Summary: Blends based on poly(ethylene terephthalate), PET, with poly(amino ether) (PAE) contents up to 40% were obtained by the addition of 20% poly(butylene terephthalate) (PBT) to the PET matrix. PBT mixed with PET led to a decrease in the Tm of the matrix that was enough to produce homogeneous blends by mixing in the melt state. Despite the presence of a single peak observed by dynamic‐mechanical analysis, the blends were biphasic, with amorphous phases in which minor amounts of the other component, both reacted and mixed, were present. This presence of minor components gave a fine morphology and significant adhesion that, together with the higher orientation of PAE in the blends, produced blends with a clear synergism in the modulus of elasticity, notched impact strength similar to that of the neat components, and high ductility up to 30% PAE.
Summary: A thermoplastic poly(hydroxyl‐amino ether) polymer (BLOX) was blended with a diglycidyl ether of bisphenol A monomer (DGEBA). This system may be used as a crosslinkable thermoplastic. It means that it may be processed in an extruder like a classic thermoplastic, and cured by etherification reactions initiated by tertiary amine groups of the BLOX in a second step, to produce a material with good mechanical properties. In order to understand and quantify the etherification reactions occurring at high temperature (135 °C), between epoxy groups of the diepoxy and hydroxyl groups of the thermoplastic, a model system was studied based on DGEBA in excess and ethanolamine. In the model system the rate of the etherification reaction was well described by a second‐order kinetic equation. The specific rate constants and the epoxy conversion at the gel were related to the polarity of the reactive medium. The polyetherification occurring in the DGEBA‐BLOX system could also be fitted with a second‐order kinetics. A significant increase in the reaction rate was observed when using high BLOX concentrations.
Summary: The phase and thermal characteristics of blends consisting of linear low‐density polyethylene (LLDPE) (0.7 mol‐% hexene copolymer) and poly(ethylene‐ran‐butene) (PEB) (26 mol‐% butene copolymer) have been investigated using optical microscopy (OM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). An upper critical solution temperature of 162 °C was exhibited. The addition of PEB not only slowed the overall crystallization rate of LLDPE but also changed the distribution of lamellar thickness or perfection of LLDPE crystals. The equilibrium melting temperature of LLDPE in the blends was reduced and kept relatively constant in the bi‐phase state. The blends showed a single‐stage degradation and an intermediate thermal stability between those of the individual components. It could be attributed to their homogeneous states at degradation temperatures and the similar decomposing mechanisms of two components. The kinetic analysis of thermal degradation also confirmed the above results.
Summary: The swelling equilibrium of poly(acrylamide) [PAAm] and poly[acrylamide‐co‐(itaconic acid)] [P(AAm/IA)] hydrogels was studied as a function of temperature and IA content in aqueous solutions of surfactants: sodium dodecyl sulfate (SDS, anionic) and hexadecyltrimethylammonium bromide (HTAB, cationic). P(AAm/IA) hydrogels in water exhibited reentrant conformational transitions depending on temperature, whereas PAAm hydrogels were not affected with the change of temperature. The equilibrium‐volume‐swelling ratio of P(AAm/IA) hydrogels increased sharply in SDS solutions, with an increase of the mole percent of IA. However, in HTAB solution, the equilibrium‐volume‐swelling ratio of these hydrogels decreased with an increase of IA content.
The equilibrium volume‐swelling ratios of the hydrogels in water shown as a function of temperature. 相似文献
Bis(4‐fluoro‐3‐trifluoromethylphenyl)phenylphosphine oxide is synthesized and six new poly(arylene ether)s are prepared by nucleophilic displacement of the fluorine atom on the benzene ring by several diphenols under basic conditions. The products show very high glass transition temperatures of up to 252 °C and very good thermal stabilities of up to 490 °C for 5% weight loss. The polymers display very low heat release rates in the microscale combustion calorimeter test, suggesting good flame retardance. All polymers are soluble in a wide range of organic solvents. Transparent thin films cast from dichloromethane exhibit tensile strengths up to 54 MPa, a modulus of elasticity up to 0.97 GPa and elongation at break up to 47% depending on their exact repeating unit structures.
