山梨醇基非异氰酸酯聚氨酯胶黏剂的制备与表征

Preparation and characterization of sorbitol-based non-isocyanate polyurethane(NIPU)resins

聚氨酯胶黏剂是木材工业生产中的一类重要胶黏剂,但由于其原料的毒害及湿敏性问题,以及人们环保意识的提升,使得寻求不使用异氰酸酯的生物质原料制备非异氰酸酯聚氨酯(NIPU)成为研究热点。基于此,本研究采用生物质山梨醇与碳酸二甲酯(DMC)反应后再聚合己二胺(HMDA)制备了NIPU树脂木材胶黏剂,并探讨了不同催化剂,以及最优催化剂的不同添加比例对树脂胶合性能的影响。利用液相色谱/质谱(LC-MS)和傅里叶变换红外光谱(FT-IR)研究了树脂结构以及催化剂对树脂结构的影响;通过差式扫描量热仪(DSC)和热重分析(TG)研究了树脂的固化过程以及热稳定性。结果表明:山梨醇、DMC和HMDA三者共同反应成功制备了具有氨基甲酸酯结构的NIPU树脂,在添加催化剂NaHCO_(3)之后,氨基甲酸酯结构中的C=O吸收峰增强,氨基峰减弱,说明更多胺参与缩聚,促进了反应的进行。DSC和TG测试结果也证明添加NaHCO_(3)为催化剂后树脂固化反应更完全,固化后的树脂热稳定性增强。同时胶合板测试结果表明当催化剂NaHCO_(3)的添加量为山梨醇固体质量的7.5%时,所制备NIPU树脂粘接性能最佳,其干强度、24 h冷水湿强度和3 h 63℃温水湿强度分别为2.19,0.92和0.82 MPa,满足国家标准GB/T 9846—2015《普通胶合板》对二类板(强度≥0.7 MPa)的标准要求。

At present,one of the most widely used adhesives in the wood-based panel industry is the aldehyde-based synthetic resin adhesive,but there are problems such as the release of free formaldehyde and the consumption of petrochemical resources.Polyurethane(PU)refers to a polymer containing urethane repeating structural units in its molecular chain,being widely used in coatings,adhesives,elastomers,foams,and other fields.When being used as a wood adhesive,PU has excellent properties of shear strength and impact resistance,which can be used to address the problem of formaldehyde release in traditional trialdehyde adhesives,so it is highly valued by the wood industry.However,some drawbacks,such as toxic raw materials,great consumption of petrochemical resources,and high cost remained.Preparation of non-isocyanate polyurethane(NIPU)without using isocyanates as raw materials has become a hot research topic due to the toxicity and moisture sensitivity of PU raw materials.In addition,the utilization of biomass raw materials to prepare non-isocyanate polyurethane has become a top priority with the improvement of people s environmental awareness.As a biomass material with a six-carbon polyol structure,sorbitol has a melting point of about 90℃,which can be melted without adding water as a solvent under the condition of water bath heating.Therefore,in this study,non-isocyanate polyurethane(NIPU)resin wood adhesives were prepared by the reaction of the sorbitol with dimethyl carbonate(DMC)and hexamethylenediamine(HMDA).The influences of different catalysts and different addition ratios of optimal catalysts on resin bonding properties were discussed.The resin structure and the effect of the catalyst on the resin structure were explored by the liquid chromatography/mass spectrometry(LC-MS)and Fourier transform infrared spectroscopy(FT-IR).The curing process and thermal stability of the resin were investigated by the differential scanning calorimetry(DSC)and thermogravimetric analysis(TG).The structural analysis showed that the NIPU resin was successfully prepared by the co-reaction of sorbitol,DMC,and HMDA.After the addition of catalyst NaHCO_(3),the C=O absorption peak of urethane was enhanced,and the peak represented by amine was weakened,indicating that more amino molecules were cross-linked,which promoted the reaction.DSC and TG test results showed that the curing reaction of the resin was more complete,and the thermal stability was enhanced after the adding of catalyst NaHCO_(3).In addition,the plywood test results showed that,when the addition amount of catalyst NaHCO_(3) was 7.5%of the solid mass of sorbitol,the resin bonding ability were significantly improved,and the dry strength,cold water wet strength,and 63℃warm water wet strength of plywood were 2.19,0.92 and 0.82 MPa,respectively.It meets the standard requirements of the Chinese National Standard GB/T 9846-2015“Plywood for general use”(≥0.7 MPa)for the second-class boards.