Ultraviolet Protection Finishes
for Textiles
By
Eng. Dr Faiza Safdar
Why UV Protection?
• Acute and chronic health effects on the skin, eyes
e.g sunburn
• Degradation of organic compounds
• Discoloration of dyes and pigments
• Loss of mechanical properties and gloss in
polymers and plastics
• One approach is to cover the body with clothes
Spectrum of Electromagnetic
Radiations
UV Range
• UVC is totally absorbed by atmospheric ozone, water vapour,
oxygen and carbon dioxide, hence UVC has minimal penetration to
the surface of the Earth and has little effect on human health. UVC
affects DNA and other biomolecules and can be used as germicide.
• UVA and UVB have to block for protecting human health.
• UVA penetrates deeper into the skin due to its longer wavelength,
and plays a role in skin photo-ageing.
• Long term exposure to UV light can result in
acceleration of skin ageing, erythema (skin
reddening), sunburn,increased risk of
melanoma (skin cancer), eye damage and DNA
damage
• The wavelengths of maximum danger to skin
are 305–310 nm.
• Textiles must demonstrate effectiveness in the
300–320 nm range
• To quantify the protective effect of textiles, the
solar protection factor (SPF) is determined
• In Europe and Australia, SPF is called UPF
(ultraviolet protection factor)
• The SPF is the ratio of the potential erythemal
effect to the actual erythemal effect transmitted
through the fabric by the radiation and can be
calculated from spectroscopic measurements.
• The larger the SPF, the more protective the fabric
is to UV radiation
• A fabric with an SPF of > 40 is considered to
provide excellent protection against UV radiation.
Ways to Make UV Protective Textile
• Natural fibers are inherently UV protected. But
chemical processing decreases UV absorbing
chemicals. So, they need application of UV
protective finish/dye.
• Synthetic fibers are extruded with UV blocking
pigments (metal oxides).
• More cover factor, more UV protection
• Non-plain weave fabric affords advantages for
increasing fabric mass and fabric cover, and in
turn UPF ratings
• UV protective finishes are used for lightweight
woven and knitted fabrics intended for
producing shirts, blouses, T-shirts, swimwear,
beachwear, sportswear, and the like. Industrial
fabrics designed for awnings etc.
• The UV absorbers and blockers
interact with the harmful radiation to
minimize transmission through the textile
fabrics.
• If the fibres absorb all of the incident radiation, then the only
source of transmitted rays is from the spacing between the
yarns.
Then SPF can be calculated by using following relation
• The tight micro-fibre fabrics provide a better UV protection
than fabrics made from normal sized fibres with the same
specific weight and type of construction
• Many dyes absorb UV radiation as well as visible light.
• A cotton fabric dyed to a deep shade can achieve SPF values of
50 or higher just from the presence of the dye
• Summer clothes need UV protection due to low cover factor
and light shades
Ultraviolet Protection Finishes
• Mechanism of UV protection
Requirements of UV protection finish
• Convenient application to textile without
imparting any color.
• Good affinity to textiles
• UV absorber molecules must be colourless or
nearly colourless compounds having high
absorption coefficients in the UV range of 290–
400 nm spectra
• UV absorbing molecules transform the absorbed
energy into less harmful vibrational (phonon)
energy before reaching the surrounding
substrate, and exhibit good photostability.
• UV absorbers have the same need for wash
fastness and light fastness as dyestuffs.
• Laundering trials
• UV absorber and OBA
UV Protective Agents
• UV protective agent must transform high UV
energy into vibrational energy in UV absorber
molecules and then into heat energy in the
surroundings without photodegradation
Two types of UV protective agents
• Inorganic UV blocking chemicals
• Organic UV blocking chemicals
Inorganic UV Blocking Chemicals
• Metal oxides like,
• TiO2, CeO2, ZnO and Al2O3
• Mechanism involves band gap absorption and
scattering of light
• They are more robust because they are non-
toxic and chemically stable at high
temperature and UV radiation exposure
Organic UV Protection Finishes
• UV absorber molecules must be colourless or
nearly colourless compounds having high
absorption coefficients in the UV range of 290–
400 nm spectra
• UV absorbing molecules transform the absorbed
energy into less harmful vibrational (phonon)
energy before reaching the surrounding
substrate, and exhibit good photostability.
Examples
1) Phenolic compounds
a) That form intramolecular O–H–O bridges
Phenolic compounds
b) Compounds having N in their structure
forming O–H–N bridges
Examples
2) Non-phenolic UV absorbers
UV Stabilizers
• Also called photostabilizers.
• Primary Stabilizers/ Primary Antioxidant
Interfere with the oxidation cycle of substrate material
photodegradation, thus they are called ‘radical scavengers’.
• Secondary Stabilizers
Decompose hydroperoxides and prevent new oxidation cycles
from beginning, and are described as ‘peroxide decomposers’.
But some of the secondary stabilizers may have primary
characteristics.
Primary Stabilizers
• Hindered phenols (HP) and hindered amines
(HA).
• HA operate as UV protectors by combining
with oxygen when exposed to light to form
stable radicals, which trap the radicals that
have developed from the photodegradation of
polymer coating through exposure to UV rays.
Secondary Stabilizers
• These are used synergistically with a suitable
primary antioxidant, and include phosphites,
phosphonites and thiocompounds.
Evaluation of UV protection finishes
