High-pressure carbon dioxide tanning

Free of salt high-pressure deliming of animal hides

The wastewater pollution of tanneries is of high concern. The investigation of technologies to minimize the consumption of chemicals in the leather production process can reduce the environmental burden. We focus on the reduction of ammonium salts in the leather production process. Salt-free deliming of animal hides with compressed carbon dioxide as deliming agent is performed for the first time in a technical scale 20-L drum. As a result, CO₂-deliming at 30 bar and 30 °C is two times faster than conventional deliming. In addition, the deliming efficiency is slightly improved. The initial calcium (Ca) content of the hides of 8 g/kg reaches the lowest value of 2 g/kg after a process time of 3 h. However, a process time of 60 min is sufficient to reach an elimination of 50 wt% of the initial lime. The resulting Ca-content of 4 g/kg after 60 min CO₂-deliming at 30 bar is comparable with the Ca-content of conventional delimed hide. We clarify that the ampholytic character of the collagen itself enables a buffering of the pH-value at pH-7. The stable pH-value supports the selection of specific bating enzymes that decompose non-collagen proteins. No buffering salts contaminate the wastewater. The high-pressure CO₂-deliming process has high potential to reduce wastewater emissions, save costs for chemicals, and process time in industrial beamhouse applications.

Alternative tanning technologies and their suitability in curbing environmental pollution from the leather industry: A comprehensive review

Chrome tanning remains the most favourite technology in the leather industry worldwide due to its ability to produce leather with attributes desirable for high-quality leather such as excellent hydrothermal stability, better dyeing characteristics and softness. Nevertheless, the technology has been censured globally for its severe environmental detriments and adverse effects on human health and other organisms. Developing alternative eco-friendly tanning technologies capable of producing leather of high quality has remained a challenging scientific inquiry. This review article provides an assessment of various eco-friendly tanning attempts geared towards improving or replacing the chrome technology without compromising the quality of the produced leather. The reviewed publications have ascertained that, these attempts have been centred on recycling of spent liquors; chromium exhaustion enhancement and total replacement of chromium salts. The research gaps and levels of key environmental pollutants from the reviewed technologies are presented, and the qualities of the leather produced from these technologies are highlighted. Of all the examined alternative technologies, total replacement of chromium salts sounds ideal to elude adverse effects associated with chrome tanning. Combination tanning, which implies blending two tanning agents that individually cannot impart desired properties to the leather, is anticipated to be an alternative technology to chrome tanning. Apart from being an eco-friendly technology, combination tanning produces leather with similar features to those produced by chrome tanning. In this regard, blending vegetable tannins with aluminium sulphate provides a promising chrome-free tanning technology. However, further studies to optimize combination tanning technologies to suit industrial applications are highly recommended.

Supercritical Fluid Applications in the Design of Novel Antimicrobial Materials

Bacterial resistance to antibiotics is one of the biggest problems in the modern world. The prevention of bacterial spreading from hospitals to the community and vice versa is an issue we have to deal with. This review presents a vast potential of contemporary high-pressure techniques in the design of materials with antimicrobial activity. Scientists from all over the world came up with ideas on how to exploit extraordinary properties of supercritical fluids in the production of advantageous materials in an environmentally friendly way. The review summarizes reported methods and results.

Waterless tanning: chrome tanning in ethanol and its derivatives

Waterless chrome tanning in an ethanol medium is reported for leather making with comparable properties and shrinkage temperature, low chromium leaching, high exhaustion along with the possibility of recycling.