Next to the intended increase of the impact toughness, impact modification of polycarbonate generally results in an unwanted decrease in yield stress and time‐to‐failure under constant stress. It is demonstrated that this loss in strength can be fully compensated for by an annealing treatment, or by increasing the mold temperature. The influence of impact modification on the short‐ and long‐term strengths of glassy polymers is predicted by the extension of existing models with a scaling rule based on the filler volume percentage. Introduction of this scaling rule in the evolution of yield stress during physical aging even allows for the direct prediction of yield stress on the basis of processing conditions.
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.
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.
Artificial turf is robust, playable in all weathers and has a long service life. Polyamide (PA) flooring has excellent resilience but provokes abrasion injuries (friction burn); polyethylene (PE) monofilaments are skin‐friendly but tend to permanent deformation. To maximize resilience while minimizing the risk of skin abrasion, PA‐PE bicomponent fibers are developed. Numeric simulation is applied to find optimized fiber cross‐sections and material combinations, accompanied by melt‐spinning of respective filaments and validation of the model. The resulting artificial grass resembles natural turf with respect to playability and appearance and does not need any granular infill.
Sealed microchannels and simple microfluidic networks with good efficiency and controlled quality of the structures were developed from a photocurable and PCR‐compatible material based on a PEG–methacrylate oligomers mixture. The influence of UV exposure time and of conversion degree on microchannel geometry were studied to obtain structures with controlled depth, vertical sidewalls, and good reproducibility. The roughness inside channels was as low as 50–100 nm, less than that typical of alternative LOC prototyping techniques such as micromilling. Efficient channel sealing was also achieved without using a different sealing material. Surface smoothness and hydrophilicity (static contact angle below 60°) allow spontaneous water flow inside the channels by capillarity without need of surface treatments.
The long‐term viscoelastic behavior of reinforced all‐poly(propylene) composites was studied by flexural creep tests. Both unidirectional and cross‐ply laminates were prepared from PURE® coextruded tapes by vacuum bag molding in an autoclave. The specimens were subjected to isothermal creep tests at different temperatures ranging from 20 to 80 °C under an applied load. The time‐temperature superposition principle was verified for the creep data. An Arrhenius type relationship was found to better describe the shift data obtained from the creep tests. The activation energies relating to the different reinforcement architecture and different relaxation process were calculated.
Different processing approaches were adopted to obtain the best combination of strength and toughness. The approach that yielded superior properties was examined in detail to study the mechanical response of nanoscale calcium carbonate‐reinforced high density polyethylene in conjunction with unreinforced high density polyethylene. The reinforcement of high density polyethylene with nanoscale calcium carbonate increases impact strength and is not accompanied by decrease in yield strength. The addition of nanoscale calcium carbonate to high density polyethylene alters the micromechanism of deformation from crazing‐tearing in high density polyethylene to fibrillation in high density polyethylene–calcium carbonate nanocomposite.
The fabrication of tissue engineering scaffolds based on the polymerization of crosslinked polylactide using leaching and batch foaming to generate well‐controlled and interconnected biodegradable polymer scaffolds is reported. The scaffold fabrication parameters are studied in relation to the interpore connectivity, pore morphology, and structural stability of the crosslinked PLA scaffold. In vitro cell culture and in vitro degradation are used to analyze the biocompatibility and biodegradability of the scaffolds. The new crosslinked PLA thermoset scaffolds are highly suitable for bone tissue engineering applications due to their complex internal architecture, thermal stability, and biocompatibility.
Hybrid organic/inorganic acrylic nanostructured films were prepared by a UV/thermal dual‐curing process. The role of a fluorinated hydroxyl acrylate monomer (AF) as coupling agent was investigated. Increased Tg values and modulus of the dual‐cured films were achieved by increasing the TEOS inorganic precursor. The coupling agent deeply modified the surface properties of the cured films: the formation of hybrid films characterized by high hydrophobicity together with an increase on surface hardness was achieved. TEM analysis clearly evidenced the reducing of the nanosize dimensions of the inorganic silica domains by increasing the coupling agent content in the photocurable formulation.
Magnetic organosilica nanoparticles are synthesized by grafting MPB‐POSS/MMA‐based block copolymers from magnetic iron nanoparticles via surface‐initiated ATRP. The hybrid nanoparticles consist of a magnetic iron core and a PMMA/POSS composite shell. A small amount of the nanoparticles is added as “smart additive” in casting PMMA sheets for localized surface modification. It is demonstrated that the particles are readily brought to the surface of the cast piece by applying a magnet field to the molding. At 1 wt% loading, the sample has a 50‐time higher particle content in a 100 µm‐thick surface layer than in the bulk. The indentation hardness of the modified surface is increased by 30%.
