Depth profile of UV-induced wood surface degradation
Tóm tắt
The depth profile of weathering effects on wood was studied after the laboratory ultraviolet exposure of fir-wood. The ‘thin strip’ method (ie the measurement of changes in tensile properties of microtomed wood sections) was modified in terms of exposure of batches of strips packed in bundles and exposed in a QUV apparatus. The bundles of strips were exposed untreated, covered with surface strips that had been impregnated with chromium (VI) trioxide or Fe(III) nitrate, or protected with free films of clear stain with photostabilisers and without photostabilisers. It has been shown that ultraviolet (UV) light penetrates the fir-wood surface to a depth greater than 70µm, resulting in changes in the tensile strength of the fir-wood strips to a depth of 70 to 140µm. Strength changes in lower levels (down to 280µm from the surface) could not be clearly attributed to a predominant effect of UV light, and were probably controlled by hydrolytic processes. 100 hours of exposure enabled the effectiveness of several treatments to be established. The clear stain, enriched with a UV absorber (Tinuvin 1130. Ciba) and a hindered amine light stabiliser (HALS compound type) (Tinuvin 292, Ciba), was shown to offer the best protection of the treatments studied. Impregnation with aqueous solutions of chromium (VI) trioxide and Fe(III) nitrate proved ineffective in photostabilising the wood surface.
Tài liệu tham khảo
Feist W C, Role of pigment concentration in the weathering of semi-transparent stains’,Forest Prod J,38, (2), 41–44, 1988
MacLeod I T, A D Scully, K P Ghiggino, P J A Ritchie, O M Paravagna and B Leary, “Photodegradation at the wood-clearcoat interface’,Wood Sci Technol,29, (3), 183–9, 1995
Derbyshire H and E R Miller, The photodegradation of wood during irradiation. Part I: Effects on structural integrity of thin wood strips’,Holz als Roh-und Werkstoff,39, 341–50, 1981
Feist W C, E A Mraz and J M Black, ‘Durability of exterior wood stains’,Forest Prod J,27, (1), 13–16, 1977
Feist W C, ‘Protection of wood surfaces with chromium trioxide’, Research Paper FPL 339, US Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WII, 1979
Hon D N-S and S T Chang, ‘Photoprotection of wood surfaces by wood-ion complexes’,Wood and Fiber Science,17, (1), 92–100, 1985
Evans P D and K J Schmalzl, ‘A quantitative weathering study of wood surfaces modified by chromium VI and iron III compounds’,Holzforschung,43, (5), 289–92, 1989
Feist W C and R S Williams, ‘Weathering durability of chromium-treated southern pine’,Forest Prod J,41, (1), 8–14, 1991
Hon D N-S, S T Chang and W C Feist, ‘Protection of wood surfaces against photodegradation’,J Appl Polymer Sci,30, 1429–48, 1985
Williams R S, ‘Effect of grafted UV stabilisers on wood surface erosion and clear coating performance’,J Appl Polymer Sci,28, 2093–103, 1983
Kastien H, ‘Einfluß von UV-Absorbern auf die Wetterbeständigkeit farbloser Acryldispersionen’,Farbe und Lack,95, (1), 16–19, 1989
Böhnke H and E Hess, ‘Lichtschutzmittel in Lacken: Möglichkeiten und Grenzen’,Farbe und Lack,95, (10), 715–9, October 1989
Heinskill J, ‘Möglichkeiten der UV-Stabilisierung farbloser Holz-Außenanstriche’,Farbe und Lack,100, (12), 1011–5, 1994
Rogez D and M Koehler, ‘Challenges and solutions for the 21st century’, Paper 24, Second Woodcoatings Congress, The Paint Research Association, 8 Waldegrave Road, Teddington Middlesex, TW11 8LD, UK, 2000
Raczkowski J, ‘Seasonal effects on the atmospheric corrosion of spruce micro-sections’,Holz Roh-Werkst,38, 231–4, 1980
Banks W B and P D Evans, ‘The degradation of wood surfaces by water’, The international research group on wood preservation, Document No IRG/WP/3289, IRG Secretariat, Sweden, 1984
Evans P D and W B Banks, ‘Degradation of wood surfaces by water. Changes in mechanical properties of the thin wood strips’, Holz als Roh-und Werkstoff, 46, (11), 427–35, 1988
Evans P D and W B Banks, ‘Degradation of wood surfaces by water. Weight losses and changes in ultrastructural and chemical composition’,Holz als Roh-und Werkstoff,48, (3), 159–63, 1990
Derbyshire H, E R Miller, J Sell and H Turkulin, ‘Assessment of wood photodegradation by microtensile testing’, Paper presented at the XX IUFRO World Congress, Tampere, Finland, 6th to 12th August 1995
Derbyshire H, E R Miller and H Turkulin, ‘Investigations into the photodegradation of wood using microtensile testing. Part 1: The application of microtensile testing to measurement of photodegradation rates’,Holz als Roh-und Werkstoff,53, (5), 339–45, 1995
Derbyshire H, E R Miller and H Turkulin, ‘Investigations into the photodegradation of wood using microtensile testing. Part 2: An investigation of the changes in tensile strength of different softwood species during natural weathering’,Holz als Roh-und Werkstoff,54, (1), 1–6, 1996
Turkulin H, ‘Photodegradation of exterior timber building components’, Dissertation, Faculty of Forestry, Zagreb University, Zagreb, Croatia, 1996
Turkulin H and J Sell, ‘Investigations into the photodegradation of wood using microtensile testing, Part 4: Tensile properties and fractography of weathered wood’,Holz als Roh-und Werkstoff,60, 96–105, 2002
Kiguchi M, P Evans, J Eksted and S Williams, Challenges and solutions for the 21st century’, Paper 23, Second Woodcoatings Congress, The Paint Research Association, 8 Waldegrave Road, Teddington Middlesex, TW11 8LD, UK, 2000
Ifju G, ‘Tensile strength behaviour as a function of cellulose in wood’,For Prod J,21, (8), 366–72, 1964
Hon D N-S and G Ifju, ‘Measuring penetration of light into wood by detection of photoinduced free radicals’,Wood Science,11, (2), 1978
Horn B A, J Qiu, N L Owen and W C Feist, ‘FT-IR studies of weathering effects in western red cedar and southern pine’,Chemical Modification of Lignocellulosics, FRI Bull, 176, 7th to 8th November, Rotorua, New Zealand, 1992
Hon D N-S and S T Chang, ‘Surface degradation of wood by ultraviolet light’,Journal of Polymer Science: Polymer Chemistry Edition,22, 2227–41, 1984
Horn B A, J Qiu, N L Owen, and W C Feist, ‘FT-IR studies of weathering effects in western red cedar and southern pine’.Chemical Modification of Lignocellulosics. FRI Bull, 67–76, 176, 7th to 8th November, Rotorua, New Zealand, New Zealand Forest Research Institute, 1992
Turkulin H and J Sell, ‘Investigations into the photodegradation of wood using microtensile testing. Part 4: Tensile properties and fractography of weathered wood’,Holz als Roh- und Werkstoff,60, (2), 96–105, 2002