Application Note:

It is possible to triple both the modulus and strength of polypropylene resin by adding only 15 volume % carbon nanofibers.

Source Data:

Discussion:

Graph top left: Tensile strength versus modulus for 15 volume % composites using different types of CNF in polypropylene. The open circle shows the properties of polypropylene. The data shows that it is possible to triple both the modulus and strength of the polypropylene resin by adding only 15 volume % carbon nanofibers.

Graph bottom left: Loss factor vs. fiber volume fraction for CNF/polypropylene composites at room temperature. Shows the variation of the loss factor of the graphitized fiber, air-etched, and clean fiber/polypropylene composites versus fiber volume fraction. As fiber volume fraction increases, the loss factor decreases compared to the unreinforced polypropylene. The slope of the damping versus fiber volume fraction curves increases as adhesion between the fiber and the matrix increases.

Graph right: Tensile strength and modulus of composites fabricated from 15 vol% CNF produced with different gaseous feedstock residence times. Fibers grown under conditions of lower feedstock residence time are more graphitic and adhere more poorly to polypropylene.

More graphitic fibers adhere poorly to the polypropylene matrix compared to less graphitic fibers. Fiber matrix adhesion may be improved by moderately oxidizing the fibers in air or carbon dioxide. This oxidation seem to become more effective as it increases the product of the external surface area and the surface energy of the fibers; however, excessive etching can be destructive.

Better fiber-matrix adhesion increases the mechanical properties of the CNF/polypropylene composites.

    CNF designations:
  • Clean (PR-1): Carbon nanofiber with low levels of condensed PAHs on surface (an early developmental version of CNF).
  • PR-18: CNF fiber variant used primarily in rubber composite studies.
  • PR-5: Fiber variant produced during process development studies.
  • Best shot (PR-11): Production process was designed for highest feasible fiber production rate.
  • Coal-based fiber: These utilize a mixture of ground coal to supplements the natural gas and hydrogen sulfide
  • Acetylene-based fiber: These are made by using acetylene gas as the primary carbon feedstock instead of methane Graphitized fiber: PR-11 fibers fully graphitized via heating to 3000oC for 1h followed by gradually cooling in an inert gas atmosphere
  • DH (diamine salt of carboxylic acid, high concentration): PR-1 that has been oxidized and reacted with Armak 1192 (proprietary compound comprising two amine groups positioned near the end of a long hydrocarbon chain, each amine being fully neutralized by a large fatty acid)
  • LH (diamine salt of carboxylic acid, low concentration): see above
  • EH (epoxy, high concentration): PR-1 that has been oxidized and reacted with Epon 828
  • EL (epoxy, low concentration) see above
  • Air-etched fibers: PR-1 oxidized in air
  • CO2 oxidized fibers: PR-1 oxidized in carbon dioxide

Our Recommendation:

To improve the modulus and strength of polypropylene resin, PPI recommends the following products XXX



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