BLC Leather Technology Centre

Transcription

1 BLC Leather Technology Centre

2 Unhairing & Liming

3 The Objectives of Unhairing & Liming Removal of hair and epidermis (which consists mainly of the protein keratin) Removal of any residual interfibrillary components, particularly dermatan sulphate To open up the fibre structure, in preparation for tanning

4 What Happens During Unhairing & Liming? Degradation of keratin in the hair and epidermis Degradation of dermatan sulphate Swelling of the fibre structure

5 Chemicals Used Alkali Lime Sodium Hydroxide Sharpening Agents Sodium Sulphide Sodium hydro sulphide Enzymes Di methylamine

6 Alkali Swells the collagen Attacks the disulphide (S-S) bonds in keratin Removes dermatan sulphate

7 Sharpening Agent Facilitates destruction of keratin Prevents immunisation

8 Unhairing Hairburn

9 Keratin NH NH Protein which forms hair and epidermis CO CO CH. CH. S. S. CH. CH NH NH Contains the amino acid cystine (characteristic of the keratin class of proteins) CO CO Disulphide bridges occur between the amino acid cystine on adjacent polypeptide chains

10 Degradation of Keratin Sodium sulphide, sodium hydrosulphide and alkali (OH-) attack the disulphide bond (-S-S-) of the keratin (contained in the amino acid cystine) Once the disulphide bond is broken the hair and epidermis can be attacked further making the keratin soluble, so the hair is pulped

11 Three Forms of Keratin hair cystine C C = O - CH - CH 2 - S - S - CH 2 - CH NH NH reduction (eg sulphide) C = O CH - CH 2 - SH NH thiol group alkaline OH - (immunisation) C = O C = O CH - CH 2 - S - CH 2 - CH NH NH lanthionine

12 Degradation of Keratin The hair and epidermis are also vulnerable to enzyme attack and alkali-stable enzymes can be added to aid the unhairing process The weakened hair and epidermis are removed from the surface by mechanical action Some of the hair in the root will also be degraded

13 Conventional Lime/Sulphide Unhairing 1 disadvantages effluent loading high suspended solids high COD high BOD high N 2 interfibrillary proteins pulped hair undissolved/unused lime residual sulphide - usually removed by catalytic oxidation 2 production of hydrogen sulphide gas if sulphide comes into contact with acid

14 Conventional Hair-Burn Liming Compared to Total Pollution From Leather Manufacture BOD 5 COD suspended solids sulphide total nitrogen 70% 55% 55% 100% 42% (52-63 kg/t) ( kg/t) (77 kg/t) (8 kg/t) (6 kg/t)

15 Environmental Impact Bovine hides COD S2 - NH4 + Cl - (kg/t) (kg/t) (kg/t) (kg/t) Soaking Liming/unhairing Deliming

16 Methods of Reducing the Environmental Impact Hair Save Sulphide Replacement Recycling

17 Sulphide and COD Load (based on 100% float) Process Conventional lime/sulphide Sulphide (mg/l) COD (mgo 2 /l) Low sulphide (thio compounds/ amines, hairpulping) Low sulphide hair saving process (enzyme shower) Low sulphide hair saving process (enzyme thioureadioxide) Sulphide free saving process (enzyme thioureadioxide) Sulphide free enzymatic unhairing (Ref:Rohm)

18 Unhairing Hairsave

19 Hair Save Systems: 2 Steps: 1. Intact Hair Removal by manipulating the addition of lime and sulphide 2. Opening up the Fibre Structure by conventional lime/sulphide process

20 Hair Save Commercial systems 1. Blair Hair System Use of lime to immunise hair shaft then introduce hydrosulphide into hair root* 2. Sirolime System Impregnation with inactive hydrosulphide into root* then activate by increasing the ph with lime *so root has both OH and HS

21 Blair Hair (Röhm and Haas) Soaked hide run run Immunisation 100% float 1% lime % NaHS Lime/opening-up adjust Na 2 S/lime* depending on losses Intact hair removal *Typically 1% lime % Na 2 S by analysis

