摘要
为降低单宁反应活性位点之间的空间位阻,提高单宁树脂粘接质量,研究利用碳酸二甲酯(DMC)使单宁碳酸化,并与羟甲基脲(MMU)共聚制备木材胶黏剂。通过傅里叶红外光谱(FT-IR)对树脂进行结构分析,差示扫描量热法(DSC)测试树脂的固化行为,热重分析(TG)对树脂固化产物的热稳定性进行研究。同时,还对树脂的理化性能(固体含量、黏度和凝胶时间)以及胶合板胶合强度进行测试。研究结果表明:单宁在DMC作用下发生了碳酸化反应,有利于与MMU发生共聚;碳酸化单宁共聚系列树脂的固化温度呈现出先上升后下降的趋势,当每125 g树脂中MMU添加量为60 g时,固化温度更高,固化更完全;通过TG分析,每125 g树脂中MMU添加量为60 g时能形成有效交联结构。相对于无碳酸化单宁共聚树脂,碳酸化单宁共聚树脂固体含量更高,为40.0%~43.0%;凝胶时间受MMU添加量影响,呈现先下降后上升的趋势,且碳酸化单宁树脂所制胶合板呈现出更高的胶合强度。但同等的MMU添加水平下,碳酸化单宁共聚树脂对减少甲醛释放量的贡献不大。
As a natural polyphenolic compound, tannin was characterized by high degree of aggregation and high molecular weight which made the adhesive prepared by tannin to have low degree of cross-linking. Many studies reported that the introduction of bridging agents which copolymerized with tannin can improve the polycondensation reaction ability of tannin. Therefore, this study used dimethyl carbonate(DMC), a kind of chemical raw material with low toxi-city and environmental-friendly performance, to carbonize tannins and then copolymerized it with methylol urea(MMU) to prepare wood adhesives in order to reduce the steric hindrance between the reactive sites of tannins and improve the bonding quality of tannin resins. In this study, the structure of the resin was analyzed by the Fourier transform infrared spectroscopy(FT-IR);the curing behavior of the resin was tested by the differential scanning calorimetry(DSC);and the thermal stability of the cured resin product was studied by the thermogravimetric(TG) analysis. At the same time, the physical and chemical properties of the developed resin(solid content, viscosity, and gel time) and the shear strength of the plywood were also tested. The research results showed that the carbonated tannin resin had higher solid content(between 40.0% and 43.0%) and gel time, but lower viscosity compared to the non-carbonated tannin. Through the analysis of FT-IR, it was found that tannins had undergone carbonation reaction due to the action of DMC, which is beneficial to the copolymerization reaction with MMU. However, the amount of MMU was hardly to change the structure of resins. Besides, the curing temperature of carbonated tannin copolymerization series resin showed a trend of firstly rising and then falling, especially, it was showed an increased temperature when MMU was added in the level of 60 g/125 g, which indicated that the resin system had formed a completely cross-linked network. At the same time, in the TG analysis it was also found that the carbonated tannin resin had higher thermal stability than the non-carbonated resin and the level of 60 g/125 g MMU addition was the best in the experiment which formed an effective cross-linking structure. In addition, to investigate the bonding strength of plywood, it was disco-vered that the plywood made by the carbonated tannin copolymer resin exhibited higher shear strength than the non-carbonated resin. The 60 g/125 g MMU addition still had the optimal effect on the resin. However, the carbonated tannin copolymer resin did not contribute much to the reduction of the formaldehyde emission under the same MMU addition level with more formaldehyde amount.
作者
彭晋达
晏畅
杨福仙
洪梦裳
杨兆金
杜官本
周晓剑
PENG Jinda;YAN Chang;YANG Fuxian;HONG Mengshang;YANG Zhaojin;DU Guanben;ZHOU Xiaojian(Yunnan Key Laboratory of Wood Adhesives and Glued Products,Southwest Forestry University,Kunming 650224,China;Kunming Feilin Panel Board Co.Ltd.,Kunming 650403,China)
出处
《林业工程学报》
CSCD
北大核心
2023年第1期119-125,共7页
Journal of Forestry Engineering
基金
国家自然科学基金(31971595)
云南省基础研究专项重点项目(202101AS070008)
云南省“兴滇英才支持计划人才”-青年人才
昆明市院士专家工作站(YSZJGZZ-2020052)
高等学校学科创新引智计划(D21027)。
关键词
碳酸化单宁
羟甲基脲
接枝共聚
胶合性能
耐水性
carbonated tannins
methylol urea
graft copolymerization
bonding properties
water resistance
