Thermoplastic Polyurethane Elastomer (TPU) for Wire and Cable Jackets: Properties, Applications, and Future Trends
Contents
- Introduction
- Chemical Structure and Synthesis
- Key Properties of TPU for Wire & Cable Jackets
3.1. Mechanical Properties
3.2. Thermal Properties
3.3. Chemical Resistance
3.4. Electrical Properties
3.5. Weather Resistance
3.6. Flame Retardancy
3.7. Processing Properties - TPU Grades and Formulations for Wire & Cable Applications
4.1. Classification by Hardness
4.2. Classification by Ether/Ester Based
4.3. Specific Additives and Their Effects - Applications in Wire and Cable Industries
5.1. Power Cables
5.2. Control Cables
5.3. Data Cables
5.4. Automotive Wires
5.5. Robotic Cables
5.6. Specialty Cables - Processing Techniques for TPU Wire & Cable Jackets
6.1. Extrusion
6.2. Injection Molding
6.3. Co-extrusion - Advantages and Disadvantages Compared to Other Jacket Materials
7.1. Comparison with PVC
7.2. Comparison with Polyethylene (PE)
7.3. Comparison with Cross-linked Polyethylene (XLPE)
7.4. Comparison with TPEs (other than TPU) - Quality Control and Testing Standards
8.1. International Standards
8.2. Industry-Specific Standards - Environmental Considerations and Sustainability
9.1. Recyclability
9.2. Bio-based TPU
9.3. Regulations and Compliance - Future Trends and Development
- Conclusion
- References
1. Introduction
Thermoplastic Polyurethane Elastomer (TPU) is a versatile class of thermoplastic elastomers possessing a unique combination of properties, including high elasticity, abrasion resistance, chemical resistance, and flexibility. These attributes make TPU an increasingly popular choice for wire and cable jacket applications, offering superior performance compared to traditional materials like PVC and polyethylene in demanding environments. This article aims to provide a comprehensive overview of TPU as a wire and cable jacketing material, covering its chemical structure, key properties, various grades and formulations, processing techniques, advantages, disadvantages, quality control, environmental considerations, and future trends. The information presented is intended to serve as a valuable resource for engineers, material scientists, and industry professionals involved in the wire and cable industry.
2. Chemical Structure and Synthesis
TPU is a block copolymer composed of alternating soft and hard segments. The soft segments are typically derived from polyols, such as polyester polyols, polyether polyols, or polycarbonate polyols. The hard segments are formed by the reaction of diisocyanates with chain extenders, usually low-molecular-weight diols. The specific chemical structure of these segments determines the final properties of the TPU.
The synthesis of TPU generally involves a one-shot or a prepolymer method. In the one-shot method, all reactants (polyol, diisocyanate, and chain extender) are mixed simultaneously. In the prepolymer method, the polyol and diisocyanate are reacted first to form a prepolymer with isocyanate end groups. The prepolymer is then reacted with the chain extender to form the TPU. The ratio of soft and hard segments, the type of polyol, diisocyanate, and chain extender, and the reaction conditions significantly impact the mechanical, thermal, and chemical properties of the resulting TPU.
3. Key Properties of TPU for Wire & Cable Jackets
The suitability of TPU for wire and cable jacketing stems from its exceptional combination of properties.
3.1. Mechanical Properties
TPU exhibits excellent mechanical properties, including high tensile strength, elongation at break, tear strength, and abrasion resistance. These properties are critical for withstanding the stresses and strains encountered during cable installation, operation, and service life.
| Property | Typical Value | Unit | Test Method |
|---|---|---|---|
| Tensile Strength | 20-50 | MPa | ASTM D412 |
| Elongation at Break | 200-700 | % | ASTM D412 |
| Tear Strength | 30-150 | kN/m | ASTM D624 |
| Abrasion Resistance (Taber Abraser) | 10-50 | mg/1000 cycles | ASTM D4060 |
| Hardness | 60A-75D | Shore A/D | ASTM D2240 |
3.2. Thermal Properties
TPU possesses good thermal stability and can withstand a wide range of operating temperatures. Its glass transition temperature (Tg) is typically low, providing flexibility even at low temperatures. Furthermore, certain TPU grades exhibit excellent resistance to heat aging.
