Polymers

2686 KiB

Open AccessArticle

Microwave-Absorbing Properties of Rice Starch

by Daming Fan, Huijie Shen, Luelue Huang, Yishu Gao, Huizhang Lian, Jianxin Zhao, Hao Zhang and Wei Chen

Polymers 2015, 7(9), 1895-1904; https://doi.org/10.3390/polym7091487 - 22 Sep 2015

Cited by 14 | Viewed by 6044

Abstract

In the food industry, research into the characteristics of microwave-heated materials has focused on dielectric properties. However, the lack of studies on microwave-absorbing properties has hindered the application of microwave technology. The aim of the present study was to investigate the microwave-absorbing properties [...] Read more.

In the food industry, research into the characteristics of microwave-heated materials has focused on dielectric properties. However, the lack of studies on microwave-absorbing properties has hindered the application of microwave technology. The aim of the present study was to investigate the microwave-absorbing properties of rice starch. It should be noted that this was the first time that the improved arch method was used to measure the microwave reflection loss (RL) of the starch dispersion. The results showed that the microwave absorption of the liquid system corresponded to the classical quarter-wavelength resonator model. When the concentration of the native starch was increased from 1% to 30%, the RL decreased from −5.1 dB to −1.2 dB at 2.45 GHz. Therefore, the absorption rate of microwave, γ_ab, decreased from 69.1% to 24.1%. At 1.7 to 2.6 GHz, the interference effect of pregelatinization rice starch in an aqueous system on the microwave absorption properties became weak compared to native starch. Full article

(This article belongs to the Collection Polysaccharides)

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6546 KiB

Open AccessArticle

Preferential Incorporation of Azelaic Acid Units into the Crystalline Phase of the Copoly(Alkylene Dicarboxylate) Derived from 1,9-Nonanediol and an Equimolar Mixture of Pimelic and Azelaic Acids

by Angélica Díaz, María T. Casas and Jordi Puiggalí

Polymers 2015, 7(9), 1871-1894; https://doi.org/10.3390/polym7091486 - 22 Sep 2015

Cited by 4 | Viewed by 7256

Abstract

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio [...] Read more.

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P21ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface. Full article

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3487 KiB

Open AccessArticle

Preparation and Evaluation of Vancomycin-Loaded N-trimethyl Chitosan Nanoparticles

by Jiaojiao Xu, Beihua Xu, Dan Shou, Xiaojing Xia and Ying Hu

Polymers 2015, 7(9), 1850-1870; https://doi.org/10.3390/polym7091488 - 22 Sep 2015

Cited by 91 | Viewed by 12059

Abstract

Chronic intracellular infections caused by drug-resistant pathogens pose a challenge to the treatment of chronic osteomyelitis. Such treatment requires an intracellular delivery system for the sustained release of antibiotics such as vancomycin (VCM), which is an antibiotic of last resort used against many [...] Read more.

Chronic intracellular infections caused by drug-resistant pathogens pose a challenge to the treatment of chronic osteomyelitis. Such treatment requires an intracellular delivery system for the sustained release of antibiotics such as vancomycin (VCM), which is an antibiotic of last resort used against many clinically resistant bacteria. In this work, we report VCM-loaded N-trimethyl chitosan (TMC) nanoparticles and their potential application for drug delivery. The results showed that the prepared nanoparticles were predominantly spherical in shape with an average particle diameter of 220 nm, a positive zeta potential, and a loading efficiency of 73.65% ± 1.83%. Furthermore, their drug release profile followed the Higuchi model for sustained release, with non-Fickian diffusion. Over a 24-h period, 6.51% ± 0.58% of the drug within the optimized nanoparticles was released. In vitro cytology showed that osteoblasts (OBs) exhibited higher alkaline phosphatase activity (ALP) after exposure to TMC nanoparticle material. Furthermore, TMC nanoparticles increased the uptake of water-soluble quantum dots (QDs) by OBs, and both nanoparticles and VCM/TMC mixtures improved OB proliferative activity. We also investigated the minimum inhibitory concentration (MIC, 60 μg/mL), half maximal inhibitory concentration (IC50, 48.47 μg/mL), diameter of inhibition zone (DIZ, 1.050 cm), and turbidimetric (TB) assay of nanoparticles. All data demonstrated that VCM/TMC nanoparticles had excellent antibacterial activity against the Gram-positive bacterium Staphylococcus aureus. These findings suggest that VCM-loaded TMC nanoparticles have good potential for the sustained delivery of antibiotics to bone infections. Full article

