Surface densification of wood enhances the density and mechanical properties of the surface layer, increasing the value of underutilised wood species and expanding their suitability for a broader range of applications. By improving attributes such as strength and hardness, this process positions densified wood as a sustainable alternative to conventional materials such as plastics, metals and tropical hardwoods. However, despite decades of research, widespread commercial adoption remains limited, due to high production costs, variability in product performance, and the complexities of scaling densification methods for industrial use. 

This thesis addresses key barriers to industrial-scale adoption of surface-densified solid wood intended for flooring, with a focus on continuous densification processes and the optimisation of material properties. Specifically, the research aimed to: (1) evaluate the feasibility of continuous densification using a custom-designed belt press, (2) investigate the influence of growth ring orientation and knots on the densification process and resulting material quality, and (3) establish methods for characterising and optimising density profiles to improve mechanical performance and reliability of product properties.

The belt press studies demonstrated the potential for high-throughput continuous densification, achieving targeted density profiles while minimising non-value-adding steps. Pre-heating and increased heat transfer during compression were identified as critical for mitigating undesired densification and ensuring efficient plasticisation. The influence of growth ring orientation revealed significant variability in strain distribution and spring-back behaviour, underscoring the need for customised material selection and process parameters. These findings are particularly relevant for utilising low-quality or fast-growing wood species as they exhibit high variation in those features.

Mechanical characterisation of surface-densified wood revealed a strong correlation between density profiles and hardness, with the indentation depth during hardness tests shown to be significantly influenced by the density distribution beneath the surface. This relationship shows limitations in traditional hardness testing methods, which may fail to accurately assess performance due to variability in density profiles. To address these challenges, the study proposed an application-focused approach to testing the hardness of surface-densified wood, where the densification process and hardness test parameters are tailored to meet specific end-use requirements rather than relying on arbitrary mechanical metrics. Additionally, a method for predicting density profiles from hardness test data was developed, offering a practical alternative to X-ray densitometry for process control and design.

The development of machine learning models for predicting density profiles from photographic images of the materials’ cross-section offers a method for real-time quality assessment which is industry-suited. By combining this approach with the established correlation between density profiles and hardness, it may become possible to predict hardness solely from images. This integration of digital tools advances data-driven manufacturing in wood densification, providing scalable solutions.

To gain further insights into the densification process, an innovative in-situ measurement technique was developed, combining digital image correlation and computed tomography scanning (CT). This method enabled real-time analysis of density distribution changes during thermo-mechanical densification by aligning 2D strain fields with CT data and employing a constitutive model to estimate density profiles. The method was validated against experimental results and can be used in research, process optimisation, and to provide local density data to refine numerical models for precise and application-specific simulations.

This work bridges scientific principles with industrial practice, providing a foundation for the commercialisation of surface-densified wood products. By addressing critical challenges in process efficiency, material variability, and characterisation, this thesis lays the groundwork for large-scale industrial production of surface-densified flooring boards.