화학공학소재연구정보센터
Macromolecules, Vol.36, No.15, 5798-5803, 2003
Mechanical properties of drawn smectic mesophases. Poly(tetramethylenoxypropylene p,p'-bibenzoate)
A smectic main chain polymer, poly(tetramethyleneoxypropylene p,p'-bibenzoate), PPO4B, with thermal transitions T-g = 26degreesC and Ti = 88.5degreesC was studied in and after a drawing experiment. Variation of both strain rate and temperature resulted in materials with normal and anomalous orientations of smectic layers. Mechanical properties vary correspondingly. Samples from PPO4B were drawn at different strain rates and temperatures. The stress-strain curves were recorded. The resulting oriented materials were studied by wide-angle X-ray scattering. Normal orientation (i.e., smectic layer perpendicular to draw direction) is established at high strain rate and low temperature. Anomalous orientation is achieved at low strain rate and high temperature. At intermediate values of the processing parameters a bimodal structure of both normal and anomalous orientation is observed. Dynamic mechanical analysis measurements in tensile mode were carried out on strips cut from oriented sheets in three directions, 0degrees, 45degrees, and 90degrees in relation to the draw direction. The value of the storage modulus in the drawing direction is highest in the case of normal orientation (smectic layer perpendicular to the straining direction). The highest value of the storage modulus coincides with the direction perpendicular to most of the smectic layers. Thus, for anomalous orientation the worst mechanical properties are in the fiber direction.