To determine suitable tanning method for tanning ostrich skin and producing properties of ostrich leather, bulk density, thickness, resistance and elasticity of ostrich leather in the main part of the 12-14-month-old ostriches (number = 15) were studied in different tanning methods (chromium, vegetal and aluminum).
Tanning ostrich skin, the mean bulk density and ostrich leather thickness of ostriches were 0/7 ± 0/0 g / cm2 and 1/7 ± 0/1 mm.
The rupture, resistance and elasticity force of chrome ostrich leather (0/33 ± 4/9 kgf), 2/197 ± 9/23 kg / cm2 and (3/53±0/7 percent ) were more than aluminum leathers (4/27 ± 5/5 kgf), kg 7/161 ± 7/26 kg / cm2 (4/46 ± 8/7%), and vegetal ostriches leather 0/13 ± 5/4 kgf, 7/.70 ± 8/21 Kg / cm2 and (1/40 ± 4/6 percent). (P <0/05).
In general, the mechanical quality of ostrich leather was better in chrome tanning than aluminum and vegetal leather.
An Introduction to Comparison of the Effects of Different Tanning Methods on Ostrich Leather and Ostrich Skin
Nowadays, ostrich leather is considered a luxury product, especially in the European, American and Japanese markets. Ostrich skin is tanned in different ways, such as vegetal, chrome, aldehyde, synthetic and aluminum.
In ostrich skin vegetal tanning, tannin and extracted vegetable materials such as bark and minerals are used, which usually make leather brown, but the resulting color changes due to combining with other chemicals and the origin color of the skin.
This method is most often used in the manufacturing of leather which are used in calligraphy and etching, or is used as mold to make stamps because they are not water resistant and their color will change.
Meanwhile, if they are washed with detergents and dried, their sizes are reduced and lose their softness and elasticity and will be hard and dry, so if you placed them in hot water, they will be very small and partially gelatinized.
This causes extreme dryness and rigidity of ostrich leather and, as a result, fragility. Since 1858, chrome sulfate and other chromium salts are used in chrome tannings, which are commonly used.
The resulted leather from this tanning method is smoother and more flexible than vegetal tanning and is less discolored and less shrinkage in water.
A half-made or incomplete ostrich leather is called Wet Blue which is due to adsorption of chrome color.
In aldehydi, tanning, glutaraldehyde or oxazolidine compounds are used, but because of the dangers of formaldehyde for workers and causing allergy to some people they are not used currently.
In skin tanning of ostrich skin in synthetic, aromatic polymers such as novolac or noradol are used to produce white color.
In aluminum tanning, aluminum-mixed salts with different combinations of protein-containing material are used. This type of ostrich leather is used in manufacturing baby shoes or cars cabin leather because of the lack of chrome materials in it.
However, leather industry requires information on the characteristics of ostrich leather in terms of elasticity and other physical and chemical properties to find its exact application in producing of products.
Because the ostrich skin processing differs from the skin of other animals, the product and its usage vary somewhat, therefore, the purpose of this study is to investigate the effect of some common tanning methods (chrome, vegetal, and aluminum) on mechanical properties of ostrich leather
Materials and methods
To evaluate the effect of different ostriches skin tanning methods, five ostrich skins of one to one and half years old were prepared, each of skin was cut in three parts from crosspiece and totally 15 pieces, and each five pieces was processed with chrome, vegetal and aluminum tanning methods.
The tanning operations included the preparation of pickle, wet blue, wet white, vegetal tanning and making colored crust from wet blue and white crust from wet white.
These steps were the same for pickle’s preparation, including soaking, liming, deliming, enzyming, degreasing and pickling. Wet blue was used for chrome tanning and wet white for aluminum tanning.
To prepare the colored crust from wet blue and wet white of the ostrich skin, the rechorome (in wet blue), neutralization, dyeing, fatlicuring, fixing, offload, drying in the air, softening and toggling carried out.
