Polymers

16 pages, 4308 KiB

Open AccessArticle

Tailoring Epoxy Resin Foams by Pre-Curing with Neat Amine Hardeners and Its Derived Carbamates

by Christian Bethke, Sebastian Manfred Goller, Uy Lan Du Ngoc, Simon Tino Kaysser, Volker Altstädt and Holger Ruckdäschel

Polymers 2021, 13(8), 1348; https://doi.org/10.3390/polym13081348 - 20 Apr 2021

Cited by 6 | Viewed by 3071

Abstract

The use of amine-based carbamates with their dual function, acting as amine curing agents and CO₂ blowing agents after their decomposition without by-products, are promising for ecofriendly epoxy foams as high-performance materials. However, controlling cell morphology requires a proper adjustment of the [...] Read more.

The use of amine-based carbamates with their dual function, acting as amine curing agents and CO₂ blowing agents after their decomposition without by-products, are promising for ecofriendly epoxy foams as high-performance materials. However, controlling cell morphology requires a proper adjustment of the viscosity at the foaming step. The viscosity is altered not only by blending neat amine and its derived carbamate at a fixed pre-curing time, but also by changing the pre-curing time at a fixed blend ratio. Within this study, diglycidylether of bisphenol A (DGEBA) epoxy resin is mixed with different blend ratios of isophorone diamine (IPDA) and its derived carbamate (B-IPDA). The systems are characterized by DSC and rheology experiments to identify the pre-curing effects on the derived epoxy foams. Epoxy foams at a blend ratio of 30/70_w IPDA/B-IPDA showed the best foam morphology and an optimum Tg compared to other blend ratios. Furthermore, it was found that both pre-curing times, 2 h and 3 h, for the 30/70_w IPDA/B-IPDA system reveal a more homogeneous cell structure. The study proves that the blending of neat amine and carbamate is beneficial for the foaming performance of carbamate systems. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials)

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30 pages, 5060 KiB

Open AccessReview

Recent Progress in Polysaccharide Aerogels: Their Synthesis, Application, and Future Outlook

by Arbanah Muhammad, Dabin Lee, Yonghun Shin and Juhyun Park

Polymers 2021, 13(8), 1347; https://doi.org/10.3390/polym13081347 - 20 Apr 2021

Cited by 37 | Viewed by 5750

Abstract

Porous polysaccharides have recently attracted attention due to their porosity, abundance, and excellent properties such as sustainability and biocompatibility, thereby resulting in their numerous applications. Recent years have seen a rise in the number of studies on the utilization of polysaccharides such as [...] Read more.

Porous polysaccharides have recently attracted attention due to their porosity, abundance, and excellent properties such as sustainability and biocompatibility, thereby resulting in their numerous applications. Recent years have seen a rise in the number of studies on the utilization of polysaccharides such as cellulose, chitosan, chitin, and starch as aerogels due to their unique performance for the fabrication of porous structures. The present review explores recent progress in porous polysaccharides, particularly cellulose and chitosan, including their synthesis, application, and future outlook. Since the synthetic process is an important aspect of aerogel formation, particularly during the drying step, the process is reviewed in some detail, and a comparison is drawn between the supercritical CO₂ and freeze drying processes in order to understand the aerogel formation of porous polysaccharides. Finally, the current applications of polysaccharide aerogels in drug delivery, wastewater, wound dressing, and air filtration are explored, and the limitations and outlook of the porous aerogels are discussed with respect to their future commercialization. Full article

(This article belongs to the Collection Progress in Polymer Applications)

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28 pages, 6991 KiB

Open AccessReview

Is Poly(methyl methacrylate) (PMMA) a Suitable Substrate for ALD?: A Review

by Marta Adriana Forte, Ricardo Manuel Silva, Carlos José Tavares and Rui Ferreira e Silva

Polymers 2021, 13(8), 1346; https://doi.org/10.3390/polym13081346 - 20 Apr 2021

Cited by 22 | Viewed by 10085

Abstract

Poly (methyl methacrylate) (PMMA) is a thermoplastic synthetic polymer, which displays superior characteristics such as transparency, good tensile strength, and processability. Its performance can be improved by surface engineering via the use of functionalized thin film coatings, resulting in its versatility across a [...] Read more.

Poly (methyl methacrylate) (PMMA) is a thermoplastic synthetic polymer, which displays superior characteristics such as transparency, good tensile strength, and processability. Its performance can be improved by surface engineering via the use of functionalized thin film coatings, resulting in its versatility across a host of applications including, energy harvesting, dielectric layers and water purification. Modification of the PMMA surface can be achieved by atomic layer deposition (ALD), a vapor-phase, chemical deposition technique, which permits atomic-level control. However, PMMA presents a challenge for ALD due to its lack of active surface sites, necessary for gas precursor reaction, nucleation, and subsequent growth. The purpose of this review is to discuss the research related to the employment of PMMA as either a substrate, support, or masking layer over a range of ALD thin film growth techniques, namely, thermal, plasma-enhanced, and area-selective atomic layer deposition. It also highlights applications in the selected fields of flexible electronics, biomaterials, sensing, and photocatalysis, and underscores relevant characterization techniques. Further, it concludes with a prospective view of the role of ALD in PMMA processing. Full article

(This article belongs to the Special Issue Advances in Surface Functionalization of Polymer Nanostructures)

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48 pages, 5071 KiB

Open AccessReview

Recent Developments of Carboxymethyl Cellulose

by Md. Saifur Rahman, Md. Saif Hasan, Ashis Sutradhar Nitai, Sunghyun Nam, Aneek Krishna Karmakar, Md. Shameem Ahsan, Muhammad J. A. Shiddiky and Mohammad Boshir Ahmed

Polymers 2021, 13(8), 1345; https://doi.org/10.3390/polym13081345 - 20 Apr 2021

Cited by 260 | Viewed by 36733

Abstract

Carboxymethyl cellulose (CMC) is one of the most promising cellulose derivatives. Due to its characteristic surface properties, mechanical strength, tunable hydrophilicity, viscous properties, availability and abundance of raw materials, low-cost synthesis process, and likewise many contrasting aspects, it is now widely used in [...] Read more.

Carboxymethyl cellulose (CMC) is one of the most promising cellulose derivatives. Due to its characteristic surface properties, mechanical strength, tunable hydrophilicity, viscous properties, availability and abundance of raw materials, low-cost synthesis process, and likewise many contrasting aspects, it is now widely used in various advanced application fields, for example, food, paper, textile, and pharmaceutical industries, biomedical engineering, wastewater treatment, energy production, and storage energy production, and storage and so on. Many research articles have been reported on CMC, depending on their sources and application fields. Thus, a comprehensive and well-organized review is in great demand that can provide an up-to-date and in-depth review on CMC. Herein, this review aims to provide compact information of the synthesis to the advanced applications of this material in various fields. Finally, this article covers the insights of future CMC research that could guide researchers working in this prominent field. Full article

(This article belongs to the Special Issue Polymers and Fibers)

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12 pages, 4609 KiB

Open AccessArticle

Experimental Study of Straw-Based Eco-Panel Using a Small Ignition Initiator

by Linda Makovicka Osvaldova, Iveta Markova, Stanislav Jochim and Jan Bares

Polymers 2021, 13(8), 1344; https://doi.org/10.3390/polym13081344 - 20 Apr 2021

Cited by 13 | Viewed by 2391

Abstract

Straw, a natural cellulose-based material, has become part of building elements. Eco-panels, compressed straw in a cardboard casing, is used as building insulation. Eco-panel is a secondary product with excellent insulating properties. If suitably fire-treated (insulation and covering), straw panels’ fire resistance may [...] Read more.

