For example, strong acid swelling at pH-3 leads to a very slow mass transport and a high degree of tenseness that irreversibly damages the collagen fibers. The water absorption capacity and the orientation affect the tenseness and mass transport through the cross-section of the hide, dramatically (Paul and Bailey 2003). The different charges influence the hide properties as reactivity against leather chemicals, water absorption capacity, and the orientation of the collagen fibrils. As a protein, collagen is reactive towards tannins, dyestuffs, and other leather chemicals because of numerous peptide groups and its content of functional carboxy and amino groups (Reich and Taeger 2009).Ĭollagen is a polyampholyte with basic and acidic amino acids that can have negative and positive charges depending on the pH-value. 2018).Ĭollagen is with between 40 and 70 wt% of dry matter, the predominant proportion in the finished leather. The other parts of the hide are utilized in other industries or have to be disposed of (Onem et al. For the leather production, only collagen of the dermis is used. CollagenĪnimal hide consists of three merging layers: epidermis, dermis, subcutis. The aim is a low-emission, accelerated lime removal from the hide by substituting conventional ammonium salts with dense carbon dioxide as deliming agent to prepare the hides for the CO 2-intensified tanning process. Supplementary to our previous work, we investigate the application of process features of the CO 2-tanning process to the deliming process. Recently, we demonstrated a CO 2-intensified low-emission tanning process to produce high-quality leather in a 1700-L drum at 30 bar (Prokein et al. The use of dense carbon dioxide promises a high potential to reduce the environmental burden caused by the leather production process as already reviewed and highlighted by several authors (Sathish et al. According to estimations, the costs of environmental protection measures in European tanneries account for 4.3% of their turnover while their profit margin is just about 5% (Cotance 2012). As a result, beamhouse processing causes environmental challenges in developing countries and/or enormous costs in modern tanneries. All chemicals used in the beamhouse are lost with the wastewater (Buljan et al. During the preparation, hairs are removed and the hide is modified in chemical containing aqueous solutions, called floats. In the beamhouse, raw hide is prepared for the tanning process by soaking, liming, unhairing, deliming, bating, and pickling. Each category includes a variety of working steps consuming high amounts of water and process chemicals (Joseph and Nithya 2009). The production from raw animal hide to leather goods consists of 4 main categories: beamhouse, tanning, wet end, finishing. The high-pressure CO 2-deliming process has high potential to reduce wastewater emissions, save costs for chemicals, and process time in industrial beamhouse applications. No buffering salts contaminate the wastewater. The stable pH-value supports the selection of specific bating enzymes that decompose non-collagen proteins. We clarify that the ampholytic character of the collagen itself enables a buffering of the pH-value at pH-7. The resulting Ca-content of 4 g/kg after 60 min CO 2-deliming at 30 bar is comparable with the Ca-content of conventional delimed hide. However, a process time of 60 min is sufficient to reach an elimination of 50 wt% of the initial lime. 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. In addition, the deliming efficiency is slightly improved. As a result, CO 2-deliming at 30 bar and 30 ☌ is two times faster than conventional deliming. 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. We focus on the reduction of ammonium salts in the leather production process. The investigation of technologies to minimize the consumption of chemicals in the leather production process can reduce the environmental burden. The wastewater pollution of tanneries is of high concern.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |