Foam materials

Therefore, to deform the foam material at this stage, considerable energy, represented by the area under the a versus e curve in the stress-strain graph in Fig. 4.5, must be used. Collapse of the foam material due to flexure of the walls finally leads to their compaction. Young s modulus therefore increases, and further increases in deformation now require a considerable increase in stress leading to fracture. 

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Foam controllers Foamed lonomers Foamed materials Foamed plastic Foamed plastics... 

Plastic Foam Materials and Koofinginsulation, 1983—1989, Peter Sherwood Associates, Inc., White Plaias, N.Y., Apr. 1984 KoofingJ Siding Insul 61, 82 (Oct. 1984). 

Finishes Thermal insulations require an external covering (finish) to provide protection against entry of water or process fluids, mechanical damage, and ultraviolet degradation of foamed materials. In some cases the finish can reduce the flame-spread rating and/or provide fire protection. 

Glass-reinforced grades have widely replaced metals in pumps and other functional parts in washing equipment and central heating systems. In the manufacture of business machine and computer housings structural foam materials have found some use. Mouldings weighing as much as 50 kg have been reported. 

There has also been particular interest in a rigid foam material for use in aerospace, shipbuilding and medical appliances. 

Whilst initial development was primarily in the fields of fibres and rubbers, the presence of polyurethanes at about sixth position in the production league tables is largely due to the widespread use of foam materials. By 1980 global consumption was of the order of 3 X 10 tonnes per annum. 

Much effort has been expended to try and produce flat-top foams. In one process polyethylene sheets placed along the side-walls of the trough rise with the foam. In another technique the reactants are metered from the mixing head into a fixed trough in which partial expansion takes place. The foaming material is then drawn over a weir by a moving band of paper and then drawn down a slope so that the top surface maintains a constant level as the material expands. 

Example 2.9 A solid polyethylene beam is 10 mm thick and IS mm wide. If it is to be replaced with a sandwich section with solid polyethylene in the two outer skins and polyethylene foam (density = 200 kg/m ) in the centre, calculate the dimensions of the sandwich beam if it is to have optimum stiffness at the same weight as the solid beam. If the foam material costs 20% more than the solid material, calculate the increase or decrease in cost of the sandwich beam. 

Compare the flexural stiffness to weight ratios for the following three plastic beams, (a) a solid beam of depth 12 nun, (b) a beam of foamed material 12 mm thick and (c) a composite beam consisting of an 8 mm thick foamed core sandwiched between two solid skin layers 2 mm thick. The ratio of densities of the solid and foamed material is 1.5. (hint consider unit width and unit length of beam). 

Foaming materials should be operated at 0.1-0.25 in. water/ft, or better, obtain data. Actual AP/ft may run 2-5 times chart values. 

Successful development of such systems will lead to foamed materials having useful stress-absorbing characteristics in addition to controlled physics properties. Although our work in this area is currently in a very early stage, prototype materials have been successfully synthesized and assessed structurally using three-dimensional (3D) X-ray microtomography. The technique offers a unique insight into the internal microstructure of cellular materials (see Fig. 3). The diameter of the mainly open cell pores varies from approximately 100 to 250 pm (the resolution of the instrument is 5 pm), with cell walls of variable thickness. 

The extent of bleeding in a plastic is evaluated with a test known as the sandwich method. The test sample is placed between a white, smooth surface of plasticized PVC on the top and a standardized sheet of filter paper underneath. The resulting sandwich is then placed between layers of foam material, which in turn are covered by glass plates. The resulting sandwich is allowed to remain in an exposure chamber at 50°C for 72 hours [48]. 

Incorporated in plasticized PVC, P.B.15, like other phthalocyanine pigments, is usually entirely fast to migration. Moreover, it provides excellent lightfastness. P.B.15 also finds use in various types of PUR foam materials as well as in rubber. Its redder and frequently cleaner shade compared to corresponding stabilized types makes it an equally useful pigment for other media. This applies especially for water-based systems. Textile printing, paper mass coloration, paper surface treatment, and paper pulp are areas of application as suitable for the use of P.B.15 as office articles, including colored pencils, blackboard chalks for schools, and water colors. 

P.B.15 1 is also applied in polystyrene, polyamide, polycarbonate (in which it is heat stable up to 340°C), PUR foam materials, and cast resins. It should be noted, however, that the hardening of cast resins which are based on unsaturated polyesters is usually much retarded. 

P.B.15 3, like stabilized a-Copper Phthalocyanine Blue, markedly affects the hardening of unsaturated polyester cast resins. The list of applications also includes PUR foam materials, office articles, such as colored pencils, wax crayons, and water colors, as well as spin dyeing of polypropylene, polyacrylonitrile, secondary acetate, polyamide, polyester, and viscose. Used in polyester spin dyeing, P.B.15 3 satisfies the thermal requirements of the condensation process (Sec. 1.8.3.8). 1/3 and 1/25 SD samples equal step 7-8 on the Blue Scale for lightfastness. Textile fastnesses, such as stability to wet and dry crocking are perfect. 

The major issue found in testing is the corrosion of the foam material and resultant contamination of the membrane. The high manufacturing cost of the metal or carbon foam with the required pore shape, size, and distribution also is a challenge. Further study and testing of the corrosion mechanism, selection of appropriate coating, a capillary process involved in the tiny pores, and related water retention are necessary to identify whether the new material and concept can be finally applied in the plate. 

