| The oxidized starch was synthesized by gelatinizing before oxidizing, using corn starch as raw material, ferrous sulfate as catalyst and hydrogen peroxide as oxidant. Then, heating up and adding polyvinyl alcohol as continuous phase, when being mixed evenly, adding the coupling agent for oxidized starch grafted reaction. When emulsification is completed, adding olefin monomer for the graft copolymerization reaction, then adding organic additives such as bentonite, finally get the starch adhesive with advantages of green and environmental protection and high performance. In this paper, in the process of oxidized starch synthesizing, carboxyl content was used as index, the influence of various influence factors on the carboxyl content of oxidized starch was discussed systemically by using the single factor experiment method, and then obtained the optimum oxidation starch synthetic scheme. During graft copolymerization of starch, the progression of influencing factors was determined by using orthogonal method, and then the influence of main influencing factors on the adhesive shear strength and viscosity were discussed. Finally, the optimum synthesis scheme of graft copolymerization of oxidation starch was obtained. By adding additives, the obtained starch adhesive was modified to get the optimal performance. Before using adhesive to bond items, some isocyanate was often mixed to improve its performance, and this study also discussed the best proportion of additive amount.First, the oxidized starch was synthesized by using hydrogen peroxide, and it was characterized by methods of IR, XRD, TG and DSC. The gelatinization temperature, dooage of hydrogen peroxide, dosage of catalyst, and reaction time are the factors of effect on oxidized starch’s carboxyl content index, and these were studied via single-factor experiment. The results show that starch crystal structure was damaged slightly by oxidation reaction, and oxidation reaction occurs mainly in starch non-crystalline region, only a small amount in the crystalline region. At the same time, high degree of oxidation of oxidized starch is a amorphous phase, and different degree of oxidation of oxidized starch has different crystal types; The early period of the starch gelatinization was occurred in starch non-crystalline region, then oxidation occurred in non-crystalline region first, which turned to crystalline region with the increase of oxidation degree. The optimum synthetic technology conditions of oxidized starch was as follows:starch10g, distilled water100g, oxidizer40%(Mass ratio of starch), catalyst1.716%, reaction time1.5h, reaction temperature55℃. can the oxidized starch with carboxyl content of2.55%can be prepared.Secondly, the starch adhesive was synthesized by graft copolymerization. The proportion of the main raw material was determined by orthogonal experiment method, and the influence of the main influence factors on the shear strength was discussed. Oxidized starch was characterized by IR and TG, which’showed that coupling agent and olefine monomers were successfully grafted to the oxidized starch chains, at the same time, graft copolymerization significantly improved the thermal stability of the oxidized starch. The optimum synthetic process conditions of graft copolymerization of oxidized starch was as follow:starch10g, distilled water100g, oxidizer3%(Mass ratio of starch), PVA9%, silane coupling agent9%, catalyst0.1g, Vinyl acetate and butyl acrylate(molar ratio,6:4)20g. The starch adhesive with dry strength of7.88MPa and wet strength of4.09MPa can be prepared.Next, Surfaces of cast films of the adhesive samples and the fracture surface of specimens were characterized by SEM, which showed that adhesive film formed macromolecular chain by graft copolymerization, which attaching on the grafted surface of oxidized starch, and the surface was very rough. The SEM showed crack propagation in both the wood lumen and adhesive layer, a massive mushu shape rubber appeared. This is because that under shear stress, a large number of adhesive networking structure fractured, which proves that graft copolymerization reaction is very successful, at the same time, the network structure is neat, the more the fractured mushu shape rubber, the higher the shear strength.Finally, the best effect was obtained when adding0.5%(emulsion quality percentage) sodium bentonite, and the sealed storage is the best way of storage for starch adhesive. In this paper, the stable value of the prepared adhesive is1.02, and its storage life can be up to30d. When being sized, the best adding content of isocyanate is8%. |
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