| Property | Typical Value | Unit | Test Method |
|---|---|---|---|
| Glass Transition Temperature (Tg) | -50 to -20 | °C | DSC |
| Heat Aging Resistance (150°C, 7 days) | Retains >80% properties | % Retention | UL 1581 |
3.3. Chemical Resistance
TPU exhibits excellent resistance to a wide range of chemicals, including oils, greases, fuels, solvents, and acids. This resistance is crucial in harsh industrial environments where cables are exposed to various chemicals. Ester-based TPUs generally have poorer hydrolysis resistance compared to Ether-based TPUs.
| Chemical | Resistance Level |
|---|---|
| Mineral Oil | Excellent |
| Gasoline | Good |
| Acids (dilute) | Good |
| Bases (dilute) | Good |
| Solvents | Fair to Good |
| Water | Variable (Ether based is better) |
3.4. Electrical Properties
TPU offers good electrical insulation properties, including high dielectric strength and volume resistivity. These properties ensure the safe and reliable transmission of electrical signals through the cable.
| Property | Typical Value | Unit | Test Method |
|---|---|---|---|
| Dielectric Strength | 20-40 | kV/mm | ASTM D149 |
| Volume Resistivity | 1012-1014 | Ohm-cm | ASTM D257 |
3.5. Weather Resistance
TPU exhibits good resistance to UV radiation, ozone, and weathering. However, prolonged exposure to UV radiation can cause degradation, leading to discoloration and loss of mechanical properties. UV stabilizers are often added to TPU formulations to enhance their weather resistance.
3.6. Flame Retardancy
While TPU is inherently combustible, flame retardant additives can be incorporated to improve its flame retardancy. Various flame retardant systems, including halogenated and halogen-free options, are available to meet specific flammability requirements. Achieving desired flame retardancy often involves a trade-off with other properties, such as flexibility and processability.
3.7. Processing Properties
TPU is a thermoplastic material, meaning it can be repeatedly softened by heating and solidified by cooling. This allows for easy processing using various techniques, such as extrusion and injection molding, making it suitable for manufacturing wire and cable jackets.
4. TPU Grades and Formulations for Wire & Cable Applications
TPU is available in a wide range of grades and formulations tailored to specific wire and cable applications.
4.1. Classification by Hardness
TPU hardness is typically measured using the Shore durometer scale (Shore A and Shore D). Softer TPU grades (Shore A) are more flexible and are suitable for applications requiring high flexibility, while harder grades (Shore D) offer higher strength and abrasion resistance. Wire and cable jackets typically use TPUs in the range of 80A to 65D.
| Hardness Range | Typical Applications |
|---|---|
| 80A-90A | Highly flexible cables, robotic cables |
| 90A-95A | General-purpose cables, control cables |
| 50D-65D | Power cables, abrasion-resistant applications |
4.2. Classification by Ether/Ester Based
The type of polyol used in the TPU synthesis significantly affects its properties. Ether-based TPUs offer superior hydrolysis resistance and low-temperature flexibility, making them suitable for wet environments and cold weather applications. Ester-based TPUs, on the other hand, generally exhibit higher tensile strength and abrasion resistance but have poorer hydrolysis resistance.
| Polyol Type | Advantages | Disadvantages | Typical Applications |
|---|---|---|---|
| Ether-based | Excellent hydrolysis resistance, low-temp flex | Lower tensile strength compared to ester-based | Submersible cables, marine cables, cold-weather cables |
| Ester-based | High tensile strength, abrasion resistance | Poor hydrolysis resistance | General-purpose cables, automotive cables, power cables |
4.3. Specific Additives and Their Effects
Various additives are commonly incorporated into TPU formulations to enhance specific properties. These additives include:
- UV Stabilizers: Improve weather resistance and prevent degradation caused by UV radiation.
- Antioxidants: Protect the TPU from thermal degradation during processing and service life.
- Flame Retardants: Enhance flame retardancy and meet specific flammability requirements. Halogenated and halogen-free options exist.
- Plasticizers: Increase flexibility and improve low-temperature performance.
- Processing Aids: Improve processing characteristics, such as melt flow and mold release.
- Colorants: Provide desired color and aesthetic appeal.
