Processing Techniques for Different Furs

The Ministry of Science and Higher Education of the Russian Federation Kazan National Research Technological University







G. Lutfullina, V. Sysoev, E. Valeeva




                PROCESSING TECHNIQUES FOR DIFFERENT FURS




Tutorial







Kazan
KNRTU Press
2021

         UDC 675.6(075)



Published by the decision of the Editorial Review Board of the Kazan National Research Technological University

Reviewers:
Cand. Sc. (Technology) D. Semenov
Cand. Sc. (Philology) G. Mullakhmetova









         Lutfullina G.
         Processing Techniques for Different Furs : tutorial / G. Lutfullina, V. Sysoev, E. Valeeva; The Ministry of Education and Science of the Russian Federation, Kazan National Research Technological University. - Kazan : KNRTU Press, 2021. - 108 p.

         ISBN 978-5-7882-3081-8

       This tutorial focuses on different types of fur raw materials, their processing methods and technological operations using Russian and foreign chemical reagents.
       The tutorial is intended for practical classes and lectures for training Bachelor’s degree students majoring in Technologies of Textile Industry. The study guide can also be used for Doctoral and Master’s degree students conducting their research in the field of fur and leather processing.
       It has been developed at the Department of Plasma Chemistry and Nanotechnology of High Molecular Materials.

UDC 675.6(075)

ISBN 978-5-7882-3081-8    © G. Lutfullina, V. Sysoev, E. Valeeva, 2021
© Kazan National Research Technological University, 2021


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CONTENTS

INTRODUCTION.................................................... 4
1. PROCESSING OPERATIONS FOR DIFFERENT TYPES
OF FUR RAW MATERIALS ........................................... 5
  1.1. Spring types of fur raw materials ........................5
    1.1.1. Astrakhan wool ...................................... 5
    1.1.2. Merlushka lamb skins ............................... 19
    1.1.3. Fur sheepskins and wool sheepskins ..................20
  1.2. Winter types of fur raw materials........................43
    1.2.1. Rabbit skins ........................................43
    1.2.2. Dog skins ...........................................51
  1.3. Spring types of fur raw materials .......................52
    1.3.1. Mole skins ......................................... 53
    1.3.2. Marmot skins ........................................56
    1.3.3. Large-toothed souslik skins .........................59
  1.4. Winter types of fur raw materials........................60
    1.4.1. Muskrat skins ...................................... 60
    1.4.2. Squirrel skins ..................................... 66
    1.4.3. Mink skins ......................................... 67
    1.4.4. Marten skins ........................................75
    1.4.5. Arctic fox skins ....................................76
  1.5. Sea animal skins ........................................82
    1.5.1. Fur seal skins ......................................82
    1.5.2. Seal skins ..........................................84
2.  PROCESSING OF FUR INDUSTRY WASTE...........................88
3.  CHEMICALS FOR FUR AND LEATHER PROCESSING .................. 90
REFERENCES .................................................... 106

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        INTRODUCTION




     Fur processing includes a large number of various chemical materials: surfactants, antiseptics, enzyme preparations, tanning agents, acids, dyes and other compounds. The total cost of chemical materials may be more than 50 % compared to the cost of processing certain types of fur. Generally, the quality of the final product depends on the technological operations and processes used for manufacturing semi-finished fur products, quality of chemical materials, and technological equipment.
     This study guide was created according to the experience of the leading industrial companies of the fur industry. The study guide presents the research results of the Department of Plasma Technology and Nanotechnology of High Molecular Weight Materials (Kazan National Research Technological University).
     The study guide focuses on various fur raw materials, chemical and mechanical methods and technological schemes of their processing using Russian and foreign chemical reagents.

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        1. PROCESSING OPERATIONS FOR DIFFERENT TYPES OF FUR RAW MATERIALS



        1.1. Spring types of fur raw materials



     Spring types of fur raw materials include hides of horses, reindeer calfs, fur slink calfs, reindeers, goats, and sheepskins. Sheepskins are subdivided into astrakhan fur, lambskins, fur sheepskins, and woolskins. Spring types of fur raw materials are sorted according to the specific Standards. These Standards do not divide skins of spring types into strains. The quality of the skin is determined by its age-related variability and the defects of fur raw materials. Therefore, such properties as skin size, structural nature, density, height, and color of the fur, thickness of the leather are taken into account to characterize the skins of agricultural animals killed at a certain age and having approximately the same fur hair development.
     The fur of the short-haired astrakhan skins and lambskins is curly-structured. The hair of sheepskins is ripple. The long hair hides have rod-hair structure without curls.
     Depending on the breed and age, several groups of sheepskins and woolskins are distinguished: skins of embryos, lambs and young animals, skins of adult sheep.





