Polymers

15 pages, 4291 KiB

Open AccessArticle

Impact of Diisocyanates on Morphological and In Vitro Biological Efficacy of Eco-Friendly Castor-Oil-Based Water-Borne Polyurethane Dispersions

by Nadia Akram, Muhammad Usman, Sajjad Haider, Muhammad Saeed Akhtar and Kashmala Gul

Polymers 2022, 14(17), 3701; https://doi.org/10.3390/polym14173701 - 5 Sep 2022

Cited by 9 | Viewed by 2375

Abstract

The search for renewable resources that can replace petroleum products is not only nerve-wracking, but also perplexing, as there is an abundance of plants that have yet to be explored. In this project, virgin castor oil was converted to polyol in two steps: [...] Read more.

The search for renewable resources that can replace petroleum products is not only nerve-wracking, but also perplexing, as there is an abundance of plants that have yet to be explored. In this project, virgin castor oil was converted to polyol in two steps: epoxidation and hydroxylation. The resulting polyol was used to synthesize two series of water-borne polyurethane dispersions (WPUDs). The effects of the diisocyanates on the final product were evaluated. Isophorone diisocyanate (IPDI) and dicyclohexylmethane-4,4′-diisocyanate (H₁₂MDI) were used as the hard segment (HS) up to 72 wt%, along with 1–4 butanediol (BD) as the chain extender, for the dispersions. Fourier transform infrared spectroscopy (FTIR) confirmed the bonds required for the synthesis of the dispersions. Thermogravimetric analysis (TGA) showed the multistep degradation for both series: maximum degradation took place at 500 °C for IPDI and 600 °C for H₁₂MDI-based series. Scanning electron microscopy (SEM) showed phase-segmented morphology. Hemolytic activity was observed at biologically safe levels of up to 7.5% for H₁₂MDI-based series. Inhibition of biofilm formation showed comparable results against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus): up to 46%. The results were also confirmed by phase contrast microscopy. Full article

(This article belongs to the Special Issue Progress of Biocompatible and Biodegradable Polymers in Biomedicine and Environment)

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29 pages, 15034 KiB

Open AccessArticle

Adhesive Wear and Frictional Performance of Banana Fibre Reinforced Epoxy (BaFRE) Composite

by Umar Nirmal

Polymers 2022, 14(17), 3700; https://doi.org/10.3390/polym14173700 - 5 Sep 2022

Cited by 1 | Viewed by 2020

Abstract

This current work is an attempt to investigate the tribological performance of banana fibre-reinforced epoxy (BaFRE) composite in dry contact conditions. The test is conducted on a wear test rig of type Block on Ring (BOR) based on ASTM G77, G137-95 standard. Different [...] Read more.

This current work is an attempt to investigate the tribological performance of banana fibre-reinforced epoxy (BaFRE) composite in dry contact conditions. The test is conducted on a wear test rig of type Block on Ring (BOR) based on ASTM G77, G137-95 standard. Different applied normal loads (5–30 N) subjected to a stainless steel counterface at different sliding speeds (1.7–3.96 m/s) and fixed sliding distance of 6.72 km were set as the experimental parameters. The test was conducted using neat epoxy (NE) as the control tests’ specimen while BaFRE composite was in anti-parallel (AP) and parallel (P) fibre strips orientation (O). The specific wear rate (Ws), friction coefficient, temperature variation and surface roughness (RA) of the NE and BaFRE composite in AP-O and P-O were investigated. The worn surface morphology of the test samples was examined under a high-resolution metallurgy microscope. The outcome of the work revealed that AP-O exhibited excellent wear performance when compared to P-O and NE. Moreover, the lowest friction coefficient of 0.0121 is achieved when AP-O is subjected to 30 N of applied load and 3.96 m/s of sliding velocity. BaFRE composite in AP-O demonstrated the lowest range of temperature variation when it was subjected to 30 N at 3.96 m/s of counterface sliding velocity. Due to the high shear resistance at the rubbing zone incurred by the AP-O test specimen and counterface, the RA values were remarkably high for the test specimen (i.e., 1.122 µm) and the counterface wear track zone (0.166 µm) as compared to the P-O and NE test samples. The predominant wear mechanism for the AP-O test specimen was plastic deformation, detached fibre, micro crack, minor fibre debonding and micro ploughing. In conclusion, there are improvements in terms of wear and friction performance of the composite when banana fibres are used as a reinforced element in epoxy resin. The improvement in Ws and friction coefficient for the AP test specimen was 29.4% and 48.6%, respectively, as compared to NE at 30 N of applied load, 6.72 km of sliding distance and 2.83 m/s of sliding speed. Full article

(This article belongs to the Section Polymer Fibers)

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17 pages, 5971 KiB

Open AccessArticle

Comparative Study on Thermal Response Mechanism of Two Binders during Slow Cook-Off

by Xinzhou Wu, Jun Li, Hui Ren and Qingjie Jiao

Polymers 2022, 14(17), 3699; https://doi.org/10.3390/polym14173699 - 5 Sep 2022

Cited by 4 | Viewed by 2693

Abstract

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the [...] Read more.

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the changes of colors and the intensity of infrared characteristic peaks were designed to characterize the differences in the thermal response mechanisms of the HTPB and HTPE binder systems. As a solid phase filler to accidental ignition, the weight loss and microscopic morphology of AP (30~230 °C) were observed by TG and SEM. The defects of the propellant caused by the cook-off were quantitatively analyzed by the box counting method. Above 120 °C, the HTPE propellant began to melt and disperse in the holes, filling the cracks, which generated during the decomposition of AP at a low temperature. Melting products were called the “high-temperature self-repair body”. A series of analyses proved that the different thermal responses of the two binders were the main cause of the slow cook-off results, which were likewise verified in the propellant mechanical properties and gel fraction test. From the microscopic point of view, the mechanism of HTPE’s slow cook-off performance superior to HTPB was revealed in this article. Full article

(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials)

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36 pages, 57873 KiB

Open AccessReview

A Review on Natural Fiber Reinforced Polymer Composites (NFRPC) for Sustainable Industrial Applications

by Siti Hasnah Kamarudin, Mohd Salahuddin Mohd Basri, Marwah Rayung, Falah Abu, So’bah Ahmad, Mohd Nurazzi Norizan, Syaiful Osman, Norshahida Sarifuddin, Mohd Shaiful Zaidi Mat Desa, Ummi Hani Abdullah, Intan Syafinaz Mohamed Amin Tawakkal and Luqman Chuah Abdullah

Polymers 2022, 14(17), 3698; https://doi.org/10.3390/polym14173698 - 5 Sep 2022

Cited by 124 | Viewed by 24669

Abstract

The depletion of petroleum-based resources and the adverse environmental problems, such as pollution, have stimulated considerable interest in the development of environmentally sustainable materials, which are composed of natural fiber–reinforced polymer composites. These materials could be tailored for a broad range of sustainable [...] Read more.

The depletion of petroleum-based resources and the adverse environmental problems, such as pollution, have stimulated considerable interest in the development of environmentally sustainable materials, which are composed of natural fiber–reinforced polymer composites. These materials could be tailored for a broad range of sustainable industrial applications with new surface functionalities. However, there are several challenges and drawbacks, such as composites processing production and fiber/matrix adhesion, that need to be addressed and overcome. This review could provide an overview of the technological challenges, processing techniques, characterization, properties, and potential applications of NFRPC for sustainable industrial applications. Interestingly, a roadmap for NFRPC to move into Industry 4.0 was highlighted in this review. Full article

(This article belongs to the Special Issue High-Performance Biocomposite Reinforced by Natural Fibers II)

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13 pages, 1787 KiB

Open AccessArticle

Development of Polymeric-Based Formulation as Potential Smart Colonic Drug Delivery System

by Mohammad F. Bayan, Saeed M. Marji, Mutaz S. Salem, M. Yasmin Begum, Kumarappan Chidambaram and Balakumar Chandrasekaran

Polymers 2022, 14(17), 3697; https://doi.org/10.3390/polym14173697 - 5 Sep 2022

Cited by 15 | Viewed by 3014

Abstract

Conventional oral formulations are mainly absorbed in the small intestine. This limits their use in the treatment of some diseases associated with the colon, where the drug has to act topically at the inflammation site. This paved the way for the development of [...] Read more.

