Study On Multiple Blends Based On Poly(Lactic Acid)-Poly (Epichlorohydrin-Co-Ethylene Oxide) Rubber

Poly(lactic acid)(PLA)is a kind of important bio-based plastic derived from biomass.It has advantages of high mechanical strength,easy biodegradation in environment,etc.,so PLA has showed a wide application prospect.However,the disadvantages of poor toughness and low HDT greatly limits the application of polylactic acid in wider fields.In the presence of good interfacial adhesion,blending with elastomers and other biobased polymers with complementary properties is a remarkably effective method for preparing high-performance biobased PLA materials.In this thesis,renewable poly(epichlorohydrin-co-ethylene oxide)(ECO)elastomer was used as a toughening agent,and PMMA-based block copolymers were used as compatibilizers to successfully prepare a PLA-based material with excellent and balanced properties.Moreover,polyamide 11(PA11)and ECO were also used as heat-resistant modifier and toughening agent respectively for PLA to obtain high-performance biobased materials.The physical properties,miscibility and phase structure were thoroughly studied to establish the relationship between structure and physical performance.The specific research content is as follows:1.PLLA-b-PMMA block copolymers with different PMMA block chain lengths were obtained by the ring-opening polymerization(ROP)and atom transfer radical polymerization(ATRP).The broad molecular weight dispersity of PLLA was due to the transesterification reaction in the late stage of polymerization.Under the conditions of strictly removing water and quenching the catalyst's activity in time when the monomers were almost reacted,PLA with narrow molecular weight dispersity was obtained.Using PLLA as a macroinitiator,a series of PLLA-b-PMMA block copolymers with different PMMA chain lengths were obtained by controlling the reaction time and the feed ratio of MMA monomers.When PLLA with a narrow molecular weight dispersity was used as an initiator,block copolymer of a low PDI index with higher thermal stability was obtained.2.PLLA-b-PMMA block copolymers were investigated as effective A-b-C type compatibilizers for PLA and renewable ECO elastomer blends.Compared to the neat binary PLA/ECO blend,the PLLA-b-PMMA copolymers significantly improve the compatibility of the PLA and ECO phases,leading to enhanced interfacial adhesion and mechanical performance.Interestingly,by tuning the chain structure and adding content of the copolymer,two different phase structures were achieved in the blends:typical sea-island morphology for blends with low content of PLLA-b-PMMA block copolymers(<15%)and a unique tri-continuous phase morphology with a percolated PLLA-b-PMMA copolymer zone for the blend with addition of 20 wt%PLLA_22.7-b-PMMA_115.0.Both the morphological structures endowed the blends with remarkably high elongation at break(>260%)and impact strength(>63 k J/m²).Accordingly,two different toughening mechanisms were proposed for the blend with different phase structures.The PLLA-b-PMMA block copolymers provides us a high efficient and versatile A-b-C type compatibilizer to fabricate high-performance sustainable PLA-based materials for wide prospect application.3.Fully renewable ternary blends were prepared from PLA,bio-based PA11 and ECO elastomer via a melt blending method.Miscibility,phase behavior,thermal and mechanical properties of the ternary blend were thoroughly studied.Addition of the PA11 effectively improved the miscibility,thermal resistance,and toughness of the blends.PA11 continuous phases greatly increased the Vicat softening temperature of PLA above 160?.Mechanical tests proved that 42.5 wt%content of PA11 could significantly improve the tensile toughness of the blend:the elongation at break of PLA/PA11/ECO(42.5/42.5/15)reached 295%.The impact strength of PLA/PA11/ECO(60/25/15)blend with only 25 wt%PA11 increase to 47.4 k J/m².A small amount of PA11 and ECO elastomer with high interfacial adhesions played a good synergistic effect on toughening PLA.