Straw, a natural cellulose-based material, has become part of building elements. Eco-panels, compressed straw in a cardboard casing, is used as building insulation. Eco-panel is a secondary product with excellent insulating properties. If suitably fire-treated (insulation and covering), straw panels’ fire resistance may be increased. This contribution deals with monitoring the behavior of eco-panels exposed to a small ignition initiator (flame). The samples consisted of compressed straw boards coated with a 40 mm thick cardboard. Samples were exposed to a flame for 5 and 10 min. The influence of the selected factors (size of the board, orientation of flame with the sample) were compared on the basis of experimentally obtained data: mass loss. The results obtained do not show a statistically significant influence of the position of the sample and the initiating source (flame). The results presented in the article confirm the justifiability of fire tests. As the results of the experiments prove, the position of a small burner for igniting such material is also important. Such weakness of the material can also be eliminated by design solutions in the construction. The experiment on larger samples also confirmed the justifiability of fire tests along with the need for flame retardancy of such material for its safe application in construction. Full article

(This article belongs to the Special Issue New Challenges in Wood and Wood-Based Materials)

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12 pages, 1517 KiB

Open AccessArticle

Effect of Composition on Polarization Hysteresis and Energy Storage Ability of P(VDF-TrFE-CFE) Relaxor Terpolymers

by Yusra Hambal, Vladimir V. Shvartsman, Daniil Lewin, Chieng Huo Huat, Xin Chen, Ivo Michiels, Qiming Zhang and Doru C. Lupascu

Polymers 2021, 13(8), 1343; https://doi.org/10.3390/polym13081343 - 20 Apr 2021

Cited by 7 | Viewed by 3052

Abstract

The temperature dependence of the dielectric permittivity and polarization hysteresis loops of P(VDF-TrFE-CFE) polymer films with different compositions are studied. Among them, the three compositions, 51.3/48.7/6.2, 59.8/40.2/7.3, and 70/30/8.1, are characterized for the first time. Relaxor behavior is confirmed for all studied samples. [...] Read more.

The temperature dependence of the dielectric permittivity and polarization hysteresis loops of P(VDF-TrFE-CFE) polymer films with different compositions are studied. Among them, the three compositions, 51.3/48.7/6.2, 59.8/40.2/7.3, and 70/30/8.1, are characterized for the first time. Relaxor behavior is confirmed for all studied samples. Increasing the CFE content results in lowering the freezing temperature and stabilizes the ergodic relaxor state. The observed double hysteresis loops are related to the field-induced transition to a ferroelectric state. The critical field corresponding to this transition varies with the composition and temperature; it becomes larger for temperatures far from the freezing temperature. The energy storage performance is evaluated from the analysis of unipolar polarization hysteresis loops. P(VDF-TrFE-CFE) 59.8/40.2/7.3 shows the largest energy density of about 5 J·cm⁻³ (at the field of 200 MV·m⁻¹) and a charge–discharge efficiency of 63%, which iscomparable with the best literature data for the neat terpolymers. Full article

(This article belongs to the Section Polymer Physics and Theory)

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16 pages, 1875 KiB

Open AccessArticle

Synthesis and Characterization of Biocompatible Methacrylated Kefiran Hydrogels: Towards Tissue Engineering Applications

by Hajer Radhouani, Susana Correia, Cristiana Gonçalves, Rui L. Reis and Joaquim M. Oliveira

Polymers 2021, 13(8), 1342; https://doi.org/10.3390/polym13081342 - 20 Apr 2021

Cited by 7 | Viewed by 2804

Abstract

Hydrogel application feasibility is still limited mainly due to their low mechanical strength and fragile nature. Therefore, several physical and chemical cross-linking modifications are being used to improve their properties. In this research, methacrylated Kefiran was synthesized by reacting Kefiran with methacrylic anhydride [...] Read more.

Hydrogel application feasibility is still limited mainly due to their low mechanical strength and fragile nature. Therefore, several physical and chemical cross-linking modifications are being used to improve their properties. In this research, methacrylated Kefiran was synthesized by reacting Kefiran with methacrylic anhydride (MA). The developed MA-Kefiran was physicochemically characterized, and its biological properties evaluated by different techniques. Chemical modification of MA-Kefiran was confirmed by ¹H-NMR and FTIR and GPC-SEC showed an average Mw of 793 kDa (PDI 1.3). The mechanical data obtained revealed MA-Kefiran to be a pseudoplastic fluid with an extrusion force of 11.21 ± 2.87 N. Moreover, MA-Kefiran 3D cryogels were successfully developed and fully characterized. Through micro-CT and SEM, the scaffolds revealed high porosity (85.53 ± 0.15%) and pore size (33.67 ± 3.13 μm), thick pore walls (11.92 ± 0.44 μm) and a homogeneous structure. Finally, MA-Kefiran revealed to be biocompatible by presenting no hemolytic activity and an improved cellular function of L929 cells observed through the AlamarBlue^® assay. By incorporating methacrylate groups in the Kefiran polysaccharide chain, a MA-Kefiran product was developed with remarkable physical, mechanical, and biological properties, resulting in a promising hydrogel to be used in tissue engineering and regenerative medicine applications. Full article

(This article belongs to the Special Issue Biomaterials in Medical Applications)

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24 pages, 4777 KiB

Open AccessReview

Potential of Honeycomb-Filled Composite Structure in Composite Cross-Arm Component: A Review on Recent Progress and Its Mechanical Properties

by Abd Latif Amir, Mohamad Ridzwan Ishak, Noorfaizal Yidris, Mohamed Yusoff Mohd Zuhri and Muhammad Rizal Muhammad Asyraf

Polymers 2021, 13(8), 1341; https://doi.org/10.3390/polym13081341 - 20 Apr 2021

Cited by 30 | Viewed by 4568

Abstract

Nowadays, pultruded glass fiber-reinforced polymer composite (PGFRPC) structures have been used widely for cross-arms in high transmission towers. These composite structures have replaced cross-arms of conventional materials like wood due to several factors, such as better strength, superior resistance to environmental degradation, reduced [...] Read more.

