Thermoforming of fibre-based materials : an investigation into material characteristics and process variables

Abstract

Thermoforming, a method widely used in plastic manufacturing owing to its efficiency and low heat requirements, holds untapped potential for the production of fibre-based products. However, the natural porosity of pure fibre-based materials introduces complexities during thermoforming, often requiring modifications such as plastic coatings or integrating plastic components. Despite these efforts, fibre-based products typically lack depth and detail compared with plastics. Although the global thermoforming plastics market is growing, data on fibre-based materials are limited, underscoring the need for targeted research to explore their potential in thermoforming.

This study investigated the potentials and challenges of thermoforming fibre-based materials, specifically focusing on coated and mixed composite structures. Monitoring techniques aimed at evaluating the thermoformability of fibre-based materials and aiding in process control were also introduced. Furthermore, this study examined how the material characteristics, product geometry, and thermoforming process operations influence the thermoformability of these target materials. Finally, the effect of inline material moisturization through steaming on the thermoforming performance of the coated structures was analysed across various product geometries.

The research highlighted the significant impact of the material structure on thermoforming. The coated structures exhibited limitations in shape conformability and heating tolerance, whereas mixed composite structures offered greater potential for intricate geometries but faced challenges in terms of uniformity and wood-to-plastic ratios. Material density was identified as a crucial factor affecting the vacuum suction response and sensitivity to temperature, whereas tensile properties, particularly strain at break and tensile stiffness, influenced the stretchability and product distortions. This study underscored the importance of fine-tuning thermoforming operation and mould designs to address the challenges in fibre-based structures, recommending adjustments in pressure application, cooling methods, and mould dimensions. Furthermore, inline steam treatment was found to be effective in directing the material towards the sidewalls of the geometry. However, its impact on achieving the desired depth was influenced by several material-related factors, including the material's properties, composition, preparation methods, and post-forming drying.