Laminated textiles membranes

Coated and laminated textiles usually consist of a textile substrate, which will typically be a woven, knitted or nonwoven fabric, combined with a thin, flexible fdm composed of a natural or synthetic polymeric substance. A coated fabric is one in which the textile substrate has a polymer film applied directly to one or both surfaces as a viscous liquid in a solvent or water, the thickness of which is controlled by application via a blade or similar aperture. A transfer coated fabric is an intermediate product in which a thermoplastic film is first prepared on a release paper prior to thermally bonding to the textile substrate. A laminated fabric usually consists of one or more textile substrates that are combined with a pre-prepared polymer film or membrane by adhesives or heat and pressure (Hall, 2000). 

In fine wool such as that obtained from merino sheep, the cuticle is normally one cell thick (20 x 30 x 0.5 mm, approximate dimensions) and usually constitutes about 10% by weight of the total fiber. Sections of cuticle cells show an internal series of laminations (Figs. 1 and 2) comprising outer sulfur-rich bands known as the exocuticle and inner regions of lower sulfur content called the endocuticle (13). On the exposed surface of cuticle cells, a membrane-like proteinaceous band (epicuticle) and a unique hpid component form a hydrophobic resistant barrier (14). These hpid and protein components are the functional moieties of the fiber surface and are important in fiber protection and textile processing (15). 

PTFE has a remarkable range of properties. It possesses the simple monomer unit, -(CFj-CE )-, with a molecular weight of 100, an SG of 2.1-2.3 and a degree of polymerisation of 10 000. PTFE is extremely stable and inert, is not soluble in any known liquid solvent and is unaffected by concentrated acids and alkalis. It will not bum in air, is flexible down to -80 °C and dimensionally stable up to 4-250 °C. It has a low coefficient of friction, good abrasion resistance and has excellent liquid repellency properties. It is predominantly available as a thin membrane that is laminated to one or more textile fabrics. PTFE is thus well suited for use against chemicals and liquids in harsh environments. One of the special uses of the membrane is in a shock-expanded microporous form, which confers high liquid barrier properties with high water vapour permeability. In this form laminates are... 

Considerable research is devoted to high performance Sportswear and even the Ready-to-Wear segments of textiles. The desire is to maintain the body dry by wicking water away as the body generates heat and perspires. To illustrate the concept of diffusion, consider a semi-permeable membrane laminated to a fabric. Assume the sample was placed in a cell separating a column of air from a column of saturated water vapor. The membrane is permeable for water vapor but not air. At time t — 0, thanks to Brownian motion, the water molecules will traverse the membrane and then diffuse through the fabric sample to the air. (Evidently, the fabric sample is usually next to the skin—this example is for illustration purposes only.) The molecular transport through the fabric is referred to as diffusion. 

Uses Tackifier, binder, plasticizer for inks, textile sizes and finishes, latex modification, paints, adhesives adhesion promoter (acrylic pressure-sensitive adhesives) laminating heat sensitizer for rubber latex pigment binder in textile finishing protective colloid in emulsions flexibilizer, vise, control agent for photoresist coatings semiperme-able membranes (reverse osmosis plants) antistat, binder, film-former in cosmetics finish component for poly (phenyleneterephthalamide) food-pkg. resins in food-contact PU resins Regulatory FDA 21 CFR 175.105,177.1632,177.1680 Manuf/Distrib. Aldrich BASF ISP... 

A large variety of desirable properties for membranes may be provided by the fibres themselves or by their finishing and post-treatment before the production of the fabric. If these do not provide the required properties such as watertightness, dirt and oil repellence, UV protection, flame retar-dance or abrasion resistance, the fabric must be coated or laminated. Additionally an unweldable textile (e.g. PILE) may have a weldable coating applied. 

Microporous or hydrophilic membranes are fragile and do not provide a cloth-like feel. They have to be incorporated into textile products so as to maximise the desired high-tech function without adversely affecting the classical textile properties of handle, drape, and visual impression. The fabrics produced will be two-, three-, or four-layered constructions with one of the layers being coated or laminated with the breathable membrane. 

From the water vapour permeability point of view, textile materials behave in two different ways first, materials in which moisture vapour transfer takes place predominately by diffusion through air spaces betweeu yams and fibres, following Pick s law. The measured water vapour permeability values are independent of the measuring conditions. Woven, nonwoven, and semipermeable membrane laminates fall into this category. Second are textile material composites that contain a layer of hydrophilic membranes and which behave quite differently. In particular the rate of diffusion through the hydrophilic manbrane is dependent on the test conditions, such as concentration of water vapour in the layer or relative humidity. ... 

Adjustable breathability is an area where responsive barriers have already found commercial applications. For example, a thermoresponsive breathable membrane using shape memory polyurethane has been developed by Mitsubishi Heavy Industries (SMP Technologies Inc., 2010). It can be laminated onto various types of textiles to provide waterproof, windproof yet breathable clothing. Another strategy based on a temperature-activated breathable monolithic film sandwiched between two layers of spunbond microfibrous polypropylene has been used by Ahlstrom Corp. to develop medical gowns that combine protection against virases with comfort and breathabUity (Rodie, 2005). 

In the medical industry, porous thermoplastic or thermoset membranes can be used to remove extremely small particles. They are used in applications requiring surface filtration where the particles are trapped on the surface of the media. Although the polymeric membranes are able to remove particles ranging in size from the smallest ions (<0.001 pm) up to approximately one miaon particles, they tend to be expensive and fragile. By coating the membrane on a textile substrate or lamination of a polymeric membrane with a textile fabric, it is possible to combine the physical strength of the textile materials with the filtration properties of membrane materials, hi this sense. 

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