1999 рік

The effect of the rubber content on the deformation and impact behaviour of polypropylene–EPDM rubber blends is studied. The blends are made on a twin screw extruder. The rubber content ranged from 0 to 40 vol.%. The tensile modulus and the yield stress decrease linearly with increasing rubber content. The crystallinity of the PP phase as measured with differential scanning calorimetry did not change with rubber content. The fracture behaviour was studied with a notched Izod impact test and with an instrumented single edged notched tensile test at 1 mm/s and 1 m/s. The blends were studied in temperature range from 280 to 1208C. The brittle–ductile transition temperature (Tbd) decreases with increasing rubber content from 858C for pure polypropylene to 2508C for a 40 vol.% blend, a shift of 1358C. The Tbd with the notched Izod test and the SEN at 1 m/s are very comparable. The Tbd for the SEN at 1 mm/s if compared to the 1 m/s are at a 308C lower temperature. The brittle–ductile transition at the low test speed is gradual, while at high test speeds the transition is abrupt, discontinuous. A good criterion for the onset of ductility is the crack propagation displacement.

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The behavior of a closed co-extrusion process for the preparation of gradient-index polymer optical fibers is modeled theoretically. In particular, the effects of the essential parameters such as the volume ratios of the inner/outer layer, diffusivities of monomers, diffusion length, and monomer concentrations, on the distribution of refractive index (RI) are examined. The applicability of the model derived is justified by comparing with the experimental results from the literature. The latter are gathered from a system using poly(methyl methacrylate) as the host polymer, and methyl methacrylate and benzyl methacrylate as monomers. Our results show that the RI distribution of the fibers prepared by the co-extrusion process can be significantly adjusted by the essential parameters.

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Solid-state 13C-NMR analyses of the structure and chain conformation have been carried out for a main-chain thermotropic liquid crystalline polyether which was polymerized with 4,4 0 -dihydroxy-a -methylstilbene and 1,9-dibromononane. This sample was crystallized by cooling from the isotropic melt through the nematic liquid crystalline state. Differential scanning calorimetry measurements and polarizing optical microscopic observation have confirmed that the nematic liquid crystalline phase clearly exists in the wide range of temperature in both heating and cooling scans. T1C analyses have revealed that each resonance line of the methylene sequence contains three components with different T1C values and these values become significantly longer with decreasing temperature. The evaluation of 13C chemical shifts considering the g -gauche effect indicates that methylene sequences for the two components with the longer T1C values adopt the specific overall conformation, in which successive trans-gauche exchange and isolated trans conformations coexist. In contrast, all the C–C bonds of the methylene sequence for the component with the shortest T1C value, which corresponds to the supercooled liquid crystalline component, is in the rapid trans-gauche exchange conformation, reflecting the conformation in the liquid crystalline state.

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Polypropylene–EPDM blends were prepared on a twin screw extruder with a rubber content 0–40 vol%. On these materials the yield strength and the notched tensile behaviour was studied as function of test speed (10 24 –10 m/s). With an infrared temperature camera the heat development in the notched samples is studied as function of test speed. On fractured materials the structure of the deformation zone is studied in the middle of the sample, perpendicular to the fracture plane. The yield strength increases with the strain rate and at high rates this increase is stronger. The fracture energy shows a complex relationship with test speed. At low test speeds the fracture energy decreases rapidly with test speed. At intermediate test speeds however the fracture energy increases with increasing test speed. On the micrographs of the high speed deformed samples the formation of a melt zone was observed. The temperature rise in the notched samples starts at approximately 10 25 m/s, and increases almost linearly with the logarithm of the test speed. At 10 m/s a surface temperature increase to 908C was observed.

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For a binary blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile, the lower critical solution temperature (LCST) type of phase boundary was determined by thermo-optical analysis. A critical mixture, 80/20 PCL/SAN blend, initially underwent spinodal decomposition (SD) above the LCST and then crystallized at a lower temperature (40°C). Isothermal crystallization was analyzed by differential scanning calorimetry. The longer the SD duration the higher the rate of crystallization. An optimum SD time yielding the highest degree of crystallization was found to exist at a relatively early stage of SD (ca. 5 min). The blend via the optimum time of SD showed the highest melting point. In the blend, a very long and straight crystal lamella was observed by transmission electron microscopy. Thus, the effect of the degree of demixing on the succeeding crystallization was revealed.

