不同物质的量之比乙二醛?尿素?甲醛共缩聚树脂的合成与性能

为了降低木材胶黏剂中的甲醛含量,减小胶合板甲醛释放对人体健康和环境造成的危害,采用乙二醛与单羟甲基脲(MMU)反应,合成了MMU与乙二醛物质的量之比分别为0.7∶1.0,0.9∶1.0,1.1∶1.0和1.3∶1.0的乙二醛?尿素?甲醛(GUF)共缩聚树脂;采用傅里叶变换红外光谱(FT?IR)和X射线衍射(XRD)对树脂的结构进行了表征,对树脂的基本性能、固化性能、润湿性能及胶合性能进行测定,并进行对比分析。结果表明,合成制备的GUF树脂稳定性较好,均超过了10 d;外观均为酒红色均一液体。MMU与乙二醛的物质的量之比对树脂固体含量和黏度有较大影响,固体含量随着物质的量之比增大而增大,当MMU与乙二醛物质的量之比为1.3∶1.0时,树脂的固体含量为63.12%;当MMU与乙二醛物质的量之比为0.9∶1.0时,树脂黏度的最小值为23.91 mPa·s。树脂的主要官能团(N—H、O—H、C??O、C—O—C和C—N)的红外吸收峰基本不受物质的量之比的影响。树脂对杨木单板的润湿性能良好,接触角为50.8°~57.3°;MMU与乙二醛的物质的量之比为1.3∶1.0时合成的GUF树脂性能较优,胶合板干状胶合强度和湿强度分别为1.81和1.47 MPa;低物质的量之比的GUF树脂固化后会出现晶体结构。

Synthesis and performance of GUF resins with different molar ratios

As the most important type of the so-called amino plastic resins,urea-formaldehyde( UF) resins are widely used as wood-adhesive binders in manufacturing interior-use wood-based composites like particleboards,medium-density fiberboards and plywood because of their low cost,fast curing and good performance. However,the major drawback of toxic formaldehyde emission from bonded products has hindered their widely applications. With the increases of people’s living requirements and the environmental awareness,the more and more strict standard regulations of formaldehyde emission have induced considerable research focusing not only on decreasing formaldehyde emission of UF resins but also on the development of all kinds of alternative resins to UF resin. Herein,in order to reduce the formaldehyde content in wood adhesives and reduce the harm to human health and environments caused by formaldehyde emission from plywood,glyoxal( G) was selected to substitute formaldehyde to react with monomethylol( MMU) to synthesize glyoxal-urea-formaldehyde( GUF) co-condensed resin with different MMU/G molar ratios.The Fourier transform infrared spectroscopy( FT-IR) and X-ray diffraction( XRD) analysis were used to examine the structure of the resins. The basic properties,curing properties,wettability and bonding performance of the resins were measured and compared. The results showed that the synthesized GUF co-condensed resins with red wine color were of good stability within 10 d,and the color became darker with the increase of MMU/G molar ratio. The MMU/G molar ratio had a great influence on the solid content and viscosity of the resins,and the solid content of the resins increased with the molar ratio. When MMU/G molar ratio was 1.3 ∶1.0,the solid content of GUF resin was 63.12%. The minimum viscosity was 23. 91 mPa·s. The initial curing temperature was about 96 ℃ when MMU/G molar ratio was0.7 ∶1.0,while 104 ℃ for other three molar rations. FT-IR absorption peaks of the main functional groups( N-H,O-H,CO,C-O-C and C-N) remained unchanged with different MMU/G molar ratios. Furthermore,the GUF resin had good wettability to poplar veneers,and the contact angle values were within 50.8°-57.3° with MMU/G molar ratios of 0.7 ∶1.0,0.9 ∶1.0 and 1.1 ∶1.0;but it was increased to 58.4°-61.2° with MMU/G of 1.3 ∶1.0,which was probably attributed to high viscosity. The GUF resin with the molar ratio of 1.3 ∶1.0 of MMU/G had better performance and the plywood bonded with the resin had better dry bonding strength and wet strength of 1.81 and 1.47 MPa,respectively,and the crystal structure appeared in the cured GUF resin with low molar ratios.