Showing papers in "International Journal of Polymer Science in 2011"
TL;DR: An overview of the different types of scaffolds with their material properties is discussed and the fabrication technologies for tissue engineering scaffolds, including the basic and conventional techniques to the more recent ones, are tabulated.
Abstract: Current strategies of regenerative medicine are focused on the restoration of pathologically altered tissue architectures by transplantation of cells in combination with supportive scaffolds and biomolecules. In recent years, considerable interest has been given to biologically active scaffolds which are based on similar analogs of the extracellular matrix that have induced synthesis of tissues and organs. To restore function or regenerate tissue, a scaffold is necessary that will act as a temporary matrix for cell proliferation and extracellular matrix deposition, with subsequent ingrowth until the tissues are totally restored or regenerated. Scaffolds have been used for tissue engineering such as bone, cartilage, ligament, skin, vascular tissues, neural tissues, and skeletal muscle and as vehicle for the controlled delivery of drugs, proteins, and DNA. Various technologies come together to construct porous scaffolds to regenerate the tissues/organs and also for controlled and targeted release of bioactive agents in tissue engineering applications. In this paper, an overview of the different types of scaffolds with their material properties is discussed. The fabrication technologies for tissue engineering scaffolds, including the basic and conventional techniques to the more recent ones, are tabulated.
1,480 citations
TL;DR: In this paper, the surface modification of cellulose fibers by various methods is reviewed and the processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed.
Abstract: Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.
685 citations
TL;DR: The advantages and disadvantages of modifying or designing hydrogel contact lenses for extended ophthalmic drug delivery are analyzed in this paper.
Abstract: Soft contact lenses can improve the bioavailability and prolong the residence time of drugs and, therefore, are ideal drug carriers for ophthalmic drug delivery. Hydrogels are the leading materials of soft contact lenses because of their biocompatibility and transparent characteristic. In order to increase the amount of load drug and to control their release at the expected intervals, many strategies are developed to modify the conventional contact lens as well as the novel hydrogel contact lenses that include (i) polymeric hydrogels with controlled hydrophilic/hydrophobic copolymer ratio; (ii) hydrogels for inclusion of drugs in a colloidal structure dispersed in the contact lenses; (iii) ligand-containing hydrogels; (iv) molecularly imprinted polymeric hydrogels; (v) hydrogel with the surface containing multilayer structure for drugs loading and releasing. The advantages and disadvantages of these strategies in modifying or designing hydrogel contact lenses for extended ophthalmic drug delivery are analyzed in this paper.
91 citations
TL;DR: In this article, the authors evaluated the mechanical properties of polylactide composites as a function of modification of sisal fiber with two different macromolecular coupling agents.
Abstract: Mechanical properties of composites are strongly influenced by the quality of the fiber/matrix interface. The objective of this study was to evaluate the mechanical properties of polylactide (PLA) composites as a function of modification of sisal fiber with two different macromolecular coupling agents. Sisal fiber reinforced polylactide composites were prepared by injection molding, and the properties of composites were studied by static/dynamic mechanical analysis (DMA). The results from mechanical testing revealed that surface-treated sisal fiber reinforced composite offered superior mechanical properties compared to untreated fiber reinforced polylactide composite, which indicated that better adhesion between sisal fiber and PLA matrix was achieved. Scanning electron microscopy (SEM) investigations also showed that surface modifications improved the adhesion of the sisal fiber/polylactide matrix.
82 citations
TL;DR: In this article, an attempt has been made to study the utilization potential of bamboo fiber in polymer composites and also study the effect of various parameters on mechanical and erosion wear performance of reinforced epoxy composites.
