Filled Polymer Composites Research Articles

Epoxy‐hemp and epoxy‐flax composites filled with glass dust for enhanced thermal insulation: An analytical and experimental study

AbstractThis article reports on an analytical and experimental investigation on the effects of fiber and filler reinforcement on the effective thermal conductivity (keff) of epoxy‐based composites. This research aims at enhancing the thermal insulation capability of fiber reinforced composites by adding an industrial waste, WGD (waste glass dust) as particulate filler. For this, an analytical model is proposed to estimate the keff values of particle filled polymer composites with and without fiber reinforcement. The results computed from the proposed correlations are then validated with some previously reported investigations. For an experimental validation, hemp and flax fiber reinforced epoxy based hybrid composites are fabricated with WGD as the fillers in varying weight fractions of 0 to 0.2. Effects of filler content on keff of fiber‐polymer systems are studied. Their keff are measured by a Unitherm Model 2022 instrument. It is found that the predicted and measured values are in good agreement. It is observed that the keff of the epoxy composites reduced from 0.359 to 0.297 W/m K with increase in the WGD weight fraction from 0 to 0.2. The keff of hybrid composites are also reduced by 27% and 15.53%, respectively, with 20 wt% addition of WGD.Highlights Hybridization of natural fiber based polymer composites. Utilization of waste glass dust as functional filler. Model development for heat conduction across hybrid composite system. Insulation capability enhancement of epoxy using fiber/filler reinforcements. Low cost thermal insulation materials using green materials and industry waste.

Valorisation and Thermal Responsiveness of Lignin from Elaesis guineensis

In recent years, advancement in material technology and a better understanding of material propertiescoupled with the quest for bio-compactible materials has driven research towards valorisation of agro-waste like empty palm fruit bunch (EPFB). Elaesis guineensis was a potential source of biomass and was classified as an environmental pollutant and disposal burden. In this study, the valorisation of Elaesis guineensis and its thermal responsiveness as lignin for use as a filler in polymer composites are examined. Lignin from EPFB was extracted via acid hydrolysis, using Di ethyl ether ((C2H5)2O) and HCl as the pretreatment solvent. The thermal stability, crystallinity, heat flow, chemical composition, and functional group of the extracted lignin were studied for treated and untreated EPFB samples using techniques like; Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), X- ray diffrraction (XRD), X-Ray Fluorescence Spectroscopy (XRF) and Differential Scanning Calorimetry (DSC). The percent yield of 23% obtained in this work is within the range specified in literature (20.1-23.8%) using sodium hydroxide(NaOH) and calcium hydroxide (Ca (OH)2) for alkali treatment. Results of the FTIR analysis of all samples in reference to the wave numbers of lignin are in good agreement with those stated in the literature. The stretching patterns alsoindicate the presence of compounds like phenols, hydroxides, and methyl groups, which are characteristics of lignin compounds. By comparing with the cellulose standard available in the database of the XRD system, two main peaks were observed from the XRD patterns at 2θ = 22.3 and 2θ = 26.7 representing peak 002 for hemicellulose and 011 for lignin, respectively corresponding to the amorphous region of hemicellulose and lignin while peaks I002 represent the crystalline region of cellulose. From the study, it was inferred that the thermal stability of extracted lignin with a Tg of 400C is higher compared to the samples treated with di ethyl ether and untreated EPFB having a Tg of 200C. The extracted lignin has a maximum decomposition temperature of 400oC, which makes it suitable as a filler in polymer composites.

Improved printability and electrical conductivity of carbon black polymer composite with a customized nozzle of material extrusion process

Due to the interactions between the fillers, the polymer and the die, the printing of filled polymer composites using the material extrusion process is challenging. Numerical computations have been carried out to investigate the fluid dynamics and heat transfer within the hot end of the material extrusion process. Firstly, a standard nozzle equipping the majority of 3D printers is considered. However, it is not possible to print an object on a commercial printer with a composite made of polylactic acid with 20wt% of carbon black due to clogging issues. This impossibility is supported by the application of the Q-criterion, which is an indicator of flow kinematics. As a result, a novel nozzle design is proposed. The printing of the same object on the same printer equipped with the new nozzle succeeds. The electrical properties of walls printed with both the standard and the new nozzles are evaluated. The conductivity of a wall printed with the new nozzle is 42% higher than that of a wall printed with the standard nozzle. Furthermore, complementary analysis using scanning electron microscopy shows that the porosity of the walls printed with the new nozzle is reduced which is a promising improvement.

