6 Materials and methods
8.5 Limitations and future prospects
In this thesis, the effects of hardwood (birch) and softwood (primarily pine) distillates on the properties of WPCs were determined. Similar studies have not been previously conducted, even though the potential of other types of organic waste and residues as additives for WPCs has been extensively assessed (Hamzeh et al. 2011, Li et al. 2014, Madhoushi et al.
2014, Das et al. 2015a). This thesis focused on the determination of the effects of different wood distillates on the mechanical properties, water resistance and VOC emissions of WPCs.
The positive effects of both distillates on the mechanical properties of the WPCs were evident, and the underlying reason for the enhancement was anticipated to be the improvement in the interfacial bonding between the polymer matrix and wood fibers. Further investigations of WPCs with scanning electron microscopy (SEM) and spectroscopic techniques would provide more detailed information on the interactions occurring between WPC constituents before and after the additions of the distillates.
The considerably lower water absorption values for the WPCs treated with distillates were attributed to the composition of the distillates and to the ability of the distillates to fill the gaps within the WPCs. It was assumed that the distillates were hydrophobic as they were obtained from the tar phases and all the water-soluble compounds had been extracted from the distillates. However, the exact compositions of the distillates were not characterized. The chemical composition of birch distillates has been determined by Fagernäs et al. (2012a), and it was presumed, based on our other studies, that the distillate used in this thesis would be composed of similar chemical compounds. The composition of softwood distillates
was known only roughly and the analyses conducted in other publications were also used as supporting material (Vitasari et al. 2011, Miettinen et al. 2015, Özbay et al. 2015). Nevertheless, more information on the exact chemical composition of the distillates could provide further insights into the chemical interactions between distillates and WPC constituents and explain the phenomena observed in this thesis more rigorously.
In this thesis, water absorption of the WPCs was studied for 24 and 48 hours. Considerable differences between different material types were observed even at these time intervals, but it would be interesting to examine the differences after multiple weeks or months. It would also be interesting to determine the impact of cyclic weather conditions or microbial exposure on the properties of WPCs treated with wood distillates.
Nonetheless, the results of this thesis suggest that the distillates had improved the water resistance of WPCs, especially at high distillate contents. The decreased water absorption of WPCs also suggests that the addition of wood distillates could improve the fungal resistance of WPCs, and this property should be evaluated in future studies.
PTR-TOF-MS was tested to assess its suitability for determining the VOC emissions from WPCs. The applicability of PTR-TOF-MS for monitoring the concentrations of VOCs emitting from WPCs was confirmed but further analyses would be appropriate. In this thesis, the number of monitored VOCs was limited to ten compounds. It is apparent that further analyses of VOCs are needed. For example, the monitoring of hazardous VOCs, such as styrene, toluene, and naphthalene, could provide valuable information on the impact of WPCs on indoor air quality.
In study I, two kinds of WPCs were used whereas only one kind of WPC was evaluated in studies III and IV. In the future, examinations of the effects of wood distillates on the characteristics of other types of WPCs are appropriate. Wood distillates may act differently if the polymer matrix or wood fiber type is changed. Furthermore, changes in the wood fiber
content may lead to considerable changes in the properties of WPCs modified with wood distillates.
conclusions
In the present thesis, the effects of thermally extracted wood distillates on the properties of WPCs were successfully determined. The effects of the distillates were investigated through the mechanical tests, water absorption studies, and VOC emissions analyses. The main conclusions with respect to the aims are:
1. The impregnation of the WPC granules with the wood distillate, originated from either hardwood or softwood, is possible with the presented method. However, other methods, such as impregnation of the agglomerate before the granulation process, could well be more suitable. The addition of distillates improved the processability of the WPC granules.
2. PTR-TOF-MS can be applied to determine and compare the release of VOCs from WPCs. The advantages of PTR-TOF-MS include its rapid time response, high sensitivity, and ease of use. In addition, there is no need for special sample preparation. However, there are no regulatory limits for VOC emissions measured with PTR-MS.
