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17 pages, 4804 KiB

Open AccessArticle

Toughening Polylactic Acid with Ultrafine Fully Vulcanized Powdered Natural Rubber Graft-Copolymerized with Poly(styrene-co-acrylonitrile): Tailoring the Styrene–Acrylonitrile Ratio for Enhanced Interfacial Interactions

by Reza Gholami, Ibrahim Lawan, Sahar Ebrahimi, Achiraya Pattulee, Cheol-Hee Ahn and Sarawut Rimdusit

Polymers 2024, 16(16), 2254; https://doi.org/10.3390/polym16162254 - 8 Aug 2024

Viewed by 977

Abstract

This study investigated the sustainable toughening of polylactic acid (PLA) by incorporating ultrafine fully vulcanized powdered natural rubber graft-copolymerized with poly-styrene-co-acrylonitrile (UFPNR-SAN). We investigated the effect of the styrene-to-acrylonitrile ratio (ST:AN) used during the grafting process on the final UFPNR-SAN compatibility with PLA. [...] Read more.

This study investigated the sustainable toughening of polylactic acid (PLA) by incorporating ultrafine fully vulcanized powdered natural rubber graft-copolymerized with poly-styrene-co-acrylonitrile (UFPNR-SAN). We investigated the effect of the styrene-to-acrylonitrile ratio (ST:AN) used during the grafting process on the final UFPNR-SAN compatibility with PLA. The ST:AN ratio was systematically varied during the grafting reaction to prepare UFPNR-SAN with a range of different surface energies. The ST:AN ratio of 4:1 showed the highest compatibility with the PLA matrix, attributed to optimal interfacial interactions and improved dispersion, as indicated by contact angle measurements and SEM observations. This resulted in a remarkable toughening of the PLA/UFPNR-SAN composite. For instance, an obvious fully ductile behavior without crack formation and flexural strain of around 17.5% against 5% of the neat PLA was recorded. In addition, 3.5 times improvement in the impact strength of the composite at 25 wt% dosage of the UFPNR-SAN was also achieved without compromising thermal properties. Overall, this study established the suitable ST:AN ratio on the grafting onto natural rubber to enhance interfacial interactions with PLA and its effects on the properties of the resulting PLA/UFPNR-SAN bio-based composite. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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15 pages, 6144 KiB

Open AccessArticle

Stress Wave Propagation and Decay Based on Micro-Scale Modelling in the Topology of Polymer Composite with Circular Particles

by Dominik Sabol and Zuzana Murčinková

Polymers 2024, 16(15), 2189; https://doi.org/10.3390/polym16152189 - 1 Aug 2024

Viewed by 949

Abstract

This article deals with stress wave decay performance, analysing the stress wave propagation generated by an impulsive unit load in a 2D representative unit cell (RUC) of a polymer composite with circular particles representing spherical particles, elliptical particles, and short fibres. The micro-scale [...] Read more.

This article deals with stress wave decay performance, analysing the stress wave propagation generated by an impulsive unit load in a 2D representative unit cell (RUC) of a polymer composite with circular particles representing spherical particles, elliptical particles, and short fibres. The micro-scale numerical simulation uses explicit finite element analysis (FEA). The micro-response to an impulsive unit load creates a stress wave amplitude interacting with the material structure and tends to weaken and absorb energy. The stress wave damping is determined by the decaying amplitudes of Mises stress at the front of the stress wave. The stress wave damping is evaluated for different ratios of tensile modules and material densities of matrix and reinforcing material and other factors, such as percentage and particle size, applied to nine topologies of RUCs, and even the presence of an interfacial region is analysed. Moreover, the article visualises the phases of stress wave decay in various particle distributions, i.e., various topologies. Analysing the different topologies of the same particle volume (area) percentage, the study proved that the composite topology and resulting wave–particle and wave–wave interactions are other sources of material damping. The presence of even a small percentage, 3.5 area%, of reinforcing circular particles in the matrix brings a significant increase in stress wave damping up to about 40–43% (depending on the topology) compared to a homogeneous matrix with stress wave damping of 12.5% under the same conditions. Moreover, the topology with the same volume (area) percentage can increase particle stress wave damping by 15.3%. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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15 pages, 4347 KiB

