Teresa P. Ferrándiz-Gómez’s research while affiliated with University of Alicante and other places

Three ethylene vinyl acetate (EVA) copolymers with different vinyl acetate (VA) contents (28-40 wt%) were mixed with rosin ester and polyterpene resin tackifiers in a 1 : 1 (weight/weight) ratio. The rheological and thermal properties of the tackifiers were determined and the use of rheological measurements as a precise way to measure the softening point of the tackifiers is proposed. The glass transition temperature of the tackifiers was obtained from the second heating run, after the thermal history of the tackifiers was removed. The addition of the rosin ester to EVA produced a compatible mixture, whereas for the terpene resin a less compatible mixture was obtained. The increase in the VAamount decreased the crystallinity of EVAand both the storage and the loss moduli also decreased, but the peel strength and the immediate adhesion were increased. The immediate adhesion of EVA/tackifier blends was affected by both the compatibility and the rheological properties of the blends. In fact, a relationship between the mechanical storage modulus (Et′) - obtained from DMTA experiments - of the adhesives and the immediate adhesion to thin rubber substrates was obtained. The adhesives containing the T tackifier showed higher moduli than those containing the G tackifier, and therefore higher peel strength values were obtained. An increase in the VA content increased the flexibility of the adhesives and thus a decrease in peel strength was obtained.

Different amounts (50-170 php--parts per hundred parts of EVA, 33-63 wt%) of two tackifiers (hydrogenated rosin ester, polyterpene resin) were added to an ethylene vinyl acetate (EVA) copolymer containing 28 wt% vinyl acetate. The EVA and the tackifier were characterized using infrared (IR) spectroscopy, DSC measurements, and stress-controlled plate-plate rheology. The properties and compatibility of the EVA-tackifier mixtures were studied using DSC, DMTA, and stress-controlled plate-plate rheology. Immediate adhesion was measured as a quantification of tack, and the T-peel strength of roughened styrene-butadiene rubber/EVA-tackifier adhesive joints was also obtained. The increase in the amount of tackifier noticeably changed the crystallinity of polyethylene blocks in the EVA, and the temperature at the cross-over between the curves of the storage and loss moduli as a function of the temperature was displaced to a lower value. Whereas the hydrogenated rosin ester was compatible with the amorphous ethylene vinyl acetate copolymer regions of the EVA (Tg value increased) reducing its crystallinity, the polyterpene resin was compatible with the polyethylene blocks of the EVA (T g value was not modified), increasing its crystallinity. Immediate adhesion of the EVA-tackifier mixtures was improved by adding both hydrogenated rosin ester and polyterpene tackifiers. On the other hand, there was an optimum tackifier content at which the maximum T-peel strength value was obtained.

Chlorination of a synthetic vulcanized styrene–butadiene rubber with 0.5 wt% trichloroisocyanuric acid (TCI) solutions in butanone was carried out. The durability of the halogenation treatment on the surface properties of rubber was assessed using contact angle measurements, attenuated total multiple reflection method (ATR-IR) spectroscopy and SEM. Adhesion was obtained from T-peel tests of treated rubber/polyurethane adhesive joints. The failed surfaces (after peel test was carried out) were characterized using ATR-IR spectroscopy. For halogenation time lower than 2 h improved wettability was obtained and the effects produced on the rubber surface were mainly due to the solvent. After 48 h, there was a high degree of surface modification and the reaction of TCI with the rubber was the dominant effect. After long periods (up to 1 year) there was evidence for the migration of the wax to the surface and for increased roughness. Therefore, although the increase in time produced a decrease in water contact angle, the peel strength is maintained high because of the chemical and morphological modifications on the rubber surface.

Natural ultramicronized calcium carbonate and mixtures of fumed silica-natural ultramicronized calcium carbonate are proposed as fillers of solvent based polyurethane (PU) adhesives. PU adhesive containing only calcium carbonate shows similar rheological, thermal, mechanical, surface and adhesion properties than the PU adhesive without filler. Addition of 90 wt% fumed silica +10 wt% calcium carbonate mixture to PU adhesive produced a similar performance than the PU adhesive containing only famed silica. The increase in the amount of natural calcium carbonate in respect to fumed silica in the filler mixture produced detrimental effect on the rheological and mechanical properties of the PU adhesives (in respect to those provided by the PU adhesive only containing fumed silica), although the surface and adhesion properties were not noticeably modified.

