Non-reversible heat flow

Figure 3.6. Non-reversing heat flow and change in heat capacity (C ) during cure of an epoxy resin cured with an anhydride at 80 °C. The cure time needed to reach a halving of Cp is marked as t. Adapted from Van Assche et al. (1997).

Table 5.1. Effect of experimental conditions on the reversing and non-reversing heat flows in the melt region. The sum of the heat flow signals is quantitative and is defined as the initial crystallinity of the quenched PET sample (courtesy of TA Instruments Inc.)...

TMDSC total, reversing and non-reversing heat flow signals of a polymer resin in the presence of moisture. 

Temperature modulated DSC Variation of DSC (or quantitative DTA) where a sinusoidal perturbation is applied to the temperature programme resulting in a non-linear modulation of the heat flow and temperature signals, which permits decomposition of the total heat flow signal into its reversing and non-reversing heat flow components. 

This is then subtracted irom the total heat flow to obtain the non-reversing heat flow. Viz... 

Thus, it is possible to conclude that the non-reversing heat flow contains that part of the underlying signal that comes from the chemical reaction. In most cases, it is also true to a very good approximation that C = CpPCR-Thus, it is not necessary to use the phase correction in order to measure the heat capacity and then calculate the non-reversing signal. So, the simple deconvolution can be used. 

At the same time, the non-reversing heat flow is simply... 

Multiplying C by the (measured) underljdng heating rate gives the reversing heat flow, in W the non-reversing heat flow, 4>nr in W, is the difference between the total heat flow and the reversing heat flow ... 

It should be noted that the corrected heat flow phase is very small in most cases, so that the difference in value between C and Cp is negligible. For isothermal experiments, the reversing heat flow equals zero because of a zero underlying heating rate and consequently the non-reversing heat flow equals the total heat flow. 

The total heat flow obtained in quasi-isothermal MTDSC experiments agrees very well with the heat flow evolution obtained in a conventional DSC experiment, performed under the same conditions without of the modulation (Figure 2.2a). Neither changing the modulation amplitude nor the period had an effect on the reaction exotherm seen in the non-reversing heat flow. This illustrates the negligible effect of the perturbation on the cure reaction. 

Figure 2.2. Quasi-isothermal cure of an epoxy-anhydride at 100°C (a) comparison of the non-reversing heat flow obtained in MTDSC to the heat flow obtained in conventional DSC (arrow), (b) heat capacity and (c) corrected heat flow phase.

Figure 2.3. Quasi-isothermal cure of an unsaturated polyester at 30°C (a) non-reversing heat flow and complex viseosity (logarithmie seale) (b) heat capacity and heat flow phase the symbol (o) denotes the point at maximum auto-aeeeleration in the non-reversing heat flow...

Figure 2.5. Quasi-isothermal cure of a melamine-formaldehyde (MF) resin (pH 9.5 F/M = 1.7) at 119°C in closed high-pressure steel (HPS) and open A1 pans (a) non-reversing heat flow and heat capacity (b) heat flow phase.

Figure 2.6. Production of an inorganic polymer glass (IPG) for a metakaolinite (Mk) particle size of 1.8 /xm at 35°C (a) non-reversing heat flow and storage modulus (b) heat capacity and...

Figure 2.7. Non-isothermal cure of an epoxy-anhydride at 0.2 (1), 0.4 (2), and 0.7°C min (3) and for the fully-cured material (4) non-reversing heat flow and heat capacity.

Figure 2.12. Production of inorganic pol)nner glasses for different Mk particle sizes (indicated values in /rm) at 35°C (a) non-reversing heat flow (b) heat capacity (shifted according to initial reciprocal particle diameter, d (right 7-axis), with (10%) (x) and /(50%) (A) dotted...

Figure 2.16. Cure of different epoxy-amine systems at 100°C PGE-aniline in molar ratios of amine/epoxy functional groups r = 0.6 (1) andr = 1.0 (2) DGEBA-aniline with r = 0.7 (3) and r = 1.0 (4) PGE/A,A -dimethylethylenediamine at 30°C is given for comparison (5) (a) non-reversing heat flow per mole of reacted (epoxy-NH) functional groups (b) heat capacity change per mole of reacted (epoxy-NH) functional groups.

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