Supercritical carbon dioxide-soluble polyhedral oligomeric silsesquioxane (POSS) nanocages and polymer surface modification

Supercritical processing of CO 2 -philic polyhedral oligomeric silsesquioxane (POSS)-poly( l -lactic acid) composites

“…However, the structure changed due to the POSS agglomerations. These results show that the addition of CO2-philic TFPOSS, which can enrich CO2 at the polymer/TFPOSS interface, can increase the affinity to CO2 and improve the rate of pore nucleation in the polymer [39,40]. The average pore sizes of PLLA-10T and PLLA-30T films were 624nm and 857 nm, respectively.…”

“…For this, the films were processed with two different types of additives. One of them was the TFPOSS, which was shown recently to be significantly scCO2-soluble [40], and the other was OMPOSS, which was found to be insoluble in the supercritical fluid [41]. The scCO2 processing of the films were performed at 20.7 MPa and 313 K for 2 hr, after which the films were vented at a rate of 10.3…”

“…saturation times. According to the solubility data, the solubility of TFPOSS in scCO2 is expected to be greater than 1.6 × 10 -3 by mol fraction at 313 K, 20.7 MPa [40], which would allow its extraction from the polymer films during the supercritical CO2 processing. The extraction of a significant amount of the additives with scCO2 can be beneficial for applications that require higher purities such as biomedical applications.…”

“…In polymer processing with scCO2, such particles can act as heterogeneous nucleating agents, which stimulate higher rate of cell nucleation by decreasing the free energy barrier for nucleation and provide new sites for cell formation [5,38,39]. We used two types of POSS to observe their effects on the formation of pores in PLLA; a CO2-philic type, trifluoropropyl polyhedral oligomeric silsesquioxane (TFPOSS) [40], and a non CO2-philic type, octamethyl polyhedral oligomeric silsesquioxane (OMPOSS) [41]. Even though in literature it was reported that for PLLA with crystallinity greater than 30%, saturation temperatures close to the melting temperature of PLLA were required to obtain a porous structure with scCO2 processing [31,42], our results showed that up to 40% porosity could be obtained in the polymer matrix when a CO2-philic POSS was added into the PLLA with crystallinity greater than 30% and the composite was processed at the scCO2 saturation temperature and pressure of 313 K and 20 MPa, respectively.…”

Supercritical carbon dioxide and polymers: an interplay of science and technology

“…Even more interesting, from a scientific point of view, is the preparation of polymer composites, where scCO 2 can positively influence the dispersion of the filler or even help in exfoliating it (e.g. in the case of clay) . Current and future challenges for polymer functionalization and blending might be envisaged in a better understanding of the functionalization reaction mechanism (compared with the melt one) as well as in the exact influence of scCO 2 on the structure of the inorganic filler.…”