Blends of isotactic polypropylene and natural terpene resins. I. Phase structure, thermal, and dynamic-mechanical properties

This article discusses the influence of two natural terpene resins (NTR), poly(?-pinene) (P?P A115) and poly(d-limonene) (PL C115), on morphology, miscibility, thermal, and dynamic-mechanical properties of their blends with isotactic polypropylene (iPP). The NTR have interesting physical and chemical properties, and they are approved for food contact application. From the results of differential scanning calorimetry and dynamic-mechanical thermal analysis it was deduced that both the resins were completely miscible with the amorphous iPP up to the composition investigated here (70/30 wt %). Scanning electron microscopy (SEM) analysis instead showed that the 70/30 iPP/P?P A115 blend and 80/20 and 70/30 iPP/PL C115 blends contained very small domains homogeneously distributed into the matrix. It is hypothesized that the domains are likely formed by the terpene-rich phase, and the matrix by the iPP-rich phase (besides the crystallized iPP phase). The iPP-rich phase and the NTR-rich phase would have the glass transition temperatures so close that they cannot be resolved by DSC and DMTA. Finally, for the iPP/P?P A115 system an upper critical solution temperature (UCST) is proposed.