尿素-双醛淀粉-甲醛共缩聚树脂胶黏剂的制备与性能表征

Preparation and Characterization of Urea-Dialdehyde Starch-Formaldehyde Copolycondensation Resin Adhesive

为扩大淀粉的应用领域和减小脲醛树脂胶黏剂游离甲醛的含量,采用双醛淀粉与尿素、甲醛进行共缩聚反应,制得尿素-双醛淀粉-甲醛(UDSF)共缩聚树脂胶黏剂。考察了双醛淀粉用量、第一次共缩聚时间和第一次尿素比例(F/U1)对胶黏剂固体含量、黏度、水溶性、固化时间和游离甲醛含量的影响。并通过与尿素-淀粉-甲醛(USF)进行对比,得出双醛淀粉用量为0.075 mol,第一次共缩聚时间为60 min和F/U1为1.5时,所制得的UDSF树脂胶黏剂的使用操作性能较好、固化速率较快、环保性能较优、胶合强度和耐水性满足Ⅱ类胶合板要求。利用傅里叶变换红外光谱(FT-IR)、扫描电子显微镜(SEM)和热重测试仪(TGA)对UDSF树脂胶黏剂和对照样USF树脂胶黏剂进行了对比分析。结果表明,相比于原淀粉,双醛淀粉与尿素、甲醛反应活性更大,共缩聚反应更充分,显著提高了树脂的聚合度和交联度,使UDSF树脂成为连续的均相体系。解释了UDSF树脂胶黏剂固化时间缩短、游离甲醛含量降低、胶合强度和耐热性能提高的内在原因。同时UDSF树脂中游离-OH数量减少且缔合-OH数量增多,验证了UDSF树脂胶黏剂耐水性能的提高。

In order to expand the application field of starch and reduce the free formaldehyde content of urea-formaldehyde resin adhesive,urea-dialdehyde starch-formaldehyde(UDSF)copolycondensation resin adhesive was prepared by copolycondensation of dialdehyde starch with urea and formaldehyde.The effects of the amount of dialdehyde starch,the first copolymerization time and the first urea ratio(F/U1)on the solid content,viscosity,water solubility,curing time and free formaldehyde content of the adhesives were investigated.By comparing with urea-starch-formaldehyde(USF),it was concluded that when the amount of dialdehyde starch was 0.075 mol,the first copolymerization time was 60 min and F/U1 was 1.5,the UDSF resin adhesive had better operational performance,faster curing rate,better environmental protection performance,bonding strength and water resistance to meet the requirements of class II plywood.Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM)and thermogravimetric analyzer(TGA)were used to compare UDSF resin adhesives and USF resin adhesives.The results showed that dialdehyde starch had higher reactivity with urea and formaldehyde than native starch,and the copolycondensation reaction was more sufficient.The polymerization degree and crosslinking of UDSF resin were significantly improved,making UDSF resin a continuous homogeneous system.It was explained the internal reasons of shortening curing time,decreasing free formaldehyde content,improving bonding strength and heat resistance of UDSF resin adhesive.At the same time,the decrease of free-OH and the increase of association-OH in UDSF resin verify the improvement of water resistance of UDSF resin adhesive.