Precision associated with determination of dirt content of natural rubber

The precision associated with determination of dirt in natural rubber is low even when similar testing procedures are applied, All measurements leading to this estimation involve the use of an analytical balance. For this reason 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 standard error associated with dirt measurements, which was found to be +/-0.001 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 significant figures. This error would further decrease with an increase in the quantity of dirt assayed. Prolonged maturation of coagula reduced the length of rubber chains, thus increasing the ease of dissolution of test portions during dirt analysis. Higher molar mass samples were mostly associated with poor reproducibility of dirt and macrogel content determinations. increasing the mass of test portions improved the precision of dirt measurements, though the recommended sizes of these portions should be a compromise of economic considerations and practical testing conditions. (C) 2001 John Wiley & Sons, Inc.