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Sustainability in Plastics—Embracing New Approaches

By: Chris Pandis
Posted: August 31, 2011

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Foaming is not new. It has been used extensively in electronics housings, home and garden furniture, luggage and, more recently, in automotive interior parts to reduce weight and raw material use. Added to plastics during processing, foaming agents such as Clariant’s Hydrocerol masterbatches decompose to produce small quantities of carbon dioxide to form microscopic bubbles in the polymer matrix. The gas displaces the polymer so that it takes less plastic to make a bottle, closure or other packaging component.

Until recently, acceptance of foaming used to create bottles and similar components for personal care products has been limited by a relatively coarse and nonuniform cell structure that impacted appearance and mechanical strength, especially in thinner wall sections. Advances in foaming technology are now making it possible to achieve a highly uniform structure of bubbles as small as 50–100 microns in diameter—even smaller than the period at the end of this sentence. This compares very favorably to the 400 microns typical of first-generation foams and even the 200 microns, which was considered “fine” until recently. It means there is virtually no appearance or performance difference between structures produced with a CFA versus those made without one. Yet the benefits of reduced part weight and lower production costs are undeniable. Material-use reductions of 7% are common in injection molding, and some converters have reported savings of 25% in certain extrusion applications. At the same time, the CFA plasticizes the resin in the processing machine, so less heat needs to be added to melt it (energy savings); and since less heat has to be removed during cooling, cycle times are also reduced by 10 to 15%.

Even relatively small reductions in material consumption and cycle time can be very important. In fact, when millions of pounds of plastic material are processed in the course of a year, it is very easy to save hundreds of thousands of dollars. Although actual results can vary, internal trials at Clariant showed, for a typical 20 gram HDPE bottle, a weight reduction of 10%. Applying this to five million pounds of parts would generate a net raw material savings of more than $300,000. On top of this, processing-cost savings of the same order of magnitude are made possible by substantial reductions in cycle time.

The increased productivity and reduced material and energy consumption increase the sustainability credentials of the packaging in a documented manner. Less tangible, but no less important, are the benefits that arise from reducing shipping weight for both raw materials and finished products.

How Do You Want to Be Green

Foaming is a technology that can be applied to any material from conventional petroleum-based polymers to natural and biodegradable resins such as polylactic acid (PLA) and even the newest bioidentical materials. These latter polymers are made from renewable sources such as sugar and starch but have identical properties to the fossil-based materials (polyethylene, for example), except for the age of the carbon. Indeed, they are increasingly preferred over other biopolymers because they fit so well into the existing plastics processes, including recycling. PLA and other biopolymers don’t necessarily need to be recycled since they are compostable. However, one problem they pose is that easily recycled plastics such as PET can be rendered useless if contaminated by even a small quantity of PLA.