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The poly(3-hydroxyoctanoate-co-3-hydroxy-10,11-epoxyundecanoate)s, PHOEs, with epoxide pendant units of 10, 22 and 34 mole% were prepared. The PHOEs were crosslinked with a stoichiometric hexamethylene diamine (HMDA) at 90°C for 0.5–24 h. The crosslinking reaction of PHOE–HMDA system was verified from the glass transition temperature (Tg) increment and the relative storage modulus increment. Higher increment in Tg and relative modulus with increasing the amount of epoxide group in the initial PHOE was observed. Activation energies of the crosslinking reaction were determined by use of the Kissinger and the Ozawa methods. The activation energies for the crosslinking reactions have similar values for each sample, regardless of epoxide content in the PHOEs. The values obtained from the Ozawa method were slightly higher than those from the Kissinger method.

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The effect of the rubber particle size and rubber content on the fracture behaviour of polypropylene–EPR blends was studied at low and high test speeds. The particle size was varied by changing the molecular weight of the EPR phase, and ranged from about 0.5 to around 4.0 mm. The fracture behaviour was determined as a function of temperature by the notched Izod impact test (high test speed) and by a tensile test on notched Izod bars at 1 mm/s (low test speed). At high test speed the brittle–ductile transition temperature (Tbd) increases with increasing particle size. At low test speed the Tbd decreases slightly with increasing particle size. The weight average particle size gave a better correlation with the notched Izod results than the number average particle size. This suggests that the larger particles initiate the fracture more easily.

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The effects of simple shear flow on the phase behaviour of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend, which shows a lower critical temperature (LCST)-type phase diagram, have been studied by cloud point measurements, by using a special shear apparatus. The shear-induced demixing and mixing have been observed for all of the compositions at low and high shear rate, respectively. However, at higher shear rate, the cloud points were independent of the shear rate and almost constant. In addition, the shear effect was found to be composition dependent and the largest change took place near the critical composition. The effects of rotation speed and sample thickness were also studied for the sample of PS/PVME ¼ 30/70. The values of the cloud point were strongly affected by the rotation speed and the minimum of the cloud point systematically shifted to higher shear rate values with increasing rotation speed under the constant sample thickness. The sample thickness was also found to have a pronounced effect on the cloud point under constant rotation speed, where the immiscibility region in the cloud point–shear rate diagram seemed broader with increasing sample thickness. However, the samples of PS/ PVME ¼ 30/70 completely phase separated at 17°C above the quiescent cloud point at high shear rate, regardless of the applied rotation speed and sample thickness.

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Copoly[2,2⬘-bis[1,1⬘-ferrocene]benzoylylene/3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene] (III) was synthesized by two approaches. High molecular weight III was obtained by an acid catalyzed equilibrium condensation of 1,1⬘-bis[1-(3⬘,3⬘,5⬘,5⬘-tetramethyl4-oxa-3,5-disilahexyl)benzoyl] ferrocene (IV), while lower molecular weight III was synthesized by the dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) catalyzed co-oligomerization of 1,1⬘-benzoylferrocene and 1,3-divinyltetramethyl-disiloxane. Ru catalyzed reaction of benzoylferrocene and 1,3-divinyltetramethyl-disiloxane gave 1-[2⬘-ferrocenoylphenethyl]-3-vinyltetramethyl-disiloxane (II), 1,3-bis[2⬘-ferrocenoyl phenethyl]tetramethyldisiloxane (I). The electrochemistry of I, III, and IV have been examined by cyclic voltammetry. These materials show a single reversible oxidation process. The products have been characterized by 1H, 13C, 29Si NMR, IR, UV–Vis spectroscopy, as well as elemental analysis and/or high resolution mass spectrometry with peak matching. GPC, DSC and TGA of the copolymer and co-oligomer III have been determined.

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The deformation mechanism of polypropylene–EPDM rubber blends during fracture was studied by post-mortem SEM fractography. The deformation mechanism was determined for various blend morphologies and test conditions. Brittle fracture merely gives rise to voids, which are caused by voiding of the rubber particles. In the case of ductile fracture, voiding of rubber particles and strong shear yielding of the matrix takes place. In this yielding process these voids become elongated. As the fracture surface is approached the voids are more deformed. At high test speed, in ductile fracture, along the fracture surface a layer is formed without deformation. The thickness of this layer is 10– 100 mm. This layer without deformation indicates that during deformation relaxation of the matrix material in this layer has taken place. With the formation of the relaxation layer the impact energy increases. The relaxation layer has thus a blunting effect. If a blend with large EPDM particles (1.6 mm) is deformed, in the rubber particles now several cavities are formed and these cavities are positioned near the interface with the matrix. It can be expected that it is an advantage to have several small cavities instead of one large cavity. The polypropylene matrix was found to deform by a shear yielding mechanism and multiple crazing was not observed.

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