Nowadays, pultruded glass fiber-reinforced polymer composite (PGFRPC) structures have been used widely for cross-arms in high transmission towers. These composite structures have replaced cross-arms of conventional materials like wood due to several factors, such as better strength, superior resistance to environmental degradation, reduced weight, and comparatively cheaper maintenance. However, lately, several performance failures have been found on existing cross-arm members, caused by moisture, temperature changes in the atmosphere, and other environmental factors, which may lead to a complete failure or reduced service life. As a potential solution for this problem, enhancing PGFRPC with honeycomb-filled composite structures will become a possible alternative that can sustain a longer service life compared to that of existing cross-arms. This is due to the new composite structures’ superior performance under mechanical duress in providing better stiffness, excellence in flexural characteristics, good energy absorption, and increased load-carrying capacity. Although there has been a lack of previous research done on the enhancement of existing composite cross-arms in applications for high transmission towers, several studies on the enhancement of hollow beams and tubes have been done. This paper provides a state-of-the-art review study on the mechanical efficiency of both PGFRPC structures and honeycomb-filled composite sandwich structures in experimental and analytical terms. Full article

(This article belongs to the Special Issue Recent Advances in Reinforced Polymeric Composites)

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62 pages, 3523 KiB

Open AccessReview

Potential of Stimuli-Responsive In Situ Gel System for Sustained Ocular Drug Delivery: Recent Progress and Contemporary Research

by Manisha Pandey, Hira Choudhury, Azila binti Abd Aziz, Subrat Kumar Bhattamisra, Bapi Gorain, Jocelyn Sziou Ting Su, Choo Leey Tan, Woon Yee Chin and Khar Yee Yip

Polymers 2021, 13(8), 1340; https://doi.org/10.3390/polym13081340 - 20 Apr 2021

Cited by 35 | Viewed by 5102

Abstract

Eyesight is one of the most well-deserved blessings, amid all the five senses in the human body. It captures the raw signals from the outside world to create detailed visual images, granting the ability to witness and gain knowledge about the world. Eyes [...] Read more.

Eyesight is one of the most well-deserved blessings, amid all the five senses in the human body. It captures the raw signals from the outside world to create detailed visual images, granting the ability to witness and gain knowledge about the world. Eyes are exposed directly to the external environment; they are susceptible to the vicissitudes of diseases. The World Health Organization has predicted that the number of individuals affected by eye diseases will rise enormously in the next decades. However, the physical barriers of the eyes and the problems associated with conventional ocular formulations are significant challenges in ophthalmic drug development. This has generated the demand for a sustained ocular drug delivery system, which serves to deliver effective drug concentration at a reduced frequency for consistent therapeutic effect and better patient treatment adherence. Recent advancement in pharmaceutical dosage design has demonstrated that a stimuli-responsive in situ gel system exhibits the favorable characteristics for providing sustained ocular drug delivery and enhanced ocular bioavailability. Stimuli-responsive in situ gels undergo a phase transition (solution–gelation) in response to the ocular environmental temperature, pH, and ions. These stimuli transform the formulation into a gel at the cul de sac to overcome the shortcomings of conventional eye drops, such as rapid nasolacrimal drainage and short contact time with the ocular surface This review highlights the recent successful research outcomes of stimuli-responsive in situ gelling systems in treating in vivo models with glaucoma and various ocular infections. Additionally, it also presents the mechanism, recent development, and safety considerations of stimuli-sensitive in situ gel as the potential sustained ocular delivery system for treating common eye disorders. Full article

(This article belongs to the Special Issue Translation of Polymeric Biomaterials: From the Lab to the Clinic)

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17 pages, 3783 KiB

Open AccessArticle

Development and Characterization of Cellulose/Iron Acetate Nanofibers for Bone Tissue Engineering Applications

by Hamouda M. Mousa, Kamal Hany Hussein, Mostafa M. Sayed, Mohamed K. Abd El-Rahman and Heung-Myong Woo

Polymers 2021, 13(8), 1339; https://doi.org/10.3390/polym13081339 - 20 Apr 2021

Cited by 25 | Viewed by 3194

Abstract

In tissue engineering, design of biomaterial with a micro/nano structure is an essential step to mimic extracellular matrix (ECM) and to enhance biomineralization as well as cell biocompatibility. Composite polymeric nanofiber with iron particles/ions has an important role in biomineralization and collagen synthesis [...] Read more.

In tissue engineering, design of biomaterial with a micro/nano structure is an essential step to mimic extracellular matrix (ECM) and to enhance biomineralization as well as cell biocompatibility. Composite polymeric nanofiber with iron particles/ions has an important role in biomineralization and collagen synthesis for bone tissue engineering. Herein, we report development of polymeric cellulose acetate (CA) nanofibers (17 wt.%) and traces of iron acetates salt (0.5 wt.%) within a polymeric solution to form electrospinning nanofibers mats with iron nanoparticles for bone tissue engineering applications. The resulting mats were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The resulted morphology indicated that the average diameter of CA decreased after addition of iron from (395 ± 30) to (266 ± 19) nm and had dense fiber distributions that match those of native ECM. Moreover, addition of iron acetate to CA solution resulted in mats that are thermally stable. The initial decomposition temperature was 300 °C of CA/Fe mat > 270 °C of pure CA. Furthermore, a superior apatite formation resulted in a biomineralization test after 3 days of immersion in stimulated environmental condition. In vitro cell culture experiments demonstrated that the CA/Fe mat was biocompatible to human fetal-osteoblast cells (hFOB) with the ability to support the cell attachment and proliferation. These findings suggest that doping traces of iron acetate has a promising role in composite mats designed for bone tissue engineering as simple and economically nanoscale materials. Furthermore, these biomaterials can be used in a potential future application such as drug delivery, cancer treatment, and antibacterial materials. Full article

(This article belongs to the Collection Polymers in Tissue Engineering)

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17 pages, 5903 KiB

Open AccessArticle

Preparation of Ag NPs and Its Multifunctional Finishing for Cotton Fabric

by Jionglin Zhu, Hong Li, Yu Wang, Yusu Wang and Jun Yan

Polymers 2021, 13(8), 1338; https://doi.org/10.3390/polym13081338 - 19 Apr 2021

Cited by 16 | Viewed by 2487

Abstract

To explore the combination of silver nanoparticles (Ag NPs) prepared in a green manner with cotton fabrics and the washing durability of the fabric after the combination. In this paper, the natural material, honeysuckle extract, was used as a reducing agent to prepare [...] Read more.

To explore the combination of silver nanoparticles (Ag NPs) prepared in a green manner with cotton fabrics and the washing durability of the fabric after the combination. In this paper, the natural material, honeysuckle extract, was used as a reducing agent to prepare the Ag NPs’ solution. The structure and size of Ag NPs were analyzed using ultraviolet–visible spectrophotometry (UV–vis), transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy characterization. The results showed that Ag⁺ was successfully reduced to Ag⁰ by the honeysuckle extract, the particle size was about 10.59 nm, and the potential was −42.9 mV, so it had strong electrostatic repulsion and good stability. Meanwhile, it was found that the synthesized Ag NPs were well coated by the honeysuckle extract, so they would not aggregate. Then, the cotton fabric was finished with Ag NPs’ solution by the dipping method using a complex of polymaleic acid (PMA) and citric acid (CA) as a cross-linking agent to fix Ag NPs on the cotton fabric. The structures of cotton fabrics before and after finishing were characterized using FT-IR, scanning electron microscopy (SEM), XRD, X-ray photoelectron spectroscopy (XPS), and thermogravimetric (TG) analysis, and the multifunctional properties of the finished cotton fabrics were explored by measuring the antibacterial rate, the wrinkle recovery angle (WRA), and the UV protection factor (UPF) value. The results show that Ag NPs were successfully loaded onto cotton fabric, and the PMA + CA compound was successfully cross-linked to the fabric. The cross-linked Ag NPs’ cotton fiber was rougher than that before cross-linking, and its TG stability improved. The PMA + CA compound fixed Ag NPs on the cotton fabric through chemical bonds, so it still had a 99% antibacterial effect against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) after 50 washings. Compared with unfinished cotton fabric, the UPF value and WRA of the cross-linked Ag NPs cotton increased by 34.09 and 98°, respectively, and its color did not change much. Full article

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

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14 pages, 8015 KiB

Open AccessArticle

Electrical and Capacitive Response of Hydrogel Solid-Like Electrolytes for Supercapacitors

by Guillem Ruano, José I. Iribarren, Maria M. Pérez-Madrigal, Juan Torras and Carlos Alemán

Polymers 2021, 13(8), 1337; https://doi.org/10.3390/polym13081337 - 19 Apr 2021

Cited by 16 | Viewed by 3367

Abstract

Flexible hydrogels are attracting significant interest as solid-like electrolytes for energy storage devices, especially for supercapacitors, because of their lightweight and anti-deformation features. Here, we present a comparative study of four ionic conductive hydrogels derived from biopolymers and doped with 0.1 M NaCl. [...] Read more.

