Unusual formation of precursors for crystallization of ultra-high performance polypropylene and poly(ethylene terephthalate) fibers by utilization of ecologically friendly horizontal isothermal bath
Başlık çevirisi mevcut değil.
- Tez No: 400921
- Danışmanlar: PROF. RICHARD KOTEK
- Tez Türü: Doktora
- Konular: Polimer Bilim ve Teknolojisi, Polymer Science and Technology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2013
- Dil: İngilizce
- Üniversite: North Carolina State University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 308
Özet
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Özet (Çeviri)
The concept of production of new families of high performance polymers and engineering fibers has been reported many times in the technical literature. Such fibers have various end uses in industrial applications and exhibit the enhanced potential in the challenging areas such as ballistic, automotive, aerospace, bullet-proof vests, energy, and electronics. Since the first commercial synthesis of high polymers by Carothers and Hill, filament manufacturers have looked for ways to increase strength and fibers dimensional stability, thermal degradation resistance, etc., even at extreme conditions. Therefore, studies on the fine structure development and its relation with production conditions during the wet, dry, and melt spinning processes have received much attention by researchers to describe in detail the fundamental aspects of the fiber formation. The production of ultra-high performance fibers at relatively high throughputs by a simple method using fiber-forming polymers via developing an ecologically friendly isothermal bath (ECOB) is the first aim of this study. In this case, polypropylene (PP) was chosen as a semicrystalline thermoplastic polymer which is extensively used in industry and our daily lives. A unique, highly oriented precursor (fa = 0.60), and yet noncrystallized, undrawn fibers were obtained with superior mechanical properties. Fibrillated break, high crystalline and amorphous orientation factors of 0.95 and 0.87, respectively, demonstrate an unusual structural development after only 1.34 draw ratio for the treated fibers. The second melting peak increased 9 oC for the treated fibers, which implies a higher level of molecular ordering and thermodynamically more stable phase. After hot drawing and 1.49 draw ratio, the fibers tenacity was close to 12 g/d, the initial modulus was higher than 150 g/d, and the ultimate elongation was at a break of about 20 %. In the next phase of the research, the effects of horizontal isothermal bath (hIB)11 on the structural development and the production of ultra-high performance as-spun and drawn polypropylene (PP) filaments were investigated. Two different commercial fiber forming PP polymers were used with the melt flow rate of 4.1 and 36 g/10 min. The results demonstrate surprisingly different precursor morphologies for each type of polymer at their optimum process condition. Interestingly, the all treated fibers demonstrated the similar fiber performance having tenacity of about 7 g/d and modulus of 75 g/d for as-spun fibers. After fiber drawing with DR of 1.49, tenacity greater than 12 g/d and modulus higher than 190 g/d were observed. The mean value for the modulus after the drawing process for the high melt flow rate is about 196 g/d. The theoretical modulus of PP is 35?42 GPa17, 275-330 g/d, which demonstrates the hIB fiber's modulus performance is approaching its theoretical maximum values. A key aspect of the third section of this study was to obtain ultra-high performance poly(ethylene terephthalate) fibers (PET) by utilizing a low molecular weight polymer via hIB method. The resulted fibers showed the efficient polymer chain orientation and the highly crystalline and ordered structures. The highest tenacity of more than 8 and 10 g/d were observed for the as-spun and drawn fibers, respectively, after only 1.28 draw ratios. The significant effect of the temperature of hIB spinning system on the fibrillar structure and the precursor's formation of the as-spun fibers was demonstrated. The melting temperature increased 8.51 oC from 254.05 to 262.56 oC when untreated and treated fibers are compared. The most important contribution of this study is that all these various types of polymer precursors for crystallization with different molecular weights after the baths treatments were highly oriented, yet non-crystallized or just showed the initial stages of crystallization. By a subsequent hot drawing process with the low draw ratio (DR< 1.5), the treated fibers showed a well-developed chain orientation and highly crystallized structures with superior mechanical performance.
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