Search Results (140)

This study proposes a continuous preparation strategy for poly (l-lactic acid) (PLLA) scaffolds with oriented hierarchical microporous structures for bone repair. A PLLA-oriented multi-stage microporous bone repair scaffold (hereafter referred to as the oriented multi-stage microporous scaffold) was designed using a novel extrusion foaming technology that integrates fused deposition modeling (FDM) 3D printing with supercritical carbon dioxide (SC-CO₂) microcellular foaming technology. The influence of the 3D-printed structure on the microcellular morphology of the oriented multi-stage microporous scaffold was investigated and optimized. The combination of FDM and SC-CO₂ foaming technology enables a continuous extrusion foaming process for preparing oriented multi-stage microporous scaffolds. The mechanical strength of the scaffold reached 15.27 MPa, meeting the requirements for bone repair in a low-load environment. Notably, the formation of open pores on the surface of the oriented multi-stage microporous scaffold positively affected cell proliferation, differentiation, and activity, as well as the expression of anti-inflammatory and pro-inflammatory factors. In vitro cell experiments (such as CCK-8) showed that the cell proliferation rate in the oriented multi-stage microporous scaffold reached 100–300% after many days of cultivation. This work provides a strategy for the design and manufacture of PLLA scaffolds with hierarchical microcellular structures and biocompatibility for bone repair. Full article

Lorentz invariance is such a basic principle in fundamental physics that it must be constantly tested and any proposal of its violation and breakdown of CPT symmetry that might characterize some approaches to quantum gravity should be treated with care. In this review, we examine, among other scenarios, such instances in supercritical (Liouville) string theory, particularly in some brane models for “quantum foam”. Using the phenomenological formalism introduced here, we analyze the observational hints of Lorentz violation in time-of-flight lags of cosmic photons and neutrinos which fit excellently stringy space–time foam scenarios. We further demonstrate how stringent constraints from other astrophysical data, including the recent first detections of multi-TeV events in $\gamma$-ray burst 221009A and PeV cosmic photons by the Large High Altitude Air Shower Observatory (LHAASO), are satisfied in this context. Such models thus provide a unified framework for all currently observed phenomenologies of space–time symmetry breaking at Planckian scales. Full article

This study explored the innovative foaming behavior of a novel biodegradable polymer blend consisting of polylactic acid/poly(butylene succinate)/poly(butylene adipate-co-terephthalate) (PLA/PBS/PBAT) enhanced with nanohydroxyapatite (nHA), using supercritical carbon dioxide (SCCO₂) as an environmentally friendly physical foaming agent. The aim was to investigate the effects of various foaming strategies on the resulting cell structure, aiming for potential applications in tissue engineering. Eight foaming strategies were examined, starting with a basic saturation process at high temperature and pressure, followed by rapid decompression to ambient conditions, referred to as the (1T-1P) strategy. Intermediate temperature and pressure variations were introduced before the final decompression to evaluate the impact of operating parameters further. These strategies included intermediate-temperature cooling (2T-1P), intermediate-temperature cooling with rapid intermediate decompression (2T-2P), and intermediate-temperature cooling with gradual intermediate decompression (2T-2P, stepwise ΔP). SEM imaging revealed that the (2T-2P, stepwise ΔP) strategy produced a bimodal cell structure featuring small cells ranging from 105 to 164 μm and large cells between 476 and 889 μm. This study demonstrated that cell size was influenced by the regulation of intermediate pressure reduction and the change in intermediate temperature. The results were interpreted based on classical nucleation theory, the gas solubility principle, and the effect of polymer melt strength. Foaming results of average cell size, cell density, expansion ratio, porosity, and opening cell content are reported. The hydrophilicity of various foamed polymer blends was evaluated by measuring the water contact angle. Typical compressive stress–strain curves obtained using DMA showed a consistent trend reflecting the effect of foam stiffness. Full article

Expanded graphite (EG) with high infrared (IR) absorption is incorporated at low concentrations (≤2 wt%) into polystyrene (PS) foams to reduce radiative thermal conductivity and solid thermal conductivity, which account for 20~40% and 10~30% of total thermal conductivity, respectively. After systematically and quantitatively investigating thermal insulation behavior in PS/EG foams, it was found that the inclusion of 1 wt% EG in 25-fold expanded PS/EG foam blocks over 90% of the radiative thermal conductivity, with only a marginal increase in heat conduction. A great reduction in total thermal conductivity from 36.5 to 30.2 mW·m⁻¹·K⁻¹ was then achieved. By further optimization using a co-blowing agent in the supercritical CO₂ foaming process, superthermal insulating PS/EG foam with a total thermal conductivity of 19.6 mW·m⁻¹·K⁻¹ was achieved for the first time. This significant result implies that the composite material design together with the foaming process design is capable of obtaining a superthermal insulating composite foam by using the following strategy: using additives with high IR absorption efficiency, a foam with a large expansion ratio, and a co-blowing agent with low gas conductivity. Full article

