聚乙烯亚胺-尿素-乙二醛树脂的合成及性能评价

Performance evaluation and synthesis of poly(ethylenimine)-urea-glyoxal resin

为开发适合木材胶接用非甲醛系合成树脂,以聚乙烯亚胺(PEI)、尿素(U)、乙二醛(G)为原料,在不同工艺参数下制备聚乙烯亚胺-尿素-乙二醛(PEIUG)缩合树脂,并采用傅里叶红外光谱(FT-IR)、电喷雾电离质谱仪(ESI-MS)、差示扫描量热仪(DSC)等方法对合成树脂官能团组成与固化特征进行表征,结合树脂宏观特征和胶合强度,综合评价合成反应工艺条件对树脂结构与性能的影响。测试结果表明,延长反应时间不仅有利于提升树脂的固体含量和胶合强度,树脂颜色也会随之加深,而且随着尿素用量的增加,在相同反应时间下树脂的固体含量和颜色呈现出相同的变化趋势,但胶合强度会有不同程度下降,特别是耐水性能。FT-IR和ESI-MS分析发现,合成树脂体系中存在多种分子结构组分,既包含尿素与乙二醛的自缩聚组分,也有聚乙烯亚胺、尿素、乙二醛之间的共缩聚组分,且聚合物的形成主要通过醚键(C—O—C)或亚甲基桥键(—CH_(2)—)的方式进行交联,不同反应工艺参数会导致树脂体系中聚合产物比例上的差异,进而对树脂网络交联体系的形成产生不同作用。从树脂固化历程的峰值温度和固化区域变化可以得到进一步印证,增加尿素用量虽然可以降低固化温度,但树脂固化历程会变得更加复杂。因此,在本试验条件下尿素用量对树脂整体性能的调控具有决定性作用。

As an effective way for controlling the negative influence of formaldehyde to develop formaldehyde-free wood adhesives,among many aldehydes,glyoxal was considered as the best alternative to formaldehyde due to its many distinctive advantages such as low toxicity and cost,not to volatilize and easy to degrade.However,the reactive ability of glyoxal is not as formaldehyde to amine compounds used commonly,and many glyoxal-based synthetic re-sins could not meet the standard requirements.Thus,modification is necessary to obtain excellent resins.In this work,the poly(ethylenimine)-urea-glyoxal condensation resin was produced with poly(ethylenimine),urea and glyoxal as raw materials at different chemical processes.Their structures and curing characteristics,features and bonding strength were analyzed via the Fourier transform infrared(FT-IR),electrospray ionization mass spectrometry(ESI-MS)and differential scanning calorimetry(DSC),and the performance of resins was also evaluated.The results indicated that,when the materials were the same,the longer reaction time of resin,the higher solid content,bonding strength and the deeper of its color.However,when the reactive times were the same,to increase the urea content,the solid content and color of reins were also changed to higher and deeper,respectively.Their bonding strengths were declined,especially the water resistance property,which implied that the urea content was very important for resins performance.The FT-IR and ESI-MS results showed that the various polymers with different relative molecular mass components were existed in resins including self-condensation polymers between urea and glyoxal,co-condensation polymers among poly(ethylenimine),urea and glyoxal,and different kinds of polymer could be cross-linked via ether bond(C—O—C)or bridge bond(—CH _(2)—).The ratio of polymers was diverse due to different processes,resulting in different networks.The extension of reactive time was beneficial to increase the ratio of high relative molecular mass polymer due to the increase of the dimer polymer.While the urea usage was increased,the ratio of self-condensation polymers from urea and glyoxal was increased as well,and the properties of resins would be worsened.This result was also conformed from peak curing temperatures and curing region of resins.To increase merely the urea content,the peak temperature could be decreased,but the curing process was complex as well.However,when only increased the reactive time,the curing peak temperature would move towards higher temperatures.These results indicated that low relative molecular mass polymers were easier to cross-link compared to the higher relative molecular mass polymers,but the latter had an important effect on the bonding performance of resins.Hence,the reasonable design of the process is very critical to balance the relationship between the cost and performance of resins.