AbstractPolymetaphosphate and polyethylene glycol in aqueous solution are excluded completely from rayon fibers. Determinations of nonsolvent water (δ) with these reference substances give the same value which can be used as a measure of the true swelling. The polymers can, however, penetrate into porous areas present in cotton. The average polymer concentration inside these areas is lower than in the external solution. High speed centrifugation results in decreased δ values, which is explained by a compression of the porous areas. Higher δ values are obtained as the molecular weight of the reference substance is increased. With polymetaphosphate the δ values decrease when the external concentration is increased, whereas with polyglycol the δ value within a wide range is independent of the concentra
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