Raw Sourcing: Glass, Plastic or Aluminum?

August 21, 2008

Barry Sanel
Principal
Barry Sanel Packaging Advisors

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As a former packaging manager of a large beverage company, when it came to beverages I always wondered which was more environmentally friendly. Much like the old “Paper or Plastic” argument at the grocery store, which is better or is anything actually better for the environment?

The Sustainable Packaging Coalition defines four life cycle phases of key importance to determining how earth-friendly a package is: sourcing, manufacture, use and end-of-life.

Raw Sourcing:

Glass (Bottles)
Glass is made up primarily of SiO2 or silicon dioxide. Also known as silica and most commonly found in nature as sand or quartz. Silica is the most abundant mineral in Earth’s crust and the second most abundant element. Silica occurs commonly in nature as sandstone, silica sand or quartzite. It is the starting material for the production of silicate glasses and ceramics. It can exist in an amorphous form (vitreous silica) or in a variety of crystalline forms. Often it will occur as a non-crystalline oxidation product on the surface of silicon or silicon compounds.

The production of glass dates to the Egypt, Mesopotamia & Roman empires (fifteenth century). Modern glass making dates back to the late 19th century; That is, glass made by machine. Simplified: glass is made up primarily of Sand (Silicone Oxide SiO2), Soda Ash, Limestone, Feldspar and minor ingredients: (Fining agents, decolorizers & colorizers) Glass is remarkable for its strength and being chemically inert. These ingredients are mixed together (Also known as fusion casting) in a large furnace that runs at about 2800°F. Typical glass factory diagram.

Aluminum (Cans)
The chief source of aluminum is bauxite ore is mined and refined into aluminum. Bauxite is combined with caustic soda, lime, and steam to produce a sodium aluminate liquor. Impurities are filtered or settled out of the liquor and alumina hydrate is precipitated out of the mixture. The alumina hydrate is calcined to remove moisture and drive off the bonded water.

The resulting alumina is ready for smelting into aluminum. Alumina is electrolytically reduced into molted aluminum. Aluminum’s melting point is approximately 1221°F. This reaction occurs in Hall-Heroult reduction cells (called pots) where the bound oxygen in the alumina reacts with carbon electrodes to form carbon-dioxide gas and aluminum. Each ton of aluminum requires 0.4-.05 tons of carbon anodes. The resulting aluminum is formed into slab ingots that are up to 26 inches thick, 20 feet long, and weigh up to 20 tons each.

The aluminum is then rolled into sheets through the process of forming. The slab is heated in a furnace and rolled between powered rollers until the plate is approximately 1 inch thick. The plates are further reduced in finishing mills where they are hot rolled to a thickness of 0.25 – 0.4 inch. These sheets are rolled into large coils and graded for quality.

Aluminum is too reactive chemically to occur in nature as a free metal. Instead it is found combined in over 270 different minerals. Aluminum is also an abundant metal and the third most abundant after Silicone Oxide and makes up about 8% of the Earth’s solid surface. Refined aluminum is remarkable for its ability to resist corrosion.

Polyethylene terephthalate (PET)
PET is a thermoplastic polymer resin of the polyester family (Wikipedia). The raw materials are petrochemicals: crude oil, natural gas and ethylene glycol. PET is hydroscopic, meaning that it naturally absorbs water and it must have this moisture removed as much as possible before molding or extruding. Once molded, PET has a high resistance to moisture and is very strong.

Crude oil is a naturally occurring flammable liquid found in rock formations consisting on a complex mixture of hydrocarbons plus other organic compounds. Therefore, PET is an organic compound. PET was invented by DuPont chemists in the 40’s during a search to make new textiles. The PET soda bottle was patented in 1973 and a two-piece 2 liter bottle was first used by Coca Cola in 1975.

PET raw materials are either extruded or injection molded and chopped into pellets. PET has a melting point of approximately 480°F. The raw pellets are packed in large pallet sized boxes.

So what wins on raw sourcing? Since glass and aluminum are minerals and must be mined using equipment and refined in furnaces using extremely high temperatures, I have to vote for PET here. Sure, PET is refined directly from petroleum byproducts, however the energy costs used in the formation do not begin to add up to the amount of energy used to keep the mining equipment and furnaces running 24 hours a day, seven days a week. Energy that comes from Petrochemicals.

Barry Sanel is the Principal of Barry Sanel Packaging Advisors.

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Reader Comments

Mr. Sanel’s conclusion prompts a reaction because his examination is so incomplete! Where are the numbers. More importantly, where is recycling? Glass is readily recyclable, but this is not routinely done. (Likewise PET). Aluminum apparently must have a lot of value, as it is widely recycled, both industrially and all the way down to retirees picking up aluminum cans by the road. Consequently, relatively little aluminum ends up as waste. Add to the equation the high transportation costs of glass and you can see that we can rule it out. PET can match aluminum in low transportation cost, but there remains the environmental (disposal) cost of both the PET itself and the labelling applied to it. I have no axe to grind here, but pragmatically, I’d have to say aluminum seems to win easily.

Peter Hubbard | August 25th, 2008

In any discussion about life cycle assessment it is all about the boundaries and Mr. Sanel’s boundaries seem to be very constricted. When the boundaries are expanded to include refilling the container for reuse, glass is the obvious winner. Just because we have moved away from refill and reuse doesn’t mean that glass is a loser. It may be time to reconsider this tried and true method.

John Garn | August 25th, 2008

In addition to Mr. Garn’s comment on LCA – the concept of Functional Unit, a critical concept in determining the environmental burden of any product or delivery system (or packaging in the ase of beverages), is completely missing here… the information presented here is only relvant when we understand how MUCH of the material is required to produce the desired function (such as safely holding 12 ounces of my favorite beverage until I am ready to consume it). A “pound for pound” assessment of various material choices is a classic blunder of LCA neophytes that should be avoided at all costs because it usually takes us in the wrong direction.

Jeff Yorzyk | August 25th, 2008