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Taneli Väisänen: Effects of Thermally Extracted Wood Distillates on the Characteristics of Wood-Plastic Composites example, the distillates could be directly incorporated onto the surfaces of the WPC constituents. Moreover, this would permit a more precise control of the amounts of other additives used in the WPCs. It would also demonstrate whether wood distillates could replace some of the additives currently used in WPCs. 8.2 MECHANICAL PROPERTIES The results from study I indicated that an increase in cellulose fiber content in UFs enhanced the modulus of elasticity and tensile modulus, a property attributable to the higher stiffness and crystallinity of cellulose fibers compared to those of PP. A similar phenomenon, in accordance with the rule of mixtures, has also been observed in other studies (Balasuriya et al. 2002, Bouafif et al. 2009, Ashori et al. 2011). However, the maximum values of flexural and tensile strength for UFs were achieved with cellulose fiber content of 40 wt%. A similar finding was also reported by Ndiaye et al. (2013), Bhaskar et al. (2012) and Yuan et al. (2008). The decrease in flexural and tensile strength was probably due to the limited bonding between the cellulose fibers and the PP matrix. On the other hand, Huang and Zhang (2009) also postulated that when the fiber content exceeded 40 wt%, WPCs became more susceptible to the formation of fiber agglomerates that decrease the mechanical strength of the composites. When the distillate-treated LGs were added to UF20, UF30, and UF40, the resulting composites were mechanically weaker than the untreated composites. However, the addition of LG and distillate-treated LG in UF50 exerted different effects; for example, UF 50 containing LG or distillate-modified LG possessed significantly higher flexural and tensile strengths than the unmodified material. These findings suggested that the distillate improves the mechanical durability of WPCs only when there is a higher fiber content (over 40%). On the other hand, these results could also be attributed to the chemical nature of the wood fibers in LG; as LG has thermally modified 98 Dissertations in Forestry and Natural Sciences No 222
Discussion sawdust as its fiber material, i.e., the fibers are more hydrophobic, resulting in stronger interactions between the fillers and the polymer matrix – especially if there is a high fiber content. The LG composites had lower flexural and tensile strength than the UFs. In addition, only UF20 had a lower modulus of elasticity and tensile modulus than LG. As mentioned in section 4.1, the degradation of wood components during the thermal treatment process results in the formation of organic acids, such as acetic acid, and these can catalyze the degradation of wood fibers. Therefore, composites having thermally modified wood dust as their filler have lower mechanical strengths than composites with unmodified wood fibers. Wood fiber size can also have a significant effect on the strength of WPCs as discussed in chapter 3.1 and demonstrated by Bouafif et al. (2009) and Kociszewski et al. (2012). Optical microscopic analyses (unpublished) for the samples in study I revealed that LG had considerably larger fibers than UFs, which can also partly explain the differences in the results. Moreover, no distillate agglomeration was observed. The energy required to break a specimen is known to be lower for those materials containing large fibers or fiber agglomerates because the cracks tend to travel through the large particles (Griffith 1921, Weibull 1951, Bouafif et al. 2009). Incorporation of 4.2 wt% of hardwood distillate did not improve the mechanical properties for LG. Since the distillate acts like a coupling agent or any other additive that enhances the bonding between wood fibers and polymer matrix, it is possible that only a small amount of distillate would be required to enhance the properties of WPCs. The optimum amount of coupling agents in WPCs has been reported to be approximately 2 wt% (Balasuriya et al. 2002), and as mentioned in section 2.1.3, the typical amount of additives in WPCs is less than 5%. This theory was tested in study III, and the results revealed that the mechanically strongest composite was achieved when the hardwood distillate content was 1 wt%. An increase in tensile modulus is evidence that the composite had Dissertations in Forestry and Natural Sciences No 222 99
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PUBLICATIONS OF THE UNIVERSITY OF E
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Grano Oy Jyväskylä, 2016 Editors:
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ABSTRACT The use of raw materials d
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Universal Decimal Classification: 6
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Finally, I am grateful to my wife A
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TD-GC-FID/MS Thermal desorption/gas
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LIST OF ORIGINAL PUBLICATIONS This
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Contents 1 Introduction ...........
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1 Introduction The finiteness of cr
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Introduction A new and environmenta
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2 Wood-plastic composites By defini
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Wood-plastic composites additives u
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Wood-plastic composites Cellulose i
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Wood-plastic composites The propert
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Wood-plastic composites Figure 3. T
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Wood-plastic composites of lubrican
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Wood-plastic composites roughness a
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Wood-plastic composites Hosseinaei
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Wood-plastic composites the accessi
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Wood-plastic composites However, WP
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Wood-plastic composites A typical s
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Wood-plastic composites to fill the
Page 49: Wood-plastic composites absorption.
Page 52 and 53: Taneli Väisänen: Effects of Therm
Page 63 and 64: 4 Thermal processing of wood Therma
Page 65 and 66: Thermal processing of wood Figure 9
Page 67 and 68: Thermal processing of wood counterp
Page 69 and 70: Thermal processing of wood and the
Page 71 and 72: Thermal processing of wood and Miet
Page 73 and 74: 5 Aims and significance Despite the
Page 75 and 76: 6 Materials and methods Two types o
Page 77 and 78: Materials and methods heat energy f
Page 79 and 80: Materials and methods with the untr
Page 81 and 82: Materials and methods 6.2.1 Tensile
Page 83 and 84: Materials and methods 6.3 WATER ABS
Page 85 and 86: Materials and methods The emissions
Page 87: Materials and methods where Evoc is
Page 115 and 116: 9 Summary and conclusions In the pr
Page 117 and 118: Bibliography Abdolvahaba E, Lashgar
Page 119 and 120: Bibliography Ayrilmis N, Jarusombut
Page 121 and 122: Bibliography Cernansky R. State-of-
Page 123 and 124: Bibliography polypropylene composit
Page 125 and 126: Bibliography with odor assessments
Page 127 and 128: Bibliography La Mantia FP, Morreale
Page 129 and 130: Bibliography Mohan D, Pittman CU, a
Page 131 and 132: Bibliography Rinne J, Taipale R, Ma
Page 133 and 134: Bibliography Stark NM and Rowlands
Page 135: Bibliography Yeh S and Gupta RK. Im
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