Christophe Gibout

Social transaction: A relevant paradigm for the sociology of sexuality and gender?

This article explores the possible utility of the Social Transaction Paradigm approach to sexual research, sketching its theoretical outline, exploring key studies and showing its applicability as an alternative and possibly innovative approach to the study of sexuality.

The Social Transaction Paradigm (STP) was developed during the 1970's by researchers working at Louvain University (Belgium). The paradigm was initially developed as a means to investigate the crisis between the Flemings and the Walloons who disagreed fundamentally on the future of the Catholic University of Leuven and on the language(s) that had to be used for lectures. The scientific value of the STP was immediately widely recognised. Since its initial formulation, it has proven its efficiency in describing and explaining many different situations, such as environmental governance, urban policies or trans-frontiers relationships. Initially developed by

1 Unless otherwise specified, all the translations are of the author ---------------------------temporary transactional products, which return insight into the livable social situation and authorize the resilience [START_REF] Cyrulnik | Résilience: Connaissances de base[END_REF][START_REF] Segal | Winning life's toughest battles. Roots of human resilience[END_REF] without denying the conflictual nature of relationships in society. In this discussion, I will critically evaluate the usefulness of the STP for sexuality studies. First, I will briefly present the paradigm, its genesis and its theoretical foundations. Second, I will give an overview of some of the major researches concerning the question of the sexuality mobilizing the paradigm. The founding works will be presented in order to show the way this paradigm seized the question of the sex and of the gender. For its most recent works, I will use a scalar approach, from the sexuality in the public space to the interactions within the individual himself, from the transactions that mobilize numerous actors to the ones that people do with themselves. I will conclude this discussion by critically discussing the value of the STP for doing sexuality studies.

A brief overview of the STP

For a better knowledge of the STP we need to look at the social context in which it was developed and the theoretical questions it sought to address. Understanding the social transaction supposes a historically situated proofreading by its genesis and through the words of those who have "invented" it. The social transaction is the fruit at the same time of a historic circumstance -the political, academic and religious context within Belgian society [START_REF] Servais | Sociologie de la transaction sociale : repères sur la genèse de la problématique[END_REF] and the linguistic crisis within the Belgian University of Leuven during the 1960's and the 1970's -and of a critical review of Georg Simmel's works in order to solve the scientific crisis into sociology. On one hand, "the social transaction appeared in the Jean Rémy, Liliane Voyé and Emile Servais founding work (1978). It testifies of the will of his authors to go out of a double crisis, social and scientific. They were all three teachers at the Catholic University of Leuven and, when the linguistic crisis returned its inevitable partition, the French-speaking part being expelled from Leuven in Flanders, they belonged in the exit of the crisis by the creation of the Catholic University of Leuven to Louvain-la-Neuve, in Wallonia. This practice of the transaction fed their theoretical reflexion and has been its compost or its substratum" (Blanc, 2009-a : 26) On the other hand, "To produce or to reproduce? Toward a sociology of social transaction" [START_REF] Rémy | Produire ou reproduire ? Une sociologie de la vie quotidienne[END_REF] is also an answer to a scientific crisis that has crossed French speaking sociology from the 1960's to the 1970's. The hypothesis that the cleavage between structuralism -widely dominatingand the "sociology of the actor", between the "Self-Production of Society" [START_REF] Touraine | Production de la société[END_REF]) " and "the Inheritors" [START_REF] Bourdieu | Les héritiers. Les étudiants et la culture[END_REF] or the "Reproduction in Education, Society and Culture" [START_REF] Bourdieu | La reproduction. Eléments d'une théorie du système d'enseignement[END_REF] can be transcended by a transaction between these two scientific currents. As written by Georg [START_REF] Simmel | Sociologie et épistémologie[END_REF], society is crossed and structured by inflexible but necessary oppositions -one to another (male/female, tradition/modernity, innovation/preservation, closeness/distance, etc.). To reduce the tension, without ever -----------------------------------removing it totally, transactions are possible as so many temporary compromises which make possible and livable the "being-together" [START_REF] Rémy | La transaction: la notion heuristique au paradigme méthodologique[END_REF][START_REF] Rémy | Négociations et transaction sociale[END_REF]. "The paradox of the social transaction is to have to permanently reconcile the irreconcilable (…) It is here necessary to move closer to theories which are implacably brought into conflict, by avoiding a "sociological ecumenism" (Dubar, 1998: 57) which would be a superficial syncretism. The social transaction does not delete the tensions and the contradictions (…) The social transaction allows, more modestly, to make live opposed theories, while noting their incompatibility" (Blanc, 2009-a: 31) As Jean Rémy, Liliane Voyé and Emile Servais (1978) said, the social transaction is more than a notion or a metaphor but still less than a concept. By the way, this go-between situation is also an opportunity that gives the paradigm some more flexibility and a capacity to adapt itself to the present. "More than a sum of concepts, paradigm is the basic image from which an interpretation of the reality imagines itself. Paradigm is also the organizing and inductive principle of the construction of hypotheses and theoretical interpretations" (Rémy et al., 1978: 87) Using the sociology of social transaction is also a way to consider the conflict as an essential part of the society. "The negotiation and the imposition are both essential modalities of the social transaction" (ibid.). Any interaction supposes conflict that is always inevitably present. The question is how to resolve it. The sociology of social transaction is not a sociology of the consensus but, much more, a sociology of the compromise and of the negotiation within a balance of powers. "The conflict, sometimes, is solved by a negotiated compromise; but it is frequent to be in the impossibility to negotiate and the conflict is temporarily solved by a trial of strength. Between those two poles, there are all the social transactions where negotiations and imposition harmonize in variable proportions. The question of the conflicting cooperation is at the heart of the social transaction" (Blanc, in, M. Blanc et al., 1994: 15) "So social agents are involved in an on-going process, where conflict and consensus are combined. The term "social transaction" is more relevant than the world "negotiation" as its extension is broader. A social transaction is embodied in a context giving constraints and opportunities. They are effective on a cultural level (structural) and on a social level (structurel). In relation with this context, social agents have some degrees of freedom which explain a semi-random reaction. (…) In this model, central management is not underlying co-ordination and transformation (…) The social transaction paradigm offers a methodology fitted in a context in which the autonomy of social agents increases. [Now therefore] it is highly relevant for sociological research today" (Rémy & Foucart, 2013: 35) Furthermore, the opportunity of this paradigm is to facilitate the hybridization between "research in action" and "research on the action", between scientific professional and practical practices that can meet, exchange and fruit mutually. Research through this paradigm mainly focuses on the people engaged into/around the process that is analyzed and objectivation is a device negotiated by a meeting between a commitment into social action and chosen concepts and theories. By leaving of the factual reality of the survey and by resorting to reflexivity, by "studying social practices to solve the complexity without reducing it" (Rémy, 1996: 19), the social -----------------------------------------transaction offers new opportunities to seize better transformations in the heart of the investigated social situations, the underlaying values, the balance of powers in set, the said and the unspoken, the "figure and figuration of the third"2 (Simmel, 1964, 145 -169)… In this way, social transaction sociology is both a paradigm to explain and a method to do sociology. On one hand, it is a paradigm that helps us to give sense to the complexity of society by taking care on the under-textuality of relationships. On the other hand, social transaction is a way to act as a sociologist who is concernred about the multivocal character of the society and who invent, a reading of social interactions based on the conflict and the compromise as mainsprings of the society. In one phrase, the social transaction is "a hybrid stemming from a permanent invention, from contradictory orders" (Rémy, 1998: 35).

The first period: Some foundational works using the STP in sexuality studies.

There are numerous sociological papers exploring sexuality, which mobilize the social transaction paradigm. Nevertheless, before elaborating this panorama, it is advisable to return to the prolegomena of these researches on sexuality and gender, which mobilize the social transaction paradigm. In fact, these objects have been originally questioned under a three-pronged approach: sociology of family, sociology of work identities and professional subjectivities, sociology of health. Family is seen as a social structure where interactions and relationships are less codified, with a more vague and fluctuating definition of the roles and the functions of each of the members. Nevertheless sexual identities exist and family socialization allows the apprenticeship of values, standards and roles. Different research studies show that some reasonable settlements are usual in order to establish the order of the social/sexual roles and of the respective social/sexual territories in the everyday life. These adjustments are sometimes explicit but, often, they remain tacit, basing on "silent negotiations" [START_REF] Schurmans | Négociations silencieuses à Evolène[END_REF]. The works of [START_REF] Kellerhals | Transactions interindividuelles, cohésion de groupe et normes de justice[END_REF] also demonstrates that the commitment of couples in the common life are based on interpersonal transactions between different ethics and conceptions, even rival ones. So, partners with love lives develop compromises -renegotiable and renegotiated over time -, the purpose of which is the sustainability of the life of that couple. Another avenue is the research of Claude Dubar about the working identities of male and female. "Double transaction and sexual differentiation: the interpretation of two professional biographies" [START_REF] Dubar | Double transaction et différenciation sexuelle: l'interprétation de deux biographies professionnelles[END_REF] points to the existence of a double transaction "to mean at the same time the duality of the process and its progressive, groping and exploratory character" (Dubar, 1994: 114). According to Dubar, a man and a woman, develop differently their negotiations with others and with themselves to stabilize their social identity. This transaction, at the same time external and internal to the actor, is translated by the implementation of negotiations, conflicts and 2 « Die Figur des Dritten » (G. Simmel), translation of the author.

