Polymers

12 pages, 2704 KiB

Open AccessArticle

Propolis Extract: Weaving Antioxidant Power into Polymeric Composites Through Electrospinning

by Sergiana dos Passos Ramos, Leonardo Ribeiro Bernardo, Monize Bürck, Laura Ordonho Líbero, Marcelo Assis and Anna Rafaela Cavalcante Braga

Polymers 2024, 16(22), 3230; https://doi.org/10.3390/polym16223230 - 20 Nov 2024

Viewed by 498

Abstract

The manufacture of composites with bioactive compounds represents a promising strategy for developing advanced materials in biomedical, food, and industrial applications. However, challenges such as stability, bioactivity retention, and controlled release hinder their effectiveness. Electrospinning emerges as a viable technique for encapsulating bioactive [...] Read more.

The manufacture of composites with bioactive compounds represents a promising strategy for developing advanced materials in biomedical, food, and industrial applications. However, challenges such as stability, bioactivity retention, and controlled release hinder their effectiveness. Electrospinning emerges as a viable technique for encapsulating bioactive compounds, offering advantages such as high surface area, porosity, and gradual release, which are critical for maintaining the bioactivity of embedded compounds. Regarding bioactive composition, propolis has been highlighted as a potential source and has great potential as a biopolymer ingredient due to its antioxidant and antimicrobial properties. This study analyzed the composition and antioxidant activity of three commercial propolis extracts to select the most suitable extract for fiber composite production using zein and polyethylene oxide (PEO), both recognized as safe. The characterization of the electrospun fibers, including morphology, thermal properties, and antioxidant release, was conducted through various analytical techniques. The findings highlight the effectiveness of electrospinning for developing composite materials with bioactive compounds, paving the way for innovations in antioxidant technologies across multiple sectors. Full article

(This article belongs to the Special Issue Polymer-Based Materials Incorporated with Bioactive Compounds)

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16 pages, 4840 KiB

Open AccessArticle

Dulcitol/Starch Systems as Shape-Stabilized Phase Change Materials for Long-Term Thermal Energy Storage

by Martyna Szatkowska and Kinga Pielichowska

Polymers 2024, 16(22), 3229; https://doi.org/10.3390/polym16223229 - 20 Nov 2024

Viewed by 312

Abstract

In recent years, there has been an increasing interest in phase change materials (PCM) based on dulcitol and other sugar alcohols. These materials have almost twice as large latent heat of fusion as other organic materials. Sugar alcohols are relatively cheap, and they [...] Read more.

In recent years, there has been an increasing interest in phase change materials (PCM) based on dulcitol and other sugar alcohols. These materials have almost twice as large latent heat of fusion as other organic materials. Sugar alcohols are relatively cheap, and they can undergo cold crystallization, which is crucial for long-term thermal energy storage. The disadvantage of dulcitol and other sugar alcohols is the solid–liquid phase transition. As a result, the state of matter of the material and its volume change, and in the case of materials modified with microparticles or nanoparticles, sedimentation of additives in liquid PCM can occur. In this study, we obtained shape-stable phase change materials (SSPCM) by co-gelation of starch and dulcitol. To characterize the samples obtained, differential scanning calorimetry (DSC), step-mode DSC, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used, and they were also used to test for shape stabilization. The results show that the obtained systems have great potential as shape-stabilized phase change materials. The sample dulcitol/starch with a 50:50 ratio exhibited the highest heat of cold crystallization, up to 52.90 J/g, while the heat of melting was 126.16 J/g under typical DSC measuring conditions. However, depending on the applied heating program, the heat of cold crystallization can even reach 125 J/g. The thermal stability of all compositions was higher than the phase change temperature, with only 1% mass loss occurring at temperatures above 200 °C, while the phase change occurred at a maximum of 190 °C. Full article

(This article belongs to the Special Issue Natural Polymeric Materials: Polysaccharides and Carbohydrate Polymers)

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18 pages, 11153 KiB

Open AccessArticle

The Effect of Synthetic Zeolite on the Curing Process and the Properties of the Natural Rubber-Based Composites

by Sonja Stojanov, Olga Govedarica, Marija Milanović, Julijana Žeravica, Berta Barta Hollo, Dragan Govedarica and Mirjana Jovičić

Polymers 2024, 16(22), 3228; https://doi.org/10.3390/polym16223228 - 20 Nov 2024

Viewed by 239

Abstract

Zeolites, known for their unique structural and catalytic properties, are added to the natural rubber matrix to investigate their influence on the vulcanization process and the resultant properties of composites. The natural rubber-based composites were masticated with 4A synthetic zeolite (0, 5, 10, [...] Read more.

Zeolites, known for their unique structural and catalytic properties, are added to the natural rubber matrix to investigate their influence on the vulcanization process and the resultant properties of composites. The natural rubber-based composites were masticated with 4A synthetic zeolite (0, 5, 10, 15, 20, and 30 phr). The curing of the rubber compounds was monitored on a moving die rheometer at 150 °C. The isothermal DSC method was also used to study the curing process at 150 °C, 160 °C, and 170 °C. Based on the obtained results, it is assumed that there is an interaction between the components of the curing system and the surface of the zeolite particle, and that is why the vulcanization reaction starts earlier with an increase in zeolite in the rubber mixture. This underscores the significant role of zeolite in accelerating the curing reaction of natural rubber-based compounds. The composites were vulcanized in a press at 150 °C for 15 min. The chemical structure was analyzed using FTIR, and the sample morphology was examined using SEM. The degree of swelling in toluene and distilled water was determined. The tensile strength values, modulus of elasticity at 100% and 300% elongation, and elongation at break were measured using a universal testing machine. Hardness was assessed according to the Shore A scale. With a small addition of zeolite (up to 10 phr), there is no significant change in the tensile strength values. However, adding a considerable amount of zeolite to a natural rubber matrix results in a deterioration of the tested mechanical properties. It can be assumed that with large proportions of zeolite 4A MS in the composites, the mechanical properties deteriorated due to increased porosity. The amount of added zeolite affects the initial stages of thermal decomposition of the examined samples and the rest after the analysis at a temperature of 500 °C. Full article

(This article belongs to the Section Biobased and Biodegradable Polymers)

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15 pages, 4009 KiB

Open AccessArticle

Nanostructure-Dependent Electrical Conductivity Model Within the Framework of the Generalized Effective Medium Theory Applied to Poly(3-hexyl)thiophene Thin Films

by Henryk Bednarski, Ayman A. A. Ismail, Marcin Godzierz, Andrzej Marcinkowski, Muhammad Raheel Khan, Bożena Jarząbek, Barbara Hajduk and Pallavi Kumari

Polymers 2024, 16(22), 3227; https://doi.org/10.3390/polym16223227 - 20 Nov 2024

Viewed by 320

Abstract

One of the key parameters characterizing the microstructure of a layer is its degree of order. It can be determined from optical studies or X-ray diffraction. However, both of these methods applied to the same layer may give different results because, for example, [...] Read more.

One of the key parameters characterizing the microstructure of a layer is its degree of order. It can be determined from optical studies or X-ray diffraction. However, both of these methods applied to the same layer may give different results because, for example, aggregates may contribute to the amorphous background in XRD studies, while in optical studies, they may already show order. Because we are usually interested in the optical and/or electrical properties of the layers, which in turn are closely related to their dielectric properties, determining the optical order of the layers is particularly important. In this work, the microstructure, optical properties and electrical conductivity of poly(3-hexyl)thiophene layers were investigated, and a model describing the electrical conductivity of these layers was proposed. The model is based on the generalized theory of the effective medium and uses the equation from the percolation theory of electrical conductivity for the effective medium of a mixture of two materials. The results indicate a key role of the aggregate size and limited conductivity of charge carriers, mainly due to structural imperfections that manifest themselves as an increase in the number of localized states visible in the subgap absorption near the optical absorption edge. The critical value of the order parameter and the corresponding values of the Urbach energy, excitonic linewidth and band gap energy are determined. Full article

(This article belongs to the Special Issue Polymer Thin Films: Synthesis, Characterization and Applications)

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21 pages, 7368 KiB

Open AccessArticle

Study on the Effect of SBS/HVA/CRM Composite-Modified Asphalt on the Performance of Recycled Asphalt Mixtures

by Haoming Li, Hongkui Wang, Junning Lin, Jiangang Yang and Yuquan Yao

Polymers 2024, 16(22), 3226; https://doi.org/10.3390/polym16223226 - 20 Nov 2024

Viewed by 239

Abstract

To investigate the feasibility of composite modification techniques in improving the performance of recycled asphalt mixtures, in this study, the high-viscosity agent (HVA) and crumb-rubber materials (CRM) were used to modify asphalt with a styrene-butadiene-styrene block copolymer (SBS), in order to prepare SBS-HVA [...] Read more.

