Polymers

13 pages, 9962 KiB

Open AccessArticle

Shear Strain Singularity-Inspired Identification of Initial Delamination in CFRP Laminates: Multiscale Modulation Filter for Extraction of Damage Features

by Wei Xu, Yunfeng Lu, Ruihu Zhu, Maciej Radzieński, Maosen Cao and Wiesław Ostachowicz

Polymers 2022, 14(11), 2305; https://doi.org/10.3390/polym14112305 - 6 Jun 2022

Viewed by 1703

Abstract

Identification of initial delamination is crucial to ensure the safety of the fiber-reinforced laminated composite structures. Amongst the identification approaches based on mode shapes, the concept of multiscale shear-strain gradient (MSG) has an explicit physical sense of characterizing delamination-induced singularity of shear strains; [...] Read more.

Identification of initial delamination is crucial to ensure the safety of the fiber-reinforced laminated composite structures. Amongst the identification approaches based on mode shapes, the concept of multiscale shear-strain gradient (MSG) has an explicit physical sense of characterizing delamination-induced singularity of shear strains; moreover, it is robust against noise interference owing to the merits of multiscale analysis. However, the capacity of the MSG for identifying initial delamination is insufficient because the delamination-induced singularity peak can be largely obscured by the global component of the MSG. Addressing this problem, this study proposes an enhanced approach for identifying initial delamination in fiber-reinforced composite laminates. In particular, the multiscale modulation filter (MMF) is proposed to modulate the MSG with the aim of focusing on damage features, by which a new concept of enhanced MSG (EMSG) is formulated to extract damage features. By taking advantage of the MMF with the optimal frequency translation parameters, the EMSG is concentrated in a narrow wavenumber band, which is dominated by the damage-induced singularity peak. As a consequence, the delamination-induced singularity peak in the EMSG can be isolated from the global component. The capacity of the approach for identifying initial delamination is experimentally validated on a carbon fiber reinforced polymer (CFRP) laminate, whose mode shapes are acquired via non-contact laser measurement. The experimental results reveal that the EMSG-based approach is capable of graphically characterizing the presence, location, and size of initial delamination in CFRP laminates. Full article

(This article belongs to the Special Issue Advanced Joining Technologies for Carbon Fiber Reinforced Thermoplastics (CFRTPs))

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16 pages, 2896 KiB

Open AccessArticle

Utilization of Suberinic Acids Containing Residue as an Adhesive for Particle Boards

by Raimonds Makars, Janis Rizikovs, Daniela Godina, Aigars Paze and Remo Merijs-Meri

Polymers 2022, 14(11), 2304; https://doi.org/10.3390/polym14112304 - 6 Jun 2022

Cited by 15 | Viewed by 2273

Abstract

The birch (Betula spp.) outer bark is a valuable product rich in betulin. After removal of betulin extractives, suberin containing tissues are left. Suberin is a biopolyester built from α,ω-bifunctional fatty acids (suberinic acids), which after depolymerization together with lignocarbohydrate complex is [...] Read more.

The birch (Betula spp.) outer bark is a valuable product rich in betulin. After removal of betulin extractives, suberin containing tissues are left. Suberin is a biopolyester built from α,ω-bifunctional fatty acids (suberinic acids), which after depolymerization together with lignocarbohydrate complex is a potential adhesive as a side-stream product (residue) from obtaining suberinic acids for polyol synthesis. In this work, we studied the utilization possibilities in particleboards of the said residue obtained by depolymerization in four different solvents (methanol, ethanol, isopropanol and 1-butanol). The adhesives were characterised by chemical (acid number, solubility in tetrahydrofuran, epoxy and ash content) and instrumental analytical methods (SEC-RID, DSC, TGA and FTIR). Based on the results of mechanical characteristics, ethanol was chosen as the most suitable depolymerization medium. The optimal hot-pressing parameters for particleboards were determined using the design of experiments approach: adhesive content 20 wt%; hot-pressing temperature 248 °C, and hot-pressing time 6.55 min. Full article

(This article belongs to the Special Issue Eco-Friendly Wood Composites: Design, Characterization and Applications)

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16 pages, 3795 KiB

Open AccessArticle

Graphene Oxide/Polyvinyl Alcohol–Formaldehyde Composite Loaded by Pb Ions: Structure and Electrochemical Performance

by Alaa Fahmy, Badawi Anis, Paulina Szymoniak, Korinna Altmann and Andreas Schönhals

Polymers 2022, 14(11), 2303; https://doi.org/10.3390/polym14112303 - 6 Jun 2022

Cited by 4 | Viewed by 2447

Abstract

An immobilization of graphene oxide (GO) into a matrix of polyvinyl formaldehyde (PVF) foam as an eco-friendly, low cost, superior, and easily recovered sorbent of Pb ions from an aqueous solution is described. The relationships between the structure and electrochemical properties of PVF/GO [...] Read more.

An immobilization of graphene oxide (GO) into a matrix of polyvinyl formaldehyde (PVF) foam as an eco-friendly, low cost, superior, and easily recovered sorbent of Pb ions from an aqueous solution is described. The relationships between the structure and electrochemical properties of PVF/GO composite with implanted Pb ions are discussed for the first time. The number of alcohol groups decreased by 41% and 63% for PVF/GO and the PVF/GO/Pb composite, respectively, compared to pure PVF. This means that chemical bonds are formed between the Pb ions and the PVF/GO composite based on the OH groups. This bond formation causes an increase in the T_g values attributed to the formation of a strong surface complexation between adjacent layers of PVF/GO composite. The conductivity increases by about 2.8 orders of magnitude compared to the values of the PVF/GO/Pb composite compared to the PVF. This means the presence of Pb ions is the main factor for enhancing the conductivity where the conduction mechanism is changed from ionic for PVF to electronic conduction for PVF/GO and PVF/GO/Pb. Full article

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22 pages, 3061 KiB

Open AccessArticle

Equilibrium and Dynamic Surface Tension Behavior in Colloidal Unimolecular Polymers (CUP)

by Ashish Zore, Peng Geng and Michael R. Van De Mark

Polymers 2022, 14(11), 2302; https://doi.org/10.3390/polym14112302 - 6 Jun 2022

Cited by 2 | Viewed by 3268

Abstract

Studies of the interfacial behavior of pure aqueous nanoparticles have been limited due tothe difficulty of making contaminant-free nanoparticles while also providing narrow size distribution. Colloidal unimolecular polymers (CUPs) are a new type of single-chain nanoparticle with a particle size ranging from 3 [...] Read more.

