Preparation And Properties Of Biodegradable Poly(lactic Acid)/Poly(Butylene Adipate-Co-Terephthalate) Blends

Poly (lactic acid) (PLA), as a biodegradable thermoplastic, has attracted great attentiondue to its high modulus, tensile strength and commercial availability. However, the furtherdevelopment and practical applications of PLA is restricted by its brittleness. Poly (butyleneadipate-co-terephthalate) (PBAT) is a biodegradable aliphatic–aromatic copolyester with hightoughness synthesized from adipic acid, terephthalic acid and butylene glycol. Poly(lacticacid)/Poly(butylene adipate-co-terephthalate) blends are prepared by melt-extrusion, and themechanical properties, morphology, rheological behavior and crystallization properties of theblends are investigated by dynamical mechanical analysis (DMA), scanning electronmicroscopy (SEM), capillary rheometer, polarizing microscopy(POM) and differentialscanning calorimeter (DSC). The major results are summerized as following:The mechanical properties results demonstrated that the elongation at break of blendsimproved remarkably compared to pure PLA and the maximum (298%) was achieved at 0.5%TBT content , at which the impact strength of blends was also increased by 76%. SEM imagesshowed that the compatibility obetween PLA and PBAT is significantly improved with theincorporation of TBT. Dynamic mechanical analysis demonstrated the occurrence of the glasstransition temperature for both PBAT and PLA, indicating that PLA and PBAT areincompatible.The rheological properties results revealed that both PLA and its blends arepseudo-plasticity fluid, and displayed obvious shear-thinning phenomenon. PLA and itsblends melts have relatively low viscous flow activation energy, which indicated PLA meltshas low temperature sensitivity and is beneficial to the control of processing conditions.The polarized optical microscopy (POM) micrographs showed that the spherulite size has a great dependence on the crystallization temperature and TBT loading. The spherulites of thePLA/PBAT blends become smaller with the addition of TBT, which indicated that thetransesterirication reaction obstructes the formation of the larger spherulite.The isothermal and non-isothermal crystallization behavior of PLA/PBAT blends arestudied by differential scanning calorimetry (DSC). The crystallization kinetics underisothermal conditions is analyzed by the Avrami equation. The results indicated that thenucleation way of the pure PLA and its blends might be the same, that is, which iscoexistence of two-dimensional and three-dimensional growth. Moreover, the equilibriummelting temperature is determined according to Hoffman–Weeks theory.Nnonisothermal crystallization kinetics of PLA/PBAT blends was analyzed using theJeziorny method and Mo methods. The results showed that the above two method can analyzethe nonisothermal crystallization process of poly lactic acid) and its blends. The introductionof TBT has little effect on the mechanism of the nucleation and the growth of PLA crystallites.The mode of the nucleation for blends and PLA are the same, which is coexistence oftwo-dimensional and three-dimensional growth. Additionally, the relationship between theactivation energy of nonisothermal crystallization for PLA/PBAT blends and temperature wasalso obtained from Vyazovkin method.