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Effect of polyetherimide nanoparticle coating on the interfacial shear strength between carbon fiber and thermoplastic resins
Journal Pre-proofs Full Length Article Effect of polyetherimide nanoparticle coating on the interfacial shear strength between carbon fiber and thermoplastic resins Peng Zhu, Jian Shi, Limin Bao PII: DOI: Reference:
S0169-4332(20)30151-3 https://doi.org/10.1016/j.apsusc.2020.145395 APSUSC 145395
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Applied Surface Science
Received Date: Revised Date: Accepted Date:
22 August 2019 24 December 2019 13 January 2020
Please cite this article as: P. Zhu, J. Shi, L. Bao, Effect of polyetherimide nanoparticle coating on the interfacial shear strength between carbon fiber and thermoplastic resins, Applied Surface Science (2020), doi: https://doi.org/ 10.1016/j.apsusc.2020.145395
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1
Effect of polyetherimide nanoparticle coating on the interfacial shear strength
2
between carbon fiber and thermoplastic resins
3
Peng Zhua,b,*, Jian Shic, Limin Baob
4
a
5
310018, China
6
b
7
Tokida, Ueda, Nagano 386-8567, Japan
8
c
9
Akita Prefectural University, 84-4, Ebinokuchi, Tsuchiya Aza, Yurihonjo, Akita,
College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou, Zhejiang
Department of Bioscience and Textile Technology, Shinshu University, 3-15-1
Department of Mechanical Engineering, Faculty of Systems Science and Technology,
10
015-0055, Japan
11
* Corresponding author: [email protected]
12
Abstract
13
A polyetherimide (PEI) nanoparticle coating was prepared on carbon fiber (CF) surface
14
by an evaporation induced surface modification, which was confirmed by scanning
15
electron
16
nanoparticles were not perfectly spherical, but were pie shaped as observed by field
17
emission scanning electron microscopy. Thus, the PEI nanoparticles were adsorbed on
18
the CF surface instead of accumulating on the CF surface. To understand the effect of
19
PEI nanoparticles on the interfacial shear strength between CF and thermoplastic resins,
20
CF with a PEI nanoparticle coating was heated to melt the PEI nanoparticles. In
21
addition to the desized CF, these three samples were used as reinforcements and some
22
widely used engineering thermoplastic resins. The single filament fragmentation test
23
was employed to assess the interfacial shear strength with an improved sample
24
preparation process. The results show that the introduction of PEI coating increased the
microscopy
and
Fourier-transform
1
infrared
spectrometer.
The
PEI
25
interfacial shear strength between CF and the thermoplastic resins mentioned above,
26
especially the surface of the PEI coating used a nanoparticle morphology. In
27
combination with the hot-bonding experiments, the compatibility of thermoplastic
28
resins and PEI coating was shown to influence interfacial shear strength, but it was not
29
the main factor.
30
Keywords: Carbon fiber; Polyetherimide nanoparticle; Coating; Interfacial shear
31
strength; Thermoplastic resin
32
1. Introduction
33
Carbon fiber (CF) has been widely used to reinforce thermosetting or thermoplastic
34
matrices because of its high strength and low weight [1]. CF reinforced thermoplastics
35
(CFRTPs) are ideal structural materials in a variety of fields, such as the automotive,
36
electronics, and aerospace fields, due to their superior mechanical properties, good
37
processability, and good recyclability [2].
38
The mechanical properties of CFRTPs are influenced by many factors, such as the
39
interfacial property between fiber and matrix, and the aspect ratio and volume content of
40
the fiber [3]. A strong interaction between CF and the matrix is well known to be the
41
key for its mechanical properties [1]. However, CF exhibits a low adhesion to a
42
thermoplastic matrix because of its smooth and chemically inert surface [4]. In addition,
43
the sizing agent on commercial CF surfaces is mainly designed for thermosetting resins,
44
but is not suitable for thermoplastic matrices, which usually results in poor
45
compatibility and weak interaction between CF and the thermoplastic matrix [5]. In
46
recent decades, numerous methods have been proposed to modify CF to improve the
47
interlocking and interfacial interaction between the fiber and thermoplastic matrix, such
48
as oxidation treatment [2, 6], chemical grafting [5], sizing, or coating [3, 7-9]. Oxidation
49
treatment or chemical grafting led to drawbacks on the CF surface that decrease the 2
50
fiber strength [10, 11]. Among the sizing or coating methods, polymer coatings have
51
received a great deal of attention because of their advantage of enhanced interfacial
52
adhesion and improved toughness at the interface [12]. Luo et al. enhanced the
53
interfacial adhesion between CF and polypropylene (PP) using a graphene
54
oxide/polyethyleneimine coating [3]. Giraud found that PEI and polyetheretherketone
55
(PEEK) sizing can improve the interaction between CF and the PEEK matrix [9].
56
However, Naito found that polyimide (PI)-coated CF shows a similar interfacial shear
57
strength (IFSS) between the fibers and the PI matrix with the as-received CF because of
58
the smooth surface of PI-coated CF [13].
59
Due to its excellent chemical resistance, exceptional thermal stability, and
60
commendable mechanical properties, PEI has been chosen as one of the
61
surface-modification materials in some studies [9, 14, 15]. In our previous work, PEI
62
nanoparticles with controllable particle size were prepared on a CF surface via an
63
evaporation induced surface modification method [16]. In this work, the effect of these
64
PEI nanoparticles on the IFSS between CF and thermoplastic resins was studied.
65
In the past three decades, CFRTPs mainly focused on high-performance polymers,
66
such as PEEK [9], polyethersulfone [7, 8] and polyphenylene sulfide [17]. Recently,
67
studies have focused on the interfacial property of CFRTPs, in which the matrices were
68
widely used engineering thermoplastic resins, such as PP [3, 5], polyamide-6 (PA6)
69
[17], and polycarbonate (PC) [2]. In this work, some widely used engineering
70
thermoplastic resins, such as polyvinyl chloride (PVC), PC, PA6, PP, polyamide-66
71
(PA66), and PEI were used as the matrix to observe the IFSS between CF and the
72
matrices, respectively. The single filament fragmentation test (SFFT) was used to assess
73
the IFSS between CF and thermoplastic resins. To study the effect of PEI nanoparticles
74
on IFSS, the PEI-coated CF (PEI@CF) was heated to melt the PEI nanoparticles, which 3
75
was used for another comparison (named H-PEI@CF) in addition to the desized CF.
76
The chemical composition, surface morphology, and surface roughness of desized CF,
77
PEI@CF, and H-PEI@CF were tested by Fourier-transform infrared spectrometer
78
(FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM),
79
respectively. The single fiber strength of these samples was also tested.
