Effect of degumming time on silkworm silk fibre for biodegradable polymer composites

Recently, many studies have been conducted on exploitation of natural materials for modern product development and bioengineering applications. Apart from plant-based materials (such as sisal, hemp, jute, bamboo and palm fibre), animal-based fibre is a kind of sustainable natural materials for making novel composites. Silkworm silk fibre extracted from cocoon has been well recognized as a promising material for bio-medical engineering applications because of its superior mechanical and bioresorbable properties. However, when producing silk fibre reinforced biodegradable/bioresorbable polymer composites, hydrophilic sericin has been found to cause poor interfacial bonding with most polymers and thus, it results in affecting the resultant properties of the composites. Besides, sericin layers on fibroin surface may also cause an adverse effect towards biocompatibility and hypersensitivity to silk for implant applications. Therefore, a proper pre-treatment should be done for sericin removal. Degumming is a surface modification process which allows a wide control of the silk fibre's properties, making the silk fibre possible to be used for the development and production of novel bio-composites with unique/specific mechanical and biodegradable properties. In this paper, a cleaner and environmentally friendly surface modification technique for tussah silk in polymer based composites is proposed. The effectiveness of different degumming parameters including degumming time and temperature on tussah silk is discussed through the analyses of their mechanical and morphological properties. Based on results obtained, it was found that the mechanical properties of tussah silk are affected by the degumming time due to the change of the fibre structure and fibroin alignment.     

Fabrication of highly porous bioresorbable polymer matrices using supercritical carbon dioxide

A new method for fabrication of highly porous bioresorbable polymer structures on the basis of various aliphatic polyesters for tissue engineering has been successfully designed and worked out. It has been shown that injection of polymer compositions plasticized in sub- or supercritical carbon dioxide into press forms at temperatures from 20 to 40°C through a nozzle of a certain diameter under atmospheric or elevated (up to 6 MPa) CO₂ pressure allows obtaining polymer matrices with a desired structure and morphology and mean porosity of up to 96 vol % with high reproducibility and avoiding the use of toxic organic solvents. The effect of chemical composition and molecular mass of starting polymers, as well as temperature and CO₂ pressure in the reaction cell and the receiver, on the morphology and internal structure of fabricated samples was studied using the method of scanning-electron microscopy.     

Interphase phenomena in superconductive polymer-ceramic nanocomposites

Dynamic mechanical properties (elastic moduli, phase angle) for superconducting (SC) polymer–ceramic composites based on Y₁Ba₂Cu₃O_7?x SC oxide ceramic and superhighmolecular polyethylene have been investigated. The analysis of the obtained data shows a strong interaction of the polymeric binder with the surface of the ceramic grains. It is concluded that changes of packing and structure of the macromolecules occur at the ceramic–polymer interface. This is confirmed by melting enthalpy measurements of SC polymer–ceramic composites of different filler content. Scanning electron microscopy studies of the high temperature SC composites showed that the ceramic grains are evenly covered by the binder for both amorphous and crystalline polymers. EPR (electron paramagnetic resonance) spectra of polymer–ceramic composites have shown that the intensity of the EPR signals of Cu²⁺(1) depends on the nature and the content of binder. The Mn, Co, Zn, Ni containing superconducting composites have been obtained by frontal polymerization.     

Structural and dielectric properties of polyvinyl alcohol/barium zirconium titanate polymer–ceramic composite

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr_0.1Ti_0.9]O₃ (BZT) polymer–ceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement, cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymer–ceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (ε_r) and the dielectric loss (tan δ) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymer–ceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors.     

An experimental study on the effect of mesoporous silica addition on ion conductivity of poly(ethylene oxide) electrolytes

Solid polymer electrolyte (SPE) composites, which are composed of poly(ethylene oxide) (PEO), mesoporous silica (SBA-15), and lithium salt were prepared in order to investigate the influence of SBA-15 content on the ionic conductivity of the composites. The ionic conductivity of the SPE composites was monitored by frequency response analyzer (FRA), and the crystallinity of the SPE composites was evaluated by using XRD. As a result, the addition of SBA-15 to the polymer mixture inhibited the growth of PEO crystalline domain, due to the mesoporous structure of the SBA-15. Also, the PEO₁₆LiClO₄/SBA-15 composite electrolytes show an increased ion conductivity as a function of SBA-15 content up to 15 wt.%. These ion conductivity characteristics are dependent on crystallinity with SBA-15 content.     