Flexible hydrogels are attracting significant interest as solid-like electrolytes for energy storage devices, especially for supercapacitors, because of their lightweight and anti-deformation features. Here, we present a comparative study of four ionic conductive hydrogels derived from biopolymers and doped with 0.1 M NaCl. More specifically, such hydrogels are constituted by κ-carrageenan (κC), carboxymethyl cellulose (CMC), poly-γ-glutamic acid (PGGA) or a phenylalanine-containing polyesteramide (PEA). After examining the morphology and the swelling ratio of the four hydrogels, which varies between 483% and 2356%, their electrical and capacitive behaviors were examined using electrochemical impedance spectroscopy. Measurements were conducted on devices where a hydrogel film was sandwiched between two identical poly(3,4-ethylenedioxythiophene) electrodes. The bulk conductivity of the prepared doped hydrogels is 76, 48, 36 and 34 mS/cm for PEA, PGGA, κC and CMC, respectively. Overall, the polyesteramide hydrogel exhibits the most adequate properties (i.e., low electrical resistance and high capacitance) to be used as semi-solid electrolyte for supercapacitors, which has been attributed to its distinctive structure based on the homogeneous and abundant distribution of both micro- and nanopores. Indeed, the morphology of the polyestermide hydrogel reduces the hydrogel resistance, enhances the transport of ions, and results in a better interfacial contact between the electrodes and solid electrolyte. The correlation between the supercapacitor performance and the hydrogel porous morphology is presented as an important design feature for the next generation of light and flexible energy storage devices for wearable electronics. Full article

(This article belongs to the Special Issue Innovative Polymeric Systems for Advanced Energy Storage Devices)

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10 pages, 993 KiB

Open AccessArticle

Open and Anisotropic Soft Regions in a Model Polymer Glass

by Carlo Andrea Massa, Francesco Puosi, Antonio Tripodo and Dino Leporini

Polymers 2021, 13(8), 1336; https://doi.org/10.3390/polym13081336 - 19 Apr 2021

Viewed by 1298

Abstract

The vibrational dynamics of a model polymer glass is studied by Molecular Dynamics simulations. The focus is on the “soft” monomers with high participation to the lower-frequency vibrational modes contributing to the thermodynamic anomalies of glasses. To better evidence their role, the threshold [...] Read more.

The vibrational dynamics of a model polymer glass is studied by Molecular Dynamics simulations. The focus is on the “soft” monomers with high participation to the lower-frequency vibrational modes contributing to the thermodynamic anomalies of glasses. To better evidence their role, the threshold to qualify monomers as soft is made severe, allowing for the use of systems with limited size. A marked tendency of soft monomers to form quasi-local clusters involving up to 15 monomers is evidenced. Each chain contributes to a cluster up to about three monomers and a single cluster involves a monomer belonging to about 2–3 chains. Clusters with monomers belonging to a single chain are rare. The open and tenuous character of the clusters is revealed by their fractal dimension

d_{f} < 2

. The inertia tensor of the soft clusters evidences their strong anisotropy in shape and remarkable linear correlation of the two largest eigenvalues. Owing to the limited size of the system, finite-size effects, as well as dependence of the results on the adopted polymer length, cannot be ruled out. Full article

(This article belongs to the Section Polymer Physics and Theory)

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18 pages, 6263 KiB

Open AccessArticle

A Novel Application of the Hydrophobic Polyurethane Foam: Expansive Soil Stabilization

by Mohamed Ezzat Al-Atroush, Omar Shabbir, Bandar Almeshari, Mohamed Waly and Tamer A. Sebaey

Polymers 2021, 13(8), 1335; https://doi.org/10.3390/polym13081335 - 19 Apr 2021

Cited by 10 | Viewed by 3836

Abstract

The reversible shrink–swell behavior of expansive soil imposes a serious challenge that threatens the overlying structures’ safety and durability. Traditional chemical additives such as lime and cement still exhibit satisfying performance over their counterparts in terms of swelling potential reduction. Nevertheless, significant concerns [...] Read more.

The reversible shrink–swell behavior of expansive soil imposes a serious challenge that threatens the overlying structures’ safety and durability. Traditional chemical additives such as lime and cement still exhibit satisfying performance over their counterparts in terms of swelling potential reduction. Nevertheless, significant concerns are associated with these chemicals, in addition to their environmental impact. This paper proposes a novel application of the closed-cell one-component hydrophobic polyurethane foam (HPUF) to stabilize the swelling soil. An extensive experimental study was performed to assess the efficiency of HPUF in mitigating both the swelling and shrinkage response of high montmorillonite content expansive soil. Expansive soil was injected/mixed with different weight ratios of the proposed stabilizer, and the optimum mixing design and injection percentage of the foam resin were identified to be ranged from 10% to 15%. The shrink–swell behaviors of both injected and noninjected samples were compared. Results of this comparison confirmed that HPUF could competently reduce both the swelling potential and the shrinkage cracking of the reactive expansive soil, even after several wet-shrink cycles. Full article

(This article belongs to the Collection Polymer Applications in Environmental Science)

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13 pages, 5900 KiB

Open AccessArticle

Improving the Barrier Properties of Packaging Paper by Polyvinyl Alcohol Based Polymer Coating—Effect of the Base Paper and Nanoclay

by Zhenghui Shen, Araz Rajabi-Abhari, Kyudeok Oh, Guihua Yang, Hye Jung Youn and Hak Lae Lee

Polymers 2021, 13(8), 1334; https://doi.org/10.3390/polym13081334 - 19 Apr 2021

Cited by 41 | Viewed by 6947

Abstract

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form [...] Read more.

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na⁺) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m²·day, and it decreased sharply to 1.3 g/m²·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation. Full article

(This article belongs to the Special Issue Polymer Adhesion and Interfaces for Advanced Manufacturing)

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29 pages, 10195 KiB

Open AccessReview

A Short Review on Polymeric Biomaterials as Additives for Lubricants

by Gobinda Karmakar, Koushik Dey, Pranab Ghosh, Brajendra K. Sharma and Sevim Z. Erhan

Polymers 2021, 13(8), 1333; https://doi.org/10.3390/polym13081333 - 19 Apr 2021

Cited by 9 | Viewed by 4627

Abstract

With increasing environmental concerns and the depletion of petroleum resources, the development of lubricant additives from bioresources has attracted much attention recently. In this review, we reported a few polymers and polymer composites that are synthesized from vegetable oils (soybean oil, sunflower oil, [...] Read more.

