The use of nanoadditives within recycled polymers for food packaging: Properties, recyclability, and safety

A review of plastic waste nanocomposites: assessment of features and applications

Hundreds of millions of metric tons of plastic waste are generated globally every year. Processing waste into secondary raw material is preferred over energy production and landfilling. However, mechanical recycling generally deteriorates the properties of plastic waste limiting its range of potential applications. Nanocomposite fabrication is a solution to recycle plastic waste into value-added applications due to improved properties generated by nanomaterial reinforcement, however received little study. The aim of this review is to present the current status, identify research gaps and provide topics for further research of polymer nanocomposites prepared from plastic waste in respect to utilized materials, processing methods, enhanced properties, sustainability, economics, nanomaterial safety, and applications. It is found that morphological, mechanical, thermal, flame retardancy, physical, barrier, electrical and shielding properties of plastic waste can be enhanced with low loadings of different nanomaterials making them promising materials for various applications including electronic, shielding, thermal, packaging, filtration, and water treatment. Utilization of plastic waste instead of virgin polymers can be beneficial in respect to economics and sustainability, but the energy intensive and expensive production of the most nanomaterials, and the plastic waste pretreatment methods can negate these benefits. To enhance sustainability, further research should be conducted on utilization of energy friendly nanomaterials in plastic waste nanocomposites. Further research is needed also on polymer nanocomposite safety because of the unknow composition of the plastic waste and the potential for nanomaterial release during nanocomposite's life cycle. All in all, further research and national regulations and guidance are needed on virgin polymer and plastic waste nanocomposites.

Recycled high-density polyethylene plastic reinforced with ilmenite as a sustainable radiation shielding material

In this work, recycled high-density polyethylene plastic (r-HDPE) reinforced with ilmenite mineral (Ilm) in different ratios (0, 15, 30, and 45 wt%) as a sustainable and flexible radiation shielding material was manufactured using the melt blending method. XRD patterns and FTIR spectra demonstrated that the polymer composite sheets were successfully developed. The morphology and elemental composition were addressed using SEM images and EDX spectra. Moreover, the mechanical characteristics of the prepared sheets were also studied. The gamma-ray attenuation characteristics for established r-HDPE + x% Ilm composite sheets were theoretically computed between 0.015 and 15 MeV using Phy-X/PSD software. Also, the mass attenuation coefficients have been compared to their values by the WinXCOM program. It is also shown that the shielding performance of the r-HDPE + 45% Ilm composite sheet is significantly greater than that of r-HDPE. As a result, the ilmenite-incorporated recycled high-density polyethylene sheets are suited for medical and industrial radiation shielding applications.

Development and Characterization of Polylactic Acid (PLA)-Based Nanocomposites Used for Food Packaging

The present study is focused on polylactic acid (PLA) blending with bio nanoadditives, such as Tonsil^® (clay) and Aerosil^®, to obtain nanocomposites for a new generation of food packaging. The basic composition was enhanced using Sorbitan oleate (E494) and Proviplast as plasticizers, increasing the composite samples' stability and their mechanical strength. Four mixtures were prepared: S1 with Tonsil^®; S2 with Aerosil^®; S3 with Aerosil^® + Proviplast; and S4 with Sabosorb. They were complexly characterized by FT-IR spectroscopy, differential scanning calorimetry, mechanical tests on different temperatures, and absorption of the saline solution. FTIR shows a proper embedding of the filler component into the polymer matrix and DSC presents a good stability at the living body temperature for all prepared samples. Micro and nanostructural aspects were evidenced by SEM and AFM microscopy, revealing that S3 has the most compact and uniform filler distribution and S4 has the most irregular one. Thus, S3 evidenced the best diametral tensile strength and S4 evidenced the weakest values. All samples present the best bending strength at 18 °C and fair values at 4 °C, with the best values being obtained for the S1 sample and the worst for S4. The lack of mechanical strength of the S4 sample is compensated by its best resistance at liquid penetration, while S1 is more affected by the liquid infiltrations. Finally, results show that PLA composites are suitable for biodegradable and disposable food packages, and the desired properties could be achieved by proper adjustment of the filler proportions.

In situ transmission electron microscopy as a toolbox for the emerging science of nanometallurgy

Potential applications of nanomaterials range from electronics to environmental technology, thus a better understanding of their manufacturing and manipulation is of paramount importance. The present study demonstrates a methodology for the use of metallic nanomaterials as reactants to examine nanoalloying in situ within a transmission electron microscope. The method is further utilised as a starting point of a metallurgical toolbox, e.g. to study subsequent alloying of materials by using a nanoscale-sized chemical reactor for nanometallurgy. Cu nanowires and Au nanoparticles are used for alloying with pure Al, which served as the matrix material in the form of electron transparent lamellae. The results showed that both the Au and Cu nanomaterials alloyed when Al was melted in the transmission electron microscope. However, the eutectic reaction was more pronounced in the Al-Cu system, as predicted from the phase diagram. Interestingly, the mixing of the alloying agents occurred independently of the presence of an oxide layer surrounding the nanowires, nanoparticles, or the Al lamellae while performing the experiments. Overall, these results suggest that transmission electron microscope-based in situ melting and alloying is a valuable lab-on-a-chip technique to study the metallurgical processing of nanomaterials for the future development of advanced nanostructured materials.

