Polymers

Open AccessArticle

Surface Modification and Mechanical Properties Improvement of Bamboo Fibers Using Dielectric Barrier Discharge Plasma Treatment

by

Choncharoen Sawangrat

,

Parichat Thipchai

,

Kannikar Kaewapai

,

Kittisak Jantanasakulwong

,

Jonghwan Suhr

,

Pitiwat Wattanachai

and

Pornchai Rachtanapun

Polymers 2023, 15(7), 1711; https://doi.org/10.3390/polym15071711 (registering DOI) - 29 Mar 2023

Abstract

The effect of argon (Ar) and oxygen (O₂) gases as well as the treatment times on the properties of modified bamboo fibers using dielectric barrier discharge (DBD) plasma at generated power of 180 W were investigated. The plasma treatment of bamboo [...] Read more.

The effect of argon (Ar) and oxygen (O₂) gases as well as the treatment times on the properties of modified bamboo fibers using dielectric barrier discharge (DBD) plasma at generated power of 180 W were investigated. The plasma treatment of bamboo fibers with inert gases leads to the generation of ions and radicals on the fiber surface. Fourier transform-infrared spectroscopy (FTIR) confirmed that the functional groups of lignin and hemicellulose were reduced owing to the removal of the amorphous portion of the fibers by plasma etching. X-ray diffraction analysis (XRD) results in an increased crystallinity percentage. X-ray photoelectron spectroscopy (XPS) results showed the oxygen/carbon (O/C) atomic concentration ratio increased with increasing treatment time. The fiber weight loss percentage increased with increased treatment time. Scanning electron microscopy (SEM) images showed that partial etching of the fiber surface led to a higher surface roughness and area and that the Ar + O₂ gas plasma treatment provided more surface etching than the Ar gas treatment because of the oxidation reaction of the O₂ plasma. The mechanical properties of fiber-reinforced epoxy (FRE) matrix composites revealed that the F_(tr)RE-Ar (30) samples showed a high tensile strength, whereas the mechanical properties of the F_(tr)RE-Ar + O₂ sample decreased with increased treatment time. Full article

(This article belongs to the Special Issue Natural Polymers: Design, Characterization and Applications)

Open AccessArticle

Preparation and Antimicrobial Characterization of Poly(butylene adipate-co-terephthalate)/Kaolin Clay Biocomposites

by

Raja Venkatesan

,

Krishnapandi Alagumalai

and

Seong-Cheol Kim

Polymers 2023, 15(7), 1710; https://doi.org/10.3390/polym15071710 (registering DOI) - 29 Mar 2023

Abstract

The biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) starts decomposing at room temperature. Kaolin clay (KO) was dispersed and blended into PBAT composites using a solution-casting method. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used [...] Read more.

The biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) starts decomposing at room temperature. Kaolin clay (KO) was dispersed and blended into PBAT composites using a solution-casting method. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to evaluate the structure and morphology of the composite materials. PBAT/kaolin clay composites were studied by thermogravimetric analysis (TGA). The PBAT composite loaded with 5.0 wt% kaolin clay shows the best characteristics. The biocomposites of PBAT/kaolin [PBC-5.0 (37.6MPa)] have a good tensile strength when compared to virgin PBAT (18.3MPa). The oxygen transmission rate (OTR), with ranges from 1080.2 to 311.7 (cc/m²/day), leads the KO content. By including 5.0 wt% kaolin 43.5 (g/m²/day), the water vapor transmission rate (WVTR) of the PBAT/kaolin composites was decreased. The pure PBAT must have a WVTR of 152.4 (g/m²/day). Gram-positive (S. aureus) and Gram-negative (E. coli) food-borne bacteria are significantly more resistant to the antimicrobial property of composites. The results show that PBAT/kaolin composites have great potential as food packaging materials due to their ability to decrease the growth of bacteria and improve the shelf life of packaged foods. Full article

(This article belongs to the Special Issue Bioactive Materials with Antibacterial Properties)

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Open AccessArticle

Design and Construction of an Azo-Functionalized POP for Reversibly Stimuli-Responsive CO₂ Adsorption

by

Rongrong Yuan

,

Meiyu Zhang

and

Hao Sun

Polymers 2023, 15(7), 1709; https://doi.org/10.3390/polym15071709 (registering DOI) - 29 Mar 2023

Abstract

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl₃. JJU-2 exhibited reversibly stimuli-responsive CO₂ adsorption properties as a result of the trans/cis isomerization of the polymer’s azo-functionalized skeleton. Under UV irradiation and [...] Read more.

