Pre-pressing and Pre-heating via Hot-Air/Hot-Steam Process for the Production of Binderless Medium-Density Fiberboards

Abstract

The hot-air/hot-steam process was used for the first time as a combined pre-pressing and pre-heating system for the production of medium-density fiberboards (MDF) at the pilot scale. Pre-heating systems are designed to pre-heat fiber mats before pressing by hot-presses. Using such techniques, pressing times are reduced significantly and the board properties are influenced positively; both are essential for effective MDF production. In recent years, industry has searched for alternatives to petrochemical binders. Primarily, MDF are bonded by urea-formaldehyde (UF) resins in Europe. To replace UF resins, a laccase-mediator-system (LMS) was used to activate the wood fibers' self-cohesion. It was found that the internal bond strength (IB) and thickness swelling (TS) were noticeably improved by applying the hot-air/hot-steam process before final hot-pressing for both LMS and 10% UF binding systems. Simultaneously, the total pressing time could be reduced by 25% when combining the hotair/hot-steam process with hot-pressing.

Enzymatic Oxidation of Ca-Lignosulfonate and Kraft Lignin in Different Lignin-Laccase-Mediator-Systems and MDF Production

“…Adding hydrophobizers could be a solution to improve moisture resistance, but this may hinder good gluing (Mathiasson and Kubát, 1995;Kües et al, 2007;Kirsch et al, 2016). Use of a novel hot-air/hot-steam curing to achieve higher temperatures for lignin repolymerization under reduction of press times (Euring et al, 2015;Euring et al, 2016) improved physical properties of panels produced with lignin admixture (Kirsch et al, 2018). Modifying lignin prior to admixture in resins can make them more efficient as functional eco-friendly glues (Garajová et al, 2021;Karthäuser et al, 2021).…”

“…Novozym 51003 contains a thermostable laccase recombinantly produced from a gene of the ascomycete Myceliophthora thermophila (MtL) cloned in Aspergillus oryzae and is applicable for the oxidation of a broad range of lignocellulosic materials (Novozymes, 2007;Lund et al, 2016;Ernst et al, 2018). Earlier LMS studies required a 1 L incubation solution of 100 U/ml of this asco-laccase (Euring et al, 2011;Euring et al, 2013;Euring et al, 2016) or even 200 U/ ml (Kirsch et al, 2016), per 1 kg fiber mass (atro, for "absolut trocken," absolutely dry) for the production of MDF of good technical quality at the pilot plant scale. Due to its price [around 30€ per liter in year 2020 (Univar, 2020)], it could still be difficult to integrate the LMS into a cost-oriented MDF company.…”

Quality Control of the Continuous Hot Pressing Process of Medium Density Fiberboard Using Fuzzy Failure Mode and Effects Analysis

“…The production of MDF involves the application of hot pressing using various heat processing temperatures (155 • C, 165 • C, and 175 • C) for different time durations (2.5 h, 3.5 h, and 4.5 h) [2]. With the introduction of the continuous hot-pressing (CHP) technology in Germany in the beginning of the 1970s, productivity was increased, and good surface qualities were achieved [3]. Hot pressing is the most crucial process in the production of MDF [4], and it is essential to achieve the required quality of MDF.…”