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Stain Resistance

Introduction

Stain resistance refers to a textiles’ ability to withstand discolouration caused by contact with liquids, including oil and grease, and/or solid surfaces. Commonly a liquid stain occurs as a result of a fibre being Hydrophilic?, where the liquid gets absorbed by the fibre, and on drying the fibre becomes unintentionally discoloured i.e. stained. With any fabric structure pores are created during the interlacing of the yarns; yarns also have inter-fibre spaces. These porous cavities have the ability to trap potential stains as a result of Capillary Forceshttp://en.wikipedia.org/wiki/Capillary_action are responsible to drive the liquid in capillary spaces. (Click here for more information)">capillary wickinghttp://www.thesmarttime.com/articles/wetting-wicking-3.htm, depending upon the viscosity of the contact liquid. In addition, fine particles from contact with solid materials can adhere to the fibre and fabric surfaces, or become embedded into the yarn and/or fabric interstices, which also result in stains. Stain resistance is directly related to oleophobic and hydrophobic functionalities.

The basic objective of stain resistance is therefore to prevent liquid absorption and fine particles adherence to both fibre and fabric surfaces.  This objective can be by utilising the inherent properties of certain fibres or by applying stain resists (i.e. certain additives, coatings or finishes) to fabric surfaces.

Depending on the type of stain resistance treatment used, contact and penetration of the fabric or fibre can be completely inhibited, ensuring the prevention of contact staining.

Under Construction

Areas of Application

The application of stain resistant finishes gives added value to consumer products in the Apparel sector, with this technology now being widely marketed on children’s clothing and workwear, making for easier laundering and giving garments extra life. Military clothing could benefit from such finishes as the garments are required to perform in battle field conditions; less care is needed and would result in easy wearer maintenance and reduced laundering. 

In the Interiors sector stain resistant finishes have widespread use in applications such as upholstery and floor coverings. Extreme performance upholstery requires durability, stain resistance and ease of laundering. Such upholstery and trim with stain resistant characteristics is of added value in the Automotive industry in order to lengthen product life and make day to day care easier.

Nanotechnology treatments for upholstery materials;

Stain resistance of Medical and Hygiene textiles is mainly concentrated on uses such as interior textiles, carpets, curtains, bedding and uniforms including protective clothing. Preventing staining or penetration of the textile can be helpful in controlling microbial activity and cross contamination.

Regulations and Standards

There are no specific standards available from the International Standardisation Organisation or the American ASTM focussing wholly on stain resistance, this is because the property is closely interlinked with hydrophobicity and oleophobicity. ISO 23232, water/alcohol resistance test can provide information but is not intended to measure penetration and stain resistance. ISO 6530, test method for resistance of materials to penetration of liquids, can be used to measure penetration, absorption and repellence. ISO 14419 oil repellency can provide a rough index of oil stain resistance but only generally, informing of the penetration levels.

Other standards of relevance are;
The ASTM DM4265 standard for evaluating stain removal in home laundering.

AATCC Test Method 130-2010
Soil Release:  Oily Stain Release Method

AATCC Test Method 175-2008 Stain Resistance:  Pile Floor Coverings

AATCC Test Method 193-2007Aqueous Liquid Repellency: Water/Alcohol Solution Resistance Test

AATCC Test Method 42-2007
Water Resistance:  Impact Penetration Test

When marketing or labelling products in relation to their stain resistance properties it is important to adhere to the consumer claims directive EC 2005/29.

As stain resistant finishes utilise nano scale materials, the health and safety issues surrounding the applications of nanomaterials is of growing importance. There are currently no regulations which stipulate that nano materials must be stated on textile consumer products, however the fibre content of garments and textiles must be stated, and current developments in fibre technology involve the use of nanoparticles. The European commission are currently holding a public consultation towards developing a strategic action plan on nano technology. (Click here to engage)  

Voluntary responsible code on Nanotechnology.
 

