Surface modification of carbon black by plasma polymerization was aimed to reduce its surface energy in order to compatibilize the filler with various elastomers. A fullerenic carbon black was used for the modification process. Thermogravimetric analysis, wetting behavior with liquids of known surface tension, TEM and TOF‐SIMS were used to characterize the carbon black before and after modification. The state of plasma‐coated carbon black in rubber was studied by means of conductivity measurements. The behavior of the modified filler in rubber was studied using the Payne effect and stress/strain properties. The study shows that plasma‐coated carbon black results in a better dispersion in different rubber systems than the uncoated version.
A procedure for the production of carbon nanotube (CNT) reinforced poly(vinylidine difluoride) (PVDF) powders has been developed. These powders are versatile precursors for a range of nanocomposite materials. The morphology of the CNT/PVDF powder can be related to the interaction between filler and matrix, which depends on the degree of modification of the polymer with grafted maleic anhydride (MAH‐graft‐PVDF). The mechanical performance of the nanocomposite containing 2.5 wt.‐% CNT and 1.25 ppm of MAH increased in tensile modulus, tensile strength, and strain to failure by 34, 30, and 22%, respectively, as compared to PVDF.
A new flame retardant based on an ammonium phosphonate is studied with respect to its thermal decomposition and its mode of action in wood‐plastic composites (WPCs). The measurements are carried out by means of fire tests (cone calorimeter) and pyrolysis investigations (thermogravimetry, infrared spectroscopy). The flame retardant acts mainly in the condensed phase by increasing the amount of residue formed by the wood part in the WPC. Additional flame dilution is achieved by the release of water, ammonia and carbon dioxide during the decomposition of the flame retardant.
Improving the conductivity of electrospinning solutions is often achieved by adding small amounts of conductive additives. HMIMCl, a room temperature ionic liquid, and TEBAC, a quaternary ammonium salt, were added to polylactic acid in chloroform and their effects on solution properties, electrospinning, and fiber properties were investigated. Both additives increased the conductivity which decreased the fiber diameter, but differences were observed on the fiber dispersity and fiber morphology. The conductive solutions caused fiber backbuilding with aggregation and fiber fusion. Reasons for the differences in fiber diameter and fiber morphology are discussed.
Organic/inorganic hybrid nanocomposite coatings were prepared through a dual‐cure process involving the cationic photopolymerization of a vinyl ether based system and the condensation of an alkoxysilane inorganic precursor. All formulations produced transparent cured films characterized by high gel contents. An increase in glass transition temperature and an increase in storage modulus above Tg in the rubbery plateau were observed with increasing TEOS content in the photocurable formulation. TEM micrographs showed that the organic and inorganic phases were strictly interconnected with no macroscopic phase separation; the sizes of the silica domains in the polymeric matrix were 3–5 nm.
The influence of coupling agents on the melt rheological properties of natural fiber composites has been investigated in this work using capillary and rotational rheometers. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the filler wetting and the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides relatively larger increase of the viscosity of the composites. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings. Entrance pressure loss in capillaries is also influenced by polymer matrix and coupling agent used.
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.
Nature offers interesting examples of structures with a gradually changing composition that provides unique mechanical properties. Today, the transfer of biological principles to technical applications is gaining increasing attention. One prominent example of the transfer of biomimetic principles to materials science is the mussel byssus. Byssus threads possess gradually changing mechanical properties from soft to stiff in order to efficiently attach the mussel to the rock. This design is the basis for polymer gradient materials. Herein, we give a comprehensive overview of the most recent developments in the field of PGMs. In addition to basic terminology and definitions, selected highlights of PGMs are presented, followed by experimental techniques and characterization methods.
Regenerated protein fibers from plant proteins including wheat gluten lack the mechanical properties and water stability desired for usual applications. Crosslinking has been used to improve the properties of regenerated proteins fibers. Although glutaraldehyde is commonly used to crosslink proteins, the effect of various crosslinking conditions on the properties of the materials has not been studied. In this work, a systematic study of glutaraldehyde crosslinking conditions of wheat gluten fibers is presented and shows that even low concentrations of glutaraldehyde (0.05%) can improve the strength and water stability of wheat gluten fibers.
Glass fiber biobased composites have been prepared by ROMP of a commercially available vegetable oil derivative possessing an unsaturated bicyclic moiety, and DCPD. The resins and the corresponding composites have been characterized thermophysically and mechanically. Higher DCPD content yields materials with higher glass transition temperatures. Glass fibers significantly improve the tensile modulus of the resin from 28.7 to 168 MPa. These biobased composites utilize only a limited amount of a petroleum‐based monomer, while employing substantial amounts of a renewable resource.
The role of polymer/filler interactions on the mechanical and electrical properties of elastomer nanocomposites is analyzed using dielectric spectroscopy, cyclic stress/strain tests, and online dc‐conductivity measurements. Pristine and deactivated (graphitized) CBs are studied in different rubber matrices. Due to confinement effects, an interphase of strongly immobilized polymer is present between adjacent filler particles, representing stiff but flexible mechanical bonds of the filler network. Under deformation of the sample, these bonds bend and finally break. Cyclic stress/strain measurements are analyzed by fitting the data to a microstructure‐based material model that allows for the evaluation of microscopic parameters of the polymer and filler network.
