Band 39, Heft 2

The water uptake behavior of Wood Dust (WD)/Prosopis Juliflora Fiber (PJF)/Phenol-Formaldehyde (PF) hybrid composites which are immersed in distilled and seawater environments was evaluated. Three different composite samples were fabricated by reinforcing WD and PJF with PF resin. The fabricated specimens were immersed in sea and distilled water to note down the moisture content absorption of the specimens for different time intervals from 0 to 240 h. The dry and wet specimens underwent mechanical properties testing as per ASTM standards and the findings for wet and dry specimens have been compared and analyzed. It is observed that the specimens which are immersed in sea (salt) water absorb more moisture content than the specimen immersed in distilled water and the PJF-rich (30 wt% of PJF & 10 wt % of WD) specimen absorbs more water than the other specimens. The water uptake behavior of the WD/PJF/PF hybrid composite follows a non-Fickian behavior. The mechanical performance (tensile, flexural, and impact) of the 10 wt % of WD 30 wt % of PJF specimen was better than that of other specimens at dry (before immersion) conditions and lost strength when immersed in sea and distilled water. SEM analysis was also done on the broken surface of the tested specimens which were exposed to the water environment.

In many industrial applications, natural-fiber-reinforced polymer (NFRP) composites are emerging as a strong substitute for composites based on synthetic fibers. The goal of this study was to examine the mechanical and tribological characteristics, including tensile, flexural, impact, wear, hardness, and water absorption, of hybrid epoxy composites reinforced with pineapple leaf and sisal fibers at various weight fractions. First, 5 % sodium hydroxide was used to treat the pineapple leaf and sisal fibers. With a composition of 0, 10, 15, 20, and 30 wt% of pineapple leaf and sisal fibers to the epoxy resin and its hardener mixture, which had a constant weight ratio of 70 %, hybrid composites were fabricated using the compression moulding process. To create a hybrid epoxy composite reinforced with pineapple and sisal fiber, epoxy resin was used as the binder. Different types of testing were performed on the hybrid composites following ASTM standards. The outcomes were contrasted with composites made from mono-pineapple and sisal fiber composites. In comparison to other composite samples, the 15:15 composite sample exhibited the best mechanical and tribological qualities, including the highest tensile strength, impact resistance, flexural strength, hardness, water absorption resistance, and wear resistance. Using a scanning electron microscope (SEM), the fiber/matrix adhesion was investigated. The 15:15 composite sample exhibits primarily mechanical and tribological properties, making the resultant composite material simpler to use in structural and automotive applications.

The current work aimed at investigating experimentally the weave pattern effects on the mechanical and dynamic behaviors of polymer matrix composite laminates. The laminates composed of three different weave types (plain, satin, and twill) of woven glass fabric and STR Medapoxy epoxy resin were fabricated via vacuum molding. Static bending experiments were applied to determine the influence of the weave pattern on the mechanical characteristics of the samples. The failure behaviors of the samples were also examined by optical and Scanning Electron Microscopy (SEM) analyses. Additionally, Dynamic Mechanical Analysis (DMA) in the temperature range of 25–200 °C at 1 Hz frequency was conducted to investigate the dynamic characteristics of the samples. It was found that the samples having satin weave type had the best flexural modulus followed by the plain and twill weaves. However, the twill weave laminates exhibited better storage modulus at glass transition temperature values ( T g ) compared to the others. Also, an increase of 3.3 °C in glass transition temperature was observed compared to that of neat resin. This was attributed to the better fiber/matrix adhesion and the lower molecular mobility in the polymer chain by the addition of glass twill fibers.

With this study, correlations in the structuring step of pin-like joining were derived. Increased friction energy due to higher amplitude or force leads to a reduction in structuring time. Changes in thermo-mechanical properties for humid specimens result in increased process times. The theoretical geometry of the pin-like structures is well reproduced in the lower pin area, regardless of the process control. In the upper pin area, increased force and amplitude results in increased defects and air inclusions as a result of an accelerate and more inhomogeneous pin formation. Humidity does not affect the general pin geometry, but should be avoided due to increased air inclusions that can weaken the structure. For the multi-material joints, high bond strengths of up to 30 % of the base material (max. 50 % possible with the geometry used) can be achieved. Therefore, a minimum undercut is required. Once this is reached, the pin defects and the corresponding pin-foot ratio are decisive for the resulting bond quality.

