Electrically conductive composites of poly(urea‐formaldehyde) and cellulose filled with aluminum

This article addresses the preparation and characterization of composite materials obtained with compression molding of mixtures of aluminum powder and a commercial grade thermosetting resin of poly(urea‐formaldehyde) filled with α‐cellulose in powder form. The homogeneity of these composites was checked by the morphologies of the constituents (filler and matrix) by optical microscopy. The density of the composites was measured and compared with values calculated by assuming different void levels within the samples, to discuss the porosity effect, in connection with optical microscopy observations. Then, the dependence of electrical conductivity of the composites on volume fraction of the metal filler was investigated. The conductivity of the composites is <10⁻¹² S/cm unless the metal content reaches the percolation threshold at a volume fraction of V_c = 38.6 vol%, beyond which the conductivity increases markedly by as much as nine orders of magnitude, indicating an insulator–conductor phase transition. The obtained results on electrical conductivity have been well interpreted with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, V_c, the critical exponent, t, and the packing density coefficient, F, were in good accord with earlier studies. In addition, the hardness of samples remained almost constant with the increase of metal concentration. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Conducting polymer composites of zinc‐filled urea–formaldehyde

This article is concerned with the preparation and characterization of composite materials prepared by the compression molding of mixtures of zinc powder and urea–formaldehyde embedded in cellulose powder. The morphologies of the constituent, filler, and matrix were investigated by optical microscopy. The elaborated composites were characterized by density, which was compared with calculated values, and the porosity rate was deduced. Further, the hardness of samples remained almost constant with increasing metal concentration. The electrical conductivity of the composites was less than 10^?11 S/cm unless the metal content reached the percolation threshold at a volume fraction of 18.9%, beyond which the conductivity increased markedly, by as much as eight orders of magnitude. The obtained results interpreted well with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, the critical exponent t, and the packing density coefficient were in good accord with earlier studies. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2011–2015, 2005     

Thermal degradation mechanisms of epoxy composites filled with tin particles

This article reports an evaluation study of the thermal degradation mechanisms of electrically insulating and conducting epoxy/Sn composites by using solid‐state kinetic approaches and structural characterizations. Comparison of the thermoanalytical data of epoxy/Sn composites with pure epoxy shows that the addition of tin in epoxy catalyzes the thermal degradation of epoxy and the catalytic ability of tin depends upon its contents in epoxy. Kinetic modeling of the phenomena elaborates the thermal behaviors of epoxy/Sn composites in terms of the comparison of their activation parameters and reaction models. Friedman's differential and Arshad–Maaroufi's generalized linear integral isoconversional methods are used to obtain the variation in activation energies with the advancement of reaction. Advanced reaction model determination methodology is effectively employed to evaluate the reaction mechanisms of epoxy/Sn composites. Kinetic analysis suggests that tin increases the thermal degradation rate of epoxy by lowering the activation energy barrier of reaction. It is worth noticing that the parameters of the probable reaction model, i.e., Šesták Berggren have been found nearly the same for pure epoxy and epoxy/Sn composites, revealing weak epoxy–tin interactions in the composites. The mechanistic information obtained by kinetic analysis fairly agrees with the scanning electron microscopy and X‐ray diffraction results. POLYM. COMPOS., 38:1529–1540, 2017. © 2015 Society of Plastics Engineers     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Ablation properties of zinc borate and aluminum hypophosphite filled silicone rubber composites

The ablative properties of epoxy modified silicone rubber composites filled with zinc borate (ZB) and aluminum hypophosphite (AHP) were studied. The decomposition of the added fillers and covering connection of residual on the substrate contribute to the improvement of heat insulation. The ablation test shows that the formation of a dense char layer with certain strength is key to improving the ablative properties. The optimal ablative performance is achieved when the concentration of ZB and AHP is 10 and 5 phr, respectively. Under such circumstances, the linear ablation rate is as low as 0.032 mm/s, which is about 61% lower than the pure silicone rubber. Furthermore, the structure and composition of the formed char layer were analyzed using X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy.     

