1、Influence of silaned nano SiO2 on impact properties of carbon fiberInfluence of silaned nano SiO2 on impact properties of carbon fiber reinforced polyethylene composites Rong LiuSchool of Mechanical & Electronic Engineering, Hainan University, Hainan 878805, P.R. ChinaAbstractSilaned nano SiO2 was u
2、sed to improve the adhesion properties of carbon fiber/polyethylene(CF/PE) composites. The nano SiO2 were treated by silane under different discharge time. And the changes on the surface properties of the treated and untreated composites were studied by impact, three point bending tests and scanning
3、 electron microscope (SEM) analysis. The measurement showed that CF increases fracture toughness with the increase of CF content. While too much high content of CF did not further cause the increase of the toughness of CF/PE composite. The impact strength of silaned specimens is still higher than th
4、ose of the unsilaned ones. The modified composite with the good matrix/fiber adhesion possessed 20% higher interlaminar shear strengths compared to the composite having weak interface.Keywords: SiO2; CF/PE; toughness1. IntroductionDuring the last decade, considerable attention was paid to inorganico
5、rganic hybrid materials because their solid state properties could be tailored in relation to the nature and relative content of their constitutive components. Low-volume additions (15 wt.%) of highly anisotropic nanoparticles, such as layered silicates, provide property enhancement with respect to
6、the neat polymer that are comparable to those achieved by conventional loadings (1540 wt.%) of traditional fillers. Besides, unique value added properties not normally possible with traditional fillers are also observed, such as enhanced strength, electrical conductivity, electrostatic discharge, re
7、mote-actuated shape recovery and ablation resistance1-3. In other publications, fracture toughness was improved by adding spherical nanoparticles in which quality nano-dispersion is easier to achieve 4,5. Filler/matrix interaction and achieving quality dispersion seem to be the key factors for fract
8、ure toughness enhancement for nano-scale fillers.One of the major concerns in designing composite structures is their susceptibility to impact loading. Fiber-reinforced polymer-matrix composites are known to be highly susceptible to internal damage caused by transverse loads, even under low-velocity
9、 impacts6,7. The composites can be damaged on the surface as well as beneath the surface with relatively light impacts causing barely-visible impact damage, while the surface may appear to be undamaged to visual inspection. For the effective use of fiber-reinforced polymer-matrix composites for high
10、-performance applications, understanding the causes for the formation of such damage under low-velocity impact and improving the damage-resistance characteristics of the composites are important considerations which have been the topic of extensive research for the last few years. Review articles on
11、 the impact behaviour of polymer-matrix composites covering con-tact laws, impact dynamics, stress analysis, damage mechanics, post-impact residual property characterization and damage-resistance improvements are available in the literature 8,9. Many research publications are available on the impact
12、 behaviour of polymer-matrix composites covering specific aspects 10,11.Matrix deformation and micro-cracking, interfacial debonding, lamina splitting, delamination, fiber break-age and fiber pull-out are the possible modes of failure in composites subjected to impact loading. Even though fiber brea
13、kage is the ultimate failure mode, the damage would initiate in the form of matrix cracking/lamina splitting and would lead to delamination. Damage-free composites are necessary for their effective use12.In this work, SiO2 is treated by silane in order to improve the surface properties of carbon fib
14、er. The purpose of this work is to study the impact properties of the PE composites filled with surface modified CF. Some insights into the impact fracture mechanisms of the PE composite are also given. 2. Experimental2.1 MaterialsHigh density polyethylene (HDPE) Tg: 85, Tm: 130 , p: 0.95 g cm-3 and
15、 Mw: 125,000 g mol-1, were all Merck (Germany) products and used as purchased.For the present investigation, the reinforcement materials were continuous polyacrylonitrile(PAN)-based carbon fibers manufactured by Shanghai sxcarbon Technology Co. Ltd .The silane (KH550) was dissolved in ethanol before
16、 use. The particles of nano-SiO2 were dispersed in ethanol and subjected to ultrasonic agitation for 15 min, the silane solution was then introduced and the ultrasonic treatment continued for 1 h.2.2 Composite preparationPE samples were first dissolved in 40 mL of xylene in a three necked flask. Req
