Study On Mechanical Properties And Crystal Structures Of β Ippduring The Tensile Deformation Process

The mechanical properties of the polymer materials mainly depend on their final structures and the process which form the final structure, so most of the studies focused on polymer materials in the structure and performance and the relationship between them.Crystallization behavior of isotactic polypropylene (iPP) induced with aryl amide derivative (TMB-5) asβ-form nucleating agent at different temperatures were investigated via synchrotron small angle and wide angle X-ray scattering (SAXS /WAXS) and polarized optical microscopy (POM). The WAXS results indicated that TMB-5 is a temperature dependent selective nucleating agent for iPP crystallization. In another words, onlyβ-crystal orα-crystal forms at low or high crystallization temperature, bothβ-crystal andα-crystal can be found at proper crystallization temperature. A possible mechanism was proposed to understand the phenomenon and crystallization behavior of iPP with nucleating agent.SAXS/WAXS were carried out to investigate the uniaxial drawing-induced deformation and structure transitions ofβ-iPP at varying temperatures (30oC, 60oC, 80oC, 100oC and 120oC). The WAXS results indicated that the initial strain of strain inducedβ–αtransformation decreases with the tensile temperature according to the engineering stress-strain curves. The SAXS data showed that the long period increased along the equatorial direction and changed little along the tensile direction with increasing strain in the elastic deformation stage before the yield point. During the tensile test, the angle between parent and daughter lamella rotates from initial 40o or 140o to close to 90o accounts for the lateral expansion of the samples, which matches the essential auxetical behavior.β-iPP which isothermal crystallized at 135oC and 140oC were drew at varying temperatures. The results showed that the mechanical property is dominant in the system, especially at high stretching temperature. Both yield stress and fracture stress of iPP decreased with drawing temperature, while the tensile elongation at break increased with temperature. However, the nucleating agent content of 0.2% is the critical concentration for sample mechanical properties.