Synthesis And Properties Of Cellulose Diacetate Grafted Polylactic Acid

Although petroleum-based polymers have brought great convenience to people’s lives,non-degradable wastes generated after used have caused serious damage to the ecosystem.In recent years,people’s awareness of environmental protection is increasing and oil resources are becoming scarce.The development of an environment-friendly,renewable,and biodegradable polymer instead of petroleum-based polymer has attracted more and more attention.Cellulose is the most abundant bio-based material found in nature.Cellulose diacetate(CDA)can be obtained by acetylation of cellulose and hydrolysis in two steps.The average degree of substitution(DS)of acetyl groups is 2.2～2.7.Due to its good solubility and fiber forming properties,CDA can be easily processed into films,fibers,and coatings through solution treatment,and can be used in the fields of fabric,cigarette filter tip and separation film,etc.However,there are a large number of polar groups on the CDA molecular chain,forming strong intra-molecular interactions,resulting in high glass transition temperature(T_g),too narrow thermal processing window,and some limitations in thermal processing.Therefore,in order to achieve thermoplastic processing of CDA,plasticizing and reducing T_g of CDA are of great significance.In this paper,using stannous octanoate as catalyst,L-lactide as graft monomer and CDA as graft skeleton,a series of CDA-g-PLA was successfully synthesized by ring-opening copolymerization.The structure and thermal properties of the products were characterized by Fourier infrared spectroscopy(FT-IR),Nuclear magnetic resonance hydrogen spectroscopy(~1H NMR),Gel chromatograph(GPC),Differential scanning calorimeter(DSC)and Thermogravimetric analyzer(TG).The effects of the ratio of L-lactide to CDA on the structure and properties of copolymers were studied.The results showed that the polylactic acid chain segment was grafted to the CDA skeleton successfully.When the ratio of L-lactide to CDA was 6:1,the glass transition temperature of CDA-g-PLA was 53℃and the initial weight loss temperature was about 280℃.The modified CDA polymer with good thermal stability was obtained.Then,The CDA-g-PLA polymer synthesized when the dosage ratio of L-lactide to CDA was 4:1 was selected as the material.A series of CDA-g-PLA/PEG2000composite membranes were prepared by solution blending.The structure,surface morphology,hydrophilicity and mechanical properties of the CDA-g-PLA/PEG2000composite membranes were studied and analyzed by various characterization methods.The results show that when PEG2000 is added more than 30%,PEG2000 crystals appear in the composite membrane,and the composite membrane changes from brittle fracture to ductile fracture.In addition,when the addition amount of PEG2000reached 50%,the elongation at break increased by 56.9%compared with CDA-g-PLA base film,and the water contact angle was 15°,indicating that PEG2000 effectively improved the toughness and hydrophilicity of CDA-g-PLA base film.