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Polymers, Volume 17, Issue 2 (January-2 2025) – 6 articles

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19 pages, 15466 KiB

Open AccessArticle

Development of Bio-Based and Recyclable Epoxy Adhesives by Modification with Thermoplastic Polymers

by Riccardo Miranda, Marco Luciano, Vincenzo Fiore and Antonino Valenza

Polymers 2025, 17(2), 131; https://doi.org/10.3390/polym17020131 (registering DOI) - 8 Jan 2025

Abstract

This paper deals with the design of novel epoxy adhesives by incorporating thermoplastic polymers such as polyetherimide (PEI) and poly(ε-caprolactone) (PCL) into a bio-based and recyclable epoxy resin, known as Polar Bear. The adhesives were characterized by their mechanical (quasi-static and dynamic) and rheological properties, thermal stability, and adhesion properties in single-lap joints tested at three different temperatures (i.e., −55 °C, 23 °C, 80 °C). The experimental results indicated that low PEI content substantially improved the mechanical performance and toughness of the adhesive, while preserving good processability. Nonetheless, exceeding 3% weight percentage adversely affected the adhesives’ mechanical resistance and workability. Conversely, while PCL addition enhanced the adhesives’ viscosity, it also decreased mechanical performance. However, its eco-friendliness offers potential for sustainable adhesive applications. It is worth noting that regardless of temperature, the modified adhesives consistently outperformed the commercial epoxy adhesive (DP-460), used as reference, in single-lap shear joint tests. Additionally, both PEI- and PCL-modified epoxy adhesives have demonstrated recyclability through a simple acid-based process, enabling joint disassembly and recycling of the adhesive into a thermoplastic polymer. Overall, the modified adhesives represent a promising eco-friendly, high-performance alternative for structural applications, aligning with sustainable and circular practices. Full article

(This article belongs to the Special Issue Mechanical Behaviour of Polymeric-Based Systems Used in Engineering Applications)

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28 pages, 10411 KiB

Open AccessReview

Porosity Tunable Metal-Organic Framework (MOF)-Based Composites for Energy Storage Applications: Recent Progress

by Huddad Laeim, Vandana Molahalli, Pongthep Prajongthat, Apichart Pattanaporkratana, Govind Pathak, Busayamas Phettong, Natthawat Hongkarnjanakul and Nattaporn Chattham

Polymers 2025, 17(2), 130; https://doi.org/10.3390/polym17020130 (registering DOI) - 8 Jan 2025

Abstract

To solve the energy crisis and environmental issues, it is essential to create effective and sustainable energy conversion and storage technologies. Traditional materials for energy conversion and storage however have several drawbacks, such as poor energy density and inadequate efficiency. The advantages of MOF-based materials, such as pristine MOFs, also known as porous coordination polymers, MOF composites, and their derivatives, over traditional materials, have been thoroughly investigated. These advantages stem from their high specific surface area, highly adjustable structure, and multifunctional nature. MOFs are promising porous materials for energy storage and conversion technologies, according to research on their many applications. Moreover, MOFs have served as sacrificial materials for the synthesis of different nanostructures for energy applications and as support substrates for metals, metal oxides, semiconductors, and complexes. One of the most intriguing characteristics of MOFs is their porosity, which permits space on the micro- and meso-scales, revealing and limiting their functions. The main goals of MOF research are to create high-porosity MOFs and develop more efficient activation techniques to preserve and access their pore space. This paper examines the porosity tunable mixed and hybrid MOF, pore architecture, physical and chemical properties of tunable MOF, pore conditions, market size of MOF, and the latest development of MOFs as precursors for the synthesis of different nanostructures and their potential uses. Full article

(This article belongs to the Section Polymer Applications)

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16 pages, 5487 KiB

Open AccessArticle

A Micro Insight of Water Permeation in Polyurethane: Navigating for Water Transport

by Kai Chen, Zhenyuan Hang, Yongshen Wu, Chao Zhang and Yingfeng Wu

Polymers 2025, 17(2), 129; https://doi.org/10.3390/polym17020129 - 7 Jan 2025

Abstract

Polyurethane (PU) grouting materials are widely used in underground engineering rehabilitation, particularly in reinforcement and waterproofing engineering in deep-water environments. The long-term effect of complex underground environments can lead to nanochannel formation within PU, weakening its repair remediation effect. However, the permeation behavior and microscopic mechanisms of water molecules within PU nanochannels remain unclear. In this paper, a model combining PU nanochannels and water molecules was constructed, and the molecular dynamics simulations method was used to study the effects of water pressure and channel width on permeation behavior and microstructural changes. The results reveal a multi-stage, layered permeation process, with significant acceleration observed at water pressures above 3.08 MPa. Initially, water molecules accelerate but are then blocked by the energy barrier of PU nanochannels. After about 20 ps, water molecules overcome the potential barrier and enter the nanochannel, displaying a secondary acceleration effect, with the maximum permeation depth rises from 1.8 nm to 11.8 nm. As the channel width increases, the maximum permeation depth increases from 7.5 nm to 11.6 nm, with the rate of increase diminishing at larger widths. Moreover, higher water pressure and wider channels enhance the stratification effect. After permeation, a hydrophobic layer of approximately 0.5 nm thickness forms near the channel wall, with a density lower than that of the external water. The middle layer shows a density slightly higher than the external water, and the formation of hydrogen bonds between water molecules increases toward the channel center. Full article

(This article belongs to the Section Polymer Applications)

