Optical clarity of polypropylene products

When an object is viewed through an imperfectly transparent specimen, there are two ways in which the visibility may be reduced, thus two criteria exist for transparency. The first is the degree to which the specimen reduces the apparent contrast of the object this aspect of transparency is commonly referred to as milkiness or haze. The second 

As was mentioned in the introduction, optical properties of a pol5oner are determined by the complex combination of its basic scattering, transmission and reflection characteristics, but they depend also on the technique and conditions of illumination and detection. The number of determining factors and the complexity of the relations are in strong contradiction with the natural demand in practice to characterize optical properties with a simple number, such as transparency, haze etc. In spite of this controversy and difficulties in the interpretation of the dominating factors, optical properties of a polymer can be determined, reproduced and compared by the strict application of relevant standards. 

Haze is used the most often for the characterization of the transparency of a plastic product. Haze is the total flux of light scattered within the angular range from 2.5 to 90 and normalized to the total transmitted flux. The determination of haze is described by national emd international standards (ASTM D 1003, BS 2782), which define the light source, the size of the incident light, detection and other conditions of t a measurement. Commercial instruments are available for the determi. i-tion of haze according to the above-mentioned standards. Less -ambiguous is the determination of clarity, i.e. the ability of a specimei o transmit fine details of an object. Several quantities are used for s characterization and, imlike haze, no standardized, universally acce id technique exists for its determination [2]. 

Transparency is influenced both by material properties and processing conditions. The effects of these factors are interrelated. 

Increased orientation and rate of crystallization improve light transmission. As a consequence, increasing drawing and blowing ratios improve clarity. 

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