17、uired amount of CF was added into the above solution. Indole was also dissolved in 10 mL of xylene and added into the same flask. The reaction mixture was washed with distilled hot water several times, and dried in a vacuum oven at 70 for 24 h.2.3 Impact and three point bending(TPB) testsA Charpy un
18、notched impact strength test was carried out on a pendulum impact tester (Model PH 125, Amsler & Co., Schaffhouse, Switzerland) with a capacity of 0.98 J. The test span was 20 mm, measured between the two specimen supports.The specimens were impacted on the narrow 1 mm surface, with the line of impa
19、ct midway between the supports, and the direction of blow normal to the plane of reinforcement.An INSTRON 4206 electromechanical machine was used to implement the three point bending test. 3. Results and discussion3.1 impact strength Fig. 1 The impact strength of CF/PE composite with CF contentThe r
20、esults of fracture toughness measurements are shown in Fig1. As seen in this Fig, CF increases fracture toughness with the increase of CF content. While too much high content of CF did not further cause the increase of the toughness of CF/PE composite. Based on the results shown in Fig1, it can be e
21、xpected that composites made using CF show improved interlaminar fracture toughness.Fig. 2 The impact strength of CF/PE composite filled with SiO2 with and without treatmentTo study the effect of silaned nano SiO2 modification on toughness improvement of final composite against through thickness cra
22、cks, the results of impact strength versus SiO2 content for notched test specimens are reported in Fig2. It is interesting that all samples fractured through thickness and increase in modifier content led to increased impact strength. While similar type of impact test was used to evaluate impact str
23、ength of CF modified PE composites, revealed no significant improvement in impact strength of the composite(Fig1). This can be attributed to the fact that the PE used in that particular investigation was not ductile enough to be toughened by CF modification. This is why no obvious improvement in imp
24、act strength of the composite was observed. The contribution of fibers in absorbing the impact energy is not influenced effectively by CF modification. In addition, Fig2 shows that impact strength of silaned specimens are still higher than those of the unsilaned ones. The modified composite with the
25、 good matrix/fiber adhesion possessed 20% higher interlaminar shear strengths compared to the composite having weak interface. Therefore one may conclude that silaned SiO2 modification improves crack initiation energy of the composites.The mechanical benefit of these nanoscale materials appears to i
26、ncrease as stress intensity decreases. They are not capable of hindering crack propagation (fracture toughness) once a crack begins to advance, but their nano-scale dimensions enable them to better interact with the matrix before a critical crack is initiated. In addition, SiO2 maintain their high a
27、spect ratio post-processing.This allows for a delay in craze formation and coalescence prior to crack initiation. CFs do not present an aspect ratio which favours a strong interaction with the matrix, reducing creep improvement. On the other hand, the larger size of the CFs allows them to slow the g
28、rowth of the crack by deflection, pull-out and crack bridging mechanisms. When an advancing crack is presented with a CF, it is deflected following the CF/matrix interface, eventually leading to the pullout of the filament. The surface modification was said to help in exfoliating agglomerations and
29、strengthening SiO2matrix interactions.The effect of SiO2 addition on the failure behavior of CF/PE is illustrated by the SEM micrograph shown in Fig. 3. Fiber pull-out is still evident on the fracture plane and no PE matrix appears to adhere to the fiber surface. The ductile failure of the PE matrix
30、 changes to a brittle one that is associated with some limited crazing. The craze remnants on the fracture surface are clearly visible. Thus, it can be expected that, during the fracture process, the resistance to crack propagation will be reduced markedly and the samples fail in a more brittle mann
31、er. (a)(b)(c)Fig. 3 The impact fracture morphology of CF/SiO2/PE compositeAs seen, plastic deformations at the plastic zone of modified resins are accompanied by stress whitening. The size of stress whitening increases with increasing the SiO2 content; such that in 5vol% specimen, it expands to the
32、whole surface in front of the crack tip (Fig. 3a). The difference in the damage zone sizes seen in Fig. 3 is in agreement with fracture toughness data reported in Fig2.The flat and almost featureless image seen in Fig. 3a indicates the typical brittle fracture of neat PE. On the other hand, the rough fracture surface of 3vol% specimen seen in Fig. 3b shows the significant amount of plastic deformation occurred in this material prior to fracture. It is found that cavitation is a prerequisite for massive shear deformation of the matrix. The latter is known as the main source of energy abs