To investigate the feasibility of composite modification techniques in improving the performance of recycled asphalt mixtures, in this study, the high-viscosity agent (HVA) and crumb-rubber materials (CRM) were used to modify asphalt with a styrene-butadiene-styrene block copolymer (SBS), in order to prepare SBS-HVA and SBS-CRM composite-modified asphalts. The virgin asphalt mixtures, as well as three asphalt types of recycled asphalt mixtures with 50% reclaimed asphalt pavement (RAP) content, were designed. The optimal asphalt content of the four types of asphalt mixtures was analyzed, and the rutting test, the asphalt bond strength test, the moisture-induced sensitivity test, and the low-temperature cracking resistance test were conducted to investigate the performance of the four types of asphalt mixtures. The results showed that the higher the asphalt kinematic viscosity, the higher the optimum asphalt content of the asphalt mixtures under the same air voids. HVA significantly improves the adhesion between SBS-modified asphalt and aggregate under dry conditions, while SBS-CRM composite-modified asphalt performs similarly to SBS-modified asphalt. Before and after water immersion, the degree of pull-out strength decay between the asphalts and aggregates follows the sequence of SBS-CRM- > SBS- > SBS-HVA-modified asphalts. Additionally, the residual pull-out work follows the sequence of SBS-HVA- > SBS-CRM- > SBS-modified asphalt. SBS-CRM composite-modified asphalt can significantly improve the moisture sensitivity of recycled asphalt mixtures, as well as low-temperature cracking resistance, while SBS-CRM composite-modified asphalt only improves the low-temperature cracking resistance of recycled asphalt mixtures, and does not improve the moisture sensitivity. Based on the results, it is recommended to select the appropriate composite modification method based on the climate and loading conditions, to maximize the value of asphalt, and to achieve sustainable and durable pavement. Full article

(This article belongs to the Special Issue Polymer Modified Asphalt for Sustainable Pavements)

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24 pages, 3609 KiB

Open AccessArticle

On the Activation Energy of Termination in Radical Polymerization, as Studied at Low Conversion

by Majed M. Alghamdi and Gregory T. Russell

Polymers 2024, 16(22), 3225; https://doi.org/10.3390/polym16223225 - 20 Nov 2024

Viewed by 308

Abstract

The chain-length-dependent nature of the termination reaction in radical polymerization (RP) renders the overall termination rate coefficient, <k_t>, a complex parameter in the usual situation where the radical chain-length distribution is non-uniform. This applies also for the activation energy of [...] Read more.

The chain-length-dependent nature of the termination reaction in radical polymerization (RP) renders the overall termination rate coefficient, <k_t>, a complex parameter in the usual situation where the radical chain-length distribution is non-uniform. This applies also for the activation energy of termination, E_a(<k_t>), which we subject to detailed mechanistic investigation for the first time. The experimental side of this work measures E_a(<k_t>) for the dilute-solution, low-conversion, chemically initiated homopolymerization of styrene (ST), methyl methacrylate (MMA), butyl methacrylate, and dodecyl methacrylate. Values of 25–39 kJ mol⁻¹ are obtained, consistent with strong chain-length-dependent termination (CLDT) for short chains. On other hand, the reanalysis of analogous bulk polymerization data for ST and MMA finds E_a(<k_t>) values of 18–24 kJ mol⁻¹, consistent with weak CLDT for long chains. Both these results are as expected from the so-called composite model for CLDT. A simple analytic framework for understanding and predicting E_a(<k_t>) values is presented for the standard RP situation of continuous initiation. All the results of this work can be rationalized via this framework, which clearly establishes that E_a(<k_t>) is determined by far more than just the E_a of radical diffusion. This framework is extended to activation energy for the number-average degree of polymerization, E_a(DP_n), which we measure and successfully scrutinize via our CLDT model. In the final section of this work, we make interesting, testable predictions about E_a(<k_t>) and/or E_a(DP_n) in various RP systems of different natures to those studied here, most notably, systems involving acrylates, continuous photoinitiation, or dominant chain transfer. Full article

(This article belongs to the Section Polymer Chemistry)

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18 pages, 6762 KiB

Open AccessArticle

Influence of Hydroxyapatite and Gelatin Content on Crosslinking Dynamics and HDFn Cell Viability in Alginate Bioinks for 3D Bioprinting

by Lina Maria Anaya-Sampayo, Nelly S. Roa, Constanza Martínez-Cardozo, Dabeiba Adriana García-Robayo and Luis M. Rodríguez-Lorenzo

Polymers 2024, 16(22), 3224; https://doi.org/10.3390/polym16223224 - 20 Nov 2024

Viewed by 372

Abstract

This study investigates how varying concentrations of hydroxyapatite (OHAp) and the addition of gelatin influence the ionic crosslinking time of alginate-based bioinks, as well as the shear stress experienced by neonatal human dermal fibroblasts (HDFn) during extrusion. These factors are crucial for validating [...] Read more.

This study investigates how varying concentrations of hydroxyapatite (OHAp) and the addition of gelatin influence the ionic crosslinking time of alginate-based bioinks, as well as the shear stress experienced by neonatal human dermal fibroblasts (HDFn) during extrusion. These factors are crucial for validating bioinks and developing viable 3D bioprinted models. Four bioink formulations were created with a 50/50 ratio of alginate to gelatin, incorporating different calcium phosphate concentrations (0%, 1%, 5%, and 10%). The bioink compositions were confirmed via Fourier Transform Infrared (FT-IR) spectroscopy, and rheological analyses evaluated their pseudoplastic behavior, printability limits, and crosslinking times. The results indicated a notable increase in the consistency index (k) from 0.32 for the 0% OHAp formulation to 0.48 for the 10% OHAp formulation, suggesting improved viscoelastic properties. The elastic modulus recovery after crosslinking rose significantly from 245 Pa to 455 Pa. HDFn experienced a shear stress of up to 1.5436 Pa at the tip during extrusion with the HDFn-ALG5-GEL5-OHAp10 bioinks, calculated at a shear rate as low as 2 s⁻¹. Viability assays confirmed over 70% cell viability 24 h post-extrusion and 92% viability after 7 days for the 10% OHAp formulation, highlighting the potential of hydroxyapatite-enhanced bioinks in tissue engineering applications. Full article

(This article belongs to the Special Issue Functional Bio-Based Polymers and Composites for Multipurpose Applications)

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17 pages, 4244 KiB

Open AccessArticle

Plasma Surface Modification of the Inner Wall of Montgomery’s Tracheal Implant (T-Tube)

by Konstantin G. Kostov, Ananias A. Barbosa, Fellype do Nascimento, Paulo F. G. Cardoso, Ana C. P. L. Almeida, Antje Quade, Daniel Legendre, Luiz R. O. Hein, Diego M. Silva and Cristiane Y. Koga-Ito

Polymers 2024, 16(22), 3223; https://doi.org/10.3390/polym16223223 - 20 Nov 2024

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Abstract

Tracheal stenosis (i.e., the abnormal narrowing of the trachea) can occur due to a variety of inflammatory and infectious processes as well as due to therapeutic procedures undertaken by the patient. The most common cause of tracheal obstruction in patients has been prolonged [...] Read more.

