The Properties of TPU Material and Its Application in 3D Printing

1. Introduction
2. Classification of TPU
3. Pros and cons of TPU material
4. The properties of TPU material(Comparison with PLA)

Overview

As 3D printing continues to revolutionize manufacturing processes across industries, the choice of materials plays an essential role in achieving optimal results. One such material that has gained significant attention is Thermoplastic Polyurethane (TPU). Characterized by its unique combination of flexibility, durability, and versatility, TPU has emerged as a preferred choice for creating functional and intricate 3D printed objects. In this article, we delve into the properties of TPU material and explore how it shows abilities in the realm of 3D printing.

What is TPU Material?

Introduction

Thermoplastic polyurethane (TPU) is an advanced material that has found wide applications in 3D printing. It is a thermoplastic elastomer material with properties between plastics and rubber. Essentially, it is a block copolymer, the chemical structure of which consists of alternating sequences of hard and soft segments formed by the reaction of diisocyanate with short-chain diol (so-called chain extender) and diisocyanate with long-chain diol. It not only has high durability and flexibility but also has good wear resistance, heat resistance, and excellent chemical properties, enabling it to maintain performance and dimensional stability over a wide temperature range. In addition, it also has good oil resistance, solvent resistance and chemical resistance, and can resist erosion and dissolution of various chemicals. In 3D printing, as a thermoplastic elastomer that can be melt-processed, TPU can be converted into complex three-dimensional structures through fused deposition modeling (FDM) or selective laser sintering (SLS) and other thermoplastic processing techniques. Thanks to an excellent combination of physical, chemical and thermal properties as well as its environmentally-friendly nature, TPU has become an material of choice for 3D printing applications across various industries.  Engineers, manufacturers and designers in all industries increasingly favor TPU for its unique properties and eco-friendly attributes.

Classification of TPU

TPU (Thermoplastic Polyurethane) is an elastic polymer material used in 3D printing. TPU can be classified into different hardness grades based on the Shore durometer scale. The Shore hardness test measures the hardness of elastic materials such as rubber, polymers and elastomers. A higher Shore value indicates a harder material.TPU filament used in 3D printing typically have a Shore hardness ranging from 85A to 95A, some special types of TPU filaments with Shore hardness from 40A to 85A. They can be classified as:

1. Soft TPU (Shore 85A-88A): Extremely flexible and elastic. Can be stretched up to 700-1000% of its original length. Typically used for printing components that require high flexibility, such as phone cases and watchbands.
2. Medium TPU (Shore 90A): Possesses good flexibility and durability. Can be stretched approximately 500% of its original length. Used for drone components, orthotic inserts, sports equipment, etc. This is the most common type of TPU used in 3D printing.
3. Hard TPU (Shore 95A): Still flexible but more rigid. Maximum stretch of around 200-300% of original length. Suitable for applications that require a degree of flexibility as well as support, e.g. electronic enclosures, insoles, toys, handles, etc.

The wide durometer adjustability of TPU originates from its unique block copolymer structure with alternating hard and soft segments, allowing different levels of softness, hardness and haptic properties. The Shore hardness of PLA is closely related to its chemical structure and is difficult to improve through elementary means. Therefore, TPU is an ideal choice when subtle touch, extensive durometer adjustability and high resilience are required. PLA is more suitable when higher hardness and structural integrity are needed.

Pros and Cons of TPU Material

The Properties of TPU Material(Compare with PLA)

As an environmentally friendly material maturely positioned between rubber and plastics, TPU material has many characteristics that are unmatched compared to PLA 3D printing filament, which makes it a preferable choice for certain applications.

Flexibility and Elasticity

TPU is renowned for its excellent flexibility and elasticity. As a thermoplastic elastomer material, TPU exhibits high elasticity due to its loose molecular chain structure and weak secondary interactions such as hydrogen bonding. During stretching, TPU's soft segments can extend and move without directly rupturing, endowing TPU with superior plastic deformability and toughness. Its elongation at break typically ranges from 200% to 1000%, far surpassing that of PLA.

In contrast, PLA is a biodegradable thermoplastic polyester material and a relatively rigid plastic. Due to its single stiff chain structure with lack of chain mobility, PLA readily undergoes brittle fracture upon deformation. PLA's elongation at break is usually between 5-10%, indicating its limited plastic deformability. Compared to PLA, TPU's unique chemical structure makes it an ideal material choice for 3D printing soft parts which can achieve a softer and more natural feel than PLA.

