Properties of thermoplastic polyurethane adhesives containing nanosilicas with different specific surface area and silanol content

Abstract

Thermoplastic polyurethane (TPU) adhesives containing nanosilicas with different specific surface area and silanol group content were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA), X-ray diffraction, plate-plate rheology, dynamical-mechanical-thermal analysis (DMTA), transmission electron microscopy (TEM), and strain-stress test. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints.Formation of agglomerates of nanosilica particles within the polyurethane matrix were favoured by increasing the silanol content likely due to stronger hydrogen bond interactions between the silanol groups on the nanosilica over those between the polyurethane and the nanosilica. As a consequence, inter-urethane bonds formation rather than ester-urethane bonds were favoured, leaving the soft segment chains more free to interact between them. Thus, addition of nanosilica favoured the phase segregation in the thermoplastic polyurethane. The increase in specific surface area and silanol content in the nanosilica, generally enhanced the degree of phase separation in the polyurethane, being less marked for nanosilicas with more than 200 m 2 /g and 0.60 mmol SiOH/g silica . On the other hand, the addition of the nanosilica improved the tensile strength and elongation at break, and the viscoelastic properties of the polyurethane. The immediate adhesive strength of PVC/polyurethane adhesive joints increased in the filled adhesives and it was determined by the rheological properties of the polyurethane-nanosilica mixtures. By increasing the time after joint formation, the crystallization of the polyurethane was produced giving higher adhesive strength and although a cohesive failure in the PVC was always obtained, a slight though progressive increase in joint strength was found with the passage of time with the ordering of the three systems (PU-0.45, PU-0.60 and PU-0.90) remaining unchanged with the PU-0.60 system the stronger and the PU-0.90 system the weaker. This is in agreement with the trends in the viscoelastic and mechanical properties of the filled adhesives. r

The toughness of epoxy polymers and fibre composites modified with rubber microparticles and silica nanoparticles

“…10a. This excellent technique to obtain such micrographs was devised by Pearson and Yee [58] in order to help identify mechanisms occurring at crack tips. Fig.…”

Characterization polyethylene terephthalate nanocomposites mixing with nano-silica and titanium oxide

“…Other authors have confirmed this phenomenon in cases where nano-silica and TiO2 was incorporated into multilayer organic coatings [15][16][17][18][19][20][21][22].…”

Thermoplastic Polyurethanes-Fumed Silica Composites: Influence of NCO/OH in the Study of Thermal and Rheological Properties and Morphological Characteristics

“…Recent studies (Nunes et al, 2000;Nunes et al, 2001;Vega-Baudrit et al, 2006;NavarroBañón et al, 2005;Vega-Baudrit et al, 2008;Vega-Baudrit et al, 2009) have demonstrated that the addition of fillers as silica able to form hydrogen-bonds result in less direct interactions between phases, causing a higher degree of phase separation in the polyurethane. On the other hand, the interactions between the silanol groups and the carbonyl groups in the polyurethane are weaker than those between the N-H and ester carbonyl groups, and therefore the silica addition increases the polyester chain mobility in the polyurethane allowing the creation of more ordered phases with respect to the polyurethane without silica.…”

“…In recent papers are showed the results of evaluating these samples using thermal, rheological and mechanical analysis, and adhesion tests (Vega-Baudrit et al, 2006;NavarroBañón et al, 2005;Vega-Baudrit et al, 2008;Vega-Baudrit et al, 2009). …”