In situ reinforcement of polypropylene with liquid-crystalline polymers: effect of maleic anhydride-grafted polypropylene

Abstract

The effect of maleic anhydride-grafted polypropylene (MAP) on the mechanical properties of three polypropylene/liquid-crystalline polymer (PP/LCP) blends was investigated. Three LCPs were used in the study. One LCP was a poly(ester amide) and the other two LCPs were copolyesters. The tensile properties of the PP/liquid-crystal (LC) poly(ester amide) blend were affected by the addiction of MAP to a greater extent than were the tensile properties of the two PP/LC copolyester blends. The tensile strength of the former blend increased without reaching a plateau as the level of MAP was increased, whereas the tensile strength of the latter blends showed that a plateau or maximum in the strength existed. The tensile modulus of the PP/LC poly(ester amide) blend showed a 19% increase as the amount of MAP was increased above 5 wt%. Only small changes occurred in the modulus of the PP/LC copolyester blends. The effect of MAP on the mechanical properties of PP/LCP blends indicated that MAP interacted with the amide group preferentially over the ester group. An excess of MAP was also shown to change the morphology from larger elongated structures to smaller structures that can lead to reduced tensile moduli. Measurement of the contact angles of liquids on PP,PP/MAP and the three LCPs indicated that MAP lowered the interfacial tension for all three PP/LCP blends. The reduced interfacial tension and increased adhesion indicated that MAP compatibilized the PP/LCP blends. While in most polymer blends compatibilization leads to finely dispersed drops of the minor components, LCP fibrils were obtained over a large range of compatibilizer concentrations. Finally, isolation of the PP/MAP phase from the LCP phase indicated that MAP did not react with the LCP. Instead, an interaction such as hydrogen bonding was believed to be responsible for the compatibilizing effect of MAP on PP/LCP blends.