Material Properties and Applications of Fluoropolymer Hoses

Fluoropolymers are renowned for their wide-spectrum chemical resistance, useful physical properties, and excellent thermal properties - although they often come at relatively higher costs. They are applied in various industries utilizing corrosive chemicals, such as semiconductors, spray painting, and the chemical industry. Here at Langchi, we strive to provide our customers with top-grade fluoropolymer hoses and support you in selecting the best option. We provide fluoropolymer hoses made with materials like FEP, PFA, PTFE, PVDF, and ETFE, while further developing and designing the hoses to extend their already-great resistance based on working environment requirements to suit your application.

Introduction

In general, fluoropolymers can be separated into two classes: perfluorinated fluoropolymers, and partially fluorinated fluoropolymers. Partially fluorinated fluoropolymers introduce hydrogen atoms into their chemical structures, making them physically harder, more resistant against UV radiation, less chemically inert, and less thermally stable. Among the fluoropolymers that see frequent uses, PTFE, PFA, FEP, PVDF, and ETFE, PTFE, PFA, and FEP are perfluorinated, while the other two are partially fluorinated.

When PTFE was first developed, it was celebrated for its almost-universal chemical resistance. However, processing PTFE for industrial usage was hard: it cannot undergo melt-processing. Printing logos or labels, or welding hoses together to form a multi-row hose are difficult tasks for PTFE parts even as of today. Further engineering was demanded.

FEP was among the first solutions to this problem, sacrificing the working temperature ceiling (from PTFE's 260℃ to 200℃) for improved processability. It has better mechanical properties than PTFE, and is much easier to process.

PFA preserves the high working temperature ceiling of PTFE by introducing a side chain in its chemical structure. In practice, PFA's chemical, heat, and abrasion resistances are slightly worse than PTFE's.

PVDF sacrifices the working temperature ceiling (175℃) and some chemical resistance (sensitive to strong acids/oxidants under high temperature, relatively poor performances against esters and ketones) for great mechanical durability, having great tensile strength, tensile modulus, elongation at break, impact strength, flexibility, etc. More notable is its piezoelectricity and pyroelectricity properties (capability to convert pressure/heat into electric signals), granting usage in various fields.

ETFE has an even lower working temperature ceiling (150℃), but it also has a lower working temperature floor (-60℃), and is highly transparent. Its chemical resistance is also better than PVDF.

Chemical Resistance

Fluoropolymers are celebrated for their excellent chemical resistance against most common chemicals in industrial processes.

Among them, PTFE is known for having the best chemical resistance - it is inert to almost all chemicals under a standard working temperature and pressure, making it the go-to choice for transferring highly corrosive chemicals in various industries.

PFA and FEP are known for having similar chemical resistance under a default working environment. However, if the working environment is more extreme (under high temperature and pressure), PFA would outperform FEP.

ETFE is also known for resisting most chemicals in industrial production, but this material is weak against highly-corrosive solvents, oxidizers, chlorinated solvents, ketones, and esters.

PVDF also has great resistance against industrial chemicals, and is known for maintaining this resistance under elevated temperatures and pressures. It is weak against concentrated sulfuric acid and medium-concentration alkaline solutions. Some polar solvents (like ketones and esters) are known to make PVDF swell or dissolve.

Other Resistances

• Water absorption: 

Water moisture in the working environment can be absorbed by nearby plastic parts and cause undesired shape changes, water-soluble ion leakage, and changes in mechanical properties. While some effects are reversible, the damage to the plastic parts will be significant after extended use.

Fluoropolymers are known for their very low water absorption rates, typically at a magnitude of 10^-2~10^-3 percent weight. Among them, PTFE is known for having the lowest water absorption rate.

• Flame retardant: 

Flame retardancy refers to the ability to stop the spread of fire. Thanks to their chemical structures, all fluoropolymers have excellent flame retardancy. When exposed to flame, they self-extinguish quickly once removed from the flame. PTFE/PFA/FEP materials are rated UL94 V-0, as well as PVDF/ETFE. It should be noted that PVDF and ETFE slightly under-perform in this area.

