A comprehensive review of ultraviolet radiation and functionally modified textile fabric with special emphasis on UV protection

Abstract

The functionality of natural origin-based fibres can provide minimal protection against UV exposure; however, surface modification of fabrics can help to achieve better outcomes. The ability to provide protection basically depends upon several factors of textile fabric, such as fibre chemistry, yarn structural parameters, fabric weave construction, fabric areal density, cover factor, porosity, and humidity. Due to the constant reduction of the ozone layer in the atmosphere, increasing UV radiation has now raised severe concerns across the globe, which is projected to deteriorate the state of global health. According to the WHO for the year 2022, more than 2.5 million cases of cancers associated with skin and around 1.5 million cases of blindness and other health-related issues have been reported, which is projected to take a larger picture in a few years. The best way to keep ourselves safe from hazardous UV exposure is through self-protection using protective barriers. By treating fabric with different organic and inorganic UV absorbers, surface modification of textile materials can be achieved to enhance UV blocking performance with the inclusion of different grades of polymers. This review also highlighted the different influencing parameters that effect the ultraviolet protection factor (UPF) of a fabric and discusses how dyeing and finishing can affect those. Moreover, the study enumerates the current challenges and limitations that can come across while designing a protective fabric along with precautionary measures to overcome those barriers with potential future prospects.

Graphical abstract

Highlights

• •Improving human skin protection from damaging UV rays.
• •Strategies for modifying textile fabric to provide UV protection functionality.
• •Factors that influence the fabric's UV Protection Factor (UPF).
• •Cost-effective textile that offers long lasting stability and sustained efficacy.

1. Introduction

The wavelength of the electromagnetic radiation as ultraviolet light is longer than the X-rays but shorter than visible light. Ultraviolet radiation (UVR) is one type of radiant energy emitted by the sun. Infrared radiation comprises 66 % of sun's energy, followed by visible light (32 %), and ultraviolet light (2 %), which reaches the earth [[1], [2], [3]]. Worldwide, 1.5 million and more instances of skin cancer were detected in year 2020, and more than 1,20,000 fatalities were documented, according to a WHO study released in the year 2022. There are an estimated 15 million cataract-related blindness cases worldwide, 10 % of which may be due to UV radiation exposure [4]. The safety of humans against harmful UVR, which reaches surface of the earth by ozone layer's thinning, is a critical concern in modern society. According to literatures, Skin issues increased by 2.3 % when solar UVR at the earth's surface rises due to reduction in ozone layer's thickness by about 1 % [5]. Short-term insolation to UVR is beneficial for living things since it promotes bone development and vitamin absorption, but long-term exposure may inadvertently damage deoxy ribonucleic acid (DNA) and cause numerous skin problems, such as photo dermatosis, which causes acne, cancer, and sunburn-induced erythema, along with speeding up the ageing process. Thus, limited UVR exposure is required to avoid these health problems [[6], [7], [8], [9]]. Due to updated public awareness, using sunscreen and wearing UV-protective apparel has become more common. Although, sunscreen can provide UV protection, but use of sunscreen is often cumbersome and unpleasant to human skin. Furthermore, sunscreen should not be given to kids below six months owing to the chances of the chemicals contained in the formulation to penetrate their delicate skin. The cost of these creams may also pose a barrier for some individuals [7,10]. Moreover, sunscreen's effectiveness is influenced by the environment, including wind, humidity, temperature, amount applied, and the base's ability to adhere. In general, medical professionals recommend wearing clothing that provides maximum protection to the human body as possible between 10 h and 14 h during peak UVR, especially the individuals who are working outside [11,12]. To increase the effectiveness of fabric in blocking UVR, they are now being treated with various organic and inorganic UV absorbing agents. The ability of treated fabric to block UVR is also determined by the rating of UPF [13,14]. According to previous theories, textiles provide some amount of protection from UVR by itself, after thorough investigations into the efficiency of different materials for blocking UV radiation, it was found that the various parameters that should be taken into consideration most often relates to their material properties, construction, and colour [[15], [16], [17], [18]]. The penetration of UVR through various layers of skin is depicted in Fig. 1. UV protective clothing is a unique and wide area of research. Various scientific gaps still persist in this domain that includes variability in efficacy with various environmental conditions, durability and longevity challenges with several wash cycles, and reduction in stability of fabric to resist UVR after a certain time period [15,19]. Therefore, studies are necessary to develop eco-friendly and non-toxic UV absorbers, as synthetic agents although being common, are more prone to toxicity. Optimization in fabric constructional design is pre-requisite to enhance comfort and ensure protectiveness. All these motivated us in writing this review to address all the lacunas and put more emphasis for future research on developing a long term durable protective textile with few or no adverse consequences. This review will help in enhancing individual health protection by reducing the risk of causing skin maladies and aging, raising public awareness and encouraging the utilization of UV protective modern clothing for outdoor activities along with advanced scientific methods for developing fabric as a green alternative for protection.