Conventional oral formulations are mainly absorbed in the small intestine. This limits their use in the treatment of some diseases associated with the colon, where the drug has to act topically at the inflammation site. This paved the way for the development of a smart colonic drug delivery system, thereby improving the therapeutic efficacy, reducing the dosing frequency and potential side effects, as well as improving patient acceptance, especially in cases where enemas or other topical preparations may not be effective alone in treating the inflammation. In healthy individuals, it takes an oral medication delivery system about 5 to 6 h to reach the colon. A colonic drug delivery system should delay or prohibit the medication release during these five to six hours while permitting its release afterward. The main aim of this study was to develop a smart drug delivery system based on pH-sensitive polymeric formulations, synthesized by a free-radical bulk polymerization method, using different monomer and crosslinker concentrations. The formulations were loaded with 5-amino salicylic acid as a model drug and Capmul MCM C8 as a bioavailability enhancer. The glass transition temperature (Tg), tensile strength, Young’s modulus, and tensile elongation at break were all measured as a part of the dried films’ characterization. In vitro swelling and release studies were performed to assess the behavior of the produced formulations. The in vitro swelling and release evaluation demonstrated the potential ability of the developed system to retard the drug release at conditions mimicking the stomach and small intestine while triggering its release at conditions mimicking the colon, which indicates its promising applicability as a potential smart colonic drug delivery system. Full article

(This article belongs to the Special Issue Advances in Sustainable Polymeric Materials)

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16 pages, 5274 KiB

Open AccessArticle

Mechanical, Hydrophobic, and Barrier Properties of Nanocomposites of Modified Polypropylene Reinforced with Low-Content Attapulgite

by Chi-Hui Tsou, Rui Zeng, Chih-Yuan Tsou, Jui-Chin Chen, Ya-Li Sun, Zheng-Lu Ma, Manuel Reyes De Guzman, Lian-Jie Tu, Xin-Yuan Tian and Chin-San Wu

Polymers 2022, 14(17), 3696; https://doi.org/10.3390/polym14173696 - 5 Sep 2022

Cited by 12 | Viewed by 2299

Abstract

Attapulgite (ATT) has never been used as a barrier additive in polypropylene (PP). As a filler, ATT should be added in high content to PP. However, that would result in increased costs. Moreover, the compatibility between ATT and the PP matrix is poor [...] Read more.

Attapulgite (ATT) has never been used as a barrier additive in polypropylene (PP). As a filler, ATT should be added in high content to PP. However, that would result in increased costs. Moreover, the compatibility between ATT and the PP matrix is poor due to the lack of functional groups in PP. In this study, carboxylic groups were introduced to PP to form a modified polypropylene (MPP). ATT was purified, and a low content of it was added to MPP to prepare MPP/ATT nanocomposites. The analysis from FTIR indicated that ATT could react with MPP. According to the results of oxygen and water permeability tests, the barrier performance of the nanocomposite was optimal when the ATT content was 0.4%. This great improvement in barrier performance might be ascribed to the following three reasons: (1) The existence of ATT extended the penetration path of O₂ or H₂O molecules; (2) O₂ or H₂O molecules may be adsorbed and stored in the porous structure of ATT; (3) Most importantly, –COOH of MPP reacted with –OH on the surface of ATT, thereby the inner structure of the nanocomposite was denser, and it was less permeable to molecules. Therefore, nanocomposites prepared by adding ATT to MPP have excellent properties and low cost. They can be used as food packaging materials and for other related applications. Full article

(This article belongs to the Special Issue Mechanical and Structure–Property Relationships of Polymer Composites)

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11 pages, 3662 KiB

Open AccessArticle

Colorimetric Freshness Indicator Based on Cellulose Nanocrystal–Silver Nanoparticle Composite for Intelligent Food Packaging

by Seongyoung Kwon and Seonghyuk Ko

Polymers 2022, 14(17), 3695; https://doi.org/10.3390/polym14173695 - 5 Sep 2022

Cited by 17 | Viewed by 2660

Abstract

In this study, a colorimetric freshness indicator based on cellulose nanocrystal-silver nanoparticles (CNC-AgNPs) was successfully fabricated to offer a convenient approach for monitoring the quality of packaged food. AgNPs were directly synthesized and embedded in CNC via a one-pot hydrothermal green synthesis, and [...] Read more.

In this study, a colorimetric freshness indicator based on cellulose nanocrystal-silver nanoparticles (CNC-AgNPs) was successfully fabricated to offer a convenient approach for monitoring the quality of packaged food. AgNPs were directly synthesized and embedded in CNC via a one-pot hydrothermal green synthesis, and CNC-AgNP composited indicator films were prepared using a simple casting method. The AgNPs obtained were confirmed by UV-Vis diffuse reflectance spectroscopy and X-ray diffraction. The ability of the as-prepared CNC-AgNP film to indicate food quality was assessed in terms of the intensity of its color change when in contact with spoilage gases from chicken breast. The CNC-AgNP films initially exhibited a yellowish to dark wine-red color depending on the amount of AgNPs involved. They gradually turned colorless and subsequently to metallic grey. This transition is attributed to the reaction of AgNPs and hydrogen sulfide (H₂S), which alters the surface plasmon resonance of AgNPs. Consequently, the color change was suitably discernible to the human eye, implying that the CNC-AgNP composite is a highly effective colorimetric freshness indicator. It can potentially serve as an accurate and irreversible food quality indicator in intelligent packaging during distribution or storage of products that emit hydrogen sulfide when deteriorating, such as poultry products or broccoli. Full article

(This article belongs to the Special Issue Active and Intelligent Food Packaging Polymers)

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13 pages, 3174 KiB

Open AccessArticle

Functional Nanogel from Natural Substances for Delivery of Doxorubicin

by Katya Kamenova, Lyubomira Radeva, Krassimira Yoncheva, Filip Ublekov, Martin A. Ravutsov, Maya K. Marinova, Svilen P. Simeonov, Aleksander Forys, Barbara Trzebicka and Petar D. Petrov

Polymers 2022, 14(17), 3694; https://doi.org/10.3390/polym14173694 - 5 Sep 2022

Cited by 8 | Viewed by 2695

Abstract

Nanogels (NGs) have attracted great attention because of their outstanding biocompatibility, biodegradability, very low toxicity, flexibility, and softness. NGs are characterized with a low and nonspecific interaction with blood proteins, meaning that they do not induce any immunological responses in the body. Due [...] Read more.

