Measurement of oxidation stability of polyolefins by thermal analysis

Differential thermal analysis (DTA) is well known for measuring temperatures and heats of physical and chemical transitions in materials. Recent development work on improved stabilization systems for polyolefin wire insulations has required fast procedures for measuring the performance of stabilization systems. Isothermal DTA procedures have been developed into routine tools for measuring stability of polyolefins by determining the oxidative induction time at elevated temperatures. Oxidative induction time has been used to study the stability of polyethylene and polypropylene in raw material form and on wire. The dependence on temperature and antioxidant concentration have been measured. Effects of oxidation catalysts, catalyst deactivators and various environmental exposures are readily observed. Techniques and apparatus have been developed for simultaneous testing of a multiplicity of samples, providing for economical large scale use of the method.     

Effects of thioether content on thermal and optical properties of polyamides

4,4′‐Bis(4‐chloroformylphenylthio)benzene was synthesized in two steps and was reacted with diamine‐containing thioether and amide units to prepare a polyamide containing high contents of thioether groups. The intrinsic viscosities of the polyamides were 0.76–0.87 dL g^?1. These polyamides had excellent thermal properties, with glass transition temperatures of 234.8–269 °C and initial degradation temperatures of 461–469.7 °C. They showed improved solubility in polar aprotic solvents and could form moderate strength films with a tensile strength of 75.2–111.6 MPa and storage modulus of 1.0–1.3 GPa (at 220 °C). These polymer films also had good optical properties, including an optical transmittance of the aromatic polyamide film at 450 nm that was higher than 90%. Additionally, the high quantity of thioether units provided the polymers with high refractive indices of 1.700–1.704 and low birefringences of 0.007–0.008. Copyright © 2012 Society of Chemical Industry     

N-Propargyl-substituted aromatic polyamides: preparation and thermal crosslinking

A series of high molecular weight aromatic polyamide copolymers derived from 4,4′-bis(methylamino)-diphenylmethane, 4,4′-bis(propargylamino)diphenylmethane and isophthaloyl dichloride was prepared as potential candidates for use as matrix resins in Kevlar^(R) fibre composites. These polyamides, which contain pendant propargyl groups, underwent facile crosslinking at 280°C as evidenced by dramatic increases in their glass transition temperatures (T_g) and accompanying loss of solubility. Other attempts to effect crosslinking by exposure to ultraviolet light, electron beam or gamma radiation were unsuccessful.     

Effects of metal chelates on the oxidation of polyolefins at high temperatures

The oxidation of carboxy-terminated polybutadiene (CTPB) and polypropylene (PP) has been investigated at temperatures above 150°C. Studies have also been made of the effects on the oxidation of these polymers of a number of transition metal chelates, namely, the bis(3,5-diisopropyl salicylato) (DIPS) derivatives of Co(II), Ni(II) and Cu(II), bis(3,5-diisopropyl salicylato) hydroxyaquo Cr(III), the bis(N-n-butyl salicylaldimino) (NBS) compounds of Cu(II) and Ni(II), and bis(stilbene dithiolato)nickel (II) (NiSDT). At the temperatures concerned, the antioxidant activity of some of the chelates, in particular the DIPS compounds, was limited by their thermal stability. NiSDT was found to be a uniquely effective antioxidant at temperatures up to ～290°C. Mechanisms have been proposed to account for the dual role, as both catalysts and inhibitors of thermal oxidation, of the DIPS and NBS chelates.     

Effect of the melt flow index and melt flow rate on the thermal degradation kinetics of commercial polyolefins

In this study, several polyolefins, including different grades of polypropylene (PP), high‐density polyethylene, linear low‐density polyethylene, and low‐density polyethylene, were tested by thermogravimetric analysis (TGA), and the relationships of their melt flow index (MFI) and melt flow ratio (MFR) values to the thermogravimetry (TG) curves, differential thermogravimetry (DTG) curves, and activation energy of thermal degradation were investigated. Kinetic evaluations were performed by Friedman and Kissinger analysis methods, and the apparent activation energy values for the overall degradation of different grades of polyethylenes (PEs) and PPs were determined. We found that for the samples with lower MFIs, the thermograms shifted to higher temperatures. Meanwhile, a higher activation energy was needed for their thermal degradation. Also, for samples with higher values of MFR, as a means of molecular weight distribution, a lower activation energy was needed for their thermal degradation, and their TGA thermograms shifted to lower temperatures. The breadth of the DTG curves depended on the MFR in the PEs, although MFR had little effect on the DTG curves in the studied PP grades. Among all of the samples studied, the injection‐molding grades with medium MFIs and low MFRs degraded at higher temperatures and showed better thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Chlorination and oxidation of aromatic polyamides. I. Synthesis and characterization of some aromatic polyamides