Outstanding Impact Resistance

TPU exhibits a degree of chain crosslinking and strong intermolecular interactions connecting the chains, rendering them highly resistant to displacement or breakage from their fixed positions by applied stresses. Consequently, TPU displays high impact strength and can absorb substantial impact energies without failure. In contrast, the more brittle PLA demonstrates lower impact strength. 

High tensile strength

TPU generally exhibits a tensile strength between 20-100 MPa, significantly surpassing that of conventional rubber materials. This is attributed to the presence of hard segment domains in TPU that can withstand substantial stresses under applied loads. Under the buffering effect of soft segment domains, TPU is less susceptible to premature failure and retains its integrity under large deformations. In comparison, PLA has an inferior tensile strength of 50-70 MPa, limiting its applications. In summary, TPU demonstrates a superior tensile strength relative to both conventional rubbers and PLA, allowing for wider applications.

High wear resistance

The molecular chains of TPU interact via reinforced hydrogen bonding and van der Waals forces, enhancing its cohesive strength and affording TPU elevated tear strength of 10-80 kN/m. This renders TPU molded parts less prone to cracking during service. In contrast, PLA exhibits a tear strength of only 5 kN/m, markedly lower than TPU. So TPU demonstrates markedly higher resistance to wear and tearing relative to PLA, owing to its strong intermolecular interactions and high cohesive strength.

Excellent fatigue resistance

The segmental chains of TPU can stretch and deform considerably, recovering their initial conformation upon stress removal. This enables them to repeatedly withstand large deformations. Simultaneously, the inter-chain connections remain firmly adhered via robust intermolecular forces, less prone to fracture under cyclic loading. Thus, TPU demonstrates marked fatigue resistance and enhanced durability. In contrast, PLA exhibits inferior fatigue endurance due to molecular chain slippage.

Superior acid and alkali resistance

TPU contains polar hydrogen bonds and strong intermolecular interactions, giving it a compact three-dimensional network resistant to erosion and degradation by acidic and alkaline solvents. In contrast, PLA is susceptible to chain slippage under acidic and alkaline conditions due to weaker intermolecular forces, compromising its stability. Thus, TPU exhibits markedly greater acid and alkali resistance, retaining its properties when exposed long-term to solutions with pH 3-9.

Enhanced oil and solvent resistance

The dense three-dimensional structure of TPU prevents the permeation and action of many chemical solvent molecules, conferring TPU with high resistance to many common solvents. The open structure and weak intermolecular forces of PLA render it readily dissolved and penetrated by many organic solvents. Therefore, TPU is more suitable for environments involving oils and organic solvents.

Superior oxidation resistance

TPU contains antioxidants to prevent oxidation, and its compact molecular structure renders it difficult for oxygen molecules to permeate, thereby enhancing its oxidant resistance. Without added antioxidants and with an open structure permitting oxygen ingress, PLA is prone to chain scission and degradation upon oxidation. Thus, the oxidation resistance and service life of TPU far surpass those of PLA.

Enhanced radiation resistance

The dense structure and robust intermolecular interactions of TPU make its molecular chains difficult to directly impact and destroy by radiation energy. The weaker intermolecular forces of PLA render it susceptible to molecular chain scission and degradation under radiation. Therefore, TPU demonstrates greater radiation resistance and irradiation stability compared to PLA.

The Most Suitable 3D Printing Parameters(Take SUNLU TPU Material as An Example)

Unlike conventional rigid 3D printing materials such as polylactic acid (PLA),the highly elastic and flexible nature of TPU poses greater challenges for 3D printing processes.Particularly for those with limited experience, and could readily result in unsuccessful prints.

To achieve optimal results in 3D printing with TPU, the filament SUNLU TPU is used here as a case study for recommended parameters and key considerations which are as follows:

Printing parameters:

1. Extrusion temperature: :205-230°C. Higher temperatures within this range can ensure sufficient melting of TPU.
2. Extrusion multiplier: 1.05-1.15 times. For distal extrusion, the printing speed is 20-30mm/s and the retraction speed is 10-20mm/s. For proximal extrusion, conventional printing speeds can be used, and the speed can be appropriately reduced by 15-25% for more complex models. The retraction speed is reduced by 10-20% of the normal speed. Slower speeds within these ranges allow sufficient flow of TPU and increase the success rate.
3. Extrusion width: 0.40+/-0.02mm. Filament diameter: 1.75+/-0.10mm. The settings should be determined comprehensively based on the extrusion head parameters. Excessively large sizes beyond these tolerances are difficult to control.
4. Use special extrusion headsfor TPU material, such as 0.6mm diameter and TPU filament liners. conventional extrusion heads may potentially cause clogging and compromise print quality.
5. Avoid adhesion of the printing bed. Use steel mesh, double-sided adhesive paper or PET sheets to facilitate demolding.