Nanogels (NGs) have attracted great attention because of their outstanding biocompatibility, biodegradability, very low toxicity, flexibility, and softness. NGs are characterized with a low and nonspecific interaction with blood proteins, meaning that they do not induce any immunological responses in the body. Due to these properties, NGs are considered promising candidates for pharmaceutical and biomedical application. In this work, we introduce the development of novel functional nanogel obtained from two naturally based products—citric acid (CA) and pentane-1,2,5-triol (PT). The nanogel was synthesized by precipitation esterification reaction of CA and PT in tetrahydrofuran using N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC) and 4-(dimethylamino)pyridine (DMAP) catalyst system. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM) analyses revealed formation of spherical nanogel particles with a negative surface charge. Next, the nanogel was loaded with doxorubicin hydrochloride (DOX) by electrostatic interactions between carboxylic groups present in the nanogel and amino groups of DOX. The drug-loaded nanogel exhibited high encapsulation efficiency (EE~95%), and a bi-phasic release behavior. Embedding DOX into nanogel also stabilized the drug against photodegradation. The degradability of nanogel under acidic and neutral conditions with time was investigated as well. Full article

(This article belongs to the Special Issue Polymeric Carriers for Delivery Systems in Biomedical Applications – in Memory of Professor Andrzej Dworak)

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20 pages, 4001 KiB

Open AccessArticle

Polycarbonate/Titania Composites Incorporating TiO₂ with Different Nanoscale Morphologies for Enhanced Environmental Stress Cracking Resistance in Dioctyl Phthalate

by Yasir Khalid, Amine Achour, Muhammad Aftab Akram and Mohammad Islam

Polymers 2022, 14(17), 3693; https://doi.org/10.3390/polym14173693 - 5 Sep 2022

Cited by 5 | Viewed by 2327

Abstract

Polycarbonate (PC) is susceptible to environmental stress cracking (ESC) when the conditions of pre-strain and presence of fluid with a compatible solubility index are both prevalent. One approach to counter this involves using nanoscale fillers to bridge the propagating microcracks, thus, effectively inhibiting [...] Read more.

Polycarbonate (PC) is susceptible to environmental stress cracking (ESC) when the conditions of pre-strain and presence of fluid with a compatible solubility index are both prevalent. One approach to counter this involves using nanoscale fillers to bridge the propagating microcracks, thus, effectively inhibiting impending failure. In this work, we report incorporation of titania (TiO₂) with different nanoscale morphologies into polycarbonate matrix to assess its effect on ESC resistance against dioctyl phthalate (DOP). Using a hydrothermal process with a NaOH/Ti molar ratio of 72, TiO₂ nanostructures were produced containing nanosheets with large surface area and nanotubes having typical diameter and length values of 15–20 nm and a few hundred nanometers, respectively. PC/TiO₂ composites were fabricated with up to 0.5 weight percent of TiO₂ nanoparticles (NPs), nanowires (NWs), or hybrid nanostructures (HNs). ESC tests were conducted by exposing test coupons to DOP oil at different temperatures and pre-strain conditions. The results showed that, under identical test conditions, while as-received PC grade exhibited complete fracture in ~3.1 h, PC/TiO₂-0.05HN composite took ~70 h to fail via surface cracking. SEM examination of the fracture surface revealed that homogeneous dispersion and efficient load-bearing capability of TiO₂ nanotubes and nanosheets impeded localized crack propagation by bridging the gap between the PC matrix segments. Liquid nitrogen fracture of the PC/TiO₂ composite further confirmed the critical role of TiO₂ hybrid nanostructures towards improvement in ESC resistance of PC matrix composites. Full article

(This article belongs to the Collection Feature Papers in Polymer Processing and Engineering)

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17 pages, 4839 KiB

Open AccessArticle

Imidazolium Salt for Enhanced Interfacial Shear Strength in Polyphenylene Sulfide/Ex-PAN Carbon Fiber Composites

by Baptiste Gaumond, Sébastien Livi, Jean-François Gérard and Jannick Duchet-Rumeau

Polymers 2022, 14(17), 3692; https://doi.org/10.3390/polym14173692 - 5 Sep 2022

Cited by 1 | Viewed by 1785

Abstract

Processing structural or semi-structural thermoplastic-based composites is a promising solution to solve the environmental issues of the aeronautic industry. However, these composites must withstand high standard specification to ensure safety during transportation. For this reason, there is a real need to develop strong [...] Read more.

Processing structural or semi-structural thermoplastic-based composites is a promising solution to solve the environmental issues of the aeronautic industry. However, these composites must withstand high standard specification to ensure safety during transportation. For this reason, there is a real need to develop strong interactions between thermoplastic polymers and reinforcement fibers. This paper investigates relationships between the surface chemistry, microstructure and micromechanical properties between polyphenylene sulfide and ex-PAN carbon fibers. The incorporation of ionic salt such as 1,3-Bis(4-carboxyphenyl)imidazolium chloride into neat polyphenylene sulfide was able to significantly increase the interfacial shear strength measured by microbond micromechanical test combined with different carbon fiber surfaces treatment. Full article

(This article belongs to the Special Issue Mechanical Properties and Durability of Advanced Polymers and Polymer Composites)

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13 pages, 13431 KiB

Open AccessArticle

The Effect of Topology on Block Copolymer Nanoparticles: Linear versus Star Block Copolymers in Toluene

by Yuan Zhang, Peng Wang, Nan Li, Chunyan Guo and Sumin Li

Polymers 2022, 14(17), 3691; https://doi.org/10.3390/polym14173691 - 5 Sep 2022

Cited by 5 | Viewed by 2053

Abstract

Linear and star block copolymer (BCP) nanoparticles of (polystyrene-block-poly(4-vinylpyridine))_n (PS-b-P4VP)_n with arm numbers of 1, 2, 3, and 4 were prepared by two methods of polymerization-induced self-assembly (PISA) and general self-assembly of block copolymers in the low-polar [...] Read more.

Linear and star block copolymer (BCP) nanoparticles of (polystyrene-block-poly(4-vinylpyridine))_n (PS-b-P4VP)_n with arm numbers of 1, 2, 3, and 4 were prepared by two methods of polymerization-induced self-assembly (PISA) and general self-assembly of block copolymers in the low-polar organic solvent, toluene. The effect of the arm number on the size and/or morphology of the (PS-b-P4VP)_n nanoassemblies synthesized by the two methods in toluene and on the polymerization kinetics was investigated in detail. Our results show that in toluene, a low-polar solvent, the topology not only affected the morphology of the BCP nanoparticles prepared by PISA, but also influenced the BCP nanoparticles synthesized through general self-assembly. Full article

(This article belongs to the Special Issue Advances and Applications of Block Copolymers)

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21 pages, 8491 KiB

Open AccessArticle

Assessing Molecular Docking Tools to Guide the Design of Polymeric Materials Formulations: A Case Study of Canola and Soybean Protein

by Frage Abookleesh, Farag E. S. Mosa, Khaled Barakat and Aman Ullah

Polymers 2022, 14(17), 3690; https://doi.org/10.3390/polym14173690 - 5 Sep 2022

Cited by 5 | Viewed by 3669

Abstract

After more than 40 years of biopolymer development, the current research is still based on conventional laboratory techniques, which require a large number of experiments. Therefore, finding new research methods are required to accelerate and power the future of biopolymeric development. In this study, [...] Read more.

