- Author
- Nguyen, T. | Byrd, W. E. | Zarr, R. R. | Stutzman, P.
- Title
- Effects of Humidity on Chemical Structure and CFC Loss of Polyisocyanurate Foam Blown With CFC and CFC/CO₂ Mixture.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Book or Conf
- Society of the Plastics Industry of Canada's. Workshop on Long-Term Performance of Cellular Plastics, 3rd International. October 4-6, 1993, Ontario, Canada, 1-28 p., 1993
- Keywords
- polyisocyanurate foam | humidity | chemical structure | carbon dioxide
- Identifiers
- chlorofluorocarbon; microstructure
- Abstract
- The effects of humidity on the microstructure, chemical structure, and blowing agent loss of unfaced, chlorofluorocarbon (CFC) and CFC/CO²-blown polyisocyanurate (PIR) foams were investigated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The exposure environments were: [1] ambient conditions; [2] 60 deg C in dry air (<10% RH); [3] 60 deg C and 40% RH; and [4] 60 deg C and 75% RH. SEM analyses were done for CFC/CO² foam efore and after one-year exposure. FTIR measurements were conducted using 2-mm thick specimens of both foams before exposure and at regulat time intervals for up to one year. All exposure conditions caused little change of the cell microstructure of foams taken 1 mm below the exposed surfaces. However, the change in the size of KC1 particles, which were present amply on cell membrane surfaces, was a function of humidity. All exosures had little effect on the C=O, NH, or CH groups but decreased the NCO and carbodiimide groups of the foam polymers, and caused a loss of the CFC blowing agent in both CFC- and CFC/CO²-blown foams. The change in chemical structure and CFC loss were a function of humidity, the higher the humidity the faster the loss and degradation. The CFC loss was also faster at the elevated temperature than at ambient temperature. The effective diffusion coefficients of CFC from the two foams, obtained from the desorption data using the FTIR technique for the whole exposure duration, were in the 10⁻⁸ cm₂/s range. The diffusion of CFC in CFC/CO²-blown foam followed a Fickian process while that in the CFC foam did not. Information on the microstructure and chemical properties of the two foams before exposure is also given.