Aging of anhydride‐hardened epoxies in lubricants at elevated temperatures

In automotive under‐the‐hood applications, electronics respectively their packaging materials come in contact with automotive fluids. The effect of automatic transmission fluid (ATF) on an anhydride‐cured epoxy was investigated at temperatures up to 180 °C for up to 1000 h. This study has shown that ATF retards the oxidative aging of the epoxy, presumably due to oxygen consumption. Whereas in air the material underwent a thermo‐oxidative aging with a mass loss of up to 4% and a strong broadening of T_g to higher temperatures, in ATF a temperature dependent distinctive drop of T_g from 142 to 126 °C after 1000 h aging at 180 °C, and a mass loss of maximum 1% was observed which might be a thermal decomposition of the epoxy material. A slight broadening of the damping factors might indicate an intrusion of ATF components. A color change of the samples could be observed after aging in air and ATF, with the discoloration in air being more intense. An explanation for the color change might be either a minor amount of oxygen causing an oxidative discoloration reaction or the intrusion of colored ATF degradation products. While the oxidation‐kinetics in air exhibited Arrhenius temperature‐dependence the mechanism in ATF changed above 165 °C. An acceleration of aging tests at temperatures beyond 150 °C is, therefore, not possible. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44877.     

Hygrothermal aging properties of wood plastic composites made of recycled high density polypropylene as affected by inorganic pigments

The objective of this study is to investigate the hygrothermal aging properties of wood plastic composites (WPCs) made of a recycled high density polyethylene (HDPE) highly filled with wood waste, inorganic filler and pigments with a resin/filler ratio of 27/73. Hygrothermal ageing test of the prepared WPCs with three different colors (original, red, and chocolate) was carried out by immersing specimens in distilled water at 45°C for 70 days. The hygrothermal ageing properties including water absorption, moisture diffusion coefficient, surface color change, and flexural properties of the WPCs were investigated. It was found that pigment colored WPCs have better hygrothermal aging properties including lower water absorption, less total color changes, and higher mechanical property retention rate after 70 days hygrothermal aging test. POLYM. ENG. SCI., 55:2127–2132, 2015. © 2015 Society of Plastics Engineers     

Effect of temperature on hygroscopic thickness swelling rate of composites from lignocellolusic fillers and HDPE

Effect of temperature on hygroscopic thickness swelling rate of lignocellolusic fillers/HDPE (high density polyethylene) composites was investigated. The composites were manufactured using a dry blend/hot press method. In this method, powder of plastic and dried powder of lignocellolusic material were mixed in high‐speed mixer and then the mixed powder were pressed at 190°C. Lignocellolusic fillers/HDPE composites panels were made from virgin and recycled HDPE (as plastic) and wood sawdust and flour of rice hull (as filler) at 60% by weight filler loadings. Nominal density and dimensions of the panels were 1 g/cm³ and 35 × 35 × 1 cm³, respectively. Thickness swelling rate of manufactured wood plastic composites (WPCs) were evaluated by immersing them in water at 20, 40, and 60°C for reaching a certain value where no more thickness was swelled. A swelling model developed by Shi and Gardner [Compos. A, 37 , 1276 (2006)] was used to study the thickness swelling process of WPCs, from which the parameter, swelling rate parameter, can be used to quantify the swelling rate. The results indicated that temperature has a significant effect on the swelling rate. The swelling rate increased as the temperature increased. The swelling model provided a good predictor of the hygroscopic swelling process of WPCs immersed in water at various temperatures. From the activation energy values calculated from the Arrhenius plots, the temperature had less effect on the thickness swelling rate for the composites including wood sawdust compared with the rice hull as filler and the composites including recycled compared with the virgin HDPE as plastic. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Low‐temperature UV irradiation induced the color change kinetics and the corresponding structure development of PVC film

The low‐temperature ultraviolet (UV) irradiation equipment, developed in our Lab, was used to study the photo‐aging of poly (vinyl chloride) (PVC) films at low temperature. The color change kinetics and corresponding structure development of PVC film during low‐temperature UV aging were studied through L*a*b* coordinates Commission International d' Eclau‐age (CIE 1976 color space) and Ultraviolet spectrophotometer (UV–vis) and Fourier transform infrared spectroscopy (FTIR). It was found that the yellowness difference (?b*) and color difference (?E*) of the PVC film increased almost linearly with the aging time. Their values had a slower change at lower temperature. The kinetic study showed that the relationship between the velocity of coloration of the PVC film and the temperature agreed well with Arrhenius equation at low temperature. The activation energy of coloration of the PVC film was calculated. The FTIR spectra indicated that photo‐dehydrochloration, resulting in the generation of conjugated carbon–carbon double bonds, was the main reaction for PVC during photo‐aging at low temperature. Meanwhile, the photo‐oxidation was also obvious and could not be neglected. It clearly confirmed that the absorption peaks of conjugated carbon–carbon double bond increased and shifted to longer wavelength during photo‐aging in the UV‐abs analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