Tracheal stenosis (i.e., the abnormal narrowing of the trachea) can occur due to a variety of inflammatory and infectious processes as well as due to therapeutic procedures undertaken by the patient. The most common cause of tracheal obstruction in patients has been prolonged intubation. Depending on the extent of the stenosis and its exact location, the surgical insertion of a tracheal stent is the only option for addressing this issue. The Montgomery T-tube implant is a valuable tracheal stent made from medical-grade silicone that provides a functional airway while supporting the tracheal mucosa. However, its performance is subject to gradual deterioration due to biofilm colonization of the stent’s inner wall, which may explain the discomfort claimed by many patients and clinical failures. Recently, cold atmospheric plasmas (CAPs) have emerged as an alternative technology to many conventional medical procedures, such as wound healing, skin treatment, decontamination of medical devices, etc. Here, we report on plasma-induced surface modification of the inner wall of a T-tube implant, considering future biomedical applications. To generate the plasma, we employed a cold atmospheric pressure plasma jet in gas helium, which was directly inserted into the T-tube implant. To assess the treatment uniformity, the degree of surface modification and its extension along the stent’s inner wall was analyzed using different process parameters. Full article

(This article belongs to the Section Polymer Processing and Engineering)

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20 pages, 7227 KiB

Open AccessArticle

A Physics-Guided Machine Learning Model for Predicting Viscoelasticity of Solids at Large Deformation

by Bao Qin and Zheng Zhong

Polymers 2024, 16(22), 3222; https://doi.org/10.3390/polym16223222 - 20 Nov 2024

Viewed by 258

Abstract

Physics-guided machine learning (PGML) methods are emerging as valuable tools for modelling the constitutive relations of solids due to their ability to integrate both data and physical knowledge. While various PGML approaches have successfully modeled time-independent elasticity and plasticity, viscoelasticity remains less addressed [...] Read more.

Physics-guided machine learning (PGML) methods are emerging as valuable tools for modelling the constitutive relations of solids due to their ability to integrate both data and physical knowledge. While various PGML approaches have successfully modeled time-independent elasticity and plasticity, viscoelasticity remains less addressed due to its dependence on both time and loading paths. Moreover, many existing methods require large datasets from experiments or physics-based simulations to effectively predict constitutive relations, and they may struggle to model viscoelasticity accurately when experimental data are scarce. This paper aims to develop a physics-guided recurrent neural network (RNN) model to predict the viscoelastic behavior of solids at large deformations with limited experimental data. The proposed model, based on a combination of gated recurrent units (GRU) and feedforward neural networks (FNN), utilizes both time and stretch (or strain) sequences as inputs, allowing it to predict stress dependent on time and loading paths. Additionally, the paper introduces a physics-guided initialization approach for GRU–FNN parameters, using numerical stress–stretch data from the generalized Maxwell model for viscoelastic VHB polymers. This initialization is performed prior to training with experimental data, helping to overcome challenges associated with data scarcity. Full article

(This article belongs to the Special Issue Mechanical Response Characteristics and Performance Evaluation of Polymer Materials)

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22 pages, 9163 KiB

Open AccessArticle

Electrospinning of Poly-3-Hydroxybutyrate Fibers Loaded with Chlorophyll for Antibacterial Purposes

by Polina M. Tyubaeva, Ivetta A. Varyan, Roman R. Romanov, Vasily A. Merzlikin, Olga A. Gruznova, Dmitry V. Gruznov, Nikolay I. Popov, Gulizar Sh. Shcherbakova, Ekaterina N. Shuteeva, Irina P. Chesnokova, Anton V. Lobanov and Anatoly A. Olkhov

Polymers 2024, 16(22), 3221; https://doi.org/10.3390/polym16223221 - 20 Nov 2024

Viewed by 224

Abstract

This work is devoted to the creation of biocompatible fibrous materials with a high antimicrobial effect based on poly-3-hydroxybutyrate (PHB) and chlorophyll (Chl). The data obtained show the possibility of obtaining fibrous materials from PHB and Chl by electrospinning methods. The obtained electrospun [...] Read more.

This work is devoted to the creation of biocompatible fibrous materials with a high antimicrobial effect based on poly-3-hydroxybutyrate (PHB) and chlorophyll (Chl). The data obtained show the possibility of obtaining fibrous materials from PHB and Chl by electrospinning methods. The obtained electrospun matrices were investigated by the SEM, DSC and FTIR methods. Various key properties of the matrices were evaluated, including hydrophilicity and mechanical strength, as well as photodynamic and light-dependent antimicrobial effects against the conditionally pathogenic microorganism Staphylococcus aureus. The results demonstrate a significant improvement in electrospinning properties for a concentration of 0.5% Chl and a reduction in fiber formation defects, as well as an increase in the strength of nonwovens. It was found that the antimicrobial potential of Chl-PHB (with concentrations of Chl of 1.25 and 1.5%) is higher than that of Chl in free form. It was also determined that irradiation increases the inhibitory effect of Chl, both in free form and in the form of a complex with a polymer. Full article

(This article belongs to the Special Issue Biopolymer Composites for Biomedicine Applications)

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22 pages, 3075 KiB

Open AccessArticle

Co-Optimization of Mechanical Properties and Radiopacity Through Radiopaque Filler Incorporation for Medical Tubing Applications

by Alan Nugent, Joseph Molloy, Maurice Kelly and Declan Mary Colbert

Polymers 2024, 16(22), 3220; https://doi.org/10.3390/polym16223220 - 20 Nov 2024

Viewed by 312

Abstract

Medical tubing, particularly cardiovascular tubing, is a critical area of research where continuous improvements are necessary to advance medical devices and improve patient care. While polymers are fundamental for these applications, on their own they present several limitations such as insufficient X-ray contrasting [...] Read more.

Medical tubing, particularly cardiovascular tubing, is a critical area of research where continuous improvements are necessary to advance medical devices and improve patient care. While polymers are fundamental for these applications, on their own they present several limitations such as insufficient X-ray contrasting capabilities. As such, polymer composites utilizing radiopaque fillers are a necessity for this application. For medical tubing in vivo, radiopacity is a crucial parameter that virgin polymers alone fall short in achieving due to limited X-ray absorption. To address this shortcoming, inorganic radiopaque fillers such as barium sulphate (BaSO₄) and bismuth oxychloride (BiOCl) are incorporated into polymer matrices to increase the X-ray contrast of the manufactured tubing. It is also known, however, that the incorporation of these fillers can affect the mechanical, physical, and thermal properties of the finished product. This research evaluated the impact of incorporating the two aforementioned fillers into Pebax^® 6333 SA01 MED at three different loading levels (10, 20, and 30 wt.%) on the physical, thermal, and mechanical properties of the composite. Composites were prepared by twin screw extrusion and injection molding followed by characterization of the mechanical (tensile, impact, and flexural), thermal (DSC), rheological (MFI), and physical (density and ash content) properties. The performed analysis shows that BiOCl enhanced the aesthetic properties, increased stiffness, and maintained flexibility while having minimal impact on the tensile and impact properties. When comparing BiOCl to BaSO₄-filled composites, it was clear that depending on the application of the polymer composite, BiOCl may provide more desirable properties. The study highlights the importance of optimizing filler concentration and processing conditions to achieve desired composite properties for specific medical applications. Full article

(This article belongs to the Section Polymer Applications)

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23 pages, 7207 KiB

Open AccessArticle

Water-Soluble Polyglycidol-Grafted Ladder Calix Resorcinarene Oligomers with Open Chain and Cyclic Topologies: Synthesis, Characteristics, and Biological Evaluation

by Hristo Penchev, Erik Dimitrov, Christo Novakov, Emi Haladjova, Ralitsa Veleva, Veselina Moskova-Doumanova, Tanya Topouzova-Hristova and Stanislav Rangelov

Polymers 2024, 16(22), 3219; https://doi.org/10.3390/polym16223219 - 20 Nov 2024

Viewed by 366

Abstract

Ladder oligomers containing calixarene skeletons in the main chain—calix[4]resorcinarene (CRA) ladder macromolecules with open chain and cyclic macromolecules with double ring-like (Noria-type) topologies—bring particular research attention as functional materials with various applications. However, there is still a remarkable lack of studies into the [...] Read more.

