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Файл:Innovative Technologies for Manufacturing Leather and Fur Products. A Study Guide
.pdf
head part
а b
Fig. 1.2. Hides: a – cowhide; b – horsehide: 1 – shanks; 2 – bellows hides;
3 – tail; 4 – head; 5 – crup
A hide/skin with the shoulders cut off is called culatta, and a hide/skin
with both flanks and shoulders cut off is called croupon (cattlehide butt).
Cut-off flanks and shoulders are offal, and a hide with its flanks cut off is
called crop (back). A cut-off horsehide rump is called horsebutt, while the remaining part is called horsefront. Cutting hides/skins along the backbone results in getting sides (half skins), bends (half butts), half backs, horsefront
halves.
Croupon is the thickest, densest, and toughest part of a hide/skin.
In bull hides, shoulders are sometimes even thicker than croupon, but they
are looser and more extensible, and often ribby. In other types of raw materials, shoulders are thinner and looser than croupon. All types of flanks, bellows hides, and shanks are thinner, looser, and more extensible.
Pig skins come to production as whole skins or backs. A feature of
horsehide topography is the presence of two densely structured oval sections
in the rear part of the hide, at both sides of the backbone. These sections are
called crups.
Depending on the complexity of collagen bundle weaving in cowhides, there are five basic classes of corium structure.
Class 1 is characterized by very dense three-dimensional weaving of
larger collagen bundles at an angle of 60–70º with the hide surface.
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Intersections of the bundles form lozenge-shaped structures. This is
the structure of croupon.
Class 2 is notable for many diagonal bundles that sometimes form
the lozenge-shaped weaving; however, the lozenges are not of a regular
shape.
Class 3. Separate thick bundles of collagen fibers extend diagonally
and do not form any lozenges. They interlace with the comparatively thin
and small bundles. The weaving is quite dense.
Class 4 is characterized by the dense interlacing of the thin and short
bundles of fibers forming small loops. There are no diagonal bundles.
Class 5. Fiber bundles are thin, loosely laid, and interlace horizontally
only, at an angle of 5–20º.
Reticular dermis structure of the shoulders in the lower part abutting
upon croupon belongs to structural class 2, its middle part – to class 3, and
the upper one to class 4. Flanks have the reticular layer of predominantly
class 4 and, partly, 3 in the region abutting upon croupon. The thinnest and
loosest regions of flanks are bellows parts and fore shanks. This is class 5 of
the reticular layer structure.
Various regions of a fell have different qualities, such as hair cover
thickness, softness, and height and skin tissue density and thickness.
Fell consists of backbone (back) and belly (dewlap) parts. Dewlap is
only separated out on fells skinned without longitudinal section to use it as
a cased skin, e.g., squirrel, fox, Russian desman, nutria, otter, or muskrat. In
most species, sections are made through the dewlap; in such cases, the edges
of the spread fell are called “sides”.
In furriery, additional topographic regions (Fig. 1.3) are used for cutting fells into semifinished products, depending on the quality of hair covering (Fig. 1.3). Squirrel skins include hind legs (lower half of the belly) and
chest (fore region of the belly). Sheepskin has a front (the neck-related part
of skin to the line connecting the upper recesses of fore shanks), bellows
hides (unhaired skin parts at the sites where shanks are joint to belly), and
belly (sides) representing a region of skin covering the animal belly.
Fore and hind bellows hides of goatskins, woolskins and shearlings,
karakul/fur-bearing sheepskins, and merlushka lambskins are straight; therefore, they are cut off as unusable for manufacturing.
Backbone and shell are the most valuable regions in a hide/skin of
most fur-bearing species, while sides, neck, withers, dewlaps, shanks, and
tail are less valuable. However, there are exceptions. For example, nutria
dewlaps are prized higher than backbones.
Fig. 1.3. Karakul sheepskin: 1 – shell; 2 – backbone; 3 – withers; 4 – sides;
5 – thighs; 6 – shoulders; 7 – neck; 8 – dewlap; 9 – tail; 10 – head;
11 – shanks; 12 – bellows hides
Animal hair. Animal hair refers to the crop of multiple hair shafts cov-
ering the hide or skin. The primary function of animal hair is to protect
the body against thermal shocks, while that of skin is to protect it against
various mechanical actions and to preserve moisture in body tissues.
Properties of hair and skin tissues in a fell vary depending on the animal sex and age, season, area, and habitat conditions, as well as the method
of fell processing.
