Hot-pressing process modeling for medium density fiberboard (MDF)

In this paper we present a numerical solution for the mathematical modeling of the hot-pressing process applied to medium density fiberboard. The model is based in the work of Humphrey[82], Humphrey and Bolton[89] and Carvalho and Costa[98], with some modifications and extensions in order to take into account mainly the convective effects on the phase change term and also a conservative numerical treatment of the resulting system of partial differential equations.Comment: LaTeX, 11 figures. Added references. Fixed some errors. To appear in International Journal of Mathematics and Mathematical Sciences, http://jam.hindawi.co

Modeling Rheology In The Hot-Pressing Of MDF: Comparison Of Mechanical Models

The hot-pressing operation is the final stage in the MDF manufacture where the mattress of fibers is compressed and heated to promote the cure of the resin. The press cycle has a major effect on the balance of properties of the resulting panel, so rigorous control of all processing variables is necessary to improve product quality and to reduce pressing time. The rheological behavior of the mattress during pressing involves complex phenomena that are dependent on temperature, moisture content, gas pressure, and density distributions. Following a three-dimensional model of heat and mass transfer already built, mechanical models were developed to describe the viscoelastic behavior of the material. The elastic and viscous properties for the wood-resin composite were estimated based upon several kinds of "rules of mixtures," taking into account the relationship with the simulations already undertaken for temperature, moisture content, and gas pressure profiles, as well as the adhesive polymerization. These dynamic models were used to predict the evolution of compression stress, strain, modulus of elasticity, and density with time at a given position in the mattress, as well as the density profiles. The models were compared in relation to the influential factors affecting the composite compressibility. The simulation results are useful to identify the controlling factors of a hot-pressing operation and to understand better the complex mechanisms involved in panel formation

Understanding the Adhesion Mechanism in Mycelium-Assisted Wood Bonding

The increasing environmental awareness has led to an increased interest in developing more sustainable materials as alternatives to petroleum-derived products. Among different nature-based products, fungal-mycelium-based bio-composites have gained considerable attention in various applications. Multiple materials with different densities and structures and potential applications can be fabricated by inoculating filamentous white-rot fungi in lignocellulosic materials and other substrates. Different from lower-density as-grown foam-like mycelium composites, higher-density mycelium-lignocellulosic panels have the potential to replace commercial particleboard and fiberboard bonded by petroleum-based resins. This kind of composite can be produced by directly adding heat and pressure to the low-density foams or by assembling mycelium-industry wastes before hot-pressing. The main goal of this dissertation was to investigate the principal adhesion mechanisms involved in the production of hot-pressed mycelium bio-composites. The functionality of surface mycelium for wood bonding was thoroughly investigated by growing Trametes versicolor on yellow birch veneers. The presence of surface mycelium improved the interface between two wood layers and consequently enhanced bonding. The surface mycelium layer was also confirmed to be able to be utilized as a stand-alone adhesive to bond untreated wood. The exopolysaccharides and proteins located at the interface between aerial mycelium and the substrate were confirmed to play an essential role in adhesion. The bonding mechanism and functionality of mycelium were also investigated in both as-grown and hot-pressed bio-composite structures. For low-density as-grown foam structures, fungal mycelium only worked as a binder, the lignocellulosic substrate material played an essential role in sound absorption and thermal insulation properties, and the denser mycelium structure had a negative effect on these properties. In a higher-density hot-pressed panel system, fungal mycelium contributed to bonding and reinforced the bio-composite by filling the gaps. Additionally, we also demonstrated that combining the advantages of nanocellulose research at UMaine into our novel mycelium bio-composite can provide further improvements in properties to manufacture formaldehyde-free hybrid composite panels. Finally, we discovered an all-natural mycelium surface with tunable wettability that can be switched several times from hydrophobic to hydrophilic status by a simple treatment. These surfaces can have potential applications in medical microfluidics and invisible pattern printing

Dizajniranje svojstava ekološki prihvatljivih ploča vlaknatica srednje gustoće proizvedenih uporabom lignosulfonatnog ljepila

Free formaldehyde emissions from wood-based panels, especially in indoor applications, pose serious risks to human health at certain concentrations. Prolonged exposure to formaldehyde can cause adverse health effects including eye, nose and throat irritation, other respiratory symptoms and cancer. As a consequence, new formaldehyde emission limits for composite wood products were established in Europe, USA and Japan. This, together with the stricter environmental legislation are the main driving factors for shifting the scientific and industrial interest from the traditional formaldehyde-based synthetic resins to the new bio-based adhesives for production of eco-friendly wood-based panels. The lignin-based products are one of the most prospective ecological alternatives to the traditional formaldehyde resins. The main interest in lignin is due to its phenolic structure with several favourable properties for the formulation of wood adhesives such as high hydrophobicity and low polydispersity. The present article is aimed at studying the possibilities for using lignosulfonate as an adhesive for the production of eco-friendly MDF. Regression models describing the impact of lignosulfonate concentration and hot pressing temperature on the exploitation properties of MDF panels were developed. The individual and combined impact of both factors was analysed in order to determine the optimal exploitation properties of the panels.Emisija slobodnog formaldehida iz ploča na bazi drva, posebice primijenjenih u unutarnjim prostorima, u određenim je koncentracijama ozbiljan rizik za zdravlje ljudi. Dulja izloženost formaldehidu može uzrokovati znatne zdravstvene probleme, uključujući iritaciju očiju, nosa i grla, druge respiratorne simptome i rak. Stoga su u Europi, SAD-u i Japanu određene nove granice emisije formaldehida za kompozitne proizvode od drva. To je, zajedno sa strožim zakonodavstvom o okolišu, bio glavni poticaj za prebacivanje znanstvenoga i industrijskog fokusa s tradicionalnih sintetičkih smola temeljenih na formaldehidu na nova prirodna ljepila za proizvodnju ekološki prihvatljivih ploča na bazi drva. Proizvodi na bazi lignina jedna su od najperspektivnijih ekoloških alternativa tradicionalnim formaldehidnim smolama. Glavni razlog zanimanja za lignin jest njegova fenolna strukturas nekoliko povoljnih svojstava za formulaciju ljepila za drvo poput visoke hidrofobnosti i niske polidisperznosti. Cilj ovog rada jest proučavanje mogućnosti uporabe lignosulfonata kao ljepila za proizvodnju ekološki prihvatljivih ploča vlaknatica srednje gustoće (MDF ploča). Razvijeni su regresijski modeli koji opisuju utjecaj koncentracije lignosulfonata i temperature prešanja na svojstva MDF ploča. Analiziran je pojedinačni i kombinirani utjecaj obaju elemenata kako bi se odredila optimalna svojstva ploča