Effect of silica and pofa on electrical, physical and mechanical properties of linear low-density polyethylene-natural rubber composite

• Main Author: Siti Sarah Junian
• Format: Thesis
• Language: English; English
• Published: 2017
• Subjects: TA401-492 Materials of engineering and construction. Mechanics of materials
• Online Access: https://eprints.ums.edu.my/id/eprint/38964/2/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/38964/1/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/38964/

Polymer composite is a versatile material used in making electrical insulating material to be used especially in high voltage system. Through this study, a new type of electrical insulating material is made by the addition of fillers. Application of this material, especially in high voltage, is in string insulation on transmission line, underground cables and transformer bushing cables. Besides that, this research adds value to natural rubber if it is used as electrical insulating material in the future. The purpose of this study is to characterise the performance of newly developed polymer composite, which is linear low density polyethylene-natural rubber with different type of fillers, namely palm oil fuel ash (POFA) and nanosilica, at different filler concentration of 0 to 6 parts per hundred (phr) to assess its use as a potential electrical insulating material. In this study, dielectric constant and tangent delta are investigated between 20Hz to 4000Hz. Corona discharge peak-to-peak voltage is investigated at electrical stress of 30kV. Other properties that are investigated are tensile strength, elongation at break, tensile modulus and water absorption. Fourier Transform Infrared (FTIR) spectroscopy is also done to analyse the changes in absorption bands, while Scanning Electron Microscopy (SEM) is performed to analyse the surface morphology. The results revealed that as frequency increased, the dielectric constant decreased for all samples. At 50 – 60 Hz, the dielectric constant for all type of composites increased. Corona discharge test showed that LLDPE-NR composites with nanosilica at 2phr decreased the PTP voltage by 16%, which were supported by Fourier Transform Infrared (FTIR) spectroscopy. FTIR revealed that the O-H bonds intensity of nanosilica at 3500-3200 cm-1 due to corona discharge test was less than POFA. From the tensile test, it was found that the tensile strength of LLDPE-NR composite increased the highest by 0.4% at 6phr of nanosilica. Elongation at break and tensile modulus also increased the most by 7% and 42%, respectively, at 6phr of nanosilica. Meanwhile, palm oil fuel ash (POFA) could increase the tensile modulus of the composite. The value of water absorption of LLDPE-NR with nanosilica was the lowest compared to composites with POFA. LLDPE-NR composite with nanosilica content of 2phr showed the best electrical properties, while LLDPE-NR composite with 6phr of nanosilica showed the best mechanical and physical properties. Nano-sized nanosilica particles have very large surface area as compared to micro-sized POFA particles. Because of that, nanosilica particles have better dispersion and large surface interaction with LLDPE-NR matrices which inhibited the motion of charge carriers within the composite. This resulted in increasing electrical insulating properties of LLDPE-NR composite. Better dispersion of nanosilica within the composite also resulted in stronger bonding with the polymer matrices. Nanosilica would act as temporary crosslinks between the polymer chains, which provided localized regions of enhanced strength, which would resist the growth of cracks or cavities in the LLDPE-NR composite. Meanwhile, micro-sized POFA particles have smaller surface area as compared to nanosilica. Because of that, micro-sized POFA particles have smaller surface interaction with LLDPE-NR composite which caused the charge carriers to be more mobile as compared to LLDPE-NR composite with nanosilica. This resulted in the decreasing of the electrical insulating properties of LLDPE-NR composite. POFA also have higher tendency to agglomerate together due to its large size as compared to nanosilica. Agglomeration of POFA, a type of defect within the composite, would weaken the mechanical strength of composite. Overall, LLDPE-NR composites with nanosilica fared better than POFA-filled composites in terms of electrical, physical and mechanical properties.