Mechanical Properties of Rice Husk-Recycled Polypropylene Composite

The growing amount of plastic and food waste has become a serious problem around the worldwide. As a byproduct of milling rice, rice husk is an agricultural waste that is produced in bulk quantities. Rice husk has been used as filler in polymer composites in a variety of ways. However, there have only been a few reports of using rice husk as reinforcement in composites made of recycled polypropylene. The limited interfacial reaction between natural fibre and polymer is the fundamental issue in natural fibre-based composites. This prompted the development of sustainable composite manufactured from recycled polypropylene(rPP) and rice husk (RH). Thus, we investigated the intermolecular adhesion between rPP–RH composite with maleic anhydride grafted polypropylene (MAPP) as a coupling agent. Varied compositions of RH in the range of 10–40 wt% with 4 wt% of MAPP were fabricated. The rPP, RH and MAPP were blended and executed in injection moulding. The mechanical properties will be analysed through differential scanning calorimetry, rheology, tensile, flexural, impact and hardness tests. The result shows RH agglomeration and limited dispersion in the composite cause a reduction of up to 40% for tensile strength compared to neat rPP. Despite this, it demonstrates improvements in tensile modulus, flexural modulus, impact, and hardness. It is evidence of a good intermolecular between rPP matrix and RH. In conclusion, the ideal RH loading for composites occurs at a fillercontent of 40% and has acceptable mechanical properties for various composite applications.

Comparative Study of Mechanical and Physical Properties of Rice Husk Filled Polyethylene Waste Composites

Polyethylene (PE), a type of plastic, is utilized extensively in many different applications and has become a significant part of our daily life. However, numerous plastic product manufactures have a significant environmental impact. As a result, several approaches have been investigated in order to reduce waste disposal issues. Rice husk (RH), on the other hand, is a form of agricultural waste that contains lignocellulosic fiber that can be used as a filler in polymer composites. As a result, combining both PE waste and RH fiber could be a viable option for saving our world. The objective of this study was to ascertain the impact of different RH fiber loadings, including 5, 10, 15, 20, and 25 %, on the mechanical and physical characteristics of composites manufactured from used HDPE and LDPE materials. Due to inadequate bonding between the hydrophilic fiber and the hydrophobic polymer matrix, it was discovered that increasing the filler loading lowered the tensile strength, elongation at break, and impact strength of the composites. In comparison to RH/HDPE, the tensile strength of RH/LDPE composites showed a greater decline at 45 % at the highest loading of 25 % RH fiber. Both composites showed a 98–99 % decrease in elongation at break as a result of constrained chain elongation and mobility. Additionally, the impact strength value of RH/HDPE waste composites decreased by 43 % compared to 31 % for RH/LDPE waste composites. In contrast, the inclusion of fillers improved the modulus and density of the composites substantially. While the trends for RH/HDPE and RH/LDPE composites are similar, RH/HDPE waste composites demonstrated superior mechanical characteristics than RH/LDPE waste composites.

Sub-micron spherical carbon particles with hollow cores from lignin-based hybrid precursors: preparation, characterization, and electrostatic dissipative application

