Traditional Polymer Composites Research Articles

Fatigue Behaviour of High-Performance Green Epoxy Biocomposite Laminates Reinforced by Optimized Long Sisal Fibers.

In recent decades, in order to replace traditional synthetic polymer composites, engineering research has focused on the development of new alternatives such as green biocomposites constituted by an eco-sustainable matrix reinforced by natural fibers. Such innovative biocomposites are divided into two different typologies: random short fiber biocomposites characterized by low mechanical strength, used for non-structural applications such as covering panels, etc., and high-performance biocomposites reinforced by long fibers that can be used for semi-structural and structural applications by replacing traditional materials such as metal (carbon steel and aluminum) or synthetic composites such as fiberglass. The present research work focuses on the high-performance biocomposites reinforced by optimized sisal fibers. In detail, in order to contribute to the extension of their application under fatigue loading, a systematic experimental fatigue test campaign has been accomplished by considering four different lay-up configurations (unidirectional, cross-ply, angle-ply and quasi-isotropic) with volume fraction Vf = 70%. The results analysis found that such laminates exhibit good fatigue performance, with fatigue ratios close to 0.5 for unidirectional and angle-ply (±7.5°) laminates. However, by passing from isotropic to unidirectional lay-up, the fatigue strength increases significantly by about four times; higher increases are revealed in terms of fatigue life. In terms of damage, it has been observed that, thanks to the high quality of the proposed laminates, in any case, the fatigue failure involves the fiber failure, although secondary debonding and delamination can occur, especially in orthotropic and cross-ply lay-up. The comparison with classical synthetic composites and other similar biocomposite has shown that in terms of fatigue ratio, the examined biocomposites exhibit performance comparable with the biocomposites reinforced by the more expensive flax and with common fiberglass. Finally, appropriate models, that can be advantageously used at the design stage, have also been proposed to predict the fatigue behavior of the laminates analyzed.

Tensile, flexural and fatigue properties of different thermoplastic nanocomposites: experimental investigation and ANN prediction of the fatigue life

ABSTRACT Polymer-based nanocomposites have received immense attention in industrial applications as their mechanical properties are superior to traditional polymer composites. In this study, three different thermoplastic polymers, namely (a) polypropylene (PP), (b) acrylonitrile butadiene styrene (ABS), and (c) high-density polyethylene (HDPE) were used for the purpose of engineering different nanoclay-based nanocomposites. The blending of the polymer was performed by varying the nanoclay weight percentage (0.5, 1, 3, and 5 wt.%) using a twin-screw extruder. The different nanocomposites were fabricated through injection moulding process. The composites were fabricated by considering the 90 bars of injection pressure, 60 mm/s of injection speed, and 25 sec of cooling time. The effect of nanoclay inclusion on the mechanical properties of the nanocomposites was evaluated and compared with the neat polymer. The effect of nanoclay inclusion was studied through morphological analysis of the fractured tested specimens. The tensile strength and modulus of ABS-nanoclay (5%) exhibited an enhancement of 30.95% and 35%, respectively as compared to the pure ABS. Meanwhile, the fatigue life revealed an improvement of 66.01%. The tensile strength and modulus of the ABS/nanoclay (5%) were achieved as 38.6 MPa and 1.44 GPa.

Exploring the Potential of Sustainable Biopolymers as a Shield against Electromagnetic Radiations.

The increasing demand for biodegradable and environmentally friendly materials is shifting the focus from traditional polymer composites to biocomposites in various applications, especially in electromagnetic shielding. Effective utilization of biopolymers demands improved properties and can be achieved to a certain extent by functionalization. Biopolymers such as cellulose, polylactic acid, and starch are some of the potential candidates for mitigating electromagnetic pollution in next-generation electronic devices because of their high aspect ratio, flexibility, light weight, high mechanical strength, thermal stability, and tunable microwave absorption to the electromagnetic interference (EMI) shielding composites. This Review provides an overview of the current advancements in EMI shielding materials and outlines recent research on EMI shielding composites that utilize various biodegradable polymer structures.