Fig. 1.

A Schematic diagram of UVR penetration into the skin.

2. UV radiation and its effect on human health

The quantum physics of light states that light at higher frequencies has greater energy and smaller wavelengths. UVR is having a shorter wavelength and is highly energetic. The scale range of wavelength of daylight or electromagnetic spectrum (EMR) as it travels from sun towards the earth is approximately 290 nm–3000 nm [20]. UVR is the light with wavelength range in between 100 nm and 400 nm. Three distinct wavelength ranges with different energy level, make up this UVR band: UVA (320–400 nm), UVB (280–320 nm), and UVC (100–280 nm) [8,12]. Various types of EMR and calculating formula for their energy have been shown by Eq. (1) and Fig. 2 [19,21].

E = (h x c)/λ …………………. (1)

Here, E = energy of particular band of EMR, h = Planck's constant (6.63 × 10−34 J S), c = speed of light in vacuum, and λ = wavelength.

Fig. 2.

Types of electromagnetic spectrum.

The layer of ozone (O₃), O₂, and water vapour of the higher atmosphere completely absorbs UVC radiation below 280 nm, so it cannot reach the earth's crust. This is crucial because UVC radiation is the most harmful to human skin and has the most energy out of all three bands [[22], [23], [24], [25]]. Owing to the variations in wavelength and energy, high-energy UVB and fairly low-energy UVA radiation both reach the earth's crust and cause a lethal effect on living cells [26]. Skin damage from UVR could e long-lasting and detrimental due to biosynthesis of melanin. Melanin, a brown or black pigment that shields our skin and body from the harmful effects of prolonged solar exposure, is biosynthesized from human skin after being exposed to UV-radiations. Melanin protects the deeper layer of skin by blocking UVR from sunlight. UVR, in addition to causing burns and the degeneration of dermal fibres, has the capacity to cause skin cancer by affecting chromosomes. The primary component of life, DNA is damaged at the molecular level by the high intensified UVB light, which also causes tanning of the exposed skin [25,27,28]. The effect of UV exposure on different skin types has been shown in Table 1 below [2,29].

Table 1.

Effect of UV exposure on different skin types.

Type and colour of unexposed skin	UV sensitivity	Critical dose (mJ/cm2)	Self-protection time in minutes	Level of risk
I – White	Very sensitive	15–30	5–10	Burns easily and have the largest chance of causing skin cancer and the fastest rate of premature ageing.
II – White	Very sensitive	25–35	8–12	Burn and tans very rarely
III – Brownish	Sensitive	30–50	10–15	Tan and even sometimes burn
IV – Brown	Moderately sensitive	45–60	15–20	Tan and even sometimes burn
V – Brown	Minimally sensitive	60–100	20–35	It has adequate melanin levels, seldom burns, and tans readily
VI – Dark brown-black	Insensitive	100–200	35–70	Protections provided by melanin pigment levels that are adequate, very seldom gets burned and tans readily

Besides the direct impacts of UVR, environmental changes may have an indirect influence on human health. For example, UVB radiation produces photochemical smog which in turn may worsen respiratory disorders by disrupting oxygen balance. Also, a reduction in food production in view of the ozone layer's depletion and its effects on various animals and plants might have far-reaching ramifications. Hence, quantifying these indirect health impacts is far more challenging than quantifying the direct ones on human well-being [[30], [31], [32]]. Several parameters are necessary to realize the impact it will have on mankind based on the nature and intensity of radiation entering the earth's surface. Table 2 shows the different properties of UVA and UVB [33].

Table 2.

Properties of UVA and UVB radiation.

UVR	UVA	UVB
Wavelength (nm)	320–400	280–320
Percentage reaching earth surface	98.8	1.1
Average photon energy (kJ/mol)	315–350	400
Mean Intensity (W/m2)	27	5
Negative Effects	Sunburn (minor), Melanogenesis (minor), Skin cancer (minor), Elastosis (minor)	Sunburn (major), Melanogenesis (major), Skin cancer (major), Elastosis (minor)

3. Solar UV index and natural factors influencing UVR

The amount of UV radiation coming into the earth's surface is measured through solar ultraviolet index (UVI). A numerical indicator that represents the quantity of sunburn causing solar-radiations received during the day. The International Commission on Illumination (CIE) established a standard action spectrum for UV-induced erythema on human skin. This UVI is measured using certain parameters which are ozone level, predicted cloud cover, water vapours, aerosols, and city elevation. A greater UVI indicates a higher UVR entering earth's crust which is calculated by Eq. (2). The solar UVI range along with its recommended protection is enlisted in Table 3 [19,34].

$$\text{UVI}={\mathrm{K}}_{\text{er}}{\int }_{280nm}^{400nm}S\lambda \ast Se\lambda \ast \Delta \lambda \text{.}$$ (2)

Table 3.