Ladder oligomers containing calixarene skeletons in the main chain—calix[4]resorcinarene (CRA) ladder macromolecules with open chain and cyclic macromolecules with double ring-like (Noria-type) topologies—bring particular research attention as functional materials with various applications. However, there is still a remarkable lack of studies into the synthesis of fully water-soluble derivatives of these interesting macromolecules. Research on this topic would allow their bio-based research and application niche to be at least revealed. In the present study, a strategy for the synthesis of water-soluble polyglycidol-derivatized calix resorcinarene ladder oligomers with open chain and cyclic structures is introduced. A grafting from approach was used to build branched or linear polyglycidol chains from the ladder scaffolds. The novel structures were synthesized in quantitative yields and fully characterized by NMR, FTIR and UV–vis spectroscopy, gel permeation chromatography, MALDI-TOF mass spectrometry, analytical ultracentrifugation, and static light scattering to obtain the molar mass characteristics and composition. The biocompatibility and toxicity of the two polyglycidol-derivatized oligomers were investigated and the concentration dependence of the survival of three cell lines of human origin determined. The selective apoptosis effect at relatively low dissolve concentrations toward two kinds of cancerous cell lines was found. Full article

(This article belongs to the Special Issue Synthesis, Design, Preparation and Processing of Functional Polymer Composites)

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15 pages, 4896 KiB

Open AccessArticle

Enhanced Dielectric Properties and Antibacterial Activity of Natural Rubber by Modification with Poly(Acrylic Acid-Co-Acrylamide) Incorporating Silver Nanoparticles and Titanium Dioxide

by Supharat Inphonlek, Supawat Kotchapradit, Boonruang Marungsri, Yupaporn Ruksakulpiwat and Chaiwat Ruksakulpiwat

Polymers 2024, 16(22), 3218; https://doi.org/10.3390/polym16223218 - 20 Nov 2024

Viewed by 343

Abstract

This work aims to enhance natural rubber’s dielectric properties and antibacterial activity by incorporating silver nanoparticles and titanium dioxide. Deproteinized natural rubber (DPNR) was modified through the graft copolymerization of acrylic acid and acrylamide using N′, N′-Methylenebisacrylamide as a crosslinking agent, resulting in [...] Read more.

This work aims to enhance natural rubber’s dielectric properties and antibacterial activity by incorporating silver nanoparticles and titanium dioxide. Deproteinized natural rubber (DPNR) was modified through the graft copolymerization of acrylic acid and acrylamide using N′, N′-Methylenebisacrylamide as a crosslinking agent, resulting in poly(acrylic acid-co-acrylamide)-modified, deproteinized natural rubber (MDPNR). This modification facilitated coordination with silver ions and interaction with titanium dioxide. Silver nanoparticles were generated under heat and pressure. Modified natural rubber composites containing silver nanoparticles and titanium dioxide (MDPNR/Ag-TiO₂) were prepared. Scanning electron microscopy (SEM) revealed well-distributed silver in the modified natural rubber matrix, while agglomeration of titanium dioxide was observed at a high loading. Both MDPNR and MDPNR/Ag-TiO₂ showed high thermal stability compared to DPNR. The MDPNR/Ag-TiO₂ composites exhibited higher Tg and lower tan δ, indicating higher stiffness due to the restriction of chain movement compared to that in MDPNR. DPNR exhibited a low dielectric constant, enhanced by poly(acrylic acid-co-acrylamide) modification and silver nanoparticle/titanium dioxide incorporation. Incorporating 0.5 phr of AgNO₃ and 2.5 phr of TiO₂ in the composites increased the dielectric constant by 1.33 times compared to that of MDPNR. MDPNR showed no antibacterial activity, while the MDPNR/Ag-TiO₂ composites exhibited promising antibacterial activity against Staphylococcus aureus and Escherichia coli. Full article

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

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20 pages, 2942 KiB

Open AccessSystematic Review

Natural Antibacterial Compounds with Potential for Incorporation into Dental Adhesives: A Systematic Review

by Ana Catarina Sousa, Paulo Mascarenhas, Mário Polido and Joana Vasconcelos e Cruz

Polymers 2024, 16(22), 3217; https://doi.org/10.3390/polym16223217 - 20 Nov 2024

Viewed by 268

Abstract

Dental adhesives are essential in modern restorative dentistry and are constantly evolving. However, challenges like secondary caries from bacterial infiltration at the adhesive–tooth interface persist. While synthetic antibacterial agents in adhesives show promise, safety concerns have shifted interest toward natural options that are [...] Read more.

Dental adhesives are essential in modern restorative dentistry and are constantly evolving. However, challenges like secondary caries from bacterial infiltration at the adhesive–tooth interface persist. While synthetic antibacterial agents in adhesives show promise, safety concerns have shifted interest toward natural options that are biocompatible, sustainable, and effective. Therefore, this study evaluated whether natural antibacterial compounds in dental adhesives can provide effective antimicrobial activity without compromising their integrity. This systematic review followed PRISMA 2020 statement guidelines. Four databases were screened, PubMed, Scopus, EMBASE, and Web of Science, without language or publication date restrictions until July 2024. The selection criteria were in vitro studies in which natural antimicrobial substances were incorporated into dental adhesives and the resulting composites were tested for their antibacterial and physicochemical properties. A quality assessment was conducted on the selected studies. Most of the studies reviewed reported significant antibacterial activity while retaining the adhesive’s integrity, generally achieved with lower concentrations of the natural agents. Higher concentrations increase the antimicrobial effectiveness but negatively impact the adhesive’s properties. This review highlights the promising role of natural antibacterial compounds in enhancing the functionality of dental adhesives while also pointing to the need for continued research to address current challenges. Full article

(This article belongs to the Special Issue Advanced Polymer-Based Materials for Dental Applications)

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9 pages, 3960 KiB

Open AccessCommunication

Reprocessable Epoxy–Anhydride Resin Enabled by a Thermally Stable Liquid Transesterification Catalyst

by Huan Liang, Wendi Tian, Hongtu Xu, Yuzhen Ge, Yang Yang, Enjian He, Zhijun Yang, Yixuan Wang, Shuhan Zhang, Guoli Wang, Qiulin Chen, Yen Wei and Yan Ji

Polymers 2024, 16(22), 3216; https://doi.org/10.3390/polym16223216 - 20 Nov 2024

Viewed by 265

Abstract

Introducing dynamic ester bonds into epoxy–anhydride resins enhances the reprocessability of the crosslinked network, facilitated by various types of transesterification catalysts. However, existing catalysts, such as metal salts and organic molecules, often struggle with dispersion, volatility, or structural instability issues. Here, we propose [...] Read more.

