1. Introduction

Throughout the world the tanneries are looking for alternative tanning of chroming using synthetic and vegetable tannins because it is as friendly to the environment and to given close correlation between chrome tanning and to the environmental impact of leather processing, auditing the efficiency of processing operations takes on prime importance whereas a great deal of chrome containing solid wastes such as splitting and shavings are produced, which is certainly difficult to be degraded and harmful on the environment if discharged directly [1, 2]. On this pattern Alimet al. utilized 'Garad' from Acacia Nilotica to produce chrome free tanned leather with good mechanical properties whereas it had low shrinkage temperature compared to chrome tanned leather [3] which confirmed with Gold Farb in comparison study between the thermal properties of chrome free tanned leather using mimosa, quebracho and wattle and chrome tanned leather [4]. The industry currently uses certain standards based on the physical characteristics of intermediate and final product such as shrinkage, shrinkage temperature and thermal stability thus many attempts to improve the thermal properties of free chrome leather was done demonstrated that using oxazolidine [5] or resorcinol tanning agents combined with other (vegetable or synthetic agents) allows for the obtaining of quality leathers that can be used by footwear and upholstery industries [6]. Whereas Hassan, et al. carried out a methods using Sudanese rural garad for the production of semi-chrome shoe upper leathers. The results explained that the chemical properties of leathers in all trials are found to be quite normal. The shrinkage temperature of experimental leathers for all trials found above 85.4°C and the tensile strength above 103.00 Kg/cm2 [7]. Whereas Acacia nilotica (Sunt) is a member of sub-family Mimosoideae of leguminous trees. It is of multiple uses in Sudan, Africa and many Arabian countries [8]. Three subspecies of Acacia Nilotica dominated in Sudan. The first one is Tomentosa with the pods necklace-like narrowly and regularly constricted between the seeds and grows throughout Sudan. The second subspecies is Nilotica, in which glabrous pods are strongly constricted between the seeds and grows along the White Nile. The third subspecies is Adansonii, in which the pods are only slightly constricted between the seeds and grows in Western Sudan [9, 10]. The Acacia Nilotica tannins were applied in Sudan particularly pods of the subspecies Nilotica which has been known and used for tannage since long time ago [11]. Which is contain considerable amount of tannins whereas the grand powder of Acacia nilotica pods contain23% in Sudan and 16% in India [12]. Musa and Gasm elseed reported that 'Garad' tannins had a behavior like pyrogallol and catechol tannins hence 'Garad' is a mixture of pyrogallol/ catechol [13]. The chemical composition of 'Garad' pods tannin suggested being a mixture of di/tri gallic acid, which consists of five tannins C20 H19 O10, C20 H20 O10, C21 H18 O10, C21 H19 O10, and C22 H19 O10. These oligo-gallic acids hydrolyze to yield gallic acid, ellagic acid and phlobaphenes C14 H18 O4 [14]. Whereas Rao and Orwa et al. reported that the Azadirachta Indica bark contains ~12 % condensed tannins and some chemicals which were required by leather industry [15, 16]. Therefore for more application and improvement of tanning techniques, the current study is prepared to produce high quality leather, improve the physical properties such as shrinkage temperature, tensile strength and fullness, reduction the cost and replacement of the imported tanning materials utilizing blending of 'garad- neem' in eco-friendly processes to reduce the pollution load of tannage.

2. Materials and Methods

2.1 Source of materials
The tannin materials Garad were brought from blue Nile State, Sudan. Goat pelts were obtained from warehouse in Omdurman, Khartoum. Sudan. Reagents used for the experiment and analysis were of analytical grade. Preparation of tannins powder was conducted using mixture of 70: 30 % of Garad to Neem respectively. The eques mixture was dried at inlet temperature of 175°C and outlet temperature of 100°C and 1 atm pressure using spray drying instrument.

2.2 Experimental design
The experimental design was outlined in randomized complete design with two treatments; T1 traditional tanned method; and T2 improved method; 'Garad- Neem'; replicated three times.

2.3 Tanning methods
Grain goat pelts have been used for semi chrome and 'garad- Neem' spray dried powders tanning are shown in table 1, the experimental was repeated using origin 'garad' spray dried powder instate of blend as a control, the amount of chrome sulphate used for the tanning trails has been 2% Cr2 (SO4) in both experimental processes and the obtained leather was prepared to mechanical and physico-chemical testes.

Table 1: Formulation of semi chrome- 'garad'/ 'garad-neem' tanning system for grain goat pelts.

