"Sustainable Recycling of Hybrid-Molded Composites" 

Alyson Pickering, MSE PhD Candidate 

Advisor: Professor Jan-Anders Mansson

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ABSTRACT

The growing demand for sustainable materials in the automotive and consumer goods sectors is driven by both environmental concerns and increasingly strict regulatory and corporate sustainability targets. Circular design strategies, including the reuse and recycling of materials, are becoming essential as manufacturers work to reduce life-cycle emissions and material waste. However, integrating high-performance fiber-reinforced composites into closed-loop systems remains challenging due to polymer and fiber degradation that reduces performance and changes the processing of the material. Moreover, using recycled material often yields economic penalties.

This study investigates the manufacturing and recycling of hybrid molded of thermoplastic composites using continuous fiber preforms in combination with short fiber reinforced polymers to address these challenges. Parts were processed through either direct regrinding or repelletization, where some pathways leveraged virgin material addition and others included chopped preform introduced by the recycling of parts with structural preforms produced using the QTC® line.

All molding compounds were successfully injection molded using standard parameters with multiple insert types. Mechanical testing showed that the continuous fiber preform acts a strengthener and improves flexural energy absorption by a factor of 3.5, delaying the onset of catastrophic failure. Recycled compounds maintained flexural strength through three recycling rounds. Incorporating virgin material into the molding compound further stabilized performance while, small concentrations of chopped preform had no adverse impact. However, high concentrations of chopped preform reduced performance across tests, despite improved fiber length averages.

Cost modeling confirmed that recycled configurations provide substantial economic benefits. Using 80 percent recycled content reduced part cost by more than 15 percent. When combined with a continuous fiber preform, this configuration achieved the highest performance per dollar. Although the continuous preform increases material cost, its structural benefits justify the investment in performance-critical applications.