- -----------------------------------------------------------compromises, doubts and contradictions, to operate an identity conversion, here in a professional situation. The research also shows, in a rather obvious way, an effect of gender on the process of double transaction that is engaged in these experiences of professional identity conversion. Far from a logic of social reproduction, but also not obviously free to produce their own identity, women and men develop different strategies of action and mobilize different forms of identity and of social network. "The choice of one man and one woman to explain the model of the double transaction (…) ask the question of the sexual differentiation of the double transaction. [The cultural and identical differences attached to the sexes and their social roles remain. And] the hypothesis of sexual identical dynamics adorned me completely acceptable and more heuristics. [Difference of management of the professional mobility, the use of natural categories which make sexual the modes of management of the company, sexual effects of the forms of socialization, over-representation of the men in the decision-making authorities, sexual difference according career path, all have effects] It thus seems to me that the model of the double transaction allows to understand certain essential mechanisms of the disparities between men and women in the professional field. And this without reducing the professional identical forms to by-products or by-products of identity of sex" (Dubar, 1994: 121 -122) According to the last aspect, the researchers mobilize the paradigm in order to give sense to their explorations of AIDS-related sexualities and AIDS-related social relationships [START_REF] Peto | Sida: l'amour face à la peur[END_REF][START_REF] Van Campenhoudt | La relation sexuelle comme relation sociale: à partir des réactions au risque du SIDA[END_REF]. "The sexual relation establishes an interaction characterized by the interdependence between the partners. The notion of sexual relation is understood in a wide sense containing as well the sexual relations cleanly said as all the communications and the mutual actions between the partners which precedent these relations, make them possible, give them their shape and endow them with a meaning with the eyes of the partners. (…) Our feeling is that the notion of transaction, included as methodological paradigm with heuristics function, can help to report it. In reason notably of its interest to appreciate the complex and little structured situations, where the partners produce, gradually and of a groping way, the standards of their interaction, whose evolution contains substantial uncertainty and risk." (Van Campenhoudt et al., 1994: 93 -94) Interrogating these adaptations to the risk of AIDS in heterosexual relations, the authors analyze the way adults with various sexual partnerships react to the risk of AIDS and why they continue to keep this risk even when they understand it correctly. They show that it is less an evolutionary adaptation or an operating mode than a strategy. This awareness is fickle and the risk is taken into account (without being excluded) or repressed. The sexual relation is characterized by the interdependence of the partners and by the ceaseless process of production and transformation of the standards of the relation. In the heart of the loving rites and the sexual wanderings in the time of the AIDS, is revealed a shape of "conflicting cooperation" (Van Campenhoudt et al., 1994: 111) between the actors in interaction. There is cooperation between the sexual partners because, in a sense, they participate in the same production. There is conflict because games of power, of symbol, of knowledge, of influence distort the relationships. The sexual relation, as the social relation, is organized around couples of tensions (confidence / mistrust; image of self / presentation of self; ------------------------------------emotional / physiological; competition / alliance, etc.). And the strong interdependence between the sexual partners obliges a permanent process of mutual adaptation. So many aspects which prove that social transaction is a relevant paradigm to give sense to the analysis of heterosexual wandering in the time of AIDS. Next to these 3 founding research studies, which are still mobilized to analyze the social issues of sexualities and relationships between sexual stakeholders, few works in sociology of gender or of sexuality use this paradigm until a more recent period when, from the second half of the 2000's, various studies constituted a revival of this meeting and an enforcement of the paradigm.

Some contemporary examples of sexuality studies using the STP

Among the different research studies that focus on sexuality using the social transaction approach, their eclecticism is evident. A scalar approach has been chosen to show how it could be relevant at different levels for both the sociological interrogation of sexuality and the scientific questioning of the sexual fact as the social fact. Finally, there will be a review of some recent works, judged by its own standards as a study of social transaction.

Transactions, sexuality and gender in the public space

Three research studies can be presented indicatively here. The first one concerns male gallantry and the transactions of heterosexual seduction in public places in France. The second one deals with the process of socialization to masculinity of Latin-American people. The third one focuses on male cruising-for-sex in natural spaces in the South of France. [START_REF] Gourarier | Désaffecter" la galanterie masculine. La redistribution des transactions de séduction hétérosexuelles au sein de la "Communauté de la séduction" en France[END_REF] questions French men who claim a "right for the seduction" and consider themselves as a minority victim of the feminine domination. Inspired by American "Seduction Community", these men claim: "the "French Art of Seduction" able to grasp the pleasure deriving from asymmetrical heterosexual seduction transactions, simultaneously disgarding the standards of traditional gallantery that would, according to them, endure to the disadvantage of men" (Gourarier, 2013: 205) According to her analysis, the relationships between men and women is reconstructed and determined by the members of the community to define an ideal type of the attractive man. Thus, it allows to redefine the manliness and to strengthen socially dominant concepts of masculinity. Considering that they belong to "a society of frustrated men who are dominated by the women further to the triumph of the feminism" (ibid: 208 -209) and usually seen as stalkers, they want to become pursued, appropriating the feminine power to refuse or to follow up the advances of the women. If nowadays the seduction is governed by women, its appropriation by the men is a major resource of their reaction to mutual interactions. These men want to erase the expression of male interest, which they see as an expression of their ---------------------------------------------------submission to women, to reconquer an advantage in the social transaction that is the gallantry's action. The work of Fernando Carvajal Sánchez (2013-b) deals with identity construction of Colombian "halfbreed-whites", which has to compose with both marital strategies, projects of whitening and rise in social status and western social representations of manliness. Mobilizing concepts of stigma [START_REF] Goffman | Stigma: Notes on the management of spoiled identity[END_REF] and of presentation of self in everyday life [START_REF] Goffman | The Presentation of self in everyday life[END_REF], this author highlights a chain of consecutive adaptations that allow for successive compromises and practices of coexistence. He demonstrates that the identical construction of masculinity and the "europeanity" (to be white and western) for the half-bloods South American is a transactional product. During the various moments of his life (infancy, adolescence, marital choices, etc.), the boy -and then the adult -is going to integrate or to reject some standards or values of his membership groups and peers [START_REF] Dulong | Boys Don't Cry! Les coûts de la domination masculine[END_REF]. And he is going to participate actively -sometimes consciously -in the identical modifications of his close relations. To avoid losing face or to put up a good show, he is going to enter into some rites of passage and to adopt behaviors of manliness (fighting with the others, having homophobes comments, not hugging or kissing other males, etc.) and behaviors of "europeanity" (stable conjugal relation, schooled children, socially valued employment, appending a European name to the autochthonous one, etc.). All this admits him to an ideology of the masculinity which both assure him to remain aloof and satisfies his self-dignity and his relationships with others around. Another example of the research turns attention on mostly homosexual uses of natural spaces on the French Mediterranean coastline [START_REF] Audouit | Activités récréatives et Protection de l'environnement : quelles échelles de gouvernance à inventer ?[END_REF][START_REF] Gaissad | Lieux de drague dans l'espace "naturel": un patrimoine au-dessus de tout soupçon?[END_REF]. Here, the paradigm is particularly relevant to analyze a double social transaction: • The interactions between men cruisingfor-sex and the other users of the seaside but also between different cross-categories of sexual users of different sites (beach, dune) over time. • The transactions which took place between already wellestablished notorious forms of the sexual appropriation of space and recent environmental protection measures. On one hand, the places of sexual practice are characterised by the transactions that spread there. Sometimes, there is some public expression and moral disapproval of a sexual practice. But, mostly, the "articulation of the notorious and the secret reports effectively the spatial dynamics (…)" of these places of trying to pick up and authorizes "(…) places more often shared than fought" (Gaissad & Audouit, 2014: 162). Both diurnal and nocturnal sexual territories are the object of "silent transactions" [START_REF] Schurmans | Négociations silencieuses à Evolène[END_REF]. Natives or passing people, residents or summer vacationers develop a territorial appropriation that is not without clashes. But these occasional conflicts mask a continuity of secret uses, fragile and fleeting sexual transactions among which the intimacy and the durability suppose the conflict prevention by a sharing of the space according to the various categories of users (Tourists' families / sexual wanderers; People in dunes / people on beaches; sex-cruising / coastal leisure -----------------------------------activities ; etc.) and the various sexual practices (homosexuality / heterosexuality; Exhibitionism / orgy / fast meetings; vaginal sex / oral sex / anal sex; etc.). On the other hand, the research "highlights the role of public actors [local authorities, State administration, Law enforcement, etc.] and their representations and attitudes towards such "undesirable" activities as they undertake the management of these protected natural areas" (Gaissad & Audouit, 2014: 282). This sexuality, obviously gay and/or heterosexual pleasure-seekers depending of the sites, is kept in tension between the secret and the exhibition, between the said and the unspoken, between the personal freedom of the users and the environmental protection. For local authorities and administration, the question is how to deal with a problem if you do not morally admit the phenomenon and if you are still in a culture where the activity is taboo? For sex-cruisers, the question is how to maintain the tradition of the sexual practices in these places without incurring pursuits or complaints? We observe here and there forms of partial and temporary regulation of the situation, which are similar to "reasonable settlements" [START_REF] Bouchard | Fonder l'avenir. Le temps de la conciliation[END_REF]. Actors and stakeholders compromise by surrounding some places and by abandoning others, by setting up forms of regulation [START_REF] Audouit | Activités récréatives et Protection de l'environnement : quelles échelles de gouvernance à inventer ?[END_REF]) such as: rubbish bags hung on trees; spatial demarcation of the places to pick-up, collection of the worn condoms and the cigarette ends by gays associative volunteers, tolerance of the sexual activity in some dune zones and penalty in other zones with upper ornithological, zoological or floral interest. However, the formalization of the negotiation remains difficult because it is about practices which none are inclined to name. By understanding both the formal and informal compromise, by illustrating a conflicting collaboration and/or a compromise of coexistence, these researches point to a convergence between negotiation and social transaction [START_REF] Schurmans | Négociations et transactions: un fondement socio-anthropologique partagé[END_REF] Next to these social transactions in the public place, others are set up at an intermediate level, for example in the sphere of the school, the friendly network or the widened family.

