Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and LBPE/low‐density polyethylene blends

Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and the blends of LBPE/low‐density polyethylene (LDPE) were studied using 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 LBPE and LBPE/LDPE blends. The theory of Ozawa was also used to analyze the LBPE DSC data. Kinetic parameters such as, for example, the Avrami exponent (n), the kinetic crystallization rate constant (Z_c), the crystallization peak temperature (T_p), and the half‐time of crystallization (t_1/2) were determined at various scanning rates. The appearance of double melting peaks and double crystallization peaks in the heating and cooling DSC curves of LBPE/LDPE blends indicated that LBPE and LDPE could crystallize, respectively. As a result of these studies, the Z_c of LBPE increases with the increase of cooling rates and the T_p of LBPE for LBPE/LDPE blends first increases with increasing LBPE content in the blends and reaches its maximum, then decreases as the LBPE content further increases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2431–2437, 2003     

New fluorescent monomers and polymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state. III. Thermogravimetric stability study of the benzazolylvinylene derivatives

Six fluorescent benzazolylvinylene derivatives were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and related molecular parameters. The thermal stability was determined in terms of the steps of degradation and its fitting parameters, such as maximum degradation rate (R_max), maximum degradation rate temperature (T_Rmax), degradation temperature range, which is related to the half‐width at half‐height values (Γ), and the kinetic parameters: activation energy (E_a), pre‐exponential factor (A), and reaction order (n) obtained by Barrett's method. Different organic substitutes and heteroatoms do not play a fundamental role in the thermal behavior of the studied dyes. The compensation effect between pre‐exponential factor and activation energy was confirmed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 495–500, 2006     

Susceptibility of serum lipids to copper-induced peroxidation correlates with the level of high density lipoprotein cholesterol

As a first step in evaluating the significance of our recently developed method of monitoring the kinetics of copper-induced oxidation in unfractionated serum, we recorded the kinetics of lipid oxidation in the sera of 62 hyperlipidemic patients and analyzed the correlation between oxidation and lipid composition of the sera [high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides]. We used six factors to characterize the kinetics of oxidation, namely, the maximal absorbance of oxidation products (OD_max), the maximal rate of their production (V _max), and the time at which the rate was maximal (t _max) at two wave-lengths (245 nm, where 7-ketocholesterol and conjugated dienic hydroperoxides absorb intensely, and 268 nm, where the absorbance is mostly due to dienals). The major conclusions of our analyses are that: (i) Both OD_max and V _max correlate positively with the sum of concentrations of the major oxidizable lipids, cholesterol, and cholesteryl esters. (ii). The value of t _max, which is a measure of the lag preceding oxidation and therefore reflects the resistance of the serum lipids to copper-induced oxidation, exhibits a negative correlation with HDL cholesterol. Although this finding accords with the observation of shorter lags for HDL than for LDL, it is apparently inconsistent with the role of HDL as an antirisk factor in coronary heart diseases.     

Characterization of ionomer solutions. I. Division of the concentration region and viscosity–concentration functions

The solution behavior of metal maleate low density polyethylene graft ionomers (LDPE‐g‐MAMe) in extremely dilute and dilute solutions was investigated in this study. The concentration region was divided into three parts because of the different viscosity–concentration relations of these ionomers. The η_sp/C–C relations of zinc maleate low density polyethylene graft ionomers (LDPE‐g‐MAZn) were studied in detail and compared with those of low‐density polyethylene and low‐density polyethylene‐g‐maleic anhydride. Finally, the viscosity–concentration relations of LDPE‐g‐MAMe (Na, K, La) were also studied and compared with one another. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1481–1486, 2001     

Comparison between photocatalytic ozonation and other oxidation processes for the removal of phenols from water

Photocatalytic ozonation (1O₃ + VUV + TiO₂), ozonation (O₃), catalytic ozonation (O₃ + TiO₂), ozone photolysis (O₃ + VUV), photocatalysis (TiO₂ + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry     

Thermal Stability of Gamma Irradiated Low Density Polyethylene Films Containing Hindered Amine Stabilizers

Summary: The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investigated by the oxygen uptake method under constant temperature of 180 °C and normal pressure conditions. The thermo‐oxidation was run using air environment. The sigmoidal dependency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in the thermal degradation process were detected by the derivative procedure applied to the dependencies of oxygen uptake on time. It was found that the kinetic parameters of the thermal degradation process, determined by oxygen uptake, revealed the antioxidant role of HAS in γ‐irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occurring in the ungrafted moiety and the latter taking place after the antioxidant depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoxyamine structure.