The textile industry ranks among the highest water-consuming sectors globally, with annual usage reaching billions of cubic meters. In manufacturing, wet processing, including dyeing, printing, and finishing, accounts for 72% of this water demand. These stages not only require vast water volumes but also produce wastewater containing hazardous chemicals, polluting ecosystems and reducing soil fertility. Furthermore, the energy-intensive nature of these processes, combined with a heavy reliance on fossil fuels, contributes significantly to greenhouse gas emissions. In response to these environmental challenges, innovative technologies have emerged, such as waterless dyeing using supercritical carbon dioxide, digital printing, ultrasonic-assisted processing, foam dyeing, laser-based denim finishing, and dope dyeing for man-made fibers. These methods drastically reduce water consumption, lower energy use, and minimize emissions while maintaining textile quality. However, the widespread adoption of these alternatives faces challenges, including high implementation costs, process scalability, and compatibility with existing infrastructure. This review critically explores current advancements in sustainable textile wet processing, analyzing their effectiveness, limitations, and industrial viability. By addressing these challenges, the textile industry can transition toward environmentally friendly and resource-efficient manufacturing processes. Full article

Conventional techniques for incorporating active ingredients into polymeric matrices are accompanied by certain disadvantages, primarily attributable to the inherent characteristics of the active ingredient itself, including its sensitivity to temperature. A potential solution to these challenges lies in the utilization of supercritical carbon dioxide (scCO₂) for the formation of polymeric foam and the incorporation of active ingredients, in conjunction with the encapsulation of inclusion complexes (ICs), to ensure physical stability and augmented bioactivity. The objective of this study was to assess the impact of IC impregnation and subsequent foam formation on PLA films and PLA/PBAT blends that had been previously impregnated. The study’s methodology encompassed the formation and characterization of ICs with caffeic acid (CA) and β-cyclodextrin (β-CD), along with the thermal, structural, and morphological properties of the resulting materials. Higher incorporation of impregnated IC into the PLA(42)/PBAT(58) blend was observed at 12 MPa pressure and a depressurization rate of 1 MPa/min. The presence of IC, in addition to a lower rate of expansion, contributed to the formation of homogeneous cells with a size range of 4–44 um. On the other hand, the incorporation of IC caused a decrease in the crystallinity of the PLA fraction due to the interaction of the complex with the polymer. This study makes a significant contribution to the advancement of knowledge on the incorporation of compounds encapsulated in β-CD by scCO₂, as well as to the development of active materials with potential applications in food packaging. Full article

Poly (butylene adipate-co-terephthalate) (PBAT) foam sheets prepared by foaming supercritical fluids are characterized by high resilience, homogeneous cellular structure, and well-defined biodegradability. However, the inert chemical structure and the rigid hard segments restrict the diffusion of CO₂ within the PBAT matrix, resulting in extremely long gas saturation times as long as 9 h at a thickness of 12 mm. In this study, microporous structures were pre-introduced into the PBAT matrix to provide a fast gas diffusion pathway during the saturation process. After 2 h of saturation, PBAT foam sheets with expansion ratio of 10 to 13.8 times were prepared. The interaction of CO₂ with PBAT was systematically investigated, and the CO₂ sorption process was evaluated kinetically and thermodynamically using the Fickian diffusion theory. The solubility and diffusion rate of CO₂ in pretreated PBAT sheets with different microporous sizes and densities were investigated, and the effects of pretreatment strategies on the foaming behavior and cell structure of PBAT foam sheets were discussed. The introduction of a microporous structure not only reduces saturation time but also enhances solubility, enabling the successful preparation of soft foams with high expansion ratios and resilience. After undergoing foaming treatment, the PBAT pretreated sheets with a 10 μm microporous structure and a density of 0.45 g/cm³ demonstrated improved mechanical properties: their hardness decreased to 35 C while resilience increased to 58%, reflecting enhanced elastic recovery capabilities. The pretreatment method, which increases the diffusion rate of CO₂ in PBAT sheets, offers a straightforward approach that provides valuable insights into achieving rapid and efficient foaming of thick PBAT sheets in industrial applications. Full article