After more than 40 years of biopolymer development, the current research is still based on conventional laboratory techniques, which require a large number of experiments. Therefore, finding new research methods are required to accelerate and power the future of biopolymeric development. In this study, promising biopolymer–additive ranking was described using an integrated computer-aided molecular design platform. In this perspective, a set of 21 different additives with plant canola and soy proteins were initially examined by predicting the molecular interactions scores and mode of molecule interactions within the binding site using AutoDock Vina, Molecular Operating Environment (MOE), and Molecular Mechanics/Generalized Born Surface Area (MM-GBSA). The findings of the investigated additives highlighted differences in their binding energy, binding sites, pockets, types, and distance of bonds formed that play crucial roles in protein–additive interactions. Therefore, the molecular docking approach can be used to rank the optimal additive among a set of candidates by predicting their binding affinities. Furthermore, specific molecular-level insights behind protein–additives interactions were provided to explain the ranking results. The highlighted results can provide a set of guidelines for the design of high-performance polymeric materials at the molecular level. As a result, we suggest that the implementation of molecular modeling can serve as a fast and straightforward tool in protein-based bioplastics design, where the correct ranking of additives among sets of candidates is often emphasized. Moreover, these approaches may open new ways for the discovery of new additives and serve as a starting point for more in-depth investigations into this area. Full article

(This article belongs to the Collection Biopolymers: Synthesis and Properties)

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17 pages, 9140 KiB

Open AccessArticle

Synthesis of Green and Red-Emitting Polymethyl Methacrylate Composites Grafted from ZnAl₂O₄:Mn-Bonded GO via Surface-Initiated Atom Transfer Radical Polymerization

by Ming Gao, Chi-Fai Cheung, Bo Wang and Chunjin Wang

Polymers 2022, 14(17), 3689; https://doi.org/10.3390/polym14173689 - 5 Sep 2022

Cited by 3 | Viewed by 1597

Abstract

A novel dual green and red-emitting photoluminescent polymer composite ZnAl₂O₄:Mn-bonded GO/polymethyl methacrylate (PMMA) was synthesized in a single-step reaction by surface-initiated atom transfer radical polymerization (SI-ATRP). The polymer chain was surface-initiated from the ZnAl₂O₄:Mn/GO, and [...] Read more.

A novel dual green and red-emitting photoluminescent polymer composite ZnAl₂O₄:Mn-bonded GO/polymethyl methacrylate (PMMA) was synthesized in a single-step reaction by surface-initiated atom transfer radical polymerization (SI-ATRP). The polymer chain was surface-initiated from the ZnAl₂O₄:Mn/GO, and the final products have a homogenous photoluminescent property from ZnAl₂O₄:Mn and better mechanical properties strengthened by graphene oxide (GO). The morphologies of ZnAl₂O₄:Mn/GO and the polymer composites were verified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction analysis (XRD) revealed the two valence states of Mn (Mn²⁺, Mn⁴⁺) existing in the ZnAl₂O₄ host lattice, while Fourier-transform infrared spectroscopy (FTIR) spectra proved the transference of the active group, C-Br, from the initiator to the monomer during the polymerization. Gel permeation chromatography (GPC) shows the narrow dispersity of polymer composites fabricated through SI-ATRP. The SEM and FTIR results show the successful ‘graft’ of the polymer chains from the surface of ZnAl₂O₄:Mn/GO. The dual green and red-emitting polymer composites were synthesized, confirmed by the photoluminescence (PL) and photoluminescence excitation (PLE) results. Full article

(This article belongs to the Special Issue Functional Polymer Materials: Design, Synthesis and Application)

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14 pages, 3906 KiB

Open AccessArticle

Fast Granulation by Combining External Sludge Conditioning with FeCl₃ Addition and Reintroducing into an SBR

by Jun Liu, Shunchang Yin, Dong Xu, Sarah Piché-Choquette, Bin Ji, Xin Zhou and Jun Li

Polymers 2022, 14(17), 3688; https://doi.org/10.3390/polym14173688 - 5 Sep 2022

Cited by 2 | Viewed by 1774

Abstract

The separation of light and heavy sludge, as well as the aggregation rate of floccular sludge, are two critical aspects of the rapid granulation process in sequencing batch reactors (SBRs) in the early stages. In this study, we investigated the impact of a [...] Read more.

The separation of light and heavy sludge, as well as the aggregation rate of floccular sludge, are two critical aspects of the rapid granulation process in sequencing batch reactors (SBRs) in the early stages. In this study, we investigated the impact of a method to improve both sludge separation and granulation by coupling effluent sludge external conditioning with FeCl₃ addition and then reintroducing it into the SBR. By supplementation with 0.1 g Fe³⁺ (g dried sludge (DS))⁻¹, the concentration of extracellular polymeric substances (EPS) and sludge retention efficiency greatly increased, whereas the moisture content and specific oxygen uptake rate (SOUR) sharply decreased within 24 h external conditioning. Aggregates (1.75 ± 0.05 g·L⁻¹) were reintroduced into the bioreactor once daily from day 13 to day 15. Afterwards, on day 17, aerobic granules with a concentration of mixed liquor suspended solids (MLSS) of 5.636 g/L, a sludge volume index (SVI₃₀) of 45.5 mL/g and an average size of 2.5 mm in diameter were obtained. These results suggest that the external conditioning step with both air-drying and the addition of Fe³⁺ enhanced the production of EPS in the effluent sludge and improved rapid aggregation and high sludge retention efficiency. Consequently, the reintroduced aggregates with good traits shortened the time required to obtain mature aerobic granular sludge (AGS) and properly separate light and heavy sludge. Indeed, this method jump-started the aggregation, and rapid granulation processes were successful in this work. Additionally, while the removal efficiency of chemical oxygen demand (COD) and nitrogen from ammonium (NH₄⁺-N) decreased when reintroducing the treated sludge into the SBR, such properties increased again as the AGS matured in the SBR, up to removal efficiencies of 96% and 95%, respectively. Full article

(This article belongs to the Special Issue Polymeric Materials for Water/Wastewater Treatment Applications)

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10 pages, 2986 KiB

Open AccessArticle

Evaluation of the Change in Density with the Diameter and Thermal Analysis of the Seven-Islands-Sedge Fiber

by Lucas de Mendonça Neuba, Raí Felipe Pereira Junio, Andressa Teixeira Souza, Matheus Pereira Ribeiro, Pedro Henrique Poubel Mendonça da Silveira, Thuane Teixeira da Silva, Artur Camposo Pereira and Sergio Neves Monteiro

Polymers 2022, 14(17), 3687; https://doi.org/10.3390/polym14173687 - 5 Sep 2022

Cited by 6 | Viewed by 2148

Abstract

Basic properties of sedge fibers from the seven-islands-sedge plant (Cyperus malaccensis) were investigated with possible application in reinforcing composite materials. A dimensional distribution and the effect of fiber diameter on density were investigated using gas pycnometry. The Weibull method, used to [...] Read more.

Basic properties of sedge fibers from the seven-islands-sedge plant (Cyperus malaccensis) were investigated with possible application in reinforcing composite materials. A dimensional distribution and the effect of fiber diameter on density were investigated using gas pycnometry. The Weibull method, used to statistically analyze the acquired data from the diameter intervals, indicated an inverse dependence, where the thinnest fibers had the highest density values. The morphology of the fibers was obtained through scanning electron microscopy (SEM), in which a lower presence of defects was revealed in the thinner fibers, corroborating the inverse density dependence. In addition, the sedge fiber was characterized by differential scanning calorimetry and thermogravimetric analysis, which indicate an initial thermal degradation at around 241 °C. These results revealed for the first time that thinner sedge fibers might be promising reinforcement for polymer composites with a limit in temperature application. Full article

(This article belongs to the Special Issue Natural Fibre Composites and Their Mechanical Behavior)

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13 pages, 3137 KiB

Open AccessArticle

Vibrational Emission Study of the CN and C₂ in Nylon and ZnO/Nylon Polymer Using Laser-Induced Breakdown Spectroscopy (LIBS)

by Tahani A. Alrebdi, Amir Fayyaz, Amira Ben Gouider Trabelsi, Haroon Asghar, Fatemah H. Alkallas and Ali M. Alshehri

Polymers 2022, 14(17), 3686; https://doi.org/10.3390/polym14173686 - 5 Sep 2022

Cited by 10 | Viewed by 2453

Abstract

The laser-induced breakdown spectroscopy (LIBS) technique was performed on polymers to study the neutral and ionic emission lines along with the CN violet system (B²Σ⁺ to X²Σ⁺) and the C₂ Swan system (d³ П [...] Read more.