UVI range with effect level.

Solar UVI range	Level of negative effect	Recommended protection
<2	Low	No need for protection. There is no risk in staying outdoors.
3–5	Medium	Protection is necessary. Need for a sunshade during the noon hours.
6–7	High	Protection is necessary. Need for a sunshade during the noon hours.
8–10	Very High	It is necessary to use additional protection such a hat, shirt, and sunscreen. Avoid staying outdoors, particularly during the sunlight hours

Here, $S\lambda$ is the solar spectral irradiance (Wm⁻²nm⁻¹), $Se\lambda$ is the erythema reference action spectrum, $\Delta \lambda$ is the wavelength interval considered, and K_er is a constant and it is equal to 40 m²/w.

As the insolation to sun is vital for some beneficial effects, but the damaging effects of the UVR is further vulnerable which usually depends on a several of circumstances, including intensity, length of exposure, makeup of the climate etc., [34,35]. These factors are notable keep people safe from exposure to UVR [9]. Fig. 3 represents the natural influencing factors of UVR.

Fig. 3.

A Schematic diagram of natural factors influencing UVR.

4. UV protection levels of modified textiles

Surface modification of textile fabric is engineered to improve the blocking ability of UVR. The blocking level provided by the fabric is measured by UPF rating, where SPF is used for used sunscreen. Two alternative methods, such as in-vivo and in-vitro are generally used to measure SPF and UPF value of materials [[36], [37], [38]].

4.1. In-vivo method

Using this approach, the depth of sunburn is evaluated in terms of SPF. The term “SPF” mostly refers to sunscreen products, which are stated as a ratio between a harmful dose without sun protection and a harmful dose with sun protection. A high SPF value suggests stronger protection ability against sunburn. The principal factor that accounts for the disparity between the UPF and SPF ratings is the “hole effect” in the fabric [3,30,39].

4.2. In-vitro method

This procedure is much cheaper and less time-consuming as compared to in vivo approaches. Therefore, spectrophotometer tests appear to be most feasible for determining how well fabrics prevent to transmission of UVR. A spectrophotometer uses UV rays with varied wavelengths (280 nm–400 nm) to quantify UPF value following test method AATCC 183-2004. UPF is described as the difference between average UVR computed for skin that is not shielded by the test fabric and the average UVR computed for skin that is shielded. The blocking ability of fabric increases with higher UPF numbers. The UPF value is calculated using the below formula of Eq. (3) [29,[40], [41], [42]]. Besides The protection categories of textile fabric according to American society for testing and materials (ASTM) D6603 has been shown in Table 4 [36,[43], [44], [45]].

$$\text{UPF}=\frac{{\int }_{\lambda =280}^{400}E\lambda \ast S\lambda \ast \Delta \lambda }{{\int }_{\lambda =280}^{400}E\lambda \ast S\lambda \ast T\lambda \ast \Delta \lambda }$$ (3)

Table 4.

Protection categories of textile fabrics according to ASTM D6603.

UPF number	% Transmission	% UVR blocked	Protection category
15 to 24	6.7 to 4.2	93.3 to 95.8	Good
25 to 39	4.1 to 2.6	95.9 to 97.4	Very good
40 to 50+	≤2.5	>97.5	Excellent

Here, $T\lambda$ is the average spectral transmission of the sample fabric, $E\lambda$ is the relative erythemal spectral effectiveness, $S\lambda$ is the solar spectral irradiance (Wm⁻²nm⁻¹), $\Delta \lambda$ is calculated wavelength interval (nm), and $\lambda$ is the wavelength (nm).

Several key factors are responsible to influence the UPF of fabric, they are fibre type, fabric constructions, dye and additives used, finishing method, etc. Conventional finishing methods have a crucial role to impart different characteristics to the fabric that often do not lead to permanent effects and eventually lose their character after laundering or use. Shuai et al. investigated that UPF of fabric increased from 7 to 137 when cotton fabric dyed with a reactive dye [46]. Another study showed that the fabric UPF reached around 35 from 8, when disperse dye applied on a polyester fabric [43]. Dhinesh babu et al. proved in their research study, that UPF can improve to around 56 from 12, when surface modification of cotton fabric is done by coating with TiO₂/SiO₂ nanocomposite [47]. The incorporation of ZnO nanoparticles on cotton fabric surface can also increase fabric UPF value for UVB radiations from 19 to 320 [48]. An investigation by Arora et al. showed that, when polyester fabric dyed with azo disperse class dye, the UPF increased to around 72 from 7.7 [49]. The natural colour dyeing to fabric can help improve the fabric UPF values to around 19 for curcumin and around 23 for onion skin colour as reported [50].