80
2. Experimental
81
2.1. Materials
82
CF (T300, diameter: 7 m) was purchased from Toray (Tokyo, Japan). The pristine
83
CF was washed with acetone for 48 h at room temperature to remove surface sizing
84
agents and/or contaminants. The obtained fiber was denoted as desized CF.
85
polyetherimide (PEI, melt index 9 g/10 min [337 °C/6.6 kg]) and PP (isotactic, average
86
Mw ~250,000, average Mn ~67,000) were supplied by Sigma-Aldrich (St Louis, MO,
87
USA) and N-methyl-2-pyrrolidone (NMP) was supplied by Kanto (Tokyo, Japan). PC,
88
PVC, PA6, and PA66 sheets were purchased from Rigaku (Tokyo, Japan), the thickness
89
of these sheets was listed in Table 1. All chemicals were used as received.
90
2.2 Preparation of PEI-coated CF
91
PEI particles (0.2056 g) were dissolved in NMP (100 mL) at 70 °C for 2 h to produce
92
a diluted PEI solution. A bundle of the desized CF was immersed in NMP for 15 min,
93
after which the CF surface was well-infiltrated with the solvent. In addition, adsorption
94
of NMP on the surface helped to transfer the solute from regions of high concentration
95
to regions of low concentration in the subsequent treatment. The PEI solution with the
96
NMP-infiltrated CF was then sonicated (300 W, 38 kHz) in an ice bath for 20 min (the
97
sonicated CF was obtained if there were no follow-up treatments) and allowed to stand
98
for 24 h. Finally, the pretreated CF bundle was placed on a Teflon plate in a fume hood 4
99
at room temperature for 1 week. The coated CF (PEI@CF) was obtained after
100
evaporating the solvent completely. The PEI@CF was heated to melt the PEI
101
nanoparticles to produce H-PEI@CF, which was used for another comparison in
102
addition to the desized CF. Fig. 1 shows the schematics of the preparation process.
103
2.3 Preparation of PP and PEI sheets
104
A certain amount of PP or PEI particles were put into a self-made mold and then the
105
PP or PEI sheet could be obtained after hot pressing and cooling. The thickness of the
106
PP or PEI sheet was controlled at 0.2 mm.
107
2.4 Characterizations
108
The surface morphologies of CFs were examined using SEM (VE-9800; Keyence,
109
Tokyo, Japan) and field emission scanning electron microscopy (FE-SEM, S4800;
110
Hitachi, Tokyo, Japan). Their surface chemical compositions were probed by FTIR. The
111
FTIR absorption spectra were recorded between 2000 and 1000 cm−1 using a Shimadzu
112
FTIR (IR Prestige-21 infrared spectrometer; Shimadzu, Kyoto, Japan). The surface
113
roughness was also observed by AFM (SPA-400-AFM; Seiko, Tokyo, Japan). A single
114
CF was fastened on a steel sample mount and a tapping mode was used to scan the fiber
115
surface. Roughness analysis was performed on images obtained over 4 4 m using the
116
instrument software (SPIWin). Single fiber tensile strength tests were performed using a
117
tensile tester (EZ-SX; Shimadzu) with a strain rate of 1 mm/min at 20 °C and a relative
118
humidity of 65%. At least 35 specimens were tested for each sample.
119
SFFT was used to study the interfacial properties between CFs and thermoplastic
120
resins. The dogbone samples were fixed to a microtension device. The measurement
121
under a tensile load was taken at a speed of 0.1 mm/min. During the test, entire single
122
filament fragmentation was monitored by optical microscope and the number of fiber
5
123
fragmentations was counted within the 26-mm gauge length. Five specimens were
124
tested for each sample.
125
When the length of fiber fragmentation becomes too short to effectively transfer load
126
from the matrix, the number of fractures will no longer increase with increasing stress.
127
The number of fractures was used to calculate the critical fracture length and IFSS by
128
the follow equations [18]: 𝛿𝑓𝑑𝑓
129
τIFSS =
130
4 𝑙𝑐 = 𝑙𝑎𝑣𝑒𝑟𝑎𝑔𝑒 3
131
where τIFSS, interfacial shear strength; δf, single fiber tensile strength; df, fiber diameter;
132
lc, critical fiber length; and laverage, average fiber length.
2𝑙𝑐
133
Sample preparation is most difficult in the SFFT, especially when the matrix is
134
thermoplastic resin. The preparation process is completely different from that of
135
thermosetting resin. Some researchers have used the SFFT to study the IFSS between
136
fibers and thermoplastic resins [2, 19–22]. However, there was no mention of two
137
contradictory problems in the sample-preparation process: i.e., bubbles and fiber
138
bending. In this work, CFs were centered sandwich-style lengthwise between two
139
thermoplastic sheets. To keep the fiber straight, the ends of each fiber were fixed on the
140
sheet by tapes and epoxy resin (Fig. 2b). To obtain clean specimens without bubbles, a
141
vacuum hot-press (Fig. 3a) was used to hold the mold. Fig. 3b and c show the
142
hot-pressed samples with and without vacuum at the same temperature. Without
143
vacuum hot-pressing, the sample was filled with bubbles and the edges were oxidized
144
(the color turned yellow). With vacuum hot-pressing, there were almost no bubbles in
145
the sample and no obvious oxidation on the edges. To completely discharge the residual
146
bubbles in the middle of the sheets, a PTFE film (0.05-mm thick) was placed on the 6
147
center of the upper thermoplastic sheet. Fig. 2a shows the self-made mold and the
148
sandwich-preparation process.
149
The mold was then placed in the vacuum hot-press at the appropriate temperature and
150
held at touch pressure for 10 min and then held at a pressure of 4 MPa for 4 min.
151
Finally, the mold was cooled at room temperature. Each rectangular specimen was cut
152
into a dogbone shape (Fig. 2c). The heating time and temperature were determined in
153
auxiliary experiments (Table 1).
