Bioinspired Modification via Green Synthesis of Mussel

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Bioinspired Modification via Green Synthesis of Mussel-Inspired Nanoparticles on Carbon Fiber Surface for Advanced Composite Materials Bo Gao, Wentao Du, Zhenna Hao, Haifeng Zhou, Dechun Zou, and Ruliang Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03590 • Publication Date (Web): 13 Oct 2018 Downloaded from http://pubs.acs.org on October 14, 2018

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ACS Sustainable Chemistry & Engineering

Bioinspired Modification via Green Synthesis of Mussel-Inspired Nanoparticles on Carbon Fiber Surface for Advanced Composite Materials Bo Gao a c, Wentao Du b, Zhenna Hao c, Haifeng Zhou b, Dechun Zou a*, Ruliang Zhang c*. a

Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer

Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P.R. China. b

College of Chemical and Environmental Engineering, Shandong University of Science

and Technology, 266590 Qingdao, People's Republic of China. c

School of Materials Science and Engineering, Shandong University of Science and

Technology, 266590 Qingdao, P. R. China.

Corresponding Author: Dechun Zou, Ruliang Zhang Tel/Fax: +86-10-6275-9799

ACS Paragon Plus Environment

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E-mail: [email protected] (D. C. Zou), [email protected] (R. L. Zhang)

ABSTRACT Carbon fibers with excellent performances suffer from their low surface activity in many applications. Modifying fiber surfaces can improve the properties of fiber-matrix interface, which can expand the usage of carbon fiber in the field of energy. However, there are two main problems in the most traditional researches: the damaged structure of fiber by pretreatment to build the active site, and the weak interaction between fiber and nanoparticles by deposition. Herein, we first report the bioinspired copolymerization of dopamine and poly(amidoamine) on the fiber surface using polydopamine (the versatile adhesives) as an efficient and robust platform to graft poly(amidoamine) onto fiber surface at room temperature. Systematic investigations were performed to explore optimum

conditions

and

the

reaction

mechanism

of

copolymerization

of

dopamine/poly(amidoamine) at different quantities of poly(amidoamine) on carbon fiber surfaces. The novel modification can introduce sufficient functionalization groups on fiber surface without decreasing fiber tensile strength, which can significantly increase the interfacial shear strength and impact strength of the resulting composites to 124.05 MPa and 91.17 KJ/m2, respectively. The novel strategy presents a promising and “green” platform to prepare advanced composite materials for the demand of highly mechanical properties and the usages of energy conservation.


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KEYWORDS: Carbon fiber; Bioinspired modification; Polymer composites; Mechanical properties; Interface/interphase

Introduction Carbon-based structures are versatile for high performance materials.1,2 Carbon fibers (CFs) with high specific strength, specific modulus, recyclability, and good corrosion resistance are widely used in many fields for desirable properties.3-5 Carbon fiber reinforced polymer composite is an ideal structural material in engineering applications, such as aerospace field, naval vessel, automation industry and so on. The key problem is weak properties of fiber-matrix interface due to the smooth and inert surface of fiber. Recently, many efforts were made to modify carbon fiber surface that could be changed from inert to activity for high performance composites.6-11 The most popular method is that the carbon fiber was treated with acid to build the active site on the fiber surface. And the active particles were then reacted with active sites. The introduction of active particles could introduce many functional groups onto fiber surface, leading to great improvement of fiber surface properties.12-15 However, the pretreatment could damage


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fiber surface structure, which could decrease the tensile strength of single fiber.16-20 Some researchers reported that carbon nanoparticles were deposited on the fiber surface, which will not damage the fiber surface. The main problem in this method is the relatively weak integrated strength between fiber surface and the carbon nanoparticles. Further surface structure designs and materials development are essential for improving the interfacial performance of fiber-matrix. Lee at al.21 reported that dopamine can self-polymerize to form surface-adherent polydopamine films onto most inorganic and organic materials under mild reaction conditions. This idea is inspired by the adhesive proteins of mussels. In the past years, many substrates, including graphene oxide and electrospun nanofibers, have been modified using dopamine due to the amazing sticking ability.22-26 Kaminska et al.27 described that dopamine derivatives were used to simultaneously reduce and functionalize

graphene

oxide.

