Volume 14, Issue 4

Mixing has been the focal point of many experimental studies in recent years, but advances in modeling and simulation now allow for fast, accurate and useful simulation analysis. Numerous mixing indices have been developed but the majority are tailored to experimental studies. In this study, a new mixing index is developed to analyze the particle position history of the mixer. Due to its simplicity when dealing with moving boundary problems, the boundary element method is employed to model the fluid flow and track particles. Numerous geometries can be modeled and compared on a basic workstation. First the mixing index is applied to Couette flow. Analytical and boundary element simulation results compare well. Next the method is used to analyze the mixing capabilities of a Banbury mixer with different speed ratios. Further the mixing index is used to compare the mixing capabilities of triangular mixing lobes versus typical Banbury type.

This report explores the alternative of processing biodegradable polymer-antibiotic composites as a long-term drug release. Polymer-antibiotic composite beads were manufactured by a compression-sintering technique. An elution method was employed to characterize the release rate of antibiotic over a 35-day period at 37°C. Biodegradable polymer composites released high concentrations of antibiotic (well above the breakpoint sensitivity concentration) in vitro for the period of time needed to treat bone infection; i.e. 4 to 6 weeks. By changing the processing variables, one is able to control the release rate of the beads. This provides advantages of meeting the specific antibiotic requirement for patients with various surgical infections.

The paper deals with practical and theoretical investigations of the PA 6 high speed fiber spinning process in the velocity range from 3000 until 5450m/min by means of tensile force measurements in the spinning line below the fiber solidification point. The measurements were evaluated under three different goals as follows: Quantitative determination and interpretation of relations between the technological and textile-physical fiber parameters spinning speed, throughput, and fiber fineness (in the range of 4.1 to 14.8 dtex for a single filament spun from a 9-holes die). Comparison between the experimentally measured and the theoretically calculated tensile forces by means of the own fiber formation model developed in the last years. On this occasion a satisfactory concordance could be noticed between the experimental and theoretical results. In addition to this a good model parameter estimation could be proved in the force balance part of the differential equation system for the fiber formation. Spectral analytical evaluations of the measured tensile force time functions by means of their autocorrelation functions. It could be demonstrated, that higher frequency tensile force disturbances could be caused both by the spinningpump and by unevennesses in the cross quench air conditions below the spinning die. All results from the investigations above are discussed in relation to different technological process goals and their realization possibilities.

By means of ultra-violet (UV) irradiation with photoinitiator and multifunctional crosslinking agent, the crosslinking modification of ultrahigh molecular weight polyethylene (UHMWPE) fibers prepared by gel spinning was performed. Thermal and mechanical properties of fiber samples were examined using differential scanning calorimeter, thermo-mechanical analysis apparatus and tensile tester, the gel content of fibers was measured by a standard device, the fiber surface was examined by scanning electron microscope. The results indicate that the optimal irradiation time is 1 to 2 hours. The modified fiber can then preserve its original mechanical properties, or may have better behavior, meanwhile, such fibers have improved heat- and creep-resistant behaviors.

For two linear polyethylene melts, a HDPE and a LLDPE, Rheotens experiments at constant extrusion pressure and different extusion temperatures are reported. While at sufficiently small extrusion pressure Rheotens mastercurves were found, various deviations from the mastercurves were observed at higher extrusion pressures. By use of capillary rheometry and Mooney's method, these deviations could be attributed to a stick-slip transition in the extrusion die, and, in the case of LLDPE, to partial wall slip below the stick-slip transition.

The stability of a blown film extrusion process has been investigated using a simple isothermal Newtonian model. Although the Newtonian model may be an oversimplification for polymer melts, it serves as a reasonable first approximation for linear polymers (e.g., linear low density polyethylene) in extensional flow situations. The results obtained by the method of linear stability analysis indicate that the blown film process becomes unstable if the blow-up ratio (BUR) or the film thickness reduction is larger than a certain critical value. In addition, existence of an optimum freeze-line-height is predicted at which the region of stable operation is largest in terms of the BUR and the film thickness reduction. These predicted trends are in qualitative agreement with experimental observations for linear polymers such as LLDPE.

Glass mat thermoplastics (GMT) have the superior property/price ratio, they can be used in many industrial aspects. In this paper, through a 100mm-deep mold, the glass mat distribution, fiber orientation and mechanical properties of the part were studied under different blank designs. In conclusion, (1) Blank design has effect on the mat distribution and fiber orientation, and finally on the mechanical properties of the part. To a part, there is an optimum blank design, which will not greatly decrease the mechanical properties of the sheets in the final part. (2) In compression molding, interlaminar slippage, blank ejection and resin solidification result in mat distribution and fiber orientation.

In a recent paper [1], the preparation techniques, structural features, crystallization, melting characteristics, and certain properties of the β-modification of isotactic polypropylene (β-IPP) were reviewed. Possible uses of β-IPP were demonstrated through example applications. The problems involved with the processing of β-nucleated polypropylene were analyzed and the conditions of the processing technology of β-IPP end-products were discussed. In the present paper, the results of the studies on the injection moulding technology of a commercial β-nucleated polypropylene are addressed.

