Processing enhancers for rotational molding of polyethylene

Rotational molding is a zero shear process used to manufacture hollow plast ic parts. One disadvantage of this process is long cycle times, which are s ignificantly affected by the sintering rates of thermoplastic powder. The o bjective of this work was to evaluate low molecular weight additives as sin tering enhancers for polyethylene and to validate die results in rotational molding. The following additives were blended with linear low-density poly ethylene: mineral oil, glycerol monostearate and pentaerythritol monooleate . The additives resulted in decreased melt viscosity and/or elasticity at l ow shear rate. The reduction in melt elasticity was particularly significan t. Sintering studies confirmed that the additives resulted in significantly faster coalescence. In uniaxial rotational molding, the decreased melt vis cosity and elasticity obtained with mineral oil were observed to result in much faster densification and bubble removal. Part thickness was Uniform an d there was no war-page. Adding mineral oil to polyethylene reduced the cyc le time in uniaxial rotational molding and the peak impact strength was ide ntical to that obtained without any additive. Biaxial rotational molding ex periments confirmed that the use of mineral oil resulted in shorter cycle t ime without sacrificing peak impact strength.