Properties And Mechanism Of Chinese Fir Modified By Phenol Melamine Urea Formaldehyde Resin And Borates

Chinese fir(Cunninghamia lanceolata)is one of important fast-growing tree species in south China.It is difficult to be used directly in the development of high value-added products because of its natural characteristics such as soft,easy to deform and burn.In this paper,Chinese fir wood was impregnated uniformly by phenol melamine urea formaldehyde(PMUF)resin and borates in a progressive gradual infiltration process.The dimensional stability and mechanical strength of Chinese fir were improved,and the fire and decay resistance were realized.The research results have important theoretical value and practical significance for the efficient use of Chinese fir.The main conclusions of the paper are as follows:(1)PMUF resin was synthesised by adding 5% phenol in metaphase reaction of melamine urea formaldehyde resin at 85 ?.The main components of PMUF resin were hydroxymethyl urea,hydroxymethyl phenol and oligomers.In addition,the average molecular weight were 399.1 g/mol.PMUF resin solution was mixed with 4% borax and 2% boric acid to prepare a stable resin type multi-effect modifier.The weight gain rate and density of progressive infiltration modified wood samples were higher than that of vacuum pressure impregnating samples and the longitudinal density distribution of the former tended to be uniform.(2)With the increase of resin solid mass fraction,the oven-dry density,anti-swelling efficacy,bending strength and elastic modulus of resin and compound modified wood samples increased gradually,while the water absorption and impact toughness decreased.The addition of borates will further improved the oven-dry density and bending modulus of resin modified wood samples,while the anti-swelling rate,bending strength and impact toughness reduced.(3)With the increase of resin solid mass fraction,the oxygen index of resin and compound modified wood samples went up first and then showed slightly downward trend.Moreover,the time to ignition,the second heat release rate peak time and total heat release increased gradually while the total smoke release decreased.The first heat release rate peak value of resin modified wood samples were all lower than that of untreated ones but the second heat release rate peak value were higher than that of untreated ones.Two heat release rate peak values both declined after compound modification.(4)Ageing resistance from large to small: resin modified wood > compound modified wood > untreated wood.And the ageing resistance of resin and compound modified wood samples increased with the increase of resin solid mass fraction.When the resin solid mass fraction was 20%,the compound modified wood achieved decay resistance level ? and the mass loss rate was 11%~13%.Moreover,PMUF resin could significantly improve the leachibility of borates.(5)Most tracheids and pores of Chinese fir wood were filled with resin polymer,however,borates could interfere with the resin solidification.The cell wall modulus and hardness of compound modified wood samples increased by 92.5% and 63.8% respectively,which proofed the modifier could enter the cell walls of Chinese fir wood.The crystallinity of resin and compound modified wood samples was improved,indicating that the modifier could enter the amorphous region of wood cellulose.Compared with untreated wood samples,the holocellulose and acid-insoluble lignin contents of resin and compound modified wood samples both decreased,however,the nitrogen element content and O/C value on the surface of resin and compound modified wood samples increased obviously.No new peaks outside of wood and modifiers were found in both fourier infrared spectroscopy and nuclear magnetic resonance spectroscopy.(6)The thermal decomposition rate of modified wood samples was significantly lower than that of untreated ones,so the thermal stability was improved.The addition of borates and resin both could make the wood decompose in advance.The influence of resin modification on the final char yield of wood was not obvious,however,borate and boric acid promoted the increase of carbon.Py-GC/MS results showed that resin modified material produced more furan compounds,cyclopentenone and various enes and acids,and borates could inhibit the production of volatile phenol compounds in wood.