3. A small (1 wt%) addition of hardwood distillate significantly increased the tensile modulus of the WPC.
Higher distillate contents (2–8 wt%) reduced the mechanical properties of the WPC. In addition, the ability of the material to absorb water was considerably decreased in those containing the hardwood distillate. The VOC emissions increased for the WPCs containing hardwood distillate.
4. A minor (2 wt%) addition of softwood distillate
Strain and bending increased significantly when there was a high distillate content (over 4 wt%) whereas the strength of the WPC declined. The water absorption of the WPC can be reduced with distillate content higher than 2 wt%. The addition of softwood distillate increased the release of VOCs studied.
To conclude, the studies presented in this thesis emphasize that the inclusion of wood distillates originating from industrial wood processes into WPCs can enhance the properties of these materials. In addition, it was shown that PTR-TOF-MS is a feasible technique for analyzing VOCs being emitted from WPCs. The further developments in wood distillates and the discovery of new ways to incorporate the distillates into WPCs could provide novel and ecological materials based more on the renewable resources.
Abdolvahaba E, Lashgari A, Farsi M, and Nourbakhsh A. A study on the effects of nano clay particles and pistachio shell flour on the mechanical properties of wood-plastic composites. World Sci J. 2 (3), pp. 1-11, 2014.
Abou-Zaid M and Scott IM. Pyrolysis bio-oils from temperate forests:
Fuels, phytochemicals and bioproducts. In: Bergeron C, Carrier DJ, and Ramaswamy S (Eds.). Biorefinery Co-Products:
Phytochemicals, Primary Metabolites and Value-Added Biomass Prosessing. John Wiley & Sons, Ltd, West Sussex, UK, pp. 311-326, 2012.
Adhikari R, Bhandari NL, Le HH, Henning S, Radusch H-J, Michler GH, Garda M-R, and Saiter JM. Thermal, mechanical and morphological behavior of poly(propylene)/wood flour composites.Macromol Symp.315(1), pp. 24-29, 2012.
Adhikary KB, Pang S, and Staiger MP. Dimensional stability and mechanical behaviour of wood–plastic composites based on recycled and virgin high-density polyethylene (HDPE). Compos Part B - Eng.39(5), pp. 807-815, 2008a.
Adhikary KB, Pang S, and Staiger MP. Long-term moisture absorption and thickness swelling behaviour of recycled thermoplastics reinforced withPinus radiata sawdust.Chem Eng J.142(2), pp. 190-198, 2008b.
Aigner I, Wolfesberger U, and Hofbauer H. Tar content and composition in producer gas of fluidized bed gasification and low temperature pyrolysis of straw and wood-influence of temperature.Environ Prog Sustain Energ.28(3), pp. 372-379, 2009.
Akakabe Y, Tamura Y, Iwamoto S, Takabayashi M, and Nyuugaku T.
Volatile organic compounds with characteristic odor in bamboo vinegar.Biosci Biotechnol Biochem.70(11), pp. 2797-2799, 2006.
Amoore JE and Hautala E. Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution.J Appl Toxicol.
3(6), pp. 272-290, 1983.
Aprea E, Biasioli F, Märk TD, and Gasperi F. PTR-MS study of esters in water and water/ethanol solutions: Fragmentation patterns and partition coefficients.Int J Mass Spectrom.262(1), pp. 114-121, 2007.
Ashori A, Kiani H, and Mozaffari SA. Mechanical properties of reinforced polyvinyl chloride composites: Effect of filler form and content.J Appl Polym Sci.120(3), pp. 1788-1793, 2011.
Ashori A and Nourbakhsh A. Bio-based composites from waste agricultural residues.Waste Manag.30(4), pp. 680-684, 2010.
ASTM D570-98(2010)E1. Standard Test Method for Water Absorption of Plastics.ASTM International.1st April, 2010.
ASTM D638-14. Standard Test Method for Tensile Properties of Plastics.ASTM International.15th December, 2014.
ASTM D790-15. Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.ASTM International.12th January, 2015.
ASTM D1037-12. Standard Test Methods for Evaluating Properties of Wood-Based Fiber and Particle Panel Materials. ASTM International.1st May, 2012.
ASTM D6110-10. Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens for Plastics. ASTM International.1st April, 2010.