• UV radiation: 

This factor is generally considered when the need for outdoor operation arises. Under default workplace assumptions, PTFE is not recommended for prolonged outdoor service, while PFA, FEP, and ETFE are preferred in this area. PVDF is also acceptable.

• Cold flow: 

Cold flow, or creep, refers to deformation under long-term stress. The effect of cold flow becomes more severe as the ambient temperature and the pressure rise. Generally, the more fluorinated materials are more susceptible to the effect of cold flow, meaning that PTFE is very susceptible to this effect. However, slight modifications are enough to lessen its effect. Still, it is not advised to use fluoropolymer hoses at pressures above the suggested values.

Working Temperature

Another celebrated trait of the fluoropolymers is their great working temperature range. In a default environment, all fluoropolymers can work as intended under temperatures well above boiling and well below freezing. Below is the working temperature chart for Langchi fluoropolymer hoses:  

As shown in the chart, PTFE and PFA perform better under high temperatures, while ETFE and PVDF perform better under low temperatures.

Physical Properties

• Elasticity: 

In complex working environments with limited available space, users might install hoses bent. Therefore, the ability to withstand bending without deformation is valuable. Below is our size 3/8'' (OD 3/8'', ID 1/4'', or OD 9.53mm, ID 6.33mm) fluoropolymer hoses' minimum bend radii at 20 Celsius, which measures this ability.  

As shown in the chart, fluoropolymers have fine elasticity, and PTFE performs slightly better in this area. Under no additional engineering, PTFE is softer than nylon plastics. Normally, an increase in fluorine content would decrease the hardness.

• Friction: 

All fluoropolymers have low coefficients of friction. This property means fluids transferred within fluoropolymer hoses will not lose much velocity due to friction. In general, more fluorine content within the fluoropolymer means lower friction.

• Electrical: 

Generally, fluoropolymers have high electrical resistance (ETFE in particular may have a lower resistance). This grants them excellent resistance against electrical arcs and static electricity that may be generated in workplaces.

Applications

Fluoropolymer hoses see applications in various industrial branches thanks to their top-grade qualities. 

Throughout our years of service, we served many clients requesting fluoropolymer hoses. Their specific applications include:

 - Used as spray gun cores

 - Used in various industries (for example, semiconductors, chemical, energy) to transfer corrosive fluids

Material Identification

In their non-engineered forms, PFA, FEP, and ETFE are transparent, while PTFE and PVDF are opaque. We at Langchi offer color customization options for our products, but we cannot provide you with opaque PFA/FEP/ETFE or transparent PTFE/PVDF at the moment.

Fluoropolymer materials do have different flexiblities and densities. However, these attributes offer little assistance in differentiating them. While different fluoropolymers have different flexibilities, identifying them by hand would still be a task reserved only for the experienced. Density on the other end cannot be used to differentiate between PFA and FEP, the differentiation of which is typically the focal point.

When identifying a fluoropolymer hose sample’s material, we assume that its optical property is not engineered. After visual inspections, we would heat a portion of the sample up. The materials with the same optical properties have different working temperature ceilings: while PFA, FEP, and ETFE are all transparent, PFA can withstand a temperature of 260℃, while FEP's ceiling is 200℃, and ETFE's is 150℃; on the other hand, while PTFE and PVDF are both opaque, PVDF's working temperature ceiling is only 175℃, while PTFE can withstand 260℃.

We should point out that heating up fluoropolymer is highly dangerous, since this process might produce highly acidic and toxic chemicals. We do not endorse burning fluoropolymers in an uncontrolled or unprotected setting. 

Selection

Selecting which type of fluoropolymer to use heavily depends on how demanding the working conditions and the working medium are. For less demanding requirements, it is possible to choose alternatives.

PTFE normally covers all workplace conditions and working medium requirements, since it offers the most wide-spectrum chemical resistance. However, it is also the most prone to the effect of cold flow, meaning the recommended working pressure would be comparatively lower. PTFE is also hard to process, meaning parts with too many modifications cannot be made with PTFE.

