With the rapid expansion of industrial and collaborative robots, material requirements for joints and sliding components have become increasingly demanding. High wear-resistant nylon has emerged as a competitive alternative to metals and conventional engineering plastics, offering not only extended service life but also weight reduction, noise suppression, and lower maintenance costs. The wear resistance of advanced nylon materials is derived from synergistic mechanisms at the molecular and tribological levels. During sliding contact, nylon forms a stable transfer film on the counter surface, reducing friction and wear rates. Structural modification and solid lubricant incorporation further enhance performance under boundary or dry friction conditions, making these materials particularly suitable for robotic joints subjected to intermittent motion and high loads. In robotic joint assemblies, wear-resistant nylon is commonly used for bushings, sliders, gears, and liners. These components demand dimensional stability, fatigue resistance, and thermal control. Optimized crystalline morphology and molecular weight distribution help minimize frictional heat generation and maintain precise positioning accuracy. For sliding components such as linear guides and actuator interfaces, high wear-resistant nylon provides vibration damping and noise reduction advantages over metallic counterparts. Its fine and uniform wear debris reduces secondary abrasion, contributing to longer system service life even in contaminated or poorly lubricated environments.  

Surface defects remain a critical challenge in injection molding of nylon materials, as they directly affect aesthetic quality, dimensional stability, and end-user acceptance. Among these defects, silver streaks, flow marks caused by trapped gas, and sink marks are the most frequently observed. Although these phenomena may appear visually similar, their formation mechanisms and control strategies differ substantially and must be analyzed from the perspectives of material behavior, processing conditions, and mold design. Silver streaks typically appear as elongated, silvery lines aligned with the melt flow direction. Their primary cause in nylon systems is the presence of volatile substances, especially moisture. Due to the hygroscopic nature of polyamides, absorbed water rapidly vaporizes under high processing temperatures, forming microbubbles that are stretched by shear forces during injection. These elongated bubbles solidify on the surface, resulting in visible streaks. Inadequate drying, excessive melt temperature, and high shear rates significantly increase the likelihood of this defect. Gas-related flow marks differ from silver streaks in both appearance and origin. They are usually irregular or cloudy patterns formed when trapped air cannot be efficiently evacuated from the mold cavity. Poor venting, excessive injection speed, or low mold temperature can cause the melt front to seal venting paths prematurely, leading to unstable flow behavior. Optimizing vent design, adjusting injection profiles, and maintaining appropriate mold temperatures are essential to mitigate this issue. Sink marks are primarily associated with the semi-crystalline nature of nylon materials. During cooling, crystallization-induced volumetric shrinkage occurs, particularly in thick sections or areas with insufficient packing pressure. If the gate freezes too early or packing time is inadequate, molten material cannot compensate for the volume reduction, resulting in localized depressions. Proper gate design, extended packing phases, and balanced wall thickness are key measures to control sink marks. A comprehensive understanding of moisture sensitivity, crystallization behavior, and melt flow dynamics is essential for effectively controlling surface defects in nylon injection molding. Only through coordinated optimization of materials, processing parameters, and mold structures can consistent surface quality be achieved.

Polyamides are widely used engineering plastics, but their performance often needs to be further adjusted by blending with other polymers. Due to polarity differences, most PA-based blends require compatibilizers to ensure stable morphology and mechanical integrity. Recent studies on PA/PP and PA/PC blends have provided new insights into compatibilization mechanisms and material optimization. In PA/PP blends, poor interfacial adhesion caused by large polarity differences leads to severe phase separation. Maleic anhydride-grafted polypropylene (PP-g-MAH) remains the most widely used compatibilizer. Its anhydride groups react with amine end groups of PA, forming stable chemical bonds that strengthen the interface. With deeper research, it has become clear that grafting efficiency, MAH content, and molecular weight distribution significantly influence the final toughness and processability of the blend. Block copolymer compatibilizers represent a newer direction, enabling finer phase dispersion and better toughness. Nanoparticle-assisted compatibilization has also emerged, improving long-term thermal resistance and fatigue behavior of the blends. For PA/PC blends, the challenge lies in mismatched processing temperatures and complex interfacial chemistry. Epoxy-functional compatibilizers have proven highly effective, forming chemical linkages with both PA and PC end groups. As a result, thermal stability, impact strength, and dimensional stability at elevated temperatures have greatly improved. Recent developments focus on reaction rate control, ensuring that compatibilization occurs at lower temperatures to prevent PC degradation. Additives containing silicon or flexible chain segments further enhance transparency, weather resistance, and chemical durability. Compatibilization strategies are becoming increasingly sophisticated, enabling nylon blends to meet the stringent requirements of automotive, electrical, and structural applications.