Lab Report: Curing Kinetics of Epoxy Nanocomposites

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Abstract

This lab report investigates the curing kinetics of epoxy nanocomposites with varying concentrations of graphene flakes.

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Differential Scanning Calorimetry (DSC) was used to analyze the curing process under non-isothermal conditions at different heating rates. The results indicate that the presence of graphene significantly influences the curing behavior, affecting temperature profiles, heat generation, and activation energy. The findings have implications for the processing and properties of epoxy nanocomposites.

Introduction

In this study, we explore the curing kinetics of epoxy nanocomposites with the addition of graphene flakes. Curing kinetics are crucial for understanding the curing process, including conversion, reaction rate, and activation energy, which, in turn, affect the final properties of the nanocomposites.

Experimental Procedure

The epoxy nanocomposites were prepared with different concentrations of graphene flakes (0.5 wt%, 5 wt%, 10 wt%, and 20 wt%). The curing kinetics were analyzed using Differential Scanning Calorimetry (DSC) under non-isothermal conditions at various heating rates (2°C/min, 5°C/min, 10°C/min, and 20°C/min). Characteristic temperatures of the curing process, exothermic heat of curing, and degree of curing were measured using DSC.

Results

Characteristic Temperatures

The characteristic temperatures of the curing process at different heating rates are presented in Table 1. As the heating rate increased, the T_peak-1 and T_peak-2 values also increased for all graphene concentrations, indicating a shift to higher temperatures as heating rate increased.

Graphene Flakes (wt%)	Heating Rate β (°C/min)	Tinit (°C)	Tfinal (°C)	Tfinal-Tint (°C)	ΔΤ (°C)	Tpeak-1 (°C)	Tpeak-2 (°C)	Shoulder Area1 (JK/sg)	ΔH1ult (J/g)	Area2 (JK/sg)	ΔH2ult (J/g)	FWHM1
2	18.49	261.14	243.65	81.53	108.30	7.57	3.78	3.43	1.715	28.47	27.64	5
5	20.38	270.99	250.61	97.85	128.53	22.33	4.466	10.29	2.058	32.44	42.56
10	27.63	283.58	255.95	108.83	147.13	34.76	3.476	13.08	1.308	43.97	34.74
20	35.78	288.21	252.43	129.89	171.59	82.49	4.124	30.82	1.541	43.86	45.09
0.5	2	17.85	278.45	260.6	82.78	108.12	6.89	3.445	3.24	1.62	24.72	25.69
5	20.31	274.35	254.04	90.36	121.72	17.05	3.411	9.90	1.98	37.53	44.53
10	21.27	285.15	263.88	112.16	148.97	46.78	4.678	16.04	1.604	39.64	37.46
20	30.52	292.47	261.95	123.66	168.15	72.83	3.641	32.64	1.632	44.05	52.89
1.5	2	15.38	270.31	254.93	76.47	104.88	5.34	2.67	3.58	1.79	33.95	32.69
5	19.83	286.11	266.28	94.48	127.75	18.49	3.698	9.33	1.866	38.58	39.73
10	23.32	286.79	263.47	110.45	147.69	48.93	4.893	19.55	1.955	41.17	42.71
20	30.09	285.77	255.68	129.88	171.37	103.63	5.18	34.48	1.724	43.84	45.69

Exothermic Heat of Curing and Degree of Curing

The exothermic heat of curing (ΔH) and the degree of curing (α) for different heating rates and graphene concentrations are summarized in Table 2. The ΔH values slightly decrease as the heating rate increases, indicating that ΔH is almost independent of the heating rate.

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The presence of graphene lowers ΔH, suggesting that the epoxy matrix in the nanocomposites has a lower cross-linking degree compared to neat DGEBA-DDM thermoset.

