A physical model of dart impact tests of film manufactured from semi‐crystalline polyethylene resins is developed. The models treat the dart impact tests as a special case of the standard high‐speed stress/strain measurement performed on a polymer sample with a linearly changing cross section. They describe the dart impact strength as a complex function of the parameters that characterize the stress‐strain curve of the resin: stresses and strains at the yield, necking and breaking points. The models correctly predict the range of the dart impact strength (ASTM D1709, ISO 7765) and are suitable for semi‐quantitative characterization and ranking of linear low density polyethylene resins for film applications.
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.
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.
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.
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.
A new class of polymer materials is reviewed, the SPCs, in which the matrix and the reinforcement share the same chemical composition. In addition to their milder environmental impact as compared to traditional polymer composites, they show superior mechanical performance mainly due to the improved adhesion between matrix and reinforcement. Another advantage of SPCs is the missing dispersion step in their production, thus contrasting the common polymer nanocomposites. Definition, manufacturing, classification, and the application opportunities of SPCs are described. Special attention is paid on the very new members of the SPC family, the micro‐ and nanofibrillar SPCs, including the techniques for preparation of their starting neat micro‐ and nanofibrils using bulk polymers.
SSP of PET has been thoroughly investigated under the regimes of chemical reaction and particle diffusion control. However, the majority of industrial PET plants operate under conditions of surface by‐product diffusion control, mainly due to recycling cycles of the carrier gas. The presence of residual volatile by‐products in the carrier gas (especially water) may affect adversely the polymerization reaction and the resulting polymer quality. For this reason, the effects caused by varying water vapor content of the carrier gas on the course of the PET SSP are analyzed, with emphasis on the intrinsic viscosity. The presence of small amounts of water in the carrier gas is found to exert a pronounced effect on the course of polymerization, leading to significant reduction of the molar masses of the final product.
Unfilled and MWCNT‐filled PA fibers are prepared and the effect of the extensional flow on their mechanical performance and morphological variations is investigated. Morphological analyses using SEM, TEM, and SAXS suggest a stronger orientation of the MWCNTs along the fiber direction with increasing extensional flow. A particular MWCNT bundle formation in the PA drawn nanocomposite fibers is observed for the first time, and a pull‐out of the central nanotube in some bundles is noted. The maintenance of the “shish‐kebab” structure upon extensional flow is responsible for the mechanical improvements and dimensional stability in MWCNT‐filled PA fibers.
Summary: Non‐Newtonian fluid behavior has significant influence on quantities in chemical engineering like power input, mixing time, heat transfer etc. In the laminar flow region, the concept of effective viscosity by Metzner and Otto is well established. In the transition region between laminar and turbulent flow, the existing concepts use three and even more empirical parameters to determine the specific power input. Here, a unified and general but simple approach is introduced to calculate the power input for shear thinning fluids over the whole flow region using just one empirical parameter. The Metzner‐Otto relation is obtained as a limiting case for the laminar region. The empirical parameter of the new approach is related to the Metzner‐Otto constant. The concept is validated for eight different stirrer systems. Mixing time and maximum shear rate and heat transfer can also be calculated using this approach. The new concept presented should also be applicable for other apparatuses, e.g., static mixers.
Comparison of experimental data and a curve calculated according to the new method (solid line). 相似文献
Summary: In the framework of chemical recycling of polymers, leading to the generation of secondary value‐added products, PET flakes taken from post‐consumer soft drink bottles, were glycolyzed with DEG. The oligomers obtained were analyzed for their molecular weight and characterized by FT‐IR and POM. Subsequently, dimethacrylated oligoesters of PET glycolysate (PET‐GLY‐DMA) were synthesized by methacrylation of the glycolyzed PET product. The resulted monomer PET‐GLY‐DMA was studied by FT‐IR, POM and DSC. Thermal polymerization of this monomer was carried out at 80 °C in the presence of benzoyl peroxide as initiator. A UV‐curable formulation was also prepared on the basis of neat PET‐GLY‐DMA, as well as by mixing PET‐GLY‐DMA with styrene, using DMPA as photoinitiator. Nanoparticles of SiO2 were dispersed into PET‐GLY‐DMA/styrene copolymers as reinforcing agents and the mechanical properties of resins formed were studied.
Preparation of methacrylated PET glycolysate. 相似文献
Summary: The structure and properties of blends of a PCTG and a PAE resin obtained by direct injection molding have been studied. The blends were almost immiscible, and were composed of a nearly pure PAE phase and a mixed PCTG‐rich phase containing minor PAE amounts. Electron microscopy observations showed a high intermixing level between both components. The permeability data indicated an improved barrier protection of PCTG upon PAE addition. The Young's modulus and the yield stress of the blends followed a linear behavior with respect to composition, while values close or slightly below linearity were observed for the break properties. The combined effects of the small dispersed particle size and the proposed good interfacial adhesion are stated as the main factors responsible for the positive mechanical behavior. The impact strength showed an unexpected variability for PCTG‐rich blends, which is attributed to a ductile‐brittle transition of PCTG.
