Isothermal Crystallization and Melting Behavior of Composites Composed of Poly(L-lactic Acid) and Poly(glycolic Acid) Fibers

Estimating the Relative Crystallinity of Biodegradable Polylactic Acid and Polyglycolide Polymer Composites by Machine Learning Methodologies

Biodegradable polymers have recently found significant applications in pharmaceutics processing and drug release/delivery. Composites based on poly (L-lactic acid) (PLLA) have been suggested to enhance the crystallization rate and relative crystallinity of pure PLLA polymers. Despite the large amount of experimental research that has taken place to date, the theoretical aspects of relative crystallinity have not been comprehensively investigated. Therefore, this research uses machine learning methods to estimate the relative crystallinity of biodegradable PLLA/PGA (polyglycolide) composites. Six different artificial intelligent classes were employed to estimate the relative crystallinity of PLLA/PGA polymer composites as a function of crystallization time, temperature, and PGA content. Cumulatively, 1510 machine learning topologies, including 200 multilayer perceptron neural networks, 200 cascade feedforward neural networks (CFFNN), 160 recurrent neural networks, 800 adaptive neuro-fuzzy inference systems, and 150 least-squares support vector regressions, were developed, and their prediction accuracy compared. The modeling results show that a single hidden layer CFFNN with 9 neurons is the most accurate method for estimating 431 experimentally measured datasets. This model predicts an experimental database with an average absolute percentage difference of 8.84%, root mean squared errors of 4.67%, and correlation coefficient (R²) of 0.999008. The modeling results and relevancy studies show that relative crystallinity increases based on the PGA content and crystallization time. Furthermore, the effect of temperature on relative crystallinity is too complex to be easily explained.

PLGA Barrier Materials from CO2. The influence of Lactide Co-monomer on Glycolic Acid Polyesters

The combination of the predicted polymer market growth and the emergence of renewable feedstocks creates a fantastic opportunity for sustainable polymers. To replace fossil-based feedstock, there are only three alternative sustainable carbon sources: biomass, CO₂, and existing plastics (via mechanical and/or chemical recycling). The ultimate circular feedstock would be CO₂: it can be electrochemically reduced to formic acid derivatives that subsequently can be converted into useful monomers such as glycolic acid. This work is part of the European Horizon 2020 project "Ocean" in which the steps from CO₂ to glycolic acid are developed. Polyglycolic acid (PGA) and poly(lactide-co-glycolide) (PLGA) copolyesters with high lactic acid (LA) content are well-known. PGA is very difficult to handle due to its high crystallinity. On the other hand, PLGAs with high LA content lack good oxygen and moisture barriers. The aim of this work is to understand the structure-property relationships for the mostly unexplored glycolic acid rich PLGA copolymer series and to assess their suitability as barrier materials. Thus, PLGA copolymers with between 50 and 91 mol % glycolic acid were synthesized and their properties were evaluated. Increased thermal stability was observed with increasing glycolic acid content. Only those containing 87 and 91 mol % glycolic acid were semicrystalline. A crystallization study under non-isothermal conditions revealed that copolymerization reduces the crystallization rate for PLGA compared to polylactic acid (PLA) and PGA. While PGA homopolymer crystallizes completely when cooled at 10 °C·min^-1, the copolymers with 9 and 13% lactic acid show almost 10 times slower crystallization, which is a huge advantage vis-à-vis PGA for processing. The kinetics of this process, modeled with the Jeziorny-modified Avrami method, confirmed those observations. Barrier property assessment revealed great potential for these copolymers for application in barrier films. Increasing glycolic acid content in PLGA copolymers enhances the barrier to both oxygen and water vapor. At room temperature and a relative humidity below 70% the PLGA copolymers with high glycolic acid content outperform the barrier properties of polyethylene terephthalate.