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

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Results and Discussion 140 As illustrated in the Figure 3.35 a complete conversion of epoxy system in conventional DSC cure is achieved after 540 s, while in MW field the same degree of cure is obtained in only 300 s. After 240 s, when the two thermal profiles are reasonably comparable, the ratio between the degree of conversion in MW and DSC field is equal to 2,46. The ratio between α MW and α DSC until the two thermal profiles are comparable, in static conditions (2,37) is a little lower than that (2,46) obtained in dynamic conditions at the same power (1500 W). However only 175 s are necessary for achieve a complete conversion in static conditions, while 300 s are required in dynamic conditions. This behaviour can be explained, because the heating rate, during the main part of cure process, in static condition is much higher (44 ◦ C/min) than that measured in dynamic condition (20 ◦ C/min), and therefore the temperature increase during the same delay time τ, T τ takes a role more important in the first case. Resuming in static operative conditions at a power of 1500 and 2000 W and in dynamic conditions at a power of 1500 W suitable MW cure processes, with thermal profiles reproducible with a standard dynamic DSC, have been detected. The comparison between the both heating mechanisms has produced the results listed in Table 3.20. Summary of comparison MW-DSC P[W] 1500 (static) 2000 (static) 1500 (dynamic) α MW /α DSC 2,37 13,82 2,46 Table 3.20: Ratio between the conversion in MW at different powers and DSC with comparable thermal profile. The degree of cure achieved in microwave process at every time is much higher 140
Results and Discussion 141 than the corresponding value for conventional heating, though DSC thermal profile is comparable with the temperature during MW exposure (Figures 3.16, 3.17 and 3.29). These results suggest the existence of the “specific microwave effect”. 3.4 Kinetic analysis in Microwave Field with Avrami Method The profiles of degree of conversion in function of reaction time, obtained in static operative conditions, have been used for a qualitative estimation of microwave kinetic parameters 18 with the Avrami method. This method was found to account well for the autocatalytic cure behaviour of an amine-epoxy system [32, 33]. According to Avrami method the degree of cure is calculated with the following equation: α =1− e −ktp (3.29) The derivative form of Avrami equation is given below: dα dt = e−ktp pkt (p−1) (3.30) The Avrami parameters k and p are easily obtained through graphical analysis of the experimental degree of cure versus reaction time data by plotting log [−ln (1 − α)] versus log t. The slope of the line is equal to p and the “yintercept” is equal to log k according to the relationship 3.31: log [−ln (1 − α)] = log k + p log t (3.31) With the data obtained through experiments at 1500 W an example of this graphical analysis is illustrated in Figure 3.36. 18 Activation energy E a and the pre-exponential factor k 0 . 141
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UNIVERSITA’ DEGLI STUDI DI NAPOLI
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3 I thank all the lecturers of PhD
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5 Microwaves are electromagnetic ra
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CONTENTS 7 1.8.1 DielectricProperti
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CONTENTS 9 4 Conclusions and Outloo
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LIST OF TABLES 11 3.2 Average value
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List of Figures 1.1 Diglycidylether
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LIST OF FIGURES 15 2.23 Onset tempe
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LIST OF FIGURES 17 3.38 Comparison
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Introduction 19 cannot be melted an
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Introduction 21 • bismaleimides;
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Introduction 23 cold solders, casti
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Introduction 25 Average Properties
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Introduction 27 In Figure 1.4 n can
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Introduction 29 ducts and it genera
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Introduction 31 tween current-carry
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Introduction 33 that describe the p
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Introduction 35 1.3.5 Lorentz Force
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Introduction 37 Figure 1.11: Electr
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Introduction 39 Even microwaves can
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Introduction 41 production requirem
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Introduction 43 fect of the electro
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Introduction 45 following different
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Introduction 47 Debye equations bas
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Introduction 49 Although these mode
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Introduction 51 materials that have
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Chapter 2 Experimental In this chap
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Experimental 55 Characteristic Note
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Experimental 57 If the oven is used
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Experimental 59 In monomodal applic
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Experimental 61 Figure 2.5: Right s
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Experimental 63 Figure 2.8: Front v
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Experimental 65 regardless of the a
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Experimental 67 • The number of t
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Experimental 69 Figure 2.11: Surfac
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Experimental 71 Figure 2.12: Repeti
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Experimental 73 From the Figure 2.1
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Experimental 75 in the centre of th
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Experimental 77 not read the water
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Experimental 79 Test number 1 2 3 4
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Experimental 81 Figure 2.19: Plot o
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Experimental 83 2.5 Datalogger This
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Experimental 85 same reason a wood
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Experimental 87 Material Behaviour
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Page 117 and 118: Results and Discussion 117 Tables 3
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Page 167 and 168: A Brief History of Microwave Oven 1
Page 169 and 170: Bibliography [1] W. Callister, “M
Page 171 and 172: BIBLIOGRAPHY 171 [19] P. I. Karkana
Page 173: BIBLIOGRAPHY 173 [34] K. D. V. Pras
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Kinetic Analysis and Characterization of Epoxy Resins ... - FedOA

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