Research material: on Triboelectric series

TriboElectric Table

Column 1 (this col.): Insulator name. Col.2: Charge affinity in nC/J (nano ampsec/wattsec of friction). Col.3: Charge acquired if rubbed with metal (W=weak, N=normal, or consistent with the affinity). Col.4: Notes.	Affinity nC/J	Metal effect	Triboelectric Table Tests were performed by Bill Lee (Ph.D., physics). ©2009 by AlphaLab, Inc. (TriField.com), which also manufactured the test equipment used. This table may be reproduced only if reproduced in whole.
Polyurethane foam	+60	+N	All materials are good insulators (>1000 T ohm cm) unless noted.
Sorbothane	+58	-W	Slightly conductive. (120 G ohm cm).
Box sealing tape (BOPP)	+55	+W	Non-sticky side. Becomes more negative if sanded down to the BOPP film.
Hair, oily skin	+45	+N	Skin is conductive. Cannot be charged by metal rubbing.
Solid polyurethane, filled	+40	+N	Slightly conductive. (8 T ohm cm).
Magnesium fluoride (MgF2)	+35	+N	Anti-reflective optical coating.
Nylon, dry skin	+30	+N	Skin is conductive. Cannot be charged by metal rubbing.
Machine oil	+29	+N
Nylatron (nylon filled with MoS2)	+28	+N
Glass (soda)	+25	+N	Slightly conductive. (Depends on humidity).
Paper (uncoated copy)	+10	-W	Most papers & cardboard have similar affinity. Slightly conductive.
Wood (pine)	+7	-W
GE brand Silicone II (hardens in air)	+6	+N	More positive than the other silicone chemistry (see below).
Cotton	+5	+N	Slightly conductive. (Depends on humidity).
Nitrile rubber	+3	-W
Wool	0	-W
Polycarbonate	-5	-W
ABS	-5	-N
Acrylic (polymethyl methacrylate) and adhesive side of clear carton-sealing and office tape	-10	-N	Several clear tape adhesives are have an affinity almost identical to acrylic, even though various compositions are listed.
Epoxy (circuit board)	-32	-N
Styrene-butadiene rubber (SBR, Buna S)	-35	-N	Sometimes inaccurately called "neoprene" (see below).
Solvent-based spray paints	-38	-N	May vary.
PET (mylar) cloth	-40	-W
PET (mylar) solid	-40	+W
EVA rubber for gaskets, filled	-55	-N	Slightly conductive. (10 T ohm cm). Filled rubber will usually conduct.
Gum rubber	-60	-N	Barely conductive. (500 T ohm cm).
Hot melt glue	-62	-N
Polystyrene	-70	-N
Polyimide	-70	-N
Silicones (air harden & thermoset, but not GE)	-72	-N
Vinyl: flexible (clear tubing)	-75	-N
Carton-sealing tape (BOPP), sanded down	-85	-N	Raw surface is very + (see above), but close to PP when sanded.
Olefins (alkenes): LDPE, HDPE, PP	-90	-N	UHMWPE is below. Against metals, PP is more neg than PE.
Cellulose nitrate	-93	-N
Office tape backing (vinyl copolymer ?)	-95	-N
UHMWPE	-95	-N
Neoprene (polychloroprene, not SBR)	-98	-N	Slightly conductive if filled (1.5 T ohm cm).
PVC (rigid vinyl)	-100	-N
Latex (natural) rubber	-105	-N
Viton, filled	-117	-N	Slightly conductive. (40 T ohm cm).
Epichlorohydrin rubber, filled	-118	-N	Slightly conductive. (250 G ohm cm).
Santoprene rubber	-120	-N
Hypalon rubber, filled	-130	-N	Slightly conductive. (30 T ohm cm).
Butyl rubber, filled	-135	-N	Conductive. (900 M ohm cm). Test was done fast.
EDPM rubber, filled	-140	-N	Slightly conductive. (40 T ohm cm).
Teflon	-190	-N	Surface is  fluorine atoms-- very electronegative.

Symbols in the table-
Polyurethane (top) tends to charge positive; teflon (bottom) charges negative. The charge affinity listings show relative charging. Two materials with almost equal charge affinity tend not to charge each other much even if rubbed together. Column 3 shows how each material behaves when rubbed against metal, which is much less predictable and repeatable than insulator-to-insulator rubbing. The charging by metal is strongly dependent on the amount of pressure used, and sometimes will even reverse polarity. At very low pressure (used in this table), it is fairly consistent. A letter "N" (normal) in this column means the charge affinity against metal is roughly consistent with the column 2 value. The letter "W" means weaker than expected (i.e., closer to zero than expected or even reversed.) The "+" or "-" indicates the polarity. In all cases where the polarity in col.3 disagrees with col.2, it is a weak (W) effect.

Limitations of these measurements-- Testing was done at low surface-to-surface force (under 1/10 atmosphere) using 1" strips of each of the insulators that are available as smooth solids. (Cotton, for example, could not be made into a solid strip.) The charge affinity ranking of non-smooth solids was interpolated by their effect on smooth solids which had measured affinity values. At this low surface force (typical of industrial conditions), the absolute ranking of charge affinity of various insulating materials was self-consistent. Above about 1 atmosphere, surface distortions caused some rearrangements in the relative ranking, which are not recorded here. Conductor-to-insulator tests were done also, and contrary to prevailing literature, all conductors have about the same charge affinity. However, the metal-insulator charge transfer was strongly dependent on the metal surface texture in a way not seen with insulator-insulator. Metal-insulator transfer was also more pressure-dependent in an unpredictable way, so charge transfer has not been quantified for metal-insulator. The "zero" level in this table is arbitrarily chosen as the average conductor charge affinity. "Slow conductors", like paper, glass, or some types of carbon-doped rubber, had approximately the same affinity as conductors if rubbing was done very slowly. All tests were done fast enough to avoid this effect. Testing was at approximately 72 F, 35% RH, using an AlphLab Surface DC Voltmeter SVM2 and an Exair 7006 AC ion source to neutralize samples between tests. Resistivities were measured with an AlphaLab HR2 meter. Applied frictional energy per area was 1 mJ/cm². Total charge transferred was kept in the linear range, well below spark potential, and was proportional to applied frictional energy per area. All samples needed to be sanded or scraped clean before testing; any thin layer of grease of oil (organic or synthetic) was generally highly positive and would thus distort the values.