Improving Sustainability in Rotational Moulding Polymer Processing by Use of Microwave Heating
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Roberto Utzeri, Maurizio Vignolo, Fabio Bertini, Maria Teresa Buscaglia, Paola Stagnaro
The Italian manufacturing industry is highly skilled in plastic processing, and our country is ranked in the first places in Europe for rotational molding (RM). RM is indeed the process of choice to produce one-piece hollow plastic items, mainly based on polyethylene (PE), of medium-to-large size and virtually of any desired shape. The heating process involves a hollow mould that contains a measured amount of fine polymer powder while rotating it biaxially. As the mould heats up and rotates, the polymer powder melts and adheres to its inner surface. Once all the polymer sticks to the mould, the tool is cooled, allowing the polymer to solidify. The so-formed one-piece plastic item is then demoulded.
Although RM is a well-known technology, it is still one of the most energy intensive industrial polymer processes and has not been improved for a long time. Here, microwave-assisted heating was exploited in an innovative process to enhance RM sustainability, even moving from laboratory to industrial scale. The guiding idea, since PE is not sensitive to microwave, was to modify existing metal moulds to make them rapidly heatable in a microwave field.
Based on a preliminary screening of MW-active materials, which proved effective energy saving in the use of microwaves as heating source, the best responsive formulates were deeply investigated and scaled-up to be used as sustainable, versatile and cost-effective coatings to make the moulds used in classic RM technology heatable in a MW field. The parameters involved in the formulation, in terms of MW-active materials composition, their amount with respect to the mould mass, as well as the related parameters of the microwave heating were defined and optimized. Finally, high-quality PE prototypes were prepared for the first time by means of an innovative MW-assisted RM process, demonstrating its industrial feasibility.
Keywords: rotational moulding; microwave heating; polyethylene; process innovation; sustainability
Proscience vol. 10
Pp 87-92