The microcellular injection molding (MuCell^®) process, which uses supercritical fluid (SCF) as a foaming agent, is considered an important green molding solution to reduce product weight, molding energy, and cycle time and to improve the foam quality. However, maximizing the foaming density while keeping size uniformity in the foaming cell requires further attention. In this study, H₂O and the SCF N₂ were employed as cofoaming agents in the MuCell^® process of polypropylene (PP). Owing to the different critical points of N₂ and H₂O, bubble nucleation was expected to occur in interactive ways. Various process parameters were investigated, including the SCF N₂ content, the moisture content adsorbed within the resin under targeted PP weight reductions of 30% and 40%, the melt and mold temperature conditions, and the gas counter pressure. The resulting foaming morphology was examined to evaluate the foam quality in terms of the foaming density and bubble size distribution. The bubble coalescence, particularly in the skin layer, was examined, and the associated gas permeability flow rate was measured. The results indicated that H₂O-assisted foaming led to bubble coalescence and allowed for gas penetration in the direction of the part thickness direction, resulting in an overall increase in foaming density, particularly in the skin layer. Under high SCF N₂ and H₂O contents, the solid skin layer disappeared, regulating the gas permeability from one surface side to the other. Under the optimized process parameters, the gas permeability flow rate in the filter-like foaming PP material reached 300–450 mL/min. The application of gas counter pressure also helped increase the foam density and bubble coalescence, enhancing the gas permeability in the PP material to about 500 mL/min. These results demonstrate the potential application of microcellular injection molding using water as a cofoaming agent in moisture-release devices. Full article

Fruit seeds are often an underutilized side-stream of fruit processing. The most common approach to seed valorization is oil extraction due to the relative simplicity of the process. The partially or fully defatted seed meal is rarely further processed, even though seeds generally contain more protein and fiber than oil. The present study used single-screw extrusion (oil press), supercritical CO₂ extraction, and a combination of the two, to defat Japanese quince (Chaenomeles japonica) seeds, and evaluated the defatted meals as sources of functional protein. Defatting with oil press and CO₂ extraction proved similarly effective (reduced seed flour fat content from 11.75% to 6.40% and 5.32%, respectively); combining the two methods reduced fat content to 0.90%. The yield was minimally affected, but protein extract purity was defined by defatting efficiency (65.05% protein from non-defatted versus 82.29% protein from a combination-defatted meal). Defatting did not significantly affect amino acid composition but had a significant effect on every tested functional property (solubility, water, and oil binding capacity, apparent viscosity, foaming capacity, and emulsifying activity index). Of the tested defatting methods, supercritical CO₂ extraction and the combination provided the best results from most aspects. Full article

Conventional PP with a linear chain structure is not suitable for foam processing due to its poor rheological properties. In this study, PP was modified with PE through reactive melt blending of maleic anhydride-grafted PP (MA-PP) with a small amount of PE bearing glycidyl groups on its backbone (G-PE), with the aim of enhancing the melt rheological properties of PP to make it suitable for foam processing. An anhydride–epoxy reaction occurred between MA-PP and G-PE during the melt processing, resulting in the formation of a crosslinked polymer network, which was confirmed by FTIR spectroscopy, a solubility test, and the presence of a rubbery plateau above the melting point. Melt rheological tests demonstrated that the modified PP showed a pronounced shear-thinning effect and higher elasticity compared to pristine PP. Foaming tests using supercritical carbon dioxide as a foaming agent in an autoclave demonstrated that the modified PP could produce a microcellular foam with a closed-cell structure, which was not achievable with neat PP. Full article

In this manuscript, an efficient self-reinforcing technology—solid hot drawing (SHD) technology—was combined with green processing supercritical carbon dioxide (SC-CO₂) foaming technology to promote poly (l-lactic acid) (PLLA) to form an oriented micropore structure. In addition, Polydimethylsiloxane (PDMS), with a high affinity of CO₂ and biological safety, was introduced to enhance the nucleation effect in SC-CO₂ foaming and co-regulate the uniformity of oriented micropores’ structure. The results showed that orientation induced PLLA crystallization, so the tensile strength was improved; the maximum tensile strength of the oriented micropores’ PLLA reached 151.2 MPa. Furthermore, the micropores mainly improved the toughness; the maximum elongation at break reached 148.3%. It is worth mentioning that PDMS can form an antibacterial film on the surface of the material, so that the material has a continuous antibacterial effect. Full article