Kinetics of isothermal and non‐isothermal degradation of cellulose: model‐based and model‐free methods

BACKGROUND: The kinetics of the thermal decomposition of cellulosic materials is of interest from the viewpoint of flame retardancy for safety, optimization of incineration processes and reducing energy production from fossil sources and associated pollution. One essential step in these processes is the thermal degradation through mass and energy transport, which determines the rate of evolution of various types of products from cellulosic materials. RESULTS: Kinetic parameters have been determined using various model‐based and model‐free methods in the thermal degradation of cellulose up to 700 °C in helium atmosphere. The values of the activation energy obtained in isothermal processes and non‐isothermal processes have been found to be not far from each other. From the integral method, the random nucleation (F₁)‐type mechanism has been found most probable for cellulose degradation having an activation energy, E_a, in the range 156.5–166.5 kJ mol^?1, lnA = 20–23 min^?1, for first‐order reaction during its decomposition process at heating rates of 2, 5 and 10 °C min^?1. Based on the high correlation coefficient, many types of mechanisms seem equally good for non‐isothermal degradation of cellulose. CONCLUSION: The linear correlation coefficient has a limitation for verifying the correctness of a reaction mechanism in the study of degradation kinetics. Therefore, the correctness of a mechanism should be considered on the basis of comparing the kinetic parameters obtained from isothermal as well as non‐isothermal methods. Copyright © 2008 Society of Chemical Industry     

Thermal aging of bentonite‐filled ethylene propylene diene monomer composites

Bentonite‐filled ethylene propylene diene monomer (EPDM/Bt) composites were prepared using two roll mill compounding method and the effect of Bt loading on the thermal aging, swelling resistance and crosslink density of EPDM/Bt composites were studied. The effect of in situ addition of different silane coupling agents (SCAs) on the above properties at optimum Bt loading of EPDM/Bt composite was also investigated. Thermal aging test results show that the tensile strength and tensile modulus at 100% elongation (M100) increase initially for 2 days aged composites and decrease slightly after 4 days of aging, meanwhile the elongation at break (E_b) decrease gradually with aging period as compared to the unaged composites. Upon aging, swelling resistance increase initially indicating increased crosslink density of EPDM/Bt composite due to post‐curing and reduced after 4 days of aging due to crosslink destruction and EPDM chain scissioning. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4419–4427, 2013     

Thermal,dielectric, and mechanical properties of SiC particles filled linear low‐density polyethylene composites

A thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm^?1 K^?1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<10² Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Kinetic study of polypropylene nanocomposite thermo‐oxidative degradation

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo‐oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one‐dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behaviour compared with neat PP. Copyright © 2005 Society of Chemical Industry     

Thermal behavior and dielectric property analysis of boron nitride‐filled bismaleimide‐triazine resin composites

Bismaleimide‐triazine (BT) resin/hexagonal boron nitride (h‐BN) composites are prepared, and the effects of h‐BN content on the thermal and dielectric properties are studied in the view of structure–property relationship. It is found that the introduction of the BN in the BT resin dramatically improve the thermal conductivity of BT resin. The thermal conductivity of the composites is up to 1.11 W/m.K, with an h‐BN concentration of 50 wt %, which is increased by six times compared with the pure BT resin. The BT resin/h‐BN composites also exhibit excellent thermal properties, with the glass transition temperatures above 200°C, and thermal decomposition temperatures over 390°C. Moreover, the composites possess good dielectric properties. Their dielectric constant and loss tangent (tan δ) are less than 4.5 and 0.015, respectively. The results indicate that the BT resin/h‐BN composites are promising as efficient heat‐releasing materials in the high‐density electronic packaging technology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal oxidative degradation kinetics of PP and PP/mg (OH)2 flame‐retardant composites

The thermal stability and thermal oxidative degradation kinetics of polypropylene (PP) and flame‐retardant PP composites filled with untreated and treated magnesium hydroxide (MH) in air were studied by thermogravimetric analysis (TGA). The effect of the heating rate in dynamic measurements (5°C–30°C/min) on kinetic parameters such as activation energy was also investigated. The Kissinger and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy for the degradation of neat PP and flame‐retardant PP composites. The results of TGA showed that the addition of untreated or treated MH improved the thermal oxidative stability of PP in air. The kinetic results showed that the apparent activation energy for degradation of flame‐retardant PP composites was much higher than that of neat PP, suggesting that the flame retardant used in this work had a great effect on the mechanisms of pyrolysis and combustion of PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1978–1984, 2007     

