Conclusions
Polypropylene/wood flour composites with different fibre content were prepared by intensive mixing and subsequent compression moulding. The effect of fibre content and the incorporation of maleic anhydride grafted polypropylene (MAPP) on the materials tensile and fracture and failure behaviour was investigated under quasi-static loading conditions by means of uniaxial tensile and fracture mechanical tests.
Reliable fracture toughness data were obtained for different PP/ WF composites. They are useful for design purposes when these composites are used in structural applications.
An increase in Young’s modulus was obtained with the addition of wood flour to PP as expected, whereas tensile strength, strain at break and fracture toughness were found to decrease as fibre content increased. The presence of MAPP was beneficial to tensile strength and ductility and had no significant effect on fracture toughness.
From SEM analysis of fracture surfaces, the main failure mechanisms occurring in our composites were identified. In the unmodified composites, debonding and fibre pullout were found to be the main energy absorbing mechanisms, whereas in the composites with MAPP fibre breakage was dominant as a result of an increased interfacial adhesion.
The improved fibre dispersion promoted by the coupling agent and initially detected from tensile and fracture results as well as fracture surface analysis, was also confirmed from the application of a simple model for strength.
From the results obtained in this work, it can be concluded that although ductility and toughness were reduced for the composites respect to PP, environmentally friendly stiffer materials were obtained by using MAPP as a coupling agent. These materials present a significant reduction in the amount of the non-biodegradable material (PP) and also a concomitant cost saving without sacrificing strength.
Conclusions
Polypropylene/wood flour composites with different fibre content were prepared by intensive mixing and subsequent compression moulding. The effect of fibre content and the incorporation of maleic anhydride grafted polypropylene (MAPP) on the materials tensile and fracture and failure behaviour was investigated under quasi-static loading conditions by means of uniaxial tensile and fracture mechanical tests.
Reliable fracture toughness data were obtained for different PP/ WF composites. They are useful for design purposes when these composites are used in structural applications.
An increase in Young’s modulus was obtained with the addition of wood flour to PP as expected, whereas tensile strength, strain at break and fracture toughness were found to decrease as fibre content increased. The presence of MAPP was beneficial to tensile strength and ductility and had no significant effect on fracture toughness.
From SEM analysis of fracture surfaces, the main failure mechanisms occurring in our composites were identified. In the unmodified composites, debonding and fibre pullout were found to be the main energy absorbing mechanisms, whereas in the composites with MAPP fibre breakage was dominant as a result of an increased interfacial adhesion.
The improved fibre dispersion promoted by the coupling agent and initially detected from tensile and fracture results as well as fracture surface analysis, was also confirmed from the application of a simple model for strength.
From the results obtained in this work, it can be concluded that although ductility and toughness were reduced for the composites respect to PP, environmentally friendly stiffer materials were obtained by using MAPP as a coupling agent. These materials present a significant reduction in the amount of the non-biodegradable material (PP) and also a concomitant cost saving without sacrificing strength.
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