Preparation and properties of heat-treated poplar wood modified with composite silicon modifier
目的 针对木材树脂改性剂释放甲醛不环保，无机改性材吸湿性高等问题，将廉价易得的硅石粉溶液化，再有机杂化，制得高渗透、环保、防火的水溶性木材复合硅改性剂，通过真空加压浸渍处理和热处理联合改性，可以有效提高木材的物理力学和阻燃等性能。 方法 分别制备硅油复合硅改性剂（SC2）和偶联剂杂化硅改性剂（HS2），对人工林杨木进行浸渍处理，再将浸渍材进行高温热处理，测试分析复合硅改性材及其热处理材的物理力学性能和阻燃性能。 结果 热处理使未处理材和改性材的质量与绝干密度均下降，硅油复合硅改性材（W-SC2）热处理后的质量损失率与绝干密度损失率最大。与W-SC2相比，硅油复合硅改性热处理材（TW-SC2）的吸湿率增大；偶联剂杂化硅改性热处理材（TW-HS2）的吸湿率较偶联剂杂化硅改性材（W-HS2）明显降低，抗吸湿性改善明显。与杨木未处理材（W）相比，各组改性材的力学性能均显著提高，且明显优于TW-SC2。W-HS2的点燃时间比W延迟8 s，火灾指数由0.043 m2s/kW增大至0.140 m2s/kW，TW-HS2的点燃时间比W延后9 s，火灾指数比W-HS2提高了64.3%。与W相比，TW-HS2的总热释放量减小29.4%，热释放速率峰值下降，且第二热释放速率峰值出现时间延后；W-HS2和TW-HS2的总生烟量比W大；HS2浸渍改性联合热处理，可以提升木材阻燃性能。改性材的热降解速率较未处理材降低明显，热稳定性提高，说明HS2改性剂具有明显的促进成炭作用。 结论 以硅石资源为主要原料，有机杂化制得环保、高效的木材复合硅改性剂HS2，通过真空加压浸渍−热处理联合改性工艺，可有效改善人工林杨木的物理力学和阻燃等性能，实现其绿色改性，应用前景广阔。Abstract: Objective Considering the problems such as formaldehyde emission from wood resin modifier and high hygroscopicity of inorganic material modified wood, the easily available silica powder was used as the main raw material to prepare composite silicon wood modifier, which was water-soluble, high permeable, environmental friendly and fireproof. Through vacuum pressure impregnation and heat-treatment, the physical, mechanical and fire retardant properties of woods were effectively improved. Method Silicone oil composite silicon modifier (SC2) and coupling agent hybrid silicon modifier (HS2) were prepared respectively. Plantation poplar wood was impregnated, then the impregnated wood was heat-treated at a high temperature. The physical, mechanical and fire retardant properties of composite silicon modified wood and its heat-treated wood were finally tested and analyzed. Result After heat-treatment, the mass and oven-dry density of all samples decreased, and the oven-dry density loss rate and mass loss rate of heat-treated silicone oil composite silica modified wood (TW-SC2) were the largest. Compared with silicone oil composite silicon modified wood (W-SC2), the moisture absorption rate of TW-SC2 increased. The moisture absorption rate of the heat-treated coupling agent hybrid silica modified wood (TW-HS2) was significantly lower than that of the coupling agent hybrid silicon modified wood (W-HS2), and the moisture absorption resistance was significantly improved. Compared with the untreated wood (W), the mechanical properties of all the modified wood apparently improved, and were better than TW-SC2. The ignition time of W-HS2 was 8 s later than that of W, its fire performance index increased from 0.043 to 0.140 m2s/kW. The ignition time of TW-HS2 was 9 s later than that of W, and its fire performance index increased by 64.3% compared with W-HS2. Compared with W, the total heat release of TW-HS2 reduced by 29.4%, the peak heat release rate decreased, and the peak time of the second heat release rate was delayed. The total smoke release of W-HS2 or TW-HS2 was larger than that of W, the HS2 impregnation modification combined with heat-treatment can further promote the flame retardancy of wood. The thermal degradation rate of the modified wood was significantly lower than that of W, and the thermal stability was improved, indicating that the HS2 modifier had a significant effect on promoting char formation. Conclusion Taking silica as raw material, the coupling agent hybrid silicon modifier HS2, which was environmentally friendly and highly efficient, was prepared through organic hybridization. The combined modification process of vacuum pressure impregnation and heat-treatment can effectively improve the mechanical and fire-retardant properties of plantation poplar wood, realize green modification with broad application prospects.