Introducing dynamic ester bonds into epoxy–anhydride resins enhances the reprocessability of the crosslinked network, facilitated by various types of transesterification catalysts. However, existing catalysts, such as metal salts and organic molecules, often struggle with dispersion, volatility, or structural instability issues. Here, we propose to solve such problems by incorporating a liquid-state, thermally stable transesterification catalyst into epoxy resins. This catalyst, an imidazole derivative, can be uniformly dispersed in the epoxy resin at room temperature. In addition, it shows high-temperature structural stability above at least 200 °C as the synergistic effects of the electron-withdrawing group and steric bulk can be leveraged. It can also effectively promote transesterification at elevated temperatures, allowing for the effective release of shear stress. This property enables the thermal recycling and reshaping of the fully crosslinked epoxy–anhydride resin. This strategy not only enhances the functionality of epoxy resins but also broadens their applicability across various thermal and mechanical environments. Full article

(This article belongs to the Special Issue Feature Papers in Polymer Science and Technology)

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17 pages, 7016 KiB

Open AccessArticle

Sugarcane-Based Polyethylene Biocomposite Reinforced with Organophilic Montmorillonite Clay: Experimental Characterization and Performance Evaluation

by Gustavo H. A. Barbalho, José J. S. Nascimento, Lucineide B. Silva, João M. P. Q. Delgado, Jackson B. Simões, Vital A. B. Oliveira, Luis E. A. Santos, Maria J. Figueiredo, Francisco S. Chaves and Antonio G. B. Lima

Polymers 2024, 16(22), 3215; https://doi.org/10.3390/polym16223215 - 20 Nov 2024

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Abstract

With the growing human awareness of trying to reduce the environmental impact in today’s world, the development of new sustainably based materials has been the increasing focus of industry and academia. Biocomposites are environmentally friendly materials produced from raw materials synthesized from renewable [...] Read more.

With the growing human awareness of trying to reduce the environmental impact in today’s world, the development of new sustainably based materials has been the increasing focus of industry and academia. Biocomposites are environmentally friendly materials produced from raw materials synthesized from renewable sources. In this sense, this work aims to characterize and evaluate the mechanical and thermal performances of biocomposites manufactured from a thermoplastic matrix of high-density bioethylene and obtained from ethanol produced from sugarcane and reinforced with organophilic montmorillonite clay. For this, polyethylene grafted with maleic anhydride (PE-g-MA) was used as a compatibilizer. Dry biocomposites with 1, 3, and 5% organophilic montmorillonite clay, by weight, were subjected to structural (FTIR and DRX), thermal (DSC), thermogravimetric (TG/DTG), thermodynamic–mechanical (DMA), morphological (SEM and MET), and mechanical (tensile, flexural, impact, and shore D hardness tests) characterizations. The DMA experiments were carried out within the viscoelastic region of the polymer. From the obtained results, we notice that, in general, there was an increase in the properties of high-density biopolyethylene (B-HDPE) (without compromising its processability), and therefore, the automotive application of biocomposites compatible with PE-g-MA, containing low levels of organophilic montmorillonite clay, is recommended. Full article

(This article belongs to the Section Biobased and Biodegradable Polymers)

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20 pages, 3292 KiB

Open AccessArticle

Sb(III) Removal by Granular Adsorbent Synthesized with Iron-Containing Water Treatment Residuals and Chitosan

by Huiping Zeng, Yuwei Zeng, He Xu, Siqi Sun, Jie Zhang and Dong Li

Polymers 2024, 16(22), 3214; https://doi.org/10.3390/polym16223214 - 20 Nov 2024

Viewed by 239

Abstract

In this study, chitosan and iron-containing water treatment residues were used to prepare a chitosan/Fe-sludge particle adsorbent (CHFS) via the embedding method for Sb(III) removal. Various technologies were applied to characterize the CHFS, and batch experiments were used to investigate its adsorption properties. [...] Read more.

In this study, chitosan and iron-containing water treatment residues were used to prepare a chitosan/Fe-sludge particle adsorbent (CHFS) via the embedding method for Sb(III) removal. Various technologies were applied to characterize the CHFS, and batch experiments were used to investigate its adsorption properties. The results show that CHFS adsorbents are amorphous and have a specific surface area (119.95 m²/g), both beneficial for adsorption. pH and ionic strength have no impact on the adsorption. Sb(III) adsorption on CHFS occurs spontaneously and endothermically. Sb(III) adsorption by CHFS matches the pseudo-second-order kinetic model and the Langmuir model better, with a maximum adsorption capacity of 24.38 mg/g. The primary adsorption mechanism for Sb(III) is the inner sphere complexation between the Sb and Fe–O bond, while other adsorption mechanisms include chelation, pore filling, and hydrogen bonding. This study offers a reference for antimony removal and resource utilization of iron sludge. Full article

(This article belongs to the Special Issue Chitosan-Based Materials for Water and Wastewater Treatment)

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15 pages, 5929 KiB

Open AccessArticle

The Confinement Behavior and Mechanistic Insights of Organic Phase Change Material Encapsulated in Wood Morphology Genetic Nanostructures for Thermal Energy Storage

by Yang Meng, Yanping Jiang, Yuhui Chen and Jiangyu Zhang

Polymers 2024, 16(22), 3213; https://doi.org/10.3390/polym16223213 - 20 Nov 2024

Viewed by 363

Abstract

Wood, a renewable and abundant biomass resource, holds substantial promise as an encapsulation matrix for thermal energy storage (TES) applications involving phase change materials (PCMs). However, practical implementations often reveal a disparity between observed and theoretical phase change enthalpy values of wood-derived composite [...] Read more.

Wood, a renewable and abundant biomass resource, holds substantial promise as an encapsulation matrix for thermal energy storage (TES) applications involving phase change materials (PCMs). However, practical implementations often reveal a disparity between observed and theoretical phase change enthalpy values of wood-derived composite PCMs (CPCMs). This study systematically explores the confinement behavior of organic PCMs encapsulated in a delignified balsa wood matrix with morphology genetic nanostructure, characterized by a specific surface area of 25.4 ± 1.1 m²/g and nanoscale pores averaging 2.2 nm. Detailed thermal performance evaluations uncover distinct phase change behaviors among various organic PCMs, influenced by the unique characteristics of functional groups and carbon chain lengths. The encapsulation mechanism is primarily dictated by host–guest interactions, which modulate PCM molecular mobility through hydrogen bonding and spatial constraints imposed by the hierarchical pore structure of the wood. Notably, results demonstrate a progressive enhancement of nanoconfinement effects, evidencing a transition from octadecane to stearic acid, further supported by density functional theory (DFT) calculations. This research significantly advances the understanding of nanoconfinement mechanisms in wood-derived matrices, paving the way for the development of high-performance, shape-stabilized composite PCMs that are essential for sustainable thermal energy storage solutions. Full article

(This article belongs to the Section Polymer Applications)

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21 pages, 3576 KiB

Open AccessArticle

Investigation of Rheological, Mechanical, and Viscoelastic Properties of Silica-Filled SSBR and BR Model Compounds

by Anmol Aggarwal, Nico Hackel, Fabian Grunert, Sybill Ilisch, Mario Beiner and Anke Blume

Polymers 2024, 16(22), 3212; https://doi.org/10.3390/polym16223212 - 19 Nov 2024

Viewed by 217

Abstract

Active fillers such as carbon black and silica are added to rubber to improve its mechanical and viscoelastic properties. These fillers cause reinforcement in rubber compounds through physical and/or chemical interactions. Consequently, the compounds’ rheological, mechanical, and viscoelastic behavior are affected. Changing the [...] Read more.

Active fillers such as carbon black and silica are added to rubber to improve its mechanical and viscoelastic properties. These fillers cause reinforcement in rubber compounds through physical and/or chemical interactions. Consequently, the compounds’ rheological, mechanical, and viscoelastic behavior are affected. Changing the filler loading influences these properties due to the different interactions (filler-filler and filler-polymer) taking place in the compounds. In addition, rubbers with varying microstructures can interact differently with fillers, and the presence of polymer functionalization to enhance interactions with fillers can further add to the complexity of the network. In this work, the effects of different loadings (0–108 phr/0–25 vol. %) of a highly dispersible grade of silica with three types of solution styrene-butadiene rubbers (SSBR) and one butadiene rubber (BR) on their rheological, mechanical, and viscoelastic properties were investigated. It was observed that the Mooney viscosity and hardness of the compounds increased with an increasing filler loading due to the increasing stiffness of the compounds. Payne effect measurements on uncured compounds provided information about the breakdown of the filler-filler network and the extent of the percolation threshold (15–17.5 vol. %) in all the compounds. At high filler loadings, the properties for BR compounds worsened as compared to SSBR compounds due to weak polymer-filler interaction (strong filler-filler interaction and the lower compatibility of BR with silica). The quasi-static mechanical properties increased with the filler loading and then decreased, thus indicating an optimum filler loading. In strain sweeps on cured rubber compounds by dynamic shear measurements, it was observed that the type of rubber, the filler loading, and the temperature had significant influences on the number of glassy rubber bridges in the filler network and, thus, a consequential effect on the load-bearing capacity and energy dissipation of the rubber compounds. Full article