(This article belongs to the Collection Polysaccharides)

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1732 KiB

Open AccessCommunication

Biocatalytic Self-Cleaning Polymer Membranes

by Agnes Schulze, Astrid Stoelzer, Karl Striegler, Sandra Starke and Andrea Prager

Polymers 2015, 7(9), 1837-1849; https://doi.org/10.3390/polym7091485 - 21 Sep 2015

Cited by 17 | Viewed by 8063

Abstract

Polymer membrane surfaces have been equipped with the digestive enzyme trypsin. Enzyme immobilization was performed by electron beam irradiation in aqueous media within a one-step method. Using this method, trypsin was covalently and side-unspecific attached to the membrane surface. Thus, the use of [...] Read more.

Polymer membrane surfaces have been equipped with the digestive enzyme trypsin. Enzyme immobilization was performed by electron beam irradiation in aqueous media within a one-step method. Using this method, trypsin was covalently and side-unspecific attached to the membrane surface. Thus, the use of preceding polymer functionalization and the use of toxic solvents or reagents can be avoided. The resulting membranes showed significantly improved antifouling properties as demonstrated by repeated filtration of protein solutions. Furthermore, the biocatalytic membrane can be simply “switched on” to actively degrade a fouling layer on the membrane surface and regain the initial permeability. The membrane pore structure (pore size and porosity) was neither damaged by the electron beam treatment nor blocked by the enzyme loading, ensuring a stable membrane performance. Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes 2015)

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1240 KiB

Open AccessArticle

Conjugation of ß-Adrenergic Antagonist Alprenolol to Implantable Polymer-Aescin Matrices for Local Delivery

by Ewa Oledzka, Dagmara Pachowska, Marcin Sobczak, Agnieszka Lis-Cieplak, Grzegorz Nalecz-Jawecki, Anna Zgadzaj and Waclaw Kolodziejski

Polymers 2015, 7(9), 1820-1836; https://doi.org/10.3390/polym7091484 - 18 Sep 2015

Cited by 5 | Viewed by 7120

Abstract

The sustained release of alprenolol, a ß-adrenergic antagonist, could be beneficial for the treatment of various heart diseases while reducing the side effects resulting from its continuous use. The novel and branched copolymers uniquely composed of biodegradable components (lactide and glycolide) have been [...] Read more.

The sustained release of alprenolol, a ß-adrenergic antagonist, could be beneficial for the treatment of various heart diseases while reducing the side effects resulting from its continuous use. The novel and branched copolymers uniquely composed of biodegradable components (lactide and glycolide) have been synthesized using natural and therapeutically-efficient ß-aescin-initiator, and consequently characterized to determine their structures and physicochemical properties. The obtained matrices were not cyto- and genotoxic towards bacterial luminescence, protozoan, and Salmonella typhimurium TA1535. The copolymers release the drug in vitro in a sustained manner and without burst release. The value of the drug released was strongly dependent on the copolymer composition and highly correlated with the hydrolytic matrices’ degradation results. Full article

(This article belongs to the Special Issue Functional Polymers for Medical Applications)

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1210 KiB

Open AccessReview

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

by Evangelos Mavroudakis, Danilo Cuccato and Davide Moscatelli

Polymers 2015, 7(9), 1789-1819; https://doi.org/10.3390/polym7091483 - 17 Sep 2015

Cited by 45 | Viewed by 9859

Abstract

Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP) with growing interest. Nowadays, quantum chemistry (QC) can be considered a powerful and cost-effective tool for the kinetic [...] Read more.

Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP) with growing interest. Nowadays, quantum chemistry (QC) can be considered a powerful and cost-effective tool for the kinetic characterization of many individual reactions in FRP, especially those that cannot yet be fully analyzed through experiments. The recent focus on copolymers and systems where secondary reactions play a major role has emphasized this feature due to the increased complexity of these kinetic schemes. QC calculations are well-suited to support and guide the experimental investigation of FRP kinetics as well as to deepen the understanding of polymerization mechanisms. This paper is intended to provide an overview of the most relevant QC results obtained so far from the investigation of FRP. A comparison between computational results and experimental data is given, whenever possible, to emphasize the performances of the two approaches in the prediction of kinetic data. This work provides a comprehensive database of reaction rate parameters of FRP to assist in the development of advanced models of polymerization and experimental studies on the topic. Full article

(This article belongs to the Special Issue Computational Chemistry)

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3486 KiB

Open AccessArticle

Preparation and Characterization of Novel PVC/Silica–Lignin Composites

by Łukasz Klapiszewski, Franciszek Pawlak, Jolanta Tomaszewska and Teofil Jesionowski

Polymers 2015, 7(9), 1767-1788; https://doi.org/10.3390/polym7091482 - 15 Sep 2015

Cited by 53 | Viewed by 12834

Abstract

An advanced SiO2–lignin hybrid material was obtained and tested as a novel poly(vinyl chloride) (PVC) filler. The processing of compounds of poly(vinyl chloride) in the form of a dry blend with silica–lignin hybrid material and, separately, with the two components from which that [...] Read more.

An advanced SiO2–lignin hybrid material was obtained and tested as a novel poly(vinyl chloride) (PVC) filler. The processing of compounds of poly(vinyl chloride) in the form of a dry blend with silica–lignin hybrid material and, separately, with the two components from which that material was prepared, was performed in a Brabender mixing chamber. An analysis was made of processing (mass melt flow rate, MFR), thermal (thermogravimetric analysis, Congo red and Vicat softening temperature test) and tensile properties of the final PVC composites with fillers in a range of concentrations between 2.5 wt % and 10 wt %. Additionally, the effects of filler content on the fusion characteristics of PVC composites were investigated. The homogeneity of dispersion of the silica–lignin hybrid material in the PVC matrix was determined by optical microscopy and SEM. Finally, it should be noted that it is possible to obtain a PVC composite containing up to 10 wt % of silica–lignin filler using a melt processing method. The introduction of hybrid filler into the PVC matrix results in a homogeneous structure of the composites and positive processing and functional properties, especially thermal stability and Vicat softening temperature. Full article

(This article belongs to the Collection Silicon-Containing Polymeric Materials)

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2682 KiB

Open AccessArticle

Study on the Microstructure of Polyester Polyurethane Irradiated in Air and Water

by Qiang Tian, Erzsébet Takács, Ivan Krakovský, Zsolt Endre Horváth, László Rosta and László Almásy

Polymers 2015, 7(9), 1755-1766; https://doi.org/10.3390/polym7091481 - 15 Sep 2015

Cited by 24 | Viewed by 9145

Abstract

The gamma irradiation induced aging of thermoplastic polymer Estane 5703 in air and water environments was studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and X-ray diffraction (XRD). The degree of phase mixing was increased after [...] Read more.

The gamma irradiation induced aging of thermoplastic polymer Estane 5703 in air and water environments was studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and X-ray diffraction (XRD). The degree of phase mixing was increased after irradiation, accompanied by the increase of domain distance and decrease of domain size. The hard domain distance increased from 9.8 to 11.2 nm and 14.4 nm for the samples irradiated in air and water with a dose up to 500 kGy, respectively. The GPC results indicated progressive formation of larger linked structures with very high molar mass with increasing absorbed doses. The samples irradiated in water exhibited a stronger aging effect than those irradiated in air. The FTIR results suggested that the cross-linking occurred among the secondary alkyl radicals, and the interactions in hard domains weakened because of the loss of inter-urethane H-bonds. The volume fraction of well-ordered soft segments in Estane increased upon irradiation. Full article