Studies of the interfacial behavior of pure aqueous nanoparticles have been limited due tothe difficulty of making contaminant-free nanoparticles while also providing narrow size distribution. Colloidal unimolecular polymers (CUPs) are a new type of single-chain nanoparticle with a particle size ranging from 3 to 9 nm, which can be produced free of surfactants and volatile organic contents (VOCs). CUP particles of different sizes and surface charges were made. The surface tension behavior of these CUP particles in water was studied using a maximum bubble pressure tensiometer. The equilibrium surface tension decreased with increasing concentration and the number of charges present on the surface of the CUP particles influences the magnitude of the interfacial behavior. The effect of electrostatic repulsion between the particles on the surface tension was related. At higher concentrations, surface charge condensation started to dominate the surface tension behavior. The dynamic surface tension of CUP particles shows the influence of the diffusion of the particles to the interface on the relaxation time. The relaxation time of the CUP polymer was 0.401 s, which is closer to the diffusion-based relaxation time of 0.133s for SDS (sodium dodecyl sulfate). Full article

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

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10 pages, 1202 KiB

Open AccessCommunication

Loop and Bridge Conformations of ABA Triblock Comb Copolymers: A Conformational Assessment for Molecular Composites

by Jihoon Park, Je-Yeon Jung, Hyun-Woo Shin, Jong-Wan Park, Joona Bang and June Huh

Polymers 2022, 14(11), 2301; https://doi.org/10.3390/polym14112301 - 6 Jun 2022

Cited by 1 | Viewed by 2559

Abstract

We computationally investigate the conformational behavior, “bridging” chain, between different the phase-separated domains vs “looping” chain on the same domain, for two chain architectures of ABA triblock copolymers, one with a linear architecture (L-TBC) and the other with comb architecture (C-TBC) at various [...] Read more.

We computationally investigate the conformational behavior, “bridging” chain, between different the phase-separated domains vs “looping” chain on the same domain, for two chain architectures of ABA triblock copolymers, one with a linear architecture (L-TBC) and the other with comb architecture (C-TBC) at various segregation regimes using dissipative particle dynamics (DPD) simulations. The power-law relation between the bridge fraction (

Φ

) and the interaction parameter (

χ

) for C-TBC is found to be

Φ \sim χ^{- 1.6}

in the vicinity of the order-disorder transition (

χ_{O D T}

), indicating a drastic conversion from the bridge to the loop conformation. When

χ

further increases, the bridge-loop conversions slow down to have the power law,

Φ \sim χ^{- 0.18}

, approaching the theoretical power law

Φ \sim χ^{- 1 / 9}

predicted in the strong segregation limit. The conformational assessment conducted in the present study can provide a strategy of designing optimal material and processing conditions for triblock copolymer either with linear or comb architecture to be used for thermoplastic elastomer or molecular nanocomposites. Full article

(This article belongs to the Special Issue Polymer Blends and Synthesis for the Fabrication of Nanocomposites)

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14 pages, 2773 KiB

Open AccessArticle

Characterization of Immunogenicity Associated with the Biocompatibility of Type I Collagen from Tilapia Fish Skin

by Jingyi Zhang, Jeevithan Elango, Shujun Wang, Chunyu Hou, Meng Miao, Jia Li, Lixin Na and Wenhui Wu

Polymers 2022, 14(11), 2300; https://doi.org/10.3390/polym14112300 - 6 Jun 2022

Cited by 18 | Viewed by 3388

Abstract

Collagen from fish has been proven to have a low antigenicity that has no difference in the genetic codes compared with mammalian-based collagen. This study was designed to investigate the impact of tilapia skin collagen on immunogenicity and biocompatibility in vivo and in [...] Read more.

Collagen from fish has been proven to have a low antigenicity that has no difference in the genetic codes compared with mammalian-based collagen. This study was designed to investigate the impact of tilapia skin collagen on immunogenicity and biocompatibility in vivo and in vitro. The structural characteristics of both acid-soluble and pepsin-soluble collagen (ASC and PSC), determined using SDS-PAGE and atomic force microscopy imaging experiments, revealed that the collagen had the basic characteristics of type I collagen (COL-I). The in vitro biocompatibility of the collagens showed good cell proliferation against human foreskin fibroblast (HFF-1) cells. PSC and ASC were considered to be almost non-hemolytic biomaterials with favorable blood compatibility in hemolysis tests. The in vivo antigenicity of the collagen in an ICR mouse model evoked an acceptable specific inflammatory response compared to bovine collagen. The implant’s position had developed a complete granulation tissue and the sponge disappeared after 8 weeks. The level of cytokines produced by the COL-I immune response was much lower than bovine collagen, which indicated the appropriate implantable property and biodegradability of the collagens. In conclusion, the tilapia COL-I has a lower immunogenicity with better compatibility than bovine COL-I and is a potential alternative to conventional mammalian collagens in biomedical uses. Full article

(This article belongs to the Special Issue Bio-Based and Biodegradable Polymeric Composites: Synthesis, Characterization and Applications)

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11 pages, 4389 KiB

Open AccessArticle

Lignocellulose Extraction from Sisal Fiber and Its Use in Green Emulsions: A Novel Method

by Sippi Pirah, Xiaodong Wang, Muhammad Javed, Keenjhar Simair, Bijia Wang, Xiaofeng Sui and Changrui Lu

Polymers 2022, 14(11), 2299; https://doi.org/10.3390/polym14112299 - 5 Jun 2022

Cited by 8 | Viewed by 3423

Abstract

Regenerated lignocellulose nanofibrils (RLCNFs) have recently piqued the interest of researchers due to their widespread availability and ease of extraction. After dewaxing, we treated sisal fiber with alkali, followed by heating and agitation, to obtain RLCNFs, which were then vacuum oven-dried. We used [...] Read more.

Regenerated lignocellulose nanofibrils (RLCNFs) have recently piqued the interest of researchers due to their widespread availability and ease of extraction. After dewaxing, we treated sisal fiber with alkali, followed by heating and agitation, to obtain RLCNFs, which were then vacuum oven-dried. We used a variety of characterization techniques, including XRD, SEM, and FT-IR, to assess the effects of the alkali treatment on the sisal fiber. Various characterizations demonstrate that lignocellulose fibrils have been successfully regenerated and contaminants have been removed. In addition, employing the RLCNFs as a stabilizer, stable Pickering emulsions were created. The effects of RLCNF concentration in the aqueous phase and water-to-oil volume ratio on stability were studied. The RLCNFs that have been produced show promise as a stabilizer in Pickering emulsions. Full article

(This article belongs to the Section Polymer Applications)

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18 pages, 6435 KiB

Open AccessArticle

Mechanical Properties of Nano-SiO₂ Reinforced Geopolymer Concrete under the Coupling Effect of a Wet–Thermal and Chloride Salt Environment

by Qingqing Jin, Peng Zhang, Jingjiang Wu and Dehao Sha

Polymers 2022, 14(11), 2298; https://doi.org/10.3390/polym14112298 - 5 Jun 2022

Cited by 19 | Viewed by 2192

Abstract

In this study, the mechanical behaviors of nano-SiO₂ reinforced geopolymer concrete (NS-GPC) under the coupling effect of a wet–thermal and chloride salt environment were investigated through a series of basic experiments, and a simulation on the coupling effect of a wet–thermal and [...] Read more.

