The synthesis of silver nanoparticles attached on the surface of a hollow cornet‐like polymer matrix which served as a reductant and host matrix is described. This hybrid organic/inorganic macromolecular matrix is exhibiting anion‐exchange properties, porous structure and hollow morphologies, and absorptions in the visible light region. Due to the anion‐exchange property and the 3D orientation of the macromolecular chains the material is defining a new functional organic/inorganic hybrid. For the synthesis of nanoparticles, no other reducing agents were used and silver nanoparticles with a mean diameter of less than 20 nm were attached on the surface of the polymer, thus inheriting the composite with high antibacterial activity tested in bacterial strains and yeasts.
A novel technique was developed to control the deposition of electrospun polyurethane fibers using a silicone collector substrate patterned with soft lithography. This method can be used to control selective fiber deposition with broad pattern dimensions (50–500 µm) over a large area. The combination of ease of use, low cost, tunability, and generation of relatively large fiber mats available with this technique is expected to advance our ability to mimic the orientation and anisotropic properties of native tissues to generate improved tissue engineering scaffolds.
Natural fiber reinforced polymer composites are lightweight, economical and available in a variety of forms. They have low densities, comparable material properties, high molding flexibility and are environmentally friendly, making them a conceivable alternative to traditional fillers like mica, calcium carbonate and glass. By modifying either the resin system or the natural fiber, biocomposites can be designed for different applications ranging from products of commodity to aerospace, examples including electroactive papers, fuel cell membranes, controlled drug release mechanisms and biosensors. This review aims to analyze the advancement in the application of cellulose based materials in different sectors with a discussion of fundamental research in these areas.
An in situ lubrication dispersion method is developed to achieve electrical conductivity in PP containing a small amount of MWCNTs. Good dispersion of the MWCNTs in PP is observed even after a short mixing time because the interactions between the entangled nanotubes are reduced. By in situ lubrication dispersion, the electrical percolation threshold of the PP nanocomposite can be as low as 0.5–0.7 wt% MWCNT. Rheological data also support percolation at 0.5 wt% MWCNT. With 0.5 wt% MWCNT, the slope of G′ at low frequency approaches unity and shows non‐terminal behavior. The proposed dispersion method enhances the wetting of MWCNTs and improves MWCNT dispersion compared to both direct mixing of MWCNT powder with a polymer melt and conventional master batch dilution.
A straightforward method, which is termed novel handspinning, is reported for producing uniaxially aligned sPP nanofibers. As demonstrated by SEM analysis, the morphologies of handspun sPP nanofibers are strongly dependent upon the processing conditions such as spinning method and solvent system. Compared to the normal electrospun sPP nanofibers, the handspun sPP nanofibers show smoother morphologies. FT‐IR analysis demonstrates a significant difference in polymer chain conformation between the handspun and electrospun sPP nanofibers. Moreover, interestingly, the handspun sPP single nanofibers show higher Young's modulus and tensile strength than electrospun sPP single nanofibers.
Antimicrobial properties of polymer materials are required in many applications. The polyethylene/superabsorbent polymer (PE/SAP) blends containing silver nanoparticles were successfully prepared via thermal reduction during melt mixing. It was found that in situ formed silver nanoparticles are preferentially located at the interface between PE matrix and SAP particles. The expectation was that the low water uptake of the PE will be enhanced by blending with a SAP and thus the silver ion release from the material will increase. Surprisingly, the silver ion release was markedly suppressed by the addition of SAP. This finding is explained by the preferential sorption of silver ions by the SAP particles.
The purpose of the present contribution is to provide an efficient method that would help to quantify the orientational levels occurring in polymer/clay dispersions subjected to elongational flow. The extent of internal orientation developed in salt containing montmorillonite/poly(ethylene oxide) gels is investigated, combining shear and elongational rheology methods. Entropic changes indicate that the strength of the transient network present in each gel affects the orientational ability of clay particles and polymer chains. We found that an increased Hencky strain of the hyperbolic die leads to a higher variation of the calculated entropy of the material.
The influence of an elongational flow on the morphology of PE/clay nanocomposite drawn fibers was studied. An increase of the elastic modulus and the tensile strength as well as a decrease of the elongation at break are observed with increasing draw ratio. The applied elongational gradient orients the polymer chains and the clay particles along the spinning direction. When the applied flow results in the formation and the orientation of exfoliated nanoparticles, a pronounced increase of the mechanical properties is observed. The dispersed clay particles can be broken and oriented by the extensional flow, which might indicate a flow‐induced intercalated/exfoliated morphology transition.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
Dynamic and transient shear start‐up flow experiments along with TEM, WAXS, and SEM analyses are performed on PP/PET blends and nanocomposites. The TEM results along with a theoretical analysis based on a thermodynamic model reveal that the clay particles are mainly localized in the PET phase. The localization of nanoclay in PET as the matrix phase leads to a refinement of morphology. The localization of clay is also studied by analyzing changes in complex viscosity and storage modulus in oscillation mode as well as the changes in power law index obtained from steady‐state and transient shear start‐up flow experiments. The changes in the rheological behavior of the blends are attributed to formation of clay network‐like structures.