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1885 KiB

Open AccessArticle

Simplified Model for Strengthening Design of Beam–Column Internal Joints in Reinforced Concrete Frames

by Antonio Bossio, Francesco Fabbrocino, Gian Piero Lignola, Andrea Prota and Gaetano Manfredi

Polymers 2015, 7(9), 1732-1754; https://doi.org/10.3390/polym7091479 - 10 Sep 2015

Cited by 48 | Viewed by 10287

Abstract

The beam-column joints are very restricted areas in which the internal forces, generated by boundary elements, act on the concrete core and reinforcing bars with a very high gradient. They are the link between horizontal and vertical structural elements, and therefore, they are [...] Read more.

The beam-column joints are very restricted areas in which the internal forces, generated by boundary elements, act on the concrete core and reinforcing bars with a very high gradient. They are the link between horizontal and vertical structural elements, and therefore, they are directly involved in the transfer of seismic forces. Thus, they are crucial to study the seismic behavior of reinforced concrete (RC) structures. To fully understand the seismic performances and failure modes of beam-column joints in RC buildings, a simplified analytical model of joint behavior is proposed and theoretical simulations are performed. The aim of the model, focusing on internal perimetric joints, is to identify the strength hierarchy in terms of capacity for different failure modes (namely failure of cracked joint, bond failure of passing through bars, flexural/shear failures of columns or beams). It could represent a tool for the designers of new joints to quantify the performance of new structures, but also as a tool for the designers of external strengthening of existing joints in order to calculate the benefits of the retrofit and pushing the initial failure to a more desirable failure mode. Further, some experimental results of tests available in the scientific literature are reported, analyzed and compared. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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4197 KiB

Open AccessArticle

An Experimental Study on Non-Compression X-Bracing Systems Using Carbon Fiber Composite Cable for Seismic Strengthening of RC Buildings

by Kang Seok Lee

Polymers 2015, 7(9), 1716-1731; https://doi.org/10.3390/polym7091480 - 9 Sep 2015

Cited by 12 | Viewed by 8710

Abstract

Cross-bracing (X-bracing) is one of the most popular methods of seismic retrofitting, and has been shown to significantly increase the structural stiffness and strength of buildings. Conventional steel X-bracing methods typically exhibit brittle failure at the connection between the brace and the building, [...] Read more.

Cross-bracing (X-bracing) is one of the most popular methods of seismic retrofitting, and has been shown to significantly increase the structural stiffness and strength of buildings. Conventional steel X-bracing methods typically exhibit brittle failure at the connection between the brace and the building, or buckling failure of the braces. This study investigated the structural properties of a new type of non-compression X-bracing system using carbon fiber composite cable (CFCC). This non-compression X-bracing system uses CFCC bracing and bolt connections between structural members and the terminal fixer of the CFCC, instead of conventional steel bracing. The aim is to overcome the brittle and buckling failures that can occur at the connection and bracings with conventional steel X-bracing methods. We carried out cyclic loading tests, and the maximum load carrying capacity and deformation were investigated, as well as hysteresis in the lateral load–drift relations. The test results revealed that the CFCC X-bracing system installed in reinforced concrete frames enhanced the strength markedly, and buckling failure of the bracing was not observed. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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2215 KiB

Open AccessReview

Molecularly Imprinted Polymers with Stimuli-Responsive Affinity: Progress and Perspectives

by Wei Chen, Yue Ma, Jianmin Pan, Zihui Meng, Guoqing Pan and Börje Sellergren

Polymers 2015, 7(9), 1689-1715; https://doi.org/10.3390/polym7091478 - 8 Sep 2015

Cited by 116 | Viewed by 16649

Abstract

Intelligent stimuli-responsive molecularly imprinted polymers (SR-MIPs) have attracted considerable research interest in recent years due to the potential applications in drug delivery, biotechnology and separation sciences. This review comprehensively summarizes various SR-MIPs, including the design and applications of thermo-responsive MIPs, pH-responsive MIPs, photo-responsive [...] Read more.

