SYNOPSISFor the purposes of the water-selective membrane material development for pervaporation separation, poly (vinyl alcohol) (PVA) was crosslinked with a low molecular weight of poly (acrylic acid) ( PAA) . The crosslinking reactions between PVA and PAA were characterized through IR spectroscopy, differential scanning calorimetry ( DSC ), and tensile tests when varying the reaction conditions, that is, time, temperature, amounts of crosslinking agents, PAA. It was found that the crosslinking reaction was fast: in other words, that the reaction mainly occurred at the initial step of each reaction condition. The best reaction conditions for preparing the crosslinked PVA membranes were found to be: reaction time not over 1 h, reaction temperature in the range of 15O-18O0C. PAA contents of 15-20 wt % were found satisfactory with respect to the application areas. 0 1993

No abstract

To manufacture a carbon/carbon composite the coal tar pitch was used as the matrix precursor and the PAN (polyacrylonitrile)-based carbon fiber was used as the reinforcing material to weave 3-directional preform. For pressure carbonization HIP equipment was used to produce a maximum temperature of 1000 o C and a maximum pressure of 100 MPa. The carbonization was induced by altering the dwell temperature between 250 o C and 420 o C, which is an ideal temperature for the moderate growth of the mesophase nucleus that forms within the molten pitch during the pressure carbonization process. The application of high pressure during the carbonization process inhibits the mesophase growth and leads to the formation of spherical carbon particles that are approximately 30 nm in size. Most particles were spherical, but some particles were irregularly shaped. The spread of the carbon particles was larger on the surface of the carbon fiber than in the interior of the matrix pocket.

No abstract

No abstract