Hair consists of protein named keratin. Keratin is resistant against diluted acid solutions, water, and enzymes, but it is less resistant against alkali.
It contains much sulfur, which makes it different from collagen.
A hair germinates in corium. Hair consists of a root and a shaft. Root
is the hair part located in a follicle situated within the papillary dermis.
The thickening of the hair root forms its bulb. Hair root is in the hair follicle
formed by dermis tissue. The outer shell of the hair follicle is called hair sac,
while the inner one is called root sheath. The bulb is encircled, like with
a cap, with a small outgrowth of dermis, the hair papilla. Hair papilla is saturated with blood and lymphatic vessels.
In its cross-section, the ripe part of a hair shows three concentric layers: Cuticle, cortex, and medulla.
Cuticle is a very thin (0.5–0.3 μm) outermost layer of a hair, consisting
of keratinized lamellar cells that contain amorphous keratin. The cells overlap like fish scales. Cuticle is impermeable and stable against chemical
agents. The cuticle surface state determines the shine, felting resistance, water repellency, and dyeability of a hair.
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Cortex is considerably thicker than cuticle. Hair strength depends on
the cortex thickness. Cortex contains pigments that colorize the hair. It consists of spindle cells located along the hair axis. Under the microscope, it appears as a continuous mass.
Medulla of a hair consists of keratinized cells and represents a loose
porous tissue. There are pigment granules and air bubbles inside the cell.
With its medulla being strongly developed, the hair is brittle and has a lower
stretching resistance. The stronger is the medulla, the warmer is the fur.
In the reindeer hair, for instance, medulla makes 98 % of the overall hair
thickness. In the seal hair, it is not present at all. Therefore, deer fur is warm,
but brittle, while that of seals is strong, but less warm. There is no medulla
in the ripe hair tips or in the lower part of the hair roots. Presence of medulla
in the hair root provides evidence that the hair continues to grow. A growing
hair is connected to the hair follicle papilla. As a hair grows, it raises up, and
a new growing hair gradually pushes the ripe one away. Massive change of
hair is called shedding.
Hair classification of fur-bearing animals. Depending on the shaft
crimp degree, hairs can be straight, bent, jagged, wavy, corkscrew-shaped,
spiral, or kinky. There are five hair categories of fur-bearing animals:
1. Guidance hairs are rather thick and resilient, have the longest shaft,
and their tips elevate on the hair cover surface and form a kind of a veil due
to the color differences; there are not many of such hairs, about 10–15 per
1 cm2. Supporting underfur, they prettify the fur and make it opulent.
2. Guard hairs (protective hair) are shorter and thicker than the guidance ones. Like the latter ones, they function as support and protection for
fur hair (underfur).
3. Intermediate hairs are between the guard and fur ones in terms of
their thickness and length.
4. Fur hairs (underfur) are shorter and thinner than all other hairs. They
are very delicate. They form the lower, densest layer of hair cover.
5. Sense bristles (whiskers, vibrissae) can be found at certain locations
on the body, such as on upper and lower lips or under the eyes of an animal.
In ungulates (hoofed mammals), there are usually no more than 2–3 hair
categories (mostly fur and guard hairs). Hair cover of pure-bred fine-wool
sheep consists of fur hairs only.
Parameters influencing the quality of raw materials. Quality of hides,
raw fur skins, and sheepskins is evaluated organoleptically and using chemical analysis; the bacterial status of the hide is assessed, as well.
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Chemical research consists in quantitatively defining the hide components: Moisture, ash, protein- and fat-containing substances, and pH of aqueous extract. Cured hides may also contain NaCl, Na2CO3, formaldehyde,
Al salts, etc.
Bacterial status of hides is identified by studying them under microscope. Bacterial hides are those, in the papillary layer of which most hair
follicles are degraded, while collage fibers are found in their reticular layer.
1 . 2 . P r i m a r y P r o c e s s e s o f R a w M a t e r i a l s
Primary processes include:
1) Techniques used to kill an animal;
2) Preparing the carcass and flaying;
3) Trimming and degreasing the hide; and
4) Curing.
Techniques used to kill an animal. Best hides are those flayed off animals killed in autumn or in early winter. The main requirement for killing is
bleeding of animals to be as complete as possible. Remaining in the hide
vessels, blood gets decomposed or is removed in its undecomposed form
during production, which leads to developing cut marks, such as the veininess of outer skin layer.
