Foamed free rise

Examples of foaming characteristics of resol-type phenolic foams (free-rise) are shown in Table 64 in comparison with rigid urethane foam (3). Rise-profile curves, foaming-pressure curves and temperature curves for phenolic and polyurethane foams are shown in Figure 61. 

Several manufacturiag processes can be used to produce phenohc foams (59,79) continuous production of free-rising foam for slabs and slab stock similar to that for polyurethane foam (61,80) foam-ia-place batch process (61,81) sandwich paneling (63,82,83) and sprayiag (70,84). 

Box Foa.ms. A measured quantity of the reaction mixture can be placed ia an open-topped crate or box and allowed to foam ia a free rise mode. The block is removed after gelling and is cut iato end use pieces after curiag. 

Place Arcol Polyol F-3022 (100 g, 0.1 eq., 56 OH, mixed PO/EO triol from Bayer) into a suitable container. To this add distilled water (3.3 g, 0.4125 eq.), Niax Silicone L-620 (0.5 g, a silicone surfactant from OSi Specialties), and Niax C-183 (0.12 g, an amine catalyst from OSi Specialties). Thoroughly blend this mixture without incorporating air bubbles. Then add Dabco T-9 (0.25 g, stannous octoate from Air Products) and mix again. The T-9 must be added last because it is quite water sensitive, so its exposure to the water-containing polyol blend should be kept to a minimum. To this polyol blend, quickly add Mondur TD-80 (42.6 g, 0.4868 eq., a mixture of 80% 2,4-TDI and 20% 2,6-TDI isomers from Bayer) and immediately stir at 3000 rpm for 5 s. Quickly pour the reaction mixture into a suitable container such as a 1-qt paper or plastic cup and allow the foam to free-rise. The stir blade may be wiped or brushed clean. 

Here, the case of free rise in an open mold is analyzed. Because of the very low thermal conductivity of a plastic foam, an adiabatic process will be considered. The nonadiabatic case in a closed mold leads to integral-skin foams. These foams exhibit a mass density gradient, with unfoamed skins in contact with the mold walls (Marciano et al., 1986). 

A variety of formulations and their modifications are used for producing slabstock urethane foams. The formulation variations are based on available raw materials, foam properties required, product costs and production processes. Examples of formulations for producing free-rise slabstock foam are shown in Tables 16 and 17. A comprehensive list of slabstock formulations has been prepared by Iwata and his co-workers (191). The list is shown in Table 18. 

Comparative tests between free-rise urethane and pyranyl foams indicate that the total pressures obtained are similar, but that the rate of pressure build-up and pressure dissipation are faster with the pyranyl systems. This property allows short jig-dweU times. Freezer cabinets varying in storage capacity from 7 to 30 ft, have been insulated completely satisfactorily with pyranyl foam (1). 

Table 64 Foaming Characteristics of Free-Rise Foams (3)...

PU foams were prepared by the one-shot, free-rlse method. A homogeneous liquid mixture consisting of Nlax 31-28, Isonol-100, silicone surfactant DC-193 (Dow Corning), T-12, Nlax A-1 (Union Carbide), trlchlorofluoromethane (Freon llA, E.I. duPont de Nemours Co.), and water was mixed thoroughly with Isonate-143L. It was put Into a cold mold and allowed to free rise. 

Two-component IPN foams consisting of polyurethane and epoxy were prepared by the one-shot, free-rise method. The effects of PU/E ratio on the sound absorption and mechanical energy attenuation characteristics were determined with varying levels of different fillers and plasticizers. The formulations (Table IX) were based on the best elastomer results. An average of over 90X absorption was obtained at high frequencies by the Impedance tube method. However, this average drops dramatically at low frequencies. This reduction may be seen in Figs. 3 and 4 for 90/10 and 70/30 IPN foams vlth 20X... 

Foam Rise Profile. At the end-of-mixing, formulations are poured into a one or two-gallon open-topped container and free rise foaming is measured. The rise profile and rate of foam rise has been measured with a Fluidyne System (4., 5). Foam rise and rate of rise as functions of time after the end-of-mixing are received as graphical output from the Fluidyne System. 

The continuous evolution of carbon dioxide from water-blown foam from the earliest times of reaction is a mechanism for significant heat loss from free-rise foam, the magnitude of which will depend on the scale of foaming. This observation offers an explanation for the departure from adiabaticity, lower than expected maximum reaction temperature, in smaller scale foaming. 

It is also interesting to note that inside the tube a significant orientation exists. Long cylindrical cells (tunnels) parallel to the flow axis can be observed rather than the usual dodecahedra commonly found in free-rise foams. Moreover, the pattern of Plate 1 indicates appreciable shear sensitivity of the cell structure to exist at the wall where most shearing has occurred the largest cell defects are found. 

The polyether most used in practice for continuous free rise slabstock flexible PU foams are the triols, copolyethers PO-EO, containing around 10-15% EO randomly distributed (most used 10-12% EO), of MW in the range of 3000-3600 daltons (OH = 42-60 mg KOH/g). 

FIGURE 2.71 Schematic of a free-rise process for manufacture of glass-reinforced foam laminates. 

For each formulation evaluated, free rise cup foams (see Section 1.2.2.1) were poured to determine reactivities and foam shrinkage. Data recorded were gel time, full rise time and final height. The free rise cup foams were tested for final heights and free rise density after 24 hours. Height measurements were carried out using a Mitutoyo height gauge. All experimental formulations reported in this work were matched by rise profile to each control formulation. 

The machine mix free rise reactivity comparison of all formulations are shown in Tables 1.4 and 1.5. This experimental data illustrates that the overall free rise foam reactivity for both the cushion and hack formulations remains relatively the same for the beginning of the reaction. The full rise reactivities in cushion formulations II, IE and IV and back formulations VII and VIII start to deviate slightly from the control reference formulations I and V. 

The free-rise density was calculated by dividing the mass of the foam in the cup, with the capacity of the cup as shown in Equation (1) ... 

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