Plastics and the Ocean. Группа авторов
Читать онлайн книгу.
also used in building, but to a lesser extent of only about 6% of their respective production volumes.
The most‐used resin type in building construction is PVC, both as (i) rigid unplasticized compounds, uPVC, in cladding (siding), window frames, water pipes/fittings, pipes, and rainwater goods; and (ii) plasticized, flexible compounds, pPVC, in laminates as membrane roofing, flooring tiles, and cable sheaths. PVC pipes are widely used in water transport because of their low cost and convenience in installation using quick connections compared to competing water pipes. Some chlorinaed PVC (or CPVC) is also used, especially in hot‐water applications, because of its relatively higher softening temperature compared to PVC. Plastic window or door profiles, also made of uPVC, are widely used because of their ease of installation and relatively low lifetime costs. Flooring made of PVC in laminate or engineered flooring, the most‐used flooring in the US, is also popular in Asia, Australia and some parts of Europe (Pickard and Sharp 2020). HDPE, competes with PVC as a material for pipe applications but has a relatively shorter service life, but is the plastic of choice in constructing storage tanks for water.
Table 1.9 gives a comparison of the environmental characteristics of several different pipe materials for the distribution of potable water. The savings in embodied energy (EE) on using lower‐density, lower melting, non‐corrosive, and easy‐to‐assemble PVC, in place of conventional ductile iron, concrete, or clay pipes is easy to appreciate (Uni‐Bell 2017).
Another important application is the use of plastic foam insulation in building and refrigeration, that exploits their low density as well as their very low thermal conductivity. The closed cells in polyurethane foam contain inert gases that are very good thermal insulators. Until recently, the inert gas used as a blowing agent for PU foam was Freon (especially, trichlorofluoromethane), but after these were identified as ozone‐depleting chemicals, pentanes were substituted in their place. The thermal conductivity of PU foam depends on the cell size and generally varies between 0.02 and 0.03 W/m K, at atmospheric pressure. PU foam is used in applications such as refrigeration and cold storage as well as in insulation.
Table 1.9 Embodied energy and carbon data for 8‐inch diameter water pipes.
Source: Calculated from Du et al. (2013).
| Iron‐concrete lined (DICL) | PVC | Concrete (reinforced) | Cast Iron | HDPE | |
|---|---|---|---|---|---|
| Embodied Energy (MJ/100‐ft) × 103 | 33.94 | 19.18 | 9.53 | 25.5 | 23.79 |
| Embodied Carbon (MTCO2‐e/100 ft) | 14.4 | 9.69 | 2.08 | 10.76 | 218 |
| Weight (Lbs/ft) | 22 | 5.619 | 60 | 34 | 6.65 |
| Expected pipe burst (50 years) | 1 | 1 | 18 | 3 |
1.7.3 Plastics in Transportation
The advantage of plastics in construction, that combines strength that can exceed those of metal, but at a much lower density (mass per unit volume), is best illustrated by their applications in transportation. Airplane design, where weight and strength are particularly critical, presently uses increasing amounts plastic composites in place of aluminum. An exceptional example is the Boeing 787 Dreamliner aircraft that is 50% by weight (and 80% by volume) made of plastics or composites. Not only is the molded modular construction faster and less tedious to assemble compared to aluminum structures, but the finished lighter aircraft incurs 20% fuel savings in operation as well as significantly lower carbon emissions during its manufacture. With close to 1000 of these in the air at the time writing and another 500 on order, the energy savings achieved in the aviation industry by the use of plastics are considerable. Other models of aircraft also use increasing amounts of composites in their design.
The same is true of watercraft, a prime example being the Visby class submarine of the Swedish Navy, that uses composites for hull manufacture. The weight advantage of using plastic composites in the vessel is close to 50%, with the added strategic advantage of lower radar, magnetic, and acoustic signatures, compared to traditional metal designs (Rubino et al. 2020). Automobiles where light‐weight is critical to ensure fuel savings, also use increasing amounts of plastics. Most of the plastic components in automobiles in the North American market in 2017 were made of PP, PU nylon, and PVC (32%, 17%, 10%, and 6%). In addition to the fuel efficiency that comes with a reduced weight of the automobile, plastics also contribute to corrosion resistance and design flexibility, allowing appealing and safe innovations at a reasonably low cost compared to traditional materials.
1.7.4 Plastics in Textile Fibers
A significant tonnage of plastic resin is used to spin textile fibers (73.5 MMT in 2019) but three plastics dominate the application. In 2020, of the total textile fiber market (including natural fiber) was >52% polyester, 5% Nylon, and 6% rayon fiber (Textile Exchange 2020). Unlike in the early days of the industry, the recent trend of fast‐changing fashions, results in a very short service life, often less than a season, for comfort fabric. Clothing today provides physiological as well as psychological well‐being to the consumer and needs to be easily laundered. Post‐consumer clothing can in theory be recycled, but, only about 15% of all textile is globally recycled at present despite the benefits of the strategy in terms of savings in embodied energy and reduced externalities. Recycling textiles, however, introduces a serious complication. The process generates microfibers from mechanical fragmentation, that are difficult to contain and are released to the environment with waste water.
1.7.5 Plastics in the Energy Industry
Wind turbines generate about 11% of the energy used in the US (especially electricity) and 10–15% of that in Europe. It is the fastest‐growing renewable energy source at this time, but they have significant infrastructure costs. Blades of windmill installations span 100–150 ft and have to be made of a lightweight material such as wood. Polymer composites fit the requirement ideally, and glass fiber, carbon fiber, aramid, and basalt fibers are used to reinforce either thermoplastics or thermoset polymers in the design of windmill blades (Mishnaevsky et al. 2017). Plastic blades can be conveniently molded into the complex aerodynamic geometries and are now beginning to be even recycled.
Plastics also play a significant role in the design of photovoltaic (PV) panels for production of solar energy. The active layer is encapsulated in plastic, sealing it from moisture and oxygen. Other parts of the module such as the back sheet, adhesive, and the protective film over glass, are made of plastics in modern PV modules. Another application of plastics in the energy industry is their use as a transparent exposure chambers for suspensions of microalgae in vertical algae farms employed in biodiesel production. To get high yields of oil, it is important to have a monoculture of selected oil‐rich algae, by growing them in media enclosed in thin plastic tubes or bags and exposed to solar radiation. With hundreds of closely spaced transparent algae bags exposed outdoors, plastic (rather than glass) is best suited for the application.
References