Filler Agglomeration Research Articles

Enhancing the Thermal and Mechanical Characteristics of Polyvinyl Alcohol (PVA)-Hemp Protein Particles (HPP) Composites

AbstractThis paper aims to describe the thermal, mechanical, and surface properties of a PVA/HPP blend whereby the film was prepared using a solution casting method. The improvements in thermal and mechanical properties of HPP-based PVA composites were investigated. The characterization of pure PVA and PVA composite films included tensile tests, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results of TGA and DSC indicated that the addition of HPP increased the thermal decomposition temperature of the composites. Mechanical properties are significantly improved in PVA/HPP composites. The thermal stability of the PVA composite increased with the increase of HPP filler content. The tensile strength increased from 15.74 ± 0.72 MPa to 27.54 ± 0.45 MPa and the Young’s modulus increased from 282.51 ± 20.56 MPa to 988.69 ± 42.64 MPa for the 12 wt% HPP doped sample. Dynamic mechanical analysis (DMA) revealed that at elevated temperatures, enhanced mechanical properties because of the presence of HPP was even more noticeable. Morphological observations displayed no signs of agglomeration of HPP fillers even in composites with high HPP loading.

"All Polyimide" Mixed Matrix Membranes for High Performance Gas Separation.

To improve the interfacial compatibility of mixed matrix membranes (MMMs) for gas separation, microporous polyimide particle (AP) was designed, synthesized, and introduced into intrinsic microporous polyimide matrix (6FDA-Durene) to form “all polyimide” MMMs. The AP fillers showed the feature of thermal stability, similar density with polyimide matrix, high porosity, high fractional free volume, large microporous dimension, and interpenetrating network architecture. As expected, the excellent interfacial compatibility between 6FDA-Durene and AP without obvious agglomeration even at a high AP loading of 10 wt.% was observed. As a result, the CO2 permeability coefficient of MMM with AP loading as low as 5 wt.% reaches up to 1291.13 Barrer, which is 2.58 times that of the pristine 6FDA-Durene membrane without the significant sacrificing of ideal selectivity of CO2/CH4. The improvement of permeability properties is much better than that of the previously reported MMMs, where high filler content is required to achieve a high permeability increase but usually leads to significant agglomeration or phase separation of fillers. It is believed that the excellent interfacial compatibility between the PI fillers and the PI matrix induce the effective utilization of porosity and free volume of AP fillers during gas transport. Thus, a higher diffusion coefficient of MMMs has been observed than that of the pristine PI membrane. Furthermore, the rigid polyimide fillers also result in the excellent anti-plasticization ability for CO2. The MMMs with a 10 wt.% AP loading shows a CO2 plasticization pressure of 300 psi.

Synthesis and Properties of Polymerization-Filled Composites Based on Polypropylene and Single-Wall Carbon Nanotubes

Composites based on polypropylene and single-wall carbon oxygen-containing nanotubes with a specific surface area of 360 and 500 m2/g are synthesized in the medium of liquid propylene using the catalytic system rac-Me2Si(2-Me-4-PhInd)2ZrCl2/МАО. Optimum polymerization conditions ensuring a fairly high rate of the process are determined, and the composites with the filler content in the range from 0.3 to 13.0 wt % are obtained. It is shown that the presence of functional groups enhances the filler agglomeration tendency during composite formation. Effects of the type of carbon nanofiller on the thermal stability, thermo-oxidative resistance, and thermal and electrophysical characteristics of the composites are studied. It is found that the filler inhibits the processes of oxidation and destruction of polypropylene crystallites.

Largely improved thermal conductivity of HDPE composites by building a 3D hybrid fillers network

Hybrid fillers of different geometries are increasingly utilized for the development of functional polymer composites. We herein report the role of HDPE-g-MAH as a compatibilizer for ternary composites consisting of HDPE, multi-walled carbon nanotubes and hexagonal boron nitride (BN). Through melt blending, HDPE-g-MAH can reduce the agglomeration of fillers and facilitate the formation of network structure. Due to the synergistic effect, ternary composites have demonstrated significantly higher thermal conductivity than those binary composites, and their maximum increase relative to the matrix is 262%. The mechanical performance and thermal conductivity are explained from perspectives of the morphology and crystallinity of the composites. The rheological properties of both binary and ternary composites have close relationship with their thermal conductivity. Although a high fraction of BN nanosheets can greatly reduce the electrical conductivity of ternary composites, they posed little effect on the electromagnetic interference shielding performance, owing to their electrical insulating nature. This research can provide new clues for the development of functional materials.

