As more and more compounders and processors are exploring alternatives to fossil-based virgin materials, machinery companies are sitting up and taking notice. Already, some have taken steps to tailor their products to the requirements of the new materials in order to meet growing demand from the market.
Turin, Italy-based Bausano, a manufacturer and supplier of customised extrusion lines is one such company. The company saw the interest in biodegradable and compostable plastics rise steadily over the past years.
After discovering that, for example, polyvinyl alcohol, or PVA, a water-soluble thermoplastic polymer predominantly used in food packaging, is expected to show a compound annual growth rate of more than 6% between 2021 and 2026 period, Bausano has now developed a range of special extrusion lines, marketed under the MD Nextmover name, specifically designed for the production of water-soluble bioplastic granules. These are ideal for subsequent blown film extrusion for the production of bio-based films.
“Polyvinyl alcohol is a material that has a low environmental impact, as it is fully biocompatible and non-toxic. It also has low oxygen permeability in the absence of moisture,” said Alessandro Ruotolo, Bausano’s Materials Engineer.
“As a result, PVA films are increasingly used for the packaging of food, pharmaceuticals and personal care products, as well as in disposable packaging, such as detergent tablets.”
He added that water-soluble bioplastics made from plant-based raw materials are also available as an alternative to polyvinyl alcohol. In both cases, the complexity of the material makes it necessary to adopt a different granulation process than used for traditional plastics.
For example, when processing water-soluble bioplastics, counter-rotating twin-screw extruders are preferred over co-rotating extruders. Configuring these correctly requires a number of factors to be taken into consideration. In the first place, the length of the barrel is critical: the material must pass through in the time that is strictly needed for the screws to process it. If it remains in the barrel too long, it will be subject to excessive stress.
The second aspect is temperature. Processing occurs at much higher temperatures than a resin such as PVC, for example. Moreover, to produce a granule without impurities, the gel point must be determined with absolute accuracy. Another important consideration is the choice of head and cutting technology, which help determine the correct way to cool the extrudate. Unlike polyolefins, water-soluble resins cannot be cooled in water. This cooling step requires careful attention to ensure a good-quality granule is produced.
Bausano is currently allocating considerable resources for further research and development efforts to develop researching and developing new technologies to process eco-friendly plastics. “Efforts are therefore being made to support all manufacturers who, in these times of ecological transition, are entering this business,” said Ruotolo.