While researching the properties of crosslinked polyethylene, i had made
many searches by the internet to find a method of determination the degree of crosslinking
of PE. And i found some standarts like ASTM D2765, EN579, ISO 10147. But all of them
were for a cost of above 50$. Even they were for 1$ i would not buy them. I used to find
all the things (scientific) for free (because i am only a student). Many days of thinking
finally i had found a method of determination the degree of crosslinking of PE.
In order to show the method , first of all let's formulize what the degree of crosslinking
of PE is.
The degree of crosslinking of PE - is a ratio of mass of crosslinked state of a PE to the
whole mass of PE.
But how can we know which part of PE is crosslinked?
In order to answer to this question first we should the dissolver of PE.
As it's known that PE dissolves in many organic dissolvers like xylol, toluol, etc., and
above 80 degree Celcius. But the crosslinked state of a crosslinked PE does not dissolve,
It only becomes a gel. By this way volume of a gel increases. And the size of a
macromolecule increases too.
Then i guessed a little technology:
I took a cylinderic container made of a metall(Aliminium).
The dimensions of a container is shown below:

Height of the cylinderic container was 30 millimeters.
Diameter of the base of cylinderic container was 20 millimeters.

Then i made many holes (approx. 40-60) onto this container (mainly onto the bottom).
The diameter of holes should be as little as 0.2-0.3 millimeters.

But in my case the diameter
of holes were 0.5 millimeters, because i could not find a drill with a diameter less than
0.5 millimeters.
And then i took a sample of crosslinked PE (crosslinked with dicumyl peroxide) and cut it
with a knife. The cut samples were ~0.3 millimeters of thin and 15-20 millimeters of length.
The mass of cut samples was 1 gramm. I replaced them into the container and closed the
"mouth" of the container with aliminium
foil made some little holes on it. Then replaced
the container into a flask filled with toluol. And connected the "mouth" of the flask with
backflow condenser. And replaced the flask into the hot water bath - a vessel, hot water
in it and that vessel located on top of an electric range. By this water boiled and the
temperature reached 96 degree Celcius so was the temperature in the flask. So that the
whole process continued 8 hours (minimum required time). After that ( 8 hours left) took the
container and dryied it at temperature 130-140 C approximately 3-4 hours. And got its mass.
And after some calculations ,

C = (mP - mC)*100/(mS-mC), %.

C - the degree of crosslinking of PE.
mP - the mass of the container after the whole process.
mC - the mass of the dry (nothing in it) container.
mS - the mass of the container with crosslinked PE in it before the whole process.

got the results. I did the whole process 5 times. And took the arithmetic mean of the
results.



This article can be useful for students who are researching on the properties of crosslinked
PE and who are searching the standarts like ASTM D2765,
EN579, ISO 10147 and who does not
have money to buy them ) .

Determination of crosslink density
Determination The Degree Of Crosslinking Of Polyethylene

Is there any procedure available to determine the crosslink density of cured sample other than crumb rubber sample???


-question by Arun H