Abstract:
This study deals with the effect of two conductive fillers (viz boron nitride (BN) and single walled carbon nanotubes (SWCNT)) on the properties of the linear low density polyethylene (LLDPE) matrix and LLDPE/paraffin wax blend. The pure LLDPE and paraffin wax/LLDPE blend (30/70) were melt-mixed with 1,2 and 3 wt.% content of BN and SWCNT, respectively. Because it is well-known that both conductive fillers are able to improve the thermal conductivity of the paraffin wax/polymer blends, the aim of this study was to focus on the effect of both conductive fillers on the dispersion of paraffin wax into LLDPE matrix, mechanical properties, crystallization behaviour, and thermal stability of the LLDPE/wax blend. Scanning electron microscopy (SEM) images of the LLDPE/paraffin wax blends depicted a phase separated system, which was further supported by two separate peaks from the differential scanning calorimetry (DSC). The SEM images of 2wt.% BN incorporated into the LLDPE matrix without paraffin wax showed an agglomerated BN nanoparticle within the matrix. It was further shown from the morphology that the addition of BN into the LLDPE/paraffin wax blend had no affinity with the paraffin wax, while the addition of SWCNT showed better dispersion into the LLDPE/paraffin wax/BN blend composites. This better dispersion is attributed to a high affinity between the carbon-based filler and paraffin wax. There was an enhancement in the crystallization temperature and degree of crystallization in the presence of both BN and SWCNT, which is due to the nucleating effect of the two conductive fillers into the LLDPE and LLDPE/wax blend. From the thermal gravimetric analysis (TGA), it is evident that the incorporation of the SWCNT and its synergy with BN enhanced the thermal stability of the LLDPE by forming a heat barrier that could have prevented the entrance of heat into LLDPE matrix. Generally, there was a reduction in tensile strength with the addition of paraffin into the BN/LLDPE and SWCNT/LLDPE composites, which is due to wax crystals crystallizing on the amorphous region of polymer, thereby acting as defect points for the initiation as well as propagation of stress cracking. Furthermore, the incorporation of BN into the LLDPE matrix reduced the impact strength of the composites, with this behaviour being attributed to BN particles acting as crack nucleation sites thereby it is easier for crack to form in the composites and as a result reducing the overall impact strength. The presence of wax into the LLDPE composites was found to reduce the impact strength of the system, which may be ascribed to the low viscosity of paraffin wax which might have acted as flaws with the matrix, acting as a catalyst for initiation as well propagation of stress cracking.
