Difference Between UHMW and HDPE

Key Difference – UHMW vs HDPE

 

UHMW and HDPE are thermoplastic polymers that have a similar appearance. The key difference between UHMW and HDPE is that UHMW contains long polymer chains with very high molecular weights whereas HDPE has a high strength-to-density ratio.

UHMW stands for Ultra High Molecular Weight polyethylene. It is also denoted by UHMWPE. The term HDPE stands for High Density Polyethylene.

CONTENTS

1. Overview and Key Difference
2. What is UHMW 
3. What is HDPE
4. Similarities Between UHMW and HDPE
5. Side by Side Comparison – UHMW vs HDPE in Tabular Form
6. Summary

What is UHMW?

UHMW is ultra-high molecular weight polyethylene. It is a type of thermoplastic polymer. This polymer compound contains extremely long polymer chains having high molecular weights (around 5-9 million amu). Therefore, UHMW has the highest molecular density. However, the appearance of this compound is indistinguishable from that of HDPE.

Properties of UHMW

Important properties of UHMW are as follows.

• It is a tough material.
• Has a high impact strength
• Odorless and tasteless
• High sliding ability
• Crack resistance
• It is highly non-adhesive
• The compound is non-toxic, and is safe.
• It does not absorb water.

All polymer chains in UHMW are very long, and they align in the same direction. Each polymer chain is bonded with other surrounding polymer chains via Van der Waal forces. This makes the whole structure very tough.

UHMW is produced from the polymerization of the monomer,  the ethylene. The polymerization of ethylene forms the base polyethylene product. The structure of UHMW is very different from that of HDPE due to the production method. UHMW is produced in the presence of metallocene catalyst (HDPE is produced in the presence of Ziegler-Natta catalyst).

Applications of UHMW

• Production of star wheels
• Screws
• Rollers
• Gears
• Sliding plates

What is HDPE?

HDPE is high density polyethylene. It is a thermoplastic polymer material. This material has a high density when compared to other forms of polyethylene. The density of HDPE is given as 0.95 g/cm3. Since the degree of polymer chain branching in this material is very low, the polymer chains are packed tightly.  This makes HDPE relatively hard and provides high impact resistance. HDPE can be handled under temperatures around 120°C without any harmful effect. This makes HDPE autoclavable.

Properties of HDPE

Important properties of HDPE include,

• Relatively Hard
• High  impact resistant
• Autoclavable
• Opaque or translucent appearance
• High strength-to-density ratio
• Light weight
• No or less absorption of liquids
• Chemical resistance

HDPE is one of the plastic materials that is easiest to be recycled. These properties determine the applications of HDPE.

Applications of HDPE

Some important applications include followings.

• Used as containers for many liquid compounds such as milk and to store chemicals such as alcohols.
• To produce plastic shopping bags
• Trays
• Pipe fittings
• HDPE is also used for cutting boards

What are the Similarities Between UHMW and HDPE?

• UHMW and HDPE are made of ethylene monomers.
• Both are thermoplastic polymers.
• Both have an indistinguishable appearance.

What is the Difference Between UHMW and HDPE?

UHMW vs HDPE

UHMW is ultra-high molecular weight polyethylene. HDPE is high density polyethylene.  

Structure

UHMW has very long polymer chains. HDPE has short polymer chains compared to UHMW.

Molecular Weight of Polymer Chains

The polymer chains of UHMW have very high molecular weights. The polymer chains of HDPE have low molecular weights compared to UHMW.  Production UHMW is produced in the presence of metallocene catalyst. HDPE is produced in the presence of Ziegler-Natta catalyst.

Water Absorption

UHMW does not absorb water (zero absorption). HDPE may absorb water slightly.

Summary – UHMW vs HDPE

Both UHMW and HDPE are made of ethylene monomers via polymerization. The key difference between UHMW and HDPE is that UHMW contains long polymer chains with very high molecular weights whereas HDPE has a high strength-to-density ratio.

Reference:

1. “Ultra-High-Molecular-Weight Polyethylene.” Wikipedia, Wikimedia Foundation, 27 Mar. 2018, Available here.
2. Thomas, G.P. “Recycling of High-Density Polyethylene (HDPE or PEHD).” AZoCleantech.com, 24 July 2017, Available here.
3. Vanderveer Industrial Plastics. “HDPE vs. UHMW Machining.” Vanderveer Industrial Plastics, Available here.

Image Courtesy:

1. “Stainless steel and ultra high molecular weight polythene hip replacement (9672239334)” By Science Museum London / Science and Society Picture Library – Uploaded by Mrjohncummings (CC BY-SA 2.0) via Commons Wikimedia
2. “Symbol Resin Code 2 HDPE” By Bhutajata – Own work (CC0) via Commons Wikimedia