Abstract: The application of natural fibers as reinforcement in polymer composites has been continuously growing during the last few decades. These composites find diverse applications in hostile environment where they are exposed to external attacks such as solid particle erosion. Also, in many respects, the mechanical properties of different polymer composites are their most important characteristics. Therefore, improvement of the erosion resistance and mechanical behavior of polymer composites are the prime requirements in their applications. Bamboo fiber which is rich in cellulose, relatively inexpensive, and abundantly available has the potential for reinforcement in polymers. To this end, an attempt has been made in this paper not only to study the utilization potential of bamboo fiber in polymer composites but also to study the effect of various parameters on mechanical and erosion wear performance of bamboo fiber reinforced epoxy composites.
76 citations
TL;DR: In this article, the surface and morphology of cellulose-derived fibers were analyzed to determine how treatment time affected the bonding sites in natural fibers, and the mechanical behavior was also characterized, and tensile testing reported a 61% increase in strength and a 25 percent increase in modulus in fibers treated for 16 hours.
Abstract: Properties of cellulose-derived fibers are extremely sensitive to surface treatment. Many studies have investigated the effects of varying surface treatment parameters in natural fibers to improve fiber-matrix bonding; however, work is still needed to assist with developing better quality control methods to use these fibers in more load-bearing composites. Kenaf fibers were alkali treated, and the surface and morphology were analyzed to determine how treatment time affected the bonding sites in natural fibers. The mechanical behavior was also characterized, and tensile testing reported a 61% increase in strength and a 25% increase in modulus in fibers treated for 16 hours. The increase in tensile properties was assumed to result from increased intermolecular interaction and increased crystallinity in cellulose, which was supported by XRD. On the other hand, FTIR spectroscopy and XPS showed that the amount of hydroxyl groups needed for fiber-matrix bonding decreased at longer treatment times.
57 citations
TL;DR: It is anticipated that fine control of PEG composition in PHB-based composite biomaterials can be utilised to support their applications in medicinal and tissue engineering applications.
Abstract: Polyhydroxybutyrate (PHB) is a biomaterial with potential for applications in biomedical and tissue engineering; however, its brittle nature and high crystallinity limit its potential. Blending PHB with a variety of PEGs produced natural-synthetic composite films composed of FDA-approved polymers with significant reductions in crystallinity, from 70.1% for PHB films to 41.5% for its composite with a 30% (w/w) loading of PEG2000. Blending also enabled manipulation of the material properties, increasing film flexibility with an extension to break of for PHB films and for films containing 30% (w/w) PEG106. Significant changes in the film surface properties, as measured by porosity, contact angles, and water uptake, were also determined as a consequence of the blending process, and these supported greater adhesion and proliferation of neural-associated olfactory ensheathing cells (OECs). A growth rate of cells per day for PHB films with 30% (w/w) PEG2000 loading compared to for PHB films was observed. Furthermore, while cytotoxicity of the films as measured by lactate dehydrogenase release was unaffected, biocompatibility, as measured by mitochondrial activity, was found to increase. It is anticipated that fine control of PEG composition in PHB-based composite biomaterials can be utilised to support their applications in medicinal and tissue engineering applications.
43 citations
TL;DR: In this article, the authors discuss natural fibers and nanocomposites and give a brief introduction to the papers in this special issue, which is an editorial review of the paper.
Abstract: This is an editorial article in which the authors discuss natural fibers and nanocomposites and give a brief introduction to the papers in this special issue.
42 citations
TL;DR: In this article, the optical properties of ZnO thin films on polyethylene terephthalate (PET) substrates were determined through the optical transmission method using an ultraviolet-visible spectrophotometer.
Abstract: Zinc oxide thin films of different thicknesses ranging from 100 to 300 nm were prepared on polyethylene terephthalate substrates with thermal evaporation in a vacuum of approximately Torr. X-ray diffraction patterns confirm the proper phase formation of the material. From atomic force microscopy (AFM) images, it was found that the root mean square roughness of the film surface increased as the film thickness increased. The optical properties of ZnO on PET substrates were determined through the optical transmission method using an ultraviolet-visible spectrophotometer. The optical band gap values of ZnO thin films slightly decreased as the film thickness increased.
