Properties of PLA films with cinnamic acid: Effect of the processing method
Ramón Ordoñez, Lorena Atarés, Amparo Chiralt
Abstract
• PLA films with cinnamic acid (C) were obtained by casting or thermo-processing (TP). • C could be incorporated up to 10% w/w into TP films but only up to 3% in cast films. • Cast films retained solvent and exhibited more plastic behaviour than TP films. • Barrier properties were improved by C incorporation in both cast and TP films. • No significant bacterial growth inhibition was detected due to small release of C. Polylactic acid (PLA) is a sustainable material for food packaging applications. The incorporation of cinnamic acid (CA) into PLA films was studied to obtain antimicrobial films, using two different techniques for film production, namely casting and thermal processing (TP). Whereas CA could be successfully incorporated at 5 and 10% w/w into TP films, only 3% w/w could be used in cast films without observing any crystallisation of CA. The acid reduced the glass transition temperature in TP films, while also improving their thermal resistance. Cast films retained a little proportion of the casting solvent which contributed to their plasticisation. The processing method greatly affected the mechanical properties of the films, with the cast films being significantly more plastic and stretchable. CA reduced the film’s stiffness and resistance to break and improved their water vapour and oxygen barrier capacity. Antibacterial assays with Listeria innocua did not show significant growth inhibition for any film, but the observed inhibition could be related to the acid concentration. This suggested that only a small amount of acid near the film surface could be released. Further research to promote the superficial concentration of cinnamic acid into PLA films is required to obtain active materials.