Poplar Veneer Multi-Layer Impregnation Densification Enhancement And Performance Research

Natural fast-growing poplar wood is widely used as a green renewable material in furniture and building materials,but its defects of porous and lax,low density,weak mechanical properties,and flammability limit its application scope.In this paper,a simple and feasible method was used to prepare multilayer impregnated densified reinforced wood by first removing lignin from natural poplar veneer,then oxidizing the main chemical components of wood cell wall by TEMPO oxidation method,and finally stacking and hot-pressing multiple layers of TEMPO-oxidized veneer impregnated with calcium ions,polyacrylic acid and sodium silicate,respectively.By impregnating calcium ions,polyacrylic acid,sodium silicate and hot pressing,a large number of hydrogen and chemical bonds were formed inside the multilayer impregnated densified reinforced wood,which effectively improved the density,mechanical properties,flame retardancy,thermal stability,aging resistance and hydrophobicity of natural poplar wood.The main studies are as follows.（1）After treatment with a mixture of sodium hydroxide and sodium sulfite,the mass of natural poplar veneer was reduced by 24.2%,and the contents of hemicellulose and lignin decreased by 43.3%and 23.7%,respectively,and the intensity of the characteristic lignin peaks at 1508 cm^-1,1455 cm^-1 and 1265 cm^-1 of the delignified veneer decreased,and the area between 1000 cm^-1 and 1200 cm^-1 was reduced.The absorption peaks of TEMPO-oxidized veneer at 1600 cm^-1 and 1730 cm^-1 were enhanced,indicating that some of the hydroxyl groups（-OH）on the cellulose of the cell wall had been transformed into carboxyl groups（-COOH）;the thermal stability of TEMPO-oxidized veneer was The thermal stability of TEMPO-oxidized veneer was significantly improved;compared with natural poplar,the cellulose crystallinity of delignified veneer and TEMPO-oxidized veneer was increased by 16.5%and 11%,respectively.（2）TEMPO oxidized veneer impregnated with calcium ions and then prepared LDCIW with good overall performance by multi-layer stacking and hot pressing;LDDW prepared by multi-layer delignified veneer stacking and hot pressing.The bending strength of LDCIW is3.46 times that of NW,the bending modulus is 5.11 times that of NW and 2.47 times that of LDDW;the specific bending strength of LDCIW is 1.12 times and 3.34 times that of NW and LDDW,respectively;the tensile strength of LDDW and LDCIW is 2.98 times and 3.89 times that of NW,respectively;compared with the specific tensile strength of NW and LDDW,the specific tensile strength,LDCIW increased by 25.5%and 30.2%,respectively;the unnotched impact strength of LDCIW was 3.27 times that of NW;the interfacial bond strength of LDCIW increased by 52.9%compared with LDDW;the ignition time of LDCIW was 67s,which was extended by 33s compared with NW,and the ignition time increased by 97.1%;it was extended by 21s compared with LDDW,and the ignition The maximum HRR peak of LDCIW decreased by 37.4%compared with NW,and the peak appearance time was delayed by 170s;the total heat release per unit mass of LDCIW was also lower than that of NW;the overall color change of LDDW and LDCIW was small,and the color aging resistance was significantly improved under UV irradiation,and the hydrophobicity was improved.The thermal stability of LDDW and LDCIW is also improved.（3）LDPW prepared by stacked hot press molding of TEMPO oxidized veneer impregnated with polyacrylic acid in multiple layers and LDSW prepared by stacked hot press molding of TEMPO oxidized veneer impregnated with sodium silicate in multiple layers.The FTIR spectral curves of LDPW show significantly enhanced-C=O anti-symmetric and symmetric stretching vibration peaks of-COONa at 1580 cm-1 and 1410 cm^-1 compared to NW,with a new-C-O stretching vibration peak at 1262 cm^-1;the absorption peak near 778 cm^-1 of the FTIR spectral curve of LDSW is the characteristic peak of Si-O-Si indicating that sodium silicate has been impregnated within the veneer,and the absorption peak near 1055 cm^-1 is the stretching vibration peak of Si-O-C;compared with NW cellulose crystallinity,LDPW and LDSW have improved by 12.9%and 18%,respectively;compared with LDPW bending strength and bending modulus,LDSW has improved by 27.59%and 11.32%,respectively;compared with LDCIW bending strength The tensile modulus of LDCIW,LDPW and LDSW increased by 2.08%,60%and 51%respectively compared to NW;the tensile strength of LDSW was 1.31 and 1.33 times higher than that of LDCIW and LDPW respectively;the unnotched impact strength of LDSW was 1.23 times higher than that of LDCIW and LDPW respectively.LDSW has the highest interfacial bond strength,specific tensile strength,specific bending strength and specific bending modulus.LDSW has better flame retardancy,thermal stability and hydrophobicity.In summary,natural poplar veneer was treated with a mixture of sodium hydroxide and sodium sulfite to remove lignin and TEMPO oxidation,followed by impregnation of TEMPO oxidized veneer with calcium ions,polyacrylic acid and sodium silicate,respectively,and finally the multi-layer impregnated veneer was stacked and hot pressed to prepare a high-strength multi-layer densified impregnated wood with good overall performance.