TPU Polyurethanes > ▶ Types TPU Polyurethanes

Las diferencias entre el TPU éter y TPU éster

Thermoplastic Polyurethane (TPU) is mainly classified into two types according to its molecular structure: TPU Polyether and TPU Polyester.

TPU ether offers greater resistance to hydrolysis (water-induced deterioration) and microbial degradation, as well as good flexibility even at low temperatures. Polyether polyurethane can be used in the presence of water. It is an odorless and environmentally friendly material that is resistant to hydrolysis, has high strength, high abrasion resistance, good tear resistance, tensile strength, and peel resistance, high air tightness, strong hardness, and is not easy to yellow. TPU ether is susceptible to oxidation caused by sun exposure (UV rays), which can yellow TPU. Environmentally safe and non-toxic. Durable, cold-resistant, weather-resistant, and maintains good flexibility below 35 degrees Celsius; especially suitable for use in inflatable water entertainment products.

TPU ester is notable for its UV resistance. It also excels in its extreme resistance to wear, abrasion, and high temperatures. Polyurethane polyester TPU, compared to ester TPU, has greater hysteresis and less elasticity, resulting in greater shock absorption. It is notable for its resistance to oils, greases, organic solvents, and detergents, but less so to water and heat. It is often chosen for applications requiring excellent mechanical properties. However, it is not resistant to hydrolysis. After a certain period of use, its internal components will dissolve in water, yellowing and becoming harder than polyether TPU. It is not suitable for aquatic applications.

Key differences between TPU Ester and TPU Ether

Water resistance: It is highly resistant to moisture and does not degrade easily due to hydrolysis.
Climate and cold: Maintains excellent flexibility even at extremely low temperatures.
Common use: Ideal for outdoor applications, humid environments or where contact with water is required.
Mechanical resistance: Offers superior resistance to abrasion, tearing and physical wear.
Chemicals: It is very resistant to oils, fuels and solvents.
Common use: Preferred for heavy industrial applications and high-impact parts.

The difference in smooth segmentation has the following effects on physical properties:

Tensile strength: Polyester TPU > Polyether TPU
Tear resistance: Polyester TPU > Polyether TPU
Abrasion resistance: TPU polyester > TPU polyether
Chemical resistance: Polyester TPU> Polyether TPU
Moisture vaporization: Polyester TPU
Low-temperature impact: Polyester TPU
Transparency: TPU polyester > TPU polyether.
Bactericidal properties: Polyester TPU

Differences between polyester and TPU polyether

Daw materials used

The raw materials for the production of TPU polyether are mainly 4,4'-diphenylmethane diisocyanate (MDI), polytetrahydrofuran (PTMEG), 1,4-butanediol (BDO), where the amount of MDI is approximately 40%, PTMEG represents approximately 40% and BDO represents approximately 20%.
The raw materials for TPU polyester production mainly include 4,4'-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), and adipic acid (AA), where the amount of MDI is approximately 40%, AA represents about 35%, and BDO represents about 25%.

Molecular mass distribution and impact

The relative molecular mass distribution of polyether follows a Poisson probability distribution, resulting in a narrow distribution. The relative molecular mass distribution of polyester diol follows a Flory probability distribution, resulting in a wider distribution. The molecular weight of the soft segment affects the mechanical properties of polyurethane. Generally speaking, if the molecular weight of the polyurethane is the same and the soft segment is polyester, the strength of the polyurethane increases as the molecular weight of the polyester diol increases. With ether, the strength of the polyurethane decreases as the molecular weight of the polyether diol increases, but the elongation increases. This is because the polyester soft segment is inherently more polar, has a larger molecular weight, a more regular structure, and therefore more strong, while the polyether soft segment is weaker. If the molecular weight increases, the relative content of the polyether hard segment decreases, and the strength decreases.

Mechanical properties

Polyols, polyesters, and other oligomeric polyols constitute a soft segment. Soft segments represent the majority of polyurethanes, and different oligomeric polyols differ from polyurethanes prepared with diisocyanates in their properties. Polyurethane elastomers and foams obtained using polar polyester as a soft segment have better mechanical properties. Because polyurethane made from polyester contains a polar ester group, it can not only form hydrogen bonds between the hard segments, but also allow the polar groups in the soft segment to partially bond with the polar groups in the hard segment. This bonding allows the hard phase to be distributed more evenly within the soft phase, functioning as an elastic crosslinking point. Certain polyesters can form soft segment crystals at room temperature, which affects the polyurethane's properties. Polyester polyurethane has higher strength, oil resistance, and thermal oxidation stability than the polyether type PPG, but its hydrolysis resistance is lower.

