Preparation of core-shell impact modifier particles for PVC with nanometric shell thickness through seeded emulsion polymerization

摘要

The improvement in toughness of rigid polymers like poly(vinyl chloride) (PVC) has been of great interest for developing their applications. This could be provided by designing impact modifiers which could be blended with the polymeric matrix. Here, core-shell type impact modifier particles with different glass transition temperatures of the shell and specifically, with nanometric shell thickness were prepared through seeded emulsion polymerization. The core consisted of polybutadiene particles and the shell was made of poly(methylmethacrylate-co-butyl acrylate) that was grafted onto the surface of the seed particles. The polymerization reaction was optimized and the resulting latex particles were well characterized by several techniques such as DSC, DLS, SEM, and TEM. It was found that the core-shell particles have diameters of about 350-360 nm, including the shell with thickness of almost 20-30 nm and glass transition temperatures ranging between 70 and 120 ℃. The prepared particles were blended with PVC and the corresponding impact strengths of the moldings were measured by means of Izod impact test. The impact results revealed that by decreasing T_g of the shell in impact modifier particles, the impact resistance of the molded sheets increased remarkably. Also the brittle-ductile transition temperatures (BDTT) of the prepared blends were studied and an increase in BDTT was found with lowering T_s of the shell.