Saturday, April 6, 2019

Finishes: Waterproof and Water-Repellent Fabrics
Art Resource

Marie-Therese Wisniowski

Preamble
This is the eighty-sixth post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.

Other posts in this series are:
Glossary of Cultural and Architectural Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General
Woven Pile Fabrics
Chenille Yarn and Tufted Pile Fabrics
Knit-Pile Fabrics
Flocked Pile Fabrics and Other Pile Construction Processes
Glossary of Paper, Photography, Printing, Prints and Publication Terms
Napped Fabrics – Part I
Napped Fabrics – Part II
Double Cloth
Multicomponent Fabrics
Knit-Sew or Stitch Through Fabrics
Finishes - Overview
Finishes - Initial Fabric Cleaning
Mechanical Finishes - Part I
Mechanical Finishes - Part II
Additive Finishes
Chemical Finishes - Bleaching
Glossary of Scientific Terms
Chemical Finishes - Acid Finishes
Finishes: Mercerization
Finishes: Waterproof and Water-Repellent Fabrics
Finishes: Flame-Proofed Fabrics
Finishes to Prevent Attack by Insects and Micro-Organisms
Other Finishes
Shrinkage - Part I
Shrinkage - Part II

There are currently eight data bases on this blogspot, namely, the Glossary of Cultural and Architectural Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, the Glossary of Colors, Dyes, Inks, Pigments and Resins, the Glossary of Fabrics, Fibers, Finishes, Garments and Yarns, Glossary of Art, Artists, Art Motifs and Art Movements, Glossary of Paper, Photography, Printing, Prints and Publication Terms and the Glossary of Scientific Terms, which has been updated to Version 3.5. All data bases will be updated from time-to-time in the future.

If you find any post on this blog site useful, you can save it or copy and paste it into your own "Word" document etc. for your future reference. For example, Safari allows you to save a post (e.g. click on "File", click on "Print" and release, click on "PDF" and then click on "Save As" and release - and a PDF should appear where you have stored it). Safari also allows you to mail a post to a friend (click on "File", and then point cursor to "Mail Contents On This Page" and release). Either way, this or other posts on this site may be a useful Art Resource for you.

The Art Resource series will be the first post in each calendar month. Remember - these Art Resource posts span information that will be useful for a home hobbyist to that required by a final year University Fine-Art student and so undoubtedly, some parts of any Art Resource post may appear far too technical for your needs (skip over those mind boggling parts) and in other parts, it may be too simplistic with respect to your level of knowledge (ditto the skip). The trade-off between these two extremes will mean that Art Resource posts will hopefully be useful in parts to most, but unfortunately may not be satisfying to all!


Introduction
Few fabrics are waterproof unless they are fabrics with a plastic coating. Coats made of these materials are waterproofed for heavy downpours but are not comfortable for frequent wear. No body moisture can escape and the wearer may become damp from perspiration rather than from rain.

Two women in shiny raincoats.

Water-repellent finishes have been developed, which help fabrics resist wetting, and which can be penetrated only by continuous exposure to water. Chemicals are used that interact with the surface of individual fibers in such a way that water is repelled. The spaces between the fibers are not closed and thus air and water vapour can move through with comfort.

Professional water repellent one-piece women's swim suit.

Some finishes are non-durable and need to be replaced after every cleaning; others are durable and will withstand proper laundering and dry-cleaning.

Top part of the fabric has been ironed after re-treatment washing and this heat application has re-vitalized the repellency of water. Bottom part of the fabric has not been ironed after re-treatment washing and the water is still wetting out the fabric.



An easy test for water repellency is to place a drop of water on the flat surface of the fabric. If the drop flattens out, it has wet the surface and the cloth is not water repellent. If it takes on a spherical or round shape, it has not wet the surface and will probably roll off.

Water droplet on a DWR coated surface.
Note: DWR is an ultra-thin treatment, a durable water repellent polymer that is applied to the outermost fabric layer. DWR penetrates the fibers and lowers the surface tension of the fabric, causing water to bead up and roll off this outer layer of fabric, instead of being absorbed.

Water repellency is dependent on surface tension and fabric penetrability and is achieved by: (i) finish and; (ii) cloth construction.

In general there are five main types of waterproof, breathable fabrics which are manufactured slightly differently: (i) Tightly Woven Fabrics – great for the outdoors; an Egyptian cotton, woven very tightly. When it gets wet the cotton swells and makes the weave even tighter.
(ii) Fabrics with Membranes – Polytetrafluoroethylene (PTFE) and Polyurethane (PU) are polymers most frequently used to make microporous coatings for fabrics.
(iii) Fabrics with a Continuous Hydrophilic Coating – made from a solid, water-repellent coating which has no pores but it is impermeable to air. Normally a mix of PU and polyethylene oxide (PEO).
(iv) Biocomponent Microporous and Hydrophilic Laminates – modern Gore-Tex. Impermeable to air with excellent breathability. Very durable.
(v) Nanoparticles are increasingly used as coatings on clothing to make it waterproof, microbicidal, UV-blocking or antistatic.