Livestock may be slaughtered by electrocuting followed by bleeding,
for which purpose neck vessels are cut at their chest cavity exit sites using
a special knife. Sheep, goats, and pigs are slaughtered without pre-stunning,
just by slitting neck blood vessels.
Fur-bearing animals are killed using shotguns, body-gripping traps,
leghold traps, live traps, etc. Caged minks, white foxes, red foxes, and sables
are killed by intramuscularly injecting a special chemical solution or electrocuted with 30 V. Then the operators bleed the carcasses.
Flaying. Carcasses are cooled and then flayed. Flaying techniques:
– Splitting is the flaying technique for larger animals, such as bear or
tiger, for marine animals, such as fur seal or seal, and for lambs, sheep, goatlings, calves, beefs, and colts. They are sectioned along the white line, i.e.,
in the middle of chest, abdomen, and limbs;
– Pulling is the flaying technique for fur-bearing animals, such as er-
mine, Siberian weasel, sable, etc. A section is made around the mouth, and
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nose cartilages are cut through to ensure that the snout remains with the fell.
Then, holding the head with one’s left hand, they turn the upper lip up
to the eyes. After that, they pull off the fell from the lower lip and chin. Thus,
by turning up the skin from below and from above interchangeably, they pull
it to the ears. Having cut through ear cartilages, they put off the fell from
the head. Tail is either pulled out or cur open with a longitudinal section
along the underside;
– Case-handling is used to flay snow leopard, squirrel, beaver, wolf,
hare, etc. The main section is made by a sharp knife on the internal side of
hind legs and then of fore legs. Tail skin is cut open. They start flaying from
the hind legs and tail. Then they suspend the carcass with a stick running
through the tendons of hind legs. From the suspended carcass, the fell is
practically pulled off. They call it “case”, because the carcass with its rump
and oral region open looks like a case;
– Lateral section forming two croupons (the upper one and the lower
one), each of which more uniform and more homogenous in their structure
and physical-mechanical properties than the hide of the same animal.
This technique is used to flay pigs and hogs.
Trimming and degreasing. At the trimming/degreasing stage, operators remove subcutaneous fat, excess fleshes, muscles, and tendons, as well
as the topographic areas that are not used in dressing. They also remove dirt,
blood, and adhering dung.
When trimming peltries, operators remove cartilages of ears, bones of
legs, and tail vertebrae. Otherwise, peltries cannot get dried properly and
may deconcoct. Non-degreased peltries get cured 3–4 times slower than
the degreased ones, since fat hinders the diffusion of curing substances. Unremoved fat spots the fur and distorts the color of leather fabric. In non-degreased peltries stored for a long time, hair connection to corium becomes
weaker, and hair slip occurs.
Peltry fat layer is removed using a knife or a scraper, blocking
the peltry or putting it onto a straining board. Peltries can only be degreased
from the hind end to head, otherwise hair roots may be cut through. Upon
degreasing, they wipe the peltry out with a bag cloth and degrease additionally with non-fat wood chips moisture with benzine or white spirit. The chips
are shaken out upon degreasing.
Curing. Freshly flayed hide is called “green” (or raw) hide. There are
up to 20 bacteria species on a green hide. After 8 hours, one bacterium may
produce over 4 million microorganisms. The hide starts putrefying. Color of
the fresh side of leather changes, off odor occurs, and the connection
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between hair and corium becomes weaker. Hair slip occurs, and then the stratum corneum exfoliates. After being flayed, the hide must be cured within
at most 2 hours.
All curing techniques are aimed at log reduction or at creating conditions unfavorable to their growth.
Curing is performed by chilling, drying, brining, dry salting, pickling,
or souring.
Chilling. At a low temperature, microorganisms stop being active.
If a hide is chilled in the wind and at a very low temperature, it dehydrates
considerably. White spots (spues) appear on it, which are resistant to tanning.
Chilling is a temporary measure. Chilled raw materials are defrosted and
cured by brining. Weight of the chilled raw materials must be 95 % of
the green hides, i.e., weight loss must be 5 %. Weigh of spue-marked hides
reduces by 25 %.
