Increasing the strength and stiffness of structural laminated timber using natural fibre composites

Abstract

Structural timber with low mechanical properties and/or large defects will be downgraded to non-structural uses with a subsequent loss in value. Using a low-cost natural fibre reinforced polymer (NFRP) material with a high stiffness and strength in conjunction with laminated timber veneer products, such as laminated veneer lumber (LVL) and plywood, may allow for the use of lower quality timber in structural applications. A NFRP veneer-like sheet is proposed to be included as outer layers of LVL and plywood products. Two minimal-processing methods were identified for the fabrication of industrial hemp stems into unidirectional-fibre composite sheets with high tensile strength and stiffness at a low cost. Comparison to reported properties in literature and the plywood stress grading system indicate strong stiffening potential of the hemp composite in structural applications. Finite Element (FE) models were validated with 4-point flexural testing of timber laminates and used to compare the cost and performance of using hemp composite sheets as outer layers of plywood and scaffold plank laminates. This suggests that the addition of the composite is able to reduce costs for both constant bending stiffness and constant thickness laminates based on estimated costs of timber plies and the composites materials. Small-scale timber laminates incorporating hemp composite sheets pointing towards further applications of the hemp composite including decorative panels requiring an aesthetic finish. The successful implementation the hemp composite in timber laminates could boost the profitability of Queensland and Australia’s timber industry, allowing for cheaper or downgraded timber to be used in high stiffness laminates.