Impact resistance enhancement of PVC compounds with novel core-shell silicone-acrylate impact modifiers: Synthesis, characterization and mechanical properties

Researchers have paid special attention to core-shell impact modifiers to improve toughness and impact strength of PVC. This study describes preparation of a novel core-shell silicon-acrylate impact modifier (SAIM) via emulsion polymerization. Silicone-acrylate monomer (SAM) was synthesized by chemical modification of hydroxyl terminated polydimethylsiloxane (HT-PDMS) under specific conditions. SAIM consists of a poly methyl methacrylate (PMMA) shell obtained from seeded emulsion polymerization onto poly (butyl acrylate/SAM) (P (BA/SAM)) copolymer as the core with different compositions. The crosslinking effect was investigated after the incorporation of varying weight fractions of ethyleneglycol dimethacrylate (EGDMA) in the core formulation. DLS and SEM analyses revealed that the particles are spherical with average core size of 68-84 nm. Then, PVC was compounded with SAIM powder through melt mixing, and the effects of SAM composition and its cross- linking on thermal and mechanical properties were assessed by TGA, DSC, and DMTA analyses. Cross-sectional SEM images demonstrated that the crosslinked SAIM particles were well dispersed within PVC matrix in contrast to the non-crosslinked ones. Direct correlation was found between toughness of the compounds and siloxane and gel content of SAIM, particularly at 0 and- 23 degrees C. Impact strength of the compounds improved from 3.9 to 9 kJ/ m2 with the increase in SAM content of the core in particles at-23 degrees C. Furthermore, a higher siloxane content combined with reduced crosslinking led to a decrease in tensile modulus and a slight increase in elongation at break. These new SAIM impact modifiers exhibited excellent performance, particularly at very low temperatures.