Open AccessArticle

Physicochemical Characterization and Biological Properties of Polysaccharides from Alpiniae oxyphyllae Fructus

by Risi Wang, Xinmei Ruan, Jun Chen, Lizhen Deng, Wei Zhou, Xixiang Shuai, Ruihong Liang and Taotao Dai

Polymers 2024, 16(12), 1705; https://doi.org/10.3390/polym16121705 - 14 Jun 2024

Viewed by 809

Abstract

Polysaccharides (AOPs) were extracted from Alpiniae oxyphyllae fructus using three distinct methods: hot water (AOP-HW), hydrochloric acid (AOP-AC), and NaOH/NaBH4 (AOP-AL). This study systematically investigated and compared the physicochemical properties, structural characteristics, antioxidant activities, and α-amylase inhibitory activities of the extracted polysaccharides. Among [...] Read more.

Polysaccharides (AOPs) were extracted from Alpiniae oxyphyllae fructus using three distinct methods: hot water (AOP-HW), hydrochloric acid (AOP-AC), and NaOH/NaBH4 (AOP-AL). This study systematically investigated and compared the physicochemical properties, structural characteristics, antioxidant activities, and α-amylase inhibitory activities of the extracted polysaccharides. Among the three AOPs, AOP-AC exhibited the highest yield (13.76%) and neutral sugar content (80.57%), but had the lowest molecular weight (121.28 kDa). Conversely, AOP-HW had the lowest yield (4.54%) but the highest molecular weight (385.42 kDa). AOP-AL was predominantly composed of arabinose (28.42 mol%), galacturonic acid (17.61 mol%), and galactose (17.09 mol%), while glucose was the major sugar in both AOP-HW (52.31 mol%) and AOP-AC (94.77 mol%). Functionally, AOP-AL demonstrated superior scavenging activities against DPPH, hydroxyl, and ABTS radicals, whereas AOP-AC exhibited the strongest inhibitory effect on α-amylase. These findings indicate that the extraction solvent significantly influences the physicochemical and biological properties of AOPs, thus guiding the selection of appropriate extraction methods for specific applications. The results of this study have broad implications for industries seeking natural polysaccharides with antioxidant and enzymatic inhibitory properties. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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19 pages, 8589 KiB

Open AccessArticle

Effect of Nano Spinel Ferrites Co_0.9Cu_0.1Fe₂O₄ on Non-Isothermal Cold Crystallization Behaviours and Kinetics of Its Composites with Polylactic Acid

by Wael H. Alsaedi, Khulood A. Abu Al-Ola, Omaima Alhaddad, Zyzafon Albelwe, Renad Alawaji and Ahmed M. Abu-Dief

Polymers 2024, 16(9), 1190; https://doi.org/10.3390/polym16091190 - 24 Apr 2024

Cited by 1 | Viewed by 999

Abstract

Nanoparticles of spinel ferrites with a composition of Co_0.9Cu_0.1Fe₂O₄ (AM NPs) were effectively synthesized via a hydrothermal route. The structure of ferrite nanoparticles was characterized with X-ray diffraction, which showed a single cubic spinel phase. Energy-dispersive [...] Read more.

Nanoparticles of spinel ferrites with a composition of Co_0.9Cu_0.1Fe₂O₄ (AM NPs) were effectively synthesized via a hydrothermal route. The structure of ferrite nanoparticles was characterized with X-ray diffraction, which showed a single cubic spinel phase. Energy-dispersive X-ray (EDX) spectroscopy and field emission-scanning electron microscopy (FE-SEM) were employed to analyse elemental composition and surface morphology, respectively. Moreover, the effects of the Co_0.9Cu_0.1Fe₂O₄ on the morphology of [PLA = polylactic acid] nanocomposites were examined through polarized light optical microscopy (POM) and X-ray diffraction (XRD). The thermal behaviours for tested samples were studied through [DSC = differential scanning calorimetry] and [TGA = thermal gravimetric analysis]. A great number of minor PLA spherulites were detected using POM in the presence of the Co_0.9Cu_0.1Fe₂O₄ ceramic magnetic nanoparticles (AM), increasing with AM nanoparticle contents. X-ray diffraction (XRD) analysis showed that the presence of nanoparticles led to an increase in the intensity of diffraction peaks. The DSC findings implied that the crystallization behaviours for the efficient PLA as well as its nanocomposites were affected by the addition of AM nanoparticles. They act as efficient nucleating agents because they shift the temperature of crystallization to a lower value. The Avrami models were used to analyse kinetics data. The experimental data were well described using the Avrami method for all samples tested. The addition of AM to the PLA matrix resulted in a decrease in the crystallization half-time t_1/2 values, indicating a faster crystallization rate. TGA data showed that the occurrence of AM nanoparticles decreased the thermal stability of PLA. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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12 pages, 2869 KiB