36 citations
TL;DR: In this paper, the polycarbonate film (PC) surface was treated using glow discharge low-pressure air plasma and the modified surface was characterized by contact angle, FTIR, XRD, AFM, and XPS analysis.
Abstract: The polycarbonate film (PC) surface was treated using glow discharge low-pressure air plasma. The modified surface was characterized by contact angle, FTIR, XRD, AFM, and XPS analysis. The surface-modified samples were further investigated using T-peel test for technical applications. The surface energy of the sample was estimated by measuring contact angle. The results show that, after plasma treatment, the root mean square (RMS) roughness of PC film was gradually increased with exposure time. Plasma treatment modified the chemical composition of the polymer surface and it made the surface to be highly hydrophilic. It was found that the air plasma treatment increases the polar component of PC film.
36 citations
TL;DR: In this paper, the authors used two fillers: conventional Corax N220 carbon black or electrically conductive carbon black Printex XE-2B which has a very high specific surface area.
Abstract: Natural rubber based composites have been prepared using various amounts of two fillers: conventional Corax N220 carbon black or electrically conductive carbon black Printex XE-2B which has a very high specific surface area. The composites have been studied by dynamic mechanical thermal analysis, dielectric thermal analysis and SEM. It has been established that all vulcanizates investigated are in the glass state in the C to C interval. The storage modulus increases with the increasing filler content in the C to
TL;DR: In this paper, the incorporation of natural fibres (hemp, cellulose, cotton linter, sugarcane, coconut) in the starch foam induced a density reduction up to 33%, a decrease in water absorption, and an increase in mechanical properties according to the fibre content and nature.
Abstract: Starches and polylactic acids (PLAs) represent the main biobased and biodegradable polymers with potential industrial availability in the next decades for “bio” foams applications. This paper investigates the improvement of their morphology and properties through processing and materials parameters. Starch foams were obtained by melt extrusion in which water is used as blowing agent. The incorporation of natural fibres (hemp, cellulose, cotton linter, sugarcane, coconut) in the starch foam induced a density reduction up to 33%, a decrease in water absorption, and an increase in mechanical properties according to the fibre content and nature. PLA foams were obtained through single-screw extrusion using of a chemical blowing agent that decomposed at the PLA melting temperature. A void content of 48% for PLA and 25% for cellulose fibre-reinforced PLA foams and an improvement in mechanical properties were achieved. The influence of a fibre surface treatment was investigated for both foams.
TL;DR: In this article, a soy-based unsaturated polyester resin was used as synthetic matrix, and glass and flax fiber fabrics were used as reinforcement to improve the mechanical and flammability properties of reinforced composites by introducing nanoclay particles in the resins.
Abstract: Liquid composite molding (LCM) processes are widely used to manufacture composite parts for the automotive industry. An appropriate selection of the materials and proper optimization of the manufacturing parameters are keys to produce parts with improved mechanical properties. This paper reports on a study of biobased composites reinforced with nanoclay particles. A soy-based unsaturated polyester resin was used as synthetic matrix, and glass and flax fiber fabrics were used as reinforcement. This paper aims to improve mechanical and flammability properties of reinforced composites by introducing nanoclay particles in the unsaturated polyester resin. Four different mixing techniques were investigated to improve the dispersion of nanoclay particles in the bioresin in order to obtain intercalated or exfoliated structures. An experimental study was carried out to define the adequate parameter combinations between vacuum pressure, filling time, and resin viscosity. Two manufacturing methods were investigated and compared: RTM and SCRIMP. Mechanical properties, such as flexural modulus and ultimate strength, were evaluated and compared for conventional glass fiber composites (GFC) and flax fiber biocomposites (GFBiores-C). Finally, smoke density analysis was performed to demonstrate the effects and advantages of using an environment-friendly resin combined with nanoclay particles.
TL;DR: In this article, an inorganic nanoparticle impregnation (INI) technique was used to improve the compatibility between kenaf bast fibers and polyolefin matrices.
