Permeation in polymer coatings

Abstract

This work is aimed at developing methodologies to quantify permeability, diffusivity and solubility of a model system coating. The model system, provided by AkzoNobel, is a cured epoxy coating with Epikote 828 and Ancamine 2500 as the reactants, and methyl isobutyl ketone (MIBK) and xylene as solvents. Initially, the reagents were characterized by TGA, NMR and DSC experiments. Epikote 828 is DGEBA-type epoxy resin, while Ancamine 2500 has a quite complex composition with two types of amines, i.e., AEP (18 w%) and MXDA (14 w%), plasticizers and solvents. The presence of these components was confirmed by NMR measurements.
Next, the curing reaction and the produced coatings were studied by TGA, MTDSC, and gravimetry to verify the production of sufficiently stable sample coatings for further characterization of their transport properties. The exothermic heat of the curing reaction was measured at 300 J/g by DSC and MTDSC analysis and it was predicted that reaction mixtures without adding solvents reaches a plateau of 90% conversion after 20 hours, based on microcalorimetry measurements. The product coating, cured at room temperature for 24 hours, has a glass transition temperature of about 50°C only. Application of a post-curing schedule of 4 h at 150°C, under vacuum conditions, was sufficient to deliver the maximum Tg of about 120°C for the network, as derived from MTDSC results. A drying schedule of 48 h at 130°C and under vacuum conditions resulted from gravimetry analysis for drying coatings disbonded from their substrate.
At this stage, methodologies for the sample preparation of permeation measurements were developed for gravimetry, TGA, microcalorimetry and MTDSC. The average permeabilities for each technique were in the same order of magnitude at similar temperatures. Permeabilities by permeation measurements accord with values stated in literature, as well as to theoretical estimations. Sorption measurements by both gravimetry and FT-IR show similar anomalous diffusion behaviors.
Permeation and sorption measurement techniques developed in this work, showed particular advantages and disadvantages, making these techniques complimentary measurements in case of certain coating thickness, time of measurement, number of measurements and etc. Finally, diffusion coefficients calculated by three different methods for dry and wet state of coating were compared to one another and values in literature, as well as used for discussing molecular diffusion mechanism in the model system. Calculated values for the dry state of the coating were 5.1×10^(-14) m²/s and 6.1×10^(-14) m²/s. This diffusion coefficient for the wet state is 2.95×10^(-13) m²/s. Analysis of the diffusion coefficients, together with sorption data, points to the common conclusion that the model system coating is plasticized by water.

Date of Award	6 Sept 2018
Original language	English
Awarding Institution	Vrije Universiteit Brussel
Supervisor	Guy Van Assche (Promotor), Robrecht René Verhelle (Advisor) & Herman Terryn (Co-promotor)