Open AccessArticle

Theoretical Analysis of Thermophysical Properties of 3D Carbon/Epoxy Braided Composites with Varying Temperature

by Li-Li Jiang, Zhen-Guo Li, Dong-Ye Wang, Jun-Jun Zhai and Xiang-Xia Kong

Polymers 2024, 16(8), 1166; https://doi.org/10.3390/polym16081166 - 21 Apr 2024

Viewed by 1045

Abstract

A three-dimensional helix geometry unit cell is established to simulate the complex spatial configuration of 3D braided composites. Initially, different types of yarn factors, such as yarn path, cross-sectional shape, properties, and braid direction, are explained. Then, the multiphase finite element method is [...] Read more.

A three-dimensional helix geometry unit cell is established to simulate the complex spatial configuration of 3D braided composites. Initially, different types of yarn factors, such as yarn path, cross-sectional shape, properties, and braid direction, are explained. Then, the multiphase finite element method is used to develop a new theoretical calculation procedure based on the unit cell for predicting the impacts of environmental temperature on the thermophysical properties of 3D four-direction carbon/epoxy braided composites. The changing rule and distribution characteristics of the thermophysical properties for 3D four-direction carbon/epoxy braided composites are obtained at temperatures ranging from room temperature to 200 °C. The influences of environmental temperature on the coefficients of thermal expansion (CTE) and the coefficients of thermal conduction (CTC) are evaluated, by which some important conclusions are drawn. A comparison is conducted between theoretical and experimental results, revealing that variations in temperature exert a notable influence on the thermophysical characteristics of 3D four-directional carbon/epoxy braided composites. The theoretical calculation procedure is an effective tool for the mechanical property analysis of composite materials with complex geometries. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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20 pages, 7075 KiB

Open AccessArticle

A Novel In Situ Sol-Gel Synthesis Method for PDMS Composites Reinforced with Silica Nanoparticles

by Aldo Cordoba, Juan Valerio Cauich-Rodríguez, Rossana Faride Vargas-Coronado, Rodrigo Velázquez-Castillo and Karen Esquivel

Polymers 2024, 16(8), 1125; https://doi.org/10.3390/polym16081125 - 17 Apr 2024

Cited by 2 | Viewed by 1658

Abstract

The addition of nanostructures to polymeric materials allows for a direct interaction between polymeric chains and nanometric structures, resulting in a synergistic process through the physical (electrostatic forces) and chemical properties (bond formation) of constituents for the modification of their properties and potential [...] Read more.

The addition of nanostructures to polymeric materials allows for a direct interaction between polymeric chains and nanometric structures, resulting in a synergistic process through the physical (electrostatic forces) and chemical properties (bond formation) of constituents for the modification of their properties and potential cutting-edge materials. This study explores a novel in situ synthesis method for PDMS-%SiO₂ nanoparticle composites with varying crosslinking degrees (PDMS:TEOS of 15:1, 10:1, and 5:1); particle concentrations (5%, 10%, and 15%); and sol-gel catalysts (acidic and alkaline). This investigation delves into the distinct physical and chemical properties of silicon nanoparticles synthesized under acidic (SiO₂-a) and alkaline (SiO₂-b) conditions. A characterization through Raman, FT-IR, and XPS analyses confirms particle size and agglomeration differences between both the SiO₂-a and SiO₂-b particles. Similar chemical environments, with TEOS and ethanol by-products, were detected for both systems. The results on polymer composites elucidate the successful incorporation of SiO₂ nanoparticles into the PDMS matrix without altering the PDMS’s chemical structure. However, the presence of nanoparticles did affect the relative intensities of specific vibrational modes over composites from −35% to 24% (Raman) and from −14% to 59% (FT-IR). The XPS results validate the presence of Si, O, and C in all composites, with significant variations in atomic proportions (C/Si and O/Si) and Si and C component analyses through deconvolution techniques. This study demonstrates the successful in situ synthesis of PDMS-SiO₂ composites with tunable properties by controlling the sol-gel and crosslinking synthesis parameters. The findings provide valuable insights into the in situ synthesis methods of polymeric composite materials and their potential integration with polymer nanocomposite processing techniques. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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19 pages, 2050 KiB

