The high brittleness of Poly(lactic acid) is a major drawback for flexible food packaging applications. The aim of this work is to evaluate the potential use of commercial adipates as PLA plasticizers to obtain transparent films with enhanced mechanical properties. Processing conditions were optimized. The effect of plasticizers was characterized by a decrease on the glass transition temperature and an increase in PLA chains mobility, which induced crystallization on heating. Thermal stability was not significantly affected, and mechanical properties showed an increase in ductility with the plasticizer content. Oxygen transmission rate was also measured to evaluate the effect of the microstructures generated by the presence of these additives in PLA-based films. The monomeric adipate presented lack of homogeneity that makes films plasticized with this additive not useful for the intended application. Good compatibility was observed between polyadipates (up to 20 wt %) and the matrix, making them promising materials for biodegradable films manufacturing. V
This work describes the generation of novel PHAs (named PHACOS) with a new monomer composition containing thioester groups in the side chain, which confers new properties and made them suitable for chemical modifications after their biosynthesis. We have analyzed the PHACOS production abilities of the wild-type strain Pseudomonas putida KT2442 vs. its derived strain P. putida KT42FadB, mutated in the fadB gene from the central metabolic β-oxidation pathway involved in the synthesis of medium-chain-length PHA (mcl-PHA). Different fermentation strategies based on one- or two-stage cultures have been tested resulting in PHACOS with different monomer composition. Using decanoic acid as inducer of the growth and polymer synthesis and 6-acetylthiohexanoic acid as PHA precursor in a two-stage strategy, the maximum yield was obtained by culturing the strain KT42FadB. Nuclear magnetic resonance and gas chromatography coupled to mass spectrometry showed that polymers obtained from the wild-type and KT42FadB strains, included 6-acetylthio-3-hydroxyhexanoic acid (OH-6ATH) and the shorter derivative 4-acetylthio-3-hydroxybutanoic acid (OH-4ATB) in their composition, although in different ratios. While the polymer obtained from KT42FadB strain contained mainly OH-6ATH monomer units, mcl-PHA produced by the wild-type strain contained OH-6ATH and OH-4ATB. Furthermore, polyesters showed differences in the OH-alkyl derivates moiety. The strain KT42FadB overproduced PHACOS when compared to the production rate of the control strain in one- and two-stage cultures. Thermal properties obtained by differential scanning calorimetry indicated that both polymers have different glass transition temperatures related to their composition.
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