Dependencies of oxygen uptake on time at the thermal degradation of LDPE irradiated at 812 kGy. (‐□‐) free of additive; (‐○‐) Tinuvin 123; (‐?‐) Sanduvor PR 31; (‐?‐) Uvasil 299.     

Comparative effects of cobalt carboxylates on the thermo‐oxidative degradation of LDPE films

This article reports the effect of three cobalt carboxylates—cobalt stearate (CoSt₃), cobalt palmitate (CoPal₃), and cobalt laurate (CoLau₃)—on the thermo‐oxidative degradation of low‐density polyethylene (LDPE) films prepared by sheeting process. The carboxylates were blended with LDPE in the concentration range of 0.05–0.2% (w/w). The degradation was monitored by techniques such as FTIR spectroscopy, change in the mechanical properties (tensile strength and elongation at break), viscometry, surface electron microscopy, melt flow index measurements, and apparent density measurements. Studies indicate that films containing these additives are highly susceptible to thermo‐oxidative degradation. Oxygen containing functionalities such as carbonyl and vinyl species are generated on the surface of polyethylene because of thermo‐oxidation, as indicated by FTIR studies. This oxidative process is accelerated in the presence of cobalt carboxylates. The degradation of LDPE was found to increase proportionally with concentration as well as with increasing chain length of the cobalt carboxylate, and follow the order CoSt₃ > CoPal₃ > CoLau₃. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3758–3765, 2007     

The Processes Running during the Induction Period of Inhibiting Oxidation of Polyethylene

Abstract

Oxygen absorption in the induction period of polyethylene oxidation inhibited by a strong amine antioxidant N-phenyl-N-cyclohexyl-p-phenylenediamine (PCHA) in the temperature range of from 200°C to 230°C is investigated.

It is found that the rate of O₂ absorption during the induction period in the presence of antioxidant varies in the range of from 2 × 10^?6 to 2 × 10^?5 mol/kg (210°C).

It is also stated that the main method of antioxidant consumption during the induction period consists of its direct oxidizing by molecular oxygen. The rapid oxidation of the polymer is shown to begin after the current antioxidant concentration reduction to the critical value.

Kinetic parameters of the oxidation reaction in a wide range of initial antioxidant concentration are determined.     

Effect of fatty acid composition of phospholipids on their antioxidant properties and activity index

Various phospholipids may act as antioxidants or prooxidants. This study investigated the effects of three phospholipid classes and their fatty acid composition on antioxidant activity. Antioxidant properties of sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine from salmon and menhaden oil were measured by oxidation induction time. An antioxidant activity index was determined in these systems with the Rancimat 617. Fatty acid profiles of the individual phospholipids and total oils were determined by gas-liquid chromatography before and after oxidation. The index was significantly (P<0.05) influenced by the headgroup and fatty acid composition of the phospholipid. Lipids with a choline headgroup had oxidation induction times greater than 60 h in the salmon oil system. The choline-containing phospholipid also offered better (P<0.05) protection from oxidation to the n-3 and total polyunsaturated fatty acids in salmon oil. Phospholipids containing more saturated fatty acids had longer oxidation induction times (>84 h) and higher antioxidant index (>9). Chainlength of the fatty acids may have contributed to the observed index, as phospholipids with longer chains (i.e., C₁₈ and above) had longer oxidation induction times. Phospholipids tested in this study had little or no antioxidant activity in menhaden oil, nor did they offer protection to n-3 or total polyunsaturated fatty acids in this oil. These findings suggest that fatty acid profiles of individual oils may influence the antioxidant index of each phospholipid.     

Immobilization of antioxidant on nanosilica and the antioxidative behavior in low density polyethylene

Nanosilica was firstly modified with an aminosilane coupling agent (AEAPS) and then reacted with the reactive antioxidant, 3,5-di-tert-butyl-4-hydroxycinnamic acyl chloride (AO-Cl), to form a nanosilica-immobilized antioxidant, AO-AEAPS-silica. FT-IR, XPS and TGA measurements confirmed that the reactive antioxidant was chemically immobilized onto the nanosilica surface. SEM observation showed that the nanosilica-immobilized antioxidant was homogeneously dispersed into the matrix of low density polyethylene (LDPE). It has been found that the antioxidative efficiency of AO-AEAPS-silica was superior to the corresponding low molecular counterpart (AO), based on the measurement of the oxidation induction time (OIT) of the LDPE/AO-AEAPS-silica and the LDPE/AO compounds containing equivalent antioxidant component. The release of the antioxidant from LDPE films was evaluated by monitoring the OIT change upon water extraction, demonstrating that AO-AEAPS-silica retained high stability against migration.     

