Dominique Salameh

Cédric Brandam

Roger Lteif

Pierre Strehaiano

P-coumaric acid adsorption in wines to avoid ethylphenol production by brettanomyces

Keywords: p-coumaric acid, adsorption, Brettanomyces, Saccharomyces

INTRODUCTION

The p-coumaric acid is a natural polyphenol of wines, in the hydroxicinnamic acid family. The maceration process brings that hydroxycinnamic acid into grape juice in the average concentration of 60 mg/L [1]. After fermentation and wine elaboration, the p-coumaric acid concentration cannot exceed 8 mg/L [2]. It can be found in a free form, or bounded to other wine components such as tartaric acid to form the p-coumaroyltartaric acid or with glucose to form an heteroside. The esterase activity of wine enzymes liberates the p-coumaric acid. In its free form, it is transformed into 4-vinylphenol by a common enzyme to many wine microorganisms, the cinnamate decarboxylase. The 4-vinylphenol is associated to pharmaceutical compounds smell [3]. The problem occurs when wines are contaminated by Brettanomyces yeast. This yeast can turn the 4-vinylphenol into 4-ethylphenol, due to its specific enzyme presence, the vinylphenol reductase [START_REF] Dias | Food Microb (5) D[END_REF]. Nowadays, the horse sweat smell in wines is associated to the 4ethylphenol molecule. So this reaction has a bad organoleptic impact on the wine. Therefore, many works studied this bioconversion and proposed treatments to avoid its occurrence. The proposed solutions included many approaches, such as a high hygienic level to avoid brettanomyces contaminations, or physical treatments to eliminate the volatile phenol once produced [5]. This work presents a new approach based on the p-coumaric acid adsorption on yeasts and oenological components. Its removal from the wine can avoid the ethylphenol production. Adsorption on yeasts cells mentioned in bibliography [6] was verified. Effects of different factors on the adsorption by two industrial adsorbents were tested.

MATERIALS AND METHODS

Adsorption tests on Saccharomyces and Brettanomyces cells

Different concentrations of Brettanomyces and Saccharomyces yeast were obtained by fermentations. P-coumaric acid was dissolved in 1ml of pure ethanol before to be added in different concentrations in a synthetic wine medium. Two minutes after, a sample was taken, centrifuged, and then the liquid part was tested on HPLC to detect the p-coumaric acid concentration, and on GC/MS to detect the 4-vinylphenol and 4-ethylphenol content. All the tests were compared with witness samples free of yeast.

Adsorption tests on PVPP and yeast cell walls

Polyvinylpolypyrrolidone (PVPP) and yeast cell walls were used as two oenological adsorbent in the concentration of 3 g/L. The medium used was a synthetic wine medium free of p-coumaric acid. A 2 3 factorial experimental design was tested to study the variation of the adsorbed quantity Qe (mol/g) of p-coumaric acid added in different concentrations. Q e = X/m, where m is the adsorbent mass, and X = Ci (initial concentration) -C e (concentration at equilibrium). The factors tested were the pH (3-3.5 -4), the temperature (25, 30, 35 o C) and the ethanol concentration (10-11.5-13 % v/v). The agitation was fixed at 250 rpm. All the tests were compared with witness samples free of adsorbent. The p-coumaric acid concentrations tested were 2.5 and 20 mg/L, for each adsorbent and for each level of the experimental design. The contact time for adsorption was 5h.

RESULTS AND DISCUSSION

Adsorption tests in fermentations

Results showed a difference in the adsorption potential of each species. In fact, the Brettanomyces sp. showed a better adsorption than the Saccharomyces in their specific conditions (Table 1). There was no 4-vinylphenol or 4ethylphenol production. These results confirmed the bibliography datas [7]. In fact, the p-coumaric acid is the less adsorbed phenolic acid by the saccharomyces sp. Its adsorption on brettanomyces cell walls was recently defined [8].

Adsorption tests on PVPP and yeast cell walls

With the methodology of factorial experimental design, the values of Qe were assimilated to a first degree polynomial model: Qe = ao + a 1 X 1 + a 2 X 2 + a 3 X 3 + a 4 X 1 X 2 + a 5 X 1 X 3 + a 6 X 2 X 3 + a 7 X 1 X 2 X 3 ε, where X ± was to join the effect of each factor on Qe ed by an ANOVA test, in the aim to the potential of the polynomial equation to predict the were presented for two oncentrations of p-coumaric acid: 2.5 and 20 mg/L. o (a) and 0.97 for pareto (b), which indicates the good performance of the tests.

1 was Temperature, X 2 was pH and X 3 was the ethanol concentration. The aim of this polynomial model with the effect of the interactions. The EXCEL STAT 2003 as well as the STATGRAPHICS were used to analyse the complete factorial design results. The determination of the polynomial coefficient was achieved by a multilinear regression multivariable analysis. The variances of the parameters were calculat determine the significance of the effects. The Student test (t) was acquired at a 3 freedom degree level, and for a confidence level of 95%. The values of polynomial coefficients were considered significant when the student test was higher than 3,18. The R 2 coefficient represents effect of the factors. The results of the statistical analysis are presented in the Pareto graphs in figure 1 when PVPP was used. The factor effects c

When PVPP was the adsorbent, only the temperature had a significant effect on adsorption in the tested conditions. To increase temperature from 25 to 35°C improved adsorption of p-coumaric acid. The ethanol concentration, as well as the pH, had no direct effect on the adsorption, on the two p-coumaric concentrations levels. The R 2 values were 0.92 for paret On the other hand, when the yeast cell walls were the adsorbent, experimental results were less reproductible than with the used of PVPP. The interpretation reas the maximum loss f p-coumaric acid was 45% ± 12% and 72% ± 37% when the yeast cell walls espectively for 20 and 2.5 mg/L).,.

myces sp. Because of its partial adsorption on dium will avoid the horse sweat smell PVPP. Finally, with PVPP, it was nthetic wine medium. he study of p-coumaric acid adsorption in true wines is being studied as a first iol. 20(2003) 377-384.

4088.

, 50(2002), 7432-7437. of pareto graphs are more difficult and, none of the factors seemed to affect the Qe. Nevertheless, it was possible to compare the cpacity of adsorption of PVPP and yeast extract. With the same concentration of each (3g/L), PVPP was always a better adsorbent than yeast extract. For instance, at 25 o C, the maximum loss of p-coumaric acid by adsorption was 69% ± 1% and 99.4 % ± 8.4 respectively for 20 and 2.5 mg/L when the PVPP was the adsorbent whe o were the adsorbent (r

CONCLUSION

The p-coumaric acid showed different adsorption profiles on different yeast species. The brettanomyces sp. had a better adsorption potential of the pcoumaric acid than the saccharo yeast, the p-coumaric acid present in wine cannot be transformed totally into 4vinylphenol and 4-ethylphenol. The p-coumaric acid removal from the me odours if a contamination occurs. Its adsorption on oenological components can be a solution to avoid its bioconversion. The two adsorbent materials tested showed that the PVPP is a better adsorbent than yeast cell walls of this acid in wine conditions. The non significance effects of the factors pH and ethanol concentration on the p-coumaric adsorption by PVPP was proved. On the other hand, to increase temperature from 25 to 35°C favoured the adsorption on showed that it was possible to decrease drastically the p-coumaric acid concentration in a sy T step of application

Figure 1 -

 1 Figure 1-Estimated effect of the factors on Qe when PVPP was the adsorbent -(a) 20 mg/L p-coumaric acid, (b) 2.5 mg/L p-coumaric acid.On the other hand, when the yeast cell walls were the adsorbent, experimental results were less reproductible than with the used of PVPP. The interpretation

Table 1 -

 1 Adsorption of p-coumaric acid on Brettanomyces sp. and Saccharomyces sp. in fermentation conditions

		Initial concentration (mg/L)	Concentration found (mg/L)	Population (10 6 Cell/ml)
	Saccharomyces	10	9,83	60
		10	9,53	120
		10	9,09	240
	Brettanomyces	10	9,1	3
		10	8,4	360
		10	5,2	450


