Mohammad Razavi-Nouri

Effect of block ratio and strain amplitude on thermal, structural, and shape memory properties of segmented polycaprolactone-based polyurethanes

In this work, the effects of changing molecular weight of polyol (2000, 3000, and 4000) and block ratio as well as deformation amplitude on thermal, structural, and shape memory properties of polyester urethanes based on diphenylmethane diisocyanate, polycaprolactone diol, and 1,4-butanediol were investigated. Fourier transform infrared spectroscopy was used to check the accomplishment of the polyurethanes synthesis. Thermal, structural, and shape memory properties of synthesized SMPUs were measured using differential scanning calorimetry, wide angle X-ray diffraction, and tensile cyclic tests, respectively. It was found that as the crystallinity of soft segments increased, the ability of the samples in fixation of temporary shape was higher. On the other hand, the shape recovery was dominated by the hard segment content and there was a minimum critical HSC for the samples to show appropriate shape memory effects.

Thermal and dynamic mechanical properties of metallocene polyethylene

A comprehensive study has been made of a metallocene polyethylene (m-PE) characterising the isothermal crystallisation kinetics, melting and crystallisation behaviour, crystal growth and dynamic mechanical properties in order to understand the relationship between molecular structure and mechanical properties of this new class of polyethylene. The melting behaviour after step-wise crystallisation showed that m-PE consisted of molecular fractions with different molecular weight and branch distribution. Dynamic mechanical property studies showed that three transitions existed in m-PE with the α-transition increasing in intensity and shifting to higher temperatures in samples crystallised at higher temperature compared with rapidly cooled samples.

Finite element analysis of flow of thermoplastic elastomer melt through axisymmetric die with slip boundary condition

Abstract A finite element model for the flow of thermoplastic elastomers in extrusion dies has been developed. The rheological behaviour of the polymer melt is assumed to be described by the generalised Newtonian models and as a special case, the well known, power law equation was selected. Owing to the very low variation of the temperature field, the flow regime was considered to be isothermal. The set of governing equations are solved using the finite element method in a cylindrical (r, z) coordinate system. Slip–stick of the polymer melt on the solid wall, encountered in the flow of highly viscous fluids, is incorporated into the model by the use of Naviers slip condition. A new method based on a technique developed previously is described for the inclusion of this condition in the working equations. The applicability of the model was verified by a comparison between the results of the simulation of a polypropylene–nitrile/butadiene rubber thermoplastic elastomer with experimentally measured data. These comparisons show that there are very good agreements between the model predictions and actual data, provided that the slip of the polymer melt during the flow in extrusion die has been taken into consideration.

Effect of ionic group content on thermal and structural properties of polycaprolactone-based shape memory polyurethane ionomers

In this work, the effect of ionic group content on thermal, structural, and shape memory properties of segmented polyurethane ionomers based on polycaprolactone diol, diphenylmethane diisocyanate, 1,4-butanediol, dimethylol propionic acid, and triethyl amine was investigated. Fourier transform infrared spectroscopy was used to check the accomplishment of the synthesis. Thermal, structural, and shape memory properties of the synthesized shape memory polyurethanes were measured using different techniques such as differential scanning calorimetry, thermogravimetric analysis (TGA), wide-angle X-ray diffraction, and tensile cyclic tests. It was found that the ionomers with higher amount of ionic groups have relatively stronger crystallization tendency. In addition, the glass transition temperature of soft segments was influenced by the degree of phase separation. It was observed that the degree of phase separation improved when the amount of ionization was higher than a critical value. The increased polarity difference of soft and hard phase upon ionization could be the driving force for increased phase separation. The results obtained from TGA showed that the thermal stability of the ionomers was lower than that of the non-ionomer sample. This can be attributed to the reduction of hydrogen bond formation and decrease of cohesion in the hard domains of ionomers. In addition, ionic group content affected the shape recovery of the material, where this parameter increased with the increase of ionic groups.

Modelling of polymer fluid flow and residence time distribution in twin screw extruder using fictitious domain method

Abstract The flow behaviour of a polymer melt in the conveying region of an intermeshing corotating twin screw extruder was studied using the combination of mixed finite element and fictitious domain method. The model was a combination of the governing equations of continuity and momentum with Carreau rheological model in a three-dimensional Cartesian coordinate system. The equations were solved by the use of a mixed Galerkin finite element technique. The Picard’s iterative procedure was used to handle the non-linear nature of the derived equations. The particle tracking technique was used to obtain residence time distribution and analyse distributive mixing in conveying region. The shear rate distribution was investigated as a criterion for dispersive mixing. The applicability of this model was verified by the comparison of experimentally measured pressure and simulation results for high density polyethylene melt. This comparison shows that there is a good adequacy between experimental data and model predictions.