Volume 38, Issue 2

As the final stage of the mixing process, the final mixing has a profound impact on the properties of rubber compounds. The influence of the process parameters of a continuous final mixer on the properties of carbon black/rubber composites is studied. It is found that there are two factors affecting the performance of the composite: the rotating speed of the dual rotors and the temperature of the continuous final mixer. When the temperature is unchanged, the extruding temperature of the final-mixing rubber compound increases with increasing rotating speed, and the Mooney viscosity, T10, T90 and rolling resistance gradually decrease. The Payne effect decreases first and then increases, and the overall trend gradually decreases. When the rotating speed is constant, as the temperature of the continuous final mixer rises, the extruding temperature also rises, and the temperature difference between feeding and extruding increases. Mooney viscosity and tensile strength increase. The Payne effect is more significant. T10, T90 and rolling resistance gradually decrease. The M300 of a vulcanized sample shows the following laws: When the control temperature is low, the influence of rotational speed is small, the fluctuation range is small, and has a steady rising trend; however, when the temperature is higher, M300 fluctuates greatly under the influence of rotational speed. The optimal process parameters of the rubber continuous final mixer are determined: the double rotor speed is 30RPM, and the temperature control temperature is 60–70 °C.

Process monitoring systems are playing an increasingly important role in reducing production capacity losses in injection molding. Process monitoring and optimization systems are mostly based on processing data of injection molding machine control systems. These data consist of scalar data and time series. This paper introduces a novel approach to modelling injection molding processes using only time series data and evaluates the quantitative influences of varying sampling times on calculation of integral values and model quality. On the basis of the first experiment, it is shown that the sampling rates of these time series have a large influence on information which can be derived from this data (e.g. injection work). These findings provide an assessment of whether the effort is justified for the respective requirements on the accuracy of the injection work and other parameters derived from the time series. In the second experiment, a model is presented which uses only the injection flow and injection pressure profile as input and achieves high coefficients of determination for the prediction of the part weight, despite the absence of mold sensor data and scalar data. It is shown that higher sampling rates of time series results in higher prediction quality of these models. This improves the understanding of the data needed for high quality machine learning models of injection molding processes and enable users to estimate a lower bound for the sample rates of time series for their use cases.

The present study investigates the effect of carbon fiber hybridization and graphene nanoplatelets inclusion on the vibration damping properties of glass fiber reinforced polymer composites. The hand layup method was utilized with hot press molding in hybrid/non-hybrid composite plate production. A total of sixteen laminates, eight containing pure glass/epoxy and pure carbon/epoxy, and the remainder containing glass/carbon, were stacked in four different arrays and impregnated with an epoxy matrix to provide a hybrid/non-hybrid configuration. In the first hybrid configuration, the glass fiber fabric is on the outer surface and the carbon fiber fabric is on the inside of the composite plate; in the second configuration, the opposite of this sequence was used. Graphene Nanoplatelets (GNPs) were added into the epoxy resin in different weight fractions (0, 0.1, 0.25, and 0.5 wt%). Experimental modal analysis was performed to evaluate the natural frequency and damping ratios of the GNPs modified/unmodified test samples. According to the results obtained, carbon fiber hybridization not only increased the natural frequency but also caused a decrease in the damping ratio of the glass fiber reinforced composite material. On the other hand, incorporating 0.5% by weight of GNPs into the epoxy matrix improved damping ratios by approximately 42.1, 51.6, 16.7 and 17.2% for the G05, GC05, CG05 and C05 samples, respectively, compared to the pure samples. Also, a decrease in natural frequency and loss storage values were observed at high GNPs content.

The practical applications of poly (vinyl chloride) have been constrained due to its poor thermal stability, low dielectric constant and inability to shield against ultraviolet (UV) radiation. In this study, we tried to improve the optical properties, thermal stability, temperature-dependent electrical conductivity and dielectric constant using copper alumina (Cu–Al 2 O 3 ) nanoparticles reinforced poly (vinyl chloride) (PVC). Optical absorption measured with an ultraviolet-visible (UV-visible) spectrometer emphasises the blueshift in absorption edges and decreasing bandgap energies of PVC/Cu–Al 2 O 3 nanocomposites compared to PVC. The presence of Cu–Al 2 O 3 in PVC and its interaction with the polymer were confirmed by FTIR spectroscopy. Thermogravimetric analysis (TGA) demonstrates that nanocomposites have higher thermal stability than PVC, and that thermal stability increases with filler loading. Scanning electron microscopy (SEM) indicates the homogeneous dispersion of nanosized Cu–Al 2 O 3 in the polymer matrix. The activation energy determined by the Arrhenius equation revealed that AC conductivity increases with the addition of nanoparticles up to a specific loading. The dielectric constant increases as a function of temperature and decreases with frequency. The magnitude of AC conductivity and dielectric constant were highest for 7 wt% loaded nanocomposites. The dielectric constant predicted by the Bruggeman and Maxwell-Garnet models were in good agreement with the experimental permittivity. The semiconducting nature of nanocomposites was investigated by impedance analysis. The semi-circular nature of Cole-Cole plots manifests the combination of parallel capacitance with low bulk resistance. The enhanced optical, thermal, electrical and dielectric properties of PVC/Cu–Al 2 O 3 nanocomposites can be utilized in fabricating optoelectronic devices with excellent charge-storing ability.

