Semi-Chrome Upper Leather from Rural Goat Vegetable Tanned Crust

43 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48

Semi-Chrome Upper Leather from Rural Goat Vegetable Tanned Crust (1)

(2)

A.E Musa1 and G.A Gasmelseed2 Department of Leather Technology, College of Applied and Industrial Sciences, University of Bahri, Khartoum, Sudan, P.O.Box 12327 E mail: [email protected] Telephone: +249919440560 Department of Leather Technology, College of Applied and Industrial Sciences, University of Bahri, Khartoum, Sudan, P.O.Box 12327 E mail: [email protected] Telephone: +249919634134 (Received: February 17, 2013; Accepted: March 15, 2013)

Abstract- Semi-chrome leather is used as substitute for chromium tanned goatskin, particularly when a heavier substance is required, for example, for unlined casual footwear and slippers. Among solo tannages, the effect of chromium (III) appears unique in conferring high hydrothermal stability. The present work was carried out to improve Sudanese rural garad tanned crust leathers for production of semi-chrome shoe upper leathers. The crust leather is carefully sorted for size, substance, and grain quality, so that the customers’ requirements can be met accurately. The usual process sequence consists of stripping, bleaching, retannage with Basic chromium sulphate (BCS), neutralization, dyeing, fat liquoring, drying and finishing. The physical and chemical characteristics of the leathers produced are compared with control leathers and standard physical properties showed very good agreement. The leathers produced are full, soft, and flexible with high tensile strength. However, the stripped rural garad tanned leathers were retanned with 8% Basic chromium sulphate (BCS); giving a high shrinkage temperature of 104 oC. The results gave leathers with good organoleptic and strength properties. Thus the possibility of making upper leather using semi-chrome tanning appears to be promising. Index Terms- Semi-chrome, Rural garad, BCS, Stripping

I. INTRODUCTION Upper leathers of commercial interest made from kid and goatskins are glazed kid, softie kid, shrunken grain kid, and finally suede kid and goat. All these types are mainly used for ladies’ fashion footwear, but a little kid is used in some countries for men’s footwear. Goatskin leathers are, in the main, fine leathers of thin substance, good softness, suppleness, high tensile strength, and excellent durability [1]. Semi-chrome leather is used as substitute for chromium tanned goatskin, particularly when a heavier substance is required, for example, for unlined casual footwear and slippers. The classical raw material for this leather is East Indian goatskin from India exported in the lightly vegetable tanned crust state. Alternative

and expanding supplies are available from Pakistan, East and West Africa, and the Middle Eastern countries. The quality of these leathers has improved recently as far as the process in itself is concerned; but commercial factors affect their qualities, which suffer from the fact that these skins are mainly produced by small tanners, who cannot afford the high prices paid by the larger chrome tanners for their raw skins. These leathers are sold by weight in the crust, so that they are often adulterated with Epsom salts (magnesium sulphate), colloidal earths, added fats. The incidence of faults attributable to the presence of large quantities of natural and added fats in increasing, particularly in suede leathers, so that solvent degreasing of the crust goatskins is being carried out by some dressers [1]. Semi-chrome leather is first vegetable tanned and subsequently retanned with chrome salts. The usual processes are a light surface detannage or stripping, in order to obtain increased uptake of chromium in retannage plus giving a light degreasing thus improving dyeing properties and feel of the finished leather neutralization, dyeing, fatliquoring, preferably paste drying follow with a final application of a corrected grain finish [1]. Leather processing involves cleaning of the skins or hides to remove unwanted fibrillary and inter-fibrillary and other extraneous materials, followed by preparing them for tanning and subsequently tanning to stabilize the collagen, the main fibrous protein of hides and skins against microbial degradation. The various processes involved in leather making are given in Fig. 1 [2]. Sudan has various indigenous tanning materials. Some of these, such as Garad pods (Acacia nilotica sub. sp. nilotica) and Talh bark (Acacia seyal) are used extensively in the Sudan by rural tanners. The tannin content of garad pods is fairly high and amounts to approximately 30% of the total weight, soluble nontans are nearly 20%, while moisture and insolubles make up the remainder.

