"Effects of Thermally Extracted Wood Distillates on the Characteristics of Wood-Plastic Composites",
, no. 222, Eastern Finland University Library / Sales of publications P.O. Box 107, FI-80101 Joensuu, Finland, Publications of the University of Eastern Finland Dissertations in Forestry and Natural Sciences, 2016.
<p>The use of raw materials derived from renewable sources is increasing due to the finiteness of crude oil reserves. In wood-plastic composites (WPCs), the plastic in a material is partially replaced by wood, which is an abundantly available and inexpensive raw material. WPCs are materials that encompass a wide range of performance levels such that they have diverse applications, e.g., in fencing and decking as well as in the manufacture of automobiles. The use of WPCs in indoor applications is also becoming increasingly popular. Despite the increasing popularity of WPCs, certain inherent limitations mean that these materials are unsuitable for some applications. Examples of the limitations associated with WPCs are their insufficient mechanical strength and their susceptibility to excess water absorption. Furthermore, the VOC (volatile organic compound) characteristics of WPCs have not been widely studied and therefore, a better understanding of these properties of WPCs would be of great importance. The properties of WPCs and their constituents can be altered by incorporating additives. However, some additives are rather expensive and their incorporation into WPCs is not straightforward. There is a clear need for novel, affordable and effective filler materials, especially those that would minimize the use of expensive constituents. Wood distillates are products originating from thermal processes where the components of wood are partly or completely decomposed into charcoal, condensable vapors, and non-condensable gases. Although the liquid components of wood have many potential applications, large volumes of liquids are still being discarded and not exploited in industrial applications. Thus, the incorporation of more of wood distillates into WPCs would enhance the use of raw materials and secondary products from the wood-processing industries. This would be both economically valuable and environmentally friendly since it would represent sustainable development by making commercial use of a potentially hazardous waste product. The main aim of this thesis was to investigate whether wood distillates could be used as WPC components. Another aim was to assess the possibility to improve the mechanical properties and water resistance of the WPCs with wood distillates. Furthermore, the applicability of proton-transfer-reaction time-of-flight massspectrometry (PTR-TOF-MS) in determining the VOC emission characteristics of WPCs was studied. The effects of incorporating hardwood and softwood distillates into WPCs were examined by characterizing the mechanical properties, water resistance and VOC emissions of these WPCs modified with the distillates. The distillate content varied from 1 wt% to 20 wt%. The suitability of PTR-TOF-MS for analyzing VOC emissions from WPCs was assessed by measuring VOC emissions from a WPC deck during a 41-day trial and comparing VOC emission rates between seven different WPC decks. Both hardwood and softwood distillates exerted positive effects on the water resistance of the WPC; the addition of hardwood distillate decreased the water absorption of the WPC by over 25% whereas at least a 16% decrease was observed for the WPC with the softwood distillate. Moreover, a 1 wt% addition of hardwood distillate into the WPC led to a highly significant increase (11.5%, p < 0.01) in the tensile modulus as well as achieving minor enhancements in some other mechanical properties. Similarly, when 2 wt% of softwood was added to the WPC, a highly significant increase in the tensile strength (5.0%, p < 0.01) was observed. Even though the addition of the distillates increased the total release of VOCs, the emission rates of harmful compounds, such as benzene, remained low. Nonetheless, the results from the VOC analyses indicated that some of the compounds investigated in this thesis may be smelled from the WPCs because their odor thresholds were exceeded. Wood distillates displayed good potential as natural additives in WPCs as they improved the mechanical properties and water resistance. The results of this thesis provide a basis for the further development of wood distillates as bio-based additives in WPCs</p>