Production of Wet Blue Cow Hides

Leather technology

Dayalbagh Education Institute(Dayalbagh , Agra)

Flow Chart of Wet Blue Production1. Selected raw stock 2. Trimming 3. Weighing 4. Soaking 5. Liming 6. Fleshing 7. Selection(if required) 8. Weighing 9. Chemical Wash 10. De liming 11. Bating 12. Pickling 13. Chrome tanning(with or without pre tanning) 14. Basification 15. Drain out the chrome liquor and pile up for 4-7 days for

completion of fixation and polymerization reactions

Leather: Leather is a durable and flexible material created via tanning from putrescible raw hides and skins, primarily from cattle hide.Tanning is the process of controlled denaturation of protein of the raw hides and skins.

Selection,Trimming and Weighing

1. At first select raw hides/skins and put aside the putrefied stock to treat separately

2. Next we trim the unnecessary part of the hides or skins

3. After that measure weight, because we use chemical till fleshing based on this weight.

SoakingIt is a process of rehydration of preserved raw hides or skins

Quality ControlpH Check-9.0 to 9.5(if pH is 10,no problem)Cross Section Check-Take cross section, if the entire part feel wet uniformly then soaking has done.Duration-22to24 hours in industry. Agitate the drum for 10 minutes interval of every hour

Different checks-1.Two hour after soaking, touch the hides with hand,if it feels softy then its ok. 2.Drop the soaked hide from high place,if it falls down in a place uniformly then its ok. 3.If flesh side become slippery then soaking has done

We use NaCl to remove Hyaloglunic acidBaume check- Conc.check of salt. It's measured during soaking and pickling(sometime in liming).For soaking the value is 3-4(in several tannery they keep 2-3)If the pH goes over 11,it is called immunization of soaking. In this case hair gets fixed in its root and cause problem in liming process.

Soaking

• Soda Ash or Na2CO3- It increases the pH & works as bleaching agent. It helps to keep pH within 6.5 to 7.0 of raw h/s

• Caustic Soda or NaOH- It works as Soda ash

• Wetting agent-It wets back wet or dry salted leather during soaking. Some wetting agents are:- 1.LD600(buckman) 2.Lissapol EF(ACI) 3.Eusapon FB(BASF) 4.Sinteral BD(Alpha) 5.Metapol WA 6.7794

• Bactericide- It prevents bacteria's growth in raw h/s

• Soaking Enzyme- It works as catalyst to return the wet condition completely in h/s just like green condition and also remove loose plunk which grows during mechanical agitation of soaking.It also assists to control the pH in optimum level.

Chemicals

Liming-Liming is the treatment of soaked h/s with milk of lime(CaO) with or without addition of Na2S to remove the hair from the grain surface of the h/s.

Objectives Remove the hair from h/s Swelling & plumping the collagen fiber Split up the fiber structure at the fibril bundle layer Remove the non collagenous substances Remove inter fibrillary cementing materials Emulsify fats and greases Opening up more reactive site for tanning Hydrolysis the peptide bonds, amide side chains,

guanine side chains Removal of dermatan sulfate

pH-12 to12.5

Cross section test-Drip phenolphthalein in the cross section of limed pelt, if deep pink color appears, liming is confirmed.

Layer- If double layer appears in the cross section of limed pelt, then liming has done.

Swelling & Plumping- If the pelt uniformly distended then that’s plumping, it needs 8000lb pressure to bring the water from inside. If the pelt inflate in different place that’s called swelling, it requires 48000lb pressure to bring out the water.

Duration- 24 hours in industries, but it varies in laboratory.

Hair Slip test-Before soaking we should test hair slipness, if hair slips then the raw stock is putrefied.

Controls

Chemicals1. Sodium Sulfide (Na2S)2. Calcium Oxide (CaO)Conditions If the hide has great thickness and areaSodium Sulfide (Na2S)-3.5%Calcium Oxide (CaO) -3.25% If the hide has mediocre thickness and areaSodium Sulfide (Na2S)-3.5%Calcium Oxide (CaO)-3.5% If the hide is thin and small in sizeSodium Sulfide (Na2S)-3.5% to 3.75%Calcium Oxide (CaO)-4.0% In case of goat skin(Any size and thickness)Sodium Sulfide (Na2S)-5.0%Calcium Oxide (CaO)-7.0% to 7.5%

Chemicals & Use condition

Different facts of liming CaO inflates the hides and skins

Normally after 3 months the h/s got Wrinkle, after that h/s got Jam in belly portion

In liming we have to add water in afternoon

If the stock got Wrinkle we have to take water less than the stock equal to two joint segment of finger, if the stock got Jam then we have to add water more than three joint segments of finger.

We should add reactive chemicals in three steps in 30 minutes interval or applicable time interval

Piled up limed pelt

ObjectsLowering the pH from 12-12.5 to 8.5-9.0Remove the limeRemove swelling and plumpingDepleting the pelt

Deliming: It is an intermediate process between liming and pickling

Quality Control

pH- 8.2 to 8.8

Cross section test-Drip phenolphthalein in the cross-section, if light pink color appears or the pelt become colorless deliming has done

After deliming we press the pelt by hand, if it feels soft, then it does mean the protein inside pelt has prepared for fixation reaction

Deliming ChemicalsWe can use anything which has ability to reduce pH, but the popular chemical is NH4ClWaterHydrochloric acidSulfuric acidBoric acidLactic acidFormic acidAcetic acidAmmonium sulfateCarbon di oxide

If the pelt is thick and large (NH4)2SO4- 2.75% to 3.0% (duration-75 mins)

Medium thick and medium size pelt(NH4)2SO4- 2.5% (duration-75 mins)

Less thick and small pelt(NH4)2SO4- 2.0% to 2.25% (duration-50 min-60min)

For all types and sizes goat and sheep skin(NH4)2SO4- 1.5% (duration- 45 min)If bath falls down, upload the pelts in the drum, add 80% water and 0.25% (NH4)2SO4 then run the drum for 10 minutes

Condition

Purpose: Peptizing the fiber structure and eliminate the alkali swelling with the aid of specific enzyme.

