From: "Barry L. Ornitz" <ornitz@dpnet.net>
Subject: Re: Is hot glue Polyethylene?
Date: 24 May 1999
Newsgroups: rec.radio.amateur.homebrew

AMDX wrote in message <01bea630+ACQ-972b7040+ACQ-cfb14d0c+AEA-default>...
>If hot glue is polyethylene it should have low loss
>and a low dielectric constant.


Mike and all,

Most hot-melt glues are a mixture of amorphous polypropylene and some
tackifier resins.  The RF loss properties are almost as good as
polyethylene.

Polyethylene hot-melt glues are available but they require temperatures
above those of home glue guns.  I remember seeing a company that sold
emergency connector kits.  These consisted of a large collection of
different pins and sockets of all sizes.  These were fitted to the existing
connector and the wires were attached.  A form was placed around this and
molten polyethylene from a high temperature glue gun was squirted in.  It
did a wonderful job making connectors to weird military plugs and jacks.  I
tried using polyethylene in my home glue gun and wound up destroying it.
These generally are thermal limited for safety and my gun got hot enough to
soften the polyethylene and plug the gun up.

Roy Lewellyn made some Q measurements on some toroids a while back trying
to determine the effect of coatings.  A few of the poor materials gave low
Q, but most good dielectrics had little effect on the coil Q.  Some good
ones were: polyethylene, polypropylene hot melt, RTV silicones (after
curing), polystyrene, and paraffin wax (not beeswax).  The wax is
especially nice when experimenting as it is so easy to remove.
Cyanoacrylate (super glue), RTV and epoxies do OK for permanent
installations.

As someone else pointed out, most common RTV (room temperature vulcanized)
silicone sealers release acetic acid when curing.  These have a strong
vinegar smell, and they can corrode nearby materials.  There are silicone
materials that do not release acid when curing.  I believe GE makes one
version in their professional builder's supply line.  Read the label
carefully to make sure you have the right one.


        73,  Barry L. Ornitz     WA4VZQ     ornitz+AEA-dpnet.net

From: "Barry L. Ornitz" <ornitz@dpnet.net>
Subject: Hot-Melt Adhesives, was Re: How to mount toroids securely
Date: 11 Dec 1998
Newsgroups: rec.radio.amateur.homebrew

Ian White, G3SEK wrote in message <7frRSDAhSWc2EwnB@ifwtech.demon.co.uk>...
>Barry L. Ornitz wrote:
>>Hot melt adhesives can be of several types.  The polyvinyl acetate types
>>have moderately high dielectric losses but the amorphous polypropylene type
>>is excellent.
>
>How does one tell the difference?


Roy asked me the same question.  Read below.

>I just tested a general-purpose glue stick in the microwave oven and the
>losses at 2.45GHz were very low (lower than the glass that was used to
>hold it upright).
>
>Needless to say, there was no information on the pack. If it helps you
>to identify the material, Barry, it was very similar to polyethylene in
>its translucent color and flexibility, but had a slightly sticky feel at
>room temperature rather than the waxy feel of PE. It is low-melting and
>rapidly becomes much more sticky at higher temperatures; it also pulls
>out very easily into fine filaments.
>
>It seems to work well for general-purpose waterproofing of HF antennas,
>although that is not a very severe test of RF losses.
>
>>Something easy to use that has excellent dielectric
>>properties is ordinary paraffin wax like that used in home canning and in
>>candles.
>
>Thanks for reminding us that sometimes we don't need high technology!

Ian and Roy (and others),

Most of the white hot-melt adhesive sticks for home use are the amorphous
(atactic) polypropylene variety.  As Ian noted, they are usually
translucent white and waxy feeling.  The "stickiness" is obtained by the
addition of chemical "tackfiers".  Once molten, the polypropylene become
fairly tacky by itself, but additions are generally made to improve its
sticking properties.  Other things like fillers and antioxidants like
Vitamin E are also added.  My former employer, Eastman Chemical Company,
was one of the major producers until they sold the business to H. B. Fuller
several years ago.  Their big competitor, Huntsman, is still in the
business.

[Originally amorphous polypropylene was a waste material when the desired
product was isotactic polypropylene (isotactic = all methyl groups are on
the same side of the polymer chain, atactic = randomly distributed methyl
groups).  Once good uses were found for it, Eastman "mined" large
quantities of it from a landfill where it was previously disposed.  Today
the trend is for block polymers where portions of the chain are isotactic
(hard and crystalline) and adjoining portions are atactic (rubbery and
soft).  The result is like a fiber reinforced material - the hard chains
are held together within a softer material to make a strong, but tough,
composite. ]

I had previously mentioned the polyvinyl acetates and polyvinyl alcohols
that were also used as hot melt adhesives.  These tend to be found in
industrial applications like corrugated box construction.   While not a
hard and fast rule, they tend to be tan or brown.  These have poor
electrical properties not because they are vinyls (polyethylene and
polypropylene are technically vinyl polymers).  It is because there are
highly polar groups attached to the vinyl backbone.  In PVC, these are
chlorine atoms.  In polyvinyl alcohol, PVOH, the polar groups are
hydroxyls.

Paraffin wax, which I had mentioned earlier, is electrically similar to
polyethylene but with a much shorter polymer chain.  It is a great material
for potting electrical circuits because it has low losses, is moisture
resistant, and can usually be removed readily with a heat gun.  Just be
careful of its flammability.

     73,   Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net

From: "Barry L. Ornitz" <ornitz@dpnet.net>
Subject: Re: Is hot glue Polyethylene?
Date: 24 May 1999
Newsgroups: rec.radio.amateur.homebrew

Bill wrote in message <3749FE16.36D8@NOREPLY.inreach.com>...
>AMDX wrote:
>>
>> If hot glue is polyethylene it should have low loss
>> and a low dielectric constant.


>I believe it is a blend of polymers including polyvinyl acetate and
>waxes

This combination is used in some glue sticks.  They tend to be be somewhat
"sticky" at room temperature.  The glue sticks that look like RG-8 center
dielectric are generally amorphous polypropylene and tackifier resins.

The material using polyvinyl acetate is not a good dielectric, while that
using the polypropylene is.

Thanks for mentioning this.

        73,  Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net