2.4 The mechanical, physico-chemicals tests and hand evaluation of leathers
Samples for various physical tests from experimental crust leathers have been obtained as per (SLTC, 1996) [17]. Specimens have been conditioned at 20 ± 2°C and relative humidity 65% ± 2% during 48 hours before use in a test. Physical properties such as thickness, tensile strength, percentage elongation at break and Shrinkage temperature have been measured as per standard procedures [17] where distention and strength of grain (bally flexometer), stitch tearing strength and tong tears strength were measured according to (ASTM D.2261 and 4705) [18, 19]. Experimental crust leathers have been assessed for softness, fullness, grain smoothness and general appearance by hand. For physic-chemical analysis, leather of all kinds must be ground in a cutter mill according to SLTC [17]. The ground material obtained was used to determined the moisture %, fat%, total soluble solid%, total ash content%, and chrome content% according to standard procedures (SLC 1, 2, 3, 4, 5, 9 and 8) [17].

2.5 Statistical analysis
The data mechanical, physicochemical analyzed using the statistical package for science (SPSS) at a significant level p=0.05 using (ANOVA) [20].

3. Result and Discussion

No	Description	T1	T2	BIS	Mean	Std	Sig. 0.05
1	Thickness/mm	1.1	1.1	1.0	1.067	0.0485	1.00
2	Tensile strength N/cm2	18.5	22	20	20.6	1.456	0.00
3	Elongation%	31	52	40	41.00	8.2247	0.00
4	Tear strength N/cm	2.3	4.8	3	3.367	1.0691	0.00
5	Stitch tear strength N/cm	8.9	10.3	10	9.733	0.61229	0.00
6	Distension and strength of grain/mm	8.2	10.3	9.9	9.4667	0.9233	0.00
7	Shrinkage temperature°C	91	100	100	97	4.304	0.00
8	Moisture content%	9	8.7	10	9.2	0.5697	0.00
9	Ash content%	3	3.1	4.5	0.3.53	0.694	0.08
10	Fat content%	10	10.2	10.7	10.3	0.2987	0.00
11	Total soluble matter content%	1.2	0.6	0.7	0.833	0.266	0.001
12	Chrome content%	1.0	1.1	2.5	1.5333	0.6945	0.08

Table 2: Mechanical and Physico-chemical properties of leathers which produced using semi chrome retanned by the blend.

Tannage is a chemical process that converts animal skins and hides into leather by involving additional cross-links to collagen. The efficiency of tanning depends on the binding activity of the tanning agents to the functional groups in collagen and between them [21]. It also depends on the pre- tannage and the thickness of the animal skins or hides. Thus utilizing 2% of chrome sulphate accelerate both garad/ garad-neem tannins to penetrate through cross-section of pelts and lead to uniform distribution of these agents and satisfactory tanning thus leathers showed a good cross-section, fullness, smoothness and general appearance, therefore results table 2 showed that there are no significant difference in thickness compared to standard requirement of shoe upper leather, BIS, and SS [22, 23].

The chrome tanning improve the strength properties of the leather such as tensile, tear and stitch tear, strengths, whereas tensile strength was measured as the force required to rupture a leather specimen of unit cross sectional area. The tensile strength was thus the combined breaking strength of all the fibers which are taking part to fight against the applied load therefore represent the maximum applied stress for ultimate tensile strength [24]. Thus according to that the tensile strength table 2 of this semi metal/ 'garad-neem' tanning gave competitive results to produce shoe upper leather than those tanned with semi metal /'garad' powder and they comply with the standards required for high quality upper leather, IS, and SS [22, 23]. Retanning is a key operation in leather making with the purpose of it is to obtain leathers with some special characteristics [25]. The strengths were significantly affected by the types and content of tannins however condensed tannins penetrate rapidly and aggregate more readily in the cross-section deposited very large molecules than hydrolysable types, so that in current study blends garad which contain considerable amount of hydrolysable tannins [26] and neem bark contain existence of considerable amounts of condensed tannins [27] to improve the tannins properties and raised the tanning power of blending tannins and introduction of blend tannins into the semi chrome tanning system produces a definitive improvement in the strength properties of the leather. This due to the fact that the fibre bundles are well separated in the case of chrome/garad tanned leather; while chrome/ garad-neem tanned leather shows cemented fibres bundles and this would lead to that the chrome/ garad-neem tanned leather would exhibit high tensile strength and tear with good softness where as chrome/garad tanned leather would exhibit low strength with normal softness Generally collective actions of the leather quality increase with homogenous interaction of tensile; tear and stitch tear strengths that recommended for good leather. Hence good strengths leather due to the behavior of chrome and garad-neem tannins.