Open AccessArticle

Hygroscopy as an Indicator of Specific Surface Area in Polymer Materials

by Andrey V. Smagin and Nadezhda B. Sadovnikova

Polymers 2024, 16(5), 593; https://doi.org/10.3390/polym16050593 - 21 Feb 2024

Cited by 1 | Viewed by 1297

Abstract

Specific surface area (SSA) is an integral characteristic of the interfacial surface in poly-disperse systems, widely used for the assessment of technological properties in polymer materials and composites. Hygroscopic water content (W_h) is an obligate indicator of dispersed materials prior [...] Read more.

Specific surface area (SSA) is an integral characteristic of the interfacial surface in poly-disperse systems, widely used for the assessment of technological properties in polymer materials and composites. Hygroscopic water content (W_h) is an obligate indicator of dispersed materials prior to any analysis of their chemical composition. This study links both indicators for the purpose of the express assessment of SSA using widely available W_h data, on the example of natural (starch, cellulose) and synthetic (acrylic hydrogels) polymer materials. The standard BET analysis of SSA using water vapor desorption was chosen as a reference method. In contrast to the known empirical correlations, this study is based on the fundamental thermodynamic theory of the disjoining water pressure for the connection of the analyzed quantities. The statistical processing of the results for the new methodology and the standard BET method showed their good compliance in a wide range of SSA from 200 to 900 m²/g. The most important methodological conclusion is the possibility of an accurate physically based calculation of hydrophilic SSA in polymer materials using their W_h data at a known relative humidity in the laboratory. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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18 pages, 6034 KiB

Open AccessArticle

Hybridization Effect on Interlaminar Bond Strength, Flexural Properties, and Hardness of Carbon–Flax Fiber Thermoplastic Bio-Composites

by Mohsen Bahrami, Juan Carlos del Real, Mahoor Mehdikhani, José Antonio Butenegro, Juana Abenojar and Miguel Ángel Martínez

Polymers 2023, 15(24), 4619; https://doi.org/10.3390/polym15244619 - 5 Dec 2023

Cited by 3 | Viewed by 2104

Abstract

Hybridizing carbon-fiber-reinforced polymers with natural fibers could be a solution to prevent delamination and improve the out-of-plane properties of laminated composites. Delamination is one of the initial damage modes in composite laminates, attributed to relatively poor interlaminar mechanical properties, e.g., low interlaminar strength [...] Read more.

Hybridizing carbon-fiber-reinforced polymers with natural fibers could be a solution to prevent delamination and improve the out-of-plane properties of laminated composites. Delamination is one of the initial damage modes in composite laminates, attributed to relatively poor interlaminar mechanical properties, e.g., low interlaminar strength and fracture toughness. This study examined the interlaminar bond strength, flexural properties, and hardness of carbon/flax/polyamide hybrid bio-composites using peel adhesion, three-point bending, and macro-hardness tests, respectively. In this regard, interlayer hybrid laminates were produced with a sandwich fiber hybrid mode, using woven carbon fiber plies (C) as the outer layers and woven flax fiber plies (F) as the inner ones (CFFC) in combination with a bio-based thermoplastic polyamide 11 matrix. In addition, non-hybrid carbon and flax fiber composites with the same matrix were produced as reference laminates to investigate the hybridization effects. The results revealed the advantages of hybridization in terms of flexural properties, including a 212% higher modulus and a 265% higher strength compared to pure flax composites and a 34% higher failure strain compared to pure carbon composites. Additionally, the hybrid composites exhibited a positive hybridization effect in terms of peeling strength, demonstrating a 27% improvement compared to the pure carbon composites. These results provide valuable insights into the mechanical performance of woven carbon–flax hybrid bio-composites, suggesting potential applications in the automotive and construction industries. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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17 pages, 6020 KiB