Analysis of Organic-Inorganic Compatibility to Synthesis Defect Free Composite Membrane: A Review

Despite the excellent potential separation performance of the composite membrane, the incompatibility of organic membrane matrix with inorganic nanofiller has been remained as the major concern in producing a defect free composite membrane. Indeed, incompatibility between polymer and nanofiller caused fillers agglomeration, consequently, formed the interfacial void defect. When nanofillers are dispersed in the polymer dope, agglomeration tends to happen due to relatively large van der Waals forces of interaction. In the case of filler and polymer are not compatible, these forces will be dominant among the fillers, which caused the nanoparticles to attract to each, then induces aggregation. Such membrane defects inevitably lower the separation performances of the membrane. This review discussed the development of mixed matrix membrane, particularly on the concern of compatibility between polymer and nanofiller. Techniques to improve polymer-filler compatibility has been further discussed based on various modification and cross-linking strategies. Currently, the linker is studying experimentally to promote affinity between inorganic filler and the organic polymer. Indeed, this is time consuming and involves expensive research cost. In this review, an alternative technique using molecular dynamics (MD) simulation has also been elaborated to determine the efficiency of coupling agent to improve the matching of organic-inorganic materials, through the calculation of the molecular bonding energy. Theoretically, a multi-component system with lower energy than the total energy from its respective individual component can define as stable; hence, achieving polymer-filler compatibility.

Biocarbon reinforced polypropylene composite: An investigation of mechanical and filler behavior through advanced dynamic atomic force microscopy and X-ray micro CT

Polymer composites were manufactured using biocarbon particles as a reinforcing filler to improve the mechanical and thermal properties. However, a detailed examination of dispersion and agglomeration of filler is essential to correlate the filler matrix and the filler and filler interactions with the mechanical properties of the product. We investigated the variations of mechanical, agglomeration behaviour of fillers, and thermal properties of polypropylene coconut shell biocarbon composites. PP CSB composites were prepared by melt mixing process varying the CSB content using a Brabender mixer. The nanomechanical mapping of the composites studied using Atomic Force Microscopy revealed an increase in Youngs modulus from 1.6 to 2.9 GPa when CSB loading increased from 0 to 20 weight percentage. The dispersion and agglomeration of CSB filler in the PP matrix were investigated using 3D reconstructed images with the help of X-ray micro CT, and a dedicated 3D reconstruction software. The thermal stability of the PP CSB composites also improved with an increase in CSB content in PP.

Highly dispersible silicon nitride whiskers in asymmetric porous separators for high-performance lithium-ion battery

The separator plays a pivotal role in the safe operation of rechargeable batteries. In this work, a novel separator fabricated by incorporating Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) with silicon nitride (Si3N4) whiskers was reported for the first time. Compared with introducing nano powders as inorganic fillers, incorporating inorganic whiskers into polymetric substrates not only suppresses the agglomeration of fillers, but also maintains high structural stability at high temperatures by forming a concrete composite structure. Systematical comparison of “powder-in-polymer” and “whiskers-in-polymer” separators demonstrated that the whisker filler can suppress unexpected dimensional shrinkage at high temperatures and improve electrochemical stability. The composite separator with 60 wt% silicon nitride whiskers exhibits enhanced ionic conductivity of 0.884 mS/cm at 25 °C, stable coulombic efficiency, higher capacity retention rate of 97.4% after 100 cycles and high specific capacity of 103.9 mAh·g−1 at 5 C.