Abstract: The objective of this study was to investigate an inorganic nanoparticle impregnation (INI) technique to improve the compatibility between kenaf bast fibers and polyolefin matrices. The Scanning Electron Microscopy (SEM) was used to examine the surface morphology of the INI-treated fibers showing that the CaCO3 nanoparticle crystals grew onto the fiber surface. Energy-dispersive X-ray spectroscopy (EDS) was used to verify the CaCO3 nanoparticle deposits on the fiber surface. The tension tests of the individual fiber were conducted, and the results showed that the tensile strength of the fibers increased significantly (more than 20%) after the INI treatments. Polymer composites were fabricated using the INI-treated fiber as reinforcement and polypropylene (PP) as the matrix. The results showed that the INI treatments improved the compatibility between kenaf fibers and PP matrix. The tensile modulus and tensile strength of the composites reinforced with INI-treated fibers increased by 25.9% and 10.4%, respectively, compared to those reinforced with untreated kenaf fibers.
TL;DR: The CPSRT with pore sizes ranging from 50 to 150 μm was cytocompatible because it did not provoke the additional production of IL-8 and TNF-α by pHEK cultures and serves as an ideal template for skin tissue engineering.
Abstract: Chitosan is a copolymer of N-acetylglucosamine and glucosamine. A bilayer chitosan porous skin regenerating template (CPSRT) has been developed for skin tissue engineering. The pore size of the CPSRT was assessed using a scanning electron microscopy (SEM). The in vitro cytocompatibility of the CPSRT was tested on primary human epidermal keratinocyte (pHEK) cultures by measuring lactate dehydrogenase (LDH) levels and skin irritation by western blot analysis of the interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α) secretions. The ability of the CPSRT to support cell ingrowth was evaluated by seeding primary human dermal fibroblasts (pHDFs) on the scaffold, staining the cells with live/dead stain, and imaging the construct by confocal microscopy (CLSM). The CPSRT with pore sizes ranging from 50 to 150 μm was cytocompatible because it did not provoke the additional production of IL-8 and TNF-α by pHEK cultures. Cultured pHDFs were able to penetrate the CPSRT and had increased in number on day 14. In conclusion, the CPSRT serves as an ideal template for skin tissue engineering.
TL;DR: In this paper, the effect of alkali and enzymatic treatments on flax fiber morphology, mechanical, and adhesion properties was investigated, and it was observed that gentle treatments of the fibres, down to the oriented microfibrils, are favorable to a better adherence with a PLA drop.
Abstract: The effect of alkali and enzymatic treatments on flax fibre morphology, mechanical, and adhesion properties was investigated. The multilength scale analysis allows for the correlation of the fibre’s morphological changes induced by the treatments with mechanical properties to better explain the adherence properties between flax and PLA. The atomic force microscopy (AFM) images revealed the removal of primary layers, upon treatments, down to cellulose microfibrils present in the secondary layers. The variation in mechanical properties was found to be dependent, apart from the crystalline content, on interaction between cellulose microfibrils and encrusting polysaccharides, pectins and hemicelluloses, in the secondary layers. Finally, microbond tests between the modified fibres and PLA emphasize the important role of the outer fibre’s surface on the overall composite properties. It was observed here that gentle treatments of the fibres, down to the oriented microfibrils, are favourable to a better adherence with a PLA drop. This paper highlights the important role of amorphous polymers, hemicellulose and pectin, in the optimisation of the adhesion and mechanical properties of flax fibres in the biocomposite.
TL;DR: In this paper, the manufacturing feasibility and structural characterization of natural fiber reinforced structural insulated panels (NSIPs) using NFRP laminates as skin was studied, and the results showed significant increase in the mechanical properties of resulting NSIP panels mainly a 53% increase in load-carrying capacity compared to traditional OSB SIPs.
