Particle foams

Polyurethane is pulverized to iacrease its bulk density, mixed with 30—80% of a thermoplastic mol ding material, gelled, and then granulated to give coated urethane foam particles 0.1 to 0.15 mm in size (48). The particle bulk density is three times that of the polyurethane, while the volume is 15% less. This material may be injection molded or extmsion molded into products (49). Other technologies for recycling polyurethanes have also been reported. 

Patent Number US 6150427 A1 20001121 2000 FOAMING PROPYLENE COPOLYMER, AND FOAMED PARTICLES AND FOAMS THEREOF... 

Patent Number US 5747549 A 19980505 FOAMED PARTICLES OF POLYPROPYLENE HOMOPOLYMER AND MOULDED ARTICLE OF THE FOAMED PARTICLES... 

Patent Number EP 823443 A2 19980211 FOAMED PARTICLES OF MODIFIED POLYPROPYLENE RESIN AND METHOD OF PREPARING SAME... 

Patent Number US 5391581 A 19950221 PRODUCTION METHOD OF FOAMED PARTICLES OF UNCROSSLINKED ETHYLENE-BASED RESIN... 

Most food products and food preparations are colloids. They are typically multicomponent and multiphase systems consisting of colloidal species of different kinds, shapes, and sizes and different phases. Ice cream, for example, is a combination of emulsions, foams, particles, and gels since it consists of a frozen aqueous phase containing fat droplets, ice crystals, and very small air pockets (microvoids). Salad dressing, special sauce, and the like are complicated emulsions and may contain small surfactant clusters known as micelles (Chapter 8). The dimensions of the particles in these entities usually cover a rather broad spectrum, ranging from nanometers (typical micellar units) to micrometers (emulsion droplets) or millimeters (foams). Food products may also contain macromolecules (such as proteins) and gels formed from other food particles aggregated by adsorbed protein molecules. The texture (how a food feels to touch or in the mouth) depends on the structure of the food. 

Tokoro, H. Tsurugai, K. Shioya, S. Oikawa, M. Flame-retardant foamed particles of polyolefin resin. PCT US Patent 5,569,681 assigned to JSP Corporation, 1996. 

Nussinovitch, A., Cohen, G., and Peleg, M. (1991). Comparison of the compressive characteristies of puffed popcorn and polystyrene foam particles. J. Cell. Plast., 27, 527-539. 

Polyurethane is a very common crosslinked polymer and many materials produced from it end up as waste. Given the quantity of material, recycling is a major problem. Cryogenic pulverization systems have been developed which can process PU foam to particles smaller than 1 mm (preferably <100 pm)/ " These particles are homogenized with polyol and then reacted with isocyanates to produce foam. This foam with 5% pulverized PU foam has a density equivalent to a similar foam produced without the recycled material. A further increase in filler content causes a density increase. Pulverized PU foam particles were also tried as a filler in natural rubber vulcanizates with good results. Figure 12.10 shows the effect of PU... 

Efficient immobilization of C. pubescens cells is possible in a semirigid matrix of polyurethane foam particles (107,162). The influence of immobilization on alkaloid production has not been studied. 

In the formation of polymer colloid particles in the size region of 1 pm, de-wetting of the particles can also occur as the monomer is used up and the surface tension of the aqueous phase rises adsorption of the particles at the air-water interface in this case can lead to a particle-stabilized foam. Particles of this sort can also be spread on a Langmuir trough and will form a hexagonally close-packed monolayer [76]. 

To date, the autoclaving process has been the one most frequently used to produce foam particles, in particular EPP (expanded polypropylene). In the autoclaving process, a suspension of compact polypropylene microgranulate and a liquid is placed under a pressurized atmosphere with inert gas and blowing agent while... 

Fig. 23 Schematic technical diagram extrusion of foam particles (altered according to Berstorff)...

In the process, 50 % of the blowing agent remains in the foam particle. The fresh beads can then be further processed 1 day to 1 week after prefoaming (expanding). 

Water steam is used as the energy carrier in the molding process. The steam heats up and melts the foam particles inside the forming mold. Mold walls permeable to steam and air are necessary to expose the beads inside the cavity to the steam at all. The mold is located inside a steam chamber, split into two halves like the mold to facilitate ejection by an opening stroke. 

The production of molded articles made of particle foams such as expanded polypropylene (EPP) or expanded polystyrene (EPS, also known under the brand name Styropore) is carried out by welding individual foam particles together into a formed part or molding. In the conventional steam chest molding process the source of energy used is steam, which heats and welds the foam particles in the mold into a formed part (Fig. 15). 

Supercritical C02-assisted extrusion applications mainly involve polymer blending, microcellular foaming, particle production, and reactive extrusion. Of course, supercritical CO2 can also be used as an interfacial agent, foaming agent, or plasticizer in other appUcations. 

Suprasec 1042 Suprasec 1249 Suprasec DND Suprasec DNR Hexacal F Hexacal SN Hexacal LN 2-7 Low viscosity polymeric MDI. Low density rigid foams. Semi-rigid foams. Isocyanurate foams. Particle binders. Insulating foams. Energy absorbing foams. Isocyanurate foam building panels. Mine-face consolidation. Chipboard and foundry sand binders. 

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