154
To identify whether the compatibility of these thermoplastic resins and PEI coating
155
affects the IFSS between CF and thermoplastic resins, a hot-bonding experiment was
156
designed according to ISO 4587-2003 “Adhesives – Determination of tensile lap-shear
157
strength of rigid-to-rigid bonded assemblies.” Hot bonding was used to replace the
158
adhesive. The heating and pressure conditions were the same as in the SFFT to simulate
159
compatibility during sample preparation in the SFFT. The hot-bonding sample was
160
shown in Fig. 4. Identifying the breaking force of different hot-bonding combinations
161
was performed using an INSTRON 3367 tensile tester (Illinois Tool Works, Glenview,
162
IL, USA) with a strain rate of 10 mm/min at 20 °C and a relative humidity of 65%. At
163
least 10 specimens were tested for each sample. In the standard (ISO 4587-2003), the
164
lap shear strength is calculated by dividing the breaking force by the adhesive area. The
165
resin sheets deformed in the hot-bonding process; therefore, the hot-bonding area could
166
not be calculated. Thus, the breaking force was used to roughly express the
167
compatibility of these thermoplastic resins and PEI coatings.
168
3. Results and discussion
169
3.1 Surface chemical composition, morphology, and roughness.
170
FTIR was used to determine the chemical group change in the CF after coating. Fig. 5
171
shows the FTIR spectra of desized CF, PEI@CF, and neat PEI. Almost no obvious 7
172
peaks were detected on the desized CF (Fig. 5a), which could be attributed to the low
173
number of functional groups, low transmittance of black material, and low content of
174
sizing agents [5, 6]. The results of the neat PEI membrane (Fig. 5c) exhibit
175
characteristic absorption bands at 1772 cm−1, 1710 cm−1 (asymmetric and symmetric
176
C=O stretching vibration, imide band I), 1342 cm−1 (C–N stretching, imide band II) [14,
177
23]. Vibrations at 1259, 1228, 1066, and 1010 cm−1 are due to aryl ether bonds [24]. All
178
these characteristic peaks of PEI also appear in the FTIR spectra of PEI@CF (Fig. 5b),
179
confirming that the PEI was successfully coated on the CF surface. The intensity of the
180
characteristic peaks is weak because of the low PEI contents in the treatment solution.
181
The morphologies of the samples before and after modification were obtained by
182
SEM/FE-SEM (Fig. 6). The surface of desized CF in Fig. 6a is very smooth, but shows
183
some grooves along the fiber axis. Many PEI nanoparticles appeared on the PEI@CF
184
surface after PEI coating (Fig. 6b, c). The average particle diameter measured by
185
measurement software in SEM was 200 nm. Fig. 6f shows the FE-SEM image of
186
PEI@CF from the approximate cross-section direction, which shows that the PEI
187
nanoparticles are not perfect spheres, but are pie shaped. Thus, the PEI nanoparticles
188
were adsorbed on the CF surface instead of accumulating on the CF surface. Some
189
grooves were filled after heating (Fig. 6d, e). The PEI nanoparticles on the surface of
190
PEI@CF completely melted, aggregated together, and formed many irregular flat PEI
191
blocks.
192
AFM was used to characterize the surface morphology and surface roughness of the
193
desized CF, PEI@CF, and H-PEI@CF. The surface of desized CF is relatively neat and
194
smooth (Fig. 7a), leading to a relatively low surface roughness (Ra = 55.04 nm). The
195
surface roughness of PEI@CF obviously increases to 96.95 nm due to the appearance of
196
PEI nanoparticles (Fig. 7b). After heating (Fig. 7c), the roughness of H-PEI@CF (Ra = 8
197
46.14 nm) significantly reduces, even below that of desized CF, because the PEI
198
nanoparticles were melted and many grooves filled with the melted PEI after heating.
199
3.2 Single fiber strength
200
Single fiber tensile strength is usually used to assess the effect of grafting
201
modification on the tensile strength of the fiber. Fig. 8 shows the detailed data. The
202
single fiber tensile strength of the sonicated CF was 3.14 GPa, which means that the
203
tensile strength of CF was still maintained after dipping and sonication. Similarly to
204
previous studies, the addition of PEI coating increases the single fiber strength [25, 26].
205
The introduction of PEI coating on the CF surface could help heal cracks on the fiber
206
surface and reduce stress concentrations, resulting in an improved single fiber tensile
207
strength (3.39 GPa), 7.6% higher than that of desized CF (3.15 GPa). However, after a
208
heating process during which some new defects could be formed, the PEI blocks could
209
cause stress concentrations during fiber stretching; therefore, the strength of H-PEI@CF
210
is lower than that of PEI@CF.
211
3.3 Interfacial shear strength
212
The SFFT results (Fig. 9) indicate that the existence of PEI nanoparticle coating
213
greatly increases the IFSS between CF and all studied thermoplastic resins (i.e., PVC,
214
PC, PA6, PP, PA66, and PEI) by 20.5%, 37.7%, 52.7%, 49.6%, 42.5%, and 58.0%,
215
respectively. The IFSS decreased sharply after the PEI nanoparticles were melted,
216
which indicates that the PEI nanoparticles in the molding process are easier to blend
217
with the thermoplastic resin. On the one hand, this has a great effect on IFSS. On the
218
other hand, the IFSS of the H-PEI@CF sample is still higher than that of the desized CF
219
sample, which was increased by 9.7%, 19.4%, 23.5%, 10.6%, 19.5%, and 20.8%,
220
respectively. The experimental results show that the interfacial property between CF
221
and PVC or PP is very poor. The PEI nanoparticle coating can significantly improve the 9
222
IFSS between CF and PVC or PP, but the IFSS value is still far less than that of other
223
samples.
224
A hot-bonding experiment was designed to explore whether the compatibility of these
225
thermoplastic resins and PEI coating affects the IFSS between CF and thermoplastic
226
resins after introducing PEI coating. The breaking force results of different hot-bonding
227
combinations (Fig. 10.) and the SFFT results indicate that PP has poor compatibility
228
with CF and PEI. The IFSS of PP/PEI@CF, PP/H-PEI@CF and PP/desized CF were not
229
high, but the value of PP/PEI@CF increased due to the presence of PEI nanoparticles.
230
PC and PEI are highly compatible with both CF and PEI; therefore, their enhancement
231
of interfacial strength is obvious after introducing the PEI coating. However, the results
232
of PA66 or PA6 and the results of PVC are the opposite. The compatibility of PVC and
233
PEI is good, but the IFSS is very poor. The compatibility of PA66 or PA6 and PEI is
234
not very good, but the IFSS is very strong. The deformation of PEI coating during the
235
preparation played a significant role. The PEI coating will deform more fully at the
236
temperature condition in PA6 or PA66 composite preparation, but not at the temperature
237
condition in PVC composite preparation. The IFSS results also confirmed that the
238
interface enhancement effect was more significant in the presence of PEI nanoparticles
239
because the nanoparticle coating was more prone to thermal deformation due to its
240
larger specific surface area. Therefore, the compatibility of thermoplastic resins and PEI
241
coating has an impact on the IFSS between CF and thermoplastic resins, but the most
242
important factor is the deformation of PEI coating during sample preparation.