Improving thermal insulation and fire resistance of ceramifiable EVA/ceramic hybrid composites via low temperature sintering and foaming strategy

Energy efficient buildings, propulsion components and thermal protection systems require materials with high thermal protective properties. Traditional polymer composites or ceramic materials have limited comprehensive applications because of their poor thermal protective properties or poor processability. Herein, a novel fire resistant and thermally insulating polymer/ceramic hybrid ceramifiable composite was developed based on low temperature sintering principle and foaming on fire strategy. Specifically, the influences of raw materials of low temperature ceramics, such as glass frit, phosphate, etc, on the properties of ceramifiable ethylene-vinyl acetate (EVA) composites were investigated. Its fire resistance and thermal insulation properties were evaluated by simulating different sintering environments. The results show that the ceramifiable composite exhibits the highest improvement in fire resistance because a crystalline phase was formed at high temperatures. Gas evolution from the thermal decomposition of ammonium polyphosphate (APP) and EVA contributes to the formation of the porous structure in ceramic residues. The optimal system can resist above 1000 °C flame for 30 min without disintegration, and the temperature of the unfired side was maintained around 200 °C. The reliability of the strategy was verified by the effective medium theory model.

A review on biodegradable polymer: Shortcomings, developments, and future direction

With the continuous progress and development of the world's economy and science, people's awareness of environmental protection has gradually increased. Polymer materials have brought great convenience to modern people's daily life and work, and their application fields are becoming wider. However, on the one hand, the comprehensive application of polymer materials has greatly improved our level of people's daily life, and on the other hand, it also brings a certain pollution to the environment. Because some traditional polymer composites can not degrade immediately, there may be a big problem of pollution and emission. Therefore, how to develop a biodegradable polymer material has become a research hotspot. This paper reviewed the current market share of biodegradable polymers, the classification of current biodegradable polymers, and the applications of biodegradable polymers. By providing that information, this paper aims to help understand the big picture of biodegradable polymers and contribute to their future developments.

Synthesis of starch-derived biopolymer reinforced Enset fiber green composite packaging films: Processes and properties optimization

The use and disposal of traditional fiber-reinforced polymer composites is an important environmental challenge as one of the factors contributing to worsening climate change. The primary objective of this research is to synthesize thermoplastic starch (TPS) from edible banana skins which can potentially be used as a matrix to produce bio-composite films. For the synthesis of TPS, the preparation of banana peels was performed followed by plasticization to obtain the banana peels TPS. For bio-composite film fabrication, the TPS was mixed with short false banana fibers (FBF) (10–30% by weight of the film) with an electronic blender to form a uniform dispersion of the fibers in the TPS. The FBF/TPS blend was applied uniformly on the surface of the rectangular metal mold. The autoclave method has been adopted for curing and molding the bio-composite film. Then, it was hot pressed varying the temperature and pressure from 131–141 OC to 3–6 MPa, respectively, to obtain the final cured film. The specimen was then solidified or hardened at ambient temperature. Finally, optimization of process parameters, fiber content, and their interaction effects on the tear strength, tensile strength, and bending modulus of the bio composite films were conducted using response surface methodology. The results indicate that both the effects of one factor and the interaction of factors have a significant effect on the mechanical properties of composite films. The optimum processing parameters for TPS production are a temperature of 50 OC and a drying time of 24 h. The optimal result indicates that, at 30% fiber loading, the optimum processing temperature and pressure are 135.14°C and 4.33 MPa, respectively, resulting in a composite film with good mechanical properties.

Mechanical and Three Body Abrasive Wear Behaviour of Nano-Filler Filled, Chopped Glass Fiber Filled Hybrid Composites

Polymer matrix composites are developed for tribological applications due to the possibility of optimizing the properties with the addition of special filler materials as reinforcement. Filler filled polymer matrix composite systems are used in many automotive parts and components like brake pads or clutches which require high coefficient of friction coupled with low wear. However, in most cases it is the primary concern to develop polymer composites that posses low friction and low wear properties under dry sliding conditions against smooth metallic counterparts e.g., gears or bearings, chute liners and coal handling equipments in power plants, gear pumps handling industrial fluids, agricultural machine components. Polymer composites operate in applications where fluid and grease lubricants fail, and have superior tribological performance to traditional polymer composites. Particulate fillers or fibres or solid lubricants have been a part of notable reductions in the wear rate of the polymer matrix at very low loading, and there exists a wide scope on the development of polymer composites on the tribological behaviour. The incorporation of fillers in polymer could provide a synergism in terms of improving mechanical properties and wear performance, which has not been adequately explored so far. The research on nano fillers such as nano clay, Glass fiber and Titanium di-oxide (TiO2) in epoxy system is scarcely reported and further they focus on a few specific issues only. The present study was focused on investigating Mechanical - Tensile, Hardness, and three body abrasive wear characteristics of thermosetting based Epoxy composites and the effect of incorporation of nano clay, TiO2 nanoparticles and chopped glass fiber on microstructure, hardness, friction and abrasive wear are determined and analyzed. The main aim was to investigate the effect of applied load, sliding distance /abrading distance, sliding speed and percentage of filler. The surface morphology of the worn out surfaces were examined using SEM, to get a better understanding of the wear mechanisms.

