Testing and selection of plastics
Testing plastics is a key step in ensuring their quality and applicability, and covers tests of physical properties, chemical properties, mechanical properties, and other aspects. Physical property testing includes the determination of indicators such as density, melting point, and water absorption. These data can help determine whether the plastic meets the requirements for use in a specific environment. For example, plastic parts used in humid environments need to be tested for water absorption. If the water absorption is too high, it may cause the plastic parts to swell and deform during use. Chemical property testing focuses on the corrosion resistance and solvent resistance of plastics. Plastic parts that are frequently exposed to chemical substances, such as components of chemical equipment, must pass strict chemical property testing to ensure that they will not undergo chemical changes and fail during long-term use.
Mechanical properties testing is one of the most important aspects of plastics testing, encompassing tests such as tensile strength, impact strength, and flexural strength. Tensile strength reflects a plastic’s ability to resist fracture under tension, while impact strength reflects its resilience to sudden impact. These properties directly impact the reliability of plastic parts in actual use. For example, plastics used in mechanical parts require high tensile and flexural strength to withstand the various forces exerted during operation; plastic cushioning materials used to package fragile items require good impact strength for effective protection. Mechanical properties testing can identify plastic materials that meet application requirements and prevent product failures caused by insufficient material properties.
The selection of plastics requires comprehensive consideration of multiple factors, starting with the environment in which the plastic will be used. Different environments have significantly different performance requirements for plastics. For plastics used in high-temperature environments, heat-resistant plastics such as polytetrafluoroethylene and polyimide should be selected; for plastics used in low-temperature environments, cold-resistant plastics such as polyethylene and polypropylene should be selected. Furthermore, factors such as ambient light, humidity, and corrosiveness must also be considered. For example, plastics used outdoors require excellent weather resistance to resist the aging effects of ultraviolet rays. Only by selecting plastics appropriately for the intended use environment can the lifespan and performance stability of the plastic parts be guaranteed.
The structure and size of a plastic part are also important factors influencing the selection of plastic. For parts with complex structures and uneven wall thickness, plastics with good fluidity, such as polyethylene and polystyrene, should be selected. This facilitates filling and molding the plastic within the mold, reducing the occurrence of defects such as bubbles and shrinkage cavities. For parts requiring high dimensional accuracy, plastics with low shrinkage, such as polyoxymethylene and polycarbonate, should be selected to ensure that the part meets the designed dimensions after molding. Furthermore, the weight of the plastic part also influences the selection of plastic. For products with high lightweight requirements, such as parts in the automotive and aerospace industries, plastics with low density should be preferred to reduce overall weight.
The cost and processing technology of plastics are also factors to consider when selecting a plastic. Different types of plastics vary significantly in price. While meeting performance requirements, it’s important to choose lower-cost plastics to reduce production costs. Processing performance is also crucial. For example, different processes, such as injection molding and extrusion, require different properties like fluidity and thermal stability. For example, injection molding requires good fluidity and thermal stability to accommodate rapid molding processes, while extrusion molding places higher demands on melt strength. Therefore, when selecting a plastic, consider the production equipment and process conditions, choosing a plastic material that is easy to process and mold, improving production efficiency and minimizing production complexity.
