Formation Mechanism of a Silane‐PVA/PVAc Complex Film on a Glass Fiber Surface

Abstract

Mechanical properties of glass fiber reinforced composite materials are affected by fiber sizing. A complex film formation, based on a silane film and PVA/PVAc (polyvinyl alcohol/polyvinyl acetate) microspheres on a glass fiber surface is determined at 1) the nanoscale by using atomic force microscopy (AFM), and 2) the macroscale by using the zeta potential. Silane groups strongly bind through the Si-O-Si bond to the glass surface, which provides the attachment mechanism as a coupling agent. The silane groups form islands, a homogeneous film, as well as empty sites. The average roughness of the silanized surface is 6.5 nm, whereas it is only 0.6 nm for the non-silanized surface. The silane film vertically penetrates in a honeycomb fashion from the glass surface through the deposited PVA/PVAc microspheres to form a hexagonal close pack structure. The silane film not only penetrates, but also deforms the PVA/PVAc microspheres from the spherical shape in a dispersion to a ellipsoidal shape on the surface with average dimensions of 300/600 nm. The surface area value Sa represents an area of PVA/PVAc microspheres that are not affected by the silane penetration. The areas are found to be 0.2, 0.08, and 0.03 μm(2) if the ellipsoid sizes are 320/570, 300/610, and 270/620 nm for silane concentrations of 0, 3.8, and 7.2 μg mL(-1), respectively. The silane film also moves PVA/PVAc microspheres in the process of complex film formation, from the low silane concentration areas to the complex film area providing enough silane groups to stabilize the structure. The values for the residual silane honeycomb structure heights (Ha ) are 6.5, 7, and 12 nm for silane concentrations of 3.8, 7.2, and 14.3 μg mL(-1), respectively. The pH-dependent zeta-potential results suggest a specific role of the silane groups with effects on the glass fiber surface and also on the PVA/PVAc microspheres. The non-silanized glass fiber surface and the silane film have similar zeta potentials ranging from -64 to -12 mV at pH's of 10.5 and 3, respectively. The zeta potentials for the PVA/PVAc microspheres on the glass fiber surface and within the silane film significantly decrease and range from -25 to -5 mV. The shapes of the pH-dependent zeta potentials are different in the cases of silane groups over a pH range from 7 to 4. A triple-layer model is used to fit the non-silanized glass surface and the silane film. The value of the surface-site density for Γ(Xglass) and Γ(Xsilane), in which X denotes the Al-O-Si group, differs by a factor of 10(-4), which suggests an effective coupling of the silane film. A soft-layer model is used to fit the silane-PVA/PVAc complex film, which is approximated as four layers. Such a simplification and compensation of the microsphere shape gives an approximation of the relevant widths of the layers as the follows: 1) the layer of the silane groups makes up 10% of the total length (27 nm), 2) the layer of the first PVA shell contributes 30% to the total length (81 nm), 3) the layer of the PVAc core contributes 30% to the to...

Thermal curing and water re-exposure of silane-PVA/PVAc complex film on glass fiber surface

“…A role of the coupling agent is to provide an interaction between the substrate and the film former. The silane film (note, as silane in the following text) vertically stabilizes, in the honeycomb fashion, the hexagonal close pack structure of deposited PVA/PVAc microspheres (note, as microspheres in the following text) on the glass fiber surface (note, as glass in the following text) . This interaction between silane and microspheres might be presumably enhanced by an increase of curing temperature.…”

“…A relatively rough surface was observed in the case of E 2 , because of the spherical shape of microspheres, where the value of R a is 7.3 nm. Note that the value of 7.3 nm is relatively low in comparison with R a value of microspheres without the presence of the silane, which is approximately 56 nm . In other words, the silane is smoothing the overall surface by stabilizing in the honeycomb fashion of the hexagonal close pack structure of deposited microspheres.…”

“…The silane on the glass fiber surface generates a structured topography forming islands on surface along with homogeneous film areas. The value of average roughness ( R a ), which is the arithmetic average of the absolute values of the surface height deviations, for silanized glass fiber surface after deposition of silane is approximately 6.5 nm, while R a for unsized glass fiber surface is only 0.6 nm …”

The influence of 3-methacryloxypropyltrimethoxysilane on thermostability, tensile behavior and water resistance of polyvinyl acetate/clay nanocomposite

“…However they did not study other properties such as mechanical properties and water resistence. L. Liu et al [2] prepared PVAc- Moreover, special attention has been given to the silane coupling agents which have the ability to form a durable bond between organic and inorganic material [18][19][20][21][22][23][24][25][26]. Silane coupling agents are widely employed in research and development for surface modification of inorganic materials and find their largest applica tion in the area of polymers since they provided a com bination of good mechanical properties, high resil ience, excellent adhesion and water resistance [27][28][29][30][31][32].…”

“…M. Abdelmouleh et al [21] used silane coupling agents and fibres load ing reinforced polyethylene and natural rubber com posites and the mechanical properties of the compos ites increased significantly. D. Repovsky et al [22] investigated the formation mechanism of a silane PVA/PVAc complex film on a glass fiber surface. They found silane groups strongly bind through the Si-O-Si bond to the glass surface and the silane groups on the glass fiber surface generate a structured topography by forming islands on the surface.…”