Interrelationships between reaction conditions and material properties of thermosetting and high Tg polymers are discussed from the point of view of a generalized time-temperature-transformation (TTT) diagram

Formation and properties of thermosetting and high Tg polymeric materials

Absorbed moisture can degrade the physical properties of an epoxy resin, jeopardizing the performance of an epoxy-based component. Although specific water- epoxy interactions are known to be very important in determining transport behavior, the role of network topology is not clear. In this article, a series of epoxies in which the topology is systematically varied (and the polarity held constant) is used to explore how topology influences the kinetics of moisture transport. The topology is quantified via the positron annihilation lifetime spectroscopy technique in terms of the size and volume fraction of electron density heterogeneities 5- 6 A in diameter, a dimension comparable to the 3-A kinetic diameter of a water molecule. Surprisingly, the volume fraction of such nanopores does not affect the diffusion coefficient (D) of water in any of the resins studied. For temperatures at and below 35 °C, there is a mild exponential dependence of D on the average nanopore size observed. Otherwise, the kinetics of moisture transport do not appear to depend on the nanopores. However, the initial flux of moisture into the epoxy does appear to correlate with the intrinsic hole volume fraction. That this correlation persists only in the initial stages of absorption is partially understood in terms of the ability of the water to alter the nanopore structure; only in the initial stages of uptake are the nanopores, as quantified in the dry state, relevant to transport. The role of specific epoxy-water interactions are also discussed in terms of transport kinetics. The lack of a correlation between the topology and transport sug- gests that polar interactions, and not topology, provide the rate-limiting step of trans- port. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 776 -791, 2000

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/35005/15_ftp.pdf;sequence=1

Contributions of the nanovoid structure to the kinetics of moisture transport in epoxy resins

Corrosion protection by epoxy coating containing multi-walled carbon nanotubes

Effect of chemical structure on the water sorption of amine-cured epoxy resins

A novel experimental approach, based on time-resolved two-dimensional (2D) ATR-FTIR spectroscopy has been used to study water diffusion behavior of novolac epoxy resins cured with novolac resin and novolac acetate resin named as EP and EPA, respectively. The diffusion coefficients calculated by a nonlinear curve fitting are quite consistent with the results of gravimetric analysis. In 2D-IR spectra, the splitting of the water OH vibration band at 2800-3700 and 1500-1800 cm -1 shows that there are two different states of water in epoxy networks, in which one could be confined into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved), while the other could be attributed to bound water forming strong hydrogen-bonding with hydrophilic groups of epoxy networks. The sequential order of intensity changes of the two water bands elucidates that, in the process of water diffusion into epoxy networks, water molecules first bind with specific hydrophilic groups as bound water and then diffuse into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved). The wavenumber difference of OH vibration band appearing from bound water between EP and EPA indicates that water molecules form much stronger hydrogen-bonding with EP networks than with EPA networks.

Two-dimensional (2D) ATR-FTIR spectroscopic study on water diffusion in cured epoxy resins

The effect of different time—temperature paths of cure on the water absorption of high Tg epoxy resins has been investigated. The resins were cured isothermally for different times, with the following results: as extent of cure increased, the glass transition temperature (Tg) increased, the room temperature (RT) modulus decreased, the RT density decreased, the RT diffusion coefficient appeared to decrease, and the RT water absorption increased. The decrease in RT density is related to an increase in free volume, which controls the amount of water absorbed. A qualitative model accounts for the increase in RT free volume with increasing cure. The model is based on a restricted decrease of free volume on cure due to the rigid molecular segments in the cured resin systems. The sorption isotherms can be characterized by the dual mode theory at low activities but at high activities the sorption is complicated by penetrant clustering. A thermodynamic approach, independent of the absorption model, can correlate sorption data at different temperatures. The diglycidyl resin was also cured for extended times at three temperatures, in an effort to achieve full cure at each temperature. For these, the higher the cure temperature, the lower the RT density, which could result from the lower initial density of materials cured at higher temperatures. The equilibrium water absorption increased with increasing cure temperature, consistent with the decrease in RT density. The systems studied were a diglycidyl ether of bisphenol A cured with an aromatic tetrafunctional diamine, trimethylene glycol di-p-aminobenzoate (Tg∞ = 156°C), and a triglycidyl ether of tris(hydroxyphenyl)methane cured with the same amine (Tg∞ = 268°C).

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X. Peng

Papers

Effect of time‐temperature path of cure on the water absorption of high Tg epoxy resins