Diffusion and permeation of water through unsaturated polyester resins—influence of resin curing
Introduction
Water diffusion and permeation frequently occur through polymer films (or materials) due to the presence of water vapor and liquid water in the surrounding medium of the materials. Depending on the polymer nature and the absolute water vapor pressure, the permeation flux may be very low. It is likely the case for the glassy, hydrophobic unsaturated polyesters. This makes the determination of the diffusion coefficient very difficult, as a quantitative detection of very small amounts or concentrations of water is required.
Unsaturated polyester resins (UPR) with styrene as the crosslinking agent are widely used in the coating technologies. They are inexpensive and can easily accomodate defined specifications by changing either the nature of the unsaturated polyester chain or the ratio of styrene/polyester amounts. The thermal cycles leading to the final products consist generally in curing and post-curing periods, and eventually a final curing at high temperature. The final products exhibit thermosetting characteristics, e.g. insolubility and infusibility. The chemical processes involved in the curing steps were investigated by several authors, using infrared spectroscopy (IR) [1], [2], [3], differential scanning microscopy (DSC) [4], [5], or nuclear magnetic resonance [6]. UPR resins find numerous applications in military, space and naval industries, especially in association with fibres in reinforced composite systems. Due to the importance of the naval application area, the sorption behaviors of the UPR as well as the chemical reactions involved in the immersion of the resins in water were largely studied [7], [8], [9], [10]. Indeed, the UPR materials may suffer from chemical modifications/degradations when the materials are exposed to atmospheric moisture or are in contact with liquid water for a long time. This can lead to a loss of adhesive strength, a production of cracks, a leaching of polymer fragments, a corrosion of metallic substrates and a rotting of wood. These damages result from the diffusion of water molecules throughout the polymer chains causing plasticization, local strain, chain rupture and chemical reactions [11], [12]. Although the knowledge of water diffusivity and permeability in the UPR matrices and their composites is of utmost importance, few data are available in the literature, especially when the materials are in direct contact with liquid water.
In a previous paper [13], we described the method and the experimental set-up which makes it possible to measure low water permeation fluxes for the study of diffusion and permeation phenomona. The present paper deals with the water diffusion and permeation properties of unsaturated copolyester, especially those of the raw copolyester resin during its curing at room temperature and at different curing temperatures. The water migration is then discussed on the basis of the change in the infrared spectra and the resin chemical structure during the curing process.
Section snippets
Theoretical background
The measurement principle and procedure were described in a previous paper [13]. When the upstream face of an initially dry film is suddenly in contact with pure water (activity a=1), and the downstream face is swept with a dry gas at the flow rate f, a water permeation flux J occurs through the film. The initially nil flux increases progressively with time up to a limit Jst typical of the steady state. The variation of the reduced water flux J/Jst with time depends on the values of the
Materials
The UPR precursor provided by Cray Valley-Total Corporation consists of a copolymer of maleic acid (25% mol.) and isophthalic acid (25% mol.) with propanediol (50% mol.), styrene (38 wt% styrene), and a small amount of polymerization inhibitor (hydroquinone). The resin is hardened via a radical process by using an initiator. To harden the precursor of a 6 wt% solution of cobalt octoate (Akzo), an activator is first mixed with the resin (0.2 wt% on the precursor basis). Then 1.5 wt% of
Influence of permeation procedure and material preparation
Before starting the permeation study, we must ensure that the sample is not affected by the permeation procedure. To check the reproducibility of the permeation procedure obtained with a sample in an early curing stage, i.e. a sample whose permeation properties was still changing with time, the permeation experiment was performed on a UPR sample after a two-day curing at 25°C, then the permeation experiment was repeated on the same sample after its drying in the cell. The transient permeation
Conclusion
The use of a water sensitive permeameter associated with a new method of determination of the transport properties in polymer films allowed us to determine the concentration-dependent parameters related to the water transport in UPR. The knowledge of the concentration-dependent law of diffusion would make it possible to precisely predict the steady-state or the transient flux of water through a UPR layer in the real application cases, i.e. the case in which the water vapor pressures on both
References (22)
- et al.
Eur Polym J
(1992) - et al.
Polymer
(1993) - et al.
Polymer
(1985) - et al.
Polymer
(1982) - et al.
Polym. Proc. Eng.
(1988) - et al.
Polym Bull
(1989) - et al.
Macromol Symp
(1995) - et al.
Composites
(1990) - et al.
Proc Roy Soc (A)
(1967) - et al.
Polym. Compos.
(1986)
J Appl Polym Sci
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