Twin-screw extrusion, stability

Such machines are particularly suitable when there is a requirement for compounding as well as extrusion—as with unplasticized PVC. If compounding and extrusion of the formulation can be carried out in series, so that it is not necessary to heat it twice, the quantity of heat stabilizer added can be reduced. For reasons such as this the manufacture of unplasticized PVC pipe has become a typical use for twin-screw units. 

The tremendous growth of rigid PVC markets, especially of pipe and profiles, coupled with the increasing use of low-shear multiscrew extruders permitting lower stabilizer levels, prompted the development of lower-cost mixed metal barium/ butyltin or calcium/butyltin stabilizer systems, which provided adequate processing stability for most low-cost, twin-screw extrusion formulations. Many of these, however, could not be run well on single-screw extruders, thus limiting their versatility. 

This work presents a novel method for the continuous dispersion of carbon nanotubes in a polymer matrix. Ultrasound assisted twin screw extrusion of polyetherimide (PEI)/MWNT has been carried out. PEI was chosen because of its extensive use in composites for aerospace applications due to its desirable combination of mechanical and thermal properties. They have outstanding dimensional and thermo-oxidative stability with desired processability required for space applications. The effects of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties were studied. 

Optically transparent nanocomposites were prepared via twin-screw extrusion of a medical-grade flexible PVC resin and an organically modified montmorillonite. Intercalation and orientation of the montmorillonite layers were observed via x-ray diflfaction. A positive influence on barrier properties was noted, ineluding a five-fold increase in oxygen barrier at minimal clay loading. Consistent with the literature, no significant changes in thermal stability in air were observed. 

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