Search Results (13)

Recycling production waste in the reactive injection molding (RIM) process is a step towards sustainability and efficient material usage. The recycled thermoset composite (RTC) material obtained by shredding the production waste is reused with a virgin thermoset composite (VTC). This study presents a mold-filling simulation approach considering this polydisperse suspension of RTC and VTC. Mold-filling simulations can assist in predicting processability and assessing the impact of reinforced RTC on the final part of production. State-of-the-art mold-filling simulations use the Cross–Castro–Macosko (CCM) model or anisotropic fiber-orientation-dependent viscosity models. The rheological parameters are determined either for the VTC or neat resin. However, these models do not account for changes in viscosity due to the reinforcing of fillers such as RTC. An effective viscosity model is developed by extending the CCM model using the stress–strain amplification approach to overcome this gap. This model is implemented in the computational fluid dynamics code OpenFOAM, and simulations are performed using an extended multiphase solver. To validate the simulations, experimental trials were executed using a two-cavity mold equipped with pressure sensors. Molding compounds with different compositions of VTC and RTC were injected at different speeds. Reinforcing VTC with RTC increases the viscosity. Results demonstrate that RTC-reinforced compounds require higher injection pressure for mold filling than VTC alone. The qualitative agreement of pressure profiles from simulations and experiments for different proportions of reinforcing RTC and different injection speeds shows that the implemented viscosity model can reproduce the experimental mold-filling behavior. Full article

Composites of synthetic bone mineral substitutes (BMS) and biodegradable polyesters are of particular interest for bone surgery and orthopedics. Manufacturing of composite scaffolds commonly uses mixing of the BMS with polymer melts. Melt processing requires a high homogeneity of the mixing, and is complicated by BMS-promoted thermal degradation of polymers. In our work, poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) composites reinforced by commercial β-tricalcium phosphate (βTCP) or synthesized carbonated hydroxyapatite with hexagonal and plate-like crystallite shapes (hCAp and pCAp, respectively) were fabricated using injection molding. pCAp-based composites showed advanced mechanical and thermal characteristics, and the best set of mechanical characteristics was observed for the PLLA-based composite containing 25 wt% of pCAp. To achieve compatibility of polyesters and pCAp, reactive block copolymers of PLLA or PCL with poly(tert-butyl ethylene phosphate) (C1 and C2, respectively) were introduced to the composite. The formation of a polyester-b-poly(ethylene phosphoric acid) (PEPA) compatibilizer during composite preparation, followed by chemical binding of PEPA with pCAp, have been proved experimentally. The presence of 5 wt% of the compatibilizer provided deeper homogenization of the composite, resulting in a marked increase in strength and moduli as well as a more pronounced nucleation effect during isothermal crystallization. The use of C1 increased the thermal stability of the PLLA-based composite, containing 25 wt% of pCAp. In view of positive impacts of polyester-b-PEPA on composite homogeneity, mechanical characteristics, and thermal stability, polyester-b-PEPA will find application in the further development of composite materials for bone surgery and orthopedics. Full article

During the impregnation of reinforcement fabrics in liquid composite molding processes, the flow within fiber bundles and the channels between the fiber bundles usually advances at different velocities. This so-called “dual-scale flow” results in void formation inside the composite material and has a negative effect on its mechanical properties. Semi-empirical models can be applied to calculate the extent of the dual-scale flow. In this study, a methodology is presented that stops the impregnation of reinforcement fabrics at different filling levels by using a photo-reactive resin system. By means of optical evaluation, the theoretical calculation models of the dual-scale flow are validated metrologically. The results show increasingly distinct dual-scale flow effects with increasing pressure gradients. The methodology enables the measurability of microscopic differences in flow front progression to validate renowned theoretical models and compare simulations to measurements of applied injection processes. Full article

