Dynamic mechanical properties and morphology of polypropylene/maleated polypropylene blends

The dynamic mechanical properties of both homopolypropylene (PPVC)/Maleated Poly-propylene (PP-g-MA) and ethylene-propylene block copolymer (PPSC)/Maleated Poly-propylene (PP-g-MA) blends have been studied by using a dynamic mechanical thermal analyzer (PL-DMTA MKII) over a wide temperature range, covering a frequency zone from 0.3 to 30 Hz. With increasing content of PP-g-MA, α relaxation of both blends gradually shift to a lower temperature and the apparent activation energy ΔE_α increases. In PPVC/PP-g-MA blends, β relaxation shifts to a higher temperature as the content of PP-g-MA increases from 0 to 20 wt % and then change unobviously for further varying content of PP-g-MA from 20 to 35 wt %. On the contrary, in the PPSC/PP-g-MA blends β₁ relaxation, the apparent activation energy ΔE_β1 and β₂ relaxation are almost unchanged with blend composition, while ΔE_β2 increases with an increase of PP-g-MA content. In the composition range studied, storage modulus É value for PPSC/PP-g-MA blends decreases progressively between β₂ and α relaxation with increasing temperature, but in the region the increment for PPVC/PP-g-MA blends is independent of temperature. The flexural properties of PPVC/PP-g-MA blend show more obvious improvement on PP than one of PPSC/PP-g-MA blends. Scanning electron micrographs of fracture surfaces of the blends clearly demonstrate two-phase morphology, viz. the discrete particles homogeneously disperse in the continous phase, the main difference in the morphology between both blends is that the interaction between the particles and the continuous phase is stronger for for PPVC/PP-g-MA than for PPSC/PP-g-MA blend. By the correlation of the morphology with dynamic and mechanical properties of the blends, the variation of the relaxation behavior and mechanical properties with the componenet structure, blend composition, vibration frequency, and as well as the features observed in these variation are reasonably interpreted. © 1996 John Wiley & Sons, Inc.