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl₃. JJU-2 exhibited reversibly stimuli-responsive CO₂ adsorption properties as a result of the trans/cis isomerization of the polymer’s azo-functionalized skeleton. Under UV irradiation and heat treatment, this porous material displayed various porous structures and CO₂ adsorption properties. The initial Brunauer-Emmett-Teller (BET) surface area of JJU-1 is 888 m² g⁻¹. After UV irradiation, the BET surface area decreases to 864 m² g⁻¹, along with the decrease of micropores around 0.50 nm and 1.27 nm during the trans-to-cis isomerization process. In addition, CO₂ sorption isotherms demonstrate an 8%t decrease, and the calculated Qst of CO₂ has decreased from 29.0 kJ mol⁻¹ to 26.5 kJ mol⁻¹ due to the trans to cis conversion of the azobenzene side group. It is noteworthy that JJU-2′s CO₂ uptakes are nearly constant over three cycles of alternating external stimuli. Therefore, this azo-functionalized porous material was a potential carbon capture material that was responsive to stimuli. Full article

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

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Open AccessArticle

Tension and Compression Properties of 3D-Printed Composites: Print Orientation and Strain Rate Effects

by

Tom Fisher

,

José Humberto S. Almeida, Jr.

,

Brian G. Falzon

and

Zafer Kazancı

Polymers 2023, 15(7), 1708; https://doi.org/10.3390/polym15071708 (registering DOI) - 29 Mar 2023

Abstract

This study examines the impact of three factors on the tensile and compressive behaviour of 3D-printed parts: (1) the addition of short carbon fibres to the nylon filament used for 3D printing, (2) the infill pattern, and (3) the speed at which the [...] Read more.

This study examines the impact of three factors on the tensile and compressive behaviour of 3D-printed parts: (1) the addition of short carbon fibres to the nylon filament used for 3D printing, (2) the infill pattern, and (3) the speed at which the materials are strained during testing. The results show that adding carbon fibres to the nylon filament reduces variability between tests and emphasises the effect of print orientation. When the infill pattern is aligned with the direction of loading, the tensile strength of all samples increases, with the largest increase of 100% observed in the carbon fibre-reinforced samples, compared to a 37% increase in the strength of nylon samples. The carbon fibre-reinforced samples are also highly dependent on strain rate, with a 60% increase in tensile strength observed at a faster testing speed of 300 mm/min (9 min

^{- 1}

) compared to 5 mm/min (15 min

^{- 1}

). Nylon samples show a decrease of approximately 10% in tensile strength at the same increased speed. The compressive strength of the composite samples increases by up to 130% when the print path is parallel to the loading direction. Increases of up to 50% are observed in the compressive modulus of the composite samples at a test speed of 255 mm/min (9 min

^{- 1}

) compared to 1.3 mm/min (0.05 min

^{- 1}

). Similar trends are not seen in pure nylon samples. This study is the first to report on the variation of Poisson’s ratio of short carbon fibre-reinforced 3D-printed parts. The results show increases of up to 34% and 76% in the tensile and compressive Poisson’s ratios, respectively, when printing parameters are altered. The findings from this research will contribute to the design and numerical modelling of 3D-printed composites. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

Open AccessArticle

Evaluation of Interface Shear Strength Coefficient of Alternative Geogrid Made from Para Rubber Sheet

by

Anubud Liangsunthonsit

,

,

,

and

Polymers 2023, 15(7), 1707; https://doi.org/10.3390/polym15071707 (registering DOI) - 29 Mar 2023

Abstract

In this work, elastic natural rubber compound sheet (RCS) and ribbed smoked sheet grade 3 (RSS) were studied as alternative replacements for polymer geogrid for soil reinforcement. In order to investigate the reinforcing effectiveness in three distinct environments using the interface shear strength [...] Read more.

In this work, elastic natural rubber compound sheet (RCS) and ribbed smoked sheet grade 3 (RSS) were studied as alternative replacements for polymer geogrid for soil reinforcement. In order to investigate the reinforcing effectiveness in three distinct environments using the interface shear strength coefficient (R_in) by the large-scale direct shear test, the RSS and RCS geogrids were installed independently in sand, lateritic soil, and clay. Using either an RSS geogrid or RCS geogrid, the average R_in is progressively smaller in reinforced sand, lateritic soil, and clay, respectively. Higher tensile strength of reinforced materials using the RCS geogrid than those using the RSS geogrid is encouraged by the better elastic characteristics of the RCS geogrid. Thus, utilizing the RCS geogrid-reinforced materials can better increase the shear strength of coarse-grained soil such as sand and gravel. Full article

(This article belongs to the Special Issue Polymers and the Circular Economy Model)

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Open AccessArticle

On the Donor: Acceptor Features for Poly(3-hexylthiophene): TiO₂ Quantum Dots Hybrid Materials Obtained via Water Vapor Flow Assisted Sol-Gel Growth

by

,

,

and

Polymers 2023, 15(7), 1706; https://doi.org/10.3390/polym15071706 (registering DOI) - 29 Mar 2023

Abstract

Here, we present a novel methodology for the preparation of P3HT:TiO₂ quantum dots hybrid materials via water vapor flow-assisted sol-gel growth focusing on the structural, optical and electrical property characterization complemented with first-principles calculations as a promising donor–acceptor system for polymer and [...] Read more.

