Dielectric properties of Hybrid Carbon Nanotube (CNT) cellulosic fibre filled PLA composites

There is overflowing plastic pollution with a record of over 85% of marine litter being plastic and one of the solutions is to provide a sustainable environment while conserving the resources and environment. Therefore, the biodegradable and renewable hybrid composites were produced using polylactic acid (PLA) as the matrix. However, due to the polymer matrix having low dielectric properties, 2 types of fillers with different weight loadings which are cellulosic fibres (10, 20, 30 wt%) comprise of bamboo fibre (BF), sugarcane fibre (SF) and banana pseudo-stem fibre (BPF) and carbon nanotube (CNT) (1, 3, 5 wt%) were reinforced in the composite. In addition, when 2 types of fillers were added into the composite, it is difficult to determine the hybrid filler ratio and to have good interfacial properties between the matrix and fillers.Thus, this study aims to characterize the dielectric properties, thermal, composition and morphology of porous cellulosic fibre-filled PLA and CNT-filled PLA composites and to investigate the optimum loading for low dielectric constant of hybrid cellulosic fibre CNT-filled PLA composites. The cellulosic fibres undergo water retting process, manually extracted, and were treated with alkali treatment (sodium hydroxide), and the composites were fabricated using the solvent casting particulate leaching (SCPL) method. The optimum loading weight of the two different fillers was decided according to the low dielectric constant value range based on the previous study before the hybrid composites were produced. Besides, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyse the thermal behaviour, composition, crystallinity, and morphology of the PLA composites. The dielectric constant values presented that the optimum loading for cellulosic fibres and CNT were 30 wt% and 5 wt% respectively. All the composites eventually presented increasing values of dielectric constant and dielectric loss with the increasing frequencies whereas the conductivity values decreased when the frequency increased. In addition, the dielectric properties of the composites improved when cellulosic fibre filler was added into PLA composite. However, the value was too low to be used as low-k material. Therefore, CNT was added to form hybrid PLA composites and resulted dielectric properties which were suited to be a porous low dielectric material. Moreover, the TGA analysis showed good thermal stability with higher degradation temperature compared to pure PLA with the incorporation of cellulosic fibre fillers and CNT. Whereas the XRD analysis presented excellent crystallinity due to the nucleating ability of CNT and the alkali treatment done on cellulosic fibres. The FTIR analysis showed that both cellulosic fibres and CNT were present in the PLA composites and SEM analysis results also showed the porous structure was achieved by the SCPL method and the fillers were successfully grafted on the PLA matrix. In conclusion, the hybrid PLA composites were successfully fabricated having low dielectric properties with optimum loadings of 5 wt% for CNT and 30 wt% for cellulosic fibres.