The elasticity, softness characteristics and flexibility of both experimental and control leathers are observed to be quite normal. Indigenous garad tannins are known to produce hard/ durable leathers and are generally employed for producing firm leathers for out sole, pelts, etc. Hence, it is important to evaluate the extent of softness contributed by neem tannins on the final leathers. The experimental leathers garad-neem exhibited better softness compared to the garad control leathers.. The trend in the object assessment of softness values are in accordance with the data shown in table 2. The obtained values of the grain crack and grain break in this study are normal and indicate good strength of the leather produced. Whereas the flexibility after 100,000 flexes for the experimental leathers compared with the grey scale indicates good flexibility and the semi chrome leathers produced could be accepted for shoe upper leather manufacture, IS, and SS [22, 23].

garad hydrolyzable tannins undergoes hydrolyzis releasing nontannins such as chebulinic acid, gallic acid, etc, which drops the pH of the tannins liquor and causes unlikely collagen swell/ plumping, producing very firm leather, thus the method of blend 'Garad-Neem’ and used natural salt was adopted to control the pH of the tanning liquor and organized swelling/ plumping of the pelts and developed softness, flexibility, strength and thermal stability of produced leather. This is coincided with Looney, who mentioned that pH values of 3.5-4.0 produce flexible leather whereas dropping of pH below than 3.0 produce very firm leather [28]. The shrinkage temperature of both control and experimental leathers were shown in table (2) the thermal stability of collagen is an important property for the assessment of the quality of skin, as it indirectly indicates any structural destabilization of the skin matrix due to microbial attack. The thermal stability of chrome tanned leathers is well known to be greater than 100°C, [21] where the vegetable tanned is much less than chrome. The hydrolysable tanned leather recorded rang of 70 ± 6°C and condensed tanned leather over 80°C [8]. It is seen from the table 2 that just by the utilize 30% of neem in blending of garad in semi chrome tanning exhibited about 10°C increase in shrinkage temperature compared to semi chrome/ garad control leathers. his due to an increase in the amount of tannin fixed in the presence of condensed tannins and increased exhaustion of garad observed can be semi-quantitatively related to the increase in shrinkage temperature of semi tanning systems, and which attribute to the bonding between condensed?collagen-chrome and condensed-chrome-collagen composite which can be explained by bring about countless weak hydrogen bonding between the numerous hydroxyl groups (-OH) of the polyphenols and the countless of (-NH3+) peptide groups, which support of the junction of leather fiber.

The chemical analysis values of experimental leathers (semi chrome/ garad -neem) and control (semi chrome/ garad) are given in Table 2. The chemical analysis data for the experimental leathers is comparable to that of control leathers, however the water soluble matters for the control leathers is more compared to the experimental leathers.
ANOVA analysis data Table 2 confirmed that there are significant differences of (tensile, tear, stitch tear) strengths, shrinkage temperature and total soluble mater of semi metal/ blend tanned leather compared to semi metal/ garad control tanned leathers.

4. Conclusion

quality parameters of semi-chrome/ 'garad-neem' tanned leathers were measured and compared to measured mechanical and physio-chemical properties of semi-chrome/ 'garad' tanned leathers as control and the requirements of shoe upper leather Sudanese standard. The experimental recipe result of semi metal/ 'Garad-Neem’ in leathers proved acceptable properties of strength, hydro-thermal stability, softness and flexibility which act an important viability for the ‘Garad-Neem’ spray dried powder in commercial tanning. The mechanical and physio-chemical properties of the leathers prepared compiled quite well with the standard requirements, the leather concerned revealed the best performance in terms general appearance when used the blend tannins which granted homogeneous interaction and hydrothermal stability of leather compared to garad. This the semi-metal/ blend recipe, besides the acceptable properties of the produced leather is also easily applicable from an industrial point of view.

Acknowledgement

The authors wish to express their deep thanks to Sudan University for Science and Technology for their valuable support. Also our great thanks extended to National Leather Center, IRCC, Sudan for their help and financing. Not only but also our thanks extended to every person who has direct or indirect valuable support.

