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Solving Vein Marks Defects Problem through Wet End Process by
K. Gowthaman, S. Vikram, N. Nishad Fathima* and J. Raghava Rao*
Chemical Laboratory, Central Leather Research Institute, Council of Scientific and Industrial Research,
Adyar, Chennai-60002, India
Abstract
Introduction
Leather grading is done on the basis of number of defects found on the leather. Defects either ante mortem or post mortem thus affect the final quality and price of the leather. In this study, we have investigated one of the ante mortem defects namely vein marks and have developed a process for upgrading leathers with this defect. SEM studies clearly depict the groove or indentation due to the vein marks. Upgradation using finishing often results in affecting the breathability of leathers. Hence, we have adopted a strategy of changing the post tanning recipe for upgradation of leathers with vein marks. The optimized post tanning recipe resulted in upper leathers with visibly reduced vein marks and the strength and organoleptic properties are on par with that of control leathers. Thus, this study shows that vein marks defect in leathers can be overcome by suitable post tanning process modifications.
Reduction in value of the final quality of leather made depends on various factors. First factor is poor animal husbandry including inadequate and poor quality feeds, inadequate parasite and disease management, and branding, which leads to low quality of hides and skins. This factor is classified as ante mortem defects. Second factor is that hides and skin produced in rural areas outside organized slaughter houses, due to inappropriate slaughtering, flaying, collection and initial processing methods used lead to spoilage and rejection in the market. This is classified as post mortem defects. Third possible factor could be that the technology used at various stages from raw hides to finished leather products may be inappropriate or poor, which in turn could lead to poor quality products. Low tensile strength, pinholes, rib, loose grain and cockle are considered as most common troublesome abnormalities in sheepskin.1 The ante mortem defects like thin substance, vein marks, scratches, rub marks, yoke marks, scabies, pox brand marks etc. also lead to poor quality raw material.2,3
* Corresponding authors’ e-mail:
[email protected];
[email protected]; Fax: +91 44 24911589; Tel: +91 44 24411630. Manuscript received March 5, 2014, accepted for publication June 12, 2014. JALCA, VOL. 109, 2014
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Vein marks can arise because of both ante mortem and post mortem defects. If, owing to poor cure or old age, for example, the structure around them becomes loose, the skin is said to be veiny, and the branching pattern of the veins usually shows through on the grain side. Pronounced veininess is caused due to inherent problems in the feeding/starvation of cattle and so on. Blood vessels can be seen on the flesh side as branching lines. Inadequate bleeding of the hide where the blood residues, which remain in the veins, encourages the development of microorganisms and thus increased putrefaction along the blood veins. This also leads to a veiny appearance on the leather (grooves). Also, improper curing results in putrefactive destruction of either vessel walls in skins with hair slip4 or of the tissue surrounding the vessels5,6 Due to the marks, the collagen fibre structure in that particular area is permanently changed. It is also reported that vein marks is more pronounced and difficult to remove in thin skins when compared to plump skins.7 Owing to this the vein marks leathers are not suitable for making high quality leathers for applications such as upper leathers.
Physical Testing of Leather Samples The samples for physical testing were obtained as per IULTCS methods.12 The samples were conditioned at 80±4 oF and 65±2% R.H. for 48 hrs. Physical properties such as tensile strength, % elongation and grain crack strength were investigated as per standard procedures.13,14 Each value reported is an average of four (2 along the backbone, 2 across the backbone) experiments on each skin.
Earlier microscopic studies on vein marks have suggested that filling of the voids created by veins, either by plumping the fibers with a suitable retannage or by use of impregnating materials.8 Few efforts and suggestions have been made in beamhouse operations towards minimizing vein marks with enzymes and also through use of high quality sodium sulfide along with sodium hydrosulfide but they have disadvantages like tendency to reduce the total hide substance and over loosening of fiber structure etc associated with them. Enzymes used in the bating operation have been shown to have some positive effect in reduction of vein marks.9 However, complete elimination of vein marks has not been achieved through process changes in pretanning operation. Also, most of the raw material sale happens in wet blue stage, where this defect would not have been addressed in pretanning operations. Recently, successful attempts have been made to develop different types of leathers from thin substance wet blue material by modification in post tanning chemicals.10 Hence, in this work, we have attempted upgrading of vein marks wet blue leathers through wet end process by suitable selection of post tanning chemicals. The leathers made have been characterized for various physical-chemical properties and the results are reported.
