Preparation Of Epoxy-functionalized Core-shell Starch Nanoparticles And Study On Modified PLA

Polylactic acid(PLA)is a kind of biodegradable polymer material,however,its inherent brittleness limited the large-scale application of PLA.Therefore,it is necessary to toughen PLA.In this paper,starch core-shell nanoparticles with different epoxidation degrees(G_x-CSS)were used to toughen neat PLA.Then SiO₂was mixed with G₁-CSS to improve the tensile strength of PLA.Furthermore,the nucleating agent TMC-200 was mixed with G₁-CSS,which then were blended with PLA to prepare PLA blends with balanced stiffness and toughness.The research was mainly divided into three aspects:(1)First,esterified starch(ES)with long alkyl chain and reactive sites was prepared.Then,the core-shell starch-based nanoparticles(CSS)were fabricated by soap-free emulsion copolymerization of ethyl acrylate to form poly(ethyl acrylate)(PEA)layer on surface of ES.After that,G_x-CSS were prepared by graft copolymerization of CSS with GMA,which was confirmed by the ATR-FTIR characterization.Transmission electron microscopy(TEM)images showed that G_x-CSS formed a typical core-shell structure,in which the core was consisted of ES and the shell was PEA.Finally,G_x-CSS were melt-blended with PLA to prepare PLA/G_x-CSS blends.Tensile tests showed that when 10 wt%G₁-CSS was added to PLA,the tensile elongation at break of the blend was improved from 5.8%to 387.0%,which was 66times higher than that of neat PLA.The impact strength was increased from 2.5 kJ/m²to 35.9kJ/m²,which was about 13 times higher than that of neat PLA.At the same time,the tensile strength of the blend was still remained at 39.4 MPa.In a word,G_x-CSS can improve significantly the toughness of PLA and retained the higher tensile strength of PLA.DSC and XRD tests showed that G_x-CSS have a certain nucleation effect.With the increase of epoxidation degree,the nucleation effect of G_x-CSS was gradually weakened;In addition,the?-crystal structure of PLA was not changed with the incorporation of G_x-CSS.DMA and SEM tests showed that G_x-CSS with moderate epoxidation degree have good compatibility with PLA.(2)G₁-SiO₂ blend was obtained by blending G₁-CSS emulsion and SiO₂ with particle size of 100 nm.Then,G₁-SiO₂ was melt-blended with PLA to prepare blends.Mechanical properties test showed,when 10 wt%G₁-SiO₂ was added,the elongation at break of PLA blends was increased from 5.8%to 329.7%,the impact strength was increased from 2.5 kJ/m² to 35.0 kJ/m²,and the tensile strength reached to 46.9 MPa.In conclusion,compared with PLA/G₁-CSS blends,SiO₂ particles can further improve the tensile strength of PLA,while the elongation at break and impact strength were maintained at a high level.DSC and XRD tests showed that compared with PLA/G₁-CSS blends,the addition of SiO₂particles could further improve the crystallization properties of PLA without changing the?crystal structure of PLA.DMA test showed that the compatibility of PLA/G₁-SiO₂blends was slightly reduced due to the addition of SiO₂ particles.At the same time,the SEM test showed that the pre-emulsion blending of G₁-CSS and SiO₂ particles could effectively improve the dispersibility of SiO₂ particles in PLA.(3)PLA/G₁-CSS/TMC-200 blends(PLA/G₁/TMC)were prepared by melt blending.The tensile test showed that compared with the PLA/G₁-CSS blends,when 0.3 wt%TMC-200 was added,the tensile strength of PLA/10G₁/TMC blend reached 49.9 MPa,elongation at break was328.7%,and impact strength was 30.9 kJ/m².In short,the addition of TMC-200 can significantly improve the tensile strength of PLA,the impact strength and elongation at break of the blends was maintained at a high level.DSC and XRD tests showed that TMC-200 had a good nucleation effect and did not change the?crystal structure of PLA.The crystallinity of PLA/G₁/TMC blends were not less than 35.0%.