Joint effects of long-chain branching and specific nucleation on morphology and thermal properties of polypropylene blends

Abstract

The influence of long-chain branching and specific β-nucleation on polymorphic composition, melting and crystallization, and morphology of polypropylene blends were investigated by wide-angle X-ray scattering, differential scanning calorimetry, and scanning electron microscopy. Linear polypropylene and long-chain branched polypropylene were used for the preparation of blends in various proportions. N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide was introduced (0 or 0.03 wt%) as a β-specific nucleating agent into prepared blends. It was found that LCB-PP strongly induces γ-phase formation in the blends and suppresses the nucleation activity of a β-specific nucleating agent. Blends containing a predominant amount of α-and γ-phases showed higher thermodynamic stability within melting, as compared to the samples rich in β-phase. During crystallization, LCB-PP in the blends increases nucleation density by self-seeding effect, manifesting itself in the shift of crystallization temperature. β-phase in the blends is distinctly separated in spherulites, while α-and γ-phases coexist on the lamellae level.