In this study, the mechanical behaviors of nano-SiO₂ reinforced geopolymer concrete (NS-GPC) under the coupling effect of a wet–thermal and chloride salt environment were investigated through a series of basic experiments, and a simulation on the coupling effect of a wet–thermal and chloride salt environment and SEM test were also included. During the experiments for the coupling effect of the wet–thermal and chloride salt environment, an environment simulation test chamber was utilized to simulate the wet–thermal and chloride salt environment, in which the parameters of relative humidity, temperature, mass fraction of NaCl solution and action time were set as 100%, 45 °C, 5% and 60 d, respectively. The content of nano-SiO₂ (NS) particles added in geopolymer concrete (GPC) were 0, 0.5%, 1.0%, 1.5% and 2.0%. The result indicated that the mechanical properties of NS reinforced GPC decreased under the coupling effect of the wet–thermal and chloride salt environment compared to the control group in the natural environment. When the NS content was 1.5%, the cube and splitting tensile strength, elastic modulus and impact toughness of GPC under the coupling environment of wet–thermal and chloride salt were decreased by 9.7%, 9.8%, 19.2% and 44.4%, respectively, relative to that of the GPC under the natural environment. The addition of NS improved the mechanical properties of GPC under the coupling effect of the wet–thermal and chloride salt environment. Compared to the control group without NS, the maximum increment in cube compressive strength, splitting tensile strength and elastic modulus of NS–GPC under the coupling effect of the wet–thermal and chloride salt environment due to the incorporation of NS reached 25.8%, 9.6% and 17.2%, respectively. Specifically, 1.5% content of NS increased the impact toughness, impact numbers of initial crack and the ultimate failure of GPC by 122.3%, 109% and 109.5%, respectively. Full article

(This article belongs to the Special Issue Fiber-Reinforced Composite)

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25 pages, 5997 KiB

Open AccessArticle

Research on Improving the Partial Discharge Initial Voltage of SiC/EP Composites by Utilizing Filler Surface Modification and Nanointerface Interaction

by Xupeng Song, Wei Yang, Shouchao Huo, Kun Wang, Yuanyuan Wu, Yun Chen, Jian Qiao, Boyang Shen and Xingming Bian

Polymers 2022, 14(11), 2297; https://doi.org/10.3390/polym14112297 - 5 Jun 2022

Cited by 4 | Viewed by 2491

Abstract

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at [...] Read more.

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%. Full article

(This article belongs to the Special Issue Detection and Diagnosis of Polymer Composites for Electrical and Electronic Engineering Application)

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19 pages, 6283 KiB

Open AccessArticle

Flexural and Viscoelastic Properties of FRP Composite Laminates under Higher Temperatures: Experiments and Model Assessment

by Getahun Tefera, Sarp Adali and Glen Bright

Polymers 2022, 14(11), 2296; https://doi.org/10.3390/polym14112296 - 5 Jun 2022

Cited by 4 | Viewed by 2550

Abstract

This study investigates an experimental and analytical study on the flexural, failure, and viscoelastic properties of hybrid and non-hybrid composite laminates at increasing temperatures and frequencies. Carbon, glass, and hybrids of the two fibre materials with stacking sequences of [0/90]_s were considered, [...] Read more.

This study investigates an experimental and analytical study on the flexural, failure, and viscoelastic properties of hybrid and non-hybrid composite laminates at increasing temperatures and frequencies. Carbon, glass, and hybrids of the two fibre materials with stacking sequences of [0/90]_s were considered, and specimens were prepared via the resin transfer moulding method. Three-point bending and dynamic mechanical analysis tools were used. The failure surfaces of the laminates were examined using a scanning electron microscope. The results indicated that the flexural strength, modulus, and strain at failure of all groups of laminates decreased as the temperature increased. In particular, the storage modulus, damping factor, flexural strength, and flexural modulus properties of all groups of laminates increased as the hybrid ratio decreased on each targeted temperature and frequency test. However, the strain at failure increased as the hybrid ratio increased. Additionally, results obtained from the scanning electron microscope images confirmed that combinations of delamination and debonding failure modes were observed on the stacking sequences of [0]_s and [90]_s layers of bidirectional laminates. Finally, a comparison between the storage modulus results of all groups of laminates was conducted with three empirical models. The empirical model developed by Gibson et al. provided the most accurate prediction for all groups of laminates in the targeted temperature and frequency range. The predictions using the remaining empirical models were broadly similar. Further work is needed to optimise the empirical parameters and minimise the errors. Full article

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

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12 pages, 1371 KiB

Open AccessArticle

The Properties of Poly(ester amide)s Based on Dimethyl 2,5-Furanedicarboxylate as a Function of Methylene Sequence Length in Polymer Backbone

by Konrad Walkowiak, Izabela Irska, Agata Zubkiewicz, Jerzy Dryzek and Sandra Paszkiewicz

Polymers 2022, 14(11), 2295; https://doi.org/10.3390/polym14112295 - 5 Jun 2022

Cited by 5 | Viewed by 2360

Abstract

A series of poly(ester amide)s based on dimethyl furan 2,5-dicarboxylate (DMFDC), 1,3-propanediol (PDO), 1,6-hexylene glycol (HDO), and 1,3-diaminopropane (DAP) were synthesized via two-step melt polycondensation. The phase transition temperatures and structure of the polymers were studied by differential scanning calorimetry (DSC). The positron [...] Read more.

A series of poly(ester amide)s based on dimethyl furan 2,5-dicarboxylate (DMFDC), 1,3-propanediol (PDO), 1,6-hexylene glycol (HDO), and 1,3-diaminopropane (DAP) were synthesized via two-step melt polycondensation. The phase transition temperatures and structure of the polymers were studied by differential scanning calorimetry (DSC). The positron annihilation lifetime spectroscopy (PALS) measurement was carried out to investigate the free volume. In addition, the mechanical properties of two series of poly(ester amide)s were analyzed. The increase in the number of methylene groups in the polymer backbone resulted in a decrease in the values of the transition temperatures. Depending on the number of methylene groups and the content of the poly(propylene furanamide) (PPAF), both semi-crystalline and amorphous copolymers were obtained. The free volume value increased with a greater number of methylene groups in the polymer backbone. Moreover, with a lower number of methylene groups, the value of the Young modulus and stress at break increased. Full article

(This article belongs to the Special Issue Bio-Nanocomposites: Modifications and Applications)

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29 pages, 8808 KiB

Open AccessArticle

Systematic Experimental Assessment of POFA Concrete Incorporating Waste Tire Rubber Aggregate

by Akram M. Mhaya, S. Baharom, Mohammad Hajmohammadian Baghban, Moncef L. Nehdi, Iman Faridmehr, Ghasan Fahim Huseien, Hassan Amer Algaifi and Mohammad Ismail

Polymers 2022, 14(11), 2294; https://doi.org/10.3390/polym14112294 - 5 Jun 2022

Cited by 18 | Viewed by 2716

Abstract

Several researchers devoted considerable efforts to partially replace natural aggregates in concrete with recycled materials such as recycled tire rubber. However, this often led to a significant reduction in the compressive strength of rubberized concrete due to the weaker interfacial transition zone between [...] Read more.

