Thermal measuring and testing – Transformation point determination – By electrical condition of specimen
Reexamination Certificate
2001-10-19
2003-04-08
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Transformation point determination
By electrical condition of specimen
C374S016000, C374S035000, C324S663000
Reexamination Certificate
active
06543931
ABSTRACT:
FIELD OF THE INVENTION
The absorption of molecular species by diffusion in a polymer material leads to a decrease in the glass-transition temperature (Tg) through plasticization, which modifies the properties and the performances of the material. The examples hereafter show why knowledge of the plasticized Tg is a determining factor as regards applications. In the case of epoxy resins, the Tg loses about 20° C. per percent of absorbed water according to Ellis and Karasz (Ellis, T. S., Karasz, F. E., Polymer, 25, 664, 1984). These resins are conventionally used as a protective anti-corrosion coating, but the range of operating temperatures must be adjusted as a function of the plasticized Tg, because the barrier properties decrease greatly when the Tg is reached. In the case of amorphous or semicrystalline thermoplastic polymers, the Tg is marked by a drop in the mechanical properties thereof. In this case also, the plasticized Tg value has to be taken into account for the range of temperatures used.
Furthermore, the diffusion of molecular species outside a polymer material formulated with plasticizing organic compounds can lead to a Tg increase which modifies the properties and the performances of the material. Following such a phenomenon is also essential in order to be able to control it.
Conventional Tg measuring methods using differential enthalpy analysis (DSC), thermomechanical analysis (TMA) or dynamic mechanical analysis (DMA) lead to overestimated plasticized Tg values because of the dynamic temperature sweep, which leads to a partial desorption of the solute during measurement. Besides, modern industrial practices increasingly involve non-destructive evaluation techniques, which ideally allow to follow certain properties of the materials during use.
BACKGROUND OF THE INVENTION
Thus, dielectrometry emerges as an interesting technique for following the evolution of the resistance and capacitance properties of a polymer material in the presence of fluids, in particular in the presence of water (Hasted, J. B.,
Aqueous Dielectrics,
Chapman and Hall, London, 1973). However, it is now an established fact (Maffezzoli, A. M., Peterson, L., Seferis, J. C., Kenny, J., Nicolais, L.,
Dielectric characterization of water sorption in epoxy resin matrices,
Polym. Eng. Sci. 1993, 33, 2, 75-82) (Duval, S., Camberlin, Y., Glotin, M., Keddam, M., Ropital, F., Takenouti, H.,
The influence of thermal transition to the evaluation of water-uptake in surface polymer film by EIS method,
Proceedings of the 198
th
meeting of the Electrochemical Society, October 2000) that follow-up of the dielectric properties of a polymer material immersed in water is suitable for studying the diffusion conditions of the solute, but that it does not systematically provide a quantitative measurement of the water uptake, therefore an evaluation of the plasticized Tg by means of Couchman and Karasz type mixing laws (Couchman, P. R., Karasz, F. E., Macromolecules, 11, 117, 1978).
The glass transition of a polymer material corresponds to the development of a generalized mobility on a molecular scale. The complex permittivity ∈* of a polymer material, which is the sum of dipolar and ionic components, can be used as an indicator of the state of the material, and more particularly of the glass transition stage (McCrum, N. G., Read, B. E., Williams, G.,
Anelastic and dielectric effects in polymeric solids,
Wiley, J. & Sons, New York 1967). In fact, the development of cooperative dipolar relaxations associated with glass transition (change to high temperatures or low frequencies, because of the kinetic character of the glass transition that follows time/temperature equivalence laws) induces:
an increase in the dipolar component of the real part of the complex permittivity, ∈′
d
;
a dissipative peak on the dipolar component of the imaginary part of the complex permittivity, ∈″
d
.
In cases where ions are present in the medium (for example in form of impurities in the case of thermosetting resins), the glass transition Tg leads to an increase in the ionic conductivity as a result of the mobility development of the chains, hence:
an increase in the ionic component of the real part of the complex permittivity, ∈′
i
, if the accumulation of ions at the electrodes causes a polarization phenomenon;
an increase in the ionic component of the imaginary part of the complex permittivity, ∈″
i
.
U.S. Pat. No. 5,317,252 by Kranbuehl describes in particular how to follow the life of a plastic material exposed to an aggressive environment by means of the dielectric permittivity characteristics of a sensor. Among other properties, he claims the follow-up of the Tg by correlating the permittivity measurements of the material in the initial state with those of the material during use. In fact, temperature and/or frequency dynamic dielectric measurements allow to detect the glass transition (McCrum, N. G., Read, B. E., Williams, G.,
Anelastic and dielectric effects in polymeric solids,
Wiley, J. & Sons, New York 1967) which is reflected in the development of cooperative dipolar relaxations in the medium. However, so far, no method allowing quantitative determination of the Tg of a polymer material exposed to an aggressive environment has been proposed.
Furthermore, in the case of measurement of the Tg of a polymer material in the presence of fluids, using the electrodes claimed in patent U.S. Pat. No. 5,317,252 provides no satisfactory answer:
(i) In the case of interdigitated comb sensors on an inert support (Al
2
O
3
substrates or glass as described in patents U.S. Pat. No. 4,710,550 and U.S. Pat. No. 4,723,908), the impervious character of the substrate leads to an accumulation of the solute at the interface, hence a sensor response saturation before the steady state is established (see Maffezzoli, A. M., Peterson, L. and Seferis) by short-circuit of the two electrodes.
(ii) In the case of interdigitated comb sensors on an organic substance (thermosetting and thermoplastic substrates) deposited at the surface of the polymer material to be studied, the response connected with the polymer material studied cannot be distinguished from that of the polymer substrate.
(iii) In the case of plane/plane sensors to be embedded in the polymer to be studied, the imperviousness of each electrode blocks the free circulation of the solute in the inter-electrode space. The dielectric measurement is therefore not representative of the material in mass in the stationary or transient state.
(iv) Finally, in the case of <<coupon >> sensors exposed to the same environment as the polymer material to be studied, whose complex permittivity changes would be connected by a chart to the evolution of the properties of the polymer material to be studied, the reliability of the sensor is difficult to guarantee, as underlined by D. E. Kranbuehl himself in patent U.S. Pat. No. 5,614,683.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a method of evaluating the glass-transition temperature of a polymer part during use, and a device suited for implementing this method.
The first object of the invention is a method allowing to evaluate the plasticization/deplasticization of the Tg of a polymer material in the presence of fluids from dynamic measurements of the components of the complex permittivity ∈* of the material (∈*=∈′−i∈″). The method is applicable in the laboratory as well as in an industrial context (in-situ measurements on coatings, sheaths, etc., in particular in the petroleum sphere). At a fixed temperature, the frequency measurements of ∈′ and ∈″ are carried out, then adjusted by means of a Havriliak-Negami type parametered equation (Havriliak, S.Jr., Negami, S., J. Polym. Sci. Part C, 1966, No.14, p.99) in order to determine the characteristic time of the glass transition &tgr; and consequently the plasticized Tg, by considering the previously established relaxation chart of the polymer material
Duval Sébastien
Sauvant Valérie
Antonelli Terry Stout & Kraus LLP
Gutierrez Diego
Institut Francais du Pe'trole
Verbitsky Gail
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