The synthesis is described of some aromatic polyamides based on unsubstituted, and methyl-, carboxy-, and sulfo-substituted diamines by interfacial polycondensation. Some of them are crosslinked and some of them contain heterocyclic aromatic rings. Their chemical structures are characterized by IR and ¹³C solid-state NMR spectra and the spectra are interpreted. © 1996 John Wiley & Sons, Inc.     

Biowastes from wine as natural additive of polyolefins: Thermo‐ and photo‐oxidation efficiency

Biowastes generated from agricultural industries constitute a new source for added value products that can be used in the polymer industry. Grape marc, a residue of the winery industry, is well‐known to be a rich source of polyphenols. The present work reports the use of polyphenol cocktail extracted from black Pinot grape marc as natural antioxidant in polyolefins. The purpose is to advance in the field of green stabilizer, by using an innovating approach based on the direct use of an efficient cocktail rather than a single original molecule to stabilize polymer. The antioxidant efficiency of polyphenol cocktail is measured against photo‐ and thermo‐oxidation conditions in the well‐known polypropylene polyolefin. Attention is paid to molecular structure evolution by rheology, and the efficiency to delay oxidation by‐product formation is monitored with infrared. The results confirm that cocktail approach is a promising route to develop green stabilizers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46607.     

Hysteretic thermal behavior of amorphous semi-aromatic polyamides

The hysteretic thermal behavior of two amorphous semi-aromatic polyamides, subjected to cyclic loading at high stress levels, has been investigated. The two polymers, called 1I and 1.8T, were selected with regards to chain mobility and plastic deformability considerations. This work reports the exothermal response of these materials to high level cyclic stress (of the order of σ_y), with emphasis on the initial thermal peak, normally observed in commercial polycarbonate (PC) and not in commercial polymethylmethacrylate (PMMA). The investigated materials exhibit noticeable initial thermal peaks, which are similar, to some extent, to those observed in PC. The present results suggest that chain mobility may indeed be partially responsible for the initial exothermal peak, thus supporting the hypothesis that it may be related to the transition from shear deformation zones to chain disentanglement crazing.     

Aerobic photochemical oxidation in mesoporous Ti-MCM-41: epoxidation of alkenes and oxidation of sulfides

Irradiation with visible light of a secondary alcohol, benzhydrol, in the presence of molecular oxygen within a titanium-substituted mesoporous molecular sieve, Ti-MCM-41, led to the formation of the α-hydroperoxoalcohol and then hydrogen peroxide. The peroxide species reacted in situ with alkenes and sulfides and led to the titanium center catalyzed selective formation of epoxides from alkenes and sulfoxides from sulfides. The cascade of reactions represents a new method for the photoactivation of oxygen in the presence of alcohols. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of molecular weight distribution on flow properties of commercial polyolefins

The aim of this work is to investigate the effects of molecular weight distribution on some conventional flow properties of polyolefins like melt flow index, melt flow ratio, and power law index. The study is designed in two steps. First, the statistical correlation analysis was carried out for proper choice of input variables for each output property and to find the most relevant mathematical forms of the considered parameters for the modeling section. Then the considered property was correlated to the entire molecular weight distribution using spline functions. The best fit was achieved by variation of the number of spline nodes and their values. The proposed methodology is able to be coupled with a polymerization model to correlate the polymerization conditions to the final properties of the product and design a polymerization control loop. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

聚烯烃产品中低聚物的分析

通过对CX（淤浆均聚 + 淤浆共聚 + 离心脱除低聚物）工艺产品中离心机脱除低聚物前后聚合物的分子量分布的分析对比,得出离心机可以脱除低聚物,最终产品中低聚物含量降低;通过力学和热稳定性的研究,证明了产品经离心机脱除低聚物后力学及热性能均有所提高;利用核磁分析了烯烃淤浆聚合工艺难以生产高共聚单体含量的聚乙烯牌号的原因。     

