Abstract
Poly(lactic acid) (PLA) nanocomposites with antimicrobial fillers have been increasingly explored as food packaging materials that are made of a biobased matrix and can minimize food loss due to spoilage. Some of the most commonly studied fillers are zinc oxide (ZnO), titanium dioxide (TiO2), and silver nanoparticles (AgNPs). In this work, nanocomposites with 1 wt.% of each filler were prepared by melt mixing. An extensive study of thermally stimulated processes such as crystallization, nucleation, degradation, and their kinetics was carried out using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). In detail, non-isothermal cold crystallization studies were performed with DSC and polarized light microscopy (PLM), and kinetics were analyzed with multiple equations. The activation energy of the non-isothermal cold crystallization was calculated with the methods of Kissinger and Friedman. The latter was used to also determine the Hoffman–Lauritzen parameters (Kg and U*) by applying the Vyazovkin method. Additionally, effective activation energy and kinetic parameters of the thermal decomposition process were determined by applying the isoconversional differential method and multivariate non-linear regression method. According to TGA results, metal oxide nanofillers affected the thermal stability of PLA and caused a decrease in the activation energy values. Moreover, the fillers acted as heterogenous nucleating agents, accelerating the non-isothermal crystallization of PLA, thus reducing its activation energy. It can be concluded that metal oxide nanofillers catalytically affect the thermal degradation and crystallization of PLA samples.
Highlights
With the shift of modern society from a linear to a circular economy model, biobased polymers have emerged as alternatives to the common, petroleum-sourced polymers that are an integral part of everyday life
Some of the most common antimicrobial nanofillers are clays as well as metals and metal oxides [13,14], such as Ag nanoparticles (AgNPs), titanium dioxide (TiO2 ), and zinc oxide (ZnO) [15,16,17,18,19]. While their effect on the antimicrobial activity and the mechanical and thermal properties of Poly(lactic acid) (PLA) have been widely explored [17,18,20,21,22,23,24,25], their influence on crystallization and thermal degradation kinetics has been the topic of only a handful of studies [26,27,28,29,30,31]
The kinetic model and the kinetic parameters of the thermal decomposition process were determined by the multivariate non-linear regression method
Summary
With the shift of modern society from a linear to a circular economy model, biobased polymers (i.e., polymers from renewable resources) have emerged as alternatives to the common, petroleum-sourced polymers that are an integral part of everyday life. Some of the most common antimicrobial nanofillers are clays as well as metals and metal oxides [13,14], such as Ag nanoparticles (AgNPs), titanium dioxide (TiO2 ), and zinc oxide (ZnO) [15,16,17,18,19] While their effect on the antimicrobial activity and the mechanical and thermal properties of PLA have been widely explored [17,18,20,21,22,23,24,25], their influence on crystallization and thermal degradation kinetics has been the topic of only a handful of studies [26,27,28,29,30,31]. The kinetic model and the kinetic parameters of the thermal decomposition process were determined by the multivariate non-linear regression method
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