Abstract: Natural fibers are emerging in the fields of automobile and aerospace industries to replace the parts such as body panels, seats, and other parts subjected to higher bending strength. In the construction industries, they have the potential to replace the wood and oriented strand boards (OSB) laminates in the structural insulated panels (SIPs). They possess numerous advantages over traditional OSB SIPs such as being environmental friendly, recyclable, energy efficient, inherently flood resistant, and having higher strength and wind resistance. This paper mainly focuses on the manufacturing feasibility and structural characterization of natural fiber reinforced structural insulated panels (NSIPs) using natural fiber reinforced polymeric (NFRP) laminates as skin. To account for the use of natural fibers, the pretreatments are required on natural fibers prior to use in NFRP laminates, and, to address this issue properly, the natural fibers were given bleaching pretreatments. To this end, flexure test and low-velocity impact (LVI) tests were carried out on NSIPs in order to evaluate the response of NSIPs under sudden impact loading and uniform bending conditions typical of residential construction. The paper also includes a comparison of mechanical properties of NSIPs with OSB SIPs and G/PP SIPs. The results showed significant increase in the mechanical properties of resulting NSIP panels mainly a 53% increase in load-carrying capacity compared to OSB SIPs. The bending modulus of NSIPs is 190% higher than OSB SIPs and 70% weight reduction compared to OSB SIPs.
TL;DR: In this paper, the authors developed a hermetical alkali digestion process to obtain single cellulosic fibers from kenaf bast, which produced fibers with high cellulose content (84.2-92.3%) due to the removal of lignin and hemicelluloses.
Abstract: The objective of this study was to develop a hermetical alkali digestion process to obtain single cellulosic fibers from kenaf bast. Kenaf bast were hermetically digested into single fiber using a 5% sodium hydroxide solution for one hour at four different temperatures (80°C, 110°C, 130°C, and 160°C). The hermetical digestion process used in this study produced fibers with high cellulose content (84.2–92.3%) due to the removal of lignin and hemicelluloses. The surface hardness and elastic modulus of the fibers digested at 130°C
and 160°C were improved significantly compared with those digested at 80°C. The tensile modulus and tensile strength of the individual fibers reduced as the digestion temperature increased from 110°C to 160°C. Micropores were generated in fiber cell wall when the fibers were digested at 130°C
and 160°C. The studies on the composites that were made from polypropylene reinforced with the digested fibers indicated that the compatibility between the digested fibers and polypropylene matrix was poor.
TL;DR: In this paper, a mixture of polyhydroxybutyrate (PHB) and ethyl-cellulose (EtC) was used to reduce PHB crystallinity and promote its degradation under physiological conditions without undue influence on biocompatibility.
Abstract: Polyhydroxybutyrate (PHB) is widely used as a biomaterial in medical and tissue-engineering applications, a relatively high crystallinity limits its application. Blending PHB with ethyl-cellulose (EtC) was readily achieved to reduce PHB crystallinity and promote its degradation under physiological conditions without undue influence on biocompatibility. Material strength of composite films remained unchanged at 6.5 0.6 MPa with 40% (w/w) EtC loadings. Phase separation between the two biopolymers was determined with PHB crystallinity decreasing from 63% to 47% for films with the same loading. This reduction in crystallinity supported an increase in the degradation rates of composite films from 0.39 to 0.81% wk−1 for PHB and its composite, respectively. No significant change in morphology and proliferation of olfactory ensheathing cells were observed with the composites despite significant increases in average surface roughness (Ra) of the films from 2.90 to 3.65 m for PHB and blends with 80% (w/w) EtC, respectively.
TL;DR: In this paper, a novel enzymatic fiber pretreatment was developed to facilitate the isolation of cellulose microfibrils and explores effectiveness of biotreatment on the intermolecular and intramolecular hydrogen bonding in the fiber.
