European Journal of Wood and Wood Products (2023) 81:557–570
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In addition, most collected waste wood resources at recy- cling centers or companies are mixtures of different wood types such as particleboard, fiberboard, plywood and OSB. Fiberboard accounts for about 5–15% of the amount of these waste wood resources and normally is not easy to separate from the mixture by traditional sorting methods (Fechter 2021). This amount will generate challenges (e.g. dust dur- ing chipping process of waste wood into particles and higher consumption of adhesives at gluing stage) when using it for the manufacture of industrial particleboards. For the time being, sorting technologies are developed that can sort out most of the fines from the waste wood mixture. Great effort is made to increase the recovery of MDF by different tech- nologies besides improved sorting such as steaming at high pressure, ohmic heating or microrelease. 3.2.2.3 OSB For the production of OSB from waste wood, Mirski and Dorota (2011a, b) stated that 75% of recycled wood particles could replace virgin ones in the core layer of OSB with MUPF and PMDI, complying with the mechani- cal and physical property values of standard EN 300. On the other hand, Schild et al. (2019) indicated that the substitu- tion up to 100% of unsorted waste wood particles in the core layer of OSB with PF is possible and the MOE, MOR and IB of the boards comply with standard requirements, except for TS and WA. However, MOE and MOR decrease when the waste wood content increases, whereas IB, thickness swelling and water absorption increase with the increase in waste wood proportions. These effects could be due to the inhomogeneous distribution of strands and particles and particles contaminants (e.g., wood preservatives, resonated waste wood particles, paints) in the face and core layers of OSB resulting in high-density variations in core layer and the whole board.
ability will result in better board properties. Laskowska and Maminski (2018) and Yang et al. (2007) stated that boards made from PF showed better properties than UF boards, whereas Wang et al. (2007) indicated that panels produced from PMDI showed higher properties than PF ones. Further- more, Hameed et al. (2018a) demonstrated that the combina- tion of TF and PMDI at the ratio of 30%:70% and 40%:60% in particleboard manufactured from waste wood material complied with the standard values of type P2 strength. 3.2.2.2 Fiberboard In the sector of fiberboard produced from the mixture of waste wood fiber and virgin wood, Hong et al. (2018), Roffael et al. (2016), Mantanis et al. (2004) and Krzysik et al. (1997) found that the strength properties (MOE, MOR and IB) of the panel decrease ten- dentially with the increase in waste wood fiber content. It could be explained by the fact that the handling process (e.g., hammering, cooking, refining) of recycled fiberboard into fiber resulted in shortening the fiber length of recycled fiber leading to the reduction in mechanical properties. There was a controversial finding in hygroscopic properties of investigated fiberboard. Hong et al. (2018) and Krzysik et al. (1997) found that TS and WA of investigated fiber- board increased with the higher proportion of recycled fiber content, whereas Roffael et al. (2016) and Mantanis et al. (2004) stated that TS and WA were improved and decreased when more recycled fibers are used. However, the differ- ence could be explained by the fact that the adhesive con- tent in recycled fiberboard contributes to the increase in TS and WA. Moreover, the interaction of cross-linking of the lignocellulose fibers with existing UF-pre-polymers in UF resin could be a reason for this effect (Andrews et al. 1985). Another possibility may be the effects of contaminants from adhesives, coating layers or surface laminate types (e.g., polyethylene terephthalate) in recycled fiberboard. There- fore, the findings indicated that it is only feasible to substi- tute 20% (Hong et al. 2018) to 25% (Mantanis et al. 2004) of recycled fiber in the UF wood mixture to produce fiber- boards, reaching mechanical and physical properties com- parable to virgin wood fibers. At industrial scale, fiberboard recycling is facing a major problem of effectively collecting, sorting and disintegrating the wood fibers. Recycled fiberboards from off-cuts, machin- ing errors, and transport and storage losses contain differ- ent types of wood adhesives and coating surface materials. These cause difficulties in applying appropriate technolo- gies (e.g. mechanical, thermo-hydrolytic and chemical) to disintegrating fiberboard waste wood into reclaimed fiber completely in a single step used for fiberboard production. Therefore, the combination of mechanical, thermal and chemical technologies is requested. However, this combi- nation will lead to the quality reduction in recovered fibers (Irle et al. 2019; Buschalsky and Mai 2021).
3.2.3 Formaldehyde emission
Table 4 shows the summarized data of studies conducted on formaldehyde emission of wood-based panels (particle- board, OSB, fiberboard) produced with various waste wood ratio and adhesives types. Tendentially, the amount of formaldehyde emission of particleboard and OSB produced from waste wood particles increases with higher proportion of waste wood mixture. Martins et al. (2007) indicated that particleboards produced from higher waste wood ratio (from 50 to 100%) and same UF content showed higher formaldehyde emission. Mirski and Dorota (2011a) found the same tendency in the pro- duction of OSB from recycled wood. The reason for this is probably due to the former concentration of formaldehyde included in the glue of recycled wood. In contrast, Hong et al. (2018) and Roffael et al. (2016) found that the amount of formaldehyde emission of fiberboards made from waste
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