The Removal of Cured Urea-Formaldehyde Adhesive towards Sustainable Medium Density Fiberboard Production: A Review

Abstract

Medium density fiberboard (MDF) is an engineered wood product that has density and specific gravity similar to solid wood, ranging from 600 to 800 kg/m3 of density and 0.6 to 0.8 of specific gravity. This makes MDF suitable to partially replace solid wood, particularly for interior application. Approximately over than 100 million m3 of MDF are produced in 2020, resulting in a large amount of waste MDF will be generated in the next 20 years. MDF is produced using urea-formaldehyde (UF) resins adhesive. UF resins adhesive is a poly-condensation product of urea and formaldehyde via an alkaline acid two-step reaction. Sustainable MDF production is required as the world is facing climate change and deforestation. Recycling is a way to support sustainable production in the engineered wood products manufacturing. Many attempts have been done to find ways to recycle waste MDF. The main problem is UF resins, which bond the MDF panel fibers. In order to re-manufacture the waste MDF into new recycled MDF, UF resins should be eliminated from the waste MDF before being used. The presence of UF resins in MDF can interfere with the utilization of the recycled fibers, whether it will be used as a raw material for new MDF or other composite products. This paper reviews the process of removal of cured UF resins from waste MDF panel by considering the hydrolytic stability of cured UF resins for MDF recycling, providing a comprehensive review of how cured UF resins can be removed from waste MDF and characterization of recycled fibers obtained from recycling prior to re-manufacturing of recycled MDF panel.Keywords: hydrolysis, medium density fiberboard, resin, recycling, resin removal, urea-formaldehyde

Urea-Formaldehyde Resin Removal in Medium-Density Fiberboards by Steam Explosion: Developing Nondestructive Analytical Tools

“…Hydrothermal treatments previously described in the literature on MDF recycling lead to a fiber shortening of ∼30% . Steam refining performed in comparable conditions lead to a fiber yield of ∼75% .…”

“…Hydrothermal treatments previously described in the literature on MDF recycling lead to a fiber shortening of ∼30%. 11 Steam refining performed in comparable conditions lead to a fiber yield of ∼75%. 14 In this study, regardless of the experimental SE or SEW conditions considered (Table 1, runs 2−15), a comparable fiber yield of 80% w/w (±2%) was achieved.…”

“…10 As a result, hydrolytic strategies have been proposed for UF removal prior to the reuse of wood-based panels. 11 Neutral and acidic hydrolysis can remove ∼50 and ∼70%, respectively, of UF resin from MDF fibers. 12 Hydrothermal treatment led to a reduction in resin content, but it also resulted in a reduction in the average length and width of the fibers, thus reducing the potential for further fiber recovery.…”

“…It has been shown in previous studies that the presence of residual cured UF resin on the surface of the wood fibers negatively impacts the properties of the panels formed from recycled wood. , Cured UF resins have a relatively low water resistance and can be degraded by hydrolysis . As a result, hydrolytic strategies have been proposed for UF removal prior to the reuse of wood-based panels . Neutral and acidic hydrolysis can remove ∼50 and ∼70%, respectively, of UF resin from MDF fibers .…”

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

“…According to the findings reported by the same research, 25% of the MDF panels end their life cycle within one year, and within 10 years, this percentage increased to 80% [8]. Consequently, this is associated with the greatly increased accumulation of waste MDF panels and difficulties in their disposal [9]. It is well known that 1 m 3 of MDF is produced from 1.6 to 2.0 m 3 of wood [10].…”