Effect Of Biomass Fiber And Modified Lignin On Crystallization Properties Of PLA

Polylactic acid?PLA?is a biodegradable thermoplastic polyester produced by polycondensation of lactic acid.It is obtained by fermentation of carbohydrates such as corn,sugarcane or cassava.In terms of energy consumption and CO₂ emissions,PLA is superior to some petroleum-based polymers.PLA is biodegradable,biocompatible and the mechanical properties are excellent.PLA can be applied in some substitutes of petroleum-based plastics and has attracted wide attention.On the other hand,PLA is usually in an amorphous state due to its slow crystallization rate,and its heat resistance is poor.Therefore,it is necessary to enhance the crystallinity and heat resistance of PLA materials to be applied in a wider range of fields.Aiming at the shortcomings of slow crystallization rate,low crystallinity and poor heat resistance of PLA materials,the following three aspects have been done to improve the crystallinity and heat resistance of PLA materials.Modified lignin?MZS?was selected as nucleating agent of PLA and treated biomass fiber?BF?as crystallization reinforcer to investigate the effect of BF and MZS on the crystallization properties of PLA materials.The results show that the crystallinity of the material reached a maximum of 67.1%in the case of nanocomposites containing 15 wt%BF and 1wt%MZS.The crystallization property of PLA was improved by the addition of BF and MZS,and the crystallinity was 54.7%at the cooling rate of 50?/min.The addition of BF and MZS did not change the crystalline forms of PLA.The PLA material added crystallization accelerator and nucleate agent was annealed.The annealing conditions were different in temperature,medium and time.The results show that the addition of BF and MZS could effectively reduce the annealing temperature and shorten the annealing time of PLA.When the additives were combined with annealing treatment,the crystallinity and heat resistance of PLA materials could be improved more effectively.When the PLA/BF/MZS?84/15/1?was annealed at 95?in water for 30 seconds,and the thermal deformation temperature reached 112.3?.Compared with annealing in air,the thermal resistance of PLA materials could be improved more obviously.The crystal forms of PLA were not changed by annealing treatment.The MZS was selected as nucleating agents for the toughening system PLA/EVA,and the best mass ratio for PLA crystallization was selected.While the nucleating agent was added,the temperature,speed and ratio of hot stretching were controlled to carry out hot stretching treatment for PLA.The effects of different hot stretching conditions on the crystallization ability of PLA materials were studied.The results show that the toughness and crystallinity of PLA materials were effectively enhanced by the addition of EVA and MZS.The crystallization of PLA materials was closely related to the tensile conditions.At the same stretching rate and different temperatures,the temperature of 70?was the most suitable condition.When the stretching ratio reached 3,the crystallinity was increased rapidly.The crystallinity of PLA reached a maximum when the drawing ratio was 3 and the drawing rate was 300 mm/min.