Polycarbonate(PC)/ABS is a very common immiscible polymer blend. The internal structure such as distribution of each component in the injection moldings of PC/ABS would be strongly affected by the processing parameters. Especially, the weld line formed by meeting two melt flows and the internal structure at the weld area would be a very complex form. By observing the etched samples of PC/ABS injection moldings using scanning electron microscopy, a weld part with fine dispersion of ABS was found in the area below V-notch. When tensile load was applied perpendicular to the weld line, the fracture initiated from the V-notch, but the crack propagated along the interface between the weld part with fine dispersion and the part behind the weld part. This leads to unique characteristics of the weld strength.

The rotational molding technique was utilized in the fabrication of hollow femur models for the expressed purpose of photostress analysis. Advances in computer control coupled with the development of proper experimental protocols enabled the consistent and automated reproduction of the joint model. Such considerations proved to be critical in overcoming the limitations of prevailing rotational molding operations. The use of hollow rotation molded models was advantageous as it better represented the physiologic constitution of real bones, thereby, conferring a greater degree of accuracy in the photostress experiments. The fabrication of the hollow models entailed flow visualization studies, which assessed the variation in rotational speeds with time as well as the optimum relative rotation speeds to be adopted. The preferred mode of rotational motion was also determined through a series of simulated experiments to determine whether steady or repetitive cyclical rotational modes were more beneficial. The fabricated hip models were loaded and the stress profiles examined. Contour maps of the stress fringes manifested in the photoelastic analysis indicated several sites of stress concentrations. These sites coincided with physiologic patterns of hip fractures, verifying the validity of the hollow femoral models. Computer controlled rotational molding has proven to be a feasible manufacturing process in the development of hollow physiologically representative femur models.

A composite model for the buildup and the relaxation of residual stresses and birefringence during the injection molding of semicrystalline polymer is proposed. This model takes into account the flow-induced crystallization occurring under nonisothermal conditions. The effects of crystallization on the variations of mechanical and physical properties are considered. The viscoelastic constitutive equation due to Giesekus and Leonov is employed for the calculation of the buildup and relaxation of flow stresses, whereas the Morland-Lee constitutive equation of linear viscoelasticity is utilized for the calculation of the buildup and relaxation of thermal stresses during the molding. The overall residual stresses in the molding are determined based upon the addition of residual flow and thermal stresses. The multilayered micro-structure in the moldings arising due to the flow-induced crystallization is determined. Flow birefringence is related to flow stresses according to the stress-optical rule. An expression is proposed to evaluate the overall residual birefringence based upon the resultant microstructure pattern and residual low birefringence in the moldings. As a result, numerical simulations for idealized injection molding process are formulated to calculate the residual stresses and birefringence in molded semicrystalline polymers. Based upon the above theoretical approach, the numerical simulation schemes are formulated, and a computer program is developed. Based upon the simulations, the effects of molding conditions and molecular weights on the overall residual stresses and birefringence are further evaluated.

The viscoelastic process simulation of the idealized injection molding process for various isotactic polypropylenes having different molecular weights are conducted by using the theoretical formulation developed in the first part of the present study. Molding experiments are performed under a variety of molding conditions, and birefringence measurements are carried out on the molded samples. Based upon the experimental and simulated results of the residual stresses and birefringence, the effects of molding conditions and molecular weights are studied. The influences of flow-induced crystallization kinetics on the buildup and relaxation of residual stresses and birefringence in the moldings are discussed. It has been found that, due to the absence of the flow-induced crystallization in the core region, the flow stresses and birefringence introduced in that region during the filling stage relax shortly after the cavity is filled. Moreover, the low stresses and birefringence get frozen-in due to the occurrence of the low-induced crystallization are relatively large and located within a very narrow region close to the mold wall. The main contribution to the overall residual stresses is found to be due by the residual thermal stresses that are introduced by the progression of crystallization during the postfilling stage. The distribution of the residual birefringence in the moldings is closely related to that of the crystalline microstructure pattern and less dependent upon the level of overall residual stresses.

In this paper, a generalized predictive observer-controller (GPOC) is developed for injection moulding with input delay and non-measurable states. First, based on a general state-space model with time delay and subject to process disturbances, a generalized predictive control (GPC) is appropriately formulated with a steady-state Kalman filter. Second, important and useful closed-loop characteristics relating to the stability and robustness of the proposed controller are provided. Finally, the proposed scheme is applied to the injection moulding to improve the control performance.

We present a finite element method for predicting the fiber orientation patterns in 3-D injection molded features, and compare the predictions to experiments. The predictions solve the full balance equations of mass, momentum, and energy for a generalized Newtonian fluid. A second-order tensor is used to describe and calculate the local fiber orientation state. A standard Hele-Shaw molding filling simulation is used to provide inlet boundary conditions for the detailed inite element models, which are limited to the local geometry of each feature. The experiments use automated image analysis of polished cross-sections to determine fiber orientation as a function of position. Predictions compare well with experiments on a transverse rib, where the detailed calculation can be 2-D. Results of a 3-D calculation for a flow-direction rib also show generally good agreement with experiments. Some errors in this latter calculation are caused by not simulating the initial filling of the rib, due to computational limits.