6/27

Excrétion théorique des anticancéreux administrés lors des prélèvements Excrétion théorique des antibiotiques administrés lors des prélèvements 80 0,05 à 0,2 g 1,2 g Rifampicine 80 (S) 0,18 (S) g 1,5 à 2,2 (T) g 3,7 g Sulfamethoxazole (S) triméthoprime (T) < 5 2,1 à 3,9 g 6 g Métronidazole > 2,1 g 2,3 g Amikacine > 3,2 g en 16 j 4 g Teicoplanine env 18 g 20 g Vancomycine env 39 g 40 g Levofloxacine 14 1,37 1,8 g Ciprofloxacine 20 0,64 g 0,8 g Ofloxacine 30 9,1 g 13 g Imipenem -cilastatine 20 (T) 64 g (P) 6,4 g (T) 64 (P) 8 (T) g Piperacilline (P) -tazobactam (T) < 20 5,22 g 6 g Aztréonam Temps de Séjour Hydraulique: Temps moyen de passage du liquide dans le réacteur. (V Réacteur/Débit entrée).

Age de Boues: Temps moyen de rétention de la biomasse dans le réacteur (V Réacteur/Q purge)

• Conséquences:

Concentrations en biomasse importantes.

Etablissement d'un bio-consortium plus complexe avec de plus larges possibilités physiologiques comparées à des procédés à bas âges de boues.

Meilleures performances d'élimination de la DCO, N et de composés difficilement biodégradables.

Diminution de la production de boues.

13/27

Double objectif

• Evaluer le potentiel d'un BàM pour la dégradation de médicaments anticancéreux (Cyclophosphamide + Métabolites).

• Rechercher l'effet du cyclophosphamide et ses principaux métabolites sur le fonctionnement du procédé.

14/27

Protocole expérimental

BaM R1 -COCKTAIL + Eau usée (CP+ + métabolites stoechiométrie « humaine ») Cyclophosphamide (5000 ng/L).

Acroleine (2250 ng/l), Moutarde phosphoramide (8883 ng/l), 4-Keto-cyclophosphamide (580 ng/l),

Nor-Nitrogen Mustard (517 ng/l)). Traitement tertiaire R0 • Ils induisent une modification de la liqueur mixte entrainant une augmentation du colmatage de la membrane (Accumulation DCO, EPS, fragilisation des flocs). Rôle prépondérant de la membrane du BàM R1(+CP) sur l'élimination de la DCO.

BaM R2 -eau usée seule-Pas de COCKTAIL

• Effet sur l'activité des populations bactériennes, rôle important de l'acclimatation (effet âge de boue)

• Le bioréacteur à membrane externe permet une élimination du CP et de son métabolite 4-KetoCP autour de 75%.

  prend en compte que l'administration du jour, il reste une quantité résiduelle des produits injectés la veille. **En % molaire du produit parental 7/27

**

  Ceci ne prend en compte que l'administration du jour, il reste une quantité résiduelle des produits injectés la veille. **En % molaire du produit parental Ceci ne prend en compte que l'administration du jour, il reste une quantité résiduelle des produits injectés la veille. **En % molaire du produit parental

  Effluent modèle -2 réacteurs en parallèle Vo = 24l -J = 20l/j -HRT = 48h -SRT = 50 (I)/70 (II) days MLSS R2 > MLSS R1 (plus évident après le changement de vitesse)

  Pas de rétention par la membrane, même colmatée Adsorption et/ou biodégradation?

►

  Rétention CP eau dans Milli-Q faible, due à des encombrements stériques typiques.►Adsorption entre CP et surface membrane faible mais nonnégligeable, peut conduire à une sous estimation de la rétention.►RO membrane excellente rétention (>90%) qq soient les conditions opératoires ► BaM-NF et BaM-RO peuvent être considérés comme prometteurs. de CP et ses principaux métabolites, dans les conditions opératoires étudiées, ne diminue pas la capacité épuratrice (en termes de DCO et d'azote totale) du bioréacteur à membrane.

  The cyclophosphamide is detected at average level of 146 ng/l in hospital effluent, with peaks at 4500 ng/l.(Steger-Hartmann et al, 1997) Non-degradated in WWTP (Steger-Hartmann et alDCO (mg/L) L'évolution de la concentration en DCO du perméat est attribuée à deux facteurs : L'activité des microorganismes et la rétention de la membrane. la membrane du BàM R1(+CP) sur l'élimination de la DCO.

de prélèvement % de survie Evolution de la toxicité d'effluents hospitaliers sur les lentilles d'eau lemna minor suivant les heures de prélèvement (échantillons du 01/09/2007)

						120
						100
						80
						60
						40
						20
	o i n	1 1 h	1 2 h	1 3 h	1 4 h	1 5 h heures 0 1 6 h 1 7 h 1 8 h 1 9 h 2 0 h 2 1 h 2 2 h 2 3 h 2 4 h T é m o i n	1 1 h	1 2 h	1 3 h	1 4 h	1 5 h	1 6 h	1 7 h	1 8 h	1 9 h	2 0 h	2 1 h	2 2 h	2 3 h	2 4 h

heures de prélèvement % de survie Evolution de la cytotoxicité d'effluents hospitaliers suivant les heures de prélèvement et après 48h d'incubation (échantillons du 02/09/2007)

	140
	120
	100
	80
	60
	40
	20
	0
	T é m o i n	1 h	2 h	3 h	4 h	5 h	6 h	7 h	8 h	9 h	1 0 h

heures de prélèvement % de survie Evolution de la toxicité d'effluents hospitaliers sur les lentilles d'eau lemna minor suivant les heures de prélèvement (échantillons du 02/09/2007)

		Effluents hospitaliers: bilan Bioréacteur à membrane Bioréacteurs à membranes
	Cytotoxicité (Hep H) Procédé couplant deux fonctions:		Croissance Lemna minor
	30 juillet 2007 2. Séparation par membrane Des quantités de l'ordre du g pour 70 patients environ 1.Biodégradation de la matière organique Eau traitée/microorganismes
		Effet cyclique environ 10 heures, liés à ??? P2 P3
	1 sept
	2007	Quantification des molécules permé	120
	20 40 60 80 100 Bilan en cours sur certaines dans l'effluent de sortie. % de survie at P1 pomp
	e	purge	0 T é m o i n	1 h	2 h	3 h Air heures de prélèvement 4 h 5 h 6 h 7 h comprimé U ER	8 h	9 h	1 0 h
									10/27 11/27 12/27

• Souplesse

du procédé (TSH et Age de Boue):

R1 + CP R2 Controle Matière en suspension

		Epuration conventionnelle (DCO, N) Pression transmembranaire
		14
		12
	COD removal (%)	0 2 4 6 8 0 Sludge concentration g/L 5 0 0 5 0 10 2 4 6 8 10 Sludge concentration g/L	10 5 15 Cyclophosphamide and 15 20 25 30 35 40 45 First day: Addition of metabolites to R1 10 15 20 25 30 35 40 metabolites to R1 20 25 30 35 40 45 50 55 50 45 Cyclophosphamide end Cyclophosphamide end First day: Addition of metabolites to R1 First day: Addition of	55 50 60 Operation time (d) 60 65 70 75 80 85 90 95 55 60 65 70 75 80 85 90 95 100 100 105 105 110 110 65 70 75 80 85 90 95 100 105 110 115 120 115 115 125 120 120 130 125 125 135 130 130 140 135 135 145 140 140 150 145 145 155 150 150 160 155 155 Increasing crossflow velocity from 4 to 5 m/s. Change of velocity from 4 to 5 m/s. membranes ±10% Increasing crossflow Change of velocity from 4 to 5 m/s. membranes Increasing crossflow membranes ±10% Change of ±5%	160 160
			Operation tim e (d) Operation tim e (d) R1 cyclophosphamide R2 control
		R1 g/L R2 g/L Control R1 g/L 95 to 98 %, pharmaceutics compounds lead to weakening the non affectée par la présence CP+Metab. biomass structure in R1
					17/27 18/27

albasi@ensiacet.fr claire.albasi@ensiacet.fr Degradation CP et 4-KetoCP

	•Adsorption ou Biodégradation ?
	•Des tests d'adsorption révélateurs d'adsorption sur la phase solide, malgré Kow faibles Merci pour vôtre attention •Des soupçons sur les colloïdes comme « pièges » des molécules toxiques. Importance de la membrane Removal of about 75 % of CP and 80% 4-Keto CP
	• Potentialité de couplage NF ou RO, mais quid des « concentrats » ? Oxydation couplée? Analyses of other metabolites are in progress.
	27/27

claire.