Vegetal tanning from pickle was carried out during soaking, washing, adjusting ion load, vegetal tanning with myrobalan, mimosa, basintan, tamol, lubricating, fixing and drying, and other operations were carried out to make leather like chrome and aluminum tanning.
The leather sample was taken from the main area of the ostriches skin or crown area (Fig. 1)
The mechanical properties of ostrich leather were determined by the national standard methods of Iran.
To determine the bulk density, three samples were taken from the original leather sample in the form of a circular cylindrical roller perpendicular to leather face with an approximate diameter of 70 mm. The mean of four points’ thickness of the sample was determined with a caliper.
By using Vernier caliper, the diameter of the samples was measured with a half-millimeter approximation and with millimeter ruler in two directions perpendicular to the ostrich grain and in two directions perpendicular to the thickness was measured again.
The mass of the test sample was weighted with a precision of one thousandth of gram and the bulk density was obtained from formula (1):
1) Da = 1.273 × 10 m / td2
In this equation, m is the mass (g), t is the thickness (mm) and d2 is the diameter (mm).
To measure the rupture force, resistance to rupture and elasticity, leather samples in dimensions of 10 to 50 mm was prepared.
The samples were fitted between pins of the puller (instron Model 4001) and after the rupture of the sample, the maximum recorded force was noted as the rupture force and the distance between the pins was noted as the sample length at the point of rupture (elasticity).
To determine the rupture resistance of 10 (Tn) was used from formula (2)
In this equation, F is the registered force (Kg), W is the sample width (mm) and t is the sample thickness (mm). The increase percentage of length at the rupture point (Eb) was obtained from formula (3).
In this equation, l1 is the distance between the pins at the rupture point and l0 is the initial distance between the pins.
One-way model (4) was used for analysis of figures in SAS software:
In this formula, yij is each of observations, u is average, i is the effect of three tanning methods and ij is the effect of the random error of each observation.
Results and discussion
The morphological structure of the ostrich skin is similar to the skin of the poultry, but some of its features are similar to the skin of mammals.
For this reason, the characteristics of ostrich leather can be compared with light and heavy leather.
The thickness of the skin of the studied ostriches was 1.5 mm, with a range of 1.3 to 2.5 mm (Table 1). Similar figures for the thickness of ostrich leather were recorded.
In one study, the skin thickness of ostriches of 5 to 14 months was determined to be 66/0 ± 05/0 to 13/1 ± 05.0 mm, indicating getting more thickness of the skin with age gaining.
The thickness of the ostrich skin varies depending on the species, variety, age, sex, and areas of the ostriches body, so that the thickness of the leather of different species of livestock such as blue neck ostrich, black neck ostrich, goat, lamb and buffalo have been reported 1, 9/1, 9/0 , 7/0 and 1/1 mm respectively.
As you can see, the thickness of ostrich leather in the current survey is as high as the figures reported for ostrich leather and is more than leather thickness of often livestock species.
Table 1: The average and the standard error of physical characteristics of ostrich leather and skin.
And: ** in each column is the significant difference in mean values at the level (P <0/05) and (P <0.01) : ns, the means difference was not significant (P <0/05)
In the present study, tanned vegetal leather had a higher but insignificant thickness of chrome and aluminum leather (Table 1).
The optimum thickness of leather clothes, handbags and boots is respectively 85/0, 25/1 and 45/1 mm, as well as lining and upper leather of women handbags are respectively, 5/0 and 8/0 mm respectively. Considering these cases, the most appropriate usage of ostrich leather is in the manufacturing of bags and boots, and is less suited to leather suits.
A wide range of forces (76/0 to 50 kg) was observed for tears in the studied leather (Table 1).
The amount of force needed to tear blue neck ostrich, black neck ostrich, goat, lamb and buffalo were registered at 32, 43, 26, 12 and 82 kg, respectively.
