Feasibility of Recycled Polypropylene for Reusable Food Packaging: Effects of Reuse Conditions on Packaging Performance, Material Properties, and Microbial Safety

Polypropylene (PP) recycling has always been challenging because the polymer is highly susceptible to thermooxidative degradation during extrusion. Recycled (degraded) PP is normally blended with virgin PP to achieve reasonable mechanical properties after reprocessing operations. However, impurities present in recycled PP tend to degrade even the virgin PP in this process. In this study, standard recycled PP was produced in a laboratory by repeated extrusion and pelletization operations of virgin PP. This material was blended with virgin PP in a ratio from 3 : 7 to 7 : 3. An attempt was made to stabilize the recycled blend by adding a peroxide decomposer (triphenylphosphite, TPP) and a slipping agent (zinc stearate) in contrast to radical scavengers normally used in reprocessing. It was found that by using 0.3–0.5 wt % of TPP and 2 wt % of zinc stearate, this degradation could be effectively attested. Compared to the tensile strength retention of 68% (based on strength of pure virgin PP) of a 60 : 40 (recycled : virgin) PP blend without any stabilizer, a value of 77% was obtained for the same blend with the above-mentioned stabilizers. This stabilization effect was attributed to decomposition of unstable hydroperoxides to stable compounds in the recycled materials by TPP, and lower generation of new radicals in the presence of zinc stearate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3247–3251, 2004

For the last few decades, plastics have been the material of choice for food packaging applications. Combining mechanical performance with barrier properties and transparency, plastics have been a cost-effective solution for safely distributing food produce. Unfortunately, most plastic packaging is based on a linear model where packaging is designed for single use, resulting in vast amounts of post-consumer waste being generated annually. In response to this concern, many public and private bodies globally have set ambitious sustainable development targets with the goal of reducing plastic waste. To assist in meeting these targets, the implementation of reusable packaging schemes has been suggested. These schemes aim to prolong the lifespan and worth of plastic packaging and have the potential to reduce the environmental impact of single-use plastics, provided all aspects of their design are carefully considered. One design aspect often neglected is the influence of repeated use on the properties of the packaging material. Very little literature exists investigating the effects that repeated contamination and washing can have on the material's intrinsic properties. This review article aims to comprehensively review the functions and properties of various food packaging materials to assess their suitability for reusable food packaging applications.

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.

Waste polypropylene (PP) polymer was collected, washed, dried and mechanically recycled into granules. Natural fibers are a sustainable and renewable resource, and in this work, Corchorus olitorius jute fiber was used as a reinforcing agent with waste PP. Jute fiber was collected from local market, cleaned, dried and cut into 1-2 mm in length for the production of waste PP-jute composites. The molecular structure of waste PP and virgin PP were characterized by the attenuated total reflection-fourier transform infrared (ATR-FTIR). The purpose of the current research was to examine the effectiveness of waste PP by comparing waste PP-jute composites and virgin PP-jute composites. The injection molding process was utilized to make jute fiber reinforced waste PP composites with various jute fiber loadings (5%, 10%, 15%, 20%, 25%, and 30% in weight).The same process was used to produce virgin PP composites reinforced with jute fiber. All composites undergo water absorption and tensile testing in order to assess the recycled PP. Injection molded virgin and waste PP's physico-mechanical, thermal, and tensile strengths are also examined. In comparison to waste PP, virgin PP has a 6% greater tensile strength and a 19% higher elongation at break. Results from waste PP-jute composites and virgin PP-jute composites did not significantly differ from one another. Products made from recycled PP can thus be both economically and environmentally viable.

An experimental study on recycled polypropylene and high-density polyethylene and evaluation of their mechanical properties

Several composites based on recycled—virgin polypropylene, wood flour and organically modified montmorillonite (commonly called ‘nanoclay’) were prepared by melt compounding. This paper aims to evaluate the potential for the use of recycled polypropylene and underutilized wood flour as material for the development of wood–plastic composites, as well as reinforcement effect of organically modified montmorillonite on them. In order to improve the poor interfacial interaction between the hydrophilic wood flour and hydrophobic polypropylene matrix, as well as polypropylene–organically modified montmorillonite, maleic anhydride-grafted polypropylene was used as a compatibilizer. Some mechanical and physical properties were evaluated. Findings of this work show that both recycled and virgin polypropylene can be used in manufacture of wood–plastic composites and there is no significant difference in the properties of resulting nanocomposites. It was found that mechanical properties of polypropylene containing 40wt% wood flour reinforcement remain essentially unchanged when the virgin polypropylene in the matrix is replaced be recycled polypropylene. Morphologies of the nanocomposites were analyzed by scanning electron microscopy and X-ray diffraction, and the results showed increased d-spacing of clay layers indicating enhanced compatibility between polypropylene and clay and wood flour. Consequently, polypropylene recycled from postconsumer applications can be used in high-value nanocomposites without going the expense of separating out impurities from the polymer.

UV accelerated aging of unidirectional flax composites: Comparative study between recycled and virgin polypropylene matrix

Polypropylene (PP)-based recyclates obtained specifically from mechanical recycling are increasingly used and visible in various application, e.g., bottles and containers in non-food applications. A big drawback of mechanical recyclates is that they contain besides the target polymer type, also other polymers and inorganic fillers, which are not soluble under the conditions required for polyolefins. These components make the analysis of recyclates with standard methods difficult. For virgin polypropylenes, it was shown that Crystex (CRYStallization EXtraction) analysis was capable of accurately determining the key properties for PP composition, like the amount of xylene cold soluble (XCS), the ethylene content, and the intrinsic viscosity (IV) of the whole material as well as of the crystalline and amorphous fractions. In this work, defined compounds with the same polypropylene composition but various filler contents were used for proving that the Crystex technique is a suitable analysis technique to determine the key properties of PP-based compounds in a fast and accurate way. Different types of sample preparation for removal of insoluble components prior to Crystex analysis were investigated and validated by different complex compounds, recycled PP, and PP-based compounds containing recycled material. It was concluded that by the usage of a newly developed online filter system, the key parameters in PP-based compounds and recycled PP can be determined without disturbance. Additionally, a new methodology was developed for a more accurate estimation of the non-intended polyethylene (PE) amount that does not originate from heterophasic PP (HECO-PP) in post-consumer recycled (PCR) PP material.

