V. Michaud

Impregnation of Compressible Fiber Mats with a Thermoplastic Resin. Part I: Theory:

In many cases of composite processing by liquid matrix impregnation, the fiber reinforcement is compressed when it comes in contact with the liquid and then relaxes as the matrix flows within its pores. This phenomenon can be analyzed in terms of local fluid flow, mass conservation and mechanical equilibrium. A model is proposed to simulate the kinetics of impregnation, and the evolution of the fiber volume fraction profile as the resin front progresses, as well as after the front has reached the end of the mold. The analysis is then applied to the case of infiltration of needled glass fiber preforms by a polypropylene matrix, used in the production of Glass Mat Thermoplastic blanks. Aquantification of the effects of applied pressure and fluid viscosity on total process time is provided. It is shown that the time for preform relaxation after the fluid has filled the preform may be much larger than that for impregnation. As a result, an apparently well impregnated part may exhibit an inhomogeneous distribution of the reinforcement, in turn inducing a modification of the mechanical behavior and residual stress distribution.

Impregnation of Compressible Fiber Mats with a Thermoplastic Resin. Part II: Experiments:

The impregnation of compressible glass fiber mats by a thermoplastic resin in the transverse direction is investigated with application to the Glass Mat reinforced Thermoplastics (GMT) lamination process in a double belt press. Amodel proposed in Part I to simulate the kinetics of impregnation and the evolution of the fiber volume fraction profile as the resin front progresses across the fiber mat, as well as after macro-impregnation is complete, is further developed to include micro-impregnation effects. The predictions are compared with experimental results obtained using model systems such as polyethylene glycol and glass fiber mats, as well as an industrially relevant system consisting of polypropylene and glass fiber mats used in the production of GMT blanks. It is shown that significant compression of the fiber mat may occur during impregnation, with subsequent relaxation on a much longer time-scale. Also, fiber bundle impregnation generally occurs after macro-impregnation is complete, the driving force being the local pressure in the resin around the bundles, dictated by the local state of compression of the mat. The model is then used to provide guidelines for optimization of the preform impregnation conditions for a given material configuration.

Dynamic Properties of Materials for Alpine Skis

The aim of the present research has been to quantify the influence of different materials on the global dynamic response of a ski. The properties of the individual constituent materials were characterized as a function of temperature and frequency using dynamic mechanical analysis. At the same time, the dynamic behavior of skis with different designs was investigated in a cold room at between −15 and 25 °C using specially developed apparatus. The results indicated the overall behavior to be influenced significantly by the polymeric topsheet, which showed a strong damping peak at about 0 °C. Elasticity-based FEA accounted well for the experimental results for the two first flexural vibrational modes of the skis. For higher modes, however, the viscoelastic nature of the polymeric components led to significant discrepancies between the predicted and observed behaviors.

Formation of aminosilane-oxide interphases

The aim of this work is to understand the interactions and interphase formation mechanisms between a liquid aminosilane oligomer (γ-APS) and glass, steel or gold surfaces as a function of the pH of the liquid aminosilane. When basic liquid γ-APS (pH 11.4) is applied onto a gold coated substrate, no interphase is detected. Similarly, when liquid γ-APS controlled at pH 8 is applied onto steel or glass substrates and cured, properties are the same as the bulk ones. In contrast, when the liquid γ-APS (pH 11.4) is applied onto steel or glass substrates and cured, an interphase, with chemical, physical and mechanical properties quite different from those of the bulk oligomer, is created between the substrate and the oligomer. Using various analytical techniques (DSC, FTIR, ICP, SEM, AFM, nano-indentation and XPS) it was shown that the amino-silane chemically reacts with and dissolves the oxide or hydroxide layers. Then metallic ions diffuse through the organic layer to form a complex, assumed to be of coordination type with the amine function of the oligomer molecule. These organometallic complexes are insoluble at room temperature and crystallize in the form of sharp needles. The Youngs modulus of the resulting crystal is equal to approximately 5 GPa, i.e.over two orders of magnitude higher than that of the silane. In other words, these organometallic complexes act as a short fiber in a matrix.

Phase separation at the fiber-matrix interface in composites based on a thermoplastic/polyester blend

A study of the microstructure developing at the surface of glass fibers in a poly(vinyl acetate) (PVAc)/polyester blend is presented. Three different experimental methods are used: a technique based on the Wilhelmy method to measure the wettability of the fibers before curing, and both optical microscopy and atomic force microscopy in the pulsed-force mode to characterize potential phases splitting at the fiber–matrix interface after curing. It was found that, depending on the curing conditions and the concentration in PVAc, the surface treatment of the fiber could have a significant influence on the microstructure. For a concentration in PVAc lower than 5 wt% and a curing temperature of 80°C, extreme cases, such as the development of layers of one of the phases at the surface or the formation of lenses of one phase, were observed. In other cases, in particular for elevated temperatures and higher concentrations in PVAc, the fibers did not exert a significant influence on the morphology. It was also found that in such a reactive system, surface tension considerations alone are insufficient to explain the configuration of the phases at the surface of the fibers.

Wettability of Glass Fibers in Reactive Thermoplastic/Polyester Blends: Comparison between Compatible and Incompatible Thermoplastics

The evolution of morphology of reactive thermoplastic/unsaturated polyester blends at the surface of glass fibers is investigated during curing. The study focuses on two different types of thermoplastics, incompatible and compatible respectively with the polyester resin. Poly(dimethylsiloxane) and poly(methyl methacrylate) are chosen as incompatible thermoplastics, and poly(vinyl acetate) as a compatible thermoplastic. In the presence of incompatible thermoplastics, the blends form an emulsion during the entire course of curing. In that case, a correlation exists between the surface tensions of the components of the blend measured before curing and the final morphology at the surface of the fibers. For a compatible thermoplastic, on the other hand, a reaction-induced phase separation occurs during curing. In that case, the morphology at the surface of the fiber after phase separation cannot be fully determined by the surface tensions of the components.