Ian Robert Shankland

Blowing Agents: The Next Generation

The most promising long term replacements for the HCFC blowing agents are likely to be the HFCs. Although other chemicals such as fluoroethers are feasible, much less is known concerning their toxicological and chemical stability properties. Amongst the HFCs two general options are possible: liquid blowing agents and gaseous blowing agents. Gaseous HFCs which are already commercially available or are likely to become available in the near future include HFCs 152a, 134a, 32, 125 and 143a. These gases are not as efficient thermal insulators as HCFC-141b or HCFC-22. Nor are they as soluble in polyols on a theoretical substitution basis as HCFC-22, which may have some effect on foam processing characteristics. Although a large number of HFC liquids are known, many of them are impractical because of high molecular weights or are flammable

CFC alternatives for thermal insulation foams

Abstract Low density polymeric foam material expanded with chlorofluorocarbon (CFC) blowing agents have found widespread use as highly efficient thermal insulation materials in the construction, refrigeration appliance and transportation industries. The advent of regulations which are reducing the production and consumption of the fully halogenated CFCs for environmental reasons has prompted the development of environmentally acceptable substitutes for the CFC blowing agents. This paper summarizes the physical properties and performance of the leading alternatives for CFC-11, which is used to expand rigid polyurethane and polyisocyanurate foams, and the leading alternatives for CFC-12 which is used to expand extruded polystyrene board foam. Although the alternatives, HCFC-123 and HCFC-141b for CFC-11 and HCFC-142b and HCFC-124 for CFC-12, are not perfect matches from the performance viewpoint, they represent the optimum choice given the constraints on environmental acceptability, toxicity, flammability and performance.

Evaluation of Next Generation Blowing Agents

As we move toward final phaseout of chlorofluorocarbon blowing agents, new compounds and technologies are emerging to produce the polyurethane foams essential to so many products. In considering zero-ozone-depleting compounds that are currently available, the potential hydrofluorocarbon (HFC) candidates are gases at ambient conditions. Development programs are under way to understand feasibility and demonstrate use of one candidate, HFC-134a, to replace CFC-11. This paper summarizes basic data developed to support commercial process conversion from CFC-11 to HFC-134a. Topics include a comparison of physical properties, results of vapor pressure and solubility studies with different polyols, effects of different surfactants on HFC-134a solubility, confirmation of product stability in foaming applications, B-side system viscosity effects, and materials-of-construction compatibility data. With respect to processing, the paper summarizes experience developed in modifying equipment to handle higher B-side mixing and storage pressures, and discusses effects of process settings on foam quality.

A Performance Evaluation of Environmentally Acceptable Foam Blowing Agents

ecently proposed global and U.S. domestic regulations governing Rthe production and consumption of fully halogenated chlorofluorocarbons (CFC’s) will impact the use of these substances in all areas of application, including the foam industry. The largest CFC application within the foam industry is the use of CFC-11 (CCLF) as an expansion agent for flexible and rigid polyurethane foams as well as polyisocyanurate foams; published market studies [1] also indicate that this particular application is the single largest market for CFC-11. In the case of rigid polyurethane/polyisocyanurate foams, CFC-11 has been the blowing agent of choice because it possesses many of the desirable characteristics of an ideal blowing agent. With planned regulations limiting the future availability of CFC-11, fluorocarbon suppliers and the polyurethane foam insulation industry are actively pursuing the development of environmentally acceptable substitutes for CFC-11.

Measurement of Gas Diffusion in Closed-Cell Foams

The aging process in closed-cell thermal insulation foams refers to that phenomenon which results in a degradation of insulation value of the foam over a period of time and is generally attributed to diffusion of atmospheric components into the foam and diffusion of expansion agent out of the foam. In this paper an apparatus is described for measuring the effective or apparent diffusion coefficient of atmospheric and other rapidly permeating gases in closed-cell polymeric foams. The technique is based on a solution of the transient diffusion equation, which is outlined along with the method of data reduction. The diffusion cell is designed to accommodate cylindrical foam specimens of varying sizes up to 7.6 cm (3 in.) in diameter and up to 5.1 cm (2 in.) thick. Other features of the apparatus include quick and convenient interchange of foam samples as well as automatic data acquisition. Major sources of experimental error are discussed; those aspects of the experimental technique designed to reduce the magnitude of the experimental uncertainty are also mentioned. Results obtained with the apparatus for a number of different foams are presented and discussed in terms of various foam diffusion models described in the literature. Interpretation of the data in this manner gives some insight into the cellular structure of the foam and also provides a correlation for estimating the diffusion coefficient of other gases in the foam sample.

Blowing Agent Emission Calculations for a Refrigerator

This paper presents an outline of a model which can be used to estimate the concentration of blowing agents emitted from the foam insulation into the cavity of a domestic refrigerator. The basic assumption of the model is that blowing agent is emitted from the foam via a diffusion process and finds its way into the refrigerator cavity via holes and slots (for feed-throughs, shelves, etc.) which are cut in the plastic liner. The concentration of blowing agent inside the refrigerator decays asymptotically with time and depends on the diffusion coefficient and initial concentration of blowing agent in the foam, the number and surface area of holes through the plastic liner, whether or not the foam is adhered to the plastic liner, and the air exchange rate for the refrigerator. The model calculations indicate that, under normal operating conditions, the blowing agent concentration inside the refrigerator is very low, typically, parts per billion by volume. It is believed that the assumptions on which the model is based are conservative, i.e., the model over-estimates the concentration of blowing agent in the refrigerator. The sensitivity of the calculated concentrations to these assumptions is also discussed.

Blowing Agent Emissions from Insulation Foams

This paper presents an outline of a mathematical model that can be used to estimate the concentration of blowing agent emitted from foam insulation, which may be present in a house. The basic assumption of the model is that the blowing agent emission process is a diffusion process. Other assumptions on which the model is based are also discussed. Estimated concentrations of CFC-11 and HCFC-141b in the house are presented. The sensitivity of the calculations to the input parameters is also discussed