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Ranjan Bera. Marcelo Protz. Response of Maize Varieties to Phosphorus and k Lvels. Shivam Mehra. Its condition, as a result of previous treatment, affects not only its physical structure but also its chemical structure.
The degree of opening of the fibres, the availability of reactive sites for vegetable tanning, the degree of hydration, the presence of salts and the extent of swelling of the skin are all-important in practical vegetable tanning.
Quite a lot of complex phenomena are involved and there is a further complication of one working against another. There is still no decided conclusion as to what are the groups of protein involved in vegetable tannage and even, whether vegetable tannage is a chemical action or strictly a physical absorption. The generally accepted mechanism for vegetable tannage is through hydrogen bonding to the CO- NH peptide backbone of the protein collagen through the phenolic hydroxyl group of the vegetable tannin [14].
This type of interaction is concluded from reaction studies with polyamides. Also it is known that polyphenols interact with side chain functional groups; to amino side chains by electrostatic salt links with carboxylate or hydrogen bonding with carboxylic acid groups depending on pH. It is also now known that condensed tannins have an additional mechanism for reaction, because they are more resistant to removal by hydrogen bond breakers. Thus the vegetable tannins are essentially unionized through the entire vegetable tanning range, and the ionization of the phenolic hydrogen is not the main factor for fixation.
The protein, on the other hand, increases its hydrogen ion fixation with the lowering of the pH; therefore, fixation of the vegetable tannin is dominated by the reaction of the hydrogen ion with the protein, rather than the hydrogen ion on the vegetable tanning material. At the high pH values in the neighborhood of pH 5, the hydroxyl groups on the vegetable tannin material become ionized and the fixation of the vegetable tannin decreases distinctly.
The S-shaped curve near the iso-electric point emphasizes the fact that the reaction is not strictly chemical. The swelling characteristics of the protein are such that hydration of the molecule is least near the isoelectric point but increases both on the acid and the alkaline sides of the isoelectric point.
Increase in pH causes an increase in hydration and in the fixation of the vegetable tanning material at pH values just above the isoelectric point. As vegetable tannage proceeds, the fiber is no longer dominated by water of hydration, but rather has changed in character as a result of the fixation of the vegetable tannins.
The hydration factor becomes less significant, and the eventual fixation curve is a smoother sweep from the neutral pH range to a high fixation at the strong acid range.
The quantity of vegetable tanning material is important to bring about proper tannage is much greater than one would expect from a chemical point of view. The physical size i. Vegetable tannage can be considered as being a partial reaction between the protein and the tannin, the reaction being blocked as a result of the physical size of the hide fiber and of the vegetable tanning extract particles.
As tannage proceeds, additional vegetable tanning materials are deposited on and between the hide fibers, resulting in eventual coating of the fibers and filling of the voids of the hide with vegetable tanning materials. Pollution load studies put forward sodium metasilicate as an effective tanning agent for pelts to apply at small industrial scale also. As temperatures increase, density decreases. When the solid content increases, density increases. Weight ratio is the most important silicate variable.
Ratio is either the weight or molar proportion of silica to alkali. Total solids are the sum of the silica and the alkali. The tanning salt is white in colour similar to that of other alkaline salts Figure 2. The pH value of silicates does not truly reflect the alkali content of solution, due to the strong buffering capability of silica. This means the pH of a silicate solution is kept constant until almost complete neutralization. Silica-this is the primary constituent of all silicates, alkali-a key component of soluble silicates.
Aqueous sodium silicate solutions appear to contain the low [SiO2 OH 2]2-but, depending on the pH and concentration, polymerized species are also present. XSiO2 are metal oxides of silica. Using silicates to tie up metal ions is an inexpensive way to enhance the performance of many processes. Soluble silica reacts with all multivalent cationic metal ions to form the corresponding insoluble metal silicates. Silicates will precipitate these metals out of solution and render them insoluble or non-reactive.
The reactant by-product normally displays long term stability. The problem confronting the tanners is to prepare a very stable solution of silica.
A sol of silica purified is much too sensitive for practical use as the silica is precipitated by very small amount of electrolytes, such as would ordinarily be carried by the skins. As is well known that silicate is easily soluble in water when a soluble silica monomer Si OH 2 is formed at concentration greater than about ppm as SiO2 that is greater the solubility of the solid phase of amorphous silica, the monomer polymerizes by condensation to form higher molecular weight species of silicic acid that depend upon the conditions, separate in the form of solution or aggregate in to three dimensional network and form gels.
