STEP BY STEP UV FINISHES MECHANISM

1. compiled by Tanveer Ahmed 1

2. compiled by Tanveer Ahmed 2

3.  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.
compiled by Tanveer Ahmed 3

4.  Solar radiation striking the earth’s surface is composed of light
waves with
 wavelengths ranging from the infrared to the UV
compiled by Tanveer Ahmed 4

5.  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.
compiled by Tanveer Ahmed 5

6.  The actual damage to human skin from UV
radiation 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.
compiled by Tanveer Ahmed 6

7.  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
compiled by Tanveer Ahmed 7

8.  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.
compiled by Tanveer Ahmed 8

9.  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.
compiled by Tanveer Ahmed 9

10.  When radiation
strikes a fibre
surface, it can be
reflected,
absorbed,
transmitted
 through the fibre or
pass between fibres
compiled by Tanveer Ahmed 10

11.  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 the
4) 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
compiled by Tanveer Ahmed 11

12.  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
compiled by Tanveer Ahmed 12

13.  If the fibres absorb all  Using a SPF value of 50
of the incident as the goal,
radiation,  a fabric with a cover
 then the only source factor of 0.98
of transmitted rays is  And composed of
from the spacing fibres that absorb all of
between the yarns. the non-reflected UV
 By definition, the radiation
theoretical maximum  will provide its wearer
SPF is the reciprocal of with excellent
1 minus the cover protection against
factor. solar UV radiation.
compiled by Tanveer Ahmed 13

14. compiled by Tanveer Ahmed 14

15.  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
compiled by Tanveer Ahmed 15

16.  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.
compiled by Tanveer Ahmed 16

17. compiled by Tanveer Ahmed 17

18. compiled by Tanveer Ahmed 18

19.  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.
compiled by Tanveer Ahmed 19

20. compiled by Tanveer Ahmed 20

21.  The reversible chemical reaction, induced by
UV absorption
 of hydroxy-phenyl structures of UV absorbers,
compiled by Tanveer Ahmed 21

22.  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.
compiled by Tanveer Ahmed 22

23. compiled by Tanveer Ahmed 23

24.  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
compiled by Tanveer Ahmed 24

25.  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
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26.  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
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