PARTIAL MASKING OF CELLULOSIC FIBER HYDROPHILICITY FOR COMPOSITE APPLICATIONS - WATER SORPTION BY CHEMICALLY-MODIFIED FIBERS

Cotton cellulosic fibers have been treated with alkyl isocyanates, mod ified polypropylene or other aliphatic agents in more or less swelling mediums. Their hydrophilicity can be reduced and this effect is studi ed by the associated techniques of microgravimetry and microcalorimetr y. For the non-treated sample, a sorption mechanism is proposed: two w ater molecules linked by a double H bond are sorbed per amorphous gluc ose unit with a high molar energy (-65 to -58 kJ/mol(-1)) up to P/P-o = 0.85. Above this pressure, the water is sorbed with the liquefaction molar energy (-44 kJ/mol(-1)). For the treated fibers, the two preced ing stages are always observed as a function of P/P-o, but interesting results are obtained for alkyl isocyanate modifed samples, with varyi ng lengths of the alkyl chains: C8H7-, C8H17- or C18H37-. These result s show the importance of a critical length of the alkyl chain (between three and eight carbons) for reducing the amount of sorbed water by 2 5% and modifying the mean diffusion coefficient. These effects would b e due to the blocking by the linked agents of some water diffusion pat hs. (C) 1996 John Wiley & Sons, Inc.