Atomic oxygen erosion behaviors of PBO fibers and their composite: Microstructure, surface chemistry and physical properties

Polymer Degradation and Stability 133 (2016) 275e282

Contents lists available at ScienceDirect

Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab

Atomic oxygen erosion behaviors of PBO fibers and their composite: Microstructure, surface chemistry and physical properties Lei Chen, Caifeng Wang, Zijian Wu, Guangshun Wu, Yudong Huang* MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 August 2016 Received in revised form 6 September 2016 Accepted 9 September 2016 Available online 10 September 2016

Poly(p-phenylene benzobisoxazole) (PBO) fibers are ideal candidates for cables in tether application and reinforcements in advanced composites. Upon exposure to atomic oxygen (AO) in low earth orbit (LEO), PBO fibers are severely eroded. In this study, the AO erosion behaviors of PBO fibers and their composite were investigated in simulated AO environment, based on the evaluation of microstructure, surface chemistry, thermal stability and mechanical properties. Surface morphologies and crystalline structure confirmed that PBO fibers were significantly eroded after AO irradiation. X-ray photoelectron spectroscopy (XPS) showed that the relative content of CeC decreases with the increase of AO irradiation time, suggesting a chain scission of PBO fibers. After 8 h AO exposure, the tensile strength of PBO fibers was decreased by 31.6%, and the onset decomposition temperature was reduced by 30.8
C. Monofilament pull-out tests showed that the interfacial shear strength (IFSS) of PBO/epoxy composite was as low as 61.3% that of pristine composite due to the interface damage caused by AO penetration. © 2016 Elsevier Ltd. All rights reserved.

Keywords: PBO fiber Atomic oxygen Erosion Tensile strength Interface

1. Introduction Nowadays, numerous satellites, space stations and other spacecrafts are being launched into low earth orbit (LEO) altitudes, ranging from 200 to 800 km [1e4]. At the LEO altitudes, the most abundant species is atomic oxygen (AO), which is produced by dissociation of molecular oxygen under UV sunlight. Although the number density of AO is low, spacecrafts move through it at high velocities of about 8 km/s. The translational energy of AO collisions is approximately 5 eV, which is sufficient to break the polymer bond and induce oxidative decomposition [5e8]. The reaction of materials with AO in low earth orbit presents a safety concern on spacecraft operation. Consequently, much attention has been paid to the reaction between the energetic AO and materials used in the exterior of a spacecraft, such as polymer and solid lubricants [9e14]. Over the past few decades, the field of high-performance fibers has witnessed considerable growth [15e22]. Poly(p-phenylene benzobisoxazole) (PBO) fibers, representative of high-performance fibers, are characterized by superior specific tensile strength,

* Corresponding author. E-mail address: [email protected] (Y. Huang). http://dx.doi.org/10.1016/j.polymdegradstab.2016.09.013 0141-3910/© 2016 Elsevier Ltd. All rights reserved.

outstanding thermal stability and good chemical resistance [23,24]. Based on the superior natures, PBO fibers have attracted significant interest as cables for tether application and reinforcements for advanced composites [25,26]. Tether satellite which connects two satellites with flexible cable, needs synthesized fibers with a highmodulus cable material. PBO fibers are one of the potential candidates for cable material in tether application due to the excellent mechanical properties. For this application, PBO fibers are suffered by the direct AO attack without matrix. Moreover, PBO fibers are frequently used as reinforcements of composite materials in various space applications. Although fiber reinforcements covered by matrix are not directly subjected to AO attack, the interface of composite would be destroyed in long-term missions [27e29]. Till now, most of studies focus on their surface modification for improving the interfacial adhesion and UV resistance [30], whereas the AO erosion behaviors of PBO fibers and PBO fiber reinforced epoxy resin composite have not been systematically investigated yet. In this work, the effects of AO irradiation on PBO fibers and their composite were investigated through artificial AO accelerated aging. The microstructure, surface chemistry and physical properties of PBO fibers and their composite exposed to AO were comprehensively studied for the first time, and the AO erosion mechanisms of them were also discussed. We anticipate that these evaluations

276

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

Fig. 1. Molecular structure of PBO fiber.

may provide some useful insights into their degradation behaviors in AO environment. 2. Experimental 2.1. Materials The PBO fibers (Zylon, HM) with a filament diameter of 12 mm were supplied by Toyobo Ltd., Japan. The molecular structure of PBO is demonstrated in Fig. 1. Epoxy resin (E-51) and 4, 40 -methylene-bis(2-ethylaniline) (H-256) as curing agent were provided by Shanghai research institute of synthetic resins, China. 2.2. AO exposure tests

Fig. 3. Effect of AO exposure time on the crystal structure of PBO fibers.

