Study On Preparation And Properties Of Thermosetting Wood Adhesives Based On Starch

The paper aimed to prepare starch wood adhesive based on addition agents with waxymaize starch as reaction material which will be graft-copolymerized with compoundmonomers, with oxidization and acidolysis as pretreating methods. The final resultsdemonstrated that many characteristics of starch adhesives get close to white latex from themarket and some are even more excellent.First, the experiment studied preparation technics and characteristics of waxy maizedialdehyde starch with waxy maize starch and sodium periodate as raw material and oxidantrespectively, with aldehyde content as index and obtained better technical conditions throughsingle factor experiments: the mol ratio of oxidant and starch is1.1:1, pH of reaction solutionis3.0, reaction temperature and time are30℃and2h respectively, the starch milkconcentration is8%. The aldehyde content of final sample reached87.36%. The study oncharacteristics indicated that polarization cross of dialdehyde starch gradually disappearedalong with the increase of aldehyde content, starting point of gelatinization temperatureincreased, peak viscosity decreased, cold paste viscosity also lowered greatly and crystalstructure of dialdehyde starch was destroyed.Second, the experiment studied preparing technics of waxy maize dialdehyde starchadhesive which was made with polyvinyl alcohol as protective colloid and emulsifier andvinylacetate as reaction monomer in connection with additional agents.The optimized technicparameters are as follows: aldehyde content of oxidized starch is20%, mass ratio of starchand grafted monomer is1:2.5, the amount of PVA is75%of dry starch base, volume ratio ofvinylacetate and ethyl-acrylate is3:1, dry and wet shear strengthes of adhesive reached3.0MPa and2.5MPa respectively. Infrared Spectrum and X-ray diffraction demonstrated thatstarch grafted with monomers successfully and crystal structure of reaction productdisappeared.Third, the prepared technics conditions of acidified starch adhesive were determined.The adhesive was made with acidolysis as pretreating methods, PVA was added into reactionsystem before graft-copolymerization which went on whithout pumping nitrogen.Theexcellent technic parameters are as follows: hydrochloric acid solution concentration was 2.0mol/l, starch milk concentration was20%, the amount of initiator and PVA were1.2%and40%of dry starch base respectively, volume of monomers was40ml, volume ratio of VAc andEA was3:1, grafting reaction temperature was70℃, the dry and wet shear strengthes ofadhesive reached4.2MPa and3.6MPa respectively.Finally, characteristics of starch adhesives were compared with white lates from themarket. Characteristics on appearance、wood polluting、ash content、solid material content、viscosity and stability were close to white latex and even surpassed white latex. Thermalstability of starch adhesive was weaker than that of white latex and starch adhesive had stongaging property; grain diameter of starch adhesive was a little larger than white latex; threeadhesives belong to shear-thinning fluid and starch adhesive has more obvious shear-thinningproperty.