Viscoelastic Behaviour of Wood Fibres during the Hot Pressing of Medium Density Fibreboard

Holzforschung ◽  
2003 ◽  
Vol 57 (4) ◽  
pp. 391-399 ◽  
Author(s):  
J. van Houts ◽  
D. Bhattacharyya ◽  
K. Jayaraman
Keyword(s):  
Relative Humidity ◽  
Hot Pressing ◽  
Viscoelastic Behaviour ◽  
Relaxation Behaviour ◽  
Medium Density ◽  
Taguchi Experimental Design ◽  
Load Relaxation ◽  
Medium Density Fibreboard ◽  
Wood Fibres ◽  
Effects Of Temperature

Summary Sufficient stress relaxation within a medium density fibreboard (MDF) mat during hot pressing is critical for producing a panel with acceptable mechanical properties and dimensional stability. This paper describes a series of load relaxation tests of wood fibres conducted at temperatures and moisture contents similar to those within an MDF mat during the hot pressing process (temperatures ranging from 80°C to 100°C with relative humidity levels ranging from 9% to 68%). The results clearly show an increase in relaxation when either the temperature or relative humidity is increased. The relaxation behaviour of MDF is also measured and the trends observed are comparable to those of the wood fibres. Taguchi experimental design is employed to analyse the effects of temperature, moisture content and initial stress on the viscoelastic behaviour of MDF.

Modelling the Heat and Mass Transfer during Hot Pressing of Medium Density Fibreboard

2013 ◽  
Vol 8 (1) ◽  
pp. 27-39 ◽  
Author(s):  
Arun Gupta ◽  
Patrick Jordan ◽  
Shusheng Pang
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Hot Pressing ◽  
Urea Formaldehyde ◽  
Hot Compression ◽  
Formaldehyde Resin ◽  
Medium Density ◽  
Differential Algebraic Equation ◽  
Medium Density Fibreboard

Abstract This paper discusses the development of a one-dimensional mathematical model to describe the heat and mass transfer during the hot-compression of medium density fibreboard (MDF) composite panels. Five primary variables were considered during the model development: air content, water vapour content, bound water content, and temperature within the mat, and the extent of the cure of the adhesive system, characterized by the cure index. Different heat and mass transfer processes were identified for the transport of the heat and the moisture phases. The heat was transported by conduction and convection due to a temperature gradient, and the exothermic energy released by the curing of the urea formaldehyde resin, while the water phases were transported by bulk flow and diffusion due to total pressure and concentration gradients. The resulting differential-algebraic equation system was solved by the finite difference method. The mathematical model predicted temperature, moisture content, partial vapour pressures, and extent of adhesive cure within the mat structure under a typical hot-compression process. The model results allow a better understanding of the interacting mechanisms involved in a complex production process. The model can also assist to optimize the hot-pressing parameters for improved quality of MDF panel products, while reducing pressing time.

scholarly journals Effects of adding nano-wollastonite, date palm prunings and two types of resins on the physical and mechanical properties of medium-density fibreboard (MDF) made from wood fibres

2018 ◽  
Vol 335 ◽  
pp. 49 ◽  
Author(s):  
Hamid R. Taghiyari ◽  
Farzad Arbabi Ghamsari ◽  
Ehsan Salimifard
Keyword(s):  
Mechanical Properties ◽  
Date Palm ◽  
Physical And Mechanical Properties ◽  
Medium Density ◽  
Medium Density Fibreboard ◽  
Propriétés Mécaniques ◽  
Wood Fibres ◽  
Propriétés Physiques ◽  
Propriétés Physiques Et Mécaniques ◽  
Proprietes Mecaniques

L’étude porte sur les effets de l’ajout de nano-wollastonite (NW) et de résidus de palmier-dattier sur les propriétés physiques et mécaniques de panneaux de fibres à densité moyenne. Des résines d’urée-formaldéhyde (UF) et d’isocyanate (IC) ont été utilisées à 10 % et 5 %, respectivement, du poids sec du matériau pour produire les panneaux. NW à granulométrie < 100 nm a été utilisé à 5 et 10 % du poids sec des résines, mélangé et pulvérisé sur le matériau avant formation du tapis de fibres. Les résultats ont été ensuite comparés à ceux pour les panneaux sans NW. Ils indiquent clairement une moindre absorption d’humidité et un moindre gonflement en épaisseur pour les panneaux produits avec ajout de résine IC. L’ajout de résidus de palmier-dattier a augmenté significativement les valeurs IB des panneaux produits avec les deux résines, UF et IC. L’ajout de NW a réduit les propriétés mécaniques des panneaux produits avec la résine UF, et amélioré celles des panneaux produits avec la résine IC. En conclusion, les résidus de palmier-dattier peuvent être considérés comme matière première potentielle pour la production de panneaux de fibres à moyenne densité en utilisant les deux résines, UF et IC. D’autre part, l’ajout de NW est recommandé pour la production de panneaux composites avec 10 % de résidus de palmier pour compenser en partie leur moindre résistance mécanique.  