Air drying. At a humidity of 20–30 %, bacteria stop developing. Air
drying is based on this fact. Material is dried at the temperature of 20–35 °C,
relative humidity of 45–60 %, and permanent room ventilation. Hides should
not be dried near heating facilities, at fire, or in the sun. If drying is too intense, the superficial layers shrink locking in moisture in the internal layers
where bacteria may develop. Moisture contents usually reduce from 70–75
to 12–16 %. This technique is simple and cost-neutral. Pelts are light in terms
of weight. It is easy to sort and transport them. Pelts are usually dried on
special frames, otherwise they may spring. Pulled off pelts are thoroughly
flattened and dried on frames or poles.
Brining. The widest-spread technique of hide curing. Hides may be
cured by this technique through salting (dry salting) and brining proper
(the hide is placed in a saturated salt solution brine).
In dry salting, raw materials are processed by dried pure dairy salt
containing at most 5 % of moisture. This produces a saturated salt solution
buried in the hide, which blocks the development of microorganisms. A well
salted hide must have a dense and resilient corium and wet, but not moist
hairs tightly bound to corium. The pulled-off hide shall be spread with its
flesh side up and thoroughly flattened on a wooden rack sprinkled with sodium chloride and squinting towards edges for brine to drain. Salt should be
sprinkled onto the flesh side in such a manner that its largest layer is on
the thickest topographic areas. The second hide should also be put onto
the first one, with its flesh side up, shoulder to shoulder and shell to shell,
and salted in the same manner. This should be continued until a pile is
formed of 1–1.5 m high. Smaller pelts become salty within 4–5 days, while
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the larger ones within 6–7 days. Salt consumption is 40–45 % of the weight
of green hides. Antiseptic should be added to sodium chloride: Paradichlorobenzene or white tar, 1 or 0.8 % of sodium chloride weight, respectively.
In sprinkling hides with dry salt, a thin layer of the saturated sodium
chloride is formed on the hide surface. Due to high osmotic pressure, the free
water of the hide diffuses in the saturated sodium chloride solution on
the hide surface, sodium chloride simultaneously diffusing into the hide
structure, i.e., the hide gets dehydrated. Sodium chloride diffuses in the hide,
and the hide is dehydrated, until the sodium chloride concentrations inside
of the hide and on its surface become well-balanced. Water with salt dissolved in it runs down along the rack sides as a solution containing blood,
lymph, and other protein-containing substances.
Brining consists in keeping hides in the concentrated sodium chloride
solution, followed by adding some dry salt in stacks. Additional salting can
be replaced with sprinkling hides with calcine soda suspension in the presence of an antiseptic agent. Diary salt concentration in the brine is maintained by adding it every 6 hours. Antiseptics are added to the solution, too.
The total duration of brining shall be 16–24 hours, the float ratio (FR) being
2.5–4.0 and temperature being 10–20 °C. Salt consumption is 50–60 % of
the green-hide weight. Hides may be brined in pits, paddles, or drums. Upon
being unloaded, hides should drain for at least 2 hours.
Curing by dry salting and by brining is based on the same (diffusionosmotic) principle; the only difference is that the dairy salt concentration is
lower in the brine, and water osmosis prevails over the salt diffusion
in the hide. Then, while hides are salted additionally, salt diffusion prevails.
When brining cattlehides or pig skins, one may increase the temperature up to 40 °C and use ammonium sulfate as an additive. All this will result
in accelerating diffusion-osmotic processes within the hide. The total process duration gets reduced. Advantages: Hides cured by brining have a better
storage stability, higher curing evenness, fewer defects, and lower contents
of dirt and soluble proteins than those cured by dry salting. Leather yield
increases in terms of area. Disadvantages: High salt consumption (50–60 %
of green-hide weight), high labor intensity, and large water consumption for
preparing the brine.
In brining, hide loses moisture and absorbs salt. Moisture content reduction reaches up to 30 % of its weight. Weight decreases, since the hide
loses more moisture than it absorbs salt. Reducing the hide weight during
brining is called weight lose. Mass yield of all types of green hides but pig
skins makes 83–87 %. Area yield of pig skins is 90–95 %.
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Brining is also used to cure sealskin, sheepskin, and dogskin.
Dry salting. It is used to cure lambskins of all sheep breeds, such as
caracul, karakultcha, yakhobab, krimmer, saksak, or kid pelts, sheepskins,
and dogskins. Dry salting represents a combination of brining and drying.
First, green hides are brined. Dairy salt consumption is 20–25 % of the greenhide weight. Then the material is dried. Weight yield of dry-salted materials
is 50 % of green-hide weight. Area yield is 94 % for sheep- or goatskins.