Several researchers devoted considerable efforts to partially replace natural aggregates in concrete with recycled materials such as recycled tire rubber. However, this often led to a significant reduction in the compressive strength of rubberized concrete due to the weaker interfacial transition zone between the cementitious matrix and rubber particles and the softness of rubber granules. Thereafter, significant research has explored the effects of supplementary cementitious materials such as zeolite, fly ash, silica fume, and slag used as partial replacement for cement on rubberized concrete properties. In this study, systematic experimental work was carried out to assess the mechanical properties of palm oil fuel ash (POFA)-based concrete incorporating tire rubber aggregates (TRAs) using the response surface methodology (RSM). Based on the findings, reasonable compressive, flexure, and tensile strengths were recorded or up to 10% replacement of sand with recycled tire fibre and fine TRAs. In particular, the reduction in compressive, tensile, and flexural strengths of POFA concrete incorporating fibre rubber decreased by 16.3%, 9.8%, and 10.1% at 365 days compared to normal concrete without POFA and rubber. It can be concluded that utilization of a combination of POFA and fine or fibre rubber could act as a beneficial strategy to solve the weakness of current rubberized concrete’s strength as well as to tackle the environmental issues of the enormous stockpiles of waste tires worldwide. Full article

(This article belongs to the Special Issue Cement-Based Polymeric Composites: Design, Synthesis and Properties)

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17 pages, 2197 KiB

Open AccessArticle

Synthesis of Chitosan-Based Gold Nanoparticles: Antimicrobial and Wound-Healing Activities

by Amr H. Hashem, Amr M. Shehabeldine, Omar M. Ali and Salem S. Salem

Polymers 2022, 14(11), 2293; https://doi.org/10.3390/polym14112293 - 5 Jun 2022

Cited by 66 | Viewed by 4733

Abstract

The global spread of multidrug-resistant bacteria has become a significant hazard to public health, and more effective antibacterial agents are required. Therefore, this study describes the preparation, characterization, and evaluation of gold nanoparticles modified with chitosan (Chi/AuNPs) as a reducing and stabilizing agent [...] Read more.

The global spread of multidrug-resistant bacteria has become a significant hazard to public health, and more effective antibacterial agents are required. Therefore, this study describes the preparation, characterization, and evaluation of gold nanoparticles modified with chitosan (Chi/AuNPs) as a reducing and stabilizing agent with efficient antimicrobial effects. In recent years, the development of an efficient and ecofriendly method for synthesizing metal nanoparticles has attracted a lot of interest in the field of nanotechnology. Colloidal gold nanoparticles (AuNPs) were prepared by the chemical reduction of gold ions in the presence of chitosan (Chi), giving Chi/AuNPs. The characterization of Chi/AuNPs was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and X-ray diffraction (XRD). Chi/AuNPs appeared spherical and monodispersed, with a diameter ranging between 20 to 120 nm. The synergistic effects of AuNPs and Chi led to the disruption of bacterial membranes. The maximum inhibitory impact was seen against P. aeruginosa at 500 µg/mL, with a zone of inhibition diameter of 26 ± 1.8 mm, whereas the least inhibitory effect was reported for S. aureus, with a zone of inhibition diameter of 16 ± 2.1 mm at the highest dose tested. Moreover, Chi/AuNPs exhibited antifungal activity toward Candida albicans when the MIC was 62.5 µg/mL. Cell viability and proliferation of the developed nanocomposite were evaluated using a sulphorhodamine B (SRB) assay with a half inhibitory concentration (IC₅₀) of 111.1 µg/mL. Moreover, the in vitro wound-healing model revealed that the Chi/AuNP dressing provides a relatively rapid and efficacious wound-healing ability, making the obtained nanocomposite a promising candidate for the development of improved bandage materials. Full article

(This article belongs to the Special Issue Advances in Smart Polymer Materials)

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17 pages, 4412 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Porous Chitosan/Saccharomycetes Adsorption Microspheres

by Wei Song, Qingzhu Zhang, Yuxin Guan, Wanyan Li, Siyu Xie, Jin Tong, Mo Li and Lili Ren

Polymers 2022, 14(11), 2292; https://doi.org/10.3390/polym14112292 - 5 Jun 2022

Cited by 7 | Viewed by 2832

Abstract

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres [...] Read more.

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres was characterized by X-ray diffraction. The results showed that the adsorption sites of amino and hydroxyl groups had been provided by the porous chitosan/saccharomycetes microspheres for the removal of preservatives, pigments, and other additives in food. The surface roughness of microspheres could be improved by increasing the mass ratio of saccharomycetes. The increase in silica gels could make the microsphere structure more compact. The porous chitosan/saccharomycetes microspheres could be used as adsorbents to adsorb doxycycline in wastewater. Full article

(This article belongs to the Section Polymer Chemistry)

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20 pages, 13492 KiB

Open AccessArticle

Microporous Formation Mechanism of Biaxial Stretching PA6/PP Membranes with High Porosity and Uniform Pore Size Distribution

by Wenxiang Fang, Guixue Liang, Jiang Li and Shaoyun Guo

Polymers 2022, 14(11), 2291; https://doi.org/10.3390/polym14112291 - 5 Jun 2022

Cited by 4 | Viewed by 2582

Abstract

The low porosity and wide pore size distribution of biaxial stretching PP microporous membranes continue to be the primary impediments to their industrial application. To solve this problem, there is a critical and urgent need to study the micropore-forming mechanism of PP membranes. [...] Read more.