The physical perspective on the solid and molten states associated with the mechanical properties of eco‐friendly HDPE/Pinus taeda wood‐plastic composites

The manufacture of wood plastic composites (WPCs) by reutilizing post‐consumed polymeric materials and post‐industry wood wastes contributes to reduce the environmental impact and the consumption of virgin plastics. In this work, the influence of interfacial adhesion on the solid and molten states of high density polyethylene (HDPE) containing WPCs wood dust of recycled Pinus taeda (PT) was evaluated. The composites were prepared by extrusion in a twin screw extruder using maleic anhydride as compatibilizer. The samples were analyzed by dynamic‐mechanical analysis (DMA), tensile and impact strength measurements, oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). DMA analysis showed increase in module and an improved interface with physical interaction between the WPCs phases. The higher molecular interactivity interface improved the mechanical properties relative to pure HDPE. Melting state analysis showed increased WPCs flow restriction, this feature being correlated with reduction in the molecular degree of freedom during flow, which consequently reduces the crystalline degree changes in microstructure as well as in processing parameters of the material. These results lead to consider the development of an eco‐friendly and economic effective technology to reuse abundant recycled solid wastes in a new market. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42887.     

A method for determination of time‐ and temperature‐dependences of stress threshold of linear–nonlinear viscoelastic transition: Energy‐Based Approach

A methodology for determination of time‐ and temperature‐dependences of stress threshold of linear–nonlinear viscoelastic transition is proposed and validated by example of uniaxial creep of epoxy resin. Energy approach is applied for characterization of the region of linear viscoelasticity (LVE) and the threshold of LVE is given in the stress–strain representation as the master curve independent of time and temperature. Time‐ and temperature‐dependences of the stress threshold are calculated by extending LVE theory and time–temperature superposition principles (TTSP) to the energy relations. Reasonable agreement between experimental data and calculations is obtained. It is shown that number of tests required for characterization of LVE region in a wide range of test time and temperatures can be considerably reduced by applying the proposed methodology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Kinetics and thermal properties of epoxy resin cured with Ni(II)‐tris‐(O‐pheneylendiamine) bromide

Diglycidyl ether of bisphenol A (DGEBA) is cured with a nickel complex of O‐phenylendiamine (OPD) as a ligand. The structure of the synthesized curing agent is confirmed through IR and elemental analysis. The curing kinetics of DGEBA/Ni(OPD)₃Br₂ system is studied by the dynamic DSC and isothermal FTIR techniques. In all cases, we have observed at least two exothermic peaks during DSC traces up to 350°C. Dynamic activation energies are calculated by using the two isoconversional, Kissinger and Ozawa, methods applied to peak maximum. A two‐parameter (m, n) autocatalytic model (Sestak–Berggren equation) is found to be the most adequate model to describe the cure kinetics of the observed thermal events. Isothermal kinetic parameters are estimated using the Horie model. The onset decomposition temperature and char yield (at 700°C) of the crosslinked material were 290°C and 27%, respectively. The activation energy of the solid‐state thermal degradation process is evaluated by Ozawa approach, resulting in 95–138 kJ/mol on a range of 2–20% decomposition conversion. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1257–1265, 2006     

Effect of core‐shell morphology evolution on the rheology,crystallization, and mechanical properties of PA6/EPDM‐g‐MA/HDPE ternary blend

