Modified nylon can be prepared through physical blending and chemical modification. Physically blended modified materials are often produced using injection molding.
Modified nylon is highly hygroscopic and requires thorough drying before processing, typically in 80-90°C hot air circulation until the moisture content does not exceed 0.3%. It is a crystalline material with a high melting point, narrow melting temperature range, and poor thermal stability. It is prone to oxidation and degradation at high temperatures and decomposes above 300°C; therefore, excessively high melt temperatures and prolonged residence times should be avoided. It has excellent fluidity, with a flash value of approximately 0.02mm, making it prone to overflow; self-locking nozzles are required. Molding shrinkage is significant and its range is large, with pronounced directionality, making it susceptible to defects such as shrinkage cavities and sink marks. The cooling rate of the melt significantly affects crystallinity; therefore, mold temperature should be carefully controlled. Lower mold temperatures are recommended for thin-walled parts, while higher mold temperatures are recommended for thick-walled parts. The gating system should be appropriately enlarged in form and size to avoid shrinkage cavities and sink marks. The wall thickness of the finished product should be as uniform as possible, and the draft angle should be large. When using a screw-type injection molding machine, a high compression ratio screw is recommended. A check ring should be installed on the screw head. The barrel temperature depends on the type of raw material, the shape of the plastic part, and the injection molding type, primarily determined by its melting point. To stabilize product performance, post-processing moisture conditioning is often necessary.
Chemical modification methods include preparing dodecalactam-modified casting nylon through activated anionic copolymerization under adiabatic conditions, or synthesizing nylon 6 resin containing amine modifiers by adding reactive composite amine modifiers during caprolactam hydrolysis polymerization. Another method is to use maleic anhydride-grafted polyolefins or olefin copolymers as toughening agents. Adding 8%–10% toughening agent can significantly improve nylon toughness, and adding 15%–20% can achieve the performance requirements of ultra-tough nylon.