243
Fig. 11 shows a schematic illustration of the cross-section of different CFs and
244
CFRTPs. The breaking force results and the SFFT results indicate that the interfacial
245
property of interface II and interface III/interface III in both PEI@CF and H-PEI@CF
246
samples was better than that of interface I in the desized CF sample. Due to the presence 10
247
of the PEI nanoparticles, the interfacial property of interface III in PEI@CF was better
248
than that of interface III in H-PEI@CF after molding because the PEI nanoparticle
249
coating was more prone to thermal deformation than the PEI coating without PEI
250
nanoparticles.
251
4. Conclusion
252
In this work, a vacuum hot-press, the necessary pressure, and a PTFE film were used to
253
eliminate bubbles and minimize fiber bending in the SFFT between CF and
254
thermoplastic resins. A PEI coating with uniform PEI nanoparticles was formed on the
255
CF surface. The existence of this PEI nanoparticle coating greatly increased the IFSS
256
between CF and all the thermoplastic resins used in this work (i.e., PVC, PC, PA6, PP,
257
PA66, and PEI). The IFSS decreased sharply when the PEI nanoparticles were melted;
258
therefore, the PEI nanoparticles in the molding process were easier to blend with the
259
thermoplastic resins. On the one hand, this has a great effect on the IFSS. On the other
260
hand, the IFSS of the H-PEI@CF sample was still higher than that of the desized CF
261
sample. Therefore, the interfacial property of the two interfaces in both PEI@CF sample
262
and H-PEI@CF sample was better than that of the interface in the desized CF sample.
263
The compatibility of thermoplastic resins and PEI coating has an impact on IFSS
264
between CF and thermoplastic resins, but the most important factor is the deformation
265
of the PEI coating during sample preparation. In conclusion, the PEI coating formed by
266
evaporation induced surface modification can be used as a method to improve the IFSS
267
between CF and thermoplastic resins. The effect is even better if the surface of PEI
268
coating is nanoparticle morphology.
269 270 271 11
272
Acknowledgments
273
This work was supported by the Natural Science Foundation of Zhejiang province,
274
China (Grant No.LQ20E030001) and Research Initiation Fund Project from Zhejiang
275
Sci-Tech University (Grant No.18012278-Y).
276 277
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368
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fiber,
Compos
Sci
377 378
16
Technol.
69
(2009)
1319-1322.
379
Figure legends
380
Fig. 1. Schematic illustration of the preparation of PEI@CF and H-PEI@CF.
381
Fig. 2. (a, b) The fabrication process of the sandwich specimen. (c) The dimensions (in
382
mm) of the dogbone shape specimen.
383
Fig. 3. (a) The vacuum hot-press. (b) A hot-pressed sample without vacuum. (c) A
384
hot-pressed sample with vacuum at the same temperature.
385
Fig. 4. The dimensions (in mm) of the hot-bonding combination.
386
Fig. 5. FTIR spectra of (a) desized CF, (b) PEI@CF, and (c) neat PEI.
387
Fig. 6. SEM images of (a) desized CF; (b, c) PEI@CF; (d, e) H-PEI@CF; and (f)
388
FE-SEM image of PEI@CF from the approximate cross-section direction.
389
Fig. 7. AFM images of (a) desized CF; (b) CF treated with 0.2% PEI; and (c) CF treated
390
with 0.2% PEI after heating for 40 min at 260 °C.
391
Fig. 8. Single fiber tensile strength of desized CF, PEI@CF, and H-PEI@CF.
392
Fig. 9. IFSS between CF and thermoplastic resins.
393
Fig. 10. Breaking force of different hot-bonding combinations.
394
Fig. 11. Schematic illustration of the cross-section of different CFs and CFRTPs.
395 396
397
Table legend
398
Table 1. Heating time and temperature in the sandwich preparation process.
399 400 401 402 403 17
404 405
Fig. 1. Schematic illustration of the preparation of PEI@CF and H-PEI@CF.
406
407 408
Fig. 2. (a, b) The fabrication process of the sandwich specimen. (c) The dimensions (in
409
mm) of the dogbone shape specimen. 18
410 411
Fig. 3. (a) The vacuum hot-press. (b) A hot-pressed sample without vacuum. (c) A
412
hot-pressed sample with vacuum at the same temperature.
413 414
415 416
Fig. 4. The dimensions (in mm) of the hot-bonding combination.
417
19
418 419
Fig. 5. FTIR spectra of (a) desized CF, (b) PEI@CF, and (c) neat PEI.
420 421 422
20
423 424
Fig. 6. SEM images of (a) desized CF; (b, c) PEI@CF; (d, e) H-PEI@CF; and (f)
425
FE-SEM image of PEI@CF from the approximate cross-section direction.
426 427
21
428 429
Fig. 7. AFM images of (a) desized CF; (b) CF treated with 0.2% PEI; and (c) CF treated
430
with 0.2% PEI after heating for 40 min at 260 °C.
431
432 433
Fig. 8. Single fiber tensile strength of desized CF, Sonicated CF, PEI@CF and
434
H-PEI@CF.
435
22
436 437
Fig. 9. IFSS between CF and thermoplastic resins.
438
439 440
Fig. 10. Breaking force of different hot-bonding combinations. 23
441 442
Fig. 11. Schematic illustration of the cross-section of different CFs and CFRTPs.
443 444
Table 1. Heating time and temperature in the sandwich preparation process. Process conditions Sample Step 1
Step 2
PVC (0.3 mm)
180 °C, 0 MPa，10 Min 180 °C,4 MPa，4 Min
PC (0.5 mm)
215 °C, 0 MPa，10Min 215 °C, 4 MPa，4 Min
PA6 (0.3 mm)
220 °C, 0 MPa，10Min 220 °C, 4 MPa，4 Min
PP (0.2 mm)
250 °C, 0 MPa，10Min 250 °C,4 MPa，4 Min
PA66 (0.3 mm)
260 °C, 0 MPa，10Min 260 °C, 4 MPa，4 Min
PEI (0.2 mm)
340 °C, 0 MPa，10 Min 340 °C, 4 MPa，4 Min
Step 3
Cooling down in room temperature
445 446 447 448 24
without pressure.
Highlights
Polyetherimide coating with nanoparticle morphology was prepared on CF surface. Evaporation-induced surface modification was used as the surface treatment method. This method increased the interfacial shear strength between CF and thermoplastics. This nanoparticle morphology had a great influence on the interfacial property.
