Clay was intercalated and exfoliated by neutralized dimethylol butanoic acid (DMBA) and used to fabricate rigid polyurethane foam (RPUF)/clay nanocomposites. Cream time, gel time, and tack-free time increased with the addition and increasing amount of clay whereas foam density and compression strength decreased. Cell size, closed cell content, volume change upon heating and cooling, and thermal conductivity of the foam decreased with the addition and increasing amount of clay with a minimum at 2 pphp (parts per 100 polyol by weight). The glass transition and decomposition temperatures increased with increasing clay content due to the restricted motion of chains and barrier property of the clay platelets.
SynopsisThe effect of dissymetrical units on the properties of thermotropic liquid crystalline copolyesters based on hydroxyhenzoic acid (HBA) , terephthalic acid (TPA) , and poly (ethylene terephthalate) (PET) units was examined. The dissymmetrical units employed included 2,7-&hydroxynaphthalene (2,7-DHN), 1,4-dihydroxynaphthalene ( 1,4-DHN), and bromo-hydroquinone (Br-HQ). All of these polymers exhibited turbid melts. The flexible PET units lower the melting and/or stick temperature, and between 10 to 20 mol 9% is a critical level to achieve values in the range of 250°C or lower. The copolyesters based on 2,7-DHN have the highest glass transition temperatures and maintain stiffness to the highest temperatures. The properties of each series of copolyesters are discussed in terms of the efficiency of molecular packing. The effects of chemical and physical inhomogeneity are emphasized.
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