Band 30, Heft 5

In this paper, the residual stress in polyethylene terephthalate (PET) bottles, which was processed using blow-molding, was analyzed theoretically and numerically. First, the process of blow-molding was analyzed theoretically, which had considered both blowing process and curing of the polymer. The creep model was used to describe the relation between the deformation and the pressure in the blowing process, and thermo-chemical model was used to describe the curing process of the PET bottle. Then, a simulation was carried out using ABAQUS based on the creep model and thermo-chemical curing model. The deformation, residual stresses, heat flux vector and strain of the PET bottle during the blow-molding process were obtained. Finally, the effect of loading path on the residual stress was analyzed numerically, which shows that the longer the pressure was applied, the larger the residual stress.

Two different types of inorganic silica fillers, nano-silica powder (NSP) and colloidal silica sol (CSS) were added into isotactic polypropylene (iPP) with low silica content (0.2 wt%) and the influence of the two silica fillers on the crystallization behavior and mechanical properties of iPP were investigated. Differential scanning calorimeter (DSC) results showed that the crystallization temperature of iPP with CSS and NSP were increased by 4.1 °C, and 2.4 °C, respectively. The tensile strength, flexural strength, and izod impact strength of iPP/CSS (33.75 MPa, 33.04 MPa, and 4.80 kJ/m 2 ) were higher than that of iPP/NSP (32.09 MPa, 32.27 MPa, and 4.25 kJ/m 2 ). In addition, the haze value of iPP/CSS was decreased from 37.6 % to 27.6 %, which was 4.7 % lower than that of iPP/NSP (32.3 %). The better performance of CSS as ascribed to its better dispersion ability in iPP matrix than NSP, and it was verified by scanning electron micrograph (SEM) and transmission electron microscope (TEM). Overall, these results indicated that inorganic silica sols had a potential application in the nanoparticle-reinforced composites field.

This study proposed a processing technology using a multi-axis magnetic roller for micro-structure transfer embossing development. First, dynamics deduction and ANSYS numerical simulation were used to explore the impact of the upper axis on the medium and lower axis, under the conditions of different parameters. This study also-developed and established a multi-axis magnetic roller micro-structure transfer embossing system for analysis, simulation, and discussion, on the technological characteristics of the multi-axis auxiliary roller embossing replication and transfer embossing processing technology. By taking advantage of the feature of the uniform contact pressing of the magnetic roller during the roller embossing process, coupled with the coordinated force application of the three axis rollers, this study attempted to achieve complete, uniform transfer embossing and replication of the micro-structure during the roller embossing process. The results of multi-axis transfer embossing process simulation and experimental analysis showed that multi-axis transfer embossing technology can transfer and replicate a micro-structure on the roller in a more uniform and more effective manner. The proposed multi-axis magnetic roller micro-structure transfer embossing system can smoothly replicate a micro-structure by roller embossing with good replication moldability and optical performance characteristics, in order to sufficiently achieve uniform embossing results

Initial heating conditions and temperature effects have an important influence during the injection stretch blow molding process of PET preforms. The paper provides a simplified modeling of the infrared (IR) flux provided by the IR lamps and the convection heat transfer with air, for the finite element simulation of the heating of PET samples. This modeling enables fast thermal simulations in industrial context. First, a complete 2D simulation of the air convection around a PET sheet sample is conducted using ANSYS/FLUENT to compute the local convection heat transfer coefficient. The distribution of this coefficient along the PET wall is then interpolated by a best linear fit function of the wall position to provide the boundary condition of the convection heat transfer thereafter. This boundary condition, coupled with the calculation of the infrared flux absorbed by the PET sheet sample, allows a 3D calculation of the time evolution of the sample temperature. This calculation is validated by comparing the experimental temperature distribution of the PET sheet obtained from an IR camera with the numerical results of the simulation. Second, we focus on the modeling of the heating of a cylindrical PET preforms by IR lamps. In our approach, the IR heating flux is calculated using the spectral and surfaceto-surface radiation laws adapted to the sample geometry. The air convection effect around the preform is modeled using the heat transfer coefficient identified from the 2D plane sheet case. It is applied on the boundaries of a simpler model in Comsol where only the preform is meshed. The temperature distribution on the outer surface of the preform is compared to experimental measurements by thermal imaging. A good agreement is observed which validates the whole approach used.

