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Strange chemical reaction from PVC grommets

Discussion in 'General Electronics Discussion' started by sacentre, Feb 18, 2016.

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  1. sacentre


    Sep 27, 2014
    This may be more of a chemistry question but here goes. Some years back, I bought an RS P.V.C Grommet Kit (see photo 1) and over the years, the PVC of the grommets has reacted with the yellow plastic of the box (Photo 2) just as if it has melted where the grommets came into contact.

    The grommets themselves seem completely unaffected but the yellow plastic of the box seems to have softened and molded itself to the shape of the grommets even to the extent of extruding a cylindrical column through the centre hole of soime of the smaller ones. I had to dig many of them out as they had become deeply embedded. As I say, they seem to be quite serviceable.

    I was wondering if anyone had seem this effect before and can tell me what the reaction might have been. I assume this may have been as a result of a faulty batch or defective composition of the box material.


    Trevor 1.jpg 2.jpg
    KeithM likes this.
  2. AnalogKid


    Jun 10, 2015
    Outgassing from the components affected the plastic. It's not much, but when trapped for a few years slowly works its magic. Some foam speaker cover material disintegrates after a few years. Looks fine until you touch it, then it turns to powder. All petrochemical plastics degrade over time, some more quickly than others.

    Tha fios agaibh likes this.
  3. Crystal Wizard

    Crystal Wizard

    Feb 10, 2016
    Sounds like what has happened to the insulating foam that my ICs have been stored in for 20 years!
    Just touch the stuff and it falls to dust!
  4. duke37


    Jan 9, 2011
    PVC is hard and brittle and used for things like water guttering. To make it more malleable it is mixed with plasticizer which can migrate out of the PVC. Uncovered cables in walls will often show where they are hidden after a few years. I have a vague memory that it has hormone effects.
  5. Martaine2005


    May 12, 2015
    My ex liked pvc........Is that why our marriage ended?
    I told her leather was better!:p

    davenn likes this.
  6. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Can you elaborate?
    I don't think I've ever seen this and I'm an electrician.
    Martaine2005 likes this.
  7. Martaine2005


    May 12, 2015
    John, you are a chief electrician.. (did I get that right)?
    Oops, master electrician..:D
    I think Trevor means that cables on older houses with older broken/sheaths have a tendancy to bleed through after a re-paint. Water based paints obviously bring out the rust in older steel cables and can be seen quite easily by rust marks on the walls. Also happens with rendered walls which has iron in. The obvious trade mark of that is rust marks seeming to come from stones in rough cast render.
    All or most houses have two or three rust runs that give the game away.

  8. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Martaine, you can call me Master spark jockey. Lol
    Trevor said "in walls" so I'm thinking paint bleed through was not what he meant.
    I'll wait for him to explain himself.

    Besides, On this side of the pond we are not allowed to have unprotected cables on walls. I find cables that are painted do hold up nicely without bleeding through.
    The only caveat is the amperage rating has to be derated because the paint layer insulates the cable.

  9. davenn

    davenn Moderator

    Sep 5, 2009
    Try sending it back to them and claim a replacement :) :)

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