Materials feature: flexible plastics

Tess Raine, Packaging News, 01 February 2007

 

Flexible packaging has come a long way in the last five years and is branching out to use different materials and methods.

 

As recently as five years ago, predictions on the market and uses for flexible plastic in packaging in 2007 focused primarily on polyethylene (PE) and polypropylene (PP).

 

But manufacturers now find the choice is no longer that simple. Consumers are aware that packaging can salve their environmental conscience if it’s produced from renewable resources, so the production of PLA in a flexible form has proved popular with brands wanting to help consumers feel good about themselves. (PLA stands for polylactic acid, a polymer derived from renewable agricultural resources like maize or sugar beet that can be processed to make a plastic which will biodegrade under the right conditions to water and carbon dioxide.)

 

 

Five years ago PLA was only really thought of as a packaging material for rigid plastic trays or bottles, because of its supposedly brittle nature. Despite high transparency, 100% PLA had limitations as a flexible packaging material, but the right mixture of additives and manufacturing processes has extended the use of PLA into flexible applications.

 

 

Indeed, in some cases, there are benefits to using PLA over other flexible plastic materials, says Andy Sweetman, Innovia’s market development manager for sustainable technologies.

 

“Although in the overall scheme of things biodegradables are still a baby, there’s major potential for them – especially in the fresh food market. In that area, their moisture permeability can be a real technical advantage,” he says.

 

Flexible friend

Flexible PLA can now be used for a variety of packaging applications, including folding carton windows, bag windows, bag laminations, container lidding, twist wraps and floral wraps, as well as shrink film.

 

 

German film producer Treofan makes biaxially-oriented polypropylene film (BOPP) and cast PP film as well as bio-degradable PLA film under the brand name Biophan. Made from NatureWorks PLA, the production process of Biophan requires 30-50% less fossil fuel than conventional plastic materials.

 

Biophan is a biaxially-oriented film, stretched in both a longitudinal and transverse direction to increase its strength. It can be thermo-laminated to paper or board and may be used in direct contact with all kinds of food. It is suitable for flexographic and rotogravure printing with recommended nitrocellulose-based or water-based inks.

 

 

Sales of single- and three-layer Biophan films more than doubled in 2005 and 2006 and UK sales manager Carey Ashworth expects similar growth in 2007.

 

 

The NatureWorks PLA polymer is also used to produce films with shrink properties. Decorative Sleeves was the first European shrink-sleeve manufacturer to use PLA. Multinational packaging producer Alcan is also looking to use PLA in future applications. It has developed a very-high-barrier film, Ceramis PLA, targeted at the modified atmosphere fresh food markets. This uses a very thin transparent barrier layer to impart high moisture and gas barriers to PLA film without affecting the compostability of the base film.

 

Using materials made from renewable resources isn’t the only way to entice users to flexible plastics. Degradability is also key to ensuring media and public attention, but using materials that will eventually break down can make it difficult to produce packaging tough enough to do the job.

 

National Flexible is offering its SuperEco made from PP with an additive to make it degradable and biodegradable. Marketing manager Andy Smith says: “What we’re hoping for this bio-film is that customers don’t have to do different jobs with a biodegradable film. We want them to know we’re not offering a different material. It’s just a different version.” This different version offers the same performance levels as standard OPP but it breaks down to CO2, water and biomass when composted.

 

Unlimited possibilities

National Flexible feels it is still at the start of producing and marketing this relative newcomer to the flexible plastic market. Smith says degradable films have big potential, but stresses that compostable films are still relative newcomers and haven’t, as yet, taken as much market share as you might expect.

 

“Regular polyester and laminate films still dominate our business,” says Smith. “But there has been so much demand from our customers for degradable films.”

 

“It’s still generally slightly more expensive than traditional plastic films,” admits Smith. But he says the cost in mass production of PLA or other degradable plastic films is estimated to be similar to that of petrochemical plastics.

 

 

“The uses for flexible plastic packaging are pretty much unlimited,” says Smith. “Generally it uses fewer raw materials than other types of packaging and producers and retailers are constantly looking at ways to produce even less waste from flexible packaging.”

 

 

There are many other flexible plastic materials that are degradable, but they are not made from PLA. Innovia offers NatureFlex, a transparent, compostable packaging film, which was first produced in 2003 and is made up of a cellulose base layer with compostable plastic coatings to give it heat sealability and moisture barrier properties.

 

 

Sweetman says the firm has two “families” of NatureFlex film: those with barrier properties and those with permeable layers. “For fruit and veg you need a permeable film that evacuates the excess moisture,” he says. “But for sugar confectionery we might formulate in moisture barrier properties.