Open cell PU foam

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... 

Some General Properties of Open Cell PU Foams for Vacuum Insulated Panels... 

This chapter will focus on the open cell PU foams, even though many general aspects and recent developments of the technology, dealing with films, getters and manufacturing processes, can be also applied, with minor changes, to other micro porous fillers. 

In the case of the open cell PU foams detailed expressions for the first two terms of Equation (1) have been given by Kodama and co-workers [9j. 

Dimensional stability tests carried out on open cell PU foam-filled vacuum panels showed that creep problems should not occur for properly prepared panels, provided the open cell foam preparation has been optimised [15]. 

Selected physical properties of some open cell PU foams are listed in Table 4.1. 

Table 4.1 Some physical properties of open cell PU foams ...

To fully exploit the insulating performances of the open cell PU foams, pressure in the panel has to be kept preferably below 1.0 Pa during its life. To achieve this demanding target, the foam must be 100% open celled and with a very low outgassing rate. 

In spite of the increasing use of open cell PU foam, data from the literature on its vacuum properties are quite scarce. 

Before being used in a vacuum panel, the open cell PU foam needs a preliminary heat treatment in air, generally carried ont at 120-150 °C for 10-60 minutes to remove water and other volatile species which otherwise would desorb and rapidly cause the vacuum to deteriorate. The result of a typical outgassing test carried out at 23 °C on a foam sample baked at 120 °C for 30 minutes is shown in Figure 4.4 for all desorbed gases but water. Water is difficult to quantify since it sticks to the walls of the system and only partially reaches the mass spectrometer. Water can be estimated as the difference between the total absolute pressure and the sum of the partial pressures of the other gas species, which can be accurately quantified with the mass spectrometer. 

Figure 4.4 Outgassing rate for an open cell PU foam. Water is not shown.

Results shown in Figure 4.4 and Table 4.2 can vary from sample to sample depending on the open cell PU foam preparation technique, its microstructure and density and the pre-treatment. 

An additional factor which may have an impact on the vacuum properties is the closed cell content of the PU foam. All the open cell PU foams so far presented in the literature for VIP applications are quoted to be 100% open cell based on pycnometric measurement. On the other hand, the accuracy of this test method is generally close to 0.2% [15], so that the possibility of a small fraction of closed cells cannot be completely ruled out and has to be considered as an additional potential source of pressure build-up in the panel. 

In general, for household appliances, depending on the surface coverage of the cabinet and the panel thickness, energy savings from 10% to 30% have been reported using open cell PU foam-filled panels packaged in a 6 pm aluminium foil-based barrier [12, 15, 52, 56]. 

Bezazi, A. and Scarpa, F. Tensile fatigue of conventional and negative Poisson s ratio open cell PU foams. Int. J. Fatigue 31, 2009, 488 94. 

Strandfoam, developed by Dow, is said to be an easy to shape polyolefin foam consisting of thousands of joined strands of foam. The structure is said to improve cushioning and insulation properties and may replace some open cell PU applications. The process is briefly described and utilises ethylene-acrylic acid in a PE carrier. DOW EUROPE SA... 

To overcome some of the drawbacks associated with the use of these materials, new families of fillers, based on PU [9, 10, 11, 12] and, more recently, polystyrene (PS) [13] open cell foams, have been developed and proposed to the market. Both open cell PU and polystyrene foams are now being considered as interesting options due to their moderate outgassing, good thermal insulation values, low weight, ease of handling and cost effectiveness. 

The open cell PU cores are produced according to various preparation technologies, such as lamination and block foaming. In both cases, after the foam has been grown, a cutting operation is usually necessary to remove the outer skin of the material, which... 

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

PU foam stabilizers PU foam cell openers Defoamer oils Emulsifiers... 

Figure 2.4 shows the remaining fragments of a cell window after cell opening as foimd in the fully cured foam. It is very obvious that the opening of a flexible PU foam is not a... 

As shown by Equations (1-5), the insulation properties of an open cell foam depend on a complicated interplay of different parameters such as the PU thermal conductivity, foam density, cell size and cell size distribution, cell morphology and anisotropy, which have to be optimised during the foam preparation to obtain the best trade-off among the three thermal conductivity contributions, and... 

A different approach to making open cell foam slabs has been proposed recently [11], which is based on the use of the PU fluff obtained from the recycling of used refrigerators (Recycled Urethane Fluff, or RUF panel). 

The same company has developed a new generation of highly flame resistant open cell flexible PU/CR hybrid foam materials. The polyurethane and chloroprene are prepared using a brand-new technology called Foam-One. This is a batch process for making flexible slabstock under variable pressure that may range from 1 psi to 25 psi. PU base foams are post-treated with a polychloroprene compound to obtain the hybrid grades. 

Insulation (noise and seismic vibrations), sonor foams Laminates of rubber (mostly natural/chloroprene), polyphenylene oxide (PPO, UF foams, open cell foams of PU, PIR, PS... 

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