Graphical Abstract
Author statement
Peng Zhu: Corresponding author, Conceptualization, Methodology, Experiment, Data curation, Writing- Original draft preparation. Jian Shi: Reviewing and Editing. Limin Bao: Reviewing and Editing.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0169-4332(20)30151-3 https://doi.org/10.1016/j.apsusc.2020.145395 APSUSC 145395
To appear in:
Applied Surface Science
Received Date: Revised Date: Accepted Date:
22 August 2019 24 December 2019 13 January 2020
Please cite this article as: P. Zhu, J. Shi, L. Bao, Effect of polyetherimide nanoparticle coating on the interfacial shear strength between carbon fiber and thermoplastic resins, Applied Surface Science (2020), doi: https://doi.org/ 10.1016/j.apsusc.2020.145395
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© 2020 Published by Elsevier B.V.
1
Effect of polyetherimide nanoparticle coating on the interfacial shear strength
2
between carbon fiber and thermoplastic resins
3
Peng Zhua,b,*, Jian Shic, Limin Baob
4
a
5
310018, China
6
b
7
Tokida, Ueda, Nagano 386-8567, Japan
8
c
9
Akita Prefectural University, 84-4, Ebinokuchi, Tsuchiya Aza, Yurihonjo, Akita,
College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou, Zhejiang
Department of Bioscience and Textile Technology, Shinshu University, 3-15-1
Department of Mechanical Engineering, Faculty of Systems Science and Technology,
10
015-0055, Japan
11
* Corresponding author: [email protected]
12
Abstract
13
A polyetherimide (PEI) nanoparticle coating was prepared on carbon fiber (CF) surface
14
by an evaporation induced surface modification, which was confirmed by scanning
15
electron
16
nanoparticles were not perfectly spherical, but were pie shaped as observed by field
17
emission scanning electron microscopy. Thus, the PEI nanoparticles were adsorbed on
18
the CF surface instead of accumulating on the CF surface. To understand the effect of
19
PEI nanoparticles on the interfacial shear strength between CF and thermoplastic resins,
20
CF with a PEI nanoparticle coating was heated to melt the PEI nanoparticles. In
21
addition to the desized CF, these three samples were used as reinforcements and some
22
widely used engineering thermoplastic resins. The single filament fragmentation test
23
was employed to assess the interfacial shear strength with an improved sample
24
preparation process. The results show that the introduction of PEI coating increased the
microscopy
and
Fourier-transform
1
infrared
spectrometer.
The
PEI
25
interfacial shear strength between CF and the thermoplastic resins mentioned above,
26
especially the surface of the PEI coating used a nanoparticle morphology. In
27
combination with the hot-bonding experiments, the compatibility of thermoplastic
28
resins and PEI coating was shown to influence interfacial shear strength, but it was not
29
the main factor.
30
Keywords: Carbon fiber; Polyetherimide nanoparticle; Coating; Interfacial shear
31
strength; Thermoplastic resin
32
1. Introduction
33
Carbon fiber (CF) has been widely used to reinforce thermosetting or thermoplastic
34
matrices because of its high strength and low weight [1]. CF reinforced thermoplastics
35
(CFRTPs) are ideal structural materials in a variety of fields, such as the automotive,
36
electronics, and aerospace fields, due to their superior mechanical properties, good
37
processability, and good recyclability [2].
38
The mechanical properties of CFRTPs are influenced by many factors, such as the
39
interfacial property between fiber and matrix, and the aspect ratio and volume content of
40
the fiber [3]. A strong interaction between CF and the matrix is well known to be the
41
key for its mechanical properties [1]. However, CF exhibits a low adhesion to a
42
thermoplastic matrix because of its smooth and chemically inert surface [4]. In addition,
43
the sizing agent on commercial CF surfaces is mainly designed for thermosetting resins,
44
but is not suitable for thermoplastic matrices, which usually results in poor
45
compatibility and weak interaction between CF and the thermoplastic matrix [5]. In
46
recent decades, numerous methods have been proposed to modify CF to improve the
47
interlocking and interfacial interaction between the fiber and thermoplastic matrix, such
48
as oxidation treatment [2, 6], chemical grafting [5], sizing, or coating [3, 7-9]. Oxidation
49
treatment or chemical grafting led to drawbacks on the CF surface that decrease the 2
50
fiber strength [10, 11]. Among the sizing or coating methods, polymer coatings have
51
received a great deal of attention because of their advantage of enhanced interfacial
52
adhesion and improved toughness at the interface [12]. Luo et al. enhanced the
53
interfacial adhesion between CF and polypropylene (PP) using a graphene
54
oxide/polyethyleneimine coating [3]. Giraud found that PEI and polyetheretherketone
55
(PEEK) sizing can improve the interaction between CF and the PEEK matrix [9].
56
However, Naito found that polyimide (PI)-coated CF shows a similar interfacial shear
57
strength (IFSS) between the fibers and the PI matrix with the as-received CF because of
58
the smooth surface of PI-coated CF [13].
59
Due to its excellent chemical resistance, exceptional thermal stability, and
60
commendable mechanical properties, PEI has been chosen as one of the
61
surface-modification materials in some studies [9, 14, 15]. In our previous work, PEI
62
nanoparticles with controllable particle size were prepared on a CF surface via an
63
evaporation induced surface modification method [16]. In this work, the effect of these
64
PEI nanoparticles on the IFSS between CF and thermoplastic resins was studied.
65
In the past three decades, CFRTPs mainly focused on high-performance polymers,
66
such as PEEK [9], polyethersulfone [7, 8] and polyphenylene sulfide [17]. Recently,
67
studies have focused on the interfacial property of CFRTPs, in which the matrices were
68
widely used engineering thermoplastic resins, such as PP [3, 5], polyamide-6 (PA6)
69
[17], and polycarbonate (PC) [2]. In this work, some widely used engineering
70
thermoplastic resins, such as polyvinyl chloride (PVC), PC, PA6, PP, polyamide-66
71
(PA66), and PEI were used as the matrix to observe the IFSS between CF and the
72
matrices, respectively. The single filament fragmentation test (SFFT) was used to assess
73
the IFSS between CF and thermoplastic resins. To study the effect of PEI nanoparticles
74
on IFSS, the PEI-coated CF (PEI@CF) was heated to melt the PEI nanoparticles, which 3
75
was used for another comparison (named H-PEI@CF) in addition to the desized CF.
76
The chemical composition, surface morphology, and surface roughness of desized CF,
77
PEI@CF, and H-PEI@CF were tested by Fourier-transform infrared spectrometer
78
(FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM),
79
respectively. The single fiber strength of these samples was also tested.