Development and Performance Evaluation of Cellulose Acetate-Bentonite Mixed Matrix Membranes for CO2 Separation

Membrane science is a state-of-the-art environmentally green technology that ascertains superior advantages over traditional counterparts for CO2 capture and separation. In this research, mixed matrix membranes (MMMs) comprising cellulose acetate (CA) with various loadings of bentonite (Bt) clay were fabricated by adopting the phase-inversion technique for CO2/CH4 and CO2/N2 separation. The developed pristine and MMMs were characterized for morphological, thermal, structural, and mechanical analyses. Several techniques such as scanning electron microscopy, thermogravimetric analysis, Fourier transformed infrared spectroscopy, and nano-indentation investigations revealed the promising effect of Bt clay in MMMs as compared to pristine CA membrane. Nano-indentation test identified that elastic modulus and hardness of the MMM with 1 wt. loading was increased by 64% and 200%, respectively, compared to the pristine membrane. The permeability decreased with the incorporation of Bt clay due to uniform dispersion of filler attributed to enhanced tortuosity for the gas molecules. Nevertheless, an increase in gas separation performance was observed with Bt addition up to 1 wt. loading. The opposite trend prevailed with increasing Bt concentration on the separation performance owing to filler agglomeration and voids creation. The maximum value of ideal selectivity (CO2/CH4) was achieved at 2 bar pressure with 1 wt. % Bt loading, which is 79% higher than the pristine CA membrane. For CO2/N2, the ideal selectivity was 123% higher compared to the pristine membrane with 1 wt. % Bt loading at 4 bar pressure.

Investigation of mechanical properties of jute epoxy composite with fruit waste (Citrullus vulgaris peel) filler for automotive applications

In the current investigation, the mechanical behavior of watermelon (Citrullus vulgaris) peel nano debris (described as a fruit filler) with different weight composition (0 wt. %, 1 wt. %, 2 wt. %, 2.5 wt. %, 5 wt. %, 7.5 wt. % and 10 wt. %) is reinforced with jute fabric in an epoxy matrix. The effect of filler concentration on tensile, hardness, flexural and impact strength are investigated as per ASTM standards. The findings indicate that the addition of fruit filler improves the mechanical property of jute composite. It is found that the presence of 2.5 wt. % filler in the nanocomposite records the highest value of tensile strength, flexural strength, and hardness of the jute epoxy composite and the 10 wt. % filler nanocomposites achieve a noticeable projection in impact strength. The fracture surfaces are examined for the fiber alignment, fiber-matrix adhesion, voids, filler agglomeration, and fiber fracture. Furthermore, a glass visor was developed to show the best mechanical performing potential and analyzed for deformation behavior and modal analysis using ANSYS.

Wood flour‐high density polyethylene composites: Influence of silanization and esterification on mechanical properties

AbstractSilanization and esterification are strategies used to treat wood flour (WF) to produce surface functionalized hydrophobic WF leading to an improvement in dispersion and compatibility between wood phase and polymer phase. Silanization involves functionalization of alkyl groups by coupling trimethoxy (propyl) silane (MPS), and esterification functionalizes WF with ester groups, using acetic anhydride (Ac). Modified WF was incorporated into recycled high‐density polyethylene (HDPE) to form reHDPE/mod‐WF composite system. Both modifications produced highly hydrophobic WF surfaces which improved the dispersion in the reHDPE matrix; resulting in a significant difference in impact strength, specifically at 20 wt% filler, from 74.5 Jm−1 to 146.3 Jm−1 and 113.5 Jm−1, that is, up to 96% and 52% for MPS‐WF and Ac‐WF, respectively. However, filler agglomeration higher than 20 wt% reduces the composite impact strength. The results herein demonstrate that alkyl‐functionalized WF show excellent dispersion in the reHDPE system and is the preferred technique to improve system mechanical resilience as compared to esterification.

Polypropylene nanocomposites with high-loading conductive carbon nano-reinforcements for multifunctional applications

Lightweight automotive parts fabrication is an essential criterion for the improvement of the efficiency of vehicles. In this work, different weight (wt) content of commercially developed carbon nanofiber (CNF) and granulated graphitized graphene (GRP) were melt extruded with polypropylene (PP) with the aim of improvement in mechanical and electrical properties. The CNF–PP and GRP–PP nanocomposites were developed by injection molding technique, and mechanical as well as electrical properties at different reinforcement content were studied. A three-point bending test showed that flexural strength and modulus increases with increment in nanofiller content, and maximum mechanical properties were obtained by 45 wt% CNF–PP and 60 wt% GRP–PP nanocomposites. Electrical conductivity of 1.4 and 0.4 S/cm were achieved by incorporating 60 wt% CNF and 60 wt% GRP in PP nanocomposites. Thermal stability was studied by thermogravimetric analysis (TGA), and maximum thermal stability was achieved by 45% CNF–PP nanocomposites. Morphological study by scanning electron microscopy (SEM) showed considerable aligned CNF selectively located in the PP matrix and exhibited oriented dispersion while filler agglomeration phenomena observed for GRP at high loading, which made nanocomposites have significant enhancement of mechanical and electrical properties using CNF reinforcement.

