Cotton cellulosic fibers have been treated with alkyl isocyanates, modified polypropylene or other aliphatic agents in more or less swelling mediums. Their hydrophilicity can be reduced and this effect is studied by the associated techniques of microgravimetry and microcalorimetry. For the non-treated sample, a sorption mechanism is proposed: two water molecules linked by a double H bond are sorbed per amorphous glucose unit with a high molar energy (–65 to –58 kJ/mol−1) up to P/Po = 0.85. Above this pressure, the water is sorbed with the liquefaction molar energy (–44 kJ/mol−1). For the treated fibers, the two preceding stages are always observed as a function of P/Po, but interesting results are obtained for alkyl isocyanate modified samples, with varying lengths of the alkyl chains: C3H7−, C8H17− or C18H37−. These results show the importance of a critical length of the alkyl chain (between three and eight carbons) for reducing the amount of sorbed water by 25% and modifying the mean diffusion coefficient. These effects would be due to the blocking by the linked agents of some water diffusion paths.
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Joly et al. (1996) studied this question.