Dimensional stability of compound modification on fast-growing Populus cathayana with alkali lignin and hyperbranched polyacrylate emulsion
目的 为提升木质素对人工林速生材的尺寸稳定性，本研究提出利用碱木质素与超支化聚丙烯酸酯乳液（HBPA）对速生青杨复合改性的方法。 方法 通过在碱木质素中引入HBPA乳液，配制了质量分数1.31%的碱木质素与质量分数4%、8%的HBPA乳液的复配乳液（4HL、8HL组），然后分别将碱木质素、HBPA乳液及复配乳液浸渍处理速生青杨，基于改性材的质量增加率、增容率及扫描电镜探究浸渍效果；利用傅里叶变换衰减全反射红外光谱分析HBPA乳液的聚合情况以及改性材化学组分的变化；通过吸水、吸湿性试验对试材的尺寸稳定性进行评价；并对试材的顺纹抗压强度进行测试。 结果 微观上，随着乳液质量分数增大，固化后黏附在细胞腔内的乳液越多，整体被改性剂填充的导管和木纤维的数量也相应增多。宏观上，随着乳液质量分数的增大，改性材的质量增加率和增容率也相应提高，复配乳液改性材的4HL组质量增加率和增容率为8.14%和3.14%，8HL组质量增加率和增容率为15.05%和3.36%，且复配乳液改性材的质量增加率大于碱木质素、HBPA乳液改性材的质量增加率之和；相对于未改性材，复配乳液改性材4HL组和8HL组在吸水192 h时，吸水率分别降低了29.4%、35.3%，体积膨胀率分别降低了28.5%、29.7%，在相对湿度84%的条件下吸湿21 d后，含水率分别降低了6.9%和11.5%，体积湿胀率分别降低21.3%、26.0%；HBPA乳液及复配乳液有效提升了速生青杨的顺纹抗压强度，但其变化趋势与HBPA乳液质量分数相关不大。 结论 相对于碱木质素、HBPA乳液改性材，复配乳液改性材的质量增加率和增容率更高，吸水性和吸湿性降低更明显，尺寸稳定性提升更明显，说明碱木质素与HBPA乳液对速生青杨具有复合改性效果。Abstract: Objective To improve the dimensional stability by lignin on fast-growing wood, this work proposed a compound modification method by alkali lignin and hyperbranched polyacrylate emulsion (HBPA) for fast-growing poplar (Populus cathayana). Method By introducing HBPA emulsion into alkali lignin, compound emulsions (group 4HL and 8HL) composed of 1.31% alkali lignin and 4% and 8% HBPA emulsion were prepared, and then the alkali lignin, HBPA emulsion and their compound emulsions were used separately to treat fast-growing poplar. Mass percentage gain, bulk capacity and scanning electron microscope of the modified wood were used to explore the impregnation effect; the Fourier transform attenuated total reflection infrared spectroscopy was applied to analyze the polymerization of the HBPA emulsion and the composition change of the modified wood; dimensional stability was evaluated through water absorption and moisture adsorption; and longitudinal compressive strength of the samples was tested. Result Microscopically, as the concentration of the emulsion increased, more emulsion was observed to adhere to the cell cavity after solidification, and the amount of vessels and wood fibers fully filled with the modifiers increased as well. Macroscopically, with emulsion mass fraction increased, the mass percentage gain and bulk capacity of the modified wood also rose. Specifically, the mass percentage gain and bulk capacity of the 4HL group were 8.14% and 3.14%, and those for the 8HL group were 15.05% and 3.36%, respectively, and the mass percentage gain of the compound emulsion modified samples was greater than that of the sum for alkali lignin and HBPA emulsion individual treatment. Compared with the alkali lignin, unmodified wood, water absorption rate at 192 h for the 4HL and 8HL groups of the compound emulsion modified wood reduced by 29.4% and 35.3%, and the corresponding volume swelling rate decreased by 28.5% and 29.7%, respectively. After 21 d of moisture adsorption under 84% relative humidity, moisture content reduced by 6.9% and 11.5%, and the corresponding volume swelling rate decreased by 21.3% and 26.0%, respectively. HBPA emulsion and compound emulsion effectively enhanced the longitudinal compressive strength of treated wood, but this change trend was not related to the mass fraction of HBPA emulsion. Conclusion Compared with alkali lignin and HBPA emulsion modified wood, the mass percentage gain and bulk capacity of the compound emulsion modified wood were higher, the water absorption and moisture adsorption decreased significantly, and the dimensional stability was promoted greatly, confirming the compound modification effect of lignin and HBPA emulsion on fast-growing poplar.
