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TOPIC: Peroxide decomposition temperature

Peroxide decomposition temperature 2 years 10 months ago #690

What is approximate temperature to which the peroxide starts to decompose into XLPE insulation compounds
Last Edit: 2 years 7 months ago by Archived Forum Admin.
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Re: Peroxide decomposition temperature 2 years 10 months ago #691

Hi again Bighead,

I suggest you contact your polymer supplier for this information because you must know what organo-peroxide they are using.

The following is some information I learned from Chemicalland21.com. The important thing to notice that as far as decomposition temperatures are concerned, they talk in terms of half life against time and temperature.

White Powder
"Dicumyl peroxide is a strong free radical source ; used as a polymerization initiator, catalyst and vulcanizing agent. The half-life temperatures are 61 C (for 10 hours), 80 C (1 for 1 hour) and 120 C (for 1 minute). DCP decomposes rapidly, causing fire and explosion hazard, on heating and under influence of light. It reacts violently with incompatible substances or ignition sources (acids, bases, reducing agents, and heavy metals). It is recommended to store in a dry and refrigerated (< 27C or 39 C max) and to keep away from reducing agents and incompatible substances." Source: www.chemicalland21.com/specialtychem/per...CUMYL%20PEROXIDE.htm

Clear Liquid
"Di-tert-butyl peroxide, DTBP, is used to as a catalyst of polymerization for olefin copolymers and crosslinking agent for unsaturated polyesters. It is also used as a fuel additive and chemical intermediate. It is a strong free radical source containing more than 10.9% of active oxygen. The half-life temperatures are 126 C (for 10 hours), 149 C (1 for 1 hour) and 193 C (for 1 minute). It decomposes rapidly, causing fire and explosion hazard, on heating and under influence of light. It reacts violently with incompatible substances or ignition sources (acids, bases, reducing agents, and heavy metals). It should be stored in a dry and refrigerated (< 27C recommended or 38 C max) area and to keep away from reducing agents and incompatible substances."
Source: www.chemicalland21.com/specialtychem/per...BUTYL%20PEROXIDE.htm

As far as safety goes, there is little concern re fires and explosions unless you are using peroxide injection and thus handling Di-tert-butyl peroxide. With purchased XLPE compounds the dicumyl peroxide is already properly distributed inside the pellets and thus is waiting heat activation.




As reference, here is a copy of the the answer to your other question:

"This is a very interesting question and somewhat difficult to answer as most seemingly straightforward technical questions are. In fact, you really should be discussing this with your chemical laboratory and your XLPE polymer suppliers.

As I recall, the temperature to achieve crosslinking is somewhere around 210C (410F) with a range of 210C (410F) to 215C (419F).

If, in saturated steam, steamcure, the gage pressure is around 18 to 20 bar (260 psi to 290 psi gage).

If you are using an electrically heated tube with an inert gas atmosphere (drycure), you need a gage pressure somewhere between 5 and 10 bar (72.5 and 145 psi gage) to prevent the formation of voids due to organo-peroxide (dicumyl or di-tert-butyl peroxide) decomposition products.

Now, there is one fundamental thing that must be achieved in any CV tube. The inside surface of the polyethylene insulation, immediately adjacent to and in intimate contact with the conductor must get up to that 210C-215C temperature for a period of time. This takes time because the heat comes from the outside of the insulation and that necessary time for the heat transfer controls the line speed against the length of the curing tube. This is why conductor preheaters are used with triple crossheads - anything to reduce the cooling effect of the conductor itself on the inside surface of the insulation. The driving force for the heat transfer is the higher temperature of the outside surface of the insulation and in a dry cure line this is even thermally more complex because of both radiation and convective heating by the CV tube itself.

In drycure lines, the temperature of the outside surface of the XLPE must not get so high (For the dry nitrogen pressure you are using.) that the cooling water begins to boil at the cooling section interface when the polyethylene is quenched. If this happens you would have in effect inadvertently created a steamcure line. This will also give very high high insulation shrinkback and excess organo-peroxide decomposition products in the dry cure atmosphere itself. (And on the surface of the cooling water at the gas-water interface.)

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
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