Influence of Pressing Schedule and Adhesive Content on the Rheological Behavior of Wood Fiber-Furnish Mats.

Heiko Thoemen,Ali Shalbafan

doi:10.3390/ma15041413

Abstract

In this study, for a better understanding of the hot-pressing process, the influence of adhesive content (AC) on various features of a typical pressing schedule for medium-density fiberboard (MDF) production, including fiber mat compressibility, heat transfer during hot-pressing, density profile and board properties, were evaluated. It was found that increasing the AC (urea formaldehyde) leads to faster heat transfer towards the mat’s central plane, mainly due to higher heat release from the adhesive polycondensation reaction. Moreover, the results indicate that the time needed to reach the critical mark of 100 °C in the central plane of the mat depends on the duration of the first densification level (FD). Importantly, the pressure peaks (pmax and p2nd) needed for mat densification are significantly reduced when increasing the AC, which might be attributed to the slippery effect created by the adhesive on the fiber surfaces. The duration of the FD also showed obvious effects on the intermediate density maxima (ρinter) and the core layer density (ρcore). In general, the physical and mechanical properties of MDF panels are significantly impacted by the pressing schedule and AC. All in all, the results of this study are valuable information for refining existing rheological models to improve their accuracy and their ability to simulate the vertical density profile during industrial production.

Highlights

Demand for wood-based panels (WBPs), as a furniture and building material has increased considerably in recent decades
The core layer temperature started to increase after nearly 50 s of pressing time in all panels, rapidly reached 100 ◦C and maximum temperature, and eventually was constant prior to press opening
The lower density of the mat following code A results in reduced thermal conductivity and, in reduced heat transfer. This finding is in accordance with that presented by Thoemen and Ruf [11]

Summary

Introduction

Demand for wood-based panels (WBPs), as a furniture and building material has increased considerably in recent decades. In the WBP industry, the raw material features (e.g., type of raw materials and their geometry) influence the board properties, the hot-pressing operation is one of the most critical steps of the whole panel production, as the properties of the final product depend heavily on the pressing conditions of the wood-furnish mat [3,4,5]. A fundamental understanding of the pressing process is crucial for optimizing production speed, costs and energy consumption, as well as manipulating board properties and for the development of new technologies and products [6,7]

Methods

Results

Conclusion