Effect of Density and Fiber Size on Porosity and Thermal Conductivity of Fiberboard Mats

Pamela Rebolledo,Martin-Claude Yemele,Alain Cloutier

doi:10.3390/fib6040081

Pamela Rebolledo, Martin-Claude Yemele + Show 1 more

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https://doi.org/10.3390/fib6040081

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Abstract

The thermal conductivity and porosity of fiberboard mats are crucial parameters for efficient energy consumption of the hot-pressing process and for final panel quality. In this work, the effect of fiber size and mat density on porosity and thermal conductivity of the mat were investigated. The fiber size was characterized as fine, medium and coarse. The mat porosity was measured by image analysis using the black and white contrast method. The thermal conductivity was determined at different density levels with a temperature gradient of 1.6 °C mm−1 and 7.6% (s = 0.3) moisture content. The results showed that fiber size was a dominant variable governing heat conduction and mat porosity. The mats made with medium size fibers showed a higher resistance to compression. The thermal conductivity of coarse fiber mats decreased drastically between 700 kg m−3 and 810 kg m−3. This was likely due to a higher fracture frequency observed for coarse fibers in comparison to the other fiber sizes studied. Hence, the fine and medium fibers conducted heat more efficiently. Moreover, fiber bundles and fractured fibers were observed during the mat porosity measurements, principally in mats made with fine fiber size.

Highlights

Medium density fiberboard (MDF) is a wood-based composite widely used in residential applications and recognized for its easy machining, excellent surface properties and finishing quality.In the industrial manufacture of MDF, hot pressing is a key step due to its impact on the performance of the final panel and the plant productivity
The local density evolution can be linked to local mat thermal conductivity and porosity
The knowledge of how mat density is linked to local mat thermal conductivity and porosity

Summary

Introduction

Medium density fiberboard (MDF) is a wood-based composite widely used in residential applications and recognized for its easy machining, excellent surface properties and finishing quality.In the industrial manufacture of MDF, hot pressing is a key step due to its impact on the performance of the final panel and the plant productivity. There is a common agreement that hot pressing of fiber mats involves two different mechanisms: Heat and mass transfer and mat rheological behavior [1,2,3,4,5]. Heat and mass transfer take place in the fibrous material and in the void spaces of the fiber mat. This heat is transferred from press platens to the fiber mat by conduction. Mat porosity may affect this moisture transfer and the mechanical behavior of the fiber mat during the development of the density profile through the mat thickness

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