Rubberwood composite – chip off a new block?

Wood Focus magazine
22 Sep 2012

A hybrid particleboard composite may address the problem of rising supply demand in the developing world – and help lower prices of indigenous raw materials, say researchers at Universiti Teknologi MARA in Selangor, Malaysia.

In Malaysia, the traditional raw material for particleboard or chipboard is rubberwood, from which latex is produced. After the trees have finished commercial production they are felled and the wood is used to make items such as furniture and, in sawdust form, particleboard. But the demand for solid rubberwood for furniture has been forcing up the wood’s cost for particleboard manufacturers, and although mixing the wood with agricultural waste such as ground coconut shell can mitigate this, the mechanical performance of such mixtures is poor.

To counter these factors, the team came up with two hybrid composites of rubberwood and coconut shell particles reinforced with textile fabrics – one type using cotton (dubbed CtHRC), the other polyester (PeHC).

The composites were made by mixing equal parts of ground rubberwood and coconut shell, binding with urea formaldehyde then ‘sandwiching’ the mixture in moulds with two, three or four layers of the particular fabric. Each sample was then cured, producing panels 12mm thick, then tested for flexural and impact strength.

For flexural tests, the team used a three-point bending scheme on an Instron 3382, in accordance with British Standard EN 310:1993. The falling-weight impact tests were conducted on a Dynatup machine.

The results show that both types of composite outperformed the control samples. Overall, CtHRC performed better in flexural tests, showing a maximum improvement of more than 200% over the control, while PeHC performed better in impact tests, showing a maximum improvement of nearly 270%. The researchers also found that the best results for both composites were achieved using three layers of cotton and three of polyester for flexural strength, and four-layer samples for impact strength.

The team says CtHRC did better than PeHC in the flexural tests due to better adhesion between the cotton and the rest of the composite, but that the performance of PeHC should improve once this issue has been addressed. By contrast, they claim PeHC did better in the impact tests because of polyester’s ability to stretch by 30–40% of its original length, and that it is this ductility that enhances the composite’s ability to absorb impact.

The hybrids should be cheaper and more sustainable than traditional composites, although the two cannot be directly compared, says Professor Mohd Iqbal Misnon, who led the research. ‘We use 50% less rubber wood than existing products. We also use coconut shell that would otherwise just be thrown away or burned, and we use less than 5% cotton and polyester fabric. Unlike traditional composites, though, ours are more suitable for interior low load-bearing applications such as nonstructural and furniture components.’

Although the focus of the study is on the issues faced by manufacturers in Malaysia, he says, the technology could be applied in other developing countries. ‘As it is here in Malaysia all the raw materials can be sourced locally – rubberwood from sawmills, the shell from coconut palm farms, textiles from fabric manufacturers and the binder from chemical companies.’

The composites can be produced using existing particleboard fabrication procedures, he says, but the material is still in the process of being patented. ‘The secret lies in the resin preparation and how we distribute the proportions between the mix of materials.’

The team is now looking to finish prototyping the composites and hopes to establish a production process for producing commercial-size panels.