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首页> 外文学位 >Investigation of dynamics and structure development during uniaxial stretching of PET films at different molecular weights using fully automated spectral birefringence technique.
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Investigation of dynamics and structure development during uniaxial stretching of PET films at different molecular weights using fully automated spectral birefringence technique.

机译：使用全自动光谱双折射技术研究在不同分子量的PET薄膜的单轴拉伸过程中的动力学和结构发展。

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In order to develop non-intrusive automated control protocols to tailor final properties during film processing, an understanding of structural development is essential. Recently developed real-time the Spectral Birefringence system fulfills all these requirements to couple optical properties with structural details of polymer films through its measure of optical anisotropy.; The Spectral Birefringence method is optimized for noise reduction to monitor rapid optical changes during uniaxial stretching of different molecular weight PET films. A tensile stretcher is designed and built in our laboratory that keeps the center of the dumbbell-shaped sample at a constant position for optical measurements. A laser width measurement system is also incorporated in this stretching system to assess the true mechanical response of the material at the middle portion of the film.; The relationship between birefringence and true stress development of various molecular weight PET films uniaxially stretched at 2, 20, and 200 mm/min at 90°C shows that there are three stress-optical regimes with different characters.; In the first well-known stage, birefringence develops linearly with true stress. In the second stage, the linear relationship gains a nonlinear character close to the strain hardening point. Finally in the third stage, birefringence reaches a plateau at the higher values of true stress.; Structural studies performed by WAXS, DSC and Raman are used to elucidate these three stages of birefringence development during stretching: in the first stage, the deformation of polymer chains takes place while they remain in amorphous state. At the end of this stage, chains start to orient to form oriented crystals that are responsible for the breakdown of linear birefringence development. After the breakdown, in the second stage, the deformation causes the chains to orient and crystallize substantially as it is shown by crystallinity and trans conformer fraction increase. The second stage is identified by an accelerated increase of birefringence. Finally, in the third stage, birefringence increase slows down and almost reaches a plateau; crystallinity conversion becomes almost negligent; and the trans conformer fraction continues to increase, indicating that chains are still responding to deformation by becoming oriented and taut.
机译：为了开发非侵入式自动控制协议以在胶片处理过程中调整最终性能，对结构发展的理解至关重要。最近开发的实时光谱双折射系统满足了所有这些要求，通过光学各向异性的测量将光学性能与聚合物薄膜的结构细节耦合在一起。光谱双折射方法经过优化，可降低噪声，以监测不同分子量PET薄膜单轴拉伸过程中的快速光学变化。在我们的实验室中设计并建造了一个拉伸担架，可将哑铃状样品的中心保持在恒定位置以进行光学测量。该拉伸系统中还装有激光宽度测量系统，以评估膜中间部分材料的真实机械响应。在90°C下以2、20和200 mm / min单轴拉伸的各种分子量的PET薄膜，双折射与真实应力发展之间的关系表明，存在三种具有不同特征的应力光学体系。在第一个众所周知的阶段，双折射随着真实应力线性增长。在第二阶段，线性关系获得接近应变硬化点的非线性特性。最终，在第三阶段，双折射在较高的真实应力下达到平稳状态。由WAXS，DSC和Raman进行的结构研究用于阐明拉伸过程中双折射的这三个阶段：在第一阶段，聚合物链发生变形，而它们保持非晶态。在此阶段结束时，链开始取向形成定向晶体，该晶体负责线性双折射的产生。击穿后，在第二阶段，变形使链基本取向并结晶，如结晶度和反式构象分数增加所表明的。第二阶段是通过加速双折射来确定的。最后，在第三阶段，双折射的增加变慢并且几乎达到平稳状态。结晶度转变几乎变得疏忽了；反式构象分数继续增加，表明链仍然通过定向和拉紧来响应变形。

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