4 Advice to Choose a UHMWPE Lined Tubing

Ultra High Molecular Weight Polyethylene (UHMWPE) is increasingly becoming notable across various industries with the need for materials that possess qualities like high strength, durability and chemical resistance. Compared to traditional plastics, this polymer showcases outstanding properties like abrasion resistance, low friction coefficient and impact resistance. 

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As demand grows for lightweight materials that are reliable in manufacturing, UHMWPE rises as a sustainable and cost-effective alternative to metals or wood. In , statistical research stated that UHMWPE market cap was valued at USD 998.2 million and is estimated to grow up to USD .4 million by the year .

For engineers, understanding the properties and use cases of this polymer is essential. In this article, we will explore everything you need to know about UHMWPE. Read on to learn more!

UHMWPE morphological structure (Image Source: Researchgate)

Key Properties of UHMWPE

UHMWPE’s key properties are extreme toughness and durability, low friction, excellent abrasion resistance, chemical and moisture resistance, and biocompatibility. These attributes jointly position this material as the top choice across different industries. 

From heavy-duty industrial and engineering applications to life-saving medical interventions, where reliability, longevity, and performance are paramount, UHMWPE caters for all. Let’s have a detailed look at its properties!

1. Extreme Toughness and Durability

UHMWPE’s resilience in difficult industrial situations is really remarkable as its molecular structure forms a hardened bond that resists distortion even under extreme force. This inherent toughness is characterized by its long chain of ethylene monomers which translates to an impeccable impact resistance, a quality that is withstanding even at temperatures below zero degrees.

Whether enduring harsh impacts or navigating frigid climates, UHMWPE ensures reliability and longevity in the most demanding conditions.

2. Low Friction and Excellent Abrasion Resistance

A standout feature of UHMWPE is its low coefficient of friction, making it an ideal choice for applications requiring smooth, sliding surfaces thus minimizing the need for lubrication, thereby cutting down on maintenance costs and enhancing operational efficiency. 

Industries ranging from manufacturing to food processing benefit from UHMWPE’s low friction characteristics, which improve performance and extend the lifespan of critical industrial machinery.

3. Chemical and Moisture Resistance

UHMWPE’s resistance to chemicals makes it invulnerable to the corrosive natures of various substances. This makes it the preferred for deployment in hostile environments. 

Its ability to absorb low moisture further enhances its effectiveness in damp or wet conditions better than traditional materials. Industries that operate in humid and semi-humid areas tend to rely on UHMWPE to deliver seamless durability and reliability ensuring increased lifespan of the industry equipment.

4. Biocompatibility and Medical Use

UHMWPE has been a game-changer in the medical field due to its biocompatibility nature and wear resistance. Its inert state and compatibility with body tissues makes it a vital material for joint replacements and prosthetics. 

Patients benefit from its ability to seamlessly integrate into the body while enduring the asperity in day-to-day activities. With an aging population and a projection in demand for joint replacements, UHMWPE plays a pivotal role in improving the quality of life for countless individuals.

Industrial and Commercial Applications

UHMWPE, with its impressive array of properties, has a vast application paradigm in industrial and commercial sectors, offering solutions to a variety of challenges.

Marine Industry

UHMWPE forms the part of the backbone that enhances safety and durability in the marine industry. Dock fender pads and pile guards, typically exposed to harsh conditions and constant impact from vessels, benefit from UHMWPE’s outstanding rigidness and abrasion resistance.

These components endure relentless forces without giving in to wear and tear, ensuring prolonged service life and reduced maintenance costs. Moreover, anti-skid walkways made from UHMWPE provide secure footing for personnel, minimizing the risk of slips and falls in maritime environments.

Material Handling 

Material handling operations depend on UHMWPE for its ability to curb wear and noise while improving efficiency. Chute liners, hopper linings, and truck bed liners crafted from UHMWPE offer robust protection against abrasive materials and heavy loads. 

By reducing friction and dampening noise levels, UHMWPE liners enhance material flow and contribute to a noise reduced environment. Various industries ranging from mining, construction to agriculture benefit from these durable and low-maintenance solutions.

UHMWPE cord (Image Source: Amazon)

Food Processing 

UHMWPE comes up as a preferred material for different components in food processing industries where hygiene and corrosion resistance are crucial. Its smooth surface is easy to clean and disinfect thus making it ideal for food contact surfaces such as conveyor belts, cutting boards and processing equipment. 

Additionally, UHMWPE’s  resistance to corrosion and chemical exposure ensures compliance with food safety regulations. Whether in meat processing plants, breweries, or dairy facilities, UHMWPE components contribute to the production of safe and high-quality food products.