Open AccessArticle

Numerical Study on the Damage of a Carbon Woven Composite Panel Subjected to Blast Loading

by Alessandro Vescovini, Luca Lomazzi, Marco Giglio and Andrea Manes

Polymers 2023, 15(21), 4269; https://doi.org/10.3390/polym15214269 - 30 Oct 2023

Viewed by 1336

Abstract

Blast loading represents a critical dynamic condition for engineering structures. While the response of metal materials to such a condition has been studied in detail, the behavior of composites has not been properly addressed yet. In this context, this work leverages numerical methods [...] Read more.

Blast loading represents a critical dynamic condition for engineering structures. While the response of metal materials to such a condition has been studied in detail, the behavior of composites has not been properly addressed yet. In this context, this work leverages numerical methods to assess the damage that occurs in a carbon-fiber-reinforced polymer plate subjected to close-range blast loading. Numerical analyses were carried out using two methods, i.e., the pure Lagrangian and hybrid coupled Eulerian–Lagrangian approaches. The simulations were validated against observations from a benchmark experimental test taken from the literature. The results showed that (i) the hybrid approach seems to be the most promising solution in terms of efficiency and accuracy; (ii) the Lagrangian approach can accurately reproduce the experimental observations, even though it comes with strong limitations; and (iii) the numerically predicted damage adheres to the experimentally observed damage, although the simulation outcome is influenced by the modeling technique used to describe the behavior of the composite material. We consider the approaches presented in this paper promising for investigation of blast-loaded composite structures, and further improvements can be achieved by (i) refining the description of the material behavior, e.g., by including the strain rate sensitivity; and (ii) better modeling the boundary conditions. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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22 pages, 3693 KiB

Open AccessArticle

Exploring the Potential of Fique Fiber as a Natural Composite Material: A Comprehensive Characterization Study

by Oscar Muñoz-Blandón, Margarita Ramírez-Carmona, Leidy Rendón-Castrillón and Carlos Ocampo-López

Polymers 2023, 15(12), 2712; https://doi.org/10.3390/polym15122712 - 17 Jun 2023

Cited by 5 | Viewed by 2046

Abstract

Many studies available in the literature focus mainly on the mechanical characterization of fiber, leaving out other physicochemical and thermogravimetric analyses that allow for establishing its potential as an engineering material. This study characterizes fique fiber for its potential use as an engineering [...] Read more.

Many studies available in the literature focus mainly on the mechanical characterization of fiber, leaving out other physicochemical and thermogravimetric analyses that allow for establishing its potential as an engineering material. This study characterizes fique fiber for its potential use as an engineering material. The fiber’s chemical composition and physical, thermal, mechanical, and textile properties were analyzed. The fiber has a high holocellulose content and low lignin and pectin content, indicating its potential as a natural composite material for various applications. Infrared spectrum analysis revealed characteristic bands associated with multiple functional groups. The fiber had monofilaments with diameters around 10 μm and 200 μm, as determined by AFM and SEM images, respectively. Mechanical testing showed the fiber could resist a maximum stress of 355.07 MPa, with an average maximum strain at which breakage occurs of 8.7%. The textile characterization revealed a linear density range of 16.34 to 38.83 tex, with an average value of 25.54 tex and a regain of 13.67%. Thermal analysis showed that the fiber’s weight decreased by around 5% due to moisture removal in the range of 40 °C to 100 °C, followed by weight loss due to thermal degradation of hemicellulose and glycosidic linkages of cellulose ranging from 250 to 320 °C. These characteristics suggest that fique fiber can be used in industries such as packaging, construction, composites, and automotive, among others. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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21 pages, 5448 KiB

Open AccessArticle

CRYSTAF, DSC and SAXS Study of the Co-Crystallization, Phase Separation and Lamellar Packing of the Blends with Different Polyethylenes

by Xuerong Yao, Ying Shi, Yujing Tang, Chunxia Luo, Liping Hou, Minqiao Ren, Cui Zheng and Li-Zhi Liu

Polymers 2023, 15(8), 1940; https://doi.org/10.3390/polym15081940 - 19 Apr 2023

Cited by 5 | Viewed by 2098

Abstract

The crystallization of polyethylene (PE) blends is a highly complex process, owing to the significant differences in crystallizability of the various PE components and the varying PE sequence distributions resulting from short- or long-chain branching. In this study, we examined both the resins [...] Read more.