(This article belongs to the Section Polymer Applications)

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31 pages, 8437 KiB

Open AccessArticle

Multifunctional Ag-Poly(N-isopropylacrylamide/itaconic Acid) Hydrogel Nanocomposites Prepared by Gamma Irradiation for Potential Application as Topical Treatment Dressings

by Jelena Spasojević, Milica Milošević, Sašenka Vidičević-Novaković, Jelena Tasić, Petar Milovanović, Marija Djurić, Dragan Ranković, Zorica Kačarević-Popović and Aleksandra Radosavljević

Polymers 2024, 16(22), 3211; https://doi.org/10.3390/polym16223211 - 19 Nov 2024

Viewed by 302

Abstract

Today, hydrogel dressings that can protect injury sites and effectively promote healing have become highly desirable in wound management. Therefore, multifunctional silver-poli(N-isopropylacrylamide/itaconic acid) (Ag-P(NiPAAm/IA)) hydrogel nanocomposites were developed for potential application as topical treatment dressings. The radiolytic method, used for the [...] Read more.

Today, hydrogel dressings that can protect injury sites and effectively promote healing have become highly desirable in wound management. Therefore, multifunctional silver-poli(N-isopropylacrylamide/itaconic acid) (Ag-P(NiPAAm/IA)) hydrogel nanocomposites were developed for potential application as topical treatment dressings. The radiolytic method, used for the crosslinking of the polymer matrix as well as for the in situ incorporation of silver nanoparticles (AgNPs) into the polymer matrix, enables the preparation of hydrogel nanocomposites without introducing harmful and toxic agents. Moreover, materials produced using γ-irradiation are simultaneously sterilized, thus fulfilling one of the basic requirements regarding their potential biomedical applications. The NiPAAm/IA ratio and the presence of AgNPs influenced the microstructural parameters of the investigated systems. Increasing the IA content leads to the formation of a more porous polymer matrix with larger pores, while the incorporated AgNPs act as additional junction points, decreasing the porosity and pore size of the resulting nanocomposite hydrogels. Swelling studies showed that most investigated systems uptake the fluids from their surroundings by non-Fick diffusion. Further, the Ag⁺ ion release, antibacterial activity, and cytotoxicity of Ag-P(NiPAAm/IA) hydrogel nanocomposites were examined to evaluate their biomedical potential. All hydrogel nanocomposites showed an initial burst release of Ag⁺ ions (useful in preventing bacteria adherence and biofilm formation), followed by a slower release of the same (ensuring sterility for longer use). An antibacterial activity test against Escherichia coli and Staphylococcus aureus showed that Ag-P(NiPAAm/IA) hydrogel nanocomposites, with silver concentrations around 10 ± 1 ppm, successfully prevent bacterial growth. Finally, it was shown that the investigated hydrogel nanocomposites do not exhibit a cytotoxic effect on human keratinocyte HaCaT cells. Therefore, these multifunctional hydrogel nanocomposites may promote wound repair and show promising potential for application as functional wound dressing. Full article

(This article belongs to the Special Issue Polymer Hydrogels: Synthesis, Properties and Applications)

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21 pages, 22949 KiB

Open AccessArticle

Development of Sustainable Cement Asphalt Mortar Using Agricultural Waste-Derived Bio-Oil and Latex–Acrylic Polymers for Enhanced Durability

by Yeong-Min Kim, Kyungnam Kim and Tri Ho Minh Le

Polymers 2024, 16(22), 3210; https://doi.org/10.3390/polym16223210 - 19 Nov 2024

Viewed by 321

Abstract

Cement Asphalt Mortar (CAM) is widely applied in infrastructure, particularly in railways, bridge expansion joints, and pavements, due to its combination of cement’s load-bearing capacity and asphalt’s flexibility. Conventional CAM formulations, however, often encounter challenges such as extended setting times, high shrinkage, and [...] Read more.

Cement Asphalt Mortar (CAM) is widely applied in infrastructure, particularly in railways, bridge expansion joints, and pavements, due to its combination of cement’s load-bearing capacity and asphalt’s flexibility. Conventional CAM formulations, however, often encounter challenges such as extended setting times, high shrinkage, and limited durability under extreme environmental conditions. This study addresses these limitations by integrating bio-oil and polymer additives to enhance both the sustainability and performance of CAM mixtures. CAM mixtures were evaluated with cement-to-asphalt emulsion (C/AE) mass ratios of 75:25 and 50:50, incorporating bio-oil contents of 2% and 4% by mass and latex–acrylic polymer proportions ranging from 1% to 2% by mass. The optimized mix design, with a 75:25 cement-to-asphalt emulsion (C/AE) mass ratio, 2% bio-oil, and 1.5% polymer, improved flowability by 25%. This formulation achieved a flow diameter of approximately 205 mm and reduced the flow time to 72 s. Compressive strength tests indicated that this formulation reached an early-stage strength of 10.45 MPa (a 20.8% improvement over the control) and a 28-day strength of 24.18 MPa. Thermal stability tests at 45 °C demonstrated that the optimized CAM retained 86.6% of its compressive strength, compared to a 25% reduction in unmodified mixtures. Chemical resistance assessments in 5% sulfuric acid and 5% sodium hydroxide solutions showed strength retention of 95.03% and 91.98%, respectively, outperforming control mixtures by 17% and 13%. SEM examination revealed a dense, cohesive microstructure, reducing shrinkage to 0.01% from 0.15% in the control. These findings underscore the potential of bio-oil and latex–acrylic polymers to improve the performance and sustainability of CAM mixtures, making them well suited for resilient, rapid-setting infrastructure applications. Full article

(This article belongs to the Special Issue Functional Polymeric Materials for Engineering and Environmental Applications)

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18 pages, 7800 KiB

Open AccessArticle

Demonstrating the Efficacy of Core-Shell Silica Catalyst in Depolymerizing Polycarbonate

by Onofrio Losito, Pasquale Pisani, Alessia De Cataldo, Cosimo Annese, Marina Clausi, Roberto Comparelli, Daniela Pinto and Lucia D’Accolti

Polymers 2024, 16(22), 3209; https://doi.org/10.3390/polym16223209 - 19 Nov 2024

Viewed by 309

Abstract

Polycarbonate (PC) is a highly versatile plastic material that is extensively utilized across various industries due to its superior properties, including high impact strength and heat resistance. However, its durability presents significant challenges for recycling and waste management. Polycarbonate is a thermoplastic polymer [...] Read more.

