Recycling of blends made of polypropylene and an iron-based oxygen scavenger – Influence of multiple extrusions on the polymer stability and the oxygen absorption capacity

Effect of catalyst carrier type and concentration on oxygen-scavenging property and characteristics of iron-based active films

The presence of oxygen can degrade food quality, making it essential to remove oxygen from the packaging headspace of food products. In this study, the effect of catalyst type and concentration on iron-based oxygen-scavenging films was investigated to enhance the oxygen removal efficiency in food packaging films. Among the investigated catalysts, calcium chloride and lipophilic silica improved the oxygen-scavenging capacity more than sodium chloride and hydrophilic silica. As the catalyst content was increased from 0.1 to 6.0 %(w/w), the oxygen content (%) in the package decreased from 3.90 to 0.36%. Application of oxygen-scavenging films in apple packaging decreased the apple browning index from 52.87 to 38.13 and reduced the oxygen concentration inside the package from 9.8 to 0.0%. Therefore, the food packaging film developed in this study can be used as a food packaging material that removes oxygen and thus prevents food quality deterioration.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01520-4.

Packaging Weight, Filling Ratio and Filling Efficiency of Yogurt and Relevant Packagings Depending on Commercial Packaging Design, Material, Packaging Type and Filling Quantity

Yogurt is a diverse dairy product category. It is available in different packaging designs made of different materials. To identify potential for improvement for these packagings, a better understanding about used materials and packaging efficiencies is necessary. For this study, 150 dairy products and some yogurt relevant desserts were bought from various supermarkets, street markets and discounters in the Munich region (Germany) in spring 2022. Commercial types of packaging are cups, buckets, pouches, bottles, glass packagings and bricks. The filling ratio of most packagings is above 70%, the rest of the volume is headspace. Poly(1-methylethylene) (PP) and poly(1-phenylethene) (PS) dominate as main materials for the different types of packaging. For bottle packagings, poly(ethylene terephthalate) (PET) and polyethene high-density (PE-HD) are used. Interestingly, poly(lactic acid) (PLA) is not found. Closures (caps) are responsible for 5 to 30% of the total packaging weight. Typical filling efficiencies are 20 to 40 g food product packaged in one gram of packaging material. For glass packagings, the values are 1.5 to 2 g food product packaged in one gram of packaging material. Therefore, plastic packaging results in an at least ten-times lower packaging use per unit of food, at single use packagings. With increasing product weights, we observe a tendency towards higher packaging efficiencies. By using paper/carton wrapping at cups, plastic use is reduced for the whole packaging.

Comparison of Properties with Relevance for the Automotive Sector in Mechanically Recycled and Virgin Polypropylene

Polypropylene (PP) has a high recycling potential. However, the properties of mechanically recycled PP (R-PP) have not been fully compared to those of virgin PP (V-PP). Therefore, in this study, properties of R-PP and V-PP were compared using data from recyclers, virgin plastic suppliers, and the literature. The properties of recyclates could not be directly correlated either with the properties of the virgin polymers from which the recyclates were made or the recycling parameters. It was found that the MFR of R-PP was higher; MFR R-PP had a median value (m) of 11 g/10 min while MFR V-PP had a median value of 6.3 g/10 min (at 230 °C and with 2.16 kg). In terms of mechanical properties, in many cases R-PP exhibited stiffer and more brittle behavior, with a slightly higher Young’s modulus (ER-PP = 1400 and EV-PP = 1200 MPa), a reduced elongation at break (ɛbR-PP = 4 l.-% and ɛbV-PP = 83 l.-%), and notched charpy impact strength (NCISR-PP = 4.8 and NCISV-PP = 7.5 kJ/m2). However, the values for every property had a broad distribution. In addition to existing information from the literature, our research sheds fresh light on the variation of the characteristics of recycled polypropylenes presently on the market.

Elaboration and Characterization of Active Films Containing Iron-Montmorillonite Nanocomposites for O2 Scavenging

Iron particles of sizes between 6 and 20 nm forming aggregates of 57 ± 17 nm were synthesized by chemical reduction of iron precursors on the surface of montmorillonite (MMT). This active MMT-Fe powder was then uniformly distributed in a linear low-density polyethylene (LLDPE) matrix by extrusion at atmospheric conditions, as confirmed by wide-angle X-ray scattering (WAXS), which also detected a partial exfoliation of the nanoclays. Thermogravimetric analysis (TGA) did not detect any significant modification of the degradation temperature between nanocomposites and active nanocomposites. 57Fe Mössbauer spectroscopy evidenced the formation of a majority of iron boride in MMT-Fe as well as in the active film containing it. The LLDPE.Fu15.MMT-Fe3.75 and LLDPE.Fu15.MMT-Fe6.25 films had oxygen-scavenging capacities of 0.031 ± 0.002 and 0.055 ± 0.009 g(O2)/g(Fe), respectively, while the neat powder had an adsorption capacity of 0.122 g(O2)/g(Fe). This result confirms that the fresh film samples were partially oxidized shortly after thermomechanical processing (60% of oxidized species according to Mössbauer spectroscopy). No significant difference in oxygen permeability was observed when MMT-Fe was added. This was related to the relatively small film surface used for measuring the permeability. The reaction-diffusion model proposed here was able to reproduce the observed data of O2 adsorption in an active nanocomposite, which validated the O2 adsorption model previously developed for dried MMT-Fe powder.

Gallic Acid as an Oxygen Scavenger in Bio-Based Multilayer Packaging Films

Oxygen scavengers are used in food packaging to protect oxygen-sensitive food products. A mixture of gallic acid (GA) and sodium carbonate was used as an oxygen scavenger (OSc) in bio-based multilayer packaging films produced in a three-step process: compounding, flat film extrusion, and lamination. We investigated the film surface color as well as oxygen absorption at different relative humidities (RHs) and temperatures, and compared the oxygen absorption of OSc powder, monolayer films, and multilayer films. The films were initially brownish-red in color but changed to greenish-black during oxygen absorption under humid conditions. We observed a maximum absorption capacity of 447 mg O₂/g GA at 21 °C and 100% RH. The incorporation of GA into a polymer matrix reduced the rate of oxygen absorption compared to the GA powder because the polymer acted as a barrier to oxygen and water vapor diffusion. As expected, the temperature had a significant effect on the initial absorption rate of the multilayer films; the corresponding activation energy was 75.4 kJ/mol. Higher RH significantly increased the oxygen absorption rate. These results demonstrate for the first time the production and the properties of a bio-based multilayer packaging film with GA as the oxygen scavenger. Potential applications include the packaging of food products with high water activity (a_w > 0.86).