The Rotational Molding process utilizes a number of commodity based materials. The most widely used material for rotomolding is Polyethylene (PE). PE comes in a variety of different offerings such as Linear Low Denisty Polyethylene, Medium Density Polyethylene, High Density Polyethylene and Cross Link Polyethylene. Other materials that are available to rotomolders include Polypropylene, Nylon, PVC, Vinyls, Polycarbonate and some other less processed materials. Because of the nuances of the process, most all materials for rotational molding are offered as a powder, typically a 35 mesh. Some materials are offered as a micro-pellet, as some more capable molding companies are capable of processing the micro-pellets.
Raw materials vary greatly across physical properties, uses, additives and various other physical properties and traits. Learn more about some of the rotational molding materials below.
PE is a thermoplastic material that is part of the polyolefin polymer family. PE is further categorized into groups according to its density as indicated in the following abbrevations LLDPE (Linear Low Density Polyethylene), HDPE (High Density Polyethylene), MDPE (Medium Density Polyethylene), LDPE (Low Density Polyethylene), XLPE (Cross Link Polyethylene), etc.
Linear Low Density Polyethylene (LLDPE)
Linear low density polyethylene exhibits medium stiffness properties, is extremely durable, easy to rotationally mold and offers excellent chemical and environmental stress crack resistance abilities. It is necessary to be pulverized to powder form for the rotational moldig process. Commonly processed with UV stabilization additives and AO packages, LLDPE can also feature anti-microbial additives, FDA approved grades for food and medical contact and more. LLDPE applications include rotationally molded furniture, chemical tanks, industrial tanks, agricultural tanks, shipping containers, plastic pallets, toys, tornado shelters, secondary containment, drainage products, playground equipment and more!
High Density Polyethylene (HDPE)
High density polyethylene offers the stiffest properties of all of the different grades of polyethylenes. Like all other polyethylene materials, HDPE has excellent resistance to a wide array of chemicals and solvents. It features great processing ability for the rotational molding process. Like LLDPE, HDPE must be pulverized to a powder form for it to be processed. It is commonly processed with UV stabilizer additives and AO packages. Commonly used in FDA/USDA approved food grade applications. Common applications for HDPE in rotationally molded products include wall barriers, chemical tanks, agricultural tanks, Cargo Containers, dock floats and more!
Low Density Polyethylene (LDPE)
Low density polyethylene was the first grade of polyethylene developed by Imperial Chemical industries in 1933. Like all PE grades, LDPE is commonly recycled. Some reports show that in the last decade, world-wide LDPE consumption has exceeded a volume of 23 billion US-Dollars. LDPE has a lower tensile strength and lower density than HDPE materials. LDPE generally offers a density in the range of .910-.940 g/cm³.
Cross Linked Polyethylene (XLPE)
Cross-Linked Polyethylene contains a cross-linking agent which reacts with the material during the rotomolding process, forming a cross-linked molecule similar to a thermoset material. This reaction during the molding process drastically improves the toughness, durability, environmental stress-crack resistance and tear resistance. Applications for XLPE include Fuel Cells, Chemical Tanks, Piping, Waste Management products and more. Due to the cross-linking process, products molded from XLPE are not recycleable.
Ethylene Vinyl Acetate is the copolymer of ethylene and vinyl acetate. The polymer is comprised of 10-40% vinyl acetate with the remaining composition of the polymer being ethylene. This polymer behaves similar to elastomeric materials in softness and flexibility, yet it is processed like other PE materials. It exhibits good barrier properties, stress crack resistance, ability to withsand low temperatures, hot melt adhesive water proof properties and resistance to UV. EVA is often comparable and competitive with rubber and vinyl products.
PVC compounds can be molded in both liquid and powder forms. The liquid form of the plastisols are fluid suspensions of very fine partical size resins in plasticizing liquids. PVC compounds are moderate in costs and are easily processed with the proper equipment and dispensing systems. The PVC compounds can be engineered to produce parts that range from flexible to semi-rigid durometer hardness ranges of 60 Shore A to 65 Shore D. Applications include teething rings, planters, dolls, toys, Dog Toys, novelty items and more.
Nylon comes in 2 different grades for rotomolding, Nylon 6 as well as Nylon 12. Nylon 6 displays outstanding tensile strength, rigidity and impact strength. Nylon exhibits very high heat resistance so properties are maintained at raised temperature levels. It excels in chemical resistance. These properties make it a great candidate for fuel cells and other applications where temperature elevation and exposure to chemicals are necessary. Nevertheless, the costs of Nylon are realtively substantial if comparing aginst PE.
Nylon 12 has a much lower melting point compared to Nylon 6. It additionally shows mechanical properties less than Nylon 6 but easier to process than Nylon 6. It has excellent moisture absorbtion characteristics. Numerous applications for Nylon 6 as well as Nylon 12 consisting of Fuel Cells, heating and air ducts, Chemical Storage tanks and more!
Polycarbonate displays very strong physical properties including stiffness, tensile strength and creep resistance. Highest impact of all rigid plastics. Polycarbonate has very high heat resistance. If processed correctly, can be molded clear. Applications include light fixtures, snowmobile components, Air Craft Containers, shipping containers, etc.
PP displays physical properties that make it stiffer than PE. Polypropylene also has a higher heat distortion temperature, autoclavable, excellent chemical and environmental stress crack resistance. However, Polypropylene is extremely brittle and has very low impact properties currently. It is moderately expensive in comparison to PE. Currently many material suppliers are working on improvements to Polypropylene's impact properties. Polypropylene is commonly used to manufacture Food Industry products due to it's ability to be very resistant to abrasions.
Various materials for rotomolding are used in a variety of products and applications. The materials utilized will depend on the design and intended function of the rotationally molded products. Learn more about the rotational molding process to better understand how these materials are processed!