AO exposure tests were conducted on a ground-based AO effect simulation facility designed by Beijing university of aeronautics and astronautics [31]. The AO flux was calculated to be 2.1  1015 atoms/ cm2$s from mass loss of Kapton® H. In the experiment, all samples

including PBO fibers and PBO/epoxy composites were placed in a vacuum environment (1.5  101 Pa) at ambient temperature, and AO with a peak energy of 7 eV attacked the sample surface in a

Fig. 2. Surface morphologies of a), b) PBO-AO-0, c) PBO-AO-2, d) PBO-AO-4, e) PBO-AO-6 and f) PBO-AO-8.

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282 Table 1 Effect of AO exposure time on the surface chemical composition of PBO fibers. Sample

PBO-AO-0 PBO-AO-2 PBO-AO-4 PBO-AO-6 PBO-AO-8

Atomic percent (%) C

O

N

87.63 75.17 77.97 74.36 75.68

7.93 20.47 18.46 20.12 19.4

4.44 4.36 3.57 5.52 4.92

vertical direction. The samples were periodically taken out for property testing. The AO exposure time was within 8 h, which was approximately equivalent to the exposure of a satellite surface to a LEO environment for 17 days in an orbit of 300 km [32]. For convenience, the AO irradiated PBO fibers were designated as follows, for example, PBO-AO-2 indicated that the AO exposure time was 2 h. The AO irradiated PBO/epoxy composites used the same expression.

277

2.3. Characterization The surface morphologies of PBO fibers were observed by scanning electron microscope (SEM, Hitachi S-4700, Japan). The crystal structure of PBO fibers was examined by X-ray diffractometer (XRD, RIGAKU D/MAX-rb, Japan), which used a Cu Ka radiation (l ¼ 0.15406 nm) as the source generated at 40 kV and 100 mA. The surface chemical composition of PBO fibers was obtained by a X-ray photoelectron spectrometer (XPS, Thermo Scientific, USA). The surface roughness (Ra) of PBO fibers was determined in an area of 4 mm  4 mm by an atomic force microscope (AFM, Solver-P47H, NTMDT, Russia). 2.4. Physical property tests Thermogravimetric analysis (TGA) was carried out by a simultaneous thermal analyzer (Mettler Toledo TGA/DSC1, Switzerland) with a heating scan from 25 to 800
C under nitrogen atmosphere at a heating rate of 10
C/min. Monofilament tensile tests were conducted on a universal testing machine (Instron 5566, USA) according to the ASTM D3379-

Fig. 4. Fitting curves of C1s spectra of a) PBO-AO-0, b) PBO-AO-2, c) PBO-AO-4, d) PBO-AO-6 and e) PBO-AO-8.

278

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

Table 2 Concentration of functional groups on the surface of PBO fibers after different AO exposure time. Sample

Concentration of functional groups (%)

PBO-AO-0 PBO-AO-2 PBO-AO-4 PBO-AO-6 PBO-AO-8

CeC

CeN

CeO

N]CeO

O]CeO

66.92 33.23 35.19 35.28 22.06

15.58 25.1 32.3 25.47 55.15

11.01 31.34 27.48 35.29 15.44

6.49 7.38 3.53 3.96 7.35

e 2.95 1.5 e e

75. A gauge length of 100 mm and cross-head speed of 10 mm/min were used for all samples. At least 60 specimens were tested for each fiber type, and then the tensile strength results were analyzed by a Weibull statistical method. Dynamic contact angle (DCA) was measured by a CA meter (DCAT21, Data-Physics Instrument, Germany). Deionized water (gf ¼ 72.8 mJ/m2, gdf ¼ 21.8 mJ/m2) and diiodomethane (gf ¼ 50.8 mJ/m2, gdf ¼ 50.8 mJ/m2) were used as the testing liquids. Advanced CA was determined from the mass change during immersion of PBO fibers into the testing liquids using Wilhelmy's Equation (1):

