Development of an impact test for evaluation of weatherability of rigid plastics

Abstract

he evaluation of both initial and long-term properties T of rigid plastic materials for outdoor use must be based on the requirements of specific applications. Plastic parts for architectural use frequently serve decorative or protective functions requiring no structural strength beyond self support. Such parts must withstand abuse in the form of impact from hail, ladders, car doors, and various types of assault by children and lawn mowers.It must not be assumed that a stable color and surface appearance indicate retention of impact or abuse resistance. Many plastic materials suffer gradual embrittlement when exposed to weathering conditions. This embrittlement appears to proceed much faster in thin sections than many common test methods would indicate. Materials with very high initial impact strength do not always remain more durable after years of ex-I C MANDREL SPEC1 PEDESTAL 4 I Figure 1. Variable height impact tester. 124 posure than materials of low-to-moderate initial impact strength.Preliminary work indicated that a variable height impact test, such as the Gardner Tester, performed on samples of extruded products yielded more meaningful weatherability data than did a variety of test methods previously employed. Specimen GeometryA test which will measure properties of a specimen representative of the end products involved is obviously desirable. The influence of ultra-violet excitation, moisture, and constantly varying temperature will be much more profound on a thin sample with its large surface area per unit volume than on a thick sample. Weatherability evaluations should be made with specimen thick. nesses typical of the application considered.The necessity for die cutting or machining specimens introduces errors regardless of project design. Machining prior to exposure introduces surfaces and surface characteristics to exposure which are not present in product usage. Machining after exposure allows error through heat build up in the sample and variations due to wear of the cutting tools. The most desirable specimens will require little or no special preparation.

An evaluation of the cavity transfer mixer for the extrusion of rigid PVC on both single and twin screw extruders

“…A selection of photomicrographs showing the presence of unfused grains without the CTM and absence of such grains with the CTM are shown in Figs. [5][6][7][8].…”

“…Impact testing was carried out using 50 mm square specimens cut from the center of the extruded strips (the edges being discarded) with a Gardner type variable height falling weight impact machine (5). A visual assessment was made of surface finish and general appearance, and the presence of secondary particles identified by optical microscopy using microtomed sections.…”