The polymerization behaviour of silica as well as the polymerization degree and the size of the colloidal particles, depend on several factors, the most effective being the pH and the presence of salt. The maximum stability of the solution occurs at pH 1. To obtain better penetration, it is necessary that the colloidal silica is present in solution as stable solution of small size particles. Since the presence of salt in the tanning solution is necessary to avoid swelling of the skin, silica gelling is inevitable.
It is thus necessary to operate in pH ranges in which the gelling time as longer as possible [15]. The sols formed are stable only in a basic or a strongly acid medium. The figure 2. Ganguly, showing the stability link of these sols a formation of their pH values of their concentration. The solution formed is stable only in a basic or in a strong acidic medium.
So research is going on to find out the best eco-friendly system of leather tanning which encounter the requirements what chrome tanned leather have. It has been reported that silicon dioxide and sodium silicate are used for manufacturing wet-white leathers.
Silica based tanning produces white leathers hence, the concept of wet-white tanning as a potential alternative to wet blue tanning is appealing. Silica is used for tanning in the form of solution not in the form of powder itself. The ratio of silica absorbed by the skins and the feel of leathers produced were markedly different. From previous studies on silica it is observed that: 1 the silica is absorbed by the skin like any other tanning material, but it can, according to the application conditions, give either leather showing all the characteristics of a full tannage or products keeping the feel of untanned skin, although their silica content is high; 2 The penetration of silica in to the skins is possible only with monomeric or very weakly polymerized products.
However those products have no tanning action. To produce tanning it is necessary that polymerization of the solution occurs during the tanning time. However there are reports on prior silica tannage hindering the vegetable tannage [16]. Aluminium, tannic acid and silica combination tanning is one of the chrome free tanning system of leather tanning in which silica is involved. The presence of silica in that combination tanning system gives rise to produce supple, soft, smooth, fluffy and fuller leathers because it has an ability to fill the loose portions as well as lubricate due to its inherent gelling nature of the leather [7].
Skins stabilized with silicates could be adapted to shaving readily. In the other studies silica was used in chromium tanning. Since polymeric silica may interact with chromium salts through chelate like coordination bonds, thus improving adsorption of the chrome salt on the silica particles and forming synergism effects to favour the chromium penetration and fixation process [15]. More importantly chromium was at zero discharge because chrome was not used in this experimental process.
Another interesting result was that the nano-SiO2 shavings produced in this process could be easily reused. High quality gelatin without chromium was obtained and large amount of water and chemical materials was saved in recovery processes, so the secondary pollution caused by the traditional recovery of chrome shaving could be avoided.
However, the drawbacks associated with the solo tanning with silica are the lack of desired shrinkage temperature and strength properties in the leathers [17, 18, 19, and 20]. To reduce this drawback of silicate, it is required to use combination tanning and improves the required properties of the leather produced. These authors studied the stability of silica solutions as the function of acidity and in the presence of several acids. They pointed out that the kind of acid used had little or no influence, and that ionic acidity only must be considered.
The maximum stability is obtained at lower pH. However, chambard and lasserre assumed it was possible in those solutions very rich in silica, that there would be a high state of polymerization and that this condition could influence the solution stability and their penetration power.
This product is the only one of the series of commercial silicates which is relatively well defined. It is not a viscous solution, but a solid semi crystalline product [21]. Hence, use of silica as a co-tanning agent is expected to improve the properties of Tara tanned leathers. Monomer Linear trimer Figure 2. Hence hydrogen bonding is the weak bond results lower shrinkage temperature to leather.
It reduces the pollution load of chrome, Cost wise it is cheaper than Cr and it is easily available, it possesses tanning property and facilitates buff ability in case of suede leather, bright shades could be obtained with sodium silicate tanned leather on dyeing, silicate tanned leather retains soft even on washing, perhaps due to the lubricating nature of silicates, fullness of the leathers is improved considerably, it imparts high tensile strength to the leather [7].
Silica in the form of colloidal silica, silicic acid has applications in leather processing in the context of wet white that it will be useful. The reagent binds to collagen via hydrogen bonding, so it is not unexpected that there is no an increase in shrinkage temperature.
