Band 38, Heft 3

In a range of applications, such as the automotive, aerospace, and shipbuilding sectors, where weight reduction is essential, sandwich structures are getting more popular. The performance of sandwich structures in bending can be enhanced by using lightweight core topologies. In this study, six different novel and new core topologies were designed with CATIA V5. Polylactic acid (PLA) sandwich structures with new core designs were produced using the fused deposition modeling (FDM) additive manufacturing method. In order to determine the mechanical characteristics of these six designed core topologies, three-point bending tests on sandwich structures were performed. The influence of core topology on the flexural characteristics of lightweight sandwich structures was investigated to appropriately choose and design the core topology of the sandwich structures to meet desired structural requirements. To evaluate the flexural behavior of sandwich structures, finite element simulation using ANSYS Workbench 2021 R2 was also performed. Both the experimental data and simulation were in good agreement and clearly showed that the sandwich structure with the triple bow core exhibited the highest mechanical properties. These results provide new perspectives on the investigation of the mechanical response of sandwich structures, which can be beneficial for many other industries and applications.

In the present investigation, a polyacrylamide (PAM) – graphene oxide (GO)-single-walled carbon nanotubes (SWNTs) composite has been prepared through a cost effective solution cast method and physical properties (electrical and mechanical) measurements have been carried out. The GO sheets contain oxygen functional groups which enhance the interfacial adhesion with the polymer matrix, while the SWNTs act as wires joining the GO together in the composite matrix. This interconnected network creates a conducting path, lowering film resistance and improving PAM films’ electrical, mechanical, and thermal properties. Raman study demonstrated that carbon nanofiller (SWNTs, GO) and polymer PAM have good interfacial bonding. The electrical conductivity and mechanical characteristics (hardness and elastic modulus) of these composite films were enhanced at a loading of 15 wt% GO and 15 wt% SWNTs in PAM matrix. Electrical conductivity of GO (15 wt%) – SWNTs (15 wt%)-PAM composite film was found to be 2.8 × 10 −2  S/cm, which is five orders of magnitude higher than that of the PAM polymer. In comparison to pure PAM polymer, the elastic modulus and hardness are found to be 1.14 and 65 times higher, respectively.

A new environmental friendly flame retardant manganese phytate (MnPa) was prepared by a direct precipitation method and the polyurethane foam (PUF) modified with MnPa was obtained by a one-step all-water foaming method. The thermal stability and combustion performance of the MnPa-modified PUF (MnPUF) were investigated by using thermogravimetric (TG), thermal decomposition kinetics, smoke density characterization, limiting oxygen index (LOI) and UL-94 horizontal combustion test. The results indicated that the addition of MnPa significantly improved the thermal stability and combustion performance of the modified PUF. On the basis of the thermogravimetric analysis, Flynn-Wall-Ozawa method, Kissinger method and Coats Redfern method, it could be concluded that PUF with 7.5 wt% MnPa (MnPUF3) had the highest activation energy and the best thermal stability. Smoke density analysis, LOI and horizontal combustion analysis also showed that the addition of MnPa was positively correlated with smoke suppression, LOI value and burning time. The current research results can provide a reference for the subsequent flame retardant modification of PUF.

To improve the processability of LLDPE, a binary processing aid composed of polyethylene glycol (PEG) and hydrocalumite was designed. Hydrocalumite containing HPO 3 2− was successfully synthesized with co-precipitation of calcium and aluminum hydroxide in the presence of phosphorous acid. Scanning Electron Microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Thermogravimetric analyses (TGA) and Ion chromatography were utilized for the characterization of the synthesized hydrocalumite. SEM images showed the layered structure. Ion Chromatography demonstrated the molar ratio of Ca 2+ /Al 3+ was 2:1.3 as an interlayer ion. The influence of PEG/hydrocalumite with the different ratios as a processing aid on the rheological properties of LLDPE was investigated by capillary rheometry. The results obtained showed that PEG/hydrocalumite processing aid with a ratio of 1:3 exhibited the best effect on the reduction of critical stress due to the best coverage of the extruder surface. The measurement of processing parameters in the blown film extruder revealed that hydrocalumite interacted with metallic oxides, created a slippery film layer on the die wall. This leads to a decrease in the die pressure and power consumption by 11% and 21%, respectively. SEM analysis confirmed a delay in Sharkskin instability at a higher shear rate.

Poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA), both available on the market, are blended on a technical scale. Using a special process control, the two materials are blended in a twin-screw extruder at a mass throughput rate of 2 kg/h, resulting in a stereocomplex Poly(-lactide) (PLA) blend. Thermal analysis indicates only one melting point at 235 °C. Both the Raman spectra and X-ray powder diffraction patterns show characteristic features for the stereocomplex PLA. With the available amount of this blend PLA fibers with technical strengths can be developed by melt spinning. As such, the application of the biopolymer PLA can be expanded, leading to substitute the conventional plastics for conserving both the resources and the environment.

An experiential research on mechanical and tribological characteristics of snake grass and sisal fiber reinforced hybrid polymer (epoxy) composites was carried out and reported in this article. The snake grass and sisal fibers were initially treated with 5% sodium hydroxide (NaOH). Hybrid composite samples were fabricated using a compression moulding technique with a total fiber weight ratio of 30% and an epoxy resin weight ratio of 70%. The proportions of snake grass and sisal fibers in the hybrid composites were 70:30, 50:50, and 30:70. The fabricated hybrid composite samples were subjected to flexural, tensile, interlaminar shear strength, Shore D hardness, water absorption, and wear tests as per ASTM international standards, and the outcomes were compared with the results of snake grass and sisal mono fiber composites. The results disclosed that the 30:70 (SG:S) hybrid composite has higher mechanical characteristics than those of other hybrid and mono fiber composites. Also, the 30:70 hybrid sample performed at par with the sisal mono composite in wear and water absorption characteristics. Optical microscopy examination of alkali-treated natural hybrid and mono fiber composites displayed excellent results in terms of interfacial bonding between polymer and fiber.

Polylactic Acid (PLA) experiences widely spread applications in Fused Filament Fabrication (FFF) owing to its relatively high stiffness, strength, and environmentally friendly biodegradability. Reinforcing inclusions like short carbon fibers are introduced to virgin PLA feedstock aiming to improve the mechanical performance of FFF-made products. Nevertheless, the rigid fibers significantly reduce the ductility of the overall fabricated parts. This study prepares sandwich specimens with PLA as core and its 10 wt% chopped carbon fiber reinforced composites (i.e., CF/PLA) as shell via a low-cost FFF-based multi-material additive layered manufacturing method. The sandwich specimen has three layers, which are changed according to different material volumes, which is able to design the local strength and toughness performances of a printed part. Tensile properties of these sandwich samples printed in the different volumetric rates of virgin PLA constituents are measured. It is found that the strength of sandwich specimens with 20% vol of PLA reduces noticeably as compared to the full CF/PLA specimens. The 80% vol specimens exhibit a competitive strength as compared to the 40% and 60% vol specimens, while its toughness increases notably as compared to the other cases. Finite element simulations of the layered manufacturing process show that the thermal residual stresses of 20% vol sandwich accumulates most significantly. We also explore the effects of thermal annealing on the prepared sandwiches. Experimental results indicated that the post-annealing process improved the strength and stiffness of the sandwich specimens, while enhancing the stability of the mechanical properties of the FFF printed sandwich.

A modified White-Metzner viscoelastic constitutive equation is incorporated into the state-of-the-art Three Dimensional Computational Fluid Dynamics (3D-CFD) framework for performing isothermal and non-isothermal entry flow simulations of a polymer melt. As a result, the corner vortex becomes smaller with increased isothermal temperature, namely, the so-called temperature-induced vortex reduction. In addition, the vortex grows with raising wall temperatures, whereas the vortex reduction is found under high inlet temperatures. Through the visualized flow patterns, it is significant to investigate the dramatic variations of vortex size in relation to fluid temperature, weighted viscosity and extension rate, as well as Weissenberg number and Trouton ratio.

This study produced a box-like product through injection molding, and pressure sensors were installed at the nozzle in the injection molding machine and mold cavity. Injection molding experiments were conducted with various process parameters to understand the correlations between the pressure of the cavity, nozzle, and oil pump. A high correlation ( R  > 0.95) between oil pressure and nozzle pressure could be found in the study. The oil pressure in the injection molding machine could fully describe the pressure variation of the molten plastic at the nozzle. However, the correlation between nozzle pressure and cavity pressure was slightly reduced due to changes in injection speed, melting temperature, and packing time. Thus, a suitable molding window can improve the correlation between oil pressure, nozzle pressure, and cavity pressure. This study provides a correlation between the three pressures and a reference for the future selection of process variables, an essential pretreatment for online monitoring.

The extrusion of large or heavy technical rubber profiles is usually assisted by a conveying device. Such a device can be a conveyor belt or a series of rollers, and its use is necessary mainly for being able to achieve the process. Within the context of numerical simulation of extrusion flows, a conveying device brings additional downstream constraints to the flow governing equations. In the present paper, we propose a simple engineering approach for modelling a roller conveyor used in rubber tire tread extrusion, and we apply it to the extrusion simulation of a flat tire tread profile as typically encountered in the tire manufacturing industry.