This paper presents the novel development of a shape memory polymer foam based on polymer–polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO₂ foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time. Full article

This study investigates the modeling and experimental validation of cell morphology in microcellular-foamed polycaprolactone (PCL) using supercritical carbon dioxide (scCO₂) as the blowing agent. The microcellular foaming process (MCP) was conducted using a solid-state batch foaming process, where PCL was saturated with scCO₂ at 6 to 9 MPa and 313 K, followed by depressurization at a rate of −0.3 and −1 MPa/s. This study utilized the Sanchez–Lacombe equation of state and the Peng–Robinson–Stryjek–Vera equation of state to model the solubility and density of the PCL-CO₂ mixture. Classical nucleation theory was modified and combined with numerical analysis to predict cell density, incorporating factors such as gas absorption kinetics, the role of scCO₂ in promoting nucleation, and the impact of depressurization rate and saturation pressure on cell growth. The validity of the model was confirmed by comparing the theoretical predictions with experimental and reference data, with the cell density determined through field-emission scanning electron microscopy analysis of foamed PCL samples. This study proposes a method for predicting cell density that can be applied to various polymers, with the potential for wide-ranging applications in biomaterials and industrial settings. This research also introduces a Python-based numerical analysis tool that allows for easy calculation of solubility and cell density based on the material properties of polymers and penetrant gases, offering a practical solution for optimizing MCP conditions in different contexts. Full article

Microcellular injection molding (MuCell^®) using supercritical fluid (SCF) as a foaming agent to achieve weight reduction has become popular in carbon emission reduction. In the typical MuCell® process, SCF N₂ is commonly used. Although SCF CO₂ exhibits high solubility and can achieve a high weight reduction, controlling the foaming is not easy, and its foaming cells are usually larger and less uniform, which limits its industrial application. Our previous studies have shown that gas counter pressure (GCP) can improve the foaming quality effectively. Here, we investigated whether or not the CO₂ SCF foaming quality could be improved, and weight reduction was achieved for polycarbonate (PC) material. This is quite important for the electronics industry, in which most of the housing for devices is made of PC materials. MuCell^® was subjected to molding experiments using the parameters of the SCF dosage, melt temperature, mold temperature, and injection speed. The results revealed that using CO₂ gas for the PC material can reduce the size of microcellular cells to 40 µm and increase the cell densities to 3.97 × 10⁶ cells/cm³. Using GCP significantly improved the microcellular injection-molded parts by reducing the cell size to 20.9 µm (a 45.41% improvement) and increasing the cell density to 8.04 × 10⁶ cells/cm³ (a 102.48% improvement). However, implementing GCP may slightly decrease the target weight reduction. This study reveals that microcellular injection molding of PC parts using SCF CO₂ can achieve high-quality foaming and reduce the weight by about 30%. Full article

Supercritical carbon dioxide (SCCO₂) is a non-toxic and environmentally friendly fluid and has been used in polymerization reactions, processing, foaming, and plasticizing of polymers. Exploring the behavior and data of SCCO₂ sorption and dissolution in polymers provides essential information for polymer applications. This study investigated the sorption and diffusion of SCCO₂ into polyetherimide (PEI). The sorption and desorption processes of SCCO₂ in PEI samples were measured in the temperature range from 40 to 60 °C, the pressure range from 20 to 40 MPa, and the sorption time from 0.25 to 52 h. This study used the ex situ gravimetric method under different operating conditions and applied the Fickian diffusion model to determine the mass diffusivity of SCCO₂ during sorption and desorption processes into and out of PEI. The equilibrium mass gain fraction of SCCO₂ into PEI was reported from 9.0 wt% (at 60 °C and 20 MPa) to 12.8 wt% (at 40 °C and 40 MPa). The sorption amount increased with the increasing SCCO₂ pressure and decreased with the increasing SCCO₂ temperature. This study showed the crossover phenomenon of equilibrium mass gain fraction isotherms with respect to SCCO₂ density. Changes in the sorption mechanism in PEI were observed when the SCCO₂ density was at approximately 840 kg/m³. This study qualitatively performed FTIR analysis during the SCCO₂ desorption process. A CO₂ antisymmetric stretching mode was observed near a wavenumber of 2340 cm⁻¹. A comparison of loss modulus measurements of pure and SCCO₂-treated PEI specimens showed the shifting of loss maxima. This result showed that the plasticization of PEI was achieved through the sorption process of SCCO₂. Full article