Rotational molding, of polymers

Kontopoulou, M. Bisaria, M. Vlachopoulos, J. An experimental study of rotational molding of polypropylene/polyethylene copolymer. Int. Polym. Process. 1997,12, 165-173. 

Throne, J.L. Some factors influencing cooling rates of rotational molding parts. Polym. Eng. Sci. 1972, 12 (5), 335-339. 

A possibility to avoid the CM stage is offered by the modified method for preparation of in situ MFCs based on consecutive slit or rod extrusion, hot stretching and quenching [32,37,38,42,43,47,62] used to process thermoplastic polymer blends, mostly polyolefins and PET. Rotational molding of LDPE/PET beads has also been attempted for the same purpose [34], but the reinforcing effect was insufficient due to the uneven distribution of the reinforcing fibrils and due to their reversion to spheres losing their MFC structure in this particular case. 

Rotational Molding. Large containers and some toys are manufactured with a specialized technique caHed rotational mol ding. A rotational mol ding machine contains several large metal molds that can be rotated in two perpendicular planes. A load of fine LLDPE particles is introduced into each mold, and the mold assembly is transferred into an oven. Inside the oven, heated molds rotate at speeds ranging from 10 to 40 rpm. The polymer powder melts and is uniformly distributed on the internal surface of each mold. After the container is formed, the mold assembly is removed from the oven and cooled at which point the plastic containers are removed. 

The crossed polarizer effects of both types are used in analysis work. The concentration of optically active organic materials is determined by the degree of rotation. In plastic processing the residual strains in molded materials as well as the degree of orientation of polymers is determined by the effect on polarized light. Crossed polarizers are used with special wave plates to control the amount of light that passes through an optical system. 

Gravimetric hoppers feed a mold with a prescribed weight of polymer. The feed stock is either a finely divided powder or a liquid plastisol. A plastisol is a suspension of a resin powder, typically polyvinyl chloride, in a plasticizer, used to manufacture. Rotational molders use liquids and powders in their process since both flow freely. This property permits the easy addition of the materials to the mold. More importantly, they flow smoothly around the interior of the mold as it rotates. In doing so, they coat the entire surface. 

---