Ductility of PCTG/PAE blends vs. composition. 相似文献
A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.
Time series of video frames showing capsules being compressed into a constriction. 相似文献
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.
Summary: Novel poly(cyclotriphosphazene‐co‐sulfonyldiphenol) microtubes were successfully prepared via one‐pot synthesis using special templates generated in situ during the polymerization. The templates could be easily removed by dissolution in water. This approach overcame the multi‐step nature of general template methods. The as‐synthesized microtubes were 1–3 µm in width, about 100 µm in length and contained hexagon‐shaped channels. IR and NMR spectroscopies confirmed the covalently crosslinked chemical structure of the polymer tubes, and the tubes are thus mechanically and thermally stable. The polymer microtubes are of interest for use as chemical or biological sensors, controlled release and delivery of drugs, tissue engineering materials, absorbants and many other microscale investigations.
SEM images of triethylamine hydrochloride crystals produced in situ during formation of the tubes (left) and the polymer microtubes (right). 相似文献
Summary: Different styrene‐ and acrylate‐based organic‐inorganic polymer composites incorporating magnesium hydroxide were successfully synthesized using MPTMS as a coupling agent and MgCl2 as an inorganic precursor. The polymer composites were prepared by free‐radical emulsion polymerization following different procedures. The samples were investigated by means of FT‐IR spectroscopy, XRD, TGA, DSC, and rheometry. It is shown that the preparation method does only affect the ratio of organic to inorganic component, but not the chemical structure of the composites. The obtained polymer composites consist of Mg(OH)2 particles which are linked covalently via MPTMS groups to the polymer backbone.
Scheme of Mg(OH)2 crosslinked with MPTMS units as proposed for the emulsion polymer composite. 相似文献
The flame retardancy mechanisms of aluminium diethylphosphinate (AlPi) and its combination with melamine cyanurate (MC) in glass‐fibre‐reinforced poly(butylene terephthalate) (PBT/GF) were analysed using TGA including evolved gas analysis (TGA‐FTIR), cone calorimeter measurements using various irradiations, flammability tests (limited oxygen index, LOI, UL 94) and chemical analyses of residues (FTIR, SEM/EDX). AlPi decomposed mainly through the formation of diethylphosphinic acid and aluminium phosphate and influenced the decomposition of the PBT only slightly. AlPi acted mainly through flame inhibition. A halogen‐free V‐0 PBT/GF material was achieved with a LOI of 44%. Additional charring influenced the flammability. MC decomposed independently of the polymer and showed some fuel dilution effects.
A new kind of binary polymer brushes was synthesized from two immiscible polymers, PMMA and PEG, on GPS‐modified silicon wafers. Surface composition, layer thickness, coverage, chain density, wetting ability, morphology and protein adsorption of the binary brushes were investigated by XPS, ellipsometry, AFM and contact angle measurements. The results show that both PMMA and PEG were successfully grafted onto the surface. The surface coverage and the chain density of PMMA and PEG brushes can be controlled by modulating the reaction temperature and time. This kind of binary polymer brushes exhibits a distinct microphase‐separated structure and excellent protein‐preventing property.
Hybrid nanocomposite coatings were prepared by the UV‐curing technique with a methacrylic oligomer and multifunctional methacrylic polyhedral oligomeric silsesquioxane blocks (POSS®). The results obtained from the polyhedral compounds were compared with those of a disordered framework obtained by the condensation of a silica precursor (MEMO). The inorganic domains generated during synthesis created constraints in movement of polymer segments, which reflected in an increase in Tg of the hybrid nanocomposite coatings. The films were transparent. The random structure obtained by the condensation of the MEMO showed a stronger effect on Tg than that observed by introducing POSS®. The effect of inorganic domains reflected on thermal stability, surface hardness and mechanical properties of the hybrid nano‐composite coatings.
Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane‐1,6‐diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard‐to‐soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard‐to‐soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress‐strain curves in tack experiments.
The storage modulus of the adhesives as a function of frequency at 70 °C. 相似文献
During their working life, plastics can be exposed to contaminating media which limit their recyclability. A continuous extraction process with supercritical CO2 has been developed. Contaminated material is extruded through two twin‐screw extruders in a cascade. The first extruder purifies with scCO2 and the second extruder is for degassing and hot‐cut pelletisation. Post‐consumer automotive diesel fuel tank material has been processed. A direct flow and a counter‐flow process with different screw configurations have been developed. Characterisation has been performed by headspace gas chromatography. Results show that contaminants were extracted out of the plastic for both process variants. However, direct flow yielded better extraction efficiency.