Cytotoxicité surnageant / permeat

Formation d'un deuxième pic autour de 1-2 µm de diamètre moyen de particules, plus proéminent pour le MBR1 que pour le MBR2.

R1 + CP R2 Contrôle

Cp + métab = Fragilisation des flocs


Edgardo-D Carosella

Hugues Chabot
email: hugues.chabot@univ-lyon1.fr

The Academy's best kept secrets

In 1976, under the impetus of its perpetual secretary Paul Germain, the French Academy of sciences undertook a profound reform of its statutes, which then dated back to 1816, the year of their previous revision. Among the specialized committees created on this occasion, a commission was set up to assess the sealed notes that had never been asked to be opened, either by their authors or their families, and that were more than one hundred years old. The innovation implemented the right established by a regulation of 1860 to open, publish, preserve, or even destroy (!) unclaimed deposits. By the end of the 1980s, all the sealed notes dating from before 1870 had been opened (about 5,000 of them). Pierre Costabel devoted a regular column to a few of them in La Vie des sciences, the Academy's publication for the dissemination of scientific knowledge. In the updated academy regulations from 2003, the procedure for depositing sealed notes remains in place, as does the role of the commission in charge of examining them, including the out-of-date materials. Today, the biennial meeting of the sealed notes commission is the occasion to open between 200 and 400 envelopes deposited at the Academy over a century ago.

The present book is a collective work by the current commission, composed of two mathematicians, three physicists, two chemists, two physicians, a palaeontologist and a historian and philosopher of science (Claude Debru). The project has been coordinated by the Academy's librarian-archivist Christine Foulcher. From the Academy's point of view, the sample of examples gathered here should serve to promote the mission of the Academy, by preserving the memory of the institution's science. The approach offers a representation of the history of science through the prism of the contemporary disciplinary affiliation of the members of the commission. The reasons for the choice of the materials selected are not explicit, but the classification that is used suggests a form of sentimental history of science -a "peculiar and original" history, as we can read on the back cover -aimed at a wider, albeit scientifically informed, public. Actually, the four themes are listed as follows: touching sealed notes, outstanding sealed notes, quaint sealed notes, sealed notes reflecting a period. The 21 subsequent contributions have no other ambition than to draw attention to remarkable pieces, without aiming to establish any kind of historiographical overview. Echoing the work of evaluation assigned to the members of the sealed envelopes commission, these different texts are very brief retrospective analyses of the scientific content of some of the most astonishing notes entrusted to the secrecy of the Academy over the course of nearly three centuries.

It is not surprising to come across the famous names of Buffon, Lavoisier, Ampère, and Pasteur, whose sealed notes precede a formal publication by a few weeks or a few months. These authors used this method to ensure the priority of a discovery or an idea, the main motivation for resorting to the procedure of depositing these secret notes with the Academy. In addition to those of these leading French scientists, many of the sealed notes mentioned are already well known to historians (for example, Scott de Martinville's note on the recording of the human voice, or Jackson on a method of anaesthesia, or Joliot-Curie on nuclear chain reactions, or those of the pioneers of photography in France). Some have been the subject of significant publications in the history of science (for example, the discovery some twenty years ago by Bernard Bru of a major contribution to the theory of probability by the mathematician Döblin, who died at the age of 25). More unexpectedly, a sealed note deposited by Poincaré in 1883 was (re)discovered very recently by Étienne Ghys, who here puts it into context and describes its limits. Finally, three texts that address this historical material from a thematic point of view are worth mentioning. Jean-Paul Poirier and Robert Guillaumont have unearthed about thirty sealed notes related to the (false) discovery of N rays at the very beginning of the twentieth century, and they draw up a chronological list that is somewhat frustrating for the reader. In this particular case, there would have been a good opportunity to study the role played by the sealed notes procedure in the publication strategy of the researchers involved in this fiasco (which was brilliantly studied by Marie Jo Nye some forty years ago). Similarly, one of the longest contributions of the book reviews some of the 90 sealed envelopes deposited at the Academy during the First World War, but the historical perspective to contextualize these notes is to be found elsewhere, in the proceedings of a recent colloquium on academies at war published under the direction of Claude Debru. Appropriately, in one of the most interesting texts in the book, Debru plays the game of systematically associating sealed envelopes with publications in the Comptes rendus hebdomadaires des séances de l'Académie des sciences, working on a few pages devoted to the impact of phylloxera in France in the last third of the 19th century.

In the introduction of the book, the current president of the sealed notes commission, Edgardo-D. Carosella, provides some partial (if not contradictory) quantitative data, which can be advantageously complemented by a short article published in 1986 in the Revue d'histoire des sciences by Pierre Berthon, the first titular archivist of the Academy appointed in 1960. Notably, the reader will find there an accurate description of the three registers recording the sealed notes from 1735 to 1896, then from 1897 to 1949, and finally from 1950 on, as well as a list of the forty or so sealed envelopes analysed between 1977 and 1983 in the Comptes rendus. In addition, Berthon wrote a study of the sealed notes that can be found in the archives of the Academy (with a detailed analysis of the notes concerning medicine). Moreover, Claude Debru informs us that Pierre Buser, a former president of the sealed notes commission, also wrote, in 2004, an unpublished text entitled "Secrets de l'Académie des sciences, Coup d'oeil sur les plis cachetés", which is also housed in the archives of the Academy.

The procedure of depositing sealed envelopes did not attract great interest until the nineteenth century. While there were barely 300 of them in the period 1735-1792, their total number exceeded 6,000 at the beginning of the twentieth century. In his landmark study on the history of the French Academy of Sciences, Maurice Crosland states that the growth became exponential in the 1820s, reaching a maximum in the middle of the century. Today, the cumulative number of sealed notes is close to 19,000. The magnitude of such a corpus can only fascinate the historian. There is a database, but it is only available at the archives of the Academy, and when it becomes more widely accessible it will surely reveal many more secrets. In an article published in 2013 in the French edition of Scientific American (Pour la Science), Carosella and Buser provide some clues (probably derived from this database) about the authors of the sealed envelopes from 1760 to 1960. For this period, it seems that they counted a whole of 7,000 different authors, and that they encountered among them 1,500 engineers, 1,400 physicians, 1,360 teachers and scientists, 800 members of the Academy, 400 military officers, 280 craftsmen, and so on. The subject definitely deserves further investigation using more explicit quantitative historical methods. Approached correctly, this unique archive can inform a major area of research for the historians of the French Academy of Sciences as for historians of science more generally.


