German engineers have developed and demonstrated a process that could dramatically lower the cost of plastic bottle production. Polymer expert Zimmer claimed that its new approach could reduce the cost of manufacturing preforms for polyethylene terepthylate (PET) bottles by as much as 10 per cent.
Preforms are injection-moulded bottles that are yet to be blown and stretched into their final shape. With around 10 million tonnes of these 'embryonic' bottles manufactured every year, a 10 per cent saving could represent an enormous economical stride.
The process by which plastic bottles are made - injection stretch-blow moulding - is relatively simple. Molten polymer is injected into a cavity to produce a preform, which is dropped into a blow-mould area where it is stretched and blown into the desired bottle shape.
There are two traditional approaches to PET bottle moulding. The one-step method, typically used on small to medium-scale production lines, uses one machine to complete all the processes - from PET granule to finished bottle. An injection-moulded preform is withdrawn from the injection cavity while still hot and immediately stretch blown to form the finished bottle. This method is highly suited to small and medium-scale production lines.
More common, however, is a two-step method carried out on two separate machines, typically at different sites. An injection-moulding machine is used to make the preforms, which are shipped to the filler or customer where they're reheated and stretch blown on a separate machine. While the two-step process means that the bottles must essentially be heated twice, it is typically more efficient for large-scale processes because small bottles can be shipped to the customer more cheaply.
However, both approaches have another step that adds considerable expense. Anke Ruettgers, head of marketing at Zimmer, explained that typically, before injection moulding can begin, the raw material - polyester - must be treated in a polymerisation plant. This produces a low-viscosity resin which, to have suitable properties for bottle production, must then be put through an additional process known as Solid State Polymerisation (SSP).
Following SSP, the resin then has to be cooled down to allow it to crystallise. It is then stored until use, during which time it is affected by humidity. This means it then has to be dried, and finally reheated in preparation for the injection-moulding machine.
Ruettgers explained that the Zimmer process essentially dispenses with these early processing stages. Instead of making a high-viscosity resin, Zimmer has developed a reactor that produces a high-viscosity melt directly from the polyester. This melt can then be injected directly into the moulding chamber.
'We omit solid state polymerisation, transport, storage and drying prior to injection moulding, instead going directly from polymerisation into the preform (injection-moulding) machine,' said Ruettgers.
A pilot plant is already up and running in Frankfurt demonstrating the technology on a small scale. It is claimed to have the capacity to produce around 12,000 bottle preforms per day and is also able to satisfy the demand by different bottle customers for different grades.
While Ruettgers said that the factory is still at the development stage, full commercialisation is, she claimed, just around the corner. 'We are convinced that we will be able to market the process by the end of the year,' she said.
With massive and imminent growth predicted in global consumption of PET bottles, Zimmer's breakthrough is timely. Whether these savings translate as cheaper products for consumers, however, remains to be seen.