Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

Results and Discussion 103
of instantaneous enthalpy dH i has been performed, through the trapezium rule as
illustrated in the following equation:
dH i = (φ i+1 + φ i )(t i+1 − t i )
2
· 60 (3.5)
φ i and φ i+1 are the specific heat flow [W/g], respectively at time t i [min] and at the
following instant t i+1 , measured by the DSC instrument. The isothermal enthalpy
has been calculated, according to the following equation:
∆H ISO =
n∑
dH i (3.6)
i=1
The sum is extended up to the last instant for t n =40min.
The energy developed during an ideal isothermal DSC should be equal to that
generated in a dynamic test. Instead the ∆H ISO is always lower than the ∆H TOT ,
because in every case there is a loss of data, due to the initial instrumental set-up.
For reducing the influence of this problem, for every temperature the first value of
instantaneous enthalpy dH 1 has put equal to the difference between the total cure
energy ∆H TOT 4 and the isothermal enthalpy ∆H ISO .
The degree of cure at every instant α i is calculated using the following equation:
α i =
dH i
∆H TOT
(3.7)
The reaction rate α ′ i
has been computed as incremental ratio of degree of cure:
α ′ i = dα i
dt ≈ α i+1 − α i
t i+1 − t i
(3.8)
3.2.3 Reaction Rate-Degree of Cure Plot
The curve of reaction rate versus degree of cure has been traced, using the
experimental values, calculated with the equations 3.7 and 3.8.
In Figure 3.8 the plot of α ′ versus α for the isothermal DSC at 100 ◦ C is illustrated.
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