Website Link (Journal by Velásquez et. al.)
Currently, reducing packaging plastic waste and food losses are concerning topics in the food packaging industry. As an alternative for these challenges, antimicrobial and antioxidant materials have been developed by incorporating active agents (AAs) into biodegradable polymers to extend the food shelf life.
In this context, developing biodegradable active materials based on polylactic acid (PLA) and natural compounds are a great alternative to maintain food safety and non-toxicity of the packaging. AAs, such as essential oils and polyphenols, have been added mainly as antimicrobial and antioxidant natural compounds in PLA packaging. In this review, current techniques used to develop active PLA packaging films were described in order to critically compare their feasibility, advantages, limitations, and relevant processing aspects.
The analysis was focused on the processing conditions, such as operation variables and stages, and factors related to the AAs, such as their concentrations, weight losses during processing, and incorporation technique, among others.
Recent developments of active PLA-based monolayers and bi- or multilayer films were also considered. In addition, patents on inventions and technologies on active PLA-based films for food packaging were reviewed. This review highlights that the selection of the processing technique and conditions to obtain active PLA depends on the type of the AA regarding its volatility, solubility, and thermosensitivity.
CONCLUSION AND PERSPECTIVES
The melting-based processes, such as extrusion and injection molding, are the most attractive methods because these conventional techniques are widely used to produce flexible and semi-rigid food packaging in the plastic industry.
The nature of the AA can determine the selection of the process and operational conditions. Mostly, natural agents as EOs are used due to their biocompatibility and safety, but weight losses of these compounds can occur using melt blending techniques because high temperatures may cause their partial evaporation or thermal degradation.
Therefore, casting, coating, electrospinning, or supercritical impregnation become more convenient processes when using thermosensitive AAs. However, the AA losses occur also during solvent-casting and electrospinning depending on the solvent evaporation rate during processing.
The operating variables are set depending on the nature of the polymers and AAs, as well as additives such as plasticizers or fillers. In all methods, the complete mixing of PLA and the AA is crucial to obtain homogenous materials with adequate properties. Besides, adequate operating temperatures are essential to avoid AA volatilization or degradation.
Single PLA-based bi- and multilayer films have been produced through different processing techniques to improve physical-mechanical properties and reduce active compound losses. Combining polymers and adding nano- or micro-fillers to improve physical-mechanical properties is an attractive alternative considering that AAs can affect PLA mechanical performance.
In the second part of this review, the effect of processing and AAs addition on the physical-mechanical properties, compostability, and the controlled release of AAs from active PLA films was critically reviewed and analyzed.