Band 34, Heft 2

The main objective of this paper is to numerically investigate the use of fiber-dependent viscosity models in injection molding simulations of short fiber reinforced thermoplastics with latest commercial software. We propose to use the homogenization-based anisotropic rheological model to take into account flow-fiber coupling effects. The 4th-order viscosity tensor is approximated by an optimal scalar model and then implemented in the Moldflow Insight API framework. Numerical simulations are performed for a test-case rectangular plate with three fiber orientation models. The resulting coupled flow kinematics and fiber evolutions are then compared to the standard uncoupled simulations. Interpretations are given based on detailed post-processing of the field results. Certain deformation conditions are expected to be better taken into account, which may also in return lead to an improved fiber orientation prediction. Preliminary confrontation between flow-fiber coupled simulations and existing experimental data is then presented at the end of the paper.

Air, water, and DINCH (Di-isononyl-cyclohexane-1,2-dicarboxylate) were selected as the cooling media to prepare polypropylene hollow fiber membranes by melt spinning. The effects of various cooling ways with different cooling rates on the row-nucleated lamellar crystallization were investigated. The crystallinity, orientation and arrangement of the crystals were examined by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). Membrane morphology was observed by SEM. The less uniform pores, a layer of amorphous phase, and only a small part of slit-shaped pores were observed on the surface of samples when water and DINCH were used as the heat transfer medium because the fast cooling rate froze the surface molecules and decreased the crystallinity and orientation. However, when air was used as the cooling medium, the higher crystallinity and the better orientation of the annealed hollow fibers were obtained mainly due to the slow cooling rate. Corresponding hollow fiber membranes prepared by stretching had better interconnectivity of pores and larger pure water flux. Thus this study explains why air was selected as the cooling medium to prepare polypropylene hollow fiber membranes which can have larger pure water flux. Also, it provides new insights into the structure control of polypropylene hollow fiber membranes by stretching in order to prepare membranes with high strength.

A finite volume technique in a commercial computational fluid dynamics (CFD) code is employed in this study to simulate transient, incompressible, non-Newtonian and non-isothermal rubber mixing. The simulation processes are conducted in a two-dimensional(2D) domain, where a mixing chamber partially-filled with rubber is equipped with a pair of two-wing non-intermeshing counter-rotating rotors. The main objective is to assess the effect of different fill factors of rubber on dispersive and distributive mixing characteristics by simulating 15 revolutions of the rotors rotating at 20 min −1 . 50%, 60%, 70%, 75%, 80% and 90% are the six different fill factors chosen for the study. An Eulerian multiphase method has been applied to solve for the two different phases, rubber and air. The non-Newtonian property of rubber is handled using the shear rate dependent Carreau-Yasuda model, along with an Arrhenius function to include the temperature dependency. In addition to the governing equations related to the conservation of mass, momentum and energy, the volume of fluid (VOF) method is chosen to track the interface between air and rubber. With regard to the results, flow patterns, thermal distributions, viscosity behavior and volume fraction are analyzed for the different fill factors. In addition, dispersive and distributive mixing behavior is also assessed in detail using Lagrangian statistics, such as mixing index, cumulative distribution of maximum shear stress, cluster distribution index (CDI), scale of segregation (SOS) and length of stretch (LOS), calculated from massless particles. Both the Eulerian and Lagrangian results showed that fill factors between 70% and 80% presented the most reasonable and efficient mixing scenario, and also exhibited the best dispersive and distributive mixing characteristics combined.

Polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) blends were prepared by melt blending using PP-g-MAH as a compatabilizer. The microstructure and rheological behavior of PP/EVOH blends were studied. The results showed the that EVOH particles were uniformly dispersed in the PP matrix and inhibited the mobility of PP chains. The isothermal crystallization kinetics and morphology development of PP/EVOH blends were compared with that of pure PP. It was found that the EVOH essentially acted as an effective nucleating agent for PP, which could significantly increase the nucleation rate because the EVOH molecules in PP/EVOH blends aggregated together to form interface. Therefore, the introduction of EVOH increased the overall rate of isothermal crystallization compared with pure PP, although the PP molecular chains would be hindered seriously if excessive amounts of EVOH were added. X-ray diffraction showed that pure PP and PP/EVOH blends exhibited an identical crystal structure, and the crystallinity of the PP phase in the blends was not significantly different from that of pure PP.

