ТОП просматриваемых книг сайта:
Plastics and the Ocean. Группа авторов
Читать онлайн.Название Plastics and the Ocean
Год выпуска 0
isbn 9781119768418
Автор произведения Группа авторов
Жанр Химия
Издательство John Wiley & Sons Limited
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) for different beverage containers (Ghenai 2012) are shown in Table 1.8. Note however, that these values are based on LCA and therefore, may vary with location, time, and technology used (Figure 1.14).
The limited analysis has several shortcomings, but shows the plastic jug to have the second‐lowest embedded energy as well as carbon emissions. Not captured in Table 1.8 is the water demand, especially in pulping and bleaching of paperboard, as well as the impact of toxic releases from any of the steps. Paperboard enjoys the unique advantage of being based on a renewable feedstock, partly reflected in the value of E1 (it is also biodegradable in the environment). These estimates assume that only virgin materials are used, and if recycling is included, given the high contributions of of E1 and C1 to EE nd EC, these estimates can decrease considerably.
Figure 1.14 Schematic representation of manufacturing a package.
Table 1.8 Energy and carbon footprint associated with packaging milk in various containers. (The percentage of embodied energy and carbon associated with material production phase is shown in parantheses).
| Container | Mass of package (kg) | Volume L | Embedded energy (1010 J) (E1%) | Carbon footprint (kg) (C1%) |
|---|---|---|---|---|
| HDPE jug | 0.051 | 0.946 | 2.95 (82.2) | 1219 (67.7) |
| Aluminum can | 8.1 | 50 | 17.52 (95.9) | 10263 (94.7) |
| Glass bottle | 0.41 | 1 | 5.82 (68.7) | 3820 (62.0) |
| Paperboard carton | 0.057 | 0.942 | 0.65 (84.8) | 278 (73.4) |
Data from Ghenai, 2012
Using packaging with a high environmental cost is justified with food that also has high EE (MJ/kg) and a large carbon footprint (e.g. meats, cheese, coffee, chocolate) as it minimizes waste, and extends shelf life, assuming the consumer will responsibly dispose the packaging waste. If responsible disposal can be assured, plastics would indeed be the ideal packaging material available. A common product that does not conform to the above criteria is bottled water, a popular beverage in the US, with 13.85 Billion gallons sold worldwide in 2018. The environmental cost of the packaging, however, is several orders of magnitude higher than that of the water. The embodied energy of the PET bottle of ~8 MJ/L is enormous by comparison to that of the water of (<0.2 MJ/L) Also, the carbon footprint of the PET bottle is ~42 kg CO2‐e while it is negligible for the water! When transportation, labeling, display, and promotional costs are added, the environmental price tag of bottled water is unacceptably high, especially for water imported from other countries. It is still popular because of its convenience in serving large numbers of people and the misperception that it is more hygienic compared to tap water. An interesting, related comparison is between the environmental merits of paper grocery bags versus plastic bags is pointed out in Box 1.3.
Box 1.3 Paper or Plastic?
A cradle‐to‐grave LCA study in the US (Chet and Yaros 2014) compared the environmental impacts of HDPE bags, biodegradable PE/PLA bags, and Kraft paper bags (with 30% recycled fiber content). The embodied energy for the HDPE bag was 71% lower, and the gobal warming gas (GWG) emissions, 50% lower, compared to the heavier paper bag. Water demand in the manufacture of the HDPE bags was only ~5% of that used to make the paper bags. A 2018 Danish study (DEPA 2018) that included 7 bag types, as well as a 2011 British study (Edwards and Fry 2011), were in general agreement with the conclusions. A plastic bag was the better choice based on these criteria.
The two main problems with HDPE bags, not captured in such studies, are the recalcitrance of plastic bag litter in the environment (not an issue with biodegradable paper bags) and the toxicity of water/air emissions from the manufacture of either type of bag. The acid rain emissions (NOx and SOx) for HDPE bags was ~11% of that associated with paper bags (Chaffee and Yaros 2014). These values are are highly variable, depending on the location of manufacture and consumer littering behavior, and therefore difficult to quantify. The debate on whether the paper or the plastic grocery bags are better for the environment has been in the news for years. With ~5 trillion paper bags used globally each year (or over 150 000 bags a second!) clear guidance to the conscientious consumer will help the environment.
1.7.2 Plastics in Building
As with packaging, only a handful of different plastics are used in building construction; these, along with the percentage of global production used in building, are PVC (69%), HDPE (20%), PUR (29%) and PS (28%). The percentages shown are for that of the global production in 2015