Enhancing Color Stability of Sterilizing Radiation of Polymer Compositions

Further illustration of this invention is set forth in the following examples. There is no intention to limit the scope of the invention to merely what is shown.

The following resins were used in the formulations of the examples:

Polycarbonate--LEXAN.RTM. 145 resin, poly(bisphenol-A carbonate), General Electric Company (contains 0.06% by weight of a conventional phosphite stabilizer).

Poly(ester-carbonate)--an ester content of 75% mole % and being 93 mole % isophthalate and 7 mole % terephthalate.

Polycarbonate/polyester blend--80 weight parts polycarbonate with 20 weight parts KODAR A150 resin, Eastman Kodak Company, poly(1,4-cyclohexanedimethanol-terephthalate-co-isophthalate) and a phosphorous acid stabilizer.

Unless otherwise noted, the formulations containing 100 weight parts of the indicated resin or blend were extruded on a sterling single screw (13/4') extruder at a melt temperature of T1. Test plaques 1/8' in thickness were injection molded on a 3 oz. Van Dorn using a T2 melt set temperature, a T3 mold cavity temperature, and a 10/20 cycle time. T1, T2, and T3 were set according to the resin or blend used:

The samples were irradiated by one of the following methods:

Gamma Irradiation--samples were exposed to a Co.sup.60 source on a continuous conveyor system, dosimetry was monitored with a calibrated NBS, radiochromic, nylon dosimeter and different Co.sup.60 sources were used.

Electron Beam Irradiation--samples irradiated on one side in air using a linear cathode electron beam system, 5 Mrad dose, 20 ft/min line speed, 5 mA beam current, 200 KV terminal voltage, dosimetry monitored with a calibrated NBS, radiochromic, nylon dosimeter.

Unless otherwise noted, testing of the samples has been conducted with gamma radiation and yellowness index, Y.I., measured on a Gardner colorimeter in accordance with ASTM D1925 both before and after radiation. The less change in Y.I. upon irradiation, the more effective the stabilizer.

The following formulations were extruded at from 271.degree. to 299.degree. C. and injection molded into test plaques 1/8' in thickness using a melt temperature of from 271.degree. to 288.degree. C. and a mold temperature of from 49.degree. to 82.degree. C. Measurement of yellowness index was made on a Pacific-Scientific Spectrogard II unit in accordance with ASTM D1925.

The following composition was extruded from 260.degree. to 316.degree. C. and injection molded into test plaques 1/8' in thickness using a melt temperature of from 260.degree. to 304.degree. C. Measurement of yellowness index was made on a Pacific Scientific Spectrogard II unit in accordance with ASTM D-1925.