Epoxy rubber toughened

Epoxy, rubber toughened epoxies Dow BASF Paints, coatings, adhesives, pipes, circuit boards... 

Fig. 2. Morphology model of a core-shell, rubber-toughened epoxy adhesive.

J. C. Hedrick, N. M. Patel, and J. E. McGrath, Toughening of Epoxy Resin Networks with Functionalized Engineering Thermoplastics, in Rubber Toughened Plastics, K. Riew (Ed.), American Chemical Society, Washington, DC, 1993. 

While the surface modification is not effective to suppress cavitation, Yee and coworkers performed an experiment to suppress the cavitation mechanically in a rubber-modified epoxy network. They applied hydrostatic pressure during mechanical testing of rubber toughened epoxies [160]. At pressures above BOSS MPa the rubber particles are unable to cavitate and consequently no massive shear yielding is observed, resulting in poor mechanical properties just like with the unmodified matrix. These experiments proved that cavitation is a necessary condition for effective toughening. 

Fond et al. [84] developed a numerical procedure to simulate a random distribution of voids in a definite volume. These simulations are limited with respect to a minimum distance between the pores equal to their radius. The detailed mathematical procedure to realize this simulation and to calculate the stress distribution by superposition of mechanical fields is described in [173] for rubber toughened systems and in [84] for macroporous epoxies. A typical result for the simulation of a three-dimensional void distribution is shown in Fig. 40, where a cube is subjected to uniaxial tension. The presence of voids induces stress concentrations which interact and it becomes possible to calculate the appearance of plasticity based on a von Mises stress criterion. 

Swelling experiments showed that a lignin epoxide resin of 0.11 epoxy equivalents per lOOg formed a network polymer when cured with DETA, PA, or ATBN. Phase separation was observed in the rubber-toughened lignin epoxide network. Cured epoxides had lignin derivative contents of up to 95%. 

Figure 13.5 Comparison between theoretical predictions of Kinloch s model ( ) and the experimental results ( ) at different test rates and temperatures of a rubber-toughened epoxy. (Huang and Kinloch, 1992a, with kind permission from Kluwer Academic Publisher.)...

Siebert, A. R., Riew, C. K., The Chemistry of Rubber Toughened Epoxy... 

Adhesives. Two single part, rubber toughened hot cured structural epoxy adhesives were used throughout the current research. Both adhesives were provided by Dow Automotive,... 

A variant of rubber toughening involves the use of preformed core-shell rubbers comprising a highly cross-linked polybutadiene core with a grafted shell of a vinylic polymer. In this case, the particles are small, typically ca. 0.1 pm, and thus have little effect on the observed viscosity of the epoxy. One of the principal advantages of this over simple rubber toughening is the ability to produce predetermined controllable morphology in the cured polymer. " ... 

Huang, Y. Kinloch, A.J. The role of plastic void growth in the fracture of rubber-toughened epoxy polymers. J. Mater. Sci. Lett. 1992, 11, 484-489. 

In many systems, such as epoxy resins, the rubber toughener may be soluble in the other phase, such as epoxy resin, so the phase separation must be achieved during cure. This is an example of phase separation during reactive processing. 

Figure 1.34. Change in the phase boundary (UCST) during the cure reaction for a system of a rubber (e.g. CTBN) dissolved in an epoxy resin. Toughening requires that phase separation be achieved during the cure cycle. After Pascualt et al. (2002).

Pearson and Lee (1991) examined the effects of particle-size and particle-distribution effects on rubber-toughened epoxy resins. They examined a variety of CTBN liquid rubbers and a methacrylated butadiene styrene core-shell particle in a DGEBA-piperidine system. They found that the toughening mechanism for small particles was internal cavitation of the... 

Predictive Modeling of the Properties and Toughness of Rubber-Toughened Epoxies... 

We have used this model to investigate stress distributions in and around the rubber particle, or around a void, in a matrix of epoxy polymer. This chapter describes the modeling of stress concentrations in rubber-toughened epoxy and gives a simple model for predicting the fracture energy, Gc, of such a material. 

Under unidirectional loading, the shape of the deformed sphere of isotropic material is an ellipsoid. This deformed shape must also be attained by a cell of rubber-toughened epoxy because the overall material is isotropic. This shape would not be attained from application of the load alone constraints... 

The application of pure hydrostatic stress leads to the prediction of the bulk modulus, K, for the rubber-toughened epoxy. For an isotropic material, the value of the bulk modulus is related to the value of Youngs modulus, E, and the Poisson ratio, v, by... 

Some linear-elastic results were obtained for direct comparison with experimental values of mechanical properties available in the literature. The materials were rubber-toughened epoxy resin (5) and epoxy resin filled with glass beads (22). The material properties used for these analyses are shown in Table II. 

Kinloch and Guild. Predictive Modeling of Rubber-Toughened Epoxies 11... 

Figure 6. Comparison of experimental and predicted values of Youngs modulus of epoxy resin toughened with rubber particles. Finite-element predicted values were calculated using two values of the Poisson ratio of the rubber phase and the predicted bounds using the Ishai and Cohen model (26).

Stress Distributions in Rubber-Toughened Epoxy. The toughening mechanisms described in the introduction of this chapter are observed ahead of a crack, in a triaxial stress field. The simplest triaxial stress field that can be applied to the spherical cell is a pure hydrostatic stress. This stress field can be directly imposed by the application of stress, without prior knowledge of the material properties of the overall material. The shape of the deformed grid is automatically spherical, and this is the correct deformed shape. Pure hydrostatic stress was used for the detailed investigation of the stress distributions and the effect of rubber properties. 

Figure 11. Growth of a localized shear zone in rubber-toughened epoxy, obtained using the spherical model. The yielded elements at the different steps are shaded. The applied strain (loading direction) is 3.0% (top), 4.0% (middle), and 5.0% (bottom).

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