| Biodegradable green plastic poly?lactic acid??PLA?,which can be derived from biomass resources,is widely used in our daily life because of its good mechanical strength and processability.However,the disadvantages of poor toughness,slow crystallization rate,poor thermal stability and slow degradation rate in natural environment severely limit the further application of PLA.In this paper,a kind of biodegradable polyester elastomer particles?BEP?/graphene oxide?GO?compound powder in which GO and BEP were adhered and GO sheets were isolated from each other was designed and prepared.The high toughness and biodegradable PLA/BEP/GO ternary nanocomposites were prepared by blending PLA with BEP/GO compound powder,and the effects and its mechanism of BEP type,particle size,BEP loading and GO type on the toughness,thermal stability,crystallization property and biodegradability of the composites were discussed.1.Preparation of PLA/BEP/GO ternary nanocomposites.Vulcanized polyester emulsion was prepared by melt polycondensation,polyester emulsification and radiation vulcanized processes.The hydroxyl terminated BEP?HBEP?and carboxyl terminated BEP?CBEP?with particle sizes of 200 nm,500 nm and 1?m were prepared by spray drying from vulcanized polyester emulsion,and saline BEP?SBEP?was prepared by salinization of CBEP.Different kinds of BEP/GO compound powders were prepared by spray drying after the vulcanized polyester emulsion was evenly mixed with single-layer high-oxygen??50 wt%?GO?GO-O?,single-layer low-oxygen??30 wt%?GO?GO-S?and multi-layer low-oxygen??30 wt%?GO?GO-M?.PLA/BEP binary composites and PLA/BEP/GO ternary nanocomposites were prepared by melt-blending of PLA with BEP and BEP/GO compound powder,respectively.2.Study on mechanical properties of PLA/BEP/GO ternary nanocomposites.Both the BEP and BEP/GO compound powder can significantly improve the toughness of PLA.The elongation at break and notched impact strength of the PLA/BEP binary composites with 7.5 phr CBEP?500 nm?are 17.1 and 2 times than that of neat PLA,respectively.At the same time,the addition of GO can improve the tensile strength of PLA composites.The tensile strength of the PLA/BEP/GO ternary nanocomposites with CBEP/GO-O?200 nm?loaded is 4.9%higher than that of the corresponding PLA/BEP binary composites,and the elongation at break and notch impact strength are 9.8 and 1.6times than that of neat PLA,respectively.3.Study on the thermal stability and electrical/thermal conductivity of PLA/BEP/GO ternary nanocomposites.The thermal stability of PLA/BEP binary composites was slightly lower than that of neat PLA,while the PLA/BEP/GO ternary nanocomposites was higher than that of neat PLA.The initial decomposition temperature of the PLA/BEP/GO ternary nanocomposites with the addition of HBEP/GO-S?1?m?was 10.4°C higher than that of neat PLA.BEP/GO compound powder can also improve the electrical and thermal conductivity of PLA,of which BEP/GO-S compound powder has the best effect.The electrical conductivity of PLA/BEP/GO ternary nanocomposites which loading 0.6 phr of GO-S increases from5.4×10-16 S/m of neat PLA to 6×10-10 S/m,and the thermal conductivity increases from0.079 W/?m?K?of neat PLA to 0.137 W/?m?K?.4.Study on crystallization properties of PLA/BEP/GO ternary nanocomposites.Both BEP and BEP/GO compound powder can be used as heterogeneous nucleating agents to improve the crystallization properties of PLA.The isothermal melting crystallization half-time of the PLA/BEP binary composites with 7.5 phr SBEP?200 nm?is shortened by 32.7%compared to neat PLA,and the crystallinity is increased by 0.23times than neat PLA.The crystallization half-time of the PLA/BEP/GO ternary nanocomposites with SBEP/GO-O?200 nm?compound powder is shortened by 19%compared to neat PLA,and the crystallinity is increased by 0.18 times than neat PLA.The addition of BEP or BEP/GO compound powder did not change the crystal shape and crystallization mechanism of PLA.The nucleation speed of neat PLA in the crystallization process is slow and the spherulite size is large,while the BEP and BEP/GO compound powder not only can improve the nucleation speed and the number of crystal nucleus of PLA,but also reduce the spherulite size and increase the spherulite density.5.Study on the degradability of PLA/BEP/GO ternary nanocomposites.Both BEP and BEP/GO compound powder can increase the water absorption and degradation rate of PLA in different environments.For the weight loss rate after 500 U/mL lipase degradation for 15 days and soil burial degradation for 4 months:the PLA/BEP binary composites with 10 phr of SBEP?200 nm?was 11.5 and 8.5 times of neat PLA,while the PLA/BEP/GO ternary nanocomposites with addition of SBEP/GO-S?200 nm?compound powder was 11.3 and 8.3 times of neat PLA.The surface of PLA/BEP binary composites and PLA/BEP/GO ternary nanocomposites after 4 months of soil burial degradation showed a large number of holes and furrows compared with neat PLA,and the surface roughness increased significantly. |
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