) is an organic compound and the primary constituent of cell walls in green plants, many forms of algae, and oomycetes. Being the most abundant organic polymer on Earth, it serves as a primary source of nutrition for herbivores through a process called cellulolysis. Composed of linear chains of several hundred to many thousands of β(1→4) linked D-glucose units, it differs from starch, another glucose-based polymer, in that humans and many animals cannot directly digest cellulose due to its β-glycosidic bonds. However, certain animals like ruminants and termites can break it down with the help of symbiotic microorganisms. Industrially, cellulose is vital for producing paper and paperboard and serves as a raw material for derivative products such as cellophane and rayon. Its derivatives, including cellulose acetate and nitrate, find uses in coatings, inks, and more. Its renewable nature has also positioned cellulose as a potential resource for sustainable biofuel production.
Plastics offer a lightweight, cost-effective alternative to traditional optical materials like glass and crystal, making them an increasingly popular choice for a variety of optical applications. Common optical plastics include polymethyl methacrylate (PMMA), polycarbonate, and cyclic olefin copolymer (COC), each with its own set of advantages and limitations. For instance, PMMA is known for its excellent light transmittance and ease of fabrication, while polycarbonate provides higher impact resistance. Plastics are widely used in consumer electronics, automotive lighting, and even in some medical devices, where their lightweight nature and moldability offer distinct advantages. They are particularly well-suited for mass production techniques like injection molding, which allows for the creation of complex optical elements at scale. However, plastics generally have lower refractive indices and can exhibit higher levels of optical dispersion compared to glass, which can be a limitation in high-precision applications. They are also more susceptible to environmental factors such as temperature fluctuations and UV degradation, requiring special additives or coatings for long-term stability. Advances in polymer science are leading to new types of optical plastics with improved characteristics, including higher refractive indices and lower levels of dispersion, expanding their range of potential applications. Overall, plastics provide a versatile and economically viable option for many optical systems, and ongoing research promises to further extend their capabilities.