Polycarbonate (PC) is a highly versatile plastic material that is extensively utilized across various industries due to its superior properties, including high impact strength and heat resistance. However, its durability presents significant challenges for recycling and waste management. Polycarbonate is a thermoplastic polymer representative of the class of condensation reaction polymers obtained from the reaction of bisphenol A (BPA) and a carbonyl source, such as phosgene or alkyl and aryl carbonate. The recycling processes for PC waste include mechanical recycling, blending with other materials, pyrolysis, and chemical recycling. The latter is based on the cleavage of carbonate units to their corresponding monomers or derivatives through alcoholysis and/or hydrolysis and ammonolysis, normally under basic conditions and without catalysts. This study investigates the efficacy of the use of several heterogeneous catalysts based on silica gel as a robust support, including Sc(III)silicate (thortveitite), which has been previously reported for the preparation of polyesters, core-shell Si-ILs, and core-shell Si-ILs-ZnO, which has never been used before in the depolymerization of polycarbonate, proposing a sustainable and efficient method for recycling this valuable polymer. We chose to explore core-shell catalysts because these catalysts are robust and recyclable, and have been used in very harsh industrial processes. The core-shell silica catalysts used in this study were characterized by XRD; SEM_EDX, FT-IR, and ICP-OES analysis. In our experimental protocol, polycarbonate samples were exposed to the catalyst under controlled conditions (60–150 °C, for 12–24 h) using both oxygen and nitrogen nucleophiles. The depolymerization process was systematically monitored using advanced analytical techniques (GC/MS and GPC chromatography). The experimental results indicated that core-shell silica catalyst exhibits high efficacy, with up to 75% yield for the ammonolysis reaction, producing monomers of high purity. These monomers can be reused for the synthesis of new polycarbonate materials, contributing to a more sustainable approach to polycarbonate recycling. Full article

(This article belongs to the Special Issue Chemical Recycling of Polymers)

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12 pages, 5910 KiB

Open AccessArticle

Extraction of Lignocellulose from Rice Straw and Its Carboxymethylation When Activated by Microwave Radiation

by Abdirakym Nakyp, Elena Cherezova, Yuliya Karaseva, Kaiyrzhan Shalmagambetov, Aleksandr Aleksandrov, Rakhmetulla Zhapparbergenov, Nurgali Akylbekov and Rakhymzhan Turmanov

Polymers 2024, 16(22), 3208; https://doi.org/10.3390/polym16223208 - 19 Nov 2024

Viewed by 294

Abstract

The paper presents the process of cellulose extraction from rice straw using water–alkaline solution treatment and the subsequent process of carboxymethylation of the obtained product when activated by microwave radiation. After mercerization of rice straw, the obtained product contained 89.2% cellulose and 6.7% [...] Read more.

The paper presents the process of cellulose extraction from rice straw using water–alkaline solution treatment and the subsequent process of carboxymethylation of the obtained product when activated by microwave radiation. After mercerization of rice straw, the obtained product contained 89.2% cellulose and 6.7% lignin. The X-ray diffraction pattern of the obtained lignocellulose shows three diffraction peaks in the region typical for the polymorphic modification of cellulose Iβ (2θ = 15.50(78), 21.70(145), 34.70(52)). The degree of crystallinity was 65%. The product was heat-stable up to 247 °C. The synthesis of carboxymethylcellulose (CMC) based on the obtained product included successive processes of thermostating in alcohol–alkali solution and cellulose esterification reaction using monochloroacetic acid. To activate the carboxymethylation process, microwave radiation was used (350 W for 90 s), which made it possible to reduce the reaction time by more than 100 times. Functional group analysis of the carboxylated lignocellulose from rice straw was carried out using an FTIR spectrometer. In the IR spectra, a band with a maximum of 1742 cm⁻¹ was recorded, corresponding to stretching vibrations of >C(O)OH groups. The degree of polymerization was recorded by mass spectrometry. Full article

(This article belongs to the Special Issue Recent Progress on Lignocellulosic-Based Polymeric Materials)

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19 pages, 5197 KiB

Open AccessArticle

Expanded Polystyrene/Tyre Crumbs Composites as Promising Aggregates in Mortar and Concrete

by Karamat Subhani, Krishnamurthy Prasad, Nishar Hameed, Mostafa Nikzad and Nisa V. Salim

Polymers 2024, 16(22), 3207; https://doi.org/10.3390/polym16223207 - 19 Nov 2024

Viewed by 302

Abstract

A composite material comprising expanded polystyrene (EPS), granulated tyre rubber (GTR), and a compatibilizer is demonstrated as a possible replacement for fine and coarse agglomerates in mortar and concrete systems, respectively. Two different polymer blending processes (solvent/low shear blending and melt/high shear blending) [...] Read more.

A composite material comprising expanded polystyrene (EPS), granulated tyre rubber (GTR), and a compatibilizer is demonstrated as a possible replacement for fine and coarse agglomerates in mortar and concrete systems, respectively. Two different polymer blending processes (solvent/low shear blending and melt/high shear blending) are used, and the resulting composite material utilized as aggregate to replace sand and cement for mortar and concrete block development. Critical properties such as workability, compressive and flexural strengths, water absorption, bulk density, and porosity are measured before and after aggregate replacement. The novel composite material led to significant improvements, boosting compressive strength by 7.6% and flexural strength by 18% when sand was replaced and further increasing compressive strength by 22.2% and flexural strength by 5.26% with cement replacement. However, a decrease in compressive and flexural strength was observed when plain EPS and plain GTR were used separately as aggregate replacements. This work proposes a pathway for the successful reincorporation of difficult-to-recycle materials such as EPS and GTR, otherwise destined for landfill, back into the supply chain for the construction industry. Moreover, this research represents the first reported work where the overall properties of mortar have surpassed those of standard mortar when substituted with recycled EPS or GTR. Full article

(This article belongs to the Special Issue Renewable, Degradable, and Recyclable Polymer Composites)

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11 pages, 3528 KiB

Open AccessArticle

A Novel Rhodamine B Fluorescent Probe Derived from Carboxymethyl Chitosan for the Selective Detection of Fe³⁺

by Mei Yang, Zixi Tang, Chunwei Yu and Jun Zhang

Polymers 2024, 16(22), 3206; https://doi.org/10.3390/polym16223206 - 19 Nov 2024

Viewed by 272

Abstract

In this study, we synthesized a fluorescent material by modifying the C-2 amino group of carboxymethyl chitosan with a rhodamine B derivative, which was proposed and demonstrated using ¹H NMR and FT-IR measurements. A series of experiments including selectivity, sensitivity, reversibility, pH, [...] Read more.

In this study, we synthesized a fluorescent material by modifying the C-2 amino group of carboxymethyl chitosan with a rhodamine B derivative, which was proposed and demonstrated using ¹H NMR and FT-IR measurements. A series of experiments including selectivity, sensitivity, reversibility, pH, and water content were conducted to investigate the fluorometric and colorimetric properties of the grafted polymer. Utilizing a Fe³⁺-induced ring-opening mechanism of the rhodamine B spirolactam, we found that the grafted polymer exhibited a highly selective fluorescence response to Fe³⁺, with enhanced fluorescence at 583 nm compared to other tested metal ions and anions, accompanied by the characteristic absorption peak of rhodamine B that appeared at 561 nm with a noticeable color change from colorless to pink, facilitating visual observation. Additionally, the modified probe, composed of carboxymethyl chitosan, was easily regenerated through treatment with EDTA. Full article

(This article belongs to the Special Issue Preparation and Application of Biodegradable Polymers)

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15 pages, 4675 KiB

Open AccessArticle

Novel Recycling of Epoxy Thermosets by Blending with Reversible Diels–Alder Epoxy Resin

by Isaac Lorero, Blanca Rico, Mónica Campo and Silvia G. Prolongo

Polymers 2024, 16(22), 3205; https://doi.org/10.3390/polym16223205 - 19 Nov 2024

Viewed by 274

Abstract

The introduction of Diels–Alder (D-A) bonds into epoxy resins is a promising pathway to convert these unrecyclable materials into sustainable materials. However, D-A bonds make epoxy resins extremely brittle materials and hinder their practical usability. Nonetheless, the reversibility of D-A bonds allows the [...] Read more.

