Porous membranes were fabricated using chitosan and poly(DL ‐lactide) or poly(L ‐lactide) blends through a combinatorial technique. Well‐controlled porous structures could be achieved by optimizing processing conditions. The ductility and toughness of dry porous membranes were improved by incorporating an increased amount of chitosan, and the physical strength and dimensional stability of hydrated porous membranes were preserved if the components were used in a suitable ratio. Although there were measurable differences in the pore‐size distributions of membranes with the same composition prepared under identical conditions, this showed no effect in their dry states.
Summary: Various output heaters were extruded with CB‐filled HDPE composites. The effects of crystallinity on the PTC and thermal reproducibility of the quenched, annealed, and E‐beam crosslinked heaters were examined during heating and cooling cycles at an applied voltage of 220 V. Conductor resisitivity and PTC effect of the heaters increased as crystallinity of composites increased. During the thermal cycling test, significant changes in heater‐output and resistivity for annealed and quenched heaters were observed. However, for quenched/E‐beam radiated and annealed/E‐beam radiated heaters no significant difference was found. These results indicate that the annealing process did not affect the thermal and electrical reproducibility of HDPE/CB heaters significantly.
Acetylene black aggregates in polyethylene matrix. 相似文献
The rheological behavior, morphologies, and tensile properties of reactively compatibilized PVDF/TPU blends are reported. Using PVDF‐g‐AAc as the compatibilizer, PVDF/TPU 90/10 and 10/90 blends are prepared. The carboxylic acid groups of PVDF‐g‐AAc react with the urethane linkages of TPU during melt blending to generate in situ PVDF‐g‐AAc‐g‐TPU which leads to compatibilization of PVDF/TPU blends. The introduction of PVDF‐g‐AAc into the PVDF/TPU blends causes an increase in viscosity. The rheological behavior of the compatibilized PVDF/TPU 90/10 and 10/90 blends are well described by the generalized Zener model. The addition of the compatibilizer PVDF‐g‐AAc reduces the dispersed‐phase domain size and narrows the size distribution. ?Author: The summary has been shortened to comply with the maximum of 700 characters. Pls check/confirm changes!?
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
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.
Summary: Blending of the commercial LC‐polyester Rodrun LC‐3000 with the bisphenol‐A‐diglycidyl ether based diepoxide DOW D.E.R.330 alone and with the mixture of the diamine (MCDEA) and D.E.R.330 by means of a twin‐screw extruder has been investigated. Conditions to suppress curing of epoxide and amine during blending have been established. Due to the very low solubility of Rodrun in the diepoxide only LCP‐rich blends with a minimum content of 60 wt.‐% Rodrun could be obtained. The blends were investigated by SEM and thermal analysis (DSC, DMTA). Binary blends are immiscible while ternary blends appear miscible from DMTA up to 30 wt.‐% of epoxy/amine.
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.
In the present work, we report on the synthesis and characterization of poly(vinylidene fluoride) (PVDF) with N‐isopropylacrylamide (NIPAAM) polymer side chains from molecular graft copolymerization in solution. The copolymer can be readily cast into temperature‐sensitive microfiltration (MF) membranes by the phase inversion technique. The copolymer approach to membrane fabrication allows a much better control of the physicochemical nature of the membrane pores through the variation in graft concentration, membrane casting temperature and concentration of the membrane casting solution.
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.
This paper deals with immiscible blends of poly(ethylene terephthalate) obtained by melt blending with polycarbonate. A large survey of the current knowledge in the field of these blends is presented. Resolved and unresolved issues concerning the effect of exchange reactions on the miscibility of the components are addressed. The experimental part of the paper focuses on the rheological behavior of PET/PC blends. Blends containing various polymer ratios were obtained by melt blending with and without transesterification catalysts. Oscillatory shear flow in the melt was used to characterize the rheology of the various samples. A plot of the oscillatory data, similar to the Van Gurp Palmen plot, is used to point out the broadening of the co‐continuity window when in situ compatibilization takes place.
Summary: Melt elasticity of a series of conventional and metallocene‐catalyzed PEs is investigated. The samples show very noticeable differences in their molecular architecture, including a variable degree of LCB and MWD. Four parameters (De, RSI, recoverable shear and steady state compliance), determined through dynamic viscoelastic measurements, are correlated with molecular architecture and blown film properties. RSI parameter shows a particular capacity to discern the LCB effect from the MWD effect on PE melt elasticity. Enhancing melt elasticity improves bubble stability, but provokes more haze and poorer impact properties in the film.
