| Polylactide(PLA) is a thermoplastic aliphatic polyester chemically synthesized from renewable resources.Its raw materials derived from plants and PLA eventually can be degraded into carbon dioxide and water.With its unique environmental protection,good biocompatibility and mechanical properties,PLA has become one of the most widely used biodegradable material,which has a wide range of applications in the packaging materials,textile fabrics,biomedical and other fields.However,PLA is hard and brittle,with poor toughness,which limited its practical application.Therefore,the study on the toughening modification of PLA has been one of the key research topics in this field.In this paper,thermoplastic silicone polyurethane elastomer(TPSiU) was used as the toughener,and the toughening modification behavior of PLA by TPSiU was systematically studied.Polycarbonized diimine(PCDI) was further used as the compatibilizer,and the effects of the addition of PCDI on the compatibility and toughening modification of the blends was studied.The main conclusions are as follows:The study of structure and performance of TPSiU showed that TPSiU was amorphous polymer,its molecular chain contained organosilicon segment,and had good solubility in strong polar solvents such as tetrahydrofuran(THF),N,N-dimethyl formamide(DMF) and so on.The melt processing temperature of TPSiU was above 180?,while it had good thermal stability.PLA/TPSiU blends were prepared by melt blending.The effects of TPSiU content on the structure and properties of the blends were studied.The experimental results showed that the cold crystallization peak of PLA moved towards higher temperature with the addition of TPSiU,and the crystallinity decreased slightly,the initial thermal decomposition temperature of the blends also decreased slightly.The poor thermodynamic compatibility between PLA and TPSiU resulted in the"sea-island"structure of PLA/TPSiU blends.The addition of TPSiU had a significant effect on the mechanical properties of PLA/TPSiU blends.When the content of TPSiU was 10wt%,the elongation at break and notched impact strength of blends improved significantly,suggesting the favorable toughening effect,while the tensile strength reduced.Rheological behavior studies showed that PLA/TPSiU melt was typically shear thinning.As the content of TPSiU increased,the apparent viscosity of PLA/TPSiU blends showed a trend of rising first and then falling,and its non-newtonian flow index gradually increased.PLA/10wt% TPSiU blends with better comprehensive mechanical properties was selected as the research object.Polycarbodiimide(PCDI) was used as compatibilizer to modify the poor thermocompatibility between PLA and TPSiU.The results showed that the addition of PCDI made the glass transition temperature of PLA and TPSiU phase closer,while the particle size of TPSiU dispersed phase decreased,and the interface between the two phases became indistinct,indicating a good compatibilizing effect was generated,which therefore improved PLA's toughness.With the increase of PCDI content,the elongation at break and the notched impact strength of the compatibilizing blends increased firstly and then decreased,while the tensile strength and elastic modulus increased gradually.When the PCDI content was 1.0wt%,the compatibilization blends had the best toughness,and the elongation at break was 25.3%,which was 5.6 times of pure PLA;and the impact strength was 13.9KJ/m~2,which was 3.6 times of pure PLA.In addition,the cold crystallization temperature of PLA matrix shifted towards higher temperature and the crystallinity decreased owing to the addtion of compatibilizer PCDI,and the initial thermal decomposition temperature increased by 7-10? compared with the uncompatibilized blends,suggesting its thermal stability was improved.In summary,TPSiU used as toughening agent and PCDI as compatibilizer could effectively improve the impact toughness of PLA while retaining its tensile strength,indicating the favorable toughening modification effect. |
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