In the leather of domestic goats, the value of this attribute was 5/25 kg. (2)
As you see, the average of leather tear force amount of ostriches in this study is lower than mentioned figures in other studies on leather of ostrich, goat, and buffalo but higher than sheep leather,
In the present study, the average total skin resistance was 10/137 ± 68/19 (50 to 273 kg / cm2), which is less than mentioned figures in other studies, 163 to 214 kgf / cm2, 178 to 194 Kgf/cm2 and 10/137 ± 1/23 kgf / cm2 (see Table)
The range of goat and cattle leather resistance was reported as 94/203 to 93/254 and 93/254 to 92/305 kgf / cm2, respectively. Probably the difference is due to the difference in the thickness of the experimental ostrich leather with other sources.
The minimum resistance to rupture for full grain leather, furniture leather and outerwear of ostriches leather is 200, 170 and 200 kg / cm2, respectively.
Cowhide, upper and lining leather of bag, should have at least 150, 180, 40 and 30 kg/cm2 resistance respectively.
The results obtained in this review are close to standard leather suits and more than upper and lining leather standards, and are therefore of good use in making ostriches leather clothes if they are well-processed and have a good thickness.
In this experiment, the highest mean values for tear, resistance and elastic force were obtained in tanned leather by chromium method (P <0.05), and then these values were reduced in aluminum leather and eventually vegetal tanned leather.
Particularly, there was a sharp decrease in in vegetal leather against chrome leather. Therefore, it can be said that the vegetal tanning method has an inverse effect on the physical properties of ostrich leather
A source of different tanning methods on ostrich skin was not obtained, so the influences of these effects were not obtained too, but according to the mechanical properties of furniture leather, for vegetable and chrome tanning respectively, 200 and 375 kgf/cm2, industrial leather products from 150 to 375 kgf/cm2 and chrome tanning leather for cloths and gloves 250 kgf/cm2, chrome tanned leather in this test can have better usage than aluminum and vegetal for the above goods, but due to the hardness of vegetal leathers, mostly they are used in hard and firm products such as luggage bags and book covers and aluminum leather can be used in car seat covers for tropical areas due to the lack of chromium oxide production.
The average elasticity of ostriches leather was 20/46 ± 05/4, which is as high as the mentioned figures for ostriches leather (50%) and goat leather (40%) and is less than
The maximum tensibility of vegetal and chrome furniture leather products and is 50% and 75% respectively, and industrial leather goods are between 20% and 50%.
Considering the higher elasticity of chrome leather compared to vegetal and aluminum leather in this study, the use of chrome leather in furniture leather is better, although due to the unique properties derived from nodules of the ostrich skin, this type of leather is usually used for decorative and covering items (Table 1).
As it was said, vegetal leather is more suitable for making hard and industrial leather goods due to its less flexibility, and vegetal tanned ostrich skin can be used properly in manufacturing of bags, luggage, book covers and much more.
The resulting density is less than the apparent density of Shoe soles leather (1 and 1.5 g / cm 2) and to an acceptable level for other types of leather (Table 1).
In this study, there was a positive nonsignificant correlation between thickness with resistance such as leather of domestic goat’s leather, while in the evaluation of camel leather, a decrease in the amount of tear, resistance and elasticity was observed with increasing thickness of the sample (Table 2).
The most important issue which was considered in correlation between mechanical properties of ostrich leather, was positive correlation (3/0+) between firmness and elasticity (P <0.01)
Table 2: The correlation of physical features of ostrich leather
Due to the high growth of breeding of this bird in the country, it is necessary to propose suitable strategies for the use of ostrich products especially for ostrich skin.
Meanwhile, how ostriches skin is processed for leather products is very important, and if methods used properly, it will play an important role in the production of optimal ostrich leather products and, ultimately, the economics of breeder and the leather industry.
The study found that ostrich leather has a good mechanical quality, such as other livestock, and, given the difference between different tanning methods, it is necessary to conduct wider practical studies to access higher quality, especially in vegetable leather.