Microhardness of compatibilized blends of polypropylene with a semiflexible liquid-crystalline polymer

The Vickers microhardness of blends of isotactic polypropylene and a semiflexible liquid-crystalline polymer (iPP/LCP 90/10 and 80/20 w/w), compatibilized with 2.5, 5 or 10 wt% PP-g-LCP copolymers with different composition has been studied. It has been shown that the microhardness values of uncompatibilized blends are close to the additive ones, while for compatibilized blends a strong positive deviation from additivity has been established. This result is interpreted by the increase in the degree of crystallinity of PP, by the decrease in the surface free energy of PP crystals and by the decrease in the surface free energy of the LC domains when the PP-g-LCP compatibilizer is present. The effect of the composition and concentration of the compatibilizer on the experimental hardness values has also been studied. The values of the microhardness/modulus of elasticity of some of the materials have been obtained. It is demonstrated that according to these values the compatibilized blends take a position closer to the elastic material in the elastic-plastic spectrum than the uncompatibilized blends. The results are interpreted by the compatibilizing efficiency of PP-g-LCP copolymers towards iPP/LCP blends.