            1.1.1. Astrakhan wool



     Astrakhan wool is made of lamb skins of purebred Persian sheep. Usually they are three days old. Astrakhan wool is distinguished by a peculiar form of curls as well as silky and shiny hair. Persian sheep were bred on the territory of modern Uzbekistan many centuries ago. Sheep of this breed are well adapted to the desert conditions. The main producers of astrakhan wool are Uzbekistan, Turkmenistan, Kazakhstan, Tajikistan, and Moldova.



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     Depending on the age of the sheep, various types of fur and wool are obtained: astrakhan wool, broadtail skins, beaver-lamb, and woolskins.
     In the first days after birth, the hair of Persian lambs is curled. A hair has a spiral shape, the axis of which is parallel to the surface of the skin. Starting from the age of three days, the curls become looser and eventually break into separate strands.
     To sort astrakhan wool, the quality of its fur and skin, the quality of preliminary processing and the skin size are determined.
     To assess the quality of the fur, we should pay attention to its silkiness, shine, density, type and size of the curl, as well as to the nature of the distribution of the pattern over the area of the skin. The hides are sorted according to the hair softness. While the hair of some skins is soft and silky, other skins have rough and tough structure. The astrakhan wool of the highest quality has silky and soft hair.
     The hair gloss is one of the main properties. It characterizes the quality of astrakhan wool. Fur skins of the highest grades are distinguished by a beautiful glossy shine. On the other hand, low-grade skins have matte or low-sheen hair.
     Purebred astrakhan beaver-lambs, astrakhan wool and broadtail skins have a short hair, a wide tail at the base narrowed to the end with an appendage.
     Preliminary processing. The skins of lambs are removed in a layer by a long cut along the midline of the dewlap to maintain the area from the head to the end of the tail and from the legs to the feet. The skins should be cleaned of meat, fat, cartilage, dirt, and blood. They should be well defatted, straightened symmetrically without folds, and preserved by the dry-salted method and pickling.
     Astrakhan wool is sorted according to:
     -  the type;
     -  the method of preservation (dry-salted method, pickling);
     -  the skin thickness (up to 0.7 mm and more);
     -  the hair color (black, gray, brown, dapple, etc);
     -      by region of origin (Central Asian - Uzbek or Bukhara, Turkmen, Kazakh; European - Astrakhan, Moldavian, Ukrainian);
     -      by defects (without defects, with defects of the first group, with defects of the second group. It is allowed to combine skins without defects and with defects of the first group in one batch). Low-grade skins are assembled in separate batches. The batches are counted and weighed. A technical passport is issued for each batch. Each skin is marked using a needle punch. A mark indicates the grade and type of a skin.

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     Astrakhan skins and lambskins are characterized by the deep bedding of the hair roots. The thickness of the papillary layer makes up most of the thickness of the skin. In the thickness of the dermis, the fibers are located almost parallel to the surface of the skin, close to one another and form a continuous mass at the border of the papillary and reticular layers. Skin collagen fibers have a looped structure. The papillary layer is penetrated with hair ends, that leads to the formation of a characteristic fracture on its surface during peeling of the mesh layer. The hair height varies depending on the topographic areas from 4.2 to 7.8 mm.
     The weight of the curried skin is on average 275 g (preserved by the fresh-dry method) and 325 g (preserved by pickling). The weight of the skin as a semi-finished product is 225 g.
     Application. Women's coats, short coats, jackets, women's and men's hats and collars are made of astrakhan skins.
     Sorting. Purebred astrakhan skins are sorted according to GOST 9296-74. They are divided according to the fur quality: various degrees of silkiness and shine, consisting of curls of various shapes, covering the entire area of the skin; the neck is covered with curls with a straightened hair length of no more than 30 mm; the fur of the head and paws has a special pattern or curls; on the hind legs, below the hock joint, smooth hair is allowed; the tail is wide at the base, narrowed towards the end, covered with elastic or loose spreading curls.
     The skins should be removed in a layer saving all parts, symmetrically straightened with a tightening to the width, with the paws spread out to the width. The fur should be clean, uniformly colored deep black. The skin should be soft, clean, uniformly and evenly colored blue or dark blue, and stretch in all directions. Tears, crowbars, holes, bald patches, worn-out places must be removed without breaking the symmetry of the skin. Inserts and attachments are selected in accordance with the curl shape, fur quality and skin color. Skins selected for industrial processing are not repaired, but the tears on them should be sewn up.
     Astrakhan skins are sorted by size: large, medium, small, extra small. In addition, the shape and size of the curls are taken into account.
     The purebred dyed skins, depending on the quality of the fur and the shape of the curls, are divided into 26 grades, including large and medium-sized skins. Depending on the defects, purebred skins are divided into four groups.
     Purebred gray undyed skins are sorted according to GOST 3157-69. Purebred dyed skins are sorted according to GOST 3595-74.