Here, we present a novel methodology for the preparation of P3HT:TiO₂ quantum dots hybrid materials via water vapor flow-assisted sol-gel growth focusing on the structural, optical and electrical property characterization complemented with first-principles calculations as a promising donor–acceptor system for polymer and hybrid solar cells. X-ray diffraction and UV-Vis spectroscopy analyses suggest that the increasing concentration of TiO₂ quantum dots leads to the formation of higher amounts of amorphous regions while the crystalline regions exhibited interesting aspect ratio modifications for the P3HT polymer. Raman spectra evidenced the formation of charge carriers in the P3HT with increasing TiO₂ quantum dots content and the P3HT:TiO₂ 50:50 weight ratio resulted in the best composition for optimizing the bulk electronic conductivity, as evidenced by impedance spectroscopy studies. Our DFT calculations performed for a simplified model of the P3HT:TiO₂ interface revealed that there is an important contribution of the thiophene carbon atoms states in the conduction band at the Fermi level. Finally, our DFT calculations also reveal an evident gain of electron density at the TiO₂ (101) surface while the thiophene rings showed a loss of the electron density, thus confirming that the P3HT:TiO₂ junction acts as a good donor–acceptor system. In our opinion, these results not only present a novel methodology for the preparation of P3HT:TiO₂ quantum dots hybrid materials but also reveal some key aspects to guide the more rational design of polymer and hybrid solar cells. Full article

(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Uruguay (2021,2022))

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Open AccessArticle

Effect of a New Additive Based on Textile Fibres from End-of-Life Tyres (ELT) on the Mechanical Properties of Stone Mastic Asphalt

by

Gonzalo Valdés-Vidal

,

Alejandra Calabi-Floody

,

Cristian Mignolet-Garrido

and

Cristian Díaz-Montecinos

Polymers 2023, 15(7), 1705; https://doi.org/10.3390/polym15071705 (registering DOI) - 29 Mar 2023

Abstract

Stone Mastic Asphalts (SMA) are asphalt mixes with discontinuous granulometry and a high content of asphalt binder. In order to prevent draindown of the asphalt binder and ensure good performance, these mixes must be strengthened with cellulose or mineral fibres and/or polymer additives. [...] Read more.

Stone Mastic Asphalts (SMA) are asphalt mixes with discontinuous granulometry and a high content of asphalt binder. In order to prevent draindown of the asphalt binder and ensure good performance, these mixes must be strengthened with cellulose or mineral fibres and/or polymer additives. This study was designed to evaluate the effect of a granular additive based on waste tyre textile fibres (WTTF), developed as a replacement for cellulose commercial additives in SMA mixes. Use of the WTTF-based additive will encourage the development of sustainable mixes by recycling a by-product of end-of-life tyres (ELT), which currently constitute a major environmental problem around the world. To this end, in the present experimental study we evaluated the replacement of cellulose-based commercial fibre with different percentages of WTTF-based additive (0%, 50%, 75%, 100%) in an SMA asphalt mix. The following design and performance properties were evaluated: resistance to cracking, stiffness modulus, sensitivity to moisture, and resistance to permanent deformation. The results indicated that replacing 100% of the cellulose commercial additive in the SMA mix by the WTTF-based additive allowed the mix to meet its design properties and showed good performance in the mechanical properties evaluated, with behaviour similar to that of the reference SMA mix. Full article

(This article belongs to the Collection Biopolymers and Biopolymer Based Composites: Processing, Properties, Durability)

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Open AccessArticle

Potentially Health-Promoting Spaghetti-Type Pastas Based on Doubly Modified Corn Starch: Starch Oxidation via Wet Chemistry Followed by Organocatalytic Butyrylation Using Reactive Extrusion

by

Oswaldo Hernandez-Hernandez

,

Lesbia Cristina Julio-Gonzalez

,

Elisa G. Doyagüez

and

Tomy J. Gutiérrez

Polymers 2023, 15(7), 1704; https://doi.org/10.3390/polym15071704 (registering DOI) - 29 Mar 2023

Abstract

Extruded spaghetti-type pasta systems were obtained separately either from native or oxidized starch prepared via wet chemistry with the aim of evaluating the effect of oxidation modification of starch. In addition to this, the butyrylation reaction (butyrate (Bu) esterification—short-chain fatty acid) using native [...] Read more.