Graphene-Based Reinforcing Filler for Double-Layer Acrylic Coatings.

This study aims to demonstrate the remarkable features of graphene-based fillers, which are able to improve the protective performance of acrylic coatings. Furthermore, the joint application of a cataphoretic primer and a spray top coat, containing graphene and functionalized graphene oxide flakes, respectively, enables the deposition of a double-layer coating with high conductivity and abrasion resistance properties, capable of offering excellent corrosion resistance to the metal substrate. The surface morphology of the single- and double-layer coatings was investigated by optical and electron microscopies, analysing the defectiveness introduced in the polymer matrix due to the filler agglomeration. The behavior in aggressive environments was assessed by exposure of the samples in the salt spray chamber, evaluating the blister formation and the adhesion level of the coatings. Electrochemical impedance spectroscopy measurements were employed to study the corrosion protection properties of the coatings, whose conductivity and abrasion resistance features were analysed by conductivity assessment and scrub tests, respectively. The incorporation of graphene-based fillers in the cataphoretic primer improves the corrosion protection properties of the system, while the graphene flakes provide the top coat spray layer with high conductivity and excellent abrasion resistance features. Thus, this work demonstrates the possibility of employing different types of graphene-based fillers and deposition methods for the creation of multifunctional coatings.

Process Optimization of Ultra-High Molecular Weight Polyethylene/Cellulose Nanofiber Bionanocomposites in Triple Screw Kneading Extruder by Response Surface Methodology.

Incorporation of nanocellulose could improve wear resistance of ultra-high molecular weight polyethylene (UHMWPE) for an artificial joint application. Yet, the extremely high melt viscosity of the polymer may constrict the mixing, leading to fillers agglomeration and poor mechanical properties. This study optimized the processing condition of UHMWPE/cellulose nanofiber (CNF) bionanocomposite fabrication in triple screw kneading extruder by using response surface methodology (RSM). The effect of the process parameters—temperature (150–190 °C), rotational speed (30–60 rpm), and mixing time (30–45 min)—on mechanical properties of the bionanocomposites was investigated. Homogenous filler distribution, as confirmed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis, was obtained through the optimal processing condition of 150 °C, 60 rpm, and 45 min. The UHMWPE/CNF bionanocomposites exhibited improved mechanical properties in terms of Young’s and flexural modulus by 11% and 19%, respectively, as compared to neat UHMWPE. An insignificant effect was observed when maleic anhydride-grafted-polyethylene (MAPE) was added as compatibilizer. The obtained results proved that homogenous compounding of high melt viscosity UHMWPE with CNF was feasible by optimizing the melt blending processing condition in triple screw kneading extruder, which resulted in improved stiffness, a contributing factor for wear resistance.

Thermal insulation using biodegradable poly(lactic acid)/date pit composites

The usage of green insulation in building construction improves the thermal management with respect to buildings and allows the usage of environmentally friendly materials for insulation. Herein, we developed novel green polymer composites using biodegradable poly(lactic acid) (PLA) and date pit powder (DPP) as the building insulation material. The PLA–DPP composites were melted and blended and were subjected to compression molding. Then, they were characterized based on their physical (water absorption), thermal (thermal conductivity, thermal diffusivity, and degree of crystallization), and mechanical properties. Results indicate that the thermal conductivity decreased from 0.0794 to 0.0682 W/m.K when the DPP content increased from 10% to 40% (w/w). Similarly, the thermal diffusivity decreased with the increasing DPP content and became 0.034 mm2/s. However, this increased the water absorption (~5.6% at 40 wt.% in cold water). The compressive strength decreased with the addition of DPP, which was attributed to the filler agglomeration and low compatibility between PLA and DPP. The compressive strength of the PLA–DPP composite was higher than those of the commonly used insulating materials and comparable to those of the construction materials (84.3–64.4 MPa). The characteristics of the PLA–DPP composites indicate that they are stable composites with promising insulation and construction capacity. The composite developed herein could replace traditional insulators and a portion of the concrete in the wall panel, increasing the overall thermal resistance of the wall panel. The developed materials may be used in the handles of kitchen utensils and other materials that require thermal insulation.

