Rotational Molding Materials
Materials for Rotational Molding
Rotational molding utilizes various petroleum based materials such as Polyethylene (Linear Low Density Polyethylene, Medium Density Polyethylene, High Density Polyethylene), Polypropylene, Nylon, PVC, Vinyl, Polycarbonate and various other materials.
All polyethylene is made from petroleum feedstocks also known as hydrocarbons. Both the feedstocks (and raw materials) and polyethylene are composed of only hydrogen and carbon (hydrocarbon). In North America, the feedstock is typically natural gas. Where as in most parts of the world, Oil is still being used.
Generally, there are (2) major requirements for the various materials supplied to the Rotational Molding & Rotocasting industry. The material must be capable of flowing through the construction of the cavity of the mold as the mold rotates. The materials must also be thermally stable to be able to be processed at the temperatures the oven cycle is operating at for the duration the cycle requires.
Approximately 80% or more of the materials processed by Rotational Molding companies is Polyethylene.
Polyethylene
Polyethylene (PE) is a thermoplastic material belonging to a group of polymers called polyolefins. It is categorized by its density as indicated in the abbreviations LLDPE, HDPE, MDPE, LDPE, XLPE, etc.
-LLDPE
(Linear Low Density Polyethylene) exhibits Medium stiffness, extremely durable and tough, easy to process, has excellent chemical and environmental stress crack resistance properties. Processed in Rotational Molding in powder form. Commonly processed with UV stabilization additives, Anti-Microbial additives, FDA approved grades and more. LLDPE applications include Chemical Tanks, Industrial Tanks, Shipping Containers, Toys, Tornado Shelters, Secondary Containment, Furniture and much much more!
-HDPE
(High Density Polyethylene) displays the stiffest properties of all the different polyethylenes. Like all other polyethylene materials, it has excellent chemical resistance, easy processing ability. Processed in Rotational Molding in powder form. It too is also commonly processed with UV stabilization additives, etc. Commonly used in FDA/USDA approved Food Grade applications. Applications include Wall Barriers, Chemical Tanks, Tornado Shelters, Pallets, Air Craft Containers, Cargo Containers, Dock Floats and much much more!
-LDPE
(Low Density Polyethylene) was actually the first grade of polyethylene developed by Imperial Chemical Industries in 1933. As with majority of polyethylene grades, LDPE is commonly recycled. Some reports show that in 2009, the worldwide LDPE market reached a volume of 22.2 Billion US-Dollars (Market Study: Polyethylene LDPE. Ceresana Research). LDPE has a lower tensile strength and lower density than HDPE. LDPE generally has a density range in the .910-.940 g/cm³.
-XLPE
(Cross-Linked Polyethylene) contains a cross-linking agent which reacts with the material during the molding cycle, forming a cross-linked molecule similar to a thermoset. This reaction in the process drastically improves the toughness, environmental stress-crack resistance and tear resistance. Applications range from Seating, Fuel Cells, Chemical Tanks, Piping, Waste Management products and so much more! Due to the cross linking process, the cross linked materials are not recycleable.
-EVA Co-polymer
(Ethylene Vinyl Acetate) is the copolymer of ethylene and viny acetate. The weight percent vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. This polymer approaches elastomeric materials in softness and flexibility, yet it is processced like other polyethylene materials. It exhibits good barrier properties, stress crack resistance, low temperature durability, hot melt adhesive water proof properties and resistance to UV. EVA is often competitive with rubber and vinyl products.
-Polyvinylchloride
PVC compounds can be molded in both liquid and powder forms. The liquid form of the plastisol are flud suspensions of very fine partical size resins in plasticizing liquids. PVC compounds are moderate in costs and are easily processed with the proper equipment. 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
Nylon comes in 2 different grades, Nylon 6 and Nylon 12. Nylon 6 exhibits excellent tensile strength, stiffness and impact strength. Very high heat resistance so properties are maintained at elevated temperatures. It excels in chemical resistance. However, the costs of Nylon are realtively significant if comparing aginst PE.
Nylon 12 has a much lower melting point than Nylon 6. It also displays mechanical properties lower than Nylon 6 but more easily processed. It has good moisture absorbtion properties. Many applications for Nylon 6 and Nylon 12 include Fuel Cells, Heating and Air Conditioning ducts, Chemical Tanks, etc.
-Polycarbonate
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.
-Polypropylene
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.
