Wet-air oxidation of p-nitrophenol

Summary Wet air oxidation rates of p-nitrophenol in the presence of excess oxygen, at different temperatures and oxygen pressures conditions were investigated. The experiments were carried out at between 120 and 200^oC and at 1.0-3.0 MPa partial pressures of oxygen, in a glass vessel inserted in a stainless steel reactor. Initial p-nitrophenol concentration was 3.59x10^-4 mol/L. Copper sulfate (CuSO₄.5H₂O) was used as a catalyst. Presence of Cu²⁺ ions in the reaction medium accelerated oxidation reaction slightly. Oxidation kinetics have also been investigated with respect to p-nitrophenol disappearance and TOC results.     

Nitric acid oxidation of irradiated polyethylene

Samples of high-density polyethylene were irradiated with x-rays and oxidized with concentrated nitric acid to determine the location of unsaturated groups. Vinyl groups initially present in the polymer were rapidly oxidized to the extent of 85% and are assumed to be excluded from the crystals. Vinylene groups show a rapid oxidation followed by slow oxidation. The initial oxidation is about 35%, which is slightly greater than the 25% amorphous content of the polymer prior to irradiation. Diene groups are rapidly oxidized by nitric acid but are formed at about the same rate in crystalline and amorphous samples. This is interpreted to indicate that diene groups are formed throughout the polymer but form large defects in crystalline regions and are accessible to oxidation. Defects formed in crystalline regions during irradiation lower the melting point to a greater extent than predicted by the mole fraction of noncrystallizable units.     

Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends

A systematic investigation of the dynamic mechanical properties of high-density polyethylene (HDPE)/high-impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.     

Miscibility of polycaprolactone/chlorinated polyethylene blends

Blends of polycaprolactone (PCL) with chlorinated polyethylenes (PECls) having chlorine contents of 25, 30, 36, 42, and 48% by weight were prepared and studied by differential scanning calorimetry and small-angle light scattering (SALS). It was found that blends made with PECls containing 30% or more chlorine are completely miscible with PCL (a single glass transition temperature T_g is found) while the PCL/PECl(25) blends are immiscible. PCL crystallizes in the miscible blends at any composition and it has an enthalpy of fusion which decreases only slightly with PECl content. Blends in the PECl composition interval of 0–80% are spherulitic, as shown by SALS, but a rodlike morphology is found at the 85% composition and dispersed crystals are observed at higher compositions. It is suggested that the k parameter of the Gordon-Taylor equation can be taken as a measure of the strength of the specific interaction between PCL and PECl. Low values of k (0.26 and 0.35) are found for PCL/PECl blends but a higher value of k (0.51) has been reported for PCL/poly(vinyl chloride) (PVC) blends, indicating a stronger interaction in the latter mixtures. In agreement with these findings poly(α-methyl-α-n-propyl-β-propiolactone) and poly(valerolactone) are not miscible with PECl, whereas they were previously shown to be miscible with PVC.     

Kinetic patterns for thermal oxidation of binary and ternary blends based on polylactide and polyethylene

Russian Chemical Bulletin - The effect of introduced aged low density polyethylene (LDPE-A) on structure and properties of mixed blends based on polylactide (PLA) and low density polyethylene...     

Effect of metals on melt oxidation of polyethylene

Oxidation of polyethylene (PE) melts in contact with metals (Cu, Pb, Au, Al, Zn, Ag) has been studied by infrared spectroscopy and differential thermal analysis (DTA). These metals may be divided into two groups, depending on their activity for oxidizing PE: namely, high-activity metals (Cu, Pb, Ag, Zn) and low-activity metals (Al, Au). During the oxidation of PE in contact with high-activity metals dissolution of the surface layer of metal is observed with accumulation of metal-containing compounds (salts of carboxylic acids) in the bulk of the polymer. With low-activity metals these phenomena are not observed. The rate of oxidation of PE on low-activity metals approaches the oxidation rate of nonmetals (polytetrafluoroethylene and inorganic glass). With certain high-activity metals (Cu, Pb) the process of oxidation is accelerated only in the early stage of oxidation; then the oxidation rate slows down and the oxidation process ceases. PE films separated from metal after being oxidized on it possess chemical memory, i.e., their oxidation rate depends on the nature of the metal with which they had been in contact, and on the duration of the contact oxidation. The effect of salts of carboxylic acids (metal stearates) on the oxidation of PE melts was also studied. Based on the data obtained, it is concluded that the rate of oxidation of PE melts on high-activity metals is controlled by metal-containing compounds which are the products of contact reactions.     