Extruded spaghetti-type pasta systems were obtained separately either from native or oxidized starch prepared via wet chemistry with the aim of evaluating the effect of oxidation modification of starch. In addition to this, the butyrylation reaction (butyrate (Bu) esterification—short-chain fatty acid) using native or oxidized starch was analyzed under reactive extrusion (REx) conditions with and without the addition of a green food-grade organocatalyst (l(+)-tartaric acid) with the purpose of developing potentially health-promoting spaghetti-type pasta systems in terms of increasing its resistant starch (RS) values. These would be due to obtaining organocatalytic butyrylated starch or not, or the manufacture of a doubly modified starch (oxidized-butyrylated—starch oxidation followed by organocatalytic butyrylation) or not. To this end, six pasta systems were developed and characterized by solid-state ¹³C cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) spectroscopy, degree of substitution (DS), attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), pancreatic digestion, free Bu content analysis and in vitro starch digestibility. The results obtained here suggest that starch oxidation hydrolytically degrades starch chains, making them more susceptible to enzymatic degradation by α-amylase. However, the oxidized starch-based pasta systems, once esterified by Bu mainly on the amylose molecules (doubly modified pasta systems) increased their RS values, and this was more pronounced with the addition of the organocatalyst (maximum RS value = ~8%). Interestingly, despite the checked chemical changes that took place on the molecular structure of starch upon butyrylation or oxidation reactions in corn starch-based spaghetti-type pasta systems, and their incidence on starch digestibility, the orthorhombic crystalline structure (A-type starch) of starch remained unchanged. Full article

(This article belongs to the Special Issue Bioplastics: Starch and Cellulose)

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Open AccessArticle

Synthesis of Novel 2,9-Disubstituted-6-morpholino Purine Derivatives Assisted by Virtual Screening and Modelling of Class I PI3K Isoforms

by

,

,

and

Polymers 2023, 15(7), 1703; https://doi.org/10.3390/polym15071703 (registering DOI) - 29 Mar 2023

Abstract

The phosphatidylinositol-3 kinase (PI3K) pathway is one of the most frequently activated pathogenic signalling cascades in a wide variety of cancers. In the last 15 years, there has been an increase in the search for selective inhibitors of the four class I isoforms [...] Read more.

The phosphatidylinositol-3 kinase (PI3K) pathway is one of the most frequently activated pathogenic signalling cascades in a wide variety of cancers. In the last 15 years, there has been an increase in the search for selective inhibitors of the four class I isoforms of PI3K, as they demonstrate better specificity and reduced toxicity in comparison to existing inhibitors. A ligand-based and target-based rational drug design strategy was employed to build a virtual library of 105 new compounds. Through this strategy, the four isoforms were compared regarding their activity pocket availability, amino acid sequences, and prone interactions. Additionally, a known active scaffold was used as a molecular base to design new derivatives. The virtual screening of the resultant library toward the four isoforms points to the obtention of 19 selective inhibitors for the PI3Kα and PI3Kγ targets. Three selective ligands, one for α-isoform and two for γ-isoform, present a ∆ (∆G_binding) equal or greater than 1.5 Kcal/mol and were identified as the most promising candidates. A principal component analysis was used to establish correlations between the affinity data and some of the physicochemical and structural properties of the ligands. The binding modes and interactions established by the selective ligands in the active centre of the α and γ isoforms of PI3K were also investigated. After modelling studies, a synthetic approach to generate selective ligands was developed and applied in synthesising a set of derivatives that were obtained in good to excellent yield. Full article

(This article belongs to the Special Issue Modelling and Simulation of Proteins, Biopolymers and Biocompatible Materials)

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Open AccessArticle

Dielectric, Mechanical, and Thermal Properties of Crosslinked Polyethylene Nanocomposite with Hybrid Nanofillers

by

Nurul Iman Abdul Razak

,

Noor Izyan Syazana Mohd Yusoff

,

Mohd Hafizi Ahmad

,

Muzafar Zulkifli

and

Mat Uzir Wahit

Polymers 2023, 15(7), 1702; https://doi.org/10.3390/polym15071702 (registering DOI) - 29 Mar 2023

Abstract

Crosslinked polyethylene (XLPE) nanocomposite has superior insulation performance due to its excellent dielectric, mechanical, and thermal properties. The incorporation of nano-sized fillers drastically improved these properties in XLPE matrix due to the reinforcing effect of interfacial region between the XLPE–nanofillers. Good interfacial strength [...] Read more.