5. Textile materials and UV protection

There are three methods to protect us from solar radiation: first, by avoiding the sun's rays; second, by wearing protective clothing while going outdoors; and third, by using sunscreen accessories or lotions. As is well known that, UVR is composed of two UV rays with varying energies, UVA and UVB. While yarn is a twisted component of a bundle of fibres, most wearable textiles are nothing more than an interlacement or interloping of yarns with pores. When UV radiation strikes a textile fabric surface, it splits into several components. Some part of the radiation is reflected at the fabric's surface periphery, while another portion is absorbed and shifted into a different energy form as it travels through the fabric. The final portion of the UVR is transmitted through the fabric and reaches the skin area (Fig. 4). By lowering the detrimental effect of solar wavelengths via reflection, absorption, and scattering, textile fabric has the capacity to offer protection from incoming UV radiation [29,43,51,52]. The fabric's form, design, and construction factors are the most valuable factors that alter the protecting ability of the textile fabric. During weaving of woven fabric for good UVR protection, few aspects must be considered like composition of the fibres where natural fibres transmit more UVR as compared to synthetic fibre, tightness factor of the weave where a jammed woven fabric transmits less UVR than a normal fabric, colour of fabric in which dark colour of a same fabric will absorb more UVR than light shaded fabric, likewise stretched fabric has a lower UPF than a rigid one [22,33,53,54].

Fig. 4.

An illustrative representation of UVR exposure on textile fabric surface.

6. Textile parameters effecting UPF

As already mentioned in the previous sections, UVR is beneficial up to a certain level, but if our skin gets exposed to too high levels, it might be extremely harmful. Another best method to shield our skin from UV rays is by wearing UV protective cloths [35,55]. But there are several additional parameters that should be taken care of while designing a protective fabric.

6.1. Fibre chemistry

The chemical properties of fibre have a profound impact on fabric's UPF [56]. Due to some natural components such as pigments, pectin, and waxes present in grey cotton fibre, it has a greater UPF than bleached cotton fibre, whereas bleached fabric does have a higher UV transparency [12,57]. Likewise, the presence of lignin, which serves as a UVR absorber, may be one such reason for grey jute fibre having higher UPF. Although lignin is available in linen and hemp fibres too, still the jute fibre demonstrates better UV absorption than the other one [58]. Compared to cotton and wool, silk has been found to absorb more UV light. Over 280–400 nm and even beyond 400 nm, wool fibre has a decreased transmittance. Furthermore, dull viscose fibre exhibits better UVR absorption than glossy viscose fibre. Natural fibres like cotton, silk, and wool absorb relatively lower proportion of UVR as compared to synthetic fibres like polyester [59,60]. Furthermore, polyester fibre absorbs more ultraviolet radiation than acrylic and polyamide fibre. In comparison to aromatic polyamides, aliphatic polyamides are substantially less efficient against UPF [11,61,62]. The colour, strength, and resilience of fibre are all negatively impacted by prolonged UVR exposure.

6.2. Moisture content of fibre

Depending on the hydrophobicity and hydrophilicity of fibre, greater humidity is to blame for the higher moisture availability in the material. The fibre's moisture content and atmosphere's relative humidity have a profound impact on fabric's UPF. First, owing to fibre swelling, fibres with a higher moisture absorption capacity will form a larger cross-section. By increasing the fibre surface area and decreasing the gap across the ends and picks, the fabric density rises and UV transmittance decreases. Alongside, moisture in the fibre decreases the impact of UVR scattering since its refractive index is near to fibre polymers than air, leading to increased UV transmission as compared to lower UPF. A change in UVR contact and UVR scattering intensity on swelled fibre will indicate a change in UPF. Among viscose and silk, viscose fibre has a better swelling characteristic and an improved ability to absorb water. Thus, they are more dependent on humidity [26,63,64]. Despite having weak swelling qualities, silk's very fine texture and a larger quantity of fibres per yarn cross-section causes it to swell more owing to capillary absorption, which in turn reduces UV transmission. UV light transmission is decreased by finishing treatments applied to materials to prevent swelling. In general, a stronger association between hygroscopic fibres and their UPF is known. However, very few synthetic fibres like polyester, have a little moisture absorption and swelling but possess higher UPF, which is why the UPF cannot be correlated with humidity [58,65,66].

6.3. Yarn structural chemistry

Although different kinds of yarn are employed to make fabrics, the one fundamental factor that affects the fabric's UPF is the structure of yarn. The efficacy of fibre packing in the thread and its impact on the surface qualities both contribute to a fabric's UV protection capabilities. According to Stankovic et al. the yarn structure significantly affects the UV protection qualities of high UPF fabrics by having an impact on the air volume spread within the fabric, or the fabric's openness. The proportion of free open space on the fabric's surface is generally confirmed by the yarn spacing. Since yarn twist changes both the core and surface geometry, it is vital to know about the surface characteristics of the yarn so as to accurately predict the uniformity of pores in textile fabric. Additionally, there is a negative correlation between yarn count and fabric UPF. The thinner fabric constructed with finer yarns might be a probable reason for this [45,67]. It could also be attributed to greater fabric porosity for textiles made with finer fibres [68].

