Journal of Cellular Plastics

The ever increasing amount of legislation on fire performance tests in many parts of the world indicates the decisive roll of FR-performance on the further development of the polyurethane-foam business in general. Because of this, the use of flame retardants is imperative for many applications but attempts were made to evaluate other factors which also influence the FR-performance of the polyurethane foam, as well.

The focusing point of our work was the question whether there are practical ways to implement results into actual production processes.

For example the influence of foam porosity on FR-performance is well known. Nevertheless, it may not be a factor to be changed under production conditions due to foam specifications.

In this paper research will be shown regarding the question in which way FR-performance and production safety can affect formulation changes without changing foam porosity.

Other topics of special interest to us are the melting performance and the influence of surface morphology on the burning of flexible slabstock foam. This also relates to the use of fillers in slabstock formulations and their effects on the flammability of foams.

Another important aspect that has been considered is the influence of the silicone surfactant structure, especially with regard to the ethylene oxide content of the utilized polyethers in the surfactant. The dependence among silicone surfactant structure, the amount of silicone surfactant within a foam and the resulting influence on FR-performance is another very important aspect to consider for optimum FR-properties. Differences between the use of conventional, universal and FR-surfactants will be shown and explained.

Based on the results of our work the parameters to design surfactants with enhanced FR-performance will be discussed.

In view of the ozone depletion potential of HCFC-141b and other HCFCs, processing challenges with gaseous HFC-134a, and flammability potential with pentanes as blowing agents, significant efforts have been deployed in the development of environmentally friendly, all carbon dioxide blown rigid polyurethane spray foams. These foams are primarily used for the insulation of roofs, storage tanks, vessels, walls and piping. The Mannich base initiated Polyol A, developed by The Dow Chemical Company [1], with viscosity of ∼2000 cps at 77°F and OH# of ∼312 was manufactured using patented technology. This OH# is significantly lower than that of the dominating spray foam polyols (OH# 470). The low viscosity and higher equivalent weight of this polyol are designed to alleviate the processing difficulties of typical carbon dioxide blown spray applied systems.

Some of the important requirements in spray systems are the flammability characteristics. Most carbon dioxide blown foams, however, suffer from high heat release, smoke and weight loss in small scale burn tests like the Ohio State University (OSU; ASTM E-906) test when compared to the corresponding results with HCFC-141b as the primary blowing agent. A series of formulations containing Polyol A, aromatic polyester polyols and commercially available fire retardants were evaluated at different isocyanate indices. Flammability properties were determined using a variety of small scale test methods including cone calorimeter and ASTM E-906. In an attempt to understand factors contributing to burn properties, several analytical techniques, such as FTIR (Fourier Transform Infrared Spectrometry), TGA (Thermo-Gravimetric Analysis) and DMS (Dynamic Mechanical Spectroscopy) were utilized. Analysis of the FTIR spectra leads to an estimate of conversion of isocyanate end groups and trimerization reactions where applicable. TGA reflects the chemical stability of the polymer network to thermal decomposition and DMS reflects the physical stability of the polymer network. A correlation of these data with the weight loss data after burning has been investigated. A combination of these techniques leads to a systematic approach for the development of spray polyurethane foams with improved flammability characteristics.

During the last year all major European Appliance Manufacturers have chosen the cyclopentane options as blowing agent for polyurethane insulation as the optimum solution for the phase-out of CFCs. The reason for this choice is due to several factors, including: zero-ODP, environmental acceptance, reasonable low initial thermal conductivity, appropriate boiling point and proven availability. These factors outweighed the disadvantage of cyclopentane flammability and the related safety problems.

This paper presents the results of ICI Polyurethanes studies with cyclopentane foam in terms of:

• processing and safety, including engineering advice for the modification of existing equipment, storage facilities and handling procedures

• the VOC emission during handling and foaming process

• the exothermicity of the reaction, overpack and pressure generation

• the initial properties of the foam: thermal conductivity and thermal insulation efficiency on the cabinets, mechanical properties, dimensional stability, blowing efficiency and foam flowability

• anticipation of long term performances, including diffusion and condensation phenomena, identification of accelerated method for the prediction of aged foam physical properties

• the performances in domestic appliances in terms of the aging phenomena, the solubility of the cyclopentane in the PU foam and compatibility with plastic liners

• the plasticizing effect on the PU matrix

• the aspect related to the environmental impact

This paper also addresses the further developments being carried out with leading appliance manufacturers towards the improvement of key requirements, such as thermal conductivity, foam morphology and mechanical properties.

Efforts are continually being made to improve the insulation efficiency of appliance foam to reduce dependency on fossil fuels and to meet federally mandated product energy use requirements. These efforts have become even more important due to impending elimination of chlorofluorocarbons (CFCs) as the blowing agent for polyurethane and polyisocyanurate foams. Conversion to hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) generally leads to decreased insulation value of foams and therefore, decreased overall energy efficiency for the appliances.

The effects of incorporating carbon black to reduce thermal conductivity of HCFC-141b blown appliance foams are discussed. The work was jointly carried out by Miles Inc. and the Center for Applied Engineering. Studies previously conducted at the Center had demonstrated that carbon black is well suited for use in rigid insulating foams, particularly in urethane-modified isocyanurates. The Celotex Corporation has now commercialized this technology in the building insulation market.

Improvements of 6-9% in initial k-factors were observed when carbon black dispersed in polyols or isocyanates was used either in TDI- or PMDI-based appliance systems. The use of carbon black in HCFC-141b blown systems has the potential to produce foams with insulation values equivalent to CFC-11 blown production foams.

The very fine particle size and inert character of commercially available carbon blacks allow loadings up to 12% by weight in foam polymer. Since the dispersions can result in excessively high viscosities, efforts were also directed towards modifying formulations to improve flow characteristics. Various approaches were taken to optimize carbon black loading in reactants as well as to facilitate processing in the foam process equipment.

With the scheduled phase out of CFCs near at hand, many companies have been investigating completely water-blown (CO2) rigid foams. Several problems surfaced immediately such as a substantial increase in k-factor, a reluctance for the foaming mass to flow and fill molds properly, and a tendency for the foam to be dimensionally unstable in the density range commonly considered.

Several applications do not require that k-factor be the primary concern. For instance, the insulation provided by some units containing rigid foam is affected by the tightness of the lid to the case, and insulation is required for only a limited, not an extended period of time, as for example, a picnic cooler. In such applications, a water-blown foam provides sufficient insulation and rigidity in the cooler walls to provide a satisfactory result. However, the foam in such cases must be dimensionally stable, i.e., over a period of time in which the cooler may be subjected to a number of heating and cooling cycles, the foam must not shrink, expand, or distort. One method to accomplish this is to use open-celled foam, since the cells contain no trapped gas to exert internal pressure on heating or cause a semi-vacuum on cooling.

At BASF we have uncovered a family of additives which act as cell openers when added to resin formulations. Using standard rigid foam polyols, we have prepared foams with densities as low as 0.90 pcf which show less than 5% dimensional changes when kept at 158°F and 100% R.H. for 28 days. The measured closed cell content can be as low as 3-5%, although foams in the 1.1-1.4 pcf density range were found to be dimensionally stable at closed cell contents as high as 88%.