表 1 改性杨木的绝干密度和质量损失率
Table 1. Oven-dry density and mass loss rate of modified poplar wood
Mass loss rate/%
Untreated poplar wood (W)
0.325 (3.5%) 2.873 (2.8%) 杨木热处理材
Heat-treated poplar wood (TW)
0.321 (1.6%) 1.2 2.712 (2.1%) 5.6 硅油复合硅改性材
Silicone oil combined with silica treated wood (W-SC2)
0.613 (2.3%) 4.806 (5.8%) 硅油复合硅改性热处理材
Heat treated silicone oil composite silica modified wood (TW-SC2)
0.513 (2.4%) 16.3 3.610 (4.9%) 24.9 偶联剂杂化硅改性材
Coupling agent hybrid silica treated wood (W-HS2)
0.528 (1.4%) 4.344 (4.6%) 偶联剂杂化硅改性热处理材
Heat treatment coupling agent hybrid silica modified wood (TW-HS2)
0.516 (1.3%) 2.3 4.196 (3.6%) 3.4 注：括号内为变异系数。下同。Notes: data in brackets are variation coefficients. Same as below.
表 2 改性杨木的抗吸湿率
Table 2. Anti-moisture efficiency of modified poplar wood
时间 Time/h 12 24 36 60 84 120 156 204 264 528 W-SC2 58.8 54.7 54.2 47.9 41.6 29.0 21.9 5.7 −2.1 −29.9 TW-SC2 42.9 37.6 40.6 34.7 30.1 16.9 3.5 −10.8 −29.4 −61.3 W-HS2 50.0 39.0 41.6 39.9 32.4 19.7 20.3 −2.8 −21.9 −58.3 TW-HS2 51.0 40.1 44.6 45.5 42.1 29.3 24.2 13.1 −6.2 −23.6
表 3 改性材的力学性能
Table 3. Mechanical properties of the modified wood
顺纹抗压强度 Compressive strength along grain/MPa W 57.7 (5.45%) 7.2 (0.31%) 43.7 (2.19%) W-SC2 96.9 (7.03%) 12.9 (0.90%) 87.2 (4.54%) TW-SC2 79.8 (3.46%) 9.3 (0.89%) 70.2 (1.37%) W-HS2 127.8 (4.57%) 14.1 (1.10%) 97.4 (1.23%) TW-HS2 121.9 (3.25%) 13.3 (1.28%) 90.3 (4.15%)
表 4 复合硅改性热处理杨木的燃烧性能
Table 4. Combustion properties of composite silicon modified heat-treated poplar wood
组别 Group tTI/s p1/(kW·m−2) p2/(kW·m−2) FPI(m2·s·kW−1) TH/(MJ·m−2) TS/m2 W 8 184.9 178.0 0.043 112.3 1.60 W-HS2 16 114.2 159.2 0.140 94.9 2.80 TW-HS2 17 74.0 96.8 0.230 79.3 1.85 注：tTI为点燃时间；p1为第一热释放速率峰值；p2为第二热释放速率峰值；FPI为火灾指数；TH为总热释放量；TS为总生烟量。Notes：tTI is the time to ignition, p1 is the first heat release rate peak, p2 is the second heat release rate peak, FPI is the fire performance index, TH is total heat release, TS is total smoke release.
表 5 样品的热降解特征值
Table 5. Thermal degradation characteristic values of samples
组别 Group TA/℃ mLA/% TF/℃ mLF/% Tp/℃ mLp/% TF –TA/℃ mLF–mLA/% R/% W 222.0 6.9 454.7 83.9 366.3 65.7 232.7 77.0 13.3 W-HS2 166.8 4.3 524.2 53.4 273.8 27.7 357.4 49.1 45.3 TW-HS2 193.3 4.9 499.7 48.4 273.3 23.1 306.4 43.5 49.6 注：TA为第三阶段的起始温度；mLA为第三阶段起始温度时的质量损失率；TF为第三阶段的结束温度；mLF为第三阶段结束时的质量损失率；Tp为DTG曲线的峰值温度；mLp为温度达到Tp时的质量损失率；R为热解最终剩余物质量占热解前质量的百分数。Notes：TA is the start temperature of the third stage, mLA is the mass loss rate at the start temperature of the third stage, TF is the end temperature of the third stage, mLF is mass loss rate at the end of the third phase, Tp is the expectation of the DTG curve temperature, mLp is mass loss rate when the temperature reaches Tp, R is the mass percentage final residue.
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