Structural modification of sepiolite (natural magnesium silicate) by thermal treatment: effect on the properties of polyurethane adhesives

• Published in: International journal of adhesion and adhesives 1997-01, Vol.17 (2), p.111-119
• Main Authors: Torró-Palau, Ana, Fernández-García, Juan C., Orgilés-Barceló, A.César, Pastor-Blas, M.Mercedes, Martín-Martínez, JoséMiguel
• Format: Article
• Language: English
• Subjects: A. polyurethane; A. solvent based; Applied sciences; B. rubber; B. surface treatment; C. dynamic mechanical analysis; C. infrared spectra; C. rheology; D. viscoelasticity; Exact sciences and technology; Miscellaneous; Physical properties; Polymer industry, paints, wood; Properties and testing; Technology of polymers
• ISSN: 0143-7496; 1879-0127
• DOI: 10.1016/S0143-7496(96)00039-5

A sepiolite silicate was heat-treated at 550 and 1000°C to modify its structure, and was used as a filler in a solvent-based polyurethane (PU) adhesive. The treated sepiolites were characterized by X-ray diffraction and infra-red spectroscopy, and it was observed that the water was irreversibly removed from the structure and pores of the sepiolite, changing the structure. The increase of temperature produced a collapse of the sepiolite structure. The rheological, mechanical, thermal and adhesion properties of the filled PU adhesives were measured. In general, the addition of treated sepiolite to PU adhesives resulted in a loss of adhesive properties with respect to the blank (PU adhesive with untreated sepiolite). The loss in properties was more noticeable as the treatment temperature increased. Thus the PU adhesives containing treated sepiolite had reduced rheological properties (lower viscosity, lower storage and loss moduli, and they did not provide thixotropy and pseudoplasticity to the solutions) with respect to the PU adhesive filled with untreated sepiolite. On the other hand, the addition of treated sepiolite decreased the mechanical and thermal mechanical properties of PU films. The T-peel strength of roughened and roughened + chlorinated (with 1 wt% trichloroisocyanuric acid in 2-butanone) styrene-butadiene rubber/PU adhesive joints was improved if the PU adhesive contained untreated sepiolite, but it decreased if the sepiolite was heat-treated. Interactions between the untreated sepiolite, the solvent and the polyurethane were responsible for the improved properties of PU adhesives. These interactions disappeared when the sepiolite was heat-treated, because of the destruction of the structure of the sepiolite and the removal of surface silanol groups.