Polyurethane foams are one of best insulators used for various kinds of industries. Blowing agents expands polyurethane into a foam material and give it good insulating capability. Conventional blowing agents such as CFC-11, HCFC-141b etc., have been replaced with new ones which render no potency to the depletion of the ozone layer and less potency to global warming. However, these eco-friendly foaming agents have a disadvantage of high thermal conductivity. In this paper, we summarize factors affecting thermal insulating performance of polyurethane foam and introduce the effective methods to enhance properties of polyurethane foam made of eco-friendly blowing agents.
Polyurethane foams are one of best insulators used for cryogenic industries including Liquefied Natural Gas (LNG) carriers, LNG pipe, LNG storage tank and so on. Blowing agents expands polyurethane to be a foam material and give it good insulating capability to be trapped in the closed cell in gas phase. ChloroFluoroCarbons (CFCs) (1st generation blowing agents) had been widely used as blowing agents, solvents, and refrigerants since 1930s. But Montreal Protocol on Substances that deplete the Ozone Layer restricted the use of CFCs after it was known that CFCs depletes the ozone layer in the stratosphere. CFCs had phased out in the developed countries since 1995.
HydroChloroFluoroCarbons (HCFCs) (2nd generation blowing agents) came to the markets to replace CFCs and were adopted as substitute for CFCs in various fields such as refrigerators, freezers, air conditioning system and also insulating foams. But HCFCs still depletes the ozone layer although the strength is small compared to CFCs (about 1/10). The use of HCFCs has been prohibited practically in the developed countries since 2005.
The substitutes for CFCs and HCFCs are HydroFluoroCarbons (HFCs) (3rd generation blowing agents) having zero Ozone Depletion Potential (ODP). Although ODP of HFCs is zero HFCs have high level of Global Warming Potential (GWP). Nowadays the earth has been having a hard time due to climate change caused by global warming. So the regulation on HFCs has been emerged and the use of HFCs can be banned in the near future. The one of promising substitutes is HydroFluoroOlefins (HFOs). There are many requirements asked for new blowing agents as shown in Table 1.