Shirin Enferad

Salvatore Pillitteri

Geoffroy Lumay

Claire Gaiani

Sebastien Kiesgen De Richter

Michaël Marck

Syrym Umbetov

Nicolas Vandewalle

Mathieu Jenny

Shirin Enferard

Powder flow behavior governed by the surface properties of glass beads

Keywords: Flowability, glass bead, hydrophobic formulation, humid control 1

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Powders are omnipresent in our daily life and they are extensively used in various industries such as pharmaceutical, cosmetics, chemical, food and construction. Despite numerous studies on powder rheology [START_REF] Guerin | Rheological characterization of pharmaceutical powders using tap testing, shear cell and mercury porosimeter[END_REF][START_REF] Xiang | Effect of Fuller-fine sand on rheological, drying shrinkage, and microstructural properties of metakaolin-based geopolymer grouting materials[END_REF][START_REF] Grabowski | Nutritional and rheological characterization Journal Pre-proof of spray dried sweetpotato powder[END_REF][START_REF] Coussot | Rheometry of pastes, suspensions, and powders: applications in industry and environment[END_REF][START_REF] Salameh | Physico-chemical and rheological properties of Lebanese kishk powder, a dried fermented milk-cereal mixture[END_REF][START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF][START_REF] Shah | Influence of particle properties on powder bulk behaviour and processability[END_REF] their behavior is not fully understood, due to their complexity.

In fact, the flow behavior of a powder depends on many factors including surface properties, size, shape of particles [START_REF] Castellanos | The relationship between attractive interparticle forces and bulk behavior in dry and uncharged fine powders[END_REF] and environmental conditions such as humidity [START_REF] Stoklosa | Effects of storage conditions, formulation, and particle size on moisture sorption and flowability of powders: A study of deliquescent ingredient blends[END_REF]. However, understanding the powder's flowability is one the most important objectives in powder industries. Indeed, it can allow them to anticipate the powder's characteristics by knowing the condition that they encounter during process. In order to identify the pertinent parameters governing the powder's flow, using different test methods that represent the state of stress and strain rate of interest is very important. These methods can provide different points of view and indices to assess powder flowability with several mechanical and dynamical conditions that have been explained in the following.

It is known that the Hausner ratio is an efficient and rapid method to estimate the powder behavior based on bulk density [START_REF]European pharmacopoeia 7.0[END_REF], Hausner ratio correlated to the ratio between settled bulk density and tapped bulk density. It has been reported that low compressible powders have the best flowability [START_REF] Carr | Evaluating flow properties of solids[END_REF]. Similarly, a study on copper powder indicated that the Hausner ratio can be representative of friction condition between particles [START_REF] Hausner | Friction conditions in a mass of metal powder[END_REF].

Apparition of powder electrostatic charges as a result of particle-particle interaction and powders interaction with manipulating equipment during powder process is a know phenomena in industries. In addition, depending on the different surface chemical formulation of powders, the electrostatic charge can increase or decrease which impacts the powder bulk behavior [START_REF] Wang | Molecular surface functionalization to enhance the power output of triboelectric nanogenerators[END_REF][START_REF] Fulchini | Relationship between surface area coverage of flow-aids and flowability of cohesive particles[END_REF].

Whereby, an increase in powder electrostatic charge can lower its flowability [START_REF] Rescaglio | Combined effect of moisture and electrostatic charges on powder flow[END_REF][START_REF] Mersch | Effect of an electric field Journal Pre-proof on an intermittent granular flow[END_REF]. Powder characterization based on their electrostatic charge is of great interest [START_REF] Da | Fabrication of 3d objects via electrostatic powder deposition[END_REF][START_REF] Stichel | Electrophotographic multi-material powder deposition for additive manufacturing[END_REF][START_REF] Zafar | Evaluation of a new dispersion technique for assessing triboelectric charging of powders[END_REF].

Moreover, rotating drum is a method to characterize the macroscopic properties of powders under aeration condition, it fluidizes the powder and reports evolution of cohesion under rotation [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF]; this technique measures powder flow at high shear rate condition. Furthermore, one of the most used methods in industry is applying vibration during process. This technique optimizes powder flowability consequently enhances saving energy. In addition, this method is convenient to control the different steps of industrial process consisting of feeding, conveying and even parts of the equipment such as hopper, etc [START_REF] Sloot | Theoretical and experimental study of the transport of powders by inclined vibratory conveyors[END_REF][START_REF] Gaudel | Bulk and local rheology in a dense and vibrated granular suspension[END_REF]. The mentioned technique has been studied recently by implementing a rheometer attached to a shaker [START_REF] Gaudel | Bulk and local rheology in a dense and vibrated granular suspension[END_REF]. Based on vibrational rheology, the powder flow can be assessed at low shear rate condition.

On the other side, studying and understanding the influence of environmental condition like as humidity on powder behavior is very significant and of great interest. A large number of theoretical and experimental studies in the literature are devoted to figuring out the link between air humidity and powder flow behavior [START_REF] Lumay | Effect of relative air humidity on the flowability of lactose powders[END_REF][START_REF] Vandewalle | How relative humidity affects random packing experiments[END_REF][START_REF] Fiscina | The compaction dynamics of wet granular assemblies[END_REF][START_REF] Colbert | Identification of inter-particular forces by atomic force microscopy and how they relate to powder rheological properties measured in shearing tests[END_REF][START_REF] Forsyth | Effect of cohesive interparticle force on the flow characteristics of granular material[END_REF][START_REF] Jones | Adhesion forces between glass and silicon surfaces in air studied by AFM: Effects of relative humidity, particle size, roughness, and surface treatment[END_REF][START_REF] Landi | Flow properties of moisturized powders in a Couette fluidized bed rheometer[END_REF][START_REF] Landi | Modelling and experiments on the effect of air humidity on the flow properties of glass powders[END_REF][START_REF] Teunou | Effect of relative humidity and temperature on food powder flowability[END_REF]. A decrease in flowability with increasing relative air humidity has been reported for granular material [START_REF] Forsyth | Effect of cohesive interparticle force on the flow characteristics of granular material[END_REF][START_REF] Jones | Adhesion forces between glass and silicon surfaces in air studied by AFM: Effects of relative humidity, particle size, roughness, and surface treatment[END_REF][START_REF] Landi | Modelling and experiments on the effect of air humidity on the flow properties of glass powders[END_REF] and food powders [START_REF] Colbert | Identification of inter-particular forces by atomic force microscopy and how they relate to powder rheological properties measured in shearing tests[END_REF][START_REF] Teunou | Effect of relative humidity and temperature on food powder flowability[END_REF]. This paper focuses on studying the influence of surface treatment on powder flowability Journal Pre-proof and sensitivity of powder flowability to the external condition. Therefore, first in section III.A, the influence of surface treatment on the behavior of raw and hydrophobic glass beads has been studied in ambient temperature without humid control. Different methods utilised to figuring out the macroscopic flow and the rheology of powders under different processing dynamics. Then in section III.B, the influence of humidity on powder behavior has been studied. In this case, two different methods of humid control and powder rheology utilized to characterize the powders and finally their results have been compared.

First, the humid control was done inside a rotating drum with humid-air controlled flow.

The powders were kept for 1 h in each selected humid range.

A second experiment with a different humid control method was conducted at the same time, in order to compare and to link the dependency of the humidity on the shear rate with the electrostatic charge of powders and their cohesion.

In this case, the powders were kept in a humid chamber for 72 h at 20°C in a given humidity ranging from 35 % up to 90 % RH. The humid control time kept long enough to be sure that the powders took enough humidity at each humid value and at the end of humid control the humidity value of powders were confirmed by TH200 thermoconstanter. Then the rheology of powders was performed in a dry room in ambient temperature during maximum 30 min of measurement. The apparent viscosity of powders has been measured with Discovery HR3-Rheometer. The rheometer was attached to a shaker in order to ensure a reproducible packing state and collect data at low shear rate condition. All results have been collected by imposing shear stress.