Hydrolytic stability

When thermoplastic polyester polyurethane is protected with carbodiimide, its hydrolysis resistance is improved. Polyether ester-type and polyether thermoplastic polyurethanes exhibit the best hydrolysis resistance at high temperatures.
Polyester is susceptible to breakdown by water molecules, and the acid formed by hydrolysis can further catalyze additional hydrolysis of the polyester. The type of polyester has some influence on the physical properties and water resistance of the elastomer. As the number of methylene groups in the polyester diol raw material increases, the water resistance of the resulting polyester polyurethane elastomer improves. A lower ester group content also results in good water resistance. Similarly, polyester elastomers synthesized using a long-chain dibasic acid exhibit better water resistance than polyester-based polyurethanes made with a short-chain dibasic acid.

Microbial resistance

Soft polyester thermoplastic polyurethanes are exposed to wet soils for prolonged contact with microorganisms, whereas soft or polyether thermoplastic polyurethanes and polyether thermoplastic polyurethanes or rigid thermoplastic polyurethanes are generally not subject to microbial attack.

Price comparison

Polyether polyurethane elastomers are significantly more expensive than polyester polyurethane elastomers. The main reasons are:

Polyurethane polyether elastomer has good resistance to hydrolysis, resistance to low temperatures, and flexural strength.
In comparison with polyester polyols, polyether polyols, which make up the soft segment of TPU, have higher production raw materials.
The production process for polyether polyol is much more complicated than that for polyester polyol.
Polyether polyols are difficult to control under process conditions.
When producing polyether polyols, the requirements for production equipment are high. At the same time, certain protective measures must be taken during the production process.

Differences in processing

Drying:
As we know, polyurethane is a polar polymer that slowly absorbs moisture when exposed to air. Moisture-absorbing TPU granules form in a molten state, and the water vaporizes at the processing temperature, resulting in a non-smooth product surface, internal bubbles, and reduced physical properties. Therefore, to ensure product performance and prevent bubbles caused by moisture vaporization during the melting process, it is generally necessary to dry the TPU pellets before processing.
We have also analyzed the hydrolytic stability of TPU esters and ethers in the past. Polyester is easily broken down by water molecules, and the acid formed by hydrolysis can catalyze further hydrolysis of the polyester. Under the same conditions, polyester TPU has a much higher water content than polyether TPU. Therefore, polyester TPU requires special attention during the drying process. It must be completely and strictly dry. The conditions are controlled.

Pressure Maintenance Stage
When molten polymer is injected, whether in the pre-plastic stage or the injection stage, the melt is subjected to a combination of internal static and external dynamic pressure. During the packing phase, the molten polymer is subjected to high pressure. Under this pressure, the free volume between the molecular segments is compressed. Due to the decrease in free volume between the molecular chains, the proximity of the macromolecular segments increases intermolecular forces. That is, the apparent viscosity is enhanced. Furthermore, since polyether TPU has a lower cohesive energy of the ether bond and a smaller rotational barrier of the bond, the effect of strengthening the tight chain between the molecular chains is less, so when compressed, the relative displacement of the chain molecules is large, and therefore the viscosity appears to vary over a wide range. Furthermore, because the molecular chain of polyether TPU is much more flexible than that of polyester TPU, permanent deformation is difficult to achieve. Therefore, when polyether TPU is pressed during processing, it tends to fuse with the polyester TPU. In contrast, polyether TPUs require longer holding times.

Processing Time
: In general, molecular weight increases the length of the molecular chain. The slower the center of gravity of the molecular chain moves, the greater the relative displacement between segments, and the greater the flexibility of the long molecular chain. This leads to more entanglement, release, and slippage of the chain, making it more difficult for it to move and increasing the resistance to the flow process. This, in turn, increases the time and energy required, demonstrating the sensitivity of viscosity to shear. Generally, polyester TPU has a higher molecular weight than polyether TPU, so the processing and molding time is longer.

