The pressure to reduce packaging waste is leading many producers to remove excess material from their containers. However, this is triggering an unwanted side effect in some plastic packaging. John Grover, director of sales, Americas at Selig Group, talks about plastic lightweighting, the problem of distortion and how it can be resolved.
Over the years, producers have worked out the delicate balance between container plastic wall thickness and the maintenance of the packaging’s integrity. With the impending Deposit Return Scheme (DRS) and Extended Producers Responsibility (EPR), Scottish producers will come under increasing financial as well as environmental pressure to lightweight containers.
Lightweighting delivers
When it comes to lightweighting of plastic containers, the benefits can be significant. A case in point from the food sector is HDPE plastic bottles for milk. Turning back the clock to 1992, containers weighed 34.04g. Over the next ten years this was dropped to 25.95g; a 23.8% reduction in weight. In addition, the PE cap on the bottle was dropped from 3.1g to 1.5g, a 41.6% saving in material. These great gains were achieved using an induction heat seal, to give the lightweighted containers both stability and tamper evident product security.
Challenges to lightweighting
Fast forward to today and lightweighting is being undertaken across an even broader spectrum of products. This is good news for material reduction targets, however it can cause container distortion problems, particularly when done to the plastic packaging of products prone to off-gassing, such as home and garden chemicals. Also, the trend for more ‘concentrated’ forms of these products can acerbate the packaging distortion issue.
The two main distortion issues that can occur are panelling or bloating. Panelling is when the walls of a plastic container collapse inwards and bloating is when they swell or bulge outwards. The former tends to happen as vacuum pressure is created due to product oxygen scavenging, or elevation or atmospheric pressure changes.
Bloating on the other hand is a result of gas buildup inside the packaging, such as in the case of concentrated bleaches, peroxides, and other household cleaners and chemicals.
Alternatively, if the product absorbs gas – which tends to occur with solvent-based products and those containing essential oils, then there can be panelling.
Venting to maintain appearance
Although panelling and bloating do not tend to have an impact on the container’s contents, they can communicate to consumers that product spoilage might have occurred, reducing their shelf-appeal. So, how can these symptoms be avoided, whilst continuing to meet lightweighting plastic reduction goals? The answer lies in ensuring proper venting.
Venting is the use of a sealing liner that has been designed to allow pressure equalisation through letting gas in or out. Microporous membranes, slit or pressure-relief valves and two-piece vented liners can all resolve the panelling and bloating issue.
However, it is important to choose the right vent, as some only work if the container is stored upright, and the incorrect vent liner choice can leak if the membrane is compromised.
When it comes to containers for items prone to bloating and panelling, Selig’s technical team recommends choosing closure liners that include a hydrophobic or oleophobic membrane. These membranes will allow gas to pass through but block liquid escape, maintaining a secure, leak-free seal, even under pressure.
Selig’s solution development team of engineers can help fillers and brand-owners identify the proper venting materials and liner materials for each application, to ensure the right balance of venting properties and sealing characteristics.
Selig’s family of container venting liner materials, Circumvent™ and AirFoil™ are helping many producers lightweight their containers, whilst eradicating potential panelling or bloating issues. Other venting solutions for use on specialised containers or in custom closure systems are also available from Selig.
As the balancing act continues between sustainability and maintaining the container’s on-shelf appeal, vented liners are an unsung hero in the packaging producer’s toolbox. By choosing the right container venting solution, it is possible to deliver both plastic reduction and container integrity in even the more challenging applications.