Sports and Leisure

Sports and leisure industries utilize the impact resistance of UHMWPE to enhance safety and performance in various applications. Protective gear such as helmets, pads, and body armor infuse UHMWPE fibers to absorb and minimize impact forces. This reduces the risk of injuries like blunt force traumas during sports and recreational activities. 

UHMWPE’s abilities discussed earlier like durability and low friction allow for smooth gliding and swift maneuvers on various surfaces when used on components such as ski bases, snowboard bottoms and skateboard decks.

Manufacturing Processes and Fabrication

The manufacturing and processing techniques employed for Ultrahigh Molecular Weight Polyethylene (UHMWPE) play an important role in shaping its properties and determining its suitability for various applications. We are going to look at the different stages of UHMWPE production and key processing methods utilized.

1. Polymerization of UHMWPE

The first step in UHMWPE manufacturing is the polymerization process. UHMWPE is produced through a process called Ziegler-Natta polymerization.

Using a catalyst system, ethylene monomers are polymerized resulting in formation of long polymer chains with ultrahigh molecular weight. Controlling the molecular weight distribution of the polymers is essential to warrant the desired properties of UHMWPE. 

2. Melt Processing Techniques

The melting processing techniques are used commonly to shape and mold UHMWPE into desired forms. These techniques majorly involve heating the UHMWPE resin to a molten state then using different molding methods to transform it into a desired shape.

3. Ram Extrusion

Ram extrusion is a popular processing method for UHMWPE that is used to force the molten UHMWPE through a die using a ram or piston. This method allows for the production of continuous profiles, such as rods, tubes, and sheets, with precise dimensions and excellent surface finish. 

4. Compression Molding

In this step, the molten UHMWPE is placed into a mold cavity then pressure is exerted to shape into the required form. The compression molding technique is suitable for products that will have a varying thickness in post-production.

Advanced Grades and Modifications

Ultra-high-molecular-weight polyethylene is available in various grades tailored for specific user needs. These grades include:

• Natural Virgin: It is the most basic cost-effective option since it’s tough, resistant to wear, collisions, and chemicals, making it suitable for many use cases.
• Reprocessed: This grade is more budget-friendly and  best used for less demanding jobs compared to the virgin grade.
• Anti-Static: It is a UHMWPE designed to prevent static buildup especially in places where static build could be a potential cause for problems, like around flammable materials.
• Tivar: This grade is optimized for the protection of machinery parts like chain guides and rollers. It’s also excellent at reducing wear and tear.
• Tivar HOT: It is formulated to maintain its strengths and properties even at high temperatures, making it useful in hot environments.
• Tivar 88: This is a premium grade mainly used for lining equipment in bulk material handling. It offers high-level protection and longevity.
• Tivar DrySlide: This grade combines anti-static properties with self-lubrication, reducing friction and wear.
• IPX : It is an advanced polyethylene with better benefits than standard UHMWPE. It’s engineered for superior performance in demanding applications.

Each of these grades has its own strengths, allowing for a wide range of applications across industries while being cost-effective and user-friendly.

Sustainability Aspect of UHMWPE

Environmental effects may result from the disposal of UHMWPE which are frequently dumped in landfills or burned. Because of its molecular structure, it is difficult to recycle overused materials. 

Potent greenhouse gasses like Methane can be produced when they are dumped in landfills thus affecting the quality of water and soil. Burning of UHMWPE may also produce ash that must be dumped in landfills and tend to emit greenhouse gasses that pollute the atmosphere. 

On the other hand, the processes used to produce Ultra-high molecular weight polyethylene i.e removal of raw materials, production of the polymer and creation of the final product, use energy and materials that produce emissions and trash.

UHMWPE is produced using ethylene, a hydrocarbon that can be found in crude oil or Natural Gas and thus doesn’t require a lot of resources to produce. However, the processing and extraction of these raw materials may have adverse effects on the environment, including water use and pollution risk.

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Currently there are few possibilities for the responsible disposal of UHMWPE. Nonetheless, setting up strategies to recycle this polymer can help in reducing its negative effects on the environment.

Recycling can assist in conserving resources and lower the need for raw materials but it can also be challenging to recycle due to its molecular makeup. And even so, there are currently few methods of recycling.

UHMWPE hose pipe (mage Source: Chemical Support)

Conclusion

UHMWPE is definitely a cutting-edge innovation in the world of polymers, offering a unique combination of resilience, strength and low friction setting it apart from other plastics with an array of benefits.

These benefits include but are not limited to: improved efficiency, cost-reduction, performance enhancement of countless products and processes. Whether you are an engineer seeking reliable materials or simply curious about plastics, UHMWPE deserves your attention. 

