EFFECT OF ACRYLIC POLYMER DISPERSIONS ON WATER VAPOUR PERMEABILITY AND SOME OTHER PHYSICAL PROPERTIES OF FINISHED LEATHERS

EFFECT OF ACRYLIC POLYMER DISPERSIONS ON WATER VAPOUR PERMEABILITY AND SOME OTHER PHYSICAL PROPERTIES OF FINISHED LEATHERS

Abstract

The effects of acrylic polymer dispersions on water vapor permeability and some other properties of finished leather were investigated. We investigated the properties of AE 558 Nycil, a commercial acrylic-based binder, and investigated the effect of applying a finish on some of the physical properties of first retanned leather. The binder had an intrinsic viscosity of 227 dL/g and a viscosity molecular weight (Mv) of 4.03×10 5 . This was obtained by performing solution viscosity measurements of the solid polymer in toluene at 25°C. The melting temperatures of the solid binders were found to range from 361.7 oC to 370 oC. These physical property results suggest that this is a very high molecular weight polymer with high thermal stability. Leather finishing formulations containing various proportions of 125g, 150g, 175g, 200g and 250g of binder were prepared and applied to leather substrates corresponding to respective samples A1, A2, A3, A4 and A5 respectively. Several physical properties of these coated samples were tested. The water vapor permeability of the originally retanned (uncoated) leather decreased significantly after finishing. A1 has the lowest permeability at 125g of binder in the formulation and A5 has the highest permeability at 250g of binder in the formulation. In general, the water vapor permeability of coated leather increases with increasing modulus of change in this test. A3 had the highest Shore A value at 175g binder in the formulation, while A5 had the lowest Shore A value at 250g binder in the formulation. Coating the leather improved the elongation and bursting strength of the uncoated leather. However, there was no particular trend with increasing amount of binder in the finish. The robustness of the coated samples generally increased with increasing amount of binder in the finish formulation, with sample A5 showing the best resistance to wet abrasion. chapter One

1.0 Introduction

Acrylic is an ester of acrylic acid, the product formed by the reaction of acrylic acid and alcohol. Esters of acrylic acid readily polymerize to give highly transparent plastics. They are commonly used in applications requiring a clear, durable finish such as: in the aircraft and automotive industry. Acrylic surface coatings are often used. The physical properties of acrylics (gloss, hardness, adhesion, flexibility, etc.) can be modified by changing the composition of the monomer mix used in the polymerization process. Acrylics are used in a variety of industries and the list below is just some of the more common examples.
Adhesives, textile industry (e.g. production of sponge fillers for padded jackets), paper coatings, paint industry, especially road marking paints.

The polymerization process readily occurs in the presence of a catalyst and can be carried out in four different ways:
Emulsion, bulk, solution or suspension.

Emulsion polymerization occurs in water/monomer emulsions using water-soluble catalysts. Emulsion polymerization is the primary process used to manufacture acrylic polymers.

Bulk polymerization takes place without solvent. A catalyst is mixed with the monomer and the polymerization is allowed to proceed over time. This is the process commonly used to make acrylic plates.

Solution polymerization takes place in a solvent in which both the monomer and subsequent polymer are soluble. Only low molecular weight polymers can be produced by this method, as high molecular weight polymers cause very high viscosities.

Suspension polymerization is carried out in the presence of a solvent, usually water, in which the monomers are insoluble and suspended by stirring. A protective colloid is added to prevent the monomer droplets from coalescing and the polymer from solidifying. Suitable colloids include bentonite, starch, polyvinyl alcohol and magnesium silicate. In contrast to emulsion polymerization, the catalyst is monomer-soluble and dissolves into the suspended droplets. Polymers are made from monomers resulting from the reaction of acrylic acid and alcohol. These are then polymerized with free radical initiators in water emulsions.

The emulsion polymerization reaction requires the following ingredients:
monomer

Monomers are made by a reversible reaction between acrylic acid and alcohol.

CH2=CR-COOH + R’OH CH2=CR-COOR’ + H2O Alcohol acrylate Alkyl acrylate

The main monomers used are ethyl acrylate, methyl methacrylate, butyl acrylate, and similarly acting non-acrylic monomers such as vinyl acetate and styrene.

Surfactant:
Surfactants are substances composed of mutually repelling polar and non-polar ends. The surfactant surrounds each monomer droplet with a layer of surfactant and the polar ends align with the surrounding water, forming micelles.

water:
Water is used as a medium to disperse these micelles. During the process, water acts as a solvent for surfactants and initiators and as a heat transfer medium.

initiator:
Commonly used initiators (catalysts) are water-soluble peroxide salts such as ammonium or sodium peroxydisulfate. This reaction can be initiated by either thermal initiation or redox initiation. Thermal initiation dissociates the peroxydisulfate into two SO4 radicals.

–O3S—O—O—SO3– → 2SO4– • peroxydisulfate radical

Redox initiation uses a reducing agent (usually Fe2+ or Ag+) to donate electrons and dissociate peroxydisulfate into sulfate radicals and sulfate ions.

Fe2+ ​​+ –O3S—O—O—SO3– → Fe3+ + SO4– • + SO42-

peroxydisulfate radical

The emulsion polymerization process can be carried out in a reaction vessel equipped with heating and cooling jackets to allow temperature control during the reaction.