Biomass soybean oil-based polyol rigid polyurethane foam (RPUF) was modified and prepared by expandable graphite (EG). The effects of EG on the thermal stability and flame retardant properties of soybean oil-based polyol RPUFs were investigated by thermogravimetric analysis, pyrolysis kinetic analysis, conical calorimetry and flue gas toxicity analysis. The results showed that modified RPUF (RPUF-4) with EG content of 20 wt% had the highest initial and end temperatures, the highest activation energy E , the lowest Ds (17.6), and the highest light transmittance (73.6 %). At the same time, RPUF-4 had the lowest heat release rate (10.1 and 16.5 kW/m 2 ), the lowest total heat release (1.5 and 2.1 MJ/m 2 ), and the lowest average toxic gas emissions. The current study indicated that RPUF-4 had better thermal stability and flame retardant performance, which provided a useful reference for subsequent biomass flame retardant modified RPUFs.

In this work, the fabrication process of electrospun nanofibers from a blend of polyhydroxy butyrate (PHB) and polyvinyl chloride (PVC) has been investigated. PVC/PHB nanofibers have been fabricated from solutions using different PVC and PHB ratios. The influence of technical parameters of the electrospinning process on the fabrication, morphology, and diameter of nanofibers has been evaluated. The chemical structure and thermal properties of PVC/PHB have been studied. The results show that the diameter of PVC/PHB nanofibers increases as the PHB content increases. In addition, the optimal technical parameters of the electrospinning process for each PVC and PHB ratio are different. Infrared spectroscopy analysis revealed an enhancement of the crystalline phase of the polymer composite with increasing PHB content. The thermal properties of PVC/PHB nanofibers were evaluated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The change in PHB ratios leads to a change in the glass transition temperature of PVC/PHB nanofibers. The thermal degradation process of PVC/PHB includes two steps. Increasing the PHB content leads to an enhancement in the mechanical strength of PVC/PHB nanofiber mats; however, it also results in a reduction in tensile elongation. Based on the results of structural, morphological, interaction analysis, and mechanical properties of PVC/PHB nanofibers, this study contributes to the optimization of the fabrication of nanofibers from PVC and PHB. PVC/PHB nanofibers have the potential to be used for air filtration applications.

Natural fibers have received a lot of attention from academia as well as industry in the context of sustainable materials. Since they are more environmentally friendly than traditional synthetic materials, their physico-mechanical and frictional properties such as porosity, moisture absorption, high strength, modulus, toughness, and wear resistivity make them appropriate for a variety of industrialized applications where issues involving a significant quantity of dumping must be taken into account. The paper introduces an attempt to use epoxy-based composites reinforced with wood dust for various applications. The composites are prepared with various wood filler stacks (0, 2.5, 5, 7.5, 10, and 12.5 wt%) embedded with epoxy resin and subjected to tensile and flexural testing. The highest ultimate tensile strength achieved at 7.5 wt% wood dust support is 22 MPa, whereas the highest flexural modulus is 0.48 GPa at 12.5 wt% composites. The composite’s wear properties is examined under dry, wet, and heated contact conditions using a pin-on-disk (POD) machine. In dry condition, coefficient of friction (COF) varies from 0.10 to 0.38 whereas, in wet condition, the value of COF decreased by 70–83 %. In heated state, the COF is increased by up to 15 % when varying the temperature from 40 °C to 80 °C. The composite exhibits better wear behavior in the lower filler support than in the higher filler support due to the sturdy connection between the matrix and filler. On the other hand, the wet state’s tribological performance is superior to the dry and heated states. During surface morphology analysis, it is found that various voids, crack formation, wear debris, and thin transfer layer formation take place on the composite.

