摘要
酚醛(PF)树脂胶合强度高、耐水(湿)耐候性强、阻燃性能较好,但固化后的PF树脂呈现出高聚合度三维网络结构,脆性较高、韧性不足,胶层在外力特别是冲击载荷作用下易于产生裂纹并迅速扩展,导致胶层开裂甚至失效。针对PF树脂胶黏剂固化后脆性大、韧性差的不足,探究引入端羧基丁腈橡胶(CTBN)对其增韧改性(添加量5%~25%)后试制杨木胶合板。通过傅里叶变换红外光谱、X射线衍射、固体核磁等方法分析表明,CTBN柔性链段不仅有效嵌入PF树脂固化体,而且通过活性端基(—COOH)与PF树脂羟甲基发生接枝反应。纳米压痕测试结果表明,随着CTBN添加量的增加,PF树脂固化体的硬度和杨氏模量均出现下降趋势,表明改性PF树脂固化体具有良好的韧性。胶合强度结果表明,当CTBN添加量为15%时,干胶合强度提升幅度最大,达到了110.5%;当CTBN添加量为5%时,湿胶合强度提升幅度最大,达到了48.33%。数字散斑结果表明,CTBN的加入有效减少了杨木胶合板受到外力作用时胶层应力集中的现象。研究结果证实了CTBN增韧PF树脂并提高木材胶合性能的理论和技术可行性。
Phenolic(PF)resin has high bonding strength,high water(wet)weathering resistance,and better flame-retardant properties,which is widely used as an adhesive for outdoor wood-based panels.The cured PF resin shows a high degree of polymerization of three-dimensional network structure,high brittleness,lack of toughness,the adhesive layer in the external forces.Especially the impact load is easy to produce cracks and rapid expansion,resulting in adhesive layer cracking or even failure.Toughening and modification of the PF resin can improve the impact resistance of wood-based panels and their products on the basis of retaining its inherent excellent bonding properties,which can further broaden the application scenarios of the products.This study investigated the introduction of terminated carboxylated nitrile butadiene rubber(CTBN)with toughening modification(5%-25%application)for trial production of poplar plywood.Analyses by Fourier transform infrared spectroscopy,X-ray diffraction,and solid-state NMR showed that the flexible chain segments of CTBN were not only efficiently embedded in the curing body of the PF resin,but also grafted to the hydroxymethyl group of the PF resin through the reactive end group(—COOH).The nanoindentation test results showed that the hardness and Young's modulus of the PF resin cured body showed a decreasing trend with the increase of CTBN addition,and the modified PF resin cured body had lower hardness and Young's modulus compared to the unmodified PF resin cured body,which indicated that the modified PF resin cured body had good toughness.The results of the bonding strength showed that the addition of CTBN had a significant effect on the bonding strength of plywood.When CTBN was added by 15%,the dry bonding strength was 2.03 MPa,which was 110.5%higher than that of pure PF plywood,and when CTBN was added by 5%,the wet bonding strength was 1.50 MPa,which was 48.33%higher than that of pure PF plywood.Overall,the optimal addition amount of CTBN was 5%,and the plywood could be used in a wider range of application scenarios.The failure modes of the specimen glued interface were mainly cohesive damage and mixed damage.The digital scattering results proved that the addition of CTBN made the strain distribution at the interface between liquid adhesive and wood veneer more uniform,which was more conducive to stress transfer and less likely to produce stress concentration phenomenon.The findings in this study confirmed the theoretical and technical feasibility of CTBN for toughening PF resins and improving wood bonding properties.
作者
朱春锋
田飞宇
吴玉涛
靳愿愿
徐信武
ZHU Chunfeng;TIAN Feiyu;WU Yutao;JIN Yuanyuan;XU Xinwu(Co-Innovation Center of Efficient Processing and Utilization of Forest Resources,Nanjing Forestry University,Nanjing 210037,China)
出处
《林业工程学报》
CSCD
北大核心
2024年第5期36-43,共8页
Journal of Forestry Engineering
基金
湖北省技术创新专项重大项目(2019ABA097)。
关键词
酚醛树脂
增韧改性
端羧基丁腈橡胶
纳米压痕
phenol formaldehyde resin
toughening modification
CTBN
nanoindentation