Similarly,

the

way,

chemically

grafting

3,4-

dihydroxyhydrocinnamic acid onto PVA which was electrospun into nanofibers, was revealed by Son et al..28 Expectedly, CFs as amphiphobic substrates can be modified with PDA film, and the fiber surface can be transformed from inert and smooth to activity and roughness. Herein, we first report the copolymerization of dopamine (DA) and Poly(amidoamine) (PAMAM) on the fiber surface using polydopamine as an efficient and robust platform to graft PAMAM on the fiber surface. The novel method does not require pretreatment (like


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acid treatment) to build the active site on the fiber surface. The modification is achieved by one-step copolymerization of DA and PAMAM on the fiber at room temperature, which could significantly improve fiber surface properties without decreasing the tensile strength of single fiber. The PDA, known as versatile adhesives, can firmly introduce the PAMAM onto fiber surface. Therefore, sufficient fuctionalization groups can be adhered on fiber surface by this way, which can greatly increase the interfacial properties between carbon fiber and epoxy matrix. In addition, the intervention of PAMAM can change the morphology of PDA, which is also beneficial to improve interface properties of fibermatrix. Scheme 1 depicts the detailed functionalization processes. The satisfactory effect was confirmed by the excellent interfacial properties of carbon fiber-epoxy matrix. Our strategy will provide an interesting research guidance in the future of design and manufacture of advanced composite materials and the usages of energy conservation. The surface properties of carbon fiber were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectra, and scanning electron microscope (SEM). Mechanical properties of carbon fiber/epoxy composites were also investigated. The systematic study was carried out for physicochemical properties of functionalized fibers and the properties of the resulting polymer composites, which revealed the optimized conditions.


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Scheme 1. Schematic of copolymerization of DA/PAMAM on carbon fiber surfaces at room temperature. Experimental Section Materials Carbon fibers (T700-12K-50C, average diameter 7 μm) were manufactured by Toray Industries Inc. All chemicals were used as received unless stated otherwise. Dopamine hydrochloride was supplied by Sigma-Aldrich. Tris(hydroxymethyl)- aminomethane (Tris) were purchased from Aladdin (China). The matrix system is epoxy resin with 350-400 of molecular weight and hardener H-256 (3,3'-diethyl-4,4’-diaminodiphenyl methane,


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DEDDM). Other chemicals were obtained from Aldrich. The solvents are of analytical grade. Materials Carbon fibers were first treated by acetone to remove sizing agent (denoted as desized CFs). The copolymerization of DA and PAMAM on fiber surface was achieved by immersed desized CFs in the mixed aqueous solution of DA and PAMAM at room temperature for 4 h, 7 h, 10 h. There are six sets of experiments. The weight of DA is 0.2 g in per group, while the weights of PAMAM are 0.1 g, 0.2 g 0.4 g, 0.6 g, 0.8g, 0.9, respectively (CFPDA/PAMAM0.1,

CF-PDA/PAMAM0.2,

CF-PDA/PAMAM0.4,

CF-PDA/PAMAM0.6,

CF-

PDA/PAMAM0.8, CF-PDA/PAMAM0.9). The results were washed with water several times and then dried at 80 ℃ under vacuum for 12 h to obtain functionalized carbon fibers. Characterization of carbon fibers The fiber surfaces and the fractured surface morphologies of fiber reinforced composites were examined by a field emission scanning electron microscope. A SPEX 1403 (SPEX, USA) microscopic confocal Raman spectrometer was used to carry out Raman spectra. Fourier transform infrared spectra (FTIR) were conducted using a Perkin Elmer spectrometer (Spectrum one, USA). X-ray photoelectron spectroscopy (XPS, ESCALAB 220i-XL, VG, UK) spectra were performed with a monochromated Al Ka source (1486.6 eV) at a base pressure of 2 × 10-9 mbar. Interfacial evaluation equipment (Tohei Sayon


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Corporation, Japan) was performed to obtain interfacial shear strength (IFSS) of fibermatrix by single fiber micro-debond test. A universal testing machine (Instron 5500R, USA) as per ASTM D3379-75 was carried out to evaluate the tensile strength of single fiber. The interlaminar shear strength (ILSS) of carbon fiber composites was characterized using a universal testing machine (5569, Instron, USA) by the short-beam shear test according to ASTM D 2344. The drop weight impact test system was used to perform the impact tests (9250HV, Instron, USA). The specimens with dimensions of 55 mm × 6.5 mm × 2 mm were tested at an impact span of 40 mm. Results and Discussion Possible Mechanism of copolymerization of DA/PAMAM on fiber surface Lu et al. demonstrated the typical polymerization mechanism of DA.29 Two reaction pathways for the formation of polydopamine was presented in Figure S1 (Supporting Information). It is well known that the amino containing groups can be reacted with the quinone groups oxidized from the catechol moieties in PDA by Michael addition or Schiff base reactions, which can form the bond types of −C−NH or −CN under the alkaline solution.30-33 According to the summary above, the PDA and PAMAM (the molecular structure is showed in Figure S2 Supporting Information) could be cross-linked together on carbon fiber surface by copolymerization, and the mechanism was shown in Figure 1.


