The effect of ultraviolet light on the viscosity of cellulose acetate and cellulose nitrate has been studied in atmospheres of air, nitrogen, and oxygen. In air and oxygen the degradation of these cellulose esters is accelerated. The effect of a nitrogen atmosphere is to retard degradation. In all atmospheres the drop in viscosity for cellulose acetate was gradual; for cellulose nitrate the viscosity dropped more rapidly during the initial part of exposure and then leveled off.
A modified Bingham-type rheometer, designed for operation at temperatures up to 500°F and at pressures up to 2000 p.s.i. is described. Interchangeable orifice plates permit wide variation of shear conditions. With this instrument flow properties may be studied under conditions approximating those encountered in the actual processing of thermoplastics, e.g., by molding or extrusion. Typical results are presented for cellulose acetate, polystyrene, and polyvinyl resin plastics, and correlation with practical experience is pointed out. The instrument is slow, and this limits its usefulness for other than research investigations.
The physical properties of plastics are markedly influenced by the ambient temperature, but comparatively few quantitative data on polystyrene have been published. The variation of flexural strength and deflection at break for compression-moulded polystyrene and for a number of other compression-moulded plastic materials at temperatures from —70° to +200° C was described by Nitsche and Salewski. Jenckel and Lagally determined the tensile strength of extruded polystyrene filaments at 30° to 60° C. The elongation at 20° to 90° C was reported for extruded and racked polystyrene foil by Müller. Since the mechanical properties of plastic materials are profoundly influenced by the methods used in preparing the test specimens, data on such properties are meaningless unless the details of preparation also are known. This paper describes variations in some of the mechanical properties of injection-moulded polystyrene over the range from —75° to +100° C. This method was chosen because injection moulding is by far the most commonly Used commercial process for the fabrication of polystyrene.
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