In this post not all of these approaches will be detailed, rather only an overview will be presented.



Finishes: Waterproof and Water-Repellent Fabrics
Waterproof fabric and waterproof material fabric is a generalized term for any materials which are resistant, either fully or partially, to penetration by water. There is a difference between “waterproof” and “water-resistant”: Fabrics and materials which are described as waterproof are fully resistant to the penetration of water, whereas water-resistant fabrics can only withstand partially for a limited time. Water-repellent fabrics are usually woven materials, that have been manufactured to partially repel water.

Water-Repellent Finishes
Finishes that can be applied to a fabric to make it repellent are wax emulsions, metallic soaps, and surface active agents. They are applied to fabrics such as twill, poplin, and rayon and cotton satin, all of which have a very high warp count and are made with fine yarns.

Sud-merged Women's Water Repellent Mini Wrap Skirt - Black.

Wax emulsions and metallic soaps coat the yarns but do not fill the interstices between the yarns. These finishes are not permanent but tend to come out when the fabric is washed or dry-cleaned. They can be renewed.



Wax Proofed Clothing - Long Coat.

Most of the original waterproofed finishes, produced by the application of rubber, waxes and oxidised oils, have been replaced by applying an impervious film of polyvinyl chloride - PVC plastic. The low cost of this application, associated with the very light weight of the waterproof fabric produced compensates for the lack of comfort in the garment produced.

Cotton canvas and tarpaulins are usually waterproofed by impregnation with cuprammonium hydroxide solution. This causes a slight and partial surface dissolution of the fibers which on drying re-solidifies and at the same time fuses adjacent fibers. The result is a fabric that is nearly impervious to water. Fabrics proofed in this manner are mainly used for covers. tenting and the like, where handling and comfort are not important.

Tarp construction.

Surface active agents (surfactants) have molecules with one end that is water repellent and one end that will react with the hydroxyl groups (-OH) of cellulose. After they are applied, heat is used to seal the finish to the fabric. This finish is permanent to washing and dry cleaning.

Waterproof fabric is usually a textile which is compounded with polymer waterproof, breathable materials. Above is an OilCloth matt fabric.

If fabrics for clothing are to be comfortable, the finishes must allow air to circulate i.e. moisture release from the body must be able to ventilate into the surrounds. These finishes are water-resistant rather than waterproof. Various water resistant finishes have been developed over the years with the first commercially successful product being Velan PF.

Velan PF is applied from a buffered aqueous solution, cured at 125 - 150 oC and rinsed and dried. It is thought that Velan PF decomposed to a fatty hydrophobic compound, which reacts with the cellulosic material and results in a water repellant finish. As each fiber will now be covered with a film of this compound, the textile material will be water-resistant. The fatty nature of this water-resistant finish often softens the handle of the textile material to which it has been applied. The success of this process led to using the fatty compound as a water repellant substance in lieu of using Velan PF.

Fabrics can also be made water-repellent with thermo-setting silicone resins. Their application involves impregnation of the fabric with an aqueous dispersion of partially polymerized resins. On curing, the the silicone resins polymerize and combine with the cellulose polymers. The silicone resins are hydrophobic because they are "fatty".

Water repellent finishes can also be obtained by the application of perflouro fatty compounds. These fatty compounds not only repel water, but they tend to repel greasy soil. Such water-soil-repellent finishes (e.g. Scotchgard) are most successfully applied to cellulosic fabrics.

Cloth Construction
Cloth construction can be water-repellent without a finish. Shirley Cloth developed at the Shirley Institute in England (now British Textile Technology Group) is similar in construction to the canvas bags found in Egyptian tombs. They were plain weave with two warp threads woven in one. They were always made of flax. Studies showed that cotton and flax swell about the same amount. It was then decided that twist made the difference between cotton and the flax. Shirley cloth is made of long, fine cotton fibers, three-ply yarns of very low twist, and oxford weave. It is a nearly waterproof fabric. It is cool and porous when dry, but moisture causes the yarns to swell and close the interstices between them.

It is more difficult to select a water-repellent coat than a waterproof coat because the finish is not obvious and one must depend on the label for information. However, the consumer can recognise some guides for buying. The cloth construction is far more important than the finish. The closer the weave, the greater the resistance to water penetration. The kind of finish used is as important in selection, because it influences the cost of the upkeep. The use of two layers of fabric across the shoulders gives increased protection, but the inner layer must also have a water-repellent finish or it will act as a blotter and cause water to penetrate.



Care is important in water-repellent fabrics. The greater the soil on the coat, the less water-repellent it is.



Water-repellent finishes render fabrics spot and stain-resistant. Some of the finishes are resistant to water-borne stains, and some to both. Durable water-repellent finishes often hold greasy stains more tenaciously than untreated fabrics. Unisec, Scotchgard and Zepel etc. are trade names for finishes that give resistance to both oily and water borne stains. Hydro-Pruf and Syl-mer, older finishes, are silicon finishes that give resistance to water-borne stains.


References:
[1] N. Hollen and J. Saddler, Textiles, 3rd Edition, MacMillan Company, London (1968).

[2] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).

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