高碘酸钠修饰阿拉伯胶-大豆分离蛋白胶黏剂的热固化行为及胶合板制备工艺

Plywood preparation process using sodium periodate modified gum arabic-soy protein isolate adhesive and its thermal curing behavior

以阿拉伯胶(GA)、大豆分离蛋白(SPI)为主要原料,通过添加氯化亚铁(FC)为催化剂,制备了一种阿拉伯胶-大豆分离蛋白-氯化亚铁胶黏剂(GA-SPI-FC),并在此基础上探讨了高碘酸钠(SP)修饰GA-SPI-FC胶黏剂的修饰工艺、热固化行为以及用该胶黏剂制备胶合板的热压工艺。通过研究SP的添加量和反应时间对胶合性能的影响,得到最佳修饰工艺为添加质量分数6%、反应时间9 h;通过测定在不同加热温度下经SP修饰和未修饰的GA-SPI-FC胶黏剂的不溶解率,得出在SP修饰下胶黏剂的固化温度显著降低;通过分别对比经SP修饰和未修饰的GA-SPI-FC胶黏剂的热重分析(TG)及差示扫描量热分析(DSC)结果可知,经SP修饰后GA-SPI-FC胶黏剂在快速热降解温度和吸热反应温度方面有明显的下降,从而提高了热固化效率。通过衰减全反射傅里叶变换红外光谱(ATR-FTIR)分析了经SP修饰GA-SPI-FC胶黏剂的反应机理,表明了SP能够氧化GA形成醛基,与SPI的NH 2/OH基团交联形成希夫碱连接。利用扫描电子显微镜(SEM)观察经SP修饰和未修饰GA-SPI-FC胶黏剂(固化后)微观形貌,经SP修饰后胶黏剂固化表面气孔数量、气孔孔径以及表面平整度都得到改善,微观形貌更加致密。最后,根据以上研究,探索经SP修饰后的GA-SPI-FC胶黏剂制备胶合板的工艺参数,得出热压温度150℃和热压时间10 min条件下,胶黏剂所制胶合板的湿剪切强度为0.78 MPa,满足GB/T 9846—2015《普通胶合板》对Ⅱ类胶合板的要求(≥0.7 MPa)。

In this study,a kind of gum arabic soy protein isolate ferrous chloride adhesive(GA-SPI-FC)was prepared using gum arabic(GA)and soy protein isolate(SPI)as the main raw materials and adding ferrous chloride(FC)as the catalyst.On this basis,the modification process,heat curing behavior and hot-pressing process of the GA-SPI-FC adhesive modified by the sodium periodate(SP)were discussed.By studying the influence of SP mass ratio and reaction time on the adhesive properties,the best modification process was obtained as 6%of SP mass ratio and 9 h of modification time.By measuring the insolubility of the SP modified and unmodified GA-SPI-FC adhesives at different heating temperatures,it was found that the insolubility of the SP modified GA-SPI-FC adhesive increased by 52%at 150℃,indicating that the curing temperature of the SP modified adhesive was significantly reduced.The thermogravimetric analysis(TG)and differential scanning calorimetry(DSC)of the SP modified GA-SPI-FC adhesive and the unmodified GA-SPI-FC adhesive were compared,respectively.The results showed that the rapid thermal degradation temperature and endothermic reaction temperature of the GA-SPI-FC adhesive modified by SP decreased significantly,and all occurred at 140℃,thereby improving the thermal curing efficiency.The changes of chemical functional groups before and after the SP modification of the GA-SPI-FC adhesive were analyzed by the attenuated total reflection Fourier transform infrared spectroscopy(ATR-FTIR),and the reaction mechanism was explored.It was shown that SP could oxidize GA to form aldehyde group and cross link with NH 2/OH group of SPI to form Schiff base connection.The scanning electron microscope(SEM)was used to observe the micro morphology of the SP modified and unmodified GA-SPI-FC adhesives(after curing).After the SP modification,the number of pores on the cured surface of the adhesive,pore diameter and surface smoothness were improved,and the micro morphology was denser.This showed that the cross-linking density of the GA-SPI-FC adhesive modified by SP was increased and a denser cross-linking network was formed.Finally,according to the above research,the process parameters of preparing plywood with the GA-SPI-FC adhesive modified by SP were explored,and it was concluded that the wet shear strength of the prepared adhesive was 0.78 MPa at 150℃and 10 min,meeting the requirements of the ClassⅡplywood in GB/T 9846-2015“General plywood”(≥0.7 MPa).This research lays a theoretical foundation for the preparation of formaldehyde-free adhesives for wood-based panels using sugars as the main raw materials,expanding the application of environmentally friendly adhesives in the wood industry.