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

2. 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.

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

4. 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

5. 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

6. 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

7. 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.

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

9. 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

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

11. Influence of ultrasound waves on various foaming conditions

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

13. 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

14. (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.

15. 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.

16. 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

17. 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.

18. Comparison of morphologyb d c
(a,b)Conventional foams (c,d) Auxetic foams

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

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

21. 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

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

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

24. Simulation-modeling of wave fronts in ultrasonic tank

25. Simulation study on cell wall rupturing mechanics under ultrasound waves

26. Modeling of cavitation flow through the tortuous path in porous foams

27. Thank You
Questions ?????