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Figure 1. Possible reaction mechanism between PDA and PAMAM. Optimum reaction time The reaction times of copolymerization between DA and PAMAM on fiber surfaces are 4 h, 7 h, 10 h, respectively, in this study. The morphologies of PDA/PAMAM on fiber surface at different reaction times were characterized by scanning electron microscopy (SEM). After incubation in buffer solution with DA and PAMAM for 4, 7, 10 h, Figure 2 (ac), the surface topographies of the modified CFs are distinctly different compared with desized CF. As shown Figure 2 b, a uniform layer with many nanoparticles was formed on the carbon fiber surface after 7 h of polymerization. Interestingly, after polymerization for 10 h, the surface morphology of CF-PDA/PAMAM is similar with the ones of 7 h. The results indicate that the polymerization morphologies of PDA/PAMAM on fiber will be changed as the reaction time increase and remain unchanged for more than 7 h.


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Therefore, the optimum reaction time can be considered as 7 h. In the following, the reaction time was set at 7 h to functionalize carbon fiber. Surface topography of carbon fibers Surface morphologies of CFs play a significant role on the surface properties of fiber and the interfacial properties of carbon fiber-epoxy matrix. As shown in Figure 2(d-j), SEM was used in this study to characterize the surface morphologies of CF-PDA/PAMAM0.0-0.8. As expected, the surface topography and roughness are distinctly different between desized and modified CFs. The surface of desized carbon fiber is smooth and neat, which is unfavorable to the mechanical properties of composite materials, Figure 2d. After PDA coated, a layer of polymer was formed on the fiber, leading to the increased roughness of fiber surface. Interestingly, the introduction of PAMAM in polymerization can change the morphologies of polymer coated on fiber surfaces. The nanoparticles were formed as the increased introduction of the amount of PAMAM, Figure 2(f-j). The nanoparticles were becoming more and more homogeneous from CF-PDA/PAMAM0.1 to CF-


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PDA/PAMAM0.6,

leading

to

a

very

uniform

layer

Figure 2. SEM images of carbon fiber surfaces: (a-c) the reaction times 4, 7, 10 h of carbon fibers in the buffer solution with 0.2 g PDA/0.6 g PAMAM, d) desized CF, e) CFPDA, f) CF-PDA/PAMAM0.1, g) CF-PDA/PAMAM0.2, h) CF-PDA/PAMAM0.4, i) CFPDA/PAMAM0.6, j) CF-PDA/PAMAM0.8.


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Scheme 2. The reaction mechanism of copolymerization of DA/PAMAM at different quantities of PAMAM on carbon fiber surfaces. of nanoparticles coated on the surface of CF-PDA/PAMAM0.6. The amount of PDA/PAMAM on fiber surface was also characterized by Thermogravimetric analysis (TG/1600LF, Switzerland). The results indicate that the most polar groups were existed on the CF-PDA/PAMAM0.6 in Figure S3 (Supporting Information). The uniform nanoparticles formed on the carbon fiber surface can greatly improve the surface properties, which can effectively increase mechanical properties of the resulting composites. However, the amount of nanoparticles decreased for CF-PDA/PAMAM0.8. Therefore, we also explored the causes of the experimental result and revealed the possible mechanism of polymerization at different amount of PAMAM by a diagram. In the process of