In the water and gas distribution industry, electrofusion is one of the main techniques used for welding polyethylene pipes. In order to help understanding the origin of some defects discovered recently and to optimize and predict the welding quality, we developed a coupled numerical and experimental approach. Our numerical model, that computes a weld quality index based on molecular interdiffusion, is able to reasonably well predict whether welding will occur or not depending on the welding conditions imposed.

In this study, we describe the synthesis of amides and evaluate their use as slip additive agents in polypropylene films. The additives N-isopropyl-stearamide and N,N-diisopropyl-stearamide were synthesized and characterized and then used to prepare masterbatches. Erucamide, a commercial masterbatch, was used as the reference standard. A 3 2 factorial experimental design was used to create the different compositions of slip additives in polymer films. The films were processed via flat-die extrusion and stored in an oven at a constant temperature of 40 °C for seven days. The following are the properties evaluated in the study: thermal decomposition temperature, fusion temperature, fusion enthalpy, coefficient of friction, surface energy, contact angle, and seal initiation temperature. The results were evaluated by analysis of variance (ANOVA) at a 90 % confidence interval. The analysis of the results showed that N-isopropyl stearamide and N,N-diisopropyl stearamide do not provide an adequate surface slip for polypropylene films at the conditions used in the study. In turn, at the same conditions, erucamide, the commercial amide, also does not provide the required surface energy for printing and lamination processes required for polypropylene films.

A linear dependency of zero shear, constant shear-rate and constant shear-stress viscosities with temperature and hole fraction (“thermo-occupancy” function) was derived for polyacrylonitrile-butadiene-styrene (ABS), polypropylene (PP) and polystyrene (PS). The relation of viscosity parameters, such as transmission coefficient and a measure of activation energy coefficient, with shear-rate and shear-stress was also investigated and some conclusions on the differences for the studied polymers were discussed. In particular, it was found that, for all materials, the derivative of logarithm of viscosities at zero shear, constant shear-rate and constant shear-stress decreases with decreasing rate with the hole fraction.

The purpose of this study was to improve toughness of inherently very brittle polylactide (PLA) without sacrificing strength and thermal properties, so that biopolymer PLA could be used in engineering applications. For this purpose, PLA was blended with various amounts of two different thermoplastic elastomers; TPU (petroleum-based thermoplastic polyurethane) and TPE (bio-based thermoplastic polyester). Melt blending and specimen shaping were achieved by using a twin-screw extruder and injection molder, respectively. SEM analysis indicated that TPU and TPE were immiscible forming fine and uniform round domains in the PLA matrix. It was revealed that rubber-toughening mechanisms of TPU and TPE were very effective. For instance, using only 10 phr of TPU or TPE increased Charpy impact toughness of PLA more than 300 %, while increases in fracture toughness (K IC and G IC ) values of PLA were as much as 35 % and 130 %, respectively. Other mechanical tests (tension, flexure, hardness) and thermal analyses (DSC) revealed that there were no significant detrimental effects of using 10 phr TPU or TPE on the engineering performance of PLA.

The paste extrusion process of two types of PTFE has been studied in capillary extrusion using dies having different reduction ratio (RR) and die entrance angles. The extrusion pressure shows a weak increase with shear rate over a wide range of flow rates and a more significant increase with reduction ratio. Moreover, the extrusion pressure exhibits a minimum for entrance angle at around 30°. A simple analytical model based on the radial flow hypothesis (previously developed) has been found to represent the extrusion pressure adequately as a function of flow rate (shear rate) and geometrical characteristics of the capillary dies. The extrudates collected at different processing conditions were dried and tested in uniaxial extension to assess their effect on mechanical properties. The tensile modulus, yield stress and ultimate tensile strength of the obtained extrudates were found to be increasing functions of reduction ratio, although the opposite effect was found for the ultimate elongational strain. These mechanical properties are also found to be insensitive to changes in the die entrance angle although the ultimate tensile strength has shown a maximum at the entrance angle of about 60°. The PTFE paste extrudates show a Poisson's ratio equal to zero in tensile experiments, thus exhibiting expansion (significant density reduction with stretching). Finally, a simple model was derived for the density change in tensile deformation by taking into the account the Poisson's ratio and the strain recovery (recovery of the elastic energy stored upon removal of the tensile stress).