44 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48 The main constituent of the garad tannin is presumably leucocyanidin gallate i.e. gallic acid esterified with a flavanoid. Garad tannin is reported to contain chebulinic acid, gallic acid and to have a high sugar content, factors which are common in hydrolysable tanning materials. Garad tannins are therefore

mixed tannins i.e. containing condensed tannins as well as hydrolysable tannins containing gallic acid esterified with glucose [3]. The most widely condensed tannins are based on flavan-3-ols (-)- epicatechin (+) - catechin (Fig. 2) [4].

Figure 1: Process flow sheet for conventional leather processing

OH

OH

OH

OH HO

HO

O

O

OH

OH OH

OH

Epicatechin

Catechin Figure 2: Flavan-3-ols

When garad pods are crushed, they disintegrate into three parts, the husk with about 12% pure tannins, the seeds with no tannin content and the grain powder with approximately 55%

tannins. The seeds and husk form about 63.6% of the weight of the pod, the remainder being the grain powder [3].

45 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48 Natural leather is processed from hides and skins of animals. There is a need to understand the properties of processed natural leather to select proper material for an application. During the past 20 years, leather researchers have used experimental and theoretical approaches to investigate several methods for stabilizing collagen structure. Insight gained from these studies and those of leather and biomaterials scientists will be evaluated as steps toward a still elusive, comprehensive mechanism for stabilization of collagen in leather and other biomaterials. The main process of skin or hide converting into leather is tanning. Chromium has been used as primary tannage for many leathers for over 100 years. In the early days the tanning form, Cr(III), was produced from Cr(VI) by reduction of the chrome by sugars at low pH. When basic chrome sulphate was introduced as a product ready to be used for tanning, tanneries changed to the use of these products either as an aqueous solution or a dry product [5]. During the last 20 years new tanning methods, which allow avoidance of toxic chromium compounds, have been developed. Although such tanning methods enable the avoidance of chromium compounds, it does not mean that the leather is free from inorganic salts (aluminium, silicon, titanium etc.). Due to increasingly strict requirements for leather and with regard to recycling of leather wastes, the manufacture chromium-free leather becomes very important [6]. Developing of environmentally friendly tanning technologies, most perspective is the combination of inorganic (aluminium, silica, zinc etc.) and organic (vegetable tannins, resins, aldehydes etc) chrome-free materials [7-10]. Chrome-tanned leathers are stable in the presence of heat and moisture. The characteristic shrinkage temperature (Ts) of at least 100oC is a standard to which leathers tanned by other processes are compared. Considerable research has shown that the tanning effects of minerals other than chromium (Al, Zr, Ti, or Fe) are enhanced when they are used in combination with vegetable tannins, aldehydes, or other organic molecules [11, 12]. Leathers tanned with these combinations had Ts of near 100oC and physical-mechanical properties adequate for variety of applications. Nevertheless, these combination tannages have not been widely adopted.The vegetable tanning has advantages such as comfort, compatibility with skin, high-dimensional stability and ease of disposal. The drawbacks of vegetable tanned leather are that they lack softness as they are very hard and firm and lack the affinity for anionic fat liquors. The vegetable tanned leathers also lack the degree of hydrothermal stability required. Studies on combination of vegetable–oxazolidine [13] and vegetable–zinc [14] produced good results. Hence, in this work, an attempt has been made to evaluate the upgrading of rural garad-tanned crust leather for production of upper leather. II. MATERIALS AND METHODS

