The influence of particle size on the fracture toughness of a PP-based particle composite

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Polymeric particulate composites with thermoplastics, especially polypropylene (PP) matrix and mineral fillers are of great practical importance due to the possibility of modifying mechanical properties and reducing the price/volume ratio of resulting material. PP composite filled by CaCO3 is one of the most widely utilized material with thermoplastic matrix. The properties of the particles themselves (size, shape, material properties) can have a significant effect on the global behaviour of the composite. Generally, the addition of rigid particles to a polymer matrix will have an embrittling effect on the composite. The presence of particles significantly influences the cure reaction, resulting in the formation of the third phase known as the interphase, which possess property distinct from those of the matrix and the particles. The interphase resides in a region between the constituents of the composite with a size of a few to a few thousand nanometers. This region controlled the adhesion between particles and matrix and plays deciding role in the evaluation of the driving force of micro-cracks [1,2]. In the present contribution the interaction of micro-crack propagating in the matrix filled by rigid particles covered by the interphase is analyzed. The stress distribution was determined for variety of particle size and material properties of the interphase. The corresponding values of the stress intensity factors for a micro-crack lying in the matrix were evaluated. On the basis of the numerical model the determining role of the interphase on the final crack path was found. Generally, a crack propagating in the matrix has a tendency to deflect to regions with stiffer materials (particles). If the particle is coated, this effect is shielded by the existence of the interphase and under certain conditions (given by its thickness and material properties) the trend of crack propagation is characterized by the attraction to the particle. This effect is depends on the ratio between particle size and interphase thickness, so the particle should be of small size to have a positive effect on fracture toughness. Consequently, numerical calculations can help design polyprophylene based composite with specifically requested material properties.

PP-based particle composite, particle size, fracture toughness

HUTAŘ, P.; MAJER, Z.; ŠESTÁKOVÁ, L.; NÁHLÍK, L.; KNÉSL, Z.

26. 5. 2008

Institute of Polymer Mechanics, University of Latvia

Riga, Latvia

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