Extrusion processes ultrasound

Influence of Ultrasound on the Channels of the Forming Head in Extrusion Processes... 

To harness the full potential of amorphous systems for all types of chemical compounds, alternate technologies are constantly being added to the toolbox. Ultrasonic-assisted compaction is a modified tabletting process that can provide heat, pressure, and shear due to ultrasonic energy to the powder mixture during compaction. The application of ultrasound to solubility enhancement is based on the fusion method and in some ways mimics the extrusion process (Fini et al. 1997 Sancin et al. 1999). The ultrasonic frequency vibration is applied at the same time as compaction force. The key features of the technology include ... 

ULTRASOUND ASSISTED SINGLE SCREW EXTRUSION PROCESS FOR DISPERSION OF... 

CONTINUOUS DISPERSION OF CARBON NANOTUBES IN POLYMERS USING ULTRASOUND ASSISTED EXTRUSION PROCESS... 

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22], A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofdler in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24]. 

To our knowledge, there has been no work done to improve the dispersion of carbon nanotubes in polyimide matrix with the help of ultrasound assisted extrusion process. 

P.D. Coates, S.E. Barnes, M.G. Sibley, E.C. Brown, H.G.M. Edwards and I.J. Scowen, In-process vibrational spectroscopy and ultrasound measurements in polymer melt extrusion. Polymer, 44, 5937-5949 (2003). 

Coates, P.D. Barnes, S.E. Sibley, M.G. Brown, E.C. Edwards, FEG.M. Scowen, I.J. In-Process Vibrational Spectroscopy and Ultrasound Measurements in Polymer Melt Extrusion Polymer 2003, 44, 5937-5949. 

Ultrasound can be scaled up to large volumes in batch or continuous flow systems. It can also be combined with an extruder, where it speeds up extrusion and allows the processing of polymers of higher molecular weight that may have improved tensile strength. It is a technique that deserves to be used more often, for it can often save money by reducing reaction times. 

Mathematical description of the process of polymer melting in the extrusion channel is complex when ultrasound is used. The description requires firstly, consideration of the mass flow of the polymer, knowledge of the flow characteristics of the melt, the temperature and pressure of extrusion, sizes of the channel and frequency of ultrasonic oscillations. Secondly, coefficient of swelling of the extrudate, effective viscosity of polymer, pressure of melt, and frequency of oscillations. 

Based on these results we investigated different methods for the formation of water droplets in the organic phase. The emulsions were generated by extrusion from syringes through capillaries or a thin brass disk with narrow pores in the low micrometer range. In addition, sonication with ultrasound, electrospray and a microemulsion system were analyzed in term of droplet size and stability for the phase transfer process. In all these experiments, we used different techniques to generate water droplets with various sizes and encapsulated compounds. 

The ultrasonic treatment of PET/LCP blends leads to improvements in the mechanical properties of the homopolymers and some blends. The increase in the viscosity and mechanical properties of neat PET and LCP, as well as some of their blends at certain amplitudes, points toward homo- and copolymerization. The increase in viscosity of PET after ultrasonic treatment is attributed to possible esterification reaction. The presence of hairy structures on the surface of LCP droplets in the core region of 90/10 PET/LCP blends after ultrasonic treatment at an amplitude of 7.5 otm illustrates the improved adhesion between the PET and LCP phases, and possible copolymer formation under the action of ultrasound. Low residence times in the ultrasonic zone and energy saving due to reduced pressure render ultrasonic extrusion a viable method for the compatibilization of thermoplastic polymer/thermotropic LCP blends. Further refinement of processing conditions could allow one to achieve greater enhancements in the performance of LCP, and its blends with PET. 

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. 

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