Rheological model of konjak powder-chitosan-polyvinyl alcohol blending adhesive

Abstract: With the rapid development of our country's economy, the environmental pollution has become more serious. Developing environment-friendly wood adhesive and understanding its key processes in plywood production are important for Chinese wood industries. Our studies showed that the konjak powder-chitosan-PVA blending adhesive had good bonding strength performance and water resistance performance that complied with the national standards. This study also verified that blending the three kinds of polymer materials had good compatibility. Hot pressing process parameters including gelling temperature, glass transition temperature, hot pressing temperature, gel time were obtained from the rheological behavior of blending adhesive. The rheological behavior of blending adhesive was further investigated by using TA Rheometer through scanned konjak powder-chitosan-PVA blending adhesive. The results indicated that curing process mainly occurred at 100-160℃ dynamic temperature could sweep from 20-190℃.The relationship between complex viscosity and time at 120, 130, 140 and 150℃ was characterized based on the steady-state curves and dynamic rheological curves. A chemrheological model based on Dual-Arrhenius equation was developed for this adhesive from estimate of zero shear viscosity and other model parameters. Finally, the viscosity and process conditions of the adhesive were predicated. The results showed that : By dynamic temperature sweep, when the temperature was low, the complex viscosity of adhesive decreases slowly; when the temperature increases to the gelation temperature , the complex viscosity decreased rapidly; when the temperature increased to about 160℃, the complex viscosity arised a plateau and increased sharply above 160℃. When controlling the temperature of 120~150 ℃ for experimental research of viscosity -temperature-time, the visctsity increased with the increasing of time. Based on the isothermal time sweep, complex viscosity of adhesive increased gradually at beginning, and then it rose sharply through their respective inflection points, the higher the temperature the shorter curing thickening time. This adhesive followed the Cox-Merz Rule, the corresponding relationship of the complex viscosity and shear viscosity can be developed by comparing the steady-state curves and dynamic rheological curves. The relative viscosity characteristics of adhesive followed the Dual-Arrhenius equation at 100~160℃. The ideal pressure time was after reaching the temperature at 130℃ about 15 - 20min. The model simulation results are in good agreement with the experimental data. This model can be used to predict the technological parameters of hot-pressing process of plywood, and simulate the viscosity changes dynamically throughout the hot-pressing process.