Mechanical, barrier, and photodegradation properties of biodegradable PLA-based blend films

In this work, films based on blends of polylactide (PLA), poly(ε-caprolactone), (PCL), and the compatibilizer ElvaloyPTW were prepared by blown film extrusion; neat PLA was used as a reference material. Adding 30% PCL to PLA resulted in films with decreased modulus, yield strength, and tear resistance. However, when ElvaloyPTW was added to the 70/30 PLA/PCL blend, films featuring high ductility and improved gas barrier properties were achieved. The photodegradation of blown films based on PLA/PCL (100/0/0 and 70/30/0 wt%) and PLA/PCL/c (c = compatibilizer (ElvaloyPTW), 70/30/3 wt%) blends was comprehensively investigated under accelerated conditions using a xenon arc lamp for up to 168 h of UV irradiation. The photo-degraded samples were characterized using gel permeation chromatography (GPC), ¹H-NMR, FTIR-ATR, thermogravimetric analysis (TGA), polarized light optical microscopy (PLOM), and differential scanning calorimetry (DSC). The results indicate that the photodegradation of PLA/PCL/c films proceeds via a bulk erosion mechanism. This suggests that UV penetrates the specimens with no significant reduction in intensity, irrespective of the polymer blends' chemical structure and crystallinity. PLA and PCL chains were susceptible to photodegradation even within the crystalline regions; however, their photodegradability was lower in the crystals than in the amorphous regions. A significant decrease in molecular weight was observed with photodegradation time. The combined results of FTIR and thermal analysis allowed us to establish that the PLA phase in the blends experiences a much faster degradation rate in the presence of PCL and/or PCL/compatibilizer. Finally, the effect of photodegradation increased the crystallization rate of PLA and affected the morphology of PLA spherulites.