Extensional flows generally take place in a channel with varied cross-sectional areas. During polymer processing with a variety of complex geometric features, it is difficult to separate extensional rates from shear rates in state-of-the-art predictive engineering tools of computational fluid dynamics. The recently proposed method of Tseng [Tseng, H.-C., “A Revisitation of Generalized Newtonian Fluids,” J Rheol 64 493–504 (2020)] decomposed the generalized strain rate as the characteristic shear and extensional rates via the rate-of-deformation tensor rotated along streamline coordinates. As validation for an isothermal center-gated disk flow, the predicted flow field profiles fairly matched the analytical solution for Newtonian fluid. Under injection molding simulations, an objective indicator is defined to visualize the colorful contours of extensional flows encountered in the gate-vicinity and the mid-plane of the cavity’s thickness direction, as well as contraction-expansion channels.

The mechanical, thermal and dielectric properties of lanthanum manganite (LaMnO 3 ) epoxy nanocomposites reinforced with silane coated E-glass fiber are reported. Structural and morphological characteristics of the LaMnO 3 , synthesized by the solution combustion method, were studied via X-ray diffraction, EDAX and scanning electron microscopy. LaMnO 3 /epoxy composites containing various percentages of LaMnO 3 (LME) were prepared via hand lay-up method and tested for tensile, flexural and impact strength. Improved properties were obtained with the addition of LME compared to plain epoxy composites. The thermal stability of the composites remains almost unaltered by the filler loading. Variation in the dielectric characteristics with filler loading is attributed to the percolation of charge carriers due to the interfacial zonal overlapping in the nanocomposite resulting in a change of the dielectric characteristics.

Research based on numerical simulation with the CFD software ANSYS POLYFLOW is conducted on the mixing properties for the wave screw elements, as well as barrier screw elements, by using statistical tools. Then, the investigation is conducted in detail on the relationship between pressure, maximum shear rate, mixing index and other flow field characteristics of the two above screws under the same simulation conditions. It is found that polymer melt flow in the wave screw possesses various advantages compared with the normal barrier screw, such as acquiring larger pressure, stronger shearing and stretching action, better mixing and efficiency, which mainly result from the periodic depth change design in the screw groove. On the other hand, the increased wave bulge in the wave screw lessens the space for the polymer melt to be conveyed forward, which can greatly reduce the original function of the secondary flight. Also, the convergent and divergent zones in the wave screw groove produce a much stronger stress favoring the shear and elongation rates, and also lead to a sharp increase of the axial force load on the wave screw. Consequently, for the optimization of the wave screw configuration it is suggested to reduce the axial force without decreasing the effect of the excellent distributive and dispersive mixing.

In this work, a comparative study on the electrical conductivity ( σ ) and thermal properties of polypropylene (PP)/carbon microparts with different part thickness (namely, 0.85 and 0.50 mm) is reported. Two different types of carbon filler (i.e., CNT and CB) were adopted to study the efficacy of different carbon fillers in improving the σ of PP/carbon microparts. In general, the σ of 0.85 mm thickness microparts were higher than the 0.50 mm thickness microparts, regardless of the carbon filler type and testing directions. This suggested that higher shearing conditions that prevailed in the microinjection molding (μIM) process were unfavorable for the formation of intact conductive pathways in corresponding moldings, albeit the distribution of carbon fillers turned better with increasing shear rates, as confirmed by morphology observations. Differential scanning calorimetry results showed that prior thermomechanical histories (including melt blending and μIM) experienced by the polymer melts had an influence on the thermal behavior of subsequent moldings. Also, there existed a strong shear flow-induced crystallization of polymer chains during μIM because the crystallinity of microparts was higher than that of feed materials.

Rubber latex industry has been looking for techniques to rapidly estimate the dry rubber content (DRC) of rubber latex with accuracy, at a low cost, and to be used by non-technical people in the field. The basis of electrical charge in terms of proton-electron transfer (P.E.TF) was used to develop a new prototype. The prototype was created with the P.E.TF system, two electrode probe detectors, and a new code program on Arduino board. The data was collected using the P.E.TF system of fresh natural rubber latex and presented as the P.E.TF number and the percentage of dry rubber content (%DRC). The standard method (ISO126:2005(E)) was used to calculate %DRC. The comparison of the %DRC measurement using the prototype and the standard method was studied. It was found that the new code program on Arduino board could evaluate the data. In real-time, it converted the P.E.TF number into %DRC on the LCD screen. The %DRC measurement using the prototype was close to that calculated using the standard method. The correlation between the two methods is 0.9814 of Rsqr. Therefore, the novel measurement system can replace the standard method for the %DRC measurement of fresh natural rubber latex. The prototype is simple, fast to detect, small, and low-cost without operator training.

