Preparing Nanocomposites with a Three Roll Mill - Nanoparticle Dispersion

The strong tendency for nanoparticles to form clumps and clusters (“agglomerates”) is a serious technological problem that impedes the effective use of nanoparticles in many applications. For example, the nanoclay aggregates (as large as 10μm) could result in reduction of strength in nanoclay/epoxy composites.

Three roll milling is a dispersion technique that employs both shear flow and extensional flow created by rotating rolls of different speed to mix and disperse CNT, CNF, Graphene, or other nanoscale particles into polymers or other viscous matrixes. It is a very appealing process that benefits the environment by eliminating the solvent. Three roll mill is an extremely effective dispersion tool for nanocomposites containing fiber-like filler such as carbon fiber, glass fiber, carbon nanotube etc. Because of the powerful shear force, the mixer can reach a higher degree of intercalation/exfoliation within a short period of time.

Example - Nanocomposites with Carbon Nanotubes

Polymer matrix nanocomposites with filler such as carbon fiber, fiber glass or other polymer fibers render high mechanical properties, high electrical conductivity, high electrostatic discharge, high electromagnetic interference, and high thermal conductivity, with which the regular polymer can’t provide. Carbon nanotubes have high mechanical properties from their high aspect ration, high electrical conductivity, high thermal conductivity, and high thermal stability. By adding carbon nanotube into the polymer, it is potential to improve the polymer matrix in terms of solvent resistance, stiffness, glass transition temperature (Tg) and reduce thermal shrinkage. However, it requires a high loading (about 10 to 25 wt%) and a good dispersion to reach the desired polymer properties. The smooth sidewall surface of carbon nanotube, that is incompatible with most solvents.

The most commonly employed methods to disperse CNT include ball milling, ultrasonication, and three roll milling.

To obtain narrow length and diameter distributions of CNTs and to open the nanotubes for improved sorption capacity for gases, ball-milling is a very useful method. However, it has also been observed that a large amount of amorphous carbon is created which clearly indicates that the tubes are damaged in different ways and that ball milling is a destructive method.

Ultrasonication is a very effective method of dispersion and deagglomeration of CNTs, as ultrasonic waves of high-intensity ultrasound generates cavitation in liquids. However, cavitation, the formation and implosion of bubbles, can also damage the CNT structure. A study showed hardness deteriorated after sonication for greater than 10 minutes.

In comparison, due to the powerful shearing forces of the three roll mill, the dispersion of the agglomerates for the carbon nanotubes is ideal. The carbon nanotubes remain undamaged and the requisite high aspect ratio (length to diameter) is retained. The surface area of the carbon nanotubes wet by epoxy resin continues to grow. As a result, the viscosity rises steadily from 10 cPoise to as much as 100.000 cPoise.

Another unique advantage of this technique is that the gap width between the rollers can be mechanically or hydraulically adjusted and maintained, thus it is easy to obtain a controllable and narrow size distribution of particles in viscous materials. In some operations, the width of gaps can be decreased gradually to achieve the desired level of particle dispersion.

Nanotechnology Three Roll Mill Specifications

Parameter T65 Nano Mill T65B Nano Mill
Diameter of Roller 2.5” (65mm) 2.5" (65mm)
Length of Roller 5.0” (127mm) 10" (254mm)
Roller Speed Ratio (Fixed) 1:2:4 1:2:4
Speed of Roller
RPM
Slow Roller 0~108 0~108
Mid Roller 0~216 0~216
Fast Roller 0~432 0~432
Motor Power 3/4HP / .55kW 3/4HP / .55kW
Weight 165 lbs (75kg) 175 lbs (80kg)
Dimensions 25”x11”x15”
(635mmx280mm
x381mm)
30"x11"x15" (770mmx280mm
x381mm)
Throughput Up to 20 L/h Up to 45 L/h
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Safety Features

  • Large mushroom style red emergency stop button
  • Emergency pull cord
  • VFD enabled wash-up operation mode
  • Nip guard