Scanning Electron Microscopic Analysis Wet blue vein marks substance sample was dehydrated by gradual dehydration process using methanol and acetone.16 The specimens were then coated with gold using Edwards E306 sputter coater. A FEI Quanta 200 Environmental scanning electron microscope was used for the analysis. The micrographs for the grain surface and cross section were obtained by operating the SEM at an accelerating voltage of 20 KV with different lower and higher magnification levels.
Experimental Post Tanning Operations Vein marks wet blue (goat skin) was taken as raw material. The post tanning recipe for making upper leather from this raw material is given in Table I. Control upper leathers were made using conventional post tanning recipe.11
Evaluation of Organoleptic Properties Crust leathers were assessed for softness, grain smoothness, grain tightness, fullness and general appearance by tactile evaluation. Experienced tanners rated the leathers in a scale of 0-10 points for each functional property. Wet and Dry Rub Fastness Samples of appropriate size (5 x 14 cm) were cut from the official sampling position and after conditioning as mentioned before were tested according to IS 6191-1971 (LF:10)31 using SATRA Crockmeter.15
Results and Discussion The objective of the study is to improve the grade of leathers, which have vein marks through post tanning operations. With this in mind the post tanning recipe was designed by choosing appropriate syntans and fatliquors. Strategy Followed for Optimization of the Post-tanning Recipe Vein marks are associated with hard fibers with improper fiber opening. Hence, the main strategy involved is to open up the fibers in that area using a protease enzyme. The product Bluzium 4M Polv, is a protease, which is especially used for opening of hard dried fibers. Hence, the use of enzyme enhances the fiber opening and loosens the area. Then the opened areas are filled using syntans and fillers. The choice of chemicals chosen for this experiment varied from protein fillers, filling resins and melamine based resins. These filling type of syntans results in uniformly filled fiber matrix. Opening of the fiber structure followed by proper filling of the void spaces results in overcoming the vein marks problems in
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TABLE I Process Recipe for making Upper Leather from Wet Blue Vein Marks. %
Chemicals
200
Water
0.2
Wetting Agent
25
Water
1
Sodium formate
1
Bluzium 4M Polv
0.5
Degreasing agent
100
Water
Time (in mins)
Remarks Drain
15
20 60
1
Formic acid
20
5
Acrylic Resin
30
5
Chrome syntan
5
Synthetic Resin
2
Synthetic Hydrocarbon based fatliquor
1
Natural reactive esters
drain/wash/drain
Check pH 3.2
60
40
0.5
Wetting agent
100
water
10
Sodium formate
20+20
Check pH 3.8 Leave Over Night
Next day run for
30
Drain/wash/drain
2
100
water
2
Organic complex syntan
1
Sodium formate
0.5
Sodium bi carbonate
2
Synthetic Hydrocarbon based fatliquor
50
Water
5
Protein filler
5
Retanning resin
3
Reactive resin
Table I continues on next page. JALCA, VOL. 109, 2014
20 40 30
45 30
Check pH 5.0-5.2 Drain/Wash/Drain
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Table I continued. 5
Synthetic tannin derivative
5
Styrene Maleic Resin
3
GS powder
3
Organic sulphonated derivative
3
Dye (brown RC)
4
Ester derivative
2
Fatty esters synthetic compound
2
Ester synthetic derivative
0.2
40
30 Check penetration
60
Emulsifier
1
Reactive resin
2
Styrene Maleic Resin
2
Retanning resin
2
Formic acid
15 20 20+30
Drain/wash/drain
150
hot water
1
brown RC
20
1
Formic acid
20
Drain/Wash/Drain
20
Drain/rinse/pile
150
hot water
0.5
Fatty ester synthetic
the leathers. However, due to usage of more quantity of filling syntans, proper choice of fatliquors is essential to provide a flexible leather matrix. Hence, mostly ester and hydrocarbon based fatliquors were chosen. The ester based fatliquors are known to give better softness and lubrication. The ester based fatliquors also give better strength properties to the leathers.
Upgradation in Vein Marks Leathers Following the post tanning recipe, the grade upgradation of vein mark wet blue leathers was from Lining-II to Upper. This high level of upgradation achieved would offset the higher cost of chemicals that would be incurred on increased offer of syntans.
The various post tanning chemicals used for making upper leather along with the optimized recipe is presented in Table I. The comparison of the post tanning chemicals used in conventional and experimental leathers are shown in Table II. It can be seen from the table that the % offer of syntans has increased by about 10% and the % offer of fatliquors has decreased by 2%. The increased offer of syntans is for selective filling of the void created by the vein marks.
