The most convenient method of constructing such a calibration curve is to aerate samples of the solution with known air mixtures containing 0.10, 0.20, 0.30, and 0.40% carbon dioxide (Matheson & Co., Inc.). Such solutions have true pC02's of 0.10, 0.20, 0.30, and 0.40% atm., respectively. If SUMMARY Table III, Comparison of Direct Absorption and Colorimetric Methods on Polygard Analysis Polygard Re-Std.

(1) Styrene-butadiene rubber (SBR) is very susceptible to oxidative degradation unless an effective stabilizing agent is incorporated in the polymer during manufacture. (2) Degradation of SBR appears as discoloration or resinification during drying of the polymer or during storage. Changes in the polymer may appear as variation in Mooney viscosity or as an increase in gel content. (3) Deterioration of inadequately stabilized SBR may also show up during processing operations when the polymer is subjected to heat—as in the Banbury or on a hot mill. (4) Deterioration of SBR polymer will appear as degraded physical properties in the cured vulcanizate. (5) The rubber goods manufacturer will benefit from the use of a really effective SBR stabilizer incorporated in the polymer during manufacture or by adding additional stabilizer to provide more protection against heat degradation in his operations. (6) Tris(nonylated aryl) phosphite exhibits unusual effectiveness as a stabilizer for SBR. (7) The presently widely used method of salt-acid coagulation of SBR polymer leaves room for improvement as far as polymer stability is concerned. (8) The more effective SBR stabilizers exhibit benefits in the aging of SBR vulcanizates.

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