Abstract: The use of cellulose nanofibres as high-strength reinforcement in nano-biocomposites is very enthusiastically being explored due to their biodegradability, renewability, and high specific strength properties. Cellulose, through a regular network of inter- and intramolecular hydrogen bonds, is organized into perfect stereoregular configuration called microfibrils which further aggregate to different levels to form the fibre. Intermolecular hydrogen bonding at various levels, especially at the elementary level, is the major binding force that one need to overcome to reverse engineer these fibres into their microfibrillar level. This paper briefly describes a novel enzymatic fibre pretreatment developed to facilitate the isolation of cellulose microfibrils and explores effectiveness of biotreatment on the intermolecular and intramolecular hydrogen bonding in the fiber. Bleached Kraft Softwood Pulp was treated with a fungus (OS1) isolated from elm tree infected with Dutch elm disease. Cellulose microfibrils were isolated from these treated fibers by high-shear refining. The % yield of nanofibres and their diameter distribution (<50 nm) isolated from the bio-treated fibers indicated a substantial increase compared to those isolated from untreated fibers. FT-IR spectral analysis indicated a reduction in the density of intermolecular and intramolecular hydrogen bonding within the fiber. X-ray spectrometry indicated a reduction in the crystallinity. Hydrogen bond-specific enzyme and its application in the isolation of new generation cellulose nano-fibers can be a huge leap forward in the field of nano-biocomposites.
TL;DR: In this paper, two kinds of environmental friendly composites were prepared based on sustainable matrices, respectively, defatted cross-linked soy flour and thermoplastic polyhydroxybutyrate cohydroxyvalerate, reinforced by natural fibers from Caroa and Kenaf plants.
Abstract: Two kinds of environmental friendly composites were prepared based on sustainable matrices, respectively, defatted cross-linked soy flour and thermoplastic polyhydroxybutyrate cohydroxyvalerate, reinforced by natural fibers from Caroa and Kenaf plants. The obtained composites were compared in terms of moisture tolerance, thermal and mechanical properties, and thermoregulation ability. It was found that this ecofriendly systems have suitable properties for indoor applications in housing and transportation.
TL;DR: In this paper, the effects of titanate as a coupling agent and some particulate nanoscale particles such as TiO2, CaCO3, and ZnO on thermal and mechanical properties of emulsion polyvinylchloride (E-PVC) were investigated by thermogravimetric analysis (TGA), and mechanical tests.
Abstract: The effects of titanate as a coupling agent and some particulate nanoscale particles such as TiO2, CaCO3, and ZnO on thermal and mechanical properties of emulsion polyvinylchloride (E-PVC) were investigated by thermogravimetric analysis (TGA), and mechanical tests. In this research, it was found that, in the presence of nanoparticles of CaCO3, TiO2, and ZnO, the peak temperature of dehydrochlorination of E-PVC was shifted to higher temperatures, and the rate of mass loss was decreased. Also results of differential scanning calorimetry showed that the addition of nanoparticle of CaCO3, TiO2, and ZnO led to an increase in glass transition temperature. The impact strength, elastic modulus and toughness of the samples were enhanced after addition of 0–10 part of filer in hundred parts of resin (phr) nano-CaCO3, nano-TiO2, and nano-ZnO due to improvement of compatibility of the polymer and the nano-particles. Also UV and thermal stability of the samples were enhanced by means of the nanoparticles. It was found that, in the presence of titanate as coupling agent, content of additives that could be used in the composite of PVC shifts to higher amounts.
TL;DR: In vivo bone-marrow tests with Sprague-Dawley rats revealed far-reaching significant osseoconductivity increases from bisphenyl-polymer/carbon-fiber composites when compared to state-of-the-art titanium-6-4 alloy controls.