Intelligent stimuli-responsive molecularly imprinted polymers (SR-MIPs) have attracted considerable research interest in recent years due to the potential applications in drug delivery, biotechnology and separation sciences. This review comprehensively summarizes various SR-MIPs, including the design and applications of thermo-responsive MIPs, pH-responsive MIPs, photo-responsive MIPs, biomolecule-responsive MIPs and ion-responsive MIPs. Besides the development of current SR-MIPs, the advantages as well as the disadvantages of current SR-MIPs were also displayed from different angles, especially preparation methods and application fields. We believe this review will be helpful to guide the design, development and application of SR-MIPs. Full article

(This article belongs to the Special Issue Stimuli-Responsive Polymers and Colloids)

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5539 KiB

Open AccessArticle

Polymeric Shape-Memory Micro-Patterned Surface for Switching Wettability with Temperature

by Nuria García-Huete, José María Cuevas, José Manuel Laza, José Luis Vilas and Luis Manuel León

Polymers 2015, 7(9), 1674-1688; https://doi.org/10.3390/polym7091477 - 8 Sep 2015

Cited by 30 | Viewed by 7588

Abstract

An innovative method to switch the wettability of a micropatterned polymeric surface by thermally induced shape memory effect is presented. For this purpose, first polycyclooctene (PCO) is crosslinked with dycumil peroxide (DCP) and its melting temperature, which corresponds with the switching transition temperature [...] Read more.

An innovative method to switch the wettability of a micropatterned polymeric surface by thermally induced shape memory effect is presented. For this purpose, first polycyclooctene (PCO) is crosslinked with dycumil peroxide (DCP) and its melting temperature, which corresponds with the switching transition temperature (Ttrans), is measured by Dynamic Mechanical Thermal Analysis (DMTA) in tension mode. Later, the shape memory behavior of the bulk material is analyzed under different experimental conditions employing a cyclic thermomechanical analysis (TMA). Finally, after creating shape memory micropillars by laser ablation of crosslinked thermo-active polycyclooctene (PCO), shape memory response and associated effect on water contact angle is analyzed. Thus, deformed micropillars cause lower contact angle on the surface from reduced roughness, but the original hydrophobicity is restored by thermally induced recovery of the original surface structure. Full article

(This article belongs to the Special Issue Shape-Memory Polymers)

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5844 KiB

Open AccessArticle

Preparation and Characterization of Mn/N Co-Doped TiO₂ Loaded on Wood-Based Activated Carbon Fiber and Its Visible Light Photodegradation

by Xiaojun Ma and Yin Chen

Polymers 2015, 7(9), 1660-1673; https://doi.org/10.3390/polym7091476 - 7 Sep 2015

Cited by 14 | Viewed by 6873

Abstract

Using MnSO₄·H₂O as manganese source and urea as nitrogen source, Mn/N co-doped TiO₂ loaded on wood-based activated carbon fiber (Mn/Ti-N-WACF) was prepared by sol–gel method. Mn/Ti-N-WACF with different Mn doping contents was characterized by scanning electron microscopy, X-ray [...] Read more.

Using MnSO₄·H₂O as manganese source and urea as nitrogen source, Mn/N co-doped TiO₂ loaded on wood-based activated carbon fiber (Mn/Ti-N-WACF) was prepared by sol–gel method. Mn/Ti-N-WACF with different Mn doping contents was characterized by scanning electron microscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopies (XPS), and ultraviolet-visible spectrophotometer. Results showed that the loading rate of TiO2 in Mn/Ti-N-WACF was improved by Mn/N co-doping. After calcination at 450 °C, the degree of crystallinity of TiO₂ was reduced due to Mn/N co-doption in the resulting Mn/Ti-N-WACF samples, but the TiO₂ crystal phase was not changed. XPS spectra revealed that some Ti⁴⁺ ions from the TiO₂ lattice of Mn/Ti-N-WACF system were substituted by doped Mn. Moreover, new bonds formed within N–Ti–N and Ti–N–O because of the doped N that substituted some oxygen atoms in the TiO₂ lattice. Notably, the degradation rate of methylene blue for Mn/Ti-N-WACF was improved because of the co-doped Mn/N under visible-light irradiation. Full article