Assessment of lifetime of hot-water polyethylene pipes based on oxidation induction time data

A method is presented for assessment of lifetime of polyethylene pipes undergoing thermal oxidation (Stage III failure) based on oxidation induction time (OIT) data obtained by DSC. The method requires pressure testing for limited time periods, sampling from unexposed and exposed pipes, the establishment of a linear relationship between the OIT and the antioxidant concentration, and the taking of OIT profiles through the pipe wall. The method is not applicable to pipes with improper dispersion of the antioxidant. A mathematical procedure based on a model for the migration and chemical consumption of the antioxidant system is used to extrapolate short-term OIT profiles to obtain the OIT profiles after extended exposure. The lifetime prediction is also based on the empirical establishment of a criterion, a critical OIT value, for the onset of thermal oxidation of the polymer (Regime C). The total lifetime is then obtained under the assumption that the time period of Regime C constitutes 10% of the total lifetime. The pressure testing time required to obtain adequate data for modeling is only a fraction (20% to 70%) of the failure times of the pipes studied. The average difference between the actual and predicted times was 15% for the MDPE pipes studied.     

Isothermal crystallization behavior of poly(L‐lactic acid)/organo‐montmorillonite nanocomposites

The isothermal crystallization behavior of poly(L ‐lactic acid)/organo‐montmorillonite nanocomposites (PLLA/OMMT) with different content of OMMT, using a kind of twice‐functionalized organoclay (TFC), prepared by melt intercalation process has been investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods (t_i) and half times for overall PLLA crystallization (100°C ≤ T_c ≤ 120°C) were affected by the temperature and the content of TFC in nanocomposites. The kinetic of isothermal crystallization of PLLA/TFC nanocomposites was studied by Avrami theory. Also, polarized optical photomicrographs supplied a direct way to know the role of TFC in PLLA isothermal crystallization process. Wide angle X‐ray diffraction (WAXD) patterns showed the nanostructure of PLLA/TFC material, and the PLLA crystalline integrality was changed as the presence of TFC. Adding TFC led to the decrease of equilibrium melting point of nanocomposites, indicating that the layered structure of clay restricted the full formation of crystalline structure of polymer. The specific interaction between PLLA and TFC was characterized by the Flory‐Huggins interaction parameter (B), which was determined by the equilibrium melting point depression of nanocomposites. The final values of B showed that PLLA was more compatible with TFC than normal OMMT. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The application of an extrusion slit die in the rheological measurements of polyethylene composites with calcium carbonate using an in‐line rheometer

This article has reported the results of rheological testing of low‐density polyethylene (LDPE) and its calcium carbonate composites containing 7, 14, 21, and 28 wt% filler, respectively. The polymer composites were produced in a twin‐screw extrusion process. The assessment of the rheological properties of the polymeric materials was made under extrusion process conditions, using an in‐line rheometer with an extrusion slit die (W = 20, H = 2, L = 150 mm), at temperatures of 170°C, 180°C, and 190°C, respectively. The rheological parameters were determined based on the Ostwald‐de‐Waele power law model. The employed testing stand enabled the assessment of the effect of filler addition and slit die temperature on the variations in viscosity, power law index (n), consistency index (K), maximum flow velocity (V_max), and maximum flow profiles (V_z), under the conditions of technological processing (extrusion) of plastics. POLYM. ENG. SCI., 59:E16–E24, 2019. © 2018 Society of Plastics Engineers     

Kinetics of Adhesion Interaction of Polyolefins with Metals Under Conditions of Contact Thermooxidation

The development of peel strength of adhesive joints between a PE containing organic peroxide (dicumy1 peroxide) and steel has been studied. It has been found that the kinetics of this process are controlled by the contact oxidation processes in a thin boundary layer. The peel strength, A, as a function of the contact time, t, is determined by the content of dicumy1 peroxide, c _per, in the adhesive, contact temperature, T, and the content of oxygen in the contacting environment. The value of A reaches its maximum, A _max, at a certain contact time, t _Amax..

The kinetic characteristics A _max and t _Amax as well as the initial growth rate of A,A ^{= t}=0 = lim da/dt _t=0, are determined by c _per and T. There is a growth of A _max and A ⁼ _t=0 with c _per and a decrease of t _Amax with T.