Transactions, sexuality and gender at a meso-level

Among the research studies that took place with this focus, two are particularly appropriate. The first focuses on the guile in the (homo)sexual transaction in popular circles in Casablanca (Morocco) and the reason why some gay Moroccans immigrate to Belgium to live their sexuality. The second focuses on the sexist violence and violence of gender in the school, in particular the effects of heterosexual normativity, on the homophobia and transphobia in academic system. Marien [START_REF] Gouyon | Parcours homosexuels du Maroc à la Belgique: l'émigration comme moyen d'émancipation?[END_REF] explains that, in Morocco, gender identities seem to be fossilized and the non-respect of their codes is likely to engender calls to order and confusion. Over there: "the impossibility of expressing one's homosexuality cannot be perceived as the incapacity to imagine homosexuality. Thus leaving the country in order to express one's sexuality has no connection with social reality. The departure that is linked to sexuality is to be connected with the break in the social experience of an individual's personal story" (Gouyon, 2010: 312 -313) The reason for this self-exile is not homosexuality per se but the physical and/ or mental inability to live this sexuality. Gay Moroccans choosing to be immigrants have to compromise: live their sexuality or stay in the native country, live in the shadows or come out, precariousness at home or instability over there … This study expresses the anguish linked to weakening compromises, how transactions are transitional, precarious and sometimes suffered but always defined in order to keep both the opportunity of self-realization and the possibility to live together. For those -often the poorest and the less educated -who stayed in Morocco [START_REF] Poquelin | Analphabètes[END_REF][START_REF] Taïa | L'armée du salut[END_REF], Marien [START_REF] Gouyon | La ruse dans la transaction sexuelle: une liaison constitutive des rapports sociaux homosexuels de milieu populaire à Casablanca[END_REF] notice they are engaged in exchanges and renewed tacit agreement practices that connected them in a coordinated action. The study emphasized the tacit zone through which the social connections are made and remade. The author suggests "an overviewing reading of the social transaction, which will help understand how young men from Casablanca emancipate themselves thanks to daily events that arise" (Gouyon, 2013: 217). Getting organized in cliques, the young gays of Casablanca use guiles, gestural or linguistic codes bound to the dominant culture and to the west, lies, manipulation or thefts of the Westerners in order to make a better place into the society even they have popular social background, they are effeminate and often prostitute themselves. By introducing a culture of the guile, the precariousness and the coping strategies in their sexual and para-sexual transactions, the boys of the clique succeed to manage on their own and negotiate emancipatory spaces in the Moroccan society. Caroline Dayer (2013) uses the same paradigm when she questions gender-related violence in a school context and the way it is endured by Swiss pupils. Her analysis of rejection mechanisms linked to sexual orientation or gender identity is based on the more general problematic of discrimination and on the idea of a heterosexist matrix. She shows how pupils deal with their sexual identity and face up to sexist or homophobic violence. Stigmas, stereotypes and prejudices generate a "minority stress" [START_REF] Meyer | Prejudice, social stress and mental health in lesbian, gay and bisexual populations; Conceptual issues and research evidence[END_REF]. The person spends a considerable energy not to be the target of violence, which has physical ad psychological consequences. A more traumatising stigma as that it is not generally shared in the family, unlike the ethnic or religious stigmas. So the child has no respite and they have to make up permanently to leave an acceptable life role (Dayer, 2013: 135 -136). The social transactions that the pupil then has to commit concern not only their peers but also, sometimes, teachers and educational authorities. So they take in a range of constraints and contingencies. The stakeholders are multipleand few support them -and their minority status obliges them to compromise even more. If school will foster identity-building and a sense of belonging within community, and if identity construction is a transactional product, it seems that the conflicting cooperation is very much more difficult for sexual minorities and that their social acceptance is more a recurring question [START_REF] Dayer | Souffrance et homophobie. Logique de stigmatisation et processus de socialisation[END_REF][START_REF] Dayer | Suffering from Homophobia. A general analysis and a study on francophone Switzerland[END_REF].

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Transactions, sexuality and gender at a micro-level and in the presentation of self in everyday life

We saw previously that double transactions could be operated both in relationships with the others and in the internal dialogue of the person. Now we will focus on this second aspect of the transaction by focusing on the identity formation process of transsexual people. The trans-identity journey conforms to a logic of "restraining to metamorphosis" and can be deployed in six phases [START_REF] Sironi | Psychologie(s) des transsexuels et des transgenres[END_REF]. The paradigm of social transaction is useful: "to analyse the different biographic and inter-personal transaction [START_REF] Dubar | Double transaction et différenciation sexuelle: l'interprétation de deux biographies professionnelles[END_REF] working in each of the phase (…) [and] to determine the particularity of the different identity transitions from several people assigned to a gender at birth but having engaged or concluded a re-assignation in the claimed gender" (Carvajal Sánchez, 2013-a: 179) The transactions take place in serial. There are at the same time negotiations, compromises and conflicts between the actors but also doubts and contradictions within transsexuals and transgenders subjects themselves. This involves recognizing that gender claims are an obstacle course to overcome the resistances and convince stakeholders. Re-assignation is a long term process where, permanently and in a non-linear way, individuals have to negotiate with others and with themselves: What is my real-life identity? What is my received identity? What rate of estrogens or testosterone for which identity? What role of clothes in the process and when to change them? What surgical operations and when? What roles play the secondary sexual signs (Mustache, breast, hip, etc.) or the secondary identical signs (Nail polish, lipstick, make-up, masculine or feminine clothes, etc.)? With whom -man or woman -to be in couple? Which kind of couple, homosexual or heterosexual? When and how to change identity papers (passport, driving licence, etc.)? How to react in front of the looks or attitudes of the family, colleagues, administrations and others? Empirically, various transactional levels can be observed [START_REF] Dayer | Suffering from Homophobia. A general analysis and a study on francophone Switzerland[END_REF](Dayer, & 2013)). The first level of transaction deploys to oneself (Dayer, 2013: 198 -199). The progressiveness and the trial-and-error-deal in the sexual conversion are intrapersonal. It deals with the selfacceptation, the process of finding adequate vocabulary, the whom to say. The second level of transaction is interpersonal. It regards with the confrontation with others, the mobilization of retort or defense speeches, the fact of continuous managing with "evolutionary arms" and on unequal terms. The third level is societal (Dayer, 2013: 200 -201). It concerns the capacity to be an actor exercising agency in their own lives, to interact with the various authorities of their close or distant circle of acquaintances. These three levels interact on each other. At every level the people compromise and negotiate, develop practical compromises, the purpose of which is the possibility of living and managing one's own identity. To conclude this review of social transaction approaches to gender and sexuality in a micro-level, we do not have to forget that social representations, norms, roles and "emotions are data which come into the transaction and at the same time modulate the normed social frame that governs the transaction" (Bernard, J., 2009: 79 -80). And that, even if -sometimes -the transaction take place in a psycho-sociological level, it impacts on the community and the society, according to the fact that - ----------------------------"the social action is thought and it develops itself in the interaction with the others" (Schurmans, 2003: 56).

Transactions without STP : a read again of works

Finally, some other works could be read again by mobilizing the social transaction approach. As an example, when Jacquelyne Luce (2013) studies lesbian, bi and queer women's experiences of thinking about and trying to become a parent, she looks at the contexts within which women's experience occurred and draw attention to issues such as "contracting" relationships to meet a donor or to "organize" insemination, mediating understandings of biology and genetics, and decision-making amidst various social, legal and medical developments. These different issues could be seen as interactions in a public arena where women have to develop their argumentation and face contradictory speeches. A public scene where practical compromises must be brokered in an instant and whose validity is temporary, passing and resultant of the presence of different forces and stakeholders. The autonomy of the women is set against the autonomy of other social agents. The uncertainty of the situation is more important in a way that women have to compromise and that both side, have to compromise often and concerning questions that are varied. The work of Paola [START_REF] Tabet | La construction sociale de l'inégalité des sexes: des outils et des corps[END_REF][START_REF] Tabet | La grande beffa. Sessualità delle donne e scambio sessuo-economico[END_REF] could also usefully be reviewed by using the SPT. In a certain way, as Mister Jourdain made it in prose (Molière, 2013), she uses this paradigm without knowing it. It is commonly held that constraints connected to the reproductive capacities of the women determine their place in society and justify the sexual division of the work. Paola [START_REF] Tabet | La construction sociale de l'inégalité des sexes: des outils et des corps[END_REF] describes the social and historic construction of the "said-natural constraints" that assign their place to women. She shows the strength of the prejudices and the social or cultural representations with which women have to adapt and deal with in order to take their place in society. Besides, she questions the remuneration for sexuality which makes of a woman 'a whore' [START_REF] Tabet | La grande beffa. Sessualità delle donne e scambio sessuo-economico[END_REF]. According to her, sexuality appears as an asymmetric exchange and not reciprocal between men and women. Not an exchange peer-to-peer, with one sexuality against the other, but as a male compensation for a feminine service that becomes consistently a benefit. So, she suggests a transaction on an unequal social market where the balance of power is against the women. A precarious compromise where the men take systematically advantage of their dominant situation. By exploring the asymmetric relation in the sexuality, by questioning the border between the wife and the prostitute, the author shows that women compromise in a range of constraints and negotiate, according to circumstances and strengths, the forms of their sexual commitment. An exchange -vice versa -but whose stakeholders are in unequal dispute, with possible cooperating alliances which impede the reciprocity; an exchange which, in fact, is widely similar to a social transaction.

