No abstract

Several materials derived from kraft lignin have been shown to exhibit distinct antioxidant activity for the stabilization of raw rubber against heat accelerated degradation. Selected lignin derivatives alone or in combination with amine or sulfide antioxidants were effective stabilizers for an oil‐extended styrene‐butadiene rubber (SBR). Synergism with a phosphite has been demonstrated with unextended SBR. Candidate stabilizers were screened using the relatively rapid torsional braid analyzer (TBA) technique. Pertinent samples were then tested with the conventional, but slower, technique of measuring Mooney viscosity. Mooney and TBA tests correlated for lignin derivatives, but the TBA predictions were low for typical commercial stabilizers such as phenyl‐beta‐naphthylamine (PBNA). Apparently the more volatile stabilizers, such as PBNA, escape during the aging process from the thin rubber sample employed in TBA testing. This observation limits the utility of the TBA technique to samples of similar and preferably low volatility. Lignin derived stabilizers are unique in that they are non‐discoloring, nonstaining, and relatively low in volatility and cost.