The potential of supercritical (SC) CO2 as solvent or plasticizer for the processing of polymeric materials is reviewed in this study. The results suggest that SC CO2 due to its excellent properties, good solubility and plasticizing effect in polymers can be successfully used in processing biomaterials.
Poly(ε-caprolactone) is used for biomedical applications due to its biocompatibility and biodegradability. Its processing with supercritical carbon dioxide represents a sustainable alternative to the classical methods involving toxic and environmentally hazardous organic solvents. In the presentwork, the behavior of poly(ε-caprolactone) in the presence of supercritical CO2 has been studied. The influence of CO2 on the melting point and crystallinity content of the polymer was analyzed, the solubility and diffusivity of gas into poly(ε-caprolactone) was measured, and the experimental data were correlated using Sanchez-Lacombe equation of state and PC SAFT model. Supercritical CO2 was then used for foaming poly(ε-caprolactone) to obtain tissue engineering scaffolds, and the connection between process parameters (temperature, pressure), gas solubility in the polymer, and foam morphology was studied.
Aerogels of natural polysaccharides possess both biocharacteristics of polysaccharides, such as good biological compatibility and cell or enzyme-controlled degradability, and aerogel characteristics, such as very high porosity and specific surface areas that makes them highly attractive in drug delivery. Biodegradable alginate aerogels were synthesized via a sol-gel process. In the present work two methods of ionic cross-linking were used to prepare alginate hydrogels as monoliths and spheres, which can be further easily converted to high surface area aerogels. The aerogels obtained were further used as drug carriers. We investigated the effect of process parameters, such as starting concentration and viscosity of alginate solution, on synthesis products and on model drug (nicotinic acid) release. The results indicate that by using the internal setting cross-linking method for obtaining monolithic aerogels nicotinic acid was released in a more controlled manner. The aerogels thus obtained also exhibited smaller volume shrinkage than the ones described in other publications. However, with increasing alginate concentration in both types of synthesis more compact and cross-linked aerogels were formed.
The aim of this work was to investigate the properties of polyethylenes (PE) of various densities (low-density and high-density) under pressure of CO2 and propane. The phase equilibria of PE of different density in presence of CO2 and in presence of propane in dependence of pressure and temperature were investigated. The phase transitions of PE at atmospheric pressure were determined by differential scanning calorimetry (DSC). Furthermore, phase transitions of polymers under pressure of gases were measured by using an optical high pressure cell. Measurements of phase transition were performed in range of pressure of 1–90 MPa. The results show that melting points of LDPE decreased in presence of CO2 and in presence of propane. For high-density polyethylene (HDPE) the melting point decrease was observed only in presence of propane, while in presence of CO2 melting point increases with increasing pressure. The melting points of LDPE and HDPE decrease in average for 10–20 K in presence of propane, while in presence of CO2 the melting point decrease for both LDPE was lower (5–10 K). Solubility and diffusivity of supercritical CO2 in two low-density polyethylenes (LDPE) and in high-density polyethylene (HDPE) were measured at temperature 373 K and pressures up to 30 MPa using a magnetic suspension balance (MSB). The solubility data were used for estimating the binary diffusion coefficients. The solubilities increased with increasing density. The diffusion coefficient shows strong CO2 density and CO2 solubility dependence. Diffusion coefficient starts to decrease with increasing density and solubility of CO2.
The Sanchez-Lacombe equation of state and the Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the polyethylene glycol-CO2 systems. The Aspen Plus software was used and polyethylene glycol with various molecular weights was investigated. The results were compared with previously obtained experimental values for solubility. The phase equilibrium was calculated at a temperature of 343 K, in the pressure range of 10-30 MPa and for polyethylene glycol molecular weights from 1000 to 100,000 g/mol. The binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both models are reliable in describing the phase equilibrium of the polyethylene glycol-CO2 systems at the proposed conditions. Moreover, the molecular weight of the polymer affects the behaviour of the system, as observed from the variation of solubility values and of binary interaction coefficients.