Perceptive textile finishes

Textile finishes generate value through perceptive and protective effects, points out Dr Ashok Athalye.

The way a textile is finished can change its personality. Conventional textile finishes help modify basic handling of the fabric and provide surface softness or stiffness. Functional effect finishes impart comfort and performance properties like managing moisture management, retarding flame, repelling oil and water, protecting from sun and improving hygiene. Functional finishes also correct deficiencies or introduce specific properties. Textile substrates which are deficient in some properties or where some improved properties are desired are treated with specialty effect finishes. So, conferring desired effects, meeting end-use expectations, ensuring sustainable ECO norms and enhancing value for money are major considerations for such perceptive and protective finishes.

Functional finishes are categorised as:

1. Sensory perceptive - As the name suggests, these impart effects which impact senses such as touch, smell, visual appeal and offer physical comfort.

2. Protective and repelling - effects that can shield the wearer from external factors

•  Skin care - rejuvenating

•  Health care - antimicrobial

• Aroma - fragrance

• Fire protective - flame retardant

• Sun protection - UV absorbers

• Soil free - anti-static

•  Stain free- oil and water repellent

• Quick dry - moisture management

• Wrinkle free - resins

Selection criteria - depends on desired functional effect and various factors such as

i) Intended end-use

ii) Desired effect - either singular or multiple properties

iii) Regulatory norms - Ecological, toxicological, sustainable

iv) Requirements of international brand

v) Fastness testing and evaluation methods

vi) Washing method and durability expectations

Further, there are regulations for environment protection, liquid effluent discharge, landfills and safeguarding human health which the textile material is expected to maintain.

Application methods:

Each treatment has its own application. This could be padding through low liquor ratio or spraying with suitable equipment or coating to achieve different effects on two sides of a fabric with two different finishes (moisture management on inner side and water repellant on outer side). Some are put through micro-encapsulation or active ingredient application while others go through multi layer or layer on layer application or even electro-chemical deposition.

1. Skin care

Finishes can generate a feel-good factor by providing skin nourishing chemicals through textile. These chemicals provide various effects such as moisturising during dry or low humidity conditions, antioxidants like Vitamin E to overcome wrinkle formation or delayed ageing.

3. Aroma Sensual

The wearer and those in close proximity enjoy unique benefits from aromatic chemicals and fragrances that impart a pleasant smell. These stimulate different moods like relaxation and encouraging sleep.

The chemicals are volatile. Fragrance is transported to and detected by the olfactory system in the upper part of the nose which transmits the stimuli to the brain where it is perceived as a pleasant odour.

The pleasant smell tends to elicit a variety of feelings and emotions such as relaxation, happiness and well-being. Various essential oils like lavender, rosemary, and jasmine were used in this finish. These are used in home textiles such as bed linen, pillow covers, bed sheets to keep them fresh even with everyday use. Also, aroma compounds infuse a feeling of well-being and freshness. Aroma fabrics have several uses in medicine and alternative healing.

The following table gives a list of those aroma chemicals.

Table 2 List of aroma-imparting chemicals

4.Fire protection

Fire protective finishes make textiles flame-resistant. They minimise risk of a fire starting in case of contact with a small heat source. The fabric does not ignite or the process is delayed. When a fire starts, retardants reduce spread of flames and rate of fire spreading. Fire retardants interfere with combustion at different stages of the process like during heating, decomposition, ignition or spreading of the flame.

•  Increase decomposition temperature

•  Decrease the amount of combustible gases

•  Promote char formation

•  Prevent access of oxygen to the flame

• Increase combustion temperature

Commonly used chemicals include boric acid or borax, tetrakis (hydroxymethyl) phosphonium chloride (THPC) and phosphoric acid derivatives. Flame-retardant fibres confer high comfort and safety to textiles and are, thus, preferred for use in garments and in decorative fabrics and home textiles.

Table 3 - Test methods and evaluation of water and oil repellants

6. Antistatic finish

Static electricity is produced or created when two non-conducting surfaces such as synthetic textiles rub together. The two surfaces become oppositely charged and an electrical charge builds up. The wearer can experience electric shocks and the fabric clings to the body. Anti-static finishes are chemical substances applied to reduce and eliminate static charge. They absorb moisture from the atmosphere and reduce dryness of the fabric that causes static charge build up. These finishes

•  Avoid charge creation upon rubbing

•  Provide wicking effect

•  Impart soft handle

•  Improve fat and soil release

• Avoid impairment of whiteness

Table 4 - Common evaluation methods

7. Moisture management

The ability of a garment to transport moisture away from the skin is one of the key performance enhancement criteria in modern sports and active outdoor wear. This phenomenon is termed moisture management. Various factors including the physio-chemical characteristic and construction of the textile coupled with application of different type of finishing chemicals help impart this effect.

Generally, the hydrophobic textiles repel moisture and the insufficient transport of moisture leads to damper feeling, restricting evaporative cooling. Whereas, the hydrophilic textiles have more moisture absorption, but at the same time retains moisture due to slower drying and leads to clinging and sagging. However, a combination of inner hydrophobic and outer hydrophilic textile can provide desired rapid transport of moisture from skin and then evaporated from the outer surface.

Such finishes are used in combination to impart additional desirable properties like antibacterial, antistatic and soil release effects. They control moisture balance between the garment and skin and keep body temperature constant by evaporating moisture both from the skin and from outside of the textile material. The schematic mechanism of moisture management is given below.

The common methods of determination and evaluation are:

• AATCC 195

• Wicking- vertical wicking test (BS 3424 or AATCC 197:2011)

•  Water Absorbency (AATCC 79: 2000)

•  Air permeability

8. Thermal protection

Textile material capable of absorbing or releasing heat energy can provide desired thermal protection under adverse climatic conditions. The chemicals that provide such effect are called phase-change material. Such chemicals have the ability to change their state with a certain temperature range. These materials absorb energy during the heating process as phase change takes place and releases energy to the environment during a reverse cooling process.

These chemical finishes have the capability of melting during heat absorption and crystallising during heat release, maintaining temperature of the wearer constant under varying surrounding conditions. Certain specialty paraffin microcapsules are applied on the textile substrate for such thermo-regulating and temperature controlling effects.

9.Sun protection

Sunlight consists of harmful ultra violet radiation in the wavelength region of 150 to 400 nm, which can result in acceleration of skin ageing, photodermatosis (acne), erythema (skin reddening), sunburn, melanoma (skin cancer) on prolonged exposure. Though the intensity of UV radiation is much less than that of visible or infrared radiation, the energy per photon is significantly higher.

When radiation strikes the surface of a fibre, it can be reflected, absorbed, transmitted through the fibre or pass between fibres. The relative amounts of radiation reflected, absorbed or transmitted depend on many factors, including fibre type, fibre surface smoothness, fabric cover factor and the presence or absence of fibre delustrants and dyes.