The low porosity and wide pore size distribution of biaxial stretching PP microporous membranes continue to be the primary impediments to their industrial application. To solve this problem, there is a critical and urgent need to study the micropore-forming mechanism of PP membranes. In this research, the interfacial micropore formation mechanism of PA6/PP membranes during biaxial stretching was investigated. PA6/PP membranes containing spherical PA6 and fibrillar PA6 were found to exhibit different interfacial micropore formation mechanisms. Numerous micropores were generated in the PA6/PP membranes, containing PA6 spherical particles via the interface separation between the PP matrix and PA6 spherical particles during longitudinal stretching. Subsequent transverse stretching further expanded the two-phase interface, promoting the breakdown and fibrosis of the PP matrix and forming a spider-web-like microporous structure centered on spherical PA6 particles. In PA6/PP membranes with PA6 fibers, fewer micropores were generated during longitudinal stretching, but the subsequent transverse stretching violently separated the PA6 fibers, resulting in a dense fiber network composed of PA6 fibers interwoven with PP fibers. Crucially, the PA6/PP biaxial stretching of microporous membranes presented an optimized pore structure, higher porosity, narrower pore size distribution, and better permeability than β-PP membranes. Furthermore, this study explored a new approach to the fabrication of high-performance PA6/PP microporous membranes, with good prospects for potential industrial application. Full article

(This article belongs to the Section Polymer Membranes and Films)

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4 pages, 215 KiB

Open AccessEditorial

Electrospun Composite Nanofibers for Functional Applications

by Sana Ullah, Motahira Hashmi and Ick Soo Kim

Polymers 2022, 14(11), 2290; https://doi.org/10.3390/polym14112290 - 5 Jun 2022

Cited by 5 | Viewed by 1919

Abstract

Summary of the Special Issue: [...] Full article

(This article belongs to the Special Issue Electrospun Composite Nanofibers for Functional Applications)

14 pages, 3218 KiB

Open AccessArticle

Facile Fabrication of Superhydrophobic Graphene/Polystyrene Foams for Efficient and Continuous Separation of Immiscible and Emulsified Oil/Water Mixtures

by Chunxia Zhao, Haoran Huang, Jiaxin Li, Yuntao Li, Dong Xiang, Yuanpeng Wu, Ge Wang and Mingwang Qin

Polymers 2022, 14(11), 2289; https://doi.org/10.3390/polym14112289 - 5 Jun 2022

Cited by 5 | Viewed by 2258

Abstract

Three-dimensional superhydrophobic/superlipophilic porous materials have attracted widespread attention for use in the separation of oil/water mixtures. However, a simple strategy to prepare superhydrophobic porous materials capable of efficient and continuous separation of immiscible and emulsified oil/water mixtures has not yet been realized. Herein, [...] Read more.

Three-dimensional superhydrophobic/superlipophilic porous materials have attracted widespread attention for use in the separation of oil/water mixtures. However, a simple strategy to prepare superhydrophobic porous materials capable of efficient and continuous separation of immiscible and emulsified oil/water mixtures has not yet been realized. Herein, a superhydrophobic graphene/polystyrene composite material with a micro-nanopore structure was prepared by a single-step reaction through high internal phase emulsion polymerization. Graphene was introduced into the polystyrene-based porous materials to not only enhance the flexibility of the matrix, but also increase the overall hydrophobicity of the composite materials. The resulting as-prepared monoliths had excellent mechanical properties, were superhydrophobic/superoleophilic (water/oil contact angles were 151° and 0°, respectively), and could be used to continuously separate immiscible oil/water mixtures with a separation efficiency that exceeded 99.6%. Due to the size-dependent filtration and the tortuous and lengthy micro-nano permeation paths, our foams were also able to separate surfactant-stabilized water-in-oil microemulsions. This work demonstrates a facile strategy for preparing superhydrophobic foams for the efficient and continuous separation of immiscible and emulsified oil/water mixtures, and the resulting materials have highly promising application potentials in large-scale oily wastewater treatment. Full article

(This article belongs to the Special Issue Graphene-Based Polymer Composites and Their Applications)

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13 pages, 3933 KiB

Open AccessArticle

Controlling Morphology and Physio-Chemical Properties of Stimulus-Responsive Polyurethane Foams by Altering Chemical Blowing Agent Content

by Sayyeda Marziya Hasan, Tyler Touchet, Aishwarya Jayadeep and Duncan J. Maitland

Polymers 2022, 14(11), 2288; https://doi.org/10.3390/polym14112288 - 4 Jun 2022

Cited by 4 | Viewed by 2393

Abstract

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is [...] Read more.

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is a function of physio-chemical material properties. In this study, concentrations of the chemical blowing agent for the foam were altered and the resulting effects on morphology, thermal and chemical properties, and actuation rates were studied. Lower concentration of chemical blowing agent yielded foams with thick foam struts due to less bubble formation during the foaming process. Foams with thicker struts also had high tensile modulus and lower strain at break values compared to the foams made with higher blowing agent concentration. Additionally, less blowing agent resulted in foams with a lower glass transition temperature due to less urea formation during the foaming reaction. This exploratory study provides an approach to control thermo-mechanical foam properties and morphology by tuning concentrations of a foaming additive. This work aims to broaden the applications of shape memory polymer foams for medical use. Full article

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

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31 pages, 4594 KiB

Open AccessReview

Biopolymeric Nanoparticles–Multifunctional Materials of the Future

by Andrey A. Vodyashkin, Parfait Kezimana, Alexandre A. Vetcher and Yaroslav M. Stanishevskiy

Polymers 2022, 14(11), 2287; https://doi.org/10.3390/polym14112287 - 4 Jun 2022

Cited by 34 | Viewed by 4746

Abstract

Nanotechnology plays an important role in biological research, especially in the development of delivery systems with lower toxicity and greater efficiency. These include not only metallic nanoparticles, but also biopolymeric nanoparticles. Biopolymeric nanoparticles (BPNs) are mainly developed for their provision of several advantages, [...] Read more.

Nanotechnology plays an important role in biological research, especially in the development of delivery systems with lower toxicity and greater efficiency. These include not only metallic nanoparticles, but also biopolymeric nanoparticles. Biopolymeric nanoparticles (BPNs) are mainly developed for their provision of several advantages, such as biocompatibility, biodegradability, and minimal toxicity, in addition to the general advantages of nanoparticles. Therefore, given that biopolymers are biodegradable, natural, and environmentally friendly, they have attracted great attention due to their multiple applications in biomedicine, such as drug delivery, antibacterial activity, etc. This review on biopolymeric nanoparticles highlights their various synthesis methods, such as the ionic gelation method, nanoprecipitation method, and microemulsion method. In addition, the review also covers the applications of biodegradable polymeric nanoparticles in different areas—especially in the pharmaceutical, biomedical, and agricultural domains. In conclusion, the present review highlights recent advances in the synthesis and applications of biopolymeric nanoparticles and presents both fundamental and applied aspects that can be used for further development in the field of biopolymeric nanoparticles. Full article

(This article belongs to the Special Issue Natural Degradation: Polymer Degradation under Different Conditions)

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12 pages, 3099 KiB

Open AccessArticle

Facile Fabrication of Cellulose Nanofibrils/Chitosan Beads as the Potential pH-Sensitive Drug Carriers

by Meiyan Wu, Wangfang Deng, Yidong Zhang, Chao Chen, Zhexuan Liu, Pedram Fatehi and Bin Li

Polymers 2022, 14(11), 2286; https://doi.org/10.3390/polym14112286 - 4 Jun 2022

Cited by 5 | Viewed by 2374

Abstract

It is highly desirable to develop a safe, highly efficient, and biodegradable drug carrier with an enhanced drug transport efficiency. Cellulose nanofibrils (CNF) and chitosan (CS) composite hydrogels are promising candidate carriers with biological compatibility and non-cytotoxicity. Herein, the CNF/CS composite beads were [...] Read more.

