Studies On The Preparation And Properties Of Water-resistant Starch-based Wood Adhesive

This paper mainly studied several different ways to improve water-resistance of starch-based adhesive, such as different preparing ways on starch, adding cross linking agent during the process of graft copolymerization and modifying agent addition, on the basis of process on corn starch as raw material after thin-modified, oxidized and graft copolymerized to prepare starch-based wood adhesive. The optimal directions for preparing adhesive were achieved by orthogonal experiment. Properties and storage characters of this adhesive were also analyzed.The effect of different preparing ways of starch on the water-resistant property of adhesive was initially discussed. The result showed that the viscosity, the content of COOH- group and water-resistance of adhesive made from normal corn starch was much better than that of tapioca starch; the modifying conditions of starch corresponded to a reaction temperature of 60℃, and a catalyzing agent concentration of 0.5mol/L. Choosing acetic corn starch ester with DS of 0.15, and mixing acetic corn starch ester with thin-modified, oxidized corn starch at a rate of 1:5.The effect of cross linking agent on grafting parameter, compressive dry sheer strength and water-resistance of adhesive during graft copolymerization was studied. The result showed that the water-resistance of adhesive increased as the viscosity molecular weight of grafted line increased. The raw conditions of reaction were obtained by single-factor test on four factors, and the optimal conditions of reaction achieved by response surface analysis corresponded to adding quantity of 0.41% of starch (db), adding time of 2h after grafting, adding concentration of 0.05g/mL, and net adding time of 19min. Adhesive prepared in this way got 5.036 MPa as compressive dry sheer strength and 3.074 MPa as water-resistance.After the effect of modifying agent on water-resistance of adhesive was studied, the result showed that the compressive dry sheer strength, water-resistance and other properties of adhesive made from polyvinyl alcohol(PVA) with higher DP value , were much better than that of PVA with lower DP value. By orthogonal experiment, the optimal direction for preparing adhesive were that quantity of PVA, borax and urea were 15%, 0.5%, and 22% of starch (db) respectively, and concentration of PVA, borax and urea were 10%, 1.5% and 40% respectively.The properties and storage character of adhesive prepared at optimal conditions were analyzed. The water-resistance of improved adhesive was better than before, and its properties were almost the same with the normal polyvinyl acetate adhesive in market; by analyzing the storage character of adhesive, conclusions could be got that, compressive dry sheer strength, and water-resistance of adhesive remain fine after stored for long time; the adhesive remain flake plastic fluid, and Tg increased properly because of starch degradation and changed little after a period of time during storage.The water resistance of modified starch-based wood adhesive was much better than that of non-modified adhesive, and it has already got the middle level of polyvinyl acetate adhesive; it will have a good application in wood industry.