Investigations on Primary and Secondary Recycling of PLA and its Composite for Biomedical and Sensing Applications

Polylactic acid (PLA) and PLA-hydroxyapatite (Hap)-chitosan (CS) composite have been extensively used for biomedical applications, and numerous studies were reported on their recycling in the past two decades. But hitherto less has been testified on the effect of primary (1°) and secondary (2°) recycling of PLA and its composite for biomedical and sensing applications. In this study, 1° and 2° recycling of PLA and PLA-Hap-CS composite were performed with twin-screw extrusion (TSE) followed by preparation of feedstock strand for 3D printing. Further rheological, electrical, mechanical, morphological properties and bond characteristics of prepared strands were compared for 1° and 2° recycled PLA and its composite. Results of the study suggest that while 1° recycling of PLA there was a 73.99% increase in flowability (after 1st cycle) whereas in the case of 2° recycling of PLA flowability increase was 125.83%. As regards tensile properties, it was observed that while 1° recycling of PLA (after 1st cycle), there was a reduction of 8.86% in peak strength, whereas, in the case of 2° recycling, 23.25% reduction was noticed. On the other hand, significant improvement in Young’s modulus ( E ) was noticed while 1° and 2° recycling after the 2nd cycle. Further, based on the surface analysis of the prepared feedstock strand, it was observed that the porosity was increased in both 1° and 2° recycling of PLA and its composite. The electrical characteristics reveal that the electric resistance was increased for both 1° and 2° recycling. The study suggests that when the strand prepared by TSE is recycled 2nd time (for both 1° and 2° recycling), it shows better sensing properties for biomedical applications. The results are supported with scanning electron microscopy (SEM), energy-dispersive spectroscopy, Fourier transformed infrared spectroscopy-attenuated total reflectance analysis.