# Utilization of Partially Liquefied Bark for Production of Particleboards
## 4 Conclusions  
Bark as an abundant and easily accessible industrial waste has not been economically and significantly used. The current paper provides a new method for developing bio-based panels from  
Figure 8: Results of thickness swelling and water absorption of particleboard without (**a**,**c**) and with MUF (**b**,**d**) after 2 and 24 h of testing. Values labelled in the same colored letter (small blue for 24 h, and capital red for 2 h) are not statistically different from each other (ANOVA, [PERSON]’s HSD test, \(p<0.05\)).  
Figure 9: Scanning Electron Microscopy (SEM) micrographs showing the interaction of partially liquefied bark (PLB) and wood particles in the particleboard: (**a**) reference; (**b**) with 20% PLB and no MUF; (**c**) with 9.1% PLB and 10% MUF; and (**d**) with 20% PLB and 10% MUF.  
-pine bark with the partial liquefaction technique. In this study, pine bark was partially liquefied and then used to produce single-layer particleboard. Four particleboard panels were produced (I-IV) with wood particles and different load levels of PLB (4.7%, 9.1%, 20%, and 33.3%), and five boards (V-IV) were manufactured with wood particles, 10% MUF adhesives and different load levels of PLB (0, 4.7%, 9.1%, 20%, and 33.3%).  
Characterization of bark and solid residues of PLB (oven-dried PLB and purified PLB) revealed that the cleavage of the glucoside linkage of cellulose and the \(\beta\)-O-4 bonds of lignin occurred during the partial liquefaction for forming intermediates. PLB and purified PLB decomposed faster than bark during the thermogravimetric analysis because the bark was degraded in the partial liquefaction. PLB and purified PLB were more hydrophilic than bark at higher RHs, meaning that PLB has more hydroxyl groups accessible to water. Excessive hydroxyl groups can be attributed to the bonding between particles and PLB.  
Production of particleboard by replacing wood particles with PLB was possible with or without adding MUF adhesives. However, the boards made without MUF adhesives exhibited inferior mechanical properties as compared to the ones with MUF. The mechanical properties and thickness swelling of the non-MUF boards were considerably improved by increasing the content of PLB from 9.1% to 20%. The best mechanical properties were obtained in the particleboard with MUF adhesives and a PLB content of 9.1%. However, up to 20% of PLB content can be used for manufacturing particleboard for meeting the standard requirements. The boards manufactured with 4.7% and 9.1% PLB (I and II) without MUF adhesives showed very poor water resistance, while further addition of PLB at 20% and 33.3% in boards III and IV significantly enhanced the hydrophobicity of the boards. The boards bonded with MUF and different load levels of PLB from 4.7% to 33.3% exhibited significantly lower TS and WA values than the reference board V. The above results indicated that PLB acted as a good water-resistant substance in the particleboard.  
Conceptualization, W.J., S.A., M.P., M.S., and S.M.; methodology, S.M. and R.H.; software, W.J.; validation, W.J. and S.M.; formal analysis, W.J.; investigation, W.J., R.H., and J.Z.; resources, M.P. and M.S.; data curation, W.J.; writing--original draft preparation, W.J.; writing--review and editing, S.A., R.H., and J.Z.; visualization, W.J.; supervision, S.A. and S.M.; project administration, S.A.; funding acquisition, S.A. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Formas project 942-2016-2 (2017-21) titled \"Utilization of renewable biomass and waste materials for production of environmental-friendly, bio-based composites\".  
The authors would like to thank [PERSON] from Ikea Industry AB, Hultsfred, Sweden for his technical support in testing internal bond strength.  
The authors declare no conflict of interest.