Controlled photodegradation

The main conclusion from the above measurements is that a critical step in photodegradation is adsorption of the organic substrate on the surface. Therefore the parameters that control photodegradation are directly related to the parameters that govern adsorption processes, and include van der Waals forces, dipole-dipole interaction, ion-exchange, hydrogen bonding, hydrophobic interactions, n-n interactions, and donor-acceptor interactions. 

The above discussion pertains mostly to the pure polymer most, polymers used in practical applications, especially those used outdoors tend to be compounded with a variety of additives. Some of these such as opacifiers, UV absorbers, and light stabilizers are intentionally added to the compound to control photodegradation and related oxidation reactions, to extend the outdoor lifetime of the material. Others such as fillers, reinforcing agents, lubricants, and... 

Fig. 5. Time-controlled photodegradation of LDPE stabilized with different concentrations of the photosensitize iron dithiocarbamate (FeDRC) and the photostabilizer nickel dithiocarbamate (NiDRC). Numbers on curves are antioxidant concentration in 10- mol/100g(156).

The wide application of plastics in agriculture has a decisive influence on cultivation practices. Plastic films used as a growing aid in the form of mulch and tunnel covers have increased yields. The debris of these films left behind after the harvest poses a serious disposal problem. The controlled photodegradation of plastics affords a workable solution not only to this problem but opens new possibilities of the programmed removal of the films even during the growing period of the crops when this is desirable. 

Generation of Large Pretilt Angles by Controlled Photodegradation... 

The advantages of microreactors, for example, well-defined control of the gas-liquid distributions, also hold for photocatalytic conversions. Furthermore, the distance between the light source and the catalyst is small, with the catalyst immobilized on the walls of the microchannels. It was demonstrated for the photodegradation of 4-chlorophenol in a microreactor that the reaction was truly kinetically controlled, and performed with high efficiency [32]. The latter was explained by the illuminated area, which exceeds conventional reactor types by a factor of 4-400, depending on the reactor type. Even further reduction of the distance between the light source and the catalytically active site might be possible by the use of electroluminescent materials [19]. The benefits of this concept have still to be proven. 

Topochemical [24-2] photoreactions of diolehn crystals has been reviewed. The reactions clearly depart from typical solution chemistry crystal-lattice control offers a unique synthetic route into photodegradable polymers, highly strained [24-2] paracyclophanes, stereoregular polymers, and absolute asymmetric synthesis. However, achieving the desired type of crystal... 

The solid circulation rate (Gs, kgm-2s-1) can be controlled by aeration gas in the loop-seal to adjust pressure balance in the CFB loop. Solid circulation rate is a unique operating variable in the CFB system as a function of pressure drop across loop-seal of a CFB photoractor [10] and directly related to solid holdup in the riser where the photodegradation of TCE occurs. 

Weather insensitivity Atrazine efficacy is relatively unaffected by weather. Since it is not particularly susceptible to photodegradation or to volatility, it can be applied under a variety of conditions and still be expected to deliver weed control benefits when rain occurs. The mode of action of atrazine in higher plants is such that the sensitivity of susceptible plants is only minimally affected by environmentally induced changes in plant growth, unlike many alternative herbicides that work well only in rapidly growing plants. 

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