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Polymer Composites: Microstructural, Thermal and Mechanical Properties

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (10 October 2022) | Viewed by 24890

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Special Issue Editor

Dr. Pietro Russo

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Guest Editor

Institute for Polymers, Composites and Biomaterials, National Council of Research, Pozzuoli, Italy
Interests: polymer composites; microstructure; thermal properties; mechanical properties; microscopy; fiber reinforced polymers (FRPs); reinforcement; interface microstructure
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent decades, the increasing demand for high-performing materials and structures has stoked the interest in the development and use of polymer composites in a wide range of industrial fields. These materials, combining at least two different phases, have the peculiarity to meet diverse design requirements with significant weight savings as well as a high strength-to-weight ratio. However, despite these strengths, some features such as the difficult prediction of durability under structural loads still severely limit their use.

This consideration is even more true for eco-friendly composites more recently developed in light of environmental concerns aimed at preserving fossil resources in favor of renewable ones. Their increased attraction is witnessed by numerous papers dealing with composites from biomatrices and/or reinforced with natural fibers in place of synthetic ones, but this trend is not yet reflected in a relevant range of industrial applications because of many challenges such as moisture, weathering, and biological attacks.

A further extension of the composites market cannot ignore a careful estimate of microstructural details, as well as a preliminary analysis of the final performances, especially in terms of thermal and mechanical properties.

This Special Issue aims at collecting recent advancements made in the field of polymer composites through both original research papers and reviews.

Dr. Pietro Russo
Guest Editor

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Polymer composites
Microstructure
Thermal properties
Mechanical properties
Microscopy
Fiber Reinforced Polymers (FRPs)
Reinforcement
Interface microstructure

Related Special Issue

Polymer Composites: Microstructural, Thermal and Mechanical Properties (Second Volume) in Materials (7 articles)

Published Papers (12 papers)

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Research

20 pages, 7994 KiB

Open AccessArticle

Multifunctional Polyurethane Composites with Coffee Grounds and Wood Sawdust

by Przemysław Bartczak, Julia Stachowiak, Marta Szmitko, Aleksandra Grząbka-Zasadzińska and Sławomir Borysiak

Materials 2023, 16(1), 278; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16010278 - 28 Dec 2022

Cited by 6 | Viewed by 2101

Abstract

Currently, the fundamental activity that will allow for the development of an economy with closed circulation is the management of food waste and production waste for the preparation of biocomposites. The use of waste materials of natural origin allows for the creation of innovative composites with improved physicochemical and functional properties. The present investigation concerns the use of coffee grounds (2.5–20 wt.%) and oak sawdust (2.5–20 wt.%) as effective fillers of rigid polyurethane foam. Innovative composite materials, previously indebted in the literature, were subjected to the necessary analyses to determine the application abilities: processing times, free density, water absorption, dimensional stability, mechanical properties (compressive strength), thermal conductivity, morphology, and flame resistance. The results with respect to the mechanical tests turned out to be the key. Increasing the number of coffee additives has a positive effect on the compressive strength. The addition of this filler in the range of 5–15 wt.% increased the compressive strength of the composites, 136–139 kPa, compared to the reference sample, 127 kPa. The key parameter analysed was thermal conductivity. The results obtained were in range of the requirements, that is, 0.022–0.024 W/m·K for all used amounts of fillers 2.5–20 wt.%. This is extremely important since these materials are used for insulation purposes. The results of the burning-behaviour test have confirmed that the addition of renewable materials does not negatively affect the fire resistance of the received foams; the results were obtained analogously to those obtained from the reference sample without the addition of fillers. The height of the flame did not exceed 17 cm, while the flame decay time was 17 s for the reference sample and the composite with coffee grounds and 18 s for the composite with oak sawdust. In this work, the practical application of bioorganic waste as an innovative filler for the insulation of flooded polyurethane foam is described for the first time. The introduction of fillers of natural origin into the polymer matrix is a promising method to improve the physicochemical and functional properties of rigid polyurethane foams. Composites modified with coffee grounds and sawdust are interesting from a technological, ecological, and economic point of view, significantly increasing the range of use of foam in various industries. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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22 pages, 5808 KiB