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modification, polydopamine is used as an efficient and robust platform to grafting PAMAM on the fiber surface. The first stage is the polymerization of DA on the fiber surface and the PDA/PAMAM can be then copolymerized on fiber surface. As shown in Scheme 2, there are a large number of DA molecules can reach the surface of carbon fibers and effectively copolymerize with PAMAM on fiber surface. Under this circumstance, almost PAMAM molecules could participate in the polymerization and be coated on the fiber. With the increased introduction of PAMAM molecules, the probability of DA molecular contact surface decreases gradually because the DA molecules are more dispersed among PAMAM molecules. In a word, an appropriate quantity of PAMAM molecules can effectively improve the surface topography of carbon fibers. Chemical analysis of functionalized carbon fibers The carbon types of carbon fibers can be effectively evaluated by Raman spectrum. Figure 3a showed the Raman spectra of desized CF, CF-PDA/PAMAM0.1, CFPDA/PAMAM0.6 in the Raman shift range of 200-3000 cm-1. There are two typical peaks at around 1350 (D band, the amorphous structures of carbon) and 1600 cm-1 (G band, the graphitic structures of carbon which is related with sp2 hybridized carbon-based material).34-37 The peak intensity of D and G band have been distinctly changed from desized CFs to PDA/PAMAM functionalized fibers. Interestingly, the ID/IG ratio (the area ratio of D to G band) of modified carbon fibers become higher compared with desized fiber. The highest ID/IG ratio is existed in CF-PDA/PAMAM0.6. The more introduction of


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PAMAM causes the increase of ID/IG ratio, which indicates the decrease of graphitic domains and the increase of active elements (such as N, O). This result reveals the more and more PAMAM molecules are participating in the copolymerization on the fiber surfaces. FTIR was performed to investigate the chemical groups on the carbon fibers without and with PDA/PAMAM. The FTIR spectrum of desized carbon fiber has no discernable and typical peaks in Figure 3b. In contrast, many distinct absorption peaks appear after copolymerization of PDA and PAMAM on carbon fiber surface. In the spectrum of CFPDA/PAMAM, the new adsorption peaks at 3470 cm-1, 3280 cm-1, 2940 cm-1, 1650 cm-1, 1530 cm-1, and 780 cm-1 appear. The new peak at 3470 cm-1 can confirm that the hydroxyl groups are introduced by PDA.38 The intense


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Figure 3. The Raman spectra (a) and FTIR spectra (b) of desized CFs and CFs after copolymerization of DA and PAMAM. of new peak at 3280 cm-1, 1530 cm-1, and 780 cm-1 can be ascribed to the effect of symmetric and asymmetric stretching vibration of −NH2 groups.39,40 As we all know, the synergistic effects of stretching vibration of −OH and stretching vibration of −NH2 lead to the broad and intense spectrum ranged from 3580 to 3000 cm−1.16,38,41,42 In addition, the intense of C=O groups in spectra increased from CF-PDA/PAMAM0.2 to CFPDA/PAMAM0.6 because of the more amount of PAMAM molecules on carbon fiber surfaces. These results suggest that the hydroxyl and amino groups were successfully introduced onto carbon fiber surface by copolymerization of PDA/PAMAM, which could significantly improve the surface wettability of fiber. XPS carbon core line spectra, corresponding with changes of carbon environment, shows changes in the binding energy of the ejected photoelectrons. XPS is an effective


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characterization means to determine the chemical composition of materials.43 XPS was performed to investigate the chemical composition of the desized CF, CF-PDA/PAMAM and the results were shown in Figure 4a and Table S1 (Supporting Information). Compared to that of desized CF, the peak intensity of N, O element showed a gradually increasing trend for the XPS survey spectra from desized CF to CF-PDA/PAMAM0.6. The N, O content significantly increases to 9.31%, 21.47 %, respectively, of CF-PDA/PAMAM0.6 from 1.09%, 9.20 % for desized CF. Especially, the N/C, O/C ratios greatly rise from 1.22%, 10.30 % to 13.59%, 31.35 %, respectively, in Table S1 (Supporting Information). However, the N, O content of CF-PDA/PAMAM0.8 and CF-PDA/PAMAM0.9 decreased to 5.96%, 17.03% and 4.65%, 17.54%, respectively. These results are consistent with the previous SEM research results, which reveal that 0.2 g/0.6 g of DA/PAMAM is the best ratio to modify carbon fiber.