Novel sub-micron, spherical, bio-based carbon materials with hollow-core characteristics were synthesized from spherical lignin particle (SLP) hybrid precursors via thermo-stabilization and carbonization. Primarily, the mixture of bagasse lignin (BG-L) and palm kernel shell lignin (PKS-L) with an addition of dicumyl peroxide (DCP) at different BG-L:PKS-L:DCP ratios was utilized to prepare SLPs through anti solvent precipitation. Interestingly, as-prepared SLPs having a 250–331 nm diameter contained hollow cores of 41–223 nm inside the spherical particles. A mechanism of hollow-core formation was also proposed. Effects of BG-L:PKS-L:DCP ratio, heating rate (HR), oxygen flow rate (O2 FR), and stabilization time (SBT) on spherical shape retention of SLPs after thermo-stabilization were systematically investigated, and a cross-link pathway was suggested. The spherical aspect of SLPs having hollow cores was successfully maintained at optimal conditions of 250 °C for 1 h with a HR of 0.3 °C/min under O2 FR of 3 L/min using a BG-L:PKS-L:DCP ratio of 1:1:1 by wt. After carbonization at 900–1200 °C, spherical carbon particles (SCPs) with hollow cores were obtained, possessing a high carbon (C) element of ≅ 93–96%, a high specific surface area of ≅ 308–593 m2/g, and a high order of graphitic structure (ID/IG ratio ≅ 1). The average particle size of SCPs and hollow-core dimensions were ≅ 171–224 and 80–107 nm, respectively. The polylactic acid (PLA)/SCP composite films were prepared using SCPs at different carbonization temperatures and loadings via a solution casting technique. The composite film containing 20 wt% of SCPs carbonized at 900 °C (SCPs-900) provided a surface resistance of ≅ 3 × 105 Ω and a tribo-charge voltage of 0 V, appropriate for electrostatic dissipative (ED) applications. The Young's modulus and elongation at break of the PLA/SCP-900 (20 wt%) composite film were ≅ 3.4 MPa and 2.0%, respectively. These findings demonstrate a feasible and effective approach to utilize biomass-based lignin for producing carbon particles with unique features as renewable and sustainable conductive fillers in polymer composites.

Investigations on thermal contact resistance between filled polymer composites and solids using micro thermography

This article reports the use of a new measurement technique based on micro thermography for determining the thermal contact resistances (TCRs) between filled polymers and solids. The thermal conductivity of polymers can be significantly increased by using thermally conductive fillers. For numerous applications, not only is a high intrinsic thermal conductivity required but also a good thermal transfer between the filled polymer and an adjacent solid surface. The physical principles of thermal transport when considering this type of contact have not yet been investigated in detail, and only a few experimental results are available. The most common measurement techniques determine a macroscopic resistance and project it onto the contacting surface. However, the heterogeneous microstructure of a filled polymer causes the TCR to be a volumetric phenomenon in the overall boundary region. The utilized IR camera system takes thermal images with a spatial resolution of less than per pixel. The new method resolves the TCRs spatially and gives new insights into the microscale effects on the particle level. In addition to the common zero-gap extrapolation for the extraction of TCRs, we propose another evaluation method that considers all microscale effects of the boundary layers and evaluates TCR as a volumetric phenomenon. For the first systematic study, samples consisting of two aluminum substrates and a filled epoxy polymer were prepared and investigated. We studied the effects of filler size, filler material, filler volume fraction, and surface structure, focusing on monomodally filled polymers with filler amounts between and . The obtained results and the uncertainties of the new method are discussed within this paper.

Injection molding of highly filled microcrystalline cellulose/polycaprolactone composites with the aid of reversible Diels-Alder reaction

To tackle the challenge of producing highly filled polymer composites using the traditional injection molding technique, which is characterized by the fairly high melt viscosity that makes mold filling difficult, the authors propose a solution based on dynamic covalent chemistry. As demonstrated by the proof-of-concept experiments, the 4-arm star-shaped polycaprolactone (PCL) oligomers and microcrystalline cellulose (MCC) are crosslinked by the reversible Diels-Alder (DA) bonds. The flowability of the compounds greatly decreases due to the dissociation of the intercomponent DA bonds at the retro-reaction temperature, and the networked architecture is reconstructed during cooling as a result of the forward DA reaction. Consequently, the high-loading MCC fillers are well distributed in the matrix and covalently bonded to the nearby PCL, forming a striking contrast to the control in which linear PCL acts as the matrix. The DA bonds crosslinked biodegradable PCL composites exhibit decent mechanical strength (20.7 MPa) even at the MCC fraction of 65 wt%, which is superior to those (5–12.2 MPa) of the highly filled PCL composites (with filler contents of 50–63.8 wt%) reported so far. The proposed approach has sufficient expansibility for the fabrication of the highly filled polymer composites constructed by other types of matrix and fillers.

