1. A Comparison of HDPE and PET: Life Cycle Analysis
By: Kristie Apgar

2. The Cycle

3. Process 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.

4. Overview of HDPE Formation

5. HDPE Process

6. Formation of PET

7. Major Producers
HDPE
Dow
Equistar
ExxonMobil
PET
Dupont
Hoechst

8. Types of Molding
There are several different molding processes, HDPE (milk jugs) and PET (drink containers) are usually made by:
Injection molding
Blow Molding

9. From Plastic Producer to Consumer: 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.

10. Recycling There are 4 main types of recycling: Primary Secondary
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

11. Collection Voluntary Drop-Off Buy-Back Centers Curbside
The curbside is the most expensive to maintain.
Recovery Rates %
10-15
15-20
70-90

12. Sorting at the MRF Manual Identification Automated 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
Natural HDPE bottles (e.g., milk, water) 85-95

13. Reclamation Granulation and air classification Washing Separation
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

14. Different 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.

15. PET 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.

16. Recycled 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
PET
Recycle
Virgin
HDPE
Recycle
Virgin

17. Incineration
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.

18. An Incinerator

19. Landfilling 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.

20. 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.

21. 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.

22. Economics
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.

23. Comparison of HDPE and PET
Millions of Pounds of Recycled Plastic
Total PET Bottles
Total HDPE Bottles

24. Recycling Rate of PET

25. Actual Products Made of Recycled Materials
HDPE
Lumber
Traffic cones and barriers
Pipe
Trash cans
PET
Drink Bottles
Fiber fill for pillows
Insulation for ski jackets
Sleeping bags
Carpeting

26. Summary
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.