Preparation Of Flexible Polylactide(PLA) Film

General plastic packages always lead a few environmental problems, such as "white pollution". In this study, we tryed to solve these problems by preparing the flexible PLA film and developing blowing molding technology. The methods and mechanism of PLA toughness and flexibility modification was discussed. The effect of additives in PLA on uv-irradiation degradation and the compost degradation under the condition of high temperature and high humidity were also studied. These works will promote the application of PLA, an entirely bidegradation polymer, as a common package material. Firstly, PLA was blended with various plasticizers,flexibilizers in the mixer of Haake torque rheometer in melting state. The PLA sheets were prepared by hot-press molding with plate vulcanizer. The tensile mechanical properties, dynamic mechanical property, thermal property were tested.And also the relationships between toughing PLA Stress-strain behaviors, phase transformation behaviors and the kind and content of plasticizers, flexibilizers were studied in order to optimize the processing technology of the flexible PLA film.Secondly, PLA film was prepared by blowing molding in single-screw extruder.According to the practical application, a few studies were carried out. These studies included film mechanical properties testing (tensile-strength, elongation at break,tearing strength) ,and the effect of additives in PLA film on the compost degradation under the condition of high temperature and high humidity and uv-irradiation degradation in the self-made uv-irradiation device. The conclusions were summarized from this paper as following:(1) PEG plasticizers has plasticization effect on PLA. The elongation at break of blend was increased slightly. The optimized content of PEG with different molecular weight was 10% wt. Different plasticization effects were detected due to the molecular weight of PEG, while PEG6000 is the best one. However, PEG was not a stable plasticizer of PLA because the toughness of plasticized PLA would deterioration with the increase of time when keeping in the room tempreture.(2) Four ester plasticizers all had good effect on increasing PLA flexibility.After their application on PLA, the elongation at break was increased greatly.Among them, TPPi and DBS plasticizers have better effect than TBC and DOP plasticizers. PLA plasticized by the former two plasticizers has ductile fracture behavior and yield cold-drawing phenomenon can be observed in extending process.The results of DSC showed that ester plasticizers lowered the glass transition temperature(T_g), melting point(T_m) and cold crystalline temperature(T_c) of PLA,while increasing the crystallinity of PLA.(3) Polyester A and B can toughen PLA by melting state blend and modify PLA brittleness, but elongation at break was increased slightly.(4) Self-made built toughen system could increase PLA flexibility obviously.The highest elongation at break of blends was about 400% when the tensile-strength still maintained at 30 MPa.(5) DMA showed that built toughen system could effectively increase the mobility of molecular chains of PLA, while reducing theαtransition temperature and cold crystalline temperature. With the content of built toughen system increasing,the storage modulus of PLA decreases and the peak of tgδatαtransition temperature moved towards the lower temperature zone.(6) SEM indicated that both flexibility and built toughen system dispersed in PLA matrix as spherical particle. Toughening mechanism is crazing and shear yield in the majority.(7) According to the the degradation experiments under the high temperature and high humidity compost and uv-irradiation, it indicated that PLA blowing molding film had good degradation ability. In the early compost degradation process, the longitudinal tensile-strength of PLA film decrease firstly then increase, elongation at break reduced gradually. The blowing molding film was susceptible to uv-irradiation and decreased greatly in the form of mechanical properties.(8) The mechanical properties test of flexible PLA film indicated the film optimized by this study could be widely used as daily package film or bags and could replace the general polyolefin blowing molding film.