Production of the thermoplastic composites with electromagnetic shielding property

While smart mobile phones, electronic devices, electric vehicles, wireless internet networks, satellite, radar, communication or sensor systems, which are indispensable by entering our lives as a result of the developments in technology in the 21st century, make human life easier, the negative effects on human health caused by the electromagnetic (EM) radiations emitted by these devices are gradually increasing. In addition, electromagnetic interference prevents the devices from working properly. In recent years, the importance of electromagnetic shielding materials has increased with the awareness of the society on this issue and the publication of guidelines and standards by relevant institutions on EM interference prevention and exposure limits to electromagnetic field. In this respect, EM shielding materials gained critical importance especially for recyclable thermoplastic materials which are used extensively in electronic devices and systems or vehicles, in terms of reducing environmental problems, human health and device safety. The aim of this thesis is to develop thermoplastic composites with EM shielding properties, which can be used in electronic devices, automotive, aerospace and defense sectors, using poly(butylene terephthalate) (PBT) matrix, a recyclable thermoplastic polymer, and nickel-coated carbon fiber and titanium dioxide-nickel-coated carbon fiber reinforcements and TiO2 nanoparticles in the matrix as additives. In this thesis, first of all, optimum coating parameters for nickel and TiO2-Nickel coating on carbon fiber by electrodeposition method were determined. Electrical, morphological and structural properties of coated carbon fibers were investigated. Afterwards, carbon fibers coated with nickel and TiO2 nanoparticles were mixed with PBT polymer by melt mixing method with a twin screw extruder and composite test plates were produced by injection molding method. The effects of additive types and ratios on the thermal, mechanical, electrical properties and EM shielding efficiency of the developed composites were investigated. In the last part, in order to examine the effect of TiO2 nanoparticles added to the matrix; PBT granules were coated with TiO2, then mixed with nickel-plated carbon fibers with a twin screw extruder, and composite test plates were produced by injection molding method. The effects of TiO2 nanoparticle amount and additive types on the thermal, mechanical, electrical properties and EM shielding efficiency of the produced composites were investigated. As a result, an average of 55.1 dB (99.9997%) EM shielding efficiency was achieved in the 8 - 13 GHz frequency range with PBT composites with a thickness of 3 mm containing 30% by weight TiO2-Nickel coated carbon fiber, an average of 18.4 dB EM xxiii shielding efficiency (98.4151%) was obtained in the 500 MHz - 4 GHz frequency range. It was concluded that the use of TiO2 nanoparticles as dispersed in the matrix instead of coating the carbon fibers with nickel contributes more to the EM shielding properties both in the low frequency range (500 MHz - 4 GHz) and in the high frequency range (8 - 13 GHz). With the addition of 3% by weight TiO2 to the 3 mm thick PBT composite containing 20% by weight of nickel-plated carbon fiber, the average EM shielding value in the 8 - 13 GHz frequency range increased by 18.2%, reaching from 44.1 dB (99,9961%) to 51.7 dB (99.9994%). In addition, an efficiency close to the EM shielding value (56.0 dB, 99.9997%) of the PBT composite containing 30% nickel-coated carbon fiber was obtained. With the contribution of TiO2 nanoparticles, the EM shielding efficiency was increased in the 8 - 13 GHz frequency range with the composite with lower weight and density. It was concluded that there is a synergistic effect between nickel coated carbon fiber with electrical conductivity and magnetic properties and TiO2 nanoparticles with dielectric properties. Developed composites can be used in electromagnetic shielding applications in electrical-electronics, automotive, aerospace and defense industries.