白土对三聚氰胺-尿素-甲醛共缩聚树脂性能影响

Effect of clay on properties of melamine-urea-formaldehyde resin

为降低可食用面粉在木材胶黏剂行业的使用量同时保证胶合板预压性能,采用价格低廉的白土代替面粉并同时添加增稠剂作为三聚氰胺-尿素-甲醛(MUF)共缩聚树脂填料,研究白土及增稠剂的添加对MUF树脂黏度、膨胀率及制备胶合板的预压性能、胶合强度、甲醛释放量的影响。结果表明:白土主要是以物理填充的形式存在于胶黏剂基质中,当受到外力冲击时,可引发银纹效应。添加20 g(占填料总质量的80%)白土作为填料时,MUF3树脂制备胶合板的胶合强度提高到1.17 MPa,甲醛释放量为1.29 mg/L,满足E1级标准;随白土添加量增加,胶黏剂黏度下降,MUF3树脂制备胶合板预压后,单板翘曲面积大于30%,不能满足生产要求;MUF3树脂中加入1 g增稠剂后,胶液膨胀对比率达到102%,制备胶黏剂的黏度提高,保证了胶黏剂的初黏性,制备胶合板预压后,没有出现单板翘曲现象,预压性能良好。同时,所制备胶合板的胶合强度提高到1.25 MPa,甲醛释放量为1.03 mg/L,满足E1级标准。白土最高可替代80%(质量分数)的面粉作为MUF树脂填料,同时添加少量的增稠剂,即可满足胶黏剂预压性能,又可提高胶合强度,有望替代可食用面粉在人造板行业应用。

The addition of flour in urea-formaldehyde and its modified resin not only improve the initial viscosity of adhesive and the prepressing performance but also reduce the usage and cost of adhesives.In the plywood production,the addition amount of flour is about 10%-30%(accounting for the total weight of resin).In China,the plywood production industry consumes about 300,000 t of flour every year,which is a great waste of edible flour.The single addition of inorganic filler instead of flour as the resin fillers can improve the resin bonding strength,but often lead to low resin viscosity and poor prepressing performance.To reduce the use of edible flour in the wood adhesive industry and ensure the prepressing performance of resultant plywood,low-cost white clay and thickener were adopted as melamine-urea-formaldehyde(MUF) resin fillers.The effect of the clay and thickener addition on the viscosity of the MUF resin,prepressing performance,bonding strength,and formaldehyde emission of the resultant plywood was studied.The results showed that the clay existed in the adhesive matrix mainly in the form of physical filling and could initiate silver grain,absorb impact energy,and terminate crack propagation.When 20 g(80% of the total mass of filler) of clay was added as filler,the bonding strength of the plywood prepared with the MUF3 adhesive was increased to 1.17 MPa,and the formaldehyde emission was 1.29 mg/L,which met the requirements of E1 standard.With the increase of clay content,the viscosity of adhesive decreased.Because the resin viscosity was too low,the warpage area of the plywood prepared by MUF3 resin was more than 30%.In the process of veneer loading,it is easy to dislocate,which could not meet the production requirements in the industry.When 1 g thickener was added to the MUF3 resin,the expansion contrast ratio of glue solution reached 102%,and the viscosity of the prepared adhesive was improved.After the prepressing of plywood,there was no veneer warpage.At the same time,the bonding strength of the prepared plywood was increased to 1.25 MPa and the formaldehyde emission was 1.03 mg/L,which met the requirements of E1 standard.Clay could replace up to 80% of flour as MUF resin filler.Adding a small amount of thickener into adhesive could not only enhance the prepressing performance but also improve the bonding strength.It is expected to replace flour in the wood-based panel industry.