This review reports on recent advances in the design of biodegradable polymers built from petroleum and renewable resources using reactive extrusion processing. Reactive extrusion represents a unique tool to manufacture biodegradable polymers upon different types of reactive modification in a cost‐effective way. Partially based on our ongoing research, ring‐opening polymerization of biodegradable polyesters will be approached as well as the chemical modification of biodegradable polymers, particularly natural polymers. The development of environmentally friendly polymer blends as well as (nano)composites from natural polymers, including natural fibers and nanoclays, through reactive extrusion, as an efficient way to improve the interfacial adhesion between these components, will be also discussed.
The effect of carbon nanoreinforcements of different shapes on the mechanical properties of epoxy‐based composites is studied. It is found that while nanodiamond and fibrous (carbon nanotube and nanofiber) particles provided better tensile properties, platelet (graphene oxide) nanoreinforcements lead to a considerable increase in the fracture toughness of the composites. The trend of the results is explained on the basis of the geometrical characteristics of the reinforcements. The accuracy of several micromechanics‐based criteria for predicting the Young's modulus of composites is investigated for different nanoparticle shapes. The state of dispersion of nanofillers and the fracture surface features of all composites are examined using TEM and SEM.
PA nanocomposites are prepared from clays organophilized with a phosphonium and an ammonium salt, and sodium montmorillonite is used as reference. The analysis of mechanical and micromechanical properties of the composites reveal that several micromechanical deformation processes occur in the PA/MMT composites. The matrix cavitates at relatively small stress. Processes related to non‐exfoliated clay structural units are initiated at larger stresses. Sound is emitted mainly by the fracture of particles, but debonding may also occur. The plastic deformation of the matrix dominates at larger stresses and deformations. The various local deformations are independent of each other and composite properties are not determined by silicate related processes but by the deformation of the matrix.
The thermal conductivity of a rubber compound is studied as a function of its state of curing. The device is presented and the calculations in order to obtain samples with controlled and homogeneous vulcanization rates are performed. The hot disk technique is used to measure the thermal conductivity of the rubber. This transient, plane‐source and non‐destructive method allows rapid and accurate measurement of the thermal conductivity based on the measurement of the electrical resistance of a plane sensor placed between two identical samples. The obtained results show that the thermal conductivity may vary significantly as a function of vulcanization rate. The effect of this variation on the prediction of the reaction progress is discussed.
The morphological structure of CB networks in elastomers and their flocculation dynamics under heat treatment and especially during vulcanization are analyzed by dynamic mechanical and dielectric spectroscopy. Dielectric spectra in the MHz range show that nanoscopic gaps between adjacent CB particles develop during heat treatment or vulcanization. These gaps are maintained by immobilized polymer layers acting as flexible bonds between the particles. Low‐frequency dielectric data indicate that the static percolation model qualitatively describes the dielectric properties of the conducting CB network on large length scales, but a superimposed kinetic aggregation process takes place on smaller length scales.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
Fully exfoliated PS/clay nanocomposites were prepared via FRP in dispersion. Na‐MMT clay was pre‐modified using MPTMS before being used in a dispersion polymerization process. The objective of this study was to determine the impact of the clay concentrations on the monomer conversion, the polymer molecular weight, and the morphology and thermal stability of the nanocomposites prepared via dispersion polymerization. DLS and SEM revealed that the particle size decreased and became more uniformly distributed with increasing clay loading. XRD and TEM revealed that nanocomposites at low clay loading yielded exfoliated structures, while intercalated structures were obtained at higher clay loading.
We present a new strategy for fabricating thermally responsive adjustable stiffness materials. A microfabricated heater embedded within a composite film is used to modulate the temperature of a low melting point polymer. Currents ranging from 0 to 200 mA were applied to the microheater and modulated material stiffness ≈100‐fold between 1.03 GPa and 10.9 MPa. The outside temperature of the composite ranged from 23 to 45.5 °C over this range of currents, suggesting its possible use in biomedical applications. The softened composite was bent into arbitrary shapes and allowed to restiffen, highlighting the reconfigurable nature of the material.
Porous cellulose acetate butyrate foams with a bimodal cell size distribution were produced using supercritical carbon dioxide as a blowing agent. It is demonstrated that the cell size distribution is tunable, due to the semi‐crystalline nature of the polymer. The resulting morphology will either be homogeneous or bimodal, depending on the depressurization rate. Mercury intrusion porosimetry shows that the produced cellulose acetate butyrate foams possess an open cellular structure.
Continuous and uniform yarns of thermoplastic nanofibers were prepared via direct melt extrusion of immiscible blends of thermoplastic polymers with CAB and subsequent extraction removal of CAB. Ratios of thermoplastic/sacrificial polymers, melt viscosity, and interfacial tensions affect the formation of nanofibers. Dominating sacrificing polymer content in the blends and low interfacial tensions between thermoplastic polymer and CAB are two key factors. This fabrication process possesses features of high productivity, versatility of thermoplastics, controllability, and environment friendliness in manufacturing thermoplastic nanofibers.