Physical Strength Characteristics, Organoleptic Properties and Rub Fastness Measurements Tensile, tear strength and grain crack strength for upper leathers processed using the modified post tanning recipe are given in Table III. It is often felt that an increase in the offer of syntans may affect the physical strength properties negatively. However, it is seen that the physical properties of leathers made using the modified recipe are comparable and/or better JALCA, VOL. 109, 2014
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TABLE II Comparison of Post Tanning Chemicals for Conventional and Experimental Upper Leathers from Vein Marks Wet Blue. Chemicals
Conventional
Experimental
acrylic resin (Oratan 540)b: 2%
synthetic resin (Acton RM)a: 5%
aldehyde: 3%
protein filler (Tafigal P)c: 5%
vegetable: 10%
Syntans
retanning resin (Basyntan FB6)b: 10%
neutralizing syntan (Selassol NG)f: 1.5%
reactive resin (Relugan RE)b: 4%
phenolic syntan (Basyntan DI)b: 5%
Styrene maleic resin (Adusin MT)e: 7%
(Total composition: 28.5%)
(Total composition: 39%)
reactive resin (Relugan RE)b: 3%
synthetic tannin derivative (Vernatan OS)d: 5%
melamine based syntan (Basyntan FFS)b: 4%
GS Powder: 3%
Natural reactive ester (Coripol EF)f: 1%
fish oil: 2%
Synthetic hydrocarbon based derivative (Balmol SXE/ Balmol SX 20)g: 4%
synthetic fatliquor: 4% Fatliquors
licethin fatliquor: 5%
Organic sulphonated derivative (M7 polv)h: 3%
lanoline : 4%
Ester synthetic derivative (Pellastol ES)i: 6%
vegetable: 3%
Fatty ester synthetic (Sirial WK)j :2%
(Total composition: 18%)
(Total composition: 16%)
a: ATC; b: BASF; c: MUNZING; d: COLOUR CHEM; e: CURTIN SA; f: TFL; g: (BALMER & LAWERIE); h: KEMIA TAU; i: ZSCHIMMER & SCHWARZ; j: PULCRA
TABLE III Physical Strength Characteristics and Rub Fastness Characteristics of Various Leathers Made From Vein Marks Wet Blue. Sample
Tensile strength (Kg/cm2)
Tear strength (Kg/cm)
Load at grain crack (Kg)
Distention at grain crack (mm)
Wet rub fastness (256 rubs)
Dry rub fastness (512 rubs)
Control
139.70
42.01
23
11.68
4
3/4
Experimental
179.87
58.03
24.33
8.53
4
4/5
than the control leathers. The bulk properties of the control and experimental leathers were assessed by standard tactile evaluation by experienced tanners. The comparative ratings for each property are given in Figure 1. The figure shows that leathers made using the designed process recipe have better / comparable organoleptic proper ties. Rub fastness measurements were also carried out on the upper leathers made from vein marks wet blue and the results are given in Table III. An average rub fastness of about 4/5 has been achieved.
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Scanning Electron Microscopy and Optical Studies Figure 2 shows the flesh side and grain side of the vein mark area of the wet blue. The figure clearly depicts the indentation or the groove in the area of vein marks in the flesh side and the raised line in the grain side. Understandably, selective filling of this groove will reduce the vein marks. Figure 3 shows the optical photographs of leathers with vein marks before and after post tanning using the optimized recipe. It can be seen that visible reduction of vein marks is feasible by changing the post tanning recipe.
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generally affects the feel of the leather, achieving a high quality leather through post tanning modification will pave way for getting higher value for the upgraded leather.
Acknowledgement Figure 1. Organoleptic properties of control and experimental leathers.
Financial support from CSIR under Supra-institutional project STRAIT is acknowledged. The authors thank CSIR for funding the Supra Institutional Project – S&T Revolution in Leather with a Green Touch STRAIT -CSC0201. CSIR-CLRI communication code: 1079.
References
Figure 2. Scanning electron micrographs showing (i) the cross section of the vein marks wet blue raw material at different magnification (a) X300 (b) X1000. (ii) the grain of the vein marks wet blue raw material at different magnification (a) X500 (b) X300.
Figure 3. Comparison of photographs of vein marks leathers at a) wet blue stage and b) crust stage
Conclusions Upgradation of vein marks wet blue leathers has been carried out by bringing about suitable changes in the post tanning recipe. Physical strength and organoleptic properties have been found to be comparable to that of the control leathers. Considering the fact that upgradation in finishing operation
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