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Assessments of the amount of light scattering or haze caused by the abrasion of transparent plastics when measured with a collimated beam hazemeter at reduced beam diameter are shown to be affected by differences in amount of beam reduction. The data presented illustrate that most of the light scattered from a sample abraded with a Taber Abraser® is found in the angular cone between 0 and 2.5°. This is also the region subtended by the 1.3° annulus between the lightbeam and the exit port of a hazemeter conforming to ASTM Test for Haze and Luminous Transmittance of Transparent Plastics (D 1003). For this reason, measurement of abraded specimens is very sensitive to the beam geometry of the hazemeter.
Since conventional (nonabraded) specimens produce very diffuse scattering patterns, changes in beam diameter and thus the size of the annulus do not significantly affect haze readings. However, to obtain reproducible results on abraded specimens, modification is required to the geometry of the hazemeter so that the image of the entrance window is focused at the exit port of the sphere. Good interlaboratory agreement was obtained when suitably modified hazemeters were used to measure a set of polymethylmethacrylate (PMMA) specimens. Modifications that have been made to ASTM Test for Resistance of Transparent Plastics to Abrasion (D 1044) are discussed.
Manager—Advanced ProductsMember of ASTM, Pacific Scientific Co., Silver Spring, MD
Group leaderMember of ASTM, American Cyanamid Co., Stamford, CT
Stock #: JTE10242J