Info

Total energy Natural gas Petroleum

□ Industry HI Transportation Ej Residential & commercial

H Plastics industry

Figure 1.8. Estimated energy consumption by U.S. plastics industry relative to that by other sectors (based on Franklin, 1990) [29].

relatively small volume of plastic resin used in this application resulted in a strong, exceptionally durable fishing gear that increased the "catchability" by a factor of 2-12 times relative to the conventional natural-fiber gear [31], very significantly increasing the profitability of the industry. In transportation applications, particularly in automobile and aircraft design, the replacement of metal parts by the lighter polymeric materials contributes to energy savings far in excess of the minimal cost of raw materials involved in resin production.

Several case studies illustrate instances where the use of a relatively small amount of a plastic material leads to significant energy savings (as well as emission levels). These findings are based on comprehensive cradle-to-grave-type analysis reported for the relevent materials. Other instances of energy savings using plastics will be discussed in chapters that deal with specific areas of application.

• Case Study The switch over from metal or asbestos cement pipes to lighter plastic pipes in the building industry is estimated to deliver substantial savings in energy (estimated at 330 trillion Btu in the United States). The energy needed to fabricate a vinyl sewer pipe is about a third of that needed to make the same out of cast iron [32].

• Case Study In residential buildings, the use of plastic wrap to reduce air infiltration was recently estimated to save 12-60 million Btu annually (360-1800 million Btu over a 30-year period). Assuming the plastic reduces the infiltration by 50%, energy savings incurred from its use on all new houses in the United States between 1980 and 1997 was estimated to be 9 x 109 billion Btu! Yet, the energy cost of the plastic wrap itself was only 1-2 million Btu! The wraps are manufactured using high-density polyethylene (HDPE) or polypropylene (PP) fibers that weigh only 15-33 lb per typical house [33].

Along with the saving in energy, the environment also benefits from reduced emission of greenhouse gases into the atmosphere. The study estimated the reduction in release of emissions from each house to be 1600-8100 lb of CO2 equivalents per year. This translates into very significant emission reductions when all residential properties in the United States are taken into account. A similar claim might be made for the lightweight vinyl window frames that can effectively replace aluminum window frames. The heat loss through a vinyl frame is smaller than that through an aluminum frame by a factor of about 1000 [34]! Replacing selected conventional building materials with vinyl can result in very significant energy savings.

• Case Study Polyurethane (PU) foam is the most commonly used insulation material in the manufacture of refrigerators and freezers today. Effectiveness of the foam might be compared to that of fiberglass insulation used in the past for the same application. The energy requirement for appliances using polyurethane insulation was estimated to be only 61% of that for the appliances with fiberglass insulation. This translates into 98 million Btu over the life of a single unit (there were 140 million units in the United States alone in 1997). The total greenhouse gas emissions would be reduced by 62-64% when polyurethane was used instead of fiberglass. The energy costs to manufacture the small quantity of polyurethane foam per unit is less than 1% of the energy expended in using the appliance over its entire lifetime. But, the foam delivers disproportionately large savings in the energy cost to run the equipment over its useful lifetime. (The energy for manufacture of the appliance itself was, of course, not included in these estimates [35].)

• Case Study The use of plastics in automobiles leads to indirect but large savings of energy. For example, a small 1% reduction in the weight of the vehicle by replacing metal parts with plastic parts might be assumed to result in a 1% saving in fuel consumption. At a fuel consumption rate of 1 kg per 10 km and 150,000 km of driving over the lifetime of the vehicle, the savings in crude oil consumed was estimated at 180 kg of fuel. This is about 10 times the cost of production of the plastic parts (10 kg for a 1000-kg vehicle) which is about 17 kg of crude oil [36].

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