Ayrilmis N, Jarusombuti S, Fueangvivat V, and Bauchongkol P. Effect of thermal-treatment of wood fibres on properties of flat-pressed wood plastic composites. Polym Degrad Stab. 96 (5), pp. 818-822, 2011.
Bakhiya N and Appel KE. Toxicity and carcinogenicity of furan in human diet.Arch Toxicol.84(7), pp. 563-578, 2010.
Balasuriya PW, Ye L, Mai Y-W, and Wu J. Mechanical properties of wood flake-polyethylene composites. II. interface modification. J Appl Polym Sci.83(12), pp. 2505-2521, 2002.
Basu P. Biomass Gasification, Pyrolysis and Torrefaction: Practical Design and Theory.Academic Press, London, UK, 2013.
Beyler CL and Hirschler MM. Thermal decomposition of polymers. In:
DiNenno P (Ed.). SFPE Handbook of Fire Protection Engineering.
National Fire Protection Association, Quincy, MA, US, pp. 110-131, 2001.
Bhaskar T, Bhavya B, Singh R, Naik DV, Kumar A, and Goyal HB.
Thermochemical conversion of biomass to biofuels. In: Pandey A (Ed.). Biofuels: Alternative Feedstocks and Conversion Processes.
Academic Press, London, UK, pp. 51-77, 2011.
Bhaskar J, Haq S, and Yadaw S. Evaluation and testing of mechanical properties of wood plastic composite.J Thermoplast Compos Mater.
25(4), pp. 391-401, 2012.
Björklund Jansson M and Nilvebrant N. Wood extractives. In: Ek M, Gellerstedt G, and Henriksson G (Eds.). Wood Chemistry and Wood Biotechnology. Walter de Gruyter, Berlin, Germany, pp. 147-172, 2009.
Bledzki AK, Faruk O, and Huque M. Physico-mechanical studies of wood fiber reinforced composites.Polym Plast Technol Eng.41(3), pp. 435-451, 2002.
Bledzki A, Letman M, Viksne A, and Rence L. A comparison of compounding processes and wood type for wood fibre—PP composites.Compos Part A-Appl S.36(6), pp. 789-797, 2005a.
Bledzki AK, Zhang W, and Faruk O. Microfoaming of flax and wood fibre reinforced polypropylene composites.Holz Roh Werkst.63(1), pp. 30-37, 2005b.
Bouafif H, Koubaa A, Perré P, and Cloutier A. Effects of fiber characteristics on the physical and mechanical properties of wood plastic composites. Compos Part A-Appl S. 40 (12), pp. 1975-1981, 2009.
Bourmaud A and Baley C. Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites. Polym Degrad Stab.92(6), pp. 1034-1045, 2007.
Bridgwater A. Thermal Biomass Conversion and Utilization: Biomass Information System. Office for Official Publications of the European Communities, Luxembourg, 1996.
Brown RC and Brown TR. Biorenewable Resources: Engineering New Products from Agriculture. John Wiley & Sons, West Sussex, UK, 2014.
BS EN 15534-1. Composites made from cellulose-based materials and thermoplastics (usually called wood-polymer composites (WPC) or natural fibre composites (NFC)) - Part 1: Test methods for characterisation of compounds and products.European Committee for Standardization.9th November, 2014.
Butylina S, Martikka O, and Kärki T. Properties of wood fibre-polypropylene composites: Effect of wood fibre source. Appl Compos Mater.18(2), pp. 101-111, 2011.
Callister W. Fundamentals of Materials Science and Engineering: An Integrated Approach.John Wiley & Sons, Hoboken, NJ, US, 2005.
Cernansky R. State-of-the-art soil.Nature.517(7534), pp. 258-260, 2015.
Chowdhury JU, Bhuiyan MNI, and Mohammed Y. Chemical composition of the leaf essential oils ofMurraya koenigii (L.) spreng andMurraya paniculata (L.) jack.Bangladesh J Pharmacol.3, pp. 59-63, 2008.
Clemons C. Raw materials for wood-polymer composites. In: Oksman Niska K and Sain M (Eds.). Wood-Polymer Composites.CRC Press, Cambridge, UK, pp. 1-22, 2008.
