| This paper adopts corn starch as raw materials to prepare nonpoisonous wood adhesive whichhas low cost and high performance. Corn starch was thin-modified, oxidized and graftcopolymerized. Modifying agent and crosslinking agent were added into compound modified starchslurry, them increase temperature for gelatinization. After temperature was decreased and thendiluent, plasticizer and defoamer were added in turn, starch-based wood adhesive was obtained.Acid modification, oxidation and grafting copolymerization of corn starch were studied. Formulaand process of adhesive were designed. Properties of adhesive were researched and cost wasanalyzed.The mechanisms of oxidization and initialization of ammonium persulfate were discussed.With biochemistry light instrument, the effect factors of production of original free radicals inaqueous ammonium persulfate solution were systematically investigated. The results showed thatammonium persulfate could oxidize starch. There is linear relationship between concentration ofpersulfate and the quantity of original free radical. The quantity of original free radical increaseswith increasing of the concentration of persulfate and rising of temperature. However, it is smallwhen pH value is too low or high. Ammonium persulfate can produce most original free radicals atlow pH value(pH=3～4).Preparation and properties of the acid-thinned and oxidized starch were studied. Theacid-thinned and oxidized starch was prepared via the reaction of corn starch with hydrochloric acidas acid catalyzer and ammonium persulfate as oxidant. It has a low viscosity and carboxyl content.The result showed that the optimal conditions of reaction correspond to a concentration of 30%(db)for starch slurry, an reacting time of 60min, a hydrochloric acid concentration of about 0.5mol/L, areacting temperature of 60℃ and a ammonium persulfate quantity of 2.25% of dry starch weight.The acid-thinned and oxidized starch has better properties than acid-modified starch. So it has abetter application in adhesive industry.Reaction of grafting copolymerization of vinyl acetate onto acid-thinned and oxidized starchusing ammonium persulfate as initiator was investigated. The graft copolymer of starch wascharacterized. The results showed initiator was a very important factor in the reaction. Ammoniumpersulfate should be added by stages. The optimum dosages of initiator were 2.25% and 0.45% ofdry starch weight respectively. By single-factor tests, the optimum graft copolymerizationconditions with higher grafting efficiency and grafting percent ratio correspond to anacid-modification and oxidation time of 1h, mass ratio of monomer and starch of 0.8, amonomer-dripping time of 1.5h, pH value of 3～4, a grafting reaction temperature of about 70℃and a grafting reaction time of about 3h. With the aim of assessing the effects of these variables ongrafting percent ratio, grafting efficiency and monomer conversion efficiency, temperature ofgrafting reaction and pH value were varied according to a central composite design. The responsesurface analysis was used to determine the function relationship between factors and the graftingparameter. The optimum level of the effects was also obtained. The results showed that whentemperature of grafting reaction is 70℃ and pH value is 4, the grafting percent ratio, graftingefficiency and monomer conversion efficiency can reach maximums, these are 28.2%, 49.1%,99.8% respectively. The grafting copolymerization of vinyl acetate onto acid-thinned and oxidizedstarch was determined by infrared spectrum, X-ray diffraction and SEM.Starch-based wood adhesive was prepared using the acid-thinned and oxidized starch graftvinyl acetate copolymer and vinyl acetate homopolymer as binder. By single-factor tests, the resultsshowed that presences of the PVA, borax and urea could improve the properties of adhesive verymuch. Plasticizer and defoamer were indispensable to adhesive. By orthogonal experiment based onsingle-factor tests, the optimal directions for producing the adhesive were that the quantities of PVA,borax and urea were 12%, 0.2% and 40% of dry starch weight respectively, the plasticizer wasglycerol and the defoamer was tributyl phosphate. Under optimal directions, solids content,viscosity, compressive shear dry strength and wet strength were 38.5%, 2.20Pa.s, 16.32MPa and7.88MPa.At last, the properties of starch-based wood adhesive prepared at optimal conditions wereanalyzed. Properties of starch-based wood adhesive were compared with polyvinyl acetate adhesiveand Country standard of polyvinyl acetate wood adhesive. The cost of adhesive was estimated. Theresults showed that all properties of starch-based wood adhesive reached Country standard ofpolyvinyl acetate wood adhesive. Especially compressive shear strength including dry strength andwet strength went beyond Country standard much. So starch-based wood adhesive has goodproperties. Furthermore, starch-based wood adhesive has low cost;its commercial cost was abouthalf of polyvinyl acetate adhesive.Starch-based wood adhesive has good properties and low cost, so it will have a very goodapplication in wood industry.
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