The present study evaluates the effect of heat treatment on electrospun poly(lactide‐co‐glycolide) fibrous membranes. Both a temperature (75–150 °C) and a treatment time range (5–40 min) are tested. The effect on the fibrous structure is investigated in terms of morphology, showing that with increasing temperature or longer treatment time the fusion of fibres progresses continuously. Additionally, the tensile properties of the various scaffolds deliver results on the effect of increasing fibre‐to‐fibre linkages. Both modulus and yield increase within the heat treatment procedures. The elevated stiffness of the membranes accompanies a loss in porosity. These findings deliver insights into the tailoring of membranes that might be used in the fabrication of customised scaffolds intended for cell culture in tissue engineering.
Nanoporous polyimide films were prepared in two steps. The first step is the preparation of poly(urethane‐imide) films by casting blend solutions containing various weight percentages of poly(amic acid) and phenol blocked polyurethane prepolymer (from 1,6‐hexamethylene diisocyanate and poly(ethylene glycol)). Three poly(amic acid)s were obtained from biphenyltetracarboxylic dianhydride (or) 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride with 1,4‐phenylenediamine (or) 2,5‐dimethyl‐1,4‐phenylenediamine. Poly(urethane‐imide) films were characterized by density and surface energy measurements, AFM, DSC, TMA, mechanical properties and TGA. In the second step, these films were thermally treated above 300 °C to give nanoporous polyimide films. During thermal treatment, less thermally stable urethane domains decomposed, leaving porous polyimide films. The presence of pores was confirmed by scanning electron microscopy (SEM). The dielectric constant of the polyimide film was found to decrease with increasing amounts of urethane content.
The influence of talc loading on phase morphology of PLA/PCL/talc composites and improvement in resulting properties are reported. Talc‐based composites of PLA/PCL blends were prepared by melt blending. SEM analysis demonstrates that PLA appears as discrete domain phase, while PCL acts as a bulk phase in the blend. Talc addition decreases PLA domain sizes and voids in the matrix. This results in significant improvement of oxygen and water vapor barrier properties of composite by 33 and 25%, respectively, at 3 wt.‐% talc loading. DSC shows that talc acted as nucleating agent for PCL phase in the composite and improves its crystallinity. Various theoretical models based on dispersion and filler geometry are used to predict the tensile modulus and oxygen permeability.
Plastic foam with nano‐/micro‐scale cellular structures was prepared from a poly(propylene) (PP)/propylene‐ethylene copolymer (PER) blend by controlling bubble nucleation sites and bubble growth in disperse PER domains. Batch foaming experiments using a CO2 pressure quench method were conducted at room temperature. The bubble size and location were highly controlled in disperse PER domains by exploiting the differences in CO2 solubility and viscoelasticity between the PER domains and the PP matrix. The average cell diameter of PP/PER blend foams can be controlled within 0.5–2 µm by the PP/PER ratio, depressurization rate, and foaming temperature.
Summary: To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetra‐functional epoxy monomer was incorporated into PBT/[ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E‐MA‐GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E‐MA‐GMA and the effect of the epoxy monomer were investigated. It was found that E‐MA‐GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E‐MA‐GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E‐MA‐GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact‐fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt.‐% or more elastomer.
SEM micrographs of freeze‐fractured surfaces of PBT/E‐MA‐GMA blend illustrating the finer dispersion of E‐MA‐GMA in the presence of epoxy monomer. 相似文献
Summary: A novel phosphorus‐containing polymeric retardant, WLA‐3, was synthesized from phenylphosphonic dichloride (PPD) and 2‐(6‐oxido‐6H‐dibenz〈c,e〉〈1,2〉oxaphosphorin‐6‐yl) 1, 4‐benzenediol (ODOPB). The flame‐retardant element, phosphorus, was bonded both in the main chains and in the pendant chains of flame‐retardant polymer molecules, and reached a content of 13.8%. The high phosphorus content and rich aryl group structures of WLA‐3 contribute an excellent flame retardancy to poly(ethylene terephthalate) (PET) without a considerable decrease of mechanical properties. WLA‐3 is also very effective in improving flame retardancy of epoxy resin and unsaturated polyester.
Stable layers of nearly monodisperse spheres of β‐polymorphic poly(vinylidene fluoride) with iridescent properties are prepared. The colloidal crystalline arrays (CCAs) were characterized by optical microscopy, differential scanning calorimetry (DSC), and FT‐IR spectroscopy. FT‐IR spectroscopic and wide‐angle X‐ray scattering (WAXS) studies revealed a β‐polymorphic PVF2 structure, the DSC study showed that the level of crystallinity in the CCA was much higher than that in the melt‐crystallized sample, and UV‐visible spectroscopy showed extinction peaks at 323 and 510 nm in the CCAs. The β‐polymorphic PVF2 structure, along with the optical extinction properties of these CCAs, raises the prospect of their application in optical filters and/or piezoelectric sensors.