Developing Post-Consumer Recycled Flexible Polypropylene and Fumed Silica-Based Nanocomposites with Improved Processability and Thermal Stability

Collection and mechanical recycling of post-consumer flexible polypropylene packaging is limited, principally due to polypropylene being very light-weight. Moreover, service life and thermal-mechanical reprocessing degrade PP and change its thermal and rheological properties according to the structure and provenance of recycled PP. This work determined the effect of incorporating two fumed nanosilica (NS) types on processability improvement of post-consumer recycled flexible polypropylene (PCPP) through ATR-FTIR, TGA, DSC, MFI and rheological analysis. Presence of trace polyethylene in the collected PCPP increased the thermal stability of the PP and was significantly maximized by NS addition. The onset decomposition temperature raised around 15 °C when 4 and 2 wt% of a non-treated and organically modified NS were used, respectively. NS acted as a nucleating agent and increased the crystallinity of the polymer, but the crystallization and melting temperatures were not affected. The processability of the nanocomposites was improved, observed as an increase in viscosity, storage and loss moduli with respect to the control PCPP, which were deteriorated due to chain scission during recycling. The highest recovery in viscosity and reduction in MFI were found for the hydrophilic NS due to a greater impact of hydrogen bond interactions between the silanol groups of this NS and the oxidized groups of the PCPP.

Feasibility of Valorization of Post-Consumer Recycled Flexible Polypropylene by Adding Fumed Nanosilica for Its Potential Use in Food Packaging toward Sustainability

The food industry has a current challenge of increasing the recycling of post-consumer plastics to reduce plastic waste towards a circular economy, especially flexible polypropylene, which is highly demanded in food packaging. However, recycling post-consumer plastics is limited because service life and reprocessing degrade their physical-mechanical properties and modify the migration of components from the recycled material to the food. This research evaluated the feasibility of valorization of post-consumer recycled flexible polypropylene (PCPP) by incorporating fumed nanosilica (NS). For this purpose, the effect of concentration and type (hydrophilic and hydrophobic) of NS on the morphological, mechanical, sealing, barrier and overall migration properties of PCPP films was studied. Incorporating NS improved Young's modulus and, more significantly, tensile strength at 0.5 wt% and 1 wt%, where a better particle dispersion was confirmed by EDS-SEM, but it diminished elongation at breakage of the films. Interestingly, NS tended to increase the seal strength of PCPP nanocomposite films more significantly at higher NS content, showing a seal failure of the adhesive peel type which is preferred for flexible packaging. NS at 1 wt% did not affect the water vapor and oxygen permeabilities of the films. Overall migration of PCPP and nanocomposites exceeded the limit value of 10 mg dm^-2 allowed by European legislation at the studied concentrations of 1% and 4 wt%. Nonetheless, NS reduced the overall migration of PCPP from 17.3 to 15 mg dm^-2 in all nanocomposites. In conclusion, PCPP with 1 wt% of hydrophobic NS presented an improved overall performance of the studied packaging properties.

Occurrence, potential release and health risks of heavy metals in popular take-out food containers from China

Global consumption of take-out food increased rapidly and the chemicals in their containers become a potential source of human exposure. However, available information on heavy metals in the containers is extremely limited and the associated health risks remain poorly understood. We investigated Cd, Cr, Pb, Sb, Mn, Ni and Co in the popular take-out food containers from China and found the concentrations of these metals were moderate in comparison to the concentrations reported in other food contact materials. The metal concentrations in sampled containers by material type differed significantly, and higher concentrations of Cd, Pb, Sb, Mn and Co were observed in expanded polystyrene samples. The metals in the containers likely originated from intentional addition and/or contamination of materials. The potential release of the metals from containers was simulated and found the median leaching rates of Cd, Pb, Sb, Ni and Co in the range of 0.36-4.80% under typical conditions, which depended largely on the material types. Based on the observed leaching rates, we estimated that the summed carcinogenic risks of Cd, Pb, Ni and Co were unacceptable under specific exposure frequency, although the total non-carcinogenic risks from metal intake were low.

