Volume 35, Issue 1

The fluid-powered projectile-assisted injection molding (FPAIM) technique can be used to produce wholly or partially hollowed plastic parts through the introduction of a projectile driven by pressurized fluid. It greatly improves the quality, applications, and design freedom of hollowed parts. The operation principles, variants, advantages and disadvantages, as well as the process factors of FPAIM, are discussed in detail in this paper. In addition, some developments of FPAIM in the areas of both-end openings, projectile, variable cross-section, pipes with branches, closed voids, and elastomeric hollow parts, as well as combinations with other processes, are also introduced. Some applications of FPAIM are briefly presented. Finally, the future development of the FPAIM technique is also discussed.

Recently, the research on low rolling resistance tires attracted interest for its reduction of petrol consumption, which is related to the hysteresis loss of rubber composites. Here, four common methods representing the hysteresis loss of rubber composites in lab were contrasted to explore the potential connections between them. The results indicated that tan δ obtained by DMA showed good positive linearity with that obtained by RPA without distinguishing the rubber species and filler types, also for the positive relation between tan δ and hysteresis loop area (HLA). The rolling power loss (L) captured by the rolling resistance testing machine appeared to have a positive correlation with tan δ from DMA or RPA in NR composites, while a negative connection showed up in SBR composites. Further, considering the influence of strain on rolling energy loss, the 100% modulus was introduced leading to a good positive quadratic equation connection between tan δ/100% modulus and L in all common rubber composites.

An extensive modeling study is presented on viscoplastic flows in the single screw extruder. An effective modeling procedure is developed, and fully three-dimensional Non-Newtonian FEM computations are performed to design the screw and die characteristics which may be implemented into the global model of the process. ANSYS Polyflow software is applied to model these viscoplastic flows. An analysis is performed for the flow with yield stress effects both in the screw and in the die. Screw characteristics and die characteristics are calculated and modeled for various viscoplasticity parameters. The effect of yield stress parameters on the extruder operation has been discussed.

Twin screw extruders (TSE) are widely used in polymer blending and compounding operations, since the relatively high stresses they impart on melts and controllable residence times make them highly suitable for mixing operations. However, the mixing action in the industry-standard kneading blocks (KB) is shear-dominated and shear flows are inefficient for dispersive mixing compared with extensional flows. A novel static extensional mixing element (EME) was developed recently by our group with the objective of providing extension-dominated flow during blending and compounding. Dispersive mixing in the EME is provided by flow through stationary hyperbolic converging-diverging (C-D) channels placed along the screw. The improvements in dispersive mixing for immiscible blends using EMEs with wide hyperbolically channels, i.e., low contraction ratios, has been proved. In this work, we begin by performing computational investigations of more extreme contraction geometries to determine the design flexibility limits for the EME. The contractions again showed more extension-dominated flow patterns than the original EME, the drawback being the obvious increase in the pressure drop. However, at extremely high contraction ratios, the entry angle is so shallow that recirculation zones appear at the entrance, which are undesirable, implying that there are geometrical limits above which the EME ceases to be an effective dispersive mixer. Next, experimental validation on the EMEs with different degrees of aggressiveness of the C-D channel were performed and dramatic improvement in droplet breakup (dispersive mixing) in case of immiscible blends is clearly observed at all viscosity ratios and with increasing degree of EME aggressiveness.

Natural fiber reinforced polymer composites have the advantages of low density, low cost and renewability. However, the inferior mechanical property restricts the application. In this work, EPDM-g-GMA has been added to straw/PP composites to improve the properties. The mechanical properties, thermal stability, crystallinity and melt viscosity have been invested. The results reveal that the mechanical properties of straw/PP/EPDM composites are improved remarkably and the impact strength more than doubles compared to straw/PP composites. Surface microstructure analysis reveals that the composite has good interfacial compatibility and dispersing performance. The maximum decomposition temperature, the melting enthalpy and crystallinity increased. The glass transition temperature and process ability are also improved by the addition of EPDM.

A coextrusion apparatus was developed to fabricate low-density polyethylene/polyamide 6 (LDPE/PA6) multilayer films. Unlike the feedblocks used in conventional coextrusion, the apparatus consists of a stirring rod, which stretches and folds the polymer components. On rotating the stirring rod, the lower viscosity phase migrates to high shear regions (stirring rod surface), thereby contributing to the formation of a multilayer structure. The desired multilayer structure was achieved at the optimum stirring speed (0.013 m s −1 ), volumetric flow rate of LDPE (5.8 × 10 −6 m 3 s −1 ), and volumetric flow rate of PA6 (1.5 × 10 −6 m 3 s −1 ). The LDPE/PA6 multilayer film had higher tensile and puncture resistance properties compared to that produced from conventional coextrusion, indicating the potential of the proposed apparatus for multilayer polymer film production.

