Thermoplastic composites using natural fibres are studied intensively and widely used in applications including automotive, packaging, consumer goods and construction. Good balance of mechanical properties, processability and low cost are great advantages of these materials on top of the environmental benefits. Recently, there have been various efforts to amplify the positive effects on the environment by replacing the conventional polymers by bio-derived renewable polymers in the composites. Recent studies conducted from our research group showed competitiveness of plant fibre-thermoplastic composites. Implementing the promising results and experience, a new composite design using renewable polyethylene as the matrix material was studied. This polyethylene is a renewable thermoplastic that was derived from sugar cane ethanol. The objectives of this study were to employ renewable high density polyethylene (HDPE) into composites using wheat straw and flax fibre to extend the range of properties of the HDPE while keeping the amount of renewable content to nearly 100%. The chemical resistance of these materials has not been reported before and it was investigated here by measuring and comparing the properties before and after accelerated chemical ageing. Both wheat straw and flax fibre had two different grades in size. Each of them was compounded with HDPE and additives (antioxidant and coupling agent) in a co-rotating twin screw extruder. The concentrations of fibres were varied from 0 to 30 wt-%. Then, injection molded samples were prepared for measurement of properties: tensile, flexural, impact tests. The effects of reinforcing fibre size were studied first. Both length and aspect ratio were considered. For both types of fibre composites, a general trend was observed. There was no clear evidence of improvements in flexural (strength and modulus) and tensile (strength, percentage elongation at break) properties with respect to the change in fibre size. However, impact (IZOD impact strength, Gardner impact failure energy) properties showed some improvements. This result was due to no substantial difference in size and aspect ratios in post-processed fibres that were actually residing in the matrix. There were remarkable improvements in flexural strength and modulus when the fibre content increased. However, minor decreases in tensile properties were observed. Furthermore, the impact properties were very sensitive to the concentration of fibres. As the fibre concentration went up, there were significant decreases in both IZOD impact strength and Gardner impact failure energy. Chemical resistance of these composites was studied by exposing them in six different chemical solutions (hydrochloric acid, acetic acid, sodium hydroxide, ethyl alcohol, industrial detergent, water) for up to thirty days. The increase in weight and leaching behaviour was observed. As the fibre content increased within the composites, the weight gain was more rapid during chemical ageing. Because there were more fibres exposed on the surface after chemical ageing, it is likely that they contributed to the higher flux of liquids (used for chemical ageing) inside the sample. Among the physical properties, tensile properties were most susceptible to the chemical ageing. One possible reason could be due to the exposed surface area to volume ratio, which was the highest in tensile bars and therefore faster mass transfer taking place into the matrix per volume. Finally, morphological study using scanned electron spectroscopy (SEM) revealed the damage on the surface when exposed to the chemicals. The fibres on the surface had been leached out in the sodium hydroxide solution leaving empty spaces. The fractured surface was also monitored via SEM. Though there was not enough evidence of strong interfacial interactions between the fibre and the polymer, good dispersions were observed.

