Understanding the Dynamics of Polymer Extrusion: Simulation of Thermoplastics Processing with Planetary Roller Extruders.

Resource efficient processing of polymers is of paramount importance to minimize energy consumption, processing time, and material losses in the polymer industry. This study is concerned with polymer processing in planetary roller extruders. A three-dimensional numerical flow simulation was tailored to understand the polymer flow through the extruder in detail. Using the simulation software ANSYS Polyflow, we quantified both directly measurable process parameters, such as pressure build-up, and more intangible parameters, such as material shear. By varying operational and material parameters in a sensitivity analysis, we showed that the dynamics, material stress and pressure build-up are controlled primarily by the number of spindles and their rotational speed. Notably, this work provides the first successful validation of a 3D simulation of a polymer flow in a planetary roller extruder against actual experimental data. The simulation showed robust agreement between the simulated and experimental values, provided that a critical backpressure length is reached. This computational approach minimizes labor-intensive experimental testing in polymer processing.

Green Processing of Neat Poly(lactic acid) Using Carbon Dioxide under Elevated Pressure for Preparation of Advanced Materials: A Review (2012-2022).

This review provides a concise overview of up-to-date developments in the processing of neat poly(lactic acid) (PLA), improvement in its properties, and preparation of advanced materials using a green medium (CO2 under elevated pressure). Pressurized CO2 in the dense and supercritical state is a superior alternative medium to organic solvents, as it is easily available, fully recyclable, has easily tunable properties, and can be completely removed from the final material without post-processing steps. This review summarizes the state of the art on PLA drying, impregnation, foaming, and particle generation by the employment of dense and supercritical CO2 for the development of new materials. An analysis of the effect of processing methods on the final material properties was focused on neat PLA and PLA with an addition of natural bioactive components. It was demonstrated that CO2-assisted processes enable the control of PLA properties, reduce operating times, and require less energy compared to conventional ones. The described environmentally friendly processing techniques and the versatility of PLA were employed for the preparation of foams, aerogels, scaffolds, microparticles, and nanoparticles, as well as bioactive materials. These PLA-based materials can find application in tissue engineering, drug delivery, active food packaging, compostable packaging, wastewater treatment, or thermal insulation, among others.

Supercritical CO2 - assisted production of PLA and PLGA foams for controlled thymol release.

Amorphous, medical grade poly(d,l-lactic acid) (PLA) and poly(d,l-lactic-co-glycolic acid) (PLGA) were used to develop systems for controlled release of a natural bioactive substance - thymol. Supercritical carbon dioxide (scCO2) was successfully used both as an impregnation medium for thymol incorporation into the polymer matrix and a foaming agent in a single-step batch process. Impregnation of samples using low to moderate scCO2 densities (273 kg/m3 and 630 kg/m3) and short processing times (2 h and 4 h) enabled thymol loading of 0.92%-6.62% and formation of microcellular foams upon system depressurization. Thymol effect on structural and thermal properties on foamed samples was proven by FTIR and DSC. The effect of CO2 under elevated pressure on the neat polymers was analysed by high pressure DSC. Foaming of polymers with lower molecular weight by CO2 of higher density yielded foams with smaller pores. All tested foams released thymol in a controlled manner in phosphate buffered saline (PBS) at 37 °C within 3 to 6 weeks. Higher loading and lower cell density favoured thymol release rate, while its concentration in PBS for the tested period depended on foam interaction with the medium. Representative PLGA foam sample with the highest thymol loading (6.62%) showed controlled thymol release within 72 h in mediums having pH values from 1.1 to 7.4.

Supercritical CO2 impregnation of PLA/PCL films with natural substances for bacterial growth control in food packaging.

Biodegradable polymers with antibacterial properties are highly desirable materials for active food packaging applications. Thymol, a dietary monoterpene phenol with a strong antibacterial activity is abundant in plants belonging to the genus Thymus. This study presents two approaches for supercritical CO2 impregnation of poly(lactic acid)(PLA)/poly(ε-caprolactone)(PCL) blended films to induce antibacterial properties of the material: (i) a batch impregnation process for loading pure thymol, and (ii) an integrated supercritical extraction-impregnation process for isolation of thyme extract and its incorporation into the films, operated in both batch or semi-continuous modes with supercritical solution circulation. The PCL content in films, impregnation time and CO2 flow regime were varied to maximize loading of the films with thymol or thyme extract with preserving films' structure and thermal stability. Representative film samples impregnated with thymol and thyme extract were tested against Gram (-) (Escherichia coli) and Gram(+) (Bacillus subtilis) model strains, by measuring their metabolic activity and re-cultivation after exposure to the films. The film containing thymol (35.8 wt%) showed a strong antibacterial activity leading to a total reduction of bacterial cell viability. Proposed processes enable fast, controlled and organic solvent-free fabrication of the PLA/PCL films containing natural antibacterial substances at moderately low temperature, with a compact structure and a good thermal stability, for potential use as active food packaging materials.