Effect of Hydrolysis Regime on the Properties of Fibers Obtained from Recycling Medium-Density Fiberboards

Abstract

Unlike the recycling of particleboards, the recycling of medium-density fiberboards (MDF) is not a widespread industrial practice, and currently, most waste MDF panels are landfilled or incinerated after the end of their life cycle. Therefore, it is of great importance to develop cost-effective methods for MDF recycling. The extraction of resins used for bonding the panels, mostly urea–formaldehyde (UF) resins, is carried out mainly with hydrolysis. Hydrothermal hydrolysis is a more environmentally friendly and cheaper recycling technique compared to acid hydrolysis and allows obtaining a high yield of recycled fibers. The aim of this research work was to investigate and evaluate the effect of hydrolysis regime applied on its efficiency and on the properties of the recycled MDF fibers. For this purpose, thermal hydrolysis was carried out in an autoclave with saturated steam as a heat carrier. The main novelty of the research is the preliminary preparation of the recyclable MDF in samples with dimensions close to those of pulp chips. The effect of hydrolysis regime characteristics, i.e., process time and temperature on the properties of recycled MDF wood fibers, was studied. The hydrolysis temperatures used were 121 °C (saturated steam pressure of 0.2 MPa) and 134 °C (saturated steam pressure of 0.3 MPa); for each temperature, three durations were applied—30, 45, and 60 min. After hydrolysis, the resulting fiber fraction was refined using a hammer mill. The fractional and elemental composition of the recycled fibers obtained were evaluated. The hemicellulose content after each hydrolysis treatment was also determined. The chemical oxygen demand (COD) was defined as an indicator of wastewater contamination and as an indirect indicator of the quantitative yield of the process. The results revealed no significant changes in the elemental composition of the recycled fibers, and the hydrolysis regimes used showed no decrease in pentosan content. The recycled MDF fibers exhibited similar fiber morphology and fractional composition, being shorter than fibers from industrial pulp. The increased temperature and time of hydrolysis resulted in a significant increase in COD values. Based on the obtained results, with a view to the slightest contamination of wastewater (as determined by COD), the most promising hydrolysis regime was at a temperature of 121 °C and a time of 30 min. It should be emphasized that for a confirmation of this statement, the properties of MDF panels fabricated with fibers recycled in different regimes should be subsequently investigated.

The Impact of Hydrolysis Regime on the Physical and Mechanical Characteristics of Medium-Density Fiberboards Manufactured from Recycled Wood Fibers

“…Such extracts were also reported in the study by Hagel et al [42]. Another study [10] reported that, even at a hydrolysis temperature of 121 • C and a hydrolysis time of 30 min, the presence of amino compounds was observed in the pulp, indicating the disintegration of UF resin [47,48]. However, the impact of the hydrolysis regime on the physical and mechanical characteristics of MDF panels fabricated from recycled wood fibers obtained using the thermal hydrolysis of waste MDF panels was investigated in previous studies [10].…”

“…The thermal hydrolysis process was conducted using a TS 14 B+ autoclave (Cixi Tonsor Medical Instrument 146 Co., Ltd., Ningbo, Zhejiang, China). More detailed characterization of the processing parameters of hydrothermal recycling and the properties of the recycled fibers obtained can be found in Savov et al [10].…”

“…It should be noted that, while the recycling of particleboards is relatively well-developed at an industrial scale [7][8][9], the recycling of MDF panels is associated with specific technical difficulties, mostly related to the reduced slenderness of the recycled wood fibers [10][11][12][13][14][15][16]. The recycling of MDF panels can be carried out with or without removing the resins [17][18][19][20][21].…”

“…Studies on hydrothermal hydrolysis regimes are relatively limited. In the research by Savov et al [10], an investigation was conducted to examine the impact of the hydrolysis regime on the characteristics of the recycled fibers obtained. It was found that the recycled fibers were shorter compared to the natural ones, and spherical structures were observed in the pulp from such fibers.…”

“…Another study [10] reported that, even at a hydrolysis temperature of 121 • C and a hydrolysis time of 30 min, the presence of amino compounds was observed in the pulp, indicating the disintegration of UF resin [47,48]. However, the impact of the hydrolysis regime on the physical and mechanical characteristics of MDF panels fabricated from recycled wood fibers obtained using the thermal hydrolysis of waste MDF panels was investigated in previous studies [10]. Thus, the aim of this research was to investigate and evaluate the impact of the hydrothermal hydrolysis regime on the physical and mechanical properties of MDF panels fabricated from recycled wood fibers (rMDF).…”