In this article, polyamide 6 (PA6), maleic anhydride grafted ethylene‐propylene‐diene monomer (EPDM‐g‐MA), high‐density polyethylene (HDPE) were simultaneously added into an internal mixer to melt‐mixing for different periods. The relationship between morphology and rheological behaviors, crystallization, mechanical properties of PA6/EPDM‐g‐MA/HDPE blends were studied. The phase morphology observation revealed that PA6/EPDM‐g‐MA/HDPE (70/15/15 wt %) blend is constituted from PA6 matrix in which is dispersed core‐shell droplets of HDPE core encapsulated by EPDM‐g‐MA phase and indicated that the mixing time played a crucial role on the evolution of the core‐shell morphology. Rheological measurement manifested that the complex viscosity and storage modulus of ternary blends were notable higher than the pure polymer blends and binary blends which ascribed different phase morphology. Moreover, the maximum notched impact strength of PA6/EPDM‐g‐MA/HDPE blend was 80.7 KJ/m² and this value was 10–11 times higher than that of pure PA6. Particularly, differential scanning calorimetry results indicated that the bulk crystallization temperature of HDPE (114.6°C) was partly weakened and a new crystallization peak appeared at a lower temperature of around 102.2°C as a result of co‐crystal of HDPE and EPDM‐g‐MA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Rheological and mechanical characterization of polypropylene‐based wood plastic composites

The aim of this article is to investigate the influence of filler content and temperature on the rheological, mechanical, and thermal properties of wood flour polypropylene composites (WPCs). Testing WPCs at high temperatures and percentages of filler is extremely challenging because of reduced linear viscoelastic region, high viscosity, and degradation. In this work, a complete characterization of WPCs with different filler percentages (0–70 wt%) has been made. Rheological tests are performed at 170°C for the WPCs and in the 170–200°C range for neat polypropylene. A single master curve is obtained using two shift factors that can be described by a modified Eilers model and a Williams‐Landel‐Ferry equation. This master curve, fitted with a Carreau‐Yasuda model, can be very useful for predicting the viscosity of WPCs at temperatures that are typically used during processing and for any percentage of filler. POLYM. COMPOS., 37:3460–3473, 2016. © 2015 Society of Plastics Engineers     

Color Change Kinetics of American Ginseng (Panax quinquefolium) Slices During Air Impingement Drying

The color change kinetics of American ginseng (Panax quinquefolium) slices were investigated in an air impingement dryer under different drying temperatures (35, 45, 55, and 65°C) using the CIE Lab color parameters (L*, a*, b*) as the assessment indicators. Results illustrated that all three color parameters (L*, a*, b*) increased with drying time. The L* value decreased with increasing drying temperature. However, a* and b* values increased with the increase in drying temperature. Furthermore, at the initial drying stage the change rate of L* increased significantly, while towards the end of drying it reduced significantly. As regards a*, it slowly changed at the initial and final drying stages rather than in the intermediate drying stage. In the case of b*, it increased with increasing drying time and drying temperature during the whole process. The zero-order, first-order, and fractional conversion models were fitted to the experimental data, and the model's parameters were determined using linear regression analysis. By comparing the fitting of kinetic models to the experimental data, the most suitable model was selected to describe the color change kinetics. An Arrhenius equation was used to calculate the activation energy for color change kinetics and it was found that the values were 33.87–38.55, 56.48, and 74.03 kJ/mol for L*, a*, and b*, respectively. The findings of this work contribute to a better understanding of ginseng color changes kinetics during drying, and the established change kinetics models are a good tool for predicting, evaluating, and controlling of color change of American ginseng during its drying process.     

Phase Evolution upon Aging of Air‐Plasma Sprayed t′‐Zirconia Coatings: I—Synchrotron X‐Ray Diffraction

Phase evolution accompanying the isothermal aging of free‐standing air‐plasma sprayed (APS) 7–8 wt% yttria‐stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) is described. Aging was carried out at temperatures ranging from 982°C to 1482°C in air. The high‐temperature kinetics of the phase evolution from the metastable t′ phase into a mixture of transformable Y‐rich (cubic) and Y‐lean (tetragonal) phases are documented through ambient temperature X‐ray diffraction (XRD) characterization. A Hollomon–Jaffe parameter (HJP), T[27 + ln(t)], was used to satisfactorily normalize the extent of phase decomposition over the full range of times and temperatures. Comparison to vapor deposited TBCs reveal potential differences in the destabilization mechanism in APS coatings. Furthermore, the lattice parameters extracted from Rietveld refinement of the XRD patterns were used to deduce the stabilizer concentrations of the respective phases, which suggest a retrograde tetragonal solvus over the temperature range studied. In concert with a complementary microstructural study presented in Part II, this effort offers new insights into the mechanisms governing the phase evolution and raises implications for the high‐temperature use of 8YSZ ceramics.     

