Photochemical degradation surface treatment

Figures 4-10 to 4-12 show the effects of ultraviolet exposure followed by reaction with alkaline hydrogen peroxide for different times (15 min to 2 h). The effects of the alkaline peroxide on ultraviolet exposed hair are to dissolve parts of the cuticle, providing for even less structural differentiation. Part of the cuticular proteins are solubilized by these combined chemical treatments into gelatin-like glue that is redeposited between the fibers, see Figure 4-11. This effect was produced after only 15 min exposure to alkaline peroxide after photochemical degradation. The total lack of surface structural definition is seen in the most extreme case in Figure 4-12 where no cuticle scale definition exists after 2h of treatment with alkaline hydro-...

Polyvinyl chloride has been modified by photochemical reactions in order to either produce a conductive polymer or to improve its light-stability. In the first case, the PVC plate was extensively photochlorinated and then degraded by UV exposure in N2. Total dehydrochlorination was achieved by a short Ar+ laser irradiation at 488 nm that leads to a purely carbon polymer which was shown to exhibit an electrical conductivity. In the second case, an epoxy-acrylate resin was coated onto a transparent PVC sheet and crosslinked by UV irradiation in the presence of both a photoinitiator and a UV absorber. This superficial treatment was found to greatly improve the photostability of PVC as well as its surface properties. 

Basagran has a herbicidal activity but a high bioconcentration factor (Kinkennon, 1995). Diquat is able to undergo natural photochemical decomposition after application to plant surfaces. Studies show that 50 mg of herbicide is depleted to below 6 mg/kg within 7 days after treatment. In soil, diquat is biodegraded at a rate of 10% per year. In aqueous environments, diquat was degraded to levels that were undetectable in less than 30 days. 

The principal direction of the published photochemical research to date has been to elucidate pathways which might be responsible for the degradation of these refractory substances in nature. This basic research has not been extensively applied either to on-or off site treatment of hazardous substances. In this chapter we extend the existing PCB photochemistry literature by considering this potential. The development and fabrication of a prototype surface photoreactor, and its preliminary evaluation at a PCB-contaminated site are described. Photochemical treatments may be applicable to many other classes of hazardous chemicals as well including the polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF) about which this monograph is chiefly concerned. 

Lao et al. [75] compared the surface functionalization of PHBHV by HEMA grafting via UV treatment and via thermal free radical polymerization. The photochemical grafting was realized with BP and H Oj at room temperature by an indirect method to avoid HEMA homopolymerization. The study of the enzymatic degradability demonstrated that the presence of PHEMA affected the degradability of the grafted PHBHV films (Fig. 6.7). 

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