The crystallization of polyethylene (PE) blends is a highly complex process, owing to the significant differences in crystallizability of the various PE components and the varying PE sequence distributions resulting from short- or long-chain branching. In this study, we examined both the resins and their blends through crystallization analysis fractionation (CRYSTAF) to understand the PE sequence distribution and differential scanning calorimetry (DSC) to investigate the non-isothermal crystallization behavior of the bulk materials. Small-angle X-ray scattering (SAXS) was utilized to study the crystal packing structure. The results showed that the PE molecules in the blends crystallize at different rates during cooling, resulting in a complicated crystallization behavior characterized by nucleation, co-crystallization, and fractionation. We compared these behaviors to those of reference immiscible blends and found that the extent of the differences is related to the disparity in crystallizability between components. Furthermore, the lamellar packing of the blends is closely associated with their crystallization behaviors, and the crystalline structure varies significantly depending on the components’ compositions. Specifically, the lamellar packing of the HDPE/LLDPE and HDPE/LDPE blends is similar to that of the HDPE component owing to its strong crystallizability, while the lamellar packing of the LLDPE/LDPE blend is approximately an average of the two neat components. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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15 pages, 1157 KiB

Open AccessArticle

Comparative Evaluation of the Stiffness of Abaca-Fiber-Reinforced Bio-Polyethylene and High Density Polyethylene Composites

by Faust Seculi, Francesc X. Espinach, Fernando Julián, Marc Delgado-Aguilar, Pere Mutjé and Quim Tarrés

Polymers 2023, 15(5), 1096; https://doi.org/10.3390/polym15051096 - 22 Feb 2023

Cited by 11 | Viewed by 2440

Abstract

The use of bio-based matrices together with natural fibers as reinforcement is a strategy for obtaining materials with competitive mechanical properties, costs, and environmental impacts. However, bio-based matrices, unknown by the industry, can be a market entry barrier. The use of bio-polyethylene, which [...] Read more.

The use of bio-based matrices together with natural fibers as reinforcement is a strategy for obtaining materials with competitive mechanical properties, costs, and environmental impacts. However, bio-based matrices, unknown by the industry, can be a market entry barrier. The use of bio-polyethylene, which has properties similar to polyethylene, can overcome that barrier. In this study, composites reinforced with abaca fibers used as reinforcement for bio-polyethylene and high density polyethylene are prepared and tensile tested. A micromechanics analysis is deployed to measure the contributions of the matrices and reinforcements and to measure the evolution of these contributions regarding AF content and matrix nature. The results show that the mechanical properties of the composites with bio-polyethylene as a matrix were slightly higher than those of the composites with polyethylene as a matrix. It was also found that the contribution of the fibers to the Young’s moduli of the composites was susceptible to the percentage of reinforcement and the nature of the matrices. The results show that it is possible to obtain fully bio-based composites with mechanical properties similar to those of partially bio-based polyolefin or even some forms of glass fiber-reinforced polyolefin. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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17 pages, 5435 KiB

Open AccessArticle

Numerical Analysis of Curing Residual Stress and Strain in NEPE Propellant Grain

by Xiangyang Liu, Xuyuan Xie, Dongmo Zhou and Ruimin Wang

Polymers 2023, 15(4), 1019; https://doi.org/10.3390/polym15041019 - 17 Feb 2023

Cited by 3 | Viewed by 2111

Abstract

In order to investigate the formation mechanism of the residual stress and residual strain in a nitrate ester plasticized polyether (NEPE) propellant grain during the curing and cooling process, the temperature, curing degree and stress/strain of the NEPE propellant grain during the curing [...] Read more.