A low-pressure gas RF plasma-treatment has been used to improve the adhesion of a synthetic vulcanized rubber to polyurethane adhesive as an environmentally friendly alternative surface treatment to the conventional chemical treatments. A sulfur vulcanized styrene-butadiene rubber (R2) containing a noticeable amount of zinc stearate and paraffin wax (both providing a lack of adhesion) in its formulation was used. Two different gases (oxygen and nitrogen) were used to generate the RF plasma, which was performed at 50 Watt for 1–15 min. The modifications produced on the R2 rubber surface by the RF plasma treatments were assessed by using advancing and receding contact angle measurements, ATR-IR spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Force Microscopy (SFM), and Scanning Electron Microscopy (SEM). Adhesion evaluation was obtained from T-peel tests of joints produced between plasma treated R2 rubber and a polyurethane adhesive. The plasma treatment produced a decrease in advancing and receding contact angle values on R2 rubber, irrespective to the gas used to generate the RF plasma. The treatment with RF plasma produced the partial removal of hydrocarbon moieties from the rubber surface and the generation of oxygen moieties. An increase in surface roughness was also produced. The degree of oxidation and the amount of hydrocarbon-rich layer removed from the R2 rubber surface was more important by treating with oxygen plasma. The treatment of rubber in oxygen plasma for 1 minute was enough to noticeably increase adhesion of R2 rubber to polyurethane adhesive. However, an extended treatment (15 min.) was needed when nitrogen plasma was applied to R2 rubber. The loci of failure in the joints produced between the plasma treated R2 rubber and the polyurethane adhesive was assessed by using ATR-IR spectroscopy. A mixed failure (partially adhesional and partially cohesive failure in the rubber) in the joints produced with plasma treated R2 rubber joints was always obtained.

Four silicas, two fumed silicas (one hydrophilic and one hydrophobic) and two precipitated silicas (one hydrophilic and one hydrophobic), were added as filler to solvent-based polyurethane (PU) adhesive formulations. In general, the addition of silica increased the viscosity, the storage and loss moduli of the PU adhesives but only the hydrophilic fumed silica exhibited pseudoplasticity and thixotropy. The rheological properties imparted by adding filmed silicas to PU adhesive solutions were more noticeable than that of precipitated silicas. Interactions between the hydrophilic fumed silica, the polyurethane and/or the solvent seemed to be responsible for the improved rheological properties of filled PU adhesives.

Three thermoplastic block styrene–butadiene–styrene (TR) rubbers were treated with sulfuric acid to improve their adhesion to polyurethane adhesives. T-peel test, scanning electron microscopy (SEM), contact-angle measurements (water, ethane diol), infra red spectroscopy (ATR-IR) and stress–strain experiments were used to analyze the nature of surface modifications produced in the rubber. The length of the treatment and the neutralization procedure (with and without ammonium hydroxide) were considered in this study. The treatment produced the sulfonation of the butadiene units of the rubber and the creation of highly conjugated CC bonds, which produced a change in the color of the TR rubbers. The treatment also produced a decrease in the tensile strength and the elongation at break of the TR rubbers. This suggests that the treatment with sulfuric acid was not restricted to the rubber surface but also produced a bulk modification. The lower the styrene content in the TR rubber, the more significant modifications were produced on the surface. The styrene content (33–55wt%) in three thermoplastic styrene–butadiene (TR) rubbers affected the extent, but not the nature of the surface modifications produced by treatment with sulfuric acid. The H2SO4 treatment increased the T-peel strength of S1 and S2 rubber/polyurethane adhesive joints and produced a mixed failure mode (adhesion+cohesive failure in the rubber). Sulfonation of the TR rubbers is fast and needs only a 30s immersion in sulfuric acid to produce high adhesion. Furthermore, the neutralization of the acidic surface with ammonium hydroxide is critical to assure an adequate durability of the adhesive joints.

Natural ultramicronized calcium carbonate and mixtures of fumed silica + natural ultramicronized calcium carbonate are proposed as a filler for solvent-based polyurethane (PU) adhesives. The PU adhesive containing only calcium carbonate showed similar thermal, mechanical, surface, and adhesion properties to those of the PU adhesive without a filler. The addition of 90 wt% fumed silica + 10 wt% calcium carbonate mixture to the PU adhesive produced a performance similar to or improved over that of the PU adhesive containing only fumed silica. The increase in the amount of natural calcium carbonate with respect to fumed silica in the filler mixture had a detrimental effect on the rheological and mechanical properties of the PU adhesives, although the surface and final adhesion properties were not noticeably modified. The immediate adhesion (45 min after joint formation) was noticeably increased in the joints produced with the PU adhesives containing fillers, mainly in those with a higher fumed silica content; a cohesive failure in the adhesive was produced in those joints and the mechanical and rheological properties of the PU adhesives determined the immediate adhesion. The failure in the joints peeled 72 h after joint formation was adhesional and the adhesion properties were mainly determined by the surface properties of the PU adhesives. All the adhesive joints showed a similar final adhesion because they have similar surface properties.