The long cycle of manufacturing continuous carbon fiber-reinforced composite has significantly limited its application in mass vehicle production. High-pressure resin transfer molding (HP-RTM) is the process with the ability to manufacture composites in a relatively short forming cycle (<5 min) using fast reactive resin. The present study aims to investigate the influence of HP-RTM process variables including fiber volume fraction and resin injection flow rate on void characteristics, and flexural properties of manufactured CFRP components based on experiments and numerical simulations. An ultrasonic scanning system and optical microscope were selected to analyze defects, especially void characteristics. Quasi-static bending experiments were implemented for the CFRP specimens with different void contents to find their correlation with material’s flexural properties. The results showed that there was also a close correlation between void content and the flexural strength of manufactured laminates, as the flexural strength decreased by around 8% when the void content increased by ~0.5%. In most cases, the void size was smaller than 50 μm. The number of voids substantially increased with the increase in resin injection flow rate, while the potential effect of resin injection flow rate was far greater than the effect of fiber volume fraction on void contents. To form complicated CFRP components with better mechanical performance, resin injection flow rate should be carefully decided through simulations or preliminary experiments. Full article

In this work, green composites have been developed and characterized using a bio-based polymeric matrix such as BioPBSA and the introduction of 30 wt.% short hemp fibers as a natural reinforcement to obtain materials with maximum environmental efficiency. In order to increase the interfacial adhesion between the matrix and the fiber to obtain better properties in the composites, a reactive extrusion process has been carried out. On the one hand, different additives derived from bio-based itaconic acid have been added to the BioPBSA/HEMP composite, such as dibutyl itaconate (DBI) and a copolymer of PBSA grafted with itaconic acid (PBSA-g-IA). On the other hand, a different copolymer of PBSA grafted with maleic anhydride (PBSA-g-MA) was also tested. The resulting composites have been processed by injection-molding to obtain different samples which were evaluated in terms of mechanical, thermal, chemical, dynamic-mechanical, morphological and wettability and color properties. In relation to the mechanical properties, the incorporation of hemp fibers resulted in an increase in the stiffness of the base polymer. The tensile modulus of pure BioPBSA increased from 281 MPa to 3482 MPa with 30% fiber. The addition of DBI shows a remarkable improvement in the ductility of the composites, while copolymers with IA and MA, generate mechanically balanced composites. In terms of thermal properties, the incorporation of hemp fiber and compatibilizing agents led to a reduction in thermal stability. However, from the point of view of thermomechanical properties, a clear increase in rigidity is achieved throughout the temperature range studied. As far as the color of the samples is concerned, the incorporation of hemp generates a typical color, while the incorporation of the compatibilizing agents does not modify this color excessively. Finally, the introduction of lignocellulosic fibers greatly affects water absorption and contact angle, although the use of additives helped to mitigate this effect. Full article

Pultrusion of thermoplastic composites has been the hotspot of manufacturing high-performance thermoplastic composites in recent years. The optimization of process parameters in the pultrusion usually needed repeated attempts, which wasted lots of manpower and material resources. A numerical simulation method can accelerate the optimization of process parameters. In this work, the impregnation process of reactive injection pultrusion for glass fiber reinforced nylon 6 (GF/PA6) composites was modeled and numerically simulated by a finite element/controlled volume (Fe/CV) method. Based on Darcy’s law, the impregnation process can be regarded as the two-phase flow (liquid resin and air) in porous media (undirectional glass fibers). The distribution of resin flow during the impregnation was explored. The effects of pulling rate and injection pressure on the impregnation time and resin reflux distance were analyzed, and the appropriate range of relevant process parameters was determined. The results showed that increasing the pulling rate can significantly control the reflux distance of resin in the impregnation mold and shorten the impregnation time, but too high a pulling rate would increase the impregnation time. Increasing the injection pressure can greatly shorten the resin impregnation time, but it would significantly increase the resin reflux distance. This work can effectively guide the subsequent optimization of process parameters of reactive injection pultrusion for GF/PA6 composites. Full article

The presented research focused on improving the mechanical properties of PLA-based composites reinforced with buckwheat husks (BH) particles. The research work was carried out in two stages. Firstly, the blend was prepared with the addition of polybutylene adipate terephthalate (PBAT) and thermoplastic starch (TPS), manufactured by injection molding technique, then the selected materials were prepared with the addition of BH filler, and the samples were prepared using the fused deposition modeling method (FDM). All samples were subjected to the assessment of material properties. Thermal and thermomechanical properties were evaluated using differential scanning calorimetry analysis (DSC) and dynamic thermal mechanical analysis (DMTA). Mechanical characteristic was evaluated using static tensile and flexural measurements and Charpy impact resistance tests. The research was supplemented with scanning electron microscopy analysis (SEM). It was found that the addition of PBAT and TPS greatly improves impact strength and elongation, especially with the addition of reactive compatibilizer. As expected, TPS, PBAT, and BH reduced the stiffness of the composites during DMTA testing. The presence of BH particles in the polymer matrix was observed to improve the crystallization behavior of PLA. The optimal content of BH filler in the composite was found to be 10%, which allowed to preserve good mechanical properties. Full article

