# Enhancing the Ultrasonic Welding of Wood Using 3D Printed Lignin Energy Directors

## TL;DR

This paper introduces a sustainable method to improve ultrasonic wood welding using 3D printed lignin, resulting in stronger and more durable wood joints.

## Contribution

The novel use of lignin-based energy directors enhances ultrasonic welding of wood, enabling strong and multifunctional joints.

## Key findings

- Lignin-based energy directors significantly improve lap shear strength and wet durability of wood joints.
- The method achieves performance comparable to traditional adhesives while being eco-friendly.
- The joints show conductivity, enabling potential for strain sensing and multifunctional applications.

## Abstract

Ultrasonic wood welding is an ecofriendly method for rapidly joining wooden components in less than 2 s. However, this dynamic process results in low mechanical performance and poor durability under wet conditions. Inspired by natural wood's robust interlocking cellular structure, which leverages lignin fusion to enhance structural integrity, lignin fusion at wood interfaces is optimized, significantly improving lap shear strength and wet durability. These results demonstrate that enhanced lignin fusion at interfaces is crucial for obtaining strong wood joints by positioning lignin as a sustainable energy concentrator, promoting greener manufacturing of sustainable structures into complex shapes. The joints exhibit lap shear strengths and wet durability comparable to those achieved with water‐based wood and epoxy adhesives, while also demonstrating conductivity which could be leveraged for multifunctional features such as strain sensing. The approach can be extended to other manufacturing methods, such as hot‐pressing and continuous robotic manufacturing, emphasizing its potential for scalability and broad industrial adoption.

Sustainable manufacturing for lightweight structures using ecofriendly materials will be key to reducing material consumption and lowering carbon footprints. Here, an approach is presented to weld wood using ultrasonic vibrations with material at the joint interface to direct energy. Energy directors are produced from fully biobased constituents that can be augmented with multifunctional features such as sensing to result in smart sustainable structural joints.