Opportunities and interests of a transactional reading of the gender and the sex

After the presentation of STP in its theorical form and an outline of the major research studies that are based on it, conclusion provides an opportunity to answer the question in the title. If there is huge differences inside sex and gender studies -national, disciplinary, theoretical variations, in particular on the tradition of materialistic social criticism -, all of them agree on four aspects (Dortier, 2014: 32) : • The social construction of the phenomenon • Many relational process are organized around a binary relation man / woman • Relationships man / woman are marked by relationships of domination • The male domination is imbricated in other relations of power (economic, social, ethnic, etc.) Obviously, these four aspects start resonating with STP, which is built on pairs of inflexible oppositions, balance of power and domination, attention on the complexity of the social and on the interweaving of social phenomena (Blanc, M., 2009-b;[START_REF] Foucart | Penser et agir dans l'incertain: l'actualité de la transaction sociale, Numéro thématique[END_REF]Gibout et al., 2009: 7 -11;[START_REF] Rémy | La transaction: la notion heuristique au paradigme méthodologique[END_REF]Schurmans, 2014). Sexual and gender relationships could be seen as unstable and temporary transactional products that represent the livable social situation and authorize the resilience [START_REF] Segal | Winning life's toughest battles. Roots of human resilience[END_REF] without denying the conflictual nature of the society. If we consider that the relations of gender and sex are balance of power as well as part of the order of physical and/or symbolic violence, we can see that negotiations within the relational systems are investigated as a kind of resilience, i.e. a search for a new balance consecutive to a shock or a trauma [START_REF] Cyrulnik | Résilience: Connaissances de base[END_REF]. Considering these negotiations as social transactions is a way to show that resilience is not opposed to coping [START_REF] Paulhan | Stress et coping: Les stratégies d'ajustement à l'adversité[END_REF]. The adjustments are made in the hic-et-nunc but they are neither definitive nor linear. Individuals and groups compromise and their compromises are passing and changing throughout the situation, reflecting a state of the strengths in presence. So the social transactions give opportunities to analyze relationships of sex or gender as a kind of do-it-yourself, which is similar to the "savage mind" [START_REF] Lévi-Strauss | La pensée sauvage[END_REF] as far as it tries to build an order with ill-assorted elements, but this order is ceaselessly made by temporary artefacts both to keep its nimbleness and its intelligence giving sense and direction to the world surround and to keep life together possible. Already, some prospects and future developments could be imagined. Besides those studies already mentioned, other research areas in sexuality studies could benefit from using the STP. For example, the study of women or gay men who are engaged in "traditional male sports". I try to do this in a study of rugby women players [START_REF] Gibout | Rugby Women Transacting, presentation at Sports, Genders and Sexualities: Social, Ethical and Political Challenges[END_REF], where the STP helps to understand explicit and implicit transactions the sportswomen are engaged in. Also, the analysis of gay people engaged in heteronormative sport's team [START_REF] Anderson | Openly gay athletes. Contesting hegemonic masculinity in a homophobic environment[END_REF][START_REF] Anderson | Openly lesbian team sport athletes in an era of decreasing homohysteria[END_REF] could usefully use STP. How have sports' institutions managed to include or exclude gen ----------------------------------der and sexual diversities? How have sports people managed to enter into "traditional clubs" and how do they manage themselves and their social position/identity within sexist and heteronormative culture? Among such a lot of questions, this topic shows how people and institutions have to enter into transactions with the in order to stabilize a social position inside one "field of strengths and tensions". As another example, could be question the relationship between sexual consent, sexual literacy and sexual well-being, and the problems of sexual law and citizenship [START_REF] Claes | Why Sexual Ethics and Politics? Why Now? An Introduction to the Journal[END_REF][START_REF] Reynolds | Disentangling privacy and intimacy: Intimate citizenship, private boundaries and public transgressions, 'Human Affairs' Special Issue On 'Intimacy And The Civic Arena: Exploring Needs, Expectations & Conflicts; Negotiating Transformations[END_REF]. How to build an identity from divergent positions? How, in the everyday life, to deal with the social pressures and prevailing views about gender identities and gender normativity? How to tinker a stable political identity from contradictory speeches according to the sexual identities? Are not stakeholders obliged to make compromises to make their life possible? Furthermore, STP goes a long way in respecting the agency of those who are being researched, while at the same time locating that research within the community being researched. It acknowledges the input of original works of experimental research, proposing that be re-read through STP, suggesting a paradigm that does not deny other approaches and tries to complete and improve them, keeping attention both on conflict and its practical resolution by stakeholders. Also, by inviting researchers to study quotidianity and to analyze commonplace activities, STP suggests a "macro sociology of everyday life in which anguish is established as a sociological concept" (Javeau, 1980: 31). An anxiety that is the translation of a social order to permanent compromise. In his experiences of ordinary life, everyone has to order their acts and argue their choices by making possible and regularly questioned compromises. STP invites researchers to think of the social acts of everyday life as so many factors organising necessary choices each of us has daily to face in order to keep one's face and to keep possible (and livable in?) society. To conclude, STP could be a real contribution to contemporary sexuality studies. It does not pretend to revolutionise the approach of sexuality as a social phenomenon. But, at the least, STP could improve contemporary sexuality studies by overcoming a sociology of the conflict and reconciling it with a sociology of the consensus, and by granting additional attention to everyday life in sociological understandings


Baptiste Quienne

Florian Cuminet

Julien Pinaud

Mona Semsarilar

Didier Cot

Didier Cot b , Vincent Ladmiral

Sylvain Caillol
email: sylvain.caillol@cnrs.fr

Baptiste Quienne

Upcycling biobased polyurethane foams

Keywords: Polyurethane foams, biobased polymers, covalent adaptable network, reshaping, transcarbamoylation, upcycling, recycling

come   L'archive ouverte pluridisciplinaire

Introduction

The development of renewable materials is a current major concern to reduce the impact of human activities on the environment and on the climate, and to ensure sustainable consumption and production. [START_REF] Un | Transforming Our World: The 2030 Agenda for Sustainable Development[END_REF] In 2019, 368 million tons of plastics were produced in the world representing 10 % of the global fossil feedstocks and only less than 1 % were biobased. [START_REF]Plastics -the Facts[END_REF][START_REF] Ferreira-Filipe | Are Biobased Plastics Green Alternatives?-A Critical Review[END_REF] Regardless of the feedstock, this production translates directly into plastic wastes that need to be recycled. Nevertheless, infrastructures are still not able to manage this massive inflow, and 79 % of plastic wastes end up in landfills or are discarded in natural environments in which they affect ecosystems for hundreds to thousands of years. [START_REF] Geyer | Use, and Fate of All Plastics Ever Made[END_REF][START_REF] Hahladakis | An Overview of Chemical Additives Present in Plastics: Migration, Release, Fate and Environmental Impact during Their Use, Disposal and Recycling[END_REF] Henceforth, it is crucial that plastic production, which is constantly growing, become a sustainable and circular framework. [START_REF] Thiounn | Advances and Approaches for Chemical Recycling of Plastic Waste[END_REF][START_REF] Sheldon | Green Chemistry and the Plastic Pollution Challenge: Towards a Circular Economy[END_REF] To initiate this transition, the production of biobased monomers has been widely developed to achieve sustainable polymers such as polyamides, polyurethanes, epoxy-resins and polyesters. [START_REF] De | Furandicarboxylic Acid (FDCA), A Versatile Building Block for a Very Interesting Class of Polyesters[END_REF][START_REF] Skoczinski | Bio-Based Building Blocks and Polymers-Global Capacities, Production and Trends 2019-2024[END_REF][START_REF] Winnacker | Biobased Polyamides: Recent Advances in Basic and Applied Research[END_REF][START_REF] Jiang | Enzymatic Synthesis of Biobased Polyesters and Polyamides[END_REF][START_REF] Caillol | Bio-Sourced Epoxy Monomers and Polymers[END_REF] Polyurethanes (PUs), produced via step growth polymerization of polyisocyanates and polyols, are the 6 th most produced polymer in the world with almost 20 Mt per year and their demand is constantly growing due to their excellent properties and their high versatility. They are present in a wide range of applications such as coatings, elastomers and sealants for example, but two third of their production is devoted to foams. [START_REF] Eling | Current and Future Trends in Polyurethanes: An Industrial Perspective[END_REF][START_REF] Singh | Recent Advancement in Plant Oil Derived Polyol-Based Polyurethane Foam for Future Perspective: A Review[END_REF][START_REF] Tenorio-Alfonso | A Review of the Sustainable Approaches in the Production of Bio-Based Polyurethanes and Their Applications in the Adhesive Field[END_REF][START_REF] Wendels | Biobased Polyurethanes for Biomedical Applications[END_REF][START_REF] Liu | Continuous Production of Water-Borne Polyurethanes: A Review[END_REF][START_REF] Gorbunova | Recent Advances in the Synthesis and Application of Thermoplastic Semicrystalline Shape Memory Polyurethanes[END_REF] PU foam (PUF) production represents around 12 Mt per year, mostly from fossil-based resources and leads to accumulation of foam wastes.