For a newly developed thermoset injection molding process, glass fiber-reinforced phenolic molding compounds with fiber contents between 0 wt% and 60 wt% were compounded. To achieve a comparable remaining heat of the reaction in all compound formulations, the specific mechanical energy input (SME) during the twin-screw extruder compounding process was used as a control parameter. By adjusting the extruder screw speed and the material throughput, a constant SME into the resin was targeted. Validation measurements using differential scanning calorimetry showed that the remaining heat of the reaction was higher for the molding compounds with low glass fiber contents. It was concluded that the SME was not the only influencing factor on the resin crosslinking progress during the compounding. The material temperature and the residence time changed with the screw speed and throughput, and most likely influenced the curing. However, the SME was one of the major influence factors, and can serve as an at-line control parameter for reactive compounding processes. The mechanical characterization of the test specimens revealed a linear improvement in tensile strength up to a fiber content of 40–50 wt%. The unnotched Charpy impact strength at a 0° orientation reached a plateau at fiber fractions of approximately 45 wt%. Full article

This research reports the manufacturing and characterization of green composites made from recycled polypropylene obtained from the remnants of polypropylene non-woven fabrics used in the textile industry and further reinforced with short hemp fibers (SHFs). To improve the interaction of the reinforcing fibers with the recycled polymeric matrix, two types of compatibilizing agents (maleic anhydride grafted, PP-g-MA, and maleinized linseed oil, MLO) were added during melt-processing, the percentage of which had to remain constant concerning the amount of fiber loading to ensure complete reactivity. Standardized test specimens were obtained by injection molding. The composites were characterized by mechanical (tensile, impact, and hardness), thermal (DSC, TGA), thermomechanical, FTIR, and FESEM microscopy tests. In addition, color and water uptake properties were also analyzed. The results show that the addition of PP-g-MA to rPP was satisfactory, thus improving the fiber-matrix interaction, resulting in a marked reinforcing effect of the hemp fibers in the recycled PP matrix, which can be reflected in the increased stiffness of the samples. In parallel to the compatibilizing effect, a plasticizing effect was obtained by incorporating MLO, causing a decrease in the glass transition temperature of the composites by approximately 6 °C and an increase in ductility compared to the unfilled recycled polypropylene samples. Full article

The presented study focuses on the development of flax fiber (FF) reinforced composites prepared with the use of poly(lactic acid)/poly(butylene adipate-co-terephthalate)—PLA/PBAT blend system. This type of modification was aimed to increase impact properties of PLA-based composites, which are usually characterized by high brittleness. The PLA/PBAT blends preparation was carried out using melt blending technique, while part of the samples was prepared by reactive extrusion process with the addition of chain extender (CE) in the form of epoxy-functionalized oligomer. The properties of unreinforced blends was evaluated using injection molded samples. The composite samples were prepared by compression molding technique, while flax fibers reinforcement was in the form of plain fabric. The properties of the laminated sheets were investigated during mechanical test measurements (tensile, flexural, impact). Differential scanning calorimetry (DSC) analysis was used to determine the thermal properties, while dynamic mechanical thermal analysis (DMTA) and heat deflection temperature (HDT) measurements were conducted in order to measure the thermomechanical properties. Research procedure was supplemented with structure evaluation using scanning electron microscopy (SEM) analysis. The comparative study reveals that the properties of PLA/PBAT-based composites were more favorable, especially in the context of impact resistance improvement. However, for CE modified samples also the modulus and strength was improved. Structural observations after the impact tests confirmed the presence of the plastic deformation of PLA/PBAT matrix, which confirmed the favorable properties of the developed materials. The use of PBAT phase as the impact modifier strongly reduced the PLA brittleness, while the reactive extrusion process improves the fiber-matrix interactions leading to higher stiffness and strength. Full article

