Structure And Properties Of PLLA/PBAT Blends Based On Reactivity Compatibilization

Poly(L-lactic acid)(PLLA)is a linear aliphatic polyester,which has excellent mechanical strength and biocompatibility,and is compostable and renewable.However,the low toughness of PLLA limits its wide range of applications.In order to solve the problem of low tensile toughness and impact toughness of PLLA,this dissertation used flexible degradable PBAT to blend and modify PLLA.Furthermore,the phase morphology and crystalline structure of the PLLA/PBAT blends were regulated by reactivity compatibilization and thermal annealing.The PLLA/PBAT blends with excellent mechanical properties were prepared,meanwhile,the compatibilization mechanism and toughening mechanism were discussed.(1)Triglycidyl isocyanurate(TGIC)was used as the compatibilizer,and the interfacial compatibility of PLLA/PBAT blends was significantly improved by two-step melt blending,which endowed PLLA/PBAT/TGIC blends with high tensile toughness.When the PLLA/PBTA ratio was 70/30 and the TGIC dosage was 4%,the two-step(PBAT/4%T)/PLLA blend showed the smallest dispersed phase size and the strongest interface adhesion.The significant improvement of interfacial compatibility and the thickening of interfacial layer promoted the stress transfer from the PLLA matrix to the PBAT dispersed phase,and the elongation at break was 25.6 times that of PLLA/PBAT blend.(2)TGIC and toluene diisocyanate(TDI)were used as synergistic compatibilizers,combined with thermal annealing treatment,the interface compatibility and matrix crystallinity of PLLA/PBAT blends were greatly improved.The PLLA/PBAT/TGIC/TDI blends with high impact toughness,high mechanical strength and good tensile toughness were prepared.The epoxy groups of TGIC and the isocyanate groups of TDI could react to form oxazolidone,which synergistically promoted the interfacial compatibility between PLLA and PBAT.When the ratio of PLLA/PBTA was 70/30 and the dosage of TGIC and TDI were both 4%,the PLLA/PBAT/ 4%T/4%TD blends exhibited the smallest dispersed phase size and the robust interface bonding.It is therefore that the tensile strength and elongation at break were enhanced simultaneously.After annealing,the crystallinity of PLLA/PBAT/4%T/4%TD blends increased,and its tensile strength and impact strength improved by 21.5% and 68.0%,respectively,compared with the unannealed samples.(3)PLLA/PBAT(90:10)blending fibers with good strength and flexibility were prepared by melt spinning-hot drafting process.The(PBAT/4%T)/PLLA and PLLA/PBAT/TGIC/TDI blends had good spinnability,and after the action of hot drafting field,the diameter and the surface roughness of the fibers decreased,and the evenness of the strip improved.In PLLA/PBAT/TGIC/TDI blending fibers,PBAT formed a highly oriented and well-arranged in-situ nanofiber structure after 8 times of hot drafting.The nanofiber structure effectively promoted the stress-induced crystallization of PLLA matrix and the PLLA/PBAT/4%T/4%TD fiber had the highest crystallinity and tensile strength.In addition,due to the synergistic compatibilizing effects of TGIC and TDI,the interfical compatibility was significantly improved,which guaranteed the best tensile toughness of PLLA/PBAT/4%T/4%TD blending fiber.