Julien E Bois

Dr Philippe G Sarrazin
email: philippe.sarrazin@ujf-grenoble.fr

Robert J Brustad

David O Trouilloud

François Cury

Role Modelling Behaviours and Perceptions of their Child's Competence

Keywords: children's physical activity, parental socialization, role modelling, perceived competence, parental beliefs, motivation

published or not. The documents may come

Parental influence on physical activity 3

The role of physical activity (PA) in contributing to the physical, psychological, and social health and development of children cannot be underestimated. Research has demonstrated a moderate association between PA levels and physical health variables for children.

Physically active children tend to have lower blood pressure levels and more favourable blood lipid profiles than sedentary children (e.g., [START_REF] Suter | Relationship of physical activity, body fat, diet, and blood lipid profile in youths 10-15 yrs[END_REF]. Moreover, active participation in sport and exercise has beneficial social and psychological effects, such as increased social acceptance (e.g., [START_REF] Weiss | The relationship between physical competence and peer acceptance in the context of children's sports participation[END_REF], and elevated self-esteem and feelings of well-being (e.g., [START_REF] Martinsen | Exercise and mental health in clinical and free living populations[END_REF]. In addition, research suggests that PA levels during childhood could partially predict PA levels in adulthood (e.g., [START_REF] Sallis | Determinants of physical activity and interventions in youth[END_REF]. Therefore, increasing PA during childhood carries with it numerous physical, psychological, and social benefits.

Researchers have initiated attempts to identify the factors that shape children's PA behaviour (e.g., [START_REF] Sallis | Determinants of exercise behavior[END_REF][START_REF] Sallis | Determinants of physical activity and interventions in youth[END_REF]. A complex arrangement of influences seems to be involved, among which several social sources of influence clearly impact children's PA and sport involvement. These include peers, coaches/teachers and parents (see [START_REF] Brustad | Youth in sport: Psychological considerations[END_REF]. As a starting point, socialization within the family (i.e., parents and siblings) should be a fundamental form of influence because the family constitutes an important initial element of socialization influence for children and because the majority of children's free time prior to adolescence is spent within the context of the family [START_REF] Brustad | Integrating socialization influences into the study of children's motivation in sport[END_REF][START_REF] Greendorfer | Sport socialization[END_REF]. Unfortunately, only a limited amount of research has examined how parents influence children's PA behaviour, and some of this research suffers from methodological problems that affect our interpretation of findings.

Several forms of parental influence have been suggested in the literature. The most frequently studied relate to parental role modelling practices and parental belief systems, particularly parental perceptions of children's competence. Role modelling, or children's Parental influence on physical activity 4 vicarious identification with their parents [START_REF] Bandura | Social foundations of thought and action: A social cognitive theory[END_REF], has been proposed as a form of influence whereby children reproduce the behaviours of their parents through observational and social learning processes. Studies that have tested this hypothesis in the PA domain have found mixed results. Some investigations have found a moderate to strong relationship between the PA involvement of parents and their children (e.g., [START_REF] Freedson | Familial aggregation in physical activity[END_REF][START_REF] Moore | Influence of parents' physical activity levels on activity levels of young children[END_REF] whereas other studies have found weak or no relationships between activity levels of parents and children (e.g., [START_REF] Brustad | Who will go out and play? Parental and psychological influences on children's attraction to physical activity[END_REF][START_REF] Dempsey | Parental influence on children's moderate to vigorous physical activity participation: An expectancy-value approach[END_REF][START_REF] Kimiecik | Parental beliefs and children's moderate-to-vigorous physical activity[END_REF]. These discrepant findings may be a function of differences in measures, such as objective indicators, children's perceptions, and parents' self-reports [START_REF] Fredericks | Parental influences on youth involvement in sports[END_REF]). Therefore, it seems important to design studies that use methods that are capable of providing a strong test for the effects of parental role modelling on children's physical activity involvement.

Parental belief systems can also constitute an important form of socialization influence on children's physical activity involvement. The relation between parents' beliefs and children's motivation and achievement has been well established in the educational literature (e.g., [START_REF] Eccles | Motivation to succeed[END_REF]. According to the parental socialization model of Eccles and her colleagues (see [START_REF] Eccles | Motivation to succeed[END_REF][START_REF] Fredericks | Parental influences on youth involvement in sports[END_REF], the beliefs that parents hold for their children influence their patterns of interaction with the child, such as extent of encouragement and the provision of opportunities and experiences that, in turn, affect their children's motivation.

Important components of parental belief systems include parents' perceptions of the child's competencies in various achievement domains, parents' beliefs about the relative value or importance of various achievement domains (e.g., academics, art, music, sport), and parents' expectations that their child will attain success in a given domain. As proposed by Eccles and colleagues (e.g., Eccles, et al.1983;[START_REF] Fredericks | Parental influences on youth involvement in sports[END_REF][START_REF] Wigfield | Expectancy-value theory of achievement motivation[END_REF], parental beliefs about their child's physical competence can shape their children's activity choices indirectly through effects on the children's own perceptions of competence and perceptions about the relative value of various activities.

Given that competence perceptions assume a central role in contemporary theoretical frameworks on motivation (e.g., [START_REF] Bandura | Self-efficacy: The exercise of control[END_REF][START_REF] Harter | The development of competence motivation in the mastery of cognitive and physical skills: Is there a place for joy[END_REF], and as perceived physical competence has been among the most studied self-perception variables for the purpose of understanding individual differences in motivated behaviour [START_REF] Weiss | Self-esteem and perceptions of competence in youth sport: Theory, Research, and enhancement strategies[END_REF], understanding how children form competence perceptions in the physical domain is a primary focus of this study. In extending Eccles' theory to the physical domain, it is anticipated that parents are likely to influence their children's time spent in PA indirectly by shaping children's domain-specific self-perceptions of competence which, in turn, influence children's PA involvement.

Several studies have revealed a correspondence between parents' perceptions of their child's competence and the child's own perceived physical competence (e.g., [START_REF] Babkes | Parental influence on children's cognitive and affective responses to competitive soccer participation[END_REF][START_REF] Mccullagh | Motivation for participation in physical activity: Comparison of parent-child perceived competence and perceived motives[END_REF], even in cases in which actual levels of physical ability were statistically controlled [START_REF] Bois | Mothers' expectancies and young adolescents' perceived physical competence: A year long study[END_REF][START_REF] Felson | The effect of parents on the self-appraisals of children[END_REF]. However, some limitations to these studies have to be acknowledged. To support the presence of a relation between parents' perceptions of their child's competence and the child's perceived physical competence, longitudinal designs, including autoregressive influence, are necessary [START_REF] Maccallum | Applications of structural equation modeling in psychological research[END_REF]. That is, if it is hypothesized that variable A at time 1 (A1; e.g., parent's perception of child's ability) influences variable B at time 2 (B2; e.g., child's selfperception of ability), the child's initial perceived competence (B1) also should be measured and included in the model to understand the relation between B1 on B2 as well as the relation between A1 and B1 [START_REF] Gollob | Interpreting and estimating indirect effects assuming time lags really matter[END_REF]. But much previous work Parental influence on physical activity 6 has been cross-sectional in nature, making causal interpretation problematic, or did not include the autoregressive effect [START_REF] Jacobs | The impact of mothers' gender role stereotypic beliefs on mothers' and children's ability perceptions[END_REF].

