Visualizing the Microdistribution of Zinc Borate in Oriented Strand Board Using X-Ray Microcomputed Tomography and SEM-EDX

Philip D Evans,Vinicius Lube,Holger Averdunk,Andrew Kingston,Ajay Limaye,Timothy J Senden,Michael Turner

doi:10.1155/2015/630905

Philip D Evans, Vinicius Lube + Show 5 more

Open Access

https://doi.org/10.1155/2015/630905

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Abstract

Oriented strand board (OSB) is an important wood composite used in situations where fungal decay and termite attack can occur. To counter these threats, powdered zinc borate biocide is commonly added to OSB. The effectiveness of biocides depends on their even distribution within composites and resistance to leaching, but little is known about the distribution of zinc borate in OSB. Zinc is denser than wood and it should be possible to map its distribution in OSB using X-ray micro-CT. We test this hypothesis and chemically register zinc in OSB using SEM-EDX. Zinc borate particles aggregated at the wood-adhesive interface in OSB, creating interrupted lines of zinc oriented in the x-y plane. Zinc borate particles were also found in the lumens of wood cells. Zinc was distributed throughout OSB, although slightly less was present in the core of the composite than in surface layers. A network of zinc remained in OSB after leaching in water. The resistance of zinc to leaching may be due to its incorporation in glue-lines within OSB, in addition to its low water-solubility. We conclude that X-ray micro-CT is a powerful tool for studying the distribution of zinc in OSB and other wood composites containing zinc borate.

Highlights

Oriented strand board (OSB) is a composite made by compressing and bonding together wood flakes with a thermosetting adhesive
Our results clearly demonstrate that zinc borate is distributed throughout the OSB as interrupted lines of particles concentrated at the wood adhesive interface and oriented in the x-y plane and, less commonly, as individual particles located in the lumens of the wood fibres in OSB strands
High intensity regions that are white in scanning electron microscopy (SEM) images could be clearly seen at the surface of unleached and leached oriented strand board (OSB) specimens when they were examined using field emission scanning electron microscopy

Summary

Introduction

Oriented strand board (OSB) is a composite made by compressing and bonding together wood flakes with a thermosetting adhesive. OSB is used for sheathing of buildings (walls, floors, and roofs), webs in structural I-beams, furniture frames, and industrial packaging (pallet tops, export crates, and boxes). In some of these end-uses OSB can be exposed to water for short periods of time. Zinc borate is used to protect other bio-based composites from fungal and insect attack, for example, waferboard, oriented structural straw-board, particleboard, medium density fibreboard, laminated strand lumber, bamboo scrimber, and wood plastic composites [4,5,6]. The resulting composite is resistant to both fungal and termite attack, higher loadings of zinc borate are required to prevent such attack when wood composites are subjected to severe leaching with water [7]

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