Compatibilizing effect of isocyanate functional group on polyethylene terephthalate/low density polyethylene blends

To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET microdispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447–453, 1998     

Photooxidative behaviour of polyethylene/polyamide-6 blends

The photochemical behaviour of several polyethylene/polyamide-6 blends was studied under conditions of artificial accelerated weathering. Particular attention was paid to five different compositions ranging from pure polyethylene to pure polyamide with blends of PE/PA-6 of various compositions: 75/25, 50/50 and 25/75 wt/wt%. Analysis by infrared spectroscopy of the chemical modifications caused by photooxidation showed that exposing the polyethylene/polyamide-6 blends to UV-light irradiation led to the formation of oxidation photoproducts in both polymer phases. In agreement with both the mechanical and spectroscopic analyses, the photooxidation rate of the blends was observed to be much higher than that of the homopolymers. The results given in this paper suggest that photooxidation of the PE/PA blends starts in the polyamide phase and that the subsequent photooxidation of the polyethylene phase may be initiated by the radicals coming from the oxidation of PA.     

Researches on the aromatic azo compounds The oxidation of p-dimethylamino-phenylazo-pyridines

This paper concerns the mono-oxidation of the three isomeric p-dimethylamino-phenylazopyridines by perbenzoic acid. The 2-isomer leads only to the amino-oxide; the 3-isomer yields mainly the amino-oxide, and small amounts of the 1-oxide. With the 4-isomer a mixture was obtained, from which only the 1-oxide was isolated. These results are discussed on the basis of the absorption spectra and resonance structures of the azo compounds.     

Liquid phase oxidation of p-chlorotoluene to p-chlorobenzaldehyde over cobalt-doped mesoporous titania with a crystalline framework

Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated.     

Elongational rheometry of polyethylene terephthalate/bisphenol-a polycarbonate blends

The elongational deformation properties of polyethylene terephthalate (PETP) and bisphenol-A polycarbonate (PC) blends were determined using a Rutherford elongational rheometer. The effects of temperature (in the thermoelastic region) and strain rate were studied on blends containing up to 50% PC. Addition of low levels of polycarbonate permits the thermoelastic processing of PETP over a wider temperature range. PETP is particularly sensitive to changes in temperature. Over the range studied, the effect of strain rate on elongational deformation is not very marked. However, the deformation temperature changes the strain levels at which strain stiffening occurs, an important observation in respect of processing and optimisation of physical properties of uniaxially oriented products. The effect of the addition of a phenoxy resin on the blend was studied, and although TEM analysis suggests that it did not compatibilise the blend, it did increase the available extension at higher temperatures.     

The compatibilization effect of ethylene/styrene interpolymer on polystyrene/polyethylene blends

In this study, ethylene/styrene interpolymer (ESI) was used as compatibilizer for the blends of polystyrene (PS) and low‐density polyethylene (LDPE). The mechanical properties including impact, tensile properties, and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Impact measurements indicated that the impact strength of the blends increases slowly with LDPE content up to 40 wt %; thereafter, it increases sharply with increasing LDPE content. The impact energy of the LDPE‐rich blends exceeded that of pure LDPE, implying that the LDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI. Tensile tests showed that the yield strength of the PS/LDPE/ESI blends decreases considerably with increasing LDPE content. However, the elongation at break of the blends tended to increase significantly with increasing LDPE content. The compatibilization efficiency of ESI and polystyrene‐hydrogenated butadiene‐polystyrene triblock copolymers (SEBS) for PS/LDPE 50/50 was further compared. Mechanical properties show that ESI is more effective to achieve a combination of LDPE toughness and PS rigidity than SEBS. The correlation between the impact property and morphology of the ESI‐compatibilized PS/LDPE blends is discussed. The excellent tensile ductility of the LDPE‐rich blends resulted from shield yielding of the matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2136–2146, 2007     

Polymer blends—I. Mechanical and morphological behaviour of polyethylene/polyvinyl chloride blends

As part of a fundamental study of the behaviour of mixed plastics during reprocessing and in service, blends of low density polyethylene (LDPE) and polyvinyl chloride (PVC) have been investigated. It was found that Young's modulus increased steadily from pure LDPE to pure PVC whereas both tensile strength at break and elongation at break passed through a minimum at about 5% PVC. Optical and scanning electron microscope studies have related this mechanical behaviour to morphological changes in the two phase system under stress.     

An efficient aerobic oxidation for p -xylene to p -toluic acid catalyzed by cobalt (II) hydroxamates with benzo-15-crown-5

Cobalt (II) hydroxamates with the benzo-15-crown-5 (B15C5) pendant have been synthesized and characterized. These complexes were successfully employed to the oxidation of p-xylene to p-toluic acid with air at 110°C under normal atmospheric pressure. The effects of the B15C5 pendant, the length of chain bonding of B15C5 in these complexes and the addition of alkali metal ions on the oxidation for p-xylene are also investigated by the comparison with the crown-free analogue.     

