Structure And Properties Of Liquid-like Nanofluids Filled In Polylactic Acid Composites

As a kind of biodegradable thermoplastic polyester with high modulus and high strength,Polylactic acid?PLA?is one of the most promising materials with excellent biocompatibility and environmental friendliness.However,PLA has native brittleness,which greatly limits its further development and application.Recently,domestic and overseas scholars have taken up many researches on reinforcing and toughening PLA matrix with macromolecule polymer and inorganic nanoparticles,but the agglomeration of reinforcements always affects properties of PLA composites.In this paper,solvent-free nanofluids were prepared by using organic polymer and inorganic nanoparticles as core materials,which can successfully improve their dispersion and interface compatibility in the PLA matrix,and then nanofluids/PLA composites with antibacterial activity,antistatic property,moisture absorption,high strength and toughness were fabricated.The main contributions are as follows:1. The covalently bonded starch fluids,which composed of carboxymethyl starch as the core and polyethylene glycol-substituted tertiary amines as the shell,was prepared by chlorination.FTIR,TG and TEM were used to characterize the chemical structure and properties of starch fluids,which suggested that the obtained starch fluids had a good dispersion and exhibited the core-shell structure.Dynamic rheology tests showed that starch fluids displayed liquid-like behavior at room temperature.Starch fluids/PLA membrane was obtained by loading starch fluids into PLA matrix by solution casting method.Results from XRD test proved that starch fluids,acted as a plasticizer,can not only improve the interfacial interaction between starch and PLA matrix,but also enhance the toughness of PLA composite membrane.The tensile and thermal conductivity tests suggested that PLA composite membrane with 10 wt%loading of starch fluids can improve the toughness and thermal conductivity at the same time,elongation at break increased remarkably from 6.88%to17.81%?raised nearly 1.6 times?.Thermal conductivity was increased from 0.141 Wm^-1 K^-1for pure PLA to a maximum value of 0.31 Wm^-1 K^-1for 10 wt%loading of starch fluids.Four-probe tester indicated that the organic chains grafted on the outer layer of starch fluids can promoted the polarization process of PLA chains,increasing the electrical conductivity from5.07×10^-5 to 4.995 S cm^-1 with the increment of current.2. TiO₂ nanofluids were prepared by ion exchange reaction with polysiloxane quaternary ammonium salt and nonylphenol polyoxyethylene ether sulfate as the shell grafted on TiO₂nanoparticles as core materials.TG and rheological tests suggested that TiO₂ nanofluids had a good thermal stability,dispersibility and exhibited the liquid-like fluidity.After homogeneous mixing of TiO₂ nanofluids and PLA matrix,uniform electrospun TiO₂ nanofluids/PLA fiber was obtained by electronspinning.TiO₂ nanofluids can bring a high charge density to the solution,which results in uniform fibers with a narrow diameter distribution.We explored the functionary mechanism of TiO₂ nanofluids on PLA matrix,which was characterized by AFM and tensile tests.It was proved that TiO₂ nanofluids,acted as plasticizer and crystallization promoter,can overcome the brittleness of PLA matrix,simultaneously reinforcing and toughening PLA at the same time.When TiO₂ nanofluids content were 5%,tensile stress and Young's modulus had increased 4 and 8 times,respectively.When TiO₂ nanofluids content were 20%,elongation at break reached the maximum of 74%,which was 2.3 times than pure PLA fibers.WCA,antibacterial efficiency and rejection were utilized to investigate the influence of TiO₂ nanofluids on PLA composites with wettability,antibacterial activity and separation properties.Amphipathy of TiO₂ nanofluids provided PLA composites an excellent wettability,and after ion-exchange reaction polysiloxane quaternary ammonium salt can work as an antimicrobial against E.coli and S.aureu.