With increasing environmental concerns and the depletion of petroleum resources, the development of lubricant additives from bioresources has attracted much attention recently. In this review, we reported a few polymers and polymer composites that are synthesized from vegetable oils (soybean oil, sunflower oil, rice bran oil, and castor oil) and used as multifunctional additives in the formulation of eco-friendly lubricant compositions. We mentioned the preparation of vegetable oil-based homo- and copolymers and their characterization by different spectral techniques (FTIR/NMR). The average molecular weights of the polymers are determined by gel permeation chromatography (GPC). Performance evaluations of the polymeric materials mainly as a viscosity index improver (VII), pour point depressant (PPD), and most importantly antifriction additives when blended with lubricating base oils are indicated. Standard ASTM methods have been applied to evaluate their performances. The findings have shown that all the additives discussed are non-toxic, biodegradable, and showed excellent performances compared to commercial petroleum-based additives. Full article

(This article belongs to the Special Issue Polymeric Materials as Lubricant Additives)

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11 pages, 6328 KiB

Open AccessArticle

Synthesis of New Amino—β-Cyclodextrin Polymer, Cross-Linked with Pyromellitic Dianhydride and Their Use for the Synthesis of Polymeric Cyclodextrin Based Nanoparticles

by Kinga Kozieł, Jakub Łagiewka, Beata Girek, Agnieszka Folentarska, Tomasz Girek and Wojciech Ciesielski

Polymers 2021, 13(8), 1332; https://doi.org/10.3390/polym13081332 - 19 Apr 2021

Cited by 5 | Viewed by 3347

Abstract

New water soluble amino β-cyclodextrin-based polymer was synthesized by reaction between amino cyclodextrin derivatives and pyromellitic anhydride. This experiment presents amino derivatives, which were synthesized by attaching amino groups to β-cyclodextrins (β-CDs) used mono-6-azido-6-deoxy-β-cyclodextrin (β-CD-N₃) and triphenylphosphine (Ph₃P) in [...] Read more.

New water soluble amino β-cyclodextrin-based polymer was synthesized by reaction between amino cyclodextrin derivatives and pyromellitic anhydride. This experiment presents amino derivatives, which were synthesized by attaching amino groups to β-cyclodextrins (β-CDs) used mono-6-azido-6-deoxy-β-cyclodextrin (β-CD-N₃) and triphenylphosphine (Ph₃P) in anhydrous N,N-dimethylformamide (DMF). An amino blocking reaction was conducted. The obtained polymer was purified by ultrafiltration. In addition, an attempt was made to create nanospheres by encapsulating the polymer with chitosan (CT) in an acidic condition. For the first time, nanospheres were obtained in the reaction between an amino β-cyclodextrin polymer and chitosan. Scanning electron microscopy (SEM). ¹H NMR and ESI-MS methods for confirmation of reaction product and for structural characterization were employed. The differential scanning calorimetry (DSC) studies of polymers were also carried out. Full article

(This article belongs to the Special Issue Biodegradable and Natural Polymers)

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11 pages, 2082 KiB

Open AccessArticle

Photocatalytic Activity and Filtration Performance of Hybrid TiO₂-Cellulose Acetate Nanofibers for Air Filter Applications

by Miyeon Kwon, Juhea Kim and Juran Kim

Polymers 2021, 13(8), 1331; https://doi.org/10.3390/polym13081331 - 19 Apr 2021

Cited by 12 | Viewed by 2878

Abstract

A facile method to prepare hybrid cellulose acetate nanofibers containing TiO₂ (TiO₂-CA nanofibers) by emulsion electrospinning technique was developed for the denitrification and filtration of particulate matters (PMs). This work found that hybrid TiO₂-CA nanofibers mainly contain the [...] Read more.

A facile method to prepare hybrid cellulose acetate nanofibers containing TiO₂ (TiO₂-CA nanofibers) by emulsion electrospinning technique was developed for the denitrification and filtration of particulate matters (PMs). This work found that hybrid TiO₂-CA nanofibers mainly contain the anatase form of TiO₂, contributing to the photodecomposition of NO gas under UV irradiation. The TiO₂-CA nanofibers also showed an excellent filtration efficiency of 99.5% for PM_0.5 and a photocatalytic efficiency of 78.6% for NO removal. Furthermore, the results implied that the morphology of the TiO₂-CA nanofibers, such as micro-wrinkles and protrusions, increased the surface hydrophobicity up to 140°, with the increased addition of TiO₂ nanoparticles. The proposed TiO₂-CA nanofibers, as a result, would be promising materials for highly efficient and sustainable air filters for industrial and home appliance systems. Full article

(This article belongs to the Special Issue Advances in Polymer Nanofibers II)

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11 pages, 2636 KiB

Open AccessArticle

Recycling and Utilization of Polymers for Road Construction Projects: An Application of the Circular Economy Concept

by Muhammad Kashif Anwar, Syyed Adnan Raheel Shah and Hatem Alhazmi

Polymers 2021, 13(8), 1330; https://doi.org/10.3390/polym13081330 - 19 Apr 2021

Cited by 22 | Viewed by 5066

Abstract

Numerous environmental issues arise as a result of a linear economy strategy: reserves become scarce and end up in landfills and as greenhouse gases. Utilizing waste as a resource or shifting towards a circular economy are among the effective strategies for addressing these [...] Read more.

Numerous environmental issues arise as a result of a linear economy strategy: reserves become scarce and end up in landfills and as greenhouse gases. Utilizing waste as a resource or shifting towards a circular economy are among the effective strategies for addressing these issues. To track this shift, appropriate measures that concentrate on sustainable development while taking practical contexts into consideration are required. In this paper, we utilize plastic wastes as a replacement for bitumen for reuse aiming at a circular economy. The use of plastic waste materials, i.e., plastic bottles (PET) and gas pipes (PE) in asphalt materials as a bitumen modifier was studied through series of experimental lab test methods. Marshall samples were prepared using a conventional Marshall method containing five different percentages (0%, 5%, 10%, 15%, and 20%) of plastic content by total weight of bitumen. Samples were tested after 1 and 30 days and the result shows that the stability of plastic-modified asphalt concrete was increased after 30 days, while still meeting standard criteria with plastic contents up to 20%. Moreover, the addition of waste plastic in road construction is a very effective strategy for reusing plastic waste, which also provides economic and social benefits for a sustainable approach to road pavements. Full article

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

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20 pages, 5360 KiB

Open AccessArticle

“All Polyimide” Mixed Matrix Membranes for High Performance Gas Separation

by Maijun Li, Zhibo Zheng, Zhiguang Zhang, Nanwen Li, Siwei Liu, Zhenguo Chi, Jiarui Xu and Yi Zhang

Polymers 2021, 13(8), 1329; https://doi.org/10.3390/polym13081329 - 19 Apr 2021

Cited by 3 | Viewed by 3236

Abstract

To improve the interfacial compatibility of mixed matrix membranes (MMMs) for gas separation, microporous polyimide particle (AP) was designed, synthesized, and introduced into intrinsic microporous polyimide matrix (6FDA-Durene) to form “all polyimide” MMMs. The AP fillers showed the feature of thermal stability, similar [...] Read more.

