Precision associated with determination of dirt content of natural rubber

The precision associated with determination of dirt in natural rubber is lo w even when similar testing procedures are applied, All measurements leadin g to this estimation involve the use of an analytical balance. For this rea son the contribution of associated errors to the ultimate precision of dirt measurements was evaluated using analytical balances of varying degrees of precision. A mathematical model was proposed to estimate the compound stan dard error associated with dirt measurements, which was found to be +/-0.00 1 mg. This signifies that, during dirt assay, the masses of test portions, empty sieves, and sieves containing dirt must be estimated to at least 3 si gnificant figures. This error would further decrease with an increase in th e quantity of dirt assayed. Prolonged maturation of coagula reduced the len gth of rubber chains, thus increasing the ease of dissolution of test porti ons during dirt analysis. Higher molar mass samples were mostly associated with poor reproducibility of dirt and macrogel content determinations. incr easing the mass of test portions improved the precision of dirt measurement s, though the recommended sizes of these portions should be a compromise of economic considerations and practical testing conditions. (C) 2001 John Wi ley & Sons, Inc.