Isloation of Eco-Friendly Leather Tanning Agents from the Indigenous Plants of Northern and Central Punjab of Pakistan.

Abstract

The use of hexavalent chromium “Cr(VI)” for leather tanning is carcinogenic and harmful for human health. Therefore special attention is being paid on use of vegetable tanned leather instead of chrome tanned leather throughout the world. Vegetable tanning is eco-friendly technique in leather processing. It refers to the use of vegetable tannins extracted from plants to process animal hides into leather. The leather industry of Pakistan has great interest in environmental- friendly tanning process but unfortunately no commendable work has been done so far. The present study was focused on the vegetable tanning of leather by the isolation of tanning agents from the selected plants of Northern and Central Punjab of Pakistan. Plants having maximum tannin content were selected by random sampling. Tannins were isolated by TLC and identified by UV spectrophotometer. Extraction of tannins was followed by purification, concentration and spray drying to get powder extract. The isolated tannins were tested for leather tanning and the quality of leather was compared to commercially available tanning agents (Tara and Mimosa) used in tanning industry. Comparison study was carried out to check the quality of leather and to check the standards of leather as per approved by the IUP/4, International Union of Leather Technologists and Chemists Societies (IULTCS) and by ISO 2589:2002. A comparison of physical properties of leathers tanned with local vegetable tanning materials and those tanned with commercial mimosa and tara indicated significant results. All the ten vegetable tanning materials had an adequate shrinkage temperature range of 50-93°C. Q. incana and P. roxburghii tanned leather samples showed no shrinkage at all. The C. deodara showed highest tensile strength i.e., 27.1 N/mm2 as compared to standard Mimosa used in this study which had 22N/ mm2. The A. indica had a value of 24.26N/mm2 and Q.dilatata had a value of 26N/mm2. The values of xxii tensile strength of A. nilotica was (16.8), A. pindrow (19.4), E. globules (10.67), P. roxburghii (15.61), P. wallichiana (12), Q.incana (12). In this study, the percentage elongation of standard Mimosa and Tara was found to be 40.48% and 61.84% respectively. The values of percentage elongation of P. roxburghii was 38.1%, P. wallichiana (39.1%), E. globulus (37.7%), C. fistula (39.3%), A. pindrow (59.6%), Q. dilatata (39.1%), Q. incana (38.32%), A. nilotica (48.42%), A. indica (42.52%), C. deodara (39.36%). In present research, it was discovered that the tearing force of all the vegetable tanned leathers was greater than 20 N with Eucalyptus globulus, 31.6 N, Acacia nilotica 56.05 N, Azadirachta indica 68.6 N, Pinus wallichiana 65.95 N, Pinus roxburghii 63.15 N, Cedrus deodara 74.05 N, Quercus dilatata 62.2 N, Abies pindrow 56.05 N, Cassia fistula 50.3 N, Quercus incana 39.71 N, Tara 44.99 N, Mimosa, 44.05 N. ). Flexing test was applied to the vegetable tanned leathers and there was no crack or damage at 50,000 flexes to any of the leathers The skin of fish is regarded as exotic and advanced type of leather, in different fashion and fabric industries. The bark tannin powder of five plants i.e., P. roxburghii, P. wallichiana, C. fistula, Tara, A.indica were used for the tanning of fish skins. All plants showed good results but the P. roxburghii and C. fistula tannin powder had best tanning results on Fish skins. It is highly recommended to consider P. roxburghii as an eco-friendly tanning agent. The study recognized and identified ten indigenous trees from Pakistan as a source of vegetable tanning materials. The present work indicated the percentage of tannins in various barks of plants. For example in Acacia nilotica; 8.7%, Pinus roxburghii; 10.06%, Eucalyptus globulus; 7.77%, Pinus wallichiana; 13.06%, Cassia fistula; 10.06%, Quercus dilatata; 7.28%, Quercus incana; 8.15% , Azadarichta indica; 10.76%, Abies pindrow; 11.6%, Cedrus deodara; 8.97%. The spectra for tannins are usually found in the range of 230-290 nm. The xxiii bands were recorded at 270 - 280 nm with different absorbance values. The results of UV-Vis spectroscopy and TLC proved the presence of tannins. In conclusion, this study found the good quality of leathers tanned with vegetable tanning materials as comparable to those tanned with commercial standards and all of them had showed best results. Present study also revealed that isolated tannins are a good source of natural tannins for leather tanning, which will help local tanning industry, by providing eco-friendly, non-carcinogenic and non-dangerous leather tanning agents at low cost. This study will give strength to the economy through sustainable product and save our environment.