Material The selected rural garad-tanned crust leathers were dipped in water, piled for several hours to condition uniformly, and then shaved at 1.2 mm – this weight was used in subsequent processing. Chemicals used for post tanning processes were of commercial grade. Chemicals used for the analysis of spent liquor were analytical reagents. Upgrading of goat rural garad-tanned crust leathers The rural garad-tanned crust leathers were divided into two equal sides. The right sides were used for experimental trial and the left ones used as control. The experimental process using 8% basic chromium sulphate (BCS) in two feeds, 4% in each, is given in Table 1. The post tanning process in Table 2 was followed for both experimental and control leathers. Measurement of hydrothermal stability of leathers The shrinkage temperature of control and experimental leathers has been determined using a Theis shrinkage tester [15]. 2X0.5 cm2 piece of tanned leather cut from the official sampling position has been clamped between the jaws of the clamp and has been immersed in solution containing 3:1 glycerol: water mixture. The solution has been continuously stirred using mechanical stirrer attached to the shrinkage tester. The temperature of the solution has been gradually increased and the temperature at which the sample shrinks has been measured as the shrinkage temperature of the leathers. Physical testing and hand evaluation of leathers Samples for various physical tests from experimental and control crust leathers have been obtained as per IULTCS methods [16].Specimens have been conditioned at 20  2 oC and 65  2 % R.H (relative humidity) over a period of 48 hrs. Physical properties such as tensile strength, percentage elongation at break [17], grain crack strength[18] and tear strength[19] have been measured as per standard procedures. Each value reported is an average of four samples (2 values along the backbone and 2 values across the back bone). Experimental and control crust leathers have also been assessed for softness, fullness, grain smoothness, grain tightness (break), general appearance and dye uniformity by hand and visual examination. Three experienced tanners rated the leathers on a scale of 0-10 points for each functional property, where higher values indicate better property of leathers. Chemical analysis of leathers Total ash content, % moisture, % oils and fats, % water soluble, % hide substance, % insoluble ash, degree of tannage and chromium oxide were carried out for control and experimental leathers according to standard procedures [20].

Table 1: Formulation of the experimental trial for semi-chrome leathers from rural garad tanned crust leathers

46 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48 Process

%

Product

Duration

Remarks

(min) Wetting back Stripping Bleaching

Semi chrome tanning Basification

100 100 1 100

Water

50

Water Sodium bicarbonate Water

60

1 4 4 0.75

Oxalic acid Basic chromium sulphate (BCS) Basic chromium sulphate (BCS) Sodium bicarbonate

60

60 60 3  15

Single feed, washed well after stripping 1 feed, pH should be 3.5 drain 50% of bath Check for penetration in cross section Check the pH to be 4. Drain the bath and pile overnight. Next day sammed and shaved to 1.2 mm. The shaved weight noted.

Table 2: Formulation of post-tanning process for control and experimental leathers Process

%*

Product

Washing Neutralization Pre-retannage Pre-fatliquor

200 0.75 100 2 2

Dyeing Fatliquoring

2 3 3

Water Sodium bicarbonate Water Relugan RE (Acrylic syntan) Lipoderm liquor SAF (Synthetic fatliquor) Basyntan DI Acid dye brown Lipoderm liquor SAF (Synthetic fatliquor) LB II Basyntan DI Basyntan FB6 (phenolic syntan) Formic acid

Retanning Fixing

4 3 4 1

III. RESULTS AND DISCUSSION Upgrading of rural garad-tanned crust leathers Experimental sides leathers treated with 8% basic chromium sulphate (BCS) resulted in shoe upper leathers with higher shrinkage temperature (104°C) compared to control sides (84°C). Performance of leathers Organoleptic properties of crust leathers for experimental and control Crust leather from both control and experimental processes has been evaluated for various bulk properties by hand and visual evaluation. The average of the rating for the leathers has been calculated for each property and is given in Fig. 3. Higher numbers indicate a better property. It is observed from Fig. 3, that experimental crust leathers exhibited good fullness compared to control leathers with better organoleptic properties. This is assigned to the penetration and fixation of chrome in the experimental process. Other properties such as softness, grain

Duration (min) 10 3  15

Remarks

pH: 5-5.5

40 40 30 30

40 40 3  10 + 30

pH 3.5

tightness, smoothness, dye uniformity and general appearance are comparable to that of conventionally processed leathers. The overall appearance of experimental leathers is better than that of control leathers. Physical strength characteristics of experimental and control crust leathers It is essential to study the influence of the tanning system on the strength of leathers. The physical measurement results viz., tensile strength, elongation, tear strength, load at grain crack and distension at grain crack results for the control and experimental crust leathers are given in Table 3. It is observed that the tensile strength, elongation, tear strength of experimental-tanned crust leathers is higher than that of the control leathers. Chemical analysis of the crust leather The chemical analysis of crust leathers from control and experimental tanning trials are given in Table 4. The chemical analysis data for the experimental leathers is comparable to the

47 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48 control leathers. However, the water soluble matter for the

control leathers is more than the experimental leathers.