5. Applications in Wire and Cable Industries
TPU is used in a wide range of wire and cable applications due to its versatility and performance.
5.1. Power Cables
TPU is used as a jacketing material for power cables requiring high abrasion resistance, chemical resistance, and flexibility. Examples include industrial power cables and portable power cables.
5.2. Control Cables
TPU is ideal for control cables used in automation and robotics due to its excellent flexural fatigue resistance and chemical resistance.
5.3. Data Cables
TPU is used in data cables requiring high flexibility and signal integrity, such as Ethernet cables and communication cables.
5.4. Automotive Wires
TPU’s resistance to oil, fuel, and abrasion makes it a suitable material for automotive wiring harnesses. Its flexibility is also important in tight spaces.
5.5. Robotic Cables
Robotic cables require exceptional flexibility and resistance to repeated bending and twisting. TPU’s excellent flexural fatigue resistance makes it an ideal choice for these demanding applications.
5.6. Specialty Cables
TPU is used in specialty cables requiring specific properties, such as submersible cables, marine cables, and welding cables. The versatility of TPU allows for customization to meet specific application requirements.
6. Processing Techniques for TPU Wire & Cable Jackets
TPU can be processed using various techniques, including extrusion, injection molding, and co-extrusion.
6.1. Extrusion
Extrusion is the most common method for applying TPU jacketing to wires and cables. The TPU is melted and forced through a die to form a continuous coating around the conductor. Precise control of temperature, pressure, and screw speed is crucial to ensure a uniform and defect-free jacket.
6.2. Injection Molding
Injection molding is used to produce complex cable connectors and other molded components. The molten TPU is injected into a mold cavity, where it cools and solidifies into the desired shape.
6.3. Co-extrusion
Co-extrusion involves extruding two or more different materials simultaneously to form a multi-layered jacket. This technique can be used to combine the desirable properties of different materials, such as a TPU outer layer for abrasion resistance and a different polymer for specific electrical properties.
7. Advantages and Disadvantages Compared to Other Jacket Materials
TPU offers several advantages over traditional wire and cable jacketing materials, but it also has some limitations.
7.1. Comparison with PVC
| Feature | TPU | PVC |
|---|---|---|
| Abrasion Resistance | Excellent | Fair |
| Flexibility | Excellent | Fair to Good (plasticizer dependent) |
| Chemical Resistance | Good to Excellent | Good |
| Temperature Range | Wide (-40°C to +125°C) | Limited (-20°C to +105°C) |
| Flame Retardancy | Requires additives | Inherently flame retardant (with Cl) |
| Environmental | Recyclable, potentially bio-based | Concerns about plasticizers and chlorine |
| Cost | Higher | Lower |
7.2. Comparison with Polyethylene (PE)
| Feature | TPU | PE |
|---|---|---|
| Abrasion Resistance | Excellent | Poor |
| Flexibility | Excellent | Good (LDPE) to Fair (HDPE) |
| Chemical Resistance | Good to Excellent | Excellent |
| Temperature Range | Wide (-40°C to +125°C) | Limited (-40°C to +85°C) |
| Flame Retardancy | Requires additives | Requires additives |
| Environmental | Recyclable, potentially bio-based | Recyclable |
| Cost | Higher | Lower |
7.3. Comparison with Cross-linked Polyethylene (XLPE)
| Feature | TPU | XLPE |
|---|---|---|
| Abrasion Resistance | Excellent | Fair |
| Flexibility | Excellent | Poor |
| Chemical Resistance | Good to Excellent | Excellent |
| Temperature Range | Wide (-40°C to +125°C) | Wide (-40°C to +150°C) |
| Flame Retardancy | Requires additives | Requires additives |
| Environmental | Recyclable, potentially bio-based | Not easily recyclable |
| Cost | Higher | Moderate |
7.4. Comparison with TPEs (other than TPU)
| Feature | TPU | Other TPEs (e.g., TPE-E, TPE-S) |
|---|---|---|
| Abrasion Resistance | Excellent | Variable, typically lower than TPU |
| Flexibility | Excellent | Variable, can be comparable to TPU |
| Chemical Resistance | Good to Excellent | Variable, depends on the specific TPE |
| Temperature Range | Wide (-40°C to +125°C) | Variable |
| Flame Retardancy | Requires additives | Requires additives |
| Cost | Generally higher | Variable, can be lower than TPU |
8. Quality Control and Testing Standards
Rigorous quality control and testing are essential to ensure the performance and reliability of TPU wire and cable jackets.
