Effect of Compatibility on the Foaming Behavior of Injection Molded Polypropylene and Polycarbonate Blend Parts

A lightweight polyurethane-carbon microsphere composite foam for electromagnetic shielding

In this study, we have produced a lightweight foam composite material by a simple freeze-drying method, which is composed of carboxylated multi-walled carbon nanotubes (MWCNTs), mesoporous carbon hollow microspheres (MCHMs), water-based polyurethane (WPU), and polyvinyl alcohol (PVA). MCHMs were prepared by a novel and facile method. We found that the electromagnetic shielding performance of foam composites can be adjusted by adjusting the density of foam composites, and the electromagnetic shielding performance of composites can be enhanced through the synergistic effect of hollow mesoporous carbon and MWCNTs. The composite material with a density of 232.8042 mg·cm−3 and 40 wt% MWCNT has a δ of 30.2 S·m−1 and SE of 23 dB. After adding 10 wt% MCHMs to the composite material, δ reaches 33.2 S·m−1, and SE reaches 28 dB. Both absorption losses accounted for 70%. The increase in the content of MWCNT, the increase in density, and the introduction of MCHMs all have a positive effect on the δ and SE of the composite material.

Dynamic Mechanical Analysis and Thermal Expansion of Lignin-Based Biopolymers

Biodegradable materials investigation has become a necessity and a direction for many researchers worldwide. The main goal is to find sustainable alternatives which gradually replace plastics based on fossil resources from the market, because they are very harmful to the environment and to overall quality of life. In order to get to the stage of obtaining different functional parts from biodegradable materials, it is necessary to study their properties. Taking into account these shortcomings, this paper aims at the mechanical characterization (DMA—Dynamic Mechanical Analysis) and thermal degradation (thermogravimetric analysis (TGA)) of lignin-based biopolymers: Arboform LV3 Nature^®, Arboblend^® V2 Nature, and Arbofill^® Fichte Arboform^® LV3 Nature reinforced with aramid fibers. The tested samples were obtained by using the most common fabrication technique for polymers—injection molding. The obtained results for the DMA analysis showed separate polymeric-specific regions for each material and, based on the tanδ values between (0.37–0.54), a series of plastics could be proposed for replacement. The mechano-dynamic behavior could be correlated with the thermal expansion of biopolymers for temperatures higher than 50/55 °C, which are thermally stable up to temperatures of at least 250 °C.

Evaluating the gas-laden ability of polymer melt under atmospheric conditions using a modified torque rheometer

To investigate the effects of incorporating gas and the associated influencing factors on polymer melt, a method of evaluating the gas-laden ability using modified rheometric measurements was proposed. In this study, common and widely used thermoplastic materials—polypropylene (PP) and high-density polyethylene (HDPE), and their blends with different weight ratios—were selected, and the rheological properties of neat melt and gas-laden melts were tested using a modified torque rheometer. The foamed samples were also produced using a regular injection-molding machine, and the foamed morphology was examined by scanning electron microscope (SEM). The comparison of rheological curves of neat melt and gas-laden melt indicated that the incorporation of gas influenced the rheological properties of the gas-laden polymer melts as evidenced by a decrease of zero-rotational torque and an increase in the melt flow index. The results also suggested that the gas-laden ability of polymer melt could be evaluated quantitatively by the decay (due to desorption) of gas using the modified rheological measurement method. This study also demonstrated that the gas-laden ability can be used to predict the foaming behavior of polymer melts.

Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene

Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding.

A Novel Hybrid Foaming Method for Low-Pressure Microcellular Foam Production of Unfilled and Talc-Filled Copolymer Polypropylenes

Unfilled and talc-filled Copolymer Polypropylene (PP) samples were produced through low-pressure foam-injection molding (FIM). The foaming stage of the process has been facilitated through a chemical blowing agent (C₆H₇NaO₇ and CaCO₃ mixture), a physical blowing agent (supercritical N₂) and a novel hybrid foaming (combination of said chemical and physical foaming agents). Three weight-saving levels were produced with the varying foaming methods and compared to conventional injection molding. The unfilled PP foams produced through chemical blowing agent exhibited the strongest mechanical characteristics due to larger skin wall thicknesses, while the weakest were that of the talc-filled PP through the hybrid foaming technique. However, the hybrid foaming produced superior microcellular foams for both PPs due to calcium carbonate (CaCO₃) enhancing the nucleation phase.