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Temporally Programmed Stretching of Polymer Films: Influence of Nanoparticles

Seif, Sylvain S.

Abstract Details

2009, Doctor of Philosophy, University of Akron, Polymer Engineering.

This research provides an in-depth analysis on the effects of organoclay inclusion in PLA film on the evolution of structural hierarchy during constant and variable rate uniaxial and biaxial stretching processes. At lower deformation rates and/or higher temperatures PLA exhibits three regime stress-optical behavior: In Regime I, the material remains amorphous while obeying the traditional linear Stress Optical Rule (SOR), in Regime II strain crystallization occurs in conjunction with a positive deviation from SOR, and in Regime III, birefringence increases slowly with stress as the chains reach their finite extensibilities or are locked in place by an oriented crystalline network. This is due to partial chain relaxation at these conditions which allows the highly oriented adjacent chains to register themselves into the crystal lattice formation. Lower temperature and/or higher rates, on the other hand, evoke a nematic-like phase consisting of high orientation but significant translational disorder, bringing about Regime I-III behavior with absence of Regime II. As the organoclay filler content increases, higher temperatures and/or lower rates are required to overcome the confinement effect on the PLA chains in the vicinity of the high aspect ratio organoclay platelets and/or to relax the chains that are quickly being pulled and oriented by the clay. The 3D ordered crystal zones in filled material don’t all orient in the MD, as many of the PLA chains that are entangled between and interconnected with the organoclay platelets’ surfaces deform and crystallize away from the MD as the platelets separate during stretching. This phenomenon leads to lower Regime I-II slopes and end-birefringence values with an increase in clay loading.

Application of very low stretch rates early on in the deformation process (Exponential (EXP) profile) was found to delay the strain crystallization mechanism which leads to rapid orientation development in the material. For the same value of strain, the highest birefringence values are evidenced in the Logarithmic (LOG) profile, whereas the lowest values are seen in the EXP profile. Furthermore, higher crystallinity values for the same strain values are obtained in the LOG profile, while lower values are obtained in the EXP profile. This implies that the chains orient and crystallize more efficiently when high rates are applied early on in the deformation process. Intermediate levels of crystallinity are induced when Linear (constant stretch rate) or Sigmoidal (high stretch rates at intermediate stages of deformation) deformation profiles are applied. Incorporation of Cloisite 30B organoclay speeds up the oriented crystallization process, bringing about significantly higher crystallinity levels at the lower deformation levels. However, as the deformation proceeds to high extension levels, higher crystallinity levels are noted in neat PLA.

Mukerrem Cakmak, PhD (Advisor)
412 p.

Recommended Citations

Citations

  • Seif, S. S. (2009). Temporally Programmed Stretching of Polymer Films: Influence of Nanoparticles [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1248047899

    APA Style (7th edition)

  • Seif, Sylvain. Temporally Programmed Stretching of Polymer Films: Influence of Nanoparticles. 2009. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1248047899.

    MLA Style (8th edition)

  • Seif, Sylvain. "Temporally Programmed Stretching of Polymer Films: Influence of Nanoparticles." Doctoral dissertation, University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1248047899

    Chicago Manual of Style (17th edition)