Potential of Lauryl Gallate as Stability and Recyclability Improver of Poly (Butylene succinate-co-adipate)

Abstract

In the present study, Lauryl Gallate (LG), a natural antioxidant, was used to improve polymer thermal stability and recyclability of a biodegradable polyester as poly(butylene succinate-co-adipate) (PBSA). Neat PBSA and PBSA/LG (0.5 wt% LG) blends were processed by melt extrusion and subjected to multiple consecutive extrusion cycles at 170 °C to prevent the occurrence of thermo-oxidative radical degradation processes of the polymer. Thermal, rheological, morphological, FTIR, and GPC analyses showed the beneficial effect of LG in delaying PBSA thermo-oxidative degradation, reducing polymer fragmentation at low-mid molecular weights compared to the reprocessed virgin PBSA. The use of LG limits the drop of both complex viscosity η* and zero-shear stress viscosity η0 as well as the reduction of crystallinity degree and the enhancement of melt flow rate (MFR). This molecular degradation produces low molecular weight polymer fractions and oligomers that solely affect molten PBSA fluidity. In the presence of 0.5 wt% of LG, the processability of PBSA doubles from six (neat PBSA) up to twelve extrusions until presenting the first signs of degradation of the molten polymer while preserving the mechanical characteristics at the solid state. These mechanical properties remain equivalent to the neat PBSA (Young’s modulus 0.33 GPa, yield strength 19.2 MPa, stress at break 24.4 MPa, and elongation at break 350%). Consequently, LG can be successfully employed as a natural PBSA stabilizer to extend the polymer lifecycle and contribute to the circular economy practice within the processing and manufacturing industry, particularly in the field of PBSA agricultural applications and injection moulded disposable products.