cos q ¼

mg

pdf gl

(1)

where q is the DCA between PBO fibers and the testing liquids; m is the weight of PBO fibers; g is the gravitational acceleration; df is the average filament diameter of PBO fibers and gl is the surface free energy of testing liquids. The surface free energy, dispersive component and polar component of PBO fibers were calculated according to the Owens-

Fig. 6. Effect of AO exposure time on the thermal stability of PBO fibers.

Wendt model described in Equations (2) and (3):

qffiffiffiffiffiffiffiffiffiffiffi

qffiffiffiffiffiffiffiffiffiffiffi

gl ð1 þ cos qÞ ¼ 2 gdl gdf þ 2 gpl gpf

(2)

gf ¼ gdf þ gpf

(3)

where gf, gdf and gpf are the surface free energy of PBO fibers, its dispersive and polar component, respectively; gl, gdl and gpl are the surface free energy of testing liquids, its dispersive and polar component, respectively. Monofilament pull-out tests were performed to determine the interfacial shear strength (IFSS) of PBO/epoxy composites using an

Fig. 5. a) Typical stress-strain curves of PBO fibers after different AO exposure time; Effect of AO exposure time on the b) tensile strength, c) elongation at break, and d) Young's modulus of PBO fibers. The insets of Fig. 5b show the tensile failure morphologies of PBO-AO-0 and PBO-AO-8.

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

279

Fig. 7. Surface morphologies of a), b) PBO/epoxy-AO-0, c) PBO/epoxy-AO-2, d) PBO/epoxy-AO-4, e) PBO/epoxy-AO-6 and f) PBO/epoxy-AO-8 composites.

interfacial strength evaluation equipment (Tohei Sanyon Co., Ltd., Japan). The values of IFSS were calculated from the following Equation (4):

IFSS ¼

Fmax pdl

(4)

where Fmax is the peak pullout force; d is the average filament diameter of PBO fibers; l is the embedded length of monofilament in epoxy resin. 3. Results and discussion 3.1. AO erosion behavior of PBO fibers Fig. 2 shows the surface morphologies of PBO fibers before and after AO irradiation. The samples exhibit different morphologies with the increase of AO exposure time. It is evident from Fig. 2a and b that the surface of PBO-AO-0 is neat and smooth. In the case of PBO-AO-2 (Fig. 2c) and PBO-AO-4 (Fig. 2d), some projections appear on the surface of PBO fiber, which is caused by the attack of high-energy AO beam. After 6 h AO exposure (Fig. 2e), PBO fiber is severely eroded and roughened, giving a “corduroy-like” appearance. The dramatic changes of the surface morphologies can be attributed to the oxidative nature of AO. AO diffuses into the fiber

and reacts with some atoms such as carbon, nitrogen, and hydrogen to form volatile products, resulting in the formation of the feature [6]. As the AO exposure time further increases to 8 h (Fig. 2f), PBO fiber is eroded more severely. Fig. 3 shows the XRD patterns of PBO fibers before and after AO irradiation. Obviously, the diffraction peaks of PBO fibers appear at 16.1
(200), 25.6
(010), 27.3
(210) and 32.4
(400). When the AO exposure time is less than 4 h, AO does not give rise to a visible change in the intensity and shape of the diffraction peaks. Kitagawa et al. [33] demonstrated that PBO fibers had a core-shell structure, in which the shell of 1e2 mm thickness had fewer voids and a higher degree of order compared with the core. AO erosion only occurs at the shell structure of PBO fibers within 4 h, and thereby does not affect the stacking of their molecular chains. As the AO exposure time progresses, the peak intensities of PBO fibers reduce gradually, which implies the deterioration in crystal structure of PBO with AO erosion. The surface chemical composition of PBO fibers before and after AO irradiation is analyzed by XPS. As listed in Table 1, the surface of PBO-AO-0 is mainly composed of carbon (87.63%), oxygen (7.93%) and a small amount of nitrogen (4.44%). The strong oxidizing AO can react with the carbon atoms, therefore, some of these atoms are transformed to volatile gases. After 2 h AO exposure, the carbon content decreases from 87.63% to 75.17%, whereas the oxygen