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Figure 4. a) Wide XPS spectra, and respective C 1s fitting analysis of b) desized CFs, c) CF-PDA/PAMAM0.1, d) CF-PDA/PAMAM0.4, e) CF-PDA/PAMAM0.6, and f) CFPDA/PAMAM0.8. In order to elucidate the detailed information of the changed chemical groups on fiber surface, the XPS C1s core-level spectrum of desized CF and CF-PDA/PAMAM are presented in Figure 4 (b-f). The C1s spectra can be curve-fitted with four or five peak


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components at the binding energies (BEs), Table S2 (Supporting Information). In Figure 4b, there are four peaks (O=C-O, C-O, C-N and C-C) in C1s spectra of desized CFs. As for CF-PDA/PAMAM, it emerged carbonyl carbons CIV (C=O) as compared to the characteristics of desized CFs. In addition, the peak intense of carbonyl carbons CIV (C=O), oxygenated carbons CIII (C-O), and nitrous carbons CII (C−N) show a clearly increased trend from desized CFs to CF-PDA/PAMAM. Specially, the C-N and C=O contents dramatically increase from 8.71% and 0% (desized CFs) to 13.58% and 3.22% (CFPDA/PAMAM0.1), 20.10% and 5.66% (CF-PDA/PAMAM0.4), 23.85% and 8.24% (CFPDA/PAMAM0.6), respectively. The introduced network of PDA/PAMAM on the fiber surface would significantly improve the surface energy and wettability of carbon fibers by supplying many polar groups, resulting in the dramatically increased strength of carbon fiber-epoxy matrix interface. As expected, the active content on the fiber surfaces presents a decrease trend as the content of PAMAM continues to increase. The C-N and C=O contents drop from 23.85% and 8.24% for CF-PDA/PAMAM0.6 to 20.00% and 5.58% for CF-PDA/PAMAM0.8. These results can further confirm that the 0.2 g DA/0.6 g PAMAM is the best ratio for functionalizing carbon fiber.


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Figure 5. The respective N1s fitting analysis of a) desized CFs, b) CF-PDA/PAMAM0.1, c) CF-PDA/PAMAM0.4, d) CF-PDA/PAMAM0.6, e) CF-PDA/PAMAM0.8, and f) CFPDA/PAMAM0.9. Nitrogen-containing functional groups, especially −NH2 groups, play a significant role on improving the interfacial strength of the resulting composites. The detailed differences/similarities of nitrogen-containing groups between desized CFs and CFPDA/PAMAM were further analyzed by N1s spectra of the investigated samples. Figure 5 shows the N1s XPS core-level spectra for desized CFs and CF-PDA/PAMAM. The N1s corelevel XPS spectra of carbon fibers are decomposed into two Gussian peaks with the binding energy of 399.8 and 400.9eV respectively, which arise from N-H structure and CN structure.44,45 The relatively detailed information is shown in Table S3 (Supporting Information). From the N1s XPS core-level spectra, the N-H content increased from 45.40% for desized CFs to 49.22% for CF-PDA/PAMAM0.1, 56.11% for CF-PDA/PAMAM0.4,


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and 64.52% for CF-PDA/PAMAM0.6, respectively. The increased and sufficient amino groups could greatly improve the surface energy and wettability of fibers, which can be further reacted with epoxy molecules to form covalent bond between carbon fiber and epoxy matrix, leading to dramatically increased mechanical properties of carbon fiber reinforced composites. In addition, the amino groups can promote the curing of epoxy resin, which would be favorable to the properties of the resulting composites. However, the N-H contents of CF-PDA/PAMAM0.8 and CF-PDA/PAMAM0.9 decreased to 56.05% and 51.24% due to the excess addition of PAMAM molecules. The reaction mechanism was summarized in Section 3.3. Mechanical properties of carbon fibers and the resulting composites. The aim of modifying carbon fiber surfaces is to change the surface from inert and smooth to polar and rough, which can improve the surface energy and wettability of fiber surfaces (Table S4 (Supporting Information)), resulting in the increased interfacial strength between carbon fibers and epoxy matrix. The IFSS is an effective test means to characterize the ideal interfacial properties of fiber reinforced composites, which is performed by single-filament pull-out tests and calculated with Equation 1: IFSS = Fmax/πdl

(1)

where Fmax is the maximum load, d is the single fiber diameter, and l is the embedded length of a composites droplet. As shown in Figure 6 (a), the IFSS value of desized CFs