Teak wood flour (TWF) reinforced HDPE composites were prepared and characterized in terms of mechanical, morphological and thermal properties using 2% polyethylene grafted with maleic anhydride (PE-g-MAH) as compatibilizer. The composites were prepared by twin screw extrusion and samples were prepared by injection molding. Mechanical properties increased with the incorporation of TWF, Starch and PE-g-MAH. Tensile strength and Young's modulus increased by 96% and 207%, respectively for TWF (40%)-HDPE composite as compared to virgin matrix. Scanning electron microscopy revealed good interface between TWF and matrix. FT-IR spectra confirmed the esterification reaction and H-bond between anhydride group of PE-g-MAH and cellulose of TWF. The DSC results showed that the melting temperature increased from 129°C to 137°C while crystallization (%) decreased from 40.49% for HDPE to 34.77% for 40% TWF composites, respectively. The storage modulus increased for all the composites at low temperature. Glass transition temperature practically remained unaffected by filler loading.

Three-dimensional, transient, non-isothermal calculations have been carried out using a commercial computational fluid dynamics (CFD) software in a two-wing rotor-equipped chamber partially-filled (75% fill factor) with rubber, to analyze the mixing efficiency for three different rotor speed ratios of 1, 1.125 and 1.5. The moving mesh technique has been used to incorporate the motion of the rotors. The Eulerian based volume of fluid (VOF) method has been used to track the interface between the two fluids, which are rubber and air. To assign the highly viscous and non-Newtonian properties of rubber, the Carreau-Yasuda model along with an exact Arrhenius formulation that accounts for the shear and temperature dependent viscosity, has been used here. Governing equations including the continuity, momentum and energy equations have been solved to characterize the flow field and various mixing parameters. Eulerian-based fields such as velocity magnitude, viscous heat generation, and average temperature and viscosity are compared between cases with different speed ratios. Dispersive and distributive mixing behaviour are assessed through a Lagrangian approach that tracks the paths of a set of massless particles. Statistical quantities such as cumulative distribution of maximum shear stress, cluster distribution index, and axial and inter-chamber particle transfer rates are calculated and presented as well. Results showed that the speed ratio of 1.5 displayed the best dispersive and distributive mixing characteristics in comparison to the other cases.

Hot embossing was used to fabricate a microneedle array on poly(methyl methacrylate) (PMMA) substrates. Both experimental and numerical researches were carried out to investigate the whole formation process. The results showed that the edge effect would significantly influence the replication rate of final products. An optimization design of convex flow barrier was proposed to improve the replication efficiency and structure uniformity. Furthermore, optimum parameters of the flow barrier were found to be 2 mm in length and 0.2 mm in height. Reasonable high molding temperature and force were conducive to reduce the filling time and increase the average height of microneedles.

The method of preparing polyolefin foam with good flame retardancy, thermal stability, and physical and mechanical properties was investigated. Foaming condition of linear low density polyethylene (LLDPE) was investigated with triphenyl phosphate (TPP) as plasticizer, NaHCO 3 as foaming agent. The influence of modified expandable graphite (EG P ) and ammonium polyphosphate (II) on foam density, compression strength, combustion characteristics and thermal stability was explored. Results verified that EG P presented better dilatability and flame retardancy than the normal expandable graphite. Addition of EG p improved the limiting oxygen index (LOI) of 15NaHCO 3 /100 LLDPE TPP /30EG p foam from 18.8% to 24.6%. Furthermore, the combination of EG p and ammonium polyphosphate (II) (APP) at the mass ratio of 2:1 improved the LOI of 15NaHCO 3 /100 LLDPE TPP /20EG p /10APP sample to 27.9%, and the vertical burning UL-94 level reached V-0, indicating that this material was flame retardant. Although these additives made 15NaHCO 3 /100 LLDPE TPP /20EG p /10APP composite exhibit a high density of 142.5 kg m −3 , which was increased by 12.3 wt% relative to the 15NaHCO 3 /100 LLDPE TPP foam, it could improve the compressive strength to 0.4747 MPa, which was about 2.7 times that of the matrix. The thermal stability of the material was also enhanced.

As the demand for individualized products rises, the development and need for additive manufacturing (AM) techniques such as selective laser sintering (SLS) has strongly increased. The industrial use of these procedures for prototypes or small-scale production lines has grown due to their specific characteristics like the high achievable complexity. With the increasing demand for electrification and functionalization, the combination of AM with laser-direct structuring (LDS) gains interest. Therefore, the powder used for the investigation is dry coated with a LDS-additive, which enables laser activation and a metallization of the activated sections in a metallization bath. To characterize the influence of the LDS-additive on the process, the powder properties were investigated for unfilled and successive increased additive content. The thermal process window was identified by standard and process adapted isothermal differential scanning calorimetry. This showed a decrease of the isothermal crystallization time due to nucleation effects of the additive. Subsequently, parts were produced with a parameter study and showed a demand for a higher energy density. The resulting parts were then metallized with a parameter variation and characterized by stereomicroscopy. To investigate the influence of the different parameter sets and the LDS content, the mechanical properties were determined.