Dart impact values vs. relaxation spectrum index. 相似文献
The influence of the stabilizer/SWNT ratio on the transport behavior of latex‐based polymer nanocomposites is examined in an effort to improve electrical conductivity while maintaining or improving the Seebeck coefficient (i.e., thermopower). Results show that phonon and electron transport are significantly affected by tube/tube junctions, and the carrier transport across the junctions can be manipulated by altering the stabilizer concentration. Electrical conductivity of composites containing 10 wt.‐% SWNT nearly doubles, becoming greater than 900 S · m?1, by changing the SWNT:GA ratio from 1:3 to 10:1, while thermal conductivity and Seebeck coefficient remain relatively constant (near 0.25 W · m‐K?1 and 40 µV · K?1, respectively).
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.
PET/PE blends are prepared with and without different types of organo‐modified montmorillonites (OMMT) using a extrusion process. The droplet size of PE dispersed phase decreases upon organoclays addition, however without any direct dependence on the organoclay initial surface tension. To assess the effect of the organomodifier without MMT, PET/PE blends are then compounded adding solely the surfactants (similar to those used to modify the various organoclays). Whatever the chemical nature of the surfactant, a refinement of the PE droplets is observed, interestingly similar to those previously observed in presence of clay. This shows unambiguously that the key factor for organoclay compatibilization efficiency, in the case of PET/PE blends, is the surfactant modifier itself and not the MMT platelets.
Poly(lactic acid) (PLA) and soy protein concentrate (SPC) were compounded using poly(2‐ethyl‐2‐oxazoline) as compatibilizer by twin‐screw extrusion, and the resulting blends were foamed by a chemical blowing agent (CBA) using the same extruder. Effects of foaming temperature and CBA content on cell density and foam density were investigated. Polymeric methylene diphenyl diisocyanate (pMDI) as a co‐compatibilizer was added prior to foaming extrusion and its effects on foam morphology and properties were also studied. The results showed that cell density and foam density were greatly influenced by foaming temperature and CBA content. Using the strong interfacial modifier pMDI in PLA/SPC blends resulted in high‐cell density and low‐foam density when CBA concentration was low.
Summary: The compatibilization of polyethylene/polyaniline (PE/PANI) blends and the preparation of plasticized PANI/camphorsulfonic acid (CSA) complexes suitable for melt blending were studied. Rheological properties of the components essentially affected the morphology of the blend and thereby the electrical conductivity. The hydrogen bonds between the PANI complex and the functionalized metallocene PE used as compatibilizer compensated the unfavorable viscosities of the components. Mechanical properties of PE/PANI blends were improved, and electrical conductivity of the blends remained the same or increased through addition of functionalized metallocene polyethylene. Plasticized PANI/CSA complex with good electrical conductivity was successfully prepared.
Compatibilization of PANI/CSA complex and OH‐functionalized polyethylene. 相似文献
Oriented precursors of MFCs consisting of HDPE and PA6 or PA12 are studied during strain‐controlled slow load‐cycling. In the PA6‐containing blends a strongly retarded nanostrain response is detected. Compatibilization induces nanostrain heterogenization. Stress fatigue is lower in the PA12 blends, but hardly decreased by the compatibilizer. Selective migration of the compatibilizer into a disordered semi‐crystalline fraction of the HDPE matrix can explain the findings. The semi‐crystalline HDPE entities in PA6 blends appear more disordered than in PA12‐blends. An analysis of the HDPE nanostructure evolution during cycling reveals epitaxial strain crystallization. Uncompatibilized PA6 blends cycled about high pre‐strain show plastic flow but nanoscopic shrinkage in the semi‐crystalline stacks.
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.
Summary: Blends of different compositions were prepared from: a thermoplastic elastomer (EPDM), a low density polyethylene (PE), a polystyrene crosslinked with a small amount of divinylbenzene (PS‐co‐DVB) and an inorganic proton conductor: antimonic acid (HSb). The blends obtained were sulfonated heterogeneously with chlorosulfonic acid and were then structurally and electrically characterized by means of the following techniques: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), crystallization kinetics under non‐isothermal conditions and complex impedance spectroscopy.
Dynamic mechanical analysis for EPDM and EP‐3 blends series. 相似文献
Repetitive processing was employed to assess the recyclability of in situ microfibrillar poly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) blends which were fabricated through a “rectangular slit die extrusion–hot stretching–quenching” process. For comparison, the conventional PET/HDPE blends were also obtained using the same processing operation but without hot stretching. The morphological observation indicated that slit die extrusion and hot stretching successfully made the dispersed PET phase deform in situ into well‐defined microfibrils. The average diameter of the microfibrils increased with the processing cycles. The rheological properties obtained from the parallel‐plate dynamic rheometer suggested that the microfibrillar blends have higher viscosity and viscoelastic moduli (storage and loss moduli) as well as better flow stability than the conventional PET/HDPE blend. More importantly, with the increase in the processing cycles, an increase in yield strength and unchanged tensile modulus were observed for in situ microfibrillar blends, while a decrease in these properties for conventional blend, indicating that the in situ microfibrillar PET/HDPE blends have promising recycling potential.