Abstract: Aerospace/aeronautical thermoset bisphenyl-polymer/carbon-fiber-reinforced composites are considered as new advanced materials to replace metal bone implants. In addition to well-recognized nonpolar chemistry with related bisphenol-polymer estrogenic factors, carbon-fiber-reinforced composites can offer densities and electrical conductivity/resistivity properties close to bone with strengths much higher than metals on a per-weight basis. In vivo bone-marrow tests with Sprague-Dawley rats revealed far-reaching significant osseoconductivity increases from bisphenyl-polymer/carbon-fiber composites when compared to state-of-the-art titanium-6-4 alloy controls. Midtibial percent bone area measured from the implant surface increased when comparing the titanium alloy to the polymer composite from 10.5% to 41.6% at 0.8 mm, P < 10-4, and 19.3% to 77.7% at 0.1 mm, P < 10-8. Carbon-fiber fragments planned to occur in the test designs, instead of producing an inflammation, stimulated bone formation and increased bone integration to the implant. In addition, low-thermal polymer processing allows incorporation of minerals and pharmaceuticals for future major tissue-engineering potential.
TL;DR: In this paper, a strategy to reduce the influence of wet ageing by adding extra layers of PLLA on the biocomposite surface was presented, which reduced weight gain by half and increased stiffness and strength after ageing.
Abstract: Biocomposites are sensitive to water, and previous work on flax reinforced PLLA showed a large drop in mechanical properties after immersion (Le Duigou et al. 2009). Unreinforced PLLA was much less sensitive. This paper presents a strategy to reduce the influence of wet ageing by adding extra layers of PLLA on the biocomposite surface. Weight gain measurements show that a PLLA coating 350 𝜇m thick reduces weight gain by half, and biocomposite stiffness and strength after ageing are improved by 100% compared to uncoated composite behaviour. Thermal analysis and microscopic examination are used to show damage mechanisms with and without protection. Property changes are shown to be quasilinearly related to weight gain.
TL;DR: In this article, the dielectric and microwave properties of carbon black/siloxane rubber-based nanocomposites have been investigated in the frequency range from 1 GHz to 12GHz according to the content of the carbon black and the frequency.
Abstract: In this paper, the dielectric and microwave properties of carbon black/siloxane rubber-based nanocomposites have been investigated in the frequency range from 1 GHz till 12 GHz according to the content of carbon black and the frequency. It has been established that the increasing frequency and filler content lead to an increase in the relative permittivity and tangent of dielectric loss angle. At higher filler content, the effects become more pronounced, especially those upon dielectric loss. It has been also established that there are two well-distinguished areas in all dependences of microwave properties on frequency and filler content increasing. The first is between 1 and 8 GHz wherein the reflection and attenuation of microwaves do not change considerably with frequency and filler content alternation while shielding effectiveness worsens. The second area is between 8 and 12 GHz wherein the reflection and attenuation of microwaves increase drastically with the increasing frequency and filler content. Shielding effectiveness improves, too. It has been established that in all cases the degree of correlation between dielectric and microwave properties evaluated on the basis of the coefficients of correlation calculation is perfect.
TL;DR: Amine-terminated poly (L-lactide) (NH2-PLLA) with various chain lengths were successfully synthesized by sequential tert-butyl-N-(3-hydroxypropyl) carbamate initiated bulk ring-opening polymerization (ROP) of L-LA in the presence of Stannous(II) 2-ethylhexanoate (Sn(Oct)2) and deprotection of the N-tert-butoxycarbonyl (Boc) group at the end of the polymer chain this paper.
Abstract: Amine-terminated poly (L-lactide) (NH2-PLLA) with various chain lengths were successfully synthesized by sequential tert-butyl-N-(3-hydroxypropyl) carbamate initiated bulk ring-opening polymerization (ROP) of L-lactide (L-LA) in the presence of Stannous(II) 2-ethylhexanoate (Sn(Oct)2) and deprotection of the N-tert-butoxycarbonyl (Boc) group at the end of the polymer chain. The polymers obtained were characterized by FT-IR, 1H NMR, and GPC method. NH2-PLLA thus prepared was used to initiate the polymerization of ω-benzyloxycarbonyl-L-lysine-N-carboxyanhydride (Lys (Z)-NCA), and the result confirmed the high nucleophilicity of the terminal amine group. This method was not only suitable for the preparation of low molecular weight NH2-PLLA, but also quite efficient in the synthesis of high molecular weight samples.