(This article belongs to the Special Issue Stimuli-Responsive Polymers and Colloids)

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4749 KiB

Open AccessArticle

Thermal, Mechanical and UV-Shielding Properties of Poly(Methyl Methacrylate)/Cerium Dioxide Hybrid Systems Obtained by Melt Compounding

by María A. Reyes-Acosta, Aidé M. Torres-Huerta, Miguel A. Domínguez-Crespo, Abelardo I. Flores-Vela, Héctor J. Dorantes-Rosales and José A. Andraca-Adame

Polymers 2015, 7(9), 1638-1659; https://doi.org/10.3390/polym7091474 - 7 Sep 2015

Cited by 30 | Viewed by 9511

Abstract

Thick and homogeneous hybrid film systems based on poly(methyl methacrylate) (PMMA) and CeO₂ nanoparticles were synthesized using the melt compounding method to improve thermal stability, mechanical and UV-shielding properties, as well as to propose them for use in the multifunctional materials industry. [...] Read more.

Thick and homogeneous hybrid film systems based on poly(methyl methacrylate) (PMMA) and CeO₂ nanoparticles were synthesized using the melt compounding method to improve thermal stability, mechanical and UV-shielding properties, as well as to propose them for use in the multifunctional materials industry. The effect of the inorganic phase on these properties was assessed by using two different weight percentages of synthesized CeO₂nanoparticles (0.5 and 1.0 wt %) with the sol–gel method and thermal treatment at different temperatures (120, 235, 400, 600 and 800 °C). Thereafter, the nanoceria powders were added to the polymer matrix by single screw extrusion. The absorption in the UV region was increased with the crystallite size of the CeO₂ nanoparticles and the PMMA/CeO₂ weight ratio. Due to the crystallinity of CeO₂ nanoparticles, the thermal, mechanical and UV-shielding properties of the PMMA matrix were improved. The presence of CeO₂ nanostructures exerts an influence on the mobility of PMMA chain segments, leading to a different glass transition temperature. Full article

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3473 KiB

Open AccessArticle

Fatigue Behaviour of CFRP Strengthened Out-of-Plane Gusset Welded Joints with Double Cracks

by Qian-Qian Yu, Tao Chen, Xiang-Lin Gu and Ning-Xi Zhang

Polymers 2015, 7(9), 1617-1637; https://doi.org/10.3390/polym7091475 - 7 Sep 2015

Cited by 11 | Viewed by 6887

Abstract

This paper investigates the fatigue behaviour of out-of-plane gusset welded joints strengthened with carbon fibre reinforced polymer (CFRP) laminates. Two notches were introduced at the weld toes adjacent to longitudinal plate ends to simulate the initial damage. Variables including the stress range, single- [...] Read more.

This paper investigates the fatigue behaviour of out-of-plane gusset welded joints strengthened with carbon fibre reinforced polymer (CFRP) laminates. Two notches were introduced at the weld toes adjacent to longitudinal plate ends to simulate the initial damage. Variables including the stress range, single- or double-sided strengthening and modulus of CFRP materials were considered. It was found that both cracks propagated under fatigue loading. All the specimens fractured along one predefined notch when the fatigue crack reached a certain length while the other crack also grew to some extent. Test results showed that the addition of composite materials significantly prolonged the fatigue life of specimens by as much as 1.28 to 8.17 times. Double-sided bond and ultra-high modulus CFRP materials led to a better strengthening efficiency. Thereafter, a series of numerical analyses were performed to study the stress intensity factor (SIF) and crack opening displacement (COD). Local debonding around the crack tip at the adhesive-steel interface was taken into consideration. Finally, the fatigue life of all the specimens was evaluated based on the linear elastic fracture mechanism (LEFM) theory and the predicted results agreed well with the experimental data. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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3660 KiB

