Application Note:

Ball milling the carbon nanofibers for two minutes prior to adding to polypropylene provides the lowest electrical resistivity (i.e., highest conductivity) because the fiber length is similar to the non-ball milled fiber, but the dispersion is better. Ball milling the carbon nanofibers for 10 minutes shortens the fiber length too much to decrease the resistivity in the polypropylene.

Source Data:


Carbon nanofiber descriptions: Clean (PR-1): Carbon nanofiber with low levels of condensed PAHs on surface (an early developmental version of CNF).
Best shot (PR-11): Production process was designed for highest feasible fiber production rate.
Graphitized fiber: PR-11 fibers fully graphitized via heating to 3000oC for 1h followed by gradually cooling in an inert gas atmosphere.
Air-etched fibers: PR-1 oxidized in air.

Best shot: fibers produced under a rapid flow condition to maximize fiber production rate, but left several monolayers of polycyclic aromatic hydrocarbons condensed of the fiber surface
Clean: fibers fabricated at a low flow rate and had a much cleaner surface than the "best shot," perhaps about one monolayer of adsorbed hydrocarbon
Air-etched: "best shot" fibers which were subsequently heated to 500o C for 20 min in flowing air to burn off adsorbed hydrocarbons
Graphitized: "best shot" fibers heat treated to 3000o C in inert gas for several hours

Top left graph: Approximate resitivity upper bound required for several applications, compared with electrical resitivity values for graphitized VGCF and clean VGCF in polypropylene. Increasing the fiber volume fraction above 3% results in rapidly decreasing volume resistivity for the graphitized VGCF/PP composites. The graphitized VGCF/PP composites have a significantly lower resistivity than the clean VGCF/PP composites at 20% fiber volume fraction.

Top right graph: Electrical resistivity for BGCF/PP and VGCF/nylon composites utilizing fibers with graphitized, clean, best shot, air-etched and sieved, and carboxylic acid treatments.

Bottom left graph: Resistivity versus fiber volume fraction for VGCF/PP composites incorporating fibers ball milled for 0, 2, and 10 minutes. Ball milling of the fiber shortens its length and length influences resistivity. The non-ball milled sample has the highest resistivity because of the agglomerates present making dispersion difficult. Ball milling for 10 minutes shortens the length too much to decrease the resistivity while ball milling only two minutes provides the lowest resistivity because the fiber length is similar to the non-ball milled, but the dispersion is better.

Table bottom right: Conductivity, critical fiber volume concentrations, and critical exponents from the curve fits to the experimental data VGCF/PP composites and literature data.

Our Recommendation:

To electrical conductivity of polypropylene, PPI recommends the following products XXX

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