UV-Protection

The discovery of CNTs gives new direction for the use of CNTs in polymeric materials to improve several properties, including UV protection. Mondal et al. have coated the cotton fabrics with 

The principal issues for the materials technology related to the basic properties for polyurethane/CNT composites were already presented in previous sections. It provided the correlation between the structural factors and the properties resulting therefrom. This section, however, is going to present a review of the latest trends in applications for the materials based on polyurethane/CNT composites. 

Two kinds of photoresponsive azobenzene polyurethane functionalized multiwalled carbon nanotube (AzoPU-MWNT) composites were synthesized by in-situ polycondensation (50). Core-shell structures with MWNTs as hard core and polymer layer as soft shell were formed and the average thickness of the grafted polymers was about 7-10 nm. The AzoPU-MWNT composites showed reversible photoisomerism behavior. 

Luo et al. have fabricated a conductive polyurethane/MWNT composite thin film with a selective vapor-induced sensing performance through in-situ dispersion polymerization (120). This kind of thin films yielded higher responsivity to some solvent vapors like benzene, toluene, acetone and chloroform than others such as carbon tetrachloride, cyclohexane, methanol and formaldehyde. 

The above analysis takes the synthesis methods, the performance affected by the dispersion of CNTs, enhanced physical properties and the latest applications of carbon nanotube/polyurethane composites described in literature reports as the reference point. In the interest of brevity, this is not a comprehensive review, however, it goes through numerous research reports and applications which have been learned and described in the recent years. Despite that, there are still many opportunities to synthesize new carbon nano-tube/polyurethane systems and to modify carbon nanotubes with new functional groups. The possibility of producing modern biomedical and shape memory materials in that way makes the challenge of the near future. 

Some applications of Na-alginate as well as Aloe vera gel in antimicrobial functionalization of cotton fabrics are shown in Table 6.4. 

Alginate micro Cotton capsules containing denim herbal extract 

Alginate-quaternary Cotton ammonium complex fabrics nanoparticles [SA-TSA, with an average size of 99 nm] 

Sodium alginate (SA]/3-(trimethoxysilyl) propyl-octadecyl-dimethylammonium chloride (TSA) complex nanoparticles were used for antimicrobial finishing of cotton fabrics by pad-diy-cure technique 

Aloe vera extract Cotton fabric Finishing of cotton fabric was 

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In vitro absorption-spectrophotometry techniques are available to assess a sunscreen s efficacy, but the preferred methods are in vivo procedures in which a small body site is irradiated with the desired wavelengths for different periods in the presence or absence of a uv protectant. Procedures vary from country to country to determine the incremental timing of the exposure that ultimately allows quantification via sun protective factor (SPE). In the United States, sunscreen preparations are considered OTC dmg products, and the SPE must be specified (54). Even in countries that do not identify these products as dmgs, SPE labeling has become customary. 

The SPE is defined as the ratio of the time required to produce a perceptible erythema on a site protected by a specified dose of the uv protectant product to the time required for minimal erythema development in the unprotected skin. An SPE of 8 indicates that the product allows a subject to expose the protected skin 8 times as long as the unprotected skin to produce the minimum erythema response. The measurement can be quite subjective unless skin color and the history of reactions to sun exposure of the test subjects are taken into account. The MED range for Caucasians at 300 nm averages 34 mj/cm. The range is 14—80 mj/cm. Perspiration or the use of artificial irradiation devices can create additional problems. 

In order to simplify the experimental problems involved in unravelling the mechanisms of UV protection by the piperidines, we have concentrated on the use of the simpler monopiperidine compounds. Although our findings are relevant to the photoprotection by the more complex multifunctional, commercial additives, some major differences may exist, and will be emphasized together with the very significant effects of the solid state on photo-stabilization. 