80
2. Experimental
81
2.1. Materials
82
CF (T300, diameter: 7 m) was purchased from Toray (Tokyo, Japan). The pristine
83
CF was washed with acetone for 48 h at room temperature to remove surface sizing
84
agents and/or contaminants. The obtained fiber was denoted as desized CF.
85
polyetherimide (PEI, melt index 9 g/10 min [337 °C/6.6 kg]) and PP (isotactic, average
86
Mw ~250,000, average Mn ~67,000) were supplied by Sigma-Aldrich (St Louis, MO,
87
USA) and N-methyl-2-pyrrolidone (NMP) was supplied by Kanto (Tokyo, Japan). PC,
88
PVC, PA6, and PA66 sheets were purchased from Rigaku (Tokyo, Japan), the thickness
89
of these sheets was listed in Table 1. All chemicals were used as received.
90
2.2 Preparation of PEI-coated CF
91
PEI particles (0.2056 g) were dissolved in NMP (100 mL) at 70 °C for 2 h to produce
92
a diluted PEI solution. A bundle of the desized CF was immersed in NMP for 15 min,
93
after which the CF surface was well-infiltrated with the solvent. In addition, adsorption
94
of NMP on the surface helped to transfer the solute from regions of high concentration
95
to regions of low concentration in the subsequent treatment. The PEI solution with the
96
NMP-infiltrated CF was then sonicated (300 W, 38 kHz) in an ice bath for 20 min (the
97
sonicated CF was obtained if there were no follow-up treatments) and allowed to stand
98
for 24 h. Finally, the pretreated CF bundle was placed on a Teflon plate in a fume hood 4
99
at room temperature for 1 week. The coated CF (PEI@CF) was obtained after
100
evaporating the solvent completely. The PEI@CF was heated to melt the PEI
101
nanoparticles to produce H-PEI@CF, which was used for another comparison in
102
addition to the desized CF. Fig. 1 shows the schematics of the preparation process.
103
2.3 Preparation of PP and PEI sheets
104
A certain amount of PP or PEI particles were put into a self-made mold and then the
105
PP or PEI sheet could be obtained after hot pressing and cooling. The thickness of the
106
PP or PEI sheet was controlled at 0.2 mm.
107
2.4 Characterizations
108
The surface morphologies of CFs were examined using SEM (VE-9800; Keyence,
109
Tokyo, Japan) and field emission scanning electron microscopy (FE-SEM, S4800;
110
Hitachi, Tokyo, Japan). Their surface chemical compositions were probed by FTIR. The
111
FTIR absorption spectra were recorded between 2000 and 1000 cm−1 using a Shimadzu
112
FTIR (IR Prestige-21 infrared spectrometer; Shimadzu, Kyoto, Japan). The surface
113
roughness was also observed by AFM (SPA-400-AFM; Seiko, Tokyo, Japan). A single
114
CF was fastened on a steel sample mount and a tapping mode was used to scan the fiber
115
surface. Roughness analysis was performed on images obtained over 4 4 m using the
116
instrument software (SPIWin). Single fiber tensile strength tests were performed using a
117
tensile tester (EZ-SX; Shimadzu) with a strain rate of 1 mm/min at 20 °C and a relative
118
humidity of 65%. At least 35 specimens were tested for each sample.
119
SFFT was used to study the interfacial properties between CFs and thermoplastic
120
resins. The dogbone samples were fixed to a microtension device. The measurement
121
under a tensile load was taken at a speed of 0.1 mm/min. During the test, entire single
122
filament fragmentation was monitored by optical microscope and the number of fiber
5
123
fragmentations was counted within the 26-mm gauge length. Five specimens were
124
tested for each sample.
125
When the length of fiber fragmentation becomes too short to effectively transfer load
126
from the matrix, the number of fractures will no longer increase with increasing stress.
127
The number of fractures was used to calculate the critical fracture length and IFSS by
128
the follow equations [18]: 𝛿𝑓𝑑𝑓
129
τIFSS =
130
4 𝑙𝑐 = 𝑙𝑎𝑣𝑒𝑟𝑎𝑔𝑒 3
131
where τIFSS, interfacial shear strength; δf, single fiber tensile strength; df, fiber diameter;
132
lc, critical fiber length; and laverage, average fiber length.
2𝑙𝑐
133
Sample preparation is most difficult in the SFFT, especially when the matrix is
134
thermoplastic resin. The preparation process is completely different from that of
135
thermosetting resin. Some researchers have used the SFFT to study the IFSS between
136
fibers and thermoplastic resins [2, 19–22]. However, there was no mention of two
137
contradictory problems in the sample-preparation process: i.e., bubbles and fiber
138
bending. In this work, CFs were centered sandwich-style lengthwise between two
139
thermoplastic sheets. To keep the fiber straight, the ends of each fiber were fixed on the
140
sheet by tapes and epoxy resin (Fig. 2b). To obtain clean specimens without bubbles, a
141
vacuum hot-press (Fig. 3a) was used to hold the mold. Fig. 3b and c show the
142
hot-pressed samples with and without vacuum at the same temperature. Without
143
vacuum hot-pressing, the sample was filled with bubbles and the edges were oxidized
144
(the color turned yellow). With vacuum hot-pressing, there were almost no bubbles in
145
the sample and no obvious oxidation on the edges. To completely discharge the residual
146
bubbles in the middle of the sheets, a PTFE film (0.05-mm thick) was placed on the 6
147
center of the upper thermoplastic sheet. Fig. 2a shows the self-made mold and the
148
sandwich-preparation process.
149
The mold was then placed in the vacuum hot-press at the appropriate temperature and
150
held at touch pressure for 10 min and then held at a pressure of 4 MPa for 4 min.
151
Finally, the mold was cooled at room temperature. Each rectangular specimen was cut
152
into a dogbone shape (Fig. 2c). The heating time and temperature were determined in
153
auxiliary experiments (Table 1).
154
To identify whether the compatibility of these thermoplastic resins and PEI coating
155
affects the IFSS between CF and thermoplastic resins, a hot-bonding experiment was
156
designed according to ISO 4587-2003 “Adhesives – Determination of tensile lap-shear
157
strength of rigid-to-rigid bonded assemblies.” Hot bonding was used to replace the
158
adhesive. The heating and pressure conditions were the same as in the SFFT to simulate
159
compatibility during sample preparation in the SFFT. The hot-bonding sample was
160
shown in Fig. 4. Identifying the breaking force of different hot-bonding combinations
161
was performed using an INSTRON 3367 tensile tester (Illinois Tool Works, Glenview,
162
IL, USA) with a strain rate of 10 mm/min at 20 °C and a relative humidity of 65%. At
163
least 10 specimens were tested for each sample. In the standard (ISO 4587-2003), the
164
lap shear strength is calculated by dividing the breaking force by the adhesive area. The
165
resin sheets deformed in the hot-bonding process; therefore, the hot-bonding area could
166
not be calculated. Thus, the breaking force was used to roughly express the
167
compatibility of these thermoplastic resins and PEI coatings.
