| Synchrotron X-ray scattering and diffraction techniques have been widely used to study the structure and property relationships of materials. It is important to first identify the driving physics and basic understanding of the structure change during mechanical usage before leading to material design for potential applications. In this thesis, the combined wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques have been used to analyze in-situ structure formation over a large range of length scale from 1 nm to 100 nm during mechanical deformation. In specific, the in-situ structural development and morphological changes in polymer plastics and rubber during tensile deformation were studied.;The chosen systems included the lamellar structural changes of uniaxially oriented semi-crystalline polyethylene (PE) fibers using in-situ WAXD and SAXS techniques. The deformation mechanism in PE was found to be driven by an initial structural rearrangement of the lamellar stacks, followed by crystallographic slippage and strain-hardening. The experimental deformation results were qualitatively compared with atomistic simulations of tensile deformation to provide further insights into the interlamellar regions and its overall effect on PE deformation. Various temperatures, strain rates, and modes of deformation were explored.;In natural rubber (NR), the behavior of strain-induced crystallization (SIC) was found to be primarily responsible for its outstanding mechanical properties, such as high tensile strength, tear strength, cut resistance, and durability. The underlying mechanism could be attributed to the pseudo-network and the non-rubber components-polymer interactions in NR. In other words, the inhomogeneity of cross-linked topology in NR leads to a microfibrillar structure composed of crystalline segments between the cross-links during stretching. A novel two-dimensional WAXD simulation method was developed to analyze the SIC of un-vulcanized NR, vulcanized NR, and synthetic polyisoprene rubber (IR). Crystallite properties, such as size, volume, orientation, crystal fractions, and crystal disordering, were obtained and compared at various temperatures from -50 to 50°C. The effects of temperature on the mechanical properties and the SIC process are discussed. |
