Difference Between TPU and PU

Main Difference – TPU vs PU

TPU and PU are very important polymers that have a wide range of applications in different industries. TPU stands for thermoplastic polyurethanes while PU stands for polyurethanes. TPU is a type of thermoplastic elastomer. It has many improved properties than other thermoplastic elastomers. PU is a polymer that is different from other polymer materials based on its nomenclature; this polymer is named based on the urethane linkages present in the polymer. There are many differences between these two types. The main difference between TPU and PU is that TPU has no cross-links whereas PU can have cross-links based on the type of polyols used.

Key Areas Covered

1. What is TPU
– Definition, Structure, Applications
2. What is PU
– Definition, Steps in the Production
3. What is the Difference Between TPU and PU
– Comparison of Key Differences

Key Terms: Cross Links, Elastomers, Isocyanates, Monomer, Polymer, Polyols, Polyurethane (PU), Thermoplastic, Thermoplastic Polyurethane (TPU), Thermosets, Urethane

What is TPU

TPU stands for thermoplastic polyurethane. It is a type of thermoplastic elastomer. Hence, it is elastic and melt-processable. It has many favorable properties such as elasticity, transparency, resistance towards oils and abrasion resistance. TPU is a form of block copolymer (contains soft and hard segments).

TPU can be colored through a number of processes, and it is also extremely flexible. This is mainly due to the composition of hard and soft segments. The hard parts are either aromatic or aliphatic. They are generally aromatic, but the aliphatic hard segments are preferable when the color and clarity retention in exposure to sunlight is more important.

The oil resistance arises with the soft segment of this block copolymer. The soft segments are often either polyether or polyester types, but this depends on the application. Polyether soft segments are important to withstand wet environments whereas polyester soft segments are important in oil resistance. Some applications of TPU are given below.

Wire and cable solutions – provide toughness and flexibility along with extended durability
Film and sheet – provide durability and flexibility
Hose and tubes
Sporting goods swim fins and goggles

Figure 1: TPU Chips

However, TPU has a high hardness when compared to other types of thermoplastic elastomers. When burnt, TPU burns with an irritating odor. The products made of TPU feel rougher.

What is PU

PU stands for polyurethane. It is a polymer material composed of urethane linkages. These are also called carbamate linkages. Most polyurethanes are thermosets. They do not melt when heated. But there are some thermoplastic polyurethanes as well.

This polymer is different from many other polymers due to the absence of a urethane monomer (other polymers are named according to the monomer used for the production; for example, polyethylene is made from ethylene monomers). The polymer is named based on the repeating linkages present in the polymer, which are urethane linkages (-R-NH-C(=O)-O-).

Figure 2: Memory Foam Cushion made of PU

Polyurethanes are produced from the reaction between alcohols (having more than two –OH groups, also known as polyols) and isocyanates (having more than one reactive isocyanate group –NCO). The linkage that is formed between alcohol and isocyanate is a urethane linkage. The production of PU has three major steps.

Production of Isocyanates

For the production of isocyanates, two major compounds are used; TDI (toluene diisocyanate), and MDI (methylene diphenyl diisocyanate). TDI is mainly used in the production of low density, flexible foam or cushions. MDI is generally used in the production of rigid foams.

Production of Polyols

The number of –OH groups present per monomer is important in determining the degree of crosslinking between the polymer molecules. This affects the mechanical properties of the polymer material.

Production of PU

A linear PU is formed if the polyols have two –OH groups per monomer and are mixed with either TDI or MDI. These polyurethane linkages are formed via condensation polymerization. If the polyols contain more than two –OH groups per monomer, then a cross-linked polymer material is produced.

Definition

TPU: TPU stands for thermoplastic polyurethane.

PU: PU stands for polyurethane.

Nature

TPU: TPU is a thermoplastic material.

PU: Most polyurethanes (PU) are thermosets, but there are some thermoplastic materials as well.

Composition

TPU: TPU contains hard and soft segments.

PU: PU contains urethane linkages.

Raw Materials

TPU: TPU is made from polyether or polyester (soft segments) or polycaprolactones.

PU: PU is made from polyols and isocyanates.

Cross-links

TPU: TPU has no cross links.

PU: PU can have cross-links based on the type of polyols used.

Conclusion

TPU stands for thermoplastic polyurethane. It is an improved form of thermoplastic elastomer. It is different from usual elastomers due to the absence of crosslinks. PU stands for polyurethanes. This polymer is different in its nomenclature because it is named considering the repeating urethane linkages. The main difference between TPU and PU is that TPU has no cross-links whereas PU can have cross-links based on the type of polyols used.

Reference:

1. Lazonby, John. “Polyurethanes.” The Essential Chemical Industry online, Available here.
2. “Engineered Polymers.” Thermoplastic Polyurethane (TPU) and Beyond – Lubrizol, Available here.
3. Polyurethanes.” Thermoplastic Polyurethane, Available here.

Image Courtesy:

1. “Chips TPU” By Luigi Chiesa – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “MemoryFoam-slow” By Johan – Own work (CC BY-SA 3.0) via Commons Wikimedia