Another consideration with previous studies has been that children's perceptions of parental beliefs have been relied upon rather than parents' own self-reports (e.g., [START_REF] Babkes | Parental influence on children's cognitive and affective responses to competitive soccer participation[END_REF][START_REF] Brustad | Attraction to physical activity in urban schoolchildren: Parental socialization and gender influences[END_REF][START_REF] Kimiecik | Relationships among children's beliefs, perceptions of their parents' beliefs and their moderate to vigorous physical activity[END_REF]. An advantage of the traditional approach is that children are likely to act upon their perceptions of their parents' beliefs as they may not effectively interpret their parents' actual beliefs. However, from a measurement standpoint, the reliance on self-reports from single sources can be problematic, in that the associations identified might be due to shared method variance rather than to actual relations involving the construct of interest. In line with that concern, a final limitation pertains to the fact that parental influence often is assessed without distinguishing between the mother's and the father's beliefs (e.g., [START_REF] Brustad | Who will go out and play? Parental and psychological influences on children's attraction to physical activity[END_REF][START_REF] Brustad | Attraction to physical activity in urban schoolchildren: Parental socialization and gender influences[END_REF][START_REF] Dempsey | Parental influence on children's moderate to vigorous physical activity participation: An expectancy-value approach[END_REF]. Fathers and mothers might not share similar appraisals of their child's aptitudes and abilities and it is likely that one parent might be more influential in shaping the child's achievement-related beliefs than the other. Because mothers typically are more fully immersed in the rearing of their children during childhood and early adolescence, mothers' perceptions might be particularly important in shaping children's achievement-related beliefs, even in stereotypically masculine achievement domains such as sport [START_REF] Jacobs | The impact of mothers' gender role stereotypic beliefs on mothers' and children's ability perceptions[END_REF].

The Present Study

The main purpose of this study was to investigate the extent to which parents' PA behaviours and beliefs about their child's physical competence could predict the child's own self-perceptions of competence and the amount of time their child dedicated to physical activity.

Parental influence on physical activity 7 Methodological precautions were taken in order to appropriately examine socialisation processes. As parental socialisation influence needs time to operate, a 12month longitudinal study was conducted with data collected at two points in time.

Structural equation modelling (SEM) was used to determine whether theoretically anticipated relationships existed. SEM, which is particularly useful in longitudinal research [START_REF] Bentler | Multivariate analysis with latent variables: Causal modeling[END_REF][START_REF] Maccallum | Applications of structural equation modeling in psychological research[END_REF], allows for examination of hypothesized relations among all of the constructs involved in a model, using a latent representation of these constructs that is less vulnerable to measurement errors, such as those that can be encountered in research with child populations.

Figure 1 shows the hypothesized model that is partly based on the Eccles et al. model of achievement-related choice (e.g., [START_REF] Eccles | Expectancies, values, and academic behaviors[END_REF][START_REF] Wigfield | Expectancy-value theory of achievement motivation[END_REF].

In the proposed model, parents' PA is presumed to directly affect their child's involvement in PA through a role modelling effect (the dotted lines in Figure 1). Parental beliefs about their child's physical competence are also presumed to indirectly shape the time that their child spends in PA through an effect on the child's perceived physical competence (the double lines in Figure 1), controlling for the child's initial level of perceived physical competence (the auto-regressive effect). In turn, children's perceived physical competence is expected to predict their own PA involvement (the thick line in Figure 1). Gender differences were also expected (the thin lines in Figure 1). In accordance with previous research, it was anticipated that boys would report higher levels of perceived competence than would girls (e.g., [START_REF] Eccles | Gender differences in sport involvement: Applying the Eccles' expectancy-value model[END_REF][START_REF] Jacobs | Changes in children's self-competence and values: Gender and domain differences across grades one through twelve[END_REF], as well as higher levels of involvement in PA (e.g., [START_REF] Dempsey | Parental influence on children's moderate to vigorous physical activity participation: An expectancy-value approach[END_REF][START_REF] Eccles | Gender differences in sport involvement: Applying the Eccles' expectancy-value model[END_REF]. Age was added as a control variable in the event that differences in the variables included in the model were affected by age-related factors.

Parental influence on physical activity 8

Another objective was to compare the specific predictive influence of mothers and fathers with regard to two hypothesized forms of influence -role modelling and parental beliefs -in order to determine if one of the parents would have a greater influence than the other, or if the influence of the two parents was additive. In contrast with some previous studies (e.g., [START_REF] Brustad | Attraction to physical activity in urban schoolchildren: Parental socialization and gender influences[END_REF][START_REF] Kimiecik | Relationships among children's beliefs, perceptions of their parents' beliefs and their moderate to vigorous physical activity[END_REF], fathers' and mothers' self-reports were both used to reduce the shared variance problems caused by the use of children's perceptions of parental beliefs.

Method

Participants

A sample of 152 intact families (mother, father and child), coming from three French cities (each with a population of 15,000 to 30,000 inhabitants), was used in this study. Only one child per family was included (no siblings participated). No child in the sample had medical or disability-imposed restrictions on physical activity. The 84 girls and 68 boys who participated ranged in age from 9 to 11 years of age (M = 9.56, SD = 0.84 yrs) at the beginning of the study, their mothers averaged 38.04 years of age (SD = 3.71) and their fathers 39.8 years of age (SD = 4.36). Thirty-six of the child participants (16 boys and 20 girls) were between 8.5 and 9.0 years of age, 69 (30 boys and 39 girls) were between 9 and 10 years of age, and 47 (22 boys and 25 girls) were between 10 and 11 years of age.

The sample was comprised primarily of Caucasian French middle to upper class families.

Measures

Child's perceived competence in physical activity. This construct was assessed through a French version (Sarrazin, Bois, & Trouilloud, 2000a) of [START_REF] Harter | Manual for the self-perception profile for children[END_REF] Perceived Physical

Competence Scale for Children. The back-translation method (see [START_REF] Brislin | The wording and translation of research instruments[END_REF]) was used to translate the original scale into French. Items were scored on a 4-point response format using [START_REF] Harter | Manual for the self-perception profile for children[END_REF] structured alternative approach. An example of one of the four items Parental influence on physical activity 9 used in this scale is, "Some kids are sure that they are good at sports but other kids don't think they are good at sport". On this scale, a score of 1 reflects a low level of perceived physical competence and 4 a high level of perceived physical competence; scores of 2 and 3 indicate intermediate levels. In previous research, this scale has been found to be valid and reliable [START_REF] Bois | Mothers' expectancies and young adolescents' perceived physical competence: A year long study[END_REF]Sarrazin et al., 2000a). In the present study, the internal consistency was satisfactory (Cronbach α = .72 and .79, respectively for Time 1 and Time 2).

Child's physical activity duration. Time spent in moderate-to-vigorous-physical activity was assessed at Time 2 with two complementary measures: (1) parents' reports of their child's PA and (2) an interviewer-administered recall of PA for children. Previous studies (e.g., [START_REF] Haaro | Validation of a questionnaire to assess physical activity of children ages 4-8 years[END_REF][START_REF] Manios | Physical activity of 6-year old children: Validation of two proxy reports[END_REF] have found that parental reports are reliable and valid tools in assessing a child's moderate to vigorous physical activity. Furthermore, [START_REF] Sallis | Assessment of physical activity by self-report: Status, limitations, and future directions[END_REF] review provided support for the validity of interviewer-administered recall with young children.