The bulk density of polymers is a crucial factor for the throughput and the pressure build-up of single screw plasticating units. It depends not only on the density of the polymeric material itself, but also on the geometry of the single pellets, on the dimensions of the screw channel and, furthermore, on the temperature and the pressure. A review of the existing models shows that there is potential for improvement, as their applicability is restricted. It is difficult to obtain model parameters, as they can only be determined by experiment, but there are only a few devices which enable temperature- and pressure-dependent bulk density to be measured. Furthermore, these devices are not standardized. This work presents a new model which can be used to calculate the bulk density as a function of pressure and temperature and an adapted approach that considers the dimensions of the single pellets and the screw channel. The model is verified by both, new data derived from experiments and data from the literature. Compared to existing models, this new model fits the experimental data better, requires fewer parameters and shows much better extrapolation behavior as well as a continuous changeover behavior at the melting temperature. Another big advantage of the new model compared to the existing ones is that the model parameters of this new model can be estimated from the stress at yield and from the melting temperature. This enables a rough estimation of the pressure and temperature dependent bulk density without having to measure it.

The present work aimed to study the influence of ABS type and compatibilizer on the thermal and mechanical properties of PC/ABS blends. For that, blends of PC with two types of ABS, with different rubber content, were prepared at 70 wt% of PC and 30 wt% of ABS, without and with compatibilizer at loadings of 1, 3 and 5 wt%. The effectiveness of those formulations was examined by means of morphological (SEM), thermal (DSC, TGA) and mechanical (tensile and microhardness) properties. It was shown that the compatibilizer had in general beneficial effects on the global properties of PC/ABS blends, and that the optimal amount of compatibilizer depends on the ABS type.

On the premise that the overall structure and composition of the parts remain unchanged, the over-molding of self-reinforced polymer composites parts (OM-SRCs parts) prepared in this paper change the aggregation structure of the parts by combining multi-component sequential molding technology with micro-injection molding technology. Thus, it improves the comprehensive performance of the parts, and achieves the purpose of self-reinforcing. The morphological feature of self-reinforced parts during over-molding are obviously different from those formed by conventional injection molding, which also leads to differences in physical properties. In this study, two types of polypropylene parts of the same size (60 × 12 × 2 mm 3 ) were prepared, and their micro-morphologies comparison were investigated by means of polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). From the results, it was found that the tensile properties of OM-SRCs parts were improved by up to 9.46% compared with the conventional parts. Through PLM observation, it is found that the section shape of OM-SRCs parts perpendicular to the flow direction shows a double “skin-core” structure, resulting in the increase of the area ratio of skin layer to 24% (16% in conventional parts). SEM was carried out on the skin layer near the fusion position of the interface, and a highly oriented “shish-kebab” structure was observed. Through DSC and 1D-WAXD pattern analysis, it was found that the overall crystallinity of OM-SRCs parts decreased by 8.53% and 5.32% compared with the conventional parts, respectively. The 2D-WAXD pattern analysis showed that the molecular orientation degree of the skin layer of OM-SRCs parts increased by 15.65%. By means of the response surface method, the molecular orientation obtained was the decisive factor affecting the performance of OM-SRCs parts. By means of the least squares' minimization procedure, a dimensionless equation between the micro-morphologies and mechanical properties was established, which makes the “adjustability” of the sample performance be preliminarily realized.

Sustainable, biodegradable and thermoplastic processable aliphatic polyesters (polybutylene succinate (PBS) and polyethylene succinate (PES)) were prepared and characterized; then, they were grafted onto cellulose micro-fibers using a simple click reaction. This modification was conducted under simple experimental conditions. The characterization (NMR and FTIR analysis), thermal properties, solubility, morphology and biodegradation process of the all products prepared were established and studied. The results show that the solubility of the prepared derivatives is improved in comparison with cellulose, while their thermal stability showed a slight decrease compared to the starting materials. The composites derived from the modified cellulose show a slight decrease in their biodegradability in comparison with that of unmodified cellulose due to several parameters.