Microcellular foaming

Patel, S.V. Venditti, R. A. and Pawlak, J. J. (2010). "Dimensional changes of starch microcellular foam during the exchange of water with ethanol and subsequent drying," BioResources, 5,121. 

In practical application, it was reported that the platinum particles dispersed in highly porous carbonized polyacrylonitrile (PAN) microcellular foam used as fuel-cell electrocatalyst160 have the partially active property. The fractal dimension of the platinum particles was determined to be smaller than 2.0 by using the potentiostatic current transient technique in oxygen-saturated solutions, and it was considered to be a reaction dimension, indicating that not all of the platinum particle surface sites are accessible to the incoming oxygen molecules. 

Ramesh, N. S., Rasmussen, D. H., and Campbell, G. A., The Heterogeneous Nucleation of Microcellular Foams Assisted by the Survival of Microvoids in Polymers Containing Low Glass Transition Particles. Part 1 Mathematical Modeling and Numerical Simulation, Polym. Eng. ScL, 34, 1685 (1994)... 

Olefins or alkenes are defined as unsaturated aliphatic hydrocarbons. Ethylene and propylene are the main monomers for polyolefin foams, but dienes such as polyisoprene should also be included. The copolymers of ethylene and propylene (PP) will be included, but not polyvinyl chloride (PVC), which is usually treated as a separate polymer class. The majority of these foams have densities <100 kg m, and their microstructure consists of closed, polygonal cells with thin faces (Figure la). The review will not consider structural foam injection mouldings of PP, which have solid skins and cores of density in the range 400 to 700 kg m, and have distinct production methods and properties (456). The microstructure of these foams consists of isolated gas bubbles, often elongated by the flow of thermoplastic. However, elastomeric and microcellular foams of relative density in the range 0.3 to 0.5, which also have isolated spherical bubbles (Figure lb), will be included. The relative density of a foam is defined as the foam density divided by the polymer density. It is the inverse of the expansion ratio . 

Table 2 Die dimensions and residence time for microcellular foam extrusion ...

STUDY OF SHEAR NUCLEATION THEORY IN CONTINUOUS MICROCELLULAR FOAM EXTRUSION... 

A theoretical analysis based on shear energy was carried out with the aim of illustrating the mechanism of shear nucleation through a slit channel die in continuous microcellular foam extrusion. The shear energies for different positions and for different experimental conditions were calculated to demonstrate the various contributions to the surface free energy required for bubble nucleation. 14 refs. 

Journal of Applied Polymer Science 88, No. 12, 20th June 2003, p.2842-50 MICROCELLULAR FOAM OF POLYMER BLENDS OF HDPE/PP AND THEIR COMPOSITES WITH WOOD FIBER Rachtanapun P SeUce S E M Matuana L M Michigan,State University... 

Journal of Injection Molding Technology 5,No.3, Sept.2001,p.l52-9 MICROCELLULAR FOAM PROCESSING IN RECIPROCATING-SCREW INJECTION MOLDING MACHINES Jingyi Xu Pierick D Trexel Inc. 

An overview is presented of TrexeTs MuCell microcellular foam extrasion technology and a description is given of its application to the manufacture of thermoformable PP sheet. The results of pilot scale thermoforming trials carried ont to optimise forming conditions and obtain data abont potential cycle time effects, measurements of the densities, flexnral modnlns and wall thicknesses of the sheets and containers made from the sheets and cell stmcture analysis are presented and discussed. 

A study on the batch processing and characterisation of microcellular foamed HDPE/isotactic PP blends is reported. The blends were used to produce materials with a variety of crystaUine and phase morphologies to enhance the subsequent microcellular foaming. Much finer and more uniform foams were produced with the blends than with neat HDPE and isotactic PP. The mechanical... 

Journal of Vinyl and Additive Technology 2, No.2, June 1996, p.167-9 MICROCELLULAR FOAMING OF POLYPROPYLENE CONTAINING LOW GLASS TRANSITION RUBBER PARTICLES IN AN INJECTION MOULDING PROCESS Chicheng Wang Cox K Campbell G A Clarkson University... 

Boston, Ma., 7th-llth May 1995, p.2183-8. 012 EFFECT OF MORPHOLOGY ON MICROCELLULAR FOAMING OF SEMICRYSTALLINE POLYMERS Doroudiani S Park C B Kortschot M T Cheung L K Toronto,University (SPE)... 

Atlanta,18-21 April 1988,p.719-22. 012 PRODUCTION OF MICROCELLULAR FOAMS IN SEMICRYSTALLINE THERMOPLASTICS... 

Difficulties in producing microcellular foams from semicrystalline polymers are discussed and nucleation... 

MAKING MICROCELLULAR FOAMS FROM CRYSTALLINE POLYMERS... 

Materials. Supercritical fluids offer many opportunities in materials processing, such as crystallization, recrystallization, comminution, fiber formation, blend formation, and microcellular (foam) formation. 

Microcellular foams can be obtained by flash spinning and are usually prepared at relatively high polymer concentrations in the spinning solution, i.e., at least 40% synthetic fiber-forming polyolefin. 

Relatively low spinning temperatures and pressures that are above the cloud-point pressure can be used. Microcellular foam fibers may be obtained rather than plexifilaments, even at spinning pressures slightly below the cloud-point pressure of the solution. 

By crosslinking, the viscosity of EVA at high temperatures is increased and the individual cells are kept in a stable condition without rupture or agglomeration. A low density microcellular foam can be thus obtained. By selecting the vinyl acetate content, the EVA foam is flexible and highly resilient with easy coloring and adherent to other materials. The application is used widely in shoe soles, sandals and cushion materials. 

Microcellular foaming, bimodal cell size distributions, and high open-celled contents of molecular composites of HT-polymers were reported by Sun et al. [33], investigating blends of a rod-like polymer polybenzimidazole with an aminated PSU and poly(phenyl sulfone) by using carbon dioxide as a blowing agent. The complex foaming behavior was related to phase separation within the otherwise... 

Siripurapu S, Gay YJ, Royer JR, DeSimone JM, Spontak RJ, Khan SA (2002) Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process. Polymer 43 5511-5520... 

Huang HX, Wang JK (2007) Improving polypropylene microcellular foaming through blending and the addition of nano-clacium carbonate. J Appl Polym Sci 106 505-513... 

Rachtanapun P, Selke SEM, Matuana LM (2003) Microcellular foam of polymer blends of HDPE/PP and their composites with wood fiber. J Appl Polym Sci 88 2842-2850... 

Ramesh NS, Rasmussen DH, Campbell GA (1994) The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass-transition particles. 1. Mathematical-modeling and numerical-simulation. Polym Eng Sci 34 1685-1697... 

Sun HL, Mark JE, Tan SC, Venkatasubramanian N, Houtz MD, Arnold FE, Lee CYC (2005) Microcellular foams from some high-performance composites. Polymer 46 6623-6632... 

Tan SC, Bai Z, Sun H, Mark JE, Arnold FE, Lee CYC (2003) Processing of microcellular foams from polybenzobisthiazole/polyetherketoneketone molecular composites. J Mater Sci 38 4013-4019... 

Microcellular foams can be produced by thermally induced phase separation (TIPS) [47, 74, 76], The induced spinodal decomposition can be optimized to generate, e.g., polylactide scaffolds with the porous morphology and physicomechanical characteristics of a foam. Interesting materials can be constructed in a simple process. These materials exhibited bundles of channels with a diameter of 400 pm. The internal walls of the tubular macropores have a porous substructure with pore diameters of " 10 pm. It appears to be remarkable that the channels have a preferential... 

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