It is highly desirable to develop a safe, highly efficient, and biodegradable drug carrier with an enhanced drug transport efficiency. Cellulose nanofibrils (CNF) and chitosan (CS) composite hydrogels are promising candidate carriers with biological compatibility and non-cytotoxicity. Herein, the CNF/CS composite beads were prepared by dissolving cellulose and CS in LiBr molten salt hydrate and regenerating in ethanol. This preparation method is facile and efficient, and the obtained porous CNF/CS beads with the weight ratio of 8:2 exhibited a large specific surface area, uniform micro-nano-sized pores, strong mechanical property, and water absorption-resistance. Moreover, these beads as drug (tetracycline hydrochloride, TH) carriers showed a higher encapsulation efficiency (47.4%) at the TH concentration of 5 mg/mL in 24 h, and a higher drug loading rate (12.0%) than pure CNF and other CNF/CS beads prepared with different ratios. In addition, the TH releasing behavior of CNF/CS (8:2) beads fitted well into the zero-order, first-order, and Higuchi models under an acid condition, indicating that the drug release of these pH-sensitive beads was mainly affected by drug concentration under an acid condition. Therefore, these CNF/CS beads have great potential to be used as drug carriers for medical applications. Full article

(This article belongs to the Special Issue (Nano)Cellulose in Biomedical Research)

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12 pages, 5517 KiB

Open AccessArticle

Construction of Three-Dimensional Network Structure in Polyethylene-EPDM-Based Phase Change Materials by Carbon Nanotube with Enhanced Thermal Conductivity, Mechanical Property and Photo-Thermal Conversion Performance

by Yunbing He, Yanfeng Chen, Cuiyin Liu, Lisha Huang, Chuyu Huang, Junhua Lu and Hong Huang

Polymers 2022, 14(11), 2285; https://doi.org/10.3390/polym14112285 - 4 Jun 2022

Cited by 5 | Viewed by 1925

Abstract

High thermal conductivity and good mechanical properties are significant for photo-thermal conversion in solar energy utilization. In this work, we constructed a three-dimensional network structure in polyethylene (PE) and ethylene-propylene-diene monomer (EPDM)-based phase change composites by mixing with a carbon nanotube (CNT). Two-dimensional [...] Read more.

High thermal conductivity and good mechanical properties are significant for photo-thermal conversion in solar energy utilization. In this work, we constructed a three-dimensional network structure in polyethylene (PE) and ethylene-propylene-diene monomer (EPDM)-based phase change composites by mixing with a carbon nanotube (CNT). Two-dimensional flake expanded graphite in PE-EPDM-based phase change materials and one-dimensional CNT were well mixed to build dense three-dimensional thermal pathways. We show that CNT (5.40%wt)-PE-EPDM phase change composites deliver excellent thermal conductivity (3.11 W m⁻¹ K⁻¹) and mechanical properties, with tensile and bending strength of 10.19 and 21.48 MPa. The melting and freezing temperature of the optimized phase change composites are measured to be 64.5 and 64.2 °C and the melting and freezing latent enthalpy are measured to be 130.3 and 130.5 J g⁻¹. It is found that the composite phase change material with high thermal conductivity is conducive to the rapid storage of solar energy, so as to improve the efficiency of heat collection. Full article

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

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10 pages, 2126 KiB

Open AccessArticle

Removal of Copper Corrosion Products by Using Green Deep Eutectic Solvent and Bio-Derivative Cellulose Membrane

by Akiko Tsurumaki, Cristina Chiarucci, Shraddha Khaire, Chiara Dal Bosco, Alessandra Gentili and Maria Assunta Navarra

Polymers 2022, 14(11), 2284; https://doi.org/10.3390/polym14112284 - 4 Jun 2022

Cited by 3 | Viewed by 2454

Abstract

A safe and environmentally friendly material for corrosion removal from metals is proposed in this article. Electrochemically corroded copper was selected as a target material, and a deep eutectic solvent (DES) composed of choline chloride and ascorbic acid, in a molar ratio of [...] Read more.

A safe and environmentally friendly material for corrosion removal from metals is proposed in this article. Electrochemically corroded copper was selected as a target material, and a deep eutectic solvent (DES) composed of choline chloride and ascorbic acid, in a molar ratio of 2:1, was developed to this end. Aqueous solutions of the DES with a concentration above 70 wt% were found to be effective in the dissolution of patina and less aggressive towards other materials such as CaCO_3, which is the main component of limestone. These concentrated DES solutions were integrated with either cotton swabs or cellulose-based membranes and used for the cleaning of electrochemically corroded copper. The membrane containing 80 wt% DES aqueous solution exhibited the most desirable cleaning ability in terms of speed and area selectivity. X-ray diffraction analysis of the corroded copper before and after the application of the membrane was performed to demonstrate the successful corrosion removal. Full article

(This article belongs to the Special Issue Advanced Polymers for Electrochemical Applications)

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11 pages, 2682 KiB

Open AccessArticle

Study on the Synthesis and Properties of Waterborne Polyurea Modified by Epoxy Resin

by Jing Wang, Jihu Wang, Song Wang, Shaoguo Wen, Kaimin Chen, Chen Xie and Chunping Yuan

Polymers 2022, 14(11), 2283; https://doi.org/10.3390/polym14112283 - 4 Jun 2022

Cited by 4 | Viewed by 3284

Abstract

The most notable features of polyurea are its fast reaction, energy-saving and high efficiency. In order to meet the needs of environmental protection, waterborne polyurea (WPUA) has become a research hotspot. However, the presence of hydrophilic groups in WPUA reduces its solvent resistance, [...] Read more.

The most notable features of polyurea are its fast reaction, energy-saving and high efficiency. In order to meet the needs of environmental protection, waterborne polyurea (WPUA) has become a research hotspot. However, the presence of hydrophilic groups in WPUA reduces its solvent resistance, heat resistance and mechanical properties. Therefore, it is necessary and valuable to develop a high-performance WPUA. In this study, epoxy-modified waterborne polyurea (WPUAE) emulsions were prepared using epoxy resin as a modifier. Fourier transform infrared spectroscopy (FT-IR) showed that E44 was successfully introduced into the molecular chain of WPUA. The WPUAE was tested for gel fraction, adhesion, contact angle, solvent resistance, tensile properties and thermal stability. The results showed that when the E44 content was 8 wt%, the performance of WPUAE was best, the adhesion of WPUAE coating film was 1.53 MPa, the gel fraction, water contact angle, water absorption, toluene absorption, tensile strength and decomposition temperature were 96.94%, 70.3°, 16.43%, 131.04%, 9.05 MPa and 365 °C, respectively. The results showed that epoxy resin as an emulsion modifier improved the comprehensive properties of WPUA. Full article

(This article belongs to the Section Polymer Chemistry)

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15 pages, 4850 KiB

Open AccessArticle

Performance Evaluation of Cross-Linked Polyethylene Insulation of Operating 110 kV Power Cables

by Man Ding, Weifeng He, Jiahe Wang and Jinpeng Wang

Polymers 2022, 14(11), 2282; https://doi.org/10.3390/polym14112282 - 3 Jun 2022

Cited by 11 | Viewed by 2635

Abstract

The ageing characteristic of XLPE insulation of operating a 110 kV power cable with different service time is studied in this paper. The microscopic morphology of XLPE films from different cables were characterized by using Differential Scanning Calorimetry (DSC), X-ray Diffraction method (XRD), [...] Read more.

