The yield strength of particulate reinforced thermoplastic composites

Abstract

The effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES). When there is perfect adhesion between constituents, an upper bound for tensile yield strength is found to be 1.33 times the matrix yield strength above a critical volume of particulate concentration. Utilizing Sjoerdsma's model for interacting stress concentration fields, one can determine the concentration dependence of the yield strength below the critical filler volume fraction. When there is no adhesion between constituents, a modified version of an equation by Nicolais and Narkis adequately describes a lower bound for the tensile yield strength. The particulate concentration and the matrix ductility are the prime factors in controlling the brittle failure of the composite. Upper and lower bounds for brittle failure strength are characterized using a strength‐of‐materials approach and stress concentration factors for both “perfect” and “zero” adhesion. The properties of calcium carbonate filled PP homopolymer were measured over a wide range of filler volume fractions. CaCO3 was either treated with stearic acid to prevent adhesion between constituents or used as received. Maleic anhydride grafted PP (MPP) was used to promote adhesion. For filler volume fractions below 0.2, yielding of the composite by combined microcavitation and shear deformation was the principal failure mechanism. At vf above 0.35, a brittle failure mechanism dominated. In the range between 0.2 and 0.35, both failure modes were observed in the populations tested. Good agreement was found between the experimental results and the proposed model.

Blends of poly(vinylidene fluoride) with polyamide 6: interfacial adhesion, morphology and mechanical properties

“…Recent studies have suggested that the yield behaviour of polymer blends is affected by the interfacial adhesion [31,[33][34]37]. Pukanszky et al [31][32][33][34][35][36][37] have proposed the upper and lower values for the yield stress, in case of extreme values of interfacial adhesion. When the interfacial adhesion is strong enough for the stress transfer to occur between two phases, the yield stress would obey the law of mixtures (the upper value):…”

Phenolic rigid organic filler/isotactic polypropylene composites. III. Impact resistance property

“…The brittle-ductile transition of the composites takes place at filler content of about 4%. According to Percolation Theory [14][15][16][17], this value is defined as the critical volume fraction of this system. At filler content of 5%, the impact strength attains the maximum.…”

Performance evaluation of synthesized acrylic acid grafted polyethylene in aluminum hydroxide highly filled polyethylene composites

“…2,3 Unfortunately, the high loading of Al(OH) 3 in PE leads to the reduction of impact strength and elongation at break, due primarily to the poor interfacial adhesion between the two components. Coupling agents act to provide a means of transferring stress from the polymer matrix to the filler particles, which ultimately result in better mechanical properties.…”

“…Halogen-based flame retardants were used to produce flame-retardant PE for many years, but they give off heavy smoke and hazardous gases during combustion. In recent years, nonhalogen flame retardants such as Al(OH) 3 and Mg(OH) 2 have therefore been considered an attractive alternative to halogen-based flame retardants and have become a major trend in the development of flame-retardant polyethylene.…”