Many biobased polyols derived from vegetables oils, carbohydrates, proteins or lignin are nowadays available in the market. [START_REF] Singh | Recent Advancement in Plant Oil Derived Polyol-Based Polyurethane Foam for Future Perspective: A Review[END_REF][START_REF] Li | Bio-Based Polyols and Polyurethanes[END_REF][START_REF] Li | Polyols and Polyurethanes from Vegetable Oils and Their Derivatives[END_REF][START_REF] Kyriacos | Biobased Polyols for Industrial Polymers[END_REF][START_REF] Lligadas | Plant Oils as Platform Chemicals for Polyurethane Synthesis: Current State-of-the-Art[END_REF][START_REF] Ge | Conversion of Lignocellulosic Biomass Into Platform Chemicals for Biobased Polyurethane Application[END_REF] Partially biobased PUs are produced from such biobased polyols and fossil-based polyisocyanates. [START_REF] Mort | Biobased Foams for Thermal Insulation: Material Selection, Processing, Modelling, and Performance[END_REF] In the same way as biobased PUs, biobased PUFs reported so far are only partially biobased and often prepared using fossil-based polymeric 4,4'-methylene bis(phenyl isocyanate) (pMDI). [START_REF] Peyrton | Structure-Properties Relationships of Cellular Materials from Biobased Polyurethane Foams[END_REF] The reaction of isocyanates and water that releases CO 2 provides a good foaming strategy, even if many other blowing agents are commercialized too. [START_REF] Coste | From Gas Release to Foam Synthesis, the Second Breath of Blowing Agents[END_REF] A wide variety of biobased polyols were used to synthesize rigid foams, for example, crude glycerol, obtained as a byproduct in the production of biodiesel, and raw citric acid fermentation waste. [START_REF] Özveren | The Use of Biodiesel Residues for Heat Insulating Biobased Polyurethane Foams[END_REF][START_REF] Liu | Facile Solvent-Free Preparation of Biobased Rigid Polyurethane Foam from Raw Citric Acid Fermentation Waste[END_REF] Sorbitol-based polyols also allowed the elaboration of PUFs with anisotropic behavior. [START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF] Biobased PUFs were also synthesized with new polyol architectures obtained from microalgae oil. [START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF] In order to achieve more sustainable PUs, non-isocyanates PUs (NIPUs) synthesized through the aminolysis of cyclic carbonates are still in development. [START_REF] Carré | From the Synthesis of Biobased Cyclic Carbonate to Polyhydroxyurethanes: A Promising Route towards Renewable Non-Isocyanate Polyurethanes[END_REF][START_REF] Cornille | A Perspective Approach to Sustainable Routes for Non-Isocyanate Polyurethanes[END_REF][START_REF] Yadav | Polymers Based on Cyclic Carbonates as Trait d'Union Between Polymer Chemistry and Sustainable CO 2 Utilization[END_REF][START_REF] Gomez-Lopez | Hydroxyurethane) Adhesives and Coatings: State-of-the-Art and Future Directions[END_REF] A few NIPUs foams (NIPUFs) have been described but their synthesis is not as optimal as PUs foams (PUF) because of the lower reactivity of cyclic carbonates making difficult to synchronize both, blowing and crosslinking reactions. [START_REF] Blattmann | Flexible and Bio-Based Nonisocyanate Polyurethane (NIPU) Foams[END_REF][START_REF] Cornille | Room Temperature Flexible Isocyanate-Free Polyurethane Foams[END_REF][START_REF] Grignard | CO2-Blown Microcellular Non-Isocyanate Polyurethane (NIPU) Foams: From Bio-and CO2-Sourced Monomers to Potentially Thermal Insulating Materials[END_REF][START_REF] Quienne | Enhanced Aminolysis of Cyclic Carbonates by β-Hydroxylamines for the Production of Fully Biobased Polyhydroxyurethanes[END_REF] Our team was the first to describe NIPUFs using the H 2 released by the reaction of amines with poly(methylhydroxysiloxane) as a blowing agent. [START_REF] Cornille | A New Way of Creating Cellular Polyurethane Materials: NIPU Foams[END_REF] Lately, Monie et al. described the first selfblowing NIPUFs by controlling the chemo-and regioselectivity of the nucleophilic additions of thiols to cyclic carbonates that allowed the release of CO 2 . [START_REF] Monie | Chemo-and Regioselective Additions of Nucleophiles to Cyclic Carbonates for the Preparation of Self-Blowing Non-Isocyanate Polyurethane Foams[END_REF] However, the foaming reaction and the lower reactivity of the cyclic carbonate-amine reaction required heat.

Recently, a few biobased polyisocyanates have emerged in the market, leading our team to report the first highly biobased PUs (until 95% renewable carbon). [START_REF] Morales-Cerrada | Fully Bio-Based Thermosetting Polyurethanes from Bio-Based Polyols and Isocyanates[END_REF] These biobased polyisocyanates are less reactive than aromatic isocyanates such as the widely used pMDI. Therefore, specific formulations are needed to reach the fast reaction rates required for the production of highly biobased PUFs.

Recycling PUF is thus a major challenge. Hence, we propose in the present study a recycling process that can be applied to commercial PU foams in order to give them new life in new applications and reduce environmental impacts. The present approach is based on biosourced polyurethanes from biosourced isocyanates with reduced toxicological profiles. Hence, it proposes a more sustainable approach to PUF recycling which has recently been extended to NIPU foams. [START_REF] Monie | Divergent Aminolysis Approach for Constructing Recyclable Self-Blown Nonisocyanate Polyurethane Foams[END_REF] The development of new biobased monomers and polymer materials is an essential pathway to increase the sustainability of plastic industries. However, not only the first synthesis step needs to be improved, but the whole life cycle of polymers and especially their end-of-life have also to be considered. Therefore, the degradability of PUs and PUFs by enzymatic degradation was studied. [START_REF] Magnin | Characterization of the Enzymatic Degradation of Polyurethanes[END_REF][START_REF] Magnin | Breakthrough in Polyurethane Bio-Recycling: An Efficient Laccase-Mediated System for the Degradation of Different Types of Polyurethanes[END_REF][START_REF] Magnin | Green Recycling Process for Polyurethane Foams by a Chem-Biotech Approach[END_REF] Besides, increased attention is currently drawn to the recyclability of thermosets, especially since the discovery of vitrimers in 2011. [START_REF] Montarnal | Silica-Like Malleable Materials from Permanent Organic Networks[END_REF] As early as 1956, Offenbach and Tobolsky reported polyurethane elastomers able to relax mechanical stresses, and attributed this behavior to a chemical exchange of the urea and urethane bonds. [START_REF] Offenbach | Chemical Relaxation of Stress in Polyurethane Elastomers[END_REF] Much later, in 2015, Fortman et al. took advantage of this feature to design a PHU vitrimer, namely a thermosetting 3D structure endowed with exchangeable covalent bonds. The dynamic nature of the hydroxyurethane bonds able to exchange by transcarbamoylation enabled the material to be reshaped upon heating. [START_REF] Fortman | Mechanically Activated, Catalyst-Free Polyhydroxyurethane Vitrimers[END_REF] Such behavior was also observed in PUs when dibutyltindilaurate (DBTDL) was added as a transcarbamoylation catalyst, [START_REF] Zheng | Thermoset Shape-Memory Polyurethane with Intrinsic Plasticity Enabled by Transcarbamoylation[END_REF][START_REF] Yan | Multifunctional Polyurethane-Vitrimers Completely Based on Transcarbamoylation of Carbamates: Thermally-Induced Dual-Shape Memory Effect and Self-Welding[END_REF] or even without a catalyst provided that an aromatic isocyanate was used. [START_REF] Zheng | Catalyst-Free Thermoset Polyurethane with Permanent Shape Reconfigurability and Highly Tunable Triple-Shape Memory Performance[END_REF] Urea bonds were proved to exchange more readily and to ease the reprocessing of such materials. [START_REF] Erice | Effect of Regioisomerism on Processability and Mechanical Properties of Amine/Urea Exchange Based Poly(Urea-Urethane) Vitrimers[END_REF] Sheppard et al. recently managed to recycle used PUFs by twinscrew extrusion of postconsumer foams with DBTDL to incorporate the transcarbamoylation catalyst in the finished material. [START_REF] Sheppard | Reprocessing Postconsumer Polyurethane Foam Using Carbamate Exchange Catalysis and Twin-Screw Extrusion[END_REF] These recent discoveries, along with the pursuit of a greener and more circular consumption model, triggered the idea to prepare highly biobased PUFs that could be recycled after the foam end-of-life.