Segregated structures induced linear mechanoelectrical responses to low strains for elastomer/CNTs composites

Carbon nanotubes (CNTs)-based polymer composites are great potential as flexible piezoresistive sensors to apply to wearable devices, electronic skins, etc. We herein prepared a type of polymer composites with a segregated structure derived from double-percolating structured polymer composites of two elastomers and CNTs. Expressly, CNTs were composited with two elastomers by melt blending, forming double-percolated structures. The composites with segregated structures were attained after removing the elastomeric phase where CNTs selectively located by solvent extraction, followed by hot compression to eliminate voids. This kind of segregated structure could reduce the percolation threshold of CNTs while maintaining superior stretchability of the elastomeric matrix. Compared to polymer composites with randomly distributed CNTs, the composites with the segregated structure posed nonrandom distribution of CNTs, forming a denser conductive network with the same content. Therefore, the composites exhibited different mechanoelectrical responses from the traditional CNTs-based polymer composites. The composites with the segregated structure showed a higher strain where the relative change of resistance increased significantly. Notably, the composites exhibited a linear (instead of the commonly nonlinear) piezoresistive response with improved sensitivity under low mechanical strains. The practical applications of the as-prepared composites as piezoresistive sensors showed reliable performance in detecting gentle touching, dropping impact, and human body motions.

A novel three-dimensional boron phosphide network for thermal management of epoxy composites

Recently, construction of effective three-dimensional (3D) heat transfer networks inside polymer has emerged as a promising design strategy to improve the isotropic thermal conductivity for electronic packaging materials. Hexagonal boron nitride (BN) sheets are popular carriers for constructing 3D networks. But removing overheat capability of BN was greatly sacrificed due to size limitation when constructing 3D network. Herein, a novel 3D heat-transferring network, interconnected boron phosphide (BP) grains in-situ growing on Ni foam, was designed to alternate 3D BN network. An isotropic [email protected] network with high-quality and integrity was successfully fabricated by a simple high temperature treatment. The synthesized [email protected] was incorporated into epoxy resin (ER) by infiltration to fabricate composites. ER/[email protected] composite, with strong interfacial adhesion between epoxy and [email protected], achieved a high thermal conductivity of 2.01 W/(mK), which corresponded to 908.53% and 402.00% enhancement compared to pure epoxy and ER/Ni composite. The coefficient of thermal expansion (CTE) of the composite reached as low as 26.95 × 10−6/°C, much smaller than epoxy of 60.69 × 10−6/°C and ER/Ni composite of 59.42 × 10−6/°C. The designed ER/[email protected] composite has distinguished heat removal and CTE with semiconductors from traditional polymer composites containing 3D BN network. This strategy is promising to promote the development of electrical packaging materials with high isotropic thermal conductivity.

Enhanced thermal conductivity of epoxy composites via bridged Al2O3 network with in situ formed silver nanoparticles

AbstractIt is of great significance to achieve excellent thermal conduction for polymer composites in electrical insulation application. However, traditional polymer composites exhibit limited thermal conduction due to the absence of efficient heat transfer pathways. Herein, Al2O3 microspheres absorbed with silver acetate (AgAc) and 2‐ethyl‐4‐methylimidazole (2E4MI) complex were prepared as fillers for constructing heat transfer paths in epoxy composites. At a suitable temperature, 2E4MI was released from Ag(2E4MI)2Ac complex and initiated the curing reaction of epoxy. Simultaneously, nano silver ions were reduced, sintered in situ and then bridged separate Al2O3 microspheres to 3D filler network, which acted as thermal transport pathways in matrix. The thermal conductivity increased from 1.38 W/mK for Al2O3/epoxy composites to 2.62 W/mK for Al2O3@Ag(2E4MI)2Ac/epoxy composites at 60 vol% Al2O3 loading. Thanks to the 3D filler network, the tensile strength of Al2O3@Ag(2E4MI)2Ac/epoxy composites was obviously improved. Both the electrical resistivity and dielectric strength of the composites were basically preserved. Al2O3@Ag(2E4MI)2Ac/epoxy composites exhibit promising application in thermal management materials for advanced electric machinery and electronic devices.