Metal-Filled Epoxy Composites: Mechanical Properties and Electrical/Thermal Conductivity

Abstract

The mechanical properties and the electrical and thermal conductivity of composites based on an epoxy polymer (EP) filled with dispersed copper (Cu) and nickel (Ni) were studied. It was shown that the electrical conductivity of the composites demonstrated percolation behavior with the values of the percolation threshold being 9.9 and 4.0?vol.% for the EP-Cu and EP-Ni composites, respectively. Using the Lichtenecker model, the thermal conductivity of the dispersed metal phase in the composites, λ_f, was estimated as being 35?W/mK for Cu powder and 13?W/mK for Ni powder. It was shown that introduction of the filler in EP led to a decrease in the intensity of the mechanical loss tangent (tan δ) peak that was caused by the existence of an immobilized polymer layer around the filler particles which did not contribute to mechanical losses. Using several models the thickness of this layer, ΔR, was estimated. The concept of an “excluded volume” of the polymer, V_ex, i.e. the volume of the immobilized polymer layer, which does not depend on the particle size and is determined solely by the value of the interaction parameter, B, was proposed.     

Improved electrical,magnetic and dielectric properties of polypyrol (PPy) substituted spinel ferrite composites

CoTb_0.03Fe_1.97O₄ ferrite and poypyrrole (PPy) polymer nano composites were prepared by mixing the nano crystalline ferrite with poypyrrole (PPy) by following the solid state reaction synthesis route. The XRD patterns of CoTb_0.03Fe_1.97O₄ spinel ferrite powders and polymer (PPy) exhibited single phase spinel structure. The amorphous nature of PPy was evidenced by the broad peaks of XRD patterns. The surface morphology unfolded heterogeneous distribution in composites and ferrite. The grains in ferrite were spherical in shape with clear boundaries. The morphology was appreciably altered by the inclusion of ferrite contents. The higher activation energy and resistivity aroused due to blocking of conduction mechanism owing to nanoparticles embedded in the PPy matrix. A downfall in the dielectric loss of the composites is observed as the frequency of the applied field is increased. The incorporation of ferrite contents optimized the magnetic parameters of the composites. The enhanced coercivity (Hc) of these nanocomposites might be beneficial for memory devices.     

PEO|Sncl2|PANI composites: as an electrolyte in solid-state battery

Solid-state polymer electrolytes possess high conductivity and have advantages compared with their liquid counterparts. The polyethylene oxide (PEO)-based polymer is a good candidate for this purpose. The PEO/SnCl₂/polyaniline composite (PSP composites) at different weight percentages were prepared in anhydrous acetonitrile media. Structural studies were carried out of the prepared composites by X-ray diffraction, Fourier transmission infrared spectroscopy, and surface morphology by scanning electron microscopy. The σ _dc was carried out by a two-probe method, and it is found that the conductivity increases with an increase in temperature. The temperature-dependent conductivity of the composites exhibits a typical semi-conducting behavior and hence can be explained by the 1D variable range hopping model proposed by Mott. The electrochemical cell parameters for battery applications at room temperature have also been determined. The samples are fabricated for battery application in the configuration of Na: (PSP): (I₂?+?C?+?sample), and their experimental data are measured using Wagner’s polarization technique. The cell parameters result in an open-circuit voltage of 0.83 V and a short-circuit current of 912 μA for PSP (70:30:10) composite. Hence, these composites can be used in polymer electrolyte studies.     

Structural, conductivity, and dielectric characterization of PEO–PEG blend composite polymer electrolyte dispersed with TiO2 nanoparticles

A solid polymer electrolyte (SPE) composites consisting blend of poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG) as the polymer host with LiCF₃SO₃ as a Li⁺ cation salt and TiO₂ nanoparticle which acts as a filler were prepared using solution-casting technique. The SPE films were characterized by X-ray diffraction and Fourier transform infrared analysis to ensure complexation of the polymer composites. Frequency-dependent impedance spectroscopy observation was used to determine ionic conductivity and dielectric parameters. Ionic conductivity was found to vary with increasing salt and filler particle concentrations in the polymer blend complexes. The optimum ambient temperature conductivity achieved was 2.66?×?10^?4?S?cm^?1 for PEO (65 %), PEG (15 %), LiCF₃SO₃ (15 %), ethylene carbonate (5 %), and TiO₂ (3 %) using weight percentage. The dielectric relaxation time obtained from a loss tangent plot is fairly consistent with the conductivity studies. Both Arrhenius and VTF behaviors of all the composites confirm that the conductivity mechanism of the solid polymer electrolyte is thermally activated.     

Synthesis of fullerene-containing polymer composites and investigation of interactions in these systems

The methods of synthesizing fullerene-containing polymer composites are analyzed. It is established that the technique of determining the intrinsic viscosity can be used for evaluating the effect of the fullerene involved in the polymer composite on the polymer chains. The influence of the synthesis procedure on the fullerene content in a water-soluble fraction is demonstrated using the poly(N-vinylpyrrolidone)-C₆₀ (PVP-C₆₀) system as an example.     