Crosslinked polyethylene (XLPE) nanocomposite has superior insulation performance due to its excellent dielectric, mechanical, and thermal properties. The incorporation of nano-sized fillers drastically improved these properties in XLPE matrix due to the reinforcing effect of interfacial region between the XLPE–nanofillers. Good interfacial strength can be further improved by introducing a hybrid system nanofiller as a result of synergistic interaction between the nanofiller relative to a single filler system. Another factor affecting interfacial strength is the amount of hybrid nanofiller. Therefore, the incorporation amount of hybridising layered double hydroxide (LDH) with aluminium oxide (Al₂O₃) nanofiller into the XLPE matrix was investigated. Herein, the influence of hybrid nanofiller content and the 1:1 ratio of LDH to Al₂O₃ on the dielectric, mechanical, and thermal properties of the nanocomposite was studied. The structure and morphology of the XLPE/LDH-Al₂O₃ nanocomposites revealed that the hybridisation of nanofiller improved the dispersion state. The dielectric, mechanical, and thermal properties, including partial discharge resistance, AC breakdown strength, and tensile properties (tensile strength, Young’s modulus, and elongation at break) were enhanced since it was influenced by the synergetic effect of the LDH-Al₂O₃ nanofiller_. These properties were increased at optimal value of 0.8 wt.% before decreasing with increasing hybrid nanofiller. It was found that the value of PD magnitude improvement went down to 47.8% and AC breakdown strength increased by 15.6% as compared to pure XLPE. The mechanical properties were enhanced by 14.4%, 31.7%, and 23% for tensile strength, Young’s modulus, and elongation at break, respectively. Of note, the hybridisation of nanofillers opens a new perspective in developing insulating material based on XLPE nanocomposite. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

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Open AccessReview

Advances in the Production of Biomaterials through Kombucha Using Food Waste: Concepts, Challenges, and Potential

by

Anelise Leal Vieira Cubas

,

Ana Paula Provin

,

Ana Regina Aguiar Dutra

,

Cláudia Mouro

and

Isabel C. Gouveia

Polymers 2023, 15(7), 1701; https://doi.org/10.3390/polym15071701 (registering DOI) - 29 Mar 2023

Abstract

In recent years, several researchers have focused their studies on the development of sustainable biomaterials using renewable sources, including the incorporation of living biological systems. One of the best biomaterials is bacterial cellulose (BC). There are several ways to produce BC, from using [...] Read more.

In recent years, several researchers have focused their studies on the development of sustainable biomaterials using renewable sources, including the incorporation of living biological systems. One of the best biomaterials is bacterial cellulose (BC). There are several ways to produce BC, from using a pure strain to producing the fermented drink kombucha, which has a symbiotic culture of bacteria and yeasts (SCOBY). Studies have shown that the use of agricultural waste can be a low-cost and sustainable way to create BC. This article conducts a literature review to analyze issues related to the creation of BC through kombucha production. The databases used were ScienceDirect, Scopus, Web of Science, and SpringerLink. A total of 42 articles, dated from 2018 to 2022, were referenced to write this review. The findings contributed to the discussion of three topics: (1) The production of BC through food waste (including patents in addition to the scientific literature); (2) Areas of research, sectors, and products that use BC (including research that did not use the kombucha drink, but used food waste as a source of carbon and nitrogen); and (3) Production, sustainability, and circular economy: perspectives, challenges, and trends in the use of BC (including some advantages and disadvantages of BC production through the kombucha drink). Full article

(This article belongs to the Special Issue Advanced Polymer in Food Industry II)

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Open AccessArticle

Modification of 3D Printable Polymer Filaments for Radiation Shielding Applications

by

Antonio Jreije

,

Swaroop Kumar Mutyala

,

Benas Gabrielis Urbonavičius

,

,

,

,

and

Polymers 2023, 15(7), 1700; https://doi.org/10.3390/polym15071700 - 29 Mar 2023

Abstract

There is a growing need to develop lead-free shielding materials that are safe, low weight, durable, environmentally friendly, chemically and mechanically stable and customizable for specific applications. Fused deposition modeling (FDM), an additive manufacturing technique based on the extrusion of a thermoplastic filament [...] Read more.

