[Next][Index][Thread]
No Subject
I thought I'd share the results of my library searches:
First, I'd like to list some of the plastics with their chemical name and
thier abreviations. Trade names are listed if they are well known.
chemical name abreviation aka notes
------------- ----------- --- ------
polyethylene PE CH2-CH2 monomer
HDPE High density PE
LDPE Low density PE
polypropylene PP replace one H in PE
by CH3
polyvinyl chloride PVC replace one H in PE
by one Cl atom
polyvinylidene chloride CPVC PVDC replace two H in PE
by two Cl
polystyrene PS replace H in PE by
a benzene ring
polyvinyl flouride PVF replace H in PE by
F atom
polyvinylidene flouride PVDF Kynar repace two H in PE
by two F atoms
polymethyl methacrylate PMMA Plexiglas
Lucite
polytetraflouroethylene PTFE Teflon replace all H in PE
by F atoms
polychlorotrifloroethylene PCTFE Kel-F replace 3 H in PE
with F one with Cl
polyamide 6 PA 6 Nylon 6
polyamide 66 PA 66 Nylon 66
polyurethane PUR
polycarbonate PC Lexan
polyethlene terephthalate PET Mylar co-polymer of PE
acrylonitrile-butadiene-styrene ABS Cycopac ter-polymer of
polystyrene
polyimide PI Kapton
OK, there are zillions of others, but these are the ones I picked because I
heard of them before...
A couple of comments: Notice that there are many polymers which share a
common structure with polyethylene, all that changes is replacing one or
more of the H atoms in (PE) with some other atom or group of atoms. Then
there are plastics which are called co-polymers or ter-polymers. A co-
polymer is just taking two different monomers and sticking them together in
a unit cell before polymerizing. Example: PET. Likewsie, a ter-polymer is
just sticking three monomers into a unit cell and then polymerizing. A very
common example is ABS which is used as sewar and drainage pipe.
Now for the useful stuff. What are the electrical properties of some of
these polymers? The most useful properties in my mind are the dielectric
constant (or permittivity), the dielectric strenght, and the dissipation
factor. All of these properties are dependent on temperature and frequency,
but amazingly they also depend somewhat on the actual thickness of the
material (as in thin films).
----A couple of notes:
All three properties mentioned above depend on frequency, but it turns out
that for many non-polar polymers (ie PE) that the dielectric constant and
dissipation factor do not depend much on frequency. I'll show some data for
some of the plastics I could find. However, nobody seems to have data on
the frequency dependence of the dielectric strength. It is best just to
assume that this was done at DC.
One property which is not well known for polymers is that the breakdown
electric field or dielectric strength (VOLTS/INCH etc...) depends on the
actual thickness of the film. Typically, as the film gets thinner, the
dielectric strength goes up!!! For example, LDPE has a strength of 800volts
per mil at 80 mils, but this goes up to 1400volts/mil at 20mils!!
Polystyrene exceeds even this!
Finally what is dissipation factor? It is a measure of how lossy the
material is to alternating electric fields (as in Tesla coils and tank
capacitors). It is defined by
Ir
--- = tangent (delta) = DF
Ic
where Ir is the resistive or dissipative current and Ic is the capacitive
or displacement or reactive current. Delta is the phase angle between
these currents (in the complex plane). Another expression which contains
the same information is the Power Factor. For those familiar with this term
they are related by:
PF=DF/SQRT(1+DF^2)
For small DF, then PF is approximately equal to DF. Obvisously, one would
like to have DF as small as possible for low loss, high Q systems.
polymer dielectric dielectric dissipation
constant strength factor
50Hz / 1Mhz (Kv/cm) 50Hz / 1Mhz (x10^-3)
-------- ----------- ----------- -----------
LDPE 2.29 / 2.28 370 .15 / .08
HDPE 2.35 / 2.34 -- .24 / .20
PP 2.27 / 2.25 240 .40 / .50
PVC-plasticized 4-8 / 4-5 270 80 / 120
PS 2.5 / 2.5 200-300 .1-.4/.05-.4
ABS 2.4-5/2.4-3.8 ~400 3-8 / 2-15
PMMA 3.3-3.9/2.2-3.2 140 40-60/4-40
PTFE 2.1 / 2.1 480 .2 / .2
PCTFE 2.3-2.8/2.3-2.5 550 1 / 20
PA-6 3.8 / 3.4 400 10 / 30
PA-66 8 / 4 600 140 / 80
PC 3.0 / 2.9 380 .7 / 10
PET 4.0 / 4.0 420 2 / 20
PI 3.5 / 3.4 560 2 / 5
PUR-linear 5.8 / 4.0 >300 120 / 70
PUR-thermoset 3.6 / 3.4 240 50 / 50
PUR-thermoplas 6.6 / 5.6 300 30 / 60
Silicone 3.6 200 5-13 / 7
Another comparison:
polymer Dielectric constant / Dissipation Factor (x10^-3)
100 Hz 1000 Hz 1 Mhz 10 Mhz
ABS 2.8/5 2.8/6 2.8/8 2.8/7
PMMA 3.6/62 3.2/58 3.1/40 2.9/33
PC 3.1/1 3.1/1.3 3.1/7 3.1/11
PE 2.3/.1 2.3/.1 2.3/.1 2.3/.1
PA-6 4.2/31 3.8/24 3.8/31 4.0/20
References:
1. Polymer Engineering Principles, Richard C. Progelhof and James Throne
2. Plastics for Electronics, Martin T. Goosey
3. Handbook of Plastics in Electronics, Dan Grzegorczyk and George Feineman
4. SPI Plastics Engineering Handbook, Society of the Plasitics Industry
Finally, I have yet to find out what the properties of dielectrics of
magnet wire are. They are given names such as Formvar, Enamel, Poly-thermal
-ease etc... anyone know?
-Ed