Foaming process

Additives have the same effect on thermoplastic foaming processes as on thermoset foaming processes. Environmental conditions are important in this case because of the necessity of removing heat from the foamed stmcture in order to stabilize it. The dimensions and size of the foamed stmcture are important for the same reason. 

For passenger car seating about 90% is made by the molded foam process. The transportation market has expedenced a decline since 1979 due to decreased automotive production and also because U.S. cars have been downsized, resulting in the use of less polyurethane foam per car. 

Process and Equipment. Rigid polyurethane foam processes use the same high or low pressure pumping, metering, and mixing equipment as earher described for flexible foams. Subsequent handling of the mixture is deterrnined by the end product desired. 

USM Foam Process, Technical Bulletin No. 655-A, Farrel Co. Division, Ansonia, Conn. 

Dow Eatex Foam Process, buUetin, The Dow Chemical Co., Midland, Mich. 

Foam spray dryiag coasists of forcing gas, usuaHy air or nitrogea, iato the product stream at 1.38 MPa (200 psi) ahead of the pump ia the normal spray dryer circuit. This method improves some of the characteristics of dried milk, such as dispersibHity, bulk deasity, and uniformity. The foam—spray dryer can accept a condensed product with 60% total soHds, as compared to 50% without the foam process. The usual neutralization of acid whey is avoided with the foam—spray dryer (see Drying Foams Sprays). 

A rather strange but nevertheless large-scale application of U-F resins is in the manufacture of firelighters, made by a modification of the foam process. The resin solution is blended with a small amount of detergent and then whisked with paraffin. A hardener is added and the resin allowed to set. In effect the product is a U-F foam saturated with paraffin. 

When an engineering plastic is used with the structural foam process, the material produced exhibits behavior that is easily predictable over a large range of temperatures. Its stress-strain curve shows a significantly linearly elastic region like other Hookean materials, up to its proportional limit. However, since thermoplastics are viscoelastic in nature, their properties are dependent on time, temperature, and the strain rate. The ratio of stress and strain is linear at low strain levels of 1 to 2%, and standard elastic design... 

Generate or release gases into selected areas of the fluid polymers (used almost exclusively to control foaming processes). 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

Most slabstock foams are open-celled, that is, the walls around each cell are incomplete. Towards the end of the foaming process, the polymer migrates from the membranes between cells to the cell struts, which results in a porous structure. In some cases, cells near the surface of the foam collapse to form a continuous skin, which may be trimmed off later. 

Figure 9.24 shows temperature-reduced plots of 2d, Nc and 5 versus Tf + ATg. All the data conform well to a reduced curve like Figure 9.23. Interestingly, when the authors used both Tg and the melting temperature (Tm) [61] depressions to conduct superposition, they recognized that the reduced curve is nicely constructed but there is no significant difference compare with the case of Tf+ ATg. This indicates that Tg depression is important in optimizing foam processing conditions but Tm depression is not a significant factor for processing because the Tf range is still below Tm after C02 saturation.

To confirm the heterogeneous nucleation and the nanocellular feature in the foam processing, TEM observation of the cell wall in the PLA/MMT-ODA foam was conducted. 

Takada, M. (2004) PhD Thesis, Crystallization control and foam processing of semi-crystalline... 

Polyurethane foam processing, 19 559 Polyurethane hydrogels, 13 739 Polyurethane industry, neopentyl glycol in, 12 672... 

Blowing Agents and Foaming Processes. Proceedings of a conference held Stuttgart, Germany, lOth-llth May 2005. 

BLOWING AGENTS AND FOAMING PROCESSES CONFERENCE 2001. Proceedings from a conference held Frankfurt, 13th-14th March 2001. 

The other foaming process is referred to as the prepolymer method. The monomers are reacted to form a low molecular-weight prepolymer. Later the prepolymer is mixed with small amounts of water and is heated. The water reacts with the free isocyanate groups to liberate carbon dioxide, which foams the polyurethane as cross-linking starts. 

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