Suchergebnisse

Polylactic acid (PLA) may be regarded as an analogue of a poly-alanine oligo/polypeptide, where the amino group has been replaced by a hydroxyl. As a consequence, a series of studies have explored the possibility that PLA can adopt peptide-type secondary structures – i.e., repetitive structural patterns characterized by intramolecular hydrogen bonds between neighboring functional groups. To this end, computational techniques (molecular mechanics, semiempirical, Hartree-Fock, density functional theory DFT) geometry optimizations of isolated oligomers of lactic acid (generally ten-unit oligomers), or oligomers attached to solid surfaces, or dimers have been reported, as well as spectral simulations thereof - looking at relative stabilities of helices (α, π, 310), and β sheets. A significant variation in the predicted structures and spectra was noted, depending on the computational method employed. With the most accurate method available (a DFT functional parametrized especially for describing non-covalent interactions), in isolated PLA models the π helix was found to be the most likely structure, closely followed by the 310 helix, and β sheets being the least stable. We review here these data and add two important elements: (1) first, a comparison with an experimentally-derived model of PLA, proposed by De Santis, and (2) second, a Ramachandran analysis of the Φ and Ψ angles in the optimized geometries. It is shown that (1) the De Santis structure is in fact slightly more stable than the helices, and (2) the optimized geometries in fact stray far from the initial Φ, Ψ values – to the extent that all of the peptide-like secondary structures in fact end up as turns (mostly type III β turns), while the DFT-optimized De Santis structure has no classical correspondent in the Ramachandran series of secondary structures.

Polylactic Acid (PLA) comes from renewable resources, has a reasonable biodegradability rate, and is used in biomedical, food packaging, textiles, and agricultural applications. PLA offers high mechanical strength and the ability to compost, similar to polyethylene terephthalate (PET) and nylon. However, the brittleness of PLA has always limited its usage. Therefore, bio-based plasticizers in the biopolymer matrices can increase flexibility (elasticity), durability, and workability. This study aims to determine the optimal blending ratio for the PLA blended with epoxidized waste cooking oil (EWCO) to enhance the mechanical and thermal properties of PLA/EWCO. The mechanical strength test consists of the hardness test (N/mm²), flexural strength (MPa), and impact energy (kJ/m) adopted to evaluate the plasticizing characteristics. The thermal stability analysis involves glass transition temperature (T_g) (°C), cold-crystallization temperature (T_cc) (°C) and melting temperature (T_m) (°C). The blending ratio is 97.5PLA/2.5EWCO, 95PLA/5EWCO, 92.5PLA/7.5EWCO and 90PLA/10EWCO. As a result, 97.5:2.5 of PLA/EWCO reduces intermolecular interactions by stimulating more free volume in biopolymer chains' mobility and enhancing the flexibility and elasticity of the PLA blends. Ultimately, the brittleness of PLA decreased with increasing EWCO bio-based plasticizer.

In tissue engineering applications, the use of natural compounds without undesired side effects is highly preferred compared to chemical drugs. Flavonoids, polyphenolic compounds distributed widely in plant-based foods, exert diverse biological effects in cultured cells and in vivo. Flavonoids exhibit anti-inflammatory, antioxidant, anti-mutagenic, anti-cancerous, antiproliferative, and proapoptotic activities, enzyme modulating activities with minimal toxicity issues. Naringenin (4′,5,7-trihydroxyflavanone) (NAR) is a flavonoid belonging to the class flavanone, predominantly found in grape fruit, bitter orange, and other citrus fruits. It has very prominent pharmacological actions like antitumor, vasoprotective, antihypertension, antiviral, and dantishockactions. As NAR can scavenge reactive oxygen species, its use in wound dressing studies is increasing. In recent years, many studies have been carried out to produce nanofibrous materials by the electrospinning method. Electrospun nanofibers have very large surface areas, controllable pore sizes, and tunable drug release profiles. Several biocompatible polymers with excellent biocompatibility and biodegradability including polylactic acid (PLA) have been widely used for the synthesis of nanofibers using the electrospun technique. In this study, nanofibers were obtained by adding NAR at different concentrations into PLA by electrospinning technique. Morphological (Scanning electron microscopy, SEM), molecular interaction (Fourier transform infrared spectroscopy, FT-IR), thermal analysis (Differential scanning calorimetry, DSC), antioxidant activity, and physical analysis were carried out after the production process. Meanwhile, the PLA nanofibers showed the largest swelling value of 220% after immersion in phosphate buffer saline (PBS) solution for 10 days. Overall, this study demonstrates that our PLA/NAR nanofiber mats are attractive candidates for wound dressing material research and application.