Graphene Flakes (wt%)	Heating Rate β [°C/min]	ΔH1ult [J/g]	ΔH1ult [kJ/mol]*	ΔH2ult [J/g]	ΔH2ult [kJ/mol]*	Degree of curing (α1)	Degree of curing (α2)
2	3.78	0.6804	1.715	0.3087	0.0081	0.0023	0.0104
5	4.466	0.8038	2.058	0.3704	0.0096	0.0028	0.0124
10	3.476	0.6256	1.308	0.2354	0.0075	0.0017	0.0092
20	4.124	0.7423	1.541	0.2773	0.0089	0.0021	0.011
0.5	3.445	0.6201	1.62	0.2916	0.0074	0.0022	0.0096
5	3.411	0.6139	1.98	0.3564	0.0073	0.0027	0.01
10	4.678	0.8420	1.604	0.2887	0.0101	0.0022	0.0123
20	3.641	0.6553	1.632	0.2937	0.0078	0.0022	0.01
1.5	2	0.4806	1.79	0.3222	0.0057	0.0024	0.0081
5	3.698	0.6656	1.866	0.3358	0.0080	0.0025	0.0105
10	4.893	0.8807	1.955	0.3519	0.0106	0.0026	0.0132
20	5.18	0.9324	1.724	0.3103	0.0112	0.0023	0.0135

Activation Energy

The activation energy (Ea) values for different graphene concentrations and heating rates are presented in Table 3. Ea was calculated using the Arrhenius equation, ln(β/T_peak^2), and 1/T_peak. The data show that the presence of graphene significantly affects the activation energy, with lower Ea values observed for nanocomposites compared to pure resin.

Graphene Flakes (wt%)	Heating Rate β [°C/min]	Tpeak-1 [°C]	ln(β/ Tpeak-1^2) [°K]	1/ Tpeak-1 [°K]	Tpeak-2 [°C]	ln(β/ Tpeak-2^2) [°K]	1/ Tpeak-2 [°K]	Ea1 [kJ/mol]	Ea2 [kJ/mol]
2	81.53	-11.04	0.002818	108.30	-11.19	0.002621	-51.09± 4.74	-44.70 ± 2.418	-95.7 ± 7.15
5	97.85	-10.22	0.002695	128.53	-10.38	0.002489
10	108.83	-9.58	0.002617	147.13	-9.77	0.002379
20	129.89	-9.00	0.002481	171.59	-9.19	0.002248
0.5	82.78	-11.05	0.002809	108.12	-11.19	0.002622	-53.20± 9.5	-43.59 ± 5.18	-96.7 ± 14.68
5	90.36	-10.18	0.002750	121.72	-10.34	0.002532
10	112.16	-9.60	0.002595	148.97	-9.78	0.002368
20	123.66	-8.97	0.002520	168.15	-9.18	0.002266
1.5	76.47	-11.02	0.002860	104.88	-11.17	0.002645	-44.38± 1.57	-41.62± 0.90	-86 ±2.47
5	94.48	-10.20	0.002720	127.75	-10.37	0.002494
10	110.45	-9.59	0.002606	147.69	-9.78	0.002376
20	129.88	-9.00	0.002481	171.37	-9.19	0.002249

Rate Constants

Rate constants (k1 and k2) and their ratios (k1/k2) at different temperatures are presented in Table 4. These constants provide insights into the reaction kinetics and how they change with temperature and graphene concentration.

T/K	k1/s-1x105	k2/s-1x105	k1/k2
298.15	308.15	318.15	328.15	338.15	348.15	358.15	368.15	378.15	388.15	398.15
50	7.20	187.56	36.88	1399.53	38.22	70	90	0.5
50	70	90	1.5

Discussion

The results obtained in this study align with previous research, indicating that the addition of graphene to epoxy nanocomposites affects their curing kinetics significantly. The shift in characteristic temperatures (T_peak-1 and T_peak-2) towards higher values with increasing heating rates is consistent with the literature[1]. The decrease in ΔH as the heating rate increases suggests that graphene hinders the epoxy-amine reaction, resulting in less perfect networks in the nanocomposites[2]. The activation energy values show that the presence of graphene reduces the energy required for the curing reaction, indicating improved catalytic effects[5].

Conclusion

This study has provided valuable insights into the curing kinetics of epoxy nanocomposites with graphene flakes. The presence of graphene affects the temperature profiles, heat generation, and activation energy of the curing process. These findings have significant implications for the processing and properties of epoxy nanocomposites, making them a promising area for further research and development.

Lab Report: Curing Kinetics of Epoxy Nanocomposites. (2024, Jan 12). Retrieved from https://studymoose.com/document/lab-report-curing-kinetics-of-epoxy-nanocomposites