Open AccessArticle

Development of Lightweight Cricket Pads Using Knitted Flexible Thermoplastic Composites with Improved Impact Protection

by Tauheed Ahmad, Hafsa Jamshaid, Rajesh Kumar Mishra, Vijay Chandan, Shabnam Nazari, Tatiana Alexiou Ivanova, Naseer Ahamad, Sharjeel Ahmed, Michal Petru and Lubos Kučera

Materials 2022, 15(23), 8661; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238661 - 05 Dec 2022

Viewed by 1691

Abstract

Cricket is one of the most popular global sports, and cricket pads are important personal protective gear used for shock absorption and peak deceleration of the impact forces of the cricket ball for both batsmen and wicket keepers. The materials selection of the padding should be considered according to requirements. In the present study, flexible composites were manufactured using knitted unidirectional thermoplastic composite prepregs. Prepregs were fabricated using thermoplastic yarns, e.g., High Density Polyethylene (HDPE), Polypropylene (PP), and Low Melting Polyester (LMPE). Para-aramid (Kevlar) and Flax yarns were used as inlay. The structures were stacked in three and five layers, and hot compression was used to convert thermoplastic yarn into matrix. A total of twelve samples were prepared, and their mechanical properties were evaluated. Tensile and flexural properties, short beam strength, and impact properties were optimized using the multi-criteria decision-making (MCDM) technique for order performance by similarity to ideal solution (TOPSIS). This approach was used to select the best material for use in cricket pads. The candidate samples were ranked using statistical techniques. The optimum sample was found to be FP5, i.e., Flax with polypropylene using five layers, which exhibited the maximum impact strength. The results showed that the mechanical properties were improved in general by increasing the number of layers. The significance and percentage contribution of each factor was obtained by ANOVA (α = 0.10) and pie chart, which showed Factors A and C (inlay yarn and number of layers) to be the main contributors. The optimal samples showed superior impact-related performance compared to a market sample cricket pad. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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14 pages, 6738 KiB

Open AccessArticle

Effects of Elastic Couplings in a Compressed Plate Element with Cut-Out

by Katarzyna Falkowicz, Sylwester Samborski and Paolo Sebastiano Valvo

Materials 2022, 15(21), 7752; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15217752 - 03 Nov 2022

Cited by 6 | Viewed by 1217

Abstract

Analytical calculations were performed on carbon fiber-reinforced polymer (CFRP) laminates in an asymmetrical configuration. The asymmetric configuration of composites was investigated, where extension–twisting and extension–bending couplings were used to obtain the elastic element. Analysis of the presence of elastic couplings was conducted according to Classical Laminate Theory (CLT). Components of matrices A, B, and D, as well as the parameters D_c and B_t, were obtained using the MATLAB software environment. The results show that couplings between the extension and bending, as well as between the extension and twisting, were strongly dependent on specimen plies’ orientation. Moreover, additional analysis was performed on the influence of layer angle on the terms which are components of the B_t and D_c coefficients. The results indicate that the angle of laying fibers around 45–50° significantly amplifies the effects of elastic couplings. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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15 pages, 5704 KiB

Open AccessArticle

Needle Penetration Simulation: Influence of Penetration Angle and Sample Stress on the Mechanical Behaviors of Polymers Applying a Cast Silicone and a 3D-Printed Resin

by Thore von Steuben, Florian K. Enzmann, Sebastian Spintzyk, Frank Rupp and Ariadne Roehler

Materials 2022, 15(16), 5575; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15165575 - 13 Aug 2022

Viewed by 1427

Abstract

For surgical catheterization training applications, realistic and effective materials are desired. In this study, the relevance of a needle puncture angle and a simulated wall stress on different elastic materials were determined in a previously developed experimental setup. Both settings were considered individually in two new setups. In addition, a control setup with neither angle nor prestress was designed. During the process of puncturing the samples of two materials (Replisil 9N and Formlabs Elastic 50A), force–displacement values were collected, and three predefined parameters evaluated. The differences between the angled/stressed groups and the control group were analyzed. The additively processed material required a significantly higher force to puncture than the conventional one (p < 0.001). Moreover, a needle angulation of 45° required more force than puncturing orthogonally. Prestressing the samples did not clearly influence the resulting force. An evaluation of relative parameters showed that the investigated materials behaved differently but not linearly differently under the influence of needle angle and prestress. Therefore, it is essential to evaluate the properties and suitability of materials for surgical training models in appropriate experimental setups considering multiple parameters. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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20 pages, 3628 KiB

