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Preparation of Protein based Surfactants from Leather Waste Fleshings and their Reutilization in Leather as a Water Resisting Agent.

Byline: HAFIZ RUB NAWAZ, BEENA ZEHRA, OMM-E-HANY, UZMA NADEEM AND BARKAT ALI SOLANGI

Summary: Tanneries generate a huge amount of highly polluting solid and liquid wastes during leather processing at different stages such as fleshings, shavings, tanning, finishing etc. Approximately, 250 kg of finished leather product is obtained from 1 ton of raw salted hide while other protein goes into wastes. Leather fleshings are about 50-60% of the total solid waste generated in leather processing. Three different surfactants have been prepared from soft wax, long chain fatty acid chlorides and leather waste protein isolated from alkaline hydrolysis of fleshings. .Products are milky in color and have been applied in goat leathers as a replacement of fat liquor and water resisting agent .The resulted crust leathers have been characterized for various physical parameters such as tensile strength, thickness, softness, tear strength, bursting load, water absorption etc, as per their standard test methods.

Leathers have also been evaluated for grain smoothness, fullness and feeling. Leathers have shown satisfactory results as per international requirement specially for water resisting. Thus a leather waste protein is converted into a useful product and reutilized in leather making.

Key words: Leather fleshings, Waste protein, Surfactant, Water resisting agent, Water resistant leather.

Introduction

Tanneries generate highly polluting solid and liquid wastes during leather processing at different stages such as fleshings, shavings, tanning, finishing etc. Approximately, 250 kg of finished leather product is obtained from 1 ton of raw salted hide while other protein goes into wastes [1]. Liming of hides and skins is a pre- tanning process, carried out with calcium hydroxide and sodium sulfide for the removal of hairs and flesh. After liming, the flesh in the hide or skin is removed by mechanical method or by using sharp knives.

The solid wastes from pre-tanning operations are highest in protein content where fleshing are about 50-60% of the total solid waste generated in leather comprising mostly collagen, bovine fat and water [2, 3].

The method commonly used for this waste disposal (landfill or incineration) presents high operational cost and environmental pollution [4]. De- liming of leather fleshings with HCL produces toxic H2S [5]. Collageneous protein in leather fleshings requires hydrolysis to be more useful as a nutrient in animal feeds and other beneficial products [6, 7]. Efforts for the utilization of limed wastes have been directed to extraction of the collagen after acid treatment with sulfuric acid, thermal hydrolysis at 125oC [8] and then pressing at high temperature for the removal of water and fat. Microbiological work has also been carried out for the utilization of tannery fleshings such as liquefaction for methane generation [9-12]. However, the handling and further processing of fleshings with some toxic material is costly and risky for the use in daily life products. Therefore, we have emphasized on the easy conversion of protein into beneficial product and its reutilization in leather.

Since water resisting surfactants are very useful products for water resisting leather due to their use in very marketable value added different leather articles. So, we have emphasized and successfully isolated protein from fleshings and converted into water resisting surfactant.

Results and Discussion

Three different fractions were isolated from hydrolyzed fleshings, as shown in Table-1. First fraction was fat content present at the top layer due to light in weight. Second and third fractions were collagen and insoluble residue at the bottom layer respectively. Second fraction was choosed for the preparation of surfactant because of its most purity and richness in amino acids, while the work on the utilization of other two fractions is in progress.

Table-1: Characteristics of recovered fractions from fleshings.

S. No.###Recovered fractions###Appearance###pH###% Yield on Moisture free Basis

01.###Fat###Light Creamy###7.0###17.35

02.###Collagen protein Hydrolyzates Light Brown###7.0###53.26

03.###Sludge###Blackish Grey###7.0###29.39

Extracted protein from leather solid waste has wide applications for different industrial purposes as reported earlier [13-23]. Protein themselves and their hydrolyzates are ampholites with surface-active properties which can be further enhanced by some chemical treatments [24, 25]. The well known is the condensation with long-chain carboxylic acids where the acid may be used in the form of chloride, anhydride or various esters [26]. The most important characteristics of the condensates as compare to untreated hydrolyzates are; much more surface- activity, better dispersing and equalizing, better stability in alkaline media, in hard water and in solutions of electrolytes. Therefore, the products were prepared by protein hydrolyzates and fatty acids chlorides and applied in goat skin leather processing (10%) at fat liquoring stage as a replacement of fat liquor as well as a water resisting agent.

