Search

We studied the long-term performance of new environmentally-friendly blowing agents for polyurethane foams. Several blowing agents, hydrofluorocarbons, hydrocarbons, and a possible hydrochlorofluorocarbon substitute (dimethoxymethane), as well as hydrochlorofluorocarbons, were analyzed. The determination of effective diffusion coefficients (knowledge of which is required to study long-term performance) was performed by means of a classical gas chromatographic technique and by a new method based on infrared spectroscopy. The reliability of the experimental procedure used is showed by comparing experimental and predicted aging, as the slope of the aging curve (i.e., thermal conductivity vs. time) depends only on effective diffusion coefficients. Our study of long-term performance of foams blown with alternative blowing agents shows that hydrofluorocarbons represent a proper alternative to hydrochlorofluorocarbons, as the foams show similar initial thermal conductivity and a slower aging rate (i.e., better long-term performance). POLYM. ENG. SCI., 45: 260-270, 2005. [c] 2005 Society of Plastics Engineers, INTRODUCTION Polyurethane foams are widely used as thermal insulator materials due to their low thermal conductivity. Otherwise, they are subjected to aging phenomena (i.e., the increase with time of thermal [...]

The effective diffusion coefficients of novel, environmentally friendly, hydrofluorocarbon (HFC) blowing agents for polyurethane foam production were measured. The method was based on gas chromatography and infrared spectroscopy measurements. The accuracy and reliability of the procedure developed were confirmed by comparisons of experimental and the predicted thermal aging curves. The slope of the aging curves (i.e., the change in thermal conductivity with time) depended only on the effective diffusion coefficients. The effective diffusion coefficients of the new HFC blowing agents were close to those of conventional hydrochlorofluorocarbon (HCFC) blowing agents, and the aging behavior of foams produced from HFC or HCFC blowing agents were similar. Polym. Eng. Sci. 44:2229-2239, 2004. © 2004 Society of Plastics Engineers., INTRODUCTION Polyurethane cellular foams are widely used as thermal insulator materials as they are characterized by a very low thermal conductivity. One major drawback concerning the use of those materials [...]

R-RIM PU (reinforced-reaction injection molding polyurethanes) from the automotive industry (production scrap and parts at the end of their life cycle) can be recycled for the production of new RIM PU by a chemical process. Among the various possible chemical processes (hydrolysis, alcoholysis, aminolysis, and pyrolysis), we have examined glycolysis, a particular form of alcoholysis, for the purpose of obtaining a mixture of oligomers sufficiently similar to a polyol to be used in the production of new R-RIM PU. Glycolysis with dipropylene glycol (DPG) of R-RIM PU forms a monophasic product that could be used in the preparation of new, highly crosslinked polymers, similar to those used in the preparation of rigid thermal insulation foams. The same product, because of its high hydroxyl number, cannot be directly re-used in the production of new RIM PU. Partial substitution of free DPG in the glycolysis product with a triol having high molecular weight forms a homogeneous mixture suitable for production of new RIM PU. This final product has been used in the original R-RIM application introducing an appropriate optimization of formulation. In comparison with RIM PU obtained from only virgin materials, the loss in properties of molded parts based on even high amounts of regenerated polyol was only marginal., INTRODUCTION RIM and R-RIM (reinforced-reaction injection molding) polyurethane/polyurea polymers are materials that, owing to their intrinsic properties, are increasingly used in the automotive industry (bumpers, fascias, side panels, door interior [...]

Physical blowing agents such as n-pentane and methyl formate and, for comparison, chemical blowing agents such as water were used to prepare structural polyurethane rigid foams of different densities by [...]