高替代率木质素酚醛树脂在胶合板中的应用性能比较

Application Performance Comparison of Lignin⁃based Phenolic Resin with High Phenol Substitution Rate in Plywood

以云杉硫酸盐法制浆黑液中的碱木质素(UL)为原料,在改性得到脱甲基化木质素(DUL)和羟甲基化木质素(HUL)的基础上,合成了高替代率(≥70%)的木质素酚醛树脂(LPF),并探讨了3种木质素羟基含量对LPF胶黏剂胶合强度和游离甲醛含量的影响。木质素的结构分析结果表明:相比原料UL,DUL和HUL的羟基比例分别提高了26.41%、 72.35%。将UL、DUL和HUL替代苯酚制备LPF并将其用于杨木单板胶合实验中,实验结果显示:UL经脱甲基化改性后进一步提高了其耐热水胶合强度(σ_(HWT)),在30%木质素替代率下,DUL的σ_(HWT)最大,达1.09 MPa,比PF(0.78 MPa)提高了39.39%。木质素替代率从30%(HUL)提高至70%(DUL),同时胶合板中游离甲醛的质量浓度从0.33 mg/L(UL)降低至0.29 mg/L(DUL),仍小于国标GB 9846.2—2004要求(<0.5 mg/L);UL经羟甲基化改性后,HUL制备LPF的胶合强度大幅提高,在30%木质素替代率下,干胶合强度(σ_(dry))为2.55 MPa,与PF(1.43 MPa)相比提高了79.02%;湿胶合强度(σ_(WST))为1.99 MPa,与PF(0.84 MPa)相比提高了135.31%。

Lignin⁃based phenolic resin(LPF)with high phenol substitution rate(≥70%)were synthesized based on alkali lignin(UL)from black liquor of kraft pulping of spruce,or based on demethylated lignin(DUL)and hydroxymethylated lignin(HUL)obtained from the modification of UL.The effects of the hydroxyl content of three types of lignin on the adhesive strength and free formaldehyde content of LPF adhesives were compared and analyzed in this paper.The results of structure analysis of lignin showed that the hydroxyl ratios of DUL and HUL increased by 26.41%and 72.35%,respectively,while compared to raw UL.UL,DUL and HUL were separately used to replace phenol for the preparation of LPF that were applied in the bonding experiment of poplar veneer.The experimental results showed that demethylation of UL could further improve the heat⁃resistant water⁃based bonding strength(σ_(HWT)).At 30%lignin substitution rate,DUL showed the largestσ_(HWT) of 1.09 MPa,which was 39.39%higher than PF(0.78 MPa).The replacement rate of lignin increased from 30%to 70%.Meanwhile,the content of free formaldehyde in plywood decreased from 0.33 mg/L to 0.29 mg/L,which was still less than the requirement of national standard GB 9846.2—2004(<0.5 mg/L).The bonding strength of LPF prepared from HUL was significantly improved after modification of UL by hydroxymethylation.At 30%lignin replacement rate,the dry bonding strength(σ_(dry))and wet bonding strength(σ_(WST))were 2.55 MPa and 1.99 MPa which increased by 79.02%and 135.31%respectively,while compared those with PF(1.43 MPa and 0.84 MPa).