New discoveries and technological advances are made gradually in the field of material science and as such we cannot help but wonder what the future holds in the innovation and creative uses involving UHMWPE plastics. This guide serves as a foundation to appreciate the potential of the polymer therefore encouraging you to further explore its benefits and applications.

There are many factors to consider when choosing the right tubing for your research. From fit and material to kink resiliency and air permeability, it’s important to understand the pros and cons of materials, sizes, and the intended application.

Choose the best tubing for your application based on seven key factors:

1. Fit - How well do the tubing dimensions match the rest of your system?
2. Material - Do the physical properties of the material make sense for your use?
3. Kink Resistance - Will the tubing need to make tight turns?
4. Compound Compatibility - How compatible is the tube material with the fluid that will be flowing through it?
5. Air Permeability - How important is it that air not permeate through the tube?
6. Suitability for Implantation - If the tube will be implanted, how suitable is it for use inside the body (animal research only)?
7. Cost - Will it fit your budget?

1. Fit

Tubing’s purpose is really quite simple: transport fluid (or gas) from point A to point B. How the tubing connects to point A and point B is important. In the human medical world, tubing connections are standardized with luers fittings and other connectors that are bonded onto the tube. These fittings make reliable connections, but they also add dead volume and cost which can make them impractical in research.

For many years Intramedic™ polyethylene (PE) tubing from the Clay Adams division of Becton Dickinson was the standard for small diameter laboratory tubing. It came in a range of sizes with a somewhat random set of inner and outer diameters. In fact, Instech’s first fluid swivel, model 375/22, had 22ga connections to fit PE-50, the most popular of the Intramedic sizes. (Actually 23ga fits PE-50 better, but PE tubing has a problem that it takes a set over time and so the founder of Instech chose 22ga for a tighter fit.) And for that reason, today 22ga is the standard for Instech’s rat system connections. 25ga is the standard for mouse systems.

While it varies with material and tubing size, in general, for an ideal friction fit the flexible tubing should have an inner diameter (ID) of 0.002-.004in (0.05-0.10mm) smaller than the outer diameter (OD) of the metal coupler onto which it will be placed. The outer diameter of stainless hypodermic tubing is almost always right on spec, but extruded tubing will vary by +/- 0.002in (0.05mm) or more due to the nature of the manufacturing process. So if you have a tube with a nominal ID very close to the OD of the connector, you can be fairly sure at some point it will disconnect or leak. Download this guide which contains a printable Guide to Tubing Fit.

2. Tubing Material

Tubing material is just as important as the dimensions for a good connection. Here is how they stack up:

Silicone is soft and stretchy, so you can have a small inner diameter stretch over a relatively large connector which is sometimes useful if you are trying to minimize dead volume. Silicone tubing does not take a set; i.e., it will come back to its original size when pulled off the connector. However, silicone is slippery and will easily pull off connectors, so it is a poor material for friction-fit connections.

Dow Corning Silastic® brand medical-grade silicone is commonly used for research tubing; beware of industrial-grade silicone which can have impurities.

Polyethylene is stiff and will not stretch far over connectors, but at first it will make a good connection. Over time, however, PE will take a set (permanently stretch out), weakening the connection. PE is not good for friction fit connections.

Polyurethane stretches well and grabs. If you try to pull a PU tube that has a good fit over a connector it will stretch down like a Chinese finger trap and grab even more; so much so that the tube might break or the connector might pull out of the device before it will disconnect. PU is a good material for friction fit connections, and the only material we recommend for subcutaneous connections.

In some cases, it is wise or necessary to take additional steps to prevent disconnection. Options include:

Bonding. Special light-cure glues can bond some tubing to the stainless steel connectors. Some glues are medical grade and can be safely implanted. PU can be bonded, but silicone and PE cannot. Instech has co-extruded PE/PVC tubing that can be bonded because the glue binds to the PVC layer. Downsides: you can’t disconnect and replace the tubing at the end of the experiment; if you are bonding a subcutaneous connection, such as a catheter to a Vascular Access Button™, your surgical procedure may need to be modified.

Sleeve. Placing a segment of thick-walled stretchy tubing, usually silicone, over the joint is a relatively simple solution that can reinforce the connection, though it is not as foolproof as bonding. A sleeve can also help prevent kinking at the connector. It can be used for external or subcutaneous connections.

Suture. If you are connecting a catheter to a connector during surgery and are already suturing the vessel, it can be a simple step to throw a loop around the connection. The only downside is the time to do it.

