SAMPE Journal - March/April 2020 - 38

FEATURE / RECYCLING PTFE WASTE
Picture of PTFE powder.

tioned fibrous morphology in order to increase
strength as described in our second paper, "Influence of addition of emulsion polymerized PTFE
powder on particle morphology and mechanical
strength of recycled PTFE compacts"3-4. This was
based on the thinking that fibrous morphology in
virgin PTFE enhances the strength.
PTFE raw material is sold in powder form like
molding powder and fine powder (which is made
by a drying dispersion) and in colloidal emulsion
liquid state called dispersion. The dispersion is
generally used for coating on base materials. PTFE
powder obtained from dispersion by coagulation is
known to be white in color, soft and adhesive, and
easily becomes fibrous when undergoing stress.
Using these characteristics, the fibrous morphology can be made to surround recycled PTFE particles. However, there have been no cases in which
the fired PTFE body was created by mixing recycled
PTFE powder and dispersion.
Mixed Dispersions Significantly Modify Recycled PTFE Outcome
Let's consider a simple example. We have 100%
buckwheat noodle here in Japan. This is buckwheat
noodle that uses no binding agent within it. On the
other hand "Nihachi soba" (a 2-8 buckwheat noodle) uses binding agent such as flour. That is to say,
the 100% buckwheat noodle is a highly pure buckwheat noodle that enables enjoyment of the original flavor whereas the Nihachi soba version has a
binding agent portion.
Similarly, a mixture of dispersion into recycled
PTFE powder means that the fired PTFE with high
purity is now born. Dispersion can be said to be
used as a binding agent as in the 100% buckwheat
vs. Nihachi soba version case. However, dispersion
is originally a kind of PTFE with similar substance.
Figure 43 shows electron microscopic images of: (a)
recycled PTFE powder, (b) dried dispersion powder, and (c) molding powder. In Figure 4(a), there is
no fibrous morphology, but fibrous behavior is observed in Figure 4(b). Granular particles in which
fine particles are coagulated are observed in Figure
4(c).
So, the question is "did the strength increase in
reality?" The strength was measured for the various
fired bodies prepared using recycled PTFE power
and dispersion, and, also the strength was measured for the fired bodies prepared using recycled
PTFE powder and molding powder as a comparison testing.

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Figure 4. Photos of (a) recycled PTFE powder, (b) dried dispersed powder,
and (c) molding powder3.

Test Result Outcomes
Let us follow the outcome. First, porosity, which
affects strength; Fired recycled PTFE bodies mixed
with dispersion became denser with an increase
in dispersion, and the porosity reached just below
1% for the fired PTFE body containing 50 w% dispersion (Figure 5- 6 ). However, fired PTFE body
containing 50 wt% molding powder (Figure 5- 8 )
did not become as dense as that containing 50 wt%
dispersion (Figure 5- 6 ).
When tensile strength and tensile elongation

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SAMPE Journal - March/April 2020

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