The laser-induced breakdown spectroscopy (LIBS) technique was performed on polymers to study the neutral and ionic emission lines along with the CN violet system (B²Σ⁺ to X²Σ⁺) and the C₂ Swan system (d³ П_g–a³ П_u). For the laser-based emission analyses, the plasma was produced by focusing the laser beam of a Q-switched Nd: YAG laser (2ω) at an optical wavelength of 532 nm, 5 ns pulse width, and a repetition frequency of 10 Hz. The integration time of the detection system was fixed at 1–10 ms while the target sample was positioned in air ambiance. Two organic polymers were investigated in this work: nylon and nylon doped with ZnO. The molecular optical emission study of nylon and doped nylon polymer sample reveals CN and C₂ molecular structures present in the polymer. The vibrational emission analysis of CN and C₂ bands gives information about the molecular structure of polymers and dynamics influencing the excitation structures of the molecules. Besides, it was further investigated that the intensity of the molecular optical emission structure strongly depends on the electron number density (cm⁻³), excitation temperature (eV), and laser irradiance (W/cm²). These results suggest that LIBS is a reliable diagnostic technique for the study of polymers regarding their molecular structure, identification, and compositional analysis. Full article

(This article belongs to the Special Issue Smart Textile and Polymer Materials)

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15 pages, 3739 KiB

Open AccessArticle

Bactericidal Anti-Adhesion Potential Integrated Polyoxazoline/Silver Nanoparticle Composite Multilayer Film with pH Responsiveness

by Xiaojiong Bao, Xiaofei Huang, Xiaoqiang Jin and Qiaoling Hu

Polymers 2022, 14(17), 3685; https://doi.org/10.3390/polym14173685 - 5 Sep 2022

Cited by 2 | Viewed by 2278

Abstract

Bacterial infections occur frequently during the implantation of medical devices, and functional coating is one of the effective means to prevent and remove biofilms. In this study, three different hydrophilic polyoxazolines with carboxyl groups (aPOx: PT1, PT2 and PT3) and bactericidal silver nanoparticles [...] Read more.

Bacterial infections occur frequently during the implantation of medical devices, and functional coating is one of the effective means to prevent and remove biofilms. In this study, three different hydrophilic polyoxazolines with carboxyl groups (aPOx: PT1, PT2 and PT3) and bactericidal silver nanoparticles (AgNPs) were synthesized successfully, and an aPOx-AgNP multilayer film was prepared by electrostatic layer-by-layer self-assembly. The effect of charge density and assembly solution concentration was explored, and the optimal self-assembly parameters were established (PT2 1 mg/mL and AgNPs 3 mg/mL). The hydrophilicity of the surface can be enhanced to resist protein adhesion if the outermost layer is aPOx, and AgNPs can be loaded to kill bacteria, thereby realizing the bactericidal anti-adhesion potential integration of the aPOx-AgNP multilayer film. In addition, the aPOx-AgNP multilayer film was found to have the characteristic of intelligent and efficient pH-responsive silver release, which is expected to be used as a targeted anti-biofilm surface of implantable medical devices. Full article

(This article belongs to the Special Issue Metal Nanoparticles–Polymers Hybrid Materials III)

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14 pages, 4254 KiB

Open AccessArticle

Slurry Homopolymerization of Ethylene Using Thermostable α-Diimine Nickel Catalysts Covalently Linked to Silica Supports via Substituents on Acenaphthequinone-Backbone

by Kening Zong, Yanhui Hou, Xiaobei Zhao, Yali Sun, Binyuan Liu and Min Yang

Polymers 2022, 14(17), 3684; https://doi.org/10.3390/polym14173684 - 5 Sep 2022

Cited by 2 | Viewed by 1914

Abstract

Four supported α-diimine nickel(II) catalysts covalently linked to silica via hydroxyl functionality on α-diimine acenaphthequinone-backbone were prepared and used in slurry polymerizations of ethylene to produce branched polyethylenes. The catalytic activities of these still reached 10⁶ g/molNi·h at 70 °C. The life [...] Read more.

Four supported α-diimine nickel(II) catalysts covalently linked to silica via hydroxyl functionality on α-diimine acenaphthequinone-backbone were prepared and used in slurry polymerizations of ethylene to produce branched polyethylenes. The catalytic activities of these still reached 10⁶ g/molNi·h at 70 °C. The life of the supported catalyst is prolonged, as can be seen from the kinetic profile. The molecular weight of the polyethylene obtained by the 955 silica gel supported catalyst was higher than that obtained by the 2408D silica gel supported catalyst. The melting points of polyethylene obtained by the supported catalysts S-C1-a/b are all above 110 °C. Compared with the homogeneous catalyst, the branching numbers of the polyethylenes obtained by the supported catalysts S-C1-a/b is significantly lower. The polyethylenes obtained by supported catalyst S-C1-a/b at 30–50 °C are free-flowing particles, which is obviously better than the rubber-like cluster polymer obtained from homogeneous catalyst. Full article

(This article belongs to the Collection Polymerization and Kinetic Studies)

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18 pages, 3201 KiB

Open AccessArticle

Rheological Method for Determining the Molecular Weight of Collagen Gels by Using a Machine Learning Technique

by Karina C. Núñez Carrero, Cristian Velasco-Merino, María Asensio, Julia Guerrero and Juan Carlos Merino

Polymers 2022, 14(17), 3683; https://doi.org/10.3390/polym14173683 - 5 Sep 2022

Cited by 1 | Viewed by 3522

Abstract

This article presents, for the first time, the results of applying the rheological technique to measure the molecular weights (Mw) and their distributions (MwD) of highly hierarchical biomolecules, such as non-hydrolyzed collagen gels. Due to the high viscosity of the studied gels, the [...] Read more.

This article presents, for the first time, the results of applying the rheological technique to measure the molecular weights (Mw) and their distributions (MwD) of highly hierarchical biomolecules, such as non-hydrolyzed collagen gels. Due to the high viscosity of the studied gels, the effect of the concentrations on the rheological tests was investigated. In addition, because these materials are highly sensitive to denaturation and degradation under mechanical stress and temperatures close to 40 °C, when frequency sweeps were applied, a mathematical adjustment of the data by machine learning techniques (artificial intelligence tools) was designed and implemented. Using the proposed method, collagen fibers of Mw close to 600 kDa were identified. To validate the proposed method, lower Mw species were obtained and characterized by both the proposed rheological method and traditional measurement techniques, such as chromatography and electrophoresis. The results of the tests confirmed the validity of the proposed method. It is a simple technique for obtaining more microstructural information on these biomolecules and, in turn, facilitating the design of new structural biomaterials with greater added value. Full article

(This article belongs to the Special Issue Smart Natural-Based Polymers)

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13 pages, 3791 KiB

Open AccessArticle

Superhydrophobic Nanosilica Decorated Electrospun Polyethylene Terephthalate Nanofibers for Headspace Solid Phase Microextraction of 16 Organochlorine Pesticides in Environmental Water Samples

by Hamid Najarzadekan, Hassan Sereshti, Irfan Ahmad, Syed Shahabuddin, Hamid Rashidi Nodeh and Nanthini Sridewi

Polymers 2022, 14(17), 3682; https://doi.org/10.3390/polym14173682 - 5 Sep 2022

Cited by 5 | Viewed by 1879

Abstract

A new solid phase micro extraction (SPME) fiber coating composed of electrospun polyethylene terephthalate (PET) nanofibrous mat doped with superhydrophobic nanosilica (SiO₂) was coated on a stainless-steel wire without the need of a binder. The coating was characterized by scanning electron [...] Read more.