6.4. Weave construction

The weave pattern of woven fabrics has an impact on how much UVR passes through them. Naturally, tighter weaves provide greater UV protection, whereas materials with looser structures offer relatively little protection for woven fabrics with the similar grammes per square metre (GSM). Twill and satin types of fabric offer substantially greater protection, whereas plain types of fabric often provide less protection in conditions like natural coloured, dyed, and bleached state. Fig. 5 shows the different kinds of weave structure of fabric [16,33,54].

Fig. 5.

Block diagram showing plain, twill, and satin weave construction of textiles.

6.5. Fabric cover factor (Cf) and porosity

Yarn density (ends per inch (EPI) and picks per inch (PPI)) and yarn count (Ne) are used to determine the amount of cloth that is covered by the warp and weft yarns in a fabric. The most important characteristics that describe the weave structure is the fabric's cover factor [69]. UPF and cover factor have an exponential connection. The fabric's ability to block UV rays is increased by a higher cover factor [33,56]. Eqs. (4)–(7) denotes the relationship between cover factor and fabric UPF.

$$\text{Cover}\text{factor}\text{of}\text{warp}\text{in}\text{fabric}\left({\text{Cf}}_{\mathrm{p}}\right)=\frac{Endsperinch}{\sqrt{Warpyarncount\left(Ne\right)}}$$ (4)

$$\text{Cover}\text{factor}\text{of}\text{weft}\text{in}\text{fabric}\left({\text{Cf}}_{\mathrm{t}}\right)=\frac{Picksperinch}{\sqrt{Weftyarncount\left(Ne\right)}}$$ (5)

$$\text{Cover}\text{factor}\text{of}\text{woven}\text{fabric}=\text{Cf}\_\left(\mathrm{p}\right)+\mathrm{C}\mathrm{f}\_\left(\mathrm{t}\right)-\left[\frac{Cfp\ast Cft}{28}\right]$$ (6)

$$\text{Fabric}\text{UPF}=\frac{100}{\left(100-Coverfactor\right)}$$ (7)

Porosity could be used to explain the positive link between fabric weights (GSM), thickness and UPF ratings. The terms “cover factor” and “porosity” both refer to the tightness of the weave [64]. The portion of the fabric's area filled by the threads increases with tighter weaving, and the fabric becomes opaquer to UV rays. As GSM rises, the cover factor grows as well. As the gaps between the yarns are closer together with heavier fabrics, hence more radiation is blocked, reducing the overall UV transmission. Thickness is a also a relevant factor in determining UPF, Apart from having a better cover factor, thicker and denser materials transmit fewer UV rays [68,70,71]. Owing to the frequent interlacing of threads, woven textiles often have larger cover factors than knitted fabrics. Knitted fabric also has wider pores than woven fabric because of larger space between the yarns. According to Pailthorpe, an Australian textile expert, moving to a coarser count while keeping the construction variables (EPI and PPI) and fibre composition unchanged would ultimately lead to an increase in cover factor, which would further improve the UPF and thus more UVR is prevented because the holes between the interlaced yarns are narrower. The ideal fabric has extremely tiny holes between the interlaced yarns and yarns that are entirely opaque to UV light. When light only comes in through the pores, UV transmission is at its best. This can be best expressed with the help of the following formula,

$$\text{Fabric}\text{UPF}=\frac{100}{Porosity\%}$$ (8)

Hence, higher the porosity, lower is the UPF [26,56,72,73]. Through a variety of dry finishing techniques, including over feeding the stenter, compressive shrinkage techniques like compacting and sanforising, which are sometimes used to provide structural stability [26].

6.6. Chemical finishing via bleaching and dyeing

In a grey cloth with the same weave pattern, bleached fabric has a much lower UPF than unbleached one made from natural fibres. This is mainly because bleaching process removes UV absorbers such as natural colours, waxes, and other components [57,64]. Bleaching is a crucial step for finishing of fabric wherein, agents such as hydrogen peroxide (H₂O₂), sodium hypochlorite (NaOCl), sodium bisulphite (NaHSo₃) etc., are used to impart white texture to the developed fabric [74,75]. This is achieved at high temperature and alkaline pH for a stipulated time. Bleaching will lead to the weight loss and enhance the absorbance capacity of fabric to assist in further processing of finishing. According to Imaizumi et al. colouring affects UV transmission on different variety of fibres [69]. However, few studies have shown that deeper shades of any colour provide more UVR protection because they transmit less UVR than lighter shades. Hence, colour is the significant feature of UPF rating. According to the findings, textiles in all shades of black, blue, and most shades of red provided not just acceptable but outstanding protection from the sun if they were weaved in satin and twill pattern [16,22]. All UPF ratings for plain textiles were clearly below 45, whereas the UPF ratings for satin and twill textiles were quite high (over 400) [33].

