Leather flexibility

Applications Coating, lacquers Flexible foams, elastomers Elastomer, prepolymers, synthetic leather Flexible foams, lacquers, coatings... 

In temperate climates extracts from some plants were found to be excellent preservatives for hides and skins. The hides, with or without hair, were placed in pits in the ground, then covered with alternating layers of bark or leaves and skins. Water was added and later, ie, days or months depending on the thickness of the hide, the hides could be removed, washed, and oiled. The resulting leather is flexible and lasts essentially forever. This procedure was used well into the seventeenth century as the most common method of tanning. In some isolated primitive societies, the method is used in the 1990s. 

Leather. Natural leather is made from hides, which are salted and cured, then taimed. Through the preparing process, useless matter which caimot be taimed, such as outerskin (epidermis) and flesh, are removed, leaving the tme skin (corium). In the tanning process, the fluid matter which maintains the skin in a flexible and moist condition is removed, and there remains nothing but the fibrous portion to be acted on by the tanning chemicals (1-3). 

Copolymerisation. Except in those rare cases where monomer segments are isomorphous (see Figure 4.11), copolymerisation, as usual, leads to less crystalline and frequently amorphous materials. As might be expected, these materials are tough, leather-like, flexible and, when unfilled, reasonably transparent. 

Cross-linkable rubbery polyesters have been produced but are now no longer produced. Rubbery polyester-amides were introduced by ICI under the trade name Vulcaprene as a leathercloth material but later were used primarily as leather adhesives and as flexible coatings for rubber goods. A typical polymer may be made by condensing ethylene glycol, adipic acid and ethanolamine to a wax with a molecular weight of about 5000. 

The market is dominated by flexible foam applications (43% in the United States) and rigid and semi-rigid foam (29%). Cast elastomers (4%) and RIM elastomers (3%) have only specialised outlets. The remaining sizeable 21% of the market cover such diverse uses as thermoplastic rubbers, surface coatings, adhesives, sealants and synthetic leathers. 

Since it possesses good properties of both PVC plastics and polyurethane elastomers, it has been used in those areas where PVC and polyurethane have traditionally played dominant roles. For example, it is a very promising replacement for flexible PVC used for medical purposes and in the food industry [I6,l7], because it essentially eliminates the concern regarding plasticizer contamination. It has been used in combination with the copolymer of butadiene and acrylonitrile (NBR) to make the abrasion-resistant aprons and rolls used on textile machines [18]. A PVC/TPU/ABS blend serves as a substitute for leather [19]. This could have a tremendous impact on the shoe industry. It has also been found to have an application as a building coating [20,21]. This trend will certainly grow and more applications will be found. This in turn should bring new developments in the material itself. 

A great variety of PVC materials have been tested in the process thus far cable, cable trays, flooring material, window frames, artificial leather, packaging, pipes, flexible hoses, ring binders and roofing material. This indicates that the process is robust and can handle a broad range of PVC materials. In terms of chlorine content, there are no restrictions. With the completion of the pretreatment pilot plant, the contents of other plastics and metals may now be reduced significantly. 

Other chemicals that are common in different RSL are phthalates. Phthalates are usually used as softening agents in plastics to obtain the required flexibility. The most common phthalates included on restriction lists for the leather industry are bis(2-ethylhexyl)phthalate (DEHP), benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), di- isononyl phthalate (DINP), D- isodecyl phthalate (DIDP) and di-n-octyl phthalate (DNOP). All these chemicals are included on the SVHC list (Candidate List), and currently (2012) there is a proposal to restrict the placing of products containing DEHP, BBP and DBP on the market in the EU. 

A formed laminate is made by relative movement of first and second contoured mould surfaces toward each other to compress a flexible sheet and vertically spaced film with a foamable liquid mixture therebetween that has substantially completed expansion but not yet substantially cured so as to form the flexible sheet and provide a collapsed foam layer bonded to the sheet. The flexible sheet is preferably porous cloth, vinyl or leather. A film which is preferably a nonadherent plastic such as PE is preferably positioned in a vertically spaced relationship with the flexible sheet either above or below the sheet with the foamable liquid mixture received therebetween for the expansion prior to the compression that provides the formed laminate. The formed laminate... 

Di(2-ethylhexyl) phthalate is widely used as a plasticizer in flexible vinyl products. Plastics may contain from 1 to 40% di(2-ethylhexyl) phthalate by weight and are used in consumer products such as imitation leather, rainwear, footwear, upholstery, flooring, wire and cable, tablecloths, shower curtains, food packaging materials and children s... 

Flexible Ebonite This can be called semi-ebonite usually loaded with mineral fillers with a lower proportion of sulphur, say 15 phr, and by incorporating into the compound synthetic rubbers like polychloroprene, polyisobutylene or butyl rubber. This ebonite will have good resistance to impact. A sheet made of flexible ebonite will look like a hard flexible leather. 

Applications. Furniture and minor vehicle upholstery is the largest market for flexible vinyl foams. Because of better aesthetics (leather-like plastics), comfort, and favorable pricing, they are expected to show good... 

These polymers commonly are described as PVC plastics or less specifically as vinyl. They are materials that may be either flexible or rigid according to what they are mixed with, and they are used in the manufacture of many familiar articles such as plastic curtains, rainwear, floor tile, synthetic leather goods, upholstery, table mats, phonograph records, insulation, plastic pipes, tubing, and packaging materials. 

Leather represents the product obf-incd by subjecting the hides of animals to suitable processes (tanning) to give them keeping properties and to impart to them certain special qualities (elasticity, flexibility, etc.). 

Ofjmportance also is the flexibility test, which is carried out by bending a strip of the leather (bloom outside) into an arc, at first with a diameter equal to ten times the thickness and afterwards with less diameters (the strip may be bent round cylindrical rollers of different diameters), any cracking and the depths of the cracks being observed. 

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