Based on an adaptation of previously used methods that have demonstrated reliability and validity (e.g., [START_REF] Kimiecik | Relationships among children's beliefs, perceptions of their parents' beliefs and their moderate to vigorous physical activity[END_REF][START_REF] Sallis | Seven-day recall and other physical activity self-reports in children and adolescents[END_REF], the measures were designed to assess the duration of each child's PA involvement over a one-week period, in this case the week immediately prior to the interview. Some evidence (e.g., [START_REF] Sallis | Seven-day recall and other physical activity self-reports in children and adolescents[END_REF] indicates that younger children can report their vigorous activities with reasonable accuracy, even over a 7-day period. Nevertheless, because recall of PA is a complex cognitive task, especially for children [START_REF] Baranowski | Validity and reliability of self-report of physical activity: An information processing perspective[END_REF], several procedures to aid recall were used (the detailed interviewer manual is available from the first author). Essentially, the procedure consisted of presenting to the child (and each parent) a list of activities in which children of this age are commonly engaged. Those activities included rollerblading, cycling, playing games (such as tag), rope jumping, Parental influence on physical activity 10 dancing, running, skateboarding, climbing activities and sport (typical activities such as soccer, basketball or rugby were given as examples), as well as an 'other' category for any activities in which the children engaged that were not present on the list. Activities were selected in such a way as to be representative of the age and culture of the children. The protocol focused on relatively intensive activities (i.e., moderate to vigorous physical activity) that should be more easily recalled than would be low intensity activities [START_REF] Sallis | Seven-day recall and other physical activity self-reports in children and adolescents[END_REF]. For this purpose, the child was asked to identify the activities that were hard enough to make her/him get tired or breathe hard or sweat. After the children were reassured that it was acceptable to report no physical activity if this were accurate in their case, the next step consisted in identifying any activities in which they had engaged in during each day of the week. To simplify the interview, activities were counted only if they totalled at least 10 continuous minutes. Then for each identified activity, children (and parents) indicated how long they were engaged. To provide them with a frame of reference, children were asked beforehand to name events that last approximately 10 minutes in duration (e.g., recess), 30 minutes in duration (e.g., school meals), etc. The interviewer assisted each child in estimating the amount of time spent in each activity on each day. The one-on-one interviews with the children lasted 10 to 15 minutes. The daily totals were summed to obtain a score representing the amount of the child's PA time in hours during the one week period. A one month test-retest correlation was conducted on a pool of 30 children and revealed satisfactory reliability for this measure (r = .68). Moreover, the correlation of this measure with the parents' recall measurement of their child's physical activity was significant (r = .46, p < .001) supporting the validity of the child's measurement. Because mothers' and fathers' reports of their children's exercise behaviour were highly correlated (r = .98), they were averaged.

Parental perceptions. Parental perceptions related to their child's ability in PA were measured by a French version [START_REF] Sarrazin | Trans-cultural validation of the measurement scales of the Eccles et al[END_REF] of Jacobs and Eccles' (1992) questionnaire on mothers' perceptions of their child's physical competence. The back-translation method [START_REF] Brislin | The wording and translation of research instruments[END_REF] was used to translate this 4-item scale into French.

A sample item was "In general how good is your child in sport?" This 5-point Likert-type scale ranged from 1 ("not good at all ") to 5 ("very good"). In previous research, this scale has been found to be valid and reliable [START_REF] Bois | Mothers' expectancies and young adolescents' perceived physical competence: A year long study[END_REF][START_REF] Sarrazin | Trans-cultural validation of the measurement scales of the Eccles et al[END_REF]. In the present study, the internal consistency was satisfactory (α = .75 and .79, respectively for mothers and fathers).

Parents' physical activity. Parents' PA was measured with a one-week recall format similar to the one parents used to evaluate their child's physical activity. Each parent was presented a list of activities and had to identify the activities in which they participated as well as the duration of their participation. The amount of time spent in each activity was summed over the week to obtain a single score representing the amount of PA performed by each parent. A one-month test-retest procedure conducted with 20 parents revealed satisfactory reliability for this measure (r = .82 and .85, respectively for father and mother).

Procedure

Agreement was obtained from both parents and from the school director for the children's participation in the study and verbal assent was obtained from each child prior to their involvement. Data were collected at two times over a one-year period (October 2000 and October 2001) from (1) questionnaires completed by parents and children, (2) and from semi-structured interviews with children to obtain the PA information. In October 2000, data for all of the parents' variables and child's age, sex and initial perceptions of competence were obtained. One year later, child's physical activity and current perceptions of competence were measured. Children completed questionnaires in the classroom in a Parental influence on physical activity 12 small group with an assistant reading the questions and providing assistance to them. The parents' questionnaire was given to the children, completed at home by the parents, and then returned to the school a week later.

Data analysis

Descriptive statistics were obtained and preliminary data analyses were conducted to investigate possible gender differences across the variables of interest. To test for anticipated relationships among the variables in the full model, we adopted [START_REF] Anderson | Structural equation modeling in practice: A review and recommended two-step approach[END_REF] two-step modelling approach intended to identify sources of poor overall model fit. On the first step, a confirmatory factor analysis (CFA) was conducted to test for the construct validity of the latent variables. Once the factor structure was supported, the second step involved a test of the relationships hypothesized in the theoretical model. Alternative models were tested in which the direct influence of parental perceptions of the child's competence on child's PA involvement was added.

Results

Descriptive Statistics and Preliminary Analyses

Means and standard deviations for all the variables are presented separately for boys and girls in Table 1. Boys presented higher scores than girls on perceived competence at Time 1 (F (1,150) = 5.08, p < .05, η² = .03), perceived competence at Time 2 (F (1,150) = 3.85, p < .05, η² = .03), and on parents' reports of their child's PA levels (F (1,150) = 4.02, p < .05, η² = .03). No other gender differences were found. To test whether parents' beliefs concerning their child's competence in PA varied as a function of their own or their child's gender, a 2 (child's sex) × 2 (mother's and father's belief concerning their child's competence) analysis of variance was conducted, with repeated measure on the last variable. Neither main effects nor significant interactions were revealed from this analysis Parental influence on physical activity 13 (p > .19). This finding indicates that mothers' and fathers' appraisals of their child's competence did not significantly differ and did not vary with the gender of the child.

Confirmatory Factor Analysis

CFA was conducted to examine the construct validity of all of the model's latent variables. Items on each subscale were aggregated randomly to form two composite scores for each construct in order to reduce the number of variables and to keep the model degrees of freedom reasonable [START_REF] Bentler | Multivariate analysis with latent variables: Causal modeling[END_REF][START_REF] Byrne | Structural equation modeling with EQS and EQS/Windows[END_REF]. Given the difficulty in precisely measuring the child's PA (see [START_REF] Sallis | Assessment of physical activity by self-report: Status, limitations, and future directions[END_REF], we decided to use a latent representation of this variable based both on parents' and children's report (r = .46, p < .001). As a result, the CFA was based on ten observed variables and five latent factors (child's perceived competence at Time 1 and Time 2, mothers' and fathers' perceptions of child competence and child's PA). The analysis was conducted with LISREL 8.3 with the maximum likelihood method of estimation. In view of the current controversy regarding measures of overall goodness of fit, it is generally considered appropriate to report multiple indices [START_REF] Bollen | Structural equations with latent variables[END_REF]. Thus, the chi-square statistic, the goodness-of-fit index (GFI), the non-normed fit index (NNFI), the comparative fit index (CFI) and the standardized root mean square residual (SRMR) all were used to evaluate the adequacy of the fit of the model to the data. For GFI, NNFI and CFI values above .95 are considered satisfactory.

For SRMR, values below .08 indicate a good fit of the model to the data.

The first run of the analysis resulted in an inadequate fit of the model to the data (χ²(25, N = 152) = 67.65, p < .001, GFI = .92, NNFI = .85, CFI = .92, SRMR = .067).