6.6.1. Influence of OBA

As already disclosed in the previous literatures, optical brightening agents (OBA) affect UPFs when employed in fabric finishing processes and wash cycles. The fabric's whiteness is often improved by OBA via UV ray excitation and visible blue emission [76]. Emission and excitation are induced by the shifting of p-orbital electrons from aromatic and conjugated molecules. Excitation maxima for the majority of optical brighteners lie between 340 and 400 nm. Cotton and blended cotton may have their UPF improved by OBA, but 100 % nylon and polyester textiles cannot [63]. OBA may improve the UPF number from 16.3 to 32.2 in P/C blends to a level of 0.5 %, which is almost comparable to the outcome of utilizing UV absorbers at a 0.2 % concentration (UPF 35.5). When materials with OBA treatments are washed, the UPF decreases and so after around 10 launderings, it equals to that of an untreated fabric, demonstrating the semi-permanent character of the finish and protection [77]. Many OBAs have another drawback of absorbing 93 % of the daytime spectrum in only the UVA region [78].

6.6.2. Impact of dyeing

The UVR protecting ability of the dye sources depends upon absorption characteristics of the functional group present in the chemical structure. Sankaran et al. reported that the UVR protection ability of cotton fabrics was effectively improved when dyed with vegetable and animal dyes from madder, indigo and cochineal [79]. Some direct, reactive and vat dyes with darker shade are capable of giving a UPF of greater than 50 due to the nature of dye-fibre bonds. Multiple studies investigated that the potential role of few natural dyes like curcumin and onion skin dye on fibre or fabric by providing UV protective characteristics. The combinational effect of dyes and UV absorbers together on fabric can also reduce the transmission of UVR. The dye shades substantially increase the UPF value of bleached cloth when compared with non-bleached fabric [43,46,74]. Although, light colours reflect solar radiation more efficiently than dark ones but part of the radiation penetrates more easily through the fabric. Since the dye's absorption bands extend to UVR, all types of dye function as UV absorbers (280–400 nm). The capacity of dyes to raise a fabric's UPF depends on the extinction coefficient. Another experimental result revealed that the colour depth and dye concentration are the most essential factors influencing the UV protection property of cotton knitted fabrics. Therefore, the UVR blocking ability of textiles are enhanced with increase in ingredient concentration with either a dye or pigment or a delustering agents or other additives [80,81].

6.6.3. Natural agents for finishing

Polyphenolic substances, flavones, flavonoids, tannins, and lipid fractions from plants have been shown to absorb the visible section of light and UVB radiations [81]. Tannins are water soluble phenolic compounds that have been used on textiles for several hundred years both as a pre-treatment and post-treatment factor to increase wash fastness and light fastness. Metallic salt mordants have also been reported to contribute to enhancing UV-protective properties of naturally dyed cotton wool, and silk [82].

7. Modification of textiles for UV protection

The treatment strategies of textile for providing UV protection are achieved using different categories of UV absorbers which are organic or inorganic components in nature that absorb short-wave sun light (280–400 nm) to prevent body penetration and also release it as heat without degrading yarn and fabric quality. During the finishing process of fabric, UV-absorbing compounds are added to the surface of a yarn or fabric by various methods which makes the fabric robust at blocking UV rays as shown in Fig. 6 [19,29,71]. These methods are direct dipping method by incorporating UV absorbing agent directly by dipping the fabric in solution bath. This is the simplest method so far in which the concentration of entities gets uniformly spread across the fabric surface. In this method nanoparticles of UV absorber can also be imparted on to the fabric for better distribution and long-term efficacy [39,62]. Another is pad-dry-cure method in which the surface modification of textile is achieved by passing the same into a solution bath and squeezing a roller for efficient impregnation and to remove the excess solution from the fabric, followed by drying in a hot air oven and finally solidifying the compound through curing that ensures regular distributions. This method is used widely to attach microcapsules, nanoparticles etc., in the textile providing a control release pattern of the compounds with wide shelf life [83,84].

Fig. 6.

A Schematic diagram showing protective action of fabric with and without protective coating.

7.1. Organic compound as UV absorber

Organic UV absorbers are colourless, aromatic molecules with conjugate double bonds that absorb UV light and allow the molecules to enter an excited state. The light is then turned into vibrational energy inside the UV absorber molecule. When the molecules go back to their normal state, they release heat energy into the air [[85], [86], [87]]. The chemical structures of some of the widely used absorbers are shown in Fig. 7. To enhance UV protection, cotton fabric is coated with an aloe vera and chitosan nanocomposite [39]. Microcapsules of photochromatic dyes and chitosan also improve the protection ability of cotton fabric when coated with sodium alginate [88]. Green tea's polyphenolic components act as a defence barrier against UVR and also prevents from its detrimental effects [89]. As reported in some literatures, lutein and lutein esters, two carotenoid substances, were utilized to increase the cloth's UV protections [39,90]. Saewan & Jimtaisong (2013) found out that, baicalein, an extract of Scutellaria baicalensis, has the ability to increase the silk fabric's UV protection [91]. Additionally, UV absorbers on cellulosic fibre include flavonoids, tannins, and amino acids [39]. There are additional reports that natural zeolite; clinoptilolite may act as a UV protector [92]. Derivatives of ethylene diamine and triazine are also reported to improve the UV protection of fabric apart from acting as a UV absorber [93]. Additionally, β-cyclodextrin has UV absorption characteristics, when treated with cotton fabric; it was testified to have an absorbance peak at around 300 nm wavelength [14].

