Novel silver/polymer composites based on thiol‐ene chemistry are prepared by an in situ bottom‐up approach. The in situ synthesis of silver particles inside the polymer matrix is achieved in one pot by photoreduction reaction in presence of a silver precursor and the concurrent crosslinking reaction. XPS analysis confirms the formation of silver particles; TEM morphological investigation shows a very good dispersion and distribution of the nanometric silver particles within the thiol‐ene network. Antimicrobial properties of the photocured hybrids are also evaluated.
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.
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.
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.
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.
A composite material consisting of hydroxide‐modified hemp fibres and euphorbia resin was produced. The composites were tested in tension, short‐beam interlaminar shear stress and in impact. There was an increase in the tensile strength and modulus for resins with high‐hydroxyl‐group based composites. Similar results were obtained for interlaminar shear stress while low‐hydroxyl group euphorbia resin based composites exhibited high impact strength. The euphorbia resin with high hydroxyl content yielded composites with high stiffness. The use of euphorbia‐based resins in composite manufacture increases the value of the euphorbia oil as well as creating a new route of composite manufacturing.
Electrospray deposition has been investigated as a substitute for photoresist spin coating. The morphology of Microposit S1813 photoresist films has been studied as a function of several spray conditions including resist concentration, substrate surface, and flow rate. Film morphology is controlled by three process parameters: the surface energy determines the equilibrium conditions of resist on the substrate; the viscosity and volume flux determine the relaxation time for the depositing resist solution after impact on the substrate. Electrosprayed photoresist films have been used for photolithographic patterning and it has been demonstrated that electrospray deposition is an effective method for deposition of photoresist on top of fragile, thin films, which can be used for multilayered thin film fabrication.
The pyrolysis and fire behavior of halogen‐free flame‐retarded DGEBA/DMC, RTM6 and their corresponding 60 vol.‐% carbon fibers (CF) composites were investigated. A novel phosphorous compound (DOPI) was used. Its action is dependent on the epoxy matrix. DGEBA/DMC and DOPI decompose independently of each other. Only flame inhibition occurs in the gas phase. RTM6 shows flame inhibition and a condensed phase interaction increasing charring. Both mechanisms decrease with increasing irradiance, whereas in RTM6‐CF charring is suppressed at low ones. RTM6 + DOPI shows a higher LOI (34.2%) than DGEBA/DMC + DOPI and a V‐0 classification in UL 94. Adding CF only enhances the LOI, DOPI + CF leads to a superposition in LOI for DGEBA/DMC‐CF + DOPI (31.8%, V‐0) and a synergism for RTM6‐CF + DOPI (47.7%, V‐0).
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.
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.
A variety of polymer parts used in microsystems technology is produced by injection molding. For dimensioning and design of these products, both the material properties and changes during the life cycle have to be taken into account. The aging behavior of parts with decreasing dimensions or of parts processed under different cooling conditions is discussed in terms of their morphological and mechanical long‐term properties. The results indicate that a decreasing part size leads to higher post‐crystallization and higher thermo‐oxidative degradation. This leads to size‐dependent changes in mechanical properties. Adjusted process conditions by application of thermal low‐conductive mold materials can favor the process‐related properties and thus the long term properties can be improved.
Synthesis, properties, and patterning of new acrylic/silsesquioxane hybrid materials are reported. PMA‐functionalized PHSSQ was synthesized by hydrosilylation and then formulated with acrylate monomer mixtures to yield the photocurable materials. Experiments suggest that the thermal/mechanical properties of the parent acrylic polymers could be significantly enhanced by incorporating nano‐sized silsesquioxane moieties. The refractive index and optical loss were reduced by increasing the silsesquioxane content. The hybrid materials could be photocured and developed a Y‐shape channel pattern; potential applications include uses in patterned electronic and optoelectronic devices.
A composite of boehmite alumina nanoparticles and a PP/PA12 blend is prepared. WAXD and SEM suggest that a low filler loading enhances the coalescence of PA12, whereas a higher loading reverses the situation. DSC, DMA and TGA reveal that the final properties of the blend composites such as crystallization temperatures, flexural storage moduli, or thermal degradation temperatures improve with increasing nanoparticle loading. The data are compared with the neat polymers and the compatibilized blend, and the results show that the compatibility increases only at high nanoparticle loading, and most of the thermal properties improve with increasing nanoparticle content in the blends. The presence of interfacial interactions between the polymer matrices and the filler was confirmed via FTIR.
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.
To improve the poor mechanical properties of uniaxially ultra‐drawn films along the transverse direction, lamination of two ultrahigh molecular weight polyethylene/ethylene dimethylaminoethyl methacrylate copolymer blend films was carried out in the rectangular elongation direction by a microwave heating method. The characteristics of the successful laminated films were analyzed theoretically and experimentally. The original orientation of the crystallites for the blend films was maintained perfectly after lamination, and the preferential directions intersected each other. The Young's modulus increased symmetrically with respect to the 45 ° direction. This is the first report concerning a drastic improvement of the Young's modulus in the transverse direction for films ultra‐drawn along one direction.
The design and synthesis of new fouling‐resistant coating materials, specifically PC‐substituted polyolefins, and their application to water purification membranes is described. Greatly improved fouling resistance is found for coated membranes subjected to environmentally relevant emulsified oil foulants. The coating method proves effective for reducing fouling on both UF and RO membranes, and for maintaining high rejection of organic material and salt. Providing membranes of various types with a coating that simultaneously gives high flux, fouling resistance, and foulant rejection represents a significant advance in membrane materials, and a promising route to extend membrane applications beyond what has been possible using conventional, known materials.
Developing co‐continuity in a polymer blend determines a multiphase system with enhanced properties which originate from the synergism of its constituents. Filling a blend with nanoparticles is a promising route to guide its morphology and eventually affect the co‐continuity transition. We add different kinds of nanoparticles to an HDPE/PEO blend to study how they affect the morphology of the blend as function of their surface properties and form factor. We find that PEO drop size is drastically reduced by particles adsorbed at the HDPE/PEO interface. However, we show that a drastic shifting of the co‐continuity threshold may only be achieved when particles affect the rheology of the interface.
Recycling of PET was examined using hydrolytic depolymerization in an alkaline solution under microwave irradiation. The reaction was carried out in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. The main products were the monomers TPA and EG. The effect of reaction temperature, time, amount of PET and alkaline concentration on the degree of PET depolymerization and TPA recovery was investigated. Microwave irradiation was found to reduce the time needed to achieve a specific degradation of PET significantly, with almost complete depolymerization occurring in 30 min at 180 °C and only 46 W of microwave power. Using a phase transfer catalyst (TOMAB) resulted in the same amount of unreacted PET but at significantly lower depolymerization temperatures.
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 new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.
