UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR
| Main Author: | |
|---|---|
| Language: | English |
| Published: |
University of Akron / OhioLINK
2016
|
| Subjects: | |
| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=akron1460505451 |
| id |
ndltd-OhioLink-oai-etd.ohiolink.edu-akron1460505451 |
|---|---|
| record_format |
oai_dc |
| collection |
NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Polymers |
| spellingShingle |
Polymers Kang, Jia UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| author |
Kang, Jia |
| author_facet |
Kang, Jia |
| author_sort |
Kang, Jia |
| title |
UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| title_short |
UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| title_full |
UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| title_fullStr |
UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| title_full_unstemmed |
UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR |
| title_sort |
uniaxial plastic deformation of isotactic polypropylene studied by solid-state nmr |
| publisher |
University of Akron / OhioLINK |
| publishDate |
2016 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=akron1460505451 |
| work_keys_str_mv |
AT kangjia uniaxialplasticdeformationofisotacticpolypropylenestudiedbysolidstatenmr |
| _version_ |
1719439464667807744 |
| spelling |
ndltd-OhioLink-oai-etd.ohiolink.edu-akron14605054512021-08-03T06:35:32Z UNIAXIAL PLASTIC DEFORMATION OF ISOTACTIC POLYPROPYLENE STUDIED BY SOLID-STATE NMR Kang, Jia Polymers <p>At alleviated temperatures, some semicrystralline polymers can be stretched to very large deformation ratios. Such deformations of semicrystalline polymers have been extensively studied since 1960s. Based on experimental observations and theoretical investigations, solid-state transformation (three stage model) proposed in 1971 and local melting and recrystallization in 1978 have been considered two major mechanisms to explain the deformations of polymer crystals. With the elucidation of molecular dynamics in the last two decades, it was proposed in 1999 that helical jump motion plays an important role in crystal deformation. On the other hand, the new structures induced by deformation also influence the molecular motions and resultant properties of deformed polymers. Such processing-structure-property relationship is very important to understand the polymer behaviors as well as to inform the polymer industry.</p><p>However, to conclude the deformation mechanism of semicrystalline polymer is still challenging, because there is no appropriate tools to trace structural evolution of polymer chains inside the polymer bulk. And detailed understanding of the relationships between hierarchical structures and specific motions and properties need to be achieved.</p> <p>In this dissertation, using the advanced tool of solid-state NMR (ss-NMR), we achieve three goals: Firstly, we investigate the hierarchical crystalline structural changes of isotactic polypropylene (<i>i</i>PP) upon high temperature stretching to understand the deformation process. Secondly, we evaluate the roles of local packing structure and crystal thickness in determining the stem motions and thermal properties of deformed a-form <i>i</i>PP. Thirdly, we utilize <sup>13</sup>C-labeled isotactic polypropylene (<i>i</i>PP) to trace the change of chain folding number as a function of <i>e</i> to conclude molecular-level deformation mechanism.</p> <p>To realize the first and second goals, the chain packing, crystal thickness, molecular dynamics, and melting temperature (T<sub>m</sub>) of a-form <i>i</i>PP drawn uniaxially at high temperatures of 100 - 150 °C were investigated using solid-state (SS) NMR and DSC. Two types of <i>i</i>PP samples with disordered (a<sub>1</sub>) and relatively ordered (a<sub>2</sub>-rich) packing structures were prepared via different thermal treatments and drawn up to an engineering strain (<i>e</i>) of approximately 20. High-resolution <sup>13</sup>C NMR detected continuous a<sub>2</sub>-to-a<sub>1</sub> transformations in the original a<sub>2</sub>-rich samples over the entire deformation range at all drawing temperatures (T<sub>d</sub>s). A sudden a<sub>1</sub>-to-a<sub>2</sub> transformation was found to occur in the original a<sub>1</sub> sample in the small e range of approximately 3 - 8 at T<sub>d</sub> = 140 °C. Then, in the late stage, the newly grown a<sub>2</sub> structure reversely transformed into a<sub>1</sub> structure with further increase in <i>e</i>, as observed in the original a<sub>2</sub>-rich sample. These results indicate that at least two different processes are involved in large deformations. On the basis of crystallographic constraints, the continuous a<sub>2</sub>-to-a<sub>1</sub> transformation over the entire deformation range is attributed to molecular-level melting and recrystallization facilitated by chain diffusion. The steep a<sub>1</sub>-to-a<sub>2</sub> transformation in the smaller <i>e</i> range is assigned to isotropic melting and recrystallization induced by stress. After the large deformations (<i>e</i> ˜ 20) of the original a<sub>2</sub>-rich and a<sub>1</sub> samples at Td = 150 and 140 °C, respectively, 1H spin diffusion verified increases in the crystal thickness in both the former (14.1 nm at <i>e</i> = 0 and 20.1 nm at <i>e</i> = 20) and the latter (9.2 to 17.0 nm). Centerband-Only Detection of EXchange (CODEX) NMR at 120 °C demonstrated that the correlation time (t<sub>c</sub>) of the helical jump for the former drastically decreased from t<sub>c</sub> = 52.4 ± 5.2 at <i>e</i> = 0 to 9.3 ± 1.8 ms at <i>e</i> = 20 but slightly increased from 4.2 ± 1.3 to 7.1 ± 0.9 ms for the latter. Additionally, DSC indicated that the melting temperature (T<sub>m</sub>) for the former decreased considerably from 173 °C at <i>e</i> = 0 to 165 °C at <i>e</i> = 20, whereas the melting temperature (T<sub>m</sub>) remained nearly invariant at 163 °C for the latter. Based on these findings, we conclude that the local packing structure plays a crucial role in determining the molecular dynamics of the stems and T<sub>m</sub> of largely deformed <i>i</i>PP materials. The established relations among the structures, the dynamics, and the thermal properties provide a useful guide to achieving improved properties of <i>i</i>PP materials under processing.</p><p>To realize the third goal, <sup>13</sup>C-<sup>13</sup>C Double Quantum (DQ) NMR was applied to trace the structure evolution of <sup>13</sup>C-labeled <i>i</i>PP chains inside the crystallites under stretching at 100 ºC. DQ NMR based on spatial proximity of <sup>13</sup>C labeled nuclei proved conformational changes from the folded chains to the extended ones of the <i>i</i>PP chains induced by stretching. By combining experimental findings with literature results on molecular dynamics, it was concluded that transportation of the crystalline chains plays critical role to achieve the large deformability of <i>i</i>PP.</p> 2016-06-09 English text University of Akron / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=akron1460505451 http://rave.ohiolink.edu/etdc/view?acc_num=akron1460505451 unrestricted This thesis or dissertation is protected by copyright: some rights reserved. It is licensed for use under a Creative Commons license. Specific terms and permissions are available from this document's record in the OhioLINK ETD Center. |