To improve the interfacial compatibility of mixed matrix membranes (MMMs) for gas separation, microporous polyimide particle (AP) was designed, synthesized, and introduced into intrinsic microporous polyimide matrix (6FDA-Durene) to form “all polyimide” MMMs. The AP fillers showed the feature of thermal stability, similar density with polyimide matrix, high porosity, high fractional free volume, large microporous dimension, and interpenetrating network architecture. As expected, the excellent interfacial compatibility between 6FDA-Durene and AP without obvious agglomeration even at a high AP loading of 10 wt.% was observed. As a result, the CO₂ permeability coefficient of MMM with AP loading as low as 5 wt.% reaches up to 1291.13 Barrer, which is 2.58 times that of the pristine 6FDA-Durene membrane without the significant sacrificing of ideal selectivity of CO₂/CH₄. The improvement of permeability properties is much better than that of the previously reported MMMs, where high filler content is required to achieve a high permeability increase but usually leads to significant agglomeration or phase separation of fillers. It is believed that the excellent interfacial compatibility between the PI fillers and the PI matrix induce the effective utilization of porosity and free volume of AP fillers during gas transport. Thus, a higher diffusion coefficient of MMMs has been observed than that of the pristine PI membrane. Furthermore, the rigid polyimide fillers also result in the excellent anti-plasticization ability for CO₂. The MMMs with a 10 wt.% AP loading shows a CO₂ plasticization pressure of 300 psi. Full article

(This article belongs to the Special Issue Advanced Polyimides and Other High Performance Polymers)

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11 pages, 7175 KiB

Open AccessArticle

A Study on the Interfacial Compatibility, Microstructure and Physico-Chemical Properties of Polyimide/Organically Modified Silica Nanocomposite Membrane

by Md A. Wahab, Mohammad R. Karim, Muhammad O. Aijaz, Bidita Salahuddin, Shazed Aziz and Abu A. I. Sina

Polymers 2021, 13(8), 1328; https://doi.org/10.3390/polym13081328 - 18 Apr 2021

Cited by 8 | Viewed by 3270

Abstract

Polyimide-silica (PI-Silica) composites are of tremendous research interest as high-performance materials because of their excellent thermal and mechanical properties and chemical resistance to organic solvents. Particularly, the sol-gel method of fabricating such composites is popular for manipulating their properties. In this work, PI-silica [...] Read more.

Polyimide-silica (PI-Silica) composites are of tremendous research interest as high-performance materials because of their excellent thermal and mechanical properties and chemical resistance to organic solvents. Particularly, the sol-gel method of fabricating such composites is popular for manipulating their properties. In this work, PI-silica composite films are synthesized by the sol-gel method and thermal imidization from the solution mixtures of hydrolyzed tetraethoxysilane (TEOS) (or glycidoxypropyltrimethoxysilane (GPMS)) modified silica and an aromatic polyamic acid (PAA) based on 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA)–p-phenylenediamine (PDA). The phase morphology of composites is found to be controlled by the substitution of TEOS with GPMS. Solid-state NMR spectroscopy is used to confirm the structural components of silica and GPMS-modified silica, whereas FT-IR results confirm the complete imidization of polyimide and composite film and suggest successful incorporation of Si–O–Si bonds into polyimide. The thermal, optical transmittance, and dielectric constant characterizations of pure polyimide and composite films are also carried out. Thermal stability of pure polyimide is found to be increased significantly by the addition of silica, whereas the partial substitution of TEOS with GPMS decreases the thermal stability of the composite, due to the presence of the alkyl organic segment of GPMS. The optical transmittance and dielectric constant of the composite films are controlled by manipulating the GPMS content. Full article

(This article belongs to the Special Issue Polymer Composites for Structural Applications)

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19 pages, 22909 KiB

Open AccessArticle

Preparation and Characterization of Nanofibrous Scaffolds of Ag/Vanadate Hydroxyapatite Encapsulated into Polycaprolactone: Morphology, Mechanical, and In Vitro Cells Adhesion

by Hany El-Hamshary, Mehrez E. El-Naggar, Ayman El-Faham, M. A. Abu-Saied, M. K. Ahmed and Mosaed Al-Sahly

Polymers 2021, 13(8), 1327; https://doi.org/10.3390/polym13081327 - 18 Apr 2021

Cited by 16 | Viewed by 2454

Abstract

Series of nanofibrous composites of polycaprolactone (PCL) were fabricated in different compositions of modified hydroxyapatite (HAP). The encapsulated HAP was co-doped with Ag/vanadate ions at different Ag contributions. XRD and FTIR techniques confirmed the powder and fibrous phase formation. Further, the morphological and [...] Read more.

Series of nanofibrous composites of polycaprolactone (PCL) were fabricated in different compositions of modified hydroxyapatite (HAP). The encapsulated HAP was co-doped with Ag/vanadate ions at different Ag contributions. XRD and FTIR techniques confirmed the powder and fibrous phase formation. Further, the morphological and mechanical behaviors of the electrospun nanofibrous scaffolds containing hydroxyapatite were investigated. The nanofibrous phases were biologically evaluated via studying contact angle, antibacterial, cell viability, and in vitro growth of human fibroblasts cell line (HFB4). It is obvious that silver ions cause gradual deviation in powder grains from wafer-like to cloudy grains. The maximum height of the roughness (R_t) ranged from 902.0 to 956.9 nm, while the valley depth of the roughness (R_v) ranged from 308.3 to 442.8 nm, for the lowest and the highest additional Ag ions for powdered phases. Moreover, the highest contribution of silver through the nanofibrous phases leads to the formation of lowest filaments size ranged from 0.07 to 0.53 µm. Further, the fracture strength was increased exponentially from 2.51 ± 0.35 MPa at zero concentration of silver ions up to 4.23 ± 0.64 MPa at 0.6 Ag/V-HAP@PCL. The fibrous phases were biologically evaluated in terms of antibacterial, cell viability, and in vitro growth of human fibroblasts cell line (HFB4). The nanofibrous composition of 0.8 Ag/V-HAP@PCL reached the maximum potential against E. coli and S. aureus and recorded 20.3 ± 1.1 and 19.8 ± 1.2 mm, respectively. This significant performance of the antibacterial activity and cell viability of co-doped HAP distributed through PCL could recommend these compositions for more research in biological applications, including wound healing. Full article

(This article belongs to the Section Polymer Applications)

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34 pages, 4747 KiB

Open AccessReview

Polylactic Acid (PLA) Biocomposite: Processing, Additive Manufacturing and Advanced Applications

by R.A. Ilyas, S.M. Sapuan, M.M. Harussani, M.Y.A.Y. Hakimi, M.Z.M. Haziq, M.S.N. Atikah, M.R.M. Asyraf, M.R. Ishak, M.R. Razman, N.M. Nurazzi, M.N.F. Norrrahim, Hairul Abral and Mochamad Asrofi

Polymers 2021, 13(8), 1326; https://doi.org/10.3390/polym13081326 - 18 Apr 2021

Cited by 226 | Viewed by 18140

Abstract

Over recent years, enthusiasm towards the manufacturing of biopolymers has attracted considerable attention due to the rising concern about depleting resources and worsening pollution. Among the biopolymers available in the world, polylactic acid (PLA) is one of the highest biopolymers produced globally and [...] Read more.

