textfiles/science/polymers

New inclusions to the old stuff:
Info on magnet wire coatings!


From all the discussion on this group about building ones own capacitors 
and what types of materials make good coil forms, I became interested in 
obtaining some hard (or semi-hard) data on different types of polymers. I 
was also interested when someone (?) asked whether ABS was a good material 
for coil forms - I had no idea. It seems that it is much preferable to PVC 
as Richard guessed.

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		polythene-British!
						
							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
							*wire wrap insul.

polymethyl methacrylate		PMMA		Plexiglas
						Lucite
						Perspex (Jim Oliver)

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

polyamide-imide			PAI		Torlon

polyurethane			PUR

polycarbonate			PC		Lexan

Polyacetal			POM		Delrin

polyethlene terephthalate	PET		Mylar	co-polymer of PE

cellulose actetate butyrate	CAB		Butyrate

cellulose nitrate		CN		"Laquer" *typical constituent
							laquers	

acrylonitrile-butadiene-styrene	ABS		Cycopac	ter-polymer of 
							polystyrene
						* warning Jim Oliver says
						this name may apply to
						may many diff materials

polyimide			PI		Kapton

polyvinyl formal		?		Formvar	wire coating

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. In fact, 
for the purposes of approximation, the Q of a capacitor with low DF or PF 
is simply Q=1/DF=1/PF

Absolute power lost in the system is:
1. goes up with the square of the voltage gradient (electric field)
2. goes up linearly with the volume of the dielectric in the field
   ( as Richard said, make your coil forms thin)
3. goes up linearly with increasing dielectric constant
4. generally increases with frequency


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
POM		3.7 / 3.7	400		5 / 5
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
CAB		3.7 / 3.5	400		6 / 21
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


Magnet wire coatings from Phelps-Dodge:
All data pertain to 18 gauge magnet wires
Build= thickness of coating

Coating			What's it made of	Build		DC 
----------		-----------------	-----		breakdown

Thermaleze-T (TZT)	polyester-imide		2.8mils		11kV

Armored Polythemaleze				3.05mils	11kV
(APTZ)			modified polyester&
			modified polyamide-imide

Imideze (ML)		Aromatic polyimide	2.9mils		12kV

Formvar			modified polyviynyl	3.0mils		10kV
			formal			

Sodereze		modified polyurethane	2.9mils		8.5kV

Nyleze			Polyurethane		2.9mils		8.5kV 
			& polyamide

* Note: for the dielectric breakdown, I'm not exactly sure of what they're 
takling about since for some of the materials one would get 12kV/3mils
=4KV/mil which doesn't realyy make sense - it's too big by a rather wide 
margin, I think. 1Kv/mil is more reasonable.
Anyway, here's the dielectric constant/DF numbers for these matearials:

Material		Dielectric Const. / DF x 10^-3

		1kHz		100kHz		1Mhz		rating
TZT		3.7/5.6		3.56/16.4	3.58/21.5	3rd

APTZ		3.86/6.9	3.69/22.1	3.67/26.6	5th

ML		3.34/0.9	3.3/5.7		3.36/9.8	2nd to 
								teflon

Formvar		3.6/11.2	3.41/25.2	3.37/28.4	5th

Soldereze	3.85/11.3	3.66/20.7	3.66/23.1	4th

Nyleze		4.07/19.7	3.78/27.1	3.75/27.2	6th


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
5. Electrical Engineer's Handbook, Pender - 4th Edition
6. Phelps-Dodge magnet wire product data

Plastics sources: probably best to check your local distributors, but there 
is a mail order company called US Plastic Corp @800-537-9724 (catalog). 
They have rod/sheet/tubing of PVC, PMMA, CAB, POM, PE, PS. Of particlular 
note:
	Butyrate tubing up to 6 " diameter * lower loss coil forms
	Polystyrene tubing to 4 " dia * very low loss coil form
	4x8ft LDPE sheet 60mil or other * Richard's Capacitors

If you all are sick of seeing this I'll refrain from futher posts!

-Ed