Poly(propylene carbonate) (PPC)/polypropylene (PP) spunbond nonwoven slice has gained more attention, owing to its excellent properties, such as biodegradability, flexibility, biocompatibility, and CO 2 utilization. However, the applications of this green material are limited due to the poor thermodynamic incompatibility between PPC and PP. In this paper, PP grafted with maleic anhydride (MAH) and styrene (St) (PP- g -(MAH- co -St)), prepared by a mechanochemical method and having a grafting percentage G MAH  = 1.40 %, was used as a compatibilizer to prepare a biodegradable PPC/compatibilizer/PP composite-spunbond nonwoven slice by melt-blending. The effects of compatibilizer content on the tensile strength, elongation at break, melt flow rate, thermal properties, and micro-morphology of PPC/PP- g -(MAH- co -St)/PP were systematically studied. Furthermore, the mechanism of compatibilization of PP- g -(MAH- co -St) in the PPC/PP spunbond nonwoven composite slice is discussed. The results indicated that this green PP- g -(MAH- co -St) exhibited a clear reactive compatibilization effect. Therefore, it can be considered as a good compatibilizer for the biodegradable PPC/PP spunbond nonwoven slice.

The use of naturally derived eco-friendly biocomposites became more popular due to growing environmental concerns and hunt for sustainable materials. Biocomposites can reduce the residual waste and carbon emission to the environment during their lifecycle. The present study aims to develop biocomposites by reinforcing flax fiber (F) and kenaf fiber (K) laminates with bio-epoxy matrix at four different arrangements (FFF, FKF, KFK, and KKK). The biocomposite samples were fabricated with three laminated thicknesses (3 mm, 4 mm and 5 mm) and the thermo-mechanical performance was investigated. The results showed that FFF biocomposites recorded higher tensile, flexural, and interfacial properties with lower density and absorption of water compared to KKK biocomposites due to higher cylindrical lumen diameter of flax laminates. The hybridization of flax with kenaf fiber at different stacking sequences provided greater strength, modulus, toughness, stiffness, thermal stability and degradation behaviour due to greater interfacial interaction between laminated fiber and bio-epoxy. The FKF biocomposites showed maximum impact strength (52.96 kJ/m2), tensile strength (110.21 MPa), and compressive strength (139.64 MPa) at 5 mm laminated thickness while, flexural (158.67 MPa) and shear strength (39.45 MPa) were maximum at 4 mm thickness with the highest degradation temperature (336 °C). The optimal biocomposite configuration has been identified through employability of a novel decision-making framework encompassing interval-valued intuitionistic fuzzy sets, TOmada de DecisaoInterativaMulticriterio (TODIM) and Schweizer–Sklar operations. The inclusive evaluation with regard to the applied framework has revealed that FKF and KFK biocomposites with 4 mm thickness (Lam 5 and Lam 8 ) configuration to have the optimal configuration. On the other hand, Lam 10, i.e., KKK_3 mm turned out to be inferior to all the considered biocomposite configurations.

Objectives Electrospinning is one of the most well-known approaches to producing polymer nanofibers from a polymer solution by applying a potential difference (voltage) between the spinner and the collector, which is used in various industries such as medicine and military. This method has some significant restrictions, like low process efficiency due to the evaporation of the solvent, remaining solvent on the fibers, which are sometimes toxic, and inability to control the geometry of the produced fibers. On the other hand, preparing some solvents used in the electrospinning of polymer solutions is costly. Polymer melt electrospinning writing is a replacement for this type of electrospinning, which can be mentioned in terms of economy, efficiency, and production of solvent-free fibers. Therefore, in this research, a melt polymer electrospinning device was designed and manufactured according to existing extrusion-based additive manufacturing (AM) devices (3D printer). Methods Changes in an extrusion-based 3D printer to convert it into a writing electrospinning device experimentally. Results PLA and PCL fibers with diameters ranging from 8 to 84 μm were produced. The effect of process variables on the produced fibers’ diameter was investigated: Applied potential difference between the nozzle and the substrate: As its increases, the fiber diameter decreases. Increasing temperature: As its increases, the fiber diameter decreases. Distance between the nozzle and the substrate: As its increases, the fiber diameter increases. Flow rate: As its increases, the fiber diameter increases. Conclusions By presenting a 3D printer-electrospinning device, it is possible to control the fiber’s diameter and the 3D geometry in the 3D printing-electrospinning process.