The ageing characteristic of XLPE insulation of operating a 110 kV power cable with different service time is studied in this paper. The microscopic morphology of XLPE films from different cables were characterized by using Differential Scanning Calorimetry (DSC), X-ray Diffraction method (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) methods, and the dielectric, mechanical, and electrical properties of XLPE were also measured. The relationship of several typical property parameters with the cable service time were established, and the ageing mechanism of XLPE insulation of the operating cable was also analyzed. It was found that XLPE insulation would endure a recrystallization process in the initial operation stage during which the microscopic morphology would become more perfect with higher crystallinity and denser crystal structure. Then, the thermal oxidation would dominate the ageing process of XLPE with the molecular chains broken and more micromolecular products generated after the cable had operated for more than 10–15 years. The AC breakdown strength decreases with the increase of cable service time, with lower decreasing rate in the initial operation stage and a larger rate after 10–15 years. The Pearson correlation coefficient between the cable service time with the characteristic parameters were calculated, and some of them were found to be effective to be used as indicators for operation state detection of operating power cables. Full article

(This article belongs to the Special Issue Detection and Diagnosis of Polymer Composites for Electrical and Electronic Engineering Application)

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17 pages, 5264 KiB

Open AccessArticle

Study of SPRC Impact Resistance Based on the Weibull Distribution and the Response Surface Method

by Song Chen, Ziling Xu, Zeli Liu, Chen Wang and Jiuhong Jiang

Polymers 2022, 14(11), 2281; https://doi.org/10.3390/polym14112281 - 3 Jun 2022

Cited by 2 | Viewed by 1964

Abstract

Silica-fume–polyvinyl-alcohol-fiber-reinforced concrete (SPRC) is a green and environmentally friendly composite material incorporating silica fume and polyvinyl alcohol fiber into concrete. To study the impact resistance of SPRC, compressive-strength and drop hammer impact tests were conducted on SPRC with different silica-fume and polyvinyl-alcohol-fiber contents. [...] Read more.

Silica-fume–polyvinyl-alcohol-fiber-reinforced concrete (SPRC) is a green and environmentally friendly composite material incorporating silica fume and polyvinyl alcohol fiber into concrete. To study the impact resistance of SPRC, compressive-strength and drop hammer impact tests were conducted on SPRC with different silica-fume and polyvinyl-alcohol-fiber contents. The mechanical and impact resistance properties of the SPRC were comprehensively analyzed in terms of the compressive strength, ductility ratio and impact-energy-dissipation variation. Based on the impact resistance of the SPRC, the impact life of SPRC with different failure probabilities was predicted by incorporating the Weibull distribution model, and an impact damage evolution equation for SPRC was established. The impact life of SPRC under the action of silica-fume content, polyvinyl-alcohol-fiber content and failure probability was analyzed in depth by the response surface method (RSM). The research results show that, when the content of silica fume is 10% and the content of polyvinyl alcohol fiber is 1%, the compressive strength and impact resistance of SPRC are the best. The RSM response model can effectively predict and describe the impact life of SPRC specimens under the action of three factors. Full article

(This article belongs to the Special Issue Advances in Polymer-Reinforced and Fibre-Reinforced Concrete)

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20 pages, 11729 KiB

Open AccessArticle

Investigation of Efficient Alkali Treatment and the Effect of Flame Retardant on the Mechanical and Fire Performance of Frost-Retted Hemp Fiber Reinforced PLA

by Percy Festus Alao, Raimond Press, Heikko Kallakas, Jussi Ruponen, Triinu Poltimäe and Jaan Kers

Polymers 2022, 14(11), 2280; https://doi.org/10.3390/polym14112280 - 3 Jun 2022

Cited by 8 | Viewed by 2465

Abstract

This research investigates an effective alkali (NaOH) treatment and fire-retardant coating to produce biocomposites from frost-retted hemp fiber and PLA. The fiber surface treatment with various NaOH concentrations was investigated throughout a range of soaking times. The results show that the extracted non-cellulosic [...] Read more.

This research investigates an effective alkali (NaOH) treatment and fire-retardant coating to produce biocomposites from frost-retted hemp fiber and PLA. The fiber surface treatment with various NaOH concentrations was investigated throughout a range of soaking times. The results show that the extracted non-cellulosic fiber content increases with treatment duration and NaOH concentration, while the fraction of targeted components removed remains nearly unchanged after soaking for 1, 2, and 4 h with a 5 wt.% NaOH solution. At the composite level, the treatment with 5 wt.% NaOH solution for 1 h emerged as the most efficient, with tensile strength, Young’s modulus, flexural strength, and flexural modulus of 89.6 MPa, 9.1 GPa, 121.6 MPa, and 9.6 GPa, respectively, using 30 wt.% fibrous reinforcement. The fire performance of the examined batches of biocomposites improved significantly with the novel fire-retardant (Palonot F1) coating. However, the tensile strength notably decreased, while the flexural properties showed only a slight reduction. In most cases, the biocomposites with the alkali-treated hemp fiber had delayed ignition during the 5 min exposure to the cone heater. The findings in this work contribute to studies that will be required to give design guidelines for sustainable building options. Full article

(This article belongs to the Special Issue Flame-Retardant Polymer Composites)

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15 pages, 2590 KiB

Open AccessArticle

Chitosan Graft Copolymers with N-Vinylimidazole as Promising Matrices for Immobilization of Bromelain, Ficin, and Papain

by Andrey V. Sorokin, Svetlana S. Olshannikova, Maria S. Lavlinskaya, Marina G. Holyavka, Dzhigangir A. Faizullin, Yuriy F. Zuev and Valeriy G. Artukhov

Polymers 2022, 14(11), 2279; https://doi.org/10.3390/polym14112279 - 3 Jun 2022

Cited by 14 | Viewed by 2706

Abstract

This work aims to synthesize graft copolymers of chitosan and N-vinylimidazole (VI) with different compositions to be used as matrices for the immobilization of cysteine proteases—bromelain, ficin, and papain. The copolymers are synthesized by free radical solution copolymerization with a potassium persulfate-sodium [...] Read more.