The effect cannot be called tanning. However the presence of silica within the fibber structure has the effect of reducing the ability of the fibre structure to slip over itself when subjected to distorting pressure.
When the shaving blade applies pressure to untreated pelt, the surface can ripple ahead of the blade, until the pressure gets too much and the blade slips over the surface, generating fractional heat. If the pelt is treated with silica it is stiffened, so the shaving blade cuts rather than distorts the surface. The shrub has been cultivated in Southern Italy, sardhina and in former Indian colonies.
In North Africa, it has been found to grow well, especially in morocco. Tara parts are also known in trade as cevalina or carabin, but this name is not in use. The pods are similar to divi-divi and algorabilla, all three being member of the same genus. Tara is one of the hydrolysable vegetable tanning agents. The tannins from Tara are well known in the leather industry and they are appreciated because their light colour and light fastness compared with other traditional vegetable tannins.
For this reason, demand of Tara increased during the last decades at the time high performance leather production for automobile upholstery has experienced a growing demand. However, there are no specific promotions and researches for the use of Tara tannins.
Its application as tanning agent remains in the technical departments of the chemical suppliers. Tannery technicians obtain very little information from their technical product information-sheets that only specify few recommendations and provide minimum quality values such as concentration of tannins, solids and humidity [23, 24]. Since, Tara and silica produce white leathers, the leathers obtained using these tanning agents are light colour, which are ideal for pastel shade dyeing.
Tara is cultivated as a source of high value products from its pods as tannins based on a gallotannic structure used in the leather industry [25]. Hydrolyzing vegetable tannins cannot increase the shrinking temperature. Usually tara mills and several machines used during the leather processing for mechanical operations contain parts made with iron and the risk of such dark spots is quite high[10].
The following are some of the important properties required for a leather to be used as an upper. Moreover, the quality of raw material nowadays is not same. Hence, some quality enhancements are carried out through processing steps after main tanning. Also, the kind of targeted article or final leather is decided at this stage. Some of the main objectives of post tanning operation are as mentioned below.
With chromium tanning, the pH tends to further decrease since protons are released by hydroxyl bridges of chromium complexes olation. Since the isoelectric point is higher, the skin protein is in cationic form and is too reactive with regard to the syntans, dyestuffs and fatliquors, all in anionic form, employed in the subsequent steps.
The pH value is then raised from 4. Such a transformation is mainly aimed to obtain the desired handle in terms of fullness of the final article and different tanning chemistries can be used here with respect to the main tannage. The introduction of one or more sulphonic functional groups is necessary to make the molecule water soluble and to allow an electrostatic bonding with the cationic amino groups of collagen.
For a good penetration the reactivity of the substrate should be minimized by raising the pH value. Treatment leathers with fatliquor also prevent the leather fibres from sticking together during drying. This results in giving leather softness, strength and suppleness [22]. Fatliqours are required for all types of leathers. Fixation is obtained by lowering the pH, typically with formic acid. They may also vary within the same tannery from time to time. The wastewater from beamhouse process viz.
The wastewater from tanyard process viz. Effluent from vegetable tanning contains high organic matter. The chrome tanning wastes contain high amount of chromium mostly in the trivalent form. The extent of fastness that is the extent of colour removal, colour staining on the contact material is assessed with a set of graded scales called Grey scales.
Grey scale used to assess the colour change in leather surface is called colour change scale. Grey scale used to assess the colour transfer to the rubbing felt or contact fabric material is called colour transfer scale SATRA TM8: The grey scale has five grades from grade one up to five.
The medium size pickled pelts were taken for preliminary tanning experiments. For optimization one pickled goat skin was cut and used for four trials one skin cut in to four equal parts.
The optimized process is used for matched pair comparison with conventional chrome tanned control. All right side of the skins were used for the experimental trials and corresponding left sides for control. Then the leathers were analysed for the organoleptic properties, chemical and physical tests by comparing chrome tanned leathers after post tanning operation at crust stage using standard procedures for testing as these tests are essential in determining the suitability of the tanning chemicals for upper leather manufacture.
The leather chemicals used for processing are of commercial grade. These are the chemicals to be consumed during the leather making starting from soaking to pickling and retanning to finishing as in the conventional method of leather manufacture.