In this study, PUFs from biobased polyols and polyisocyanates have been synthesized. To the best of our knowledge, they are the first highly biobased PUFs reported so far from biobased isocyanates.

Pripol® 2033, a diol obtained via the dimerization of fatty acids was used in combination with diglycerol as crosslinker. Those polyols were formulated with two different biobased diisocyanates, Tolonate™ X FLO 100 and the L-Lysine ethyl ester diisocyanate (LDI) derived from the corresponding amino acid. Four biobased PUFs were prepared by varying the nature of the diisocyanate used and the molar ratio of the two polyols. Thermomechanical and physical properties of the PUFs were studied by DSC, TGA and DMA. The use of dibutyltin dilaurate (DBTDL) as catalyst allowed on one hand the foaming process at room temperature and on the other hand the recycling PUFs and PUFs mixtures by compression molding.

Materials & Methods

Materials

L-Lysine ethyl ester diisocyanate (purity 97 %) was purchased from Alfa Aesar (Kandel, Germany). Tolonate™ X FLO 100 (NCO equivalent: 341 g/eq) was kindly supplied by Vencorex® Chemicals (Saint Priest, France). Laponite-S 482 was kindly supplied by BYK-Chemie GmbH (Wesel, Germany). Pripol® 2033 (OH value: 207 mgKOH/g, purity 98 %) was kindly supplied by Croda (East Cowick, United Kingdom). Dibutyltin dilaurate (DBTDL, purity 95 %) and diglycerol (purity 80 %, mixture of isomers) were purchased from TCI EUROPE N.V (Zwijndrecht, Belgium). All materials were used as received.

Characterizations Fourier Transform Infrared Spectroscopy

Infrared (IR) spectra were recorded on a Nicolet 210 Fourier transform infrared (FTIR) spectrometer.

The characteristic IR absorptions mentioned in the text are reported in cm -1 . Materials analyses were recorded using an ATR accessory.

Thermogravimetric Analyses

Thermogravimetric Analyses (TGA) were carried out using a TG 209F1 apparatus (Netzsch).

Approximately 10 mg of sample were placed in an aluminum crucible and heated from room temperature to 580 °C at a heating rate of 20 °C/min under nitrogen atmosphere (60 mL/min).

Differential Scanning Calorimetry

Differential Scanning Calorimetry (DSC) analyses were carried out using a NETZSCH DSC200F3 calorimeter, which was calibrated using adamantine, biphenyl, indium, tin, bismuth and zinc standards. Nitrogen was used as purge gas. Approximately 10 mg of sample were placed in a perforated aluminum pan and the thermal properties were recorded between -100 °C and 150 °C at 20 °C/min to observe the glass transition temperature. The T g values were measured on the second heating ramp to erase the thermal history of the polymer. All the reported temperatures are average values.

Dynamic mechanical analyses

Dynamic mechanical analyses (DMA) were carried out on a Metravib DMA 25 with Dynatest 6.8 software. Foam samples (10 x 15 x 12 mm 3 ) and bulk material samples (1 x 30 x 5 mm 3 ) were tested in the uniaxial tension mode at a frequency of 1 Hz with a fixed strain of 10 -5 m, while applying a temperature ramp at a rate of 3 °C/min from -60 °C to +150 °C. The T α was determined as the maximum of the loss modulus E''.

Compression experiments

Compression experiments were performed on 17 x 7 x 12 mm 3 samples with a ThermoScientific Haake Mars 60 rheometer equipped with a 60-mm plane-plane geometry as compression holders, at room temperature. The samples were compressed following the axis of the largest dimension of the samples (17 mm). A 20 N axial force was applied to the samples. Reported compression strength values were determined at 30 % of strain.

Stress-relaxation experiments

Stress relaxation experiments were performed on a ThermoScientific Haake Mars 60 rheometer equipped with a lower electrical temperature module and an active upper heating system, with a textured 8-mm plane-plane geometry. A 1 N axial force was applied to ensure proper contact between the plates and the samples. A 1 % torsional strain was applied on 8 mm diameter and 2 mm thickness circular samples, and the rubbery modulus evolution with time was monitored at different isotherms.

Swelling index

Three samples from the same material, of around 30 mg each, were separately immersed in 5 mL THF for 24 h. The swelling index (SI) was calculated using Equation 1, where m 2 is the mass of the swollen material and m 1 is the initial mass. Reported swelling index are average values of the three samples.

Equation 1

Gel Content

Three samples from the same material, of around 30 mg each, were separately immersed in 30 mL of THF for 24 h. The samples were then dried in a ventilated oven at 70 °C for 24 h. The gel content (GC) was calculated using Equation 2, where m 2 is the mass of the dried material and m 1 is the initial mass.

Reported gel content are average values of the three samples. Equation 2Density Parallelepipedic foam samples were measured with a caliper and weighed to determine the apparent foam density.

Scanning Electron Microscopy

Scanning Electron Microscopy (SEM) analyses were conducted using a Hitachi S-4500 (Tokyo, Japan) instrument operating at spatial resolution of 1.50 nm at 15 kV energy. The samples were dried and coated with an ultrathin layer of electrically conducting platinum deposited by high-vacuum evaporation.

Optical microscopy

Optical microscopy analyses were conducted using a ZEISS Stemi 508 instrument. Cell size was determined with optical microscope pictures, reported values are average values of 100 cells.

General procedure of PUFs synthesis

Materials were synthesized with a NCO/OH molar ratio of 1.1/1.0. As an example, PUF1 was prepared as follows. Pripol® 2033 (3.941 g, 0.7 eq.), diglycerol (0.259 g, 0.3 eq.), DBTDL (0.098 g, 0.0075eq.), Laponite-S 482 (0.150 g, 1 wt%) and water (0.074 g, 0.4 eq.) were mixed using a SpeedMixer™ for 1 min at 2,500 rpm. Then, Tolonate™ X FLO 100 (10.626 g, 1.5eq.) was added to the mixture and stirred once again 1 min at 2,500 rpm.The resulting homogeneous mixture started to foam at room temperature for PUF3 and PUF4. The same procedure was applied for PUF2, PUF3 and PUF4 by varying the monomer nature and molar ratios. The resulting PUF1 mixture and the PUF3 foam were then cured for 30 min at 150 °C, while PUF2 mixture and PUF4 foam were cured for 1 h at 100 °C.

Reshaping procedure

The material was manually cut into flakes (≈ 1 mm 3 ) and then pressed in a PTFE mold for 30 min at 160 °C under a 6 tons load using a Carver 3960 manual heating press. For the foams mix, the same mass of flakes from each foam was weighed and the flakes were then mixed together, prior to compression-molding.

Results & Discussion

PUFs Synthesis and Formulation In order to obtain highly biobased PUFs, monomers were chosen with care. Indeed, commercially available biobased polyols are very common nowadays. However, only very few biobased isocyanates are available in the market. The first biobased diisocyanate chosen was Tolonate™ X FLO 100. Derived from hexamethylene diisocyanate (HDI), it contains a poly(ethylene glycol) backbone and an aliphatic part derived from palmitic acid, with an overall 32 % biobased carbons content. On the other hand, L-Lysine ethyl ester diisocyanate (LDI) is obtained from the essential L-Lysine amino acid and contains 80 % of biobased carbons. According to MSDS of supplier, LDI is not a hazardous substance or mixture according to Regulation (EC) No. 1272/2008. Tolonate™ X FLO 100 allows us to study regular HDI-based PUF with a lower toxicological profile. It is classified as GHS07 irritating, whereas HDI is classified GHS06 and GHS08 toxic. To synthesize flexible PUFs, the fully biobased Pripol® 2033 derived from fatty acids was chosen for its long aliphatic chains which give flexibility.

Diglycerol, obtained from glycerol and therefore fully biobased, was used as a crosslinking agent to bring rigidity to the polymer network (Figure 1).

To obtain flexible PUFs with different mechanical properties, two Pripol® 2033 / diglycerol molar ratios (0.7/0.3 and 0.3/0.7) were studied. (Table 1) Water was added to the formulation as foaming agent. The reaction of water with isocyanates leads to urea linkages and the formation of CO 2 allows the foaming process. Laponite-S 482 was added for rheological control of the foam, and DBTDL was used to increase the reactivity of isocyanates toward water and polyols. DBTDL allowed the PUF3 and PUF4 formulations to fully foam at room temperature, without any external heating but thanks to the exotherm of the reaction (Supporting Video), while Tolonate-based PUF1 and PUF2 were only in the nucleation phase, nevertheless, the four PUFs were then cured at 100 or 150 °C depending of their diglycerol content. LDI is smaller compared to Tolonate™ X FLO 100, enabling a higher density of reactive species in the mixture leading to a higher exotherm able to trigger the complete foaming of PUF3 and PUF4. As Tolonate™ X FLO 100 is only partially biobased, PUF1 and PUF2 presented the lowest biobased carbon contents with 41 % and 47 % respectively. LDI-based foams, PUF3 and PUF4, had higher biobased carbon contents of 90 % and 93 % respectively. PUF2 and PUF4 formulations, containing more diglycerol, were cured at 100°C for 1 h. PUF1 and PUF3 were cured 30 min at 150°C, the curing temperature was increased to prevent the collapse of the foam. Indeed, as these formulations contained less crosslinking agent, the gel point was reached at longer reaction times at lower curing temperature and the fragile foam structure tended to collapse when the polymer network was not crosslinked quickly enough. The full conversion of isocyanates was confirmed by FTIR analyses (Figure S1) with the disappearance of the isocyanate band at 2 275 cm -1 and the appearance of the urethane carbonyl elongation band at 1 715 cm -1 . Moreover, the complete crosslinking of the materials was confirmed by the high gel content values, 93 % and 97 % for PUF1 and PUF2 respectively and 99 % for both PUF3 and PUF4 (Table 2). PUF1 and PUF3 with lower diglycerol contents were dense foams with densities of 266 kg/m 3 and 390 kg/m 3 respectively.

