Effect of surface functionalization on the surface and interfacial properties of thermoplastic-coated carbon fibers
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摘要: 本文利用混酸氧化以及乙二胺接枝的方法得到羟基和氨基官能化炭纤维(CF―OH和CF―NH2),之后进行磺化聚醚醚酮上浆处理,制备了热塑性上浆剂涂层改性的功能化炭纤维(CF―OH―SPEEK以及CF―NH2―SPEEK),并研究表面官能团对热塑性涂层改性炭纤维表面以及复合材料界面性质的影响。结果表明,经表面功能化处理后,炭纤维的表面官能团含量以及表面润湿能力得到了明显的提高。核磁氢谱分析显示,引入的—OH、—NH2等基团与磺化聚醚醚酮发生化学反应,提高炭纤维和上浆涂层之间的结合能力。因此,与磺化聚醚醚酮直接涂层改性的退浆炭纤维(Desized-SPEEK)相比,CF―OH―SPEEK以及CF―NH2―SPEEK与聚醚醚酮复合时界面剪切强度分别提高了6.2%和14.0%,证明表面功能化处理有利于提高热塑性涂层改性的炭纤维复合材料的界面结合能力。Abstract: Hydroxyl- and amino- functionalized carbon fibers (CF―OH and CF―NH2) were prepared by surface oxidation with an acid mixture (H2SO4∶HNO3 of 3∶1 v/v) followed by grafting with ethylenediamine. The functionalized CFs were sized with a sulfonated poly (ether ether ketone) (SPEEK) sizing agent to prepare CF―OH―SPEEK and CF―NH2―SPEEK materials. The effect of surface functionalization on the surface properties of the CFs and their interfacial properties in PEEK matrix composites were investigated. Results showed that the content of polar functional groups and wettability of the CFs increased significantly after surface functionalization. Chemical reactions between the modified CFs and the sizing agent, improved the interfacial adhesion between them. The interfacial shear strengths of CF―OH―SPEEK and CF―NH2―SPEEK reinforced PEEK matrix composites were increased by 6.2% and 14.0%, respectively, compared with that of the composites reinforced with desized-SPEEK CFs. The surface functionalization helps improve the interfacial adhesion of thermoplastic-coated CF/PEEK composites.
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Table 1. The surface energy and its components of test liquids.
Test
LiquidsPolar
component
γp (mN/m)Dispersion
component
γd (mN/m)Surface
free energy
γ (mN/m)DI 51 21.8 72.8 CH2I2 0 50.8 50.8 Table 2. Surface roughness of CFs.
CFs Types Sa (nm) Desized CF 5.6±1.1 Desized−SPEEK 12.7±2.3 CF−OH 23.4±3.2 CF−OH−SPEEK 18.3±2.9 CF−NH2 27.2±4.8 CF−NH2−SPEEK 21.7±3.6 Table 3. Surface elemental compositions of CFs.
CFs Types Elemental compositions (%) O/C (%) C N O S Si Desized 83.70 0.85 12.70 − 2.75 15.17 Desized−SPEEK 82.46 − 15.73 0.53 1.28 19.08 CF−OH 73.95 − 23.98 − 2.07 32.43 CF−OH−SPEEK 75.29 − 22.97 0.64 1.10 30.51 CF−NH2 73.69 4.08 20.73 − 1.50 28.13 CF−NH2−SPEEK 75.07 3.21 19.67 0.69 1.36 26.20 Table 4. The fitting results of C1s curves.
CFs Types Peak assignment (%) Polar
functional
group (%)C—C C—N C—O C—S C=O O—C=O Desized 77.90 2.56 16.36 − − 3.18 22.10 Desized−SPEEK 72.90 − 17.70 2.43 3.38 3.59 27.10 CF−OH 67.06 − 20.89 − 4.89 7.16 32.94 CF−OH−SPEEK 68.12 − 21.12 2.50 4.25 4.01 31.88 CF−NH2 66.78 9.00 16.54 − 4.09 3.59 33.22 CF−NH2−SPEEK 67.20 7.18 16.94 2.46 4.15 2.07 32.80 Table 5. The dynamic contact angles and surface free energy results of CFs.
CFs Types Contact angle (°) γp(mN/m) γd(mN/m) γ(mN/m) DI CH2I2 Desized 72.99 52.81 8.12 32.69 40.81 Desized-SPEEK 59.28 36.66 12.26 41.25 53.51 CF-OH 48.82 24.31 16.00 46.39 62.39 CF-OH-SPEEK 52.74 29.22 14.59 44.54 59.13 CF-NH2 48.11 23.62 16.29 46.63 62.92 CF-NH2-SPEEK 51.15 27.15 15.14 45.36 60.50 Table 6. The results of tensile strength and Weibull modulus.
CFs Types Tensile strength(GPa) Weibull modulus(m) Desized CF 4.68 9.97 Desized−SPEEK 4.79 10.02 CF−OH 4.36 7.64 CF−OH−SPEEK 4.52 7.94 CF−NH2 4.37 6.79 CF−NH2−SPEEK 4.46 7.46 -
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