SAMPE Journal - May/June 2011 - 40

improve ablative properties of carbon phenolic nanocomposites. High shear mixing has proved to provide good dispersion and exfoliation of nanoparticles12,13. Therefore, this dispersion technique was used to blend MWNT into phenolic resin. The mixer was used with water cooling systems. Tap water was constantly circulated thorough the double walls of mixing chamber and hopper to avoid overheating of the mixer and resins. Figure 8 displays cooling lines on the high shear mixer. The motor frequency and mixing time were 40 Hz (shear rate of 76,906 s-1) and 25 min, respectively. The temperature of the resin and the mixing chamber was constantly monitored with IR thermometer. The temperature was maintained below 50ºC. Phenolic resin was mixed in batches with MWNT in three different proportions: 1, 2, and 3% by weight. Figure 7. Four thermocouples were attached to the back of specimens. Temperature Measurements Front and back side temperatures were measured during thermal testing. The heat panel was first heated for 15 min. Then, the specimen was attached on the steel stand. Specimen was placed at 15 cm from radiant heat source to experience a heat flux of 15 kW/m211. Four thermocouples were taped to the back side of specimens; two in the middle and two on the sides (Figure 7). Thermocouples were attached between the composite specimen and the steel sample holder. Temperatures were recorded at each second for 20 min of exposure using a four channel data-logger thermometer. An infrared (IR) pyrometer was used to record the front side temperatures of the specimens during testing. The pyrometer was held in the fixed position with a fixed angle to the specimens. The specimens were placed in exact same position to avoid errors occurring from positioning of the IR pyrometer at an angle. There was no smoke generated on the surface of the specimens during the testing, which could affect readings. The experimental setup is shown in Figure 6. Introduction of MWNT to Phenolic Resin Multi-walled carbon nanotubes (MWNTs) were used to High Shear Technique High shear mixing is a very effective technique to disperse solid nanoparticles in liquid polymer resins. Koo and coworkers have successfully used high-shear mixing techniques to incorporate carbon nanotubes, layered silicates, nanosilicas, carbon nanofibers, and POSS to form polymer nanostructured materials in several of their research programs14. Layered silicates and carbon nanofiber, and POSS were incorporated separately into resole phenolic using high-shear, non-sparking paint mixing equipment to form different polymer nanocomposites1,6. High Shear Mixer (IKA® Labor Pilot 2000/4) with a DR module was used in this research. It is 3-stage disperser for application with high shear requirements. It has 3 generators (stator and rotor together are known as generator), 2 medium and 1 fine. The motor speed is controlled using digital controller by changing motor frequencies. Shaft speed depends on the belt drive that connects motor and shaft. According to manufacturer’s data, the radial (grinding) gap between stator and rotor is fixed to 0.2 mm. The diameter of rotor (D) was 57 mm. Shaft speed determines the shear rate. The rotational speed of shaft was measured with tachometer at different motor frequencies to calculate the real ratio of drive and shaft. More details about this mixer could be found in previous report by Tate et al.15.

Figure 8. High shear mixer with cooling jackets - tap water runs through the double walls and drained.
40 SAMPE Journal, Volume 47, No. 3, May/June 2011

SAMPE Journal - May/June 2011

Table of Contents for the Digital Edition of SAMPE Journal - May/June 2011