280

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

Fig. 8. a) Effect of AO exposure time on the IFSS of PBO/epoxy composites; b) Possible AO erosion mechanism of PBO/epoxy composite. The insets of Fig. 8a show the debonding surface morphologies of PBO/epoxy-AO-0 and PBO/epoxy-AO-8 composites.

content considerably increases from 7.93% to 20.47%, indicating that the fiber surface is activated as a result of oxygen atom incorporation. As the AO exposure time increases, the oxygen content does not show obvious changes. This is because an excessive ablation effect acts on the fiber surface and some inherent oxygen atoms or oxygen-based fragments are released from the fiber surface under bombardment of the high-energy particles in the AO beam [34]. By comparison, the nitrogen content does not change a lot during the AO exposure process, indicating that no nitrogen atoms are incorporated onto PBO fibers. The high resolution C1s spectra are deconvolved in Fig. 4 to investigate the functional groups variation on the fiber surface, and the quantitative analysis results are listed in Table 2. As shown in Fig. 4a, the C1s spectra of PBO-AO-0 can be fitted to four peaks at 284.6, 285.4, 286.5 and 288.3 eV, which are ascribed to CeC, CeN, CeO and N]CeO groups, respectively. In the case of PBO-AO-2 (Fig. 4b) and PBO-AO-4 (Fig. 4c), an additional binding energy peak at 289.6 eV is observed, which is ascribed to O]CeO group. The peak intensity and areas of PBO fibers before and after AO irradiation in the C1s spectra are quite different. The concentrations of correlative functional groups are calculated from the related peak areas. After 2 h AO exposure, the relative content of CeC group sharply decreases from 66.92% to 33.23%, and that of CeN, CeO and N]CeO groups increases from 15.58%, 11.01% and 6.49% to 25.1%, 31.34% and 7.38%, respectively. After 4 h AO exposure, the relative content of O]CeO group decreases from 2.95% to 1.5%. When the AO exposure time is 6 h (Fig. 4d), O]CeO group disappears, and the relative content of CeC group has little change. Meanwhile, the

relative contents of CeN, CeO and N]CeO groups demonstrate dynamic changes. As the AO exposure time increases to 8 h (Fig. 4e), the relative content of CeC group further decreases to 22.06%, suggesting a serious degradation of PBO fibers, which is consistent with the previous XRD testing results. PBO fibers play an important role in absorbing load in the composites, which have significant influences on the service life of the spacecraft structure. Tensile tests are taken to investigate the degeneration of mechanical properties of PBO fibers in AO environment (Fig. 5). As presented in the typical stress-strain curves (Fig. 5a), the tensile strength, elongation at break and Young's modulus decreases as the AO exposure time goes on. It can be observed from Fig. 5b that the tensile strength retention ratios of PBO-AO-2 and PBO-AO-4 are 91.7% and 90.3% respectively, indicating that the structure of PBO fibers is not destroyed. As the AO exposure time further progresses, tensile strength declines quickly. After 8 h AO exposure, the tensile strength retention ratio is only 68.4%. The differences of tensile failure morphologies between PBO-AO-0 and PBO-AO-8 are presented in the insets of Fig. 5b. Apparently, the surface of PBO-AO-0 shows no crack propagation after breakage. In contrast, PBO-AO-8 shows the lateral cracks (marked by arrow) propagate along the axial direction of the fiber. The decrease in tensile strength can be explained by the defects such as large cracks introduced onto the fiber surface caused by AO erosion [9]. During the AO exposure process, the elongation at break (Fig. 5c) and Young's modulus (Fig. 5d) of PBO fibers display similar changes with that of tensile strength. The elongation at break and Young's modulus retention ratios of PBO-AO-8 are 78.3% and 82.8%, respectively. The above results indicate that AO deteriorates the mechanical properties of PBO fibers, especially for the tensile strength. The thermal stability of PBO fibers before and after AO irradiation is studied by TGA, as shown in Fig. 6. PBO-AO-0 begins to degrade at about 642.6
C in nitrogen atmosphere, exhibiting excellent thermal resistance. The onset decomposition temperature of PBO-AO-2, PBO-AO-4, PBO-AO-6 and PBO-AO-8 are 632.2, 631.8, 625.7 and 611.8
C, respectively. Clearly, the thermal stability of PBO fibers declines gradually with the increase of AO exposure time due to the strong oxidation.

3.2. AO erosion behavior of PBO/epoxy composite Resin matrix is crucial to adhering, supporting and protecting the fiber reinforcements and transferring stress in the PBO/epoxy

Fig. 9. IFSS of different AO-irradiated PBO/epoxy composites.

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

281

Fig. 10. AFM images of a) PBO-AO-0 and b) PBO-AO-6.

Table 3 Contact angles and surface free energies of different PBO fibers. Sample

qwater (
)

qdiiodomethane (
)

gdf (mJ/m2)

gpf (mJ/m2)

gf (mJ/m2)

PBO-AO-0 PBO-AO-6

78.3 40.5

41.1 36.9

39.1 41.1

4.2 22.8

43.3 63.9

composite. Once the resin matrix is destroyed, AO can penetrate into the interfacial region of the composite, leading to the severe damage [35]. The surface morphologies of resin matrix before and after AO irradiation are observed to further understand the erosion behavior of the interface. Fig. 7 shows a striking difference in surface morphologies of epoxy micro-droplet before and after AO irradiation. Compared to the intact and smooth surface of PBO/ epoxy-AO-0 (Fig. 7a and b), large-area hollows appear on the surface of PBO/epoxy-AO-2 (Fig. 7c). After 4 h AO exposure (Fig. 7d), these hollows change into lots of ravines and crack paths with shallow depth. As AO exposure time further increases (Fig. 7e and f), the number and depth of the micro-cracks increase remarkably. IFSS testing results of PBO/epoxy composites before and after AO irradiation are shown in Fig. 8a. After 2 h and 4 h AO exposure, the IFSS retention ratios of PBO/epoxy composites are 94.1% and 89.5% respectively, indicating that the interface of the composites is not seriously affected. As the AO exposure time goes on, the IFSS declines quickly, After 8 h AO exposure, the IFSS retention ratio is only 61.3%. The de-bonding surfaces of PBO/epoxy-AO-0 and PBO/ epoxy-AO-8 are observed by SEM (see insets). These observations are consistent with the IFSS results: the higher the IFSS retention ratio, the rougher de-bonding surface of PBO fibers. The appearance of gap at interfacial region (marked by frame) also indicates poor interfacial properties of PBO/epoxy-AO-8. Fig. 8b demonstrates the possible AO erosion mechanism of PBO/epoxy composite. After long-term AO exposure, numerous defects are formed on the resin surface, which serve as channels for AO penetration. Consequently, the interfacial adhesion between the fibers and the matrix is destroyed. 3.3. Surface modification of PBO fibers using AO irradiation Plasma irradiation has been proved to effectively increase the surface roughness and wettability of PBO fibers, leading to enhanced interfacial properties of the resulting composite [36,37]. Inspired by the approach, it is reasonable to infer that AO irradiation may improve the interfacial adhesion between PBO fibers and resin matrix. In this work, we fabricate AO-irradiated PBO fibers

and epoxy resin into composites, and then examine their interfacial properties. As shown in Fig. 9, the IFSS of all AO-irradiated PBO/ epoxy composites are higher than that of PBO-AO-0/epoxy composite. As the AO exposure time increases to 6 h, the IFSS reaches maximum with an increase of 113.4%. Such an increase is attributed to two aspects. On one hand, the Ra increases from 26.6 to 73.1 nm (Fig. 10). On the other hand, leads to the improvement of surface wettability of PBO fibers, as summarized in Table 3. After 6 h AO exposure, the DCA of deionized water decreases from 78.3
to 40.5
, and that of diiodomethane decreases from 41.1
to 36.9
. Meanwhile, the gf increases from 43.3 to 63.9 mJ/m2 due to the polar groups formed by AO oxidation. However, when the AO exposure time further increases to 8 h, the IFSS has a sharp decrease. After the long-term exposure, AO may penetrate into the deep inside of PBO fibers, resulting in the poor adhesion between shell and core structures [27]. Therefore, the interfacial adhesion of resulting composites is unavoidably damaged. As the AO flux or exposure time can be easily adjusted, and large-scale treatment can be achieved, this effective approach may open a novel interface design strategy for developing advanced composites. 4. Conclusions In summary, the AO erosion behaviors of PBO fibers and their composite were systematically investigated from exposure experiments. AO seriously eroded the surface of PBO fibers, resulting in chain scission. The tensile testing results showed that tensile strength of PBO fibers declined more significantly in comparison with that of elongation at break and Young's modulus. Meanwhile, the thermal stability of PBO fibers declined gradually with the increase of AO exposure time. Furthermore, AO could penetrate into the interfacial region of PBO/epoxy composite through the surface defects of matrix, and deteriorate the interfacial properties. It is noteworthy that AO irradiation may be an alternative method for the interface enhancement of high-performance fiber reinforced polymer composites. Acknowledgements We gratefully acknowledge financial support by the Chang Jiang Scholars Program. References [1] R. Verker, E. Grossman, I. Gouzman, N. Eliaz, Residual stress effect on degradation of polyimide under simulated hypervelocity space debris and atomic

282

L. Chen et al. / Polymer Degradation and Stability 133 (2016) 275e282

oxygen, Polymer 48 (1) (2007) 19e24. [2] F. Awaja, J.B. Moon, S.N. Zhang, M. Gilbert, C.G. Kim, P.J. Pigram, Surface molecular degradation of 3D glass polymer composite under low earth orbit simulated space environment, Polym. Degrad. Stabil. 95 (6) (2010) 987e996. [3] F. Awaja, J.B. Moon, M. Gilbert, S.N. Zhang, C.G. Kim, P.J. Pigram, Surface molecular degradation of selected high performance polymer composites under low earth orbit environmental conditions, Polym. Degrad. Stabil. 96 (7) (2011) 1301e1309. [4] A. Rahnamoun, A.C. van Duin, Reactive molecular dynamics simulation on the disintegration of Kapton, POSS polyimide, amorphous silica, and teflon during atomic oxygen impact using the Reaxff reactive force-field method, J. Phys. Chem. A 118 (15) (2014) 2780e2787. [5] T.K. Minton, B.H. Wu, J.M. Zhang, N.F. Lindholm, A.I. Abdulagatov, J. O'Patchen, S.M. George, M.D. Groner, Protecting polymers in space with atomic layer deposition coatings, ACS Appl. Mater. Interf. 2 (9) (2010) 2515e2520. [6] T.K. Minton, M.E. Wright, S.J. Tomczak, S.A. Marquez, L.H. Shen, A.L. Brunsvold, R. Cooper, J.M. Zhang, V. Vij, A.J. Guenthner, B.J. Petteys, Atomic oxygen effects on POSS polyimides in low earth orbit, ACS Appl. Mater. Interf. 4 (2) (2012) 492e502. [7] S.B. Jin, G.S. Son, Y.H. Kim, C.G. Kim, Enhanced durability of silanized multiwalled carbon nanotube/epoxy nanocomposites under simulated low earth orbit space environment, Compos. Sci. Technol. 87 (2013) 224e231. [8] H.E. Misak, V. Sabelkin, S. Mall, P.E. Kladitis, Thermal fatigue and hypothermal atomic oxygen exposure behavior of carbon nanotube wire, Carbon 57 (2013) 42e49. [9] L. Ghosh, M.H. Fadhilah, H. Kinoshita, N. Ohmae, Synergistic effect of hyperthermal atomic oxygen beam and vacuum ultraviolet radiation exposures on the mechanical degradation of high-modulus aramid fibers, Polymer 47 (19) (2006) 6836e6842. [10] L. Ghosh, H. Kinoshita, N. Ohmae, Degradation on a mechanical property of high-modulus aramid fiber due to hyperthermal atomic oxygen beam exposures, Compos. Sci. Technol. 67 (2007) 1611e1616. [11] L.M. Su, L.M. Tao, T.M. Wang, Q.H. Wang, Phenylphosphine oxide-containing aromatic polyamide films with high atomic oxygen erosion resistance, Polym. Degrad. Stabil. 97 (6) (2012) 981e986. [12] X. Sui, L.C. Gao, P.G. Yin, Shielding Kevlar fibers from atomic oxygen erosion via layer-by-layer assembly of nanocomposites, Polym. Degrad. Stabil. 110 (2014) 23e26. [13] X.F. Lei, M.T. Qiao, L.D. Tian, P. Yao, Y. Ma, H.P. Zhang, Q.Y. Zhang, Improved space survivability of polyhedral oligomeric silsesquioxane (POSS) polyimides fabricated via novel POSS-diamine, Corros. Sci. 90 (2015) 223e238. [14] X.F. Lei, M.T. Qiao, L.D. Tian, Y.H. Chen, Q.Y. Zhang, Evolution of surface chemistry and morphology of hyperbranched polysiloxane polyimides in simulated atomic oxygen environment, Corros. Sci. 98 (2015) 560e572. [15] B. Larin, C.A. Avila-Orta, R.H. Somani, B.S. Hsiao, G. Marom, Combined effect of shear and fibrous fillers on orientation-induced crystallization in discontinuous aramid fiber/isotactic polypropylene composites, Polymer 49 (1) (2008) 295e302. [16] B. Wei, H.L. Cao, S.H. Song, Degradation of basalt fibre and glass fibre/epoxy resin composites in seawater, Corros. Sci. 53 (1) (2011) 426e431. [17] Q. An, A.N. Rider, E.T. Thostenson, Electrophoretic deposition of carbon nanotubes onto carbon-fiber fabric for production of carbon/epoxy composites with improved mechanical properties, Carbon 50 (11) (2012) 4130e4143. [18] C.Y. Li, K.Z. Li, H.J. Li, Y.L. Zhang, H.B. Ouyang, D.J. Yao, L. Liu, Microstructure and ablation resistance of carbon/carbon composites with a zirconium carbide rich surface layer, Corros. Sci. 85 (2014) 160e166. [19] A.L. Forster, A.M. Forster, J.W. Chin, J.S. Peng, C.C. Lin, S. Petit, K.L. Kang, N. Paulter, M.A. Riley, K.D. Rice, M. Al-Sheikhly, Long-term stability of UHMWPE fibers, Polym. Degrad. Stabil. 114 (2015) 45e51. [20] H.Q. Wang, C.F. Zhang, Z.X. Chen, H.K. Liu, Z.P. Guo, Large-scale synthesis of ordered mesoporous carbon fiber and its application as cathode material for

lithium-sulfur batteries, Carbon 81 (2015) 782e787. [21] A.L. Wang, X.J. He, X.F. Lu, H. Xu, Y.X. Tong, G.R. Li, Palladium-cobalt nanotube arrays supported on carbon fiber cloth as high-performance flexible electrocatalysts for ethanol oxidation, Angew. Chem. Int. Ed. 54 (12) (2015) 3669e3673. [22] V.A. Rybin, А.V. Utkin, N.I. Baklanova, Corrosion of uncoated and oxide-coated basalt fibre in different alkaline media, Corros. Sci. 102 (2016) 503e509. [23] Z. Hu, J. Li, P.Y. Tang, D.L. Li, Y.J. Song, Y.W. Li, L. Zhao, C.Y. Li, Y.D. Huang, Onepot preparation and continuous spinning of carbon nanotube/poly(p-phenylene benzobisoxazole) copolymer fibers, J. Mater. Chem. 22 (2012) 19863e19871. [24] T. Kitagawa, K. Funaki, Morphological studies of poly-p-phenylenebenzobisoxazole (PBO) fibers on the process that determines the direction of the crystal a-axis along the radius direction during the formation of fiber structures, Polymer 82 (2016) 246e254. [25] L. Chen, Y.Z. Du, Y.D. Huang, P.F. Ng, B. Fei, Facile fabrication of hierarchically structured PBO-Ni(OH)2/NiOOH fibers for enhancing interfacial strength in PBO fiber/epoxy resin composites, Compos. Sci. Technol. 129 (2016) 86e92. [26] L. Chen, Y.Z. Du, Y.D. Huang, F. Wu, H.M. Cheng, B. Fei, J.H. Xin, Hierarchical poly(p-phenylene benzobisoxazole)/graphene oxide reinforcement with multifunctional and biomimic middle layer, Compos. A 88 (2016) 123e130. [27] L. Chen, F. Wei, L. Liu, W.L. Cheng, Z. Hu, G.S. Wu, Y.Z. Du, C.H. Zhang, Y.D. Huang, Grafting of silane and graphene oxide onto PBO fibers: multifunctional interphase for fiber/polymer matrix composites with simultaneously improved interfacial and atomic oxygen resistant properties, Compos. Sci. Technol. 106 (2015) 32e38. [28] N. Atar, E. Grossman, I. Gouzman, A. Bolker, V.J. Murray, B.C. Marshall, M. Qian, T.K. Minton, Y. Hanein, Atomic-oxygen-durable and electrically-conductive CNT-POSS-polyimide flexible films for space applications, ACS Appl. Mater. Interf. 7 (2015) 12047e12056. [29] P. Wang, Y.S. Tang, Z. Yu, J.W. Gu, J. Kong, Advanced aromatic polymers with excellent antiatomic oxygen performance derived from molecular precursor strategy and copolymerization of polyhedral oligomeric silsesquioxane, ACS Appl. Mater. Interf. 7 (36) (2015) 20144e20155. [30] B. Song, Q.X. Zhuang, L.H. Ying, X.Y. Liu, Z.W. Han, Photostabilisation of poly(p-phenylenebenzobisoxazole) fibre, Polym. Degrad. Stabil. 97 (9) (2012) 1569e1576. [31] X.H. Zhao, Z.G. Shen, Y.S. Xing, S.L. Ma, A study of the reaction characteristics and mechanism of Kapton in a plasma-type groundbased atomic oxygen effects simulation facility, J. Phys. D 34 (2001) 2308e2314. [32] M. Yi, Z.G. Shen, W. Zhang, J.Y. Zhu, L. Liu, S.S. Liang, X.J. Zhang, S.L. Ma, Hydrodynamics-assisted scalable production of boron nitride nanosheets and their application in improving oxygen-atom erosion resistance of polymeric composites, Nanoscale 5 (2013) 10660e10667. [33] T. Kitagawa, H. Murase, K. Yabuki, Morphological study on poly-p-phenylenebenzobisoxazole (PBO) fiber, J. Polym. Sci. B 36 (1) (1998) 39e48. [34] M.N. Mirvakili, S.G. Hatzikiriakos, P. Englezos, Superhydrophobic lignocellulosic wood fiber/mineral networks, ACS Appl. Mater. Interf. 5 (18) (2013) 9057e9066. [35] J. Blunt, G. Jen, C.P. Ostertag, Enhancing corrosion resistance of reinforced concrete structures with hybrid fiber reinforced concrete, Corros. Sci. 92 (2015) 182e191. [36] J.M. Park, D.S. Kim, S.R. Kim, Improvement of interfacial adhesion and nondestructive damage evaluation for plasma-treated PBO and Kevlar fibers/ epoxy composites using micromechanical techniques and surface wettability, J. Colloid Interf. Sci. 264 (2) (2003) 431e445. [37] K. Tamargo-Martinez, A. Martinez-Alonso, M.A. Montes-Moran, J.M.D. Tascon, Effect of oxygen plasma treatment of PPTA and PBO fibers on the interfacial properties of single fiber/epoxy composites studied by Raman spectroscopy, Compos. Sci. Technol. 71 (6) (2011) 784e790.