Materials and Methods

In the following, the implemented materials and the different methods for characterizing powders have been explained. The purpose of using different methods is to characterize powders under

Powders preparation and conditioning

In this study, glass beads of type S 90-150 m  have been used. Hydrophobic surface treatment has been done on the glass beads. With the purpose of preparing hydrophobic surface treatment on the glass beads [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF][START_REF] Kutelova | Functionalization and surface modification of spherical glass beads, 7th International Conference for Conveying and Handling of Particulate Solids[END_REF], first the hydrophilic surface treatment has been prepared. The hydrophilic treatment [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF] was achieved with a 3:1 mixture of sulfuric acid and hydrogen peroxide. First, 50 g of glass beads was put in a beaker and immersed in sulfuric acid then hydrogen peroxide was gently added. The mixture was kept 4 h at ambient temperature (20°C) under extractor hood. After that, the glass beads was washed with distilled water then silanization protocol has been followed.

The silanization of glass beads with mixture of toluene (500 mL) and 1H,1H,2H,2H-perfluorooctyltriethoxysilane (2.5 g) has been performed; this mixture has been kept maximum 72 h under extractor hood at ambient temperature and then the powder was filtered and washed with pure toluene and finally was kept about 72 h under extractor hood for evaporating the toluene inside the powder. At the last, with the purpose of completely dry the powder, it was kept in an oven, maximum 4 h at 70°C.

By performing contact angle measurement, the wetting behavior of hydrophobic glass beads has been measured to verify whether the surface of glass beads was chemically modified. A mono-layer of hydrophobic glass beads has been prepared on a microscope slide then a droplet of water has been put over the sample. The contact angle has been measured based on taken images from sample and five replicates were performed for each sample, under ambient conditions. The Journal Pre-proof contact angle for hydrophobic glass beads was 142° ± 3°. This value was larger than 90° which is a confirmation of hydrophobic surface formulation.

GranuDrum/Rheometer

The GranuDrum is one of the most extensively used practical geometry to study the flow behavior of granular material [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF][START_REF] Taberlet | S shape of a granular pile in a rotating drum[END_REF][START_REF] Liu | Experimental study of the lower and upper angles of repose of powders in rotating drums[END_REF][START_REF] Rajchenbach | Flow in powders: From discrete avalanches to continuous regime[END_REF]; especially non cohesive powders [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF]. GranuDrum evaluates the flow properties of powders in a free flowing regime and the only applied stress on the powders is due to their own weight [START_REF] Hausner | Friction conditions in a mass of metal powder[END_REF][START_REF] Chikosha | Chikwanda Effect of particle morphology and size on roll compaction of Ti-based powders[END_REF]. The experimental set up in this study presented in Figure 1, consists of a drum with two glass walls which rotates around its central axis with the angular velocity  . The flowing dynamics of powders inside the drum is function of this rotating angular velocity. The drum is generally half-filled with the powder whereas the length and the diameter of the drum are respectively 20 mm and 84 mm. During rotation, the drum is back lighted by using a stroboscope and a CCD camera takes pictures of powder-air interface position inside drum. For each imposed angular velocity, 50 pictures are taken, separated by 0.5 s. After monitoring the flow of powders via a camera then the images are processed by using image-processing algorithm. In the images, the granular material appears in black and the air appears in white, whereby an edge detection determines the position of the powder-air interface. From this analysis, two measurements are extracted: the average interface position and the fluctuations around this average position. Both of these measurements are calculated according to the average of 50 pictures that have been taken from powder-air interface inside rotating drum in each imposed angular velocity. Based on the average interface position, the flowing angle f  is measured in the center of the flow which is the angle between the horizontal and the average interface. Also, the standard deviation calculated from the fluctuations of the powder-air interface, this parameter is called cohesive index f  and is directly linked to the cohesion inside drum. In fact, in the range of considered rotating speed, the cohesive granular material leads to irregular flow and non-cohesive granular material leads to a continuous flow. In this study, the rotating angular velocity has been selected between 2-30 rpm.

GranuPack

Measuring the tapped density and packing dynamic of powders is very popular in powder

Journal Pre-proof characterization [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF][START_REF]European pharmacopoeia 7.0[END_REF]. The GranuPack equipment presented in Figure 2

GranuCharge

Electrostatic charges are created due to the triboelectric effect inside a powder during a flow; meaning that the particles exchange charge at the result of contact with the other particles and Journal Pre-proof devices wall. Figure 3 illustrates GranuCharge equipment, it is a very useful equipment to measure the ability of a flowing powder to be charged electrostatically. It measures electrostatic charge of the powders by putting them in motion under the influence of gravity. In this measurement, the experimental set up consists of three parts: a stainless-steel pipe, a V-tube and a Faraday cup. The stainless-steel pipe is for feeding the V-tube by automatic rotation inside the tube.

In general, the material of the V-tube can be selected in the following list: stainless steel 316 L, aluminum 6063-T6, borosilicate glass, ABS, PVC and HDPE. The Stainless Steel 316 L was used in this study. The V-tube itself consists of two tubes with the length of L = 350 mm and diameter D = 47 mm; the two parts are connected together with the angle of 90°. After feeding the tube by a stainless-steel pipe the powders flow inside V-tube and at the end they fall into a faraday cup which is connected to an electrometer to measure the powders charge obtained during flow.

Before starting each test, the whole assembly has been connected to the earth to be sure that they are discharged. The electrometer is capable of measuring charge ranging 0.1 nC -1 µC. The powder charge density is computed by dividing calculated charge by the mass of powder. The charge density unit is Coulomb per kilogram. The powders can obtain negative or positive charge after flow, based on their tendency to obtain or lose electron [START_REF] Rescaglio | Combined effect of moisture and electrostatic charges on powder flow[END_REF].

Discovery HR3-Rheometer

The rheology of powders subject to vibration has been studied in this paper as well. With this objective, the Discovery HR3-rheometer has been implemented (see Figure 4). The implemented geometry in this study is a cylindrical baffle cell (radius = 25 mm, baffle height = 8.5 mm) with a four blades vane (radius = 7.5 mm, length = 51 mm). Only 21 mm of vane height has been immersed inside the powder. Indeed, in the case of immersing the whole vane inside the powder, the torque applied to shear the powder sample exceeds the limit of the apparatus. The utilized cell is similar to the cylindrical couette cell with the annular gap = 10 mm. The characterization cell is attached to a shaker at the bottom with the computer controlled sinusoidal transmitted vibration in close-loop system; detailed information can be found in [START_REF] Ph | Rheology of dense-phase vibrated powders and molecular analogies[END_REF][START_REF] Hanotin | Vibration-induced liquefaction of granular suspensions[END_REF]. The mechanical vibrational stress corresponds to the sample vibrational energy which is defined as

  = (1/2) 22 (2 )
Af , where  is the powder density, A is the vibration amplitude and f is the vibration frequency. The frequency and amplitude of vibration which has been used in this study is 60 Hz and 100 µm, Journal Pre-proof respectively. Pre-vibration has been applied at 70 Hz during 10 min for removing any packing history before each measurement. The volume fraction of glass beads is glass   0.61 [45, 21] (

Humid control

In this stage, the measurements were performed first with the GranuDrum and the GranuCharge with the objective of studying effect of humidity. The powder was placed in a rotating drum at 1 rpm with a controlled humid air flow during 1 h. As the powder was continuously mixed under drum rotation, the humidity absorption is assumed to be sufficient to observe changes in powder behavior. With this method, the accessible range for humidity is RH = 35 95%  5%  inside the drum.

On the other side, another methodology has been utilized for the humid control of powders.

In this case, the powder has been kept in a humid chamber longer to ensure absorption of enough humidity. With this purpose, the sufficient range of humid control time has been reported to be two days as minimum and one week as maximum storage time in a humid chamber for glass beads [START_REF] Oger | Effect of grain size and material on humid granular avalanche events[END_REF][START_REF] Oger | Dynamic behavior of humid granular avalanches: Optical measurements to characterize the precursor activity[END_REF]. According to the literature the powder behavior has the same trend in both storage times.

