Biopolymers – Easy to Process - Wacker Chemie AG


Biopolymers – Easy to Process

Biopolyesters based on renewable resources are, in many cases, far worse to processthan conventional petroleum-based plastics. By adding VINNEX® as a binder, however, biopolyesters can be handled just like standard thermoplastics.

Starch-based polymer granulate with VINNEX® is the starting material for a wide variety of products made of biodegradable plastic.

Plastics essentially consist of carbon chains with attached hydrogen and oxygen atoms. The carbon in those chains can stem from petroleum – or renewable raw materials. Polymers that are not manufactured from the increasingly scarce and expensive petroleum, but renewable raw materials such as starch or cellulose, are called biopolymers. These represent promising, sustainable alternatives to petroleum-based resources, because, in principle, the starting material is available in unlimited amounts. In addition, polyester-based bioplastics are environmentally compatible, because they decompose over time. Experts estimate that bioplastics could replace up to 90 percent of all conventional plastics in the future. So far, however, biopolymers have been a side-show compared to their conventional petrochemical competitors. According to a study conducted by the industry association European Bioplastics and the University of Hannover, 2011 only saw 1.2 million metric tons produced worldwide – less than one percent of global plastics production. The reasons for this are quite obvious: the properties of bioplastics are still often not equal to those of comparable conventional plastics and bioplastics are generally more expensive and difficult to process by well-established industrial methods.

However, the chemical and plastics processing industries as well as research institutes are working intensely on developing new and improved bioplastics. The research drive is showing up in above-average market growth with global production capacity for biopolymers set to increase fivefold to six million tons by 2016.

“Companies are working on innovations to improve the properties of existing biopolymers and their discoveries may greatly change the way plastics are used in packaging applications.”

Sujatha Vijayan, Frost & Sullivan research analyst
Biodegradable food packaging is gaining in popularity. The new VINNEX® binder system now enables enhanced processing of bioplastics and reduces the film’s noise levels.

Environmentally Conscious Consumers

According to a study by consulting firm Frost & Sullivan, bioplastics are particularly sought after by the food sector, where consumers are increasingly demanding biodegradable packaging and are willing to pay higher prices for it. Reports about huge plastic garbage vortexes the size of central Europe in the world’s oceans have alarmed environmentally aware consumers. However, the Frost & Sullivan study claims that the success of the bioplastics market also depends on the development of new technologies to enhance the quality and properties of the materials used. “Companies are working on innovations in various technology fields to improve the properties of existing biopolymers and their discoveries may greatly change the way plastics are used in packaging applications,” explained Sujatha Vijayan, a research analyst at the US-based consulting firm.

New Blends Enhance Properties

One of these companies is Wacker Chemie AG: to compensate for biopolymers’ remaining shortcomings, WACKER developers are relying on the principle of polymer blends, thus a mix of synthetic and biobased polymers. Adding the VINNEX® vinyl-acetate-based binder now enables the development of significantly higher-performance biopolymer blends that cover a more diverse application and processing spectrum.

Typically, the blends contain between five and 30 percent of the added binder. The additive considerably enhances the physical properties of the bioplastics, which are otherwise difficult to process. To an extent depending on the VINNEX® content and grade, the polymer blends have higher impact strengths, are more resistant to melting or are more flexible than the pure biopolymers.

The Product

VINNEX®

is a plasticizer-free binder based on vinyl-acetate homopolymers, copolymers and terpolymers. It now also enables easy processing of biopolymer blends. For example, these new blends can be processed into food packaging materials, brochures, parts for electronic appliances or self-degradable gardening and agricultural containers.

Same Equipment Used

The polymer-blend formulations can now be adjusted so that plastics processors can use the same equipment for the bioplastics as for conventional thermoplastics – from injection molding, extrusion, blown film extrusion, vacuum forming and thermoforming, to calendering. Furthermore, thanks to VINNEX®, it is now much easier to get the bioplastics to assume the desired shape.

The enhanced binder is compatible with all kinds of biopolyesters. As the system is modular, it is also possible to combine various VINNEX® grades – either powder or solid resin – with one or more bioplastics and fillers. Thus, various polymer blends can be obtained by combining VINNEX® with starch, polylactic acid (PLA), polyhydroxyalkanoates (PHA), polybutylene succinate (PBS) or cellulose acetate (CA). As a result, the properties are customizable. In the case of PBS, since VINNEX® lessens its tendency to recrystallize and improves the melting resistance, the polymer blend can be thermoformed to yield stable, three-dimensional structures.

Completely Novel Possibilities

With the VINNEX® range, WACKER experts have made it possible to manufacture containers for hot-filling applications from PLA/PBS blends by thermoforming. This could make the binder a valuable raw material for coffee mugs and soup containers in the future. Most VINNEX® grades are suitable for use in food-contact applications.

The binder additive opens up entirely new possibilities for bioplastics. Take polylacticacid as an example. Even though PLA is a very rigid material, the addition of 20 to 30 percent VINNEX® enables very thin and highly transparent sheets to be made without any trouble. These sheets exhibit reduced noise levels and are considerably easier to weld, which makes them ideal for display and shrink films for the food sector, for example. Since VINNEX® significantly improves the adhesion of PLA to paper, new possibilities also open up for high-speed extrusion coating, e.g. for coated paper cups and storage trays.

Products Remain Biologically Degradable

Furthermore, VINNEX® expands the application range of polyhydroxyalkanoates such as polyhydroxybutyrate (PHB). This bioplastic is produced by fermentation and has different properties, depending on the composition – from hard like ABS to flexible like soft PVC. Experts rate the market potential of polyhydroxyalkanoates to be accordingly high. Thanks to VINNEX®, the material’s processing window can be expanded and undesired postcrystallization prevented. In addition, the polymer blend is less brittle and significantly more flexible than the pure bioplastic. The elongation at break of a blend containing 10 percent VINNEX® is around 220 percent – almost three times that of pure PHB – and it exhibits slightly enhanced tensile strength.

Another VINNEX® series advantage is that certain formulations can meet the biodegradability criteria for bioplastics specified in ISO 14855. Under industrial composting conditions, the biodegradability in a mixture of PLA, starch and 30 percent VINNEX® reaches the 90-percent mark within 65 days. Just as with cellulose – as the test’s reference substrate – the mixture of starch, biobased and synthetic polymers is largely degraded after two months in the ground.