Methods to Improve Properties of Polyurethane Foam Using Liquid-Type Additives

Abstract

Polyurethane is a polymer material made by the exothermic reaction between polyol and isocyante. It has many good properties that it has been widely used in various kinds of industry. [1] Especially rigid polyurethane foam is one of best thermal insulation materials and it has been used as a main insulator for cryogenic industries such as Liquefied Natural Gas (LNG) storage tanks, LNG carriers etc. [1-4] Blowing agent is a material which makes polyurethane cellular material and gives polyurethane foam insulating ability. CFCs were typical blowing agents. But they have not been used because they destroy the stratospheric ozone layer. HCFC-141b was chosen for an alternative to CFCs. However, although small ozone depletion potential (ODP) of HCFC-141b compared to CFCs, additional alternative blowing agents with zero ODP such as hydroflurocarbons (HFCs) have been needed because of tougher environmental regulations since 2000s. LNG demand has risen by an estimated 7.5% per year since 2000. [5] Nowadays the price of natural gas has become higher and the efficiency of propulsion systems of liquefied natural gas (LNG) carriers has improved. Due to these trends, required boil-off rate (BOR) has been lowered from 0.15%/day to 0.12%/day for conventional LNG carriers with sizes between 125,000 m3 and 170,000 m3. This requirement of BOR can be satisfied by using a rigid polyurethane foam (PUF) blown by 1,1-dichloro-1-fluoroethane (HCFC-141b) as an insulator but we cannot use it anymore. So new alternative blowing agent should be used instead of HCFC-141b. But the use of alternative blowing agent can make another problem like deterioration of thermal conductivity due to its relatively high thermal conductivity. [1, 3, 6-12] This research introduces HFCs as an alternative to HCFC-141b and discuss characteristics of rigid PUFs prepared with HFCs and shows its application to LNG carriers. We also discuss effects of liquid-type additives to enhance properties of rigid PUFs under laboratory atmosphere and the possibility of their adaptability to mass production type PUFs. For these three liquid-type additives, propylene carbonate (PC), perfluoroalkane (PFA), and acetone, were introduced. The addition of perfluoroalkane induced the small cell size of the PUFs. Based on the morphology, thermal conductivity, and compressive strength, it is suggested that the perfluoroalkane is an efficient liquid-type additive for the improving the thermal performance of PUFs. [13, 14] Based on this result, a mass production type rigid PUF for a LNG carrier was manufactured and evaluated for BOR, mechanical strengths over operation temperature range, coefficient of thermal expansion (CTE), and thermal shock stability for LNG carriers. The calculated BOR of the manufactured rigid PUF is below 0.12%/day, which satisfies the recent and tough BOR specification for LNG carriers. Other properties also meet the specifications for a conventional LNG carrier. [13] Consequently, it is expected that the results in this paper will bring low BOR (<0.12%/day) LNG carries with rigid PUFs using ODP free blowing agents and contribute environmental protection through saving energy and preserving the ozone layer in the stratosphere. Besides that, the product of this paper will reduce the time required to construct the raw material system and make the blending system configuration process easier.