Meng-Shung Yen

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λc) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films.

Preparation and Physical Properties of MDEA-based Polyurethane Cationomers and their Application to Textile Coatings

Cationic aqueous polyurethane (CAPU) coatings were prepared by the acetone process using 4,4-methylene bis (isocyantocyclohexane) (H12MDI), N-methyldiethyolamine (N-MDEA) and a series of various polydiols (polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetramethylene glycol (PTMG) for ether-type polyols and polycaprolactone (PCL) for ester-type polyol) with different molecular weights (Mn =1000, 2000 and 3000 g/mole). The surface tension of CAPU dispersion, contact angle, thermal properties of CAPU casting film and its tensile strength were examined. The waterproof (WP) and water vapor permeability (WVP) of coated fabric and its washing durability were also studied. Our results showed the ether-based CAPU showed a higher surface tension value, contact angle and WVP with a sequence of PEG-PU > PTMG-PU > PPG-PU > PCL-PU, and it increased with increasing M n of the soft segment. As for the thermal properties, the PEG-PU had the highest glass transition temperatures of the soft segment (Tgs) and melting point (Tms) than those of PCL -PU, PTMG-PU and PPG-PU. For the thermal stability of CAPUs casting film, the PEG-PU had ideal thermal stability, followed by PTMG-PU and PCL -PU, and the CAPU with a larger M n of the soft segment had better thermal stability. The PTMG-PU had excellent tensile strength, followed by PCL -PU and PPG-PU. For coated fabric, the trend of WVP followed the order: PEG-PU > PTMG-PU > PPG-PU > PCL -PU, while the WP followed the order: PTMG-PU > PCLPU > PPG-PU > PEG-PU. Finally, the CAPUcoated fabric had an excellent performance after washing and its wash-durability was still 80 %.