Polystyrene Based Nanocomposites with Enhanced Thermal and Mechanical properties

Abstract

In this research work, polystyrene-based various formulations of nanocomposites have been developed for multi-functional applications in two-phase experimental setup. Initially in the first experimental phase, an inexpensive general purpose polystyrene (GPPS-550P) is converted into a flame-retardant nanocomposite, while, in the second phase, the same polymer is transformed into a thermally conductive polymer nanocomposite. Polystyrene (PS) was taken as synthetic polymer matrix, while, the two different ceramic-based reinforced materials (sepiolite clay and boron nitride powder) have been separately incorporated in polystyrene, as filler. The silane coupling agents were used to increase the possible compatibility between the matrix and incorporated fillers. In the first phase the respective nanocomposites of general-purpose polystyrene (GPPS-550P), and modified sepiolite clay (m-SP) were fabricated via melt-extrusion, solvent-free technique. The inorganic, ceramic-based sepiolite clay was modified by treating with vinyl tri-ethoxy silane (VTES), to induce a silanol functional group (Si OH) at the surface of the mineral clay. The appearance of carbonyl (C-O) peak in the range of 1610 to 1710 cm-1 was more prominent and of high intensity, in the spectra of S2 and S4 samples with higher filler loading, in the fabricated nanocomposites. The FTIR peak of (Si-O-C) at 1072 cm-1 in polystyrene nanocomposites confirmed the interactions between (Si-OH) groups of m-sepiolite with polymer matrix. The ultimate compatibility was achieved due to interaction between (Si-OH) groups of the coupling agent and (-OH) groups of sepiolite, which have the affinity towards the organic polymer. Various composite formulations were fabricated by varying the concentration of clay, using twin-screw extruder (Modal, Thermo Haake Poly-lab Rheomix-600, Internal Mixer and Karlsruhe, Germany). Initially, the temperature and speed of the rollers were adjusted for successful digestion at 100 °C and 60 rpm. After the digestion, the parameters were adjusted to its optimum (200 °C and 100 rpm), where, the drop wise addition of Di-methacrylate (DMC) played its vital role to facilitate the crosslinking process. The surface morphologies of pristine PS and PS/m-SP composites were examined using scanning electron microscopy (SEM), where better dispersion of m-SP as a filler in the PS matrix was achieved. SEM micrographs revealed no such cracks and pores, which confirmed that filler was embedded in the polymer matrix. This xxiii resulted a positive increase in the mechanical properties and thermal stabilities, resulted the targeted flame-retardancy in the fabricated nanocomposites. The flame retardancy test was carried out as per ASTM Standard D4986-20, in which the calculated burning rate of the optimum sample decreased to 48%, yielding a good flame-retardant product. In the second phase, the same grade polystyrene was converted to thermally conductive polymer nanocomposite, while keeping its electrically insulative property as active, by incorporating boron nitride (BN) powder as functional filler. These are currently the demanding properties in polymers, which are potentially applicable in 5G applications, electronic industry, heat sink, heat storage, heat transfer, thermal management and several other aviation applications. The filler, boron nitride (BN) powder was treated with 10% NH3 solution, washed and sonicated simultaneously with methanol and deionized water to achieve the required modified boron nitride (m-BN). This modification helped in avoiding the cluster formation of filler within the matrix, resulted in achieving percolation threshold at 20 weight percent of the filler consumed. The FTIR analysis confirmed the modification of boron nitride (m-BN), where, the bending vibrations of (B–N) bond at 810 cm−1 becomes more prominent with increasing filler content up to 30 weight percent. These better interactions of filler and matrix, resulted in good mechanical properties, where tensile strength increased to 69.37%. The successful percolation of filler formed the targeted thermal pathways within the composite and thus an increase of 67.43% in thermal conductivity was achieved at optimum temperature.