Process-Induced Aging of Poly(lactic acid) in Additive Manufacturing Using Fused Granular Fabrication

Abstract

This study systematically evaluates the recyclability of poly(lactic acid) (PLA) in additive manufacturing via granule-based material extrusion. The objective is to define acceptance ranges and practical guidelines for regranulation, enabling higher secondary material shares and technically robust, industry-ready recycling pathways. PLA is processed through up to five mechanical recycling cycles, with standardized specimens produced under defined and consistent process parameters at each stage. Material characterization is performed using tensile testing (DIN EN ISO 527-1), three-point bending tests (DIN EN ISO 178), and oscillatory shear rheology to assess melt flow behavior and material degradation. Reprocessing recycled PLA via Fused Granular Fabrication (FGF) affects both processability and final part properties. The complex viscosity decreases by approximately 40% after five recycling cycles, indicating processing-induced material aging. Mechanical  properties exhibit reductions of 10–40%, depending on the parameter considered, while Young's modulus and flexural modulus show only minor variations. Overall, recycled PLA can be reprocessed up to five times via FGF, demonstrating its potential for industrial-scale applications.