| Highly aligned short carbon fibers (SCFs) reinforced composites can not only achieve high performances (such as high strength-to-weight ratio, high modulus-to-weight ratio and so on) mainly reinforced by continuous fibers, but also have the advantage of easy processability and low cost for preparing the complex structural shapes. Therefore, highly aligned SCFs reinforced composites can be used in some high-end fields, especially in aerospace and industry. However, how to improve the degree of alignment based on the well dispersion are scientific problems that to be solved for preparing high performance SCFs reinforced composites. Besides, how to make the production of alignment suitable for simple, highly efficient, environmentally friendly and large continuous process are engineering scientific problems. Therefore, the dispersion mechanism for SCFs was studied systematically using water as dispersion medium and biobased materials dopamine as surfactant. And the main influences on alignment of SCFs and alignment mechanism were system studied. Thus, the basic experimental datas and theoretical guidance could be provided for the preparation of aligned SCFs mats with environmentally friendly and large continuous process.pDop-SCFs was prepared successfully through self-polymerization of dopamine, and effect of dopamine modification on surface structure, activity and hydrophily was also studied. Besides, the effect of dopamine modification on mechanical properties of epoxy composites was further explored. The results showed that dopamine was successfully coated on the surface of SCFs to form smooth film of poly(dopamine) which could improve the surface activity and hydrophily. Besides, the interfacial strength was enhanced by dopamine modification, and the tensile strength and modulus rose by 18.3% and 19.8%, respectively, and the flexural strength and modulus rose by 21.2% and 27.4%.Effect of dopamine modification, dispersion viscosity, dispersion time and ultrasonic treatment on the dispersion state of SCFs in water was studied, the dispersion degree β value were used to qualitative and quantitative analysis respecively. The results showed that dispersion viscosity was the major determinant of SCFs dispersion and best dispersion state could be obtained when dispersion viscosity was about 1.0-4.0 Pa.s. Ultrasonic treatment improved the dispersion efficiency for SCFs dispersion markedly. Dopamine modification improved the stability of SCFs suspersion significantly. And besides, the mechanism of SCFs disperison was proposed:SCFs aggregate beared externally applied shear force (F) and the agglomeration force (Fr) between fibers during dispersion, and best dispersion state of SCFs could be obtained when F value was bigger than that of Fr.The laboratory-scale device was successfully designed and established based on convergent fluid induced alignment theory. The major factors affecting alignment behaviors and alignment mechanism of SCFs were studied systematically. The results showed that the high aligned SCFs mats with alignment degree of 93.4% were prepared successfully when dispersion viscosity was about 1.0-4.0 Pa.s, slit width of convergent nozzle was about 1.0 mm, the pressure was about 0.2 MPa and the conveyor speed was about 10 mm·min-1. And besides, second-order tensor quantitative characterization method for SCFs alignment was established based on SEM images of aligned SCFs mats. Furthermore, high aligned SCFs mats reinforced epoxy composites was prepared and the result showed that alignment of SCFs improved the tensile and flexural properties of composites significantly. And this will provide scientific methods for preparing high performance SCFs reinforced composites. |
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