Conductive Polymer Composites and Electromagnetic Protection Fabrics: Manufacturing Techniques and Property Evaluations

Autor: Zheng-Ian Lin, 林政彥
Rok vydání: 2016
Druh dokumentu: 學位論文 ; thesis
Popis: 104
This study aims to apply conductive polymer composites as electromagnetic protection materials and electromagnetic protection fabrics. The study on EMI SE materials is divided into three parts. In the first part, PP/multi-walled carbon nanotube (MWCNT) composites are made using melt compounding, and are evaluated for mechanical properties, MWCNT distribution, melting and crystallization behavior, crystal structure, thermal stability, electrical conductivity, and electromagnetic interference shielding effectiveness (EMI SE),thereby examining the influences of the lengths of MWCNT. The test results show that MWCNT with a short length (i.e., S-MWCNT) contribute to better mechanical properties and have a better dispersion in the matrix. Regardless of MWCNT types, the combination of MWCNT prevents the growth of PP spherulites, and thus results in spherulites of a small size. MWCNT also serves as a nucleating agent for PP, thereby increasing the crystallization temperature. Compared to L-MWCNT, S-MWCNT results in higher crystallinity. Avrami theory analyses indicate that the addition of S-MWCNT provides PP/MWCNT composites with a particularly high crystallization rate. X-Ray diffraction (XRD) results show that the combination of MWCNT does not pertain to the crystal structure. The TGA test results show that L-MWCNT outperforms S-MWCNT in improving the thermal stability of PP, although both can significantly improve it. The addition of 8 wt% L-MWCNT in PP/MWCNT composites results in an optimal electrical resistivity of 65.02 ohm-cm and an average EMI SE of -29.47 dB. In the second part, a solution mixing method is used to combine plasticized polyvinyl alcohol (PVA) as a matrix and MWCNT as reinforcement to form PVA/MWCNT films. The films are laminated and hot pressed in order to form PVA/MWCNT composites. The control group is produced using a melt compounding method. The tensile properties, dispersion, melting and crystallization behaviors, thermal stability, electrical conductivity, and EMI SE of PVA/MWCNT composites are then evaluated and compared. The test results indicate that at 1.5 wt% MWCNT, PVA MWCNT composites exhibit the highest tensile strength, along with satisfactory melting and crystallization behaviors and thermal stability. When at 2 wt% MWCNT, PVA/MWCNT composites exhibit optimal electrical conductivity and EMI SE. In the third part, PVA/graphene nano-sheet (GNS) composites are produced using solution mixing and melt compounding methods, where MWCNT is added during the process. The test results show that PVA/GNS composites composed of 0.25 wt% GNS possess optimal tensile strength, while the others composed of 2 wt% GNS have a high glass transition temperature, thermal stability, electrical conductivity, and EMI SE. The addition of MWCNT provides PVA/GNS with a synergy effects of hybrid fillers, improving the their tensile strength, thermal stability, electrical conductivity, and EMI SE. Finally, the top and bottom layers are PP/MWCNT composites that enclose a PVA/MWCNT composite or a PVA/GNS composite. The layers of sandwich-structured composites are bonded using maleic anhydride grafted polypropylene (PP-g-MA) as a coupling agent. The sandwich-structured composites constructed with different combinations are then evaluated for tensile properties and EMI SE. The test results show that the incorporation of PP-g-MA reinforces interfacial adhesion between the sandwich-structured composites, thereby increasing their tensile strength. When consisting of a PVA/MWCNT interlayer, the sandwich-structured composites have an optimal electrical conductivity of 5.8 S/cm, and EMI SE of -34.68 dB for 0 GHz-1 GHz, -36.70 dB for 1 GHz-2 GHz, and -38.65 dB for 2 GHz-3 GHz. Sandwich-structured composites that have good mechanical properties, good flexibility and high EMI SE can thus be produced using a simple and effective manufacturing method. The examination of functional fabrics is divided into two parts. In the first part, this study uses a melt extrusion method, a method used for producing wires, to coat polyester (PET) yarns with PP and MWCNT. The resulting PP/MWCNT-coated PET conductive yarns are tested for their tensile properties, processability, morphology, melting and crystallization behaviors, electrical conductivity, and applications. The test results indicate that the tensile strength of the conductive yarns increases with an increase in the coiling speed, which contributes to a more single-direction-orientated MWCNT arrangement as well as greater adhesion between PP/MWCNT blends and PET yarns. Using 8 wt% MWCNT causes the crystallization temperature to increase by 18 oC and an electrical conductivity of 0.8862 S/cm is yielded. The processing technique for conductive yarns contributes to satisfactory tensile properties and electrical conductivity, and is thus suitable for the preparation of functional woven/knitted fabrics. In the second part, PP/MWCNT-coated PET conductive yarns are made into conductive woven/knitted fabrics. The fabric structure, tensile properties, static bursting properties, electrical properties, and EMI SE of the conductive fabrics are evaluated in terms of MWCNT content. The test results indicate that the conductive fabrics have optimal tensile strength and optimal bursting strength when composed of 2 wt% MWCNT. Both the conductive woven/knitted fabrics have a greater electrical resistivity and EMI SE as a result of more MWCNT, and also have a stabilized weavability. The EMI SE of the conductive woven/knitted fabrics increases when they are composed of three layers. The conductive fabrics proposed in this study have permanent electrical conductivity, a light weight, and flexibility. Moreover, their EMI SE reaches the protection level required by standard electronic devices.
Databáze: Networked Digital Library of Theses & Dissertations
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