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PLASTICS ADDITIVES


                             5.26                        CHAPTER 5


                                        TABLE 5.23  Electrical Conductivity of Filled Polymers
                                               Material      Log volume resistivity (Ω-cm)
                                          Unfilled polymers          15 to 16

                                          Graphite-filled coatings    1 to 2
                                          Nickel-filled epoxy         0 to –2
                                          Graphite                     –3
                                          Silver-filled epoxy          –4
                                          Nickel                       –5
                                          Aluminum, copper, silver    –6


                                            TABLE 5.24  Electrical Conductivity of Reinforced
                                            Plastics: 40 Percent by Weight of Fiber

                                               Fiber    Log volume resistivity (Ω-cm)
                                             Carbon               0
                                             Aluminum            –1

                                             Brass               –2
                                             Copper              –4

                             5.2.5.8 Impermeability. Impermeability (barrier performance) is produced by plate-like
                             flakes, which increase the tortuous path that permeating molecules must seek.
                             5.2.5.9 Controlled Degradability. This has been produced by use of biodegradable fill-
                             ers such as starch powder. Once the filler has disappeared, the polymer crumbles, and the
                             high surface area accelerates oxidative and biodegradation.
                             5.2.5.10 Carbon Nanotubes. These are tiny hollow fibers made up of carbon atoms ar-
                             ranged in a hexagonal pattern, in flat sheets that roll up into seamless tubes. Diameters
                             range from 1 to 200 nm and aspect ratios up to 10,000! Their modulus, strength, and ther-
                             mal and electrical conductivity are superior to graphite and carbon fiber. Used at 1 to 5
                             percent in plastics, they provide very high modulus, strength, and thermal and electrical
                             conductivity. Processing is difficult, and cost is extremely high, but researchers are opti-
                             mistic about their future.


                             5.2.6  Technical Summary
                             The relative effects of fillers and reinforcements on plastics may be clarified by summariz-
                             ing them in tabular form (Table 5.25). In the table, (+) means an increase in the property,
                             (++) means a great increase, (–) means a decrease, (– –) means a great decrease, and (±)
                             means the effect varies depending on the specific filler, fiber, polymer, or test.





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