Over recent years, enthusiasm towards the manufacturing of biopolymers has attracted considerable attention due to the rising concern about depleting resources and worsening pollution. Among the biopolymers available in the world, polylactic acid (PLA) is one of the highest biopolymers produced globally and thus, making it suitable for product commercialisation. Therefore, the effectiveness of natural fibre reinforced PLA composite as an alternative material to substitute the non-renewable petroleum-based materials has been examined by researchers. The type of fibre used in fibre/matrix adhesion is very important because it influences the biocomposites’ mechanical properties. Besides that, an outline of the present circumstance of natural fibre-reinforced PLA 3D printing, as well as its functions in 4D printing for applications of stimuli-responsive polymers were also discussed. This research paper aims to present the development and conducted studies on PLA-based natural fibre bio-composites over the last decade. This work reviews recent PLA-derived bio-composite research related to PLA synthesis and biodegradation, its properties, processes, challenges and prospects. Full article

(This article belongs to the Special Issue Additive Manufacturing of Bio and Synthetic Polymers)

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12 pages, 2293 KiB

Open AccessArticle

Structure and Properties of Octenyl Succinic Anhydride-Modified High-Amylose Japonica Rice Starches

by Wei Zhang, Bei Cheng, Jiahui Li, Zaixi Shu, Pingping Wang and Xuefeng Zeng

Polymers 2021, 13(8), 1325; https://doi.org/10.3390/polym13081325 - 18 Apr 2021

Cited by 22 | Viewed by 2929

Abstract

Starches rich in amylose are promising functional ingredients for calory-reduced foods. In this research, a high-amylose Japonica rice starch (amylose content 33.3%) was esterified with octenyl succinic anhydride (OSA) to improve the functional properties. The OSA-modified derivatives were evaluated for structure and functional [...] Read more.

Starches rich in amylose are promising functional ingredients for calory-reduced foods. In this research, a high-amylose Japonica rice starch (amylose content 33.3%) was esterified with octenyl succinic anhydride (OSA) to improve the functional properties. The OSA-modified derivatives were evaluated for structure and functional properties, with OSA-modified normal Japonica rice starch (amylose content 18.8%) used as control. Fourier transform infrared spectra confirmed the introduction of OSA groups to starch. OSA modification made little change to morphology and particle size of high-amylose starch, but decreased the relative crystallinity and pasting temperature and increased the pasting viscosity, swelling power, emulsifying stability, and resistant starch (RS) content. The changes of properties were related to the degree of substitution (DS). Typically, OSA-modified high-amylose starch at DS of 0.0285 shows polyhedral-shape granules, with a volume-average particle diameter of 8.87 μm, peak viscosity of 5730 cp, and RS content of 35.45%. OSA-modified high-amylose starch had greater peak viscosity and RS content and lower swelling power than OSA-modified normal starch of similar DS, but the two kinds of derivatives did not have a significant difference in emulsifying stability. The OSA-modified high-amylose Japonica rice starch could be used as an emulsifier, thickener, and fat replacer in food systems. Full article

(This article belongs to the Special Issue Polysaccharides: Structure, Properties, and Applications)

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13 pages, 10249 KiB

Open AccessArticle

Behaviour of Polymer Filled Composites for Novel Polymer Railway Sleepers

by Wahid Ferdous, Allan Manalo, Choman Salih, Peng Yu, Rajab Abousnina, Tom Heyer and Peter Schubel

Polymers 2021, 13(8), 1324; https://doi.org/10.3390/polym13081324 - 18 Apr 2021

Cited by 10 | Viewed by 2825

Abstract

A novel concept of polymer railway sleeper is proposed in this study that has the potential to meet static performance requirements within the cost of hardwood timber. The existing challenges of composite sleepers, such as low performance or high cost, can be overcome [...] Read more.

A novel concept of polymer railway sleeper is proposed in this study that has the potential to meet static performance requirements within the cost of hardwood timber. The existing challenges of composite sleepers, such as low performance or high cost, can be overcome using this innovative concept. Such a proclamation is proven through limit state design criteria and a series of experimentations. Results show that polyurethane foam as an infill material can provide sufficient strength and stiffness properties to the sleeper, but the inadequate screw holding capacity could be a problem. This limitation, however, can be overcome using a particulate filled resin system. The findings of this study will help the railway industry to develop a timber replacement sleeper. Full article

(This article belongs to the Special Issue Polymer Concrete and Composites)

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24 pages, 4230 KiB

Open AccessReview

Delamination and Manufacturing Defects in Natural Fiber-Reinforced Hybrid Composite: A Review

by M. J. Suriani, Hannah Zalifah Rapi, R. A. Ilyas, Michal Petrů and S. M. Sapuan

Polymers 2021, 13(8), 1323; https://doi.org/10.3390/polym13081323 - 18 Apr 2021

Cited by 65 | Viewed by 9204

Abstract

In recent years, most boat fabrication companies use 100% synthetic fiber-reinforced composite materials, due to their high performance of mechanical properties. In the new trend of research on the fabrication of boat structure using natural fiber hybrid with kevlar/fiberglass-reinforced composite, the result of [...] Read more.

In recent years, most boat fabrication companies use 100% synthetic fiber-reinforced composite materials, due to their high performance of mechanical properties. In the new trend of research on the fabrication of boat structure using natural fiber hybrid with kevlar/fiberglass-reinforced composite, the result of tensile, bending, and impact strength showed that glass fiber-reinforced polyester composite gave high strength with increasing glass fiber contents. At some point, realizing the cost of synthetic fiber is getting higher, researchers today have started to use natural fibers that are seen as a more cost-effective option. Natural fibers, however, have some disadvantages, such as high moisture absorption, due to repelling nature; low wettability; low thermal stability; and quality variation, which lead to the degradation of composite properties. In recent times, hybridization is recommended by most researchers as a solution to natural fiber’s weaknesses and to reduce the use of synthetic fibers that are not environmentally friendly. In addition, hybrid composite has its own special advantages, i.e., balanced strength and stiffness, reduced weight and cost, improved fatigue resistance and fracture toughness, and improved impact resistance. The synthetic–nature fiber hybrid composites are used in a variety of applications as a modern material that has attracted most manufacturing industries’ attention to shift to using the hybrid composite. Some of the previous studies stated that delamination and manufacturing had influenced the performance of the hybrid composites. In order to expand the use of natural fiber as a successful reinforcement in hybrid composite, the factor that affects the manufacturing defects needs to be investigated. In this review paper, a compilation of the reviews on the delamination and a few common manufacturing defect types illustrating the overview of the impact on the mechanical properties encountered by most of the composite manufacturing industries are presented. Full article

(This article belongs to the Special Issue Mechanics of Polymer and Polymer Composite Materials and Structures)

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17 pages, 4321 KiB

Open AccessArticle

Synthesis and Characterization of Diosgenin Encapsulated Poly-ε-Caprolactone-Pluronic Nanoparticles and Its Effect on Brain Cancer Cells

by Bijuli Rabha, Kaushik Kumar Bharadwaj, Debabrat Baishya, Tanmay Sarkar, Hisham Atan Edinur and Siddhartha Pati

Polymers 2021, 13(8), 1322; https://doi.org/10.3390/polym13081322 - 18 Apr 2021

Cited by 32 | Viewed by 3719

Abstract

Diosgenin encapsulated PCL-Pluronic nanoparticles (PCL-F68-D-NPs) were developed using the nanoprecipitation method to improve performance in brain cancer (glioblastoma) therapy. The nanoparticles were characterized by dynamic light scattering (DLS)/Zeta potential, Fourier-transform infrared (FTIR) spectra, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and [...] Read more.

