María del Mar Mahíques-Bujanda’s research while affiliated with University of Alicante and other places

A new series of acrylic adhesive mixtures was specifically designed for use in strabismus surgery, more precisely to join the rectus muscles to the sclera. These two-part adhesives consisted of a mixture of ethyl cyanoacrylate (CN) and ethyl carboxyacrylate (ECA). ECA acted as a plasticizer imparting flexibility to the CN, and also as a nonreactive diluent, serving to reduce the exotherm in the reaction between CN and eye tissues. In this article, the synthesis of the ethyl carboxyacrylate is described, and the properties of different ethyl cyanoacrylate + ethyl carboxyacrylate mixtures were studied. The curing reaction of the adhesive mixtures was monitored using Fourier transform infrared (FTIR) spectroscopy and scanning differential calorimetry (DSC). The rheological properties of the cured CN-ECA adhesive films were studied using plate-plate rheometer experiments. To quantify the adhesion, single lap-shear tests produced between a rubber and the adhesive mixtures were performed and, to evaluate the adhesion to eye tissues, tensile strength measurements of superior rectus muscle/adhesive mixture/sclera joints were carried out. The 70CN-30ECA (v/v) adhesive mixture provided the most adequate balance between adhesion and mechanical properties in the joining of the superior rectus muscle to the sclera. The glass transition temperature of the CN-ECA adhesive mixtures linearly decreased with increase in the ECA content, and a lower degree of conversion during polymerization was obtained by increasing the ECA content. As a consequence, the CN-ECA mixtures were less stiff than CN, giving better performance in the joining of the rectus muscles to the sclera. Finally, the adhesion of CN was sufficiently decreased in CN-ECA mixtures, and the locus of failure was directed to the adhesive film in the joint between the rectus muscles and the sclera.

Fumed silicas of different surface areas (90–380m2/g) and primary particle size (20–7nm, 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 (130–200m2/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.

In order to improve their adhesion to polyurethane adhesives, three unvulcanized block styrene-butadiene-styrene (SBS) rubbers with styrene contents between 33% and 55% were surface-treated with solutions of 2 wt% trichloro-isocyanuric acid (TCI) in ethyl acetate. The joint strength was estimated using T-peel tests and the failed surfaces were analyzed to assess the locus of failure. The failed surfaces were analyzed using ATR-IR spectroscopy, contact angle measurements, XPS, and SEM. An unexpected trend in the joint strength was obtained because the locus of failure depended on both the styrene content and the mechanical properties of each SBS rubber. A mixed mode of failure was obtained in joints produced with S 1 rubber (33 wt% styrene content), whereas failure in the chlorinated layer was observed with S3 rubber (55 wt% styrene content); cohesive failure in the adhesive was found for the joints produced with S2 rubber (44 wt% styrene content).

Fumed silicas of different specific surface area (90-380 m/g) were added to a thermoplastic polyurethane (PU) solution. After solvent removal, solid fumed silica-PU composites were obtained. The viscoelastic properties of PU were improved by adding fumed silica and only a solid-like behavior in PU-fumed silica composites was obtained. The increase in the specific surface area of the fumed silica up to 200 m / g increased the moduli of the composites. Fumed silica-PU interactions were responsible for the improved rheological properties of the composites. The activation energies for viscous flow of the composites were 14-16 kcal/mol and increased as the specific surface area of fumed silica increased. The glass transition temperature (obtained from DMTA and DSC experiments) and the crystallization rate of fumed silica-PU composites decreased compared with PU and also decreased with increasing surface area of the fumed silica. The contact angle values were similar in all the composites and the strength of PVC/fumed silica-PU composite joints was not affected by the specific surface area of the fumed silica.

Heat-treated sepiolite silicate at 550 and 1000°C was used as a filler in solvent-based polyurethane (PU) adhesives. The increase of the treatment temperature produced a collapse of the structure, due to an irreversible removal of water from the pores of the sepiolite. The Theological, mechanical, thermal and adhesion properties of the filled PU adhesives were measured. The addition of the treated sepiolite to PU adhesives provided a loss in properties in respect to the PU adhesive containing untreated sepiolite. The loss in properties was more noticeable as the treatment temperature increased.