Clemons C. Elastomer modified polypropylene–polyethylene blends as matrices for wood flour–plastic composites.Compos Part A-Appl S.
41(11), pp. 1559-1569, 2010.
Clemons C, Rowell R, Plackett D, and Segerholm B. Wood/nonwood thermoplastic composites. In: Rowell R (Ed.). Handbook of Wood Chemistry and Wood Composites.CRC Books, Boca Raton, FL, US, pp. 473-508, 2013.
Dahmen N, Henrich E, Kruse A, and Raffelt K. Biomass liquefaction and gasification. In: Vertès AA, Qureshi N, Blaschek HP, and Yukawa H (Eds.). Biomass to Biofuels: Strategies for Global Industries.John Wiley & Sons, Ltd, West Sussex, UK, pp. 89-122, 2010.
Dányádi L, Móczó J, and Pukánszky B. Effect of various surface modifications of wood flour on the properties of PP/wood composites.Compos Part A-Appl S.41(2), pp. 199-206, 2010.
Das O, Sarmah AK, and Bhattacharyya D. A novel approach in organic waste utilization through biochar addition in wood/polypropylene composites. Waste Manage. 38, pp. 132-140, 2015a.
Das O, Sarmah AK, and Bhattacharyya D. A sustainable and resilient approach through biochar addition in wood polymer composites.
Sci Total Environ.512, pp. 326-336, 2015b.
de Gouw J and Warneke C. Measurements of volatile organic compounds in the Earth's atmosphere using proton-transfer-reaction mass spectrometry.Mass Spectrom Rev.26(2), pp. 223-257, 2007.
Decker SR, Sheehan J, Dayton DC, Bozell JJ, Adney WS, Hames B, Thomas SR, Bain RL, Czernik S, Zhang M, and Himmel ME.
Biomass conversion. In: Kent JA (Ed.). Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology. Springer US, New York, NY, US, pp. 1449-1548, 2007.
Defoirdt N, Gardin S, Van den Bulcke J, and Van Acker J. Moisture dynamics of WPC and the impact on fungal testing.Int Biodeterior Biodegrad.64(1), pp. 65-72, 2010.
Dorfner R, Ferge T, Kettrup A, Zimmermann R, and Yeretzian C. Real-time monitoring of 4-vinylguaiacol, guaiacol, and phenol during coffee roasting by resonant laser ionization time-of-flight mass spectrometry.J Agric Food Chem.51(19), pp. 5768-5773, 2003.
Downie A and Van Zwieten L. Biochar: A coproduct to bioenergy from slow-pyrolysis technology. In: Lee JW (Ed.). Advanced Biofuels and Bioproducts.Springer, London, UK, pp. 97-117, 2012.
Ek M, Gellerstedt G, and Henriksson G. Pulping Chemistry and Technology.Walter de Gruyter, Berlin, Germany, 2009.
Eriksson K and Levin J. Identification of cis-and trans-verbenol in human urine after occupational exposure to terpenes. Int Arch Occup Environ Health.62(5), pp. 379-383, 1990.
Eriksson K, Levin J, Sandström T, Lindström-Espeling K, Lindén G, and Stjernberg N. Terpene exposure and respiratory effects among workers in Swedish joinery shops.Scand J Work Environ Health.23 (2), pp. 114-120, 1997.
Espert A, Vilaplana F, and Karlsson S. Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in
polypropylene composites and its influence on their mechanical properties.Compos Part A-Appl S.35(11), pp. 1267-1276, 2004.
Esteves B and Pereira H. Wood modification by heat treatment: A review.BioResources.4(1), pp. 370-404, 2008.
Fagernäs L, Kuoppala E, and Arpiainen V. Composition, utilization and economic assessment of torrefaction condensates. Energ Fuel. 29 (5), pp. 3134-3142, 2015.
Fagernäs L, Kuoppala E, and Simell P. Polycyclic aromatic hydrocarbons in birch wood slow pyrolysis products. Energ Fuel.
26(11), pp. 6960-6970, 2012b.
Fagernäs L, Kuoppala E, Tiilikkala K, and Oasmaa A. Chemical composition of birch wood slow pyrolysis products.Energ Fuel.26 (2), pp. 1275-1283, 2012a.
