Repeated thermo-hydrolytic disintegration of medium density fibreboards (MDF) for the production of new MDF

Abstract

Medium density fibreboards (MDF) are currently not recycled after service life, but various publications report on recycling by the disintegration of MDF using various techniques and the properties of obtained recovered fibres (RF). In this study, the main aim was to put back RF into the MDF manufacturing process as closed-loop recycling using repeated thermo-hydrolytic disintegration. Compared to previous studies, the focus was on the recycling of MDF with a relatively low F:U molar ratio (1.11). Urea–formaldehyde-bonded MDF with a target density of 700 kg m−3 was subjected to thermo-hydrolytic disintegration in an autoclave using only water at 95 °C for 20–30 min. Afterwards, the properties of RF and virgin fibres (VF), of MDF produced thereof and the composition of the disintegration water (DW) were determined. The nitrogen content (NC) revealed that RF contained about 30% of the initially applied UF. The pH of the DW hardly changed during recycling and it contained considerable amounts of reducing sugars. Using RF did not result in higher formaldehyde emissions than VF. Compared to earlier studies using a higher formaldehyde content (higher F:U ratio), MDF bonded with modern UF resins can be disintegrated under clearly milder disintegration conditions with respect to temperature and time. The properties of recycled MDF were similar to those of reference MDF; up to 100% RF could be used without severely deteriorating the strength and increasing formaldehyde emissions from these panels.

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

“…The selected process parameters are consistent with the study carried out by Moezzipour, B. et al [39]. Other studies in the field show that at lower hydrolysis temperatures and similar process times, formaldehyde emissions in MDF panels fabricated with recycled fibers significantly increase [34]. That could be seen as circumstantial evidence of the incomplete disintegration of UF resins to amino compounds.…”

“…With the selected hydrolysis regimes, 100% of the binder components remained in the recycled fibers. Lubis et al [34] found that only 33.5% of the UF resin components were present in recycled fibers after performing acid hydrolysis. Another study [39] corroborated these findings.…”

“…UF resin has no resistance to hydrolysis [31][32][33]. Hydrolysis can be thermal [34], thermochemical in an acidic solution [35], or hydrolysis by electrolysis [36].…”

Seagrass Leaves: An Alternative Resource for the Production of Insulation Materials

“…In the case of WF boards, along with the chemical bonding provided by the pMDI binder, the wood fibers are interlocked with each other to form a stable structure. In addition, shorter and thinner fibers usually provide high internal bond strength [ 39 ].…”

“…The higher compression strength of WF boards can be explained by the higher glue effectiveness as well. Short and thin wood fibers have a great surface area and glue is utilized to a high extent [ 39 ].…”