The Research Of Structure And Properties Of Cellulose Modified PLA

Poly (lactic acid) (PLA ) is a biodegradable and renewable material. Having good mechanical strength, biocompatible and processing, as an important substitute petroleum-based materials, PLA has paid close attention by researchers. But the poor toughness and strong hydrophobicity of PLA affect its application.How to overcome these defects to expanding its application, is the research of PLA's hotspot.In this paper, we chose easily soluble in water, insoluble in organic solvent's methyl cellulose and soluble in organic solvents, insoluble in water's ethyl cellulose by the method of melt mixing and injection molding to modify PLA. The molecular weight of 15, 400, 1500,40000, 100000 mPa.s's methyl cellulose and molecular weight of 9?11, 40?45, 90?110,180?220, 270?330, mPa.s's ethyl cellulose,in accordance with the dosage of 1%,3%,5%,7%, 9%, were blended with PLA; Methyl ethyl cellulose modified by MDI and methyl ethyl cellulose blends modified PLA composite material. The influence of methyl ethyl cellulose's additive amount and molecular weight on tensile properties, thermal stablility, morphology of fracture surfaces, crystallization properties of PLA composite material were systematically studied. The influence of blends methyl ethyl cellulose into PLA were also observed.PLA blend with the different molecular weight and additive amount's methyl cellulose,the test results show that blend methyl cellulose into PLA, the elongation of PLA appeared first increased and then decreased. With 1% additive, the elongation of PLA reached the maximum. With the increase of additive, the elongation gradually decreased. The fracture morphology show that, with the lower additive amount, methyl cellulose can be more evenly distributed in the PLA matrix, with the increasing of additive, methyl cellulose aggregate together, which existed as the form of impurity in matrix, external force was acted on composites, It was brittle and it's breaking elongation was decreased. The thermal stability and crystallinity analysis shows that blend methyl cellulose, the thermal stability of PLA was decreasing,with 1% additive, the blend's thermal stability was best, however it's crystallinity was decreased. There was no significant correlation between PLA's tensile strength and elongation at break with methyl cellulose's molecules weight.Ethyl cellulose blend with PLA, the characterization results showed that: compared with methyl cellulose, mixed with ethyl cellulose makes the elongation of polylactic acid had been greatly improved, and the different molecular weight had an optimal additive amount, then the fracture elongation will be decreased. The elongation of the composite had positively related to the ethyl cellulose's size and molecular weight. Mixed with ethyl cellulose, the thermal stability of PLA was poor, crystallinity was decreased; composites's tensile modulus had no obvious correlation wtih the ethyl cellulose's molecular weight.Blending cellulose modified by MDI and mixed cellulose with polylactic acid, the results show that compare with pure cellulose/PLA composite, the fracture elongation of cellulose modified by MDI/PLA composite becomes small. MDI has vivace chemical can react with the active hydrogen of cellulose,which cause the cellulose's surface coated by MDI,the compatibility of cellulose in the matrix are changed, The blend's elongation at break was decreased. Blending methyl ethyl cellulose blend with poly lactic acid, compared with pure PLA, the elongation of blends had 50% increased, the crystallinity was decreased, thermal stability became worse.