Floreon technology, redefining polylactic acid
Dr Andrew Gill, CTO, and Dr Sandrine Garnier, CEO of Floreon Technology Ltd., explain how the company is redefining Polylactic Acid, starting with who they are and what they offer. Floreon Technology is an innovative company that emerged from a successful KTP (Knowledge Transfer Partnership) with the University of Sheffield in the UK. Floreon's technical team has developed expertise in using Polylactic Acid (PLA) to produce a highly robust line of biopolymers for engineering purposes.

This work reports on the design and development of nanocomposites based on a polymeric matrix containing biodegradable Polylactic Acid (PLA) and Polyhydroxyalkanoate (PHA) coated with either Graphite NanoPlatelets (GNP) or silver nanoparticles (AgNP). Nanocomposites were obtained by mechanical mixing under mild conditions and low load contents ( <10 wt %). This favours physical adhesion of the additives onto the polymer surface, while the polymeric bulk matrix remains unaffected. Nanocomposite characterisation was performed via optical and focused ion beam microscopy, proving these nanocomposites are selectively modified only on the surface, leaving bulk polymer unaffected. Processability of these materials was proven by the fabrication of samples via injection moulding and mechanical characterisation. Nanocomposites showed enhanced Young modulus and yield strength, as well as better thermal properties when compared with the unmodified polymer. In the case of AgNP coated nanocomposites, the surface was found to be optically active, as observed in the increase of the resolution of Raman spectra, acquired at least 10 times, proving these nanocomposites are promising candidates as surface enhanced Raman spectroscopy (SERS) substrates. ; Ministerio de Economía y Competitividad TEC2017-86102-C2-2R ; Junta de Andalucía ; European Union

Biodegradable and biocompatible polymers represent an excellent alternative to conventional polymers for various applications. One of the most promising biopolymers is represented by polylactic acid (PLA). During injection molding process, the cooling stage has a great importance because it ensures the dimensional stability of the produced articles. In this simulation study regarding the cooling process in the injection molding of PLA, with cold water, it was analyzed the temperature distribution in the mold-material system in the case of a polymeric plate and the cooling time was calculated. The model of heat transfer was solved in COMSOL Multiphysics software, by defining the geometry of the mold, the materials properties and the cooling conditions.

In the present work, a functionalization of polylactic acid (PLA) has been carried out to anchor maleic anhydride onto the main polymer chain to promote improvement in the compatibility of this polymer matrix with cellulose fibres. Low-molecular-weight PLA has been reacted with maleic anhydride following different procedures: a bulk reaction in an internal mixer and a solution reaction. The presence of oxygen during bulk processing did not allow for functionalization, guiding the reaction towards a decrease in the molecular weight of the material. On the contrary, a controlled reaction under an inert atmosphere in the presence of dioxane as the solvent, at reflux temperature, led to the functionalization of the polymer reaching different yields depending on the percentage of radical initiator and maleic anhydride added and reaction time. The yield of functionalization has been monitored by acid number titration as well as 1H NMR, with optimal yield values of functionalization being up to 3.5%. The PLA-functionalized formula has been used to make commercial PLA compatible with cellulose fibres derived from a thermomechanical treatment. The addition of 10% w/w of fibres to PLA increases the ultimate tensile strength (UTS) of PLA by up to 15%. The incorporation of 4 w/w of the already-functionalized coupling agent to the composite produces improvements in UTS of up to 24% regarding PLA, which confirms the functionalization from a performance point of view ; This research was funded by Spanish government MINECO in the framework of project MAT2017-83347-R

Efforts to replace petroleum-based polymers with environmental-friendly biopolymers have been intensified during recent years. Presently, polylactic acid (PLA) is one of the most developed biopolymers and chitin nanocrystals (ChNCs), a nano-reinforcement extracted from chitin in crustacean waste, can provide enhanced structural, barrier and bioactive properties to PLA. Hence, the PLA/ChNC combination is promising to produce nanocomposite films for sustainable packaging applications. In this work, PLA/ChNC nanocomposites wereprepared by a novel liquid-assisted extrusion method. To improve the compatibility between ChNCs and PLA matrix, triethyl citrate (TEC), a bio-based plasticizer, was added to the nanocomposites with different concentrations (7.5%-15%). The main objective here is to identify the minimum amount of TEC needed to improve the ChNC dispersion and toughness of the nanocomposites. The plasticized PLA/ChNC nanocomposites were investigated by microcopy techniques to determine the dispersion of ChNCs in PLA. Moreover, their transparency, mechanical performance and thermal behaviors were characterized. All results reveal that TEC plays an important role as a dispersant in the processing of PLA/ChNC nanocomposites and significant toughening effect was obtained when the TEC concentration exceeds 12.5 wt%. This project is funded by the Bio-Based Industries Joint Undertaking under the European Union's Horizon 2020 (Grant No. 792261).