168
3. Results and discussion
169
3.1 Surface chemical composition, morphology, and roughness.
170
FTIR was used to determine the chemical group change in the CF after coating. Fig. 5
171
shows the FTIR spectra of desized CF, PEI@CF, and neat PEI. Almost no obvious 7
172
peaks were detected on the desized CF (Fig. 5a), which could be attributed to the low
173
number of functional groups, low transmittance of black material, and low content of
174
sizing agents [5, 6]. The results of the neat PEI membrane (Fig. 5c) exhibit
175
characteristic absorption bands at 1772 cm−1, 1710 cm−1 (asymmetric and symmetric
176
C=O stretching vibration, imide band I), 1342 cm−1 (C–N stretching, imide band II) [14,
177
23]. Vibrations at 1259, 1228, 1066, and 1010 cm−1 are due to aryl ether bonds [24]. All
178
these characteristic peaks of PEI also appear in the FTIR spectra of PEI@CF (Fig. 5b),
179
confirming that the PEI was successfully coated on the CF surface. The intensity of the
180
characteristic peaks is weak because of the low PEI contents in the treatment solution.
181
The morphologies of the samples before and after modification were obtained by
182
SEM/FE-SEM (Fig. 6). The surface of desized CF in Fig. 6a is very smooth, but shows
183
some grooves along the fiber axis. Many PEI nanoparticles appeared on the PEI@CF
184
surface after PEI coating (Fig. 6b, c). The average particle diameter measured by
185
measurement software in SEM was 200 nm. Fig. 6f shows the FE-SEM image of
186
PEI@CF from the approximate cross-section direction, which shows that the PEI
187
nanoparticles are not perfect spheres, but are pie shaped. Thus, the PEI nanoparticles
188
were adsorbed on the CF surface instead of accumulating on the CF surface. Some
189
grooves were filled after heating (Fig. 6d, e). The PEI nanoparticles on the surface of
190
PEI@CF completely melted, aggregated together, and formed many irregular flat PEI
191
blocks.
192
AFM was used to characterize the surface morphology and surface roughness of the
193
desized CF, PEI@CF, and H-PEI@CF. The surface of desized CF is relatively neat and
194
smooth (Fig. 7a), leading to a relatively low surface roughness (Ra = 55.04 nm). The
195
surface roughness of PEI@CF obviously increases to 96.95 nm due to the appearance of
196
PEI nanoparticles (Fig. 7b). After heating (Fig. 7c), the roughness of H-PEI@CF (Ra = 8
197
46.14 nm) significantly reduces, even below that of desized CF, because the PEI
198
nanoparticles were melted and many grooves filled with the melted PEI after heating.
199
3.2 Single fiber strength
200
Single fiber tensile strength is usually used to assess the effect of grafting
201
modification on the tensile strength of the fiber. Fig. 8 shows the detailed data. The
202
single fiber tensile strength of the sonicated CF was 3.14 GPa, which means that the
203
tensile strength of CF was still maintained after dipping and sonication. Similarly to
204
previous studies, the addition of PEI coating increases the single fiber strength [25, 26].
205
The introduction of PEI coating on the CF surface could help heal cracks on the fiber
206
surface and reduce stress concentrations, resulting in an improved single fiber tensile
207
strength (3.39 GPa), 7.6% higher than that of desized CF (3.15 GPa). However, after a
208
heating process during which some new defects could be formed, the PEI blocks could
209
cause stress concentrations during fiber stretching; therefore, the strength of H-PEI@CF
210
is lower than that of PEI@CF.
211
3.3 Interfacial shear strength
212
The SFFT results (Fig. 9) indicate that the existence of PEI nanoparticle coating
213
greatly increases the IFSS between CF and all studied thermoplastic resins (i.e., PVC,
214
PC, PA6, PP, PA66, and PEI) by 20.5%, 37.7%, 52.7%, 49.6%, 42.5%, and 58.0%,
215
respectively. The IFSS decreased sharply after the PEI nanoparticles were melted,
216
which indicates that the PEI nanoparticles in the molding process are easier to blend
217
with the thermoplastic resin. On the one hand, this has a great effect on IFSS. On the
218
other hand, the IFSS of the H-PEI@CF sample is still higher than that of the desized CF
219
sample, which was increased by 9.7%, 19.4%, 23.5%, 10.6%, 19.5%, and 20.8%,
220
respectively. The experimental results show that the interfacial property between CF
221
and PVC or PP is very poor. The PEI nanoparticle coating can significantly improve the 9
222
IFSS between CF and PVC or PP, but the IFSS value is still far less than that of other
223
samples.
224
A hot-bonding experiment was designed to explore whether the compatibility of these
225
thermoplastic resins and PEI coating affects the IFSS between CF and thermoplastic
226
resins after introducing PEI coating. The breaking force results of different hot-bonding
227
combinations (Fig. 10.) and the SFFT results indicate that PP has poor compatibility
228
with CF and PEI. The IFSS of PP/PEI@CF, PP/H-PEI@CF and PP/desized CF were not
229
high, but the value of PP/PEI@CF increased due to the presence of PEI nanoparticles.
230
PC and PEI are highly compatible with both CF and PEI; therefore, their enhancement
231
of interfacial strength is obvious after introducing the PEI coating. However, the results
232
of PA66 or PA6 and the results of PVC are the opposite. The compatibility of PVC and
233
PEI is good, but the IFSS is very poor. The compatibility of PA66 or PA6 and PEI is
234
not very good, but the IFSS is very strong. The deformation of PEI coating during the
235
preparation played a significant role. The PEI coating will deform more fully at the
236
temperature condition in PA6 or PA66 composite preparation, but not at the temperature
237
condition in PVC composite preparation. The IFSS results also confirmed that the
238
interface enhancement effect was more significant in the presence of PEI nanoparticles
239
because the nanoparticle coating was more prone to thermal deformation due to its
240
larger specific surface area. Therefore, the compatibility of thermoplastic resins and PEI
241
coating has an impact on the IFSS between CF and thermoplastic resins, but the most
242
important factor is the deformation of PEI coating during sample preparation.