Multi-layer co-extrusion via the layer multiplication technique and a blow-molding set-up were used to produce bottles with a 129-layered structure of a model system of alternating polystyrene (PS) and poly (methyl methacrylate) (PMMA) layers. This method shows layer retention and thickness control with the use of melt rotation during the extrusion process. Samples were extruded and deformed angularly at different rotation speeds, blow-molded into bottles, and the overall wall thickness and analysis of individual layer thicknesses were performed. Angular rotation leads to weld line deformation and a change in layer thickness above a critical rotation speed in which the weld lines, inherited in the extrusion of the tube structures, are suitably deformed helically leading to uniform deformation during the blowing process. This method has potentially large implications for single cavity blow molding processes where high-performance properties, e.g., high barrier, insulation, mechanical, are of upmost importance, potential industries include gas transport, specialty packaging, and medical.

Data-based process monitoring in injection molding plays an important role in compensating disturbances in the process and the associated impairment of part quality. Selecting appropriate features for a successful online quality prediction based on machine learning methods is crucial. Time series such as the injection pressure and injection flow curve are particularly suitable for this purpose. Predicting quality as early as possible during a cycle has many advantages. In this paper it is shown how the recording length of the time series affects the prediction performance when using machine learning algorithms. For this purpose, two successful molding quality prediction algorithms ( k Nearest Neighbors and Ridge Regression) are trained with time series of different lengths on extensive data sets. Their prediction performances for part weight and a geometric dimension are evaluated. The evaluations show that recording time series until the end of a cycle is not necessary to obtain good prediction results. These findings indicate that early reliable quality prediction is possible within a cycle, which speeds up prediction, allows timely part handling at the end of the cycle and provides the basis for automated corrective interventions within the same cycle.

Laser processes have gained popularity in microfluidic device fabrication. This study aims to determine the optimal parameters for laser-based micro-cutting to achieve the desired width, depth, profile, and material removal, considering the thermal properties of PMMA. A CNC CO 2 laser was used, and 29 trials tested various speed and power combinations. Two theoretical models based on trial results focused on depth and width. COMSOL Multiphysics FEA software estimated surface temperature. Theoretical depth estimation matched experimental data more accurately when the P / S ratio was below 0.15 and the scanning speed was set at 500 mm/s or 750 mm/s. At 500 mm/s, width estimation was most accurate, up to 30 W. At 750 mm/s, experimental width exceeded predictions. Material removal increased proportionally with increasing P / S ratio, but beyond a threshold of 0.15, material removal remained nearly constant despite rising heat input. Laser-cut track shape varied, resembling a ‘U’ at lower and a ‘V’ at higher ratios. The groove shape transitioned from ‘U’ to ‘V’ when the temperature surpassed 1200 K. A V-shaped groove required a temperature exceeding 1500 K. Optimization confirmed a microchannel depth of 0.197 mm, width of 0.256 mm, and ‘U–V’ channel shape achievable at 30 W and 200 mm/s scanning speed, with a surface temperature of 1325 K.

Polyvinylidene fluoride (PVDF) is widely used in biotechnology due to its excellent biocompatibility, high temperature and pressure resistance, and outstanding mechanical properties. However, the hydrophobic nature of PVDF surface hinders the attachment of biological proteins. In order to enhance the wettability of PVDF surfaces, this study prepared composite films by blending PVDF with polyvinyl alcohol (PVA), and micro-patterned structures were fabricated on the material surface using a mold-replication method based on digital light processing (DLP) photopolymerization printing technology. A series of characterization techniques including surface morphology analysis, chemical composition analysis, and wettability testing were employed. The surface morphology analysis results indicated that the method of using DLP photopolymerization technology to print mold replicas and create micro-patterned structures was indeed effective in creating micro-patterned structures on both PVDF and PVDF/PVA composite films. The chemical composition analysis showed that the spin-coating of PVDF powder material resulted in PVDF β -phase crystalline structure, which has a positive effect on cell growth. Furthermore, the introduction of hydrophilic groups was achieved by mixing PVDF with PVA. Wetting test results indicate that the incorporation of the hydrophilic material PVA and micro-patterned surfaces both contribute to the improved hydrophilicity of the material. The water contact angle of the micro-patterned PVDF/PVA composite film reached 30.8°, exhibiting excellent hydrophilic properties. This study achieved the optimization of PVDF surface properties through micro-patterned surface modification and material composition design, providing novel insights for the further development of PVDF materials in the field of biotechnology.