表 1 试验分组
Table 1. Groups of specimens
HBPA mass fraction
Alkali lignin mass fraction
Control 未改性材 Unmodified wood 0 0 L 碱木质素处理 Alkali lignin treatment 0 1.31 4H HBPA乳液处理 HBPA emulsion treatment 4.00 0 8H 8.00 0 4HL 碱木质素/HBPA复配乳液处理 Alkali lignin/HBPA compound emulsion treatment 4.00 1.31 8HL 8.00 1.31
表 2 未改性与改性材的质量增加率和增容率
Table 2. Mass percent gain and bulking capacity of unmodified and modified wood samples
Mass increase rate (MPG)/%
Bulk capacity (BC)/%
L 1.51 (0.09) 1.11 (0.09) 4H 6.24 (0.59) 1.96 (0.08) 8H 11.21 (0.98) 2.46 (0.26) 4HL 8.14 (0.54) 3.14 (0.72) 8HL 15.05 (0.69) 3.36 (0.57) 注：括号中的数值分别为每组6块试材试验结果的标准偏差。Note: values in parentheses represent the standard deviation for 6 replicates of each group.
 张英豪, 奉国强. 中国木材供需现状与趋势[J]. 林业经济, 2015, 37(2):68−72.Zhang Y H, Feng G Q. China’s timber supply and demand: status and trend[J]. Forestry Economics, 2015, 37(2): 68−72.  Trinh H M, Militz H, Mai C. Modification of beech veneers with N-methylol melamine compounds for the production of plywood: natural weathering[J]. European Journal of Wood and Wood Products, 2012, 70(1−3): 279−286. doi: 10.1007/s00107-011-0554-y  郎倩. 复合改性剂对速生杨木和椿木改性效应及机理研究[D]. 北京: 北京林业大学, 2016.Lang Q. Research on properties and mechanism of fast-growing poplar and ailanthus treated by multi-functional modifier[D]. Beijing: Beijing Forestry University, 2016.  詹先旭, 张伟, 谢序勤, 等. 速生木材的增强改性研究进展[J]. 家具, 2019, 40(1):13−21.Zhan X X, Zhang W, Xie X Q, et al. Research progress on enhanced modification of wood from fast-growing trees[J]. Furniture, 2019, 40(1): 13−21.  Cannatelli M D, Ragauskas A J. Laccase-mediated synthesis of lignin-core hyperbranched copolymers[J]. Applied Microbiology and Biotechnology, 2017, 101(16): 6343−6353. doi: 10.1007/s00253-017-8325-2  Li H, Sivasankarapillai G, McDonald A G. Highly biobased thermally-stimulated shape memory copolymeric elastomers derived from lignin and glycerol-adipic acid based hyperbranched prepolymer[J]. Industrial Crops and Products, 2015, 67: 143−154. doi: 10.1016/j.indcrop.2015.01.031  Liu M, Yi Q R, Li J Y, et al. Synergistic effect of montmorillonite/lignin on improvement of water resistance and dimensional stability of Populus cathayana[J]. Industrial Crops and Products, 2019, 141: 111747. doi: 10.1016/j.indcrop.2019.111747  刘敏. 碱木质素/纳米蒙脱土协同提升速生杨尺寸稳定性研究[D]. 北京: 北京林业大学, 2019.Liu M. Synergistic effect of alkali lignin and nano-montmorillonite on improvement of dimensional stability of Populus cathayana[D]. Beijing: Beijing Forestry University, 2019.  周海珍. 碱木质素多尺度提升速生杨木尺寸稳定性研究[D]. 北京: 北京林业大学, 2018.Zhou H Z. Multiscale modifications on dimensional stability of Populus cathayana by alkali lignin[D]. Beijing: Beijing Forestry University, 2018.  Gurunathan T, Mohanty S, Nayak S K. Hyperbranched polymers for coating applications: a review[J]. Polymer-Plastics Technology and Engineering, 2016, 55(1): 92−117. doi: 10.1080/03602559.2015.1021482  谭惠民. 