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    An eco-friendly tanning method using plant barks and their combination with aluminium sulphate from kaolin for leather industry

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    Date
    2021-02
    Author
    Rolence, Cecilia
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    Abstract
    Chrome tanning has remained the most preferred tanning method worldwide in the leather industry because it produces leather of a high quality with all the desired features. However, environmental concerns of chromium shifted the focus of current research to chrome-free and greener chemical processing options. When used in combination with some eco-friendly metal salts, vegetable tannins are environmentally safe and manageable, while producing excellent quality leather, bearing shrinkage temperature above 100 °C as that of chromium tanned leather. As such, shortage of vegetable tannin supply requires characterization of non-commercialized sources locally available in Tanzania for cottage tanneries. In the present work, vegetable tannins from the stem barks of local plants namely Acacia mearnsii (A. mearnsii), Acacia xanthophloea (A. xanthophloea), Euclea divinorum (E. divinorum) and root barks of Euclea racemosa (E. racemosa) were prepared using a simple extraction technique at 30-80 °C. Extract yield, tannin, total flavonoid and phenolic content, cross-linking ability as well as properties of the tanned leather were determined. Results indicated that even at low temperature (50 °C) the barks yield vegetable tannins with features similar to that of a commercialized source of tannin. Euclea racemosa extract had low tannin, phenolic and flavonoid content and its crosslinking ability was poor; hence, was determined as an un-suitable tannin source. Despite recording less extract yield, tannin and other contents than that of A. mearnsii, the extract from E. divinorum bark demonstrated a substantial tanning ability, which is attributable to its high tannin strength. However, a broad interval between T onset and T peak of treated hide powder necessitated combination tanning with aluminium sulphate [Al 2 (SO 4 ) 3 ] to lower the interval. About 2% (w/v) aluminium oxide (Al 2 O 3 ) equivalent is an optimal dose of Al 2 (SO 4 ) 3 for extract pre-treatment. Since the main source of Al 2 (SO 4 ) 3 , bauxite, is diminishing in the world, an alternative source of Al 2 (SO 4 ) 3 was explored. The Al 2 (SO 4 ) 3 was prepared from Kaolin of Pugu hill in Tanzania and applied for combination tanning. The study has proven the suitability of kaolin as an alternative source of Al 2 (SO 4 ) 3 for combination tanning with vegetable tannins. Leather tanned with the combination of the prepared Al 2 (SO 4 ) 3 and vegetable tannin exhibited the shrinkage temperature of up to 118 °C as compared to vegetable tannins alone that showed the average of 80 °C. Mechanical strength characteristics met the standard norms. Fiber separation was good as confirmed through microscopic studies. The study provides useful information and new insights on accomplishing self-sustenance through available resources and an eco-friendly manufacturing system for leather industries in Tanzania and beyond.
    URI
    https://doi.org/10.58694/20.500.12479/1308
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