Journal of Cellular Plastics

doi: 10.1177/0021955X9903500501pmid: N/A

Takada, N.; Tamai, R.; Yamamoto, H.; Sekiya, A.; Tsukida, N.; Takeyasu, H.

doi: 10.1177/0021955X9903500502pmid: N/A

The development of blowing agents that exhibit lower thermal conductivity, shorter atmospheric lifetime, and less adverse effects on the atmosphere is an urgent issue. We investigated three fluorinated ethers as blowing agent alternatives [2,2,2-trifluoroethyl difluoromethyl ether (HFE-254mf), 2,2,3,3,3-pentafluoropropyl difluoromethyl ether (HFE-347mcf), and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE-347pc-f)] in terms of physical properties (boiling point and gaseous thermal conductivity), environmental adaptability (atmospheric lifetime), toxicity, flammability, solubility in polyols, and thermal stability.By using these fluorinated ethers as blowing agents, we experimentally produced rigid polyurethane foams, all of which showed thermal conductivities lower than or equal to foams produced with the blowing agent alternative candidates, HFC-245fa and cyclopentane.

Manini, Paolo

doi: 10.1177/0021955X9903500503pmid: N/A

Polyurethane foam is the preferred insulator material in a wide range of appliances such as refrigerators and freezers. The recent phase out of CFC-11 has however decreased its insulation performance due to the need to adopt environmentally more benign blowing agents, such as HCFCs and hydrocarbons, all having higher gas thermal conductivity. This represents a serious drawback since specific regulations to reduce the energy consumption in refrigerators have been issued in recent years, and even more demanding reductions are under debate and expected to be applied worldwide by the turn of the century. In response to these requirements, Vacuum Insulated Panels (VIPs) technology has been studied and developed. Suitable components, filler, bag and a getter to maintain the necessary vacuum, have to be selected to ensure the high super-insulation properties which can be exhibited by VIPs. Among various core materials for VIPs, open cell foams present specific advantages in terms of performance, weight, processability and cost. In the present paper, the recent developments in the VIP technology are reviewed and discussed focusing the attention on the open cell polyurethane. The various gas sources deteriorating the vacuum during the panel life have been experimentally determined and evaluated by means of outgassing, permeation and gas analysis measurements on VIP components and finished devices. A suitable getter system able to cope with the gas load and to ensure vacuum performance and reliability is also described.

Wu, J.; Albouy, A.; Mouton, D.

doi: 10.1177/0021955X9903500504pmid: N/A

The development of a third generation HFC blowing agent has achieved significant progress in the past few years. Several candidates have been identified as promising substitutes for HCFC-141b in foam applications.Elf Atochem has striven to provide alternatives after HCFC-141b phases out in foam applications. This paper summarizes our recent research activities in HFCs in rigid polyurethane foam applications. It includes determinations of the weight loss of blowing agents during the foaming process. To predict long term aging behavior of polyurethane foams, we measured effective diffusion coefficients of HFC-245fa, HFC-365mfc and HCFC-141b. Also, stability of the foam systems (PUR and PIR) using HFC-365mfc as the blowing agent will be reported. The stability is indicated by the amount of decomposition during a certain period of time. Furthermore, we have studied effects of HFC-245fa foam density on the foam insulation (k-factor), dimensional stability and compressive strength. In this study, we also determined aged k-factors of HFC-245fa and HCFC-141b foams with different foam densities. Finally, we investigated HFC-134a in PUR foam as well as its solubility in several polyols.

Baes, M.; Galina, C.; Vanlandschoot, K.

doi: 10.1177/0021955X9903500505pmid: N/A

In view of the formulation changes induced by the use of alternative physical blowing agents, the understanding of the main parameters determining the dimensional stability performance was an important issue for the rigid laminate industry. So far, the influence of formulation and processing variables on dimensional stability has mainly been described qualitatively, and new evaluation techniques have been proposed in several publications.This paper describes how the application of the so-called dimvac test has led to a better quantification of the formulation and processing parameters influencing the long-term dimensional stability performance.A series of pentane blown laminates based on different formulations and processed on a variety of equipment were evaluated at the most severe condition in the dimvac test. We found that a set of formulation and processing requirements had to be fulfilled in order to ensure the dimensional stability of the laminates in service. The requirements were different for each formulation, production line and product.To quantify the influence of polyether polyol composition and type of non-reactive liquid fire retardant, a systematic laboratory study was carried out. For foams without fire retardant, a clear model was obtained predicting the dimvac performance in terms of foam density and polymer network parameters. For formulations including fire retardants, deviations from the model were observed, and differentiation between dilution and plasticization could be made.

Zhang, X. D.; Davis, H. T.; Macosko, C. W

doi: 10.1177/0021955X9903500506pmid: N/A

Literature on the polyurethane foam cell opening mechanism is reviewed and discussed. A new cell opening mechanism is proposed. Cell opening is observed to be triggered by urea precipitation which changes the rheology of the polyurethane dramatically. The foam matrix shows extensional thinning behavior after urea phase separation. The extensional thinning behavior will lead to localized cell window thinning.The cell window thickness distribution will lead to different film rupture times for individual cell windows and will result in cell windows in different states. Some windows are totally missing and others leave torn-off films. Windows with only pin holes or totally closed were also observed. The cell opening event is shown to be a continuous process rather than a sudden event.