The production of foamed films and sheets from polypropylene and polystyrene is discussed, with particular reference to packaging applications. Advantages of foamed materials for this application are examined, and the chemical and physical foaming processes are described. Extrusion technology for film and sheet by chemical and physical foaming processes is discussed, and recent developments in the coextrusion of multilayer packaging trays for the food industry are considered. 

PP bead foams were subjected to oblique impacts, in which the material was compressed and sheared. This strain combination could occur when a cycle helmet hit a road surface. The results were compared with simple shear tests at low strain rates and to uniaxial compressive tests at impact strain rates. The observed shear hardening was greatest when there was no imposed density increase and practically zero when the angle of impact was less than 15 degrees. The shear hardening appeared to be a unique function of the main tensile extension ratio and was a polymer contribution, whereas the volumetric hardening was due to the isothermal compression of the cell gas. Foam material models for finite element analysis needed to be reformulated to consider the physics of the hardening mechanisms, so their predictions were reliable for foam impacts in which shear occurred. 16 refs. 

Patent Number US 5929127 A 19990727 FINE-CELLED POLYOLEFIN FOAM MATERIALS... 

The static and dynamic mechanical properties, creep recovery behaviour, thermal expansion and thermal conductivity of low-density foams made of blends of LDPE and EVA were studied as a function of the EVA content of the blends. These properties were compared with those of a foam made from a blend of EVA and ethylene-propylene rubber. A knowledge of the way in which the EVA content affects the behaviour of these blend foam materials is fundamental to obtaining a wide range of polyolefin foams, with similar density, suitable for different applications. 9 refs. 

Patent Number US 5616627 A 19970401 POLYPROPYLENE RESIN COMPOSITION, POLYPROPYLENE RESIN FOAMED MATERIAL AND PROCESS FOR PRODUCING THE SAME... 

This composition contains abont 90 to 60 pbw of a PP block copolymer and abont 10 to 40 pbw of a PE. The block copolymer contains abont 99 to 90 wt.% of a crystalline PP and abont 1 to 10 wt.% of an amorphons ethylene/alpha-olefm copolymer and has a melt flow rate of about 2 to 15 g/10 min and a die swell ratio, measured by a capillary rheometer, of at least 1.7. Foamed materials containing a fine and uniform foam are obtained from this composition. 

LDPE/EVA blend was irradiated using gamma-irradiation and then expanded by heat as a foamed material. The EVA content in the blend was optimised to form a gel. The effects of atmospheres and of irradiation dose rate were studied. The ETIR spectra of the foam revealed the oxidation level. The relations between gel fraction of LDPE/EVA blend, expansion ratio, apparent density, average cell diameter and tensile properties of the foam are discussed. 8 refs. 

A multi-layer foamed PP sheet was developed which efficiently inherits both characteristics of compounded and foamed material. Structure, manufacturing techniques, properties and applications of multi-layer foamed sheet are discussed. 3 refs. 

Sekisni Kaseihin Kogy Co. has started production of closed cell type PE foam board. The PE board has a low density cnshion effect and high heat insulation. Boards will be prodnced with thicknesses of 40,50 and 60mm in 1 metre widths for packaging, shock absorption and moistnre barrier uses. The company is already producing PS and PU foamed materials. This abstract includes all the information contained in the original article. 

A piece of the polymer (about 1 g) is placed in a 500 ml beaker, containing boiling water. At this temperature, the polystyrene softens and is foamed by the vaporizing pentane. The test piece is held below the surface of the water for 5 min with the aid of a piece of bent wire and is then removed.The foamed material obtained in this manner is dipped into a graduated cylinder, containing methanol, in order to determine its approximate volume it is also weighed after drying in a vacuum desiccator.The density is found to be below 0.1 g/cm (cf.,cork has a density of 0.2 g/cm ). 

As previously mentioned, the homogeneity of foamed materials and the proportion of open and closed cells can be influenced by additives such as emulsifiers and stabilizers. Emulsifiers (e.g., sodium, potassium, or zinc salts of long-chain fatty acids) cause a uniform distribution of water in the reaction mixture, ensuring homogeneous foaming, while stabilizers (certain silicone oils) prevent a breakdown of the cell structure at the beginning of the reaction and also act as pore regulators. 

In the case of foaming materials, the distillation must be carefully watched. Additional antifoaming agents can be used, but they will be coextracted and may cover some sample volatiles on the GC profile. Their use is not recommended. 

Fibrous and Foamed Materials. Most sound-absorbing materials are fibrous or porous and are easily penetrated by sound waves. Air particles excited by sound eneigy move rapidly to and fro within the material and mb against the fibers or porous material. The frictional forces developed dissipate some of the sound eneigy by converting it into heat. 

Syntactic foamed materials are classified as foamed plastics because they are formally similar in structure to cellular gas-expanded plastics in that they are heterophase, gas-solid systems. In general, however, they differ from ordinary foamed plastics in that they are not binary but tertiary systems because the filler and binder are made usually from different materials 3 5). 

It is interesting to note that microspheres were originally developed as a means of creating a floating layer to decrease the evaporation (by 90%) of oil and petroleum in tankers and large containers, and to increase the buoyancy of ships and submarines U). They are still used for this purpose, but most microspheres are now used in the manufacture of syntactic foamed materials. 

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