Therefore, here in our study each powder sample has been kept 72 h in a humid chamber and the range of imposed humid value was between 35 % up to 90 % at 20°C. The relative humidity of powders has been confirmed by using TH200 thermoconstanter(Novasina, Switzerland) at a temperature of 25°C; after taking them from the humid chamber. This apparatus has a measuring range comprised between 0.05 to 1.00 and an accuracy of ± 0.01 over a temperature range between 0 and 50°C. More precisely, 1 g sample is introduced into a polypropylene cup deposited in the sealed enclosure of the apparatus. The free water moistens or dries the air inside the enclosure until the balance is reached. The relative humidity has been measured using an electrolytic sensor. After humid control then the powder characterization has been done by Discovery HR3-Rheometer under vibration.

Results

Journal Pre-proof

Influence of surface treatment 3.1.1. Flowability

In the literature, a vast body of researches conducted to study the powder flow behavior by different shear cell tests [START_REF] Angus | Calibrating friction coefficients in discrete element method simulations with shear-cell experiments[END_REF][START_REF] Lupo | Assessment of a powder rheometer equipped with a cylindrical impeller for the measurement of powder flow properties at low consolidation[END_REF][START_REF] Yahia | Development of a virtual Couette rheometer for aerated granular material[END_REF][START_REF] Saleh | Dust generation from powders: A characterization test based on stirred fluidization[END_REF][START_REF] Tomasetta | The measurement of powder flow properties with a mechanically stirred aerated bed[END_REF][START_REF] Francia | From Quasi-static to Intermediate Regimes in Shear Cell Devices: Theory and Characterisation[END_REF]. In our previous study we studied flowability of raw and hydrophobic glass beads with shear cell [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF]. For this measurement, FT4 powder rheometer was utilized to evaluate powder flow at high shear rate by rotating shear head. In this measurement, first the powder was preconsolidated at 9 kPa normal stress. Then, decreasing normal stresses from 7 to 3 kPa by 1 kPa steps were successively applied and the shear stresses ( ) (s) required to make the powder flow (i.e. to induce preconsolidated powder bed failure) were recorded. (see Figure 5). In our measurements, the yield locus presented the same values for both powders over the entire range of normal stress showing similar flow behavior in raw and hydrophobic glass beads.

In addition, the flowing factor ff characterizes powder flowability in this measurement.

This factor is calculated by yield locus approach of software, whereby major principal stress According to the Jenike classification [START_REF] Jenike | Storage and flow of solids[END_REF], powders are considered as not flowing for < ff 1, very cohesive for 1 << ff 2, cohesive for 2 << ff 4, easy-flowing for 4 << ff 10 and free-flowing for > ff 10. Therefore, based on this criteria our powders fall into category of free-flowing powders with the same flowability at high shear rate condition.

Charge

The electrostatic charge measurement of raw and hydrophobic glass beads has been performed

with the GranuCharge equipment with the humidity and temperature range at 37-44 % and 22°C, respectively. Figure 6 represents the results corresponding to this test. Three values have been collected for each sample. These values include initial charge q 0 , final charge q f and  q = q f -q 0 .

The initial charge was measured before performing the test by directly introducing the powder inside Faraday cup and final charge is a measurement after powder flow through the V-tube. The obtained results show that both powders had almost zero initial electrostatic charge. After flow Journal Pre-proof inside stainless steel V-tube, the raw glass beads kept this tendency for having almost zero charge however hydrophobic glass beads obtained a negative charge. The quantity of each sample was 50 mL during measurement.

Cohesion

Figure 7 shows the evolution of the cohesion f  and the flowing angle f  of raw and hydrophobic glass beads. It has been observed that cohesion of both samples have been enhanced by increasing the rotating speed of the drum, meaning that their flowability decreases under motion, particularly after 10 rpm. Hydrophobic glass beads showed slightly more cohesion than raw glass beads. This could be explained by the GranuCharge measurements where hydrophobic glass beads presented more electrostatic charge than raw glass beads. This can lead to higher cohesion of hydrophobic glass beads under motion (see Figure 6).

Packing dynamics

The compaction curves of raw and hydrophobic glass beads have been recorded with the GranuPack in standard conditions of temperature and pressure and they have been presented in Figure 8. One observes the difference of density between two powders at the beginning and at the end of the compaction process. In addition, Figure 9 presents the Hausner ratio r H where the packing density before tapping 0  , after 500 tap 500  and the asymptotic packing fraction after an infinite number of tap   obtained from the equation (1). One observes a slightly higher Hausner ratio for the hydrophobic glass beads than for the raw glass beads. This can be related to the cohesion since high Hausner ratio generally corresponds to poor flowability and therefore high cohesion. Also, the slight density difference of powders can be due to the different rearrangements of particles during measurement.

Impact of humidity

Influence of humidity on flowability of raw and hydrophobic glass beads has been studied. Indeed, it has been reported that humidity can change the charging of a powder [START_REF] Rescaglio | Combined effect of moisture and electrostatic charges on powder flow[END_REF] whereby it can induce variation of cohesion and consequently it modifies powder flowability. We implemented GranuDrum with the speed of 4 rpm at standard conditions and GranuCharge equipments to Journal Pre-proof measure powders cohesion and electrostatic charge under influence of humidity. Here, the humid control has been done with a rotating drum with humid-air controlled flow. The powders have been kept shortly 1 h in each selected humid range, the accessible range for humidity is RH = 35 95% 5%  inside the drum.

Figure 10 shows evolution of the cohesive index of raw and hydrophobic glass beads inside GranuDrum after humid control. The cohesive index of raw glass beads has been increased after 80 % RH which shows high sensitivity of raw glass beads to the humidity after this value of humidity. However, the cohesive index of hydrophobic glass beads had almost constant value in all range of humid control, showing less sensitivity of this powder to the humidity. In addition, based on Figure 11, we have seen that control glass beads have almost zero electrostatic charges in all ranges of humid control. While the electrostatic charge of hydrophobic glass beads decreased by increasing the humidity up to 80 % of humidity and after this range of humidity hydrophobic glass beads lost their electrostatic charge completely. Therefore, we have observed that the powder cohesion and electrostatic charge can evolve by humidity in spite of short humid control time. As a complementary test, the evolution of viscosity of our two formulations have been considered with Discovery HR3-Rheometer Discovery at low shear rate condition (Figure 4). In this case, the powders humidity has been controlled longer during 72 h before each measurement in a humid chamber; then the rheological measurements have been done in an experimental room in ambient temperature and the humidity of room was not controlled during measurements. Based on viscosity curves, the hydrophobic glass beads presented higher viscosity than raw glass beads. This can be due to the fact that hydrophobic glass beads presented more electrostatic charge than raw glass beads in the humid range of 35-80 % (see Figure 11). In addition, the viscosity curve of hydrophobic glass beads stayed always constant even after 80 % of humidity. This is due to the tendency of hydrophobic glass beads to repel water even at 90 % of humidity. By taking into account that the rheological measurements have been done in a dry room, then a slight amount of presented water in high humidity range on hydrophobic glass beads surface evaporated rapidly due to the tendency of this powder to repel the water. The rheological measurement time was between 20-30 min which was enough for evaporating the slight surface water and getting the powder recharged again. It should be indicated that the charge measurement Journal Pre-proof time in Figure 11 which has been done with GranuCharge was a few seconds, meaning that the powders did not have enough time to recharge.

In general, raw glass beads showed lower viscosity than the hydrophobic glass beads which can be due to the lower electrostatic charge of raw glass beads compared to hydrophobic glass beads. However, after 80 % of humidity the viscosity of raw glass increased dramatically which is due to the sensitivity of raw glass beads to humidity that resulted in high cohesion. In addition, this increasing shift of viscosity of raw glass beads can be due to the condensation effect, however for the hydrophobic glass beads the viscosity was constant throughout the same range of humidity. It indicates that performing hydrophobic surface treatment on glass beads decreases the sensitivity of glass beads to the humidity therefore the viscosity of hydrophobic glass beads stayed constant in all range of humidity. In order to check the stability of hydrophobic surface formulation on glass beads, the contact angle measurement performed at the end of measurements performed by Discovery HR3-rheometer (the longest test in this paper). Hydrophobic glass beads presented the same water contact angle than before performing any test.