Efficient thermal transport network construction within epoxy composites with hybrid ceramic fillers

Polymer composites with superior thermal conduction and low dielectric constant are urgently required for thermal management applications of modern electrical devices. However, the performances of traditional polymer composites usually suffer from either low thermal transfer efficiency or high dielectric loss. Herein, we prepared a series of epoxy composites using a binary system of beta-silicon nitride (β-Si3N4) rod-like crystals and aluminum oxide (Al2O3) spheres fillers via a gravity mixing process and investigated the effect of the mass ratio and solid content of hybrid fillers on their thermal conductivity. Al2O3 spheres played a role of “hot spots” and small size β-Si3N4 rod-like crystals were homogenously dispersed between Al2O3 spheres acting as “bridges”, which constructed an efficient thermal transport network in the epoxy matrix for propagating heat flow. The thermal conductivity was efficiently increased up to 2.2 Wm−1K−1 for β-Si3N4/Al2O3 loading of 52.5 vol% at an optimum mass ratio of 3/4 in the composite, which demonstrated 899% thermal conductivity enhancement with the preservation of a low dielectric constant and dielectric loss. Moreover, a 67.3% reduction of the thermal expansion (CTE) coefficient in cryogenic temperature was achieved at the same time. The highly desirable multifunctional features of the epoxy composites were potential for the heat-dissipation demand in many fields.

Tensile and impact strength of alpaca fiber epoxy matrix hybrid composites prepared by injection moulding process

Today, there are many more applications for fibre reinforced polymer composites than there were for metals and alloys a few decades ago. Numerous research projects have focused on improving the mechanical and thermal properties of composite materials, especially when reinforced with environmentally friendly, recyclable, and biodegradable materials. This study combined alpaca fibre (AF), palm seed filler (PSF), and polypropylene (PP) to create composites that have improved properties over traditional polymer composites. Fiber loadings of 35, 30, 25, 20, 15, and 10 percent and filler loadings of 15, 10, and 5 percent were used to prepare the alpaca fiber/palm seed filler polypropylene (PP) composites using a conventional injection moulding technique (0, 5, 10, 15, 20 and 25 wt. percent ). Hydrophilicity and mechanical properties of the hybrid bio-composites were evaluated experimentally. The results showed that 15 lbs. For example, epoxy matrix composites have tensile and flexural strengths of 62 MPa, as well as hardness and impact strengths of 54 and 17.9 kJ/m2, respectively.

Mechanical and water absorption behaviour of palm seed particles based hybrid bio-composites

In the recent decades, many scholars and researchers are interested in natural fibres today because they are inexpensive, widely available, and easy to process compared to conventional fibres. Due to environmental awareness and growing concern over the greenhouse effect, the construction, automotive, and packaging industries are also looking for eco-friendly materials that can replace conventional synthetic polymeric fibres. Alpaca fiber (AF), palm seed filler (PSF), and polypropylene (PP) were combined in this investigation to create composites that outperformed traditional polymer composites in terms of properties. The alpaca fiber/palm seed filler polypropylene (PP) composites were prepared using a conventional injection molding technique with fiber loadings of 35, 30, 25, 20, 15, and 10% and filler loadings of 15, 10, and 5%. (0, 5, 10, 15, 20 and 25 wt. percent). Polypropylene (PP)/Alpaca fiber/palm seed composites with a filler content of 20 wt. % were found to be more promising than PP/Alpaca fibre composites.