LISREL output analysis revealed large residuals between manifest indicators of mothers'

and fathers' perceptions of their child's physical competence, and between the first indicator of the child's perceived competence at Time 1 and Time 2. As mothers and fathers answered the same questions, and as they certainly share similar views on their Parental influence on physical activity 14 child's competence, it is not surprising that manifest indicators of mothers' and fathers' perceptions of their child's competence are correlated. Therefore, in accordance with recommendations by [START_REF] Jöreskog | LISREL 8: User's reference guide[END_REF], two covariance errors were added between these two pairs of variables. A third large residual remained between the first indicator of child's perceived physical competence at Time 1 and Time 2 (i.e., between the same indicator assessed at Time 1 and Time 2). As recommended in longitudinal designs with auto-regressive effects [START_REF] Jöreskog | LISREL 8: User's reference guide[END_REF], a third covariance error was added between these two variables. This new model was run and provided a good fit to the data (χ²(22, N = 152) = 28.95, p > .05, GFI = .96, NNFI = .97, CFI = .99, SRMR = .04).

All λs were significant (t > 2.00). The computed reliabilities 1 for the constructs were .63 for child PA, .69 and .77 for children's perceived physical competence at Time 1 and Time 2, and .78 and .82 for mothers' and fathers' perceptions of their child's ability, respectively. Thus, the variables demonstrated adequate construct validity.

Structural model

The second step of our analysis consisted of testing simultaneously the structural and measurement models (from the CFA analysis) thus allowing us to focus on conceptual connections among the variables of the model displayed in Figure 1 (the five latent factors plus mother's PA, father's PA, child's sex and child's age, considered as manifest variables). This resulted in a model with fourteen observed variables and five latent factors.

Table 2 shows the covariance matrix used as input.

The hypothesized model provided a good fit to the data (χ²(47, N = 152) = 59.44, p > .05, GFI = .95, NNFI = .95, CFI = .97, SRMR = .05). The relation between mothers' PA and their children's PA was significant (β = .30, p < .01) whereas fathers' PA did not predict their child's PA involvement after controlling for the child's age (β = .37, p < .001) and sex (β = -.02, p > .05). Similarly, mothers', but not fathers', perceptions of their child's Parental influence on physical activity 15 ability significantly predicted the child's perceptions of their physical competence (β = .41, p < .01), independent of the child's age (β = -.25, p < .01), sex (β = -.31, p < .01), and the child's initial level of perceived physical ability at Time 1 (β = .09, p > .05). Eventually, children's perceived physical competence predicted their PA level (β = .48, p < .001).

A second model was tested in order to examine the possibility that parents' perceptions have direct effects on child's PA. Paths from both fathers' and mothers' perceptions of the child's competence to the child's PA were freely estimated, along with the other path from the former model. This alternative model had a good fit to the data (χ²(45, N = 152) = 50.27, p > .05, GFI = .96, NNFI = .98, CFI = .99, SRMR = .04), but was significantly different from the first model (∆χ 2 (2) = 9.17, p < .01). The direct path from fathers' perceptions to child PA level was significant (β = .35, p < .05) whereas the influence of mothers' perceptions on this variable was not (β = .01, p > .05). Adding these paths did not significantly affect the size of the other paths in the first model. Finally, a third model was tested in which the non-significant path between mothers' perceptions and child PA was removed. The fit of the model was good (χ²(46, N = 152) = 50.28, p > .05, GFI = .96, NNFI = .98, CFI = .99, SRMR = .04), and was not significantly different from the second model (∆χ 2 (1) =.01, p > .05). Given the equivalence of the two alternative models, the simpler model was preferred. The structural coefficients of this model are displayed in Figure 2. Collectively, the variables within the model explained 30% of the variance in children's perceptions of their physical ability and 51% of the variance in children's PA level.

Discussion

Given the importance of PA for the long-term health and psychosocial development of children (e.g., [START_REF] Martinsen | Exercise and mental health in clinical and free living populations[END_REF][START_REF] Weiss | The relationship between physical competence and peer acceptance in the context of children's sports participation[END_REF], this study Parental influence on physical activity 16 investigated the role of social and psychological factors in shaping children's physical activity behaviour. With regard to social forms of influence, both parental role modelling of PA and parental beliefs about their child's physical competence were examined in relation to their influence upon children's perceived physical competence and PA levels.

These relationships were studied over a 12-month period to better tease out the role of parental socialization influence as it shapes children's perceptions and behaviour over time.

Three significant findings emerged. First, evidence was found for the existence of direct parental socialization influences on their child's involvement in PA through PA role modelling effects. Second, support was obtained for the influence of parents' beliefs in that mothers' perceptions of their child's physical competence were related to children's perceived competence, and subsequent time spent in physical activity. Third, the findings supported the link between children's perceptions of their physical competence and their involvement in physical activity. The discussion focuses on each of these three major findings as well as upon age and gender effects.

Parental role modelling effects

Mothers', but not fathers', involvement in PA was related to their child's involvement in PA, and this finding provides partial support for the role modelling hypothesis. It appears that mothers' role modelling behaviour seems to be more salient to children in this age range than does the role modelling behaviour of their fathers. Previous studies using self-report measures of PA have generally found non significant or weak correlations between parents' and children's PA levels [START_REF] Dempsey | Parental influence on children's moderate to vigorous physical activity participation: An expectancy-value approach[END_REF][START_REF] Kimiecik | Parental beliefs and children's moderate-to-vigorous physical activity[END_REF] whereas studies using more objective assessment, such as those with Caltrac accelerometers, have found a moderate-to-strong relation between parent and child PA levels [START_REF] Freedson | Familial aggregation in physical activity[END_REF][START_REF] Moore | Influence of parents' physical activity levels on activity levels of young children[END_REF]. Perhaps the methodological precautions taken in our study (a latent representation of children's PA using two Parental influence on physical activity 17 indicators) are at the origin of the significant results found, in spite of the use of self-report measurements.

With regard to the strength of mothers', as opposed to fathers' influence, this finding is consistent with two previous studies. First, in a sample of competitive youth swimmers, [START_REF] Power | Parenting practices and age-group swimming: A correlational study[END_REF] found that mothers' role modelling was positively associated with their child's level of enthusiasm for participating in the sport whereas fathers' role modelling was not. Another study examining familial aggregation of PA habits found that mothers' PA levels, but not fathers', were related to children's PA participation [START_REF] Sallis | Aggregation of physical activity habits in Mexican-American and Anglo families[END_REF]. The extent of maternal influence identified in these three studies might be surprising to some, however, these findings seem to indicate that mothers are salient socialization agents for children of this age range perhaps because they are likely to be more involved in the day-to-day activity choices of their children. Other studies should be conducted to further address this finding.

Moreover, it will be interesting in the future to assess other "qualitative" variables (e.g., enjoyment) related to parents' PA. For example, a mother or a father who is enthusiastic about his/her PA is more likely to be imitated by children than the one who practises at the same level but does not express positive sentiments [START_REF] Brustad | Attraction to physical activity in urban schoolchildren: Parental socialization and gender influences[END_REF][START_REF] Fredericks | Parental influences on youth involvement in sports[END_REF].