Fig. 7.

Chemical structure of some organic UV absorbers.

7.2. Inorganic compound as UV absorbers

Inorganic UV absorbing agents are mostly efficient, stable, and safe. They also provide protection from UVR by physically obstructing them. Some of these include talc, ichthammol, kaolin, iron oxide, and titanium dioxide [13,94,95]. Another inorganic compound effective in blocking incoming UVR is zinc oxide (ZnO) [96]. It was observed that lowering it to the nanoscale level improves its ability to block UV light [97,98]. When ZnO nanoparticles (NPs) are applied to the surface of cotton fabric, their ability to behave as UV absorbers may be effectively transferred to the finished fabric [99,100]. While Farouk et al. reported using epoxy binder during coating to provide long-term UV protection [101]. Wang et al. grew nano ZnO crystallites on cotton textiles to gain UV-blocking properties [102]. Moreover, iron oxide (Fe₂O₃) has been found to possess UVR blocking qualities as well. This is the reason it is most often utilized with ZnO to produce synergistic effects [13]. It was observed that the metallic-coated textile fibres also provide UVR protection [103]. Thus, improved ability of UV protection for fabric may be achieved by combining ZnO with titanium dioxide (TiO₂) [104]. The incorporation of ZnO/SiO₂ nanorods to cotton fabric can increase UV protection [105]. A wide-spectrum UV blocker, TiO₂ diffuses the light to filter the UV rays [104]. Due to its photo-catalytic properties, TiO₂ nanoparticles have drawn a lot of interest. Utilizing TiO₂, textile fabrics may now offer some additional qualities like antibacterial, self-cleaning, hydrophilic, and super hydrophobicity [53,80,106,107]. It was reported by Zheng et al. that cotton textiles finished with nano-TiO₂ sols possess greater UPF values. The best way to finish cotton fabrics with nano-TiO₂ sols is to use two dips, two pads, 70 % wet pickup, and dry at 50 °C for 5 min before curing at 165 °C for 3 min [81]. The UV protection qualities of the cloth are additionally enhanced by applying nano silver to its surface [79,108]. The UPF can also be increased when certain salts, including zinc and copper acetate, are added to the polyester surface and then subjected to caustic treatment. Utilizing plasma therapy is another method for incorporating such salts; in general, nitrogen plasma treatments produce the best outcomes [82]. According to some research studies, cotton fabric may be treated with TiO₂ nanoparticles using various techniques in combination with reactive and natural dyestuff to provide long-lasting protection against dangerous UVR [24,109]. Cationized cotton textiles were dyed and finished using several formulas that included reactive dyes, henna extract, and TiO₂ nano-sol. The dyed materials demonstrated exceptional UV protection without compromising other performance characteristics. TiO₂ concentration and dyeing temperature both influence UV protection [110,111]. The proposed method for Ag/TiO₂ composite synthesis via the proposed method is suitable for long-term biological applications. Also, Ag-doped TiO₂ NPs when additionally deposited on fabric using a prolonged hydrothermal process was found to improve the UPF values [112]. Also, ZnO/Ag nanocomposites were employed to create fabrics with simultaneous UV blocking, self-cleaning, and antibacterial characteristics [113,114].

8. Characteristics of polymers for UVR protective clothing

Polymers have an exceptionally crucial role in textile manufacturing right from dyeing till finishing. At every single step, polymers play an essential role through its multifaceted application and function by enhancing protection ability, comfortability, durability, flexibility and performance for long term efficacy. These polymers are used either directly during fabric finishing or fibre productions stage for ensuring specific characteristics and structural properties [26,30,39]. A study by Zhonghua et al. proved that the use of poly (vinylsilsesquioxane) polymer with ZnO on cotton fabric can improve its UPF value drastically high [115]. It has been shown recently that chitosan and ZnO integrated composite can significantly improve the UVR protection ability of cotton fabric [116]. The use of polyurethane, an organic polymer with carbamate linkage can behave as a reliable UV absorber on fabric by reducing the amount of UVR transmission as reported by Emam et al. [117]. A study by Silva et al. reported that the application of carboxymethyl cellulose (CMC) and colouring matter can increase the UVR protection's ability of a fabric [118]. Additionally, metal nanoparticles (MNPs) with polysaccharides such as chitosan, cyclodextrins, starch and alginates can impart UV protection functionalities without compromising the intrinsic character of the textile material [119]. Shafei et al. proved that the use of reactive cyclodextrin poly-butyl acrylate preformed polymers containing nano-ZnO on cotton fabric can improve fabric functionality with reducing the UVR transmission [120]. Composites compound of poly (N-vinyl-2-pyrrolidone) on fabric can also enhance the fabric's UPF value after finishing [121]. So, polymers play an extraordinary and unique role in the textile production process. Both natural and synthetic polymers, like cellulose, keratin, and fibroin, and polyamides, polytetrafluoroethylene, polyvinyl chloride, polyurethanes, and polyvinyl alcohol, have transformed the textile industry with their distinct characteristics and remarkable capabilities, including UV protection.