243
Fig. 11 shows a schematic illustration of the cross-section of different CFs and
244
CFRTPs. The breaking force results and the SFFT results indicate that the interfacial
245
property of interface II and interface III/interface III in both PEI@CF and H-PEI@CF
246
samples was better than that of interface I in the desized CF sample. Due to the presence 10
247
of the PEI nanoparticles, the interfacial property of interface III in PEI@CF was better
248
than that of interface III in H-PEI@CF after molding because the PEI nanoparticle
249
coating was more prone to thermal deformation than the PEI coating without PEI
250
nanoparticles.
251
4. Conclusion
252
In this work, a vacuum hot-press, the necessary pressure, and a PTFE film were used to
253
eliminate bubbles and minimize fiber bending in the SFFT between CF and
254
thermoplastic resins. A PEI coating with uniform PEI nanoparticles was formed on the
255
CF surface. The existence of this PEI nanoparticle coating greatly increased the IFSS
256
between CF and all the thermoplastic resins used in this work (i.e., PVC, PC, PA6, PP,
257
PA66, and PEI). The IFSS decreased sharply when the PEI nanoparticles were melted;
258
therefore, the PEI nanoparticles in the molding process were easier to blend with the
259
thermoplastic resins. On the one hand, this has a great effect on the IFSS. On the other
260
hand, the IFSS of the H-PEI@CF sample was still higher than that of the desized CF
261
sample. Therefore, the interfacial property of the two interfaces in both PEI@CF sample
262
and H-PEI@CF sample was better than that of the interface in the desized CF sample.
263
The compatibility of thermoplastic resins and PEI coating has an impact on IFSS
264
between CF and thermoplastic resins, but the most important factor is the deformation
265
of the PEI coating during sample preparation. In conclusion, the PEI coating formed by
266
evaporation induced surface modification can be used as a method to improve the IFSS
267
between CF and thermoplastic resins. The effect is even better if the surface of PEI
268
coating is nanoparticle morphology.
269 270 271 11
272
Acknowledgments
273
This work was supported by the Natural Science Foundation of Zhejiang province,
274
China (Grant No.LQ20E030001) and Research Initiation Fund Project from Zhejiang
275
Sci-Tech University (Grant No.18012278-Y).
276 277
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Figure legends
380
Fig. 1. Schematic illustration of the preparation of PEI@CF and H-PEI@CF.
381
Fig. 2. (a, b) The fabrication process of the sandwich specimen. (c) The dimensions (in
382
mm) of the dogbone shape specimen.
383
Fig. 3. (a) The vacuum hot-press. (b) A hot-pressed sample without vacuum. (c) A
384
hot-pressed sample with vacuum at the same temperature.
385
Fig. 4. The dimensions (in mm) of the hot-bonding combination.
386
Fig. 5. FTIR spectra of (a) desized CF, (b) PEI@CF, and (c) neat PEI.
387
Fig. 6. SEM images of (a) desized CF; (b, c) PEI@CF; (d, e) H-PEI@CF; and (f)
388
FE-SEM image of PEI@CF from the approximate cross-section direction.
389
Fig. 7. AFM images of (a) desized CF; (b) CF treated with 0.2% PEI; and (c) CF treated
390
with 0.2% PEI after heating for 40 min at 260 °C.
391
Fig. 8. Single fiber tensile strength of desized CF, PEI@CF, and H-PEI@CF.
392
Fig. 9. IFSS between CF and thermoplastic resins.
393
Fig. 10. Breaking force of different hot-bonding combinations.
394
Fig. 11. Schematic illustration of the cross-section of different CFs and CFRTPs.
395 396
397
Table legend
398
Table 1. Heating time and temperature in the sandwich preparation process.
399 400 401 402 403 17
404 405
Fig. 1. Schematic illustration of the preparation of PEI@CF and H-PEI@CF.
406
407 408
Fig. 2. (a, b) The fabrication process of the sandwich specimen. (c) The dimensions (in
409
mm) of the dogbone shape specimen. 18
410 411
Fig. 3. (a) The vacuum hot-press. (b) A hot-pressed sample without vacuum. (c) A
412
hot-pressed sample with vacuum at the same temperature.
413 414
415 416
Fig. 4. The dimensions (in mm) of the hot-bonding combination.
417
19
418 419
Fig. 5. FTIR spectra of (a) desized CF, (b) PEI@CF, and (c) neat PEI.
420 421 422
20
423 424
Fig. 6. SEM images of (a) desized CF; (b, c) PEI@CF; (d, e) H-PEI@CF; and (f)
425
FE-SEM image of PEI@CF from the approximate cross-section direction.
426 427
21
428 429
Fig. 7. AFM images of (a) desized CF; (b) CF treated with 0.2% PEI; and (c) CF treated
430
with 0.2% PEI after heating for 40 min at 260 °C.
431
432 433
Fig. 8. Single fiber tensile strength of desized CF, Sonicated CF, PEI@CF and
434
H-PEI@CF.
435
22
436 437
Fig. 9. IFSS between CF and thermoplastic resins.
438
439 440
Fig. 10. Breaking force of different hot-bonding combinations. 23
441 442
Fig. 11. Schematic illustration of the cross-section of different CFs and CFRTPs.
443 444
Table 1. Heating time and temperature in the sandwich preparation process. Process conditions Sample Step 1
Step 2
PVC (0.3 mm)
180 °C, 0 MPa，10 Min 180 °C,4 MPa，4 Min
PC (0.5 mm)
215 °C, 0 MPa，10Min 215 °C, 4 MPa，4 Min
PA6 (0.3 mm)
220 °C, 0 MPa，10Min 220 °C, 4 MPa，4 Min
PP (0.2 mm)
250 °C, 0 MPa，10Min 250 °C,4 MPa，4 Min
PA66 (0.3 mm)
260 °C, 0 MPa，10Min 260 °C, 4 MPa，4 Min
PEI (0.2 mm)
340 °C, 0 MPa，10 Min 340 °C, 4 MPa，4 Min
Step 3
Cooling down in room temperature
445 446 447 448 24
without pressure.
Highlights
Polyetherimide coating with nanoparticle morphology was prepared on CF surface. Evaporation-induced surface modification was used as the surface treatment method. This method increased the interfacial shear strength between CF and thermoplastics. This nanoparticle morphology had a great influence on the interfacial property.
Graphical Abstract
Author statement
Peng Zhu: Corresponding author, Conceptualization, Methodology, Experiment, Data curation, Writing- Original draft preparation. Jian Shi: Reviewing and Editing. Limin Bao: Reviewing and Editing.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: