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Reinforced unsaturated polyester composites by chemically grafting amino-POSS onto carbon fibers with active double spiral structural spiralphosphodicholor
Accepted Manuscript Reinforced Unsaturated Polyester Composites by Chemically Grafting AminoPOSS onto Carbon Fibers with Active Double Spiral Structural Spiralphosphodicholor Dawei Jiang, Li Liu, Jun Long, Yudong Huang, Zijian. Wu, Xinru. Yan, Zhanhu Guo PII: DOI: Reference:
S0266-3538(14)00190-0 http://dx.doi.org/10.1016/j.compscitech.2014.05.035 CSTE 5835
To appear in:
Composites Science and Technology
Received Date: Revised Date: Accepted Date:
5 March 2014 2 May 2014 28 May 2014
Please cite this article as: Jiang, D., Liu, L., Long, J., Huang, Y., Wu, Zijian., Yan, Xinru., Guo, Z., Reinforced Unsaturated Polyester Composites by Chemically Grafting Amino-POSS onto Carbon Fibers with Active Double Spiral Structural Spiralphosphodicholor, Composites Science and Technology (2014), doi: http://dx.doi.org/ 10.1016/j.compscitech.2014.05.035
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Reinforced Unsaturated Polyester Composites by Chemically Grafting Amino-POSS onto Carbon Fibers with Active Double Spiral Structural Spiralphosphodicholor Dawei Jiang 1, 3, Li Liu1,*, Jun Long1, 3, Yudong Huang1, 2, Zijian. Wu 1, Xinru. Yan3, Zhanhu Guo3,* 1. School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, China 2.
.
State Key Laboratory of Urban Water Resource and Environment, Department of Applied Chemistry, Harbin Institute of Technology, Harbin, China 3. Integrated Composites Laboratory (ICL), Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont 77710 USA *Corresponding author.
E-mail: [email protected]; [email protected]
Abstract The grafting of amino-POSS on the carbon fibers (CFs) surface was achieved through the reaction of the spiralphosphodicholor (SPDPC) grafted on the CFs surface with aminopropylphenyl polyhedral oligomeric silsesquioxane (amino-POSS). X-ray photoelectron spectroscopy (XPS) showed that the phosphorus, chlorine and silicon containing functional groups were obviously increased after the modifications. Both CFs grafted with SPDPC and CFs grafted with SPDPC plus amino-POSS have been used to prepare unsaturated polyester resin (UPR）composites. The grated SPDPC and grafted with a combined SPDPC and amino-POSS improved the interfacial performance of the CFs/UPR composites, respectively. Atomic force microscopy (AFM) results showed that the surface roughness of the CFs grafted with SPDPC was lower than that of the CFs grafted with a combined SPDPC and amino-POSS. Dynamic contact angle analysis of the CFs grafted with SPDPC showed higher wettability to UPR than that of the CFs grafted with a combined SPDPC and amino-POSS. Force modulation atomic force microscopy (FMAFM) and interlaminar shear strength (ILSS) were used to characterize the interfacial properties of the composites. After grafted with a combined SPDPC and amino-POSS, the ILSS of the composites was increased by 22.9% due to the well interfacial properties that were caused by the improvement of CFs surface roughness.
Keywords: A. Carbon fibres; A. Polymer-matrix composites (PMCs); B. Impact behavior; B. Interfacial strength; B. Mechanical properties 1
1. Introduction Carbon fibers (CFs) mainly served as reinforcements in the composites have been used in aerospace, marine and automobile industries due to their unique properties including enlarged strength, high modulus and light weight [1-3]. The CFs reinforced composites normally contain three parts including CFs, hosting matrix and interphases. The interface between fibers and matrix significantly influences the performance of the composite finishing. However, a poor interface arising from the smooth and chemically inert fiber surfaces has caused poor mechanical properties of the composites [4-9]. To improve their interfacial adhesion and surface wettability or to increase the fiber surface roughness to enhance the mechanical properties [10-13], various surface treatments methods have been reported including electrochemical oxidation treatment [14], plasmas treatment [15], coating treatment [12, 16,17], and chemical grafting [11, 18]. Polyhedral oligomeric silsesquioxane (POSS), a specific cage silsesquioxane, is the smallest known silica particle with a three-dimensional Si–O cage structure and an overall diameter of 1.5–3 nm [19, 20]. POSS is in fact hybrid inorganic/organic chemical composites that possess an inner inorganic silicon and oxygen core (SiO1.5)n and external organic substituents that can feature a range of polar or nonpolar functional groups. In its structures, an inorganic Si8O12 core provides thermal and chemical stability and the surrounding inorganic cage with eight organic groups can be functionalized with non-reactive groups for an enhanced compatibility with the hosting polymer matrix or with the functional groups for chemically reacting with a polymer matrix [21-23]. The introduction of POSS cages can improve the mechanical properties of the composites, such as strength, modulus and rigidity through the improved interface adhesion of the composites and can reduce its flammability, heat evolution, and viscosity during processing [24]. These enhancements have been observed in a wide range of commercial high-performance thermoplastic and thermosetting composites [25-27]. For 2
example, Zhao et al [11] have reported octaglycidyldimethylsilyl POSS as a coupling agent through grafting on the CFs surface to enhance the interfacial adhesion of the CFs/epoxy composites. The POSS coupling agent has been demonstrated to effectively increase the polarity, wettability and roughness of the carbon fiber surface. The POSS bonded on the fibers and epoxy matrix was chemically bridged through reacting between the reactive groups on the CFs surface and the resin. All of these can improve the interfacial adhesion between CFs and matrix and thus enhance the overall mechanic properties of the resulted composites significantly [28-31]. However, the usage of spiralphosphodicholor (SPDPC) as a coupling agent to be grafted on the CFs surface has not been reported for the grafting amino-POSS on the CFs surface to increase the interfacial adhesion of CFs/unsaturated liquid polyester resin (UPR) composites. The SPDPC has attracted great interests due to its unique functions to act as one of the most important reaction intermediates for introducing more functional groups and to improve the thermal stability of polymers. Except the chemical bonding between CFs and matrix, the wettability and roughness also play a role in enhancing mechanical properties. However, whether wettability or roughness plays more roles has not been reported yet. In this paper, the aminopropylphenyl polyhedral oligomeric silsesquioxane (amino-POSS) was grated on the surface of CFs to enhance the interfacial properties through using spiralphosphodicholor (SPDPC) as an intermediate, with one end grafted on the surface of CFs and the other reacted with the amino-POSS. The molecular structure of amino-POSS is shown in Figure 1(a). The CFs with and without surface treatments were used for producing UPR composites. And the effects of wettability and roughness on the interfacial properties were compared. The surface morphologies of the CFs were observed by atomic force microscopy (AFM). The surface chemical composition of the carbon fibers was characterized by X-ray photoelectron spectroscopy (XPS). The wettability and surface free energy of untreated and functionalized fibers were investigated by 3
dynamic contact angle analysis test (DCAT). The interfacial mechanical properties of the CFs/UPR composites were characterized by short-beam bending test method (ILSS). The micro-mechanism of the composite interphase region was investigated by force modulation atomic force microscopy (AFM). 2. Experimental 2.1 Materials AROPOL MR13006 polyester and low shrinkage agent LP4016 were supplied by Ashland Inc., USA. Tert-Butyl peroxybenzoate (TBPB, 98% purity) was purchased from ACROS ORGANICS Inc, which was used as an initiator. Un-sizing polyacrylonitrile (PAN) based carbon fibers (CCF300) were obtained from WeiHai GuangWei Group (12×103 single filaments per tow, tensile strength was 3.26 GPa, average diameter was 7µm, density was 1.76 g cm–3, Shandong, China). Amino-POSS was obtained from Hybrid Plastics Co., Inc. (Texas), and was used as received.
The spiralphosphodicholor (SPDPC) coupling agent as an
intermediate product, synthesized by pentaerythritol and phosphorus oxychloride, contains two highly active functional group in both ends [32, 33] and its molecular structure is shown in Figure 1(b). 2.2 Grafting procedures First, the CFs were oxidized in a 3:1 (v/v) mixture of concentrated H2SO4/HNO3 at 60 ℃ for 2 hours, washed with deionized water until the pH of water was neutral. Second, the oxidized CFs were reduced in a solution of NaBH4 (1.0 g) in 200 mL anhydrous ethanol at room temperature for 20 hours. And then, the mixture was heated to 78℃ and maintained for 4 hours. The products were washed with deionized water until the pH was neutral and then dried. After the reduced CFs were reacted with SPDPC in acetone solutions of SPDPC (3 mass %) at 56 ℃ for 8 hours, the product was washed with absolute ethanol until the wash ethanol was neutral and then dried. The CFs-SPDPC were further reacted with amino-POSS in tetrahydrofuran (THF) 4
solutions of amino-POSS (3 mass %) at 65℃ for 12 hours. The final product was washed with deionized water until the washed water was neutral and then dried for other usage. 2.3 Preparation of CFs/UPR composites The composites of CFs reinforced UPR were prepared by compression molding method. The unidirectional prepreg carbon fibers were put into a mold to make composites. MR13006, LP4016 and TBPB were used at a mixture ratio of 105:45:1. Briefly, the CFs/UPR composites were prepared by heating the samples at 80 ℃ for one hour without pressure, a pressure of 10 MPa was applied at 100 ℃ for one hour, then the sample underwent 140 ℃ for one hour under 10 MPa, then the mold was cooled down to room temperature with the pressure being maintained. The resin content of the composites was controlled at 30±1.5 mass%, and the width and thickness of specimens were 6.5 and 2 mm, respectively. 2.4 Characterization of carbon fibers X-ray photoelectron spectroscopy (XPS, ESCALAB 220i-XL, VG, UK) was carried out to study the surface element of carbon fibers using a monochromated Al Ka source (1486.6eV) at a base pressure of 2×10-9mbar. The XPS was energy referenced to the C1s peak of graphite at 284.6 eV. The XPS Peak version 4.1 program was used for data analysis. The treatment effects on the fiber surface morphology were observed by using atomic force microscopy (AFM, Solver-P47H, NT-MDT, Russia). Individual fiber was examined in Solver P47 AFM/STM system (NT-MDT Co.). AFM was also used to investigate the microstructures of the composites. The force modulation mode was adopted to study the cross-section surfaces of the unidirectional CFs/UPR composites and the relative stiffness of the various phases, including the CFs, interface, and resin. The composites were first polished perpendicularly to the fiber axis using increasingly finer sand papers, and then polished with a Cr2O3 (50 nm) suspension, finally washer with water under ultrasonication and dried. 5
Dynamic contact angle and surface energy analyses were performed using a dynamic contact angle tensiometer (DCAT21, Data Physics Instruments, Germany). The advancing contact angle was determined from the mass change during the immersion of fibers in each test liquid using Wilhelmy’s Equation (1): [34]
cosθ =
mg π .d f .γ 1
(1)
where, df is the fiber diameter, g is the gravitational acceleration, and
γ 1 is the surface tension of the test
liquid. The surface energy ( γ f ), dispersion component ( γ f ) and polar component ( γ fp ) of the CFs were d
estimated from the measured dynamic contact angles of the test liquids with known surface tension components and calculated according to the following equations:
γ 1 (1 = cosθ ) = 2(γ 1pγ fp )1 / 2 + 2(γ 1d γ df )1 / 2
(2)
γ f = γ fp + γ df
(3)
where, γ 1 , γ 1d and γ 1p are the liquid surface tension, its dispersion and polar component, respectively. Deionised water ( γ d =21.8mJ·m-1, γ =72.8mJ·m-1) and diiodomethane ( γ d =50.8 mJ·m-1, γ =50.8 mJ·m-1, 99% purity, Alfa Aesar, USA) were used as the test liquids. Each measurement was repeated 5 times and the results were averaged. The inter-laminar shear strength (ILSS, Γ) of the CFs/UPR composites was measured on a universal testing machine (WD-1,Changchun, China) using a three point short beam bending test according to ASTM D2344. Specimen dimensions were 20 mm×6 mm×2 mm, with a span to thickness ratio of 5. The specimens were conditioned and an enclosed testing space was maintained at room temperature. The specimens were measured at a cross-head speed of 2 mm/min. The Γfor the short-beam test was calculated according to Eq. (4).[34]
Γ=
3Pb 4bh
(4)
where Pb is the maximum compression force at fracture in Newton, b is the width of the specimen in mm, and 6
h is the thickness in mm. Each reported Γ value was averaged for more than eight successful measurements. The impact tests were carried out on a drop weight impact test system (9250HV, Instron, USA). The specimen dimensions were 55 mm×6.5 mm×2 mm, the impact span was 40 mm, the drop weight was 3 kg and the velocity was 2 m/s. Each reported data was averaged value of 5 specimens.
The interfacial shear strength
(IFSS) was adopted to quantify the interfacial property between CFs and resin matrix by the interfacial evaluation equipment (Tohei Sangyo Co Ltd., Japan). The tensile strength (TS) of a single filament was performed on an electronic mechanical universal material testing machine (Instron 5500R, USA) according to ASTM D 3379-75. A gauge length of 20 mm and cross-head speed of 10 mm/min were used for all fiber samples. At least, 60 specimens were tested for each fiber type, and then the average value was considered as the tested value. 3. Results and discussion 3.1 Surface chemical elemental composition XPS was performed to determine the chemical composition of the carbon fibers surface [35]. The surface composition of the untreated and treated carbon fibers was determined by XPS and the results are given in Table 1. The C1s XPS spectra of untreated and grafted with SPDPC and a combined SPDPC and amino-POSS are shown in Figure 3. Only a small amount of oxygen was observed on the untreated carbon fibers surface. However, it is noted that 16.86% oxygen was detected on the untreated fibers surface due to the oxidation of CFs from the process of fabrication. After grafting treatment with SPDPC, the content of element was changed. The carbon content decreased from 82.03 to 63.50 % and the oxygen content increased significantly from 16.86 to 31.84 %. In addition, significant phosphrous element of 3.44% and a little chlorine of 0.16% were detected on the fibers. It was attributed to the fact that SPDPC was grafted on the surface of CFs. After SPDPC 7
being grafted, the O/C value was higher than that of the untreated CFs. The change of O element and the appearance of chlorine were helpful to graft amino-POSS on CFs surface. From Table 1, it can be seen that after amino-POSS being grafted, the silicon was appeared with an element content of 6.67%. This shows that the amino-POSS was grafted on the surface of CFs successfully. 3.2 Surface topography of carbon fibers The AFM two-dimensional and three-dimensional images of untreated, SPDPC grafted carbon fibers and SPDPC- Amino-POSS grafted on carbon fibers are shown in Figure 3. The carbon fibers surface roughness was calculated from the plane topography images by using the AFM software is shown in Table 2. The functionalization process is shown in Figure 2. From the functionalization process, the SPDPC containing two flexible chlorine groups can not only react with the reactive groups on the carbon fiber surface, but also can react with reactive groups on the amino-POSS. Through the SPDPC, the amino-POSS can be grated on the surface of CFs. Amino-POSS has only one reactive group and if the reactive group reacted with SPDPC, amino-POSS had no other group that can react with resin matrix. Significant differences of the surface topography between untreated and modified carbon fibers were observed. As shown in Figure 3(a), (d), the surface of untreated CFs has many shallow grooves and seems to be relatively smooth, which is the typical topography of CCF300. Because the surface of untreated CFs was a little smooth, its roughness is a little small. The untreated CFs surface roughness is about 56.8 nm. It can be found in Figure 3 (b), (e) that the surface topography of the SPDPC grafted fiber becomes rougher and the particles of the SPDPC molecular are scattered on the surface and in the voids of the grooves of fibers, which could be interpreted by the existence of scattered hydroxy on the surface of fibers after reduction. In addition, the surface average roughness was increased from 56.8 to 79.1 nm compared with the untreated CFs. The 8
roughness of CFs was increased by 28%. As shown in Figure 3(c), (f) on the surface of CFs-SPDPC-amino-POSS, a layer of amino-POSS particles appeared and the carbon fibers became much rougher than the untreated CFs and SPDPC grafted CFs. The protuberant area becomes bigger than that of the SPDPC grafted alone, suggesting the aggregates of POSS nanoparticles. The surface roughness of the fibers after grafted with amino-POSS was the biggest among all samples and was 112.6 nm. It increased by 50%. The increased surface roughness can significantly increase the interfacial adhesion by enhancing mechanical interlocking between the fibers and the matrix. 3.3 Dynamic contact angle analysis It is well known that the chemical composition and topography of the fiber surface can affect the fiber surface energy as well as its components. Good wettability between carbon fibers and matrix is closely related to the fiber surface energy, and integrative properties of the carbon fibers reinforced resin matrix composites are directly controlled by the wettability of fiber surface and matrix. The surface wettability of CFs was evaluated by surface free energy. The overall performance of the fibers-reinforced composites is closely related to the wettability of the fiber surface with matrix. An excellent wettability means a high interfacial strength. Generally, the fibers were pre-treated before their usage as reinforcement aiming to obtain the fibers with surface energy higher or equal to the surface energy of matrix for the improvement of wettability. In this work, the surface wettability of CFs was evaluated via a Cahn dynamic angle analysis system. The advanced contact angle( θ ), the total surface free energy ( γ ),
its dispersion
component ( γ d ) and polar component ( γ p ) of
untreated and treated CFs are summarized in Table 2. The total surface free energy of the untreated CFs was 34.46 mJ·m-1, and its dispersion component and polar component was 23.82 and 10.64 mJ·m-1, respectively. After functionalization with SPDPC, the surface energy 9
obviously increased and its dispersion and polar components of CFs-SPDPC were 33.60 and 31.26 mJ·m-1, respectively. The highest surface free energy was 64.86 mJ·m-1, which belongs to CFs-SPDPC. This may be due to the existence of polar group chlorine. The increased surface energy can effectively improve the wettability of the fibers by the resin and increase the interfacial strength. After grafted with amino-POSS, the surface energy of the CFs was bigger than that of the untreated CFs but lower than that of the CFs-SPDPC. That may be due to the lower polarity of amino-POSS than that of SPDPC, which was 58.42 mJ·m-1. 3.4 Interfacial property testing 3.4.1 Interphase modulus testing The force modulation AFM (FAFM) was used to characterize both surface topography and hardness diagram of materials. FAFM can observe different hardness and elastic area distribution of the materials and can also be used to study the change of performance between different components of the composite. The hardness of the fiber, matrix and interface area was different. The information of the shape, distribution and relative hardness of different phase (including interface phase) can be obtained from the test and characterization of the composites surface within limits, which can provide the basis for the mechanism in the analysis of interface modification [36]. The force modulation images of the interphase region between CFs and UPR matrix were obtained from the cross-section of the composites reinforced by different carbon fibers, Figure 4. Figure 4(a, b & c) show the AFM force modulation images of the untreated, SPDPC grafted carbon fibers and SPDPC-Amino-POSS grafted CFs, respectively. Figure 4(d, e & f) show the cross-sectional images of the interphase of the untreated, SPDPC grafted and SPDPC-Amino-POSS grafted CFs, respectively. From Figure 4(a), no striking interface 10
region was observed between the CFs and UPR matrix region for composites and the modulus was observed to sharply change from the CFs to the UPR matrix region, Figure 4(d). The CFs reinforcement and UPR matrix can be distinguished clearly from Figure 4(a). There was an obvious transition layer between CFs and UPR in Figure 4(b&c). The interphase was observed to have a moderate modulus, which was lower than that of the CFs and higher than that of the UPR matrix from Figure 4(e & f). For the CFs grafted with combined SPDPC and amino-POSS, the interfacial transition region was longer than that of the CFs grafted with SPDPC alone, Figure 4(b & c), which is due to the bigger roughness of CFs grafted with a combined SPDPC and amino-POSS than that of the CFs grafted with SPDPC alone. The increased surface roughness has significantly increased the interfacial adhesion by mechanical interlocking the CFs with the UPR matrix, a similar phenomenon has been reported on the epoxy nanocomposites reinforced with graphene nanosheets decorated with protruding nanoparticles [37]. A little longer interface region can decrease the effect of the applied force on the composites of CFs and UPR. 3.4.2 The inter-laminar/interfacial shear strength and impact properties Short-beam bending tests were performed to evaluate the interfacial strength of the composites. Figure 5(a) shows the ILSS of the CFs/UFR composites. After grafted with SPDPC or a combined SPDPC and amino-POSS, the ILSS of the CFs/UPR composites was increased. The ILSS of the untreated CFs/UPR composites was 47 MPa，whereas the ILSS of the CFs grafted with SPDPC and grafted with a combined SPDPC and amino-POSS was 52 and 61 MPa, respectively. The ILSS of the composites of CFs grafted with SPDPC was lower than that of the composites of CFs grafted with a combined SPDPC and amino-POSS, which was increased by 9.6 and 22.9 %, respectively. Zhao et al. [11] have reported that the ILSS of the epoxy composites was increased by 18.2% by grafting octaglycidyldimethylsilyl POSS on the CFs surface. Zhang et 11
al. [38] have reported that the ILSS of the epoxy composites was increased by 9.6% by grafting graphene oxide on the CFs. All of the percentage increase is lower than the observed ILSS value here with CFs grafted with amino-POSS. The ILSS of the composites of the CFs grafted with a combined SPDPC and amino-POSS was much higher than that of the CFs grafted with SPDPC. The ILSS was increased by 14.8% compared with that of the CFs grafted with SPDPC alone. The ILSS of the composites of the CFs grated with a combined SPDPC and amino-POSS was increased more due to both the improved surface wettability and the improved surface roughness of the CFs.
The polarity of SPDPC was higher than that of amino-POSS. Amino-POSS contains 3-D Si–O cage structure, so that the surface of CFs has aggregated amino-POSS nanoparticles after the CFs grafted with a combined SPDPC and amino-POSS. The wettability of the CFs grafted with SPDPC was higher than that of CFs grafted with a combined SPDPC and amino-POSS (Table 2), however the surface roughness of the CFs grafted with SPDPC was lower than that of CFs grafted with a combined SPDPC with amino-POSS (Table 2). Although the wettability of the CFs grafted with SPDPC was higher than that of the CFs grafted with a combined SPDPC and amino-POSS, the ILSS of the CFs grafted with a combined SPDPC and POSS was bigger than that of the CFs grafted with SPDPC. The IFSS of the composites of CFs grafted with a combined SPDPC and amino-POSS was observed significantly increased compared with the composites of CFs grafted with SPDPC and composites with untreated CFs, Figure 5 (b), indicating an improved interfacial interaction after CFs grafted with a combined SPDPC and amino-POSS. The tensile strength of the as-received, grafted with SPDPC and a combined SPDPC and amino-POSS single CF follows the Weibull distributions plots, Figure 5 (c,d&e). Single fiber tensile strength is usually performed 12
to assess the influence of the grafting modification on the tensile strength of the fibers and the Weibull distribution is a continuous probability distribution and appropriate method to deal with the strength of many fibers. The strength of a single carbon fiber obeys the single Weibull distribution, i.e., the lower the Weibull shape parameter is, the more defects the fibers have [39]. Oxidation and grafting treatment will unavoidably introduce defects on the surface of fiber, which could decrease the fiber strength. However, compared with the strength of the as-received CFs (3.26 GPa), comparable fiber tensile strength is observed for the CFs grafted with SPDPC (3.28 GPa) and for the CFs grafted with a combined SPDPC and amino-POSS (3.31 GPa), suggesting that the chemical grafting of SPDPC and amino-POSS on the fibers has no significant effects on the fiber tensile strength. The results of single fiber tensile testing imply that the functionalization would not lead to any discernable decrease in the in-plane properties of the resulting composites. The impact property tests were carried out to further examine the effects of the SPDPC and amino-POSS grafting on the impact resistance of the composites. Figure 5(b) shows the impact property testing results. The total absorbed energy of the untreated CFs/UPR composites is 1.00 J. After modification, the impact toughness is increased significantly, 1.23 and 1.49 J for the composites containing CFs grafted with SPDPC and grafted a combined SPDPC and amino-POSS, respectively. The amino-POSS interphase served as a shielding layer, which could relieve the local stress concentration, prevent the crack tips to directly contact the fiber surface and make the crack path deviate away from the fiber surface to the interphase region. In addition, numerous amino-POSS nanoparticles on the fiber surface could induce more cracks and could efficiently absorb the fracture energy when the major crack passed through them [11]. 3.4.3 Interface property of the cryo-fractured surfaces of composites Figure 6 shows the SEM microstructures of the cryo-fractured surfaces of the composites. For the untreated 13
CFs/UPR composites, Figure 6(a), some fibers were pulled out from the UPR matrix, and the interface de-bonding between CFs and UPR matrix was observed obviously. After grafted with SPDPC, the surface of the CFs had polar groups, which increased the surface energy of CFs. The wettability of the CF surface with matrix was also increased. Some de-bondings are observed in the composites containing CFs grafted with SPDPC, Figure 6(b), although it has less de-bonding than the untreated CFs/UPR composites. The interfacial adhesion was observed to be dramatically improved between CFs and UPR matrix after grafted with a combined SPDPC and amino-POSS, Figure 6(c). This strong bonding has contributed to the stronger ILSS of the composites with CFS grafted with a combined SPDPC and amino-POSS increased by 22.9 % as compared with the composites of the CFs grated with SPDPC. The interface de-bonding between CFs and UPR matrix was not observed, indicating that the surface of the CFs grafted with a combined SPDPC and amino-POSS was rougher than that the CFs grafted with SPDPC only. It also indicated that roughness play a more important role than wettability. 4. Conclusion Through the SPDPC containing two flexible chlorine groups, the amino-POSS was grafted on the surface of CFs. SPDPC and a combined SPDPC and amino-POSS were uniformly grafted on the CFs surface. Both improved the interfacial adhesion between CFs and UPR matrix. The wettability of the CFs grafted with SPDPC was higher than that of the CFs grafted with a combined SPDPC and amino-POSS. However, the surface roughness of the CFs grafted with SPDPC was lower than that of the CFs grafted with a combined SPDPC and amino-POSS. For both the CFs/UPR composites, the ILSS and the impact resistance of the CFs grafted with a combined SPDPC and amino-POSS had been dramatically increased compared with that of the CFs grafted with SPDPC. In addition, from the force modulation AFM and SEM observations of the 14
cryo-fractured test, the interfacial adhesion of the CFs grafted with a combined SPDPC and amino-POSS was also better than that of the CFs grafted with SPDPC. The surface roughness (112.6 nm) of the fibers after grafted with amino-POSS was the biggest among all samples. For the wettability, the highest surface free energy was 64.86 mJ·m-1 for CFs-SPDPC. Both the ILSS and impact energy of the CFs grafted a combined SPDPC and amino-POSS was 61 MPa and 1.49 J, respectively, higher than that of the CFs grafted with SPDPC (52 MPa and 1.23 J). All experimental evidences indicated that the roughness played more important role than the wettability. Acknowledgements The authors would like to thank the Chang Jiang Scholars Program and National Natural Science Foundation of China (No.51073047, No.51173032) for financial support and the professor Caiying Sun in Northeast Forestry University for providing SPDPC. Z. Guo acknowledges the National Science Foundation (NSF, CMMI 10–30755) USA.
References 1.
Ogasawara T, Ishida Y and Kasai T. Mechanical properties of carbon fiber/fullerene-dispersed epoxy
composites. Compos Sci Technol. 2009; 69: 2002-2007. 2.
Norris CJ, Bond IP and Trask RS. The role of embedded bioinspired vasculature on damage formation in
self-healing carbon fibre reinforced composites. Compos Part A. 2011; 42: 639-648. 3.
Zhang XZ, Huang YD and Wang TY. Surface analysis of plasma grafted carbon fiber. Appl Surf Sci. 2006; 253:
2885-2892. 4.
Galan U, Lin YR, Ehlert GJ and Sodano HA. Effect of ZnO nanowire morphology on the interfacial strength of
nanowire coated carbon fibers. Compos Sci Technol. 2011; 71: 946-954. 5.
Sharma SP and Lakkad SC. Compressive strength of carbon nanotubes grown on carbon fiber reinforced epoxy
matrix multi-scale hybrid composites. Surf Coat Technol. 2010; 205: 350-355. 6.
An F, Lu CX, Li YH, Guo JH, Lu XX, Lu HB, He SQ and Yang Y. Preparation and characterization of carbon
nanotube-hybridized carbon fiber to reinforce epoxy composite. Mater Des. 2012; 33: 197-202. 7.
He XD, Wang C, Tong LY, Wang RG, Cao AY, Peng QY, Moody S and Li YB. Direct measurement of grafting
strength between an individual carbon nanotube and a carbon fiber. Carbon. 2012; 50: 3782-3788. 8.
Wang J, Wu D, Li X, Zhang M and Zhou W. Poly(vinylidene fluoride) reinforced by carbon fibers: Structural 15
parameters of fibers and fiber-polymer adhesion. Appl Surf Sci. 2012; 258: 9570-9578. 9.
Li J. The research on the interfacial compatibility of polypropylene composite filled with surface treated carbon
fiber. Appl Surf Sci. 2009; 255: 8682-8684. 10. Yang L, He XD, Mei L, Tong LY, Wang RG and Li YB. Interfacial shear behavior of 3D composites reinforced with CNT-grafted carbon fibers. Compos Part A. 2012; 43: 1410-1418. 11. Zhao F, Huang YD, Liu L, Bai YP and Xu LW. Formation of a carbon fiber/polyhedral oligomeric silsesquioxane/carbon nanotube hybrid reinforcement and its effect on the interfacial properties of carbon fiber/epoxy composites. Carbon. 2011; 49: 2624-2632. 12. Zhang XZ, Huang YD, Wang TY and Hu LJ. Effects of silsesquioxane coating structure on mechanical interfacial properties of carbon fibre/polyarylacetylene composites. J Mater Sci. 2007; 42: 5264-5271. 13. Li J and Cai CL. The carbon fiber surface treatment and addition of PA6 on tensile properties of ABS composites. Curr Appl Phys. 2011; 11: 50-54. 14. Yue ZR, Jiang W, Wang L, Gardner SD and Pittman Jr CU. Surface characterization of electrochemically oxidized carbon fibers. Carbon. 1999; 37: 1785-1796. 15. Li H, Liang H, He F, Huang Y and Wan YZ. Air dielectric barrier discharges plasma surface treatment of three-dimensional braided carbon fiber reinforced epoxy composites. Surf Coat Technol. 2009; 203: 1317-1321. 16. Guo H, Huang YD, Liu L and Shi XH. Effect of epoxy coatings on carbon fibers during manufacture of carbon fiber reinforced resin matrix composites. Mater Des. 2010; 31: 1186-1190. 17. Zhang RL, Huang YD, Su D, Liu L and Tang YR. Influence of sizing molecular weight on the properties of carbon fibers and its composites. Mater Des. 2012; 34: 649-654. 18. Zhu J, Wei S, Ryu J, Budhathoki M, Liang G and Guo Z. In situ stabilized carbon nanofiber (CNF) reinforced epoxy nanocomposites. J Mater Chem. 2010; 20: 4937-4948. 19. Kim HU, Bang YH, Choi SM and Yoon KH. Morphology and mechanical properties of PET by incorporation of amine-polyhedral oligomeric silsesquioxane. Compos Sci Technol. 2008; 68: 2739-2747. 20. Pallavi I, Javed AM and Maria RC. A hybrid functional nanomaterial: POSS functionalized carbon nanofiber. Nanotechnol. 2009; 20: 325603. 21. Feng Y, Jia Y, Guang S and Xu H. Study on thermal enhancement mechanism of POSS-containing hybrid nanocomposites and relationship between thermal properties and their molecular structure. J Appl Polym Sci. 2010; 115: 2212-2220. 22. Wang X, Hu Y, Song L, Xing WY and Lu HD. Thermal degradation behaviors of epoxy resin/POSS hybrids and phosphorus–silicon synergism of flame retardancy. J Polym Sci Part B: Polym Phys. 2010; 48: 693-705. 23. Chiu YC, Riang L, Chou IC, Ma CCM, Chiang CL and Yang CC. The POSS side chain epoxy nanocomposite: Synthesis and thermal properties. J Polym Sci Part B: Polym Phys. 2010; 48: 643-652. 24. Scapini P, Figueroa CA, Amorim CLG, et al. Thermal and morphological properties of high-density polyethylene/ethylene–vinyl
acetate
copolymer
composites 16
with
polyhedral
oligomeric
silsesquioxane
nanostructure. Polym Int. 2010; 59: 175-180. 25. Li G and Pittman C. Polyhedral oligomeric silsesquioxane (POSS) polymers, copolymers, and resin nanocomposites. Macromolecules Containing Metal and Metal-Like Elements: Group IVA Polymers, Volume 4. 2005: 79-131. 26. Scott D. Thermal Rearrangement of Branched-Chain Methylpolysiloxanes1. J Am Chem Soc. 1946; 68: 356-358. 27. Kuo SW and Chang FC. POSS related polymer nanocomposites. Prog Polym Sci. 2011; 36: 1649-1696. 28. Zhao F and Huang YD. Preparation and properties of polyhedral oligomeric silsesquioxane and carbon nanotube grafted carbon fiber hierarchical reinforcing structure. J Mater Chem. 2011; 21: 2867-2870. 29. Zhao F and Huang YD. Improved interfacial properties of carbon fiber/epoxy composites through grafting polyhedral oligomeric silsesquioxane on carbon fiber surface. Mater Lett. 2010; 64: 2742-2744. 30. Zhao F and Huang YD. Grafting of polyhedral oligomeric silsesquioxanes on a carbon fiber surface: novel coupling agents for fiber/polymer matrix composites. J Mater Chem. 2011; 21: 3695-3703. 31. Song B, Meng LH and Huang YD. Improvement of interfacial property between PBO fibers and epoxy resin by surface grafting of polyhedral oligomeric silsesquioxanes (POSS). Appl Surf Sci. 2012; 258: 10154-10159. 32. Zhang QB, Xing HT, Sun CY, Xiang HW, Jiang DW and Qin LL. The mechanical properties and thermal performances of polypropylene with a novel intumescent flame retardant. J Appl Polym Sci. 2010; 115: 2170-2177. 33. Xiang HW, Sun CY, Jiang DW, Zhang QB, Dong CM and Liu L. Flame retardation and thermal degradation of intumescent flame-retarded polypropylene composites containing spirophosphoryldicyandiamide and ammonium polyphosphate. J Vinyl Add Tech. 2010; 16: 161-169. 34. Wu ZJ, Meng LH, Liu L, Jiang ZX, Xing LX, Jiang DW and Huang YD. Interfacial microstructure and properties of carbon fiber-reinforced unsaturated polyester composites modified with carbon nanotubes. J Adhes Sci Technol. 2014; 28: 444-453. 35. Zhang GX, Sun SH, Yang DQ, Dodelet JP and Sacher E. The surface analytical characterization of carbon fibers functionalized by H2SO4/HNO3 treatment. Carbon. 2008; 46: 196-205. 36. Li FB, Thompson GE and Newman RC. Force modulation atomic force microscopy: background, development and application to electrodeposited cerium oxide films. Appl Surf Sci. 1998; 126: 21-33. 37. Zhang X, Alloul O, He QL, Zhu JH, Verde MJ, Li YT, Wei SY and Guo Z. Strengthened magnetic epoxy nanocomposites with protruding nanoparticles on the graphene nanosheets. Polymer. 2013; 54: 3594-3604. 38. Zhang X, Fan X, Yan C, et al. Interfacial microstructure and properties of carbon fiber composites modified with graphene oxide. ACS Appl. Mat. Interfaces. 2012; 4: 1543-1552. 39. Liu Y, Liu, Y, Tan H, Wang C, Wei H, and Guo Z. Structural evolution and degradation mechanism of vectran® fibers upon exposure to UV-radiation. Polym. Degrad. Stab. 2013; 98(9): 1744-1753.
17
Table 1 Surface chemical composition of CFs with different chemical grafting method
Element content (at%) Carbon fibers Untreated CFs CFs-SPDPC CFs-SPDPC-Amino-POSS
C 82.03 63.5 68.78
O
N
Si
P
Cl
O/C
Si/C
16.86 31.84 21.58
1.1 1.06 2.18
— — 6.67
— 3.44 0.79
— 0.16 —
0.20 0.50 0.31
— — 0.09
Table 2 Surface energy and Roughness of CFs with different chemical grafting
Contact angle (o)
Surface energy (mJ·m-1)
Water
Diiodomethane
γ
Untreated CFs
74.39
56.31
23.82
10.64
34.46
56.8
CFs-SPDPC
32.52
16.81
33.60
31.26
64.86
79.1
CFs-SPDPC-Amino-POSS
42.98
25.65
32.67
25.75
58.42
112.6
CF
Ra (nm) d
γ
p
γ
Figures and Figure Captions
Figure 1. Typical structure of (a) aminopropylphenyl POSS, and (b) SPDPC.
18
Figure 2. Schematic grafting procedures of POSS functionalized CFs.
19
Figure 3. AFM images of different carbon fiber surface. (a), (d) untreated (b), (e) SPDPC grafted (c), (f) SPDPC-POSS grafted, C1s XPS spectra of the (g) untreated CFs, (h) acidized CFs, (i) reduced CFs (g) CFs grafted with SPDPC, and (k) the CFs grafted with SPDPC-POSS.
20
Figure 4. (a), (b), (c) AFM force modulation images of the untreated, SPDPC grafted CFs and SPDPC-Amino-POSS grafted CFs; (d), (e), (f) cross-sectional analysis of the interphase images of the untreated, SPDPC grafted CFs and SPDPC-Amino-POSS grafted CFs for CFs/UPR composites.
Figure 5. (a) ILSS and TS, (b) Impact test and IFFS of composites reinforced by the untreated and modified CFs; and weibull distribution plots of the (c) untreated single fibers; (d) CFs-SPDPC grafted single fibers; (e) CFs-SPDPC-amino-POSS grafted single fibers. 21
Figure 6. Morphologies of the fractured surface of CFs/UPR composites: (a) untreated; (b) CFs-SPDPC grafted; (c) CFs-SPDPC-amino-POSS grafted.
22
S0266-3538(14)00190-0 http://dx.doi.org/10.1016/j.compscitech.2014.05.035 CSTE 5835
To appear in:
Composites Science and Technology
Received Date: Revised Date: Accepted Date:
5 March 2014 2 May 2014 28 May 2014
Please cite this article as: Jiang, D., Liu, L., Long, J., Huang, Y., Wu, Zijian., Yan, Xinru., Guo, Z., Reinforced Unsaturated Polyester Composites by Chemically Grafting Amino-POSS onto Carbon Fibers with Active Double Spiral Structural Spiralphosphodicholor, Composites Science and Technology (2014), doi: http://dx.doi.org/ 10.1016/j.compscitech.2014.05.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Reinforced Unsaturated Polyester Composites by Chemically Grafting Amino-POSS onto Carbon Fibers with Active Double Spiral Structural Spiralphosphodicholor Dawei Jiang 1, 3, Li Liu1,*, Jun Long1, 3, Yudong Huang1, 2, Zijian. Wu 1, Xinru. Yan3, Zhanhu Guo3,* 1. School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, China 2.
.
State Key Laboratory of Urban Water Resource and Environment, Department of Applied Chemistry, Harbin Institute of Technology, Harbin, China 3. Integrated Composites Laboratory (ICL), Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont 77710 USA *Corresponding author.
E-mail: [email protected]; [email protected]
Abstract The grafting of amino-POSS on the carbon fibers (CFs) surface was achieved through the reaction of the spiralphosphodicholor (SPDPC) grafted on the CFs surface with aminopropylphenyl polyhedral oligomeric silsesquioxane (amino-POSS). X-ray photoelectron spectroscopy (XPS) showed that the phosphorus, chlorine and silicon containing functional groups were obviously increased after the modifications. Both CFs grafted with SPDPC and CFs grafted with SPDPC plus amino-POSS have been used to prepare unsaturated polyester resin (UPR）composites. The grated SPDPC and grafted with a combined SPDPC and amino-POSS improved the interfacial performance of the CFs/UPR composites, respectively. Atomic force microscopy (AFM) results showed that the surface roughness of the CFs grafted with SPDPC was lower than that of the CFs grafted with a combined SPDPC and amino-POSS. Dynamic contact angle analysis of the CFs grafted with SPDPC showed higher wettability to UPR than that of the CFs grafted with a combined SPDPC and amino-POSS. Force modulation atomic force microscopy (FMAFM) and interlaminar shear strength (ILSS) were used to characterize the interfacial properties of the composites. After grafted with a combined SPDPC and amino-POSS, the ILSS of the composites was increased by 22.9% due to the well interfacial properties that were caused by the improvement of CFs surface roughness.
Keywords: A. Carbon fibres; A. Polymer-matrix composites (PMCs); B. Impact behavior; B. Interfacial strength; B. Mechanical properties 1
1. Introduction Carbon fibers (CFs) mainly served as reinforcements in the composites have been used in aerospace, marine and automobile industries due to their unique properties including enlarged strength, high modulus and light weight [1-3]. The CFs reinforced composites normally contain three parts including CFs, hosting matrix and interphases. The interface between fibers and matrix significantly influences the performance of the composite finishing. However, a poor interface arising from the smooth and chemically inert fiber surfaces has caused poor mechanical properties of the composites [4-9]. To improve their interfacial adhesion and surface wettability or to increase the fiber surface roughness to enhance the mechanical properties [10-13], various surface treatments methods have been reported including electrochemical oxidation treatment [14], plasmas treatment [15], coating treatment [12, 16,17], and chemical grafting [11, 18]. Polyhedral oligomeric silsesquioxane (POSS), a specific cage silsesquioxane, is the smallest known silica particle with a three-dimensional Si–O cage structure and an overall diameter of 1.5–3 nm [19, 20]. POSS is in fact hybrid inorganic/organic chemical composites that possess an inner inorganic silicon and oxygen core (SiO1.5)n and external organic substituents that can feature a range of polar or nonpolar functional groups. In its structures, an inorganic Si8O12 core provides thermal and chemical stability and the surrounding inorganic cage with eight organic groups can be functionalized with non-reactive groups for an enhanced compatibility with the hosting polymer matrix or with the functional groups for chemically reacting with a polymer matrix [21-23]. The introduction of POSS cages can improve the mechanical properties of the composites, such as strength, modulus and rigidity through the improved interface adhesion of the composites and can reduce its flammability, heat evolution, and viscosity during processing [24]. These enhancements have been observed in a wide range of commercial high-performance thermoplastic and thermosetting composites [25-27]. For 2
example, Zhao et al [11] have reported octaglycidyldimethylsilyl POSS as a coupling agent through grafting on the CFs surface to enhance the interfacial adhesion of the CFs/epoxy composites. The POSS coupling agent has been demonstrated to effectively increase the polarity, wettability and roughness of the carbon fiber surface. The POSS bonded on the fibers and epoxy matrix was chemically bridged through reacting between the reactive groups on the CFs surface and the resin. All of these can improve the interfacial adhesion between CFs and matrix and thus enhance the overall mechanic properties of the resulted composites significantly [28-31]. However, the usage of spiralphosphodicholor (SPDPC) as a coupling agent to be grafted on the CFs surface has not been reported for the grafting amino-POSS on the CFs surface to increase the interfacial adhesion of CFs/unsaturated liquid polyester resin (UPR) composites. The SPDPC has attracted great interests due to its unique functions to act as one of the most important reaction intermediates for introducing more functional groups and to improve the thermal stability of polymers. Except the chemical bonding between CFs and matrix, the wettability and roughness also play a role in enhancing mechanical properties. However, whether wettability or roughness plays more roles has not been reported yet. In this paper, the aminopropylphenyl polyhedral oligomeric silsesquioxane (amino-POSS) was grated on the surface of CFs to enhance the interfacial properties through using spiralphosphodicholor (SPDPC) as an intermediate, with one end grafted on the surface of CFs and the other reacted with the amino-POSS. The molecular structure of amino-POSS is shown in Figure 1(a). The CFs with and without surface treatments were used for producing UPR composites. And the effects of wettability and roughness on the interfacial properties were compared. The surface morphologies of the CFs were observed by atomic force microscopy (AFM). The surface chemical composition of the carbon fibers was characterized by X-ray photoelectron spectroscopy (XPS). The wettability and surface free energy of untreated and functionalized fibers were investigated by 3
dynamic contact angle analysis test (DCAT). The interfacial mechanical properties of the CFs/UPR composites were characterized by short-beam bending test method (ILSS). The micro-mechanism of the composite interphase region was investigated by force modulation atomic force microscopy (AFM). 2. Experimental 2.1 Materials AROPOL MR13006 polyester and low shrinkage agent LP4016 were supplied by Ashland Inc., USA. Tert-Butyl peroxybenzoate (TBPB, 98% purity) was purchased from ACROS ORGANICS Inc, which was used as an initiator. Un-sizing polyacrylonitrile (PAN) based carbon fibers (CCF300) were obtained from WeiHai GuangWei Group (12×103 single filaments per tow, tensile strength was 3.26 GPa, average diameter was 7µm, density was 1.76 g cm–3, Shandong, China). Amino-POSS was obtained from Hybrid Plastics Co., Inc. (Texas), and was used as received.
The spiralphosphodicholor (SPDPC) coupling agent as an
intermediate product, synthesized by pentaerythritol and phosphorus oxychloride, contains two highly active functional group in both ends [32, 33] and its molecular structure is shown in Figure 1(b). 2.2 Grafting procedures First, the CFs were oxidized in a 3:1 (v/v) mixture of concentrated H2SO4/HNO3 at 60 ℃ for 2 hours, washed with deionized water until the pH of water was neutral. Second, the oxidized CFs were reduced in a solution of NaBH4 (1.0 g) in 200 mL anhydrous ethanol at room temperature for 20 hours. And then, the mixture was heated to 78℃ and maintained for 4 hours. The products were washed with deionized water until the pH was neutral and then dried. After the reduced CFs were reacted with SPDPC in acetone solutions of SPDPC (3 mass %) at 56 ℃ for 8 hours, the product was washed with absolute ethanol until the wash ethanol was neutral and then dried. The CFs-SPDPC were further reacted with amino-POSS in tetrahydrofuran (THF) 4
solutions of amino-POSS (3 mass %) at 65℃ for 12 hours. The final product was washed with deionized water until the washed water was neutral and then dried for other usage. 2.3 Preparation of CFs/UPR composites The composites of CFs reinforced UPR were prepared by compression molding method. The unidirectional prepreg carbon fibers were put into a mold to make composites. MR13006, LP4016 and TBPB were used at a mixture ratio of 105:45:1. Briefly, the CFs/UPR composites were prepared by heating the samples at 80 ℃ for one hour without pressure, a pressure of 10 MPa was applied at 100 ℃ for one hour, then the sample underwent 140 ℃ for one hour under 10 MPa, then the mold was cooled down to room temperature with the pressure being maintained. The resin content of the composites was controlled at 30±1.5 mass%, and the width and thickness of specimens were 6.5 and 2 mm, respectively. 2.4 Characterization of carbon fibers X-ray photoelectron spectroscopy (XPS, ESCALAB 220i-XL, VG, UK) was carried out to study the surface element of carbon fibers using a monochromated Al Ka source (1486.6eV) at a base pressure of 2×10-9mbar. The XPS was energy referenced to the C1s peak of graphite at 284.6 eV. The XPS Peak version 4.1 program was used for data analysis. The treatment effects on the fiber surface morphology were observed by using atomic force microscopy (AFM, Solver-P47H, NT-MDT, Russia). Individual fiber was examined in Solver P47 AFM/STM system (NT-MDT Co.). AFM was also used to investigate the microstructures of the composites. The force modulation mode was adopted to study the cross-section surfaces of the unidirectional CFs/UPR composites and the relative stiffness of the various phases, including the CFs, interface, and resin. The composites were first polished perpendicularly to the fiber axis using increasingly finer sand papers, and then polished with a Cr2O3 (50 nm) suspension, finally washer with water under ultrasonication and dried. 5
Dynamic contact angle and surface energy analyses were performed using a dynamic contact angle tensiometer (DCAT21, Data Physics Instruments, Germany). The advancing contact angle was determined from the mass change during the immersion of fibers in each test liquid using Wilhelmy’s Equation (1): [34]
cosθ =
mg π .d f .γ 1
(1)
where, df is the fiber diameter, g is the gravitational acceleration, and
γ 1 is the surface tension of the test
liquid. The surface energy ( γ f ), dispersion component ( γ f ) and polar component ( γ fp ) of the CFs were d
estimated from the measured dynamic contact angles of the test liquids with known surface tension components and calculated according to the following equations:
γ 1 (1 = cosθ ) = 2(γ 1pγ fp )1 / 2 + 2(γ 1d γ df )1 / 2
(2)
γ f = γ fp + γ df
(3)
where, γ 1 , γ 1d and γ 1p are the liquid surface tension, its dispersion and polar component, respectively. Deionised water ( γ d =21.8mJ·m-1, γ =72.8mJ·m-1) and diiodomethane ( γ d =50.8 mJ·m-1, γ =50.8 mJ·m-1, 99% purity, Alfa Aesar, USA) were used as the test liquids. Each measurement was repeated 5 times and the results were averaged. The inter-laminar shear strength (ILSS, Γ) of the CFs/UPR composites was measured on a universal testing machine (WD-1,Changchun, China) using a three point short beam bending test according to ASTM D2344. Specimen dimensions were 20 mm×6 mm×2 mm, with a span to thickness ratio of 5. The specimens were conditioned and an enclosed testing space was maintained at room temperature. The specimens were measured at a cross-head speed of 2 mm/min. The Γfor the short-beam test was calculated according to Eq. (4).[34]
Γ=
3Pb 4bh
(4)
where Pb is the maximum compression force at fracture in Newton, b is the width of the specimen in mm, and 6
h is the thickness in mm. Each reported Γ value was averaged for more than eight successful measurements. The impact tests were carried out on a drop weight impact test system (9250HV, Instron, USA). The specimen dimensions were 55 mm×6.5 mm×2 mm, the impact span was 40 mm, the drop weight was 3 kg and the velocity was 2 m/s. Each reported data was averaged value of 5 specimens.
The interfacial shear strength
(IFSS) was adopted to quantify the interfacial property between CFs and resin matrix by the interfacial evaluation equipment (Tohei Sangyo Co Ltd., Japan). The tensile strength (TS) of a single filament was performed on an electronic mechanical universal material testing machine (Instron 5500R, USA) according to ASTM D 3379-75. A gauge length of 20 mm and cross-head speed of 10 mm/min were used for all fiber samples. At least, 60 specimens were tested for each fiber type, and then the average value was considered as the tested value. 3. Results and discussion 3.1 Surface chemical elemental composition XPS was performed to determine the chemical composition of the carbon fibers surface [35]. The surface composition of the untreated and treated carbon fibers was determined by XPS and the results are given in Table 1. The C1s XPS spectra of untreated and grafted with SPDPC and a combined SPDPC and amino-POSS are shown in Figure 3. Only a small amount of oxygen was observed on the untreated carbon fibers surface. However, it is noted that 16.86% oxygen was detected on the untreated fibers surface due to the oxidation of CFs from the process of fabrication. After grafting treatment with SPDPC, the content of element was changed. The carbon content decreased from 82.03 to 63.50 % and the oxygen content increased significantly from 16.86 to 31.84 %. In addition, significant phosphrous element of 3.44% and a little chlorine of 0.16% were detected on the fibers. It was attributed to the fact that SPDPC was grafted on the surface of CFs. After SPDPC 7
being grafted, the O/C value was higher than that of the untreated CFs. The change of O element and the appearance of chlorine were helpful to graft amino-POSS on CFs surface. From Table 1, it can be seen that after amino-POSS being grafted, the silicon was appeared with an element content of 6.67%. This shows that the amino-POSS was grafted on the surface of CFs successfully. 3.2 Surface topography of carbon fibers The AFM two-dimensional and three-dimensional images of untreated, SPDPC grafted carbon fibers and SPDPC- Amino-POSS grafted on carbon fibers are shown in Figure 3. The carbon fibers surface roughness was calculated from the plane topography images by using the AFM software is shown in Table 2. The functionalization process is shown in Figure 2. From the functionalization process, the SPDPC containing two flexible chlorine groups can not only react with the reactive groups on the carbon fiber surface, but also can react with reactive groups on the amino-POSS. Through the SPDPC, the amino-POSS can be grated on the surface of CFs. Amino-POSS has only one reactive group and if the reactive group reacted with SPDPC, amino-POSS had no other group that can react with resin matrix. Significant differences of the surface topography between untreated and modified carbon fibers were observed. As shown in Figure 3(a), (d), the surface of untreated CFs has many shallow grooves and seems to be relatively smooth, which is the typical topography of CCF300. Because the surface of untreated CFs was a little smooth, its roughness is a little small. The untreated CFs surface roughness is about 56.8 nm. It can be found in Figure 3 (b), (e) that the surface topography of the SPDPC grafted fiber becomes rougher and the particles of the SPDPC molecular are scattered on the surface and in the voids of the grooves of fibers, which could be interpreted by the existence of scattered hydroxy on the surface of fibers after reduction. In addition, the surface average roughness was increased from 56.8 to 79.1 nm compared with the untreated CFs. The 8
roughness of CFs was increased by 28%. As shown in Figure 3(c), (f) on the surface of CFs-SPDPC-amino-POSS, a layer of amino-POSS particles appeared and the carbon fibers became much rougher than the untreated CFs and SPDPC grafted CFs. The protuberant area becomes bigger than that of the SPDPC grafted alone, suggesting the aggregates of POSS nanoparticles. The surface roughness of the fibers after grafted with amino-POSS was the biggest among all samples and was 112.6 nm. It increased by 50%. The increased surface roughness can significantly increase the interfacial adhesion by enhancing mechanical interlocking between the fibers and the matrix. 3.3 Dynamic contact angle analysis It is well known that the chemical composition and topography of the fiber surface can affect the fiber surface energy as well as its components. Good wettability between carbon fibers and matrix is closely related to the fiber surface energy, and integrative properties of the carbon fibers reinforced resin matrix composites are directly controlled by the wettability of fiber surface and matrix. The surface wettability of CFs was evaluated by surface free energy. The overall performance of the fibers-reinforced composites is closely related to the wettability of the fiber surface with matrix. An excellent wettability means a high interfacial strength. Generally, the fibers were pre-treated before their usage as reinforcement aiming to obtain the fibers with surface energy higher or equal to the surface energy of matrix for the improvement of wettability. In this work, the surface wettability of CFs was evaluated via a Cahn dynamic angle analysis system. The advanced contact angle( θ ), the total surface free energy ( γ ),
its dispersion
component ( γ d ) and polar component ( γ p ) of
untreated and treated CFs are summarized in Table 2. The total surface free energy of the untreated CFs was 34.46 mJ·m-1, and its dispersion component and polar component was 23.82 and 10.64 mJ·m-1, respectively. After functionalization with SPDPC, the surface energy 9
obviously increased and its dispersion and polar components of CFs-SPDPC were 33.60 and 31.26 mJ·m-1, respectively. The highest surface free energy was 64.86 mJ·m-1, which belongs to CFs-SPDPC. This may be due to the existence of polar group chlorine. The increased surface energy can effectively improve the wettability of the fibers by the resin and increase the interfacial strength. After grafted with amino-POSS, the surface energy of the CFs was bigger than that of the untreated CFs but lower than that of the CFs-SPDPC. That may be due to the lower polarity of amino-POSS than that of SPDPC, which was 58.42 mJ·m-1. 3.4 Interfacial property testing 3.4.1 Interphase modulus testing The force modulation AFM (FAFM) was used to characterize both surface topography and hardness diagram of materials. FAFM can observe different hardness and elastic area distribution of the materials and can also be used to study the change of performance between different components of the composite. The hardness of the fiber, matrix and interface area was different. The information of the shape, distribution and relative hardness of different phase (including interface phase) can be obtained from the test and characterization of the composites surface within limits, which can provide the basis for the mechanism in the analysis of interface modification [36]. The force modulation images of the interphase region between CFs and UPR matrix were obtained from the cross-section of the composites reinforced by different carbon fibers, Figure 4. Figure 4(a, b & c) show the AFM force modulation images of the untreated, SPDPC grafted carbon fibers and SPDPC-Amino-POSS grafted CFs, respectively. Figure 4(d, e & f) show the cross-sectional images of the interphase of the untreated, SPDPC grafted and SPDPC-Amino-POSS grafted CFs, respectively. From Figure 4(a), no striking interface 10
region was observed between the CFs and UPR matrix region for composites and the modulus was observed to sharply change from the CFs to the UPR matrix region, Figure 4(d). The CFs reinforcement and UPR matrix can be distinguished clearly from Figure 4(a). There was an obvious transition layer between CFs and UPR in Figure 4(b&c). The interphase was observed to have a moderate modulus, which was lower than that of the CFs and higher than that of the UPR matrix from Figure 4(e & f). For the CFs grafted with combined SPDPC and amino-POSS, the interfacial transition region was longer than that of the CFs grafted with SPDPC alone, Figure 4(b & c), which is due to the bigger roughness of CFs grafted with a combined SPDPC and amino-POSS than that of the CFs grafted with SPDPC alone. The increased surface roughness has significantly increased the interfacial adhesion by mechanical interlocking the CFs with the UPR matrix, a similar phenomenon has been reported on the epoxy nanocomposites reinforced with graphene nanosheets decorated with protruding nanoparticles [37]. A little longer interface region can decrease the effect of the applied force on the composites of CFs and UPR. 3.4.2 The inter-laminar/interfacial shear strength and impact properties Short-beam bending tests were performed to evaluate the interfacial strength of the composites. Figure 5(a) shows the ILSS of the CFs/UFR composites. After grafted with SPDPC or a combined SPDPC and amino-POSS, the ILSS of the CFs/UPR composites was increased. The ILSS of the untreated CFs/UPR composites was 47 MPa，whereas the ILSS of the CFs grafted with SPDPC and grafted with a combined SPDPC and amino-POSS was 52 and 61 MPa, respectively. The ILSS of the composites of CFs grafted with SPDPC was lower than that of the composites of CFs grafted with a combined SPDPC and amino-POSS, which was increased by 9.6 and 22.9 %, respectively. Zhao et al. [11] have reported that the ILSS of the epoxy composites was increased by 18.2% by grafting octaglycidyldimethylsilyl POSS on the CFs surface. Zhang et 11
al. [38] have reported that the ILSS of the epoxy composites was increased by 9.6% by grafting graphene oxide on the CFs. All of the percentage increase is lower than the observed ILSS value here with CFs grafted with amino-POSS. The ILSS of the composites of the CFs grafted with a combined SPDPC and amino-POSS was much higher than that of the CFs grafted with SPDPC. The ILSS was increased by 14.8% compared with that of the CFs grafted with SPDPC alone. The ILSS of the composites of the CFs grated with a combined SPDPC and amino-POSS was increased more due to both the improved surface wettability and the improved surface roughness of the CFs.