Delignification of intact biomass and cellulosic coproduct of acid‐catalyzed hydrolysis

The kinetics of acid‐catalyzed hemicellulose removal and also alkaline delignification of oat hull biomass were investigated. All three operational parameters namely, catalyst concentration (0.10–0.55 N H₂SO₄), temperature (110–130°C), and residence time (up to 150 min) affected the efficiency of hemicellulose removal, with 100% of hemicellulose removed by appropriate selection of process parameters. Analysis of delignification kinetics (in the temperature range of 30–100°C) indicated that it can be expressed very well by a two‐phase model for the crude biomass and also for the hemicellulose‐prehydrolyzed material. The application of acid‐catalyzed prehydrolysis improved the capacity of lignin dissolution especially at lower temperatures (30 and 65°C) and accelerated the dissolution of lignin. This acceleration of delignification by prehydrolysis was possible at all levels of temperature in the bulk phase; however, results were more significant at the lower temperatures in the terminal phase. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1783–1791, 2015     

Prediction of the colorimetric parameters and mass loss of heat‐treated bamboo: Comparison of multiple linear regression and artificial neural network method

In this study, the colorimetric parameters (L*, a*, b*) and mass loss of heat‐treated bamboo were investigated, and the obtained results were modeled by using two methods: multiple linear regression (MLR) and artificial neural network (ANN). First, bamboo samples were exposed to heat treatment at different temperatures (110°C, 140°C, 170°C, and 200°C) and durations (15, 30, 45, 60, 75, 90, and 115 minutes) in a laboratory oven. Then, the colorimetric parameters (L*, a*, b*) and mass loss of each sample were measured after each period of heat treatment. All data were modeled by using two methods separately for each parameter and the performances of these proposed methods were compared. It was found that color change and mass loss increased with increasing temperature and duration of heat treatment. Mean absolute percentage error (MAPE) values of all obtained MLR ranged from 0.64% to 10.63%, while the all MAPE values of ANN were found to be lower than 1.5%. Based on these results, it can be said that MLR and ANN could be used to evaluate the changes on the selected properties of heat‐treated bamboo samples. On the other hand, it should be emphasized that the ANN gave more accurate results than the MLR method because of its learning capability.     

Preparation and characterization of poly(ethylene terephthalate) powder‐filled high‐density polyethylene in the presence of silane coupling agents

Micron‐size crystalline particles of Poly(ethylene terephthalate) (PET), obtained from PET bottles by crystallization and grinding, were used as a filler in high‐density polyethylene (HDPE). The composite of PET particle‐filled HDPE was prepared by melt mixing at 190°C, which was well below the melting temperature of PET. Silane coupling agents (SCAs) were used to enhance the interaction between PET and HDPE in the composite. A chain extender (CE) and maleic anhydride (MA) were also used to provide further interaction with SCAs between these two materials. The ultimate tensile strength, especially at highest content 40% PET‐filled HDPE, and the impact strength of SCAs‐treated PET‐filled HDPE was found to be highly improved compared to untreated PET filling into HDPE. Dynamic mechanical analyses (DMA) demonstrated that T_g of the main matrix polyethylene was depressed from 3 to 10°C. Scanning electron microscopy (SEM) studies indicated a strong interaction between PET powder and HDPE when SCAs were present in the system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 827–835, 2001     

Accelerated crystallization of poly(L‐lactide) by physical aging

The low‐temperature physical aging of amorphous poly(L ‐lactide) (PLLA) at 25–50°C below glass transition temperature (T_g) was carried out for 90 days. The physical aging significantly increased the T_g and glass transition enthalpy, but did not cause crystallization, regardless of aging temperature. The nonisothermal crystallization of PLLA during heating was accelerated only by physical aging at 50°C. These results indicate that the structure formed by physical aging only at 50°C induced the accelerated crystallization of PLLA during heating, whereas the structure formed by physical aging at 25 and 37°C had a negligible effect on the crystallization of PLLA during heating, except when the physical aging at 37°C was continued for the period as long as 90 days. The mechanism for the accelerated crystallization of PLLA by physical aging is discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Time‐temperature superposition principle applicability for blends formed of immiscible polymers