The introduction of Diels–Alder (D-A) bonds into epoxy resins is a promising pathway to convert these unrecyclable materials into sustainable materials. However, D-A bonds make epoxy resins extremely brittle materials and hinder their practical usability. Nonetheless, the reversibility of D-A bonds allows the transition of the material to a de-crosslinked network formed by separated oligomers that can melt above 90–100 °C. This means that D-A epoxy resins can be reprocessed after being cured like thermoplastics. In the present work, a thermoset blend is made by adding spent epoxy particles to a D-A epoxy resin to increase its thermal and mechanical properties and to evaluate a possible reuse of conventional thermoset wastes. The application of hot-pressing to a mixture of epoxy particles and powder of cured D-A epoxy creates a material in which the interaction of the particles with the D-A resin increases the thermal resistance of the material and prevents the D-A epoxy from melting at high temperatures. In addition, the flexural strength is increased by 80% and the chemical resistance against organic solvents is also improved. Full article

(This article belongs to the Special Issue Application and Characterization of Multifunctional and Sustainable Polymers and Composites)

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11 pages, 2461 KiB

Open AccessArticle

Enhancing the Non-Isothermal Crystallization Kinetics of Polylactic Acid by Incorporating a Novel Nucleating Agent

by Ruijie Jin, Zehong Chen, Yidan Ouyang, Xintu Lin, Xin Dai, Shangxi Zhang, Ruilan Xu, Zhengbao Wang and Yong Peng

Polymers 2024, 16(22), 3204; https://doi.org/10.3390/polym16223204 - 19 Nov 2024

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Abstract

Polylactic acid (PLA) is a widely recognized biodegradable polymer. However, the slow crystallization rate of PLA restricts its practical applications. In this study, camphor leaf biochar decorated with multi-walled carbon nanotubes (C@MWCNTs) was prepared using the strong adhesive properties of polydopamine, and PLA/C@MWCNTs [...] Read more.

Polylactic acid (PLA) is a widely recognized biodegradable polymer. However, the slow crystallization rate of PLA restricts its practical applications. In this study, camphor leaf biochar decorated with multi-walled carbon nanotubes (C@MWCNTs) was prepared using the strong adhesive properties of polydopamine, and PLA/C@MWCNTs composites were fabricated via the casting solution method. The influence of C@MWCNTs as a novel nucleating agent on the melt behavior and non-isothermal crystallization behavior of PLA was investigated using differential scanning calorimetry (DSC). The crystallization kinetic parameters were obtained through the Jeziorny, Ozawa, and Mo methods, and the crystallization activation energy of the PLA/C@MWCNTs composites was calculated by the Kissinger method. The results show that the PLA/C@MWCNTs composites exhibit higher crystallinity and crystallization temperatures than those of PLA. Non-isothermal crystallization kinetic analysis reveals that the Mo method better describes the non-isothermal crystallization kinetics of both PLA and PLA/C@MWCNTs composites. In addition, it was found that C@MWCNTs, despite increasing the crystallization activation energy, can act as an efficient nucleating agent to increase the crystallization rate of PLA. These experimental results provide valuable insights for enhancing the slow crystallization rates associated with PLA. Full article

(This article belongs to the Special Issue Additive Agents for Polymer Functionalization Modification)

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30 pages, 14756 KiB

Open AccessArticle

Simulation and Experimental Study on Enhancing Dimensional Accuracy of Polycarbonate Light Guides

by Jiri Vanek, Martin Ovsik, Jan Hanzlik and Michal Stanek

Polymers 2024, 16(22), 3203; https://doi.org/10.3390/polym16223203 - 19 Nov 2024

Viewed by 306

Abstract

This research investigates the adaptation of conventional injection-molding techniques for producing thick-walled polycarbonate optical components, specifically targeting their application in automotive light guides. With the automotive industry’s growing demand for reliable yet cost-efficient optical products, the study examines how traditional injection-molding processes can [...] Read more.

This research investigates the adaptation of conventional injection-molding techniques for producing thick-walled polycarbonate optical components, specifically targeting their application in automotive light guides. With the automotive industry’s growing demand for reliable yet cost-efficient optical products, the study examines how traditional injection-molding processes can be refined to enhance dimensional accuracy and reduce defects. Simulations and experimental trials were conducted to evaluate the impact of critical process parameters, such as melt temperature, mold temperature, injection pressure, and gate design, on the overall quality of the final components. The results show that by carefully optimizing these parameters, it is possible to significantly reduce common defects like warpage, surface imperfections, and dimensional instability. This research highlights the potential of existing molding techniques to meet high industry standards while maintaining cost-effectiveness, offering valuable guidance for manufacturers aiming to produce high-quality optical components for demanding applications like automotive lighting. Full article

(This article belongs to the Special Issue Molding Process of Polymers and Composites)

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9 pages, 2398 KiB

Open AccessArticle

Pectin Hydrogels as Structural Platform for Antibacterial Drug Delivery

by Tejas Saravanan, Jennifer M. Pan, Franz G. Zingl, Matthew K. Waldor, Yifan Zheng, Hassan A. Khalil and Steven J. Mentzer

Polymers 2024, 16(22), 3202; https://doi.org/10.3390/polym16223202 - 19 Nov 2024

Viewed by 281

Abstract

Hydrogels are hydrophilic 3-dimensional networks characterized by the retention of a large amount of water. Because of their water component, hydrogels are a promising method for targeted drug delivery. The water component, or “free volume”, is a potential vehicle for protein drugs. A [...] Read more.

Hydrogels are hydrophilic 3-dimensional networks characterized by the retention of a large amount of water. Because of their water component, hydrogels are a promising method for targeted drug delivery. The water component, or “free volume”, is a potential vehicle for protein drugs. A particularly intriguing hydrogel is pectin. In addition to a generous free volume, pectin has structural characteristics that facilitate hydrogel binding to the glycocalyceal surface of visceral organs. To test drug function and pectin integrity after loading, we compared pectin films from four distinct plant sources: lemon, potato, soybean, and sugar beet. The pectin films were tested for their micromechanical properties and intrinsic antibacterial activity. Lemon pectin films demonstrated the greatest cohesion at 30% water content. Moreover, modest growth inhibition was observed with lemon pectin (p < 0.05). No effective inhibition was observed with soybean, potato, or sugar beet films (p > 0.05). In contrast, lemon pectin films embedded with carbenicillin, chloramphenicol, or kanamycin demonstrated significant bacterial growth inhibition (p < 0.05). The antibacterial activity was similar when the antibiotics were embedded in inert filter disks or pectin disks (p > 0.05). We conclude that lemon pectin films represent a promising structural platform for antibacterial drug delivery. Full article

(This article belongs to the Special Issue Biomedical Applications of Intelligent Hydrogel 2nd Edition)

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34 pages, 5249 KiB

Open AccessArticle

Exploring the Mechanical and Thermal Impact of Natural Fillers on Thermoplastic Polyurethane and Styrene–Butadiene Rubber Footwear Sole Materials

by Víctor M. Serrano-Martínez, Henoc Pérez-Aguilar, María Pilar Carbonell-Blasco, Cristina Llobell-Andrés, Francisca Aran-Ais, Avelina García-García and Elena Orgilés-Calpena

Polymers 2024, 16(22), 3201; https://doi.org/10.3390/polym16223201 - 18 Nov 2024

Viewed by 432

Abstract

The increasing concern for sustainability in the footwear industry has spurred the exploration of eco-friendly alternatives for materials commonly used in sole manufacturing. This study examined the effect of incorporating rice straw and cellulose as fillers into soles made from either styrene–butadiene rubber [...] Read more.

The increasing concern for sustainability in the footwear industry has spurred the exploration of eco-friendly alternatives for materials commonly used in sole manufacturing. This study examined the effect of incorporating rice straw and cellulose as fillers into soles made from either styrene–butadiene rubber (SBR) or thermoplastic polyurethane (TPU). Both fillers were used as a substitute in mass percentages ranging from 5 to 20% in the original SBR and TPU formulas, and their impact on mechanical properties such as abrasion and tear resistance, as well as thermal properties, was thoroughly evaluated. The results demonstrated that the inclusion of fillers affects the overall performance of the soles, with the optimal balance of mechanical and thermal properties observed at a 10% filler content. At this level, improvements in durability were achieved without significantly compromising flexibility or abrasion resistance. Thermal analysis revealed increased thermal stability at moderate filler contents. This research not only offers a sustainable alternative to traditional materials but also enhances sole performance by improving the composition. Furthermore, this study paves the way for future research on the feasibility of incorporating eco-friendly materials into other consumer product applications, highlighting a commitment to innovation and sustainability in product design. Full article

(This article belongs to the Special Issue Cellulose and Cellulose Micro/Nanomaterials: Recent Research and Applications)

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