Closed cell foam

Clamping plate Closed-cell foam Cohesion Cold flow... 

Closed-cell foam Cellular plastic that is composed predominantly of noninterconnecting cells. 

During construction, all possible penetrations between the crawlspace and the house should be sealed to simply prevent the passage of radon up into the living areas. Attempts to seal penetrations can be made by using expandable closed-cell foam sealants and urethane caulk. Sealing these areas can be difficult because of limited access even during construction. Areas of particular concern include9... 

Poly(aryloxyphosphazene) elastomers can be cured with peroxides, sulfur and radiation. The resulting vulcanizates are resistant to attack by moisture and oils and have been found to have desirable characteristics for electrical insulation applications where fire safety is a concern (Table II) (12). Fire resistant, low smoke, closed cell foams with excellent properties (Table III) have also been developed from poly(aryloxyphosphazene) elastomers (13). Applications for these foams, which can be produced as either slabstock or tube stock, are being developed for military, aerospace and commercial uses. (See Table II and III.)... 

Gibov et al. (9) showed that combustion vapors and air could penetrate through a typical char layer. Capillarity served to bring molten polymer to the surface where it could pyrolyze and burn. One answer to this problem is obviously to create a closed cell foam. Gibov et al. showed that the incorporation of boric acid and ammonium phosphate helped minimize penetrability of the char (Fig. 1). 

Japon, S., Leterrier, Y. and Manson, J.-A. E., Recycling of polyethylene terephthalate) into closed-cell foams, Polym. Eng. Sci., 40, 1942 (2000). 

Pre-expansion a steam flow heats the beads of EPS, which are expanded to about 40 times their original size by the boiling of the pentane. Thus, a closed-cell foam is formed. 

Under pressure in a closed mould during gelation. After cooling and demoulding, the expanded parts are re-heated (post-expansion) to obtain closed-cell foams such as life jackets. 

Foams are commercially produced several ways. Some polymerization processes produce their own foam. Polyurethanes, for example, are very exothermic. When they are formed, if a little water is present, CO2 will be a by-product. As the polymer forms, the CO2 will cause closed cell foam. As another example, a blowing agent can be injected into the molten polymer. The agent will later decompose, giving off a gas when the polymer is heated to melting. Epoxy resins are expanded into foams this way. 

Model (redrawn from a.5) of the cell air and the polymer stmcture acting in parallel in a compressed closed-cell foam... 

For closed cell foams Gibson and Ashby predict three contributions to the Young s modulus of the foam ... 

Micromechanics theories for closed cell foams are less well advanced for than those for open cell foams. The elastic moduli of the closed-cell Kelvin foam were obtained by Finite Element Analysis (FEA) by Kraynik and co-workers (a. 14), and the high strain compressive response predicted by Mills and Zhu (a. 15). The Young s moduli predicted by the Kraynik model, which assumes the cell faces remain flat, lie above the experimental data (Figure 7), while those predicted by the Mills and Zhu model, which assumes that inplane compressive stresses will buckle faces, lie beneath the data. The experimental data is closer to the Mills and Zhu model at low densities, but closer to the Kraynik theory at high foam densities. 

Simone and Gibson (a. 16) predicted the effect of wrinkled cell faces (in aluminium closed cell foams), on the Young s modulus, by FEA of a modified Kelvin... 

The faces in low density LDPE foams are partly buckled or wrinkled, as a result of processing (a.l7). This affects both the bulk modulus and the Young s modulus. The foam bulk modulus Kp is predicted, using the Kelvin closed cell foam model, to be ... 

When a closed cell foam is uniaxially compressed, it can be assumed that the compressive stress is a sum of the stresses taken by the polymer structure and that taken by the cell gas. For a foam with zero lateral expansion when uniaxially compressed, and isothermal gas compression, the latter contribution (Tg is given by (295) ... 

Mills and Gilchrist (270) analysed the heat transfer that occurs when closed cell foams are subjected to impact, to predict the effect on the uniaxial compression stress-strain curve. Transient heat conduction from the hot compressed gas to the cell walls occurs on the 10 ms... 

At strains >10%, when the polymer structure has begun to collapse, gas loss, by diffusion through the cell faces of closed cell foams, may contribute to the creep. The effect of this on the creep of LDPE and EVA foams was determined (266). The foam diffusivity for air was predicted from the polymer permeability P and the foam density p using ... 