Silane-modified polymers as interphases in glass-fibre-reinforced composites: 2. Grafting and crosslinking of interphase materials

_—This paper presents an interphase engineering technique suitable for grafting silane-modified polymers onto glass fibres to be used in composites with enhanced impact tolerance. The silane-modified polymers include ethylene polymers grafted with γ-methacryloxypropyltrimethoxysilane (MPS) and a copolymer of butyl acrylate (BuA) and MPS. The grafting of functionalized interphase materials onto glass fibres is performed in solution. By changing the concentrations of the solutions, different amounts of polymer can be deposited on the fibres. Water crosslinking of the polymer gives the possibility of producing stabilised interfacial polymer coatings over a range of thicknesses. It is concluded that acidic conditions (1) promote the grafting of silane-modified polymers on glass fibres and (2) for a given reaction time, increase the amount of crosslinked polymer in the interphase, i.e. yield more stable interphases. It is also likely that preserving acidic conditions at the fibre/polymer interface is important for maintaining bonding across the interface. It is shown that polystyrene/glass-fibre composites having SEBS at the interface are promising candidates for high-impact-tolerance composites.     

0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃(PMN-0.3PT)单晶1-3型压电复合材料的性能与单晶体积分数的关系,得出性能最优时压电相的体积分数为64%, 在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k_t高达90.1%,压电系数d₃₃大于1000pC/N,机械品质因数Q_m为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zr_xTi_1-x)O₃(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景. 关键词： PMN-PT单晶 压电复合材料 压电相 聚合物相     

Modification of Optical Characteristics of a Polymer Composite Material under Irradiation

Polymer composites based on polystyrene and modified SiO₂ are synthesized. Effect of the SiO₂ concentration on the surface (thermostatic) properties of the composites is analyzed. Surfaces of composites with different SiO₂ concentrations are microscopically studied. Minor amounts of spherical agglomerates are obtained at relatively high SiO₂ concentrations, and the size of the agglomerates may amount to 80 μm at a SiO₂ concentration of 30 wt %. Variations in the integral absorbance of solar radiation are studied for the polymer composites irradiated with vacuum-UV radiation at a temperature of 125°C.     

Giant magneto-impedance and stress-impedance effects of microwire composites for sensing applications

Composites consisting of glass-coated amorphous microwire Co_68.59Fe_4.84Si_12.41B_14.16 and 913 E-glass prepregs were designed and fabricated. The influences of tensile stress, annealing and number of composite layers on the giant magneto-impedance (GMI) and giant stress-impedance (GSI) effects in these composites were investigated systematically. It was found that the application of tensile stress along the microwire axis or an increase in the number of composite layers reduced the GMI effect and increased the circular anisotropy field, while the annealing treatment had a reverse effect. The value of matrix-wire interfacial stress calculated via the GMI profiles coincided with the value of the applied effective tensile stress to yield similar GMI profiles. Enhancement of the GSI effect was achieved in the composites relative to their single microwire inclusion. These findings are important for the development of functional microwire-based composites for magnetic- and stress-sensing applications. They also open up a new route for probing the interfacial stress in fibre-reinforced polymer (FRP) composites.     

Filler treatment effects on the weathering of talc-, CaCO3- and kaolin-filled polypropylene hybrid composites

Talc, calcium carbonate (CaCO₃), and kaolin hold considerable promise in the development of polymer composites for good mechanical properties and stability. Comparative studies on the usage of these minerals as single fillers in polypropylene (PP) have shown varying degrees of reinforcement due to their differences in terms of particle geometry, surface energy and affinity towards the matrix polymer. In this study, comparisons were made in terms of mechanical, thermal and weatherability properties between hybrid-filler PP composites (i.e. PP filled with either talc–CaCO₃ or talc–kaolin hybrid filler combinations), with particular attention directed towards the effect of surface modification of the fillers. The talc/CaCO₃ hybrid composites have shown exceptional performance in terms of flexural and impact properties. The contribution of talc in the talc–kaolin hybrid composite system has been significant in terms of enhancing the overall tensile and flexural properties. The ability of silane and titanate coupling agents in boosting the resistance of the composites to severe damage and degradation due to natural weathering has been shown.     