Achieving ultrahigh thermal conductivity in Ag/MXene/epoxy nanocomposites via filler-filler interface engineering

Polymer composites with super-high thermal conductivity have attracted many interests in aerospace and electrical fields. However, traditional polymer composites usually suffer from low thermal conductivity because of the high interfacial thermal resistance. Herein, by adopting a multi-dimensional filler composed of micro-silver (AgMP) and nano-silver (AgNP) particles, we prepare an epoxy/Ag composite with the maximum thermal conductivity of 58.3 W/m·K. Based on this, by introducing trace amount (0.12 vol%) of MXene, the thermal conductivity of the epoxy/Ag/MXene composite further increases to 72.7 W/m·K, which is 24.7% higher than that of Ag/Epoxy composites. Both of the super-high thermal conductivity enhancement in epoxy/Ag and epoxy/Ag/MXene composites should be attributed to the unique bridging effect of AgNP particles or MXene flakes. AgNP bridges AgMP via sintering while the MXene flakes bridge AgNP and/or AgMP by the strong interaction between MXene flakes and the Ag particles. The significant effect of the bridging between filler particles on the thermal conductivity of composites is elucidated and verified by FEM simulations. These findings provide new insights into the thermal transport in polymer-based composites and also suggest an approach to prepare polymer composites with super-high thermal conductivity.

Combining Alumina Particles with Three-Dimensional Alumina Foam for High Thermally Conductive Epoxy Composites

Ceramic/polymer composite with a high thermal conductivity is a candidate of insulating materials for electronic packaging. However, traditional polymer composites filled with alumina (Al2O3) powders present limited enhancement in thermal conductivity even at a high loading due to thermal resistance on the filler/filler and filler/matrix interfaces. Herein, a contiguous 3D network of alumina foam (AF) filled with different diameters of Al2O3 microparticles via vacuum-assisted filtration proves to be a promising filler structure for thermal conductivity composites. The fabricated epoxy/AF/Al2O3 composite exhibits a high thermal conductivity of 4.1 W/mK and a significant thermal conductivity enhancement (TCE) of 2097%. Further study reveals a prominent synergistic effect between the 3D interconnected AF and Al2O3 microparticles, which plays a critical role in the formation of thermal percolation networks to promote thermal conductivity dramatically. Meanwhile, compared to previous reports, the composite resulted in a lower coefficient of thermal expansion (CTE) than those of most epoxy-based composites, showing great potential for heat conduction applications in microelectronics. This result paves an effective way of developing epoxy composites with high thermal conductivity in electronic packaging applications.

Simultaneously enhance thermal conductive property and mechanical properties of silicon rubber composites by introducing ultrafine Al2O3 nanospheres prepared via thermal plasma

It is great significant to develop polymer composites with high thermal conductivity and excellent mechanical properties simultaneously. Generally, a high loading of fillers is required for thermal conductive composites. However, traditional polymer composites exhibit unsatisfactory enhancement due to poor dispersion and weak interfacial adhesion, for which lead to high interfacial resistance. Meanwhile, the mechanical properties of composites are greatly damaged because of internal defects caused by imperfect filling. Herein, Al2O3 nanospheres prepared by high frequency thermal plasma are first used as filler to increase thermal conductivity of silicon rubber (SR) and reinforce the mechanical properties of SR. The Al2O3 nanospheres show good compatibility and strong interfacial adhesion with matrix. Thus SR composites exhibit excellent thermal conductivity of 1.53 Wm−1K−1, corresponding to an enhancement of 665% compared to SR. Importantly, the SR composites still possess high tensile strength of 5.71 MPa, modulus of 9.69 MPa and fracture toughness of 1.81 MJ/m3 respectively, improving by 1630%, 3360% and 723% compared with neat SR. In addition, The Al2O3/SR composites also possess good dielectric properties, high volume resistivity and enhanced thermal stability, indicating a promising application of composites in the field of electronic packing. Therefore, this work offers a novel route to design high performance SR composites using Al2O3 nanospheres prepared by thermal plasma.

Design of network Al2O3 spheres for significantly enhanced thermal conductivity of polymer composites

It is of great significance to realize high thermal conductivity of polymer composites, which are used in electronic devices. However, traditional polymer composites exhibit limited thermal conductivity due to high interfacial thermal resistance. Herein, network Al2O3 (N-Al2O3) with multidimensional continuous structures is fabricated by a feasible strategy and first used as fillers for phenolic resin (PR), achieving significantly enhanced thermal conductivity of 4.01 Wm−1 K−1, enhanced by 1800% compared with neat matrix. The unique N-Al2O3 is responsible for the excellent thermal conductivity, which contributes to the continuous thermal transfer pathways with decreased interfacial thermal resistance. Additionally, owing to the interpenetrating structure of N-Al2O3 and PR, composites display improved mechanical properties and thermal stability. Dielectric loss tangent of composites decreases with increasing N-Al2O3, which is unusual and desired for thermal interface materials used in electronic devices. Therefore, our strategy offers new guidelines in fabricating high-quality composites for commercial applications.

