Rheological properties of thermoplastic polyurethane adhesive solutions containing fumed silicas of different surface areas

• Published in: International journal of adhesion and adhesives 1999-01, Vol.19 (4), p.321-328
• Main Authors: Jaúregui-Beloqui, Belén, Fernández-Garcı́a, Juan C., César Orgilés-Barceló, A., Mar Mahiques-Bujanda, M., Martı́n-Martı́nez, José Miguel
• Format: Article
• Language: English
• Subjects: A. Solvent based; Application fields; Applied sciences; C. Rheology; Exact sciences and technology; Polymer industry, paints, wood; PVC; Technology of polymers
• ISSN: 0143-7496; 1879-0127
• DOI: 10.1016/S0143-7496(99)00008-1

Fumed silicas of different surface areas (90–380 m 2/g) and primary particle size (20–7 nm, respectively) have been added to solvent-based thermoplastic polyurethane (PU) adhesives. Addition of silica increased the viscosity, imparted pseudoplasticity, and thixotropy or rheopexy to PU adhesive solutions. Rheological data of adhesive solutions fitted well the Casson model. Fumed silicas with intermediate surface areas (130–200 m 2/g) provided the best rheological performance to PU adhesive solutions. The increase of time after preparation of PU adhesive solutions produced an increase in viscosity, more marked pseudoplasticity and enhanced thixotropy (rheopexy was not exhibited). The reduced rheological properties of PU solutions containing Aerosil 380 have been ascribed to the relatively large size of the clusters produced by aggregation of small primary fumed silica particles, which under the experimental conditions used in this study were not fully dispersed in the PU solution. Contact angles obtained by placing adhesive drops on rubber substrates increased when the adhesive contains silica, the trend obtained was similar to that exhibited by the flow curves. This may indicate that a relationship between wettability and rheology of PU adhesive solutions may exists. Green (immediate) strength of roughened R1 rubber/PU adhesive joints was improved, if the adhesive contained fumed silica and did not vary with the surface area of the fumed silica, but the strength for (roughened+chlorinated) R2 rubber/PU adhesive joints was similar if the adhesive contained or not fumed silica, and independently of the surface area.