The physical and mechanical properties of wood-polymer composites made with virgin or recycled polypropylene, or a mixture of these were studied. The composites made with recycled polypropylene had higher density, lower porosity, and higher dimensional stability compared to the composites made with virgin polypropylene. Although the composites made with recycled polypropylene exhibited lower tensile strength than those made with virgin polypropylene, they had higher Charpy impact strength. Scanning electron microscopy analysis of the fractured surfaces of the composites showed no significant differences in the fracture mechanisms of the studied composites. The degree of crystallinity was estimated to be higher for the virgin polypropylene than for the recycled one.

Polypropylene (PP) is a versatile polymer, with a wide range of applications, from household appliances to packaging and automotive components. Unfortunately, most of the PP products have a short life, which leads to a large amount of plastic waste. Recycling PP is an efficient way to offset the environmental pressure, and several technical solutions have been already proposed for PP recycling. However, dramatically reduced thermal and mechanical properties are generally obtained in the case of PP waste materials. In this work, the influence of PP waste on thermal and mechanical properties of PP waste/virgin PP blends was studied. A PP waste material (PPRR) was melted and compounded with high flow virgin PP homopolymer. The blends were characterized by dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, mechanical tests and Fourier transform infrared spectroscopy. An increase by 20% of the tensile strength and modulus and 2.5 times increase in the melt flow index were observed in the case of the blend with 50% virgin PP as compare to PPRR, also an important increase in crystallinity. All the blends showed a better thermal stability than the virgin PP. The results recommend the blends with 30–50% virgin PP for the recycling of PP waste from raffia in high-performance applications.

Implementation of material value conservation (MVC) needs to be proven through research to determine impact upon plastic properties such as optical properties of virgin plastic and recycled plastic blends. Optical properties such as colour, transparency and gloss are important parameters for appropriate quality of plastic packaging. Degradation of optical properties occurs during recycling processes of plastic materials and the declining properties of recycled products could be improved by blending them with virgin materials. This research aims to reveal the impact of repetitive recycling on optical properties of virgin and recycled polypropylene (PP) blends based on MVC paradigm. The first step of this research was to determine composition of virgin PP and recycled PP blends. Proportion of 70% virgin PP and 30% recycled PP was selected as a blend composition. The next step of this research was repetitive recycling of virgin PP and recycled PP blends with implementation of MVC up to the 8th recycling stage. The specimens of plastic blends were made from the 1st, 2nd, 4th and the 8th recycling stage and then their optical properties were tested with the American Society for Testing Materials (ASTM) methods. Generally, degradation level of optical properties will increase during the recycling processes. Testing results show a slightly change of colour properties. Degradation level of gloss properties is gradually increased by a maximum degradation level at the 8th recycling stage as 17.46%. However, transparency had a maximum degradation level at the 4th recycling stage as 20.93%. It means that the plastic blends can be used as viable raw materials based on their optical properties with more attention to the gloss. Furthermore, the implementation of MVC will provide more benefits through extending the life cycle of recycled products, reducing virgin plastic consumption, optimizing the use of plastic waste and reducing plastic waste generation.

Modification of mechanical properties of recycled polypropylene from post-consumer containers

Plastic mechanical recycling is an attractive method for reducing the amounts of waste plastics. However, the alterations in the mechanical properties (degradation) in recycled plastics is a limitation to the material’s mechanical recycling. In this study, the mechanical recycling was enhanced by the addition of a “molten resin reservoir” unit at the end of the twin-screw extruder. Recycled polypropylene (RPP) obtained from a household was re-extruded with this developed extrusion unit. The tensile properties, type of crystalline, and conformation of polypropylene polymorphs were evaluated and compared for virgin polypropylene (VPP), recycled polypropylene (RPP) without extrusion (RPP-original), and RPP with extrusion by using a new type of extruder (RPP-extrusion). It could be found that the tensile properties of RPP-extrusion were improved, so as to be similar to those of VPP. In addition, the conformation of RPP-extrusion was similar to that of VPP by increasing the ratio between the helix and parallel band. This study succeeded in regenerating the tensile properties and inner structures in recycled PP, which could prolong the used lifetime and decrease the amount of waste from single-use plastic.

In this research, the improvement of the impact strength of wood flour–recycled polypropylene (PP) composites through impact modification was studied. For this purpose, a virgin polypropylene (VPP) was thermomechanically degraded by five extrusions under controlled conditions in a twin‐screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. PP (VPP and recycled PP at the second and fifth stages) and wood flour were compounded at 50 wt % wood flour loading in a counterrotating twin‐screw extruder in the presence different contents of ethylene vinyl acetate (EVA) to produce the wood flour–PP composites. From the results, the composites containing recycled PP exhibited significantly lower impact strengths. The addition of EVA up to 9 wt % increased the impact strengths of the composites made with PP recycled two and five times by about 63 and 41%, respectively. The composites containing VPP exhibited higher impact strengths than those containing recycled PP and EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Pyrolysis of virgin and waste polypropylene and its mixtures with waste polyethylene and polystyrene