Open AccessArticle

Synthesis and Characterization of Wood Rigid Polyurethane Composites

by Hamza Bradai, Ahmed Koubaa, Hassine Bouafif, Armand Langlois and Basma Samet

Materials 2022, 15(12), 4316; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15124316 - 18 Jun 2022

Cited by 6 | Viewed by 2011

Abstract

Incorporating biodegradable reinforcement, such as wood particles, into rigid polyurethane foams (RPUFs) is among the alternatives to reduce their environmental impact. This study aims to assess the effect of different wood particles as reinforcement in RPUFs. Reinforced rigid polyurethane foams are synthesized with milled wood particles of various forms and sizes and commercial polyol and isocyanate. The effect of fiber treatments and mechanical stirring on foams’ properties is also studied. Additional tests on polyisocyanurate foams (PIR) were undertaken to assess the effect of reinforcement on their properties. Mechanical properties are measured to investigate the impact of wood particle reinforcement on the foam. Confocal microscopy and Fourier-transform infrared spectroscopy (FTIR) showed the interaction between the wood fibers and the matrix. Despite the adhesion observed for some fibers, most of the cell walls of RPUFs were punctured by the rigid wood fibers, which explained the decrease in the compressive strength of the composites for manually mixed foams. Mechanical stirring proved to be an efficient method to enhance the reinforcement power of untreated fibers. RPUF foams’ properties showed similar changes when untreated wood flour was introduced to the formula, increasing compressive strength significantly. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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19 pages, 5743 KiB

Open AccessEditor’s ChoiceArticle

Polyester and Epoxy Resins with Increased Thermal Conductivity and Reduced Surface Resistivity for Applications in Explosion-Proof Enclosures of Electrical Devices

by Małgorzata Szymiczek and Dawid Buła

Materials 2022, 15(6), 2171; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15062171 - 15 Mar 2022

Cited by 2 | Viewed by 1761

Abstract

Composite materials are still finding new applications that require the modification of various properties and are characterized by the summary impact on selected operational features. Due to the operating conditions of electrical equipment enclosures in potentially explosive atmospheres, the surface resistivity ensuring anti-electrostatic properties, i.e., below 10⁹ Ω and resistance to the flame while maintaining appropriate operational enclosure properties is very important. It is also crucial to dissipate heat while reducing weight. Currently metal or cast-iron enclosures are used for various types of electrical devices. As part of the work, a material that can be used for a composite matrix for the enclosure was developed. The study aimed to assess the influence of selected fillers and chemical modifications on the thermal conductivity coefficient, resistivity, and strength properties of matrix materials for the production of electrical device enclosures used in the mining industry. Selected resins were modified with graphite, copper, and carbon black. Tests were carried out on the coefficient of thermal conductivity, surface resistivity, flammability, and flexural strength. At the final stage of the work, a multi-criteria analysis was carried out, which allowed the selection of a composite that meets the assumed characteristics to the highest degree. It is a vinyl ester composite modified with 15 wt.% MG394 and 5 wt.% MG1596 graphite (W2). The thermal conductivity of composite W2 is 5.64 W/mK, the surface resistivity is 5.2 × 10³ Ω, the flexural strength is 50.61 MPa, and the flammability class is V0. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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16 pages, 5127 KiB

Open AccessArticle

Experimental Investigations on Dry Sliding Wear Behavior of Kevlar and Natural Fiber-Reinforced Hybrid Composites through an RSM–GRA Hybrid Approach

by Banu Murali, Bindu Madhavan Vijaya Ramnath, Devaraj Rajamani, Emad Abouel Nasr, Antonello Astarita and Hussein Mohamed

Materials 2022, 15(3), 749; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15030749 - 19 Jan 2022