A new solid phase micro extraction (SPME) fiber coating composed of electrospun polyethylene terephthalate (PET) nanofibrous mat doped with superhydrophobic nanosilica (SiO₂) was coated on a stainless-steel wire without the need of a binder. The coating was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR) techniques and it was used in headspace-SPME of 16 organochlorine pesticides in water samples prior to gass chromatography micro electron capture detector (GC-µECD) analysis. The effects of main factors such as adsorption composition, electrospinning flow rate, salt concentration, extraction temperature, extraction time, and desorption conditions were investigated. Under the optimum conditions, the linear dynamic range (8–1000 ng L⁻¹, R² > 0.9907), limits of detection (3–80 ng L⁻¹), limits of quantification (8–200 ng L⁻¹), intra-day and inter-day precisions (at 400 and 1000 ng L⁻¹, 1.7–13.8%), and fiber-to-fiber reproducibility (2.4–13.4%) were evaluated. The analysis of spiked tap, sewage, industrial, and mineral water samples for the determination of the analytes resulted in satisfactory relative recoveries (78–120%). Full article

(This article belongs to the Special Issue Novel Wastewater Treatment Applications Using Polymeric Materials)

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10 pages, 1749 KiB

Open AccessArticle

Morphological, Chemical, and Physical–Mechanical Properties of a Clumping Bamboo (Thyrsostachys oliveri) for Construction Applications

by Zhenhua Zhang, Fei Rao and Yujun Wang

Polymers 2022, 14(17), 3681; https://doi.org/10.3390/polym14173681 - 5 Sep 2022

Cited by 7 | Viewed by 2735

Abstract

In view of the long-term utilization history as a building and furniture making material in southeast Asian countries, Thyrsostachys oliveri is considered to have great utilization potential. However, little is known about the quantitative morphological characteristics and comprehensive material properties of its culm. [...] Read more.

In view of the long-term utilization history as a building and furniture making material in southeast Asian countries, Thyrsostachys oliveri is considered to have great utilization potential. However, little is known about the quantitative morphological characteristics and comprehensive material properties of its culm. In this study, we systematically investigated the morphological characteristics, the chemical components, and the physical–mechanical properties of the three-year-old culm of T. oliveri. The morphological analysis result showed that the internode length, the diameter of internodes and the wall thickness changed with the culm height. The volume of the culm wall of a single internode increased before the 10th internode, and then it decreased to a significant level at the 20th internode. The basic chemical compositions (cellulose, hemicellulose, lignin and silicon content) of the culm wall were 346.19 mg/g, 95.32 mg/g, 33.17%, and 3.39 mg/g, respectively. These component contents were relatively stable in the bottom and middle part of the culm, but changed significantly in the upper part of the culm. The moisture content and the base density of the culm wall were 73.01% and 0.64 g/cm³, respectively. The culm wall shrinkage rate in the radial, tangential direction as well as the volumetric shrinkage reached the minimum value in the middle part of the culm. The average compressive strength, modulus of rupture and modulus of elasticity of the culm wall were 67.03 MPa, 143.74 MPa, and 7.99 GPa, respectively. These results provide valuable reference data for more rational use of this bamboo resources. Full article

(This article belongs to the Collection Wood Composites)

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14 pages, 8629 KiB

Open AccessArticle

Molecular Dynamics Simulations of the Interactions between a Hydrolyzed Polyacrylamide with the Face and Edge Surfaces of Molybdenite

by Luver Echeverry-Vargas, Darwin Estrada and Leopoldo Gutierrez

Polymers 2022, 14(17), 3680; https://doi.org/10.3390/polym14173680 - 5 Sep 2022

Cited by 2 | Viewed by 2129

Abstract

Process water used in mineral processing operations corresponds to water recovered from the thickeners and tailings dams, containing residual reagents such as hydrolyzed polyacrylamides (HPAMs). These polymers depress the flotation of different minerals, and their effect on molybdenite has been experimentally demonstrated. The [...] Read more.

Process water used in mineral processing operations corresponds to water recovered from the thickeners and tailings dams, containing residual reagents such as hydrolyzed polyacrylamides (HPAMs). These polymers depress the flotation of different minerals, and their effect on molybdenite has been experimentally demonstrated. The objective of this work was to study the interactions between a segment of a HPAM with the face and edge of molybdenite. The sigma profile, the radial distribution functions of the HPAM, and the orientation and atomic density profiles of water molecules on the face and edge surfaces of molybdenite were calculated. The results obtained from molecular dynamics simulations showed that the interactions between the HPAM and molybdenite are mainly explained by the interactions of the amide group with the faces and edges of the mineral. Molecular dynamics simulations also showed that the HPAM molecule rearranges in such a way that the amide group moves towards the molybdenite face or edge, and the carboxylate group moves away from the mineral surface. The results obtained in the simulations showed that the interactions of the HPAM with the molybdenite edge are slightly stronger than the interaction of this molecule with the mineral face. Simulations demonstrated that the presence of the sodium and hydroxide ions reduces the concentration of HPAM around the face and edge surfaces, which is expected to affect HPAM adsorption on molybdenite. The conclusions obtained through molecular dynamics simulations are in line with the results obtained in previous studies carried out at a macroscopic scale, which reported that HPAMs adsorb onto molybdenite particles and reduce their hydrophobicity. Full article

(This article belongs to the Section Smart and Functional Polymers)

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19 pages, 6310 KiB

Open AccessArticle

Long-Term Water Absorption of Hybrid Flax Fibre-Reinforced Epoxy Composites with Graphene and Its Influence on Mechanical Properties

by Amer Oun, Allan Manalo, Omar Alajarmeh, Rajab Abousnina and Andreas Gerdes

Polymers 2022, 14(17), 3679; https://doi.org/10.3390/polym14173679 - 5 Sep 2022

Cited by 16 | Viewed by 2565

Abstract

Interest in the use of natural fibres as an alternative for artificial fibres in polymer composite manufacturing is increasing for various engineering applications. Their suitability for use in outdoor environments should be demonstrated due to their perceived hydrophilic behaviour. This study investigated the [...] Read more.

Interest in the use of natural fibres as an alternative for artificial fibres in polymer composite manufacturing is increasing for various engineering applications. Their suitability for use in outdoor environments should be demonstrated due to their perceived hydrophilic behaviour. This study investigated the water absorption behaviour of hybrid flax fibre-reinforced epoxy composites with 0%, 0.5%, 1% and 1.5% graphene by weight that were immersed in water for 1000, 2000, and 3000 h. The flexural and interlaminar shear strength before and after immersion in water was then evaluated. The results showed that graphene nanoparticles improved the mechanical properties of the composites. The moisture absorption process of hybrid natural fibre composites followed the Fickian law, whereas the addition of graphene significantly reduced the moisture absorption and moisture diffusion, especially for hybrid composites with 1.5% graphene. However, the flexural and ILSS properties of the composites with and without graphene decreased with the increase in the exposure duration. The flexural strength of hybrid composites with 0%, 0.5%, 1% and 1.5% graphene decreased by 32%, 11%, 17.5% and 13.4%, respectively, after exposure for 3000 h. For inter-laminar shear strength at the same conditioning of 3000 h, hybrid composites with 0.5%, 1% and 1.5% graphene also decreased by 13.2%, 21% and 17.5%, respectively, compared to the dry composite’s strength. The specimens with 0.5% graphene showed the lowest reduction in strength for both the flexural and interlaminar tests, due to good filler dispersion in the matrix, but all of them were still higher than that of flax fibre composites. Scanning electron microscope observations showed a reduction in voids in the composite matrix after the introduction of graphene, resulting in reduced moisture absorption and moisture diffusion. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer Composites: Manufacturing and Performance)

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15 pages, 5337 KiB

Open AccessArticle

Extra-Oral Three-Dimensional (3D) Scanning Evaluation of Three Different Impression Materials—An In Vitro Study

by Eugen S. Bud, Vlad I. Bocanet, Mircea H. Muntean, Alexandru Vlasa, Mariana Păcurar, Irina Nicoleta Zetu, Bianca I. Soporan and Anamaria Bud

Polymers 2022, 14(17), 3678; https://doi.org/10.3390/polym14173678 - 5 Sep 2022

Cited by 7 | Viewed by 2692

Abstract

Impression materials are used to record and reproduce the exact morphology of the patient’s oral cavity. The dimensional stability of a material is its ability to maintain the accuracy of recording the details of the oral cavity for a longer period of time, [...] Read more.

