Journal of Cellular Plastics

The time to onset of cell opening and the modulus around the event were measured using a parallel-plate rheometer for flexible polyurethane foams. Cell opening time was compared with the visual blow-off time. The onset of cell opening occurs several seconds after phase separation, and the visual blow-off occurs several seconds (sometimes more than ten seconds) after the onset. Two series of formulations were studied, one in which the factors other than surfactant (tin catalyst level, TDI index, polyol type) were changed, and the second series in which only the surfactant was changed. In the first series, the modulus at cell opening did not change much with different formulations. However, the modulus development rate during the cell opening period (between the onset and the visual blow-off) changed significantly. Air flow was lower with higher modulus development rate. In the second series, the modulus development rate or the timing of onset of cell opening did not change even when the air flow changed considerably. The fact that the timing did not change and it is several seconds after the phase separation implies that the cell opening is triggered by sudden urea precipitation.

Light interferometry showed that the average value of the remaining cell window thicknesses in low air flow foam is higher than that of the high air flow foam. Scanning electron microscopy (SEM) of the final foam products showed that the cell windows are in a variety of stages. The windows were classified into four stages-fully open, partially open, pin holes and closed. Air flow is directly proportional to the effective fraction of open windows. SEM also showed that the cell windows are in several different states. Some window films were totally missing and others have left torn-off films. The possible mechanism of cell window rupture is discussed with respect to the results.

A microcellular plastic is a foamed polymer of a cell size in the range of 0.1 to 10 μm and a cell density in the range of 10⁹ to 10¹⁵ cells/cm³. Typically, microcellular plastics have been shown to possess superior impact strength, toughness, and fatigue life to solid polymers. Polymer/cellulosic-fibre composites make use of cellulosic-fibres as a reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the material cost and some mechanical properties such as stiffness and specific strength. These polymer/cellulosic-fibre composites are microcellular processed to create a new class of materials with unique properties. In this paper, the feasibility of the production of microcellular PVC/cellulosic-fibre composites and the effect of the fibre content on the cell morphology are studied. Particular emphasis is given to the fibre surface treatment to investigate its effect on the microcellular morphology. Each step of microcellular PVC/cellulosic-fibre composite processing is addressed including the treatment of the cellulosic-fibre surface, the manufacture of the composite by the mixing of PVC and cellulosic-fibre, the saturation of the composite with gas, and the bubble nucleation and growth. The preliminary experimental results indicate that the surface modification of cellulosic-fibre plays a strong role in determining the interface between the polymer and fibre as well as the cellular morphology of the foamed composites.

Vacuum based insulation technology results, when introduced into appliances, in a substantial reduction in energy consumption of these appliances. This reduction depends on two factors: primarily on the vacuum panel technology used, but also, very importantly, on the quality of the polyurethane foam used to fill the confined space in the refrigerator walls after incorporation of the vacuum panels. ICI Polyurethanes has now developed both an open-celled, fine-celled polyurethane foam, eminently suitable for vacuum panel technology, and a polyurethane foaming technology, based on both CO₂ and physical blowing agents, including alkanes, specifically designed to complement the vacuum panel technology. This paper reports on the status of both technologies. Since the morphology and physical properties of the open-celled polyurethane foam are substantially different from existing vacuum technologies, a complete assessment of the technical requirements for the open-celled foam has been performed. We believe the cost effectiveness, weight and ease of production weigh heavily in favour of the polyurethane foam based vacuum technology. In addition, the specific requirements for the encapsulation foam will be presented in terms of flow performance, pressure and temperature build-up and adhesion towards several liner materials. Evaluation of our technology is ongoing with a number of appliance manufacturers.

For several years, the polyurethanes industry has critically examined its products in order to meet all present, and possible future, US environmental regulations. Formulations have had to be adapted to new types of blowing agents in order to compare favourably with the thermal and fire performances previously achieved.

These changes have highlighted a need to understand the fundamental factors which determine the long term dimensional stability of foams. From the theoretical understanding, it is then possible to assess the validity of current test methods and to design improved tests for the prediction of long term dimensional stability with the new systems.

In this paper, the relevant fundamental factors have been examined individually. Factors which predominantly affect polymer strength, processing, diffusion of gases and plasticisation have been grouped together, and their combined effect, under different conditions and in different applications within construction, are discussed.

Furthermore, the prediction of long term behaviour via modelling is highlighted. Based on fundamental understanding and model calculations, a new test has been designed and a comparison made with standard predictive tests. The behaviour of several HCFC-141b and pentane blown foams in the test are also given.

It has been shown that the effect of the combined action of all parameters influencing the long term dimensional stability of foams has changed in new systems based on benign blowing agents, compared to conventional CFC-11 blown foams. It has also been shown that the new predictive test is better adapted and more critical than the standard test for these new systems.

Due to the escalating interest in zero ODP (ozone depletion potential) blowing agents throughout the world, hydrocarbons are seriously being considered as potential candidates for rigid foam applications. However, many rigid foam applications require a certain degree of fire resistance, a characteristic which the flammable nature of hydrocarbons would seem to oppose. Last year we presented a paper which detailed our initial work with hydrocarbon-blown foams produced on a lab-scale high pressure machine [1]. In that work, several techniques were explored which improve the flame resistance of isocyanurate foams. These techniques included increased index, inclusion of phosphorous, and the use of inerting co-blowing agents. This paper will present further work concerning the flammability of rigid isocyanurate foams blown with hydrocarbons, with a particular emphasis on cyclopentane as the primary blowing agent.

In this study we have investigated the use of various foaming techniques to suppress flammability. As in our previous paper, all foams were produced on a high pressure foam machine. Options which were explored include fire retardants, co-blowing agents, and increased foam indices. Results from small-scale fire tests are presented in order to compare the effectiveness of the different approaches. Mini-tunnel and hot plate test results are featured.