Falk AA, Hagberg MT, Löf AE, Wigaeus-Hjelm EM, and Zhiping W.
Uptake, distribution and elimination of �-pinene in man after exposure by inhalation.Scand J Work Environ Health.16(5), pp. 372-378, 1990.
Farsi M. Wood-plastic composites: Influence of wood flour chemical modification on the mechanical performance.J Reinf Plast Compos.
29(24), pp. 3587-3592, 2010.
Faruk O, Bledzki AK, and Nicolais L. Wood plastic composite: Present and future.Wiley Encyclopedia of Composites. pp. 1-20, 2012.
Félix JS, Domeño C, and Nerín C. Characterization of wood plastic composites made from landfill-derived plastic and sawdust:
Volatile compounds and olfactometric analysis.Waste Manage.33 (3), pp. 645-655, 2013.
Finnish Thermowood Association, ThermoWood handbook. Accessed 2/2015. 2003. Available at:
http://www.thermowood.fi/brochurestexts.
Galeski A. Strength and toughness of crystalline polymer systems.Prog Polym Sci.28(12), pp. 1643-1699, 2003.
Gao H, Song Y, Wang Q, Han Z, and Zhang M. Rheological and mechanical properties of wood fiber-PP/PE blend composites. J Forest Res.19(4), pp. 315-318, 2008.
Godavarti S. Thermoplastic wood fiber composites. In: Mohanty A, Misra M, and Drzal L (Eds.). Natural Fibers, Biopolymers, and Biocomposites.CRC Press, FL, US, pp. 348-386, 2005.
Goldstein N. Getting to know the odor compounds.Biocycle.43(7), pp.
42-44, 2002.
Gonçalves N, Teixeira P, Ferrás L, Afonso A, Nóbrega J, and Carneiro O. Design and optimization of an extrusion die for the production of wood–plastic composite profiles.Polym Eng Sci.55(8), pp. 1849-1855, 2014.
Greenberg J, Friedli H, Guenther A, Hanson D, Harley P, and Karl T.
Volatile organic emissions from the distillation and pyrolysis of vegetation.Atmos Chem Phys.6(1), pp. 81-91, 2006.
Griffith AA. The phenomena of rupture and flow in solids.Phil Trans R Soc Cond A.221, pp. 163-198, 1921.
Gwon JG, Lee SY, Chun SJ, Doh GH, and Kim JH. Physical and mechanical properties of wood–plastic composites hybridized with inorganic fillers.J Compos Mater.46(3), pp. 301-309, 2012.
Hamzeh Y, Ashori A, and Mirzaei B. Effects of waste paper sludge on the physico-mechanical properties of high density polyethylene/wood flour composites. J Polym Environ. 19 (1), pp.
120-124, 2011.
Han K, Zhang J, Wargocki P, Knudsen HN, and Guo B. Determination of material emission signatures by PTR-MS and their correlations
with odor assessments by human subjects. Indoor Air. 20 (4), pp.
341-354, 2010.
Hansel A, Jordan A, Holzinger R, Prazeller P, Vogel W, and Lindinger W. Proton transfer reaction mass spectrometry: On-line trace gas analysis at the ppb level.Int J Mass Spectrom.149, pp. 609-619, 1995.
Hill CAS. The use of timber in the twenty-first century. In: Hill CAS (Ed.). Wood Modification: Chemical, Thermal and Other Processes.John Wiley & Sons, Chichester, UK, pp. 1-18, 2006a.
Hill CAS. Thermal modification of wood. In: Hill CAS (Ed.). Wood Modification: Chemical, Thermal and Other Processes.John Wiley
& Sons, Chichester, UK, pp. 99-127, 2006b.
Hosseinaei O, Wang S, Enayati AA, and Rials TG. Effects of hemicellulose extraction on properties of wood flour and wood–
plastic composites.Compos Part A-Appl S.43(4), pp. 686-694, 2012.
Huang H and Zhang J. Effects of filler-filler and polymer-filler interactions on rheological and mechanical properties of HDPE-wood composites.J Appl Polym Sci.111(6), pp. 2806-2812, 2009.