TestspH check- 7.5 to 8.0Cross section test- Drip phenolphthalein in the cross section of

the pelt and if it turns into completely colorless, then bating has finished.

Thumb test- Press the bated pelt with thumb, if the left a print their that means bating has done

Bubble test- It basically does for goat & sheep skins as those have more compact weaved structure so it requires both acid and basic bate. We’ll wrap the bated skin if bubble comes out then it’s ok

Bating : Depending on the use of leather we treat h/s with enzymes to soften them, this process is done after deliming is called bating.

Bating-things to keep in mind

Hides bating depends on the final stage of the delimingIf light pink color exist after deliming and the pelt

remain light soft and thick duration of bating 60 minutes

If the pelt turn into colorless and become too soft then the duration of bating is 45-50 minutes

In case of sheep and goat skin, alkali bating is done prior to acid bate. Add 0.2% HCOOH in the alkali bate and revolve 10 minutes then start the acid bate and the duration will be 90 minutes

Enzymes Theoretically there are three types bating enzymes. They are:-1. Weak bating enzymes- 500 to 1000 LVU2. Mid strong bating enzymes- 1000 to 1500 LVU3. Strong bating enzymes- 1500 to 2000 LVU Practically the available enzymes are mixture of the upper

classified enzymes. There are two types available commercially, they are:-

1. Alkali bate2. Acid bate Available enzymes are-1.Oropon K (TFL, Alkali bate)2.Buzyme 146 (Buckman, Alkali bate)3.Nissabate EF (Bantage, Alkali bate)4.Tripsol D (Alkali bate)5.Oropon BRS (TFL, Acid bate)** LVU- Lohlein Volhard Unit

PicklingThe treatment of delimed or bated pelt with a solution of acid and salt is known as pickling. Recently it’s been strongly supported that by proper adjusting of salt & acid in this operation a large amount of hydrolysable tannin can be easily reduced. Objects:Preserve the pelt for further treatmentAcidify the pelt, the pH bring down from 7.8

to 2.8Oxidize hair root and remove if hair remains

after limingRemove all swelling and plumpingProduce softer, thinner white peltReduce astringency of chrome tanned leather

• pH- 2.6 to 2.9• Cross section test- CS area+BCG =yellow color (if

yellow color appear pickling done)• Beume Check- In pickling the range for beume

will be 7-8

Tests and Controls

• If light green color shows in the pelt we have to add Sulfuric acid from 0.1M to 0.6M and run 30 minutes

• If cow hides, the volume of H2SO4- 1-1.2%• If goat skins, the volume of H2SO4- 0.8%• Run 3-4 hours after adding H2SO4 in cow

hides and run 1 hour for sheep or goat skins• If pickling bath falls down, load the stock in

drum+ 80% water+ 7.5% salt+ 0.5% HCOOH and run additional 10 minutes

Emergencies in pickling

Salts & Acids Salts1. Common salt – NaCl2. Sodium Sulfate – NaSO4

3. Sodium Formate - HCOONa4. Sodium Acetate – CH3COONaAcids5. Sulfuric acid- H2SO4 6. Formic acid- HCOOH

Pickled pelt

PretannageWhich pelts are normally white those are chrome tanned and pre tanned simultaneously after pickling. The pre tanning chemicals are prepared from replacement synthetic tans. In this step the pH value is 3.4-3.6

Chrome Tanning

ControlpH check- 3.7 to 4.0CS test- CS area+BCG= If Reddish yellow turns into green, then tanning has ended

Penetration check- Take CS of wet blue leather if color is uniform through all the parts then the Cr(OH)SO4 has penetrated into the pelt.Surface tanning is known as case hardening, it’s a defect. If pickling is defective then it happens

Chrome tanning process

These are added to pickle bath

1. 4.0% Cr(OH)SO4 (run for 30 min)2. 4.0% Cr(OH)SO4

3. 1.0% HCOONa4. 0.5% Carbonyl sulfide (OCS) as chrome stable fat

Piled up pelts for fixation reaction

Wet blue leather

It’s done to fix up the Cr salt in the hide proteinIn industry MgO is used as basification agent as it reacts slowly than NaHCO3 thus basicity of the bath get increased gradually. That’s why chromium molecules get fixed up inside hide protein properly and uniformly

Basification

Advantage of Basification

• Increase strength properties1. Tensile strength- 200 kg/cm2

2. Stitch tear strength- 120-180 kg/cm2

3. Ball burst strength- 20 kg/cm2 • Increase soften property

Miscellaneous • Soaki ng & l iming i s done i n same drum• Deli ming and bating is done i n same bath• Chrome tan is accompli shed in other drum• One day prior to soaking Cao & Na2S keep mixed• Enzyme prevents hi des f rom forming loose pl unk and reduce the spots sculptured duri ng mechanica l acti on• Water leve l measurement f or industry is

1. Equal to hides level= 100% water

2. 1 segment of finger joint less= 80% water

3. 1 segment of finger joint up = 200% water

4. 2 segment of finger joint up = 300% water

• Cross section test is the major and confirmatory test for every steps except goat or sheep skin require to perform bubble test in bating

• Soda Ash

• NaHCO3

Mr. G.P Sharma

A VERY SPECIAL THANKS TO

Thanks to All

Govind Mishra