and hence Vf)
alternately increase and decrease until 300 h of UV irradiation time and, then, show a decreasing trend. The fractional free volume (Fv) varies more or less in a similar manner. Human hair (average diameter 70 lm) has a layered structure with its inner mass – cortex (90% of dry weight) being sur- rounded by a 5–10 lm thick cuticle consisting of overlapping scales of flattened keratinized cells. The cells in cortex and cuticle are cemented together by the cell membrane complex (CMC). Obviously, the cuticle receives UV light directly, and in the absence of melanin granules in it, the protein component is attacked by the incident light. This makes the fiber hygroscopic. The initial increase in the value of s3 (for UV exposure time