Construction And Properties Of Environmentally Friendly Composites With Thermoresponsive Wettability

The responsive biodegradable materials have attracted increasing attention due to the ability to mimic the fundamental reaction of living systems.These materials can respond to environmental stimuli to undergo significant physicochemical changes.Poly(N-isopropylacrylamide)(PNIPAm)is a widely studied temperature-sensitive polymer,and its critical solution temperature(LCST)is due to the hydrophilic amide group in its structure and the hydrophobic isopropyl group.The interaction between the radical and the water molecule exhibits a conformational transition between hydrophilic and hydrophobic.If it is compounded with polylactic acid(PLLA),it can not only effectively improve the hydrophobicity of PLLA but also endow PLLA with an intelligent response.Therefore,from the perspective of molecular structure,PNIPAM based polymer was synthesized by copolymerization and grafting and blended with PLLA to improve the temperature-sensitive wettability of the composite PLLA.1.Using N-isopropylacrylamide and vinyl acetate as raw materials,N-isopropylacrylamide-vinyl acetate copolymer(P(NIPAm-co-VAc))was successfully synthesized by free radical copolymerization.The composites were prepared by physical solution blending with PLLA.Scanning electron microscopy(SEM)showed that P(NIPAm-co-VAc)was uniformly dispersed in the PLLA matrix;when the blending mass ratio of P(NIPAm-co-VAc)reached 20 wt%,the composite showed a good temperature responsive wettability;its hydrophilic angle was 40.5° at 25 °C,when the temperature was increased to 45 °C,the water contact angle of the composite membrane rose to 69°,and it had good recyclability;in addition,the incorporation of 20 wt% P(NIPAm-co-VAc)had an obvious toughening effect on PLLA.2.PNIPAm-OH was synthesized by using 2-mercaptoethanol as a chain transfer radical and BPO as catalyst,and PNIPAm-PCL was prepared via ring-opening polymerization.Then PNIPAm-PCL and PLLA were blended to prepare PLLA composites.The effects of PNIPAm-PCL on the thermodynamic properties,hydrophilic properties,mechanical properties and temperature-controlled wetting properties were investigated.The PNIPAm-PCL/PLLA exhibited the optimal comprehensive properties at 20 wt% blend ratio.Although the tensile strength reduced slightly,its toughness was significantly improved,its elongation at break reaches 135.1%.and its wettability can show a good change with temperature when the temperature increased to 45 ?.The hydrophilic angle was 80.1°,and the hydrophilic angle decreased to 29.8° as the temperature decreased to0 °C;and the composite material still exhibited good temperature response after friction,indicating that the composite material had good abrasion resistance.