Nanocomposites of polyvinyl alcohol (PVA) and Cadmium selenide (CdSe) were fabricated by ex-situ casting technique. CdSe nanoparticles were prepared by thermolysis under the flow of nitrogen. Rietveld refinement of x-ray data showed that the prepared CdSe adapts cubic zinc blend structure with a lattice parameter 6.057 Å and a mean grain size of 2 nm. Samples from CdSe/PVA nanocomposite have been exposed to infrared (IR) laser fluences in the range 0–19.6 J/cm 2 . The effect of IR laser radiation on the structural and optical properties of CdSe/PVA has been investigated using XRD and UV-vis spectroscopy. UV/VIS absorption spectra confirm the formation of hybridized film CdSe/PVA nanocomposite with refractive index in the range of 1.4119–1.8621 (at 700 nm). Also, the laser radiation reduces the optical energy gap from 4.1 to 3.43 eV which could be attributed to the increase in structural disorder of the irradiated CdSe/PVA nanocomposites due to the formation of coordination reaction between OH of PVA and CdSe nanoparticles. This means that the laser radiation led to a more compact structure of CdSe/PVA nanocomposite and causes proper dispersion of CdSe nanoparticles in the PVA matrix. Further, the Commission Internationale de E'Claire (CIE units x, y and z) methodology was applied in this work for the description of colored samples. The color intensity ΔE, which is the color difference between the non irradiated sample and the irradiated ones, was increased from 11.40 to 30.57 with increasing the laser fluence up to 19.6 J/cm 2 .

In this work, long glass fibre reinforced polypropylene/intumescent flame retardants (LGFPP/IFR) composites are exposed to ultraviolet (UV) radiation with wavelength of 340 nm for 0–800 h. The effects of UV ageing on the flame retardancy, thermal stability and mechanical properties of LGFPP/IFR composites are investigated and discussed by limiting oxygen index (LOI), UL–94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), mechanical properties and energy dispersive X-ray analysis (EDAX). A slight variation in LOI values and UL-94 levels are observed, and CCT results display a lower heat release rate for all aged samples. The TGA result also shows that aged samples have a higher degradation temperature with the prolongation of the aging time. EDAX showed higher content of the O, P and N elements on the surface of samples after 600 h ageing, which means partly gathering of IFR particles. The tensile, bending and impact strengths decrease after ageing, and the fracture morphology shows that interface debonding occurs.

Poly(β-hydroxybutyrate)-co-poly(β-hydroxyvalerate) (PHBV) loaded with 1 to 10 wt.% of cork microparticles (CM) were manufactured via compression molding technique. CM were isolated by alkali, bleaching and acid hydrolysis treatments. They were then added to the PHBV matrices via solution casting technique. The filler microparticles showed typical diameters of 10 to 55 μm. Mechanical tests in tension showed that in PHBV containing 5 wt.% CM the Young's modulus and the tensile strength increased by 50% and 10% respectively. Meanwhile, the elongation at break decreased by 70% for the same CM content. The mechanical behavior of the reinforced composites was discussed in conjunction with the morphology of the samples studied by optical and electron microscopy. The temperature of initial degradation T id , the temperature at 5% weight loss T d5% and the temperature of maximum degradation T dmax increase with increasing CM content by up to 13.6°C, 10.1°C and 12.3°C respectively for the composite of 5 wt.%. The composite with 10 wt.% CM content showed the best thermal stability with temperature increments of 20°C, 14.1°C and 21.5°C respectively. DSC results showed that the presence of CM has a very weak influence on the melting/crystallization behavior of the composites.

A novel simulation technique for the flow in plastic mixers based on Element-free Galerkin Method (EFGM) has been developed in this study. To improve the simulation accuracy, a “rearrangement” scheme has been employed which eliminates errors caused by the irregular distribution of data points. Through several numerical tests, the new simulation technique has been validated to be applicable to high viscosity fluid flow with enough accuracy. Furthermore, simulation examples for realistic mixers were carried out using the developed technique. From the results, it was found that the developed technique is capable to investigate the relationship between flow behavior inside realistic mixers and operating conditions.