Polypropylene continues to be the mainstream choice thermoplastic for automotive applications. In many applications PP is filled with mineral fillers for improvement of properties. Biobased natural fillers or fibres are attractive materials to reduce the weight because of the low specific gravity of the biobased materials compared to the mineral fillers. Our group has done extensive research on the development of wheat straw fiber in thermoplastics in the past years. It is very important to understand the behaviour of single fillers on composites before studying the effects of mixing fillers or fibers (hybridization). The objective of this study is to evaluate and compare systematically the effects of wheat straw and mineral fillers in the polypropylene matrix. The study includes two types of wheat straw (WS) categorized based on their size (fine WS and medium WS) and three different types of natural minerals (Talc, Mica and Wollastonite). Three types of polypropylene (PP), Homopolymer PP, High Impact Copolymer PP and Homopolymer-Copolymer Blend PP, were investigated as the matrix. This study also evaluates the effect of combining two fillers (WS and mineral filler) in the hybrid composite. The fillers were formulated in three different percentages (20, 30 and 40wt %) and compounded via extrusion. Samples for all formulations were prepared by injection molding. The mechanical properties (flexural modulus and strength, tensile modulus and strength, impact strength), water absorption and density were measured. The properties of hybrid composites were evaluated by varying the amounts of two fillers at 10wt%-20wt%, 15wt%-15wt% and 20wt%-10wt% each, keeping the overall filler content constant at 30wt%. The effect of type of filler, filler size and filler content were critical in this work. The results obtained from this study indicated that filler type and filler content greatly influenced the mechanical properties and water absorption characteristics of the composites. The flexural modulus increased with increasing filler content. It was interesting to observe that though the impact strength decreased with the addition of fillers, increasing the filler content from 20 to 40 wt% did not affect the property. With respect to all fillers, wollastonite improved the mechanical properties significantly. Increasing the amount of WS content reduced the composite’s resistance to water absorption. Among mineral fillers, mica showed significantly higher percentage gain in weight with water absorption. Combination of fillers at varying percentages did not have any synergy effect on the mechanical behaviour of the composite. The percentage increase in weight with water absorption was observed to be increasing with increasing WS content in hybrid composites, but significantly lower than pure WS composites. The morphological study on WS composites revealed improved interaction of filler with homopolymer and polypropylene blend.

Polypropylene continues to be the mainstream choice thermoplastic for automotive applications. In many applications PP is filled with mineral fillers for improvement of properties. Biobased natural fillers or fibres are attractive materials to reduce the weight because of the low specific gravity of the biobased materials compared to the mineral fillers. Our group has done extensive research on the development of wheat straw fiber in thermoplastics in the past years. It is very important to understand the behaviour of single fillers on composites before studying the effects of mixing fillers or fibers (hybridization). The objective of this study is to evaluate and compare systematically the effects of wheat straw and mineral fillers in the polypropylene matrix. The study includes two types of wheat straw (WS) categorized based on their size (fine WS and medium WS) and three different types of natural minerals (Talc, Mica and Wollastonite). Three types of polypropylene (PP), Homopolymer PP, High Impact Copolymer PP and Homopolymer-Copolymer Blend PP, were investigated as the matrix. This study also evaluates the effect of combining two fillers (WS and mineral filler) in the hybrid composite. The fillers were formulated in three different percentages (20, 30 and 40wt %) and compounded via extrusion. Samples for all formulations were prepared by injection molding. The mechanical properties (flexural modulus and strength, tensile modulus and strength, impact strength), water absorption and density were measured. The properties of hybrid composites were evaluated by varying the amounts of two fillers at 10wt%-20wt%, 15wt%-15wt% and 20wt%-10wt% each, keeping the overall filler content constant at 30wt%. The effect of type of filler, filler size and filler content were critical in this work. The results obtained from this study indicated that filler type and filler content greatly influenced the mechanical properties and water absorption characteristics of the composites. The flexural modulus increased with increasing filler content. It was interesting to observe that though the impact strength decreased with the addition of fillers, increasing the filler content from 20 to 40 wt% did not affect the property. With respect to all fillers, wollastonite improved the mechanical properties significantly. Increasing the amount of WS content reduced the composite’s resistance to water absorption. Among mineral fillers, mica showed significantly higher percentage gain in weight with water absorption. Combination of fillers at varying percentages did not have any synergy effect on the mechanical behaviour of the composite. The percentage increase in weight with water absorption was observed to be increasing with increasing WS content in hybrid composites, but significantly lower than pure WS composites. The morphological study on WS composites revealed improved interaction of filler with homopolymer and polypropylene blend.

Dans un contexte de développement durable, des matériaux thermoplastiques multiphasés biosourcés issus de dimères d’acides gras ont été élaborés pour développer une « eco-membrane » durable pour le bâtiment. Différentes formulations intégrant des polymères thermoplastiques biosourcés, polyuréthane thermoplastique (TPU) et polyamide (DAPA), des micro-charges minérales et des renforts cellulosiques ont été élaborées et analysées. Les relations « structures-propriétés » de ces systèmes multiphasés ont été étudiées. Les architectures macromoléculaires proches ont permis d’obtenir un certain degré de compatibilité entre les polymères. Les viscosités à l’état fondu du TPU et DAPA sont comparables, ce qui permet une bonne dispersion des phases du mélange lors de la mise en œuvre. Les propriétés mécaniques et la stabilité dimensionnelle des mélanges sont améliorées par ajout de micro-charges minérales. L’impact du facteur de forme des charges sur le module d’Young a été analysé et modélisé avec un modèle micro-mécanique. Des essais du type charge-décharge ont également été menés afin d’étudier le comportement à la fatigue des biocomposites. Enfin, les interactions et les affinités entre les renforts et polymères ont été approchées. Des modifications chimiques ont été développées à la surface des fibres afin de diminuer leurs caractères hydrophiles et d’améliorer la compatibilisation avec la matrice. L’impact de ces modifications sur l’interface fibres-matrice a ensuite été analysé. Les différentes études réalisées ont permis de sélectionner pas à pas les différents constituants de l’éco-membrane pour réaliser in fine un prototype prometteur. / In the context of sustainable development, renewable multiphase systems from thermoplastics based on dimers of fatty acids were prepared to develop a renewable waterproofing material for building applications. Formulations based on thermoplastics, i.e. thermoplastic polyurethane (TPU) and polyamide (DAPA), mineral micro-fillers and cellulosic fibers were prepared with a special focus on the morphology-property relationships of the multiphase systems obtained thereof. The close macromolecular architectures promote a certain degree of compatibility between the polymers. Comparable viscosities in the melt state ensure a good dispersion of the matrices within each other during processing. The mechanical properties and dimensional stability were improved with micro-fillers. The effect of the aspect ratio of the fillers on the elastic properties was investigated and micro-mechanical modelling of the Young’s Modulus was performed. The fatigue behavior of the biocomposites was also examined through loading and unloading tests. Finally, interactions and affinities between the fibers and polymers were characterized. Chemical modifications were carried out on the surface of the fibers to decrease their hydrophilic nature and improve the fiber-matrix adhesion. The effect of the chemical modification was then investigated. Step-by-step, the studies carried out ensured the selection of the optimal components for a renewable waterproofing material enabling the production of a promising prototype.