Flow Properties Of Resins Research Articles

Acrylic‐based nanocomposite resins for coating applications

AbstractAcrylic‐based nanocomposite resins have been investigated in view of future application in water borne automotive coatings by the aid of postemulsification processes. Mechanical, flow and leveling properties of the nanocomposite resins, containing various concentrations of silicate, have been investigated. The results are related to morphological information obtained from TEM and WAXS measurements in the liquid suspension as well as from the cured film. At low silicate loadings, when flow properties are still acceptable for typical emulsification processing, a strong increase in modulus of the cured coating films is observed because of the mainly exfoliated silicate platelets. The rate of increase in modulus of the cured films decreases at higher silicate loadings. Analyzing the mechanical data, using Halpin–Tsai theory indicates that this is due to less perfect exfoliation at higher silicate loading, which is confirmed by TEM analysis. In addition at higher silicate loading, the flow properties of the resin as analyzed by DMA show solid‐like behavior. This can lead to poor film formation in future application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2146–2156, 2007

The Influence of the Rubber Carboxyl Functionality on the Processability and Properties of Solid Rubber Modified Epoxy Mixtures

AbstractSummary: A high molecular weight, carboxyl functionalised solid rubber was added to an epoxy resin‐aromatic amino system developed for autoclave curing of honeycomb core composite structures. The achievement of an optimal balance of viscous flow and viscoelasticity of the resin, by controlling the nature and extent of cross‐linking of the functionalised rubber, was proposed as a route to void‐free honeycomb skins. The aim of the present investigation is to understand how the concentration of carboxylic groups of the rubber, prereacted with one of the epoxy monomers, affects the matrix resin flow properties. The concentration of carboxyl groups was changed by reacting them with a monofunctional epoxy resin. Dynamic shear viscosity profiles varying frequency, temperature and as function of time during isothermal cure have been determined for blends with differently functionalised rubbers. Carbon fibre wettability and laminate consolidation quality have been evaluated, making composite samples according to conventional prepregging and autoclave curing processes, through electron microscopy of fracture surfaces from transverse flexural strength tests.Loss factor and storage modulus from dynamic‐mechanical torsion analysis for PWE0 blend. Loss factor and storage modulus for Nipol 1072 are reported for comparison.imageLoss factor and storage modulus from dynamic‐mechanical torsion analysis for PWE0 blend. Loss factor and storage modulus for Nipol 1072 are reported for comparison.

Visual analysis of the flow behavior of core material in a fork portion of plastic sandwich injection molding

The flow behavior of core material in the fork portion of a plastic sandwich molding was studied by using a dynamic visualization technique. High viscosity resin GPPS685 and low viscosity resin GPPS679 were used in the experiments. It was found that in the fork portion, although the molding conditions have almost no effect on the flow pattern of the skin material, they influenced the flow pattern of the core material: (1) Mold temperature slightly influences the flow patterns of the core material. (2) The flow properties of resins also affect the flow patterns of core material. An imbalanced design causes more problems than in ordinary injection molding. Low viscosity material yielded a well balanced filling more easily than high viscosity material. (3) The injection rate strongly affects the flow behavior of the core material in a complicated manner.

Phase separation influence on the performance of CTBN‐toughened epoxy adhesives

AbstractEpoxy adhesive systems were formulated and tested for their bonding behavior. Fumed silica and elastomer type and concentration were varied for the purpose of investigating their influences on intermediate and final adhesive performance properties. Of special interest was analyzing the role that flexibilized elastomer, that which does not phase separate during cure, played in these properties. Adhesive systems were tested with a commercial prepreg system using both bonded and cocured geometries. Dynamic mechanical analysis and optical microscopy showed the phase separation of the rubber was significantly influenced by the silica addition. Elastomer‐rich dispersed phase growth rates were depressed resulting in a lower percentage of toughening domains. Mode I and II fracture energies were a strong function of dispersed phase particle size, flexibilized elastomer type/content, and residual stress considerations at the resin‐resin interface. There were distinct differences between bonded and cocured fracture results with bonded samples generally outperforming cocured specimens due to changes in the surface roughness, resin flow properties, and interfacial stress build‐up. Collectively, this work illustrates the importance of phase separation behavior on the final part morphology and performance for liquid elastomer toughened epoxy adhesives.

Mechanics of the squeeze flow of planar fibre suspensions

This paper discusses the axisymmetric squeeze flow of concentrated transversely isotropic fibre suspensions in a power-law matrix and relates to the processing of composite materials such as sheet moulding compounds (SMCs) and glass mat thermoplastics (GMTs). A solution to the squeeze flow problem for a transversely isotropic power-law fluid is presented first, followed by a more detailed micromechanical analysis. In the first part of the paper a variational approach is applied to the interpretation of squeeze flow behaviour. This gives a simple expression for the total pressure, which enables the contributions due to extension and shear to be separated. Applying the procedure to GMT data suggests that the dissipation is predominantly extensional, except at very low plate separations. In the second part, a non-local constitutive equation is derived based on a simple drag law for hydrodynamic interactions. This is then used to model the pressure distribution when the effective length of the fibres is comparable to or determined by the dimensions of the squeeze flow plates. The model is shown to describe the observed squeeze flow stresses in both long and short fibre systems and to relate behaviour to the underlying resin flow properties.