Impact fracture behavior of PP/ash composites with different coupling agents

SANTIAGO GARCÍA PARDO; ESTEBAN IGARZA; VALERIA PETTARIN; L. BARRAL LOSADA; M.J. ABAD; CELINA BERNAL

Les Diablerets, Switzerland

Conferencia; 5th International Conference on Fracture of Polymers, Composites and Adhesives - 5th ESIS TC4 Conference; 2008

In the present work, the impact fracture behavior of polypropylene (PP) reinforced with fly ash derived from the biomass combustion was investigated. Different coupling agents (a silane type coupling agent and maleic anhydride grafted polypropylene) were used in the composites formulation in order to change the compatibility between PP and ash. The effect of the ash content on the fracture properties was also analyzed. Instrumented impact tests were performed on SENB specimens obtained from compression-molding plaques in three-point bending using a “falling weight” type machine at 1 m/s. In-plane fracture behavior was studied for all composites through the critical energy release rate (GIC). In the case of the composites with silane-treated ash, out-of-plane fracture properties were also studied through biaxial impact tests performed on disk shaped samples. It was observed that GIC values decrease with ash content irrespectively of the coupling agent used, suggesting that ash particles act as critical flaws for crack initiation. The incorporation of both the silane coupling agent or the maleic anhydride grafted polypropylene in the composites formulation led to better fracture properties, as a result of the improvement in the interfacial adhesion and/or in the second phase particles dispersion in the polymer matrix. Also, fracture energy obtained from biaxial impact tests showed the same trend. In addition, SEM fracture surface observations revealed that ash particles debonded from the PP matrix due to the lack of interfacial adhesion between both phases, especially in composites with silane-treated ash which exhibited the poorer matrix/filler interaction. Furthermore, the polymer matrix was unable to develop plastic yielding at the high strain rates developed under impact. Further work is in progress in order to elucidate acting deformation mechanisms by means of low blow tests.