Effect of a poly(dimethylsiloxane) modified polyolefin additive on the processing and surface properties of LLDPE

摘要

A polydimethylsiloxane (PDMS) modified polyolefin (obtained by reacting an ethylene-ethyl acrylate-maleic anhydride (EEAMA) copolymer with an amine terminated PDMS in the melt phase) was used as a processing aid to facilitate the extrusion of linear low density polyethylene (LLDPE). In blends of LLDPE and PDMS modified polyolefin (PMPO), apparent viscosity and shear stress at the die wall are reduced in comparison to pure LLDPE, and extrusion instabilities are delayed as evidenced by the fact that extrudate surface roughness only occurs at higher shear rates when the additive is present. A higher PDMS content in the PMPO leads to a more pronounced delay of extrusion instabilities. Single-screw extrusion of LLDPE compounds with a PMPO results in nearly doubled throughput per unit input energy. The reduction of viscosity and improvements in extrudate quality are attributed to the decreasing surface free energy of the PMPO with an increasing PDMS content, as determined by contact angle measurements. Chemical composition analysis of the extrudate surface and cross-section reveals silicon enrichment at the surface. The friction coefficients of pure PMPO and PMPO/LLDPE blends are measured and found to decrease as a result of the presence of PDMS.