Impact-resistant foam liners used in helmets and other protective gear are usually not breathable unless air passages are fabricated in them. Brock USA has developed a process for moulding closed-cell foam that permits three-dimensional air flow and moisture evaporation... 

Becanse there are many factors involved in the dynamic mechanical compression of polyolefin foams, the Taguchi method was employed in a Perkin Elmer DM A7 dynamic mechanical analyser to establish a method to improve the measurement process. The signal-to-noise ratio was measured to determine how the variability could be improved. Control and noise factors were evaluated and levels chosen, with details being tabulated. Appendix A describes some of the factors. Tests were conducted on two closed cell foams. NA2006 foam is 48 kg/cu m LDPE and NEE3306 foam is 32 kg/cu m EVA. Different factors were shown to influence results for E and tan delta but an optimum combination is proposed for the simultaneous measurement of both properties. The results were less variable as frequency was increased. Small differences in the dynamic response of different materials should be measurable because of the low variability in the experimental results. 18 refs. 

Cellular Polymers IV. Conference proceedings.. Shawbury, 5th-6th June, 1997, paper 15. 6124 DEFORMATION MECHANISMS EM LDPE CLOSED CELL FOAMS... 

Closed-cell foams made from metallocene-based polyolefins (MPO) have potential for use in various applications because of their uniform composition and low toxicity. Compressive stress relaxation is used to investigate the behaviour of these foams. In particular, its behaviour is compared with open-cell PU foams, a material MPO foams could possibly replace. The effect of gamma radiation on MPO foam behaviour is also... 

A study was made of the impact and recovery behaviour of three HDPE closed-cell foams with varying densities. Impact stress-strain curves were measured using a falling striker impact rig and the recovery monitored from 10s after the impact. Cell deformation was observed during compression and recovery using SEM. Recovery was found to occur by the viscoelastic straightening of the buckled faces and to be incomplete due to plastic deformation in the structure. 6 refs. 

Dow Plastics is to unveil a new resilient polyolefin foam, Strandfoam, which offers packagers of lightweight electronic equipment and components reduced package size, and savings in materials and shipping costs. Strandfoam is made of a special blend of PE and is produced by a proprietary extrusion process that yields fused strands of closed-cell foam with a network of air channels parallel to the foam strands. Strandfoam provides the required levels of protection with substantially smaller volumes of foam compared to urethane. 

Cebo UK snpply a closed-cell foamed PP seaweed, called Cegrass, which is designed to protect pipeline installations and other snbsea equipment. The artificial seaweed... 

What are the advantages of open-celled foams and how do they differ from closed-cell foams ... 

Foamed Explosives for Floating Mine. An invention fcy Stark (Ref 1) provides a floating mine which consists of an expl having a closed-cell foam structure of greater and more shattering effect than die same wt of high density expl. Buoyancies of these expls are of 20 to 50 lbs per cu ft. The foamed expls consists of HE s (such as TNT, NC, PETN or RDX) bonded by a thennosetting resin Ref H,J. Stark, USP 2845025(1958) Ordo 43, 662(Jan-Feb 1959)... 

This chapter introduces readers to the versatility of polyurethane polymers without spending too much time on the chemistry. The next chapter will discuss a more classical view of the molecule and how it is developed. Our point, however, is to present a functional view of this system. We have examined its physical characteristics, focusing our attention on the uniqueness of reticulated foams. All the chemical points we have made apply to all polyurethane polymers, whether they are open-celled foams, closed-cell foams, or thermoplastic elastomers. 

We prefer an alternative model. The expansion of the foam doubtless takes place in a high-viscosity environment. Expansion of the individual cells and a corresponding increase in foam volume continue until the transition from liquid flow to gelation. At this point, the windows between the cells are stretched beyond their elastic limit and therefore burst instead of continuing to flow. Examination of a closed-cell foam shows that the windows do indeed rupture as opposed to opening through viscous flow. 

Extruded low density foam produced I nim I.DI E is a tough, flexible, and resilient closed-celled foam used in a wide variety of applications such as cushion packaging and safety components. 

The aryloxyphoxphazene polymers, on Ihe other hand, have been used primarily in wire and cable coalings and pickets and as fire-resistant, low smoke, closed-cell foams and sound-harrier sheets. 

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