Boron nitride nanosheets endow the traditional dielectric polymer composites with advanced thermal management capability

Dielectric polymer composites with high thermal conductivity have increased applications in electrical and electronic systems. However, the increase of thermal conductivity is usually achieved by increasing filler loading, which results in deterioration of processing and dielectric property. In this work, a hybrid filler strategy for overcoming the shortcoming is reported. In the strategy, the traditional α-Al2O3 microspheres were encapsulated by boron nitride nanosheets (BNNSs). Both types of filler were treated by reactive silanes, resulting in chemical bonding between α-Al2O3 and BNNSs. Epoxy composites with the BNNS encapsulated α-Al2O3 (Al2O3@BNNS) and randomly dispersed hybrid filler (Al2O3&BNNS) were also prepared. It is interestingly found that at the same filler loading, the Al2O3@BNNS composites exhibit much higher thermal conductivity when compared with the Al2O3 composites and the Al2O3&BNNS composites. At a filler loading of 65 vol% and an optimal BNNS to α-Al2O3 ratio of 1 : 7, the Al2O3@BNNS composite exhibit a thermal conductivity of 2.43 W/(m·K), which is 73.9% higher than that of the Al2O3 composite and is also about 20% higher than that of the Al2O3&BNNS composites. This facile strategy opens a new avenue for upgrading and updating the traditional dielectric polymer composites in the field of dielectrics and electrical insulation.

Continuous network of CNTs in poly(vinylidene fluoride) composites with high thermal and mechanical performance for heat exchangers

Polymeric materials with high thermal conductivity have drawn much attention in academic and industrial field recently. Due to poor dispersion and insufficient interconnection of fillers, traditional polymer composites present not only undesirable thermal conductivity but other declined properties even with high loaded thermal conductive nanofillers. In this work, the uniform and continuous network of (3-Aminopropyl)trimethoxysilane (APTMS) modified carbon nanotubes (A-CNTs) in poly(vinylidene fluoride) (PVDF) was built up by using the simple casting method. Thermal conductivity of 2.15 Wm−1K−1 and tensile strength enhancement of 70% are achieved at 40 vol% A-CNTs loading compared with that of pure PVDF. The A-CNTs/PVDF composites exhibit an intensified thermal stability and sharply increased crystallinity (45.7%) compared with pure PVDF (28.5%). Moreover, for practical heat exchange experiment, the PVDF composites possess high heat transfer efficiency and long-last stability in corrosive water, which leads to the use of PVDF materials to supersede metal materials in heat transfers.

Effects of the total content of eutectic Sn-Cu alloy and Cu particles used as conductive filler on the structure and properties of polyamide-66 composites

Incorporating both a low-melting-point metal (LMPM) and a high-melting-point metal (HMPM) into a polymer is a promising approach to prepare highly conductive, melt-processable composites. The effects of the total content of the two metals on the structure and properties of the composites were studied in this work through a eutectic Sn-Cu alloy/Cu particles/polyamide-66 ternary system. The structure, conductivity, fluidity and toughness of the composites were characterized by scanning electron microscopy, four-point probe or two-electrode method, small amplitude oscillatory shear testing and Charpy impact testing, respectively. The results show that the morphology of metal phase in the composites transforms from isolated “islands” to a physically continuous network as the total metal content increases. The percolation threshold for the composites is lower than that of traditional metal-filled polymer composites. The complex viscosity and impact strength of the composites vary non-monotonically with the total metal content and exhibit a minimum. The enhancement in the conductivity and toughness of the composites is related to the formation of the physically continuous conductive network. Overall, the filler content dependences of the structure and properties of the LMPM/HMPM/polymer composites are different from those of traditional conductive polymer composites. The combination of LMPM and HMPM helps reduce the filler content and mitigate the composite fluidity deterioration.