Study On Curing Characteristics Of Low Molecular Weight MUF Resin Impregnated-poplar Wood

The high-quality wood resource is short with a degree of dependence on import as high as over 60%in China.However,China is rich in timber resources of fastgrowing plantations.How to realize efficiently utilization of fast-growing plantation wood is a major issue that we must face and solve.Resin impregnation modification is an important technology to improve wood density and hardness,wood dimensional stability,wood quality,and realize high-quality utilization of low-quality and fast-growing plantation wood.However,there are still many problems in the technology of resin impregnation modification wood,for example,long drying period and low efficiency,which is related to the unclear resin curing characteristics and mechanism in the drying process,resulting in the serious restriction on the popularization and application of low molecular weight resin impregnation modification technology.The curing characteristics of low molecular weight resin melamine-urea-formaldehyde(MUF)resin-impregnated poplar wood was studied in this dissertation by DSC(Differential scanning calorimeter)and other method,getting the curing regularity of MUF resin solution,MUF resinimpregnated wood(RIW)and revealing the curing characteristics and mechanism of resin in impregnated-wood by interpreting the response law of water migration and mechanical properties to resin curing in the drying process of impregnated wood.1.The curing kinetics characteristics of low molecular weight MUF resin was investigated.With the increase of concentration,the resin is more likely to cure,and wood has a certain blocking effect on the resin curing.When the resin concentration increases from 20%to 50%,the optimum curing temperature of MUF resin decreases form 93.99℃ to 79.71℃,and the corresponding apparent activation energy of curing decreases from 92.94 to 50.68 kJ/mol.The concertation has a significant effect on the optimal curing temperature and apparent activation energy of the resin.Compared with the resin solution,the optimum curing temperature of the resin in the impregnated wood increased by 10.01,7.34,5.88 and 4.57℃ respectively,and the apparent activation energy of the curing reaction increased by 24.64,9.55,15.41 and 13.7 kJ/mol respectively.2.The moisture transfer characteristics of MUF resin impregnated wood during drying were revealed.The drying rate of impregnated wood was significantly lower than that of non-impregnated wood.With the increase of resin concentration,the drying rate of impregnated wood decreased significantly.Compared with green wood and water impregnated wood,the drying rate of resin impregnated wood decreased by 5%-9%and 9%-14%respectively;When the resin concentration increased from 20%to 50%,the drying rate of impregnated wood decreased from 6.83%/h to 2.78%/h,a decrease of nearly 60%.With the increase of resin concentration,the moisture content gradient in the impregnated wood decreased during the drying process.3.The change regular of the macro mechanical strength of the impregnated wood during drying was proved.When the moisture content of green wood and water impregnated wood is above the fiber saturation point(FSP),the change of MOE and mor with moisture content is not obvious.When the moisture content is below FSP,both MOE and mor increase linearly with the decrease of moisture content.During the whole drying process,MOE and MOR of the resin impregnated wood increased linearly with the gradual reduction of moisture content and the gradual curing of resin,and the higher the resin concentration,the faster the increase of mechanical strength of the impregnated material.4.The change regular of micro mechanical strength of impregnated wood during drying was revealed.Compared with green wood and water impregnated wood.During the drying process,the resin in the impregnated wood gradually cure,and the transverse relaxation time T21 and the relaxation peak area A1 showed a continuous decreasing and increasing trend,respectively.Compared with the control wood,T21 of the dry impregnated wood decreased by about 3%and A1 increased by about 70%.With increase of concentration of MUF resin,the decreases of T21 and increases of Ai are faster.The higher the resin concentration is,the faster T21 decreases and A1 increases during drying.