scholarly journals Evolution of the viscoelastic properties of painting stratigraphies: a moisture weathering and nanoindentation approach

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Mathilde Tiennot ◽  
Davide Iannuzzi ◽  
Erma Hermens
Keyword(s):  
Mechanical Properties ◽  
Relative Humidity ◽  
Cultural Heritage ◽  
Mechanical Behaviour ◽  
Viscoelastic Properties ◽  
Viscoelastic Behaviour ◽  
Storage And Loss Moduli ◽  
Heritage Studies ◽  
Paint Films ◽  
The Impact

AbstractIn this investigation on the mechanical behaviour of paint films, we use a new ferrule-top nanoindentation protocol developed for cultural heritage studies to examine the impact of repeated relative humidity variations on the viscoelastic behaviour of paint films and their mechanical properties in different paint stratigraphies through the changes in their storage and loss moduli. We show that the moisture weathering impact on the micromechanics varies for each of these pigment-oil systems. Data from the nanoindentation protocol provide new insights into the evolution of the viscoelastic properties dsue to the impact of moisture weathering on paint films.

scholarly journals Medium Density Fibreboard Made from Kenaf (Hibiscus cannabinus L.) Stem: Effect of Thermo-mechanical Refining and Resin Content

BioResources ◽  
2014 ◽  
Vol 9 (2) ◽  
Author(s):  
Majid Dehghan Nayeri ◽  
Paridah Md Tahir ◽  
Mohammad Jawaid ◽  
Zaidon Ashaari ◽  
Luqman Chuah Abdullah ◽  
...  
Keyword(s):  
Resin Content ◽  
Hibiscus Cannabinus ◽  
Medium Density ◽  
Medium Density Fibreboard ◽  
Mechanical Refining

Reduction of Residual Stresses in Medium Density Fibreboard. Part 1. Taguchi Analysis

Holzforschung ◽  
2001 ◽  
Vol 55 (1) ◽  
pp. 67-72 ◽  
Author(s):  
J. van Houts ◽  
D. Bhattacharyya ◽  
K. Jayaraman
Keyword(s):  
Surface Layer ◽  
Residual Stresses ◽  
Internal Bond ◽  
Tensile Modulus ◽  
Thickness Swell ◽  
Subsequent Paper ◽  
Medium Density ◽  
Medium Density Fibreboard ◽  
Taguchi Analysis ◽  
Dissection Method

Summary This paper demonstrates how the Taguchi method of experimental design can be utilised to investigate methods for relieving the residual stresses present in medium density fibreboard (MDF). Panels have been subjected to heat, moisture and pressure, and after equilibration to room conditions, the changes in residual stresses through various layers have been measured using the dissection method. The application of heat and/or moisture has reduced the magnitude of residual stresses while generally the application of pressure has no effect on these stresses. The subsequent paper in this series uses Taguchi analysis to investigate how other board properties such as thickness swell, internal bond strength, surface layer tensile modulus and surface layer tensile strength are affected by the different treatment methods.

scholarly journals Effect Factors of Benzene Adsorption and Degradation by Nano-TiO2Immobilized on Diatomite

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Lijun Cheng ◽  
Yong Kang ◽  
Guishui Li
Keyword(s):  
Relative Humidity ◽  
Light Intensity ◽  
Experimental Results ◽  
Benzene Adsorption ◽  
Effect Factors ◽  
Benzene Concentration ◽  
Effects Of Temperature ◽  
Safe Concentration

Difference between adsorption of benzene by diatomite and nano-TiO2immobilized on diatomite was investigated. And effects of temperature, light intensity, relative humidity, and initial benzene concentration on adsorption and degradation of benzene by nano-TiO2immobilized on diatomite were also studied. The experimental results showed that when initial benzene concentration was2.2×10−3 mg L−1, it could be degraded to below safe concentration (1.1×10−4 mg L−1) after 50 h when temperature was 20°C, but it just needed 30 h at 35°C. When light intensity was 6750 Lx, it needed 30 h for benzene to be degraded to below safe concentration, but benzene could barely be degraded without light. When relative humidity was 50%, benzene could be degraded to1.0×10−4 mg L−1after 30 h, while its concentration could be reduced to7.0×10−5 mg L−1at the relative humidity of 80%.

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