Structural,morphological and magnetic characterization of synthesized Co-Ce doped Ni ferrite /Graphene /BNO12 nanocomposites for practical applications

Cobalt-cerium (Co-Ce) doped nickel ferrite (F) nanoparticles having formula Ni_0.8Ce_0.2Co_0.5Fe_1.5O₄ were prepared by the sol-gel auto combustion method. Graphene coated Co-Ce doped Ni ferrite (F/G) and polymer (Lugalvan BNO12) coated F/G ternary nanocomposites (F/G/P) were prepared by the dispersion method. Different characterization techniques were used to investigate the different properties of these synthesized samples. TG-DTA showed the thermal degradation of all composites up to 900 C. The FTIR spectra revealed the presence of two absorption bands that confirmed the ferrite contents in all three composites. It also showed the aromatic contents in the F/G and F/G/P composites due to the presence of graphene and polymer. The XRD patterns revealed a single phase of Ni ferrite doped with Co-Ce without other intermediate phases. The crystallite size was found to be 32.41 nm maximum for the F/G/P composites. The SEM images showed that the surface of the F/G nanocomposite was uniformly coated by Lugalvan BNO12 polymer molecular chains. EDX confirmed the presence of the respective components in all prepared composites. VSM characterization was used to measure the hysteresis loops for the determination of the anisotropy constant, magnetic moments, initial permeability, squareness ratio, remanence and saturation magnetization. These parameters showed a decrease in values in the following order F/G/P > F/G > F. F/G/P revealed the highest coercivity (279.2 G). The fascinating magnetic activity of this nanocomposite makes it a potential candidate in the applications of energy storage, adsorbents for pollutants remediation technologies, electrochemical sensors, chemical process catalysts and electromagnetic wave absorbers.     

Synthesis and study of electroactive nanoparticles and their polymer composites for novel applications

Polymer ceramic composites using a polymer binder, nanosized BaTiO₃ and metal particles were developed for radiation shielding in the microwave region. From X-ray Diffraction (XRD) the crystallinity and nanosize of BaTiO₃ was confirmed in the composite. Interesting changes in Differential Scanning Calorimetry (DSC) were observed before and after ball milling of BaTiO₃. Shielding Efficiency (SE) of microwave radiation has been measured from transmitted fraction (TF) of electromagnetic waves (EM) at different frequencies. The changes in TF were assigned to reflection and absorption of EM waves in different composites.     

Supercritical fluid fabrication of components for a sustained-release injectable risperidone dose form

The process of supercritical fluid encapsulation of pharmaceutical grade risperidone into bioresorbable D,L-polylactide microparticles via the PGSS (Particles from Gas-Saturated Solutions) method was examined. Micronization and changes in the morphology of risperidone crystals during its encapsulation into a polymer plasticized with supercritical carbon dioxide were experimentally observed. This result made it possible to prepare the polymer structures of various dispersities (from 10 to 100 μm) and morphologies containing up to 40 wt % of risperidone without the use of organic solvents. The kinetics of release of risperidone from polymer microparticles in saline solution was studied by UV spectrophotometry. It was shown that the use of D,L-polylactides of various molecular weights makes it possible to achieve a controlled increase in the time of release of risperidone from bioresorbable polymer particles prepared via the PGSS technique up to ten days.     

Polymer‐filler derived ceramics with low shrinkage using PCS/SiC/Al mixture

Active Al and inert SiC powders were dispersed in the polycarbosilane to manufacture SiC ceramic composites by a new process of active‐filler‐controlled pyrolysis of polymer. 40 wt% of active Al fillers, 40 wt% of inert SiC fillers and 20 wt% of PCS, were homogenized. The samples were obtained by pyrolysis at 1100 °C for different soaking time. The results showed that due to the incorporation of active Al fillers, formation of crystallite phases such as Al₄C₃, Al₄Si₃ and AlN occured due to the of reaction of Al particles with the polymer decomposition products and the reactive nitrogen atmosphere. The microstructural and mechanical characterization results of the composites are presented in the paper. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of Ca-P nanoparticles and fabrication of Ca-P/PHBV nanocomposite microspheres for bone tissue engineering applications

As the first step in producing totally bioresorbable osteoconductive composite scaffolds for bone tissue engineering using the selective laser sintering technology, bioresorbable nanoparticles of calcium phosphate (Ca-P) similar in composition to β-tricalcium phosphate were synthesized and Ca-P nanoparticle filled poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) microspheres were fabricated. The pH of the chemical reaction for Ca-P particle synthesis was found to have significant effects on the morphology and chemical composition of Ca-P precipitated. Ca-P particles produced at the pH of 10.0-11.0 were amorphous, had a Ca:P molar ratio of about 1.5, were spherical in shape and had sizes in the range of 10-30 nm. The Ca-P particles were used to form Ca-P nanocomposite microspheres through a solid-in-oil-in-water (S/O/W) emulsion solvent evaporation process. Ca-P nanoparticles were mostly encapsulated inside the microspheres and some Ca-P nanoparticles were superficially embedded on the microspheres. The Ca-P/PHBV microspheres had an average diameter of about 48 μm which is suitable for selective laser sintering for constructing osteoconductive composite scaffolds.