Under consumer pressure, an increasing number of converters are looking for packaging material made from renewable resources to highlight their sustainable and ecological image. These efforts to reduce both pollution and reliance on oil-based plastics, as well as continued consumer demand for sustainable and eco-friendly packaging spur demand for bio-plastics, which are biodegradable and certified to the ASTM D 6400 standard. This market segment is forecast to grow in the USA by 16.6 per cent a year by 2014, according to a recent report published by Freedonia and titled “Degradable Plastic to 2014”.
Bio-plastics are a class of polymers, which have properties comparable to conventional polymers, but are made from renewable resources or enable biodegradability of the products made from this material. Generally, raw bio-plastics (starch, PLA, PHA, PBS and others) are not easy to use and are therefore blended and compounded into more functional materials. This processing of raw bio-plastics requires special knowledge in the field of additives and a smooth compounding process.
The US bio-plastics sector is currently dominated by polylactic acid (PLA) and starch-based plastics. Corn-based plastics are made by fermenting corn sugar to produce lactic acid. This substance is then used to form PLA.
Although biopolymers have become more cost effective, they do not, as already said, perform well on their own. Rather, they must be modified and compounded with plasticizers to reach sufficient fitness for use properties to compete with petroleum-based resins. Polylactic acid (PLA) and PHA have high rigidity and are unsuitable for applications that require flexibility and toughness. The most common technique to make PLA and PHA flexible is to add a plasticizer or to compound in more flexible polymers. The predominantly used and commercially available resin used for both PLA and PHA is an aromatic/aliphatic co-polyester which is biodegradable, but not at all renewable since it is 100% derived from petroleum. Blends made from these materials tend to have reduced modulus (stiffness) and they are not optically clear.
Furthermore the fact that (blended) bio-plastic has a lower heat tolerance than some petroleum-based plastics excludes it from being used for a wide range of applications, particularly for hot-filling. Today’s PLA typically can’t take the heat of hot-filling.
To raise the ‘heat deflection temperature’ (the temperature at which a plastic material, in this case PLA, distorts) scientists of the US Government’s Agricultural Research Service (ARS) and Santa-Barbara-based private company Lapol developed a temperature deflection modifying mechanism that significantly boosts its heat resistance properties. The modifier is said to be more than 90 per cent corn based and fully biodegradable, while preliminary tests indicate that, when blended with PLA, the modifier can raise the bio-plastic’s heat-deflection temperature by at least 50˚F (10˚C).
With further research and development, the heat modifier might make it possible for food or beverage bottles or other containers made from PLA to be “hot-filled,” that is, filled at the food-manufacturing or beverage-bottling plant while the food or beverage is still hot from pasteurization. Examples might include, among other popular items, tomato ketchup or some kinds of fruit juice.
At the other end of the spectrum FKuR Kunststoff GmbH, a German bio-plastics company, developed, in cooperation with the Fraunhofer Institute UMSICHT, in Oberhausen, the world’s first sustainable deep freeze packaging made from renewable resources. The basis of this unique film structure is FKuR’s Bio-Flex range of certified compostable bio-films.
When considering the performance of deep freeze packaging the material’s mechanical properties at low temperatures are particularly crucial. High impact strength and dart drop strength at these temperatures are a must in order to succeed. Low glass-transition temperatures as well as a homogeneous material with excellent distribution of functional additives are the keys to meeting these requirements.
To obtain the film properties required for deep freeze packaging, a three-layer system made from Bio-Flex F 2110/Bio-Flex A 4100 CL/Bio-Flex F 2110 is used. This film has an appealing gloss surface together with great strength and chemical resistance along with demonstrating good barrier properties for a bio-plastics.
Both resins are based on a blend of PLA and other biodegradable materials. Bio-Flex F 2110 as well as Bio-Flex A 4100 CL are compostable according to ASTM D 6400 and are food contact approved.