8.1. International Standards
Several international standards govern the testing and performance of wire and cable materials, including:
- IEC 60811: Common test methods for insulating and sheathing materials of electric cables and optical cables.
- ISO 6722: Road vehicles — 60 V and 600 V single-core cables — Dimensions, test methods and requirements.
- UL 1581: Reference Standard for Electrical Wires, Cables, and Flexible Cords.
8.2. Industry-Specific Standards
In addition to international standards, various industry-specific standards may apply depending on the application. Examples include:
- SAE J1128: Low Tension Primary Cable (for automotive applications).
- EN 50618: Electric cables for photovoltaic systems.
These standards specify requirements for various properties, including tensile strength, elongation, tear strength, abrasion resistance, chemical resistance, electrical properties, and flame retardancy.
9. Environmental Considerations and Sustainability
Environmental concerns are increasingly important in the wire and cable industry. TPU offers several advantages from a sustainability perspective.
9.1. Recyclability
TPU is a thermoplastic material and can be recycled. Recycled TPU can be used in various applications, reducing reliance on virgin materials.
9.2. Bio-based TPU
Bio-based TPUs, derived from renewable resources such as plant oils and sugars, are becoming increasingly available. These materials offer a more sustainable alternative to traditional petroleum-based TPUs.
9.3. Regulations and Compliance
Regulations such as RoHS (Restriction of Hazardous Substances) and REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) restrict the use of certain hazardous substances in electrical and electronic equipment. TPU formulations are available that comply with these regulations.
10. Future Trends and Development
The future of TPU in wire and cable applications is promising, with ongoing research and development focused on:
- Improved Flame Retardancy: Developing halogen-free flame retardant systems that offer high performance without compromising other properties.
- Enhanced Weather Resistance: Improving UV stability and resistance to harsh environmental conditions.
- Bio-based TPU Development: Increasing the use of bio-based materials to reduce reliance on fossil fuels.
- Smart Cables: Integrating sensors and other electronic components into TPU cable jackets for monitoring and control applications.
- Nanomaterials: Incorporation of nanomaterials to improve mechanical, thermal, and electrical properties.
11. Conclusion
Thermoplastic Polyurethane Elastomer (TPU) is a high-performance material that offers a unique combination of properties suitable for a wide range of wire and cable jacketing applications. Its excellent mechanical properties, chemical resistance, flexibility, and processability make it a preferred choice over traditional materials like PVC and polyethylene in demanding environments. Ongoing research and development efforts are focused on further enhancing its properties, improving its sustainability, and expanding its applications in the wire and cable industry. As technology advances and environmental concerns grow, TPU is poised to play an increasingly important role in shaping the future of wire and cable technology.
12. References
[1] Oertel, G. (Ed.). (1994). Polyurethane Handbook. Hanser Gardner Publications.
[2] Hepburn, C. (1992). Polyurethane Elastomers. Elsevier Science Publishers.
[3] Randall, D., & Lee, S. (2002). The Polyurethanes Book. John Wiley & Sons.
[4] Brydson, J. A. (1999). Plastics Materials. Butterworth-Heinemann.
[5] Rosato, D. V., & Rosato, D. V. (2000). Plastics Engineered Product Design. Elsevier Science.
[6] Domininghaus, H., Elsner, P., Eyerer, P., & Harsch, G. (1993). Plastics: Properties and Applications. Hanser Gardner Publications.
[7] UL 1581, Standard for Electrical Wires, Cables, and Flexible Cords. Underwriters Laboratories.
[8] IEC 60811 series, Common test methods for insulating and sheathing materials of electric cables and optical cables. International Electrotechnical Commission.
[9] ISO 6722, Road vehicles — 60 V and 600 V single-core cables — Dimensions, test methods and requirements. International Organization for Standardization.
[10] SAE J1128, Low Tension Primary Cable. Society of Automotive Engineers.
[11] EN 50618, Electric cables for photovoltaic systems. European Committee for Electrotechnical Standardization.