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

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Chapter 4 Conclusions and Outlook Epoxies are the most promising thermosetting resins. These polymers have many industrial applications because after curing they possess excellent mechanical, electrical and chemical properties. However the conventional polymerization process involves time of several hours and elevated temperature, resulting in remarkable production costs. The work reported here illustrates the appealing advantages of the alternative microwave heating technology 1 in term of higher efficiency, shortening processing time, energy saving, more uniform cure and improving physical-mechanical properties. The kinetic parameters in microwave field have been qualitatively estimated, using the Avrami method, and compared with those, calculated through analysis of isothermal DSC. A remarkable decrease of the activation energy has been observed. Moreover the existence of the “specific microwave effect” has been verified, comparing the partial degree of conversion, after the same reaction time in MW and DSC cure processes, undergoing similar thermal profiles. In all the cases the 1 This heating mechanism is suitable for epoxy resins, because they contain polar functional groups. 162
Conclusions and Outlook 163 degree of cure in MW field is always much higher than the corresponding conversion achieved in DSC, and the time required for a complete polymerization of the epoxy resin is considerably lower when the system is heated with microwave radiations. Therefore, the claim of an acceleration of the reaction rate, due to the effect of the electromagnetic field 2 , can be supported. Moreover, samples microwave cured show better thermo-mechanical properties. In particular, the glass transition temperature, dynamic storage modulus and flexural elastic modulus of samples crosslinked, using both the heating mechanisms, have been measured and compared among them. An increase of the strength of the 3-D epoxy network for samples microwave cured has been noticed. As verified, through FT-IR and FT-NIR analysis, spectra of samples conventionally and microwave cured are very similar and no residual reagents, epoxies or amines, have been found in the resin cured in both the way. Finally the possible microwave heatability of non polar polymers 3 , through incorporation of suitable organic and metallic sensitizers, has been preliminarily investigated. According to these results and considerations the microwave curing process of epoxy systems can be considered a valid alternative for the polymerization of this thermosetting resin. 4.1 Outlook Further information on the cure kinetic of the epoxy resin heated in both the way can be obtained through a spectroscopic analysis. Besides the development of a microwave calorimeter can allow the performance of isothermal microwave cure and the measurement of the specific heat flow during the process. In this way 2 Not simply explainable with differences of the thermal profile. 3 Electromagnetically insensitive. 163
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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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Experimental 89 in function of the
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Experimental 91 2.6.3 Influence of
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Chapter 3 Results and Discussion Th
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Results and Discussion 95 There is
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Results and Discussion 97 Figure 3.
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Results and Discussion 99 Parameter
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Results and Discussion 101 After pr
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Results and Discussion 103 of insta
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Results and Discussion 105 1. Mecha
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Results and Discussion 107 where k
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Results and Discussion 109 Kinetic
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Page 117 and 118: Results and Discussion 117 Tables 3
Page 123 and 124: Results and Discussion 123 t MW [s]
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Page 165 and 166: Appendix A A Brief History of Micro
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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