Study On Starch-based API Wood Adhesive And Mechanism Of Curing And Retrogression

Unremitting pursuit goal is to deVelop high-performance wood adhesive by utilizing lowcost corn starch. The starch treated by composite modifier is used for the main raw materials of wood adhesive API which has been used and starch-based API has been deVeloped because poor water-resistance of traditional starch adhesive didn't meet requirement of wood bonding. Using for wood glued-product with the different requirement of shearing strength has been successful. Retrogression mechanism of glue-film is studied. Dynamic reaction mechanism of the main ingredient of starch to P-MDI is revealed. Curing reaction mechanism of starch-based API is searched.Corn starch as the main raw material produces composite modifier starch by multi-ply modifier such as acid-thinned, oxidized, graft-copolymerized starch. The optimal starch-based API is optimized in the orthogonal test by adopting composite modifier starch, second diacids, polyvinyl alcohol and P-MDI as the main elements in the paper. Adopting the different formulation of the adhesive bonds wood which can implement demand of the different water resistant bonding strength in the JIS K6806 standard and resolves paradoxical problem between water-resistance of wood glue-product and greenzation request. Physical and chemical properties are symbolized by conventional chemistry analysis and apparatus analysis. The cause for long pot lift of starch-based API by adopting the different blocking out P-MDI as cross-linking at room temperature. The reaction of corn starch and composite modifier starch to P-MDI are analyzed by DSC,FTIR,ESCA to try to reveal curing mechanism of starchbased API. Retrogression mechanism of glue-film of starch-based API is analyzed by laser Raman, ¹³C-NMR, GPC.Firstly, composite modifier starch made by grafting copolymer corn starch oxidized and acid-thinned into acrylamide is comprehensively studied.â‘ Preparation and properties of the acid-thinned and oxidized starch are studied. The acid-thinned and oxidized starch of a low viscosity and some oxidization degree is prepared in a short time with hydrochloric acid as acid-thinned catalyzer and ammonium persulfate as oxidant.â‘¡Reaction of grafting copolymerization of acrylamide to acid-thinned and oxidized starch by using ammonium persulfate as initiator is synthesized and investigated. The results show initiator is a very remarkable effect on the reaction of graft copolymer of starch. By single-factor tests, the optimum graft technology is determined primarily. The occurrence of grafting copolymerization reaction is testified by analytical means such as infrared spectrum, X-ray diffraction and SEM. Secondly, composite modifier corn starch, second diacids, polyvinyl alcohol, P-MDI as influencing elements by orthogonal test, formulations ofâ… â…¡type six starch-based API with request for bonding strength ofâ… â…¡kind of normal bonding, hot-water soakage, boiling are optimized respectively according to the different water-resistance request of aqueous polymer isocyanate wood adhesive glued wood and base on validated experiment of test results it is manufactured industrially. The results show sheafing strength of wood glued-product produced by adhesive prepared with the optimal formulation of six starch-based API wood adhesive can completely meet requirement of JIS K6806 and each property indices of adhesive satisfy demand for the practical process technology.Thirdly, dynamic reaction mechanism of starch with the different moisture content, composite modifier starch to P-MDI and curing reaction mechanism of starch-based API and bonding reaction mechanism between them and wood are studied systemically by adopting apparatus analysis methods such as FTIR, DSC and ESCA.â‘ Change regularity of—NCO content with time is systemically studied by adopting chemical analysis after the main agent of starch-based API is blended with cross-linking in proportion at room temperature and pot life of adhesive is determined.â‘¡Reaction mechanism and function, reaction activity energy and relevant reaction dynamics parameters are elicited by DSC experimental analysis on mixture of corn starch and composite modifier starch with the different moisture content, and P-MDI at the same heating rate and the constant temperature scanning.â‘¢To reveal chemical structure of curing reaction product, function-group of reaction product is qualitatively elicited, reaction regularity of corn starch of the different moisture content, composite modifier starch to P-MDI is further testified by ESCA analysis. Composite modifier starch is easier to reaction to P-MDI than corn starch under the same moisture content, which is revealed in essence.â‘£DSC, FTIR of starch-based API, birch, bonding interface between starch-based API and birch, sample with the constant temperature DSC scanning and bonding interface are analyzed by ESCA in order to reveal bonding mechanism between starch-based API and wood in the thesis. Bonding mechanism between starch-based API and birch is revealed.on retrogression-resistance of I type and I kind of starch-based API used boiling, acceleration retrogression mechanism of starch-based is revealed by laser Raman, ¹³C-NMR, GPC analysis on boiling repeatedly of glue-film cured in the normal temperature. To prove precisely chemical change of internal occurrence, under the condition that starch-based API is completely known, glue-film of I type and I kind of starch-based API which makes retrogression of adhesive cause chemical change accelerates retrogression treatment by boiling-drying repeatedly. Physical and chemical properties of glue-film and change on chemical structure of water soluble fraction or residual are analyzed by adopting Laser Raman Spectrum, ¹³C-NMR, GPC and retrogression mechanism of glue-film is studied based on these analyses.Finally, the results show Raman analysis considers chemical change of glue-film of acceleration retrogression treatment is caused by isocyanate's reaction, creation and decomposition of amine, water-solvable PVA. ¹³C-CP/MAS-NMR analysis of water soluble fraction determines that water-solvable material derives from water-solvable PVA and PVA dissolves water before boiling acceleration retrogression, but one of the chemical changes of the acceleration retrogression is formed by PVA dissolving out. GPC analysis of water soluble fraction on acceleration retrogression shows PVA macromoleeule chain of adhesive after acceleration retrogression is cut off and forming low-molecule dissolves water.