Mechanical recycling of PLA: Effect of weathering, extrusion cycles, and chain extender

Abstract

This work evaluated the reprocessing of PLA with a high melt flow index (MFI). PLA samples were prepared by extrusion using a chain extender (Joncryl ADR‐4368) and subjected to two additional extrusion cycles with or without exposure to accelerated weathering. The results showed drastic affectations of PLA properties by weathering. The MFI increased from 65 to 137 g/10 min by reprocessing, while reprocessed and weathered samples reached a MFI of 417 g/10 min after three extrusion cycles. The addition of Joncryl prevented PLA degradation (MFI of 170 g/10 min after three extrusion cycles, even when weathering was performed). Additionally, the tensile strengths of weathered samples were substantially decreased (67%) compared to only reprocessed samples (14%). In this sense, PLA mechanical recycling is a good alternative if it is not exposed to harsh weathering conditions, in which case a chain extender is needed to get reasonable properties. Otherwise, reprocessing accelerated the composting of PLA, and the chain extender addition did not limit it.

Recycled PLA for 3D Printing: A Comparison of Recycled PLA Filaments from Waste of Different Origins after Repeated Cycles of Extrusion

“…The elongation at break ( ε) progressively decreased down from initial values (ε 1PLAC = 4.08 ± 0.60 and ε 1PLAM = 3.50 ± 0.90) to (ε 5PLAC = 3.31 ± 1.18 and ε 4PLAM = 2.06 ± 0.20). In any case, these low values are characteristic for brittle materials [80].…”

“…A reduction in each recycling process was observed for the PLA-C series (Table 3), representing in total a percentage reduction of around 26% at the fifth reprocessing cycle (without considering standard deviations); on the other hand, tensile strength for PLA-M, kept constant until the third extrusion cycle. The elongation at break (𝜀) progressively decreased down from initial values ( 𝜀 = 4.08 ± 0.60 and 𝜀 = 3.50 ± 0.90) to ( 𝜀 = 3.31 ± 1.18 and 𝜀 = 2.06 ± 0.20).In any case, these low values are characteristic for brittle materials[80].The decrease of tensile strength might be attributed to a lower cohesion in the materials, according to Pillin et al[81], while the progressive diminution of elongation at break was explained by the simultaneous decrease of the molecular weight and the increase of crystallinity, favouring crack propagation.…”

Depolymerization within a Circular Plastics System

“…Therefore, the main potential recycling routes for PLA are mechanical or chemical. PLA is mechanically recyclable, however, low thermal and hydrolytic stability mean significant property deterioration occurs after even one recycle …”

“…PLA is mechanically recyclable, however, low thermal and hydrolytic stability mean significant property deterioration occurs after even one recycle. 252 Reported PLA depolymerization methods include hydrolysis and aminolysis. PLA is not water-soluble, and addition of organic cosolvents can be beneficial.…”

Carbon Recycling of High Value Bioplastics: A Route to a Zero-Waste Future

“…Above 55–60 °C, the material becomes “sticky”, making it difficult to extrude into new filament [ 168 ]. Similarly, reprocessing can more than double the melt flow index [ 173 ], which may subsequently hinder the manufacture of secondary products. To mitigate against the decrease in tensile strength due to molecular weight reduction, it is possible to add chain extenders.…”