Additives Used in Rotational Molding

Stabilizers counter the effect of the high temperatures and the oxygen rich atmosphere experienced by the resin during the rotational molding process. Since some rotational molded parts require up to one hour of residence time in the oven, such stabilizers are essential. Without them, the polymer would lose its inherent properties, becoming unfit for the final application. 

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Rotational Molding. The process of rotational molding is ideal for creating hollow parts. Polyethylene is the most common polymer used in rotational molding. Powdered plastic is introduced into a clamshell mold. Color and additives, usually a micro-pulverized blend, are added and the mold is closed. The mold is then rotated. The powder is distributed to the mold s surface by the centrifugal force. The mold is heated and a melt skin forms on the mold s surface. Spinning continues as the mold is allowed to cool. The mold is then opened, the part removed, and the process starts again. 

Polyethylene is, by far, the most commonly used resin in rotational molding processes. Low density, high density, and linear low density polyethylene are all used extensively. Additionally, crosslinked polyethylene is used for parts that require high chemical or heat resistance or enhanced impact resistance. 

Fillers are not used to any extent in products made by the rotational molding process. Rotational molding is dominated by polyethylene (close to 90% volume) to which even small addition of pigments or fillers (less than 2 wt%) causes a decrease in tensile and impact properties of the products manufactured in this process. Polyethylene is vulnerable to environmental stress cracking which is made worse if fillers are present. 

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