There is a growing need to develop lead-free shielding materials that are safe, low weight, durable, environmentally friendly, chemically and mechanically stable and customizable for specific applications. Fused deposition modeling (FDM), an additive manufacturing technique based on the extrusion of a thermoplastic filament into a 3D printed object one layer at a time, could be employed well in applications involving ionizing radiation due to its relatively low cost, design flexibility and high manufacturing precision. This study aimed at developing 3D printing composites that contain Titanium dioxide as a filler agent for shielding in a medical radiation environment. First, the effect of low-dose ionizing radiation (up to 15 Gy) on the mechanical properties of common 3D printing polymers, ABS, ULTRAT, PLA, NYLON, ASA and PETG, was investigated. Since ABS experienced the lowest variation in its ultimate tensile strength (±5%) and Young’s modulus (−5%/+11%), it was chosen as a matrix for a new extruded 3D filament containing TiO₂ at 1 wt.%, 3 wt.%, and 5 wt.%. With the incorporation of TiO₂ at different filler contents, the UTS of the ABS composites varied between 24.1 MPa and 28.4 MPa, with the highest value recorded for 3 wt.% TiO₂. Young’s modulus values were dependent on both the TiO₂ concentration and on the irradiation dose. In addition, the ABS/TiO₂ composites with a higher filler content (3 wt.% and 5 wt.%) maintained their attenuation ability even after exposure to a radiation dose of 100 Gy as opposed to pure ABS, which exhibited a ~2.5% reduction in its mass attenuation coefficient after exposure to the same dose of radiation. The pilot investigation performed demonstrated that the newly developed ABS/TiO₂ composite containing 5 wt.% of filler can be successfully employed to shield electronic devices operating in a radiotherapy room. Full article

(This article belongs to the Collection Progress in Polymer Composites and Nanocomposites)

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Open AccessArticle

Study on Improving Measures of Mechanical Properties of Geopolymer Materials and Its Effect on CO₂ Emission

by

,

,

,

,

and

Polymers 2023, 15(7), 1699; https://doi.org/10.3390/polym15071699 - 29 Mar 2023

Abstract

Using construction and demolition waste composites (CDWC) and fly ash (FA) to replace cement to produce concrete can reduce CO₂ emissions. However, the CDWC-based geopolymer materials have two imperfections: the compressive strength is prone to decrease with the increase of curing age [...] Read more.

Using construction and demolition waste composites (CDWC) and fly ash (FA) to replace cement to produce concrete can reduce CO₂ emissions. However, the CDWC-based geopolymer materials have two imperfections: the compressive strength is prone to decrease with the increase of curing age (strength shrinkage) under heat curing conditions, and the strength develops slowly under ambient curing conditions. To solve the problems of these materials, on the one hand, we designed an experiment of preparing CDWC-based geopolymer concrete (CDWGC) with pretreated CDWC at different high temperatures. We analyzed the influence of different pretreatment temperatures on the mechanical properties of CDWGC through compressive strength, SEM-EDS and XRD. On the other hand, we added CaO to improve the mechanical properties of CDWC-based geopolymer paste (CDWGP) under ambient curing conditions. Further, the CO₂ emissions of pretreating CDWC and adding CaO were calculated by life cycle assessment (LCA). The results show that: (1) Pretreatment of CDWC can effectively solve the problem of CDWGC strength shrinkage. (2) The compressive strength of CDWGP cured at ambient can be significantly improved by adding CaO, and the compressive strength can be increased by 180.9% when the optimum content is 3%. (3) Adding CaO had less impact on CO₂ emissions, a low-carbon way to improve its strength effectively. Full article

(This article belongs to the Special Issue Polymers in Concrete and Cement)

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Open AccessArticle

Effect of Heating and Citric Acid on the Performance of Cellulose Nanocrystal Thin Films

by

Emília Csiszár

,

Imola Herceg

and

Erika Fekete

Polymers 2023, 15(7), 1698; https://doi.org/10.3390/polym15071698 - 29 Mar 2023

Abstract

Cellulose nanocrystals (CNCs) were extracted from bleached cotton by sulfuric acid hydrolysis. Thin films were prepared from the aqueous suspension of CNCs by casting and evaporation with 15% glycerol as a plasticizer. Our research aimed to create stable films resistant to water. The [...] Read more.

Cellulose nanocrystals (CNCs) were extracted from bleached cotton by sulfuric acid hydrolysis. Thin films were prepared from the aqueous suspension of CNCs by casting and evaporation with 15% glycerol as a plasticizer. Our research aimed to create stable films resistant to water. The structure and the interactions of the films were modified by short (10 min) heating at different temperatures (100, 140, and 160 °C) and by adding different amounts of citric acid (0, 10, 20, and 30%). Various analytical methods were used to determine the structure, surface properties, and mechanical properties. The interaction of composite films with water and water vapor was also investigated. Heat treatment did not significantly affect the film properties. Citric acid, without heat treatment, acted as a plasticizer. It promoted the disintegration of films in water, increased water vapor sorption, and reduced tensile strength, resulting in flexible and easy-to-handle films. The combination of heat treatment and citric acid resulted in stable liquid-water-resistant films with excellent mechanical properties. A minimum heating temperature of 120 °C and a citric acid concentration of 20% were required to obtain a stable CNC film structure resistant to liquid water. Full article

