TECHNOLOGY | ACTIVE PACKAGING
Fraunhofer IVV is exploring the use of plant derived oxygen scaveners in multi-layer packaging films
powder, monolayer film and multilayer film. The films were initially brownish-red in colour but changed to greenish-black during oxygen absorption under humid conditions, demonstrating residual capacity. A maximum absorption capacity of 447 mg O2
/g gallic acid at 21°C and 100%
relative humidity was found. The incorporation of gallic acid into the polymer
matrix reduced the rate of oxygen absorption, as compared to pure gallic acid powder, because the polymer acted as a barrier to oxygen and water vapour diffusion. The institute adds that tempera- ture has a significant effect on the initial absorption rate of the multilayer films, with the activation energy being 75.4 kJ/mol, while higher relative humidity significantly increased the oxygen absorp- tion rate. Potential applications include packaging of food products containing high water levels. Fraunhofer IVV has also been involved in humid-
development,” Sängerlaub says. One of the projects Fraunhofer has worked on is the use of natural, plant-derived antimicrobials for packaging. It says the application of packaging materials that release antimicrobial substances to food surfaces is an attractive option to reduce and inhibit non-desirable microbial growth due to contamination and to prevent food loss. And natural antimicrobial compounds are often pre- ferred to synthetic substances. Fraunhofer IVV has identified suitable antimicro- bial substances – pelargonium and olive leaf extract – which are encapsulated to protect them during processing. It says they have been dispersed in polymers, coated on films, extruded and intensively tested. Work so far indicates the natural antimicro- bials are suitable for extrusion and coating, can withstand the processing temperatures involved, and exhibit a significant CFU (colony-forming unit) reduction. A question that still has to be answered is to find the right match between food and antimicrobial substance to avoid organoleptic changes in the food. In a further study, a natural and plant-derived
oxygen scavenger – gallic acid – was used in food packaging to provide additional protection to oxygen-sensitive food products. A mixture of gallic acid and sodium carbonate was incorporated in a bio-based multi-layer packaging film produced by a three-step process of compounding, flat film extrusion and lamination. Fraunhofer investigated the film surface colour as well as oxygen absorp- tion at different relative humidities and tempera- tures, and compared the oxygen absorption of the
70 COMPOUNDING WORLD | October 2017
ity regulation through the use of salts and sugars. By integrating salts in polymer structures, the materials can be modified to absorb and desorb high amounts of water vapour. In a study, films of polylactic acid and polypropylene with dispersed calcium chloride at levels of 2 and 4 wt%, were produced and biaxially stretched to form film cavities. These cavities accounted for up to 10 vol% of the film and were able to contain calcium chloride solution formed by water vapour absorption. The films were shown to absorb up to 15 wt%
water vapour at 75% relative humidity at 23°C reversibly. Fraunhofer explains this absorption behaviour is due to the effective diffusion and sorption coefficients (the effective water vapour diffusion coefficient of the films can be estimated from the permeation coefficient of the polymer and the sorption coefficient of the absorber).
PET projects The long term performance of PET bottles made with various concentrations of oxygen scavenging additives – including MXD6 from Mitsubishi Gas Chemical and Oxyclear from Invista – stored at different temperatures has also been investigated by the institute. PET bottles made with blends of PET with 2, 5 and 8 wt% MXD6 and 2 wt% Oxyclear were filled with deoxygenated water then stored at 5, 23, 38 and 55°C for up to five years. The oxygen partial pressure of the water in the bottles was measured regularly (showing an early increase at the higher temperatures because of faster exhaus- tion of the oxygen scavenger). The tests showed that the oxygen partial
pressure of the water in PET bottles with 8 wt% MXD6 was below 10 mbar even after five years
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PHOTO: FRAUNHOFER IVV
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