A Comparison of HDPE and PET: A Comparison of HDPE and PET: Life Cycle AnalysisLife Cycle Analysis

By: Kristie Apgar

The CycleThe Cycle

Process behind the production of HDPEProcess behind the production of HDPE

Ethylene is formed during the thermal cracking of crude oil.

Polyethylene is then produced using a metal oxide initiation reaction.

Overview of HDPE FormationOverview of HDPE Formation

HDPE ProcessHDPE Process

Formation of PETFormation of PET

Major ProducersMajor Producers

HDPE – Dow– Equistar– ExxonMobil

PET– Dupont– Hoechst

Types of MoldingTypes of Molding There are several different molding processes, HDPE

(milk jugs) and PET (drink containers) are usually made by:

– Injection molding

– Blow Molding

From Plastic Producer to Consumer: From Plastic Producer to Consumer: Where will it end up?Where will it end up?

A company like Equistar will sell its polyethylene to a small processing company that owns a number of injection molders and proprietary molds.

The molds are provided by a company such as Pepsi and the processing company then produces the final plastic bottle or container which is bought by the producer of the product that will be poured into the bottle.

It is then the consumers decision as to where the HDPE and PET will end up. However, this is not always the case as some smaller communities do not have any recycling centers.

RecyclingRecycling

There are 4 main types of recycling:– Primary

Consists of the preconsumer reuse of a single polymer stream for the purpose for which it was originally intended.

– Secondary Includes the collection, cleaning, and fabrication of useful

items from the post consumer waste stream.

– Tertiary Reconstitution of low molecular weight organic feedstock by

the controlled decomposition of polymeric waste.

– Quaternary Incineration

CollectionCollection

Voluntary Drop-Off Buy-Back Centers Curbside

The curbside is the most expensive to maintain.

Recovery Rates %

10-15

15-20

70-90

Sorting at the MRFSorting at the MRF

Manual Identification– This is done by visual inspection.

Automated Identification– Uses sensors to analyze the physical or

chemical properties of the plastic bottles.

Average Reclaimer Base Resin Yield (%)– PET soda bottles and custom PET bottles 75-85– Natural HDPE bottles (e.g., milk, water) 85-95

ReclamationReclamation

Granulation and air classification– Whole bottles are ground into small particles.– Then labels are separated from the heavier base resin by air classification

techniques.

Washing– May include the addition of detergents to aid the cleaning process.

Separation– Water is employed in a sink/float hydrocyclone system to separate the base

resin from attachments and contaminants based on the different densities of the materials used.

Rising/Drying Melt Filtering

– Passed through an extruder converting plastic regrind to pellets

Different Recycling ProcessesDifferent Recycling Processes Direct extrusion

– Reclaimed PET is remelted and extruded into a marketable form.

– Low cost but cannot remove color or handle impurities.

Glycolysis– The reclaimed PET is recycled by breaking the polymer chain into smaller lengths

which are partially purified, then repolymerized into new polyester resin. It is then extruded into a usable product.

– Can handle a limited amount of many more impurities.

Methanolysis– The PET is fully depolymerized into individual monomers which are purified so

that nothing but pure PET ingredients remain.– Only technology that permits close loop recycling.

PET Recycled ContentPET Recycled Content Important considerations for the use of recycled material in food

packaging include:– Polymer type– Additive levels– Cleanliness

According to the FDA– Recycled PET can be used in food applications when:

The polymer is broken down to the starting monomers. The inner core of post-consumer recycled PET is flanked by layers of virgin PET.

Hoechst was the first company to receive a no objection from the FDA to use recycled material

– Use the methanolysis process to incorporate recycled content in Coca Cola soft drink bottles.

            1996 1997 1998 1999Food & Beverage Bottles

24 41 52 68

Total US Converter Consumption

547 570 707 718

Recylced PET (RPET) mmlbs

Recycled vs. Virgin Polymer MaterialsRecycled vs. Virgin Polymer Materials

The feasibility of recycling a polymeric material depends on the cost and quality of the recycled material to that of virgin material (VM).

