Impact of thermomechanical reprocessing on multilayer plastic packaging blend

Abstract

Multilayer plastic packaging (MPP) has attracted extensive attention due to its functionality and inherent difficulty in reclamation. One primary concern is the performance of reprocessed MPP since it inherently consists of many dissimilar polymers. This study aims to assess the effect of multiple thermomechanical reprocessing cycles on the properties of a MPP blend. Low density polyethylene (LDPE)/maleic anhydride grafted linear LDPE (LLDPE-g-MA)/ethylene vinyl alcohol (EVOH) blend was manufactured and subjected to thermomechanical reprocessing, including thermal compounding, grinding, and injection molding for six cycles to characterize the impact of thermomechanical reprocessing on the blend's mechanical, morphological, thermal, and rheological properties. The tensile strength and modulus of the reprocessed blend remained consistent throughout six cycles. A pronounced decline in elongation at break was observed after four cycles of reprocessing. Toughness, as represented by the essential work of fracture, increased steadily up to three cycles of processing, followed by a decline in the following reprocessing cycles. The main property change is possibly caused by the gelling of the EVOH in the reprocessed blend, as demonstrated by larger EVOH agglomerates in the LDPE matrix. Differential scanning calorimetry results indicated that the degree of crystallization of the EVOH phase changed with increasing reprocessing cycles, suggesting EVOH degradation. Rheological behavior in the linear viscoelastic region indicated enhanced interfacial interaction between LDPE and EVOH due to the cross-linking of LLDPE-g-MA and rigid EVOH in the early reprocessing stages. After four cycles of reprocessing, decreases in storage and loss moduli were observed, indicating the possibility of phase separation caused by gelling of EVOH. Using polymer blending to reclaim LDPE-based EVOH multilayer is promising for up to four cycles of reprocessing as shown by mechanical, thermal, and rheological behaviors.