魔芋粉-壳聚糖-聚乙烯醇共混胶黏剂的流变模型

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

为了拓宽魔芋粉的应用领域，开发环境友好型木材胶黏剂，并更准确地把握该胶在胶合板生产中的工艺参数，该文在前期葡甘聚糖-壳聚糖-聚乙烯醇共混胶黏剂的胶合机理、微观结构表征和流变特性的研究基础上，通过 TA 流变仪的扫描测试进一步研究了该共混胶黏剂的流变模型。首先对胶黏剂分别进行动态温度扫描和等温时间扫描曲线分析，接着进行稳态和动态流变曲线分析建立了复数黏度与剪切黏度的对应关系，然后根据Dual-Arrhenius方程建立了复合胶黏剂的化学流变模型，最后对胶黏剂的黏度和工艺条件进行了预测。结果表明：通过动态温度扫描曲线分析，温度较低时，复数黏度缓慢下降；从玻璃化温度到凝胶化温度，复数黏度迅速下降；从凝胶化温度到160℃左右，复数黏度出现平台区；160℃以上复数黏度急剧增大；通过等温时间扫描曲线分析得到随着温度的升高，反应速率加快，温度越高固化增黏时间越短；通过对比稳态和动态流变曲线，验证了Cox-Merz定律对于该胶的有效性；100～160℃时胶黏剂体系的相对黏度特性符合 Dual-Arrhenius 黏度方程；该模型与测试结果吻合性较好，利用该模型可以预测胶合板热压工艺所需要的工艺参数，并能动态模拟整个热压工艺过程中的黏度变化；综合得出在160℃附近黏度急剧上升，黏度随时间延长增加，理想的加压时机是温度升至130℃后保温15～20 min。该研究成果为胶黏剂固化工艺条件的确定提供了理论依据。

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.