Impression materials are used to record and reproduce the exact morphology of the patient’s oral cavity. The dimensional stability of a material is its ability to maintain the accuracy of recording the details of the oral cavity for a longer period of time, including the time during imprinting and immediately after. The aim of this study was to evaluate the accuracy of three different impression materials commonly used in the dental practice with the aid of an extra-oral three-dimensional (3D) scanner using an in vitro analysis. A typodont tooth model of the maxillary dental arch and mandibular dental arch, containing 16 permanent teeth, was used for evaluation. With the aid of three different impression materials, this model was imprinted fifteen times, resulting in fifteen different plaster models. A capsule extra-oral scanner device was used to digitalize the models and the same device was later used to align, compare, and measure scanned model surfaces. After performing the Kruskal–Wallis test for each measurement category (model), only two out of the fifteen measurements showed statistically significant differences between the material groups: vestibular-oral and mesial-distal width. Post hoc analysis showed that the alginate model (mean range = 29.13) had significantly higher bias scores than the addition silicone model (mean range = 16.75) (z = 2.501, p = 0.037). The difference between the average values of the model bias made from condensation-based silicone and addition-based silicone was initially significant, but after applying the Bonferroni correction for further comparisons, this relationship did not remain significant (z = 2.197, p = 0.084). Addition-based silicone models had the highest accuracy in terms of fidelity, followed by condensation-based silicones, and then by alginate models. Silicone-based impression materials improved over time, being highly used in all areas of dentistry. Alginate impressions had the lowest pattern of accuracy among those studied. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials for Dental Applications)

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23 pages, 14107 KiB

Open AccessReview

A Scientometric-Analysis-Based Review of the Research Development on Geopolymers

by Kaffayatullah Khan, Waqas Ahmad, Muhammad Nasir Amin and Sohaib Nazar

Polymers 2022, 14(17), 3676; https://doi.org/10.3390/polym14173676 - 5 Sep 2022

Cited by 15 | Viewed by 2826

Abstract

A scientometric-based assessment of the literature on geopolymers was conducted in this study to determine its critical aspects. Typical review studies are restricted in their capability to link disparate segments of the literature in a systematic and exact way. Knowledge mapping, co-citation, and [...] Read more.

A scientometric-based assessment of the literature on geopolymers was conducted in this study to determine its critical aspects. Typical review studies are restricted in their capability to link disparate segments of the literature in a systematic and exact way. Knowledge mapping, co-citation, and co-occurrence are very difficult components of creative research. This study adopted an advanced strategy of data mining, data processing and analysis, visualization and presentation, and interpretation of the bibliographic data on geopolymers. The Scopus database was used to search for and retrieve the data needed to complete the study’s objectives. The relevant sources of publications, keyword assessment, productive authors based on publications and citations, top papers based on citations received, and areas actively engaged in the research of geopolymers are recognized during the data assessment. The VOSviewer (VOS: visualization of similarities) software application was employed to analyze the literature data comprising citation, bibliographic, abstract, keywords, funding, and other information from 7468 relevant publications. In addition, the applications and restrictions associated with the use of geopolymers in the construction sector are discussed, as well as possible solutions to overcome these restrictions. The scientometric analysis revealed that the leading publication source (journal) in terms of articles and citations is “Construction and building materials”; the mostly employed keywords are geopolymer, fly ash, and compressive strength; and the top active and contributing countries based on publications are China, India, and Australia. Because of the quantitative and graphical representation of participating nations and researchers, this study can help academics to create collaborative efforts and exchange creative ideas and approaches. In addition, this study concluded that the large-scale usage of geopolymer concrete is constrained by factors such as curing regime, activator solution scarcity and expense, efflorescence, and alkali–silica reaction. However, embracing the potential solutions outlined in this study might assist in boosting the building industry’s adoption of geopolymer concrete. Full article

(This article belongs to the Special Issue Polymer and Geopolymer Concrete Composites for Sustainable Development)

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12 pages, 1267 KiB

Open AccessArticle

Thermal Analysis of Parylene Thin Films for Barrier Layer Applications

by Sébastien Buchwalder, Aurelio Borzì, Juan J. Diaz Leon, Florian Bourgeois, Cléo Nicolier, Sylvain Nicolay, Antonia Neels, Olaf Zywitzki, Andreas Hogg and Jürgen Burger

Polymers 2022, 14(17), 3677; https://doi.org/10.3390/polym14173677 - 4 Sep 2022

Cited by 12 | Viewed by 3736

Abstract

Biocompatible polymer films demonstrating excellent thermal stability are highly desirable for high-temperature (>250 °C) applications, especially in the bioelectronic encapsulation domain. Parylene, as an organic thin film, is a well-established polymer material exhibiting excellent barrier properties and is often the material of choice [...] Read more.

Biocompatible polymer films demonstrating excellent thermal stability are highly desirable for high-temperature (>250 °C) applications, especially in the bioelectronic encapsulation domain. Parylene, as an organic thin film, is a well-established polymer material exhibiting excellent barrier properties and is often the material of choice for biomedical applications. This work investigated the thermal impact on the bulk properties of four types of parylene films: parylene N, C, VT4, and AF4. The films, deposited using the standard Gorham process, were analyzed at varying annealing temperatures from room temperature up to 450 °C. Thermal properties were identified by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods, while X-ray diffraction (XRD) analysis showed the effect of high-temperature exposure on the structural properties. In addition to thermal and structural analysis, the barrier properties were measured through the helium transmission rate (HTR) and the water vapor transmission rate (WVTR). Fluorinated parylene films were confirmed to be exceptional materials for high-temperature applications. Parylene AF4 film, 25um thick, demonstrated excellent barrier performance after 300 °C exposure, with an HTR and a WVTR of 12.18 × 10³ cm³ (STP) m⁻² day⁻¹ atm⁻¹ and 6.6 g m⁻² day⁻¹, respectively. Full article

(This article belongs to the Special Issue Polymer Surfaces and Interfaces)

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13 pages, 3235 KiB

Open AccessArticle

Revealing Nanodomain Structures of Bottom-Up-Fabricated Graphene-Embedded Silicon Oxycarbide Ceramics

by Dongxiao Hu, Gaofeng Shao, Jun Wang, Aleksander Gurlo and Maged F. Bekheet

Polymers 2022, 14(17), 3675; https://doi.org/10.3390/polym14173675 - 4 Sep 2022

Cited by 8 | Viewed by 2011

Abstract

Dispersing graphene nanosheets in polymer-derived ceramics (PDCs) has become a promising route to produce exceptional mechanical and functional properties. To reveal the complex nanodomain structures of graphene–PDC composites, a novel reduced graphene oxide aerogel embedded silicon oxycarbide (RGOA-SiOC) nanocomposite was fabricated bottom-up using [...] Read more.