In order to investigate the formation mechanism of the residual stress and residual strain in a nitrate ester plasticized polyether (NEPE) propellant grain during the curing and cooling process, the temperature, curing degree and stress/strain of the NEPE propellant grain during the curing and cooling process were analyzed via ABAQUS finite element software. The results indicate that there is a temperature gradient in the NEPE propellant grain during curing at 50 °C. The maximum temperature difference is about 5 °C and the maximum temperature is located on the center of propellant grain. At the end of curing, the temperature in the interior of the grain tends to be uniform. The curing degree in the NEPE propellant grain during the curing process has the same trend as temperature. The residual stress/strain of the NEPE propellant grain during the curing and cooling down processes are mainly composed of curing shrinkage stress/strain in the curing process and thermal stress/strain in the cooling down process. The curing shrinkage stress and strain in the curing process account for 19% and 31% of the whole process, respectively. The thermal stress and thermal strain in cooling down process account for 75% and 69% of the whole process, respectively. The thermal stress and thermal strain in the curing process can nearly be ignored. The residual stress and residual strain calculated by the traditional method is larger than that obtained in this paper. The maximum deviation of the residual stress and residual strain are about 8% and 17%, respectively. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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14 pages, 3564 KiB

Open AccessArticle

Behavior of the Flexural Strength of Hemp/Polypropylene Composites: Evaluation of the Intrinsic Flexural Strength of Untreated Hemp Strands

by María E. Vallejos, Roberto J. Aguado, Ramón Morcillo-Martín, José A. Méndez, Fabiola Vilaseca, Quim Tarrés and Pere Mutjé

Polymers 2023, 15(2), 371; https://doi.org/10.3390/polym15020371 - 10 Jan 2023

Cited by 5 | Viewed by 2506

Abstract

The growing demand for plant fiber-reinforced composites offers new opportunities to compete against glass fiber (GF)-reinforced composites, but their performance must be assessed, revised, and improved as much as possible. This work reports on the production and the flexural strength of composites from [...] Read more.

The growing demand for plant fiber-reinforced composites offers new opportunities to compete against glass fiber (GF)-reinforced composites, but their performance must be assessed, revised, and improved as much as possible. This work reports on the production and the flexural strength of composites from polypropylene (PP) and hemp strands (20–50 wt.%), using maleic anhydride-grafted PP (MAPP) as a compatibilizer. A computational assessment of the reaction between cellulose and MAPP suggested the formation of only one ester bond per maleic anhydride unit as the most stable product. We determined the most favorable MAPP dosage to be 0.06 g per gram of fiber. The maximum enhancement in flexural strength that was attained with this proportion of MAPP was 148%, corresponding to the maximum fiber load. The modified rule of mixtures and the assumption of similar coupling factors for tensile and flexural strength allowed us to estimate the intrinsic flexural strength of hemp strands as 953 ± 116 MPa. While falling short of the values for sized GF (2415 MPa), the reinforcement efficiency parameter of the natural fibers (0.209) was found to be higher than that of GF (0.045). Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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24 pages, 7223 KiB

Open AccessEditor’s ChoiceReview

Review on Heat Generation of Rubber Composites

by Ying Liu, Wenduo Chen and Dazhi Jiang

Polymers 2023, 15(1), 2; https://doi.org/10.3390/polym15010002 - 20 Dec 2022

Cited by 16 | Viewed by 4397

Abstract

Rubber composites are extensively used in industrial applications for their exceptional elasticity. The fatigue temperature rise occurs during operation, resulting in a serious decline in performance. Reducing heat generation of the composites during cyclic loading will help to avoid substantial overheating that most [...] Read more.

Rubber composites are extensively used in industrial applications for their exceptional elasticity. The fatigue temperature rise occurs during operation, resulting in a serious decline in performance. Reducing heat generation of the composites during cyclic loading will help to avoid substantial overheating that most likely results in the degradation of materials. Herein, we discuss the two main reasons for heat generation, including viscoelasticity and friction. Influencing factors of heat generation are highlighted, including the Payne effect, Mullins effect, interface interaction, crosslink density, bond rubber content, and fillers. Besides, theoretical models to predict the temperature rise are also analyzed. This work provides a promising way to achieve advanced rubber composites with high performance in the future. Full article

(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)

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