Twin-roll mill compounders

Ko-kneader improved the PHRRs compared to those with the corresponding twin-roll mill compounding (Figure 7.11). 

Compound mixing was performed on different compounding equipment. For EVA organoclay-based nanocomposites, a laboratory twin-roll mill and an internal mixer heated to 145 °C were used. A corotating twin screw extruder from Leistritz, Germany, with a 27-mm screw diameter and an aspect ration of 40 L/D was used to generate polyethylene nanocomposites. The mass temperature was 190 °C at the extruder die. 

Information on the nanocomposite morphology was obtained by transmission electron microscopy (TEM) and x-ray diffraction (XRD) observation. Compounding was done on a twin-roll mill, and exfoliated silicate sheets were observed together with small stacks of intercalated sheets." This structure may be described as a semi-intercalated semi-exfoliated structure that did not change principally with the vinyl acetate content of the EVA matrix, even a larger number of stacks were observed for EVA with lower vinyl acetate contents." There were no great differences within the morphology of these nanocomposites. 

FIGURE 7.10 Heat release rates for compounds made by twin-roll mill with various filler blends of MWCNTs and organoclays. Heat flux = 35 kW/m. (From Ref. 62, copyright 2005, John Wiley Sons, Ltd. with permission.)... 

The final quality and reproducibility of rubber compounds mixed from scratch on a two-roll mill, or finalisation of compound batches mixed in an internal mixer, depend to a large degree on the skill of the mill operative. In order to overcome to some extent the reliance on operative skill and to ensure reproducible mix quality many mills are now fitted with stock blender units. These consist of a driven twin roller system, of similar overall length to the mill rolls, fitted above the mill frame. 

The first mixer was an annular container with a spiked rotor for rubber compounding [Hancock, 1823]. The calender/two roll mill was patented by Chaffe in 1836 and manufactured by Parrel Co. A counter rotating twin shaft internal mixer with elliptical rotating discs or sigma-blades was developed by the end of the last century [Freyburger, 1876 Pfleiderer, 1880]. The first hand-operated extruder was a ram press, used for forming NR or GP, then later NC. 

The first mixer was an annular container with a spiked rotor for rubber compounding (Hancock 1823). The calendar/two-roll mill was patented by Chaffe in 1836 and manufactured by Farrel Co. A counterrotating twin-shaft internal mixer... 

There are a number of types of compounding equipment that can potentially carry out the compounding of fillers with polymers. Compounding has traditionally been carried out on two-roll mills, internal mixers and nowadays single and twin screw extruders. The extruders are being increasingly adopted as a means of giving a consistent product in a readily usable form, i.e. pellet or sheet. 

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