European Journal of Wood and Wood Products (2023) 81:557–570
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resulting in reduction of the mechanical properties of boards due to the temperature increase (Yilgor et al. 2001). Moreo- ver, these findings correspond to the research of Goldstein (1973) that the treatment temperature range should be between 110 and 170°C for recycled particles of particle- boards. Additionally, Lykidis and Grigoriou (2011, 2008) concluded that the panel made from hydrothermally treated waste wood particles at around 150 °C shows better quality than others. The effects of different waste wood ratio on the physical and mechanical properties of particleboard were investigated by Azambuja et al. (2018a, b), Laskowska and Mamiński (2018), Zamarian et al. (2017), Martins et al. (2007) and Suffian et al. (2010). The research results stated that it is possible to use 100% recycled wood particles in the produc- tion of panel products with UF as binder. In general, the higher the wood mix ratio applied, the lower the mechanical properties (MOE, MOR and IB) and the higher the hygro- scopic properties (thickness swelling and water absorption) of panel achieved. The reasons could be due to the decrease in slenderness ratio of waste wood particles formed during the chipping process, which leads to the limitation of contact area between the particles (Arabi et al. 2011). In addition, the physical contaminants from surface coating materials (e.g., polypropylene, polyethylene, polyvinylchloride) of different waste wood-mix resources ( e.g., construction and demolition, furniture, packaging) cause negative effects on glue bonding of panel production, resulting in the decline of strength properties of boards. Moreover, Czarnecki et al. (2003) confirmed that waste wood particles containing PF resin could hinder UF curing due to its alkaline character resulting in reducing MOE, MOR and IB of recycled parti- cleboard. On the other hand, Azambuja et al. (2018b) proved that the strength properties of produced particleboard con- taining up to 50% of waste wood mix are comparable to the one made from fresh wood particles and their values meet the standard of panel type P2. In general, the properties of the particleboards can be controlled based on the waste wood ratio in wood mixture. Adhesive types also strongly affect the properties of particleboards. Several investigations focused on PF, TF and PMDI adhesives instead of UF for the improvement of particleboard properties using 100% waste wood particles (Hameed et al. 2018a; Laskowska and Mamiński 2018; Yang et al. 2007; Wang et al. 2007). The key findings illus- trated that the MOE, MOR, and IB increase and TS and WA decrease when the percentages of those glues in waste wood mixture increase. This may be due to the differences in bonding properties (e.g., impregnation/absorbing ability only on surface or deeply inside middle lamella of wood) of UF, PF, TF and PMDI adhesives with wood particles/ fiber during the curing process affecting the physical and mechanical properties of produced panels. Better bonding
Hasan et al. (2011a, b) stated that the application of ED- XRF in online sorting could eliminate 92–96% of wood pre- servatives (CCA) and alkaline copper quaternary (ACQ) in recycled wood at recycling plants. This method also showed high efficiencies with certain limitations for the elemen- tal analysis of six different groups (origin, type, material, visually detected pollution, pollutant macro category and pollutant specification) from wood residues in wood recy- cling plants (Fellin et al. 2014). On the other hand, Fellin et al. (2011) stated the positive results on the application of infrared spectroscopy for the detection of pollutants in wood residues. Moreover, Mauruschat et al. (2016) indicated that near infrared (NIR) spectroscopy and automatically pneu- matic nozzles can distinguish four types of plastic granulate in WPC. In addition, this study also showed the possibility to distinguish between untreated and treated wood at differ- ent moisture contents containing inorganic and organic pre- servatives. However, these technologies need more investi- gations/improvements prior to being used on an industrial scale besides focusing on the development of new sorting techniques. Principally, the detection and sorting of most contam- inants in waste wood could be conducted by appropriate methods. However, the waste wood after sorting and pro- cessing could contain certain contaminants. Depending on types and contents, those physical and chemical contami- nants in waste wood resources will be classified whether they are problematic for the later wood-based panel products.
3.2.2 Properties of wood-based panel produced from waste wood
Table 3 presents information about the properties of wood- based panels made from recycled wood. In this part, some factors influencing physical and mechanical properties of particleboard, fiberboard and OSB produced from recycled wood such as treatment process of waste wood (e.g., hydro- thermal process), waste wood mixing ratio, and adhesives type will be addressed. 3.2.2.1 Particleboard Different investigations based on hydrothermal treatment processes were conducted at vari- ous schedules to separate waste wood into particles and use them for the production of particleboard (Andrade et al. 2015; Lykidis and Grigoriou 2011, 2008). The findings indicated that the particleboards manufactured from treated waste wood particles show stable dimensions. However, the mechanical properties (MOE, MOR and IB) and physical properties (thickness swelling and water absorption) of the panel decrease when the temperature increases. This finding is also consistent with the results of Michanickl (1996a) and Boehme and Michanickl (1998). It can be explained by the degradation of holocellulose and lignin in recycled wood
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