Thermoplastic composites using natural fibres are studied intensively and widely used in applications including automotive, packaging, consumer goods and construction. Good balance of mechanical properties, processability and low cost are great advantages of these materials on top of the environmental benefits. Recently, there have been various efforts to amplify the positive effects on the environment by replacing the conventional polymers by bio-derived renewable polymers in the composites. Recent studies conducted from our research group showed competitiveness of plant fibre-thermoplastic composites. Implementing the promising results and experience, a new composite design using renewable polyethylene as the matrix material was studied. This polyethylene is a renewable thermoplastic that was derived from sugar cane ethanol. The objectives of this study were to employ renewable high density polyethylene (HDPE) into composites using wheat straw and flax fibre to extend the range of properties of the HDPE while keeping the amount of renewable content to nearly 100%. The chemical resistance of these materials has not been reported before and it was investigated here by measuring and comparing the properties before and after accelerated chemical ageing. Both wheat straw and flax fibre had two different grades in size. Each of them was compounded with HDPE and additives (antioxidant and coupling agent) in a co-rotating twin screw extruder. The concentrations of fibres were varied from 0 to 30 wt-%. Then, injection molded samples were prepared for measurement of properties: tensile, flexural, impact tests. The effects of reinforcing fibre size were studied first. Both length and aspect ratio were considered. For both types of fibre composites, a general trend was observed. There was no clear evidence of improvements in flexural (strength and modulus) and tensile (strength, percentage elongation at break) properties with respect to the change in fibre size. However, impact (IZOD impact strength, Gardner impact failure energy) properties showed some improvements. This result was due to no substantial difference in size and aspect ratios in post-processed fibres that were actually residing in the matrix. There were remarkable improvements in flexural strength and modulus when the fibre content increased. However, minor decreases in tensile properties were observed. Furthermore, the impact properties were very sensitive to the concentration of fibres. As the fibre concentration went up, there were significant decreases in both IZOD impact strength and Gardner impact failure energy. Chemical resistance of these composites was studied by exposing them in six different chemical solutions (hydrochloric acid, acetic acid, sodium hydroxide, ethyl alcohol, industrial detergent, water) for up to thirty days. The increase in weight and leaching behaviour was observed. As the fibre content increased within the composites, the weight gain was more rapid during chemical ageing. Because there were more fibres exposed on the surface after chemical ageing, it is likely that they contributed to the higher flux of liquids (used for chemical ageing) inside the sample. Among the physical properties, tensile properties were most susceptible to the chemical ageing. One possible reason could be due to the exposed surface area to volume ratio, which was the highest in tensile bars and therefore faster mass transfer taking place into the matrix per volume. Finally, morphological study using scanned electron spectroscopy (SEM) revealed the damage on the surface when exposed to the chemicals. The fibres on the surface had been leached out in the sodium hydroxide solution leaving empty spaces. The fractured surface was also monitored via SEM. Though there was not enough evidence of strong interfacial interactions between the fibre and the polymer, good dispersions were observed.

Les processus de lavage, et plus particulièrement l'utilisation de solutions chlorées, peuvent engendrer une dégradation prématurée des membranes de filtration d'eau. Alors que le marché des technologies membranaires en PVDF est en pleine expansion, peu de travaux portent sur l'étude de leur dégradation sur le long terme. Dans ce contexte, la thèse a porté sur l'étude du vieillissement de membranes de filtration commercialisées en PVDF. Les échantillons sont immergés dans une solution d'hypochlorite de sodium et l'effet du pH sur leur dégradation est approfondi. Les propriétés mécaniques, d'hydrophilie, les performances hydrauliques ainsi que la porosité sont étudiées. L'évolution des propriétés est mise en relation avec la structure chimique étudiée à différentes échelles : moléculaire, macromoléculaire et supramoléculaire. Cette approche n'a à ce jour jamais été utilisée dans le cas des membranes fibres creuses en PVDF. Les analyses en chromatographie d'exclusion stérique révèlent les modifications les plus importantes. La dégradation du PVDF des membranes se traduit par un phénomène prédominant de coupures de la chaîne principale du PVDF accompagné, dans une moindre mesure, d'un phénomène de réticulation. Les principales modifications sont constatées à des pHs inférieurs à 10 révélant la possible action conjointe des radicaux OH•, ClO• et Cl•. Le vieillissement d'une membrane PVDF additivée montre à la fois une dégradation du PVDF et une élimination des additifs. Alors que la membrane sans additif conserve une stabilité de ses propriétés, l'élimination des additifs entraine une évolution de la porosité et une propension au colmatage plus importante. Cependant, les membranes PVDF conservent des propriétés d'utilisation acceptables au regard des conditions extrêmes de vieillissement étudiées. / The cleaning processes, especially the use of chlorine solutions, may cause the untimely degradation of the water filtration membranes. While the market for PVDF membrane-based treatment technologies is rapidly expending, only few works deal with the study of their ageing on a long-term basis. In this context, this project focuses on the study of the ageing of two PVDF filtration membranes. Samples are immersed in a sodium hypochlorite solution and the effect of the chlorine solution pH is investigated. The properties of the membranes are characterized throughout the study by tensile tests, hydrophilicity, hydraulic performances and porosity analysis. The evolution of properties is related to the chemical structure of the membranes at a molecular, a macromolecular and a supramolecular scale. Until now, this approach has never been used in the case of PVDF membranes under chlorine conditions. The size exclusion chromatography analyses revealed the most important modifications. The degradation occurs mainly by chain scissions of the PVDF and crosslinking phenomenon in lesser extent. The main modifications occurred at pH less than 10 proving the joint action of OH•, ClO• and Cl• radicals. The ageing of the PVDF membrane containing additives showed at the same time the PVDF degradation and the elimination of the additives. Whereas the properties of the additive-free PVDF membrane were preserved, the elimination of additives led to a modification of the porosity and an increased fouling. However, even if the PVDF degradation is proved, the using properties of the PVDF membranes remain acceptable taking into consideration extreme conditions of ageing studied.

