In Situ X-Ray Diffraction Study Of The Relationship Between Microstructure And Mechanical Properties Of Amorphous Sulfur And SPP

Polymer Physics concerns three main aspects: the first is the structure of the polymer, including the individual elements of the structure and aggregation of the structure of the polymer, while micro-structure directly determines the mechanical properties of materials. The second aspect is the performance of polymer materials, whose viscoelastic properties are the unique performance beyond the other materials. And the third is the relationship between structure and mechanical properties. There are a lot of scales in polymer structure, and the synergies of these structures determine the material properties. Research of the physical problems during the polymer processing can access to material changes influenced by the mechanical properties, while it also provides an experimental basis for the processing industry. This paper is divided into two parts: the supermolecular surphor for Supramolecular amorphous sulfur (amorphous polymer) in situ tensile test, and syndiotactic polypropylene sPP (crystal polymer) in situ tensile test.1) Homemade Miniature Mechanical TesterWe made a miniature mechanical tester, which can change the drawing rate and the sample temperature. With hi-precision CCD camera, it's able to get the Engineering stress-strain and the true Engineering stress-strain curve. Based on the Labview software, we can process the change of the sample's width, control the motor's rotation rate and the drawing rate. Furthermore, the homemade miniature mechanical tester is applicable for various light sources and different temperatures. After the installation onto the equipment measuring the micro-structure, it's easy to observe the material structure change online during drawing and compressing.2) Deformation Induced Linear Chain-Ring Transition and Crystallization of Living Polymer SulfurThe large bulk amorphous sulfur with a diameter of 18 mm and a thickness of 1 mm was obtained by a rapid high-pressure jump apparatus, which has a pressing rate of 100 GPa/s. The large bulk amorphous sulfur was cut into small strips with a length and a width of 12 and 1.5 mm respectively. Amorphous sulfur was studied as the representative living polymer. At high-temperature melt or amorphous state, element sulfur is in a high-molecular-weight (HMW) linear chain configuration, while sulfur crystals generally contain low-molecular-weight (LMW) rings. This is the first time to study the structure changes of the amorphous sulfur under uni-axial deformation with in-situ WAXD: (1) Drawing experiments were carried out under room temperature (25℃). Samples were mounted between two clamps of a homemade miniature mechanical tester. The mechanical error of the apparatus is less than 0.02 mm with a displacement of 100 mm. The drawing speed can be varied from 0.58 to 348μm/s with a step of 0.58μm/s. The error of the force sensor is about 0.1 N. (2) WAXS measurements were performed on a setup with Mar 345 image plate as detector and Mo KR as the source (wavelength is 0.07107 nm). The information such as changes of crystallinity, phase transition, orientation of the crysal can be extracted form the WAXD image. Corresponding to the mechanical properties of the amorphous sulfur, the conclustion is that both thermal and drawing can induce chain scission and reforming, which leads to the transition between linear chain and rings. With the large drawing rates from 1.74 to 5.8μm/s, deformation-induced chain scission dominates, which results into fibrous phase composing of HMW linear chains and LMW cyclosulfur phases (S₁₈ and S₈). Under the low deformation rates (below 1.74μm/s), the thermal effect takes over and leads to the formation of S8 phases which is similar to that under quiescent condition. 3) Streching of sPP and effect of lamellar thickness on structure evolutionsPP is one kind of the important semicrystal polymer, with many excellent properties such as transparency, surface gloss and special mechanical properties. It has been the most popular thermoplastics, used widly for the food industry, film engineering etc.As an important semi-crystalline polymer, the effect of sPP's structure on its mechanical properties should be an interesting region. Compared with amorphous polymers, crystalline polymers are complicated systems, with an amorphous phase interlaying crystalline lamellae. The strength and toughness of crystalline system are interdependent due to crystalinity, lamellae thickness, molecular orientation etc. In this investigation, sPP samples with different lamellae thickness were obtained from different prepared method: isothermally crystallization and annealed crystallization. To correlate the structure changes and the mechanical properties, the engineering force curves were divded into three regions: part (1) Complete elastic region, part (2) Plastic region (from the first yield point to the second yield point) and part (3) after necking. The (200) crysal planes were chosen to study the structure changes of the crysal lattice under deformation. The most astonishing finding is the average d-spacing changes of (200) crystal planes. Since Havard and Thackay model was insufficient to explain our experiment, we established another model, in which the changes of the grain's micro-strain agree well with that of average d-spacing.