The measurement of the morphology of closed cell foams which control the overall thermal conductivity

摘要

Means to characterize and measure morphology which affects the solid and radiative contributions in closed cell foams have been developed. From measured two-dimensional intercept area distributions, the actual cell size distribution is calculated. For each of the small-celled polyurethane foams examined, the distribution is narrow, close to the mean cell diameter. From numerical analysis of extreme cell segregation, less than 13percent error in the extinction coefficient and the radiative contribution calculated from the mean cell diameter is expected due to cell size distribution. A means to measure the fraction of solid in the strut from strut cross sectional areas is derived. For the small-celled foams analyzed, the fraction of solid in the strut decreases from 0.67 to 0.34 as mean cell diameter decreases from 0.363 mm to 0.109 mm. Smaller celled foams which show a redistribution of polymer from the struts to the cell walls as cell size decreases will exhibit a larger solid conductivity which may counterbalance the decrease in radiation which accompanies the small cell size.