3. Kink Resistance

Just like your garden hose, research tubing can kink if it makes too sharp a bend. How likely it is to kink depends on the tubing wall thickness and material. Temperature is also a factor – tubing can suddenly kink as it warms up and the material relaxes, for example when body-temperature blood flows through it.

A kink can be disastrous. In a drug infusion study a kink will stop flow completely; the catheter can clot in the meantime and you have the danger of a large bolus of fluid when the kink is released. If your pump does not have an occlusion alarm, high pressures can build up and cause a leak at the weakest point in the line.

PE-50 (polyethylene) is the most commonly used tubing in research, but unfortunately its stiffness and the relatively thin wall size makes it the most likely to kink. Once it has kinked, it is much more likely to kink again in the same place. Using PE tubing with a co-extruded layer of PVC around it practically eliminates the chance that it will kink.

Silicone is relatively resistant to kinking. Its issue is that it is so soft that if it is bent over a connector it can puncture and will leak.

Polyurethane is relatively resistant to kinking except when the tubing walls are thin. We recommend thick-walled PU tubing for external segments where tight friction-fit connections are critical. We use it inside the springs of our rodent tethers which experience a lot of pulls and movement.

A kink in an implanted catheter may be even more dangerous because it can’t be seen. It will act just like a blockage. It is a surgeon’s responsibility to know the nature of his or her catheter tubing and make sure the bends are not too tight.

4. Compound Compatibility

Chemical compatibility. Certain chemical compounds or vehicles can react with the tubing material. Other compounds can stick to tubing and release later. If you are unsure, test your compound through an isolated tubing segment before starting your experiment.

• Silicone is non-reactive but is porous and some compounds, such as oils, can permeate into it.
• Polyethylene is generally considered the most inert tubing material.
• Polyurethane is occasionally incompatible with certain compounds or chemicals; because PU makes reliable connections and is good for implantation, substitute materials often involve sacrifices.

Light sensitivity. Most tubing is translucent, which is a problem when compounds are sensitive to light. You can cover syringes with aluminum foil and surround tubing with black shrink tubing, or use PE tubing that is coextruded with a surrounding layer of black PVC for this purpose.

5. Air Permeability

If fluid is static in a tube that is permeable to air, as is often the case with the exteriorized portion of a catheter, the fluid will evaporate through the tube. In the case of an exteriorized catheter this evaporation pulls blood into the tip, which can clot and lead to a blockage.

Silicone is the most permeable tubing material.

Polyethlyene and PE/PVC tubing have very low air permeability, but are not ideal for implantation.

Polyurethane is moderately permeable to air, and this can be an issue when the tubing walls are thin as is often the case with implanted catheters. Instech’s Vascular Access Buttons™ solve this issue because no part of the catheter is exteriorized. When PU is needed for external connections, use tubing with relatively thick walls, not catheter tubing.

See the results from this study we did on air permeability in tubing

6. Suitability for Implantation

If you are choosing tubing for an implanted small animal catheter several additional considerations come into play.

Size. First, a catheter must be the appropriate size for the vessel into which it will be placed. If it is too large it will be difficult to insert, which can lead to extra time and trauma during surgery; too small and flow can be restricted. The outer diameter of a flexible catheter is measured using the French scale, where 3Fr=1mm. Most rat catheters are 3Fr; mouse jugular vein catheters are often 2Fr, whereas catheters for mouse carotid arteries and femoral veins are usually 1Fr. Intrathecal catheters are typically even smaller – 0.8Fr.

Material. Next, the material must be biocompatible and stiff enough to advance to the appropriate location in the vessel but not so stiff that it causes trauma. Polyurethane is generally considered the best material for catheters due to its biocompatibility and moderate stiffness. PE is still often used for short-term catheterizations because of its ubiquity in the lab, but it is too stiff for long-term implantation.

Tip. Sharp edges of tubing can damage the vessel wall and lead to an occlusion. Beveled tips may be easy to insert but can puncture straight through a vessel, particularly if the tube is made of a stiff material like PE. Rounded tips are generally considered the best for long-term patency, but they add cost to the catheter as they are time consuming to make and require special catheter-tipping machines. 

Sterility. Finally, per animal welfare regulations, any tubing implanted into a laboratory animal in a survival surgery must be sterile. Silicone is the only tubing material that can be autoclaved; the others should be sterilized with ethylene oxide gas. If your facility does not have a gas sterilizer, purchase either pre-sterilized polyurethane tubing segments or finished sterile catheters. 

7. Cost

Tubing cost can vary from less than $3 / meter for standard PE tubing to more than $20 / m for the very small diameter sizes. For the standard sizes, however, the cost differences are not so great that price should outweigh any of the other factors discussed here.

Price per meter (Bulk tubing offered by Instech, price list)

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