The nature of the glass fibre surface and its effect in the water absorption of glass fibre/epoxy composites. The use of fluorescence to obtain information at the interface

The effect of the nature of glass fibre surface in the water absorption of glass fibres/epoxy composites was studied. Three different silane coatings were used to change the nature of the surface of the glass fibre. Aqueous solutions of dansyl labelled silanes (5-dimethylamino-1-naphthalene-sulfonylchloride): (i) 3-aminopropyltriethoxysilane, APTES; (ii) 3-aminopropylmethyldiethoxysilane, APDES and (iii) 3-aminopropyldimethylmonoethoxysilane, APMES were used to get respectively three different coatings. Gravimetry and FTNIR measurements were used to complementary study the water absorption process in the whole composites systems. Besides, to locally study the ingress of water exactly at the interfaces of the composites the fluorescence from dansyl label was used. The presence of the silanized fibres seems to induce changes in the water absorption process of the epoxy resin decreasing the relative gain of mass at equilibrium and suggesting that the glass fibre surface may induce a change in the structure of the epoxy matrix in comparison with this polymer without reinforcement. Besides, the fluorescence measurements point out that the water accessibility to the interface is delayed respect to the water absorption of the polymer matrix and the relative amount of water absorbed by the interface depends on the nature of the glass fibre surface, being absorbed less water the lower the functionality of the silane was.