Suzuki Y, Takabayashi T, Kawaguchi T, Matsunaga K (1998) Isolation of an allelopathic substance from the crustose coralline algae, Lithophyllum spp., and its effect on the brown alga, Laminaria religiosa Miyabe (Phaeophyta). J Exp Mar Biol Ecol 225 69-77 Svensson CJ, Pavia H, Toth G (2007) Do plant density, nutrient availability, and herbivore grazing interact to affect phlorotannin plasticity in the brown seaweed Ascophyllwn nodosum. Mar Biol (in press), doi 10.1007/s00227-007-0649-5 Swanson AK, Druehl LD (2002) Induction, exudation and the UV protective role of kelp phloro-tannins. Aquat Bot 73 241-253... 

Swanson AK, Druehl LD (2002) Induction, exudation and the UV protective role of kelp phlorotannins. Aquat Bot 73 241-253... 

As well as functioning as natural UV-protective compounds, some MAAs such as mycosporine-glycine also have moderate antioxidant activity (Dunlap and Yamamoto 1995). In addition, the presumed biochemical precursor of MAAs, 4-deoxygadusol exhibits strong antioxidant activity (Dunlap et al. 1998). The photo-physicochemical properties of MAAs guarantee both a high UV-protective effectiveness in combination with antioxidant capabilities. 

A possible role of pterins as UV-protecting compounds has been suggested for the marine cyanobacterium Oscillatoria sp. since UVA radiation effectively induced... 

Sies H (1991) Oxidative stress oxidants and antioxidants. Academic Press, San Diego Shick JM (2004) The continuity and intensity of ultraviolet irradiation affect the kinetics of biosynthesis, accumulation, and conversion of mycosporine-like amino acids (MAAs) in the coral Stylophora pistillata. Limnol Oceanogr49 223-262 Shick JM, Dunlap WC (2002) Mycosporine-like amino acids and related gadusols biosynthesis, accumulation, and UV-protective functions in aquatic organisms. Annu Rev Physiol 64 223-262... 

Smith RC, Prezelin BB, Baker KS, Bidigare RR, Boucher NP, Coley T, Karentz D, MacIntyre S, Matlick HA, Menzies D, Ondrusek M, Wan Z, Waters KJ (1992) Ozone depletion ultraviolet radiation and phytoplankton biology in Antarctic waters. Science 255 952-959 Sommaruga R, Psenner R (1997) Ultraviolet radiation in a high mountain lake of the Austrian Alps air and underwater measurements. Photochem Photobiol 65 957-963 Swanson AK, Druehl LD (2002) Induction, exudation and the UV protective role of kelp phlorotannins. Aquat Bot 73 241-253... 

Color-fastness of objects to be cleaned, especially for laundry detergents Improved properties of objects to be cleaned, e.g. UV protection for laundered garment... 

UV protection/sun fade protection of fabrics (for laundry detergents only) V... 

Again, polyesters based on naphthalene-2,6-dicarboxylic acid can meet the desired properties, plus have other additional advantages. Food components containing double bonds or conjugated double bonds are extremely sensitive to light-induced reactions, such as photo-oxidation. The addition of UV stabilizers is therefore necessary to protect the content of PET bottles against UV irradiation. PET, in contrast to PEN, does not show intrinsic UV protection properties. 

Figure 18.8 Effect on color data of backing with UV-protected sheeting on Spectar UV co-ex sheeting and ABA co-ex sheeting in Miami, FL, exposure [2]. From Weathering of polyester and copolymer sheeting, presentation given by D. R. Fagerburg at the Atlas School for Natural and Accelerated Weathering (ASNAW) course, Miami, FL, May 1999, and reproduced with permission of Atlas Electric Devices Company...

UV protection can be obtained with cheap carbon blacks (but colour is grey to black) or with expensive photostabilizers. 

The growth of polyesters is hindered by their sensitivity to hot water above 60°C, fire behaviour except for FR grades, mould shrinkage for crystalline products, opacity (except amorphous PET), need of UV protection, limited chemical resistance, higher cost than commodities... 

Light UV-protection is needed Weak acids Limited behaviour ... 

PPEs are handicapped by an inherent sensitivity to fire and to common chemicals, such as hydrocarbons, chlorinated solvents and concentrated mineral acids. They have rather high coefficients of friction and are slightly attacked by UV and weathering, requiring UV protection. The number of producers is limited. 

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