Properties With Mechanisms Of Epoxy Resin/"Milled Short Carbon Fiber/Sericite" Composites

Electrically conductive polymer composites show great potential of application in such fields like electronical, electric and aerospace industries, for purposes of providing protection against electrostatic, being enclosures for electronic equipments to shield them from outside electromagnetism radiation, and fabricating molectron, linker, apparatus shell, as well as other products related to computer and even artificial organs.The epoxy resin (EP) is a widely-used commodity polymer, especially as a traditional material of electrical insulator. However, its outstanding features, such as chemical and corrosion resistance, processability and the low price make EP favorable for expanded application. In recent years, conductive carbon fiber, carbon nanotube, and graphite et al. were blended into EP to produce EP electrically conductive composites. However, only a few focused on enhancing the electrical and mechanical properties of composites at the same time. The principle of powders'complex is to blend two or several powders differing in shape, physical and chemical properties etc. together, to produce the desired synergism, which would contribute a lot to reinforce the composite or offer it some other favorable functionalities, either of powders alone can never achieve. This is very illuminating on producing EP conductive composites with obviously reinforced mechanical properties.The dissertation aims to prepare mechanically reinforced EP conductive composite with low volume resistivityρv, by means of designing the synergism between the fillers of milled short carbon fiber powder (SCF) and sericite. Firstly, the EP/SCF composites were prepared. Then, the"SCF/sericite"complex powder was filled in EP to gain the better mechanical properties than EP/SCF. The major research contents and results are stated as below:1. Using the supersonic jet mill to further pulverize and modify sericite powders with 2wt% stearic acid. Analysis of FTIR graphs of modified sericite indicated that the sericte displayed two new absorption peaks at wave number 1575 cm-1 and 1546 cm-1, which were thought as the characteristic peaks of C=O's anti-symmetric stretching in -COO- of carboxylate and correspondingly its absorption peaks at wave number between 1725 cm-1 and 1700 cm-1of C=O's anti-symmetric stretching in the carboxyl group -COOH of stearic acid vanished. Therefore, it can be safely concluded that due to the intensive mechanochemical force in the mill, hydroxyl O-H of carboxyl group -COOH in stearic acid must split to form the -COO- in process of sericite's pulverization and modification, which enable the stearic acid to chemically adsorb on sericite and form"sericite/steric acid"complex powder.2."SCF/sericite"complex powder was prepared by means of mechanical blending. The microphotographs under Scanning Electron Microscopy (SEM) and surfaces'elementary analysis by Energy Dispersive Spectrometer (EDS) on complex powder showed that two powders are so compatible that some modified sericite firmly adsorbed on the surface of SCF and thereby formed"SCF/sericite"complex powder, which greatly modified both the morpha and chemical property of SCF's surface by making it rougher and more hydrophobic. It is a interesting synergism between complex powders unreported previously.3."SCF/sericite"complex powder proved to be quite effectual to reinforce the EP and lower its volume resistivityρv simultaneously, even more effective than SCF alone. EP/SCF/Sericite (67/25/10) exhibited best all-round performance. Itsρv was lowered to 2.25×108·cm from 1.14×1015·cm of EP, and its tensile strength, tensile elastic modulus and impact toughness were 49.6 MPa, 1030 MPa and 6.96 kJ·m-2, enhanced by 29.8 MPa, 684 MPa and 3.87 kJ·m-2 respectively, compared to those of neat EP. When contrasted with EP/SCF (67/25), itsρv only rose less than one magnitude while its tensile strength rose 12.2 MPa, tensile elastic modulus 120 MPa and impact toughness 0.77 kJ·m-2.4. SEM microphotographs of fracture surfaces of EP/SCF/sericite composites, and the corresponding EDS analysis demonstrated that some interfacial substance adsorbed on pull-out part of SCF. Therefore, it can be safely concluded that due to the good compatibility between sericite and SCF, the two powders were able to compound to form"SCF/sericite/stearic acid"structure on surface of"SCF/sericite"complex powder, resulting in the superior interfacial adhesion between"SCF/sericite"and EP which is responsible for improved mechanical performance of EP/SCF/sericite composites. The assumption of producing mechanically reinforced EP conductive composites by virtue of complex powders'synergism was realized by our experiments, elementarily.