References

1. Plavan VM, Koliada M, Valeika V. An Eco-Benign Semi-Metal Tanning System for Cleaner Leather Production. Journal-Society of Leather Technologists and Chemists 101 (2017): 260-265.
2. Ludvik J. Chrome balance in leather processing, Regional Programme for Pollution Control in the Tanning Industry in South-East Asia, UNIDO (2000).
3. Ali AA EH, Gasm elseed AG, Ahmed AE. Utilization of Improved Indigenous Tannins of “Garad” In Semi Chrome Tannage. Gavin J Food Nutrit Sci 4 (2016): 1-7.
4. Gold Farb J. Principles of combination tannage: Chrome plus vegetable. Journal of the American leather chemists Association 3 (1999): 79-83.
5. Roig M, Segarra V, Bertazzo M, et al. Chrome-free leather, tanned with oxazolidine. Proceedings of XXXI IULTCS Congress, Valencia (2011).
6. Hui C, Jun G, Zhi-Hua S. A Cleaner Chrome-Free Tanning Regime: Sulfonated Urea-Phenol- Formaldehyde Condensed Polymer and Ferrous Sulfate Tanning. Journal of the American Leather Chemists Association 105 (2010): 18-24.
7. Ebtisam A Hassan, Mohamed T Ibrahim, Sally KA. Optimizations of chrome retanning process to the garad (Acacia nilotica) tanned leather. Journal of Agricultural and Veterinary Sciences 15 (2014): 9-15.
8. Ahmed M, Khirstova P, Icho G. Comparative Study of Tannins of acacia Nilotica and Indigenous Tanning Material in Sudan with Acacia Mearnsii. Suranaree J Sci Techno 12 (2005): 259-265.
9. Al-Khalifa FK, Suleiman I, Assubki H. A variation in tannin’s content of acacia nilotica (L.) Wild. ex Del. in the Sudan, Pakistan Journal of Biocal Sci 8 (2005): 1021-1024.
10. Mahdi H, Palmina K, Glavtch I. Characterization of acacia nilotica as indigenous tanning material of Sudan. J of Tropical Forest Science 18 (2006): 181-187.
11. Ismail A, Ikram EHK, Nazri HSM. Hibiscus sabdariffa L seeds-nutritional composition, protein quality and health benefits. Food Global Science Book 2 (2008): 1-16.
12. Fagg CW, James Z, Mugedo A. Dyes and tannins of Acacia nilotica, Prota (2013).
13. Musa AA, Gasm elseed AG. Utilization of indigenous tannins for chrome retanning. Industrial Research Journal 6 (2008): 90-97.
14. Lamb MJ. The Hausa Tanners of Northern Nigeria and the production of Sokoto tanned goatskins (2008).
15. Rao VSS. Vegetable tanning materials of India, (1st Edn.), Kayem packaging industries, 61/4, Muthu Mudali street, Royapettah, Chennai-600014 (2001).
16. Orwa L, Mutua A, Kindt R, et al. Pinus caribaea-Agro forestry Databases: A tree Reference. And selection guide version 4 (2009): 1-5.
17. SLTC. Official methods of analysis. Northampton: Society of Leather Trades Chemist (1996).
18. ASTM International: D2261. Standard Test Method for tearing Strength by the Tongue Tear, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States (2005).
19. ASTM International: D4705. Standard Test Method for Stitch Tear Strength of Leather, Double Hole. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States (2005).
20. Gomez KA, Gomez AA. Statistical Procedures for Agricultural Research, (2nd Edn.), Johon Wiley and Sons, Inc. New York, USA (1984): 8-20.
21. Mahdi H, Palmina K, Gurashi A, et al. Potential of vegetable tanning materials and basic aluminum sulphate in Sudanese leather industry. Journal of Engineering Science and Technology 4 (2009): 20-31.
22. Indian standard 5677. Specification for shoe upper leather for direct moulding. Indian Standard Institution, Manak, Bhavan, 9 Bhadur Shhah Zafar Marc New Delihi (1986).
23. Sudanese standard 143. General standard of shoe upper leather which tanned using mineral or vegetable (2003).
24. Dutta SS. An introduction to the principles of leather manufacture, (4th Edn.), Indian Leather Technologists Association, Calcutta (2000).
25. Keyong T, Xuejing Z, Ming Y, et al. Influence of retanning on the adsorption capacity of water on cattlehide collagen fibers: The American leather chemists association 104 (2009): 367-374.
26. Musa AA, Gasm elseed AG. Utilization of indigenous tannins for chrome retanning. Industrial Research Journal 6 (2008): 90-97.
27. Nand P, Drabu S, Gupta KR. Insignificant anti-acne activity of Azadirachta indica leaves and bark. J Pharm Negative Results 3 (2012): 29-33.
28. Looney M, Yen Truong LK, Wassenberg J. Enhancing the unique properties of kangaroo leather. A report for the Rural Industries Research and Development Corporation (2002).