The material selection of plastic sports water bottles has an important impact on their performance and transparency. Common materials include polypropylene (PP), polycarbonate (PC), polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA). These materials have their own characteristics, and their transparency, heat resistance, cold resistance and chemical resistance vary significantly. Therefore, when selecting materials, it is necessary to comprehensively consider their physical properties and application requirements.

Polypropylene (PP) is a widely used plastic material with good heat and cold resistance, but its transparency is relatively low and it is usually translucent. This is because the molecular chain structure of PP is relatively regular and the crystallinity is high, which causes light to scatter inside the material, thereby reducing transparency. Nevertheless, by improving the production process, such as rapid cooling and stretching, the crystallinity of PP can be effectively reduced and its transparency can be improved, but this will also increase production costs and technical difficulties accordingly.

Polycarbonate (PC) is known for its excellent transparency and high strength, and is widely used in products such as kettles and cups. The transparency of PC comes from the looseness of its molecular chain structure and low crystallinity, and light is not easily scattered when it propagates inside the material. In addition, PC also has good light resistance, heat resistance and impact resistance, making it an ideal choice for high-end transparent plastic water bottles. However, it should be noted that PC may contain bisphenol A (BPA) during the production process, which poses a potential risk to human health, so it is crucial to choose BPA-free PC materials to ensure the safety of water bottles.

Polyethylene terephthalate (PET) is a plastic material with high transparency and strong chemical resistance, widely used in beverage bottles and food packaging. The transparency of PET is due to the presence of benzene rings in its molecular chain structure, which makes light less scattered when it propagates inside the material. In addition, PET also has the advantages of light weight, easy processing and low cost. However, PET has relatively poor heat resistance, is easy to deform under high temperature conditions, and may precipitate harmful substances, so it is not suitable for water bottles under high temperature conditions.

Polymethyl methacrylate (PMMA) is a plastic material with extremely high transparency and gloss, which is widely used in the manufacture of transparent plastic products. The transparency of PMMA mainly comes from the ester group and methacrylic acid group in its molecular chain structure, and light is almost not scattered inside the material. In addition, PMMA also has good weather resistance, processing performance and chemical resistance. However, PMMA's wear resistance and impact resistance are relatively poor, so additional protective measures are needed during use to improve its durability.

When discussing the impact of material properties on transparency, crystallinity, molecular chain structure and refractive index are key factors. The higher the crystallinity, the more obvious the propagation and scattering of light inside the material, thereby reducing transparency. Therefore, reducing the crystallinity of the material is one of the effective ways to improve transparency. However, the process of reducing crystallinity requires a balance between performance and production costs to ensure the market competitiveness of the final product.