Abstract:

Three nanosilicas with different silanol contents were prepared by treatment of hydrophilic fumed silica with dimethyldichlorosilane. This treatment reduced the silanol content and produced the particle agglomeration of the nanosilicas. Thermoplastic polyurethane (TPU) adhesives containing nanosilicas were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), plate-plate rheology, dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and stress-strain testing. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints. The addition of hydrophilic nanosilicas favoured the degree of phase separation between the hard (i.e. isocyanate+chain extender) and soft (i.e. polyol) segments in the TPUs; the higher the silanol content on the surface of silica, the higher the degree of phase separation, and the crystallinity of the polyurethane (due to the soft segments) was also increased. Hydrogen bonds between the ester carbonyl groups in the TPU and the silanol groups on the silica surface were created and more favoured by increasing the silanol content. The tensile strength increased and the elongation at break of the polyurethane decreased by increasing the silanol content of the nanosilica. Addition of nanosilica increased the immediate adhesion of the polyurethane adhesives to PVC, irrespective of the silanol content on the nanosilica. The higher the mechanical and the rheological properties of the polyurethanes containing nanosilicas with different silanol content, the higher the final adhesive strength.

Author affiliation: Vega Baudrit, José. Universidad de Costa Rica; Costa Rica

Author affiliation: Navarro Bañón, Virtudes. Universidad de Alicante; España

Author affiliation: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina

Author affiliation: Martín Martínez, Jose Miguel. Universidad de Alicante; España

Abstract:

Three nanosilicas with different silanol contents were prepared by treatment of hydrophilic fumed silica with dimethyldichlorosilane. This treatment reduced the silanol content and produced the particle agglomeration of the nanosilicas. Thermoplastic polyurethane (TPU) adhesives containing nanosilicas were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), plate–plate rheology, dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and stress–strain testing. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints. The addition of hydrophilic nanosilicas favoured the degree of phase separation between the hard (i.e. isocyanate+chain extender) and soft (i.e. polyol) segments in the TPUs; the higher the silanol content on the surface of silica, the higher the degree of phase separation, and the crystallinity of the polyurethane (due to the soft segments) was also increased. Hydrogen bonds between the ester carbonyl groups in the TPU and the silanol groups on the silica surface were created and more favoured by increasing the silanol content. The tensile strength increased and the elongation at break of the polyurethane decreased by increasing the silanol content of the nanosilica. Addition of nanosilica increased the immediate adhesion of the polyurethane adhesives to PVC, irrespective of the silanol content on the nanosilica. The higher the mechanical and the rheological properties of the polyurethanes containing nanosilicas with different silanol content, the higher the final adhesive strength.

Author affiliation: Vega Baudrit, José. Universidad de Costa Rica; Costa Rica

Author affiliation: Navarro Bañón, Virtudes. Universidad de Alicante; España

Author affiliation: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina

Author affiliation: Martín Martínez, José Miguel. Universidad de Alicante; España

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 m2/g and 0.60 mmol SiOH/gsilica. 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.

Author affiliation: Vega Baudrit, José. Universidad Nacional. Facultad de ciencias exactas y naturales. Laboratorio de polimeros; Costa Rica

Author affiliation: Sibaja Ballester, María. Universidad Nacional. Facultad de ciencias exactas y naturales. Laboratorio de polimeros; Costa Rica

Author affiliation: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo En Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina

Author affiliation: Torregrosa-Macia, Rosa. Universidad de Alicante. Departamento de química inorgánica. Laboratorio de adhesión y adhesivos; España

Author affiliation: Martın-Martınez, Jose Miguel. Universidad de Alicante. Departamento de química inorgánica. Laboratorio de adhesión y adhesivos; España

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 m2/g and 0.60 mmol SiOH/gsilica. 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.

Author affiliation: Vega Baudrit, José. Universidad Nacional. Laboratorio de polimeros; Costa Rica

Author affiliation: Sibaja Ballestero, María. Universidad Nacional. Laboratorio de polimeros; Costa Rica

Author affiliation: Vazquez, Patricia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentina

Author affiliation: Torregrosa Maciá, Rosa. Universidad de Alicante. Departamento de química inorgánica; España

Author affiliation: Martín Martínez, Jose Miguel. Universidad de Alicante. Departamento de química inorgánica; España