Parental beliefs influences

From Eccles' theoretical perspective, a primary form of parental socialization influence occurs through the process whereby parental beliefs about children's aptitudes shape children's own self-related perceptions and subsequent motivational and behavioural patterns. A fundamental purpose of the present study was to assess the relative extent of parental belief influences in the physical domain where only a limited amount of research (e.g. [START_REF] Bois | Mothers' expectancies and young adolescents' perceived physical competence: A year long study[END_REF][START_REF] Brustad | Who will go out and play? Parental and psychological influences on children's attraction to physical activity[END_REF][START_REF] Brustad | Attraction to physical activity in urban schoolchildren: Parental socialization and gender influences[END_REF] has previously considered this form of parental Parental influence on physical activity 18 socialization influence. To demonstrate the existence of an influence between parental beliefs on children's PA behaviour it was necessary to establish that parents' perceptions of their child's ability at Time 1 predicted their child's self-perception of ability at Time 2, controlling for the child's initial self-perception of ability at Time 1 (McCallum & Austin, 2000). Secondly, for parental beliefs to have merit as contributors to children's PA behaviour, it was necessary to establish that children's self-perceptions of ability subsequently predicted their physical activity.

Results demonstrated that mothers', but not fathers', perceptions of their child's competence predicted their child's perceived physical competence 12 months later. It should be noted that these results were independent of the child's initial level of perceived competence, child's age and child's sex. These results are consistent with two other studies in the academic domain [START_REF] Eccles | Expectancies, values, and academic behaviors[END_REF][START_REF] Mcgrath | Mothers' and fathers' attitudes toward their children's academic performance and children's perceptions of their academic competence[END_REF] which found that mothers' achievement attitudes were stronger predictors of children's perceived academic competence than were fathers' achievement attitudes. In contrast, [START_REF] Felson | The effect of parents on the self-appraisals of children[END_REF] found that both mothers' and fathers' perceptions of their child's competence were influential in predicting their child's perceived competence in both academic and sport domains. Felson and Reed's sample constituted a broader and older age range (4 th to 7 th grade) than in the present study and utilized a cross-sectional design. Similar to other studies (e.g., [START_REF] Mcgrath | Mothers' and fathers' attitudes toward their children's academic performance and children's perceptions of their academic competence[END_REF], we speculate that our results could be attributed to the fact that mothers' socialization influence is greater with younger children due to their extensive involvement in their child's daily activities.

Role of perceived competence in physical activity

In accordance with theoretical perspectives on motivation [START_REF] Eccles | Expectancies, values, and academic behaviors[END_REF][START_REF] Harter | The development of competence motivation in the mastery of cognitive and physical skills: Is there a place for joy[END_REF], our results indicated that children's perceived physical competence was related to their PA involvement. That is, the more children perceived they were competent in regard to physical activity, the more likely they were to be engaged in this activity. This result is consistent with other PA studies with children (e.g., [START_REF] Dempsey | Parental influence on children's moderate to vigorous physical activity participation: An expectancy-value approach[END_REF][START_REF] Eccles | Gender differences in sport involvement: Applying the Eccles' expectancy-value model[END_REF][START_REF] Kimiecik | Relationships among children's beliefs, perceptions of their parents' beliefs and their moderate to vigorous physical activity[END_REF]. As our results also highlight the influence of mothers' competence beliefs upon children's beliefs about their own competence, it can be argued that mothers indirectly affect their children's physical activity involvement in this manner.

For fathers, a direct relationship was found between fathers' perceptions of their child's physical competence and the child's PA. This finding suggests that fathers' perceptions affect their child's PA via other variables. [START_REF] Wigfield | Expectancy-value theory of achievement motivation[END_REF] hypothesized that parents' perceptions could affect the nature, and the frequency, of opportunities for their children to play sport. On the other hand, the Eccles et al. model (e.g., Wigfield & Eccles, 2000) postulates that children's involvement in achievement activities is predicted both by children's self-perceptions and by the value they attribute to the activity. Therefore, fathers' perceptions can affect their child's PA either directly by giving him/her more or less opportunities to play sport, or indirectly via the child's values toward PA.

Further studies including the variable of value are needed and certainly constitute a promising area of investigation.

Interestingly, our study suggests that mothers and fathers have distinct patterns of influence. Mothers' influence seems to occur through role modelling and through the influence of their beliefs about the child's physical competence, whereas the fathers' influence suggests the existence of other processes. Further studies are necessary to obtain a deeper understanding of the specific role played by mothers and fathers in shaping their child's involvement in PA.

Gender differences

Parental influence on physical activity 20 Consistent with other studies (e.g., [START_REF] Eccles | Gender differences in sport involvement: Applying the Eccles' expectancy-value model[END_REF][START_REF] Jacobs | The impact of mothers' gender role stereotypic beliefs on mothers' and children's ability perceptions[END_REF], our results revealed gender differences in children's perceived competence at Time 1 and Time 2. In addition, parents of boys reported higher levels of PA for their child than did parents of girls. It was hypothesized in previous studies (e.g. [START_REF] Jacobs | The impact of mothers' gender role stereotypic beliefs on mothers' and children's ability perceptions[END_REF]) that gender differences in children's perception of competence could be due to parents' gender stereotyped perceptions. If parents' perceptions of their child's physical competence are higher for boys than for girls, the influence of parental beliefs could explain gender differences in children's own self-perceptions of physical competence. However, our results demonstrated that mothers' and fathers' estimations of their child's ability did not vary as a function of the child's gender. Our findings are consistent with [START_REF] Kimiecik | Parental beliefs and children's moderate-to-vigorous physical activity[END_REF] who found that neither mothers nor fathers held gender-differentiated perceptions of their child's physical competence. However, the existence of parental gender stereotyped perceptions should not be dismissed because stereotypes were not directly assessed in this study. Moreover, the measurement used in this study without any reference to an objective performance can mask the occurrence of gender stereotypes.

Indeed according to the shifting standards model [START_REF] Biernat | The shifting standards model: Implications of stereotype accuracy for judgement[END_REF], individuals can adjust the meaning of the subjective scales according to their appraisal for men and women regarding height, weight and competence, which removes evidence of gender stereotypes. To uncover those differences and to more assess parents' true mental representation of children, future research could use scales that are explicitly linked to an external anchor and/or direct parents' gender stereotypes.

Despite the fact that we have taken into account the influence of both mothers' and fathers' beliefs, as well as the child's age, sex, and initial level of perceived competence, our model explained only 30% of the variance in children's self-perceptions of competence. This could suggest (1) that other socializing agents, notably peers, siblings, Parental influence on physical activity 21 teachers, and coaches are likely to be instrumental in shaping children's self-perceptions at this age (see [START_REF] Weigand | Motivational climate in sport and physical education: The role of significant others[END_REF]; (2) and that children utilize many additional sources of information in assessing their competence, particularly personal sources, such as the relative ease with which they learn new skills and their perceived rate of improvement in sports and activities [START_REF] Horn | Developmental perspectives on self-perceptions in children and adolescents[END_REF]. Consequently, future studies should address the influence of other socializing agents and varied sources of competence information in addressing children's competence perceptions.

Limitations of the present study fall within four areas. Although we have used longitudinal data, our results remain correlational in nature and hence causality can only be inferred cautiously. Secondly, it is likely that the direct relationships between parents' and children's variables constitute only a first step in understanding how parents impact children's PA characteristics. For example, several mediators omitted in this study could be involved in the relation between parents' perceptions of their child's competence and children's own self-perceptions or physical activity. These might include the respective roles of children's values, perceptions of parents' beliefs (i.e., reflected appraisal), as well as parents' behaviours (e.g., extent of encouragement, provision of athletic opportunities and equipment ), and parents' affective orientations toward physical activity (enjoyment). All merit consideration in future studies. Third, the relationship between children's perceived competence and PA levels may be bi-directional. It is logical to assume that children's PA involvement should impact their self-perceptions of competence in this domain just as competence perceptions are likely to affect involvement. Therefore, the relation between these variables should be interpreted cautiously. Finally, it is important to note that our sample was limited to children with both their mothers and fathers in the home. Consequently those results are likely to be limited to this type of family. A related limitation pertains to the fact that as parents completed their questionnaires, it is possible that on some occasions the mother and the father may have completed them together.

