Preparation And Properties Of Toughening Polylactic Acid Material

Polylactic acid(PLA)is a thermoplastic polyester with the characteristics of green,compeletely biodegradable.PLA has attracted much attention due to its excellent properities.PLA possesses many excellent physicial characteristics that make it suitale for replacing traditional commodity polymers.Among its advantages are high strength,high modulus and biocompatibility.However,PLA has many drawbacks,such as brittleness,low impact strength,long degradation time,low crystallization and the poor heat resistance.These drawbacks are restricted its widespread application in packaging materials,films,disposable tableware,heat resistance fields,ect.In this dissertation,in order to improve the toughness and impact resistance of PLA,ethylene vinyl acetate(EVA)and ethylene acrylate methyl acrylate(EBA-GMA)are used as a toughening agent which has an excellent toughness.Then,the effects of EVA and EBA-GMA on the synergistic toughening and performance of PLA was investigated.In view of the long degradation time of PLA,corn starch which is modified by aluminum-zirconium agent is added into toughening system as a filler and investigated the effect of modified starch on the performance of blends.To improving the crystallization and heat resistance of the PLA/EVA/Starch blends,modified ligin as a nucleating agent and annealing treatment are introduced into the blends.For the PLA/EVA/EBA-GMA blends,when the mass ratio is 88:10:2,the compatibility of the blend is better,and the notched impact strength and elongation at break of the blend reach 8.6 kJ/m2 and 25.9%,respectively;EVA increases the thermal stability of PLA.In the low frequency region,G' and G" depend on the content of EVA.In the entire frequency range,the blends show obvious shear thinning behavior.When the EVA content is more than 10wt%,the shear thinning behavior of the blends become more pronounced with the increase of frequency.Compared with original corn starch,the interfacial adhesion and the compatibility between modified starch and blends matrix is improved.The right amount of starch can increase the toughness of the blends.When the content of starch is more than 5wt%,the mechanical properties of PLA/EVA/Starch blends is decreased.When the content of starch more than 20wt%,agglomeration is aggravated.The starch as a filler can increase the crystallinity of the blends,but it lead to the deterioration of the thermal stability of the material.Annealing treatment can improve the heat resistance of the blends.Modified lignin(MZS)as a nucleating agent can increase the crystallinity of the blends.When the weight content of MZS is 1.5wt%,the cold crystallization peak is completely disappears.And the crystallinity of the blends reach a maximum of 47.9%.With the addition of the nucleating agent MZS,the crystallization rate of PLA was accelerated and the crystallization time is shortened.Annealing treatment can improve crystal structure and crystallization of the blends,but it do not change the crystal form of PLA and it is still a stable crystal form(?-form).The crystallization rate of the blends is the fastest,while isothermal crystallization at 105 ?.Combining the nucleating agent with the annealing method can effectively improve the heat resistance of the blends.