22 ph 9-10 Blair Hair 1 Soaked Hide

23 Blair Hair 2 Immunisation of Hair Shaft OH - OH - OH - OH -

24 Blair Hair 3 Activation/Intact Hair Removal OH - HS - OH - HS - OH - HS -

25 Blair Hair 4 Hair Release OH - OH - OH - OH - OH- HS OH- HS Swelling Starts ph-12.5

26 Hair-Save Technology Principles: Sirolime system soak penetrate grain with inactive hair release agent remove inactive hair release agent from surface hair immunise hair activate hair release agent (usually OH - ) release hair filter float

27 Hair Save - Sirolime NaHS Impregnation NaHS Recycle Tank Stage Wash Oxidation Ca(ClO 3 ) 2- To Effluent Treatment or Lime Tank Lime Recycle Tank Hair Loosening Ca(OH) 2 Filtration Secondary Liming Hair

28 Possibilities for recycling. Sirolime method. Standard Sirolime Sirolime recycling method Water 250% 100% Sodiumm sulphide 1-1.5% 0.50% Sodium hydrosulphide 1% 1% kg S 2- /tonne hide Money CA Cranston RW

29 Hair Save Röhm HS Process Soak Enzyme Erhazyme and surfactant ph 9 10 Incubation 1.2% Erhavit HS2 Activation/hair Loosening Lime ph Unhairing % Sulphide Filter Relime* Overnight lime sulphide *Non sulphide liming auxiliary amine based

30 Possibilities for recycling. Erhavit HS* method. Without recycling With recycling Savings water 300% 160% 140% Sodium sulphide 1.50% 1.20% 0.30% Lime 2.50% 2.00% 0.50% kg S 2- /tonne hide * TFL product Cantera et al

31 Comparison of Conventional and Hair- Saving Technology pollution load kg/t raw hide technology conventional hair-saving reduction % SS COD S

32 Distribution of COD values for different stages of Processing COD Values (100% liquor) x1000 m g/l lim e lim e - w ash presoak mainsoak delim in g bating Pickle tan Hair-save H a ir-b u rn

33 Unhairing with organic sulphur compounds Mercaptoethanol Salts of mercaptoacetic acid (thioglycolic acid) Formamidinesulphinic acid All strong reducing agents replacing sulphide

34 Unhairing with organic sulphur compounds Reduced risk of hydrogen sulphide generation Oxidation of compounds to harmless byproducts Low sulphide consumption Higher cost

35 Enzymatic Unhairing Proteolytic alkali stable enzymes attack collagen of the grain layer Not suitable as sole application permits reduction of lime to ~1.5% permits reduction of sulphide to ~1.0% Enzyme preparations are expensive Good process control is critical

36 Enzymatic Unhairing Enzymes are applied in low levels eg NUE 0.6 at 0.03 to 0.15% Target epidermis, hair and dermatan sulphate Can attack collagen especially How do they work?

37 cuticle medulla cortex basement membrane

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41 With Sulphide note the destruction of the hair along its length

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43 With the combination of the sulphide and an unhairing enzyme the hair is broken in the zone just above the root - the prekeratinous zone

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45 Comparison of different systems COD Loadings (Liming & Total) For Tested Hair-Save Processes COD Loading (kg/t) Simple HS Sirolime Rohm HS2 Thioglycollic Acid Rohm MC Liming (hair-save) Liming (standard) Total (hair-save) Total (standard)

46 Comparison of Different systems SS LOading (kg/t) SS Loading (Liming & Total) for Tested Hair-Save Process Simple H-S Sirolim e Rohm HS2 Thioglycollic Acid Rohm MC Liming (hair-save) Liming (standard) Total (hair-save) Total (standard)

47 Advantages of Hair-Save Technology environmental benefits: lower BOD/COD lower nitrogen lower solids lower sulphide technical benefits: cleaner grain commercial benefits: can be cheaper in the long run

48 Disadvantages of Hair-Save Technology environmental hair disposal technical requires a fundamental change short hairs (roots) commercial can be more expensive initially, because extra plant is needed