Overall, this study has contributed in several ways to the literature on the socialization of children's physical activity. The results from this study provide further evidence for the need to examine the specific influence of fathers and mothers, as opposed to considering parental influence collectively. More specifically, our results showed that mothers', but not fathers', involvement in PA predicted their children's involvement in physical activity. In addition mothers', but not fathers', perceptions of their child's physical competence was related to the child's own self-appraisal of competence, after controlling for the child's initial level of perceived competence. However, fathers' perceptions directly predicted their child's physical activity. An additional important outcome from the study was the relationship between perceived physical competence and PA involvement. Clearly, enhancing children's perceived physical competence should be a goal for practitioners interested in facilitating physical activity. A particular contribution was the recognition that parents can affect their children's PA involvement in direct and indirect manners through role modelling and parental belief influences. Insofar as there is no reason to suspect cultural differences between France and other industrialized countries regarding socialization into sport, we think that these results can generalize to the other western industrialized countries where previous studies have been conducted. Nevertheless, cross-cultural studies are needed to further investigate those questions. equation: ρ = (Σλi)² / ((Σλi)² + Σδii) where λi are the factor loading and δii the error variances.

Parental influence on physical activity 30

Figure Captions Figure 1 :

 Captions1 Figure Captions

Figure 2 :

 2 Figure 2 : Structural equation model of mothers' and fathers' influences on their children perceived competence and physical activity. Standardized solutions are presented. *p < .05. **p < .01. ***p < .001.

Table 1

 1 Means and standard deviations for parent and child variables

	Boys	Girls

This study was facilitated by a grant from two French sport organizations: the 'Direction Départementale de la Jeunesse et des Sport 26' and the


Heriberto Rodríguez-Tobías

Dr Graciela Morales
email: graciela.morales@ciqa.edu.mx

Hortensia Maldonado-Textle

Dr Daniel Grande
email: daniel.grande@cnrs.fr

Heriberto Rodríguez Tobías

Long-term photo-degradation of nanofibrous composites based on poly(3hydroxybutyrate) electrospun fibers loaded with zinc oxide nanoparticles

Keywords: Photo-degradation, electrospinning, electrospraying, poly(3-hydroxybutyrate), zinc oxide nanoparticles

Composite mats based on submicron biopolyester fibers and zinc oxide (ZnO) nanoparticles have been exploited in medicine and environmental areas, as antibacterial wound dressings or filters. Generally, the resulting mats have to be subjected to UV irradiation in order to promote the formation of reactive oxygen species, thus activating the antimicrobial or photocatalytic effect of ZnO. Therefore, investigation related to the influence of ZnO on poly(3-hydroxyalkanoate) photo-degradation is required. In this context, the present paper addresses the long-term photo-degradation of nanofibrous poly(3-hydroxybutyrate) (PHB)/ZnO composites derived from two complementary electro-hydrodynamic techniques, namely electrospinning or electrospinning/electrospraying tandem processes.

A thorough investigation of the as-obtained PHB/ZnO fibrous composites implying the utilization of ATR-FTIR, SEC, and SEM was performed before and after artificial UV aging for a period of time of 500 h in order to evaluate the effect of the electro-hydrodynamic technique and ZnO content on the UV shielding properties of composite mats.

INTRODUCTION

Electrospinning-based techniques have demonstrated to be practical and economically viable processes for manufacturing polymeric fibers in the submicron scale with controlled morphological features, such as average fiber diameter, porosity ratio, fiber orientation, and in the case of composite fibers, nanoparticles distribution (on fiber surface or embedded within fibers) [1][2][3]. In this regard, the control of the aforementioned features of fibrous polymer materials make them ideal candidates for the design and fabrication of prototypes with high potential to solve environmental and health concerns, including filters for the elimination of a wide range of chemical and biological contaminants in air or water, and antimicrobial and/or wound healing mats [1,[4][5][6][7][8][9]. It is noteworthy that (bio)polyesters, such as polylactides and poly(3-hydroxyalkanoate)s (PHAs) have been extensively used for developing the aforementioned prototypes, mainly due to their renewability, biocompatibility and/or biodegradability [6][7][8][9][10][11][12].

Furthermore, the incorporation of metal oxide nanoparticles into (bio)polyester-based fibers can be considered as a synergistic approach to develop devices with improved antimicrobial and photocatalytic properties. In this regard, zinc oxide (ZnO) nanoparticles are well-known antimicrobial and photocatalytic nanostructures which can be used as multifunctional nanomaterials able to eliminate several chemical pollutants and microorganisms without collateral risks for human health and/or other species, since ZnO is catalogued as a safe component by the Food and Drug Administration [13][14][15][16][17][18][19][20].

It is needed to emphasize that there is a scarcity of publications related to PHA/ZnO electrospun composites, and the majority of them are focused on the fabrication of mats and complemented with some relevant characterization associated with the structure and morphology of the resulting fibers. As an example, Yu et al. [21] electrospun a mixed solution of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV)/ZnO, whereby composite fibers with 300 nm in size were thus obtained. The authors argued that the formation of hydrogen bonding favored the dispersion of ZnO nanoparticles into the PHBHV fibers, and they also demonstrated that the nanometal oxide restricted the crystallization. Moreover, Naphade et al. [22] obtained PHBHV/ZnO electrospun fibers ranging from 700 to 800 nm with enhanced UV emission properties which could lead to the development of biomarkers. Zviagin et al. [23] also reported the generation of poly(3-hydroxybutyrate) (PHB) fibers by electrospinning in combination with hydrothermal deposition of ZnO nanostructures, and the mats thus obtained were used for the design of piezoelectric devices.

A handful number of researchers has studied the generation of antimicrobial PHA/ZnO fibrous devices derived from electrospinning techniques. Lagaron's research group proved the antimicrobial activity of electrospun PHBHV/ZnO mats against Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes. They also analyzed the effect of ZnO content on morphological, mechanical, thermal, and optical properties of the resulting electrospun materials [24,25]. Our research consortium has also exploited the electrospinning process and its combination with the electrospraying technique for designing antimicrobial PHB/ZnO mats, whose thermal and mechanical performance was evaluated [19].

As it can be noticed in the aforementioned publications, many efforts have been made to design PHBHV or PHB mats containing ZnO nanoparticles as antimicrobial agents.

However, there is no investigation related to the photo-degradation of resulting fibrous materials, which is of outmost interest due to the activation or increase of antimicrobial and/or photocatalytic activity promoted by UV irradiation, which in turn could lead to photodegradation and, eventually, a reduction of the fibrous materials lifetime.

In this context, the aim of the present work is to investigate the photo-degradation behavior of two types of PHB-based fibrous composites, namely ZnO-embedded PHB submicron fibers engineered by mere electrospinning of the corresponding solution/dispersion, and ZnO-coated PHB submicron fibers derived from the electrospinning/electrospraying tandem technique. Further spectroscopic, chromatographic, and microscopic analyses were performed to evaluate the effect of the aging time, the employed electrohydrodynamic technique, and ZnO nanoparticles concentration/dispersion on structural and morphological changes of the PHB-based fibrous composites.