Diosgenin encapsulated PCL-Pluronic nanoparticles (PCL-F68-D-NPs) were developed using the nanoprecipitation method to improve performance in brain cancer (glioblastoma) therapy. The nanoparticles were characterized by dynamic light scattering (DLS)/Zeta potential, Fourier-transform infrared (FTIR) spectra, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and Transmission electron microscopy (TEM). The encapsulation efficiency, loading efficiency, and yield were calculated. The in vitro release rate was determined, and the kinetic model of diosgenin release was plotted and ascertained. The cytotoxicity was checked by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide)assay against U87-MG cells (glioblastoma cell lines). The obtained nanoparticles demonstrated good size distribution, stability, morphology, chemical, and mechanical properties. The nanoparticles also possessed high encapsulation efficiency, loading efficiency, and yield. The release rate of Diosgenin was shown in a sustained manner. The in vitro cytotoxicity of PCL-F68-D-NPs showed higher toxicity against U87-MG cells than free Diosgenin. Full article

(This article belongs to the Special Issue Biopolymers: Recent Progress and New Perspectives)

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16 pages, 1907 KiB

Open AccessArticle

Universal Plasma Jet for Droplet Manipulation on a PDMS Surface towards Wall-Less Scaffolds

by Cheng-Yun Peng and Chia-Hung Dylan Tsai

Polymers 2021, 13(8), 1321; https://doi.org/10.3390/polym13081321 - 17 Apr 2021

Cited by 1 | Viewed by 2457

Abstract

Droplet manipulation is important in the fields of engineering, biology, chemistry, and medicine. Many techniques, such as electrowetting and magnetic actuation, have been developed for droplet manipulation. However, the fabrication of the manipulation platform often takes a long time and requires well-trained skills. [...] Read more.

Droplet manipulation is important in the fields of engineering, biology, chemistry, and medicine. Many techniques, such as electrowetting and magnetic actuation, have been developed for droplet manipulation. However, the fabrication of the manipulation platform often takes a long time and requires well-trained skills. Here we proposed a novel method that can directly generate and manipulate droplets on a polymeric surface using a universal plasma jet. One of its greatest advantages is that the jet can tremendously reduce the time for the platform fabrication while it can still perform stable droplet manipulation with controllable droplet size and motion. There are two steps for the proposed method. First, the universal plasma jet is set in plasma mode for modifying the manipulation path for droplets. Second, the jet is switched to air-jet mode for droplet generation and manipulation. The jetted air separates and pushes droplets along the plasma-treated path for droplet generation and manipulation. According to the experimental results, the size of the droplet can be controlled by the treatment time in the first step, i.e., a shorter treatment time of plasma results in a smaller size of the droplet, and vice versa. The largest and the smallest sizes of the generated droplets in the results are about 6 µL and 0.1 µL, respectively. Infrared spectra of absorption on the PDMS surfaces with and without the plasma treatment are investigated by Fourier-transform infrared spectroscopy. Tests of generating and mixing two droplets on a PDMS surface are successfully achieved. The aging effect of plasma treatment for the proposed method is also discussed. The proposed method provides a simple, fast, and low-cost way to generate and manipulate droplets on a polymeric surface. The method is expected to be applied to droplet-based cell culture by manipulating droplets encapsulating living cells and towards wall-less scaffolds on a polymeric surface. Full article

(This article belongs to the Special Issue Polymer Scaffolds for Tissue Engineering)

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10 pages, 3920 KiB

Open AccessArticle

Nickel-Aluminum Thermal Spray Coatings as Adhesion Promoter and Susceptor for Inductively Joined Polymer-Metal Hybrids

by Erik Saborowski, Axel Dittes, Thomas Lindner and Thomas Lampke

Polymers 2021, 13(8), 1320; https://doi.org/10.3390/polym13081320 - 17 Apr 2021

Cited by 3 | Viewed by 2023

Abstract

Hybrid joints of metal- and fiber-reinforced-polymer offer great potential for lightweight applications. Thereby, a fast and reliable joining process is mandatory for mass-production applications. To this end, this study assesses inductive spot-joining in combination with prior thermal spray coating of the metal adherent. [...] Read more.

Hybrid joints of metal- and fiber-reinforced-polymer offer great potential for lightweight applications. Thereby, a fast and reliable joining process is mandatory for mass-production applications. To this end, this study assesses inductive spot-joining in combination with prior thermal spray coating of the metal adherent. A nickel–aluminum 95/5 coating was applied to achieve high adhesion through mechanical interlocking and to act as susceptor for the inductive joining process. The joint strength was assessed with lap shear specimens consisting of EN AW-6082 aluminum alloy and glass fiber reinforced polyamide 6 or polypropylene, respectively. The joints were further investigated in terms of heating time and hygrothermal cyclic loading. The results showed that significant time savings for the joining process as well as strong adhesion were achieved due to the coating. Moreover, the high strengths were even preserved under hygrothermal cyclic loading. Full article

(This article belongs to the Special Issue Polymer Hybrid Materials: Design and Applications)

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10 pages, 4041 KiB

Open AccessArticle

Hydroxyl-Terminated Saponified Natural Rubber Based on the H₂O₂/P25-TiO₂ Powder/UVC-Irradiation System

by Supinya Nijpanich, Adun Nimpaiboon, Porntip Rojruthai and Jitladda Sakdapipanich

Polymers 2021, 13(8), 1319; https://doi.org/10.3390/polym13081319 - 17 Apr 2021

Cited by 6 | Viewed by 2182

Abstract

Natural rubber (NR), a long-chain hydrocarbon polymer mostly consisting of cis-1,4-polyisoprene units, has a high molecular weight (MW) and viscosity, enabling it to show excellent physical properties. However, NR has no reactive functional group, making it difficult to react with other molecules, [...] Read more.

Natural rubber (NR), a long-chain hydrocarbon polymer mostly consisting of cis-1,4-polyisoprene units, has a high molecular weight (MW) and viscosity, enabling it to show excellent physical properties. However, NR has no reactive functional group, making it difficult to react with other molecules, especially in manufacturing processes. The functionalized low-molecular-weight NR (FLNR) is a requirement to disperse ingredients into the rubber adequately. Here, the FLNR was prepared by a photochemical degradation process under UVC-irradiation in the presence of H₂O₂ using P25-titanium oxide (TiO₂) powder as a photocatalyst. The optimum condition for the preparation of FLNR was the use of 2.0 g of TiO₂ powder per 100 g of rubber and H₂O₂ at 20% w/w under UVC-irradiation for 5 h. The hydroxyl groups were found on the NR chains due to the chain-scission of polyisoprene chains and hydroxyl radicals in the system. The weight average MW of NR decreased from 12.6 × 10⁵ to 0.6 × 10⁵ gmol⁻¹, while the number average MW decreased from 3.3 × 10⁵ to 0.1 × 10⁵ gmol⁻¹. Full article

(This article belongs to the Special Issue Advanced Rubber Composite)

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