High-thermal-conductivity polyphenylene sulfide (PPS) has both mechanical and heat dissipation properties, and its low weight and fuel efficiency make it a suitable replacement for metals in automobiles. However, this resin often causes filling defects in the injection molding process. This is due to the higher thermal conductivity, which causes the molten resin to solidify more quickly during the filling process. Therefore, it is important to predict the cooling and filling behaviors of the resin accurately using computer-aided engineering (CAE). Currently, many commercial software programs use thermal contact resistance (TCR) as the thermal boundary condition between the mold and resin. However, there is no established method to accurately evaluate TCR during filling with high spatial resolution and response, and the accuracy of CAE cannot be maintained. Therefore, we used thermography and a prismatic glass insert mold to thermally visualize and analyze the filling process of this resin. Consequently, we succeeded in evaluating TCR values with high spatial resolution and response. The obtained TCR values varied depending on the flow state and pressure. To further validate the obtained TCR values, we compared “the visualization results of real flow conditions” and “the flow prediction results of CAE considering the obtained TCR values”.

Numerous vibration-assisted methods have been adopted to solve problems in polymer processing, but the introduction of vibration fields is typically done on small extruders or injectors in school laboratories and industrial research rooms, which profoundly limits the application of vibration technology. The purpose of this study is to put forward a simple vibration excitation method for all scale extruders or injection molding machines. To recover the mixing performance of that excitation method, a numerical investigation was carried out using the CFD software ANSYS POLYFLOW 19.2, and the analysis and comparison were made between the mixing performance of a simplified screw element with and without a sinusoidal pulsating speed field. The results showed that not all dynamic states with the superimposed excitation field have better mixing performance than the steady state without any pulsating field. Nevertheless, the introduction of a pulsating speed field under certain parameters setting can indeed enhance the stretching rate, reduce the separation scale, increase the mixing efficiency, and lower the screw force. These findings are of great importance and provide valuable references for the development and application of vibration-assisted molding technology in plastics machinery.

Natural fiber-based hybrid composites are gaining more attention in industrial usage due to their low cost, environmental friendliness, and simplicity of processing. In this research, an effort was made to create hybrid natural composites using Indian almond and peepal fibers for applications in the automotive industry. Composites were prepared with different volume fractions of Indian almond and peepal fibers using the hand layup process. The mechanical and tribological properties of the composites were tested. The epoxy/40 wt% peepal composite showed superior performance compared to all other composites due to the better strength of peepal fiber. Moreover, the same composite displayed the least wear loss and coefficient of friction (COF). The present study confirms that peepal fiber composites match the strength properties of existing industrial composite materials, and that they may be some of the alternative composites for automotive applications.

Wind turbine (WT) blade fabrication typically employs thermosetting resins, whose recycling challenges post-retirement have resulted in environmental pressures. Thus, there is an urgent need to develop a low-viscosity, high-performance, and recyclable material with excellent mechanical properties that is compatible with WT fabrication processes, serving as a viable alternative to traditional epoxy resins. Poly(methyl methacrylate) (PMMA) resin is considered a promising candidate for replacing epoxy resins. However, the mechanical properties of PMMA still require improvement. In this study, we investigated the effects of introducing copolymerized monomers on the comprehensive performance of PMMA resin without affecting its viscosity, examining the influence of these copolymerized monomers on the material’s thermal and mechanical properties. Meanwhile, the mechanical properties of the synthesized PMMA-based copolymers were compared with those of blade-specific epoxy resin (WD0135). The results revealed that compared to WD0135, the flexural strength and modulus of the prepared PMMA copolymers significantly increased to 96.6 and 3158.6 MPa, respectively, with a tensile strength reaching 74.2 MPa. Consequently, this series of PMMA-based resins demonstrates immense potential for large-scale material part fabrication via casting techniques.