Nitrogen, foaming process

The matrix polymer morphology of a collection of LDPE foams manufactured from a high-pressure nitrogen solution process was analysed at different length scales. 

EFFECT OF CELL SIZE ON THE PHYSICAL PROPERTIES OF CROSSLINKED CLOSED CELL POLYETHYLENE FOAMS PRODUCED BY A HIGH PRESSURE NITROGEN SOLUTION PROCESS... 

The thermal conductivity, thermal expansion, mechanical properties at low strain rates and dynamic mechanical properties of a collection of crosslinked closed cell PE foams manufactured by a high pressure nitrogen solution process were studied as a function of the cell size. The... 

Properties of peroxide cross-linked polyethylene foams manufactured by a nitrogen solution process, were examined for thermal conductivity, cellular structure and matrix polymer morphology. Theoretical models were used to determine the relative contributions of each heat transfer mechanism to the total thermal conductivity. Thermal radiation was found to contribute some 22-34% of the total and this was related to the foam s mean cell structure and the presence of any carbon black filler. There was no clear trend of thermal conductivity with density, but mainly by cell size. 27 refs. 

Atlanta, Ga., 26th-30th April 1998, p. 1842-9. 012 PRODUCT AND PROCESS DEVELOPMENTS IN THE NITROGEN AUTOCLAVE PROCESS FOR POLYOLEFIN FOAM MANUFACTURE Eaves D E Witten N Zotefoams pic (SPE)... 

A review is presented of the nitrogen autoclave process for the manufacture of crosslinked polyolefin foams. Process and product developments over the last few years are summarised and future possibilities are described. Process developments include use of higher temperatures and pressures to produce foams having densities as low as 10 kg/cub.m. Product developments include foams based on HDPE/LDPE blends, propylene copolymers and metallocene-catalysed ethylene copolymers. The structure and properties of these foams are compared with those of foams produced by alternative processes. 5 refs. 

The applicability of the Gibson and Ashby approach, whereby deformation mechanisms are identified, to a range of thermoplastic polymer foams is explored. LDPE, EVA and PP foams were produced by the BXL Plastizote nitrogen expansion process. A full range of mechanical properties is discussed from the simpler aspects of modulus and strength to the complexities of creep and recovery performance. 8 refs. 

RIM elastomers as well as structural foams processed often include the dispersion of insoluble gas (air or nitrogen) in the form of small bubbles into the polyol component. This action results in nucleation. It is used to improve the flowability of chemical and to improve the cell structure of the final product. Improved flowability makes the melt flow more laminar and increases the throughput via a very fine pattern of cells all through the molded product. 

One observes that the tertiary nitrogen atoms in the polyol structure shown in Figure 4.39 have bulky substituents (the polyoxyalkylene chains with equivalent weight of around 1700-2000 daltons). This fact explains the modest catalytic activity in the foaming process. 

Conventional single-screw extruders may be used for the foaming process, but premature decomposition of the CBA, which causes a loss of nitrogen through the feed throat, is difficult to avoid. The object is to reach the decomposition temperature in the metering section of the screw and allow the nitrogen to go into solution... 

Because the surfactants described previously were selected for hydrocarbon-miscible flooding, the effect of hydrocarbon solvent on foam performance should be included in the surfactant screening process. Data on the characteristics of foams generated with light hydrocarbons as the gas phase are not readily available in the literature. Limited data comparing nitrogen foams with hydrocarbon solvent foams are shown in Table... 

FIGURE 2.61 Structural foam process, (a) Filling the accumulator. The blowing agent (usually nitrogen) is injected into the melt in the extruder before it is passed into the accumulator, (b) Filling the mold. The accumulator ram injects the melt into the mold where the reduced pressure allows the gas to foam the resin. 

FIGURE 49.9 Schematic representation of foaming process (1) dissolution of gas into polymer, (2) cell nucleation, (3) cell growth and expansion, and (4) SEM of hydroxypropyl methyl cellulose acetate succinate (HPMCAS) extrudate foamed with nitrogen gas. 

Techniques for continuous foaming processes for FEP and PFA have been described in this section, primarily based on the technical bulletins published by the DuPont Company. In this example a coaxial cable (RG-62) was coated ] and jacketed to meet the requirements of the military specifications MIL C-17/30B. The blowing agent was F-22 (CF2HCI) which has now been replaced by ozone-safe gases such as nitrogen. Table 11.19 lists the requirements of the RG-62 cable according to specifications. Wind-... 

Fig. 1 Micrographs of foams produced from a high-pressure nitrogen solution process, b compression molding process, c and d semicontinuous process, crosslinking by irradiation (micrographs of the same sample in two perpendicular directions)...

Fig. 6 Examples of cell shapes of closed-cell LDPE foams of a 18kg/m and b 30kg/m density produced by a high-pressure nitrogen solution process...

The WAG process has been used extensively in the field, particularly in supercritical CO2 injection, with considerable success (22,157,158). However, a method to further reduce the viscosity of injected gas or supercritical fluid is desired. One means of increasing the viscosity of CO2 is through the use of supercritical C02-soluble polymers and other additives (159). The use of surfactants to form low mobihty foams or supercritical CO2 dispersions within the formation has received more attention (160—162). Foam has also been used to reduce mobihty of hydrocarbon gases and nitrogen. The behavior of foam in porous media has been the subject of extensive study (4). X-ray computerized tomographic analysis of core floods indicate that addition of 500 ppm of an alcohol ethoxyglycerylsulfonate increased volumetric sweep efficiency substantially over that obtained in a WAG process (156). 

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