Blowing agents costs

Although carbon dioxide liberated from chemical blowing agents costs about 10 times that purchased in cylinders, the former offers advantages of simplicity of addition of powder or masterbatch pellets at the hopper. Overall, for wood-like and similar extrusions, conventional single screw extruders can be used, as for solid extrusions. 

Research and development programs have been initiated by the cellular plastics industry to develop viable substitute blowing agents. These must have similar or improved properties to their CFC counterparts at a reasonable cost. Emphasis was initially placed on HCFC 123 and HCFC 141b, both having much shorter lifetimes and considerably less effect (up to 50 times) on o2one layer depletion (22). However, various options, including gas mixtures, water, or CO2 blown foams, continue to be studied ultimately to eliminate all CFCs and HCFCs. 

The tank is typically about sixteen inches in diameter and about four to five feet tall. The top of the tank is domed upward and the bottom of the tank is also domed upward in a concave manner. The outside of the tank is insulated with a polyurethane foam insulation that is squirted into the gap between the tank and a thinner sheet metal jacket. The polyurethane is made of two different components that react and harden when mixed. Included in the mixture is a blowing agent that causes the polyurethane to expand in a foam-like manner. Prior to about 1980, water heaters were insulated with fiberglass insulation. The foam insulation process was developed to allow automation and increased manufacturing speed and reduced costs. A side benefit was improved insulating ability leading to a slight increase in efficiency. 

HCFCs. Alternative blowing agents for CFCs, for the time being, are HCFCs (hydrochlorofluorocarbons) as shown in Table 7A, in which HCFC-141b is the most feasible alternative blowing agent for CFC-11. However, HCFCs also have problems, i.e., higher costs, and a small ozone-depletion potential, and therefore, HCFCs are also expected to be phased out by 2020. 

The reasons for this Include such things as reduced density to lower cost, Increased ease of mold filling, and Improved part surface apppearance. The microcellular structure which makes these benefits realizable Is achieved by nucleatlon, either with a gas such as air or nitrogen, or by Incorporating a blowing agent In the system formulation. An IMR agent must, therefore, not affect the cell structure or the stability of the nucleated froth It must... 

A suitable blowing agent should have low toxicity, low odor, low flammability, low corrosiveness, low molecular weight, high specific gravity, non-VOC (photochemical reactivity not greater than that of ethane), low ODP, low GWP, and low cost. 

Some of the important factors to consider in the development of alternative physical blowing agents are solubility, permeability, boiling point, vapor pressure, flammability, toxicity, VOC, ODP, GWP, availability, and cost. Similarly, the key important factors to be considered in the selection of CBAs for a given polymer are decomposition temperature, gas yield, rate of gas release, environmentally acceptable decomposition products, toxicity, and dispersability in the polymer matrix. 

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