Processing Temperature
: Since polyester TPU generally has a wider molecular mass distribution than polyether TPU, the required processing temperature is higher. Because the nitrogen-oxygen bond in polyether TPU is relatively easy to break, it must be processed at a relatively low temperature.

Pressure
Since polyester TPU has a high molecular cohesive energy, the nitrogen-oxygen bond in the molecular structure is also difficult to break, so it requires high temperature and pressure to process its molecular bond.

Cooling
Since polyester TPU has high friction and high molecular cohesive energy, it is difficult to cool even if it returns to a normal state, so a long cooling time is required.

Liquidity:
Due to the low cohesive energy of the TPU polyether ether bond, the bond rotation barrier is small. As the relative molecular mass of the polyether increases, the chain becomes more flexible, exhibiting a high degree of flexibility and therefore good liquidity, whereas TPU polyester has lower liquidity.

How to detect if TPU ethers and TPU esters

Here are two ways to implement the transaction from a practical perspective:

Identification based on density.

This operation is easier to perform and the steps are simple; the density of TPU Polyether is lower than that of TPU Polyester .

Polyether TPU 1.13–1.18 gr/cm3
TPU Polyester 1.18-1.22 gr/cm³

Identification of polyurethane elastomers by color reaction

Method: (A) The TPU sample is dissolved in 5-10 mL of a suitable solvent: m-cresol, dimethyl hydrazine, or dimethyl amide are effective solvents for dissolving TPU. The dissolved TPU solution is dropped into approximately 0.1 g of p-aminobenzyl reaction reagent, and it turns yellow after a few minutes. Upon hydrolysis of TPU, the ester group reacts with hydroxylamine to form hydroxamate and then reacts with ferric chloride to form a dark red or purple complex salt, identifying the TPU as a polyester TPU. The ether compound does not show a characteristic color development.

Method: (B) Approximately 5 g of TPU is reacted with a few drops of 2 mol/L potassium hydroxide in a methanol solution with phenolphthalein, using phenolphthalein as an indicator to maintain the alkaline mixture. A few drops of hydroxylamine hydrochloride are added to the methanol (saturated solution). The mixture is heated (50°C) for a few seconds, acidified with 1 mol/L hydrochloric acid, and a drop of 3% aqueous ferric chloride solution is added. The TPU polyester immediately displays a characteristic purple color, which is prepared from castor oil or dimerized fatty acid. The polyester is brown or purplish-brown, and the TPU polyether does not develop a color. The identification method belongs to the chemical identification method, while the density identification method belongs to the physical identification method and is more reliable; it can also be adopted. However, because the operation involves many chemical reagents, the experimental steps and procedures must be strictly controlled, and the experiment is complex. Therefore, it is necessary to carry it out by professional personnel in this field. It is more demanding for general operators.

Do not mix esters with ethers

The ether group in polyether TPU differs from the ester group in polyester TPU, and their molecular structures are different. Therefore, the ether group generally has poor compatibility with ester-based resins, leading to mixing. A layering phenomenon occurs, closely related to the intermolecular strength of the ether bond. Furthermore, polyester crystallinity is generally much stronger than that of polyether, resulting in poor compatibility. However, not all ethers behave this way. Because PTMG (polytetrahydrofuran) has similar crystallinity to polyester, the compatibility of polyether TPU synthesized with PTMG and polyester TPU is slightly better. While the synthetic process is possible, the physical properties of the resulting products will be significantly reduced, a loss not worthwhile, thus avoiding mixing. It can be seen that ethers and esters cannot be mixed for processing due to differences in molecular structure, cohesive energy, intermolecular forces, crystallinity, and molecular composition. According to their compatibility, when the two are mixed, obvious lines will appear on the surface of the test piece, and turbidity will occur. Even if they can be mixed and processed together, the physical properties of the processed products will be significantly reduced, especially if they cannot be used to process particularly transparent parts. It will be very difficult to produce in large volumes. During processing, special care must be taken to avoid mixing the two.

Asistente de polímeros

TPU ether vs. esther - Polímeros termoplásticos, elastómeros y aditivos

Las diferencias entre el TPU éter y TPU éster

Key differences between TPU Ester and TPU Ether

The difference in smooth segmentation has the following effects on physical properties:

Differences between polyester and TPU polyether

Do not mix esters with ethers