Plastics and the Ocean. Группа авторов

Figure 1.13 Left: Illustration of the molecular geometry of LDPE and HDPE. Middle; LDPE sandwich bag. Right: HDPE milk jug. (Images: Courtesy of Alana Andrady)

1.7 Societal Benefits of Plastics

Behind the dramatic success of plastics as a material is the unique combination of properties that makes them particularly versatile and suitable for a broad range of applications. Plastics offer a combination of engineered functionality with a high degree of design freedom, delivered at a price that is competitive with alternative materials. To understand the consistently increasing demand for plastics worldwide, it is useful to briefly survey the main benefits of the material in several of their key application areas. Figure 1.2 that compares the mix of plastics produced worldwide annually (2015 data from Geyer et al. 2017 recalculated to exclude additives as they are not polymers) to their application areas, is a convenient starting point for the discussion. The advantages of PE and PP that account for about half the global resin in popular applications are especially impressive. Table 1.7 lists the common application areas for thermoplastics with typical uses.

Table 1.7 Applications of common types of plastics.

      Source: Rudolph et al. (2017).

      Abbreviations: ABS – Acrylonitrile‐butadiene‐styrene copolymer; PC – polycarbonate: PMMA (poly(methyl methacrylate); POM – poly(oxymethylene); and XPS – expanded extruded polystyrene.

      1.7.1 Packaging Food and Beverage

      Packaging, the leading application of plastics has a global market size exceeding US$240B. Over half the plastic packaging is used in the food and beverage sector. Industrial packaging and non‐food consumer packaging, each account for less than half of that volume. About 56% of plastic packaging is PE, with PP (22%), PET (10%), while some PS is also used (Mackenzie 2019).

      Packaging addresses a key problem of the Anthropocene, the unprecedented wastage of food in the supply chain as well as by consumers. Globally, an estimated 1/3 of food intended for human consumption invariably ends up as waste (Gustavsson et al. 2011); food wastage in the US is even higher, by at least a third, compared to that in other countries. Along with food, all the resources, including fossil fuel invested in their production, are also wasted and it is critical to minimize this waste. An industry study in the US recently found significantly less food wastage with packaged, compared to unpackaged, food (Ameripen 2018). Plastics packaging achieves this reduction primarily by extending the shelf life of food throughout the supply chain and by managing portion sizes. The weight fraction of packaging needed for this purpose is relatively low, compared to that of food or beverage. This is also true both in terms of the monetary, and the environmental cost of the package, compared to that of the food. Life cycle analysis (LCA) comparing different packaging materials for beverage, highlight the minimal environmental impacts of plastic packaging relative to that of the food it protects (Ghenai 2012; Sivenius et al. 2011; Vignali et al. 2016).

      Spoilage of produce and meats is controlled by reducing the oxygen they are in contact with, to dramatically increase their shelf life. One way to achieve this is by vacuum packaging food with flexible plastic films having high barrier properties. Vacuum sealing extends the shelf life of refrigerated vegetables three‐ to four‐fold and frozen meats from weeks, to months, or even years. Fresh meats in refrigerated displays, for instance, typically retain their desirable color only for three to seven days. Modified atmosphere packaging (MAP) used to pack the meat in an atmosphere of high oxygen (70–80%) with 20–30% CO₂ gas, extend its shelf life up to two weeks. The oxygen‐rich environment in the package retains the red color of meat, the criterion used by consumers in judging its freshness, for a longer duration. Transparent skin packaging of cured meat products, is in fact, only possible with plastic barrier films. Vegetable and fruit packaging with MAP helps reduce the use of preservatives in produce. Other approaches such as gas flushing, scavenging/desiccant sachets, or on‐package valves are all used extensively with plastic packaging to modify the atmosphere inside the package.

The use of any packaging incurs an environmental cost and often creates a post‐use solid waste issue as well. In Figure 1.14, E₁ is the embodied energy of the material made from feedstock such as aluminum from ore, or PET from fossil fuel, and E₂ is the processing energy expended to form the material into the package. Energy expenses E₃ onwards are the increments of energy expended in display at store, transporting, cooling prior to use by consumer, cooking, and its post‐use disposal. Quantities C₁, C₂, and C₃ (onwards) are the corresponding emissions associated with each step, that include the carbon footprint, the water footprint, and the solid waste generated. The scheme allows a simple comparison of the footprint of different packages such as glass or plastic, provided detailed, reliable, inventories for each step are available. Reported data for (E₁ + E₂) and (C₁)

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