(This article belongs to the Special Issue Advances in Cellulose-Based Polymers and Composites)

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Open AccessArticle

Development of Polyurethane/Peptide-Based Carriers with Self-Healing Properties

by

Luiza Madalina Gradinaru

,

Maria Bercea

,

Alexandra Lupu

and

Vasile Robert Gradinaru

Polymers 2023, 15(7), 1697; https://doi.org/10.3390/polym15071697 - 29 Mar 2023

Abstract

In situ-forming gels with self-assembling and self-healing properties are materials of high interest for various biomedical applications, especially for drug delivery systems and tissue regeneration. The main goal of this research was the development of an innovative gel carrier based on dynamic inter- [...] Read more.

In situ-forming gels with self-assembling and self-healing properties are materials of high interest for various biomedical applications, especially for drug delivery systems and tissue regeneration. The main goal of this research was the development of an innovative gel carrier based on dynamic inter- and intramolecular interactions between amphiphilic polyurethane and peptide structures. The polyurethane architecture was adapted to achieve the desired amphiphilicity for self-assembly into an aqueous solution and to facilitate an array of connections with peptides through physical interactions, such as hydrophobic interactions, dipole-dipole, electrostatic, π–π stacking, or hydrogen bonds. The mechanism of the gelation process and the macromolecular conformation in water were evaluated with DLS, ATR-FTIR, and rheological measurements at room and body temperatures. The DLS measurements revealed a bimodal distribution of small (~30–40 nm) and large (~300–400 nm) hydrodynamic diameters of micelles/aggregates at 25 °C for all samples. The increase in the peptide content led to a monomodal distribution of the peaks at 37 °C (~25 nm for the sample with the highest content of peptide). The sol–gel transition occurs very quickly for all samples (within 20–30 s), but the equilibrium state of the gel structure is reached after 1 h in absence of peptide and required more time as the content of peptide increases. Moreover, this system presented self-healing properties, as was revealed by rheological measurements. In the presence of peptide, the structure recovery after each cycle of deformation is a time-dependent process, the recovery is complete after about 300 s. Thus, the addition of the peptide enhanced the polymer chain entanglement through intermolecular interactions, leading to the preparation of a well-defined gel carrier. Undoubtedly, this type of polyurethane/peptide-based carrier, displaying a sol–gel transition at a biologically relevant temperature and enhanced viscoelastic properties, is of great interest in the development of medical devices for minimally invasive procedures or precision medicine. Full article

(This article belongs to the Special Issue Self-Healing Polymers, Proteins and Composites)

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Open AccessReview

Review of the Application of Microwave Heating Technology in Asphalt Pavement Self-Healing and De-icing

by

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and

Polymers 2023, 15(7), 1696; https://doi.org/10.3390/polym15071696 - 29 Mar 2023

Abstract

In the past decades, a large amount of research was conducted to investigate the application prospect of microwave heating technology in improving the efficiency of asphalt pavement self-healing and de-icing. This paper reviewed the achievements in this area. Firstly, the properties of asphalt [...] Read more.

In the past decades, a large amount of research was conducted to investigate the application prospect of microwave heating technology in improving the efficiency of asphalt pavement self-healing and de-icing. This paper reviewed the achievements in this area. Firstly, the properties of asphalt concrete after microwave heating were summarized, including microwave sensitivity and heating uniformity. Then, the evaluation indicators and influence factors of the self-healing properties of the asphalt mixtures heated by microwave were reviewed. Finally, the application of microwave heating in asphalt pavement de-icing was explored. In addition, asphalt pavement aging due to microwave heating was also reviewed. It was found that microwave heating technology has good prospects in promoting asphalt pavement self-healing and de-icing. There are also some problems that should be studied in depth, such as the cost-effectiveness of microwave-sensitive additives (MSAs), the performance of the pavement with MSAs, mechanism-based self-healing performance indicators, and the aging of asphalt pavements under cycling microwave heating. Full article

(This article belongs to the Special Issue Application of Polymer Materials in Pavement Design)

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Open AccessArticle

Influence of Process Parameters on the Kinetics of the Micelle-to-Vesicle Transition and Ripening of Polystyrene-Block-Polyacrylic Acid

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Polymers 2023, 15(7), 1695; https://doi.org/10.3390/polym15071695 - 29 Mar 2023

Abstract

Due to their ability to self-assemble into complex structures, block copolymers are of great interest for use in a wide range of future applications, such as self-healing materials. Therefore, it is important to understand the mechanisms of their structure formation. In particular, the [...] Read more.