Kinetic effects of silica nanoparticles on thermal and radiation stability of polyolefins

The effects of γ-irradiation as the accelerated degradation procedure were analyzed for the evaluation of material stability. Low density polyethylene, polypropylene and ethylene–propylene terpolymer were studied in formulations with SiO₂ nanoparticles (2 and 5 wt%) or as neat materials. High energy irradiation (up to 100 kGy) has revealed a faster increase in the absorption of carbonyl band in comparison with the corresponding change in hydroperoxide band. The three studied materials present increased oxidation rates as the received energy transferred from incidental rays is enhancing, because the thermal regime of degradation depends on the structural characteristics, namely initial number of tertiary carbon atoms and unsaturation level. The fate of hydroperoxides as oxidation initiators is discussed.     

Effect of oxidation progress of tributylborane on the grafting of polyolefins

Effect of the oxidation progress of tributylborane on the grafting reaction of PMMA onto high-density polyethylene (HDPE) and isotropic polypropylene (iPP) surface with tributylborane as initiator was studied in detail. The oxidation of tributylborane was triggered by the slow diffused oxygen or exposed contact to oxygen, so that the oxidation progress of tributylborane would be different. The grafted polyolefin surfaces were characterized by attenuated total reflection infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopic (XPS), scanning electron microscope (SEM) and so on. The results of ATR-IR spectroscopy and XPS analysis suggested that PMMA could be grafted onto polyolefin surfaces successfully through these two ways, but the grafting degrees were varied due to the different oxidation progresses of tributylborane. The surface morphologies of the polyolefin indicated the different grafting degrees as a result of different oxidation progress of tributylborane. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Singlet oxygen oxidation of lipids resulting from photochemical sensitizers in the presence of antioxidants

Singlet oxygen produced by photochemical sensitizers may play an important role in the oxidation of lipids in foods. Therefore, we studied the singlet oxygen oxidation of lipids and the scavenging ability of antioxidants. Singlet oxygen was generated using the photosensitizer rose bengal. The oxidation products of lipids and antioxidants were separated by high-performance liquid chromatography and monitored using post-column chemiluminescence and/or iodometric detection. The competitive reaction rates of various antioxidants and lipids were studied to elucidate the roles played by antioxidants in the prevention of food oxidation by singlet oxygen.     

Effects of dispersed phase composition on thermoplastic polyolefins

Ternary blends of polypropylene (PP), ethylene–octene copolymer (mPE), and high‐density polyethylene (HDPE) were prepared based on the phase behavior and physical properties of mPE/HDPE binary blends, and the results were interpreted in terms of morphology and both rheological and mechanical properties of the ternary blends as well as the binary blends. It was found that when mPE encapsulates HDPE in the PP matrix, compared to the encapsulation of mPE by HDPE, better blend properties were obtained, presumably because of the compatibilizing effect of mPE between PP and HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 179–188, 2004     

Valorization by thermal cracking over silica of polyolefins dissolved in LCO

A study has been made of the cracking of polyethylene (PE) and polypropylene (PP) (which are the main components of post-consumer plastic wastes) dissolved in the Light Cycle Oil (LCO) product stream of a commercial Fluid Catalytic Cracking (FCC) unit. The cracking has been carried out on a mesoporous silica (pore size between 3 and 30 nm) in the 723–823 K range. This strategy for upgrading plastics and solvents together avoids heat transfer limitations and other problems inherent to the cracking of solid plastics. The polyolefins are transformed mainly into the components that make up the pool of gasoline (C₅–C₁₂). Furthermore, the incorporation of polyolefins has a synergistic effect on the cracking of LCO and causes a major decrease in the content of aromatics of the pool of gasoline and an increase in the content of olefins, paraffins and i-paraffins.     

Graphene layers from thermal oxidation of exfoliated graphite plates

Graphite platelets of 1–5 μm in diameter consisting of a few graphenes were generated from commercially available exfoliated graphite by ultrasonic treatment in benzene (1 mg material in 20 ml solvent) for 3 h. Droplets from the suspension were dispersed on silicon wafer. The graphite platelets were characterized by atomic force microscopy (AFM). Successive oxidation of the sample was carried out at 450–550 °C in air. AFM measurements showed that the thermal oxidation removed 2–3 graphenes from the platelets and it left behind single graphene layers.