Key considerations:

1. Proximal extrusion are recommended due to their inherent advantages in flexible filament feeding.
2. Disable the fan to control the temperature drop of the model to less than 5°C/min. Use an enclosedprinterto avoid moisture affecting print quality.  
3. Limit the heightof the model. Excessive height beyond this reference value is prone to swaying at the top, affecting the success rate.
4. TPU materials should be sealed and stored in a dry and ventilated environment with relative humidity below 60% to prevent moisture damage.

When implemented appropriately, these recommendations and key considerations may help enable high quality 3D printing with flexible TPU materials such as SUNLU TPU filament.

Application of TPU Material

Thanks to to its unique chemical structure and excellent physical and mechanical properties, TPU has been widely used in many fields. It is mainly reflected in:  

1. Footwear manufacturing

TPU possesses superior elasticity and abrasion resistance, rendering it an optimal material for footwear soles and uppers. Leading athletic brands such as Adidas and Nike utilize TPU in the fabrication of running shoe soles, uppers, and various other components to enhance comfort, support, and durability while providing a highly elastic and ergonomic wearing experience for end users. Moreover, TPU can be manufactured into complex geometries to accommodate diverse design requirements.   

2. Sporting equipment

The superior tensile strength, elongation at break, and durability of TPU render it extensively utilized in the production of various sports equipment such as kayaks, bicycle tires and handlebars, rock climbing anchors, swimming goggles, snowboard boots, and gymnastics pads to enhance safety, stability, and ergonomics. Such equipment exhibits excellent abrasion resistance and protracted service life. The outstanding pliability and elasticity of TPU materials can effectively attenuate impact forces. TPU can also be manufactured in a diverse array of geometries and dimensions to satisfy the requirements of different sporting applications.

3. Engineering plastics

Owing to the superior physical and mechanical properties of TPU materials, they can serve as viable alternatives to metals for engineering plastics such as gears, bearings, bushings, and pipe fittings to achieve concomitant lightweighting and durability. Despite their flexibility, TPU 3D printed components also demonstrate high impact strength, stress resistance, and fatigue endurance.

4. Automotive industry

The pliant tactility, weatherability, and chemical resistance of TPU render it an optimal choice for automotive interior components. It is extensively utilized in steering wheel covers, gear shift knobs, instrument panels, door panels, etc. These parts exhibit robust durability and the ability to withstand harsh conditions such as extreme heat and cold. Superior impact strength and elasticity also augment vehicular safety

5. Medical and healthcare  

The biocompatibility and pliability of TPU render it a crucial constituent of medical devices and healthcare products such as oxygen masks, catheters, orthodontic brackets, wheelchairs, and crutches. These devices demonstrate excellent biocompatibility and negligible potential for adverse reactions in human subjects. They can also be fabricated in a variety of geometries and dimensions to satisfy diverse medical applications. Furthermore, they exhibit durability and the ability to withstand prolonged use and harsh conditions.

6. 3D printing

The pliability and toughness of TPU materials afford them superior 3D printability. For instance, SUNLU TPU material is extensively employed in 3D printed footwear soles, mobile phone cases, UAV components, and bags. Their 3D printed articles feature complex geometries, lightweighting, and high elasticity. TPU materials also demonstrate robust acid and alkali resistance as well as exceptional corrosion resistance. From daily necessities to fashion projects, everything can be 3D printed. 

Conclusion

In summary, the widespread applications of TPU materials substantiate its superior performance and immense potential in the domain of advanced materials. Owing to its unique properties and versatility, TPU has become an invaluable material for 3D printing. In particular, SUNLU TPU exhibits preeminent flexibility, durability, and chemical resistance, rendering it the material of choice for end users. By comprehending the specific print parameters of SUNLU TPU and leveraging its advantages, hobbyists can unleash the potential of TPU in 3D printing pursuits. Whether in consumer goods, industrial components, or medical devices, SUNLU TPU materials are enabling novel designs and applications and catalyzing more innovative products. With the sustained development of 3D printing technologies, TPU will play a pivotal role in shaping and propelling the future of additive manufacturing

WRITTEN BY: Jennie Jones