Dispersing graphene nanosheets in polymer-derived ceramics (PDCs) has become a promising route to produce exceptional mechanical and functional properties. To reveal the complex nanodomain structures of graphene–PDC composites, a novel reduced graphene oxide aerogel embedded silicon oxycarbide (RGOA-SiOC) nanocomposite was fabricated bottom-up using a 3D reduced graphene oxide aerogel as a skeleton followed by infiltration of a ceramic precursor and high-temperature pyrolysis. The reduced graphene oxide played a critical role in not only the form of the free carbon phase but also the distribution of SiO_xC_4−x structural units in SiOC. Long-ordered and continuous graphene layers were then embedded into the amorphous SiOC phase. The oxygen-rich SiO_xC_4−x units were more prone to forming than carbon-rich SiO_xC_4−x units in SiOC after the introduction of reduced graphene oxide, which we attributed to the bonding of Si atoms in SiOC with O atoms in reduced graphene oxide during the pyrolysis process. Full article

(This article belongs to the Special Issue Polymer-Derived Ceramic Materials: Design, Synthesis, and Applications)

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21 pages, 7676 KiB

Open AccessArticle

Effects of Laser Power and Hatch Orientation on Final Properties of PA12 Parts Produced by Selective Laser Sintering

by Anouar El Magri, Salah Eddine Bencaid, Hamid Reza Vanaei and Sébastien Vaudreuil

Polymers 2022, 14(17), 3674; https://doi.org/10.3390/polym14173674 - 4 Sep 2022

Cited by 38 | Viewed by 3801

Abstract

Poly(dodecano-12-lactam) (commercially known as polyamide “PA12”) is one of the most resourceful materials used in the selective laser sintering (SLS) process due to its chemical and physical properties. The present work examined the influence of two SLS parameters, namely, laser power and hatch [...] Read more.

Poly(dodecano-12-lactam) (commercially known as polyamide “PA12”) is one of the most resourceful materials used in the selective laser sintering (SLS) process due to its chemical and physical properties. The present work examined the influence of two SLS parameters, namely, laser power and hatch orientation, on the tensile, structural, thermal, and morphological properties of the fabricated PA12 parts. The main objective was to evaluate the suitable laser power and hatching orientation with respect to obtaining better final properties. PA12 powders and SLS-printed parts were assessed through their particle size distributions, X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), a scanning electron microscope (SEM), and their tensile properties. The results showed that the significant impact of the laser power while hatching is almost unnoticeable when using a high laser power. A more significant condition of the mechanical properties is the uniformity of the powder bed temperature. Optimum factor levels were achieved at 95% laser power and parallel/perpendicular hatching. Parts produced with the optimized SLS parameters were then subjected to an annealing treatment to induce a relaxation of the residual stress and to enhance the crystallinity. The results showed that annealing the SLS parts at 170 °C for 6 h significantly improved the thermal, structural, and tensile properties of 3D-printed PA12 parts. Full article

(This article belongs to the Special Issue Polymers and Their Application in 3D Printing)

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15 pages, 6344 KiB

Open AccessArticle

Comprehensive Study on the Performance of Waste HDPE and LDPE Modified Asphalt Binders for Construction of Asphalt Pavements Application

by Usman Ghani, Bakht Zamin, Muhammad Tariq Bashir, Mahmood Ahmad, Mohanad Muayad Sabri Sabri and Suraparb Keawsawasvong

Polymers 2022, 14(17), 3673; https://doi.org/10.3390/polym14173673 - 4 Sep 2022

Cited by 18 | Viewed by 4656

Abstract

This research is aimed at investigating the mechanical behavior of the bitumen by the addition of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) obtained from waste plastic bottles and bags. Polymers (HDPE and LDPE) with percentages of 0%, 2%, 4%, and 6% in [...] Read more.

This research is aimed at investigating the mechanical behavior of the bitumen by the addition of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) obtained from waste plastic bottles and bags. Polymers (HDPE and LDPE) with percentages of 0%, 2%, 4%, and 6% in shredded form by weight of bitumen were used to evaluate the spectroscopic, structural, morphological, and rheological properties of polymer-modified binders. The rheological properties for different factors; viscosity (ἠ) from Rotational Viscometer (RV), rutting factor G*/Sin (δ), fatigue characteristics G*. Sin (δ), for the modified binder from dynamic shear rheometer (DSR), Short and long-term aging from rolling thin film oven (RTFO), and pressure aging vessel (PAV) was determined. The thermal characteristics, grain size, and texture of polymers for both LDPE and HDPE were found using bending beam rheometer (BBR) and X-ray diffraction (XRD), respectively. Fourier transform infrared (FTIR) analysis revealed the presence of polymer contents in the modified binder. Scanning electron microscopy (SEM) images revealed the presence of HDPE and LDPE particles on the surface of the binder. Creep Rate (m) and Stiffness (S) analysis in relationship with temperature showed a deduction in stress rate relaxation. Results have revealed the best rutting resistance for 6% HDPE. It also showed an improvement of 95.27% in G*/Sin (δ) which increased the performance of the bituminous mix. Similarly, the addition of 4% LDPE resulted in maximum dynamic viscosity irrespective of the temperatures. Moreover, fatigue resistance has shown a significant change with the HDPE and LDPE. The festinating features of waste plastic modified binder make it important to be used in the new construction of roads to address the high viscosity and mixing problems produced by plastic waste and to improve the performance of flexible pavements all over the world. Full article

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

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12 pages, 2541 KiB

Open AccessArticle

Percolation Network Formation in Nylon 6/Montmorillonite Nanocomposites: A Critical Structural Insight and the Impact on Solidification Process and Mechanical Behavior

by Tingzi Yan, Depei Chen, Baijin Zhao, Xiaodong Jiang, Lian Wang and Yongjin Li

Polymers 2022, 14(17), 3672; https://doi.org/10.3390/polym14173672 - 4 Sep 2022

Cited by 5 | Viewed by 1994

Abstract

The incorporation of montmorillonite (MMT) into Nylon 6 can endow advantages like improved mechanical strength and thermal stability, making Nylon 6/MMT a possible ideal alternative for Nylon 66. However, the relationship between the microstructure and physical properties of nylon 6/MMT nanocomposites is unclear [...] Read more.

The incorporation of montmorillonite (MMT) into Nylon 6 can endow advantages like improved mechanical strength and thermal stability, making Nylon 6/MMT a possible ideal alternative for Nylon 66. However, the relationship between the microstructure and physical properties of nylon 6/MMT nanocomposites is unclear so far due to the complicated system, including the highly asymmetric geometry of the exfoliated MMT layer and the complicated interaction between MMT layers and entangled nylon 6 chains. Herein, we focus on two processes, namely the impact of MMT on the solidification procedure during molding and the toughness–brittleness transition during the tensile stretch, in order to elucidate the structure–property relationship of nylon 6/MMT composites. We firstly studied the solidification process of nylon 6/MMT with bending height experiments. The results showed that the solidification process occurs prior to the crystallization of nylon 6, indicating that a physical crosslinked network rather than a crystalline structure is the reason for the solidification process. Furthermore, the solidification speed has a step change at around 2 wt% MMT content, indicating that the MMT percolation network is related to the transition. We further studied the influence of MMT inclusion on the mechanical properties, and found the tensile strain at break showed a similar step change at around 2 wt% MMT content, which further confirms the existence of an MMT percolation network above 2 wt% MMT content. It was generally believed that the main effect of MMT on nylon 6 is the nanofiller enforcement; we found that the percolation effect of the highly asymmetric 2-D nanofiller plays a central role in influencing the mechanical properties and solidification behavior during molding. Full article

(This article belongs to the Section Polymer Composites and Nanocomposites)

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