Copolymers of 3,4‐ethylenedioxythiophene and 3‐methylthiophene have been prepared by recurrent potential pulses using monomer mixtures with various concentration ratios, their properties being compared with those of the corresponding homopolymers. In addition, different technological applications have been tested for the generated copolymers. Results indicate that the properties of the copolymers are closer to those of poly(3,4‐ethylenedioxythiophene) than to those poly(3‐methylthiophene). Furthermore, the ability of the copolymers to store charge and to interact with plasmid DNA suggest that they are very promising materials.
Pollen has an exine shell with remarkable chemical stability, high‐strength, and unique microstructures that suggest use as a biorenewable polymer filler. Pollen‐filled polymers may offer potential for light‐weight, high‐strength materials that can displace some petroleum‐derived content with a sustainable plant‐based alternative. We report the first demonstration of the incorporation of pollen grains (short ragweed) on the mechanical, interfacial, and thermal properties of two polymers, poly(ε‐caprolactone) (PCL) and polystyrene (PS). Under certain solvent and annealing conditions, PS mechanical properties were improved synergistically upon addition of pollen, while those of PCL were always degraded, in strong agreement with wetting behavior of the polymer–pollen interface.
A processing method based on stretching of molten polymer nanocomposites was applied to prepare dichroic films. First, dodecanethiol‐capped gold particles were embedded in low density polyethylene. The resulting isotropic films were stretched in the melt under uniaxial loading using an elongational rheometer. The melt elongation technique resulted in reproducible characteristics of the optical properties and can be directly transferred to an industrial scale. The organic coating of the metal particles plays an important role in the generation of the dichroism. A reactive surface (adsorbed perfluorophenyl azide) led to strongly agglomerated particles which obviously did not lead to dichroic films.
Soft coatings are widely used to tailor the surface chemistry of materials without altering their bulk properties. However, the strength of adhesion between the coating and the substrate must be high enough for long‐term applications. This has become a major challenge in the medical field, especially for polymer‐coated stents, mainly due to several coating failures reported after mechanical expansion during clinical implantation. In this work, the applicability of current polymer‐metal adhesion tests to polymer‐coated stents is discussed. The small punch test was proposed as an adhesion test that allows fundamental studies on the adhesion and coating properties. This adhesion test was applied to thin fluorocarbon coatings deposited by plasma on 316L stainless steel.
Multifunctional materials that are lightweight and thermally conductive but electrically insulating are important for modern electronics, computer, and telecommunication technologies. Here, a novel foam structure of a polymer/matrix composite filled with ceramic platelets with improved thermal conductivity is reported. Such improvement is caused by the stress‐induced alignment of thermally conductive fillers in the cell wall of the plastic foam. The foam structure is very promising for use as a lightweight electronic packaging material owing to its light weight, thermal conduction ability, electrical insulation, and good processability.
Epoxy/BaTiO3 hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free‐radical promoted cationic polymerization using a long‐wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well‐dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.
The preparation of functional nanocomposites by dispersion of a synthetic lamellar α‐ZrP within a styrene/butadiene random copolymer during melt compounding is described. It is shown how the physical and chemical incompatibility of filler and polymer can be overcome, and problems arising from the low viscosity ratio between slurry and polymer matrix are discussed. The aqueous phase can easily be eliminated at the end of the process. The dispersion of the ZrP requires the use of intercalants, and alkylamines were used for this purpose. XRD and TEM are used to characterize the degree of organization of ZrP in the slurries and in the matrix. DMA helps to understand the origin of the limited reinforcing effect.
MA is grafted onto both PLLA and starch in an internal mixer in the presence of DCP in a one‐step reactive compatibilization process. The effect of maleation of MA on the physical and mechanical properties and morphology of the blends was assessed. The onset decomposition temperature of the PLLA/starch blends decreased as the starch content increases due to the lower thermal stability of starch and the low effect of the maleation reaction on the thermal stability of the blends. PLLA/starch blends without grafted MA showed higher crystallinity as the starch content increased. Reactive compatibilized blends with less than 20 wt% starch had higher storage modulus, indicating that the compatibility between the two phases was improved.
Nanocomposites of cassava starch reinforced with waxy starch nanocrystals were prepared. They showed a 380% increase of the rubbery storage modulus (at 50 °C) and a 40% decrease in the water vapor permeability. X‐ray spectra show that the composite was more amorphous than the neat matrix, which was attributed to higher equilibrium water content in the composites. TGA confirmed this result and its thermal derivative suggested the formation of hydrogen bonding between glycerol and the nanocrystals. The reinforcing effect of starch nanocrystals was attributed to strong filler/matrix interactions due to the hydrogen bonding. The decrease of the permeability suggests that the nanocrystals were well dispersed, with few filler/filler interactions.
