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A brief discussion on hydrolysis resistance and UV resistance of TPU

A brief discussion on hydrolysis resistance and UV resistance of TPU
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  • Categories:Industry news
  • Author:
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  • Time of issue:2020-07-06 11:12
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(Summary description)

A brief discussion on hydrolysis resistance and UV resistance of TPU
Top

(Summary description)

  • Categories:Industry news
  • Author:
  • Origin:
  • Time of issue:2020-07-06 11:12
  • Views:
Information

Thermoplastic TPU is the first polymer material which has both rubber elasticity and plastic thermoplastic. TPU has excellent physical and mechanical properties, high tensile strength and elongation, and good wear resistance. Therefore, TPU is often used in the manufacture of sole and cable sheath. It also has excellent tear resistance and is compliant in a wide temperature range.

 

TPU abrasion resistance, tear resistance and tensile strength, tear strength is better than that of polyether type of TPU, type polyether TPU is suitable for the hydrolysis resistance, resistance to microbial degradation and low temperature resistance, requiring higher flexibility, and through the special method of synthesis of polyether ester type TPU has the characteristics of both at the same time, more excellent performance, can be used as a fire hose, cable sheath, film production, etc.

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1
The hydrolysis resistance

 

In the process of carboxylate polyester group TPU prepared from polybutanediol, a few chains are capped by carboxyl group (-CO2H) and introduced into the diol component.

 

When carboxylate polyester group TPU is hydrolyzed, a chain break occurs at the carboxylate (-COO-) chain and some new chains are formed carrying the carboxylate end. This carboxyl group formed from two sources catalyzes the further hydrolysis of TPU and accelerates the degradation process.

 

The polycarbonyl diimide structure has been shown to be a very effective hydrolytic stabilizer with poly (ester - carbamate). Its function is to react with the generated carboxyl group, acting as a neutralizer and repairing broken chains in hydrolyzed polymers.

Effect of polycarbonyl diimide (PCD) on the hydrolysis stability of TPU

 

Due to its ability to react and neutralize with carboxyl groups, polyepoxides can also be used as polyurethane hydrolytic stabilizers and can also be used to improve the TPU of broken chains.

 

The stability and stabilization of lactone polyester group TPU prepared by poly (-caprolactone) diol is very similar to that of carboxylate polyester group TPU.

 

In fact, the macromolecular diol bonds in polycaprolactam (PCL) are carboxylate bonds, but macromolecular diols are produced by lactone polymerization rather than by dicarboxylic acid-diol condensation.

 

For example, poly (adipic carbonate) diol polyester group TPU has excellent anti-hydrolysis, ester bond [such as carbonate bond (-0-C0-0-)] generates hydroxyl seal end and carbon dioxide gas on the broken chain, but the carboxyl group is further automatic catalytic hydrolysis.

 

Polybutanediol polyether TPU has obvious hydrolysis stability because the ether bond of macromolecular diols is very difficult to hydrolyze. In fact, carbamate bonds are the most sensitive in terms of poly (ether - carbamate) hydrolysis.

 

Another important factor determining the hydrolysis stability of TPU is the degree of hydrophobicity and the permeability of TPU chain. Therefore, the more hydrophobic TPU (for example, high hardness TPU) is, the less water absorption will be, which makes it more resistant to hydrolysis.

 

2
Resistance to ULTRAVIOLET radiation

The most important factor of TPU in atmospheric aging is the ultraviolet radiation with a wavelength of 330~410nm. This energy, accompanied by solar radiation, triggers the automatic oxidative degradation of TPU, which causes extensive chemical crosslinking of the chains and makes TPU embrittlement and insoluble, especially aromatic amino-ester TPU.

 

In addition, during this process, aromatic carbamate TPU produces a clear yellowish brown color, while aliphate TPU is relatively stable in color.

 

Ultraviolet degradation is thought to produce quinone imide structure in aromatic carbamate containing pre-quinone structure, and then active hydrogen may be partially added to quinone imide to form a transactionally linked TPU chain.

 

Different views have been held on the uv degradation process of this aromatic carbamate, including the light-Fleet rearrangement reaction shown in the chemical formula below to explain the color variation and cross-linking of the TPU chain.

 

The above two chemical reactions cannot be generated in aliphatic carbamate TPU because the latter has no quinone structure. In fact, the comparison between the two structures showed that aliphatic carbamate TPU showed better uv stability than aromatic carbamate TPU.

 

Undoubtedly, some degree of hydrogen peroxide may occur in the TPU chain during uV-induced automatic oxidation, regardless of the carbamate structure in TPU. According to the nature of TPU uv degradation process, the combination of UV absorber and antioxidant provides a particularly effective UV stabilization system for TPU.

 

In addition, the use of a small amount of carbon black alone can play the role of shielding uv, IT is a very effective TPU uv stabilizer.

 

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