Polyhedral oligomeric silsesquioxanes/carbon nanotube/carbon fiber multiscale composite: Influence of a novel hierarchical reinforcement on the interfacial properties
Introduction
The use of carbon fiber in advanced fiber composites has risen exponentially because of their high specific strength, low weight, outstanding thermal properties and environmental stability [1], [2], [3]. Actually, the macroscopic properties of carbon fiber reinforced composites are critically based on the microstructure and performance of an inter-phase between the fiber and matrix [4], [5]. A better interaction between the matrix and fibers help to transfer the load efficiently from fibers through the matrix, resulting in structural coherence and stronger composites [6], [7]. Because of the chemically inert and unreactive nature of the surface carbon fiber, the interaction of the carbon fiber and resin matrices is usually weak [7], [8], [9]. At the same time there has been growing interest in plasma [10], [11], irradiation [12], [13], coating [2], [9], [14] and chemical treatment [15], [16] and so on to improve wet-out for processing and to optimize the micromechanics of composites.
The majority of surface modification has centered on the amelioration of the chemical component or roughness of fiber, which is considered to be the main factor affecting the fiber–matrix adhesion [17], [18]. In this method, grafting method that will not only change the roughness but also increase the surface functional groups, which make the fiber surface more compatible with the desired polymer matrix. Especially, there has been interest in grafting nanosurface modifier, such as carbon nanotubes (CNTs) or polyhedral oligomeric silsesquioxanes (POSS) onto the carbon fiber [19], [20], [21], [22], [23]. CNTs, POSS possess extraordinary properties [24], [25], [26], [27], [28] and can develop hierarchical structures by grafting onto the carbon fibers. This new formation inter-phase layer between the fiber and resin matrix plays a key role in transferring stress from the matrix to the fiber [29], [30] and results in strengthened fiber–polymer matrix interactions [31], [32], [33].
In order to develop a realistic understanding, not only of the adhesion between the fiber and the resin matrix, but also of the adhesion between the nano-particle and the interface, it is necessary to develop a systematic procedure to quantify the physical and chemical properties of the carbon fiber surface. New hybrid reinforcement should be designed to ensure the optimal design of composites. Firstly, the new hierarchical structure should greatly increase the carbon fiber surface roughness and specific area, which is expected to provide tether to the resin and enhance mechanical interlocking. Secondly, this should introduce reactive moieties and change the surface polarity of the fiber, which can increase interact covalently and wettability of the fiber with the resin matrix. In this paper, a new hierarchical structure through co-grafting carbon nanotube and polyhedral oligomeric silsesquioxane on the surface of the carbon fiber is prepared and its mechanism is investigated. This work mainly focuses on: (1) the feasibility of grafting the CNTs and POSS onto the carbon fiber surface, (2) effect of new hierarchical structure on the characteristics of the fiber and its interfacial properties.
Considering the graphitic surface and chemical inertness of carbon fiber, a series of chemical pre-treatment process was needed before the chemical grafting. Then, carbon fiber surface grafted the amine functionalized CNTs, further grafted functionalized POSS. This newly hybrid enhancement structure on the surface topography and chemistry changes of carbon fiber are obtained by scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Wettability studies were carried out by the dynamic contact angle analysis (DCAT). The hierarchical structure evolvement on the inter-phase bonding properties of carbon fiber/epoxy (CF/EP) composites is also researched by interfacial shear strengths (ILSS).
Section snippets
Materials
The carbon fiber was purchased from Jilin Chemical Industrial Bloc (average diameter 7 μm, the density 1.78 g/cm3, the linear density 0.199–0.202 g/m). Glycidylphenyl POSS (referred to as POSS) was purchased from Hybrid Plastics (USA) as crystalline powder. Amine functionalized carbon nanotube (referred to as NH2-CNTs, diameter 8–15 nm) was purchased from Chengdu Organic Chemicals Co. Ltd. Other chemicals, reagents and solvents thionyl chloride (SOCl2), dimethylformamide (DMF), tetrahydrofuran
Fiber grafting and chemical analysis
FT-IR characterization was performed to observe the functional change of carbon fiber. As seen in Fig. 2, FT-IR spectrum of untreated fibers did not show any absorption peaks, while acyl chloride functionalized carbon fibers showed wave number range of 3450 cm−1 due to presence of the OH group [34]. The negative inductive effect of the chlorine atom in the COCl group result in a shift in the stretching vibrations of CO groups (1720 cm−1) to a higher wave number. The nature of the interaction
Conclusions
A novel hierarchical reinforcing carbon fiber was prepared through co-grafting carbon nanotube and polyhedral oligomeric silsesquioxanes in an attempt to improve interface in carbon fiber/epoxy composites in this paper. FT-IR, TG, XPS, SEM study of carbon fiber surface confirmed that POSS and CNTs were uniformly grafted on the carbon fiber surface. The wettability and DCAT results show that the surface energy and the functional groups of the carbon fiber surface increased obviously after
Acknowledgements
This work was supported by the funding from Project funded by China Post Doctoral Science Foundation (grant no. 2014M551903) and National Natural Science Fund Program of China (grant nos. 51403119 and 51302154) and the Open Project of State Key Laboratory Breeding Base for Mining Disaster Prevention and Control (Shandong University of Science and Technology) (no. MDPC2012KF08).
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2023, Applied Surface ScienceCitation Excerpt :The fiber surface of HMCF demonstrates high chemical inertness; thus, grafting efficiency would be limited, and the surface activity pretreatment would be necessary [26]. Activation with acid is commonly used to introduce polar groups and increase fiber surface activity, thereby making surface modification feasible [6,29,30]. The activation treatment can considerably improve fiber surface activity and enhance the surface wettability of CF, which are convenient for radiation grafting reactions.