Due to their ability to self-assemble into complex structures, block copolymers are of great interest for use in a wide range of future applications, such as self-healing materials. Therefore, it is important to understand the mechanisms of their structure formation. In particular, the process engineering of the formation and transition of the polymer structures is required for ensuring reproducibility and scalability, but this has received little attention in the literature. In this article, the influence of the addition rate of the selective solvent on the homogeneity of self-assembled vesicles of polystyrene-block-polyacrylic acid is demonstrated, as well as the influence of the reaction time and the mixing intensity on the morphology of the polymer structures. For example, it was demonstrated that the higher the mixing intensity, the faster the transition from micelle to vesicle. The experimental results are further supported by CFD simulations, which visually and graphically show an increase in shear rate and narrower shear rate distributions at higher stirring rates. Furthermore, it was demonstrated that the vesicle size is not only kinetically determined, since flow forces above a critical size lead to the deformation and fission of the vesicles. Full article

(This article belongs to the Special Issue Phase Transitions and Structures in Polymer Science)

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Open AccessReview

The Biomodified Lignin Platform: A Review

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Miguel Jimenez Bartolome

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Nikolaus Schwaiger

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Georg M. Guebitz

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Renate Weiss

Polymers 2023, 15(7), 1694; https://doi.org/10.3390/polym15071694 - 29 Mar 2023

Abstract

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat [...] Read more.

A reliance on fossil fuel has led to the increased emission of greenhouse gases (GHGs). The excessive consumption of raw materials today makes the search for sustainable resources more pressing than ever. Technical lignins are mainly used in low-value applications such as heat and electricity generation. Green enzyme-based modifications of technical lignin have generated a number of functional lignin-based polymers, fillers, coatings, and many other applications and materials. These bio-modified technical lignins often display similar properties in terms of their durability and elasticity as fossil-based materials while also being biodegradable. Therefore, it is possible to replace a wide range of environmentally damaging materials with lignin-based ones. By researching publications from the last 20 years focusing on the latest findings utilizing databases, a comprehensive collection on this topic was crafted. This review summarizes the recent progress made in enzymatically modifying technical lignins utilizing laccases, peroxidases, and lipases. The underlying enzymatic reaction mechanisms and processes are being elucidated and the application possibilities discussed. In addition, the environmental assessment of novel technical lignin-based products as well as the developments, opportunities, and challenges are highlighted. Full article

(This article belongs to the Special Issue Advanced Research on Lignin and Nanostructured Lignin: Biodegradation, Properties and Applications)

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Open AccessArticle

Production of Cellulose Pulp and Lignin from High-Density Apple Wood Waste by Preimpregnation-Assisted Soda Cooking

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Polymers 2023, 15(7), 1693; https://doi.org/10.3390/polym15071693 - 29 Mar 2023

Abstract

Apple wood waste (AWW), mainly tree trucks, is collectible lignocellulosic biomass from orchard rotation. The biorefinery of AWW is challenging because of the hard and dense structure. In the present work, chemical composition determination and microstructure observation was performed for the first time [...] Read more.

Apple wood waste (AWW), mainly tree trucks, is collectible lignocellulosic biomass from orchard rotation. The biorefinery of AWW is challenging because of the hard and dense structure. In the present work, chemical composition determination and microstructure observation was performed for the first time on AWW. Alkali-preimpregnation-assisted soda cooking (APSC) was developed to separate cellulose a pulp and lignin from AWW. APSC attained pulp yield of 34.2% at 23% NaOH, showing a 13.2% improvement compared to conventional soda cooking (SC). Fiber length analysis showed APSC-AWW pulp consisted mainly of medium and short fibers, which means blending with long-fibered pulp to enhance the physical strength of pulp sheets. A blend of APSC-AWW pulp and long-fibered pulp in the proportion of 80:20 attained comparable physical strength to hardwood kraft pulp. ASPC-AWW lignin was separated from spent liquor by acidification and then purified by dialysis desalination. The purified ASPC-AWW lignin showed a weight-average molecular weight of 4462 g/mol, similar to softwood kraft lignin but more uniform. Structural analysis revealed that ASPC-AWW lignin was composed of a syringyl unit (S), guaiacyl unit(G), and p-hydroxyphenyl unit (H), and an S unit was dominant with an S/G/H ratio of 74.5:18.2:7.3. It is believed the utilization of fruit tree wood waste as the feedstock of biorefinery is attractive to countries without sufficient forestry resources. Furthermore, the developed APSC is based on conventional SC, which ensures the feasibility of an industrial application. Full article

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

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