PTF: Manufacturing

Plastic resin production

The raw material for all packaging plastics is ethylene. Ethylene is a gas derived from natural gas or from a fraction of crude oil that has a composition similar to natural gas. Both natural gas and crude oil are products of fossils and are therefore not renewable.

Producing and refining ethylene uses a lot of energy, requiring combustion to achieve high reaction temperatures and refrigeration to achieve extremely low temperatures to condense and separate gases (reaching about -260 degrees Fahrenheit). Largely because refrigeration is inherently mechanically inefficient, producing ethylene consumes at least 20 megajoules (MJ) per kilogram of ethylene produced. , Twenty MJ would run a 100-watt light bulb for 56 hours. Much of this energy is generated at the production site by burning some of the feedstock of natural gas or crude oil. Therefore, producing plastics for packaging uses nonrenewable resources to heat and refrigerate as well as feedstock. This is a resource use choice, because if the resource were not dedicated to making plastic packaging, it could be either conserved or used for other applications such as generating electricity.

Once ethylene has been produced, it is combined with solvents, co-monomers, additives, and other chemicals that will participate in the planned chemical reactions. The mixture is then subjected to a chemical reaction called “polymerization” that creates long-chain molecules. (“Mono” means “one” and “poly” means “many,” so a “monomer” is a single molecule — like ethylene — that can be bound with other molecules into a “polymer.”) The new polymer is extruded, pelletized, or flaked; the product is called a “resin.” Resin is sold, re-extruded, and made into containers, films, and other products.

Energy use compared – PET plastic vs. virgin and recycled glass

Since resin manufacturing consumes so much energy, making containers with plastic requires almost the same energy input as making containers with glass despite transportation savings that stem from plastic’s light weight. The total energy required to produce, package, and transport a 16 oz. PET container is 32 MJ compared to 34 MJ for a 16 oz. glass container – virtually the same. Producing a pound of plastic resin, however, uses nearly nine times the energy of producing a pound of glass. These comparisons assume the use of virgin glass.

If the glass container uses recycled glass cullet in its feedstock, the energy required to produce it falls to less than 26 MJ for a 16-ounce glass container. That is 6 MJ less than what is needed for a new PET container. Making the glass container with recycled cullet uses only 81% of the energy needed to make a plastic container.

Size of the virgin resin market

In 1995, about 32 million tons of plastic resin were produced in the US; about 39% of this amount, or 12.6 million tons, was used for packaging. Only six resin types were used to make more than 92% of plastic packages. Their names and common uses are shown in the following table:

Table 1: Plastic Packaging; Resin Market Share; Uses

Chemical name Abbr. Resin code 1995 production (million lbs) 1995 (million tons) % of plastic packaging Typical products
polyethylene terephthalate PET 1 3,920 1.96 15.6 soda and
water bottles
high-density

polyethylene
HPDE 2 5,410 2.71 21.5 milk and water jugs, laundry detergent bottles
polyvinyl
chloride
PVC 3 520 .26 2.1 meat wrap
[linear]
low-den-
sity polyethylene
LLDPE/
LDPE
4 7,030 3.52 27.9 grocery and trash bags
polypropylene PP 5 1,610 .81 6.4 rigid
containers
polystyrene PS 6 4,620 2.31 18.3 fast food containers, meat and bakery trays
Total     23,110 11.56 91.7  



A number 7 on a plastic container indicates “other,” which typically means a combination of two or more of the six main resin types.

The use of plastics is increasing in almost all sectors of the economy, but the most rapid growth is in packaging. Globally, improved economic conditions tend to promote increased consumption and a corresponding increase in packaging. Analysts predict steady increases in the sales of most packaging plastics, particularly PET, for the foreseeable future.

The advertisement of recyclability may contribute to increases in plastic packaging sales. Modern Plastics International’s January 1995 resin report explained that double-digit growth rates in PET consumption were due, in part, to “PET’s perceived environmental benefit in regards to recycling.”

New plastic packaging materials also contribute to plastics’ market growth. The compositions of these new materials are varied and tailored to provide performance characteristics for specific applications. Container shapes and sizes are becoming less standard and more numerous. But standardized container compositions and shapes facilitate sorting and reprocessing. Thus, the unlimited use of new materials, mixtures of materials, and a diversity of container shapes work against plastic reprocessing by making it more difficult and more expensive for collectors and processors to match their output to available markets.

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