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.
Highlights
Medium density fibreboard (MDF) is a dry formed engineered wood product composed of fine lignocellulosic fibres, combined with a synthetic resin and joined under heat and pressure (Thoemen et al 2010)
The pH values of the fibres were measured after three different time spans but the differences for each fibre type were so low that only the average value was reported (Table 3)
The aim of the present study was to assess the recyclability of MDF bonded with current standard UF resins with a relatively low F:U molar ratio using repeated thermo-hydrolytic disintegration
Summary
Medium density fibreboard (MDF) is a dry formed engineered wood product composed of fine lignocellulosic fibres, combined with a synthetic resin and joined under heat and pressure (Thoemen et al 2010). MDF is used in a wide range of applications mainly for flooring, and for construction and furniture. It has substituted solid timber as well as other wood-based panels (WBP), due to its availability and wide range of thicknesses and the ability to be machined and finished to a high standard (WPIF 2014). Global MDF production, on the other hand, together with high density fibreboard has reached 98.6 million m3 in 2018 (FAO 2019). After service life, these panels will eventually become waste that is deposited in landfills
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