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reinforced composite is 69.47 MPa. After the network of PDA/PAMAM coated, the IFSS value reaches to 96.75 MPa with a 39.27% rise as compared to that of desized CF composite. As result of the introduction of PDA/PAMAM network could effectively activate the inert surfaces and increase the surface roughness of CFs, the better interfacial interaction of fiber-matrix would be obtained by enhancing resin infiltration. Interestingly, the IFSS value further increases to 107.57 MPa (CF-PDA/PAMAM0.2), and 117.19 MPa (CFPDA/PAMAM0.4) as the content of PAMAM increased. The increased PAMAM molecules will introduce more special three-dimensional structures and amino groups onto fiber surface. In addition, as shown in SEM images, the more introduction of PAMAM molecules can increase the surface roughness of fibers by forming a uniform layer of nanoparticles. CF-PDA/PAMAM0.6 reinforced composite reaches the highest IFSS value of 124.05 MPa with a 78.57% increase as compared to that of desized CF composite. With the further increased content of PAMAM, the IFSS values decrease from 124.05 MPa (CFPDA/PAMAM0.6)

to

118.36

MPa

(CF-PDA/PAMAM0.8)

and

107.01

MPa

(CF-

PDA/PAMAM0.9). This is due to the decreased amount of PDA/PAMAM network formed on the carbon fiber surfaces which can be observed in SEM images. Figure 6 (b) shows the results of the mechanical properties of carbon fibers and the resulting composites. In theory, the tensile strength (TS) of single fiber can represent its inherent mechanical property and further affect the in-plane properties of carbon fiber reinforced composites. As shown in Figure 6, it is surprising that the PDA/PAMAM hybrid


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coating introduces no deterioration to the single fiber tensile strength. The TS of CFPDA/PAMAM0.4, CF-PDA/PAMAM0.6 and CF-PDA/PAMAM0.8 rises to 4.8 GPa, 5.0 GPa and 4.7 GPa from 4.5 GPa of desized CF. The increased TS of carbon fibers could also enhance the mechanical properties of carbon fiber reinforced composites. The novel strategy would provide a new effective approach to change the fiber surfaces from inert and smooth to polar and rough without damaging the fiber tensile strength.


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Figure 6. (a) IFSS evaluation of CFs through pulling out the cured resin marbles from the single filament, (b) ILSS evaluation of carbon fiber reinforced composites by the short-beam shear test and TS evaluation of CFs, including desized CF, CFPDA/PAMAM0.4, CF-PDA/PAMAM0.6, and CF-PDA/PAMAM0.8. In addition, ILSS of carbon fiber composites were also performed by the short-beam shear test, in Figure 6 (b). The unidirectional composites were prepared with carbon fibers and epoxy resin by compression molding method. The curing process was at 363 K for 1 h, 393 K for 2 h and 423 K for 3 h and then the composites were cooled down at room temperature. Compared with desized CFs based composite (60.28 MPa), the ILSS values increase to 78.25 MPa (CF-PDA/PAMAM0.1), 85.37 MPa (CF-PDA/PAMAM0.2), 93.06 MPa (CF-PDA/PAMAM0.4), 97.89 MPa (CF-PDA/PAMAM0.6), 92.74 MPa (CF-PDA/PAMAM0.8), and 83.92 MPa (CF-PDA/PAMAM0.9). The highest ILSS value is 97.89 MPa, 62.39% increase compared with desized CFs composite. The copolymerization of PDA/PAMAM can introduce sufficient polar groups, especially amino groups, onto fiber surfaces, which can greatly improve the surface energy and wettability of fibers, leading to the significantly enhanced interfacial strength of fiber reinforced composites. Impact strength testing The interphase region between carbon fiber and epoxy matrix can affect the impact toughness properties of the composites.5 The impact strength of the resulting composites


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was performed by the drop weight impact test system. Figure 7 shows the impact strength of desized CFs and CF-PDA/PAMAM reinforced composites and a schematic illustration of the effect of the interphase on composites’ mechanical properties in the impact test. The changed trend of impact strength values is consistent to the SEM, IFSS, TS, and ILSS characterizations. The impact strength of desized CFs reinforced composites is 52.06 KJ/m2 in Figure 7 (a). After PDA/PAMAM coated, the impact strength of the resulting composites increases to 71.25 KJ/m2 for CF-PDA/PAMAM0.1, 79.54 KJ/m2 for CFPDA/PAMAM0.2, and 85.86 KJ/m2 for CF-PDA/PAMAM0.4. Surprisingly, the CFPDA/PAMAM0.6 reinforced composites reaches the highest impact strength of 91.17 KJ/m2, with a dramatical enhancement of 75.12 % as compared with desized CFs based composites. Such