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     Marking. Digital code is applied on a skin. It indicates the skin size (large - 1, medium - 2, small - 3. extra small - 4); grades; groups of defects; the skin area is expressed in dm².
     Processing of Astrakhan skins. According to the Standard Technology developed for Astrakhan skins, their processing starts with the operation of soaking, which depends on the method of preservation. To preserve skins by fermentation, the process of soaking is carried out in solutions of sodium chloride (30.0 g/dm³) and acetic acid (1.5 g/dm³). Alums (kvass) of the required acidity obtained after fermentation is also used instead of acetic acid. In case of hair slipping, zinc chloride is added to the bath, and the acidity is increased to 4.0 g/dm³ (process duration - 8-10 hours, temperature - 30 °C). Flint-dried skins are processed for 10-12 hours at 25 °C in a solution of sodium chloride (20.0 g/dm³) and zinc chloride (1.0 g/dm³).
     After fleshing, the skins are translucent on a glass table with with a lighting fixture placed under the glass. This procedure allows us to identify skins with fractures of the epidermis and papillary layer. The skins with fractures are sorted into separate batches, which are not subjected to pickling.
     Souring is used to process fur raw materials using bread kvass. This is one of the oldest methods of fur dressing. The method of pickling has narrowed the scope of souring application significantly.
     One of the most important characteristic of souring is softening. Fermentation provides high softness and ductility, and mechanical strength of the skin, while maintaining the size, reducing the thickness and weight of the skin. In addition, it reduces skin cracking and delamination. During fermentation, the microstructure of skin changes. The intertwining collagen bundles are separated into smaller structural elements during the process of pickling. The loosening of raw materials with a simple structure of skin is noticeable, when the bundles consist of fibrils. A more complex structure of the skin (fibrils-fibers-bundles) does not provide the deep fiber separation.
     Crushed grain and flour (oatmeal, barley flour) are used as initial materials for souring. During the process of softening, flour, malt sprouts, and bran are used. To protect the skin from acid grease, the composition of the fermentation and softening solutions includes a neutral salt (sodium chloride).
     Souring is used only for processing purebred Astrakhan skins after the dry-salted method. This process is characterized by a fine separation of fibers of the dermis. Softening is used to process lamb and goat skins.
     At the beginning of soaring, a fermented solution is prepared. Flour is stirred with water (110 g/dm³) at 40-42 °C and kept for a day in a special vessel. Then the solution is pumped into a drum and diluted with water until

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the acidity of the solution is 3-4 g/dm³ (in the presence of acetic acid). Then, sodium chloride (60 g/dm³) is added. The skins are loaded in the drum and processed for 5-6 days. The acidity of the ferrous solution increases up to 10-12 g/dm³ by the end of the process.
     Souring is a complex biochemical process, as a result of which the composition of the fermentation solution is constantly changing. Flour and grains contain starch, sugars, proteins, enzymes, and fibers. The process depends on starch and enzymes. There are two types of enzymes. The first type relates to degrading (saccharifying) enzymes. The second type refers to proteolytic carbohydrates, which provide the accumulation of sugars and acids, as well as the contamination of grain by microorganisms.
     Starch is the initial product from which organic acids are formed during the process of souring. It is insoluble in cold water. However, an increase in the temperature of water leads to its swelling. It forms a colloidal solution (paste) at 55-80 °C. 10 % of starch is gelatinized at 50 °C, and about 90 % of starch is gelatinized at 60 °C. The paste provides the formation of sugars from it by the action of enzymes. Non-gelatinized starch is practically not saccharified. However, the temperature of the fermentation solution is insufficient for starch gelatinization, and the bulk of organic acids is formed from simpler carbohydrates.
     Thus, starch, which makes up most of the flour, is used inefficient. Although, it can be assumed that part of the starch is gelatinized due to the long period of the process in an acidic medium,
     Enzymes hydrolyze starch and form sugars (maltose and glucose), which are the material for the formation of organic acids as a result of fermentation caused by acid-forming flora. Fermentation is a type of enzymatic process in which enzymes are produced as a result of the vital activity of bacteria, yeast and mold.
     Acids of a fermented solution are produced by lactic acid bacteria, the optimum effect of which is observed at 32 °C. They ferment glucose and maltose with the formation of mainly lactic acid (up to 70 % of the total amount). Acetic, formic and butyric acids are the by-products of the process. After 4-6 hours from the moment of preparation of the solution, the development of putrefactive and butyric acid bacteria is prevented by the acidity of the environment. Foreign cultures growth is inhibited in an acidic environment, and the development of lactic acid microflora is stimulated. The process of stirring inhibits the development of anaerobic bacteria. The use of the same vessels containing spent solutions as a ferment to prepare working solutions also inhibits the growth of foreign bacteria.

