Rheological Modeling for Production of High Quality Polymeric
The fundamental defect inherent to the thermoforming technology is wall-thickness variation of the products due to inadequate thermal processing during production of polymer. A nonlinear viscoelastic rheological model is implemented for developing the process model. This model describes deformation process of a sheet in thermoforming process. Because of relaxation pause after plug-assist stage and also implementation of two stage thermoforming process have minor wall-thickness variation and consequently better mechanical properties of polymeric articles. For model validation, a comparative analysis of the theoretical and experimental data is presented. Keywords—High-quality polymeric article, Thermal Processing, Rheological model, Minor wall-thickness variation.
Rheological modeling of plug‐assist thermoforming
Solving problems for thermoforming processes in the production of axisymmetric thin walled plastics is investigated in this research work. A nonlinear viscoelastic rheological model with a new strain energy function is suggested for improvement of physical properties of final product. For model validation, a quantitative relation between stress and technical parameters of plug-assist thermoforming is determined by comparison of theoretical and experimental results. This process with the proposed rheological model could be suggested for prevention from some technical defects such as wall thickness variations, physical instability during inflation-shrinkage, and warpage exhibited in the final part of a polymeric sheet thermoforming. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4148–4152, 2006
Development of an Analytical Method for Explosive Residues in Soil
Abstract : An analytical method was developed to determine the concentrations of HMX, RDX, TNB, DNB, Tetryl, TNT and 2,4-DNT in soil. The method involves extracting a 2-g sample with 50 mL of acetonitrile using an ultrasonic bath procedure for 18 hr. A 10-mL portion of the extract is diluted with 10 mL of water, filtered through a 0.45-micrometer Millex SR filter, and analyzed by RP-HPLC using a fixed 254-nm UV detector. Separations were obtained on an LC-18 column eluted with 50:50 water-methanol. Retention times were 2.55, 3.82, 5.16, 6.25, 7.04, 8.47 and 10.15 min for HMX, RDX, TNB, DNB, Tetryl, TNT and 2,4-DNT, respectively. Confirmation of analyte identities is recommended by RP-HPLC on an LC-CN column using 50:50 water-methanol. Kinetic studies using naturally contaminated soil indicated that equilibrium was achieved within 24 hr for the majority of soils and analytes studied. The method provides linear calibration curves over a wide range of concentrations. Reporting limits were conservatively estimated at 1.6, 1.8, 1.5, 0.5, 5.5, 0.8 and 0.8 micro grams/g for HMX, RDX, TNB, DNB, Tetryl, TNT and 2,4-DNT. Analytical precision was estimated at + or - 0.44, 0.51, 0.43, 0.13, 1.24, 0.27 and 0.20 micro grams/g, respectively, in the range of homogeneous variance near the detection limits. At higher concentrations the relative standard deviation was constant at 2% for HMX, RDX, DNB and TNB, 3% for TNT and 2,4-DNT, and 6% for Tetryl.