Caps and Plugs: How do HDPE and PP compare?

Caps and plugs can be used in a variety of applications, but how do you go about selecting the right material for your project? How does polypropylene (PP) fare – and is High-Density Polyethylene (HDPE) more efficient? To help you decide, we outline the characteristics of each. In this article we cover:

What’s the difference between HDPE and PP?
Why use HDPE for Caps and Plugs?
Why use PP for Caps and Plugs?
How to Select the Right Caps and Plugs
HDPE Caps and Plugs
Polypropylene Caps and Plugs
HDPE Vs Polypropylene: In Summary

With a wide variety of applications, including automotive components, packaging and even textiles, PP is a thermoplastic polymer manufactured from a monomer known as propylene.

Meanwhile, HDPE can be more rigid that PP, owing to its lower density. Let’s take a look at both materials’ characteristics:

Property	PP	HDPE
Tensile Strength	>0.95 - 1.30 N/mm²	0.20 - 0.40 N/mm²
Thermal Coefficient of expansion	3.0 – 30.0 Kj/m²	no break Kj/m²
Max Cont Use Temp	80˚C / 176˚F	65˚C / 149˚F
Density/p>	0.905g/cm3	0.944 - 0.965 g/cm3

 

Resistance to chemicals	LDPE	HDPE
Dilute Acid	Very good	Excellent
Dilute Alkalis	Very good	Excellent
Oil and Greases	Moderate (Variable)	Moderate (Variable)
Aliphatic Hydrocarbons	Poor	Poor
Aromatic Hydrocarbons	Poor	Poor
Halogenated Hydrocarbons	Poor	>Poor
Alcohols	Very good	Excellent

What’s the difference between HDPE and PP?

If you’re wondering if there are any distinct differences between HDPE and PP, you’d be right to wonder. The answer is ‘yes’, with a host of differences in terms of density, temperature and UV and chemical resistance.

Density is a key factor that differentiates HDPE from PP. Because HDPE has a lower density, it can be more rigid. Thanks to its lower density, though, PP, can be used when moulding parts with lower weight.

Like HDPE, Polypropylene offers good chemical resistance. UV resistance, though, is poor; if it is stabilised with additives, it can be improved. Resistant to a wealth of solvents, HDPE and PP have a wide variety of applications.

Why use HDPE for Caps and Plugs?

HDPE makes for excellent push fit caps and plugs. Offering smooth and simple assembly, they can protect critical internal and external profiles from damage and there are a wealth of types available. These include tapered, pull tab, flexible, quick-fit, and tube caps and plugs. Alongside HDPE, they can also be manufactured from LDPE, PE, PVC, Silicone, TPR or EVA.

Why use PP for Caps and Plugs?

A relatively inexpensive material, Polypropylene is a good choice when it comes to caps and plugs. It’s versatile, doesn’t suffer damage from the sun or elements in the same way as other plastics, and can withstand high temperatures.

On top of that, it does not absorb water like other plastics, making it ideal for outdoor use. It’s unlikely to shatter, too, though it is not as sturdy as, say, polyethylene. Ensuring your project – and its parts – remain functional and safe, caps and plugs may need to withstand certain chemicals.

In electrical projects specifically, Polypropylene is ideal. The reason for this is because it has a low level of electrical conductivity, meaning it can perform smoothly in electronic products and applications.

How to Select the Right Caps and Plugs

Before choosing the right caps and plugs for your particular project, there are several things you should consider. These include your environment, the application itself, the material, the production process and the removal process.

In the case of your environment, ask yourself the following questions

• Is there need for UV resistance?
• Are corrosive substances present?
• What about the atmosphere; are there high levels of moisture or humidity?
• Is there a need to conduct or dissipate electricity?
• Are there Pounds per Square inch (PSI) considerations?
• Does your application need to operate in cold or hot conditions?

You must also understand your application – and what it requires in order to perform correctly. There are a wealth of caps and plugs available, from O-rings to threaded plugs, with each offering different features.

By identifying the right material for your caps and plugs, you’ll be setting up your project for further success. Consider heat – and the heat tolerance of your chosen material. It’s also advisable to think about the environment your caps and plugs will be used in.

HDPE Caps and Plugs

So, where do you begin with HDPE caps and plugs; which is best for your project? Below, we lay out a few examples and some details on how they might be utilised in your application.

Plug or Cap Type	Plug or Cap Characteristics
UNF/Metric Threaded Sealing Caps	Limiting fluid leakage on UNF threads, the UNF or metric threaded sealing cap has a height of 452 in (11.5 mm) and reduces the potential of shearing
NPT Threaded Square-headed Plugs	The NPT Threaded Square-headed Plug has an easy-grip head for efficient removal and application. It’s also used to protect NPT threads against moisture and contaminants.
Metric Threaded O-Ring Plugs	Equipped with an O-ring to protect M8 x 1 Metric Threads from leakage, the Yellow Threaded O-Ring Plug can be applied or removed by spanner, screwdriver or socket. It can even be removed by hand, if needed.
Overfill Prevention Device Cylinder Valve Plugs	Compatible with Propane gas to protect valve threads during use and transport, Overfill Prevention Device Cylinder Valve Plugs are easy to apply via a flat strap attachment device.
UNJ/UNJS Threaded Plugs	With an easy to grip had for efficient removal and application, the UNJ/UNJS Threaded Plug protects components from dust, moisture and damage during the production, storage or shipment process.
UNF Standard Threaded Plugs	A threaded plug with a serrated grip, UNF Standard Threaded Plugs can be used in a variety of applications and can be removed by hand, hex wrench or screwdriver.

Polypropylene Caps and Plugs

Looking for Polypropylene caps and plugs? Take a look at some of the options available to you – and their characteristics:

Plug or Cap Type	Plug or Cap Characteristics
Fluid Absorption Plugs	Providing an attractive finish with a fitting height of 15.0mm, Fluid Absorption Plugs can control excess fluid residue from leaking. Easy installation is possible, too, thanks to its unique design, and the plugs are safer, cleaner and easier to use than their conventional counterparts.
UNF Standard Threaded Plugs (O-Ring optional)	Enjoy efficient application and removal with the UNF Standard Threaded Plug (O-ring optional). They can be applied or removed by hand, or with a hex wrench or screwdriver and an optional O-ring gives this component a water-tight seal.
NS & NF Class 1-2-3 Threaded Plugs (O-Ring Optional)	With an optional O-ring, which gives this component a water-tight seal, NS & NF Class 1-2-3 Threaded Plugs have an easy to grip head for efficient application and removal, and will fit NS and NF Class 1-2-3 standard threads.
Flange Protectors	Protecting a DN10 inch pipe size with a 10, 16, 25, 40 Class Pressure Rating flange, these Flange Protectors provide simple, cost-effective protection for flanges. Covering a variety of DIN sizes and pressure ratings, the outside diameter of the component is manufactured from Corrugated PP Material.

HDPE Vs Polypropylene: In Summary

Ready to choose your preferred caps and plugs? There are lots to think about, with safety, efficiency and cost amongst the key factors. Light and flexible, HDPE offers quick installation, excellent resistance and a long lifespan.

HDPE products aren’t known to transmit any chemicals, either, which deems them safe for use in everything from food packaging to automotive components.

Polypropylene, meanwhile, can withstand higher temperatures, making it ideal for hotter environments. Possessing high flexural strength, due to its semi-crystalline nature, it’s a relatively inexpensive material and can be used in a variety of applications.

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.

Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.

Questions?

Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.