Non-destructive estimation of conductive network constructed by 1D fillers in polymer composites via small angel X-ray scattering

Efficient and non-destructive estimation of conductive network in conductive polymer composites is now becoming an urgent issue than ever owing to the rapid rise of modern electronic industry. Nevertheless, traditional observation and estimation method inevitably cause damage and distortion to sample, demanding urgent development of a non-destructive fidelity detection methodology. In this study, the degree of network formation of carbon nano-fibers in polymer matrix was calculated based on small-angle X-ray diffraction (SAXS). The degree of fiber network construction based on the power law coefficient (A) has been proved to be valid and effective in comparison with other testing methods. Moreover, a mathematical model was established to predict the electrical conductivity of the conductive polymer composite. This study not only solves the problem of non-destructive testing of fiber network construction, but also provides theoretical guidance for the design of conductive polymer composites.

Isolation and characterization of agro-waste biomass sapodilla seeds as reinforcement in potential polymer composite applications

Fillers or particulate fillers find a growing utilization as reinforcement material in polymer composites due to their ability to enhance the properties of the ensuing composites. The discarded seed in sapodilla fruit is available in abundant and the shell of the seed can be used as a reinforcing filler. The primary goal of this study is to extract and characterize the sapodilla seed shell powder (SSS) physically and chemically in order to assess its potential for reinforcement as a particulate filler in polymer composites. The sapodilla seed shell filler was characterized experimentally by Physio-chemical analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Energy dispersive X-ray analysis (EDAX). The morphology and the filler size were determined by Scanning electron microscopy (SEM) and Particle size analysis. The thermal degradation behaviour was evaluated by Thermogravimetric analysis (TGA).

Waste material fly ash as an alternative filler for elastomers

AbstractFly ash (FA), a by‐product of the power generation industry, can potentially be used as a filler in polymer products. Particularly, FA has been investigated as an alternative filler to partially or fully replace commercial fillers in polymer composites. This mini‐review discusses the fundamental properties of FA, environmental pollution from commercial fillers, and the performance of FA in polymers. The properties of FA‐loaded polymer composites are discussed, including the morphological, rheological, mechanical, and thermal properties. This review highlights the potential methods and challenges for substituting, or replacing, commercial fillers in various polymers such as natural rubber (NR), epoxidized NR, epoxy, styrene‐butadiene rubber (SBR), NR/SBR blends, polyethylene, polypropylene, and polyester.

Low-voltage triggered electroactive and heat-responsive thermoplastic elastomer/carbon nanotube polymer blend composites

This study presents the synthesis and characterization of novel polymer composites that are triggered by heat and electricity. The composites were made of a blend of a styrenic block copolymer and a thermoplastic polyolefin elastomer, with multi-walled carbon nanotubes (MWCNTs) added as fillers. The composites were prepared through melt blending and the amount of MWCNTs was varied from 1 to 10 phr. The results of morphological characterization showed that the distribution of fillers within the matrix improved as the amount of MWCNTs increased. The crystallization temperature was also found to decrease due to the nucleation effect of the fillers. The reinforcing effect of MWCNTs resulted in increased values of elastic modulus, creep resistance, and storage modulus, while decreasing the values of elongation at break, creep recovery, and damping parameter (tanδ). The electrical resistance of the composites decreased with increasing amounts of MWCNTs, with the lowest resistance recorded in the composite which contains 10 phr MWCNT (10CNT) composite at 12 ohm.cm. The 10CNT composite was also able to be heated up to 75 °C by Joule heating at a voltage of 5.5 V. The shape fixing performance of the blend improved in the presence of fillers, however, despite an increase in the recovery stress value, the heat-responsive shape recovery feature worsened. The composite having 5 phr MWCNT (5CNT) showed electro-active shape recovery under 25 V in 210 s, while the 10CNT composite completed this process in 300 s under 5.5 V. The results of this study demonstrate the potential of using MWCNTs as fillers in polymer composites for various applications that require both electrical conductivity and heat responsiveness.

Thermally Latent Bases in Dynamic Covalent Polymer Networks and their Emerging Applications.