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.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
Living radical polymerization (LRP) techniques and their ability to improve the morphology of crosslinked polymer networks by controlling polymer chain growth are reviewed. Recent successes in the creation of improved molecularly imprinted polymer networks are also discussed. LRP offers the ability to control molecular weight, polydispersity, and tacticity while reducing microgel formation in polymers created via free‐radical polymerization (FRP). The improved network architecture of polymers created via LRP has great potential, especially when considering imprinted networks which have traditionally been plagued by heterogeneity in network morphology and binding affinities. Using LRP can considerably improve template recognition and further delay template transport in imprinted polymers.
Nanocomposites based on poly(vinyl alcohol) and silver nanoparticles were efficiently prepared by sun‐ and thermal‐promoted reduction processes. Uniaxial drawing of the Ag/PVA nanocomposites favoured the anisotropic distribution of silver particles, providing oriented films with polarisation‐dependent tunable optical properties. These dichroic properties were more pronounced for nanocomposites produced by sun exposition, which provided more compact and interacting metal clusters. The results obtained suggest the nanocomposite films could find potential applications as colour polarising filters, radiation responsive polymeric objects and smart flexible films in packaging applications.
PPy was synthesised by oxidative chemical polymerisation using xylan, CMC and NFC as additives. Conducting nanocomposite films were cast from aqueous slurries using doped PPy particles, CMC and NFC as the conducting and reinforcing phase, respectively. NFC‐based composites had higher conductivity and lower mechanical properties than CMC‐based homologues. SEM analysis showed that in PPy/NFC composites, PPy and NFC were arranged in two entangled networks, whereas, in PPy/NFC composites, CMC formed a continuous matrix around PPy particles, thus limiting conductivity. Mechanical properties of nanocomposite films were interpreted as reflecting the presence of different structures when using NFC or CMC as reinforcing phase.
Sunflower oil‐based HBTPU/Ag and LTPU/Ag nanocomposites have been prepared by in situ catalytic reduction of a silver salt. The virgin polymer and their nanocomposites are soluble in various polar organic solvents and amenable for both solution‐casting and hot pressing. XRD, TEM, and UV spectroscopic analyses ascertained well‐dispersed, narrow‐sized Ag nanoparticles. Tensile testing, dynamic mechanical, thermogravimetric, and DSC analyses showed desirable mechanical and thermal features with improvement upon incorporation of Ag nanoparticles and the presence of a hyperbranched component in the nanocomposites. RSM has been used to evaluate the catalytic efficacy of the nanocomposites.
Isotactic PP nanocomposites filled with Fe@FeO nanoparticles are fabricated by a facile ex situ method. The nanofillers are dispersed in a boiling PP/xylene solution. X‐ray diffraction is used to determine the nanofiller effects on the crystallinity of PP. The crystallinity along the (040) plane is found to decrease with the incorporation of nanoparticles. Thermal properties and crystallinity are studied by TGA and DSC, respectively. Enhanced thermal stability and influenced crystallinity are observed in the PP nanocomposites compared with those of pure PP. An increased dielectric property without percolation threshold is observed. In addition, the nanocomposites are found to exhibit ferromagnetic properties.
A diacrylate polysulfone oligomer is synthesized and used as the acrylic oligomer for the in situ synthesis of noble metal/PSU nanocomposites through UV‐induced simultaneous radical polymerization of acrylic functionalities and NP formation by reduction of their precursors. Thus, silver or gold NPs are formed in situ during polymer network formation. FESEM analysis of the morphology of the cured systems demonstrates that the nanoparticles of the noble metals are homogeneously distributed in the network without macroscopic agglomeration.
Thermo‐responsive PNIPAAm/PLLA nanofibrous films with tunable surface morphologies and better biocompatibility were prepared by electrospinning technique. The electrospun composite films possessed a “bead‐on‐string” structure. The wettability of nanofibrous films was observed by water CA measurements. The results showed that the electrospinning process and addition of PLLA did not change the thermo‐sensitivity of PNIPAAm. The wettability of electrospun PNIPAAm/PLLA composite films could switch from superhydrophilic to superhydrophobic when the temperature increased from 20 to 50 °C. Electrospinning is a promising way to create stimuli‐responsive surfaces with potential application in the design and tactics of controllable drug delivery system.
Reproducible and controllable hydrophilic layers were grafted on macroporous PP membranes by surface initiated grafting. Two methods were adopted, i.e., through adsorption of or entrapping the photo‐initiator on the membrane surface. The latter method yielded longer grafted chains under otherwise identical conditions. Depending on monomer solution composition, brush layers or network‐like structures were grafted onto the entire membrane surface without significant loss of water flux. The influence of the structure of grafted layers on water permeation, protein adsorption, and protein microfiltration fluxes was investigated. It was found that membranes grafted with network‐like structures have the best performance.