The tanning chemicals are both commercial and analytical grades. The chemical analysis those used reagents includes spent liquor determination COD, BOD , chromic oxide content determination nitric acid, sulphuric acid and per chloric acid fat content determination and total ash content determination. Two different tanning methods were adopted viz. Stirring is required to avoid formation of precipitate and to form homogenous solution.
The quality of the hydrochloric acid determines the percentage amount of it. If the prepared tanning system is not totally solution, it will not penetrate in to the skin matrix and it fixes on the surface of the skins that have an effect on the hydrothermal stability and physical characteristics of the leather.
The masking agents that were used in the silica solution preparation for this experiment are tri-sodium citrate and tartrate. These masking agents are used to enhance the stability of the silica tanning salt pH of precipitation point is elevated.
For ex. SC refers to silicate masked with citrate and ST refers to silicate masked with tartrate ligands. Process: The pickled pelts were taken for further tanning experiments. Add the required amount of prepared silica solution by adjusting the pickle liquor pH 2. Then, increase the pH of tanning liquor by adding sodium bicarbonate to Add the required amount of Tara to the liquor and run the drum for four and one half hours.
At the end of the process check the penetration of Tara by cutting the butt portion of the pelt and observe the exhaustion of the tanning liquor. The tanning recipe is mentioned in table 3.
The amounts of sodium metasilicate, Tara and tri-sodium citrate masking agent used to prepare a tanning agent of percentage ratio T1: S: T are The ligands used in all these experiments were tri-sodium citrate and sodium tartrate. The tanning process is mentioned here under in table 3. Table 3. B: the above recipe, table 3. The primary objective of the present work is to develop Tara and silica combination tanning system to produce upper leathers with good organoleptic properties.
Sodium metasilicate and Tara have been chosen to act as tanning adjuncts to improve the properties of leathers tanned with masking agents. The hydrothermal stability of leathers determined for the combination tanning system is presented in chapter four.
In practical it is observed that silica pre-treatment hinders vegetable Tara tannage because the hydrothermal stability of silica pretanned leather is lower, whereas silica post-treatment does not hinder Tara tannage because the hydrothermal stability of silica post treated leather is higher and the visual assessment of the tanned leather is better.
Theoretically the treatment of leather with silica will not hinder the vegetable tanning agents. Therefore, it can be concluded that tara pretanning exhibits an increase in the shrinkage temperature when compared sodium metasilicate pre-tanning and have better visual characteristics.
This enhanced hydrothermal stability of vegetable tara pre-tanning is due to new cross-links formed and consequent changes in the structure of the skin collagen. The tanning trial process was done with small sample drums shown in Fig. Fig 3. Four full pickled pelts in the range of 3. The percentage of chemicals used was based on pelt weight.
Two partial pickled goat skins were processed to upper leather and from this one half were finished and one half left in crust stage the other leather was used for physical testing. After pH adjustment, required amount of Tara was added to the liquor in three portions within an interval of one hour and drum was run for one additional hour ; totally four hours to give adequate time for the penetration of tara, then penetration of Tara into the skin matrix was check by cutting at the butt of the skin, if the penetration is ok, add the prepared masked silica solution to the tanning liquor and run the drum for two hours and check the pH of the liquor basify to pH 4 by using bicarbonate for the polymerization and the fixation of silica.
Then take out the skins and pile for 48 hours by covering with polythene covers. Next to this the sample was taken from the sampling position and the shrinkage temperature was measured. The process recipe presented in table 3. This partial pickling methodology avoids pickling and depickling process steps. After that Tara is added to the partial pickled liquor and the drum is run for four hours and penetration of Tara was checked by cutting the butt portion of the skin and the prepared masked tartrate silica solution was added and run the drum for three hours.
The pH of the liquor was Next to this drain the liquor and wash the leathers properly and out, pile it for 48 hours by covering it with polyester to keep it safe. Then the sample was taken from the sampling position and the shrinkage temperature was measured. B: Further with reference to the recipies presented in table 3.
Post- tanning processes hold a pH range of 4. A large amount of water and chemicals are consumed in post-tanning processes. A common post tanning operation was carried out for all the experimental tara-silica combination , silica, tara and chrome tanned control leathers in this study.
Here the post tanning operation started from neutralization without rechroming for all the experimental and control leathers. The combination of syntans and fatliquors used for the post tanning was chosen to produce fuller, soft and dyed upper Leathers.