A novel strategy allowing temporal control of dynamic bond exchange in covalently crosslinked polymer networks via latent transesterification catalysts is introduced. Obtained by a straightforward air- and water-tolerant synthesis, the latent catalyst is designed for an irreversible temperature-mediated release of a strong organic base. Its long-term inactivity at temperatures below 50 °C provides the unique opportunity to equip dynamic covalent networks with creep resistance and high bond-exchange rates, once activated. The presented thermally latent base catalyst is conveniently introducible in readily available building blocks and, as proof of concept, applied in a radically polymerized thiol-ene network. Light-mediated curing is used for 3D-printing functional objects, on which the possibility of spatially controlled reshaping and welding based on dynamic transesterification is illustrated. Since the catalyst is thermally activated, limitations regarding sample geometry and optical transparency do not apply, which facilitates a transfer to well-established industrial technologies. Consequently, fiber-reinforced and highly filled magneto-active thiol-ene polymer composites are fabricated by a thermal curing approach. The on-demand activation of dynamic transesterification is demonstrated by (magneto-assisted) reshaping experiments, highlighting a wide range of potential future applications offered by the presented concept.

DEFORMATION PROPERTIES OF HIGHLY FILLED METAL-POLYMER COMPOSITIONS

The deformation behavior of model highly filled metal polymer aluminum powder compositions in polyethylene glycol under simultaneous action of compression and shear studied. The compression module increases with the increase of the compression, wherein the shear module significantly reduces. The discovered effect is related to the redistribution of the elastic layer between the rigid particles of the filler in the normal direction and in the shear area. The model of behavior of highly filled polymer compositions in these conditions proposed.

Graphene Modification by Curcuminoids as an Effective Method to Improve the Dispersion and Stability of PVC/Graphene Nanocomposites.

A large amount of graphene-related research is its use as a filler for polymer composites, including thin nanocomposite films. However, its use is limited by the need for large-scale methods to obtain high-quality filler, as well as its poor dispersion in the polymer matrix. This work presents polymer thin-film composites based on poly(vinyl chloride) (PVC) and graphene, whose surfaces were modified by curcuminoids. TGA, UV-vis, Raman spectroscopy, XPS, TEM, and SEM methods have confirmed the effectiveness of the graphene modification due to π-π interactions. The dispersion of graphene in the PVC solution was investigated by the turbidimetric method. SEM, AFM, and Raman spectroscopy methods evaluated the thin-film composite's structure. The research showed significant improvements in terms of graphene's dispersion (in solutions and PVC composites) following the application of curcuminoids. The best results were obtained for materials modified with compounds obtained from the extraction of the rhizome of Curcuma longa L. Modification of the graphene's surface with these compounds also increased the thermal and chemical stability of PVC/graphene nanocomposites.

Pressure-independent through-plane electrical conductivity measurements of highly filled conductive polymer composites

Highly filled conductive polymer composites (CPCs) are widely used in applications such as bipolar plate materials for polymer electrolyte membrane fuel cells and redox flow batteries, electromagnetic interference shielding and sensors due to their useful electrical properties. A common method for determining through-plane electrical conductivities $\left(\sigma_{\rm tp} \right)$ of such highly filled CPCs applies a conductive carbon paper between electrodes and sample with application of external pressure to improve electrical contact. We show the pressure-dependence of the measured $\sigma_{\rm tp}$ can be eliminated by using a liquid metal such as the gallium-indium eutectic alloy (EGaIn) as contact material. Results indicate that EGaIn reduces contact resistances and cause three to five times larger $\sigma_{\rm tp}$ compared to measurements with carbon paper contacts and pressures up to 20 bar.