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Figure 7. (a) Impact strength of carbon fiber reinforced composites by the drop weight impact test system, (b) Schematic of the impact test of the composites reinforced with desized CFs and CF-PDA/PAMAM. an observation could be ascribed to the increase of interfacial strength as discussed above. Interestingly, CF-PDA/PAMAM0.8 and CF-PDA/PAMAM0.9 reinforced composites have the slight descendent impact strength, which may be due to the decreased amount of PDA/PAMAM on fiber surface. Figure 7 (b) shows a schematic illustration of the interphase in the resulting composites. If there exists no transition region between carbon fiber and epoxy matrix, the crack tip will extend perpendicularly to the fiber surface when the composites are suffered by external force, leading to the fiber could be easily fractured.4 After functionalizing CFs with PDA/PAMAM, the transition region corresponding to the appropriate interphase would appear in fiber-matrix interface. The interphase like a shielding layer could induce more cracks to the transition region, which would prevent the crack tips from directly extending to the surfaces of carbon fiber.4,5 Therefore, the existent interphase region will be significantly favorable to enhance the mechanical properties of carbon fiber composites. The existent interphase region was


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confirmed by EDX for the distribution of carbon element, the results are shown in Figure S4 (Supporting Information). From the distribution of carbon element, the interfacial region increases after PDA/PAMAM functionalized, which reveals the interface linkage between carbon fiber and epoxy matrix is enhanced greatly, leading to the great improvement of mechanical and thermal properties of fiber reinforced composites. Fractured surfaces of composites The fractured surfaces of the resulting composites can directly reflect interfacial properties of fiber-matrix. The fractured surface of composite samples after ILSS test was viewed under SEM, as shown in Figure S5 (Supporting Information). After PDA/PAMAM modified, there are no pulled-out fiber and fracture step, which indicates that the fiber surface wettability and mechanical interlocking of fiber-matrix were dramatically enhanced. Figure 8 shows the fractured surfaces of the resulting composites in the weft direction. As shown in Figure 8a, the desized CFs are completely separated from the matrix because of the poor interface bonding between fiber and matrix. After functionalized, the increasing number of resin fragments coated on the fiber reveals the significant enhancement of interfacial property between CF-PDA/PAMAM and epoxy matrix. The complete integration between CF-PDA/PAMAM0.6 and epoxy matrix shows the highest interfacial strength in Figure 8d. The high performance is attributed to the special structures of PAMAM and the sufficient active groups on the fiber surface. However, the


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interfacial properties decreased as the excess addition of PAMAM. These results are consistent to the above discussion.

Figure 8. The fractured surfaces of composites reinforced by a) desized CFs, b) CFPDA/PAMAM0.1, c) CF-PDA/PAMAM0.4, d) CF-PDA/PAMAM0.6, e) CF-PDA/PAMAM0.8. Conclusions With an aim to prepare advanced composite materials without damaged tensile strength of carbon fibers, we first report the bioinspired synthesis of mussel-inspired nanoparticles on fiber surfaces using polydopamine as an efficient and robust platform to graft poly(amidoamine) onto fiber surface at room temperature. The optimized conditions, including reaction time and the amount of PAMAM molecules, were researched. The network of PDA/PAMAM adhered on fiber with sufficient polar groups


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serves as an effective linker between fiber and matrix, which could release interior and exterior applied forces. The experimental results indicate that the network of PDA/PAMAM0.6 adhered on fiber can significantly enhanced mechanical properties of carbon fiber composites with dramatical increases of 78.57% for IFSS, 62.39% for ILSS, and 75.12% for impact strength of CF-PDA/PAMAM0.6 based composites. Such high values of fiber based composites are seldom reported in the literature. The novel strategy presents a promising and “green” platform to prepare high-performance composite materials, which are of great interest to the industrial field. SUPPORTING INFORMATION 1. Additional data and figures. (Figure S1-S5, Table S1-S4, Page S2-S15) 2. References (Page S14) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT This work is jointly supported by National Natural Science Fund Program of China (Grant No. 51573004, Grant No. 51773003, Grant No. 51711540302), and the Beijing Natural Science Foundation (Grant No. Z160002, Grant No. 2184134).


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For Table of Contents Use Only


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The network of PDA/PAMAM adhered on fiber with sufficient polar groups can significantly enhance the interfacial properties of carbon fiber based composites. Carbon fiber and its composites with high specific strength, recyclability, and good corrosion resistance are the sustainable material in many fields.


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113x78mm (300 x 300 DPI)


Bioinspired Modification via Green Synthesis of Mussel

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