超支化聚合物[M]. 北京: 化学工业出版社, 2005.Tan H M. Hyperbranched polymer[M]. Beijing: Chemical Industry Press, 2005.  Kim Y H, Webster O W. Water soluble hyperbranched polyphenylene: a unimolecular micelle?[J]. Journal of the American Chemical Society, 1990, 112(11): 4592−4593. doi: 10.1021/ja00167a094  Hawker C J, Chu F. Hyperbranched poly(ether ketones): manipulation of structure and physical properties[J]. Macromolecules, 1996, 29(12): 4370−4380. doi: 10.1021/ma9516706  Wang D, Jin Y, Zhu X, et al. Synthesis and applications of stimuli-responsive hyperbranched polymers[J]. Progress in Polymer Science, 2017, 64: 114−153. doi: 10.1016/j.progpolymsci.2016.09.005  Lai N J, Wu T, Ye Z B, et al. Preparation and properties of hyperbranched polymer containing functionalized Nano-SiO2 for low-moderate permeability reservoirs[J]. Russian Journal of Applied Chemistry, 2016, 89(10): 1681−1693. doi: 10.1134/S1070427216100189  Li Y F, Dong X Y, Liu Y X, et al. Improvement of decay resistance of wood via combination treatment on wood cell wall: Swell-bonding with maleic anhydride and graft copolymerization with glycidyl methacrylate and methyl methacrylate[J]. International Biodeterioration & Biodegradation, 2011, 65(7): 1087−1094.  Li X Y, Xu J F, Long L, et al. Wood composites modified with waterborne hyperbranched polyacrylate dispersed organo‐montmorillonite emulsion and the permeability investigations by surface characterizations[J]. Polymer Composites, 2020, 41(9): 3798−3806. doi: 10.1002/pc.25677  Xu J F, Li X Y, Long L, et al. Enhancement of the physical and mechanical properties of wood using a novel organo-montmorillonite/hyperbranched polyacrylate emulsion[J]. Holzforschung, 2021, 75(6): 545−554. doi: 10.1515/hf-2020-0042  Omara S S, Abdel R M H, Ghoneim A, et al. Structure-property relationships of hyperbranched polymer/kaolinite nanocomposites[J]. Macromolecules, 2015, 48(18): 6562−6573. doi: 10.1021/acs.macromol.5b01693  Macromolecule Academy. Physical properties of macromolecules[M]. Tokyo: Kyoritsu Press, 1958.  Qi M W, Zhou Y F. Multimicelle aggregate mechanism for spherical multimolecular micelles: from theories, characteristics and properties to applications[J]. Materials Chemistry Frontiers, 2019, 3(10): 1994−2009. doi: 10.1039/C9QM00442D  Wang Y L, Li B, Zhou Y F, et al. Dissipative particle dynamics simulation study on the mechanisms of self-assembly of large multimolecular micelles from amphiphilic dendritic multiarm copolymers[J]. Soft Matter, 2013, 9(12): 3293−3304. doi: 10.1039/c3sm27396b  Anandhan S, Patil H G, Babu R R. Characterization of poly(ethylene-co-vinyl acetate-co-carbon monoxide)/layered silicate clay hybrids obtained by melt mixing[J]. Journal of Materials Science, 2011, 46(23): 7423−7430. doi: 10.1007/s10853-011-5705-3  李坚. 木材波谱学[M]. 北京: 科学出版社, 2003.Li J. Wood spectroscopy[M]. Beijing: Science Press, 2003.