Effect of Uniaxial Stretching on the Crystallite Morphology of Poly(ethylene terephthalate) Film

• Main Authors: Chu, Po-Han, 朱柏翰
• Other Authors: Ching-Feng Mao
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/aa4n8n

碩士 === 南臺科技大學 === 化學工程與材枓工程系 === 106 === The processing condition of poly(ethylene terephthalate) (PET) films significantly affects the crystallinity, crystallite morphology and size of PET, which are related to the macroscopic properties, such as mechanical strength and transparency. In this study, the laboratory-scale film stretching apparatus was improved by constructing a uniform heating chamber equipped with biaxial stretching-rate controlled clamps, which are capable of uniaxial stretching as well as biaxial stretching. The effect of stretching conditions, including draw ratios, draw rates, uniaxial stretching, on properties of PET films was then investigated. Rebuilding a new laboratory-grade constant temperature film drawing machine to improve the uneven heating of the film during the stretching stage, resulting in uneven film stretching, and correcting the heating temperature and heating time. When the heating plate is set to a heating temperature of 100 ℃, the film can be maintained at 80 ℃ to constant temperature in accordance with the temperature required for PET stretching. The alkali etching technique (potassium hydroxide/ethanol), which makes use of the relatively high hydrolysis rate of the amorphous of PET to visualize the crystalline part of PET, is currently the best approach to reveal the crystallite morphology under SEM. The best crystallite morphology was obtained by etching of the dissolution solution(15 wt%) of potassium hydroxide concentration for 1~3.5 h. It is observed that PET stretch film has a variety of crystallites morphology. The draw ratio of 2.5 can be seen that the crystallites form of elliptical, and major-axis perpendicular to the stretching direction and, elliptical crystal size of about 2 ~ 5 μm. The draw ratio of 3 or more elliptical crystals beging larger in size and the major-axis parallel to the stretching direction. The crystal size is increased to 8~15 μm. As the draw ratio is increased (λ>3), the crystal form changes from elliptical to elongated, and the crystal size is about 10-15 μm. Useing the Senarmont device measuring birefringence, the birefringence of the sample is obtained from the uniaxial stretching increased with increasing draw ratio and draw rate, and the tensile stress overcomes the force between the molecular chains. So that the molecular chains are arranged toward the direction of stretch to stress-induced crystallization. Thermal properties of the material from the DSC analysis of the sample can be confirm crystallinity does increase as the draw ratio increases, but the cold-crystallization enthalpy has decreased, and the cold-crystallization temperature also observed to move toward the low temperature. The mechanical properties of the material test, the samples changes during stretching process, the draw ratio increases so that the crystallinity increases, the elastic modulus and the tensile strength of the sample was increased, but because of the crystalline regions more then the amorphous regions, the elongation was decrease.