Phase change materials based on low-density polyethylene/paraffin wax blends

Phase change materials, based on low-density polyethylene blended with soft and hard paraffin waxes respectively, were studied in this paper. DSC, DMA, TGA and SEM were employed to determine the structure and properties of the blends. The blends were able to absorb large amounts of heat energy due to melting of paraffin wax, whereas the LDPE matrix kept the material in a compact shape on macroscopic level. The hard paraffin wax was, however, much more miscible with LDPE because of co-crystallization than the soft paraffin wax. LDPE blended with hard paraffin wax degrades in just one step, while blends containing soft paraffin wax degrade in two distinguishable steps. SEM showed completely different morphology for the two paraffin waxes and confirmed the lower miscibility of LDPE and soft paraffin wax. DMA analyses demonstrated the toughening effect of the waxes on the polymer matrix. This technique was also used to follow the thermal expansion as well as the dimensional stability of the samples during thermal cycling. The most visible expansion could be seen in the first cycle, probably due to a totally different thermal history of the sample. With further cycling the dimensions stabilized after two and four cycles for soft and hard paraffin wax, respectively. Controlled force ramp testing on DMA confirmed poor material strength of the blends containing soft wax, especially at temperatures above wax melting.     

Nonisothermal crystallization kinetics and melting behavior of bimodal medium density polyethylene/low density polyethylene blends

Nonisothermal crystallization kinetics and melting behavior of bimodal-medium-density- polyethylene (BMDPE) and the blends of BMDPE/LDPE were studied using differential scanning calorimetry (DSC) at various scanning rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of BMDPE. The BMDPE DSC data were analyzed by the theory of Ozawa. Kinetic parameters such as the Avrami exponent (n), the kinetic crystallization rate constant (Z_c), the peak temperatures (T_p) and the half-time of crystallization (t_1/2) etc. were determined at various scanning rates. The appearance of double melting peaks and the double crystallization peaks in the heating and cooling DSC curves of BMDPE/LDPE blends indicated that the BMDPE and LDPE could crystallize respectively.     

Preparation and peracid oxidation of 2-(p-dimethylamino)-styryl-pyridine

The title compound is obtained by reduction of its 1-oxide, prepared in fair yield by condensation of 2-picoline-1-oxide and p-dimethylamino-benzaldehyde in pyridine in the presence of KOH. The results of the stepwise oxidation by perbenzoic acid show that the oxygen atom adds first to the amino nitrogen, appearing to indicate that the interaction effects between the dimethylamino group and the pyridine ring are small.     

热致液晶性羟乙基纤维素醋酸酯/聚乙烯共混物的热行为

本文用DSC方法研究了热致液晶性羟乙基纤维素醋酸酯（HECA）与聚乙烯（PE）共混物的相转变过程．结果表明，HECA与PE不相容，但当HECA含量＞50％时，则明显影响PE的结晶过程，使其在冷却过程中出现多重结晶。将共况物在393K退火，可改善PE结晶缺陷；在425K退火，可提高HECA液晶相的取向度。     

Structural characteristics of some high density polyethylene/EPDM blends

Blends of ethylene propylene diene terpolymer rubber (EPDM) with high density polyethylene were obtained by melt mixing. Mechanical properties of the composites, tensile strength, hardness, resilience, elongation at break, 100% modulus and tear strength were determined. Differential scanning calorimetry and wide angle x-ray diffraction were employed to study melting behavior and crystalline structure. The surface properties were analyzed using contact angle determinations. Also, compatibilization with PE-g-MA or dynamical vulcanization using phenolic resins was applied to obtain improved mechanical properties. It was found that the crystalline structure of HDPE was not changed during blending. The vulcanized composite presents a lower degree of crystallinity. Elongation at break and hardness were significantly increased for composites containing compatibilizing agent. The morphology of EPDM composites was studied by atomic force microscopy.     

Characterization and comparison of metallocene-catalyzed polyethylene/thermoplastic starch blends and nanocomposites

This study presents characterization and comparison of the properties of metallocene-catalyzed polyethylene (mPE)/thermoplastic starch (TPS) blends and nanocomposites, which contain maleic anhydride-grafted mPE (mPE-g-MA) compatibilizer and 20A-reinforced mPE-g-MA nanocompatibilizer, respectively. The results from X-ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that mPE/TPS blend-based nanocomposites were achieved with the incorporation of the nanocompatibilizer. Clay 20A was also noted to preferentially locate within the interface between mPE and TPS, as well as within the mPE matrix in the nanocomposites. The crystallization temperature of mPE increased in the blends and nanocomposites, confirming the role of TPS and 20A as nucleating agents for mPE. However, the melting temperature and the glass transition temperature of mPE hardly changed in the blends and the nanocomposites. Clay 20A also served as a heat barrier, which greatly increased the thermal stability of the nanocomposites. There was a maximum increase of up to 36% and 40% obtained in tensile strength and Young's modulus, respectively, for the nanocomposites as compared to that of the blend counterparts. It was also determined that nanocomposites have a slightly lower water uptake character as compared to the blends. Hopefully, the results presented here can pave the way for further researches on the development and innovation of environmentally friendly polymeric systems.