| As important derivatives of chitin, chitosan and carboxymethyl chitosan are active natural macromolecules characterized with extensive sources, no toxicity,biocompatibility, microbial degradation and so on. The active amido of chitosan and carboxymethyl chitosan laid foundation for their chemical modification or participating in chemical reactions. In this topic, through the radical polymerization of vinyl monomer and functional monomer acetoacetoxy ethyl methacrylate(AAEM), a certain amount of AAEM monomer were introduced into acrylic resin molecular chain to form an acrylic resin emulsion with active carbonyl on its side chain. Meanwhile a list of acrylic resin-chitosan derivative composite emulsions were prepared through the addition of chitooligosaccharide(COS) or carboxymethyl chitosan(CMC). Then the composite emulsions were utilized as a crosslinking system to prepare self-crosslinking acrylic resin at room temperature. By analyzing the basic performance of coating film tests, the effect of the crosslinking system were discussed, which aims to explore technical ideas and methods for the preparation of new type of acrylic resin.In this research, firstly, methyl acrylate(MA), methacrylic acid(MAA) and butyl acrylate(BA) were chosen as main monomers to conduct radical emulsion polymerization. During the process of acrylic resin emulsion polymerization, the effect of technologies, reaction conditions, emulsifier, and initiator on the coating performance of polymer emulsion were investigated. Optimum synthesis technology of acrylic resin emulsion was confirmed: methyl acrylate,methacrylic acid and butyl acrylate were basic monomers, pre-emulsification was firstly carried out and then the seed emulsion was applied for further emulsion polymerization. Technological parameters were as follows: the mass ratio of monomer and water was 2:3 and K-12 and OS-15 were chosen as compound emulsifiers with mass ratio of 2:1; the total dosage of emulsifiers accounted for 3% of monomer mass, and the dosage of initiator ammoniumpersulfate accounted for 0.5% of monomer mass; the stirring rate was controlled at 300 r/min.Secondly, cellulose enzyme was applied for the degradation of chitosan to get COS with different weight-average molecular weight of 923, 1127, 1394 and1497 Da. Based on the radical emulsion polymerization of methyl acrylate(MA),methacrylic acid(MAA) and butyl acrylate(BA) as main monomers, functional monomer acetoacetoxy ethyl methacrylate(AAEM) was introduced into acrylic resin molecular chain. COS was then added into the prepared acrylic resin emulsion to form self-crosslinking acrylic resin at room temperature with AAEM-COS as the crosslinking system. The crosslinking structure of the resin film was characterized using FT-IR. The influence rule of the chitosan molecular weight and dosage as well as the dosage of AAEM in AAEM-COS crosslinking system on the hydroscopicity, solvent resistance and mechanical properties of resin film were studied, in addition the effect of the crosslinking system on the coating glass transition temperature(Tg) and apparent activation energy of the resin film thermal decomposition. The results showed that dehydration condensation reaction took place between the carbonyl of AAEM and the active amino of COS. The hydroscopicity and solvent resistance of compound film was improved by the AAEM-COS crosslinking system The tensile strength and the glass transition temperature(Tg) of the film also increased. The lower the molecular weight of COS, the higher the hydroscopicity of the coating film,meanwhile the better the solvent resistance and the tensile strength. When 3% of COS(according to the mass of the emulsion) was utilized, the coating film showed good hydroscopicity, solvent resistance and mechanical properties. And when 4% of AAEM in the acrylic resin was utilized, the coating film showed good comprehensive performance. With 923 of the COS molecular weight, 4%of functional monomer dosage, 3% of COS dosage, the AAEM-COS crosslinking system could significantly increase the glass transition temperature(Tg) of the film by 24.89 ℃, and the apparent activation energy before and after crosslinking were respectively E0=182.41 k J/mol and E1=119.19 k J/mol, which apparently decreased。CMC with substitution degree of 0.63, 0.78, 0.92 and 1.21 were prepared by carboxy methylation reaction of chitosan. Through introducing a certain amountof CMC into acrylic resin emulsion containing functional monomer AAEM,self-crosslinking acrylic resin-carboxymethyl chitosan composite emulsion with AAEM-CMC as crosslinking system was prepared. The crosslinking structure of the resin film was characterized using FT-IR. The influence rule of chitosan substitution degree, carboxymethyl chitosan dosage and AAEM dosage on the hydroscopicity, solvent resistance and mechanical properties of resin film were studied, in addition the effect of the AAEM-CMC crosslinking system on the coating glass transition temperature(Tg) and apparent activation energy of the resin film thermal decomposition. Results showed that dehydration condensation reaction took place between the carbonyl of AAEM and the active amino of CMC. When the CMC substitution degree was 0.92, the coating film showed best hydroscopicity, solvent resistance and mechanical properties. And when 3%of CMC was utilized, the coating film showed good hydroscopicity, solvent resistance and mechanical properties. And when 4% of AAEM was utilized, the coating film showed good comprehensive performance. With the CMC substitution degree of 0.92, 4% of functional monomer dosage and 3% of carboxymethyl chitosan dosage, the AAEM-CMC crosslinking system could significantly increase the glass transition temperature(Tg) of the film by 26.93℃,and the apparent activation energy before and after crosslinking were respectively E0=182.41 k J/mol and E2=149.27 k J/mol,the introduction of AAEM-CMC crosslinking system can decrease the thermal decomposition apparent activation energy. |
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