Discussion

The FT4 shear cell test results from our previous study [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF] reported the same flowability for raw and hydrophobic glass beads at high shear rate condition. Whereby, these two powders classified as easy flowing powders based on Jenike classification [START_REF] Jenike | Storage and flow of solids[END_REF]. These results are in agreement with the similar study performed on raw glass beads by modified shear apparatus [START_REF] Pierrat | Effect of moisture on the yield locus of granular materials: theory of shift[END_REF], where dry raw glass beads recorded as no cohesive powder. In addition, they reported that the value of consolidation stress during measurement had no significant influence on the shear data [START_REF] Yahia | Development of a virtual Couette rheometer for aerated granular material[END_REF][START_REF] Pierrat | Effect of moisture on the yield locus of granular materials: theory of shift[END_REF].

According to the literature, the powder flowability was expected to increases when increasing particle size [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF][START_REF] Kk | Influence of particle size on the adhesion behaviour of powders, after application of an initial press-on force[END_REF][START_REF] Enferad | Compactage et vieillissement des poudres: influence de la formulation[END_REF]. In fact, surface area to volume ratio decreases with increasing size which results in better flowability of large size powders.

In addition, based on GranuPack results one observes a small difference in cohesion between the two powders which is also observed with the Hausner ratio. Indeed a high Hausner ratio generally corresponds to a high cohesion. However this difference was not significant enough to observe a change in flowability as showed in Figure 5. It should be mentioned that slightly higher value of the density in hydrophobic glass beads can be due to the different rearrangements Journal Pre-proof of particles in this case.

According to the GranuDrum measurement, the powders cohesion was increasing by increasing speed of drum. This can be due to an internal effect such as more electrostatic charge exchange because of more contact time of particles inside drum. To verify this hypothesis the cohesion measurement has been done with GranuDrum at the speed of 30 rpm with two different conditioning rotating times: 15 sec as short rotating time and 30 min as long rotating time. The measurement has been performed as usual with 50 pictures separated by 0.5 s. As illustrated in Figure 13, it has been observed that the value of cohesion is higher when the rotating time is longer (30 min). As explained already, this is due to the more charge exchange coming from more contact time, which it results in increasing electrostatic charge.

Discovery HR3-rheometer collected the data corresponding to vibrational rheology of powders after humid control. It has been observed that hydrophobic glass beads have higher viscosity than raw glass beads, which is consistent with the observations of the cohesion and the Hausner ratio. It has been reported that silanization (hydrophobic surface formulation) increases powder electrostatic charge [START_REF] Biegaj | Surface chemistry and humidity in powder electrostatics: A comparative study between tribocharging and corona discharge[END_REF] and consequently cohesion [START_REF] Hassanpour | Characterisation of flowability of loosely compacted cohesive powders by indentation[END_REF]. Here, hydrophobic glass beads presented more electrostatic charge than raw glass beads before applying vibration, therefore applying vibration induced building up more electrostatic charge consequently higher viscosity has been recorded for hydrophobic glass beads. Based on literature, the particle electrostatic charge is in inverse relation with particles size, whereby by decreasing particles size the electrostatic charge per unit area increases which is due to the more specific surface area in small size particles compared to large particles [START_REF] Zafar | Evaluation of a new dispersion technique for assessing triboelectric charging of powders[END_REF]. Furthermore, according to the collected data with Discovery HR3-rheometer, we have seen that hydrophobic treatment decreases sensitivity of glass beads to the humidity since after 80% of humidity raw glass beads presented an impressive increase in the viscosity while viscosity of hydrophobic surface treated glass beads had almost constant value from the beginning up to end of humid control. This tendency of hydrophobic glass beads has been recorded with AFM measurement on single hydrophobic glass beads over the same range of humidity in the literature [START_REF] Jones | Adhesion forces between glass and silicon surfaces in air studied by AFM: Effects of relative humidity, particle size, roughness, and surface treatment[END_REF]. In our case, we collected the bulk behavior of hydrophobic glass beads over large relative humidity range which confirms the last findings on single hydrophobic glass beads [START_REF] Jones | Adhesion forces between glass and silicon surfaces in air studied by AFM: Effects of relative humidity, particle size, roughness, and surface treatment[END_REF]. In addition, it should be indicated that based on literature was found that there is a critical relative humidity at which the raw glass beads undergoes a transition from free-flowing to stick-slip behavior [START_REF] Forsyth | Effect of cohesive interparticle force on the flow characteristics of granular material[END_REF]. In our study, this critical value of humidity seems to be Journal Pre-proof after 70% of relative humidity where raw glass beads presented a viscosity shift, this value is in agreement with the literature. In addition, this critical humidity increases with increasing particle size [START_REF] Forsyth | Effect of cohesive interparticle force on the flow characteristics of granular material[END_REF]. At the end of measurements performed by Discovery HR3-rheometer (the most longest test in this paper) the contact angle measurement performed on hydrophobic glass beads with the objective of checking the stability of hydrophobic surface formulation on glass beads.

Hydrophobic glass beads presented the same water contact angle than before performing any test.

In the following the collected raw data from different set of measurements have been presented in table 1.

Conclusion

This paper presented a study on flow behavior of raw and hydrophobic surface formulated glass Journal Pre-proof meaning that the friction between particle-particle governs the power flowability. Since raw and hydrophobic glass beads had similar surface properties therefore similar flowability has been recorded for them at frictional regime; however at low shear rate condition the flowability of powders are linked to their surface cohesion where the hydrophobic glass beads with more surface cohesion (due to the electrostatic charge) presented high viscosity. Furthermore, it has observed that by doing hydrophobic treatment on raw glass beads the sensitivity of powder to the humidity decreases, whereby even at high range of humidity it kept its flowability as in low humidity range.

However, raw glass beads lost their flowability dramatically at higher value of humidity.

Figure 1: Sketch of the GranuDrum equipment [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF]. A cylinder is half-filled with the powder and rotates around its axis. For each rotating speed, a CCD camera takes 50 successive images of the flow. A dedicated algorithm enables to measure the flowing angle f  and the fluctuations f  of the flow from the shape of the powder-air interface.

Figure 2: Sketch of the GranuPack equipment [START_REF] Lumay | Measuring the flowing properties of powders and grains[END_REF]. The powder is placed in a metallic tube and a light hollow cylinder is placed on the top of the pile to keep it flat during the compaction process.

The taps correspond to successive free falls of the tube over a distance  Z. After each tap, the height h of the pile is measured. Finally, a compaction curve is obtained. Figure 5: Flow parameters derived from shear cell test for raw and hydrophobic glass beads [START_REF] Enferad | Effect of particle size and formulation on powder rheology[END_REF].

Each test has been repeated three times and the measurements have been done in ambient temperature. Error bars represent standard errors; they are not visible as their size are inferior to the marker size.

Figure 6: Evolution of the electrostatic charge of raw and hydrophobic glass beads. 0 q is initial electrostatic charge before flow, f q is the final electrostatic charge after powder flow inside V-tube and  q is the difference between the initial and the final charge. Error bars represent standard errors (corresponding to three repeated measurements); some were not visible as their size was inferior to the marker size. The measurement performed by the GranuCharge equipment.