Thermal degradation of a phenolic resin,vegetable fibers,and derived composites

The thermal degradation behavior of resol, several vegetable fibers (two types of cotton fibers, sisal and sugar cane bagasse) and derived polymer composites have been investigated using thermogravimetric analysis (TGA). The initial thermal degradation temperature T_ONSET, the temperature at the maximum degradation rate TD_M, and the char left at 500°C corresponding to the crosslinked resol were higher than the values measured for the fibers and their composites. Thus, the addition of the fibers reduced the thermal resistance of the phenolic thermoset. The polymer and the fiber‐composites showed a complex degradation involving different thermal decomposition processes. For that reason, the DTG curves were deconvoluted and a phenomenological kinetic expression was found for each individual peak. The overall thermal decomposition curve was recalculated adding each degradation process weighted according to its contribution to the total weight loss. An increase in the activation energy corresponding to the cellulose degradation was observed in the composites, highlighting the protective action of the resin encapsulating the fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal degradation kinetics,mechanical, and flame retardant properties of epoxy‐HDPE fabric‐clay composite laminates

Addition of particulates into laminates has been found to influence thermal and mechanical properties. Composite laminates of epoxy‐high density polyethylene (HDPE) fabric‐clay were prepared by reinforcing clay in the range of 0.1–0.7 phr into epoxy‐HDPE fabric laminates. These laminates are characterized for their mechanical, thermal, and flame retardant performances. With the addition of clay, an increase was found in impact resistance, tensile strength, flexural strength, and Young's modulus to an extent of 0.2 phr clay, after which there is a decrease in these properties. The thermal stability is found to decrease with the addition of clay. The improved mechanical properties are obtained at the slight expense of thermal stability. UL‐94 tests indicate a reduction in the burning rate. Morphology of the broken samples indicate better dispersion at lower clay load and tactoid formation at higher clay loading. These materials have potential applications in agriculture, construction, and decorative purposes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40751.     

Thermal degradation of shale oils: 1. Kinetics of vapour phase oil degradation

As vertical modified in-situ retorts (VMIS) have been scaled up and tested, the overall oil yield has declined and is generally lower than that observed in an above-ground process. This reduced oil yield could adversely affect the economics of VMIS retorting. Diminished yields are attributed to a combination of factors associated with scale-up such as in complete rubblization, wide particle size distributions (large blocks of shale), and poor flow distributions. Additionally, oil losses can occur by comparatively long exposure of the oil vapours to high temperatures, by exposure to successive condensation and revaporization of the oil as it travels down the retort, and finally by long time thermal exposure of the condensed oil retained in the bottom portion of large VMIS retorts. To study such vapour phase degradation of shale oil using oil produced from Occidental Petroleum's No. 6 VMIS retort, a tubular continuous flow reactor, with an on-line gas chromatograph for gas composition monitoring was used to study thermal degradation of shale oil under retorting conditions. Oil and a combination of gases including steam were metered into the preheater and then the vapours passed into a quartz tubular reactor where the temperature and residence time of the gaseous mixture were controlled. Complete mass balances were performed giving the weight fraction of oil converted to noncondensable hydrocarbon gases and coke. This experimental design is novel because high temperature thermal degradation of shale oil was studied for the first time under steady state flow conditions with carefully controlled residence time and temperature. A range of temperatures (425–625 °C) and residence times (2–10 s) were used in a series of factorial-designed experiments (3²) to accurately determine the effects of these variables. Results of the study showed that the addition of steam to the carrier gas did not reduce oil degradation losses but did react with the coke thereby changing the product gas composition and quantity. A first-order oil degradation rate expression was used to model the rate of oil loss. The calculated activation energy was 17.3 kcal mol^?1. Chemical analyses of the product liquids and gases confirmed previously reported findings that the oil loss indices (alkene/alkane, ethylene/ethane, naphthalene/(C₁₁ + C₁₂), and gas/coke) increase with increasing oil degradation.     

Effects of ultrasonic vibration on the rheological behavior of high‐density polyethylene composites filled with flash aluminum flake pigments

The metallic effect of polymer composites was produced through the loading of flash aluminum flake pigments (FAFPs) into polymers. This production method could eliminate postprocessing techniques, such as spray coating, painting, or metallization. We used a self‐improved, ultrasound‐assisted capillary rheometer to explore the rheological behavior of high‐density polyethylene composites filled with FAFPs in the absence and presence of ultrasound treatment. The effects of the ultrasound intensity, experimental temperature, filler content, and particle size on the composite viscosity were studied. The results show that the composite viscosity not only decreased as the ultrasound intensity, experimental temperature, and particle size increased but also decreased as the filler content decreased. A viscosity model of the polymer melts was proposed to illustrate the relationship between the viscosity and ultrasonic intensity. The viscosity obeyed the equations under ultrasonic vibration. The predicted results for the composite viscosity complied greatly with the experimental values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44906.     