The influences of filler loading on tensile properties and water absorption properties of carbonized sugarcane bagasse filled high density polyethylene (HDPE) composite

This study synthesized carbonized sugarcane bagasse (CSB) filled high density polyethylene (HDPE) composites. The effect of pre-treatment reagent of SB with different concentration of sodium hydroxide (NaOH) was examined. The untreated, treated and carbonized SB were characterized by proximate analysis and functional group analysis. By considering all the characteristics, 7 wt% is the optimum concentration which gave lowest moisture content and highest fixed carbon (FC) content. It was chosen to undergo carbonization process at temperature of 600 °C to produce CSB and used as filler in composites. The filler with different loading was mixed with HDPE via extrusion process. The tensile properties, surface morphology and water absorption behaviour of the bio-composites were evaluated. As filler loading increased, the Young’s modulus was increasing gradually. Meanwhile, the tensile strength and elongation at break were increasing up to 5 wt% but then decreasing as filler content increased due to the formation of filler agglomeration in HDPE matrix. The deterioration of the interfacial adhesion of these composites was confirmed by the SEM observations. The percentage of water absorption is gradually increased with increasing the filler loading. In short, the optimum filler loading at 5 wt% imparts good tensile and water absorption properties of composites.

Predicting temperature-dependent creep and recovery behaviors of agglomerated graphene-polymer nanocomposites with a thermodynamically driven temperature-degraded process

While the subject of creep and recovery in polymers is not new, its temperature dependence in graphene-polymer nanocomposites is. In such nanocomposites, the interface activity plays a critical role that is absent in a pure polymer phase. Several recent experiments have also demonstrated the remarkable impact of temperature in such nanocomposites, but at present no theory seems to exist to predict the observed data. The issue is even more complicated when filler agglomeration is present. To achieve this goal, we invoke a two-scale agglomerate-based homogenization scheme to address the issue of filler agglomeration and a thermodynamically driven temperature-degraded process to describe the interface effect. Time-temperature superposition principle with a reduced time scale is also employed for the polymer matrix. Several key microstructural features including graphene volume concentration, aspect ratio, and dispersion state of nanofillers in the graphene-rich agglomerates and the graphene-poor matrix are all considered. The theory is developed in the Laplace transformed space. It is shown that the predicted creep strain of a graphene/polystyrene nanocomposite is significantly enhanced with the increase of temperature, but its recovery strain remains relatively flat. Graphene loading notably decreases the overall creep, but filler agglomeration and temperature-degraded process both greatly enhance it. The calculated results are all in close agreement with experiments. This work could provide guidance for tailoring creep and recovery properties of graphene nanocomposites by temperature.

Prism patterned TiO2 layers/Nafion® composite membrane for elevated temperature/low relative humidity fuel cell operation

A simple and facile way of modifying commercial membranes for effective fuel cell operation under elevated temperature/low relative humidity conditions has been developed. Instead of using the conventional casting and evaporation method involving the mixed Nafion® ionomer and inorganic fillers, a TiO2/Nafion® composite membrane was fabricated by transferring uniformly constructed porous TiO2 layers from a Si wafer to the Nafion® membrane via spin-coating, followed by a thermal imprinting process. From the process, filler agglomeration was prevented during the solvent evaporation, which secured water retention effect of the hygroscopic TiO2 layers. Furthermore, the prepared TiO2/Nafion® composite membrane was subjected to an additional prism patterning process to provide more proton pathways by enlarging the interfacial surface area between the composite membrane and the catalyst layer, and offset the reduced proton conductivity due to insertion of the inorganic fillers. The modified membrane exhibited highly improved performance compared to the pristine Nafion® 211 membrane under elevated temperature/low humidity conditions.