Optical micrograph of PVF2 CCA films cast on glass substrates. 相似文献
Summary: Propylene was copolymerized with 10‐undecen‐1‐ol using dimethylsilanylbis(2‐methyl‐4‐phenyl‐1‐indenyl)zirconium dichloride as catalyst and MAO and TIBA as cocatalysts. Comonomer incorporations from 0.1 to 0.9 mol‐% (0.5 to 3.6 wt.‐%) were obtained. These hydroxyl functionalized copolymers were applied as compatibilizers to PP/PA6 blend with a composition of 70/30. For comparison, hydroxyl functionalized polyethylene prepared with metallocene catalyst and commercial MAH grafted ethylene butyl acrylate (E/BA/MAH) and poly(propylene) (PP‐g‐MAH) were also used as compatibilizers. Effects of the compatibilizers on morphology and mechanical and thermal properties of the blends were studied. Enhanced adhesion between the blend components was observed in morphology and dynamic mechanical studies. Although improvement in toughness was not as pronounced as expected, there were indications that the hydroxyl functionalized propylene copolymers prepared with metallocene catalysts could serve as a new type of compatibilizer in polymer blends.
SEM micrograph (5 000×) of an PP/PA6/PP‐co‐OH4 blend. 相似文献
Summary: Hydrogels of high‐molecular‐weight poly(ethylene oxide) (PEO) have been obtained in situ by applying a very simple procedure that involves UV cross‐linking of PEO in aqueous solution. The efficiency of the photoactivated cross‐linking of thin layers of PEO in aqueous solution in the presence of (4‐benzoylbenzyl) trimethylammonium chloride as a photoinitiator has been determined at room temperature and in a frozen state (?25 °C). It was found that the efficiency varies with the concentration of PEO solution, the molecular weight of PEO, and especially with the temperature. When the UV cross‐linking was performed in the frozen state, porous hydrogels with very high yield of gel fraction (above 90%) and high cross‐linking density were obtained. After drying the hydrogels, films of 50–150 μm thickness were prepared. The films swell extremely fast in water and act as asymmetric membranes.
SEM of a dried PEO hydrogel obtained by UV cross‐linking of an aqueous solution at room temperature. 相似文献
Summary: A lignocellulosic flour was obtained by grinding dried cladodes of Opuntia ficus‐indica. It was used as low cost natural filler in PP and the effect of the treatment of the filler with MAPP was also investigated. The morphology and thermal properties of these composites were evaluated by SEM and DSC, respectively. MAPP coating resulted in a better adhesion between the filler and the matrix and higher homogeneity of the material. A decrease of the degree of crystallinity of the PP matrix in presence of the untreated filler was observed. Dynamic mechanical analysis and tensile properties were also studied. High‐strain tensile properties display enhanced mechanical properties for MAPP treated‐based composites only. When conditioned in highly moist atmosphere (98% RH), both the water uptake and water diffusion coefficient decrease when the filler was treated. These effects were ascribed to the promoting interfacial adhesion induced by the coating treatment. In liquid water, this increased adhesion between the filler and the matrix results in a higher weight loss of the material. It is due to the removal of the grafted polymer from the material during the dissolution of part of the filler.
SEMs of freshly fractured surface for a PP film filled with 10 wt.‐% of MAPP treated OFI cladode (top) and calcium oxalate crystallite within the PP matrix for a 3 wt.‐% filled composite (bottom). 相似文献
Plastic foams with nano/micro‐scale cellular structures were prepared from poly(propylene)/thermoplastic polystyrene elastomer (PP/TPS) systems, specifically the copolymer blends PP/hydrogenated polystyrene‐block‐polybutadiene‐block‐polystyrene rubber and PP/hydrogenated polystyrene‐block‐polyisoprene‐block‐polystyrene. These PP/TPS systems have the unique characteristic that the elastomer domain can be highly dispersed and oriented in the machine direction by changing the draw‐down ratio in the extrusion process. A temperature‐quench batch physical foaming method was used to foam these two systems with CO2. The cell size and location were highly controlled in the dispersed elastomer domains by exploiting the differences in CO2 solubility, diffusivity, and viscoelasticity between the elastomer domains and the PP matrix. The average cell diameter of the PP/TPS blend foams was controlled to be 200–400 nm on the finest level by manipulating the PP/rubber ratio, the draw‐down ratio of extrusion and the foaming temperature. Furthermore, the cellular structure could be highly oriented in one direction by using the highly‐oriented elastomer domains in the polymer blend morphology as a template for foaming.