Moisture content is 18–20 % and dairy salt 15–20 % of the hairless
hide weight.
Souring. It is processing hides using bread kvass made of oat or barley
flour with addition of dairy salt.
Souring is a complex process consisting of pickling with organic acids
(more frequently, with lactic acid), enzymatic action, and gases affecting
the corium. With this being done, the hide corium microstructure undergoes
considerable changes. Fiber bundles are divided into separate fibers and fibrillae, which results in the hide being able to be stored for a long time. Souring is used to cure caracul, karakultcha, and yakhobab previously cured by
dry salting. Caracul lambskins preliminarily cured by dry salting are soaked,
cleaned of salt and dirt, and processed with bread kvass. Soaring duration
ranges from 8 to 12 days, depending on temperature. Soaring sleeks the hair
cover, naturalizes its color, while the curls restore their natural form, tightness, and density. Corium becomes softer and more flexible.
Souring disadvantages: Use of food, long duration, and labor intensity.
Acid-salt curing. This technique is used to cure the pelts of small rodents, ondatra, fur-finished shearlings, and wool sheepskins. Acid-salt curing
differs from sprinkling with dry salt by the composition of the mixture used
to rub superficial fasciae includes both sodium chloride (up to 90 %) and
aluminum mordant (5 %), and ammonium chloride (~ 5 %). Total mixture
consumption is 35 % of the green-hide weight. When cured using this technique, sheepskins do not defects, such as hair slips, rotten spots, or pink discoloration, which all often occur in salted hides.
Other curing techniques. Compositions used in curing skins and hides
are known to frequently contain polymers. Conventional methods of disinfecting hides and skins, such as fluorine silicates, chlorine-containing agents,
or phenol-based mixtures, do not completely ensure the protection against
biological damages and are highly toxic.
Currently, fur and leather manufacturers increasingly use imported reagents characterized by quite a high quality. However, their price is much
higher than that of domestic ones. In this connection, quite promising
are polyalkylene guanidines – polymeric biocides developed by Russian
chemists. These compositions represent water-soluble polymers with a wide
spectrum of biocide effect, high stability, and low toxicity.
Currently, curing compositions are increasingly complemented with
iodine, one of highly active antimicrobial substances, which, being combined
with the copolymer of vinyl benzyl chloride and N-vinylpyrrolidone, provide
a long-lasting antimicrobial action.
Benzoic acid provides antioxidant, antimicrobial, and weakly pickling
effects. As an antioxidant, it reduces free-radical fat rusting, which considerably decreases and simplifies the taking-up if hides, since degreasing represents the most labor consuming and sensitive process. Hides processed
with benzoic acid are distinct in their market condition when stored within
three months at normal conditions, and they are contaminated with microorganisms 10–16 times less often.
There are hide curing compositions that contain aqueous polymers,
such as the mixture of carboxymethylcellulose and polyethylene glycol.
They help enhance the fur skin quality by increasing its plasticity and area
yield by 4–10 %. Moreover, the technique enables subsequent hydration
1–2 times faster, as well as does not require adding any antiseptic. This is
achieved by the fact that the composition additionally contains dairy salt, hydroquinone, and penetrator, acrylic acid polymer being used as the watersoluble polymer.
Well-known is the technique of curing caracul pelts with a mixture of
water-soluble polymers, although they are normally cured using the drybrining technique, which results in forming some defects, such as salt stains,
burnt spots, bruises, etc. High commercial quality of caracul pelts is achieved
through processing green hides preliminarily washed with clean water with
detergents with the solution of polymers, plasticizers, and antiseptics. They
are cured by the mixture consisting of 10–30 g/dm3 of carboxymethylcellulose and 5–12 g/dm3 of polyethylene glycol. Curing action of the solution
consists in polyethylene glycol quickly penetrating through all the layers of
the fur skin, carrying the particles of carboxymethylcellulose and diethylene
glycol or glycerin, which provide the fur skin with plasticity and density by
coating collagen fibers. Penetrating the fur skin, polyethylene glycol dehydrates it and, being deposited within it, ensures the beginning of curing, preserving the hides and providing whitish color to the fur skin.
Green-hide area yield can be increased by processing the green hides
while curing with a composition containing hydrolyzed polyacrylonitrile (“hy-
pan”), i.e., the product of partial hydrolysis of polyacrylonitrile with sodium
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