Abstract
The paper presents research into the changes of properties in cement-bonded particleboards caused by moisture saturation over the course of 504 h. Three particleboard variants were tested, all at the age of 18 months. The first is a standard production-line board manufactured by CIDEM Hranice, a.s. (identified as CP-R). The other two variants were modified by by-products of the particleboard manufacturing process—dust (CP-D) and a particulate mixture (CP-P). The experiment observed changes in the boards’ dimensions, volume, and mass. The effect of moisture on their basic material properties was also investigated. While the boards were being saturated by water, changes in their structure were examined using an optical microscope. It was found that the boards behave differently depending on their composition. Also there were differences in the dynamics of the property changes. The modified particleboards are more susceptible to dimensional and volume changes. Both, volume and mass undergo the most significant changes during the first 24 h. Cracks and air voids inside the wood chips begin to close upon contact with water as a result of swelling. It was observed by optical microscopy that this process occurs within 3 to 5 min since immersion in the water bath. Between 24 and 96 h the rate at which the air voids and pores are closing begins to decrease and there is a difference in the dynamics of mass and volume changes as well. Wet–dry cycling of the boards was analysed as well. Temperature and moisture fluctuations negatively affected particleboard behaviour and properties. Strength dropped up to 50%. Wider cracks in structure of the particleboards were detected by optical microscopy, namely in ITZ (internal transition zone) of cement matrix and spruce chips.
Highlights
Particleboards are composite materials consisting of small wood particles bonded by a matrix [1]
Results confirmed diverse behaviour of boards in dependence on their composition during soaking. This relates to different ratio of cement and chips in Reference cement-bonded particleboard (CP-R), Cement-bonded particleboards modified with D (CP-D) and Cement-bonded particleboards modified with P (CP-P)
Penetration of water is more difficult with increasing water amount within the boards, because porous structure is gradually filled by the water and less show the most stable properties in terms of dimensional, volume and mass changes
Summary
Particleboards are composite materials consisting of small wood particles bonded by a matrix [1]. Wang et al [2] investigated a mixture that consisted of waste wood bonded by magnesium phosphate cement. The properties of wood and the cement matrix are markedly different. Wood is a heterogeneous material consisting mostly of structural components (cellulose, hemicellulose, and lignin) and non-structural components (polysaccharides of starch, extractives, proteins, some water-soluble organic compounds, and inorganic compounds). Christensen and Kelsey [22] estimated that cellulose, hemicelluloses and lignin in Eucalyptus regnans are responsible for approximately 47%, 37% and 16% of the total water sorption of this wood species. The use of wood in cement composites is strongly influenced by the leaching of hemicellulose, which slows the hydration rate of the cement matrix; cf Janusa et al [23]
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