Influence of plasticizer on the dielectric properties of polypropylene/carbon black composites

The addition of plasticizers can improve the dispersion of conductive fillers in polymer composites. In this work, the effect of polyethylene glycol dimethyl ether (PEGDME) plasticizer on the dielectric properties of poly(propylene)/carbon black (PP/CB) composites was investigated. PP/CB composites with varying content of CB from 0 to 15 wt% were melt-mixed. PEGDME plasticizer (0 to 5 wt%) was introduced into the PP/CB composites to reduce CB particle agglomeration and facilitate CB dispersion in the polymer matrix. The electrical conductivity and dielectric constant of PP/CB composites with and without plasticizer were studied. CB loading improved the electrical conductivity and dielectric constant of the composites; however, the addition of PEGDME reduced their values. Scanning electron microscopy images revealed that the PEGDME dispersed the CB particles and hindered the continuous CB conductive network formation. Additionally, the effect of temperature on dc conductance of PP/CB composites was also investigated. The dc conductance increases when the temperature increases from 303 °K to 343 °K and then decreases with further temperature increments.

Enhanced flame retardancy, smoke suppression, and acid resistance of polypropylene/magnesium hydroxide composite by expandable graphite and microencapsulated red phosphorus

AbstractLow flame retardant efficiency and poor acid resistance of filled polymer composites are two main drawbacks of magnesium hydroxide (MH) as a flame retardant (FR). To solve these problems, expandable graphite (EG) and microencapsulated red phosphorus (MRP) were introduced into polypropylene/magnesium hydroxide (PP/MH) composite by melt compounding. The obtained PP/MH/EG/MRP quadruple composite was studied regarding its fire behavior as well as acid resistance. Obvious flame retardant synergism among MH, EG, and MRP is found in PP, which diminishes the loading of FR from 63.0 to 37.5 wt% to obtain V‐0 rating in UL‐94 test and low smoke release. Compact intumescent char with high thermo‐oxidative stability was generated on composite surface, which plays a vital role in flame retardancy. The removal of MH by acid erosion on PP/MH/EG/MRP composite surface does not affect production of intumescent char and fire behavior of this composite. The composite displays good fire retardancy, smoke inhibition, and acid resistivity concurrently. This article renders an easy and cheap route to overcome the main faults of MH.

A comparative neutron and gamma-ray radiation shielding investigation of molybdenum and boron filled polymer composites

This work presents a detailed radiation shielding study for polymer composites filled with Boron and Molybdenum additives. The chosen novel polymer composites were produced at different percentages of the additive materials to provide a proper evaluation of their neutron and gamma-ray attenuation abilities. The effect of additive particle size on the shielding characteristics was further investigated. On the gamma-ray side, simulation, theoretical and experimental evaluations were performed in a wide range of photon energies varying from 59.5 keV to 1332.5 keV with help of MC simulations (GEANT4 and FLUKA), WinXCOM code, a High Purity Germanium Detector, respectively. A remarkable consistency was reported between them. On the neutron shielding side, the prepared samples produced with nano and micron particle size additives were additionally examined by providing fast neutron removal cross-section (ΣR) and the simulated neutron transmissions through the prepared samples. The samples filled with nano sized particles show better shielding capability than the one filled with micron sized particles. In other words, a new polymer shielding material that does not contain toxic content is introduced: the sample codded N–B0Mo50 exhibits superior radiation attenuation.

Spider silk inspired bead-like aramid nanofibers via hydrogen-bond donor strategy for synergistic reinforcement of high-performance rubber composite

Aramid nanofibers (ANFs) are of significant scientific interest in various scientific and industrial fields. However, a big problem encountered in the application of ANFs is the agglomeration and the very inert surface. Herein, inspired by the shiny water droplets on a spider's web, we report a novel, green and effective method to fabricate bead-like ANFs with homogeneous knots via a hydrogen-bond donor strategy. It is revealed that γ-aminopropyl triethoxysilane is not only effective in constructing multiple hydrogen bonding interactions with the amide groups of ANFs, but also can induce the self-assembly of the interfacial polycondensation of ethyl silicate to fabricate a spindle-knots structure. The knots are rich in silanol and amino groups being able to establish covalent bonds between ANFs and polymer matrix and improve the filler dispersion in a silica hybrid system. Therefore, the bead-like ANFs synergistically reinforce the silica filled polymer composites by significantly enhancing vulcanization rate, tensile strength, elongation at break, abrasion resistance, as well as the dynamic mechanical properties. The process does not rely on any toxic and corrosive agents and the bioinspired strategy offers new insights into the design of functional aramid nanofibers and the potential application in rubber industry.