It has been found that despite hydrophilic action of protein, the use of surface modified substance resulted in an improvement of the water repellent effect. Long chain fatty acids in the range of 16-22 C-atoms were found suitable for surfactants because they support the formation of oil-in-water emulsions [27]. Crust leather was prepared, dried and subjected to physical testing. The samples were evaluated by various physical tests such as thickness, softness, grain smoothness, fullness and feeling by leather experts. Results were found superior for grain smoothness and fullness in sample 3 as compare to other leather samples. However in reference leather feeling was superior as compare to other experimental leathers. Results are shown in Table-2(a).

Leather samples were also tested for tear strength, percentage elongation at break, tensile strength, bursting load, distension and water absorption of leather, using their standard test methods .The results are shown in Table-2 (b).

The results from experiment 1-3 showed that there is significant increase in %age elongation and bursting load as compare to reference leather, while slightly fluctuation in tear strength which is common due to the natural structural difference of leather. The increase of busting strength is perhaps due to the good filling property of protein in the surfactant. Leather was also tested for water absorptions and results showed excellent water resistivity as compare to the reference product.

Basically, the absorption of water into leather completes after some steps. First of all water spreads on the upper surface of leather. After this, the water molecule penetrates inside the leather fibers network and finally wets the complete leather. In this phenomenon, tanning agents, dyes, fat-liquors, finishing polymers etc., applied in leather processing may play an important role in water penetration. Therefore, this process must be stopped at any step by the application of proper chemicals. The results for water resistance have been found a little bit different in three different experiments that are due to the action and penetration of surfactant based on carbon long chain of acids because the hydrophilic part is a same mixture of peptides, while the hydrophobic part is based on fatty acid [28]. Beside this, the water resistivity has been increased with the soft wax which fills the gaps of leather and prevents the penetration of water into the fiber network.

Experimental

Materials

All chemicals were purchased from the local market and used as received in packing. Calibrated Universal Testing Machine Tinius Olsen model H5KS was used for the physical testing of leather. Latest Tests Methods were used from Official Methods of Analysis, Society of leather Technologists and Chemists. Softness was measured on ST- 300 Softness Tester from MSA Engineering systems limited. Water absorption was measured on Bally Penetrometer 5220. Centrifugation was carried on Variable Speed Centrifuge Model 2010H Centurion from Scientific LTD, UK.

Table-2(a): Physical Characteristics of Resulted Leather from Experiments 1 -3.

Sample###Thicknessps(mm)###Softnessps(mm)###Grain Smoothness###Fullness###Feeling

Surfactant 1###1.95 +- 0.2###5.9 +- 1.0###2###2###3

Surfactant 2###1.38 +- 0.1###5.0 +- 0.5###3###3###2

Surfactant 3###1.47 +- 0.5###4.49 +- 1.0###2###2###2

Reference###1.25 +- 0.2###6.0 +- 1.0###3###3###1

Standard Deviation is given against each result, calculated from three observations of sample

Grading was awarded 1-4 (1 excellent, 2 good, 3 medium and 4 showing poor)

Table-2(b): Physical Characteristics of Resulted Crust Leather from Experiments 1-3.

###Tear Strength###%Elongation###Tensile Strength###Bursting load###Distension###Water Absorption after

###(N/mm)###(mm)###(N/mm2)###(N)###(mm)###120miutes (%)

Surfactant 1###23.602 +- 2.5###113.700 +- 1.0###5.743 +- 1.2###300.00 +- 1.0###35.380 +- 1.2###21.803 +- 0.5

Surfactant 2###16.353 +- 1.5###111.860 +- 1.5###7.379 +- 1.5###336.500 +- 0.3###37.300 +- 1.0###19.983 +- 1.1

Surfactant 3###19.536 +- 1.8###108.200 +- 2.0###7.142 +- 1.5###332.216 +- 0.7###36.421 +- 0.4###25.520 +- 1.2

Reference###17.586 +- 1.3###76.464 +- 1.7###5.321 +- 1.0###256.666 +- 0.7###44.720 +- 0.3###49.926 +- 1.6

Standard Deviation is given against each result, calculated from three observations of sample

Waste leather fleshings in wet condition were collected in polythene bags from tanneries of SITE Area Karachi. Fleshings were passed from sieves to remove bulk amount of water and to separate the solid fleshing at room temperature. Then fleshings were re-packed in polythene bag and stored in refrigerator for further experimental work.