Open AccessArticle

Polyaniline-Doped Spherical Polyelectrolyte Brush Nanocomposites with Enhanced Electrical Conductivity, Thermal Stability, and Solubility Property

by Na Su

Polymers 2015, 7(9), 1599-1616; https://doi.org/10.3390/polym7091473 - 2 Sep 2015

Cited by 28 | Viewed by 8932

Abstract

The synthesis procedure and dopant are crucial to the electrical conductivity, thermal stability, and solubility properties of polyaniline (PANI). In this paper, high-performance PANI was synthesized by means of chemical oxidative polymerization using anionic spherical polyelectrolyte brushes (ASPB) as dopant. The bonding structure, [...] Read more.

The synthesis procedure and dopant are crucial to the electrical conductivity, thermal stability, and solubility properties of polyaniline (PANI). In this paper, high-performance PANI was synthesized by means of chemical oxidative polymerization using anionic spherical polyelectrolyte brushes (ASPB) as dopant. The bonding structure, crystallographic structure, morphology, and thermal stability of the conductive nanocomposite were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermo-gravimetric analysis (TGA) respectively. Meanwhile, investigation on the electrical conductivity suggested that the room-temperature electrical conductivity of PANI doped with ASPB (PANI/ASPB) was 19.3 S/cm, which was higher than that of PANI (7.0 S/cm), PANI doped with poly(sodium-p-styrenesulfonate) (PSS) (PANI/PSS) (14.6 S/cm), PANI doped with SiO₂ (PANI/SiO₂) (18.2 S/cm), and PANI doped with canonic spherical polyelectrolyte brushes (CSPB) (PANI/CSPB) (8.0 S/cm). Meanwhile, the addition of ASPB improved the thermal stability and solubility properties of PANI. ASPB played the role of template. Conductive mechanism of PANI/ASPB nanocomposite can be explained by the theoretical models of three-dimensional variable range-hopping (3D VRH). Full article

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1433 KiB

Open AccessArticle

Effects of DMT and TMPTMA on Working Life of Acrylic Polymer Concrete Exposed to Low Curing Temperatures

by Kyu-Seok Yeon, Jin-Yun Cha and Jung Heum Yeon

Polymers 2015, 7(9), 1587-1598; https://doi.org/10.3390/polym7091472 - 26 Aug 2015

Cited by 3 | Viewed by 6151

Abstract

Ensuring an appropriate casting time window is of great importance for achieving desired quality and performance of aging materials. In this paper, the effects of promoter and cross-linking agent on the working life—the period a mixture stays in a workable condition—of low-temperature-cured acrylic [...] Read more.

Ensuring an appropriate casting time window is of great importance for achieving desired quality and performance of aging materials. In this paper, the effects of promoter and cross-linking agent on the working life—the period a mixture stays in a workable condition—of low-temperature-cured acrylic polymer concrete (PC) are investigated in order to develop mixture proportions that can be effectively applied in cold weather conditions. The experimental variables included in this study are: (1) curing temperatures (−20, −10 and 0 °C); (2) N,N-dimethyl-p-toluidine (DMT) contents (0.5, 1.0, 1.5 and 2.0 phr (parts per hundred parts of resin)); and (3) trimethylolpropane trimethacrylate (TMPTMA) contents (0, 2.5 and 5 phr). Results indicated a strong relevance between binder’s setting time and PC’s working life. Additionally, it was observed that the working life of acrylic PC was substantially shortened as the curing temperature and contents of DMT and TMPTMA increased. Results of a two-way analysis of variance (ANOVA) revealed that TMPTMA had a greater impact on the working life than DMT. Finally, this study developed an equation that can be used to estimate PC working life, based on the binder’s setting time. The findings of this study will be used as valuable information for cold weather applications of acrylic PC. Full article

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Polymers, Volume 7, Issue 9 (September 2015) – 17 articles

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