DEVELOPMENT AND INVESTIGATIONS OF BIO-BASED COMPOSITE RIGID POLYURETHANE FOAM

Abstract

Polymeric foams are used extensively in a wide range of applications such as disposable packaging, cushioning, thermal insulation and construction. Foams derived from renewable sources are a requirement of the modern world due to the increasing concern about the environment and various issues related to petroleum based foams. Much research has been conducted recently to produce foams using renewable sources; however, low mechanical strength, high flammability and low thermal stability are the matters of concern when using these foams on a commercial scale. Various approaches have been used in past to overcome these problems; including the modification of raw material or the incorporation of property enhancing fillers, with or without a surface treatment. In this research, different fillers (carbon fibre powder, zirconia powder, alumina powder, feldspar, kaolinite clay, copper powder and calcium carbonate nanoparticles) have been used as reinforcement to enhance the mechanical, thermal and flame retardant properties of the bio-based rigid polyurethane foams. It was observed that the addition of ceramic filler showed the improved mechanical and thermal properties. The best properties were shown by 6% zirconia with a compressive strength of 6.61 MPa and the flexural strength of 5.72 MPa. Zirconia also demonstrated an increase in T5% up to 260°C. It is also revealed that the foams with 8% carbon fibre concentration showed up to 288% increase in compressive strength. Furthermore, up to 28% decrease in the peak of heat release rate (PHRR) was observed on the incorporation of carbon fibre powder. The foams with 8% and 10% carbon fibre concentration show conductivity of 1.9 x 10-4 and 7.1 x 10-4 S/m respectively. Also, the foams incorporated with mineral filler demonstrated up to 182% increase in compressive strength and 351% increase in flexural strength. Thermal stability of these composite foams was also found to be enhanced on the incorporation of kaolinite clay filler, with an increase in 5% weight loss temperature (T5%) from 192°C to 260°C. [ii]

Furthermore, the total heat release (THR), the smoke production rate (SPR) and the total smoke release (TSR) were also found to decreased remarkably on the incorporation of different fillers used in this study. Present study also investigated the impact of drilling on the residual compressive strength of bio-based rigid polyurethane foam (RPUF) composites. RPUFs have been prepared by the incorporation of copper powder in castor oil-based foams. The formulation of the samples employed for the drilling experiments was optimized by performing compressive strength, thermo-gravimetric analysis (TGA) and flammability experiments. The effect of various drilling parameters (density, feed rate, spindle speed and drill diameter) on the thrust force, delamination and, residual compressive strength has been investigated. The polynomial mathematical model reliant on the Response Surface Method (RSM) employing central composite design has been developed. It was concluded that the density is the most influential factor for maximizing the residual compressive strength, Additionally, the enhancement in residual compressive strength was observed on increasing the spindle speed, while, the feed rate shows a negligible effect on the residual compressive strength. The optimized process parameters for maximizing residual compressive strength were attained as high spindle speed and low feed rate. Furthermore, the equations designated as the coded factors are also presented to identify the relative impact of the various drilling parameters.