The polarity of SPDPC was higher than that of amino-POSS. Amino-POSS contains 3-D Si–O cage structure, so that the surface of CFs has aggregated amino-POSS nanoparticles after the CFs grafted with a combined SPDPC and amino-POSS. The wettability of the CFs grafted with SPDPC was higher than that of CFs grafted with a combined SPDPC and amino-POSS (Table 2), however the surface roughness of the CFs grafted with SPDPC was lower than that of CFs grafted with a combined SPDPC with amino-POSS (Table 2). Although the wettability of the CFs grafted with SPDPC was higher than that of the CFs grafted with a combined SPDPC and amino-POSS, the ILSS of the CFs grafted with a combined SPDPC and POSS was bigger than that of the CFs grafted with SPDPC. The IFSS of the composites of CFs grafted with a combined SPDPC and amino-POSS was observed significantly increased compared with the composites of CFs grafted with SPDPC and composites with untreated CFs, Figure 5 (b), indicating an improved interfacial interaction after CFs grafted with a combined SPDPC and amino-POSS. The tensile strength of the as-received, grafted with SPDPC and a combined SPDPC and amino-POSS single CF follows the Weibull distributions plots, Figure 5 (c,d&e). Single fiber tensile strength is usually performed 12
to assess the influence of the grafting modification on the tensile strength of the fibers and the Weibull distribution is a continuous probability distribution and appropriate method to deal with the strength of many fibers. The strength of a single carbon fiber obeys the single Weibull distribution, i.e., the lower the Weibull shape parameter is, the more defects the fibers have [39]. Oxidation and grafting treatment will unavoidably introduce defects on the surface of fiber, which could decrease the fiber strength. However, compared with the strength of the as-received CFs (3.26 GPa), comparable fiber tensile strength is observed for the CFs grafted with SPDPC (3.28 GPa) and for the CFs grafted with a combined SPDPC and amino-POSS (3.31 GPa), suggesting that the chemical grafting of SPDPC and amino-POSS on the fibers has no significant effects on the fiber tensile strength. The results of single fiber tensile testing imply that the functionalization would not lead to any discernable decrease in the in-plane properties of the resulting composites. The impact property tests were carried out to further examine the effects of the SPDPC and amino-POSS grafting on the impact resistance of the composites. Figure 5(b) shows the impact property testing results. The total absorbed energy of the untreated CFs/UPR composites is 1.00 J. After modification, the impact toughness is increased significantly, 1.23 and 1.49 J for the composites containing CFs grafted with SPDPC and grafted a combined SPDPC and amino-POSS, respectively. The amino-POSS interphase served as a shielding layer, which could relieve the local stress concentration, prevent the crack tips to directly contact the fiber surface and make the crack path deviate away from the fiber surface to the interphase region. In addition, numerous amino-POSS nanoparticles on the fiber surface could induce more cracks and could efficiently absorb the fracture energy when the major crack passed through them [11]. 3.4.3 Interface property of the cryo-fractured surfaces of composites Figure 6 shows the SEM microstructures of the cryo-fractured surfaces of the composites. For the untreated 13
CFs/UPR composites, Figure 6(a), some fibers were pulled out from the UPR matrix, and the interface de-bonding between CFs and UPR matrix was observed obviously. After grafted with SPDPC, the surface of the CFs had polar groups, which increased the surface energy of CFs. The wettability of the CF surface with matrix was also increased. Some de-bondings are observed in the composites containing CFs grafted with SPDPC, Figure 6(b), although it has less de-bonding than the untreated CFs/UPR composites. The interfacial adhesion was observed to be dramatically improved between CFs and UPR matrix after grafted with a combined SPDPC and amino-POSS, Figure 6(c). This strong bonding has contributed to the stronger ILSS of the composites with CFS grafted with a combined SPDPC and amino-POSS increased by 22.9 % as compared with the composites of the CFs grated with SPDPC. The interface de-bonding between CFs and UPR matrix was not observed, indicating that the surface of the CFs grafted with a combined SPDPC and amino-POSS was rougher than that the CFs grafted with SPDPC only. It also indicated that roughness play a more important role than wettability. 4. Conclusion Through the SPDPC containing two flexible chlorine groups, the amino-POSS was grafted on the surface of CFs. SPDPC and a combined SPDPC and amino-POSS were uniformly grafted on the CFs surface. Both improved the interfacial adhesion between CFs and UPR matrix. The wettability of the CFs grafted with SPDPC was higher than that of the CFs grafted with a combined SPDPC and amino-POSS. However, the surface roughness of the CFs grafted with SPDPC was lower than that of the CFs grafted with a combined SPDPC and amino-POSS. For both the CFs/UPR composites, the ILSS and the impact resistance of the CFs grafted with a combined SPDPC and amino-POSS had been dramatically increased compared with that of the CFs grafted with SPDPC. In addition, from the force modulation AFM and SEM observations of the 14
cryo-fractured test, the interfacial adhesion of the CFs grafted with a combined SPDPC and amino-POSS was also better than that of the CFs grafted with SPDPC. The surface roughness (112.6 nm) of the fibers after grafted with amino-POSS was the biggest among all samples. For the wettability, the highest surface free energy was 64.86 mJ·m-1 for CFs-SPDPC. Both the ILSS and impact energy of the CFs grafted a combined SPDPC and amino-POSS was 61 MPa and 1.49 J, respectively, higher than that of the CFs grafted with SPDPC (52 MPa and 1.23 J). All experimental evidences indicated that the roughness played more important role than the wettability. Acknowledgements The authors would like to thank the Chang Jiang Scholars Program and National Natural Science Foundation of China (No.51073047, No.51173032) for financial support and the professor Caiying Sun in Northeast Forestry University for providing SPDPC. Z. Guo acknowledges the National Science Foundation (NSF, CMMI 10–30755) USA.
References 1.
Ogasawara T, Ishida Y and Kasai T. Mechanical properties of carbon fiber/fullerene-dispersed epoxy
composites. Compos Sci Technol. 2009; 69: 2002-2007. 2.
Norris CJ, Bond IP and Trask RS. The role of embedded bioinspired vasculature on damage formation in
self-healing carbon fibre reinforced composites. Compos Part A. 2011; 42: 639-648. 3.
Zhang XZ, Huang YD and Wang TY. Surface analysis of plasma grafted carbon fiber. Appl Surf Sci. 2006; 253:
2885-2892. 4.
Galan U, Lin YR, Ehlert GJ and Sodano HA. Effect of ZnO nanowire morphology on the interfacial strength of
nanowire coated carbon fibers. Compos Sci Technol. 2011; 71: 946-954. 5.
Sharma SP and Lakkad SC. Compressive strength of carbon nanotubes grown on carbon fiber reinforced epoxy
matrix multi-scale hybrid composites. Surf Coat Technol. 2010; 205: 350-355. 6.
An F, Lu CX, Li YH, Guo JH, Lu XX, Lu HB, He SQ and Yang Y. Preparation and characterization of carbon
nanotube-hybridized carbon fiber to reinforce epoxy composite. Mater Des. 2012; 33: 197-202. 7.
He XD, Wang C, Tong LY, Wang RG, Cao AY, Peng QY, Moody S and Li YB. Direct measurement of grafting
strength between an individual carbon nanotube and a carbon fiber. Carbon. 2012; 50: 3782-3788. 8.
