Innovating Sustainability: Transforming Wood Colors for a Greener Future

Jue Mo (left) is a PhD student in the College of Agriculture and Dipesh Tamboli (right) is a PhD student in the College of Engineering.

In a world increasingly concerned about environmental preservation, there's a growing challenge at the intersection of artistry and conservation. The problem is our insatiable demand for the rich, dark hues of tropical hardwoods, which often come at the expense of endangered species and protected forests. These exotic woods are favored in high-end markets for their natural beauty, but their unsustainable sourcing raises ethical and environmental concerns. 

On the flip side, we have abundant light-colored wood species flourishing in regions like central hardwood areas, such as Indiana. These woods are harvested sustainably, with 3.3 times more trees grown than removed. The challenge we're addressing is how to transform these lighter woods into the coveted dark shades while preserving the core strength of the wood. This transformation is essential to meet market demands for the richness of dark-colored wood without compromising the environment. 

Various methods exist for changing wood color, including chemical stains, finishes, and thermal treatments (TT). Among these, thermal treatment is a non-chemical option to enhance wood color, aligning with modern preferences for eco-friendly solutions. However, most commercial TT methods rely on energy-intensive, time-consuming processes that can weaken the wood. 

What if only the surface of the wood needs to be transformed, especially for indoor applications? This is where innovation steps in. Our study introduces a groundbreaking approach known as Surface Thermal Treatment (STT), which involves heating only the wood's surface using a heated press. This method, surprisingly underutilized, offers a remarkable solution. It can darken wood's color while preserving its core strength, significantly reducing processing time and energy consumption – less than a minute in our current research. This makes STT a promising choice for applications like siding, paneling, and flooring, where surface appearance is paramount. 

Our study focused on three common hardwood types in the United States: White Ash, Yellow Poplar, and Red Oak. We measured the wood samples' color before and after treatments using a heated press. The treatments involved varying temperature levels (225, 250, 275, 300, and 325℃) and durations (10, 20, 30, 40, and 50 seconds). 

For potential industrial production, we needed to understand how temperature and time affect the color change. To achieve this understanding and make STT predictable and controllable, we employed an Artificial Neural Network (ANN) model to correlate the variables in question. 

The ANN model played a pivotal role in accurately predicting the extent of color change with a remarkable 96% accuracy rate. This means we can use the model to achieve the desired color, reducing the number of experiments and streamlining the process. Industries can also explore integrating this ANN model into their operations, improving efficiency and sustainability. 

Our findings were nothing short of exciting. STT proved highly effective in changing the wood's color, with higher temperatures and longer durations resulting in darker wood. The treated wood exhibited a beautiful, natural, uniform color with a velvety texture. Among the three wood types, Yellow Poplar stood out as the best choice for future applications. Importantly, STT proved super-efficient, delivering consistent results without requiring the extensive experimentation typically associated with traditional methods. 

Our research brings forth an innovative technology that offers an affordable means of enjoying the rich colors of wood products while contributing to the protection of endangered trees and their habitats. This advancement represents a significant step forward in ensuring that the beauty of wood is accessible to all without causing harm to our precious forests and the wildlife that call them home. 

In conclusion, our Surface Thermal Treatment (STT) method represents a groundbreaking solution to the problem of sourcing dark-colored wood sustainably. By transforming lighter woods into the rich, dark hues consumers desire, we are taking a substantial step toward preserving our environment and its endangered species. This innovation ensures that the beauty of wood remains accessible to all without compromising the integrity of our forests. 

About the Authors: 

Jue is a Ph.D. candidate in the Department of Forestry & Natural Resources, under the supervision of Dr. Eva Haviarova. Currently, Jue is studying and working in the Wood Research Laboratory, her research is focusing on adding more value to lower-grade hardwood. Before joining Purdue, Jue obtained her master’s degree from the National Engineering and Technology Research Center of Wood-based Resources Comprehensive Utilization Center in China. She enjoys kayaking and spending time with her family and friends during her free time. 

Dipesh is a Ph.D. candidate in the Department of Electrical and Computer Engineering (ECE) at Purdue University, working under the supervision of Prof. Vaneet Aggarwal. Currently, Dipesh is immersed in diffusion model research for image generation tasks. Before pursuing his doctoral studies at Purdue, Dipesh earned his undergraduate degree in Electrical Engineering from the Indian Institute of Technology Bombay (IITB) in India. His academic journey includes a strong foundation in electrical engineering, and he has now delved into cutting-edge research in Deep Learning/Reinforcement Learning.