Why Add Plasticizers in Injection Molded Parts?
Plasticizers are commonly used additives that play a crucial role in injection molding. Their addition can significantly improve the processing properties of plastics and the performance of the final product.
1. Improving Processing Properties
Reducing Melt Viscosity: Many plastics, such as polyvinyl chloride (PVC), have high melt viscosity without plasticizers. The strong intermolecular forces between PVC molecules make it difficult for the melt to flow smoothly into the mold cavity during injection molding. Plasticizer molecules can penetrate between the polymer chains, acting as a lubricant and reducing the intermolecular forces. For parts with thin walls, good melt flow is especially important. The melt needs to fill the narrow mold cavities quickly and uniformly. By adding a plasticizer, the melt can flow more efficiently through the narrow channels, ensuring the complete formation of the part.
2. Improving Processing Temperature Range: Plasticizers can lower the glass transition temperature (Tg) of plastics. For example, pure polystyrene (PS) has a relatively high Tg, requiring a high temperature to soften during injection molding. The addition of a plasticizer lowers the Tg, allowing the plastic to exhibit good plasticity at lower temperatures. This not only reduces energy consumption during processing but also prevents problems such as plastic degradation caused by excessively high processing temperatures. Plasticizers can also broaden the processing temperature range of plastics. This means that small fluctuations in temperature during the injection molding process will have a minimal impact on the processing properties of the plastic, resulting in more stable processing and improved dimensional accuracy and quality consistency of the molded parts.
3. Enhancing the Performance of Injection Molded Parts
Increasing Flexibility and Toughness: For injection molded parts that require a certain degree of flexibility, such as plastic pipes and electrical cable jackets, plasticizers play a critical role. In the plastic matrix, plasticizers increase the mobility of the polymer chains. Plasticizers can also improve the toughness of plastics. When an injection molded part is subjected to an external impact, the plasticizer allows the polymer chains more space to absorb energy.
Improving Low-Temperature Performance: At low temperatures, many plastics without plasticizers become brittle. This is because the mobility of the polymer chains is reduced at low temperatures. The presence of a plasticizer allows the plastic to maintain a certain degree of flexibility even at low temperatures.
