Thermoplastic breakdown - improved performance and biodegradability
Iron and natural fatty acids have been added to thermoplastics to improve the performance of barrier packaging and enable biodegradability.
A Norwegian research team at SINTEF Materials and Chemistry in Oslo has developed prodegradant additives (ferric(III) stearate and stearic acid) that are incorporated into PP ﬁlms and PE-based barrier laminates. The researchers claim the additives enhance gas barrier properties, reduce ﬁlm thickness and enable biodegradation to millimetre-sized particles within three weeks, despite comprising just 2% of the material.
According to research scientist Jens Kjær Jørgensen, ‘You can just add them to normal materials, so you don’t need to buy a special material grade that is biodegradable. Instead of using 100% PE, you use 98% PE and 2% of the master batch, and you get a material that will disintegrate after it is exposed to sunlight.’
To prove the additives’ efficacy, the team conducted two tests. For the ﬁrst test, they added the prodegradant additives to a ﬁve-layer gas barrier during processing. The oxygen transmission rate was said to have improved significantly thanks to the oxygen consumption in the laminate degradation process.
‘We showed that we can go down to ﬁve microns (thickness) with the additive. The normal oxygen transmission rate is 5cm3 per square metre, and with 2% of the master batch we’re down to 1.5cm3.’
For the second part of the study, the team incorporated 2% of the master batch into ﬁve different qualities of PP and subjected them to 830 hours of accelerated weathering (using temperature cycling and UV light). At the end of this time period the material reduced from 80,000g/mole to 1,500–2,500g/mole.
Team member Ferdinand Männle explains that microorganisms will eventually eat the materials once the molecules have degraded further. ‘The biodegradability in the ﬁnal state is insurance,’ he says. ‘Normally you don’t need it, because most packaging in Europe is recycled…. (However,) if someone leaves the packaging in a park or whatever, it will disintegrate.’
Despite the performance of the prodegradants, he notes that the modiﬁed polyoleﬁns don’t fulﬁll biodegradability requirements and that industry priorities lie in other areas. ‘There is more focus on renewable sources for materials,’ he says. ‘So I don’t know how interested people are in improving polyoleﬁns. Most of our customers talk about bioplastics, but not in the way that they should be degradable and compostable.’
For Männle and his colleagues, future success could hinge on the technology’s adaptability. ‘The most interesting approach would be to incorporate the technology into bioplastics to improve properties such as material saving, recycling and degradability.’