Titanium, with the atomic number 22, is a lustrous transition metal known for its high strength, lightweight, and outstanding corrosion resistance. It is as strong as steel but 45% lighter, and twice as strong as aluminum while being only 60% heavier. This makes it highly valued in aerospace, medical implants, and high-performance sports equipment. Per gram, titanium's cost can vary widely depending on purity and form (e.g., sponge, ingot, fabricated parts), but it generally remains more expensive than common metals like steel or aluminum due to its complex extraction and processing methods. The Kroll process, developed in the 1940s, remains the primary method for extracting titanium from its ores, involving multiple steps that contribute to its final cost. Despite this, titanium's unparalleled mix of durability, lightness, and bio-compatibility justifies its expense in many high-end and critical applications.

Polypropylene (PP), a versatile thermoplastic, is primarily produced through the polymerization of propylene gas in the presence of a catalyst system. This process takes place under specific conditions of temperature and pressure. The two main methods for producing PP are the Spheripol process, which combines the polymerization section with a phase of powder purging and extrusion, and the Unipol process, which is a gas phase polymerization method carried out in a fluidized bed reactor. Both methods employ catalysts, with the Spheripol process using a Ziegler-Natta catalyst, while the Unipol process may use either a Ziegler-Natta or a metallocene catalyst. These catalysts help in controlling the molecular weight distribution and the stereochemistry of the polymer chains, thus influencing the final properties of the polypropylene. Optimization of the polymerization conditions—such as temperature, pressure, and catalyst concentration—is crucial for achieving the desired grade and properties of PP, which can range from highly crystalline, rigid plastics to flexible, copolymer plastics with elastomeric characteristics.

Cellulose is not a steroid; it is a complex carbohydrate or polysaccharide. Cellulose constitutes the principal structural component of plants' cell walls. Steroids, on the other hand, are a class of lipid molecules characterized by a carbon skeleton with four fused rings. Steroids play many important roles in organisms, including as components of cell membranes and as signaling molecules. While both cellulose and steroids are essential biological molecules, they have entirely different structures and functions. Cellulose provides structural support to plants, facilitating upright growth and stability, whereas steroids are involved in a wide range of biological processes including hormone activity, maintaining cell membrane fluidity, and modulating metabolism.