Abstract
Poly(lactic acid) (PLA), a well-known biodegradable and compostable polymer, was used in this study as a model system to determine if the addition of nanoclays affects its biodegradation in simulated composting conditions and whether the nanoclays impact the microbial population in a compost environment. Three different nanoclays were studied due to their different surface characteristics but similar chemistry: organo-modified montmorillonite (OMMT), Halloysite nanotubes (HNT), and Laponite® RD (LRD). Additionally, the organo-modifier of MMT, methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium (QAC), was studied. PLA and PLA bio-nanocomposite (BNC) films were produced, characterized, and used for biodegradation evaluation with an in-house built direct measurement respirometer (DMR) following the analysis of evolved CO2 approach. A biofilm formation essay and scanning electron microscopy were used to evaluate microbial attachment on the surface of PLA and BNCs. The results obtained from four different biodegradation tests with PLA and its BNCs showed a significantly higher mineralization of the films containing nanoclay in comparison to the pristine PLA during the first three to four weeks of testing, mainly attributed to the reduction in the PLA lag time. The effect of the nanoclays on the initial molecular weight during processing played a crucial role in the evolution of CO2. PLA-LRD5 had the greatest microbial attachment on the surface as confirmed by the biofilm test and the SEM micrographs, while PLA-QAC0.4 had the lowest biofilm formation that may be attributed to the inhibitory effect also found during the biodegradation test when the QAC was tested by itself.
Highlights
Biodegradable polymers like poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate)(PBAT), and thermoplastic starch (TPS), have great potential to replace fossil-based polymers, avoid landfill disposal of most non-recyclable polymers, and help reduce environmental impacts
The effect of the nanoclays on the initial molecular weight during processing played a crucial role in the biodegradation studies, since a lower Mn0 (≤60 kDa) seems to be correlated to the priming effect in compost
When the different nanoclays and surfactant were tested alone, it was observed that Halloysite nanotubes (HNT), organo-modified montmorillonite (OMMT), and QAC showed some inhibition regardless of the amount introduced in the bioreactors
Summary
(PBAT), and thermoplastic starch (TPS), have great potential to replace fossil-based polymers, avoid landfill disposal of most non-recyclable polymers, and help reduce environmental impacts. These materials have some properties and processing shortcomings that have limited their use in many applications, for example, brittleness, water sensitivity, low heat distortion temperature, medium to high gas permeability, and low melt viscosity [1,2]. The dispersion of hydrophilic nanofillers in a polymer matrix is challenging
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