If a market is to be found for the recycled material it should be cheaper than the VM due to its lower quality in most cases.

Recent Year End US Dollar Prices Per Pound of Recycled and Virgin Polymer Materials

Polymer Material Year 1991 1992 1993 1994

PET– Recycle 0.48 0.49 0.52 0.52– Virgin 0.66 0.66 0.66 0.76

HDPE– Recycle 0.38 0.34 0.30 0.42– Virgin 0.38 0.36 0.36 0.50

IncinerationIncineration Can be used if is not economical to recycle some of the different

types of plastics.

Municipal solid waste has a high heat combustion and newer incineration plants are designed and operated to produce the least amount of pollution possible.

Some of the equipment employed to reduce pollution includes acid gas scrubbers, filter bags, or electrostatic precipitators.

Solid residue collected afterwards may be hazardous so it must be disposed of properly.

An IncineratorAn Incinerator

LandfillingLandfilling

PET and HDPE do not biodegrade very fast.

In fact landfill linings are now being made out of HDPE.

The cost is usually cheaper to throw plastics into landfills than it is to sort them and sell them. So recycling would not be done without government subsidies.

Landfilling Cont.Landfilling Cont.

Visited the Clinton County Landfill Recycling there is not profitable and is only possible

through state subsidies from the DEP.– They were able to purchase two special pick up trucks that cost

130,000 for only 10% of the cost.– Problems include the cost of running separate collection trucks

to get the plastics and the fact that their low density but higher volume contributes to higher transportation costs.

– Market prices for plastics rise and fall. Interesting note : they deal with a marketing group that

sells their plastics anywhere in the U.S. that they can get the best price.

How does this all relate?How does this all relate?

As can be seen from the energy standpoint, tertiary recycling and incineration are not as favorable as secondary recycling due to the loss of the energy expended in the polymerization process.

Embodied Energy BTU/lbHDPE 42,200PET 45,800

Plastics Energy Landfilling Incineration ReuseReclamation/ Melt

reprocessing single polymer

Thermolysis to

Monomers

Energy Produced 0 18,000 37,200 30,200 18,200HDPE Energy Required to

Replace what was lost 42,200 24,200 5,000 12,000 24,000Embodied Energy 42,200 42,200 42,200 42,200 42,200

Energy Produced 0 18,000 40,800 33,800 21,800PET Energy Required to

Replace what was lost 45,800 27,800 5,000 12,000 24,000Embodied Energy 45,800 45,800 45,800 45,800 45,800

EconomicsEconomics

Increased demand for recycled polymer streams will raise their value.

However, virgin materials are currently inexpensive.

Landfill costs are going up in places where they are running out of space.

The real driver toward recycling may be the increase in fuel prices and the increased value in the polymer feedstock, recycled or virgin.

Comparison of HDPE and PETComparison of HDPE and PET

Millions of Pounds of Recycled Plastic

1997 1998

Total PET Bottles 649 710Total HDPE Bottles 704 734

Recycling Rate of PETRecycling Rate of PET

Total U.S.

RPET

Bottles on U.S. Shelves

Gross Recycling

(MM lbs.) (MM lbs.) Rate1995 775 1,950 39.7%1996 697 2,198 31.7%1997 691 2,551 27.1%1998 745 3,006 24.8%1999 771 3,250 23.7%

Year

Actual Products Made of Actual Products Made of Recycled MaterialsRecycled Materials

HDPE– Lumber– Traffic cones and barriers– Pipe– Trash cans

PET– Drink Bottles– Fiber fill for pillows– Insulation for ski jackets– Sleeping bags– Carpeting

SummarySummary

Many questions remain as to what the best approach is in dealing with the temporary throw away containers made of HDPE and PET.

Landfilling is bad however only 9% of MSW is made up of plastics.

Regulations can be made and subsidies given by the government to encourage recycling.

New Biodegradable polymers can be developed.

HDPE and PET are success stories because of their consumer identification and the fact that they are easier to sort than other plastics.