49 Hair-Save Unhairing Borge Garveri AS Norway in 1989 this tannery faced a capacity problem and solved it by switching from a 48 hour soak and lime to a 24 hour process today, if the hairsave process was not run, the effluent treatment capacity would be too small. The hair is also cheaper to dispose of than sludge from effluent treatment. Also the cost of making leather with the hairsave process is more or less the same as conventional processing when all costs are balanced

50 Quantity of hair recovered % drained hair Heavy bovine hides Light bovine hides Calf skin As a proportion of raw weight into process

51 Uses for recovered hair Felt production (historical use) Agricultural fertiliser Orchards, market gardens and nurseries Animal feedstuff cannot be used as sole protein (lacks lysine and methionine) Biodegradable flowerpots Cosmetics (limited applications) Gasification fuel source

52 Environmental Aspects Clean Technology Implementation Effluent volume BOD Total nitrogen Sulphide Suspended solids Sludge (Contaminated) Before 1200m 3 /day 500mg/l 300mg/1 800mg/l 1000mg/l 25000m 3 /year After 1200m 3 /day 400mg/l 200mg/l 400mg/l 500mg/l 18,000m 3 /year

53 Liming

54 What is Dermatan Sulphate Interfibrillary non-collagenous materialproteoglycan

55 Dermatan Sulphate Protein core covalently bound to collagen fibril: Possible role in maintaining the structural integrity of the collagen matrix within the fibril

56 Dermatan Sulphate Removal Dermatan sulphate is removed during unhairing/liming and is associated with opening up of the fibre structure If dermatan sulphate is not removed then the leather will be firm due to fibres that are structure stuck together Enzymes (alkali-stable) can aid the opening up process by degrading the protein backbone of dermatan sulphate The removal of dermatan sulphate can be measured at BLC and used as an indicator of efficient liming

57 Efficient Removal of Dermatan Sulphate Gives opened up fibre structure Facilitates penetration of subsequent process chemicals Produces a softer leather increases area of leather Excessive removal can result in loose, weak leather

58 Dermatan Sulphate Removal and Opening up Region (Bovine) Liming Time (h) Degradation of DS (%) Physical Testing Neck Butt Softer

59 Removal of Dermatan Sulphate Removed by highly alkaline conditions or enzymes Sheepskin Lime/sulphide 56%Removed Scour ph10 13% Removed Non-ionic detergent Neutral ph 0% Removed

60 Bovine removal of dermatan suphate using enzyme (NUE) Limed 18 hours Limed 6 hours plus NUE Dermatan sulphate Dermatan suphate removal 58% removal 56%

61 Swelling Calcium combines with proteins, therefore fewer reactive groups available to produce osmotic pressure and excess swelling Calcium hydroxide Ca(OH) 2 produces lower water uptake than Sodium Hydroxide NaOH

62 The Effect of ph on swelling

63 The Effect of Chemical Concentration and ph Increased chemical concentration and ph increases action on collagen and keratin and increases swelling Lime has low solubility (0.2%) and provides a reservoir of alkali Excessive chemical action can cause over opening up of the structure and eventually cause degradation of collagen (producing gelatin) Insufficient chemical action can result in inadequate hair removal, scud and under opening up

64 Effect of ph on shrinkage temperature A = no added salt B = 2.0 N NaCl

65 Effect of Mechanical Action Increases speed of the unhairing action Ensures removal of pulped hair and epidermis from surface Can increase uptake of water and encourage swelling Excess mechanical action can result in a number of faults including differential swelling drawn grain mottled appearance abrasion of the grain looseness weakness

66 What Can go Wrong? Overliming (longer duration) Looseness Weakness Holes Over swelling and Differential swelling Excess Mechanical Action Overplumping (irreversible) Draw, mottle Loss of grain (by scuffing)

67 What Can go Wrong? Excessive Temperature Loss of grain (nubuck or sueded grain) Shrinkage (dissociation of the collagen) Gelatinisation Skin soup Under liming Residual hair and epidermis Under opening up (resulting in firm leather)