Thermal and electrical properties of aluminum nitride/boron nitride filled polyamide 6 hybrid polymer composites

The effects of boron nitride (BN) and aluminum nitride fillers on polyamide 6 (PA6) hybrid polymer composites were investigated. In particular, the thermal and electrical conductivity, thermal transition, thermal degradation, mechanical and morphological properties and chemical bonds characteristic of the materials with crystal structure of BN and aluminum nitride (AlN) filled PA6 prepared at different concentrations were characterized. Thermal conductivity of hybrid systems revealed a 1.6-fold gain compared to neat PA6. The highest thermal conductivity value was obtained for the composite containing 50 vol% additives (1.040 W/m K). A slight improvement in electrical conductive properties of composites appears and the highest value was obtained for the 50 vol% filled composite with only an increase by 3%. The microstructure of these composites revealed a homogeneous dispersion of AlN and BN additives in PA6 matrix. For all composites, one visible melting peak around 220°C related to the α-form crystals of PA6 was detected in correlation with the X-ray diffraction results. An improved thermal stability was obtained for 10 vol% AlN/BN filled PA6 composite (from 405.41°C to 409.68°C). The tensile strength results of all composites were found to be approximately 22% lower than pure PA6.     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Thermal degradation of Kevlar fiber by high‐resolution thermogravimetry

A novel high‐resolution thermogravimetry (TG) technique in a variable heating rate mode that maximizes resolution and minimizes the time required for TG experiments has been performed for evaluating the thermal degradation and its kinetics of Kevlar fiber in the temperature range ∼ 25–900°C. The degradation of Kevlar in nitrogen or air occurs in one step. The decomposition rate and char yield at 900°C are higher in air than in nitrogen, but the degradation temperature is higher in nitrogen than in air. The initial degradation temperature and maximal degradation rate for Kevlar are 520°C and 8.2%/min in air and 530°C and 3.5%/min in nitrogen. The different techniques for calculating the kinetic parameters are compared. The respective activation energy, order, and natural logarithm of preexponential factor of the degradation of Kevlar are achieved at average values of 133 kJ/mol (or 154 kJ/mol), 0.7 (or 1.1), and 16 min⁻¹ (or 20 min⁻¹) in air (or nitrogen). The technique based on the principle that the maximum weight loss rate is observed at the minimum heating rate gives thermal degradation results that were in excellent agreement with values determined by traditional TG experiments. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 565–571, 1999     

Thermal and electrical conductivity of carbon–filled liquid crystal polymer composites

The thermal and electrical conductivity of resins can be increased by adding conductive carbon fillers. One emerging market for thermally and electrically conductive resins is for bipolar plates for use in fuel cells. In this study, varying amounts of five different types of carbon, one carbon black, two synthetic graphites, one natural flake graphite, and one calcined needle coke, were added to Vectra A950RX Liquid Crystal Polymer. The resulting composites containing only one type of filler were then tested for thermal and electrical conductivity. The objective of this work was to determine which carbon filler produced a composite with the highest thermal and electrical conductivity. The results showed that composites containing Thermocarb TC‐300 synthetic graphite particles had the highest thermal and electrical conductivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99; 1552–1558, 2006     

Effect of chemical modifications on the thermal stability and degradation of banana fiber and banana fiber‐reinforced phenol formaldehyde composites

Banana fiber has been modified by treatments with sodium hydroxide, silanes, cyanoethylation, heat treatment, and latex treatment and the thermal degradation behavior of the fiber was analyzed by thermogravimetry and derivative thermogravimetry analysis. Both treated and untreated fibers showed two‐stage decomposition. All the treatments were found to increase the thermal stability of the fiber due to the physical and chemical changes induced by the treatments. The thermal degradation of treated and untreated banana fiber‐reinforced phenol formaldehyde composites has also been analyzed. It was found that the thermal stability of the composites was much higher than that of fibers but they are less stable compared to neat PF resin matrix. Composite samples were found to have four‐stage degradation. The NaOH treated fiber‐reinforced composites have very good fiber/matrix adhesion and hence improvement in thermal stability is observed. Though both silane treatments increased the thermal stability of the composite the vinyl silane is found to be more effective. Heat treatment improves the crystallinity of the fiber and decreases the moisture content, hence an improved thermal stability. The latex treatment and cyanoethylation make the fiber surface hydrophobic, here also the composite is thermally more stable than untreated one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008