Table 3: Physical strength characteristics of experimental and control crust leathers Parameter

Semi-chrome

Control (garad )

BIS Standards

240±2

205±3

200

Elongation at break (%)

58±0.52

41±1.58

40-65

Tear strength (Kg/cm)

47±0.52

40±0. 52

30

Load at grain crack (Kg)

27±0.52

21±0.52

20

Distention at grain crack (mm)

12±0.52

10±0.52

7

Tensile strength (Kg/cm2)

Table 4: Chemical Analysis of crust leather of experimental and control Parameter

Experimental (semi-chrome )

Control (garad tanned )

Moisture % Total ash content %

15.00

13.30

3.20

2.70

Fats and oils %

5.80

3.60

Water soluble matter %

1.20

5.10

46

52

Insoluble ash %

3.00

1.20

Degree of tannage %

63.04

47.70

2.8

-

Hide substance %

Cr2O3 (%)

10

Semi- chrome Garad crust (control)

Rating

8

6

4

2

0 Softness

Softness

Fullness

Fullness

Tightness

Tightness

Smoothness General

Dye

Smoothness Generalappearance appearance Dye uniformity uniformity

Bulk properties

Figure 3: Graphical representation of organoleptic properties of the Experimental and control leather

IV. CONCLUSIONS In the present work, an attempt has been made to upgrading of rural garad tanned crust leathers to produce shoe upper leathers. It was found that experimental leathers treated with basic chromium sulphate (BCS) produced leathers with

48 Journal of Applied and Industrial Sciences, April, 2013, 1 (1): 43-48 shrinkage temperature of 104oC, which was 20oC more than the control (garad tanned) leathers. The physical and chemical characteristics of experimental leathers are comparable to control leathers. The experimental leathers are softer than the control leathers. The experimental process results in leathers with good thermal stability and organoleptic properties that is important for commercial viability of the tanning system. The physical properties of the leathers prepared compiled quite well with the standard requirements. As far as the physical and technical properties of the crust leather are concerned, the experimental trial revealed the best performance in terms of softness, fullness, grain stability and general appearance. This sequence, besides the good properties of the final leather, is also easily applicable from an industrial point of view. REFERENCES [1]. Tuck, D. H. (1981). The Manufacture of Upper Leathers. Tropical Products Institute, 56/62 Gray’s Inn Road, London, WC1 8LU.Overseas Development Administration. [2]. Suresh,V.; Kanthimathi , M.; Thanikaivelan, P.; Raghava Rao ,J.; and Unni Nair , B. (2001). An improved product-process for cleaner chrome tanning in leather processing.Journal of Cleaner Production.9, 483-491. [3]. Gasmelseed, G. A. and Mulla, T. H. A (1976). Simulation of Continuous Counter-current Leaching of Garad Pods., J. Chem. Biotech., Britain. [4]. Hagerman A.E., Zhao Y. and Johnson S. (1997). ‘Methods for determination of condensed and hydrolyzable tannins’, In: Antinutrients and phytochemicals in food, Shahidi F., ed., ACS Symposium Series No. 662. American Chemical Society, Chapter 12,.209-222. [5]. O’Flaherty, F., Roddy, W. T., Lollar, R. M. (1978). The Chemistry and Technology of Leather, Volume II, Types of Tannages. Robert E. Krieger Publishing Company Inc. Malabar Florida,: p 440. [6]. Plavan, V., Valeika, V., Kovtunenko, O., Širvaitytė, J. (2009). THPS Pretreatment Before Tanning (Chrome or Nonchrome). Journal of the Society of Leather Technologists and Chemists , 93, 186-192. [7]. Covington, A. D., Lampard, G. S. (2004). Studies on Semi-metal Tanning. Journal of the American Leather Chemists Association .99, 502-509. [8]. Rosca, I., Sutiman, D., Crudu, M., Sibieseu, D., Cailean, A., Vizitiu, M., Apostolescu, G. (2008). Study on New Complex

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