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17 pages, 3145 KiB

Open AccessArticle

A Multi-Phase Analytical Model for Effective Electrical Conductivity of Polymer Matrix Composites Containing Micro-SiC Whiskers and Nano-Carbon Black Hybrids

by Usama Umer, Mustufa Haider Abidi, Zeyad Almutairi and Mohamed K. Aboudaif

Polymers 2025, 17(2), 128; https://doi.org/10.3390/polym17020128 - 7 Jan 2025

Abstract

Multifunctional polymer composites containing micro/nano hybrid reinforcements have attracted intensive attention in the field of materials science and engineering. This paper develops a multi-phase analytical model for investigating the effective electrical conductivity of micro-silicon carbide (SiC) whisker/nano-carbon black (CB) polymer composites. First, CB nanoparticles are dispersed within the non-conducting epoxy to achieve a conductive CB-filled nanocomposite and its electrical conductivity is predicted. Some critical microstructures such as volume percentage and size of nanoparticles, and interphase characteristics surrounding the CB are micromechanically captured. Next, the electrical conductivity of randomly oriented SiC-containing composites in which the nanocomposite and whisker are considered as the matrix and reinforcement phases, respectively, is estimated. Influences of whisker aspect ratio and volume fraction on the effective electrical conductivity of the SiC/CB-containing polymer composites are explored. Some comparison studies are performed to validate the accuracy of the model. It is observed before the percolation threshold that the addition of nanoparticles with a uniform dispersion can improve the electrical conductivity of the polymer composites containing SiC/CB hybrids. Moreover, the results show that the electrical conductivity is more enhanced by the decrease in nanoparticle size. Interestingly, the composite percolation threshold is significantly reduced when SiC whiskers with a higher aspect ratio are added. This work will be favorable for the design of electro-conductive polymer composites with high performances. Full article

(This article belongs to the Special Issue Modeling of Polymer Composites and Nanocomposites)

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24 pages, 2159 KiB

Open AccessArticle

Critical Role of Rubber Functionalities on the Mechanical and Electrical Responses of Carbon Nanotube-Based Electroactive Rubber Composites

by Md Najib Alam, Siraj Azam, Jongwan Yun and Sang-Shin Park

Polymers 2025, 17(2), 127; https://doi.org/10.3390/polym17020127 - 7 Jan 2025

Abstract

Carbon nanomaterials, particularly carbon nanotubes (CNTs), are widely used as reinforcing fillers in rubber composites for advanced mechanical and electrical applications. However, the influence of rubber functionality and its interactions with CNTs remains underexplored. This study investigates electroactive elastomeric composites fabricated with CNTs in two common diene rubbers: natural rubber (NR) and acrylonitrile-butadiene rubber (NBR), each with distinct functionalities. For NR-based composites containing 2 vol% CNTs, mechanical properties, such as elastic modulus (2.24 MPa), tensile strength (12.48 MPa), and fracture toughness (26.92 MJ/m³), show significant improvements of 125%, 215%, and 164%, respectively, compared to unfilled rubber. Similarly, for NBR-based composites, the elastic modulus (5.46 MPa), tensile strength (13.47 MPa), and fracture toughness (82.89 MJ/m³) increase by 94%, 22%, and 65%, respectively, over the unfilled system. Although NBR-based composites exhibit higher mechanical properties, NR systems show more significant improvements, suggesting stronger chemical bonding between NR chains and CNTs, as evidenced by dynamic mechanical, X-ray diffraction, thermogravimetric, and thermodynamic analyses. The NBR-based composite at 1 vol% CNT content exhibits 261% higher piezoresistive strain sensitivity (GF = 65 at 0% ≤ Δε ≤ 200%) compared to the NR-based composite (GF = 18 at 0% ≤ Δε ≤ 200%). The highest gauge factor of 39,125 (1000% ≤ Δε ≤ 1220) was achieved in NBR-based composites with 1 vol% CNT content. However, 1.5 vol% CNT content in NBR provides better strain sensitivity and linearity than other composites. Additionally, NBR demonstrates superior electromechanical actuation properties, with 1317% higher actuation displacement and 276% higher electromechanical pressure compared to NR at an applied electric field of 12 kV. Due to the stronger chemical bonding between the rubber and CNT, NR-based composites are more suitable for dynamic mechanical applications. In contrast, NBR-based CNT composites are ideal for stretchable electromechanical sensors and actuators, owing to the high dielectric constant and polarizable functional groups in NBR. Full article

(This article belongs to the Special Issue Advances in Functional Rubber and Elastomer Composites II)

15 pages, 2099 KiB

Open AccessArticle

Development of an Analytical Model for Predicting the Shear Viscosity of Polypropylene Compounds

by Lukas Seifert, Lisa Leuchtenberger-Engel and Christian Hopmann

Polymers 2025, 17(2), 126; https://doi.org/10.3390/polym17020126 - 7 Jan 2025

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Abstract

The need for an efficient adaptation of existing polypropylene (PP) formulations or the creation of new formulations has become increasingly important in various industries. Variations in viscosity resulting from changes in raw materials, fillers, and additives can have a significant impact on the processing and quality of PP products. This study presents the development of an analytical model designed to predict the shear viscosity of complex PP blends. By integrating established mixing rules with novel fitting parameters, the model provides a systematic and efficient method for managing variability in PP formulations. Experimental data from binary and multi-component blends were used to validate the model, demonstrating high prediction accuracy over a range of shear rates. The proposed model serves as a valuable tool for compounders and manufacturers to optimise PP formulations and develop new recipes with consistent processing and product quality. Future work will include industrial-scale trials and further evaluation against advanced machine learning approaches. Full article

(This article belongs to the Special Issue Polymers for Circular Packaging Materials)

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