Rotational molding, also known as rotomolding, is a versatile manufacturing technique used to produce hollow plastic products. It was first developed in the 1940s but remained relatively underdeveloped due to its slow processing cycle and limited material options at the time. Initially, it was primarily used for polyvinyl chloride (PVC) paste resin. However, by the 1970s, the technology experienced significant growth and became widely industrialized. Today, rotational molding is one of the fastest-growing methods in the plastics industry, offering advantages such as high material utilization, low stress concentration in the final product, and the ability to create large and complex shapes that are difficult to achieve with other methods.
The key equipment and mold costs are lower compared to blow molding or injection molding, making it an economical choice for many applications. The materials used in rotomolding include PVC paste, polyolefins, nylon, polycarbonate, polyester, EVA, ABS, and PS. The development of powdered polyethylene in the 1960s significantly boosted the industry, and today, over 90% of rotomolding raw materials are still based on various grades of polyethylene resin. While other materials like nylon have been explored, they remain less common due to higher costs and more complex processing requirements.
Cast nylon, specifically nylon 6 (MCPA6), stands out for its excellent mechanical properties, including high molecular weight, good crystallinity, and superior impact resistance. It is widely used in engineering applications such as bearings, gears, and bushings across industries like machinery, textiles, and defense. When applied to rotational molding, cast nylon offers unique benefits, including lower energy consumption and the ability to form parts directly from monomers without the need for pre-polymerization.
One of the main challenges in rotational molding is the use of powdered resins, which can be difficult to process and may not meet the performance needs of certain applications. Liquid rotomolding systems, such as those using PVC pastes, caprolactam, or polyurethane, offer advantages like shorter heating cycles, smoother surface finishes, and better control over the final product’s properties. Cast nylon, when processed through liquid rotomolding, allows for one-step polymerization, reducing energy use and improving efficiency.
In terms of global development, companies like Rhodia, BASF, and DSM have made significant strides in creating specialized nylon resins for rotomolding. These materials are being increasingly used in automotive and industrial applications, such as fuel tanks, oil reservoirs, and insulation panels. In China, institutions like the FRP Research and Design Institute and Shanghai Jieshijie New Material Co., Ltd. have pioneered the use of cast nylon in large-scale parts, particularly in fuel tank manufacturing.
Compared to traditional metal fuel tanks, plastic alternatives—especially those made from cast nylon—offer numerous advantages, including reduced weight, greater design flexibility, and improved corrosion resistance. These benefits make them ideal for automotive and transportation applications where durability and performance are critical. With ongoing research and technological advancements, cast nylon rotomolding is expected to become a major driver of innovation in the plastics industry, offering both economic and functional value for complex, high-performance products.
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