In this work, the linear viscoelastic behavior of PP/PS and PP/HDPE blends modified with SEBS and EPDM, respectively, was studied. Small amplitude oscillatory shear measurements were carried out at different temperatures, ranging from 190°C to 240°C. The storage (G') and loss (G") moduli curves obtained were horizontally shifted and curves of angle delta (δ) (δ = atan (G"/G')) as a function of complex shear modulus (G*), known as van Gurp plots, were obtained at several temperatures, to test the applicability of time‐temperature superposition principle (TTS) to these blends. The results showed that successful application of TTS depends on the flow energy of activation and horizontal shift factors of the individual components of the blend, on the interfacial properties of the blend and on the concentration of compatibilizer added to the blend. TTS application failed for PP/PS blend, but held for PP/HDPE blend. Addition of SEBS to PP/PS blends promoted successful TTS application at specific concentrations that corresponded to interfacial saturation of the dispersed phase. Addition of EPDM did not imply sensitive change on TTS application for the PP/HDPE blends.     

Dynamic rheological properties for HDPE/CB composite melts

A study on the dynamic viscoelastic properties of carbon black (CB)‐filled high‐density polyethylene (HDPE) in the molten state was carried out. When the temperature was above 180°C in an air atmosphere, the storage modulus G′, loss modulus G″, and loss tangent δ showed particular characteristics. In the low‐frequency region, the modulus increased with increase of the testing time while the tan δ obviously decreased. Also, the higher the temperature, the more notable was the change. We can detect these changes from the deviation of G′ (G″) against ω plots from the linearity and the appearance of a characteristic plateau phenomenon. The width and height of the modulus plateau increased with increase of the temperature. When temperature was below 180°C, the testing time and the temperature had no effect on the viscoelastic parameters of HDPE. However, if we used 99% nitrogen gas as the atmosphere, substituting for air, the viscoelastic parameters revealed an undiscernible change, different from that in an air atmosphere. No changes were found under the protection of the antioxidant B215. This phenomenon indicated that HDPE can be oxidized at a temperature higher than 180°C. Nitrogen gas and an antioxidant agent can prevent HDPE from crosslinking. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2160–2167, 2003     

Investigation of kinetics of 4‐methylpentene‐1 polymerization using Ziegler–Natta‐type catalysts

The kinetics of 4‐methylpentene‐1 (4MP1) polymerization by use of Ziegler–Natta‐type catalyst systems, M(acac)₃‐AlEt₃ (M = Cr, Mn, Fe, and Co), are investigated in benzene medium at 40°C. The effect of various parameters such as Al/M ratio, reaction time, aging time, temperature, catalyst, and monomer concentrations on the rate of polymerization and yield are examined. The rate of polymerization increased linearly with increasing monomer concentration with first‐order dependence, whereas the rate of polymerization with respect to catalyst concentration is found to be 0.5. For all cases, the polymer yield is maximum at an Al/M ratio of 2. The activation energies obtained from linear Arrhenius plots are in the range of 25.27–33.51 kJ mol^?1. It is found that the aging time to give maximum percentage yield of the polymer varies with the catalyst systems. Based on the experimental results, a plausible mechanism is proposed that envisages a free‐radical mechanism. Characterization of the resulting polymer product, for all the cases, through FTIR, ¹H‐NMR, and ¹³C‐NMR studies, showed isomerized polymeric structures with 1,4‐structure as dominant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2468–2477, 2003     

Investigation of α‐iron oxide‐coated polymeric nanocomposites capacity for efficient heavy metal removal from aqueous solution

In the present study, PS@α‐Fe₂O₃ nanocomposites were prepared by chemical microemulsion polymerization approach and the ability of magnetic beads to remove Cu(II) ions from aqueous solutions in a batch media was investigated. Various physico‐chemical parameters such as pH, initial metal ion concentration, temperature, and equilibrium contact time were also studied. Adsorption mechanism of Cu²⁺ ions onto magnetic polymeric adsorbents has been investigated using Langmuir, Freundlich, Sips and Redlich–Petersen isotherms. The results demonstrated that the PS@α‐Fe₂O₃ nanocomposite is an effective adsorbent for Cu²⁺ ions removal. The Sips adsorption isotherm model (R² > 0.99) was more in consistence with the adsorption isotherm data of Cu(II) ions compared to other models and the maximum adsorbed amount of copper was 34.25 mg/g. The adsorption kinetics well fitted to a pseudo second‐order kinetic model. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) were calculated from the temperature dependent sorption isotherms, and the results suggested that copper adsorption was a spontaneous and exothermic process. POLYM. ENG. SCI., 55:2735–2742, 2015. © 2015 Society of Plastics Engineers