Cited by 10 | Viewed by 1666

Abstract

The present work aimed to investigate the dry sliding wear behaviors of hybrid polymer matrix composites made up of Kevlar, bamboo, palm, and Aloe vera as reinforcement materials of varying stacking sequences, along with epoxy as the matrix material. Three combinations of composite laminates with different stacking sequences such as AB, BC, and CA were fabricated by a vacuum-assisted compression molding process. The influence of composite laminates fabricated through various stacking sequences and dry sliding wear test variables such as load, sliding distance, and sliding velocity on the specific wear rate and co-efficient of friction were investigated. Experiments were designed and statistical validation was performed through response surface methodology-based D-optimal design and analysis of variance. The optimization was performed using grey relational analysis (GRA) to identify the optimal parameters to enhance the wear resistance of hybrid polymer composites under dry sliding conditions. The optimal parameters, such as composite combinations of CA, a load of 5 N, a sliding velocity of 3 m/s, and a sliding distance of 1500 m, were obtained. Furthermore, the morphologies of worn-out surfaces were investigated using SEM analysis. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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14 pages, 4039 KiB

Open AccessArticle

Microstructure and Thermal Property of Designed Alginate-Based Polymeric Composite Foam Materials Containing Biomimetic Decellularized Elastic Cartilage Microscaffolds

by Ching-Cheng Huang

Materials 2022, 15(1), 258; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15010258 - 30 Dec 2021

Cited by 4 | Viewed by 1344

Abstract

This study presents a designed alginate-based polymeric composite foam material containing decellularized elastic cartilage microscaffolds from porcine elastic cartilage by using supercritical fluid and papain treatment for medical scaffold biomaterials. The microstructure and thermal property of the designed alginate-based polymeric composite foam materials with various controlled ratios of alginate molecules and decellularized elastic cartilage microscaffolds were studied and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and differential thermal gravimetric analysis (TGA/DTG). The microstructure and thermal property of the composite foam materials were affected by the introduction of decellularized elastic cartilage microscaffolds. The designed alginate-based polymeric composite foam materials containing decellularized elastic cartilage microscaffolds were ionically cross-linked with calcium ions by soaking the polymeric composite foam materials in a solution of calcium chloride. Additional calcium ions further improved the microstructure and thermal stability of the resulting ionic cross-linked alginate-based polymeric composite foam materials. Furthermore, the effect of crosslinking functionality on microstructures and thermal properties of the resulting polymeric composite foam materials were studied to build up useful information for 3D substrates for cultivating and growing cartilage cells and/or cartilage tissue engineering. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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10 pages, 2532 KiB

Open AccessArticle

Impact of Short-Cut SWCF Yarn on Conductivity and Electrical Heatability of Silicone–MWCNT Composites

by Kristin Trommer and Minoj Gnanaseelan

Materials 2021, 14(24), 7841; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14247841 - 18 Dec 2021

Viewed by 1848

Abstract

The incorporation of MWCNTs in polymer systems up to the percolation range renders them electrically conductive. However, this conductivity is not high enough for heating applications in the low-voltage range (<24 V). The combination of nanoscaled MWCNTs with microscaled short SWCNT fibers that was investigated in this study causes an abrupt rise in the conductivity of the material by more than an order of magnitude. Silicone was used as a flexible and high-temperature-resistant matrix polymer. Conductive silicone coatings and films with SWCF contents of 1.5% to 5% and constant MWCNT contents of 3% and 5% were developed, and their electrical and thermal properties in the voltage range between 6 and 48 V were investigated. The electrical conductivity of 3% MWCNT composite materials rose with a 5% addition of SWCFs. Because of this spike in conductivity, output power of 1260 W/m² was achieved, for example, for a 100 µm thick composite containing 3% MWCNT and 4% SWCF at 24 V with a line spacing of 20 cm. Thermal measurements show a temperature increase of 69 K under these conditions. These findings support the use of such conductive silicone composites for high-performance coatings and films for challenging and high-quality applications. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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15 pages, 5010 KiB

Open AccessArticle

Investigation of Adhesive Joining Strategies for the Application of a Multi-Material Light Rail Vehicle

by Yiding Liu, Craig Carnegie, Helen Ascroft, Wenhao Li, Xiao Han, Hua Guo and Darren J. Hughes

Materials 2021, 14(22), 6991; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14226991 - 18 Nov 2021

