High Degree Of Substitution And High Viscosity Carboxymethyl And Graft Modified Starch

Two kinds of modified carboxymethyl starch with high degree of substitution and high viscosity was prepared by graft copolymerization of acrylic acid and acrylamide respectively.The parameters of the preparation process were optimized.Structure of the modified carboxymethyl starch was characterized,and properties of the modified carboxymethyl starch were tested.The specific research contents are as follows:1.The results of study on acrylic acid as grafting monomer show that after modification,when the degree of substitution of carboxymethyl starch is 0.2,the viscosity of starch paste is improved by about 4 times,the transparency of starch paste is improved by about 3 times,the anti-condensation ability is increased by 1.5 times,the water retention capacity is increased by 1.2times,and the salt tolerance is better at lower salt concentrations.The results of FTIR indicated that three new characteristic absorption peak of acrylic acid appeared in FTIR spectra of carboxymethyl acrylic acid graft modified starch at 1409,1577 and1710 cm^-1,the acrylic group was successfully inserted into the carboxymethyl starch.XRD results show that the carboxymethyl acrylic graft modified starch is an amorphous polymer with a small amount of submicron structure.The SEM results showed that the carboxymethyl starch was damaged after the graft copolymerization.The results of single factor experiment and orthogonal experiment showed that the optimal parameters of the preparation process were set to pH=8.5,the reaction temperature was 50℃,and the reaction time was 3 h.Under this setting,the viscosity of modified carboxymethyl starch is highest.2.The results of acrylamide as grafting monomer showed that after modification when the degree of substitution of carboxymethyl starch was 0.2,the viscosity of starch paste was increased by about 5 times,the transparency of starch paste was improved by about 4 times,anti-condensation ability is improved by about 1.5 times,the water retention capacity is improved by about 1.7 times,the thermal stability is better,but the salt-tolerance improvement is lower than carboxymethyl acrylic acid grafted modified starch.The results of FTIR indicated that three new characteristic absorption peak of acrylamide appeared in FTIR spectra of carboxymethyl acrylamide graft modified starch at 1666,2927 and3330 cm^-1,the acrylamide group was successfully inserted into the carboxymethyl starch.XRD results show that the carboxymethyl acrylamide graft modified starch is an amorphous polymer with a small amount of submicron structure.The SEM results showed that the carboxymethyl starch was broken after graft copolymerization.The results of single factor experiment and orthogonal experiment showed that the optimal parameters of the preparation process were set to pH=7.5,the reaction temperature was 50℃,and the reaction time was 3 h.Under this setting,the viscosity of modified carboxymethyl starch is highest.4.The results of study on carboxymethyl acrylamide graft modified starch which was prepared by acrylamide and carboxymethyl starch with degrees of substitution 0.4,0.6,0.8 and 1.0show that the viscosity of starch paste has been greatly improved by 5 to 24 times,and the stability of viscosity is better,improvement of anti-condensation ability is 1.5 to 2.0 times,and improvement of water retention ability is 1.88 to 2.00 times.5.Adhesive and wall putty were selected as practical applications and relevant parameters were determined.The test results show that:carboxymethyl composite modified starch wood adhesive basically meets the requirements of wood adhesive,and drying time of the putty paste made of composite modified starch is fast and it’s water resistance is good.