EXPERIMENTAL

Materials

Commercially available poly(3-hydroxybutyrate) (PHB) (Biomer, 𝑀 ̅ 𝑛 = 144,000

g•mol -1 , 𝑀 ̅ 𝑤 𝑀 ̅ 𝑛 ⁄ = 2.
3) and 2,2,2-trifluoroethanol (TFE) from Sigma-Aldrich were used as solute and solvent, respectively, of precursory solutions which eventually were subjected to the electrospinning-based techniques for generation of the fibrous materials. ZnO nanoparticles (12 nm in diameter and distribution ranging from 8 to 20 nm) were obtained by microwave-assisted synthesis as previously reported [26][27][28]. and the simultaneous electrospraying of a ZnO nanoparticles dispersion in MeOH (1-5 wt-% respect to PHB and dispersed by ultrasound bath for 1.5 h). The electrospinning was conducted under the same conditions as those used in (a), while electrospraying was carried out with a collector-to-needle distance of 5 cm and the syringe being placed at an angle of 120° relative to the direction of the other syringe.

Fabrication of fibrous materials

Artificial UV aging of PHB fibers and PHB/ZnO fibrous composites

Aging of fibrous PHB composites (2 × 2 cm samples) was conducted in a UV accelerated weathering tester (Q-Lab) equipped with a lamp at fixed wavelength and irradiance, i.e. 313 nm and 0.87 W•m2, respectively, and temperature of 60°C. Several samples were withdrawn at different aging times (50, 100, 250, and 500 h) for characterizing them by different physico-chemical techniques described in subsequent sections. It should be stressed that the wavelength was comprised within the range commonly used for activating metal oxide photocatalytic properties (UVA and UVB regions), which could be beneficial to promote antibacterial activity [13][14][15][16][17][18][19][20].

Characterization of fibrous materials

A scanning electron microscope (SEM, JEOL JSM-7401F) coupled with an energy dispersive X-ray (EDX) detector was used to analyze the morphology and composition of the as-obtained and aged mats. In addition, inner morphology of the obtained PHB mats was analyzed by a FEI Titan 80-200 transmission electron microscope (TEM). Average fiber diameter was estimated by using ImageJ software. For this purpose, several SEM micrographs were analyzed, and the diameter was estimated from 4-5 sections along 60-70 fibers (ca. 250-300 counts).

Mercury intrusion porosimetry (MIP) analyses were performed with a Micrometrics

Autopore IV equipment. The porosity features were determined by using the Washburn equation between the applied pressure (from 1.03 to 206.8 MPa) and the pore diameter into which mercury intruded, thus obtaining defined values for porosity ratio and pore size distribution from which the average pore size was estimated.

To identify any chemical change of the aged PHB/ZnO mats, infrared spectra were recorded on a Nicolet Nexus spectrometer in the attenuated total reflection mode (ATR-FTIR) between 4000 and 600 cm -1 , with 32 scan summations and a 4 cm -1 resolution.

Molar masses of aged fibrous PHB composites were estimated by size-exclusion chromatography (SEC), using three PL-gel columns with a refraction index detector at 40°C

and THF (HPLC grade) as the eluent at a flow rate of 1 mL•min -1 . Polystyrene standards were employed for calibration.

RESULTS AND DISCUSSION

Morphologic features of PHB/ZnO fibrous composites before UV irradiation

Morphology of fibrous materials derived from electrospinning techniques is of paramount significance since their applicability as filter media depends on several morphological characteristics, namely average fiber diameter (𝐷 ̅ 𝑓 ), porosity ratio (P), and average pore size (𝐷 ̅ 𝑝 ). In this context, fibrous materials based on PHB and ZnO nanoparticles were analyzed by means of SEM and MIP (Table 1).

<Table 1>

The results gathered in Table 1 demonstrated that the concentration of ZnO nanoparticles in the precursory solution or their deposition on the fiber surface by electrospraying had a negligible influence on the morphological features of PHB-based mats, since all materials exhibited 𝐷 ̅ 𝑓 values from 400 to 600 nm approximatively, P values ranging from 83 to 90 %, and 𝐷 ̅ 𝑝 values from 1.1 to 2.2 µm. Our research consortium evidenced that the similarity of the morphological features associated with mats derived from mere electrospinning was due to the fact that the electrical conductivity and viscosity of the precursory PHB solutions remained practically unchanged by the presence of ZnO nanoparticles [19]. In the case of the PHB mats derived from the electrospinning/electrospraying technique, the process was performed by using neat PHB precursory solutions, therefore, the ZnO nanoparticles sprayed on the fibers did not affect the aforementioned morphological features [19].

ZnO nanoparticles dispersion in/on the PHB fibers was assessed by means of electron microscopic techniques. In this regard, Figure 1 shows some TEM and SEM micrographs of the obtained materials, in which a homogeneous dispersion of ZnO was achieved in electrospun PHB fibers (Figure 1a,b), while electrospun/electroprayed PHB fibers exhibited some ZnO aggregates with sizes ranging from 300 to 4000 nm (Figure 1c-f). Some of these aggregates were semi-exposed on the fiber surface. These analyses evidenced that the electrospraying technique, under the experimental conditions herein used, was not suitable for obtaining well-dispersed ZnO nanoparticles, which could affect the final photodegradation behavior of PHB/ZnO composite fibers. This issue will be addressed in subsequent sections. <Figure 1>

Structures of electrospun PHB/ZnO mats after UV irradiation

Metal oxide nanoparticles, such as TiO2 or ZnO, exhibit photocatalytic activity when subjected to UV irradiation. Therefore, the presence of these nanoparticles within electrospun polyester fibers could trigger their photo-degradation. In this context, Sadi et al. [29] have extensively studied the photo-degradation of PHB in bulk, concluding that the degradation of PHB chains leads to a chemi-crystallization process, which can be evidenced by FTIR changes of carbonyl and C-O-C signals.

In this regard, Figure 2 shows FTIR spectra of neat and UV-irradiated electrospun PHB mats. In general, neat PHB mats displayed a signal centered at 1722 cm -1 which corresponded to carbonyl (C=O) stretching of the crystalline phase, along with a shoulder at higher wavenumber (1745 cm -1 ) associated with C=O stretching of the amorphous phase. In the crystalline phase, the C=O groups were close to the hydrogen atoms of a vicinal PHB chain, which reduced the polar momentum, thus provoking C=O vibrations at lower wavenumber (1722 cm -1 ). Additionally, two signals corresponding to stretching vibrations of C-O-C bonds were present at 1186 and 1230 cm -1 , the first one related to the amorphous phase and the second one associated to the crystalline phase [29,30].

<Figure 2>

Since the photo-degradation of PHB promotes chemi-crystallization of the resulting polymeric chains, the monitoring of the aforementioned FTIR signals can provide information about the effect of UV irradiation time, ZnO concentration and electrohydrodynamic technique on the PHB-based composite mats. However, carbonyl signals were overlapped, therefore only the C-O-C were considered for this monitoring. Figure 3 displays the absorbance at 1230 cm -1 to absorbance at 1186 cm -1 ratio (A1230/A1186) as a function of irradiation time and ZnO content. In general, all materials exhibited a substantial increase of A1230/A1186 ratio at 50 h of irradiation time, followed by a slight increase at 250 h, and finally this ratio exhibited a plateau at 500 h, thus suggesting the increase in the crystallinity of polymer chains.