9. Current challenges and future prospects

UV-protective fabrics play a vital role in shielding against harmful ultraviolet radiation (UVR) to minimize the damaging effects of skin cancer and other health related issues. However, several obstacles are still encountered during their development. The very first being the persistence to maintain the protection quality level of the fabric after subsequent launderings and also during prolonged exposure to solar radiation. In a long run, the exposed fabric may reduce its effectiveness and lifespan and hence cannot deliver intended outcome for a prolonged duration [24,36]. Moreover, a dense, weave or heavy fabric are required for better protections but these are less breathable, stiff, and uncomfortable in nature during warm weather condition [22,33,68,76]. Extensive research is required on the constructional approach for different weave pattern to design light weight and breathable fabric that provide optimum protection level with comfort and efficacy. The chemicals used to develop UVR protective textile can be toxic to environment which may increase sustainability concern and potential regulatory challenges [43,50,63,91]. Thus, development of a natural and eco-friendly alternatives for finishing and manufacturing process are required which will minimize environmental impact. Maintaining optimum protection level in harsh conditions of climate and altitude variations is required without compromising the safety thereby increasing the acceptance for the end user. Further research is required in testing methodologies to develop suitable material in order to maintain activity in challenging conditions. UV protective clothing may be expensive to design which can hinder the individual's accessibility when compared with a conventional fabric [71,122]. Hence, finding a cost-effective production process without compromising the quality is essential. All these concerns should be taken into consideration for developing a protective textile element.

10. Conclusion

Protection against hazardous UVR is essential as ozone layer is thinning progressively and posing a critical concern for human health. Textiles have the provision to provide basic, acceptable, or excellent protection by blocking harmful UVR depending on variable factors. This review summarized the critical factors that influence UV exposure along with potential strategies to combat those using protective clothing. The literatures revealed that the physical structure of the yarn and the chemical makeup of the fibres have a significant role on the fabric's UPF. The natural fibre in unbleached condition has been learned to possess higher UV protection capacity then the bleached one. Conversely, the synthetic fibres are more effective than natural ones as they absorb more UVR. The two significant parameters that greatly affect fabric's UPF are the cover factor and porosity. UPF increases proportionately with cover factor whereas decreases inversely with porosity. The tightness of the cloth also indirectly affects the fabric's UPF wherein a tighter fabric with compact weave pattern shall lead to the overall increase in fabric's UPF. Other parameters that notably influence UPF are the constructional characteristics of woven fabrics such as weave type, yarn count (Ne), weft and warp yarn densities (PPI and EPI) and chemical finishing. This review also revealed that a dark coloured fabric with same structure can provide more protection against UVR than light-coloured ones. Furthermore, incorporation of OBA, and organic or inorganic UV absorbers may also enhance the UPF value of fabrics. In the not-too-distant future, protective textile can serve to be an effective approach to provide defence against harmful UV radiations by shielding human skin with a comfortable and value-added fabric having substantial shelf life. This review will also engage researchers in this domain to produce ideas and build competitive products henceforth.

CRediT authorship contribution statement

Buddhadeb Saha: Writing – original draft, Software, Resources, Conceptualization. Achintya Saha: Writing – review & editing. Parikshit Das: Visualization, Resources. Ajay Kakati: Writing – original draft, Resources. Amartya Banerjee: Resources, Formal analysis. Pronobesh Chattopadhyay: Writing – review & editing, Supervision.

Data availability

Data included in article/supp. material/referenced in article.

Declaration of competing interest

The authors declared that there is no known competing financial interest to disclose.

List of abbreviations

UV

Ultraviolet

UVR

Ultraviolet radiations

WHO

World Health Organization

DNA

Deoxy ribonucleic acid

UPF

Ultraviolet protection factor

MNPs

Metal nanoparticles

SPF

Sun protection factor

AATCC

American association of textile chemists and colorists

ASTM

American society for testing and materials

UVI

Ultraviolet index

GSM

Gram per square meter

OBA

Optical brightening agents

NPs

Nano particles

EPI

Ens per inch

PPI

Picks per inch