Processing bamboo for structural composites: Influence of preservative treatments on surface and interface properties

Darshil U Shah,Bhavna Sharma,Michael H Ramage

doi:10.1016/j.ijadhadh.2018.05.009

Darshil U Shah, Bhavna Sharma + Show 1 more

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https://doi.org/10.1016/j.ijadhadh.2018.05.009

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Abstract

Engineered bamboo is being increasingly explored for structural use in the construction sector. To ensure durability, products such as laminated bamboo undergo essential preservation treatment steps during their manufacture. However, the effects of hygro-thermal caramelisation and chemical bleaching, two commonly used treatment procedures in industry, on the surface and interfacial properties of laminated bamboo are not yet known. The latter governs the structural quality of the final product. Our dynamic wettability studies through contact angle measurements revealed lower water contact angles, higher total surface energy and a slightly greater polarity ratio for bleached bamboo in comparison to caramelised and untreated bamboo. In addition, lap-joint shear tests and Weibull reliability analysis established the significantly better adhesive bonding performance of bleached bamboo with all five surveyed adhesives. Our observations are explained through the changes in chemical composition and structure of the raw bamboo material upon treatment, where changes in caramelised and bleached bamboo are dominated by hemicellulose degradation and lignin degradation, respectively. The bleaching process is conclusively identified as having favourable effects on bond strength of the glue line.

Highlights

Bamboo is an outstanding natural composite: it is rapidly growing, low-cost and abundantly available, light, yet stiffer and stronger than both timber and glass fibre composites [1,2]
Our observations reveal that the differences in surface chemistry between untreated, bleached and caramelised bamboo lead to lower adhesive bonding strengths for caramelised and untreated bamboo, and affects their affinity and bonding performance with different adhesives
Our study finds that commercial preservative treatments have significant effects on the wetting behaviour and adhesive bonding performance of the laminated bamboo material

Summary

Introduction

Bamboo is an outstanding natural composite: it is rapidly growing, low-cost and abundantly available, light, yet stiffer and stronger than both timber and (chopped strand mat) glass fibre composites [1,2]. Two methods are in primary use to modify carbohydrates in laminated bamboo [8]: a) caramelisation or steaming (a hygro-thermal treatment), using pressurised (0.20–0.25 MPa) wet steam at 120–130 °C over 5–6 h yielding a darker brown colour, or b) bleaching (a chemical treatment) in a hydrogen peroxide bath at 70–80 °C over 4 h resulting in a lighter yellow colour. Both processes are followed by steam-assisted drying at 50–60 °C for a total of 240 h for caramelised bamboo and 72 h for bleached bamboo. The selection of the treatment process in industry has been driven by the resulting colour and hue of the bamboo material and was adopted from wood processing

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