# Utilization of Partially Liquefied Bark for Production of Particleboards
## 3 Results and Discussion  
### Characterization of Bark and Solid Residues of PLB  
FTIR spectroscopy analysis detected the chemical structure of bark and solid residues of PLB (oven-dried PLB and purified PLB) (Figure 3). Raw bark showed a strong absorption peak at 3350 cm\({}^{-1}\), which corresponds to -OH stretch vibration in cellulose, lignin, and hemicellulose. Bark and oven-dried PLB illustrated two distinct peaks at 2918 and 2845 cm\({}^{-1}\), which are assigned to -CH stretch vibration in aromatic methoxyl groups and aliphatic methyl and methylene groups [38; 39]. The spectra for oven-dried PLB appears similar to that of purified PLB. A slight decrease in the -OH and -CH bonds were observed in oven-dried PLB and purified PLB compared to bark. This might be related to the degradation and dehydration of bark, and the formation of alcohol-soluble intermediates [12; 40; 41; 42]. A peak representing the C-O linkage of alcohol or ether that are typical polyol products from the complete liquefaction was found at around 1112 cm\({}^{-1}\) in oven-dried PLB and purified PLB (Figure 3). This peak verified the production of polyols through the partial liquefaction [43]. The absorption band at 1030 cm\({}^{-1}\) corresponding to -CO stretching for both PLB and purified PLB was weakened due to the cleavage of \(\beta\)-O-4 bonds of lignin [42]. The broad band between 1266 and 1030 cm\({}^{-1}\) in the spectrum for oven-dried PLB and purified PLB indicates -CO stretching in primary alcohol, secondary alcohol, ethers, and esters. The changes in the absorbance of -CO groups in bark and PLB confirmed that the liquefaction has occurred with the formation of the above intermediates. The intensive vibration at 1727 and 1605 cm\({}^{-1}\) in bark, oven-dried PLB and purified PLB correspond to -C=O in hemicelluloses and lignin, and to -C=C- stretching in lignin, which indicates the high content of lignin remained in the bark structure after partial liquefaction. Thermal degradation behavior of bark, PLB, and purified PLB was examined by TGA (Figure 4a) and derivative thermogravimetric (DTG, Figure 4b) analyses of the samples after drying in the oven at 105 \({}^{\circ}\)C for 24 h. There were apparent differences in the thermal degradation pattern of bark after partial liquefaction and purification compared to raw bark. Figure 4a shows the weight loss of the three tested samples up to a maximum of 40-60% of their initial weight. It was previously reported by [PERSON] et al. (2007) that cellulose pyrolysis occurs in a higher temperature range than lignin and hemicellulose, and lignin is the most difficult polymer to decompose with a solid residue of 45.7 wt.% [44]. As shownin Figure 4b and Table 2, decomposition of bark (T\({}_{\text{onset}}\)) initiated at 219 \({}^{\circ}\)C and reached a maximum mass loss (T\({}_{\text{max1}}\)) at 361 \({}^{\circ}\)C, thus representing typical pyrolysis of lignocellulosic material [45; 46]. The respective T\({}_{\text{onset}}\) of PLB and purified PLB were, respectively, 152 and 148 \({}^{\circ}\)C and were both lower than that of bark. The decomposition of PLB and purified PLB started earlier than bark, which might be attributed to a large number of hemicelluloses and amorphous part of cellulose that decomposed in the liquefaction due to the effect of the acid catalyst [42]. The decomposition of the intermediate products such as alcohols and esters in the PLB and purified PLB caused a shifted second maximum degradation temperature T\({}_{\text{max2}}\). As shown in Table 2, the T\({}_{\text{onset}}\), T\({}_{\text{max1}}\), and T\({}_{\text{max2}}\) of PLB and purified PLB were very close to each other but considerably lower than bark, which can be related to the lower content of volatiles in PLB and purified PLB [47]. Figure 4: Mass loss (**a**) and first derivative (DTG) (**b**) of bark, PLB, and purified PLB. Figure 3: Fourier transform infrared (FTIR) spectrum of raw bark, oven-dried partially liquefied bark (PLB), and purified PLB.