The shape of A(t) curves for a peroxide-containing PE, similar to a pure PE, is defined by the competitive influence of two principal tendencies in contact oxidation: oxidative cross-linking inducing the growth of A and oxidative destruction causing the reduction of A. There is a growth of the output of contact oxidation reactions with the increase of c _per. The empirical constants of an equation describing the A(t)-functions are calculated and the efficiency of the use of peroxides for promoting the PE-adhesion is estimated.

It has been proved that the peel strength at a fixed contact time is determined by the ratio of the gel-fraction in the polymer layer, c _gel, which is a measure of the outcome of the oxidative cross-linking, and the content of extractable low-molecular products, C _Im, characterizing the effect of oxidative destruction.     

Chain-breaking fused heterocyclic antioxidants: Antioxidant activities of 9H-xanthene-2,7-diols and α-tocopherol upon liposomal membranes

We evaluated the antioxidant activities of 9H-xanthene-2,7-diols and α-tocopherol (α-Toc) upon the oxidation of soybean phosphatidylcholine liposomal membranes, induced by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) and 2,2′-azobis(2,4-dimethylvaleronitrile (AMVN). The stoichiometric factors of 9H-xanthene-2,7-diols, initiated with water-soluble AAPH and lipid-soluble AMVN, were 1.9–2.7 and 1.2–1.8-fold greater than those of α-Toc, respectively. The consumption profile of the antioxidant confirmed that 9H-xanthene-2,7-diol was completely consumed within the induction period (t _inh) and that the 9H-xanthene-2,7-diol oxidation product was formed. When all oxidation product was depleted, t _inh was terminated, and rapid oxidation occurred. These results suggested that the antioxidant activities of 9H-xanthene-2,7-diol depend not only on the initial hydrogen abstraction from 9H-xanthene-2,7-diol but also on a second hydrogen abstraction from the residual phenolic OH group of the oxidation product. Ascorbic acid (AsA) could not scavenge the radicals by itself in the lipid bilayer. However, when 9H-xanthene-2,7-diol was located in the lipid bilayer, the addition of AsA into the aqueous phase prolonged t _inh and reduced the rate of decay of 9H-xanthene-2,7-diol.     

Development and simulation studies of an unsteady state biofilter model for the treatment of cyclic air emissions of an α‐pinene gas stream

This paper describes the development and simulation of an unsteady state biofilter model used to predict dynamic behaviour of cyclically‐operated biofilters and compares it with experimental results obtained from three, parallel, bench‐scale biofilters treating both periodically fluctuating concentrations and constant concentrations of an α‐pinene‐laden gas stream. The dynamic model, using kinetic parameters estimated from the constant concentration biofilter, was able to predict the performance of cyclic biofilters operating at short cycle periods (ie, in the order of minutes and hours). Steady state kinetic data from a constant concentration biofilter can be used to predict unsteady state biofilter operation. At a 24 h cycle period, the dynamic model compared well with experimental results. For long cycle periods (ie, hours and days), removal efficiency decreased after periods of non‐loading: the longer the period of non‐loading, the poorer the biofilter's performance at the re‐commencement of pollutant loading. At longer time scales the model did not effectively predict transient behaviour, as adsorption and changes in kinetic parameters were not accounted for. Modelling results showed that similar biofiltration performance for the cyclic and constant concentration biofiltration of α‐pinene is expected for biofilters operating solely in the first order kinetics regime. Poorer performance for cyclic biofilters following Monod kinetics spanning the entire kinetics range is expected as the cycle amplitude increases. The most important parameters affecting the performance of a cyclically‐operated biofilter with short cycle periods are: amplitude of cyclic fluctuations, C_{g, max}/C_g, relative value of the half‐saturation constant in the Monod expression, K_s, and effective diffusivity of α‐pinene in the biofilm, D_e. Copyright © 2005 Society of Chemical Industry     

Silane grafting and moisture crosslinking of polyethylene: The effect of molecular structure

The silane grafting and moisture crosslinking of different grades of polyethylene have been investigated. Three types of polyethylene (HDPE, LLDPE, and LDPE) with different molecular structures and similar melt flow indices were selected. The initiator was dicumyl peroxide (DCP), and the silane was vinyltrimethoxysilane. The grafting reaction was carried out in an internal mixer. The extent of grafting and the degree of crosslinking were determined, and hot‐set tests were carried out to evaluate the crosslink structure of the different polyethylenes. The LLDPE had the highest degree of grafting, while the LDPE had the least. The rate of crosslinking for LDPE was higher than that of HDPE and LLDPE. The gel content of LDPE was higher than that of HDPE and LLDPE. Hot‐set elongation and the number‐average molecular weight between crosslinks (M_c) were lower for LLDPE and LDPE than for HDPE. Increasing the silane/DCP percentage led to peroxide crosslinking, thereby decreasing the M_c and hot‐set elongation. The number‐average molecular weight (M_n), molecular weight distribution, and number of chain branches were the most important parameters affecting the silane grafting and moisture crosslinking. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Polyethylene terephthalate/low density polyethylene/titanium dioxide blend nanocomposites: Morphology,crystallinity, rheology,and transport properties

