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Ultraviolet protection finishes
Longterm exposure to UV light can result in
Acceleration of skin ageing, Photodermatosis (acne), Phototoxic reactions to drugs, Erythema (skin reddening), sunburn, increased risk of melanoma (skin cancer), Eye damage (opacification of the cornea) DNA damage.
Introduction
Solar radiation striking the earth’s surface is composed of light waves with
wavelengths ranging from the infrared to the UV
Introduction
Although the intensity of UV radiation is much less than
visible or infrared radiation, the energy per photon is significantly higher.
The very high energy of the UV-C photons is mostly absorbed by
ozone in the higher regions of the atmosphere decreasing their relative intensity on the earth surface to
almost zero.
But the energies of UV-A and UV-B photons that reach the earth surface exceed the
carbon–carbon single bond energy of 335 kJ mol–1, which is why UV radiation can be used to initiate chemical
reactions.
Introduction
The actual damage to human skin from UVradiation is
a function of the wavelength of the incident radiation, with the most damage done by radiation less than 300 nm.
If this erythemal effect is multiplied by the intensity of the incident solar light, as a function of
wavelength, The wavelengths of maximum danger to skin are 305–310
nm.
Therefore, to be useful in protecting the wearer from solar UV radiation,
textiles must demonstrate effectiveness in the 300–320 nm range.
Introduction
The SPF is the ratio of the potential erythemal effect (skin reddening),
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
In Europe and Australia, the SPF is referred to as the ultraviolet protection factor (UPF).
The SPF is also used with so-called ‘sun blocking’ skin creams,
giving a relative measure of how much longer a person can be exposed to sunlight before skin damage occurs
Solar Protecting Factor (SPF)
Typically, a fabric with an SPF of > 40 is considered to provide
excellent protection against UV radiation (according to AS/NZS 4399: Sun protective clothing –
Evaluation and classification, Standards Australia, Sydney).
It is possible to realise about 80 % of the theoretical maximum of SPF 200.
Industrial fabrics designed for awnings, canopies, tents and blinds may also benefit from a UV-protective treatment.
Solar Protecting Factor (SPF)
Since the most probable time for long-term solar exposure is in the summer, the most likely candidates for UV protective finishes are ◦ lightweight woven and knitted fabrics intended for
producing shirts, blouses, T-shirts, swimwear, beachwear, sportswear, and the like.
Solar Protecting Factor (SPF)
When radiation strikes a fibre surface, it can be reflected, absorbed, transmitted
through the fibre or pass between fibres
Mechanism of UV protection
The relative amounts of radiation reflected, absorbed or transmitted depend on many factors, including the
1) fibre type, 2) the fibre surface smoothness, 3) the fabric cover factor (the fraction of the4) surface area of the fabric covered by yarns) and 5) the presence or absence of fibre delustrants, 6) dyes and UV absorbers.
The effect of fibre type on the SPF of undyed fabrics of similar construction is demonstrated
Mechanism of UV protection
Cotton and silk fibres offer little protection to UV radiation since the radiation
can pass through without being markedly absorbed. Wool and polyester, on the other hand, have
significant higher SPFs since these fibres will absorb UV radiation.
Nylon falls in between these extremes. One factor influencing nylon and polyester absorbance is
the presence of the delustrant TiO2, a material that strongly absorbs UV radiation
Mechanism of UV protection
If the fibres absorb all of the incident radiation,
then the only source of transmitted rays is from the spacing between the yarns.
By definition, the theoretical maximum SPF is the reciprocal of 1 minus the cover factor.
Using a SPF value of 50 as the goal,
a fabric with a cover factor of 0.98
And composed of fibres that absorb all of the non-reflected UV radiation
will provide its wearer with excellent protection against solar UV radiation.
Mechanism of UV protection
Of course, 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
Mechanism of UV protection
Since fashion and comfort often dictate the use of
lightly coloured fabrics for summer apparel,
the need arose for UV absorbing materials that could be applied to fibres to provide the
desired SPF values in light shades.
Dyestuff and auxiliary manufacturers have responded by developing
a variety of materials suitable for use as UV protection finishes.
Mechanism of UV protection
Chemistry of UV protection finishes
Chemistry of UV protection finishes
The requirements for a material to be effective as a UV protection finish include
efficient absorption of UV radiation at 300–320 nm, quick transformation of the high UV energy into the
vibration energy in the absorber molecules
and then into heat energy in the surroundings without photo
degradation.
Further requirements are convenient application to textile fibres and lack of added colour for the treated fibre.
Chemistry of UV protection finishes
Chemistry of UV protection finishes
The reversible chemical reaction, induced by UV absorption
of hydroxy-phenyl structures of UV absorbers,
Chemistry of UV protection finishes
By careful choice of substituents, molecules can be formed that have
the required absorbance of UV radiation, lack of added colour and the necessary affinity to fibres and fastness.
In most cases, the UV absorber is applied with the dyes during the dyeing process.
Several possible application methods are described by
Haerri and Haenzi.
Chemistry of UV protection finishes
Evaluation of UV protection finishes
Several organisations around the world have developed or have proposed performance standards for UV protection fabrics. These organisations and their standards are summarised in Table
Evaluation of UV protection finishes
Although there are multiple standards for UV protective fabrics,
there are significant differences between the various organizations.
The particular standard for the intended market area should be consulted during
fabric development.
Before the development of instrumental methods, SPF values of fabrics were determined by
irradiating human subjects and measuring the critical amount of radiation necessary to cause skin reddening at
a particular wavelength with And without wearing the fabrics.
Fortunately, several methods are now available that do not result in a sunburned participant. These methods all determine
the transmittance of UV radiation through fabrics and calculate the SPF value using standard charts for the solar spectrum and the erythemal effect.
UV Standard 801 considers in addition the effects of usage of the finished textiles that normally reduce the UV protection
Evaluation of UV protection finishes
UV absorbers have the same need for wash fastness and light fastness as dyestuffs.
Laundering trials should be carried out with all new formulations to confirm that the claimed UV protection is actually active during the life of the garment.
One concern is specific to the use of UV absorbers in combination with optical brightening agents (OBA).
These brightening agents function by absorbing UV radiation and re-emitting visible light.
If a UV absorber is also present in the fibre, the brightening effect from the OBA can be greatly diminished or even absent.
Proper choice of an appropriate OBA can minimise this problem. In most other cases combination with other finishes does not reduce the UV protection.
A two-step application is necessary if the pH values of the UV protection finish bath and that of the other finishes are very different.
The UV protection finish should be applied first. Problems may arise from limited bath uptake after a repellent finish or after calendering
Troubleshooting for UV protection finishes andcombinability