Synthesis Of Cellulose Diacetate Grafting Poly Lactic Acid (CDA-g-PLA)

As one of the most popular biodegradable, biocompatibility and thermoplastic materials, Polylactic acid (PLA) would be widely used in packaging, food industry, health care and other fields in future. Due to its inherent drawbacks such as brittleness, low tensile strength and poor thermal stability, popularization and application of PLA were strongly limited. In order to solve these problems, it was proposed to modify PLA by blending with cellulose diacetate (CDA) which has a good mechanical strengthhigh, thermal stability and biocompatibility.Due to the poor compatibility of CDA/PLA blends, it is difficult to manufacture polymer alloys with application value by simple blending. Therefore, it is the technical key to modify PLA with CDA by means of blending that designing and synthesising a specific compatilizer using for CDA/PLA blend system. In this thesis, we designed and synthesised CDA grafting PLA copolymer(CDA-g-PLA) as the compatilizer of CDA/PLA blends according to the chemical and physical properties of CDA and PLA.In this work, CDA-g-PLA was prepared by using Stannous octylic acid and phosphoric acid as the catalyst, the CDA for grafting skeleton, the low molecular weight PLA (LMPLA) as the grafted prepolymer under melting condition. LMPLA was prepared with lactic acid by melt polycondensation; CDA modified with succinic anhydride (SA) was synthesized into succinic acid ester diacetate cellulose (CDA-COOH).The properties of product were mainly studied by using a variety of testing methods. The influence of reaction conditions on grafting ratio of CDA-g-PLA was mainly studied, the film-forming property and compatibility of the film that prepared with PLA/CDA blending system were evaluated. The main results were as follows:(1) FT-IR spectrogram of CDA-g-PLA proved the introduction of LMPLA side chain; the TG-DTG curves of CDA-g-PLA illustrated the strong combination between LMPLA branched-chain and CDA main chain, no obvious phase separation was found, and the copolymer had a good thermal stability; DSC showed that the glass transition temperature of CDA-g-PLA declined with the increase of grafting ratio; XRD spectra showed the crystallization capacity of CDA-g-PLA had no obvious change compared with CDA.(2) The effects of variety of catalysts, the amount of catalysts, LMPLA molecular weight, the weight ratio of raw materials, reaction temperature and reaction time on grafting ratio were studied. Results showed that the composition of stannous octylic acid and phosphoric acid as catalyst can effectively promote the grafting ratio of CDA-COOH and LMPLA; the grafting ratio of CDA-g-PLA increased to the maximum and then decreased with the increase of the amount of catalyst and LMPLA, reaction time, reaction temperature; the grafting ratio of CDA-g-PLA was decreased with the increase of molecular weight of LMPLA.(3) The film-forming property and compatibilization of the PLA/CDA blending were evaluated. The results were as follows:the film that was made of pure CDA was brittle; the brittleness of the film got improved significantly after blending with PLA, but the blending film had a poor compatibility; the compatibility and brittleness of the blending film had improved by adding of CDA-g-PLA as the macromolecules compatibilizer that was synthesized in the first step.