Summary: The combustion performance of poly(butylene terephthalate) (PBT) can be improved by the addition of red phosphorus provided it is intermolecularly cross‐linked upon irradiation with 60Co γ‐rays in the presence of triallyl cyanurate (TAC). At a content of 3 or 4 wt.‐% the latter significantly promotes cross‐linking in the presence of air. From combustion tests with samples containing red phosphorus (Pred) and having been γ‐irradiated in the presence of TAC it turned out that an improved fire resistance of PBT is achieved if the red phosphorus content is at least 12.5 wt.‐%. In this case test samples were self‐extinguishing and the UL 94 rating corresponded to V‐1. Product analysis and thermal gravimetric analysis revealed that Pred stimulates aromatization and charring. These processes involve the reaction of Pred with the polymer. 31P NMR spectroscopy revealed that the residue contained chemically bonded phosphorus.
Decomposition of anhydride groups resulting in phenyl radicals. 相似文献
The reinforced poly(propylene) (PP)/poly(ethylene terephthalate) (PET) in‐situ fiberized composites were prepared by extrusion‐drawing‐injection molding. The influences of PET weight fraction (fw) on the PET fiberization, phase morphology, and mechanical properties of the composites, together with their functional mechanisms were studied by contrast to the normal‐blended materials without drawing. The results show that as the fw rises from 0 to 20%, the number of PET fibers increases, whereas their diameter and dispersity decrease till fw = 15% and then increase, and the number of remained PET particles tends to rise. These changes of PET fiberization and phase morphology with fw were attributed to the consequence of the combined actions of breakup, coalescence, and deformation of the PET dispersed phase in the PP matrix during the extrusion drawing. Correspondingly, the tensile strength (σt) and Young's modulus (E) of the in‐situ composites increase till fw = 15% and then decrease, with maximum gains of σt and E of about 20 and 70% relative to the neat PP, respectively. This σt/fw relation was ascribed to the counterbalanced result between the reinforcing effect of the dispersed phase on matrix and the interfacial flaw effect of two immiscible phases, while the E/fw relation was considered as a representation of the rigidizing effect of the fibers on the matrix being controlled by both their number and diameter.
In‐situ PET fibres (PET/PP = 85/15) in an as‐drawn filament. 相似文献
It is still not clear why the long‐term properties of plastic weld seams can only be differentiated by the very expensive medium tensile creep tests. One hypothesis for justifying this is based on the change in the structure of the weld seam surroundings, another cites the consumption of antioxidants and the following ageing in the weld seam area to be responsible for this. Butt‐welded weld seams made of poly(propylene) were systematically produced under different process parameters. Corresponding to the particular hypothesis, these weld seams were then analyzed in various ways to find correlations or to prove one of the hypotheses. Regarding their short‐term weld seam quality, the analyzed weld seams could not be differentiated through short‐term tensile or short‐term bend test. However, the medium tensile creep tests showed significant differences in both time until failure and long‐term weld seam quality. Under long‐term loading, the start of the brittle crack could be detected in most weld seams in the fine spherulite‐zone or between this zone and the area of the flow lines. This demonstrated again that only long‐term tests are suitable for examining different weld seam qualities. Depending on the welding parameters, times until failure decline with increasing heated‐tool temperature and heating time. Though these parameters lead to a higher consumption of antioxidants in the weld seam, a degradation was not detected in the breaking area. In fact, increasing heated‐tool temperatures and heating times, as well as higher joining pressures lead to a change in the internal structure of the material. This can be seen in morphological structure analyses in the larger bend of the entire weld seam area. A larger bend, however, correlates with higher residual stresses in the weld seam. In the medium tensile creep tests, these residual stresses as well as the tensile stress in the border region and the compressive stress in the middle are superimposed by the tensile stress resulting from the test stress. Thus a greater bend of the weld seam area and higher residual stresses in the weld seam itself lead to shorter times until failure in medium tensile creep tests.
Schematic representation of the formation of residual stresses in a weld seam and residual stresses in the different bended weld seam areas. 相似文献
Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO5 nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO5 mineral pre‐treated by AlMe3, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.
SEM image of the fractured surface of a PCL‐TiNbO5 nanocomposite film. 相似文献