This work examined the effect of changing molding conditions on the physical aging of polystyrene injection moldings. First, we investigated the relationship between the molecular orientation and the molding conditions. The molecular orientation near the surface changed with changing injection rate, so we hypothesized that this molecular orientation might form during the filling stage. Because this molecular orientation did not relax under heat treatment below the glass transition temperature ( T g ), the oriented molecules near the surface were thought to be elongated owing to the high strain rate during the filling stage. On the other hand, the molecular orientation in the core layer changed with changing holding pressure and relaxed under heat treatment below T g . Thus, the molecules in the core layer might become oriented during the holding stage and not be elongated owing to the slow strain rate. Furthermore, the molecular orientation in the core layer decreased with increasing mold temperature, and the physical heat resistance improved with increasing mold temperature. Meanwhile, the excess enthalpy did not change with changing molding conditions. Therefore, the improvement in physical heat resistance with increasing mold temperature was likely caused by the decrease in the molecular orientation in the core layer. Analyzing the relaxation behavior of the molecular orientation suggested that increasing mold temperature reduced the number of oriented molecules with large deformation in the core layer.

In recent years, additive manufacturing (AM) technologies have become greatly popular in the polymer, metal, and composite industries because of the capability for rapid prototyping, and appropriateness for the production of complex shapes. In this study, a comprehensive comparative analysis focusing on the influence of post-processing types (heat treatment and water absorption) on tensile and impact responses was carried out on 3D printed PETG, PLA, and ABS. In addition, layer thickness levels (0.2, 0.3, and 0.4 mm) were selected as a major production parameter and their effect on mechanical properties was combined with post-processing type for the first time. The results showed that both tensile and impact resistance of the printed polymers increased thanks to the heat treatment. The highest tensile strength was measured for heat-treated PLA, while the peak impact endurance level was reached for heat-treated PETG. Also, water absorption caused a mass increment in all samples and induced higher tensile elongation values. Decreasing layer thickness had a positive effect on tensile features, but impact strength values dropped. On the other hand, all samples were subjected to macro and micro failure analyses to understand the deformation mechanism. These inspections indicated that for impact samples straight crack lines converted to zigzag style separation lines after the heat treatment. As for the tensile samples, the exact location of the main damage zone altered with the production stability, the water absorption capacity of the polymer, and the thermal diffusion ability of the filament.

Rigid polyurethane foam (RPUF) has been fabricated and modified by hydrolyzed keratin to improve its flame retardancy and smoke suppression. Then, the limiting oxygen index (LOI), cone calorimeter (CONE), thermogravimetric analyzer and scanning electron microscope (SEM) were used to characterize the modified RPUFs. It was found that the LOI of the modified RPUFs increased with the presence of hydrolyzed keratin. In addition, the peak heat release rate (PHRR) and total heat release (THR) of the modified RPUF tended to decrease. The HRR of RPUF-HK5 reduced 28.8 kW/m 2 compared with RPUF-0, and the THR of RPUF-HK5 was 0.74 MJ/m 2 lower than that of RPUF-0. RPUF-HK5 had the most obvious smoke suppression effect. Compared with RPUF-0, the smoke density (Ds) and light transmittance (T) of RPUF-HK5 decreased by 8.88 and increased by 11.26%, respectively. The current research results showed that hydrolyzed keratin can improve the flame-retardant and smoke-suppression performances of RPUFs and that 5 wt% hydrolyzed keratin was the most suitable ratio for the modified RPUF.

Amino trimethylphosphonate cobalt (Co 2+ -ATMP) flame retardant was prepared by ion exchange method, and rigid polyurethane foam (RPUF) modified by Co 2+ -ATMP and expandable graphite (EG) was prepared by one-pot and free-rise method. The flame retardancy, thermal stability and smoke toxicity of modified RPUF were studied by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TG) and smoke toxicity characterization. The results showed that the flame retardancy, thermal stability and smoke toxicity of RPUF modified by Co 2+ -ATMP and EG are significantly improved. When the ratio of Co 2+ -ATMP to EG is 1:5, the LOI value is the highest, and the toxicity of flue gas was the lowest. The peak heat release rate (PHRR) and total heat release rate (THR) were both the lowest, 138 kW/m 2 and 15.9 MJ/m 2 , respectively. Compared with RPUF-0, it decreased by 39.2% and 16.8% respectively. The research results can provide reference for the subsequent flame retardant modification of RPUF.

It is difficult to directly measure the steady extensional viscosity of thermoplastic composite materials, especially at high extension rates. The famous Cogswell method was derived analytically from the pressure drop of entrance flow in commercial capillary rheometers for estimating the extensional viscosity. However, using Cogswell´s extensional viscosity has always resulted in over-predictions of pressure drop. Recently, the GNF-X (eXtended Generalized Newtonian Fluid) model with a weighted shear/extensional viscosity was proposed to show the typical extension-induced vortex growth in entrance flow simulations. Under given various values of Trouton’s ratio for extensional viscosity, the GNF-X model is introduced to perform three-dimensional flow simulations of capillary rheometry over a range of apparent shear rates. The difference between the predicted pressure drops and the relevant experimental data is minimized such that the estimation of extensional viscosity is optimized herein.