Degradation and Characterization of Recycling Carbon Fiber/Epoxy Resin Composites in Supercritical n-Butanol†

doi:10.7503/cjcu20170037

Abstract

Abstract:

Recycling carbon fibers from carbon fiber/epoxy resin(CF/EP) composites using supercritical n-butanol were reported. The quantitative relationship between the degradation rate of epoxy resin and recycling process parameters was proposed through response surface methodology. The influence of process parameters on the degradation rate of epoxy resin was investigated by graphical optimization. Besides, the microstructure, the graphitization degree, the surface chemistry and the mechanical properties of the recycled carbon fibers were analyzed by scanning elcetron microscopy(SEM), atomic force microscopy(AFM), X-ray photoelectron spectrometry(XPS), Raman spectrum and single-filament tensile strength testing. The results show that the error between the actual and the theoretical degradation rate is within ±5.5%, and the reaction temperature has the greatest impact on the degradation rate of epoxy resin, followed by the reaction time, KOH concentration and n-butanol volume. Given the optimal process parameters(i.e., reaction temperature at 330 ℃, reaction time at 60 min, KOH concentration at 0.0538 mol/L, and feed ratio at 0.024 g/mL), there were no residual resin and graphitization on the surface of the recycled carbon fibers; the average roughness(R_a) and O/C ratio showed little change comparing with those of the original carbon fibers; and the average tensile strength and Young’s modulus were about 93.58% and 94.87% of those of the original carbon fibers, respectively.

Key words: Supercritical n-butanol, Degradation, Recycling carbon fibe, Carbon fiber/epoxy resin(CE/EP) composite

CLC Number:

O633.13
O69

TrendMD:

HUANG Haihong, ZHANG Baoyu, ZHAO Zhipei. Degradation and Characterization of Recycling Carbon Fiber/Epoxy Resin Composites in Supercritical n-Butanol^†[J]. Chem. J. Chinese Universities, 2017, 38(9): 1687.

Figures/Tables 15

Fig.1 CF/EP before degradation and products after degradation(A) CF/EP before degradation; (B) solid residue of CF/EP after degradation; (C) liquid residue of CF/EP after degradation.

Table 1 Process parameters and levels

Code	Process parameter	Level
Code	Process parameter	-2	-1	0	1	2
A	Reaction temperature/℃	290	300	310	320	330
B	Holding time/min	20	30	40	50	60
C	c_KOH/(mol·L^-1)	0.02	0.03	0.04	0.05	0.06
D	V(n-Butanol)/mL	400	425	450	475	500

Table 2 Analysis of variance for established mathematical model

Source	Sum of squares	Degree of freedom	F-value	P-value>F-value	Significance
Relation	0.066	12	19.53	<0.0001	Significant
A	4.773×10^-3	1	16.87	0.0007	Significant
B	0.011	1	38.60	<0.0001	Significant
C	5.367×10^-3	1	18.97	0.0004	Significant
D	6.055×10^-4	1	2.14	0.1608	Significant
AC	1.830×10^-3	1	6.47	0.0204	Significant
CD	4.442×10^-4	1	1.57	0.2263	Not significant
B²	3.353×10^-3	1	11.85	0.0029	Significant
C²	1.273×10^-3	1	4.50	0.0480	Significant
BCD	1.051×10^-3	1	3.72	0.0698	Not significant
A²B	4.726×10^-3	1	16.70	0.0007	Significant
A²D	1.287×10^-3	1	4.55	0.0470	Significant
AB²	2.735×10^-3	1	9.66	0.0061	Significant
Residual	5.093×10^-3	18
Lack of fit	4.109×10^-3	12	2.09	0.1884	Not significant
Pure error	9.843	6

Table 3 Experiments of process parameters to verify the mathematical model

No.	Reactor temperature/℃	Holding time/min	Additive concentration/ (mol·L^-1)	V(n-Butanol)/ mL	Actual degradation rate(%)	Theoretical degradation rate(%)	Error (%)
1	330	40	0.04	443	98.82	99.20	-0.38
2	300	50	0.04	450	91.19	88.90	2.58
3	320	20	0.04	500	92.98	98.34	-5.45
4	330	60	0.03	430	99.59	101.50	-1.91
5	310	50	0.05	430	97.23	96.98	0.25
6	300	60	0.04	500	80.12	77.94	-2.18

Fig.2 Effect of different process parameters on degradation rate(A) t=40 min, c=0.04 mol/L; (B) temperature=310 ℃, L= 450 mL; (C) c=0.04 mol/L, L= 450 mL;(D) t=40 min, temperature=310 ℃.

Table 4 Experiments under the optimal process parameters

No.	Reaction temperature/℃	Holding time/ min	c(Additive)/ (mol·L^-1)	V(n-Butanol)/ mL	Actual degradation rate(%)	Theoretical degradation rate(%)
1	330	60	0.0538	413	100.69	100.00
2	330	60	0.0538	413	98.17
3	330	60	0.0538	413	99.50
4	330	60	0.0538	413	98.71
5	330	60	0.0538	413	100.40
6	330	60	0.0538	413	99.87

Fig.3 SEM images of the surfaces of original carbon fibers(A) and recycled carbon fibers(B)

Fig.4 AFM images of the surfaces of original carbon fibers(A) and recycled carbon fibers(B)

Fig.5 Raman spectra of original carbon fibers(a) and recycled carbon fibers(b)

Fig.6 XPS spectrum of original carbon fibers(A) and peaks fitting(B)

Fig.7 XPS spectrum of recycled carbon fibers(A) and peaks fitting(B)

Table 5 Elemental composition of carbon fibers from XPS spectra

Species	C(%)	O(%)	N(%)	Si(%)	K(%)	O/C
Original carbon fiber	77.96	20.29	1.09	0.66	0	0.260
Recycled carbon fiber	78.46	16.70	1.86	1.71	1.27	0.213

Table 6 Oxygen functional groups of carbon fibers from XPS spectra

Species	Comporition(%)
Species	C—C	C—OH	C O	COOH	C $O 3 2 -$
Original carbon fiber	67.93	29.13	1.45	0.48	0.99
Recycled carbon fiber	33.76	44.74	18.74	1.23	1.53

Table 6 Oxygen functional groups of carbon fibers from XPS spectra

Species	Comporition(%)
Species	C—C	C—OH	C O	COOH	C $O 3 2 -$
Original carbon fiber	67.93	29.13	1.45	0.48	0.99
Recycled carbon fiber	33.76	44.74	18.74	1.23	1.53

Fig.8 Tensile strength of original carbon fibers and recycled carbon fibers

Fig.9 Young’s modulus of original carbon fibers and recycled carbon fibers

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