PETpla.net Insider 04 / 2021

MATERIALS / RECYCLING PETplanet Insider Vol. 22 No. 04/21 www.petpla.net 15 However, low weight is not a be-all and end-all. Consideration also needs to be given to the notion that a well- designed but heavier PET bottle, with a PET label, may actually in the end prove more sustainable than a lighter one that has a multilayer structure or a PVC label, both of which hinder recycling efforts. Sipa uses something called the Green Plastic Factor to show how light a bottle is in comparison with what it holds. The Green Plastic Factor (or GPF) is the ratio of the volume of the container contents in ml to the weight of the un fi lled container in g. For a collapsible 10 l bottle, the GPF is around 125, while for a single- serve 500ml bottle it is around 55. This clearly shows the high level of sustainability of large-format bottles, production of which Sipa has devel- oped speci fi c equipment. For a return- able 2 l bottle, the GPF is also low, at around 20. But if such a bottle ful fi ls its purpose and makes multiple trips, it can be assigned a “virtual” GPF, which can be close to 200. Green Plastic Factor is just one tool that Sipa uses in its design pro- jects: it is a means rather than an end. So, for example, an ultra-light 5 l water bottle may have a high GPF – pos- sibly around 85 – and also have very good performance as indicated by high top-load strength, but these have to be weighed against factors that are not so positive, such as the fact that it is single-use, and it requires the implementation of good logistics. From fl ake to preform in a single step One issue still in the balance is just how all those used PET bottles are converted back into new ones. Reducing them to fl ake, converting the fl ake into granules and then repro- cessing the granules into preforms and then bottles is the obvious solu- tion is the most obvious one – but it is not necessarily the most economic one. Xtreme Renew process incorpo- rates technologies that enable rPET to be converted in a fully integrated system directly into injection-com- pression moulded preforms. Xtreme Renew eliminates an entire section of the heat history of rPET, making it considerably more cost-effective, while offering extra bene fi ts in terms of carbon footprint. Sipa believes that for converters considering the use of high volumes of rPET, it is a highly attractive proposition. At the same time, Sipa acknowl- edges that Xtreme Renew does require investment in equipment that many converters are unfamiliar with. This is why it also supplies more conventional Xform injection mould- ing systems, and SFL or Xtra linear and rotary stretch-blow moulding systems, incorporating special fea- tures that make processing with rPET a relatively simple affair. In many cases, customers will not even have to invest in new systems, but rather make highly affordable adjustments to equipment they already have. But they will still be able to produce bot- tles with up to 100% rPET if they so choose (and if the application allows). From fl akes to preforms in a single step Modi fi ed hot runners For converters producing pre- forms, for example, it will make a lot of sense to use hot runner systems that have been upgraded to prevent accumulation of PET powder. Sipa has developed Xactive Cleaning, a patented system, which adapts the compressed air flows, normally used to move the hot runner valves stems, to also blow out the very few plastic particles that deposit inside the actuators each cycle. Cleanliness is an issue not only in hot runner systems, but also in the injection moulds that they feed. So Sipa has also been developing ways to keep mould cavities as clean as possible. A system incorporating new vacuum technology reduces the need for maintenance and increases line efficiency. Pulling a vacuum during injection All moulds incorporate tiny vent holes at key points on the surfaces of the cavities, to allow the escape of air in the cavities when the PET is injected. But the vents can become dirty if the air fl owing through them is not completely clean – impeding the passage of the air. Sipa has patented a solution that pulls the air out of the mould during injection. Net result is that the need for operations to clean the vents is also drastically reduced. Accounting for colour variations in rPET Not all rPET preforms are the same. Because the raw material usu- ally comes from a variety of sources, it is quite possible that there will be, for example, slight variations in colour. This may affect behaviour when the preforms are heated in infrared ovens, since different colours absorb differ- ent amounts of infrared energy. Sipa has developed ways to take account of such variations – making automatic adjustments to the oven settings for example – making it possible to have a high level of consistency in the way the preforms behave when they are formed into their fi nal blown shape. Preform heating can be adjusted from one batch of preforms to another, based on the variation in colour. Related to this, special vents, known and patented as X-Vents, can be inserted into the bottle moulds, making it possible to manage pres- sure changes in the cavities caused by the process adjustments relating to the different levels of energy absorp- tion of the preforms. Sipa’s Product Manager for Blow moulding Systems, says: “The speci- fi cation of any container can always be ensured. The use of X-Vents, is particularly useful for managing these situations when bottles with complex geometries are being produced, or for controlling the bases of bottles for carbonated soft drinks.” He also points out that the extra wide pro- cessing angle on the new generation of Xtra rotary stretch-blow moulding machines provides further help in pro- cessing ‘dif fi cult’ materials like rPET. www.sipasolutions.com