This work aims to synthesize graft copolymers of chitosan and N-vinylimidazole (VI) with different compositions to be used as matrices for the immobilization of cysteine proteases—bromelain, ficin, and papain. The copolymers are synthesized by free radical solution copolymerization with a potassium persulfate-sodium metabisulfite blend initiator. The copolymers have a relatively high frequency of grafting and yields. All the synthesized graft copolymers are water-soluble, and their solutions are characterized by DLS and laser Doppler microelectrophoresis. The copolymers are self-assembled in aqueous solutions, and they have a cationic nature and pH-sensitivity correlating to the VI content. The FTIR data demonstrate that synthesized graft copolymers conjugate cysteine proteases. The synthesized copolymer adsorbs more enzyme macromolecules compared to non-modified chitosan with the same molecular weight. The proteolytic activity of the immobilized enzymes is increased up to 100% compared to native ones. The immobilized ficin retains up to 97% of the initial activity after a one-day incubation, the immobilized bromelain retains 69% of activity after a 3-day incubation, and the immobilized papain retains 57% of the initial activity after a 7-day incubation. Therefore, the synthesized copolymers can be used as matrices for the immobilization of bromelain, ficin, and papain. Full article

(This article belongs to the Special Issue Polymeric Materials for Applications in the Food Industry)

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14 pages, 1911 KiB

Open AccessArticle

Research on Low-Cycle Fatigue Engineered Hybrid Sandwich Ski Construction

by Tomáš Božák, Miroslav Müller, Viktor Kolář, Martin Tichý, Jaroslava Svobodová and Štefan Michna

Polymers 2022, 14(11), 2278; https://doi.org/10.3390/polym14112278 - 3 Jun 2022

Cited by 1 | Viewed by 1902

Abstract

This research is aimed at evaluating the effect of low-cycle fatigue on a newly designed hybrid sandwich ski structure to determine the changes that may occur due to cyclic loading and thus affect its use. This is primarily concerned with the fatigue behavior [...] Read more.

This research is aimed at evaluating the effect of low-cycle fatigue on a newly designed hybrid sandwich ski structure to determine the changes that may occur due to cyclic loading and thus affect its use. This is primarily concerned with the fatigue behavior of the tested ski over different time intervals simulating its seasonal use and its effect on the mechanical properties of the ski, i.e., the durability and integrity of the individual layers of the sandwich ski structure. The ski was subjected to 70,000 deflections by moving the crossbar by 60 mm according to the ski deflection calculation in the arch. The results of the cyclic tests of the engineered ski design showed no significant changes in the ski during loading. The average force required to achieve deflection in the first 10,000 cycles was 514.0 ± 4.2 N. Thereafter, a secondary hardening of the structure occurred during relaxation and the force required increased slightly to 543.6 ± 1.7 N. The required force fluctuated slightly during the measurements and in the last series the value was 540.4 ± 0.8 N. Low-cycle fatigue did not have a significant effect on the mechanical properties of the ski; there was no change in shape or visual delamination of the individual layers of the structure. From the cross-section, local delamination was demonstrated by image analysis, especially between the Wood core and the composite layers E-Glass biaxial and Carbon triaxial. Full article

(This article belongs to the Special Issue Polymer-Based Hybrid Composites)

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23 pages, 11757 KiB

Open AccessArticle

Effect of Diluents on Mechanical Characteristics of Epoxy Compounds

by Anna Rudawska and Mariaenrica Frigione

Polymers 2022, 14(11), 2277; https://doi.org/10.3390/polym14112277 - 3 Jun 2022

Cited by 15 | Viewed by 3505

Abstract

The aim of this work is to assess the influence of different commercial diluents on some mechanical properties of two bisphenolic epoxy compounds, cold-cured by a polyamide curing agent, to be employed as epoxy structural adhesives for building and industrial applications. The diluents [...] Read more.

The aim of this work is to assess the influence of different commercial diluents on some mechanical properties of two bisphenolic epoxy compounds, cold-cured by a polyamide curing agent, to be employed as epoxy structural adhesives for building and industrial applications. The diluents under analysis were epoxy, bituminous, nitro, acrylic and extraction. The choice of these products was made on the basis of their wide commercial availability as diluents for epoxies used as adhesives and in different industrial and construction applications. The diluents were all added in small proportions, i.e., from 1 to 10 g per 100 g of epoxy resin. The cold-cured epoxy compounds were subjected to compressive (according to ISO 604) and static tensile (according to ISO 527-1) tests. The same mechanical tests were performed on both unmodified epoxy resins, for comparison purposes. On the basis of the obtained results, it was concluded that the influence of the presence of a diluent, and of its amount, on the mechanical properties of epoxy compounds depends on the type of resin and of diluent, as well as on the mechanical characteristics analyzed. Full article

(This article belongs to the Special Issue Feature Papers in Polymer Applications)

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13 pages, 5677 KiB

Open AccessArticle

Feasibility Study on the Fused Filaments of Injection-Molding-Grade Poly(Ethylene Terephthalate) for 3D Printing

by Hsi-Hsun Tsai, Shao-Jung Wu, Yu-De Wu and Wei-Zheng Hong

Polymers 2022, 14(11), 2276; https://doi.org/10.3390/polym14112276 - 2 Jun 2022

Cited by 12 | Viewed by 2545

Abstract

Unlike that of glycol-modified Poly(ethylene terephthalate) (PETG), the crystallinity of PET can be post-adjusted to enhance the mechanical properties of 3D-printed parts such as food-contact tableware and bio-implants. The aforementioned PET material could be 3D printed to produce the desired parts for performance [...] Read more.

Unlike that of glycol-modified Poly(ethylene terephthalate) (PETG), the crystallinity of PET can be post-adjusted to enhance the mechanical properties of 3D-printed parts such as food-contact tableware and bio-implants. The aforementioned PET material could be 3D printed to produce the desired parts for performance evaluation before mass production by injection molding. In this study, using differential scanning calorimetry (DSC), we examined the pellets, extruded filament, and printed specimen to identify variations in melting and crystalline temperatures, as well as crystallinity. It was also shown by Thermogravimetric Analyzer (TGA) that the addition of talcum powder increased the thermal stability of filament and resulted in an interaction between the fillers and polymer matrix. The crystallinities of the filament and printed specimen were then compared with the yield strengths and Young’s moduli to confirm the effects of the decreased molecular weight of the extruded PET filament. The talcum powder effectively improved the viscosity of the PET melted during the extrusion process for the filament and then enhanced the crystallinity of the PET, thereby achieving a significantly higher Young’s modulus. The printed PET specimen presented an excellent yield strength of 25 MPa and ductile properties with strain-at-break values of 30%, successfully indicating potential applications in food-contact tableware and bio-implants. Full article

(This article belongs to the Special Issue Recent Advances in Injection Molding of Polymers)

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