The chemicals used for post tanning was based on leather shaved weight. The process recipe followed is given in table 3. Then vacuum drying for further drying and to increase the stand of the leather and to have smooth grain surface with temperature 60oc for 30 seconds. Then overhead drying for further removal of moisture proceed and then the vibratory staking to bring its softness that it loses during drying. After staking the buffing operation had been carried out on the flesh side to see the effect of tanning material on buffeability of the leathers tanned with tara-silica masked combination and compared with chrome control leather.
From the buffed skins it was observed that the tara-silica combination tanned was better than chrome tanned. Therefore these tanning agents can be used for suede leather manufacture 3. Determination of the fat content plays its role in designing the process recipe for the manufacture of the final product.
The fat content of the Tara-silica tanned crust leather and chrome tanned control crust leather for upper was estimated by taking samples 5gm from the post tanned crust leather.
The leather sample is accurately weighed on analytical balance and transferred into a soxhlet thimble and extraction of oils and fats is done with dichloromethane in a soxhlet extraction unit for 5 hrs.
In the soxhlet the fat was extracted, dried and the solvent was separated and collected in the soxhlet tank to recover. First, the sample was carbonized on a hot plate under a fume cupboard and then placed in a furnace at about oC until the constant weight was achieved.
If it was difficult to burn off all the carbon, concentrated ammonium nitrate solution was added to the residue and it was heated again. Then it was placed in the same crucible, and then dried to the constant weight SLC, 6. The working environmental condition was The moisture content of leather will change depending on the external conditions to which it is exposed and this can often be the cause of changes in the physical properties of leather.
The loss of small amounts of volatile oils, or solvents may also be included in this weight and so this is often termed as being a determination of volatile matter. In real terms these substances are only a very small part of the total loss and so it is a very good estimation of the moisture present.
The aim is to determine the moisture content of the given sample of crust leather. The moisture content of a material is usually expressed in terms of its water content as a percentage of the mass of the dry material.
Wet blue samples from the official butt portion are taken for chromic oxide estimation. A known weight of the wet blue about 0.
Approximately 0. The flask was equipped with a small funnel to prevent the loss of acid during heating. The content was digested under gently heating in a hood until the color changes to orange. As soon as the orange color was shown stop heating and cooled it. After cooling, 10ml of distilled water was added and re-boiled for 10 minutes to evolve the free chlorine gas.
The cooled solution was transferred and made up to ml with distilled water. Sodium Hydroxide pellets were added to the final content till the pH exceeds 10 in the pH paper scale.
The chromic oxide content analysis provides us information regarding the hydrothermal and chemical resistance of the final leather to be produced. The hydrothermal stability of the wet white tanned leather is the measure of the leather to resist against hot water. This analysis is helpful in determining the suitability of the wet white leather for the production of crust as well as finished leathers. This test is conducted using a Theis shrinkage tester.
A thermometer is placed together with the sample to read the temperature at which the leather shrinks. The temperature of the water has been gradually increased and the temperature at which the sample shrinks has been measured as the shrinkage temperature of the leathers.
The wet white leather hydrothermal stability is compared with chrome tanned leather with its average shrinkage temperature 80 oc which is less than the shrinkage temperature of that of chrome tanned leather which has a shrinkage temperature oc. The process of measuring the shrinkage temperature for tanned leathers is as follows. A 2cm sample cut out at the butt area of the tanned leather was clamped between the jaws of the clamp, which in turn was immersed in water with the thermometer to read out the temperature of the water.
The temperature of the water was gradually increased and the temperature at which the sample shrinks was noted. The processes was analysed as per the standard procedure for their BOD, COD, total solids, total dissolved solids and total suspended solids. The term solids is generally used when referring to any material suspended or dissolved in waste water that can be physically isolated either through filtration or evaporation. Total solids are the term applied to the material residue left in the vessel after evaporation of the sample and its subsequent drying in an oven at a definite temperature.
Thus total solids are nothing but summation of total dissolved solids and total suspended solids. Suspended solids are part of solids in wastewater that remain present on filter paper while filtration. Dissolved solids are part of solids present in the filtrate while filtering the sample on filter paper. The various forms of solids are determined by weighing after the appropriate handling procedures. To measure total solids take a clean porcelain dish which has been washed and dried in a hot air oven at oc for three hour.