Huuhilo T, Martikka O, Butylina S, and Kärki T. Impact of mineral fillers to the moisture resistance of wood-plastic composites.Balt For.16(1), pp. 126-131, 2010.
Hyttinen M, Masalin-Weijo M, Kalliokoski P, and Pasanen P.
Comparison of VOC emissions between air-dried and heat-treated Norway spruce (Picea abies), Scots pine (Pinus sylvesteris) and European aspen (Populus tremula) wood.Atmos Environ.44(38), pp.
5028-5033, 2010.
ISO 62. Plastics - Determination of water absorption. International Organization for Standardization.28th January, 2008.
ISO 178. Plastics. Determination of Flexural Properties. International Organization for Standardization.14th December, 2010.
ISO 179-1. Plastics. Determination of Charpy Impact Properties. Part 1:
Non-instrumented Impact Test. International Organization for Standardization.19th May, 2010.
ISO 527-1. Plastics. Determination of Tensile Properties. Part 1: General Principles. International Organization for Standardization. 14th February, 2012.
ISO 16000-6. Indoor air - Part 6: Determination of volatile organic compounds in indoor and test chamber air by active sampling on Tenax TA sorbent, thermal desorption and gas chromatography using MS or MS-FID.International Organization for Standardization.
1st January, 2011.
ISO 16000-9. Indoor air - Part 9: Determination of the emission of volatile organic compounds from building products and furnishing - Emission test chamber method. International Organization for Standardization.16th January, 2006.
Jesson DA and Watts JF. The interface and interphase in polymer matrix composites: Effect on mechanical properties and methods for identification.Polym Rev.52(3), pp. 321-354, 2012.
Kim J and Pal K. Overview of wood-plastic composites and uses. In:
Kim J and Pal K (Eds.). Recent Advances in the Processing of Wood-Plastic Composites.Springer, Berlin, Germany, pp. 1-22, 2010.
Klass DL. Thermal conversion: Pyrolysis and liquefaction. In: Klass DL (Ed.). Biomass for Renewable Energy, Fuels, and Chemicals.
Academic Press, Oval Road, London, pp. 225-269, 1998.
Klyosov A. Wood-Plastic Composites.John Wiley & Sons, Hoboken, NJ, US, 2007.
Kociszewski M, Gozdecki C, Wilczy�ski A, Zajchowski S, and Mirowski J. Effect of industrial wood particle size on mechanical properties of wood-polyvinyl chloride composites. Eur J Wood Prod.70(1-3), pp. 113-118, 2012.
La Mantia FP, Morreale M, and Mohd Ishak ZA. Processing and mechanical properties of organic filler-polypropylene composites.
J Appl Polym Sci.96(5), pp. 1906-1913, 2005.
Lai Y-. Wood and wood products. In: Kent JA (Ed.). Handbook of Industrial Chemistry and Biotechnology. Springer, New York, US, pp. 1057-1115, 2012.
Lee H and Kim DS. Preparation and physical properties of wood/polypropylene/clay nanocomposites. J Appl Polym Sci. 111 (6), pp. 2769-2776, 2009.
Li C and Suzuki K. Resources, properties and utilization of tar.Resour Conserv Recy.54(11), pp. 905-915, 2010.
Li X, Lei B, Lin Z, Huang L, Tan S, and Cai X. The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties. Mater Des. 53, pp. 419-424, 2014.
Li Y. Wood-polymer composites. In: Tesinova P (Ed.). Advances in Composite Materials - Analysis of Natural and Man-made Materials.InTech, pp. 229-284, 2011.
Lindinger W, Fall R, and Karl T. Environmental, food and medical applications of proton-transfer-reaction mass spectrometry (PTR-MS). In: Adams NG and Babcock LM (Eds.). Advances in Gas-Phase Ion Chemistry.Elsevier, Amsterdam, The Netherlands, pp. 1-48,
Lindinger W, Fall R, and Karl T. Environmental, food and medical applications of proton-transfer-reaction mass spectrometry (PTR-MS). In: Adams NG and Babcock LM (Eds.). Advances in Gas-Phase Ion Chemistry.Elsevier, Amsterdam, The Netherlands, pp. 1-48,