| Polylactic acid(PLA)is a new type of biodegradable material which can be widely used in biomedicine and food packaging.However,some properties such as high brittleness and low heat denaturation temperature of PLA hinder its wide application in diverse fields.In order to solve these problems and broaden the application,PLA needs to be toughened.In this paper,a series of PLA/SBM blends were prepared by blending two brands of PLA and four SBMs with different structures.And the properties of the blends were characterized.The factors such as the properties of PLA,molecule parameters,that affect the properties of PLA/SBM were investigated.In order to improve the compatibility of SBM with PLA,SBM was modified by grafting glycidyl methacrylate(GMA)on to the chains.The research includes the following aspects.(1)PLA with lower molecule weight(PLA4032D,melt flow rate of 7g/10 min)undergoes a brittle-tough transition at a low concentration(10wt%)of SBM in PLA,and the blend gives a good toughness.The PLA with higher molecular weight(PLA2003D,melt flow rate of 6g/10 min)undergoes a brittle-tough transition at a higher concentration(15wt%).When the SBM concentration is 25wt%,the PLA4032D impact strength reaches the maximum value(9.34 KJ/m~2),and then begins to decline.PLA2003D has the highest strength when the SBM concentration is 20wt%,and the strength is10.78 KJ/m~2.The PLA/SBM blend has a two-phase structure,and the critical interpartical distance of matrix is 194 nm for PLA4032D/SBM and 119 nm for PLA2003D/SBM.The Blending with SBM,which acts as nucleating agent,could decrease the temperature of crystallization of PLA4032D,and increase the degree of crystallization.However,the degree of crystallization of PLA2003D decrease when the SBM was introduced,and the PLA2003D/SBM blend turns into amorphous as the concentration of SBM reaches 15wt%.(2)SBM E21,which has a small molecular weight and a moderate butadiene content,shows a good toughening effect on PLA.The block composition of the copolymer has a greater influence on the tensile properties of the blend.The rigidity of the PLA/SBM blend was reduced when the content of the polybutadiene component increased.Regardless of which SBM is used,the crystallinity of the PLA4032D/SBM blend can be increased.(3)SBM-g-GMA was prepared by melt grafting.When GMA,NVP(N-vinylpyrrolidone)and DCP(dicumyl peroxide)were 3%,3%and 0.3%of the total mass of the system,SBM-g-GMA has a higher grafting rate of 0.27%.PLA was toughened by reactive blending with epoxy-functionalized elastomer SBM-g-GMA,which strengthens the interfacial adhesion of the two phases and improves the compatibility of SBM with PLA.Within the experimental range,the impact strength of PLA4032D/SBM-g-GMA blends increased with the increasing content of SBM-g-GMA.When the SBM-g-GMA content is10wt%,the blend undergoes brittle-tough transition;the concentration increases to 25wt%,and the impact strength is 18.15 KJ/m~2,which is the PLA/SBM blend(SBM content is 25wt%)impact strength twice,and obvious stress blushing and necking occur during stretching,and the maximum elongation at break can be reached 28.82%.(4)CNTs are prone to agglomeration and difficult to dispersed in polymers.In this study,the“graft from”method was used to graft polymethyl methacrylate(PMMA)onto the surface of CNTs with a grafting rate of 10%.The modified CNT provides a material basis to prepare the PLA/SBM/CNT composite material in Lab in the near future. |
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