Influence of Ultrasonic Excitations on Polymeric Foam Processing Prof. Naresh Bhatnagar Department of Mechanical Engineering Indian Institute of Technology, Delhi

The Power of Ultrasound The sound waves having frequencies above the audible range i.e. above 20000Hz are called ultrasonic waves During the last 20 years we have witnessed an amazing increase in the application of ultrasonic energy in diverse fields of science and technology. In this presentation, Influence of Ultrasound waves on foaming processes has been discussed.

Cavitation phenomenon Jet formation during collapse of cavitation bubble Formation of micro-jet Ultrasound waves may develop extreme conditions in a very localized area.

Brief background Selective foaming for biomedical applications Ultrasound assisted extrusion foaming : Developed porous structure Improved elastic modulus and strength Uniform morphology SEM image of porous PMMA foams developed

Ultrasound exposure after foaming in solid-state foaming process SEM image (a) before sonication (b) post sonication Experimental setup Ultrasound settings were found very significant in developing porous foams

Ultrasound exposure during solid-state foaming process Microcellular Polystyrene foams (a) with sonication (b)without sonication Microcellular Polylactic acid foams developed with ultrasound exposure treatment revealed : Uniformity Less cell size High cell density

Research in Indian Institute of Technology, Delhi Developing porous solid-state microcellular foams using ultrasound. Developing high cell density microcellular foams using ultrasound. Continuous manufacturing of porous thermoplastic sheets using ultrasound waves. A method to control Negative Poisson’s Ratio in Auxetic foams using ultrasound waves.

Ultrasound assisted cyclic solid-state foaming for fabricating ultra-low density porous ABS foams** Process description Micrographs of ABS microcellular foams (a)200 (b) 2000. (a)P1=3 Mpa and (b) P1=6 Mpa. ** Published in Materials Letters 2013

Effect of cyclic foaming on developed microstructure Effect of cyclic foaming on developed microstructure.(a) (i) Molded sample (solid),(ii)1st foaming and (iii)2nd foaming. (b)P1=3 Mpa and (c) P1=3 Mpa,P2=3 Mpa Effect of ultrasonic irradiation on cell morphology. (a) Closed cell and (b)Ruptured ,interconnected cell

Ultrasound assisted cell nucleation in microcellular foaming process (b) Sorption-desorption curves of ABS-CO2 (a) Without ultrasound exposure (b) with ultrasound exposure

Influence of ultrasound waves on various foaming conditions

(a) (b) (d) (c) Influence of length of ultrasound exposure on morphology; 2 seconds (b) 5 seconds (c) 7 seconds (d) 10 seconds

Influence of ultrasound frequency on foam microstructure (a) Foam developed with 25 KHz frequency (b) foam developed with 45 KHz Note : The bi-modal type of morphology developed with 45 KHz frequency

(c) Continuous manufacturing of porous thermoplastic sheets using ultrasound waves Nitrogen gas was used as physical blowing agent Flexible LDPE porous foams were successfully developed through this study Permeability test results with various die temperature and screw RPMs.

Lichtenberg Acoustic Figure Dendritic acoustic pattern was observed in the push-pull ultrasonic transducer. This cavitation cloud bombards on the foam surface to rupture the closed cells Influence of ultrasound waves on foam surface. Note : Small openings appear on the foam surface due to the cavitation erosion phenomenon.

Influence of ultrasound on Auxetic foams Auxetic foams are novel class of materials which expands on extension while contracts under compression loading. Manufacturing process of Auxetic foams

Influence of processing time on morphology 10 minutes 15 minutes 20 minutes Note : The cell wall buckling phenomenon increases with the increment in processing time.

Comparison of morphology b d c (a,b)Conventional foams (c,d) Auxetic foams

Mechanics of NPR extension though ultrasound waves Conventional foams Auxetic foams Sonication Auxetic foams Mechanics of NPR extension though ultrasound waves

Sonicated Auxetic foams Influence of Sonication on Poisson’s ratio Auxetic foams Sonicated Auxetic foams

Ultrasound significantly enhances the properties and uniformity in morphological attributes, due to which a momentous research work is expected in this field in the coming years. Future research work

Influence of Ultrasound medium Aluminum foil erosion test De-Ionized water Tap water

Studying the wave distribution inside the ultrasonic tank It shows the spatial wave distribution following node-antinode pattern

Simulation-modeling of wave fronts in ultrasonic tank

Simulation study on cell wall rupturing mechanics under ultrasound waves

Modeling of cavitation flow through the tortuous path in porous foams

Thank You Questions ?????