Ultraviolet light energy

Figure 12.3 Examples of the weathering performance of (a) a stabilised HDPE nonwoven and (b) a polyamide/polyester nonwoven deliberately unstabilised against ultraviolet radiation. Both were exposed to artificial weathering using three different types of apparatus and to natural weathering in two locations. All results are plotted against radiant exposure (total ultraviolet light energy...

The heat of combustion of maleic acid is 327 Calories, and that of fumaric acid is 319 Calories. These values indicate that the change of maleic acid into fumaric acid takes place with the evolution of heat. When fumaric acid is exposed to ultraviolet light, energy is absorbed and it changes to maleic acid. 

Interestingly, the rates of some reactions are greatly increased by exposure to sunlight. This occurs because the visible or ultraviolet light energy breaks bonds in the reactant molecule(s). 

Ultraviolet spectroscopy is applicable only to conjugated systems. When a conjngated molecnle is irradiated with ultraviolet light, energy absorption occnrs and a tt electron is promoted from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). The... 

In the laboratory it is more convenient to use light either visible or ultraviolet as the source of energy to initiate the reaction Reactions that occur when light energy IS absorbed by a molecule are called photochemical reactions Photochemical techniques permit the reaction of alkanes with chlorine to be performed at room temperature... 

The alternative approach is to add a photodegradant which is an ultraviolet light absorber. However, instead of dissipating the absorbed energy as heat (as with conventional ultraviolet absorbers) the aim is to generate highly reactive chemical intermediates which degrade the polymer. One such material is iron dithiocarbamate. 

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