Physical features of polyethylene terephthalate (PET)/low density polyethylene (LDPE) immiscible blends, rich in PET, with and without titanium dioxide (TiO₂) nanoparticles are studied. These materials are of industrial interest, because they can be obtained by recycling PET bottles containing TiO₂ with their corresponding polyethylene made caps. Their potential application in packaging is investigated. Droplet-matrix morphology is observed by scanning electron microscopy; coalescence occurs during compression molding. Transmission electron microscopy results show that TiO₂ nanoparticles are located at the interface between PET and LDPE, forming a physical barrier that favors development of smaller droplets. Thermal analysis results are compatible with the morphology of the blends and the location of the TiO₂ nanoparticles. Viscosity obtained by extrusion continuous flow and oscillatory flow measurements in the linear regime show that some of the blends have viscoplastic behavior. Permeability results reveal that 80PET/20LDPE/TiO₂ blend nanocomposite shows a balanced barrier character to both oxygen and water vapor. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46986.     

Prediction of the molecular and polymer solution properties of LDPE in a high-pressure tubular reactor using a novel Monte Carlo approach

In the present work, a novel kinetic/topology Monte Carlo algorithm is developed for the prediction of molecular, topological and solution properties of highly branched low-density polyethylene (LDPE), produced in a high-pressure multi-zonal tubular reactor. It is shown that the combined kinetic/topology MC algorithm can provide comprehensive information regarding the distributed molecular and topological properties of LDPE (i.e., molecular weight distribution, short- and long-chain branching distributions, joint molecular weight-long chain branching distribution, branching order distribution, seniority/priority distributions, etc.) The molecular/topological results obtained from the MC algorithm are then introduced into a random-walk molecular simulator to calculate the solution properties of LDPE (i.e., the mean radius of gyration, R_g, and the branching factor, g) in terms of the chain length of the branched polyethylene. The validity of the commonly applied approximation regarding the random scission of highly branched polymer chains is assessed by a direct comparison of the average molecular properties of LDPE (i.e., number and weight average molecular weights), calculated by the combined kinetic/topology MC algorithm, with the respective predictions obtained by the commonly applied method of moments (MOM). Through this comparison it is demonstrated that the ambiguous implementation of the random scission reaction in the MOM formulation can result in erroneous predictions of the weight average molecular weight and MWD of LDPE. Finally, the effects of two key process parameters, namely, the polymerization temperature profile and the solvent concentration, on the molecular, topological and polymer solution properties of LDPE produced in a multi-zonal tubular reactor are investigated.     

Thermally treated low density polyethylene biodegradation by Penicillium pinophilum and Aspergillus niger

Differential scanning calorimetry (DSC), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to determine morphological, structural and surface changes (biodegradation) on thermo‐oxidized (80°C, 15 days) low‐density polyethylene (TO‐LDPE) incubated with Aspergillus niger and Penicillium pinophilum fungi, with and without ethanol as cosubstrate for 31 months. TO‐LDPE mineralization by fungi was also evaluated. Significantly morphological and structural final changes on biologically treated TO‐LDPE samples were observed. Decreases to three units on crystallinity and crystalline lamellar thickness (0.4–1.8 Å), and increases in small‐crystals content (up to 3.2%) and mean crystallite size (8.4–14 Å) were registered. An oxidation decrease (almost twice) on samples without ethanol with respect to the control was observed, while in those with ethanol it was increased (up to 2.5 times). Double bond index increased more than twice from 21 to 31 months. The higher TO‐LDPE changes and fungi‐LDPE interaction was observed in samples with ethanol, suggesting that ethanol favors the TO‐LDPE biodegradation, at least in case of P. pinophilum, probably by means of a cometabolic process. Mineralization of 0.50 % and 0.57 % for A. niger, and of 0.64 % and 0.37 % for P. pinophilum were obtained, for samples with and without ethanol, respectively. A model to explain morphological and structural changes on biologically treated TO‐LDPE is also proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 305–314, 2002