Correlations between physical properties, formulations, and ATR FTIR spectra of polyurethane foams

Abstract

. AbstractPolyurethane foams of varying surfactant, tin catalyst, and amine catalyst levels were prepared to find formulations that made "good" foams. A good foam is characterized by rise and density. Attenuated Total Reflectance spectra of the foams were collected after the foams were allowed to cure for twenty-four hours. Because the infrared spectrum shows morphology as well as structure, the ATR spectrum can be used to measure physical properties that are dependent on structure and morphology. The AIR FT-JR spectra were baseline corrected and then normalized by the area in the C-H stretch region to correct for differences in contact area with the AIR crystal. Samples were then taken from the cured foam parallel to the direction of rise to measure tensile strength and air permeability. Correlations were then made between the AIR spectra and the physical properties. Partial least squares (PLS) and principle component regression (PCR) were used to do the correlations. IntroductionPolyurethanes are of economic importance due to the varied physical characteristics that are possible. Polyurethane foams can be made soft and light for comfort products such as cushions and pillows or rigid for insulation. The physical characteristics are determined by the formulation and specific surfactant used to produce the foam.Presently, industry uses empirical methods to determine the proper formulation to produce a foam with the desired physical properties. This method is unreliable as ther is considerable lot-to-lot variability in the reactants. These problems lead to wastes of time, money, and resources on the part of industry. A means to reduce the empiricism found in polyurethane production is being sought.Our laboratory is currently involved in the development of a correlation between the physical properties and the attenuated total reflectance spectrum of the polyurethane foam. The infrared spectrum is well suited to measure these physical characteristics. The infrared spectrum shows morphological features as well as structural. It is these features that determine the characteristics of the foam. This correlation will reduce the amount of time and resources wasted in the production of foams. The correlation would reduce the amount of time needed to measure the physical properties of the foam from a week to a day.The correlations were used to predict the physical characteristics of tensile strength and air permeability. Tensile strength is the amount of pull required to break a specimen that is elongated at a constant rate. Air permeability measures the openness of the polyurethane foam cells. There are further characteristics that are of interest but the correlation was limited to these. ExperimentalComponents for the polyurethane reaction were provided by DOW Chemicals USA. Attenuated Total Reflectance spectra were collected on a BioRad FTS-60 with a SpectraTech ATR accessory. Galactic's GRAMS software and PLSP1us software was used to perform the correlations. Tensile strength was measured on an Instron Tensiometer. Four...