First, add surfactant and water to the kettle. The monomer emulsion and initiator solution (containing a redox agent to decompose the persulfate to sulfate radicals) are then transferred from the monomer feed tank to the kettle at a controlled rate. The mixture in the kettle is constantly stirred during the monomer addition. During this time, the monomer polymerizes according to the following reactions:

.SO4 + CH2=CRCOOR’ –OSO3 CH2 RC.COOR’ monomer monomer residue

. .SOCHC(COOR’) +CH=RC(COOR’) 4 2 2

monomer radical

-SO CH -RC(COOR’)CH 2 RC. COOR’ 4 2

dimer radical

When the reaction has progressed sufficiently to consume all available polymerization sites, the contents of the kettle are transferred to a stainless steel mixing vessel. The batch is then cooled, conditioned and transferred to holding tanks for storage and subsequent packaging. The quality of the final product depends on the controls in place during the manufacturing process. Regular quality control of the following characteristics is performed throughout the manufacturing process.

Solid content
pH value
viscosity
gel level
residual monomer
mechanical stability
Freeze-thaw stability
compatibility

One of the most important tests of a finished polymer is to determine its ‘glass transition temperature’, a measure of its toughness. This is done by heating the polymer at a constant rate and measuring its temperature. When plotting a plot of melt temperature versus time, there are points where the plot is flat. H. The polymer is heated, but not hot. At these points, the plastic undergoes a kind of phase change between two different solid phases. Thermal energy is used to reconfigure the structure of materials rather than simply heating them. Where and how many of these transitions occur affects the toughness of the plastic. Leather is made from animal hides and hides. Large animals like cows have skins and small animals like sheep have skins. Since animal skin is primarily composed of a protein called collagen, it is the chemical properties of this fibrous protein and the properties it imparts to the skin that are of most interest to tanners. A traditional industry that has certainly existed for over 5,000 years, the industry was established during the Code of Hammurabi (1795 B.C.-1750 B.C.). 1972). In fact, the use of animal skins is one of mankind’s oldest techniques, possibly predating tool making. In the modern world, the global leather industry exists because of the meat diet. Therefore, most of the leather produced worldwide is made from cows, sheep, pigs and goats. One of the by-products of the meat industry is skin.
Considering that the annual number of cattle slaughtered alone is in the order of 300 million he said, such 10 to 20 million tonnes of by-products would have a significant impact on the environment if not used by the tanners. will give.

The hide is primarily composed of the protein collagen, and it is the properties of this protein and the potential for chemical modification that offer tanners the opportunity to create desirable products from unattractive starting materials, thereby making it desirable. Convert to product. and useful for modern life.

Collagen is the collective term for a family of at least 28 different collagens, each with different functions in animals, most notably in connective tissue (Bailey and Paul, 1998; Comper, 1996; Kichy et al., 1993; and Kadler et al., 1993). , et al., 2007). The main component of the skin is type I collagen. Unless otherwise stated, the term “collagen” always refers to his type I collagen.

Collagen is a protein. In other words, it is made up of amino acids. They can be divided into alpha and beta amino acids. Each has a terminal amino and carboxyl group that participates in peptide bonds, and a side chain attached to a methylene group in the center of the molecule. Some amino acids are more important than others because they play specific roles in the manufacture of leather.
An important role is to create fibrous structures or participate in protein modification processing reactions. Amino acids react via a condensation process to form macromolecules, which are proteins like collagen.

An important part of the collagen structure is the role of water, which is an integral part of the collagen structure and thus its chemically modified derivatives (Bienkiewicz, 1990). was believed to be important for collagen stabilization, but the Ramachandran model (Ramachandran and Ramakrishnan, 1976).

Bjerrum’s work (1910) tells us how we can know that these complex molecules have hydroxyl bridges.

Irving 1974 summarized the chemistry of chromium(III) complexes in terms of the leather industry. Some of his more important observations can be summarized as follows.

The half-life of water exchange in the Cr(III) ligand field determined by isotope exchange of 180 is 54 h at 27 °C.
This is an associative interaction. This can be compared with other metals such as Al(III), which has a half-life of the order of 10-2 seconds.
These are dissociative interactions. This difference between associative and dissociative complexation not only affects the stability of Cr(III) complexes, but also the role of Al(III) in tanning technology. A diol complex built from two hydroxyl bridges was assumed to be the preferred form of the chromium dimer. The trimer is also claimed to be a linear version of the bridge structure.

The stability of transition metal complexes can be described in terms of thermodynamic and kinetic stability. Chromium(III) complexes with carboxylates are thermodynamically less stable than other complexes such as amines, but are more kinetically stable.
The mechanism of exchange between ligands to octahedral complexes depends on the stability of the intermediate crystal field. It is either a 5-coordinate square pyramid (SN1 mechanism) or a 7-coordinate pentagonal pyramid (SN2 mechanism). Crystal field activation energy calculations show high values ​​for both mechanisms, with the 7-coordination mechanism showing higher values. Whatever the actual dominant mechanism, the high activation energy explains that the complex is kinetically stable.
The stability of the complex between Cr(III) and carboxylate is inversely proportional to the dissociation constant of the carboxylic acid. It was first proposed by Shuttleworth (1954). A plot of log KCrL vs. log KLH shows good correlation (Chemical Society Special Publication, 1964; Tsuchiya, et al., 1964 & 1965).
Chelate complex formation is favored over complexes with monobasic carboxylates. Olation occurs in the trans position due to the fast ionization rate of the aquo ligand (Irving and Williams, 1953).
Although the modern process is customarily called “chrome tanning”, this reaction is most commonly performed using basic chromium(III) sulfate, the most commonly used reagent in the global leather industry. It is commonly done. The importance of this warning is in understanding the role of all salt components and considering alternative options.

Comparing the properties of the process to vegetable tanning reveals the reasons for the process’ popularity.

The chrome tanning reaction itself usually takes less than 24 hours.
The vegetable tanning reaction takes several weeks even with modern processes.