TL;DR: In this paper, photochromic transformations in polymer matrices were studied and the activation energy was determined based on the Arrhenius plot of the rate constant ascribed to the photochemical reaction.
Abstract: 9′-Hydroxy-1,3,3-trimethylspiro[indoline-2,3′[3H]naphtha[2,1-b]-1,4oxazine] (SPO-7OH) was used in studies of photochromic transformations in polymer matrices. Illumination with UV lamp caused opening the spirostructure of the oxazine with formation of open merocyanine species absorbing at ca. 610 nm. The kinetic studies of thermal relaxation of the open form showed that this process can be described with a biexponential function including both photochemical reaction and rheological behaviour of the polymeric environment. Basing on Arrhenius plot of the rate constant ascribed to the photochemical reaction, the activation energy was determined, which was 66.1 and 84.7 kJ/mole for poly(methyl methacrylate-co-butyl methacrylate) and poly(vinylpyrrolidone) matrix, respectively.
TL;DR: In this paper, the graft polymerization of styrene in a poly(tetrafluoroethylene) (PTFE) film was examined by time-resolved small-angle neutron scattering (SANS).
Abstract: Preirradiation graft polymerization of styrene in a poly(tetrafluoroethylene) (PTFE) film was examined by time-resolved small-angle neutron scattering (SANS). A crosslinked PTFE film, thickness of which is about 50 μm, was irradiated by γ-ray and immersed in a mixed solvent of styrene monomer and toluene. SANS elucidated that graft polymerization proceeds by two reaction processes (I) and (II). In process (I) at 0<𝑡<200 min, graft polymerization occurs at an interface between crystalline and amorphous PTFE domains and the grafted polystyrene segregates from PTFE, forming a thin layer with a sharp interface. In process (II) at 200<𝑡<600 min, grafted PS layer starts to bridge between crystalline domains. At the end of process (II), 40% of total crystalline PTFE domain is covered by the grafted PS chains.
TL;DR: In this paper, a graft copolymer was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM).
Abstract: Polystyrene, PS, was grafted from poly(vinyl alcohol), PVA, backbone by reversible addition-fragmentation chain transfer (RAFT) polymerization. The hydroxyl groups of the PVA were converted into aromatic dithioester RAFT agent and polymerization began in the presence of this agent. The structure of compounds was confirmed by FT-IR and 1HNMR spectroscopy. The graft copolymer was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Grafted polystyrene chains were cleaved from the PVA backbone by acidic hydrolysis of the PVA-g-PS, and its polydispersity index, PDI, was determined by gel permeation chromatography (GPC) showing narrow molecular weight distribution.
TL;DR: In this article, reversible addition fragmentation chain transfer (RAFT) synthesis and self-assembly of free-base porphyrin cored star polymers are reported, in the presence of a freebase PORIN cored chain transfer agent (CTA-FBP).
Abstract: Reversible addition fragmentation chain transfer (RAFT) synthesis and self-assembly of free-base porphyrin cored star polymers are reported. The polymerization, in the presence of a free-base porphyrin cored chain transfer agent (CTA-FBP), produced porphyrin star polymers with controlled molecular weights and narrow polydispersities for a number of monomers including N, N-dimethylacrylamide (DMA) and styrene (St). Well-defined amphiphilic star block copolymers, P-(PS-PDMA)4 and P-(PDMA-PS)4 (P: porphyrin), were also prepared and used for self-assembly studies. In methanol, a selective solvent for PDMA, spherical micelles were observed for both block copolymers as characterized by TEM. UV-vis studies suggested star-like micelles were formed from P-(PS-PDMA)4, while P-(PDMA-PS)4 aggregated into flower-like micelles. Spectrophotometric titrations indicated that the optical response of these two micelles to external ions was a function of micellar structures. These structure-related properties will be used for micelle studies and functional material development in the future.