Under Construction

Basic Principles of Stain Resistance

Prior to the development of finishes, stain resistance of textiles was based on the fibres inherent characteristics of water or oil repellence. This is determined by the Surface Energyhttp://en.wikipedia.org/wiki/Surface_energy and Surface Tension? interaction between the fabric and the discolouring caused by a liquid stain. A Contact Angle? of under 90° defines a hydrophillic or wettable quality. The Surface Tension? varies greatly in liquids, thus altering their interaction with the fabric surface. Porosity will influence stain adherence to textiles, as pores can provide a space for foreign matter to penetrate, in liquid substances the ability to penetrate these pores is influence by the Capillary Forceshttp://en.wikipedia.org/wiki/Capillary_action are responsible to drive the liquid in capillary spaces. (Click here for more information)">capillary wickinghttp://www.thesmarttime.com/articles/wetting-wicking-3.htm forces. In solid states the staining potential is governed by the solids ability to break up in to particles small enough to sit in the pores. However a staining ability will only be possible if the staining product is allowed to interact with the surface and the Surface Tension? property defines this.

Fabrics which do not contain inherently hydrophobic fibres have this property imparted at the finishing stage. Laminates or membranes can be applied to provide this, however they can have a detrimental affect on both breathability and softness. Chemical coatings are applied to provide this attribute, such as fluorocarbonshttp://en.wikipedia.org/wiki/Fluorocarbon, resins and silicones. 

Flurocarbon chemistry implemented in textile finishing processes was used to provide both a hydrophobic and oleophobic attribute. This created a problem of organic pollution; in certain instances the fluorocarbonshttp://en.wikipedia.org/wiki/Fluorocarbon particles were too large to break down in the environment and had a toxic effect. Flurocarbons require a binding agent to improve durability and the use of such provides further negative environmental affects.

fluorocarbonshttp://en.wikipedia.org/wiki/Fluorocarbon for textile finishing

Key Documents;

Nano whiskers Powerpoint; api.ning.com/files/...MEuOq/FINALNANOWHISKERS.ppt

Nano-finishes can be applied during traditional finishing methods such as Padding?, drip or dry coating and can be applied to a range of natural and synthetic fibres. 

Environmental Issues

Perflurochemicals have been widely used by the textile industry and are as such an organic compound. However certain variations of the compounds proved too large to break down with toxic side effects. 3M’s Scotchgard and Du pont’s Teflon were both treatments based on this chemistry and both companies took the decision in 2000 to voluntary phase out the specific type of C8 PFOS and PFOA flurocarbons in question.

The environmental impact was deemed serious enough for the EPA to legislate the 2010/2015 PFOA stewardship program, which aims to reduce C8 fluorocarbon chemicals by 100% by 2015. The use of fluorocarbonshttp://en.wikipedia.org/wiki/Fluorocarbon is still widespread, but these specific compounds, if are not already, continue to be phased out. For these reasons there is a clear drive to move away from fluorocarbon chemistry. 

Self Cleaning Textiles

The advancement of nano technology within the textile sector has made the application of stain resistant finishes which do not negatively affect the handle, look or performance of a textile a reality. Hydrophobic and super hydrophobic functions use bio mimicry, observable in plants and certain insects, such as the pond skater and the Lotus Leaf. 

Lotus Leaf 300x200

Nano scale particles or whiskers coat the fibres of the fabric, trapping air in the negative spaces, thus altering the Surface Energyhttp://en.wikipedia.org/wiki/Surface_energy. This coating does not allow liquid stains to wet the surface; they sit on the air cushion created by the structures.

A self cleaning property is observed as when water comes into contact with the surface, it naturally maintains is spherical shape. Any foreign matter of dirt present on the surface then adheres more positively to the water that the textile surface ensuring the dirt is carried away with the water, the movement enabled in the structures further aides this process, allowing little or no residue to be left behind. Nanomaterials are being implemented to provide this finish on fabrics. (Video) Demonstrates Lotus Leaf affect and dirt removal.

The unique features of Titanium dioxide at nano scale provide a self cleaning feature of organic stains. A reaction occurs on absorption of UV light which begins the degradation process of organic matter such as stains. The application of Titanium Dioxide to textiles is a process widely explored in literature.

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