## 1 Introduction  
Polyurethane (PU) is a polymer that comes under the combination of carbonate links. In the 20 th century, polyether polyols were cheaper and easier to handle. Meanwhile, they were more resistant to water compared with polyester polyols. This was the primary reason polyether polyols gained popularity. Polyurethane is conventionally molded by a combination of diisocyanate or tricyanide with polyol under exposure to UV light in the presence of a catalyst. Polyurethanes are thermosetting polymers that withstand high temperatures (120 \({}^{\circ}\)C to 300 \({}^{\circ}\)C) and have good solvent resistance [1; 2; 3]. PU foam is receiving specific interest in material science and technology, and it is demarcated as connecting the breach between plastic and rubber materials. Polyether polyols based on polypropylene, polyethylene oxide or tetrahydrofuran, aliphatic polyester polyols, aromatic polyester polyols, polycarbonate polyols, acrylic polyols, and polybutadiene polyols are the most commonly used polyols in the production of polyurethanes. Toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI) are two aromatic isocyanates commonly used in polyurethane [4]. Aliphatic isocyanates such as isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI) are used in a few applications. Aromatic types are more reactive and are used in various applications, including flexible and rigid foams [4]. Previously, petroleum-based polyols were used to fabricate PU foam. These synthetic polyols tend to be toxic, non-degradable, and high-cost, resulting in many health hazards and environmental pollution. The alternative source for synthetic polyol is a natural one which has eco-friendly, biodegradable nature, low-cost, and unique thermal properties. Therefore, regarding the ecological concern, we substitute synthetic polyol with vegetable oil-based polyol to create an organic foam [5; 6; 7]. However, various vegetable oils, such as sunflower, castor, and soybean oils, are being proposed to partially or entirely replace these oil-based polyols [8]. To make a flexible and bio-based PU foam, we use a combination of castor oil-based polyol with toluene diisocyanate (TDI) as base ingredients. During the 1960s, PU foam was more attractive in the automobile and aircraft industries, as PU foams are used for safety components such as door panels, etc. It gradually gained prominence in all technology areas and is now used in the automobile industry. Foams are widely used in auditoriums, optical fibers, engine covers, and other applications due to their acoustic, electromagnetic, and thermal properties. The use of polyurethanes and the quantity of their scrap are increasing. This PU foam is recycled in various ways to reduce waste, and it has also been reused for multiple applications [9; 10; 11]. However, they have many applications in thermal properties; they do not withstand high temperatures and they are an inferior adhesive to metal structures. To overcome these limitations, adding nanoparticle materials such as GNP, ZrO\({}_{2}\), and BC is a choice using hydrothermal processes, which provide good results due to their physical and chemical properties. Recent research has discovered that when two distinct nanoparticles are used as filler materials, they have synergistic benefits [12; 13; 14; 15]. Recently, exciting facts have been discovered about nanocomposites and they have surprised researchers with their unique properties [16; 17], and gained more scope in the field of research and development [18; 19]. Graphene nanoparticles have developed a prominent role due to their incomparable mechanical, electrical, and thermal properties. It is recorded as the finest and thinnest 2D material among all materials. It is the most in-demand material in research and development in the application of semiconductors in electric batteries and polymer composites. Over a wide range of applications, graphene is considered to have unique permittivity properties, from microwave to millimeter frequency.