A review of the plastic value chain from a circular economy perspective

Although plastic is one of the most commonly used materials in our everyday life, the current linear economy ('produce, use and dispose') engenders high risks to human health in relation to greenhouse gas (GHG) emissions and environmental pollution. As a response to these challenges, the circular plastic economy is gaining momentum, where the goal is to reduce, reuse and recycle all plastic. The transition to the circular economy should be made across the entire plastics value chain in order to ensure circular design, production, use and waste management. This study examines the current scientific literature in relation to the entire value chain of plastics. This aim of the article is to provide an overview of the existing research (and highlight research gaps) associated with the transition of plastic use to a circular model. The literature was divided into the following categories: 1) design; 2) production; 3) use; 4) end-of-life; and 5) value chain. A high proportion of the literature was found to address the end-of-life phase, suggesting that the other phases are currently neglected. The results have implications that are applicable to multiple phases; in particular, contamination of waste streams and composite materials places significant limitations on the opportunity to recycle and reuse plastic in new products. This calls for changes in the whole value chain, and for trans-sectorial collaboration to ensure systemic transparency. Therefore, future research should take a holistic approach to the transition to circular through careful mapping of implications, stakeholder involvement and collaboration.

Plastic wastes biodegradation: Mechanisms, challenges and future prospects

The growing accumulation of plastic wastes is one of the main environmental challenges currently faced by modern societies. These wastes are considered a serious global problem because of their effects on all forms of life. There is thus an urgent need to demonstrate effective eco-environmental techniques to overcome the hazardous environmental impacts of traditional disposal paths. However, our current knowledge on the prevailing mechanisms and the efficacy of synthetic plastics' biodegradation still appears limited. Under this scope, our review aims to comprehensively highlight the role of microbes, with special emphasis on algae, on the entire plastic biodegradation process focusing on the depolarization of various synthetic plastic types. Moreover, our review emphasizes on the ability of insects' gut microbial consortium to degrade synthetic plastic wastes. In this view, we discuss the schematic pathway of the biodegradation process of six types of synthetic plastics. These findings may contribute to establishing bio-upcycling processes of plastic wastes towards biosynthesis of valuable metabolic products. Finally, we discuss the challenges and opportunities for microbial valorization of degraded plastic wastes.

Effect of Organic Modifier Types on the Physical-Mechanical Properties and Overall Migration of Post-Consumer Polypropylene/Clay Nanocomposites for Food Packaging

The deterioration of the physical-mechanical properties and loss of the chemical safety of plastics after consumption are topics of concern for food packaging applications. Incorporating nanoclays is an alternative to improve the performance of recycled plastics. However, properties and overall migration from polymer/clay nanocomposites to food require to be evaluated case-by-case. This work aimed to investigate the effect of organic modifier types of clays on the structural, thermal and mechanical properties and the overall migration of nanocomposites based on 50/50 virgin and recycled post-consumer polypropylene blend (VPP/RPP) and organoclays for food packaging applications. The clay with the most hydrophobic organic modifier caused higher thermal stability of the nanocomposites and greater intercalation of polypropylene between clay mineral layers but increased the overall migration to a fatty food simulant. This migration value was higher from the 50/50 VPP/RPP film than from VPP. Nonetheless, clays reduced the migration and even more when the clay had greater hydrophilicity because of lower interactions between the nanocomposite and the fatty simulant. Conversely, nanocomposites and VPP/RPP control films exhibited low migration values in the acid and non-acid food simulants. Regarding tensile parameters, elongation at break values of PP film significantly increased with RPP addition, but the incorporation of organoclays reduced its ductility to values closer to the VPP.

An Overview of Plastic Waste Generation and Management in Food Packaging Industries

Over the years, the world was not paying strict attention to the impact of rapid growth in plastic use. This has led to unprecedented amounts of mixed types of plastic waste entering the environment unmanaged. Packaging plastics account for half of the global total plastic waste. This paper seeks to give an overview of the use, disposal, and regulation of food packaging plastics. Demand for food packaging is on the rise as a result of increasing global demand for food due to population growth. Most of the food packaging are used on-the-go and are single use plastics that are disposed of within a short space of time. The bulk of this plastic waste has found its way into the environment contaminating land, water and the food chain. The food industry is encouraged to reduce, reuse and recycle packaging materials. A wholistic approach to waste management will need to involve all stakeholders working to achieve a circular economy. A robust approach to prevent pollution today rather than handling the waste in the future should be adopted especially in Africa where there is high population growth.

Potential contribution of nanotechnolgy to the circular economy of plastic materials

The problem of plastic accumulation in the environment requires the development of effective strategies to shift the paradigm of used plastics from wastes to resources. In the present contribution, after an overview of the current plastic management strategies, the possible role of nanotechnology to this emerging field is considered. In particular, the challenges related to the use of nano-additives to improve the properties of recycled plastics is discussed based on the fundamental aspects of colloid stabilisation. Finally, the contribution of nanotechnology to the fabrication of effective catalysts for the depolymerisation of plastics into the constituent monomers is outlined.