Wang J, Wu D, Li X, Zhang M and Zhou W. Poly(vinylidene fluoride) reinforced by carbon fibers: Structural 15
parameters of fibers and fiber-polymer adhesion. Appl Surf Sci. 2012; 258: 9570-9578. 9.
Li J. The research on the interfacial compatibility of polypropylene composite filled with surface treated carbon
fiber. Appl Surf Sci. 2009; 255: 8682-8684. 10. Yang L, He XD, Mei L, Tong LY, Wang RG and Li YB. Interfacial shear behavior of 3D composites reinforced with CNT-grafted carbon fibers. Compos Part A. 2012; 43: 1410-1418. 11. Zhao F, Huang YD, Liu L, Bai YP and Xu LW. Formation of a carbon fiber/polyhedral oligomeric silsesquioxane/carbon nanotube hybrid reinforcement and its effect on the interfacial properties of carbon fiber/epoxy composites. Carbon. 2011; 49: 2624-2632. 12. Zhang XZ, Huang YD, Wang TY and Hu LJ. Effects of silsesquioxane coating structure on mechanical interfacial properties of carbon fibre/polyarylacetylene composites. J Mater Sci. 2007; 42: 5264-5271. 13. Li J and Cai CL. The carbon fiber surface treatment and addition of PA6 on tensile properties of ABS composites. Curr Appl Phys. 2011; 11: 50-54. 14. Yue ZR, Jiang W, Wang L, Gardner SD and Pittman Jr CU. Surface characterization of electrochemically oxidized carbon fibers. Carbon. 1999; 37: 1785-1796. 15. Li H, Liang H, He F, Huang Y and Wan YZ. Air dielectric barrier discharges plasma surface treatment of three-dimensional braided carbon fiber reinforced epoxy composites. Surf Coat Technol. 2009; 203: 1317-1321. 16. Guo H, Huang YD, Liu L and Shi XH. Effect of epoxy coatings on carbon fibers during manufacture of carbon fiber reinforced resin matrix composites. Mater Des. 2010; 31: 1186-1190. 17. Zhang RL, Huang YD, Su D, Liu L and Tang YR. Influence of sizing molecular weight on the properties of carbon fibers and its composites. Mater Des. 2012; 34: 649-654. 18. Zhu J, Wei S, Ryu J, Budhathoki M, Liang G and Guo Z. In situ stabilized carbon nanofiber (CNF) reinforced epoxy nanocomposites. J Mater Chem. 2010; 20: 4937-4948. 19. Kim HU, Bang YH, Choi SM and Yoon KH. Morphology and mechanical properties of PET by incorporation of amine-polyhedral oligomeric silsesquioxane. Compos Sci Technol. 2008; 68: 2739-2747. 20. Pallavi I, Javed AM and Maria RC. A hybrid functional nanomaterial: POSS functionalized carbon nanofiber. Nanotechnol. 2009; 20: 325603. 21. Feng Y, Jia Y, Guang S and Xu H. Study on thermal enhancement mechanism of POSS-containing hybrid nanocomposites and relationship between thermal properties and their molecular structure. J Appl Polym Sci. 2010; 115: 2212-2220. 22. Wang X, Hu Y, Song L, Xing WY and Lu HD. Thermal degradation behaviors of epoxy resin/POSS hybrids and phosphorus–silicon synergism of flame retardancy. J Polym Sci Part B: Polym Phys. 2010; 48: 693-705. 23. Chiu YC, Riang L, Chou IC, Ma CCM, Chiang CL and Yang CC. The POSS side chain epoxy nanocomposite: Synthesis and thermal properties. J Polym Sci Part B: Polym Phys. 2010; 48: 643-652. 24. Scapini P, Figueroa CA, Amorim CLG, et al. Thermal and morphological properties of high-density polyethylene/ethylene–vinyl
acetate
copolymer
composites 16
with
polyhedral
oligomeric
silsesquioxane
nanostructure. Polym Int. 2010; 59: 175-180. 25. Li G and Pittman C. Polyhedral oligomeric silsesquioxane (POSS) polymers, copolymers, and resin nanocomposites. Macromolecules Containing Metal and Metal-Like Elements: Group IVA Polymers, Volume 4. 2005: 79-131. 26. Scott D. Thermal Rearrangement of Branched-Chain Methylpolysiloxanes1. J Am Chem Soc. 1946; 68: 356-358. 27. Kuo SW and Chang FC. POSS related polymer nanocomposites. Prog Polym Sci. 2011; 36: 1649-1696. 28. Zhao F and Huang YD. Preparation and properties of polyhedral oligomeric silsesquioxane and carbon nanotube grafted carbon fiber hierarchical reinforcing structure. J Mater Chem. 2011; 21: 2867-2870. 29. Zhao F and Huang YD. Improved interfacial properties of carbon fiber/epoxy composites through grafting polyhedral oligomeric silsesquioxane on carbon fiber surface. Mater Lett. 2010; 64: 2742-2744. 30. Zhao F and Huang YD. Grafting of polyhedral oligomeric silsesquioxanes on a carbon fiber surface: novel coupling agents for fiber/polymer matrix composites. J Mater Chem. 2011; 21: 3695-3703. 31. Song B, Meng LH and Huang YD. Improvement of interfacial property between PBO fibers and epoxy resin by surface grafting of polyhedral oligomeric silsesquioxanes (POSS). Appl Surf Sci. 2012; 258: 10154-10159. 32. Zhang QB, Xing HT, Sun CY, Xiang HW, Jiang DW and Qin LL. The mechanical properties and thermal performances of polypropylene with a novel intumescent flame retardant. J Appl Polym Sci. 2010; 115: 2170-2177. 33. Xiang HW, Sun CY, Jiang DW, Zhang QB, Dong CM and Liu L. Flame retardation and thermal degradation of intumescent flame-retarded polypropylene composites containing spirophosphoryldicyandiamide and ammonium polyphosphate. J Vinyl Add Tech. 2010; 16: 161-169. 34. Wu ZJ, Meng LH, Liu L, Jiang ZX, Xing LX, Jiang DW and Huang YD. Interfacial microstructure and properties of carbon fiber-reinforced unsaturated polyester composites modified with carbon nanotubes. J Adhes Sci Technol. 2014; 28: 444-453. 35. Zhang GX, Sun SH, Yang DQ, Dodelet JP and Sacher E. The surface analytical characterization of carbon fibers functionalized by H2SO4/HNO3 treatment. Carbon. 2008; 46: 196-205. 36. Li FB, Thompson GE and Newman RC. Force modulation atomic force microscopy: background, development and application to electrodeposited cerium oxide films. Appl Surf Sci. 1998; 126: 21-33. 37. Zhang X, Alloul O, He QL, Zhu JH, Verde MJ, Li YT, Wei SY and Guo Z. Strengthened magnetic epoxy nanocomposites with protruding nanoparticles on the graphene nanosheets. Polymer. 2013; 54: 3594-3604. 38. Zhang X, Fan X, Yan C, et al. Interfacial microstructure and properties of carbon fiber composites modified with graphene oxide. ACS Appl. Mat. Interfaces. 2012; 4: 1543-1552. 39. Liu Y, Liu, Y, Tan H, Wang C, Wei H, and Guo Z. Structural evolution and degradation mechanism of vectran® fibers upon exposure to UV-radiation. Polym. Degrad. Stab. 2013; 98(9): 1744-1753.
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Table 1 Surface chemical composition of CFs with different chemical grafting method
Element content (at%) Carbon fibers Untreated CFs CFs-SPDPC CFs-SPDPC-Amino-POSS
C 82.03 63.5 68.78
O
N
Si
P
Cl
O/C
Si/C
16.86 31.84 21.58
1.1 1.06 2.18
— — 6.67
— 3.44 0.79
— 0.16 —
0.20 0.50 0.31
— — 0.09
Table 2 Surface energy and Roughness of CFs with different chemical grafting
Contact angle (o)
Surface energy (mJ·m-1)
Water
Diiodomethane
γ
Untreated CFs
74.39
56.31
23.82
10.64
34.46
56.8
CFs-SPDPC
32.52
16.81
33.60
31.26
64.86
79.1
CFs-SPDPC-Amino-POSS
42.98
25.65
32.67
25.75
58.42
112.6
CF
Ra (nm) d
γ
p
γ
Figures and Figure Captions
Figure 1. Typical structure of (a) aminopropylphenyl POSS, and (b) SPDPC.
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Figure 2. Schematic grafting procedures of POSS functionalized CFs.
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Figure 3. AFM images of different carbon fiber surface. (a), (d) untreated (b), (e) SPDPC grafted (c), (f) SPDPC-POSS grafted, C1s XPS spectra of the (g) untreated CFs, (h) acidized CFs, (i) reduced CFs (g) CFs grafted with SPDPC, and (k) the CFs grafted with SPDPC-POSS.
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Figure 4. (a), (b), (c) AFM force modulation images of the untreated, SPDPC grafted CFs and SPDPC-Amino-POSS grafted CFs; (d), (e), (f) cross-sectional analysis of the interphase images of the untreated, SPDPC grafted CFs and SPDPC-Amino-POSS grafted CFs for CFs/UPR composites.
Figure 5. (a) ILSS and TS, (b) Impact test and IFFS of composites reinforced by the untreated and modified CFs; and weibull distribution plots of the (c) untreated single fibers; (d) CFs-SPDPC grafted single fibers; (e) CFs-SPDPC-amino-POSS grafted single fibers. 21
Figure 6. Morphologies of the fractured surface of CFs/UPR composites: (a) untreated; (b) CFs-SPDPC grafted; (c) CFs-SPDPC-amino-POSS grafted.
22