Interfacial crystalline behavior in glass-fiber/polypropylene composites modified by block copolymer coupling agents

A kind of di-block copolymer polystyrene-block-poly(gamma-methacryloxy-propyltrimethoxysilane) (PS-b-PMPS) with different PS block length and a kind of tri-block copolymer polystyrene-block-poly(n-butylacrylate)-block-poly(gamma-methacryloxypropyltrimethoxysilane) (PS-b-PnBA-b-PMPS) with different PnBA block length were synthesized by atom transfer radical polymerization (ATRP), in which PS was a 'hard' block and PnBA was a 'soft' block. The interfacial crystallization behaviors of glass fiber/polypropylene systems modified with different coupling agents MPS, PS-b-PMPS, and PS-b-PnBA-b-PMPS were investigated on different crystallization conditions. Transcrystallinity could not be induced on non-isothermal crystallization or without maleic anhydride (10%) in polypropylene, but it appeared when glass fibers were treated with common silane coupling agent gamma-methacryloxypropyltrimethoxysilane (MPS) and di-block copolymer coupling agent PS-b-PMPS in 135 degrees C isothermal crystallization without shear and 150 degrees C isothermal crystallization with shear. However, it disappeared at the interface when the samples were treated with tri-block copolymer coupling agent (PS-b-PnBA-b-PMPS) either under static or shear-induced condition. It might be that the flexible interlayer formed by the flexible block PnBA of PS-b-PnBA-b-PMPS could relax not only the thermal stress resulted from interface temperature gradient arising from sample cooling for crystallization, but also the shear stress induced by fiber/matrix interface shear.