Heterogeneous Nucleation in Foams as Assessed by In-line Ultrasonic Measurements

Abstract

The conditions prevailing during the nucleation stage of the thermoplastic foam extrusion process in which a physical foaming agent is involved are one of the key steps in the design and optimization of the process. The conditions that induce phase separation and bubble nucleation are obviously linked to the solubility parameters, i.e., temperature and pressure at a given foaming agent content, conditions that can be probed during degassing experiments. It has been reported that adding a nucleating agent can significantly modify these degassing conditions. An in-line detection method based on ultrasonic sensors has proven to be sensitive to the onset of the phase separation. This method was used to investigate the influence of both talc and foaming agent concentrations on the nucleation cell density and degassing conditions for polystyrene-HFC-134a mixtures. A qualitative model based on foaming agent concentration gradient near the nucleating agent particles is proposed.

Keywords

thermoplastic foam nucleation talc Gibbs free energy surface tension

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References

Kieken, B. (2001). Processing and Performance of PS Foamed with HCFC-142b and HFC-134a , In: Foam Tech Meeting, June 7, 2001.

Lee, S.-T. (2000). Chapter 4: Foam Nucleation in Gas-dispersed Polymeric Systems, In: Foam Extrusion: Principles and Practice, pp. 81-124, Technomic Publishing Co., Lancaster, PA .

Chen, L. , Sheth, H. and Kim, R. (2001). Gas Absorption with Filled Polymer Systems , Polym. Eng. Sci., 41(6): 990-997 .

Areerat, S. , Hayata, Y. , Katsumoto, R , Kegasawa, T. , Egami, H. and Ohshima, M. (2002). Solubility of Carbon Dioxide in Polyethylene/Titanium Dioxide Composite under High Pressure and Temperature , J. Appl. Polym. Sci., 86(2): 282-288 .

Throne, J.L. (1996). Thermoplastic Foams, Sherwood Publishers, Hinckley, OH .

Ramesh, N.S. , Rasmussen, D.H. and Campbell, G.A. (1994). The Heterogeneous Nucleation of Microcellular Foams Assisted by the Survival of Microvoids in Polymer Containing Low Glass Transition Temperature Particles. Part I: Mathematical Modeling and Numerical Simulation , Polym. Eng. Sci., 34(22): 1685-1706 .

Lee, S.-T. (1993). Shear Effects on Thermoplastic Foam Nucleation , Polym. Eng. Sci., 33(7): pp. 418-422 .

Rodrigue, D. and Ryan, R. (2003). The Effect of Nucleating Agents on Polypropylene Foam Morphology , In: Proceedings of the Fifth International Conference on Blowing Agents and Foaming Processes, May 19-20, 2003, Munich, Germany, pp. 169-178 .

Chen, L. , Straff, R. and Wang, X. (2001). Effect of Filler Size on Cell Nucleation During Foaming Process , In: Proceedings of SPE Antec 2001, Dallas, TX, pp. 1732-1736 .

10.

Tatibouët, J. , Gendron, R. , Hamel, A. and Sahnoune, A. (2002). Effect of Different Nucleating Agents on the Degassing Conditions as Measured by Ultrasonic Sensors , J. Cell. Plas., 38(3): 203-218 .

11.

Sato, Y. , Iketani, T. , Takishima, S. and Masuoka, H. (2000). Solubility of Hydrofluorocarbon (HFC-134a, HFC-152a) and Hydrochlorofluorocarbon (HCFC-142b) Blowing Agents in Polystyrene , Polym. Eng. Sci., 40(6): 1369-1375 .

12.

Tatibouët, J. and Gendron, R. (2004). A Study of Stain-induced Nucleation in Thermoplastic Foam Extrusion , J. Cell. Plas., 40(1): 27-44 .

13.

Goel, S.K. and Beckman, E.J. (1994). Generation of Microcellular Polymeric Foams Using Supercritical Carbon Dioxide I: Effect of Pressure and Temperature on Nucleation , Polym. Eng. Sci., 34(14): 1137-1147 .

14.

Park, C.B. , Cheung, L.K. and Song, S.-W. (1998). The Effect of Talc on Cell Nucleation in Extrusion Foam Processing of Polypropylene with CO2 and Isopentane , Cell. Polym., 17(4): 221-251 .

15.

Sato, Y. , Fujiwara, K. , Takikawa, T. , Sumarno, Takishima, S. and Masuoka, H. (1999). Solubilities and Diffusion Coefficients of Carbon Dioxide and Nitrogen in Polypropylene, High-density Polyethylene, and Polystyrene under High Pressures and Temperatures , Fl. Phase Equil., 162(1-2): 261-276 .

16.

Metzner, A.B. (1985). Rheology of Suspensions in Polymeric Liquids , J. Rheol., 29(6): 739-775 .

17.

Gendron, R. , Caron, L.M. , Rohn, C. and Correa, A. (1999). On-Line Rheometry in Thermoplastic Foam Processes: Effect of Additives on the Viscosity , In: AIChE’s 1999 Spring National Meeting, Paper 73f, Houston, Texas, March 14-18, 1999.

18.

Reignier, J. , Favis, B.D. and Heuzey, M.-C. (2003). Factors Influencing Encapsulation Behavior in Composite Droplet-type Polymer Blends , Polymer, 44(1): 49-59 .

19.

Reignier, J. and Favis, B.D. (2003). On the Presence of a Critical Shell Volume Fraction Leading to Pseudo-pure Droplet Behavior in Composite Droplet Polymer Blends , Polymer, 44(18): 5061-5066 .

20.

Yildirim, I. (2001). Surface Free Energy Characterization of Powders, PhD Thesis, Virginia Polytechnic Institute and State University.

21.

Jaeger, P.T. , Eggers, R. and Baumgartl, H. (2002). Interfacial Properties of High Viscous Liquid in a Supercritical Carbon Dioxide Atmosphere , J. Supercrit. Fluids, 24(3): 203-217 .

22.

Ruengphrathuengsuka, W. (1992). Bubble Nucleation and Growth Dynamics in Polymer Melts, PhD Thesis, Texas A&M University.

23.

Seth, M. , Hatzikiriakos, S.G. and Clere, T.M. (2002). Gross Melt Fracture Elimination: The Role of Surface Energy of Boron Nitride Powders , Poly. Eng. Sci., 42(4): 743-752 .

24.

Jones, R.A.L. and Richards, R.W. (1999). Chapter 5: Adsorption and Surface Segregation From Polymer Solutions and Mixtures, In: Polymers at Surfaces and Interfaces, pp. 187-243, Cambridge University Press, Cambridge, U.K .

25.

Tatibouët, J. , Gendron, R. and Haïder, L. (2004). Ultrasonic Characterization Performed during Chemical Foaming of Cross-linked Polyolefins , Polym. Test., 23(2): 125-130 .