L'industrie alimentaire est de loin l'industrie la plus grande consommatrice d'eau potable et elle rejette environ 500 millions de m3 d'eaux usées par an contenant une charge organique très élevée. Un simple traitement de ce flux par des technologies conventionnelles échoue souvent en raison de facteurs de coûts. Aussi, récemment, l'accent a été largement mis sur la valorisation de ces effluents par récupération des éléments d'intérêt et la production d'eau de bonne qualité en utilisant des procédés à membrane intégrés. Les procédés membranaires couvrent pratiquement toutes les opérations unitaires utiles et nécessaires qui sont utilisés dans les usines de traitement des eaux usées. Ils apportent souvent des avantages comme la simplicité, la modularité, le caractère innovant, la compétitivité et le respect de l'environnement. Ainsi, l'objectif principal de cette thèse est le développement d'un procédé à membrane intégré comprenant microfiltration (MF), osmose directe (FO), ultrafiltration (UF) et nanofiltration (NF) pour la valorisation des eaux usées d'origine agro-alimentaire dans une logique de " zéro effluent liquide ". Nous avons pris les eaux de végétation provenant de la production d'huile d'olive comme support d'étude. Les défis associés au traitement des eaux usées de végétation sont: la variabilité des charges hydrauliques ou organiques, la présence de composés bio phénoliques, le colmatage des membranes et le rejet périodique de grands volumes d'eaux usées. En particulier, la présence de composés bio phénoliques rend ces eaux usées nocives pour l'environnement. Toutefois, la récupération de ces composés phytotoxiques peut également apporter une valeur ajoutée, car ils ont des activités biologiques intéressantes qui peuvent être exploitées dans les industries cosmétique, alimentaire et pharmaceutique. / The food industry is by far the largest potable water consuming industry that releases about 500 million m3 of wastewater per annum with very high organic loading. Simple treatment of this stream using conventional technologies often fails due to cost factors overriding their pollution abating capacity. Hence, recently the focus has been largely centered on valorization through combinatorial recovery of valuable components and reclaiming good quality water using integrated membrane process. Membrane processes practically cover all existing and needed unit operations that are used in wastewater treatment facilities. They often come with advantages like simplicity, modularity, process or product novelty, improved competitiveness, and environmental friendliness. Thus, the main focus of this PhD thesis is development of integrated membrane process comprising microfiltration (MF), forward osmosis (FO), ultrafiltration (UF) and nanofiltration (NF) for valorization of food based wastewater within the logic of zero liquid discharge. As a case study, vegetation wastewater coming from olive oil production was taken. Challenges associated with the treatment of vegetation wastewater are: absence of unique hydraulic or organic loadings, presence of biophenolic compounds, sever membrane fouling and periodic release of large volume of wastewater. Especially presence of biophenolic compounds makes the wastewater detrimental to the environment. However, recovering these phytotoxic compounds can also add economic benefit to the simple treatment since they have interesting bioactivities that can be exploited in the food, pharmaceutical and cosmetic industries.