Figure 3 could also be considered to investigate the effect of ZnO concentration and the implemented electrospinning technique. In the case of the electrospun PHB mats, the presence of low ZnO concentration (1 and 3 wt-%) did not change the pattern of the A1230/A1186 ratio as a function of irradiation time, which could be interpreted as these mats exhibited similar levels of crystalline phase formation associated with photo-degradation. A significant reduction of A1230/A1186 ratio was observed only at the highest ZnO concentration (i.e., 5 wt-%), which could be attributed to the UV protection by the semi-exposed ZnO nanoparticles/aggregates as displayed by SEM/TEM analyses. On the other hand, the electrospun/electrosprayed PHB mats exhibited a quite different performance, since the UV protection was the highest when the fibers contained the lowest ZnO concentration (1 wt-%).

At higher ZnO concentrations (3 and 5 wt-%), a shielding effect against photo-degradation was not perceived. This behavior could be explained in terms of ZnO nanoparticles aggregation when ZnO concentration was equal to or higher than 3 wt-%, as shown by elemental mapping (see Figure 1e,f), thus reducing the ZnO surface prone to absorb the UV irradiation [10,[31][32][33].

<Figure 3>

To further analyze the photo-degradation of electrospun PHB/ZnO composite fibers, the evolution of number-average molar mass (Mn) associated with PHB as a function of both UV irradiation time and ZnO content is plotted in Figure 4a. Firstly, a reduction of Mn values was noticed (decreasing from 144 to 25-35 kg•mol -1 ) as UV irradiation times increased and the major molar mass loss occurred at the early stage (50 h). On the other hand, a slight UVshielding effect was perceived at the highest ZnO content, which could be evidenced by a higher Mn value, thus corroborating the UV absorption by the exposed nanoparticles/aggregates. Moreover, the photo-degradation of PHB/ZnO mats induced a widening of the molar mass distributions (Mw/Mn) as demonstrated in Figure 4b. Generally, Mw/Mn values increased with UV irradiation time, and no particular trend was noticed as a function of ZnO nanoparticles content.

<Figure 4>

Regarding the photo-degradation behavior of electrospun/electrosprayed PHB/ZnO fibrous materials, SEC analyses evidenced that the ZnO content and the tandem technique did not confer a shielding effect, since Mn values were lower than those of the fibers derived from mere electrospinning in all the range of UV irradiation time analyzed (see Figure 5a).

Mn values were equal to 33-38 and 15-30 kg•mol -1 for 50 h and 250 h of UV irradiation time, respectively, and the evolution of the Mw/Mn values was practically similar to that exhibited by electrospun PHB/ZnO mats (see Figure 5b). These SEC results were in good agreement with those from the structural FTIR analyses previously discussed, i.e., electrospun mats containing high ZnO content possessed a better resistance to UV, while the tandem electrospinning/electrospraying technique was not suitable to exert a significant shielding effect. <Figure 5>

Morphologies of PHB/ZnO mats after UV irradiation

Electrospun fibrous devices for water decontamination or wound protection/healing may constitute efficient filters against pollutants and/or pathogenic microorganisms, as their high surface area-to-volume ratio favors the contact/interaction with the latters [26]. In this regard, the investigation of the effect of UV irradiation on the fibrous morphology of electrospun engineered materials is of outmost interest. In this context, Figure 6 depicts the morphology of the PHB mats derived from the electrospinning of the corresponding solution containing different ZnO concentrations (0, 1, 3, and 5 wt-%) depending on the UV irradiation time (0, 50, 250, and 500 h). All specimens showed a common morphological pattern, i.e., PHB fibers were transformed into submicron rods, which can be explained by the combination of PHB chains scission and chemi-crystallization, eventually, forming submicron rods by fragmentation. This phenomenon was more pronounced when the irradiation time was longer, since it could be observed a significant reduction of the PHB rod size (from 5-10 µm to 1-2 µm). On the contrary, no particular effect of ZnO concentration could be perceived, since all PHB mats resulted in highly degraded rods.

Regarding the fibrous materials engineered by electrospinning of a PHB solution and electrospraying of ZnO dispersions (i.e., 1-5 wt-%), the characteristic morphology gave evidence of a similar transformation than electrospun PHB mats under UV exposition during different periods of time. As a matter of evidence, Figure 7 displays the corresponding SEM micrographs, in which it could be detected the previously explained morphology transformation pattern, i.e. electrospun/electrosprayed materials evolved from continuous fibers to discontinuous rods by chains scission and chemi-crystallization. <Figure 6> <Figure 7>

CONCLUSIONS

An extensive investigation of the photo-degradation behavior of ZnO-embedded and ZnO-coated PHB mats respectively engineered by electrospinning and electrospinning/electrospraying techniques was undergone for the first time. In general, nano-ZnO within or deposited on the PHB fibers promoted a UV-shielding effect; nevertheless, FTIR and SEC analysis suggested a slightly higher extent of UV protection for the mats derived from mere electrospinning, which could be attributed to a better dispersion of ZnO nanoparticles on the PHB fiber surface. FTIR spectroscopy evidenced that UV irradiation promoted a chemi-crystallization of PHB chains whose occurrence was increased by extending the aging time. Further structural studies were performed by SEC analysis and electron microscopy (SEM and TEM) by which it was demonstrated that the exposition to UV rays led to substantial changes in the morphology and molecular changes, since the PHB/ZnO mats evolved from fibers to sub-micrometric rods with a reduction of molar mass regardless of the electro-hydrodynamic technique or ZnO content used.

Ultimately, it could be concluded that such fibrous PHB/ZnO composite mats have a high potential as wound dressings materials with good resistance to UV irradiation sterilization or membranes for UV-activated filters with a relatively short shelf life (~50 h). a Average fiber diameter as determined from SEM images by using the ImageJ software, the number after the ± symbol is the standard deviation. b Porosity ratio and c average pore size as determined by MIP, the number after the ± symbol is the standard deviation.

Fibrous

  PHB composites were engineered by two electrospinning-based technologies: (a) mere electrospinning of PHB solutions (10 wt-% in TFE) containing 1-5 wt-% of ZnO nanoparticles relative to polymer, at a flow rate of 2.7 mL•min -1 , voltage of 25 kV, cylindrical collector speed of 700 rpm, and a needle-to-collector distance of 25 cm (b) tandem process based on the electrospinning of a PHB solution (10 wt-% in TFE)

  d PHB/ZnO mats derived from mere electrospinning (E) and e obtained by combination of electrospinning/electrospraying (E/ES).

Figure 1 .

 1 Figure 1. TEM images of (a,b) electrospun and SEM images of (c,d)

Figure 2 .

 2 Figure 2. FTIR spectra of PHB electrospun fibers UV-irradiated for (a) 0 h, (b) 50 h, (c) 250

Figure 3 .

 3 Figure 3. A1230/A1186 ratio as a function of UV irradiation time and ZnO concentration for

Figure 4 .

 4 Figure 4. (a) Number-average molar mass (Mn) and (b) dispersity index (Mw/Mn) for the

Figure 5 .

 5 Figure 5. (a) Number-average molar mass (Mn) and (b) dispersity index (Mw/Mn) for the

Figure 7 .

 7 Figure 7. SEM micrographs of the electrospun/electrosprayed PHB/ZnO materials

ACKNOWLEDGMENTS

Financial support through French Mexican PCP program is gratefully acknowledged.

The authors thank CONACyT (Mexico) for providing H. Rodríguez-Tobías with a Ph.D. grant. They also thank R. Pirès (CNRS, France) for his technical assistance in issues related to electron microscopy characterization.

CONFLICT OF INTEREST