Physio Chemical Properties of Filled PTFE

PERMEABILITY of Filled PTFE

The permeability of filled PTFE is very dependent upon methods of fabrication. Since there is no chemical bonding between PTFE and the fillers used, the permeability is generally greater than that of unfilled PTFE. As the filler content increases, particularly above 10% by volume, special care, or special techniques, have to be adopted to ensure minimum permeability. Specific measurements have not been made, but from porosity tests it is concluded that permeabilities can be made close to that of unfilled PTFE if the correct method of fabrication is used.

CHEMICAL RESISTANCE of Filled PTFE

PTFE is one of the most chemically resistant materials known, and fillers can only worsen this position. Table 12 gives a list of the probable suitability of the Filled PTFE range for use with various common chemicals. As noted below this table, some of the information was obtained from direct experimentation whilst other data were predicted from a knowledge of the chemistry of the individual constituents. As with unfilled PTFE, chemical attack on the filled PTFE should not be confused with chemical attack on adjacent parts resulting from permeability of the filled PTFE.

Table 12. Suitability of Filled PTFE range for use with various chemicals at 50°C (122°F)
NB. This table is intended solely as a general guide to material selection. Because exposure conditions can vary considerably in different applications, the user is strongly advised to undertake tests under conditions relevant to the specific application

Chemical	63% Bronze+Graphite Filled PTFE	15% Glass Filled PTFE 25% Glass Filled PTFE	25% Carbon Filled PTFE 15% Graphite Filled PTFE	60% Bronze Filled PTFE
50% H2SO4	U	S*	PS	U
Conc. HCl	U	PU*	PS	U
Conc. HNO3	U	PU*	PS	U
40% NaOH	PS	PU*	PS	PS
0.880 NH4OH	U	S*	PS	U
Benzene	PS	S*	PS	PS
Phenol	PS	S*	PS	PS
Trichloroethylene	PS	S*	PS	PS
Ethanol	PS	S*	PS	PS
Fluorine	-	PU	PS	-
Chlorine	PS (dry)	PS	PS	PS (dry)
Bromine	-	PS	PS	-
HF	PS++	U	PS	PS++
SO2	-	PS	PS	-
Mercury	U	PS	PS	U

Notes
S= Satisfactory
U = Unsatisfactory
PS = Not tested, but probably satisfactory
PU = Possibly unsatisfactory
† 25% Carbon Filled PTFE and 15% Graphite Filled PTFE will be attacked only by oxidation, although there may be a slight reduction in weight when in contact with other chemicals, due to attack on the very small quantities of impurities (less than 2%) inherently present in the filler.
* The results of tests in which samples of tape 50.8mm (2 inches) square and 0.38mm (0.015 inch) thick were used in order to give the maximum surface area to weight ratio. The samples were dried, weighed and then immersed in the various liquids at 50°C (122°F). After a period of four weeks the samples were removed from the liquids, washed, dried and re-weighed to determine whether attack had occurred. Materials listed as ‘satisfactory’ showed no change in weight over the four week period and those showing some change are listed as ‘possibly unsatisfactory. Over the four week period the average change in weight of the ‘possibly unsatisfactory’ materials was 7%. The tensile properties were measured before and after the chemical resistance tests: no statistically significant changes in tensile properties were recorded in any of the tests, including those in which weight losses occurred.
++ Up to 70°C (160°F).