Weigh the empty evaporating dish in analytical balance and donate W1. Using pipette transfer 20 ml of sample in the porcelain dish then, dry the sample to get constant mass in an oven by evaporating the moisture for long duration usually 3 hours. After drying cool the container dish in a desiccator to avoid loss of mass since it is designed to provide an environment of standard dryness.
First take the weight of filter paper W3 then, add 10ml of waste water sample on the filter paper and filter it then, dry it. Then the COD content is determined based on the standard test procedure. By take 15 ml COD digestion tubes pre-washed with dilute H2SO4 to carried out the test analysis and add the required amount things in sequence.
Transfer 0. Then add 2. Next add 3. Cap and mix the contents wear gloves as contents are very hot and cool. Transfer tubes to the pre-heated COD digester at C and digest for 2 hrs. After that run 3 blanks by substituting DW for sample and proceed exactly as sample. Titration Transfer the contents of the COD digestion tube in ml beaker. Add distilled water to make the volume to 50 ml.
The sample is filled in airtight bottle and incubated at specific temperature for 5 days. The dissolved oxygen DO content of the sample is determined before and after five days of incubation at 20oc and the BOD is calculated from the difference between initial and final DO. Samples of the liquor from various experiments and control process was taken and tested with standard test method 6.
Experienced tanners rated the leathers in a scale of points for each functional property. The comparative ratings for each property are given in Fig III. The ratings are averaged values from two different tanners. The grain smoothness, roundness and dye uniformity of the leathers tanned with masked silica and Tara tanning agent from partial pickled skin has been found to be significantly better than the control leathers.
When comparing the area of the full pickled experiment leather with that of the chrome control leather which was medium size, the full pickled experimental leather is better 6. Experimental tara-silica combination tanning have been found to result in leathers with good uniformity in color.
No differential dyeing between grain and flesh has been observed for the experimental tara-silica combination tanned leather.
Post tanned with sodium metasilicate produced fuller leathers compared to pretanned with sodium metasilicate and chrome control leathers. On the whole the leathers tanned with tara-silica combination had been found to be better than chrome tanned leather. Hence use of tara-silica combination for tanning appears to be an effective option for making leathers with good organoleptic properties.
The moisture present in the leather matrix varies according the moisture relative humidity present in the working place. Temperature is also a well-known factor to influence the properties of matter. Hence it is an accepted procedure to conduct the test at a predefined test environment.
The thickness and width of the specimen were measured in the same position using a standard thickness gauge and vernier calipers, respectively, i. Then the mean thickness mm is calculated. The specimens were cut as a rectangle 50 mm long and 10 mm wide using a press knife which cuts out the specimen. The jaws of the tensile machine were set 50 mm apart, and then the sample was clamped in the jaws, so that the edges of the jaws lay along the midline.
The machine was run until the specimen was broken and the highest load reached was taken as the breaking load. The percentage of elongation is calculated as following. Double edge tear strength — Baumann Tear strength 2. Tear strength test method is intended for use with any types of leather.
The forces exerted during separation of the holders are recorded and the highest force is taken as the tearing load and expressed in newton. Tearing load can be expressed as the quotient of the load by the thickness of the sample. Cut six test specimen three test specimen from along direction and three test specimen from across directions using a cutting knife as a rectangle 50 mm long and 25 mm wide using a press knife which cuts out the specimen having a central slot in 1 operation Template machine.
Continue the test for remaining test specimen. The grain of the leather is subjected to more stain in shoe making process. Therefore the grain is liable to exhibit grain cracks on the shoe surface especially at toe area. This may be due to filling of more retanning materials into the leather matrix to give sufficient substance. Rapid tanning practices over loads the grain side instead of allowing the tanning chemicals, fatliquors and dyes to move into the entire thickness of leather.
This is also a reason for exhibiting grain cracks in shoe making process. This grain crack failure cannot be visualized by simple folding and flexing. Therefore selection of leather for shoe making has to be made after testing the leather for grain crack load and distension properties using standard test equipment called lastometer.
Three specimens cut in the circular size with diameter 50mm. The load and distension at grain crack is read out from the testing machine. By the finishing process, the grain surface of the leather is coated with various substances and is then submitted to different mechanical operations, depending upon the purpose intended whereby the appearance of leather can be highly influenced to make it more useful, attractive and appealing to users.
