The Preparation Of Starch-based Wood Adhesive And Its Characteristics Studies

To develop high performance wood adhesive by utilizing low cost biomass is unremitting pursuit goal. In our paper, a new, environmentally friendly starch-based wood adhesive high starch content was synthesized via graft polymerization of vinyl acetate monomer onto waxy corn starch, and the effects of raw materials, emulsifiers, diluents urea, nano-additives was investigated and the technological parameter of starch-based was also optimized accordingly.Firstly, the basic process of starch-based wood adhesive was studied. Physical blending and grafted copolymerization was used to prepared to starch-based wood adhesive with high starch content. The result showed that the starch-based adhesive prepared by the physical blend had poor bonding performance and poor stability for the physical phase separation. While the starch-based wood adhesive prepared by graft copolymerization had better performance than the starch-based adhesive prepared by the physical blend.Secondly, based on the basic Process, the effects of gelatinization pretreatment of starch on storage stability at low temperature and bond strength of starch-based wood adhesive were investigated. Compared with starch-based wood adhesive without gelatinization pretreatment of starch, the bonding strength of starch-based wood adhesive increased after gelatinization pretreatment, the increasement were 20.9% in dry-state and 45.8% in wet-state, respectively. The grafted parameters was also remarkably increased by the gelatinization pretreatment of starch, such as G increased by 43.5% and GE increased by 38.8%. Result of freeze-thaw stability measurement indicated that the gelatinization pretreatment of starch could effectively improve the frost resistance of starch-based wood adhesive. The results of dynamic time sweep experiments and XRD analysis demonstrated that the gelatinization pretreatment of starch could weaken intermolecular hydrogen bonds of starch, and enhance the grafted reaction of starch and VAc monomer, thereby improving the bonding properties and stability of starch-based wood adhesive emulsion.In addition, the effects of emulsifiers (SDS) on storage stability in low temperature and bond strength of starch-based wood adhesive were also investigated. Compared to starch-based wood adhesive without emulsifiers, emulsifier-fortified starch-based wood adhesive all exhibited enhanced glue strength. The optimum amount of SDS is 1% of starch content. In particularly, SDS has a most significant effect that dry strength of starch-based wood adhesive was increased to 4.75MPa and the wet strength was increased to 1.81MPa, respectively. The grafted parameters was also remarkably increased by the added of SDS, such as G increased by 80.9% and GE increased by 45.1%. The results of dynamic time sweep experiments and TEM and Low field Nuclear magnetic resonance technique (LF-NMR) showed that SDS could weaken the hydrogen bonding force of the starch molecules, and significantly enhanced the parameters of grafted reaction, thereby finally improving the bonding properties and stability of starch-based wood adhesive emulsion.In order to maximize the performance of starch-based wood adhesive, response surface methodology (RSM) was employed to optimize the grafted reaction condition. The RSM model showed that the shear strength and viscosity were related to acidolysis time (X₁), initiate APS dosage (X₂), emulsifier dosage(X₃) and initiate pH(X₄). The optimum extraction conditions were acidolysis time of 37.5min, initiate APS dosage of 0.74% of starch content (the total APS of 0.94% of starch content), emulsifier dosage of 0.84% of starch content and initiate pH of 5.85.Thirdly, in order to enhance the performance of starch-based wood adhesive, the additives which can further improve the performance of adhesive were also studied.To improve the frost resistance of starch-based wood adhesive in low temperture, the effects of urea on the performance of starch-based wood adhesive were evaluated, including freeze-thaw stability, rheological properties and bond behavior. The results indicated that starch-based wood adhesive with added urea still showed characteristics of non-Newtonian fluid. With the amount of urea increased, the non-Newtonian index would increase and the structural viscosity index would decrease. Result of freeze-thaw stability measurement indicated that added 15%(w/w)urea solution could effectively improve the frost resistance of starch-based wood adhesive. Results of dynamic time sweep experiments and LF-NMR indicated that the addition of urea could inhibit the formation of weak gel in the starch-based wood adhesive system and enhance structural stability of starch-based wood adhesive, whether the room temperature or freezing and thawing conditions. In addition, result of bond behavior indicated that urea had little influence on the bonding strength of starch-based wood adhesive. Therefore, urea can be used as an effective additive for improving storage performance starch-based wood adhesive.Furthermore, slica nanoparticles were used to improve the water resistance of starch-based wood adhesive in this study. Compared with starch-based wood adhesive without silica nanoparticles, the bonding strength of starch-based wood adhesive with 10%(w/w)of silica nanoparticles increased to 8.36MPa in dry state and 3.47MPa in wet state. The improved performance of SiO₂/starch-based wood adhesive was supported by its strengthened molecular structure, enhanced thermal stability and beneficial changes in rheological properties from the analysis results using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analyzer and rheometer.Finally, after a series of process optimization, the starch-based wood adhesive high starch content was successfully synthesized in factory, and the performance of the starch-based wood adhesive could reach the national standards of PVAc wood adhesive. The content of starch is about the 43.9% of the solid content of the starch-based wood adhesive. The economical analysis showed that the starch-wood adhesive has a lower cost, and its raw material cost is about 70% of PVAc emulsion wood adhesive. In summary, the starch-based wood adhesive is a kind of environment-friendly wood adhesives with lower cost and high performance and it will be a good extended value and market prospect in wood industy.