The humidity and temperature range are 37-44 % and 22°C, respectively. Journal Pre-proof

  different processing dynamics and to observe the influence of treatment and mainly the effect of humidity on powders flowability. Therefore, two series of tests have been performed on raw and hydrophobic glass beads. First, the characterization measurements have been done by implementing the Granutools equipments. The packing dynamics of powders has been measured with the GranuPack, the powder electrostatics charge studied with the GranuCharge and the Journal Pre-proof powder flowability and cohesion measured with GranuDrum equipment. During performing measurements with the Granutools equipments, the humidity and temperature were kept constant at 37-44 % RH and 22°C, respectively. All Granutools measurements have been repeated three times.Then the study of influence of wide range of humidity has been done on powders with the GranuDrum and the GranuCharge. These results have been confronted with the measurements of the powder behavior (after longer humid control) under vibrational rheology with Discovery HR3-Rheometer which provides possibility of powder flow at low shear rate where the cohesion of powders play a role in their flowability. The goal here was to observe clearly the effect of humidity on powders behaviors based on the strength of their surface cohesion depending on their surface treatment.

  developed to automate the procedure since it is usually realized with naked eyes. The analyzing cell is made of a tube of = 26 D mm in diameter and = 150 L mm in length. This tube is metallic to avoid the accumulation of electrostatic charges during measurement. A narrower and bottomless tube ( inserted into this measurement tube and filled with the powder to analyze. Afterward, it is slowly removed upward at the velocity =1 v mm/s. This initialization procedure avoids human intervention and then increases the reproducibility. A light hollow cylinder is placed on the top of the pile to keep it flat during the compaction process. The tube goes up and down over a height of =3 z  mm with the frequency = 1000 f ms in order to compact the granular pile. A distance sensor measures position of the hollow cylinder after each tap and computes the bulk volume V of the pile. As the introduced mass of powder is known, then the evolution of bulk density of powder b  has been calculated as a function of tap number t . The bulk density is the ratio between mass m and volume V of the powder. The packing fraction  is calculated by dividing bulk density b  by the true density of particles t  . After recording packing fraction for each tap, compaction curve has been fitted with the classical logarithmic model [39is the number of tapes, the fitting parameters   &  are asymptotic volume fraction and compaction characteristic time, respectively. The asymptotic volume fraction is representative of maximal packing fraction achieved by tapping the powders. With this parameter, one obtains the final packing fraction   consequently the more common parameter, 40, 41]. The Hausner ratio is correlated to the powder flowability whereby high value of Hr corresponds to low flowability.

3 /

 3 kg m ). All tests have been carried out at imposed shear stress with the range of 4.5-188 Pa and the measured shear rate ranged as 3

( 1 

 1 ) and unconfined yield strength ( c  ) dedicated based on yield locus approach ( 1 =/ c ff  ). The flowing factor has been recorded as 19.70 0.81  and 19.74 1.66  for raw and hydrophobic glass beads, respectively.

Figure 12

 12 Figure 12 presents evolution of the viscosity of raw and hydrophobic glass beads as a function of humidity at 35-90 % RH; the figure has been plotted in given shear rate at 51 = 5*10 s 

  beads. The objective was to evaluate the influence of hydrophobic surface treatment on glass beads as well as influence of humidity on flow behavior of raw and hydrophobic glass beads. With this objective, we considered our powders flow behavior under different processing dynamics to collect the essential factors and indices describing the behavior of a powder. Based on shear cell measurement, the powders reported similar flowability. However, GranuCharge measurement presented a charge difference between hydrophobic and raw glass beads. It reported negative charge for hydrophobic glass beads and almost zero charge for raw glass beads which was expected to influence the powders flow behavior. This difference in charge could explain the slight difference in the Hausner ratio and cohesion. This issue has been confirmed with the cohesive index values measured by GranuDrum, the hydrophobic glass beads presented higher cohesion under rotation with GranuDrum which was indicative of decreasing flowability of hydrophobic glass beads under motion due to the tendency of this powder to build up electrostatic charge. In addition, the influence of air humidity on utilized powders has been studied with Discovery HR3-rheometer at low shear rate condition. The obtained results evidenced that under vibrational rheology the hydrophobic glass beads is less flowable than raw glass beads. It was because under vibration the electrostatic charge built up by hydrophobic glass beads that it was resulted in higher viscosity in this power. At high shear rate condition with shear cell test, both powders presented same flowability while at low shear rate condition with HR3-rheometer the raw glass beads showed lower flowability. This is because at high shear rate the powders are in frictional regime

Figure 3 :

 3 Figure 3: Left: Sketch of the GranuCharge which is used to measure the electrostatic charge created inside a powder after flow in contact with a selected material. Right: Picture of the powder

Figure 4 :

 4 Figure 4: (a) Rheometer discovery (b) Schematics of couette type cell connected to shaker [45].

Figure 7 :

 7 Figure 7: Evolution of the flowing angle and cohesion of raw and hydrophobic glass beads under different rotational speed with the measurements performed by GranuDrum. Error bars represent standard errors (corresponding to three repeated measurements); some were not visible as their size was inferior to the marker size. The humidity and temperature range are 37-44 % and 22°C, respectively.

Figure 8 :

 8 Figure 8: Experimental compaction curves for respectively raw glass beads, represented by grey squares, and hydrophobic glass beads, represented by orange dots. Both curves have been fittedwith the logarithmic model (Eq.1), represented by plain curves of the same color, in order to obtain the typical compaction time and the asymptotic packing fraction after an infinite number of tap.The humidity and temperature range are 37-44 % and 22°C, respectively.

Figure 9 :

 9 Figure 9: Comparison between the Hausner ratio

Figure 10 :

 10 Figure 10: Evolution of the cohesive index of raw and hydrophobic glass beads under humid control from 35% to 95% 5%  . Error bars represent standard errors (correspond to three repeat of measurement); some were not visible as their size was inferior to the marker size. Both supplementary points out of the lines represent data from normal environmental conditions.

Figure 11 :

 11 Figure 11: Evolution of the charge difference of raw and hydrophobic glass beads under humid control from 35% to 95% 5% . Error bars represent standard errors (corresponding to three repeated measurements); some were not visible as their size was inferior to the marker size. Both supplementary points out of the lines represent data from normal environmental conditions.

Figure 12 : 51 = 5

 12515 Figure 12: Evolution of the viscosity of raw and hydrophobic glass beads under humid control from 35% to 90%. The measurement has been done with Discovery HR3-rheometer under vibration and the figure has been plotted in a given shear rate

Figure 13 :

 13 Figure 13: Evolution of the cohesive index of raw and hydrophobic glass beads as a function of rotating time in GranuDrum. The rotating speed of drum was 30 rpm, error bars represent standard errors (corresponding to three repeated measurements). The humidity and temperature range are 37-44 % and 22°C, respectively.

Figure 4

 4 Figure 4

Figure 5

 5 Figure 5

Figure 6

 6 Figure 6

Figure 7

 7 Figure 7

Figure 8

 8 Figure 8

Figure 9

 9 Figure 9

Figure 10

 10 Figure 10

Figure 11

 11 Figure 11

Figure 12

 12 Figure 12

Figure 13

 13 Figure 13

Table 1 :

 1 Recapitulation of the different values measured with the set of instruments; the humidity and temperature range are 37-44 % and 22°C, respectively. At high shear rate, raw and hydrophobic glass beads had similar flowability.  At low shear rate, hydrophobic glass beads were less flowable than raw glass beads.  Hydrophobic formulation decreased sensitivity of glass beads to the humidity.  Hydrophobic formulation increased the electrostatic charge of glass beads.

	Measures	Raw glass beads	Hydrophobic glass beads
	ff (-)	19.70 ± 0.81	19.74 ± 1.66
	 q (nC/g)	-0.30 ± 0.01	-4.55 ± 0.12
	 (a.u.) (30 rpm)	10.46 ± 0.21	13.80 ± 0.43
	f
	 (a.u.) (30 rpm)	39.73 ± 0.10	48.13 ± 3.43
	f
	0  (a.u.)	0.58 ± 0.01	0.59 ± 0.01

f  and f  are correspond to the

Figure 7. Highlights 

Acknowledgments -This study is conducted in the framework of the "PowderReg" project, funded by the European program Interreg VA GR within the priority axis 4 "Strengthen the competitiveness and the attractiveness of the Grande Région / Gro  region".

Credit Author Statement

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.