CO 2 Utilization for the dyeing of yak hair: Fracture behaviour in supercritical state

Supercritical fluid technology as a sustainable alternative method for textile dyeing: An approach on waste, energy, and CO2 emission reduction

The clothing industry is considered one of the most polluting industries on the planet due to the high consumption of water, energy, chemicals/dyes, and high generation of solid waste and effluents. Faced with environmental concerns, the textile ennoblement sector is the most critical of the textile production chain, especially the traditional dyeing processes. As an alternative to current problems, dyeing with supercritical CO2 (scCO2) has been presented as a clean and efficient process for a sustainable textile future. Supercritical fluid dyeing (SFD) has shown a growing interest due to its significant impact on environmental preservation and social, economic, and financial gains. The main SFD benefits include economy and reuse of non-adsorbed dyes; reduction of process time and energy expenditure; capture of atmospheric CO2 (greenhouse gas); use and recycling of CO2 in SFD; generation of carbon credits; water-free process; effluent-free process; reduction of CO2 emission and auxiliary chemicals. Despite being still a non-scalable and evolving technology, SFD is the future of dyeing. This review presented a comprehensive overview of the environmental impacts caused by traditional processes and confronted the advantages of SFD. The SFD technique was introduced, along with its latest advances and future perspectives. Financial and environmental gains were also discussed.

Molecular-level investigation of plasticization of polyethylene terephthalate (PET) in supercritical carbon dioxide via molecular dynamics simulation

The current study aims to use the molecular dynamics (MD) simulation method to discuss the glass transition behaviour and fractional free volume (FFV) of the pure polyethylene terephthalate (PET) and the plasticized PET induced by supercritical carbon dioxide (SC-CO₂) sorption. The adsorption concentration reproduced through sorption relaxation cycles (SRC) was firstly estimated and in an order of magnitude with the known experimental results available in the reported literature. The FFV induced by SC-CO₂ in PET polymer changes regularly, which is proportional to the capacity of SC-CO₂ adsorption with the changes in temperature and pressure. The glass transition temperature (T _g) was further estimated to be almost identical to the known experimental values and shows a gradually decreasing tendency with the increase of pressure. Meanwhile, the plasticization of PET polymer studied by radial distribution functions showed that CO₂ molecules occupying the sorption sites on the PET backbone promoted plasticization by increasing the fluidity of the PET backbone chain.

Molecular-level investigation of plasticization of polyethylene terephthalate (PET) in supercritical carbon dioxide via molecular dynamics simulation

The current study aims to use the molecular dynamics (MD) simulation method to discuss the glass transition behaviour and fractional free volume (FFV) of the pure polyethylene terephthalate (PET) and the plasticized PET induced by supercritical carbon dioxide (SC-CO₂) sorption. The adsorption concentration reproduced through sorption relaxation cycles (SRC) was firstly estimated and in an order of magnitude with the known experimental results available in the reported literature. The FFV induced by SC-CO₂ in PET polymer changes regularly, which is proportional to the capacity of SC-CO₂ adsorption with the changes in temperature and pressure. The glass transition temperature (T _g) was further estimated to be almost identical to the known experimental values and shows a gradually decreasing tendency with the increase of pressure. Meanwhile, the plasticization of PET polymer studied by radial distribution functions showed that CO₂ molecules occupying the sorption sites on the PET backbone promoted plasticization by increasing the fluidity of the PET backbone chain.

Performance and Structure Evaluation of Gln-Lys Isopeptide Bond Crosslinked USYK-SPI Bioplastic Film Derived from Discarded Yak Hair

To reduce the waste from yak hair and introduce resource recycling into the yak-related industry, an eco-friendly yak keratin-based bioplastic film was developed. We employed yak keratin (USYK) from yak hair, soy protein isolate (SPI) from soybean meal as a film-forming agent, transglutaminase (EC 2.3.2.13, TGase) as a catalytic crosslinker, and glycerol as a plasticizer for USYK-SPI bioplastic film production. The structures of the USYK-SPI bioplastic film were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). The mechanical properties, the thermal behavior, light transmittance performance, and water vapor permeability (WVP) were measured. The results revealed that the added SPI possibly acted as a reinforcement. The formation of Gln-Lys isopeptide bonds and hydrophobic interactions led to a stable crosslinking structure of USYK-SPI bioplastic film. The thermal and the mechanical behaviors of the USYK-SPI bioplastic film were improved. The enhanced dispersion and formation of co-continuous protein matrices possibly produced denser networks that limited the diffusion of water vapor and volatile compounds in the USYK-SPI bioplastic films. Moreover, the introduction of SPI prompted the relocation of hydrophobic groups on USYK molecules, which gave the USYK-SPI bioplastic film stronger surface hydrophobicity. The SPI and USYK molecules possess aromatic amino residuals (tyrosine, phenylalanine, tryptophan), which can absorb ultraviolet radiation. Thus, the USYK-SPI bioplastic films were shown to have an excellent UV barrier. The synergy effect between USYK and SPI is not only able to improve rigidity and the application performance of keratin-based composite film but can also reduce the cost of the keratin-based composite film through the low-cost of the SPI alternative which partially replaces the high-cost of keratin. The data obtained from this research can provide basic information for further research and practical applications of USYK-SPI bioplastic films. There is an increasing demand for the novel USYK-SPI bioplastic film in exploit packaging material, biomedical materials, eco-friendly wearable electronics, and humidity sensors.

Prediction of Acid Red 138 solubility in supercritical CO2 with water co-solvent

Acid Red 138, as a weak acid azo dye with a long alkyl chain, is widely used for protein fiber dyeing while it cannot dissolve in supercritical carbon dioxide. The objective of this study is to investigate the solubility of Acid Red 138 with water at the temperatures of 353.15, 363.15, 373.15, 393.15 and 413.15 K and over a pressure range of 20 to 26 MPa. The test results revealed that the phase equilibrium of water and Acid Red 138 was affected by the competition between pressure and density of supercritical carbon dioxide. Furthermore, the experimental solubilities were correlated by three types of density-based model. Good agreement with less than 3.36% of average absolute relative deviation between the calculated and the experimental data of water was achieved. In addition, the Chrastil model, Mendez-Santiago–Teja model and Sung–Shim model exhibited excellent correlation results for Acid Red 138 solubilities with the AARD values of 8.58%, 6.06% and 5.19%. Better understanding of the solubility behavior of Acid Red 138 in supercritical carbon dioxide displays potential for developing a microemulsion system for the eco-friendly dyeing of natural fibers.

The solubilities of Acid Red 138 were measured in supercritical CO₂ with water as a co-solvent to determine the influence of water.