Light Absorption and Reflection

Some of the light falling onto a polymer product will be reflected harmlessly from the surface. The rest is absorbed into the interior, particularly the layer immediately below the surface, where it can easily penetrate and where oxygen from the atmosphere can diffuse. 

The asterisked species represents an excited state, possessing sinplus energy, and removing the energy harmlessly by means of an appropriate additive is known as quenching the excited state. 

The wavelengths that are most easily absorbed by certain chemical groups are listed in Table 4.5. 

Polymers with structures containing a tertiary carbon atom, such as polypropylene and polystyrene, are more vulnerable than linear polyethylene. Head-to-head sequences of two adjacent monomer units in a polymer molecule are also weak points. 

Free-radical photo-oxidation is the main mode of degradation of the pure polymers. Polymers that contain chromophores in their structures degrade by both photo-oxidation and photolysis. 

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Infrared light absorption and reflection of the uncoated and A1 coated surfaces of polymier films were investigated and discussed in this chapter. Two commercial biaxially oriented pol q)ropylene samples coated with A1 by physical vapor deposition technique were examined. The samples called commercial film 1 and commercial film 2 were provided by POLINAS and POLIBAK companies, respectively. They were 16 pm and 19 pm thick and their one surface was coated with A1 after a corona discharge treatment. 

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