Conversely, PUF2 and PUF4 with high diglycerol contents displayed lower densities of 147 kg/m 3 and 78 kg/m 3 respectively, PUF4 even exhibits a low density similar to conventional PUFs usually between 20 to 100 kg/m 3 . [START_REF] Peyrton | Structure-Properties Relationships of Cellular Materials from Biobased Polyurethane Foams[END_REF][START_REF] Furtwengler | Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior[END_REF][START_REF] Peyrton | Biobased Polyurethane Foams Based on New Polyol Architectures from Microalgae Oil[END_REF] PUFs were observed with optical and scanning electron microscopes (SEM) (Figure 2). PUF1 and PUF3 composed of lower diglycerol content have smaller opened cells of 396 µm and 228 µm respectively, whereas PUF2 and PUF4 have larger opened cells of 667 µm and 636 µm respectively (Table 1). Nevertheless, the four PUFs have a high cell size distribution, since no surfactant was used for their synthesis. a Foams were synthesized with 0.0075 eq. of DBTDL, 0.4 eq. of water and 1 wt% of Laponite-S 482. b Cured at 150 °C for 30 min c Cured at 100 °C for 1 h.

Thermomechanical properties

The four formulations allowed to synthesize four PUFs able to cover a wide range of properties. The four PUFs exhibited T g values ranging from -29 °C to 46 °C for PUF1 and PUF4 respectively (Table 2 and Figure S3). The structure of the diisocyanate used had a significant influence on the T g values of the final foams. Indeed, Tolonate™ X FLO 100 possesses long alkyl chains and has a much higher molar mass than LDI, therefore, Tolonate-based foams presented the lowest T g as it reduces the foam crosslinking densities. Moreover, the increase of diglycerol contents from 0.3 eq. to 0.7 eq. in PUF2 and PUF4 led to higher T g values, from 12 °C to 46 °C for PUF3 and PUF4 respectively. Indeed, this can be ascribed to diglycerol content which strongly increased the crosslinking density with its high OH functionality and its small molar mass compared to Pripol 2033®. The low T g foams PUF1, PUF2 and PUF3 were soft at room temperature whereas the higher T g PUF4 was rigid.

Furthermore, the thermal stability of PUFs were studied by TGA (Figure S2) by comparing the temperatures at 5 % of degradation. Tolonate-based foams PUF1 and PUF2, which degraded at 270 °C and 273 °C respectively, were more thermally stable than the LDI-based foams PUF3 and PUF4 which degraded at 257 °C and 242 °C respectively. The higher Pripol® 2033 content increased the thermal stability of PUF3 compared to PUF4 from 242 °C to 257 °C whereas, it did not exhibit particular effect for PUF1 and PUF2. Indeed, PUF1 and PUF2 networks were mainly composed of Tolonate™ X FLO 100 with 70 wt% and 80 wt% respectively, because of its high molar mass (Table S1). Therefore, the effect of the polyol contents was lower.

Mechanical properties

Mechanical properties of the four PUFs were analyzed by an uniaxial compression experiment (Figure 3) using parallelipipedic foam samples. Three characteristic regimes were observed from the stress/strain curves. The first region, at low strain, corresponds to the linear elasticity due to the bending of the edge of the foam. This first region was observed for strain values ranging from 0 to around 5 % for PUF1 and PUF4 and from 0 to around 20 % for PUF2 and PUF3. Above these strain values, a plateau was observed where the stress was stable even if the strain increased. This second region corresponds to the collapse of the foam due to the compression of the cells. Above 40 -50 % of strain, cells were completely compressed. Therefore, the stress increased drastically. This phenomenon corresponds to the densification region (Figure S4). The compression strength (which represents the force needed to compress the foam) was determined at 30 % strain for each PUF. This strength varied with the cells characteristics and foam density but also with the composition of the PUF network. PUF1 and PUF2 (T g = -29 °C and -26 °C respectively) were very soft at room temperature and did not require a high compression strength (53 kPa and 10 kPa respectively) to achieve 30 % strain. In contrast, PUF3 and PUF4 based on LDI and which have higher T g due to their higher crosslinking density exhibited compression strength values of 127 kPa and 106 kPa respectively. In addition, the compression strength also depended on the foam density. Indeed, PUF1

which was denser than PUF2, also displayed higher compression strength. For the same reasons PUF3 had a higher compression strength than PUF4. PUFs foaming required DBTDL as a catalyst, which was reported to also activate covalent bond exchange by transcarbamoylation in cured PUs. With the discovery of vitrimers in 2011, [START_REF] Montarnal | Silica-Like Malleable Materials from Permanent Organic Networks[END_REF] the recycling of thermosets has never been so closer to reality. To assess the potential recycling of the PUFs, reprocessing trials were performed by compression molding. The foams were first powdered, then placed in a PTFE mold and pressed at 160 °C for 30 min under a 6-ton load. Flexible transparent materials were obtained out of PUF1, PUF2, PUF3 and a stiff transparent material was obtained out of PUF4 as expected given the T g of the corresponding pristine PUFs (Table 2, Figure S5). These four materials were obtained thanks to the transcarbamoylation reaction catalyzed with DBTDL already contained in the PUFs network since their synthesis, with a content between 0.65 wt% and 1.6 wt%.

Upcycling and recycling of PUFs

Several reshaping cycles were performed. The swelling indexes and gel contents were measured after each cycle for the four PUFs to assess the degradation of the polymer network, a trend was observed (Figure 5). Gel contents decreased with the number of cycles indicating some degradation of the polymer network and a decrease of the crosslinking density leading to an increase of the soluble fraction. PUF1 bulk material ended up being fully soluble after the 5 th cycle whereas PUF2, PUF3 and PUF4 bulk materials were less affected. This trend was attributed to a higher crosslinking density, either because of a higher diglycerol content (PUF2), or because of the use of LDI which is shorter than Tolonate® X FLO 100 (PUF 3), or because of both reasons (PUF 4). This difference in crosslinking density is also reflected in the Swelling Index values, as PUF 1 has the highest swelling index, whereas PUF 2 and PUF 3 have similar values and PUF 4 exhibits the lowest swelling index.

Indeed, the gel contents of PUF4 bulk materials remained above 79 % after five reshaping cycles.

Even if PUF3, as PUF1, was composed of 0.3 eq. of diglycerol, its gel content remained to 60 % after five cycles thanks to the higher crosslinking density provided by LDI. Swelling indexes of PUF2 and PUF3 increased with cycles confirming a slight decrease of their crosslinking density. In contrast the swelling index of PUF4 remained stable. Consequently, PUF4 appears to be a very promising foam because of its thermomechanical and mechanical properties, its low density and its ability to be reshaped with relatively low degradation over successive cycles. [START_REF] Swartz | Blending Polyurethane Thermosets Using Dynamic Urethane Exchange[END_REF] This possibility was assessed with the biobased PUFs described here. An equimassic mixture of the four powdered PUFs was prepared and reprocessed as described above. This reshaping procedure led to a flexible macroscopically homogeneous transparent material (mixPU). As for individual PUF up to 5 consecutive reprocessing cycles were achieved with this mixPU (Figure 4). The recycling of the four PUFs together demonstrates that a straightforward upcycling is possible for PUFs from different origins at the end of their life, if a specific collecting and recycling channel exists.

The properties of the materials obtained from mixPU reshaping steps after the first, the second and the fifth cycle were assessed by DMA (Table 3), storage modulus E' and tan(δ) were plotted against temperature (Figure 6). After the first cycle, two regimes are visible, with local tan(δ) maxima at 0 °C and 44 °C. On the DSC thermogram (Figure S6), two T g are visible at -27 °C and 44 °C on the first heating ramp (Table 4), but the second T g cannot be observed on the second ramp. This behaviour can be attributted to local heterogeneity in the material likely caused by the fact that it results from the mixing of powders from different foams. The low T g (-29 and -26 °C) PUF1 and PUF2 are responsible for the lower temperatures regime, while the higher T g (12 and 46 °C) PUF3 and PUF4 are responsible for the upper temperatures behaviour. After the second cycle both regimes were still visible on the DMA thermogram (Figure 6) but the curve was smoothed. On the DSC thermogram (Figure S7) only one T g was observed at -27 °C, though a local minimum of the derivative at 41 °C remained as an indicator of the local heterogeneity (Table 4). After the fifth cycle a broad single mode was observed by DMA, and the T g observed by DSC was -18 °C (Figure S8 and Table 4). This evolution is likely caused by the successive grinding-reshaping cycles which gradually increased the homogeneity of the material. The broadness of the mode remains a manifestation of the different T α values of the pristine PUFs. Therefore, we also could consider that five cyles are needed to obtain a new homogeneous material. On the other hand, the storage modulus on the glassy plateau E' glassy remained stable, at 3.8, 3.4 and 3.7 GPa respectively, whereas the values on the rubbery plateau decreased from 19.3 to 15.7 and 6.5

MPa respectively (Figure 6). In addition, the gel content dropped to 64 % after the second reshaping and to 50 % after the fifth cycle, which is probably due to partial degradation of the polymer.