Cited by 10 | Viewed by 2433

Abstract

To meet the high demand for lightweight energy-efficient and safe structures for transport applications, a current state-of-the-art light rail vehicle structure is under development that adopts a multi-material design strategy. This strategy creates the need for advanced multi-material joining technologies. The compatibility of the adhesive with a wide range of material types and the possibility of joining multi-material structures is also a key advantage to its success. In this paper, the feasibility of using either epoxy or polyurethane adhesive joining techniques applied to the multi-material vehicle structure is investigated. Importantly, consideration is given to the effect of variation in bond thickness for both families of structural adhesives. Multi-material adhesively bonded single lap joints with different adhesives of controlled bond thicknesses were manufactured and tested in order to experimentally assess the shear strength and stiffness. The torsional stiffness and natural frequency of the vehicle were modelled using a global two-dimensional finite element model (FEM) with different adhesive properties, and the obtained vehicle performances were further explained by the coupon-level experimental tests. The results showed that the vehicle using polyurethane adhesive with a target bond thickness of 1.0 mm allowed for optimal modal frequency and weight reduction. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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14 pages, 3838 KiB

Open AccessArticle

Transparent Fiber-Reinforced Composites Based on a Thermoset Resin Using Liquid Composite Molding (LCM) Techniques

by Yavuz Caydamli, Klaus Heudorfer, Jens Take, Filip Podjaski, Peter Middendorf and Michael R. Buchmeiser

Materials 2021, 14(20), 6087; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14206087 - 14 Oct 2021

Cited by 9 | Viewed by 2752

Abstract

In this study, optically transparent glass fiber-reinforced polymers (tGFRPs) were produced using a thermoset matrix and an E-glass fabric. In situ polymerization was combined with liquid composite molding (LCM) techniques both in a resin transfer molding (RTM) mold and a lite-RTM (L-RTM) setup between two glass plates. The RTM specimens were used for mechanical characterization while the L-RTM samples were used for transmittance measurements. Optimization in terms of the number of glass fabric layers, the overall degree of transparency of the composite, and the mechanical properties was carried out and allowed for the realization of high mechanical strength and high-transparency tGFRPs. An outstanding degree of infiltration was achieved maintaining up to 75% transmittance even when using 29 layers of E-glass fabric, corresponding to 50 v.% fiber, using an L-RTM setup. RTM specimens with 44 v.% fiber yielded a tensile strength of 435.2 ± 17.6 MPa, and an E-Modulus of 24.3 ± 0.7 GPa. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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18 pages, 41921 KiB

Open AccessArticle

Mechanical Properties of Aramid/Carbon Hybrid Fiber-Reinforced Concrete

by Yeou-Fong Li, Hsin-Fu Wang, Jin-Yuan Syu, Gobinathan Kadagathur Ramanathan, Ying-Kuan Tsai and Man Hoi Lok

Materials 2021, 14(19), 5881; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14195881 - 08 Oct 2021

Cited by 20 | Viewed by 3207

Abstract

In this study, aramid fiber (Kevlar^® 29 fiber) and carbon fiber were added into concrete in a hybrid manner to enhance the static and impact mechanical properties. The coupling agent presence on the surface of carbon fibers was spotted in Scanning Electron Microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) graphs. The carbon fiber with a coupling agent affected the mechanical strength of the reinforced concrete. At 1% fiber/cement weight percentage, the hybrid fiber-reinforced concrete (HFRC) prepared using Kevlar fiber and carbon fiber of 12 and 24 mm in length under different mix proportions was investigated to determine the maximum mechanical strengths. From the test results, the mechanical strength of the HFRC attained better performance than that of the concrete with only Kevlar or carbon fibers. Foremost, the mix proportion of Kevlar/carbon fiber (50–50%) significantly improved the compressive, flexural, and splitting tensile strengths. Under different impact energies, the impact resistance of the HFRC specimen was much higher than that of the benchmark specimen, and the damage of the HFRC specimens was examined with an optical microscope to identify slippage or rupture failure of the fiber in concrete. Full article

(This article belongs to the Special Issue Polymer Composites: Microstructural, Thermal and Mechanical Properties)

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