Hence in my case semi-aniline protein finish type of finish is used and the process recipe of finishing is given in table 3. Hence the samples for various physical tests were obtained as per SATRA TM test methods Dry rub fastness Generally this test is conducted for the following order of cycles, 8,16,32,64,,, and Cut one test specimen about 75 mm square from the finished leather.
Place the test specimen on the horizontal plat form. Secure a felt pad on to the spindle and bring in contact with the test specimen. Adjust the weight to Continue the test until specified number of cycles cycles. Remove the leather and felt pad from the machine. Place the test specimen and felt pad inside the light cabinet to view the materials at 45oangle. Assess for change in colour marring grade for leather and transfer of colour degree of staining with the help of respective grey scales. Wet rub fastness Immerse a felt pad in cold water; boil for 1 minute for complete wetting of the felt pad.
Cool, remove excess water from the wet felt by slight squeezing, attach to the spindle, adjust the weight to 7. Results and Discussions Tanning is a chemical process by which new cross-links are introduced into collagen, binding the active groups of tanning agents to the functional groups of protein Bienkiewicz, The tanning effect mainly depends on the extent of cross-linking between the collagen molecules and the thermodynamic stability of the cross-linking bonds.
A new combination tanning system based on Silica and Tara combination has been prepared as an attempt to widen the options for alternative tanning system, to combat chrome pollution.
In the present investigation, the addition of silica to Tara is expected to improve the leather properties as well as abate chrome pollution. It is hypothesised that the amount of Tara required for tanning particularly making upper leather is higher.
The shrinkage temperature of experimental leathers processed at different conditions order of addition and masking agents with higher amount of Tara is presented in Table 4. Further it is established that masking in silica tanning enhanced the thermal stability of leather greater than 5oc.
However tartrate masking is chosen for further studies in view of its less grain harshest characteristics. The order of addition with tara followed by silica resulted in thermally stable leather compared to silica followed by tara tanning as explained in table 4. Where silica can manage to find sites for interaction even after tara treatment as tara binds with collagen through non covalent interactions. Increase in the mount of Tara usage will result in higher pollution load in effluent and also affects the cost of the leather.
Therefore the shrinkage temperature of experiments and all the controls are given in table 4. Table 4. But tara and silica can only make weak hydrogen bonds with collagen as it is stated in chapter two rather they have the capacity to fill the leather and give fullness since they are bigger size molecules as compared to chromium.
Two experienced tanners rated the leathers on a scale of points for each functional property, where higher points indicate better property and lower points indicates lesser properties. Based on the indicated evidence dyeability, grain smoothness, grain tightness, roundness, softness and fullness of leathers tanned by tara-silica combination is comparable to chrome tanned crust leathers.
But all the organoleptic properties of experimental leathers are better than those of the silica tanned and tara tanned control leathers. Tara tanned leather is the lower grade from all of the experimental and control leathers in its properties especially for softness which has bony feel for hand touch. The tara tanned leather needs more amount of fatliquor or needs especial kind of fatliquors to be comparable with chrome tanned leather softness.
It is clear that the use of silica and tara did not affect the dyeing characteristics of the leather compared to control. No differential dyeing between grain and flesh has been observed for all tara followed by silica combination tanned leathers and chrome tanned leather.
Leathers pretanned with tara and post tanned with silica solution EI shows good grain smoothness, however, the partial pickled EII shows better grain tightness, roundness and overall appearance for the upper leather compared to control leathers as well as full pickled experiment EI.
Hence use of tara followed sodium metasilicate combination for tanning appears to be an effective option for making leathers with good organoleptic properties.
The value of the organoleptic properties for upper leathers are given below in table 4. The spent tan liquor analysis from tara-sodium metasilicate combination tanning was carried out to evaluate the impact of the same on environmental pollution load.
It is seen from the table that total solids load is less than from that of the chrome control tanning system, whereas the COD and BOD values are slightly higher. This proves the presence of vegetable tanning agent in tanning liquor increases the amount of BOD value. Even though the BOD and COD are higher, the wastewater can be easily treated employing simple treatment methods such as aeration, ozonization or aerobic biological treatment methods and the total solids content can be reduced by simple sedimentation or settling techniques.
It is should noted that the chrome is completely eliminated from the wastewater. The chemical analysis data for the experimental leathers is comparable to that of control leathers.
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