Degree of Gelation test

In pipes that use PEX or polyethylene network, the manufacturer is obliged to comply with the amount of gelation according to the national standard. Usually, for different networking methods, this value has a different percentage, which is mentioned in the table below, and the quality control managers must evaluate the amount of gel after the production of the pipe and the completion of the networking process. We explain how to perform the test.

Test Principles

The weight of a sample of a pipe or connection is measured before and after immersion in the solvent in a certain period of time. The degree of reticulation is expressed as the weight percentage of insoluble material in the solvent, which for PEX pipes of type b should be greater than or equal to 65%.

Materials and reagents

Xylene, an isomeric mixture with a volume purity higher than 98% and a boiling point range of 137 to 140 degrees Celsius, to which 1% by volume of antioxidant has been added.

Equipment

Refrigerant of the return flow is shown in the figure below.
Round-bottomed balloons with minimal volume
Heater, suitable for balloons used with heating capacity suitable for boiling xylene (boiling range: 137-140 degrees Celsius)
The mesh cage with a lid should be large enough to contain the test. The mesh cage should be made of aluminum or stainless steel in the form of a mesh with a hole size suitable for holding the test. Mesh wires should not be contaminated with oil, grease, or any pollutant that can be dissolved in xylene. Otherwise, it should be washed with acetone and dried before use.
Automatic cutting machine or micro cutter suitable for cutting and preparing samples
Vacuum Oven or Fan Oven
The scale, with the ability to weigh the mesh cage with or without the sample, with an accuracy of 1 mg

Guide

Identification label and thin wire connected to the mesh cage – 2. Support base – 3. Ring clamp – 4. Refrigerant – 5. Cork or connector – 6. Xylene – 7. Mesh cage for holding the sample – 8. Heater – 9. Round bottom balloon – 10. Adjustable converter – a. water exit – b. water ingress

Sample Preparation

The test is prepared based on the following instructions:

Any protective layer on the tube or test piece must be removed before the test. At least two tests must be prepared.
After cutting the pipe or connection, the sample is prepared from the cross-section of the pipe or connection and in the form of a layer with such a thickness that it is necessary to remove only the PEX layer and not to remove the adhesive layer.
The weight of the sample should be equal to or more than
The degree of reticulation may change in the thickness of the pipe or connection wall, therefore, for surface or intermediate measurements, it is necessary to use a machine to create a sample. It is recommended to use a cutting machine to prepare the sample from the pipe. It is possible to use a micro cutter or other suitable cutting tool to prepare the sample.

Test Method

1. Weigh the clean and dry mesh cage and lid carefully.

2. Place the test in the mesh cage, put the lid on it and weigh the set carefully.

3. Place the mesh cage and the sample with the cap in the balloon and make sure that there is enough solvent

There is a solution for immersing the sample in such a way that the minimum ratio of solvent weight to sample weight is 200 to 1.

The solvent can be reused after distillation by adding one volume percent of antioxidant. At 140 degrees Celsius.

In case of waste, use a fresh or distilled solution.

4. Boil the solvent for a period of time to make sure of proper corrosion in it.

5. The mesh cage and its cover along with the remaining sample after the time mentioned in the previous step

Remove the solution.

Caution – Be careful when removing the mesh cage from the boiling solution

6. Dry the rest of the sample along with the net cage for 3 hours using one of the following methods:

a. By means of a vacuum oven, keeping at a temperature under vacuum with a minimum pressure of 0.85 bar (about an absolute pressure of 0.15 bar or less).

b. By means of a fan oven, with the possibility of proper extraction, placing in the temperature

7. Allow it to cool at room temperature. Then weigh the remaining (weight) net cage and cover and the remaining weight (weight) with 1 mg precision.