Effect of pH on Chemical Components and Mechanical Properties of Thermally Modified Wood


  • Wang Wang
  • Jinzhen Cao
  • Futong Cui
  • Xing Wang


Thermally modified wood, pH value, mass loss, chemical components, mechanical properties


To investigate the correlation between acidity and degradation during thermal treatment of wood, Cathay poplar (Populus cathayana Rehd.) wood samples were impregnated with solutions of different pH values, which included disodium octoborate tetrahydrate (DOT, pH = 8.3), monoethanolamine (MEA, pH = 12), and four buffering solutions composed of boric acid and sodium hydroxide (BA/NaOH, pH = 6, 7, 8, 9). Samples were then heated for 4 h at 180, 200, and 2208deg;C, respectively. Bending MOR and MOE, mass losses, pH values, and percentages of lignin and hemicelluloses were subsequently determined in thermally modified samples and compared with control samples without pretreatment and/or thermal treatment. Results of the experiments indicated that DOT and buffering solutions decreased mass loss of thermally treated wood and increased bending MOR and MOE, whereas MEA pretreatment increased mass loss and showed comparable or even lower bending MOR and MOE than the untreated control with or without thermal treatments. Chemical analyses suggested that degradation of hemicelluloses was inhibited by DOT and BA/NaOH pretreatments within the temperature range 180-200°C, which may explain the mechanical property improvement.


Akgul M, Gumuskaya E, Korkut S (2007) Crystalline structure of heat-treated Scots pine [Pinus sylvestris L.] and Uludag fir [Abies nordmanniana (Stev.) subsp bornmuelleriana (Mattf.)] wood. Wood Sci Technol 41(3):281-289.nAlén R, Kotilainen R, Zaman A (2002) Thermochemical behavior of Norway spruce (Picea abies) at 180-225°C. Wood Sci Technol 36(2):163-171.nASTM (2007) D1106-96. Standard test method for acid-insoluble lignin in wood. American Society for Testing and Materials, West Conshohocken, PA.nAwoyemi L (2008) Determination of optimum borate concentration for alleviating strength loss during heat treatment of wood. Wood Sci Technol 42(1):39-45.nAwoyemi L, Westermark U (2005) Effects of borate impregnation on the response of wood strength to heat treatment. Wood Sci Technol 39(6):484-491.nBekhta P, Niemz P (2003) Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce wood. Holzforschung 57(5): 539-546.nBoonstra MJ, Tjeerdsma B (2006) Chemical analysis of heat treated softwoods. Holz Roh Werkst 64(3):204-211.nBoonstra MJ, Van Acker J, Tjeerdsma BF, Kegel EV (2007) Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents. Ann Sci 64(7):679-690.nBourgois J, Guyonnet R (1988) Characterization and analysis of torrefied wood. Wood Sci Technol 22(2):143-155.nDirol D, Guyonnet R (1993) Durability by rectification process. International Research Group on Wood Preservation, Document No. IRG/WP 93-40015.nEsteves BM, Domingos IJ, Pereira HM (2008) Pine wood modification by heat treatment in air. Bioresource 3(1):142-154.nFreeman MH, Shupe TF, Vlosky RP, Barnes HM (2003) Past, present, and future of the wood preservation industry. Forest Prod J 53(10):8-15.nFunaoka M, Kako T, Abe I (1990) Condensation of lignin during heating of wood. Wood Sci Technol 24(3):277-288.nGakhan G, Deniz A (2009) The influence of mass loss on the mechanical properties of heat-treated black pine wood. Wood Res-Slovakia 54(4):33-42.nKamdem DP, Pizzi A, Jermannaud A (2002) Durability of heat-treated wood. Holz Roh Werkst 60(1):1-6.nKartal SN, Hwang W, Imamura Y (2008) Combined effect of boron compounds and heat treatments on wood properties: Chemical and strength properties of wood. J Mater Process Technol 198(2):234-240.nKaygin B, Gunduz G, Aydemir D (2009) The effect of mass loss on mechanic properties of heat-treated paulownia (paulownia elongata) wood. Wood Res-Slovakia 54(2):101-108.nMcDonald AG, Gifford JS, Dare PH, Steward D (1999) Characterisation of the condensate generated from vacuum-drying of radiata pine wood. Holz Roh Werkst 57(4): 251-258.nPopper R, Niemz P, Eberle G (2005) Investigations on the sorption and swelling properties of thermally treated wood. Holz Roh Werkst 63(2):135-148.nSivonen H, Maunu SL, Sundholm F, Jämsä S, Viitaniemi P (2002) Magnetic resonance studies of thermally modified wood. Holzforschung 56:648-654.nSundqvist B, Karlsson O, Westermark U (2006) Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness. Wood Sci Technol 40(7):549-561.nTjeerdsma B, Boonstra M, Pizzi A, Tekely P, Militz H (1998) Characterisation of thermally modified wood: Molecular reasons for wood performance improvement. Holz Roh Werkst 56(3):149-153.nTjeerdsma B, Militz H (2005) Chemical changes in hydro-heat wood: FTIR analysis of combined hydroheat and dry heat-treated wood. Holz Roh Werkst 63(2): 102-111.nTuong VM, Li J (2010) Effect of heat treatment on the change in color and dimensional stability of acacia hybrid wood. Bioresource 5(2):1257-1267.nWinandy JE (1997) Effects of fire retardant retention, borate buffers, and redrying temperature after treatment on thermal-induced degradation. Forest Prod J 47(6): 79-86.nYildiz S, Gezer D, Yildiz U (2006) Mechanical and chemical behavior of spruce wood modified by heat. Build Environ 41:1762-1766.n






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