Green composites made of polylactide (PLA) and short flaxseed fibers (FFs) at 20 wt % were successfully compounded by twin-screw extrusion (TSE) and subsequently shaped into pieces by injection molding. The linen waste derived FFs were subjected to an alkalization pretreatment to remove impurities, improve the fiber surface quality, and make the fibers more hydrophobic. The alkali-pretreated FFs successfully reinforced PLA, leading to green composite pieces with higher mechanical strength. However, the pieces also showed lower ductility and toughness and the lignocellulosic fibers easily detached during fracture due to the absence or low interfacial adhesion with the biopolyester matrix. Therefore, four different compatibilization strategies were carried out to enhance the fiber–matrix interfacial adhesion. These routes consisted on the silanization of the alkalized FFs with a glycidyl silane, namely (3-glycidyloxypropyl) trimethoxysilane (GPTMS), and the reactive extrusion (REX) with three compatibilizers, namely a multi-functional epoxy-based styrene-acrylic oligomer (ESAO), a random copolymer of poly(styrene-co-glycidyl methacrylate) (PS-co-GMA), and maleinized linseed oil (MLO). The results showed that all the here-tested compatibilizers improved mechanical strength, ductility, and toughness as well as the thermal stability and thermomechanical properties of the green composite pieces. The highest interfacial adhesion was observed in the green composite pieces containing the silanized fibers. Interestingly, PS-co-GMA and, more intensely, ESAO yielded the pieces with the highest mechanical performance due to the higher reactivity of these additives with both composite components and their chain-extension action, whereas MLO led to the most ductile pieces due to its secondary role as plasticizer for PLA. Full article

In this paper, green biocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and Miscanthus giganteus fibers (MIS) were prepared in the presence of dicumyl peroxide (DCP) via reactive extrusion. The objective of this study was to optimize the interfacial adhesion between the reinforcement and the matrix, improving the mechanical properties of the final material. To this aim, two fibers mass fractions (5 and 20 wt %) and two different fiber sizes obtained by two opening mesh sieves (1 mm and 45 μm) were investigated. The impregnation of fibers with DCP before processing was carried out in order to promote the PHBHV grafting onto MIS fibers during the process, favoring, in this way, the interfacial adhesion between fibers and matrix, instead of the crosslinking of the matrix. All composites were realized by extrusion and injection molding processing and then characterized by tensile tests, FTIR-ATR, SEM, DSC and XRD. According to the improved adhesion of fibers to matrix due to DCP, we carried out an implementation of models involving that can predict the effective mechanical properties of the biocomposites. Three phases were taken into account here: fibers, gel (crosslinked matrix), and matrix fractions. Due to the complexity of the system (matrix–crosslinked matrix–fibers) and to the lack of knowledge about all the phenomena occurring during the reactive extrusion, a mathematical approach was considered in order to obtain information about the modulus of the crosslinked matrix and its fraction in the composites. This study aims to estimate these last values, and to clarify the effect caused by the presence of vegetal fibers in a composite in which different reactions are promoted by DCP. Full article

The reactive process of reinforced thermoset injection molding significantly influences the mechanical properties of the final composite structure. Therefore, reliable process simulation is crucial to predict the process behavior and relevant process effects. Virtual process design is thus highly important for the composite manufacturing industry for creating high quality parts. Although thermoset injection molding shows a more complex flow behavior, state of the art molding simulation software typically focusses on thermoplastic injection molding. To overcome this gap in virtual process prediction, the present work proposes a finite volume (FV) based simulation method, which models the multiphase flow with phase-dependent boundary conditions. Compared to state-of-the-art Finite-Element-based approaches, Finite-Volume-Method (FVM) provides more adequate multiphase flow modeling by calculating the flow at the cell surfaces with an Eulerian approach. The new method also enables the description of a flow region with partial wall contact. Furthermore, fiber orientation, curing and viscosity models are used to simulate the reinforced reactive injection molding process. The open source Computational-Fluid-Dynamics (CFD) toolbox OpenFOAM is used for implementation. The solver is validated with experimental pressure data recorded during mold filling. Additionally, the simulation results are compared to commercial Finite-Element-Method software. The simulation results of the new FV-based CFD method fit well with the experimental data, showing that FVM has a high potential for modeling reinforced reactive injection molding. Full article