JOURNAL OF COSMETIC SCIENCE 34 for tA=const, where t=0 is the start of the recovery experiment. For the analysis of the experimental data, equation 7 is combined with equation 6 and m=0.28 to yield: 0.28 (t) 1/{1 K exp[ (t/ ) ]} W R (8) where K = ΔB/B∞ is the ratio between the elastic bending rigidities of the fi laments and the matrix in the composite, respectively. The initial recovery at t=0 is accordingly given by: 0 . R (9) Fitting equation 8 to all experimental curves yielded the values for the rigidity ratio, K, and for the characteristic relaxation time, τ. The mean values for K and the related values for R0 for the various relative humidities are summarized in Table I. The water content of hair for the various humidities was deduced from sorption isotherms for similar hair material (19). Consideration of the τ-data versus aging time, tA, on a log/log-scale (1) showed that log(τ) shifts synchronously with log(tA), confi rming the value of the expected (14) aging rate, μ, for hair (11) as: A log / logt 1 P W d d (10) To correct for the effects of aging at a given water content, the parameter of the reduced, characteristic relaxation time, τ r , is introduced: W W /t r A (11) so that r log log log W W A t (12) The results for the arithmetic means of log τ r are summarized in Table I and discussed in detail in reference 1. Fibers can be regarded as non-aging as long as the experimental time is small against the aging time, such as t 0.1t A . For longer times, aging reduces the relaxation rate and in- duces deviations from the curve expected for the non-aging material (14). For a known aging rate this effect can be compensated by introducing the concept of effective time, λ, given for μ=1 by: O ) A t A ln(1 t/t (13) On the scale of effective time, the experimental data represent the recovery performance of the non-aging fi ber. Experimentally, the validity of the concept underlying equations 10–13 has been shown by Chapman, namely, for wool (20).

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