FEP and PFA's chemical resistance can match that of PTFE, and are often used as substitutes. PFA is also less prone to the effect of cold flow, making it serviceable under high temperatures and constant stress. Generally speaking, FEP offers enough resistance to cover less-demanding industrial usages at a cheaper price. However, PFA over-performs FEP under extreme working conditions in terms of chemical resistance.

ETFE and PVDF typically serve in less demanding working conditions. They are good substitutes for each other, but their maximum working temperature differs. ETFE offers better chemical resistance, while PVDF offers better physical resistance.

Usage

While fluoropolymers are strong materials, fluoropolymer hoses should still be used with caution.

• Before Installation:

Ensure that the fluid transferred is compatible with the hose’s resistance capabilities.

Ensure that the working pressure and temperature follow our recommendations.

While fluoropolymers offer some electric resistance, static electricity should still be of concern if the fluid transferred is sensitive. Use anti-static products if necessary.

• Installation:

Ensure that the installation ends do not leak and the connections are secure - working situations requesting fluoropolymers often involve highly corrosive chemicals that must not leak.

Ensure that the hoses are not overly bent.

• During use:

Be mindful of prolonged UV radiation - select the correct material before usage, or provide cover.

Be mindful of the cold flow effect - allow rest, select alternative material, or select designs with enhanced strength.

• After use:

Clean thoroughly - while fluoropolymers themselves are chemically inert, the fluids they transfer might react with each other if the hoses are not cleaned properly.

Examine regularly, and dispose of any damaged/worn/aged/deformed hoses.

• Disposal:

Common disposal methods of fluoropolymers include recycling and landfilling. Incinerating fluoropolymers will generate harmful acidic products.

Potential Failures

Like all materials, fluoropolymers can fail under uncertain working environments for various reasons. Typically, fluoropolymer failures can be due to physical, mechanical, or chemical reasons.

Physical fails occur when a part of the hose is permeated or diffused by the fluid transferred. Such fails often cause swellings, formations of blisters, or localized polymerizations, and would cause local expansions.

Mechanical fails occur when the hose is exposed to a force (tensile, compression, or vacuum-generated stresses) that exceeds its capability, eventually causing breaks or fractures.

Chemical fails occur when the hose is exposed to chemicals that can attack them. This will result in degradations in mechanical performances, and potentially introductions of impurities into the fluids transferred.

The most widely-used non-intrusive method to detect fails is through visual inspections, also known as “looking at the parts directly” - fluoropolymers are inert to most inferences, so observing them through common tools like inferred is hard. There are other methods available to find fault non-intrusively, such as spark testing (scanning a voltage through the part to seek any differences along the part - technically this method will damage the part if done repeatedly).

In general, design flaws, incorrect material choices, production flaws, or misuses can cause failures.

Langchi's Offers

Here at Langchi, we offer our customers top-grade fluoropolymer hoses. Aside from the standard virgin straight hoses, we also offer spiral hoses using the materials listed above. We assure you that this shape change not only preserves the hoses' performance, but also enhances spatial efficiency.

We also offer a modified PFA hose to provide additional static electricity resistance.

We provide after-sales support, and provide free replacements for production issues. Please contact us if you have any problems during use.

We are established in 2012 in Cixi, Zhejiang, China. We currently own our factory building with a land area of 8000 square meters, housing 28 extrusion lines, a 500 square meter cleanroom, and a lab. We specialize in R&D, manufacturing, national and international sales, and services of thermoplastic tubes with round or special shapes, with materials including PU, PA, PE, PVC, PP, POM, EVA, TPV, TPEE, and various others, aside from fluoropolymers. We serve mid-to-high-end enterprise clients, providing pipeline solutions to various workplaces, offering “one-stop” quality services. Our products see applications in equipment for electronics, electrical, automation, semiconductors, automotive, photovoltaics, energy storage, firefighting, food, medical, and other industries.