Technical development and application of supercritical CO2 foaming technology in PCL foam production

Polycaprolactone (PCL) has the advantages of good biocompatibility, appropriate biodegradability, non-toxicity, flexibility, and processability. As a result, PCL-based foams can successfully work in bone tissue engineering, medical patches, drug delivery, reinforcing materials, and other applications. A promising technology for producing PCL foam products is supercritical CO2 (ScCO2) foaming technology, which avoids using organic solvents, is green, and has low foaming agent costs. However, due to the limitations of ScCO2 foaming technology, it is no longer possible to use this technology alone to meet current production requirements. Therefore, ScCO2 foaming technology must combine with other technologies to develop PCL foam products with better performance and matching requirements. This paper systematically reviews the technological development of ScCO2 foaming in producing PCL foams. The molding process of ScCO2 foaming and the conventional preparation process of PCL foam products are discussed comprehensively, including the preparation process, advantages, and disadvantages, challenges faced, etc. Six combined technologies for ScCO2 foaming in the production of PCL foams and the applications of PCL foams are presented. Finally, the future remaining research for producing PCL foams by ScCO2 foaming is analyzed.

Fabrication of a PVDF membrane with tailored morphology and properties via exploring and computing its ternary phase diagram for wastewater treatment and gas separation applications

We report a simple approach for tailoring the morphology of poly(vinylidene fluoride) (PVDF) membranes fabricated using a nonsolvent induced phase separation (NIPS) method that sustains both the hydrophilic and hydrophobic properties. Various membrane structures, i.e. skin layers and whole membrane structures as well, were obtained via an experimental method based on the obtained and computed ternary phase diagram. The nonsolvent interactions with polymer solution resulted in the different forms and properties of a surface layer of fabricated membranes that affected the overall transport of solvent and nonsolvent molecules inside and outside the bulk of the fabricated membranes. The resulting morphology and properties were confirmed using the 3D optical profiler, SEM, FT-IR and XRD methods. The effect of binary interaction parameters on the morphology of the fabricated membranes and on their separation performance was tested using water/oil mixture and gas separation. Both hydrophobic and hydrophilic properties of PVDF showed the excellent durable separation performance of the prepared membranes with 92% of oil separation and the maximum flux of 395 L h^-1 m^-2 along with 120 min of long-term stability. CO₂ separation from H₂, N₂, CH₄ and SF₆ gases was performed to further support the effect of tuned PVDF membranes with different micro/nanostructured morphologies. The gas performance demonstrated ultrahigh permeability and a several-fold greater than the Knudsen separation factor. The results demonstrate a facile and inexpensive approach can be successfully applied for the tailoring of the PVDF membranes to predict and design the resulting membrane structure.

Unique Ivy-Like Morphology Composed of Poly(lactic acid) and Bacterial Cellulose Cryogel

This study examines the unique morphology and properties of enhanced poly(l-lactic acid) (PLLA) monoliths having a bacterial cellulose (BC) framework. Open-porous BC/PLLA monoliths were successfully prepared using thermally induced phase separation (TIPS) and a freeze-drying technique. The BC/PLLA monoliths exhibited a unique ivy-like structure composed of leaf-like PLLA units and a BC fiber network. We demonstrated for the first time that the interpenetrating BC fiber gives PLLA monoliths four times higher compressive strength than the pristine PLLA. Scanning electron microscopy observation and the N₂ adsorption test revealed that the size of PLLA units and the surface area of the monoliths can be manipulated by varying the starting PLLA concentration during the TIPS process. Moreover, the hydrophilicity of the PLLA monoliths was easily controlled by incorporating BC; the neat PLLA monoliths showed a high static water contact angle of as high as 128.8 ± 1.1°, whereas the BC/PLLA monoliths exhibited a much lower contact angle (102.1 ± 1.7°) and greater absorbability to water.