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     The souring scheme:


                                     л Organic acids
     Starch ^ Maltose ^ Glucose
                                     \ Gaseous products

     The possible release of gases in the first hours of acidification of working solutions is explained by the vital activity of yeast or mucus bacteria. Then, the formation of gases stops as a result of the rapid growth of lactic acid microflora. Therefore, the release of gases (especially at the final stage of fermentation), as well as the possible release of hydrogen, indicates that the process is proceeding under the wrong conditions. This may be associated, for example, with the development of butyric acid microflora. In this case, microorganisms do not affect the fur skin as they form only organic acids.
     Plant proteolytic enzymes (papain and bromelin) act on collagen and gelatin, breaking various bonds in the protein particle. This leads to a significant separation of the microstructure of the dermis, which determines the high plastic properties of the final fur skin.
     As a result of the fermentation reaction, a reducing medium is created in a fermentation solution, which is equivalent to the medium created by a 0.2 % solution of hydrosulfite, one of the most powerful reducing agents. This environment increases the activity of flour proteolytic enzymes. In addition, reducing agents loosen the proteins in the hide, including reticulin fibers.
     Thus, there are two main effects of the souring process. They are:
     •  proteolytic effect of plant enzymes (dominant factor);
     •  pickling effect (organic acids and sodium chloride form organic pickel).
     Factors affecting the souring (fermentation) process:
     1)      Acidity of the process. The pH of the fermentation bath influences the proteolytic activity of enzymes. The optimum value is about 7 (neutral or slightly acidic environment). As the acid accumulates and the pH decreases, the activity of these enzymes decreases.
     2)      Temperature of the process. Temperature is one of the most important parameters of the process. It influences both the enzyme activity and the development intensity of the microflora. The optimum temperature for the development of lactic acid microflora is 37-40 °C.


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     3)      Duration of the process. An increase in the processing time leads to significant changes in the skin microstructure, while the strength of the connection between the hair and the dermis decreases. Duration of the process depends on the type of skins and the technology used.
     4)      Sodium chloride. It is used to provide swelling in the presence of organic acids. It practically has no effect on enzymatic and microbiological processes.
     Therefore, during souring (fermentation, softening), the accumulation of acid in the solution, pH, sodium chloride content, solution temperature, and sourness of the skins are controlled.
     The quality of the skins after souring is checked organoleptically and histologically by its looseness and plasticity.
     The color of the flesh side of the finished skins is to be light.
     Damage to the hair follicles, causing weakening of the hair-skin bond in the groin areas of the hide, is a sign of sourness of the hides. If we detect hair slipping by slight rubbing with fingers and weak pressure on other parts of the skin, the process should be stopped immediately.
     After the process of souring, the ageing of hides is unacceptable, as it may lead to hair slipping.
     Bating. In order to save food materials, the processes of souring and pickling are combined. It is called bating. Firstly, the skins are processed in freshly prepared fermentation solutions with low acidity (1 g/dm³ in terms of acetic acid). Then, acetic or sulfuric acid is added to start the process of pickling. At the first stage, favorable conditions are created for the action of enzymes that contribute to the dissociation of the structure and the production of soft skins. At the second stage, as the acidity of the solution decreases, the action of enzymes is inhibited or completely stopped.
     Compared to souring, the process of bating may lead to hair slipping at the first stage as a result of the rapid growth of enzymatic action. In this case, the addition of mineral acid is required to lower the pH and slow down the action of enzymes. In addition, due to the lack of a stable lactic acid microflora in the softening solution, extraneous putrefactive bacteria may develop. Therefore, the use of antiseptics is recommended during the process of bating.
     Before the operations of souring or bating start, the hides are to be checked and sorted carefully. The weakening of the connection between the hair and skin resulting from the hidden defects or bacterially infections of raw materials, may lead to the additional defects of the hides during the preparatory processes.

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