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Key points of this article
- The two main reasons why chemicals cause hoses to harden are:
①Dissolving of liquid chemicals in PVC resin hoses
②Plasticizer seepage due to the chemical breakdown of bonds between PVC resins - To prevent hardening, it is important to confirm the types of chemicals being carried as well as the hose usage conditions before selecting a hose from among those with a high level of chemical resistance.
Why are PVC hoses soft?
Polyvinyl chloride (PVC) resin is often used to make general-purpose hoses. PVC resin is hard at room temperature and cannot be bent. The PVC resin used in hoses, however, is called “soft PVC resin” and offers flexibility. Soft PVC resin contains a plasticizer that softens the resin, making the PVC hose soft and easy to use even at room temperature.
Figure: Proportion of PVC to
Why do chemicals cause PVC hoses to harden?
There are two main mechanisms by which chemicals can cause a hose to harden.
①Hose hardening due to the dissolving of the plasticizer in chemicals
②Plasticizer seepage due to the chemical breakdown of bonds between PVC resins
Hose hardening due to the dissolution of the plasticizer ①can be countered by selecting hoses with a plasticizer that is not easily dissolved.
But what measures can be taken to prevent situations such as those described in②?Let’s think about this question together.
Select from among A, B, and C below.
A. Increase the amount of plasticizer additives
B. Use a PVC hose
C. Change the hose material
The correct answer is C. Change the hose material.
In the case of ①where the chemical breaks down the bond between the PVC resin molecules, causing the hose to harden—is all but impossible to prevent without changing the material of the hose itself.
Hardened hoses cannot be returned to their original condition. They must also be replaced immediately to prevent any problems. However, frequently replacing hoses at short intervals increases material and maintenance costs. This means measures must be taken to prevent hoses from hardening due to chemicals.
How can hardening due to chemicals be prevented?
There are many different types of hoses, and choosing the right type for the intended application is important. Non-PVC polyolefin resin and fluororesin hoses are often used for chemicals thanks to their high chemical resistance, and chemical-resistant stainless steel or resin couplings are also often used. Using hoses with high resistance to chemicals will allow for longer use than PVC hoses, which would become hard in just a few days.
When selecting a chemical-resistant hose, check the chemical resistance data provided by the manufacturer carefully because the chemical compatibility of hoses varies. If the chemical name cannot be found, please contact the manufacturer. In addition to chemical resistance, customers are requested to confirm usage conditions such as the temperature and pressure of chemicals being carried so that a hose appropriate for those conditions can be selected.
Toyox offers hoses with high chemical resistance, such as the TOYOFUSSO Hose series, whose inner tube is made from tetrafluororesin.
Because the ideal hose for your application will depend on what chemicals the hose is carrying, we request you to also take a look at the following Hose chemical resistance table and Coupling chemical resistance table.
Fluorine hose series
For those seeking a hose with high chemical resistance
■Hose chemical resistance table (reference material)
■Coupling chemical resistance table (reference material)
That wraps up our explanation of how chemicals can cause hoses to harden and how to prevent this from happening.
For any other inquiries or consultations, please contact the TOYOX Customer Service Office.
Using chemicals in a hose can cause the hose to harden over a short period with certain types and concentrations of chemicals. Because hardened hoses cannot be returned to their original condition and may cause various types of problems, they should be replaced as soon as possible.
In this article, Hose Adviser PRO will explain how certain chemicals can cause a hose to harden, and how to prevent this from happening.