Application of Radiation - The Preparation of Magical Heat-Shrinkable Materials

　　Radiation is typically an invisible light emitted when matter undergoes microscopic changes. It has extensive applications in military, medical and health, scientific, industrial, and agricultural fields. Here, we will only discuss the use of radiation in preparing a magical heat-shrinkable material.
　　Plastics are widely used in daily life, among which polyethylene is a collection of linear molecules polymerized from ethylene monomers, commonly found in the market. However, they do not possess heat-shrinkable properties; whether in film or pipe form, they remain as they are when purchased.
　　Heat-shrinkable materials are those that shrink and deform upon heating. For example, a thick pipe at room temperature can shrink into a thin pipe when heated, tightly adhering to the surface of the object it is attached to, thereby ensuring insulation or corrosion protection on metal surfaces. If the material is a film, it can be used to package food. Once heated, the film shrinks and tightly wraps around the food, isolating it from air and thus preserving its freshness.
　　Why does this material have such magical properties? This can be explained by examining the material's structure.
　　Ordinary polyethylene pipes do not have heat-shrinkable properties. Polyethylene is polymerized from ethylene monomers, with the molecular formula of ethylene being H2C=CH2. Under polymerization conditions, the double bonds of each ethylene monomer molecule open, and several molecules polymerize to form linear high-molecular polyethylene. The polyethylene plastic we commonly see is composed of these linear molecules stacked together.
　　However, under the influence of radiation, chemical bonds form between the linear molecules of polyethylene plastic, a process known as radiation cross-linking. The greater the radiation dose, the higher the degree of cross-linking. The result of radiation cross-linking transforms the polyethylene plastic from a linear structure into a network or three-dimensional structure. The newly formed material has a remarkable "memory effect." For example, a pipe can be expanded and then cooled to form a thick pipe. This pipe can return to its original diameter upon reheating, hence it is called a material with a "memory effect."
　　Pipes made from heat-shrinkable polyethylene materials can be conveniently used to protect cable and optical fiber joints, as well as metal pipes and rods. Heat-shrinkable materials can not only be made into radially shrinkable heat-shrink tubes but also into plastic films that shrink in both longitudinal and transverse directions. These can be used in packaging and protecting items. The magical heat-shrinkable materials will bring more extensive applications to daily life and industrial and agricultural production in the future.