Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE The graphical abstract illustrates the foaming behavior, melt strength, and free volume characteristics of HMSPP and PP samples at different foaming temperatures. HMSPP-R exhibits the highest expansion ratio, which is attributed to its superior melt strength and larger free volume, enhancing the solubility of carbon dioxide and promoting cell growth during foaming.


ABSTRACT
Compared with polypropylene homopolymer (PP-H), polypropylene random copolymer (PP-R) contains ethylene units that disrupt chain regularity and enhance chain mobility, which is expected to improve the solubility of foaming agents and promote foaming performance. However, PP-R still suffers from low melt strength as PP-H. In this study, high melt strength polypropylene (HMSPP) was prepared from both PP-H and PP-R via reactive extrusion, using benzoyl peroxide (BPO) as the initiator and vinyl polydimethlsiloxane (VS) and styrene (St) as grafting monomers. The melt strength of HMSPP-R reached 69.6 cN, which is 20.5 times that of PP-R, while HMSPP-H reached 55.9 cN, only 8.6 times that of PP-H. Combined with the rheological results, it suggests that HMSPP-R contains more branched structures than HMSPP-H. Foaming results showed that HMSPP-R achieved a maximum expansion ratio of 28.7 times, while HMSPP-H can only achieve up to 24.1 times. Solubility tests and molecular dynamics simulations further revealed that HMSPP-R has a larger free volume, enhancing the solubility of CO2 and thus improving foaming performance. This study holds significant industrial guidance value for the preparation of HMSPP suitable for foaming.