Fleshings (6.5Kg) were washed thoroughly in a washing tub with tap water. Ammonium sulfate (2%) based on the weight of fleshings was added to the washed fleshing with 100% water. Before de- liming the pH of fleshings was 9.0. While after stirring in tub for 30 minutes pH decreased to 8.0.

These de-limed fleshings were stored in a refrigerator for further experimental work.

1 Kg de-limed fleshings were weighed and hydrolyzed with alkaline mixture i.e.2% magnesium oxide and 4% sodium hydroxide with water in autoclave at 150-2500C for 2 hours. After that, the fleshings were in liquid form, dark colored viscous mass with very few insoluble particles. These particles were filtered and the filtrate collagen solution was stored in refrigerator in a separating funnel.

Methods

Protein (100gram) isolated from second fraction of leather fleshing waste in the 60% aqueous solution was used for surfactant preparation. pH of the protein solution was adjusted to 11 using 1N solution of sodium hydroxide. Fatty acid chloride product was prepared by reacting the oils and hydrochloric acid. In a typical preparation of surfactants, protein solution (100 gram each) was taken in three reaction flasks, then freshly prepared three fatty acid chlorides from Oleic acid, Lauric Acid and Palmitic Acid (0.002moles) were added drop wise into each protein solution with 100ml of distilled water in experiment 01, 02 and 03 respectively. Then, the flasks were heated to 600C for 40 minutes with constant stirring by over head stirrer. Soft Wax was melt by heating at 800C in double jacket vessel and added into reaction flask with stirring. When reaction was completed the flask was cooled at room temperature. Then product was separated by centrifugation at 4500 RPM.

The supernatant was water which was confirmed from emulsifying power test, while milky colored surfactant products were in the paste form at the bottom of the tubes. Products were stored in a cool place till application.

Four goat skins processed up to wet blue by conventional chrome tanning process were selected for the application of surfactants. Three wet-blue were used for three different prepared products, while the fourth one was processed as a reference. Surfactants were diluted with distilled water (1:5) by stirring for 10 minutes at 600 C .Wet-blue were processed with the following recipe (Table-3);

Table-3: Tannery Process.

Process###Chemical###Dosage and Duration*

Thickness of

wet blue(1.2+-0.10mm)

###300%, 10 minutes drumming

Wash###Water###(Twotimes)

Drain and wash

###Water

###Sodium bi###150%

Neutralization

###carbonate###0.2%

###Sodium###2% 90 minutes drumming

###Formate

Drain and wash well

###Water###150% 15 minutes drumming

Re-tanning###MK###3% 15 minutes drumming

###QF###4% 30 minutes drumming

Left Overnight and

drain.

Wash###250% 10 minutes (three

###Water of 60degC times) drumming

Fatliquoring###Prepared###10% 60 minutes drumming

###surfactant

###Formic Acid###0.6% 15 minutes drumming

Fixation###pH###3.8

Conclusion

Three different surfactants have been prepared from waste protein extracted from leather fleshings. Products have been successfully applied in leather processing not only as a fatliquor but also as water resisting agent. Beside this, protein present in the product also works as an excellent filling agent. Therefore, it is concluded that, the products are wealth from waste.

Acknowledgement

We are very thankful to Mr. Muhammad Zeeshan and Raja Asad Ali (Senior Technicians) for their assistance in leather processing for the application of products.

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1Leather Research Centre, PCSIR, D-102, South Avenue, SITE, Karachi, Pakistan., 2Institute of Environmental Studies, University of Karachi, Pakistan., nawazhr@yahoo.com*
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Author:Nawaz, Hafiz Rub; Zehra, Beena; Omm-E-Hany; Nadeem, Uzma; Solangi, Barkat Ali
Publication:Journal of the Chemical Society of Pakistan
Article Type:Report
Geographic Code:9PAKI
Date:Oct 31, 2012
Words:2647
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