Session: 03-11-01: Thermoplastic Composites

Paper Number: 138365

138365 - Mechanical Recyling Process of Aerospace-Grade Lm-Paek Thermoplastic Composites 

With the increasing demand for fiber-reinforced composites, the disposal of composite waste has emerged as a significant environmental issue. Consequently, regulations on waste management have been strengthened, leading to a growing emphasis on the recycling of composites. Recently, there has been active research on the recycling of thermoplastic composite materials that are more easily recyclable than thermoset plastics. Thermoplastic composites can be recycled through mechanical, thermal, and chemical methods. Among these, mechanical recycling offers an environmentally friendly approach with low energy consumption, reduced CO2 emissions, and minimal pollutant discharge compared to other methods. The mechanical recycling of conventional fiber-reinforced thermoplastic composites involves crushing the original material and then compressing and molding it. However, due to the stacking of crushed pieces with a constant fiber volume fraction, improving the moldability is challenging. Additionally, the interfaces between crushed pieces with a high resin fraction negatively impact the mechanical properties. In order to overcome these challenges, crushed pieces are often mixed with resin pellets at high temperatures to produce compounds with controlled fiber volume fractions.

In this study, a high-performance thermoplastic composite material, T700/LM-PAEK, was recycled to produce an actual part for an aerospace applicaction through the mechanical recycling process. The recycling process consists of crushing and sieving the original material, producing recycled compounds, and compression molding. Firstly, the T700/LM-PAEK material is crushed using a shredder machine with a 15 mm-size screen and a 14 mm-wide blade at a fixed rotation speed of 600 rpm. The fragmented pieces are sieved using standard sieves of 2.8 mm and 5.6 mm. Three-sizes fragments - pieces that pass through the 2.8mm sieve and pieces that are filtered by the 2.8 mm sieve and by 5.8 mm sieve - are combined in a specific mass ratio to control fiber length distribution. LM-PAEK resin pellets are added to the size-mixed fragments to adjust the fiber volume fraction for better moldability. The mixture of the shredded pieces and LM-PAEK resin is then slowly stirred at temperature higher than the melting point of the resin and produced into recycled compounds. The recycled compounds are transferred to a preheated mold and compressed into the shape of the actual part. After being demolded, the part is cooled at room temperature without applying pressure. Various inspections were performed on the recyced material to evaluate the recycling process.

Acknowledgement: This work was supported by "Overseas order-linked aviation parts industry process technology development in 2019" of the Korea Institute for Advancement of Technology (KIAT) and through the Helicopter Electric Multiple Tail Rotor Technology R&D program (RS-2022-00155776) of the Korea Evaluation Institute of Industrial Technology (KEIT), both granted financial resources from the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea.

Presenting Author: Wooseok Ji Ulsan National Institute of Science and Technology

Presenting Author Biography: Dr. Wooseok Ji is an associate professor in the Department of Mechanical Engineering at Ulsan National Institute of Science and Technology. He received his bachelor' degree from Seoul National University in 1999. After working as a tooling engineer for Korean Air Aerospace Division (currently Korean Air TechCenter) from 1999 to 2003, he pursued a postgraduate diploma and earned MS and PhD degrees in the major of Aerospace Engineering from University of Michigan in 2005 and 2008, respectively. His research efforts are put into the promotion of advanced composites for practical applications based on the fundamental understanding of their mechanics. He is a member of American Institute of Aeronautics and Astronautics (AIAA) and an associate editor of Journal of Reinforced Plastics and Composites and Functional Composites and Structures.