Surprisingly, the swelling index was stable over the five cycles and the T α did not change significantly either. Moreover, the T g increased from -27 °C to -18 °C whereas a drop of the T g is usually expected with the polymer degradation, as previously observed during the recycling of the four set apart PUFs.

Nevertheless, a theoretical final T g of -3 °C (average of the four PUF T g ) was expected for mixPU with respect to the Fox Equation. There is a significant different with the experimental value at -18 °C indicating that some degradation happened. In addition, the swelling index was supposed to increase with degradation since the crosslinking density of polymer network is usually reduced, but SI remained almost stable over the recycling cycles. Finally, in contrast with the individual PUFs, the decrease of T g and the rise of the swelling index were not observed with the degradation of mixPU.

We hypothesize that this phenomenon might be due to the homogenization of the network induced by the successive cycles applied to the mixture, and that 5 cycles are needed to homogenize the recycled material.

Dynamic properties of PUFs with DBTDL

Covalent adaptable networks (CANs) using DBTDL as transcarbamoylation catalyst in PUs have already been described. [START_REF] Zheng | Thermoset Shape-Memory Polyurethane with Intrinsic Plasticity Enabled by Transcarbamoylation[END_REF][START_REF] Yan | Multifunctional Polyurethane-Vitrimers Completely Based on Transcarbamoylation of Carbamates: Thermally-Induced Dual-Shape Memory Effect and Self-Welding[END_REF] Moreover, urea bonds are known to enhance the reprocessing of these materials. [START_REF] Erice | Effect of Regioisomerism on Processability and Mechanical Properties of Amine/Urea Exchange Based Poly(Urea-Urethane) Vitrimers[END_REF] In the present study, DBTDL was used as a catalyst to obtain the biobased PUFs, moreover, the foaming reaction of isocyanates with water led to urea bonds in the thermoset structure. To highlight the dynamic behavior of the reprocessable PUFs, mixPU was characterized by stress relaxation experiments from 160 °C to 200 °C (Figure S9). Classical non-reshapable thermosets exhibit a constant stress as their networks are fixed. On the contrary, at 200 °C the stress applied to mixPU was fully relaxed in 300 s, a feature associated with an evolving network topology. The modulus at the beginning of the relaxation G 0 decreased gradually with increasing temperature isotherms, from 0.7 MPa at 160 °C to 0.4 MPa at 200 °C, which suggests a dissociative CANs is at stakes. The relaxation was faster as the temperature increased from 160 to 200 °C (Figure 7a). The curves were fitted with a Kohlrausch-Williams-Watt equation (Table S3) and the relaxation times obtained were plotted in an Arrhenius diagram (Figure 7b). This plot fitted perfectly with a linear model (R² = 0.99647). Hence, the material flow dependence with temperature follows an Arrhenius law, a feature of vitrimer-like dissociative CANs. The activation energy (E a ) of mixPU was determined to be 140 kJ.mol -1 , in the same order of magnitude as PU CANs previously reported. [START_REF] Zheng | Catalyst-Free Thermoset Polyurethane with Permanent Shape Reconfigurability and Highly Tunable Triple-Shape Memory Performance[END_REF][START_REF] Erice | Effect of Regioisomerism on Processability and Mechanical Properties of Amine/Urea Exchange Based Poly(Urea-Urethane) Vitrimers[END_REF][START_REF] Sheppard | Reprocessing Postconsumer Polyurethane Foam Using Carbamate Exchange Catalysis and Twin-Screw Extrusion[END_REF]

Conclusion

The development of more eco-friendly materials is a major stake to ensure sustainable production and consumption. Foams are found in everyday life applications and are mainly based on polyurethanes. The recent emergence of biobased polyisocyanates in the market have made the synthesis of highly biobased polyurethanes possible (until 95% renewable carbon). Here, four highly biobased PUFs, PUF1 and PUF2 based on Tolonate™ X FLO 100 and PUF3 and PUF4 based on LDI were synthesized with a renewable carbon content ranging from 41 % to 93 %. The LDI-based formulations fully foamed at room temperature, while the heating of Tolonate-based PUFs was necessary to complete their foaming. Foams with T g ranging from -29 °C to 46 °C after curing at 100 or 150 °C were obtained. PUF1, PUF2 and PUF3 were dense foams while the PUF4 density of 78 kg/m 3 was comparable to conventional PUFs making PUF4 very promising. The DBTDL used to catalyze the foaming and the crosslinking reactions also served as transcarbamoylation catalyst to upcycle the foams to bulk PUs. The four PUFs were reshaped up to 5 times by compression molding.

Moreover, a new PU material (mixPU) was obtained from a mixture of the four PUFs using the same recycling process. The dynamic properties of the mixPU were characterized by stress relaxation experiments, demonstrating theexchanges occurring in the PUFs CANs synthesized that enable their reshaping. The upcycling and the reshaping steps applied to this mixPU highlighted the potential to recycle foams from different origins, a key parameter to achieve foam recycling on an industrial scale. This study was performed on biobased isocyanates with lower toxicological profiles. It could be extended to regular commercial PUF in order to propose a promising recycling approach that allows them new life in new applications and reduce environmental impacts. These results correspond to a transitory approach proposing to manage the present situation regarding PU wastes.

Figure 1 :

 1 Figure 1: Diisocyanate and polyol monomers used for PUFs synthesis.

Figure 2 :

 2 Figure 2 : Photographs of PUFs, optical microscopic and SEM pictures from left to right.

Figure 3 :

 3 Figure 3: Stress-strain curve of PUFs obtained by a static 20 N uniaxial compression.

Figure 4 :

 4 Figure 4: Reshaping strategy. Powdered foams were reshaped by compression molding for 30 min at 160 °C under a 6 tons load.

Figure 5 :

 5 Figure 5: Evolutions of swelling indexes (left) and gel contents (right) of PUFs over 5 reshaping cycles One of the major limitation of recycling, is the massive influx of wastes of different origins. Very selective time-consuming and labor-intensive sorting steps are necessary in order to give a second life to limited wastes. Limiting these sorting steps would be an important progress towards more cost-effective and productive recycling. One step in the right direction would be to enable wastes of different origins to be recycled together as demonstrated lately Swartz et al. by blending rigid and soft PU thermosets through transcarbamoylation.[START_REF] Swartz | Blending Polyurethane Thermosets Using Dynamic Urethane Exchange[END_REF] This possibility was assessed with the biobased

Figure 6 :

 6 Figure 6: Storage modulus (full lines) and tan(δ) (dashed lines) of mixPU during DMA experiments after several reprocessing cycles.

Figure 7 :

 7 Figure 7: (a) Normalized stress-relaxation measurements of mixPU and (b) Arrhenius diagram and linear fit of τ KWW values from 160 to 200 °C.

Table 1 :

 1 Formulations of PUFs and their biobased carbon content.

		Diisocyanate	Polyols
	Foam a	LDI (eq.)	Tolonate™ X FLO 100 (eq.)	Pripol® 2033 (eq.) Diglycerol (eq.)	Biobased Carbon Content (%)
	PUF1 b	-	1.5	0.7	0.3	47
	PUF2 b	-	1.5	0.3	0.7	41
	PUF3 c	1.5	-	0.7	0.3	90
	PUF4 c	1.5	-	0.3	0.7	93

Table 2 :

 2 PUFs properties.

	Foam	T g (°C)	T α (°C)	Compression strength (kPa)	T d5% (°C)	Gel content (%)	Density (kg/m 3 )	Cell size (µm)
	PUF1	-29	-21	53	270	93 ± 1	266 ± 35	396 ± 94
	PUF2	-26	-30	10	273	97 ± 1	147 ± 16	667 ± 191
	PUF3	12	22	127	257	99 ± 1	390 ± 61	228 ± 106
	PUF4	46	49	106	242	99 ± 1	78 ± 9	636 ± 302

Table 3 :

 3 Properties of mixPU bulk materials after several reprocessing cycles.

	Reprocessing Cycle	T g1 (°C) a	T g2 (°C) a	T α (°C)	E' glassy (GPa) b	E' rubbery (MPa) c	Swelling index (%)	Gel content
								(%)
	1	-27	44	-15	3.8	19.3	440±16	71±1
	2	-27	-	-18	3.4	15.7	453±13	64±1
	5	-18	-	-17	3.7	6.5	410±22	50±2
	a values for the first heating ramp	b at T α -50 °C	c at T α +50 °C

Acknowledgements

The authors acknowledge the Institut Carnot Chimie Balard CIRIMAT (16CARN000801) for funding the PhD Thesis of Florian Cuminet.

Associated content Supporting Information

The Supporting Information is available free of charge at Detailed PUF formulations, FTIR spectra, TGA and DSC thermograms, compression experiments, photographs and T g of recycled PUF, fitting parameters of Kohlrausch-Williams-Watts model.

Supporting video

Foaming of PUF4 at room temperature.

Authors information

Notes

The authors declare no competing financial interest.

For Table of Contents Use Only

Reprocessable biobased polyurethane foams have been synthesized and recycled highlighting that a more sustainable approach is possible.