(181az) Modeling of Diffusion in Epoxy Resin Composites

Epoxy resin composites offer a wide range of applications such as protective coatings, encapsulations and light-weight structures. If epoxy resin composites are used for the encapsulation of moisture sensitive parts, it is essential that a diffusion of steam and liquids to the sensitive parts is prevented. This project deals with the measurement and modeling of the diffusion through an epoxy cresol novolac resin with inorganic fillers.

To examine the diffusion composite samples were dried until mass no longer decreased. Then the samples were placed in various solvents and weighed in time intervals with a microbalance until the mass no longer increased. As solvents saturated water steam as well as the three different liquids water, heptane and isopropanol were used. For each solvent three different temperatures were investigated.

In order to model the diffusion, the solvent uptake in pure epoxy resin in equilibrium was modelled first. Therefore, the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state is used [1]. Due to the solvent uptake the polymer chains are stretched, which causes forces acting against a further solvent uptake. These elastic forces are taken into account by combining PC-SAFT with the network term of Miao et al. [2]. This network term was already successfully combined with PC-SAFT by Arndt and Sadowski to calculate the swelling of a hydrogel [3]. The PC-SAFT parameters of the epoxy resin were fitted to the solvent uptake in equilibrium and to its density.

After modeling the solvent uptake in equilibrium, the diffusion was modelled. Therefore the Maxwell-Stefan (MS) diffusion model is used, which is combined with the PC-SAFT equation of state. Since the MS diffusion coefficient is depending on the mixture, several models which connect the MS diffusion coefficient with the MS diffusion coefficient in infinite dilution are applied (e.g. Ogston model [4]) and discussed. The MS diffusion coefficient in infinite dilution was fitted to the measured mass increase over time.

We present the experiments of the diffusion kinetics of epoxy resins composites in saturated water steam and the three different liquids water, heptane and isopropanol. Furthermore, first modeling results are compared to the measured values and discussed.

[1] J. Gross and G. Sadowski, “Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for Chain Molecules,” Ind. Eng. Chem. Res., vol. 40, no. 4, pp. 1244–1260, 2001, doi:10.1021/ie0003887.

[2] B. Miao, T. A. Vilgis, S. Poggendorf, and G. Sadowski, “Effect of finite extensibility on the equilibrium chain size,” Macromol. Theory Simulations, vol. 19, no. 7, pp. 414–420, 2010, doi:10.1002/mats.201000009.

[3] M. C. Arndt and G. Sadowski, “Modeling poly(N-isopropylacrylamide) hydrogels in water/alcohol mixtures with PC-SAFT,” Macromolecules, vol. 45, no. 16, pp. 6686–6696, 2012, doi:10.1021/ma300683k.

[4] A. G. Ogston, B. N. Preston, and J. D. Wells, “On the Transport of Compact Particles Through Solutions of Chain-Polymers,” Proc. R. Soc. A Math. Phys. Eng. Sci., vol. 333, pp. 297–316, 1973, doi:10.1098/rspa.1973.0064.