A CFD‐DEM approach to study the breakup of fractal agglomerates in an internal mixer

AbstractIn this work we present a method to investigate the breakup of filler agglomerates in an internal mixer during a compounding operation. The method employs computational fluid dynamics (CFD) simulations along with discrete element method (DEM) simulations. CFD simulations are performed to compute the flow field inside a 2D section of a typical batch internal mixer with two tangential rotors. During the CFD simulation, we assume the filler agglomerates to behave as tracer particles, carried passively by the flow. The trajectory of the tracers, together with the experienced velocity gradients, are fed to a DEM code, built in the framework of Stokesian dynamics. The code computes the mechanical response of the agglomerates along the trajectory, from which it is finally possible to ascertain the occurrence of breakup. Simulations are performed to evaluate the robustness of the method on two different rotor speed ratio conditions and varying agglomerate strength.

Influence of Milled Glass Fiber Fillers on Mode I & Mode II Interlaminar Fracture Toughness of Epoxy Resin for Fabrication of Glass/Epoxy Composites

The present work is focused on improving mode I and mode II delamination resistance of glass/epoxy composite laminates (50 wt.% of glass fibers) with milled glass fibers, added in various amounts (2.5, 5, 7.5 and 10% of the epoxy weight). Including fillers in the interlayer enhances the delamination resistance by providing a bridging effect, therefore demanding additional energy to initiate the crack in the interlaminar domain, which results in turn in enhanced fracture toughness. The maximal increase of mode I and mode II fracture toughness and of flexural strength was obtained by the addition of 5% milled glass fiber. The mechanism observed suggests that crack propagation is stabilized even leading to its arrest/deflection, as a considerable amount of milled glass fiber filler was oriented transverse to the crack path. In contrast, at higher filler loading, tendency towards stress concentration grows due to local agglomeration and improper dispersion of excess fillers in inter/intralaminar resin channel, causing poor adhesion to the matrix, which leads to reduction in fracture toughness, strength and strain to failure. Fractured surfaces analyzed using scanning electron microscopy (SEM) revealed a number of mechanisms, such as crack deflection, individual debonding and filler/matrix interlocking, all contributing in various ways to improve fracture toughness.

Sustainable tetra pak recycled cellulose / Poly(Butylene succinate) based woody-like composites for a circular economy

Long term sustainability requires the elimination of waste products and their integration in the circular economy according to goals set by the European Union. Such is the case with Tetra pak one of the most extensively used food packaging materials in the world. More than half of the Tetra pak packaging ends up in the landfills due to the complicated disposal that requires special processing plants. The objective of this study is to investigate recycled cellulose (rCell) that has been separated from polypropylene and aluminum in the industrial processing plant as a structural filler for functional biocomposites. Cellulose-based waste products are widely used as filler materials for the composites classified as wood-plastic composites (WPC) and are one of the leading materials for sustainable building materials, furniture and packaging industry. We have selected one of the most promising bio-based and biodegradable polymers poly(butylene succinate) (PBS) that has comparable mechanical properties to polyethylene and polypropylene as a matrix for the composites. Thus, we propose a novel application route for rCell obtained during Tetra pak recycling process and evaluate its performance. High filler loading from 10 to 50 wt% has been used in the melt blending process to prepare 5 compositions that contain 55–75% bio-based carbon content. Life cycle inventory has been combined with excessive thermal and mechanical analysis to access the suitability of the composite for various application including submerging in water. The addition of 50 wt % of rCell into PBS leads to improvement of the hardness of the composites. Further, the rCell composites were found to have much higher Young’s modulus compared to pristine PBS. The dynamic mechanical analysis showed that the storage modulus and the loss modulus were significantly enhanced in measured temperature range between −70 and 70 °C. The PBS/rCell composites were biodegradable in soil under composting conditions. Scanning electron microscopy analysis of fractured composites’ surfaces testifies the filler agglomeration process in the PBS/rCell composites and generation of voids, but the FTIR measurements indicate the generation of hydrogen bonding between the polymer and cellulose components. TGA evidence the increase in thermal stability of the rCell after incorporation in the PBS/rCell composites.