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Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different co...
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Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different compounds was performed, using a differential scanning calorimeter. The isothermal tests showed double reaction peaks, due to the cure reactions of DGEBA/acid anhydride systems. The comparisons between dynamic thermograms (and between isothermal ones, too) for the different mixtures also showed that the addition of other active substances (such as a nanofiller or a flame retardant additive) does not change the mechanism of crosslinking from a qualitative point of view, but both the nanoreinforcement and the flame retardant seemed to exert an evident catalytic action on the cure reactions. A model describing the cure behavior of the aforementioned materials is proposed in this work. This model takes into account the fact that the reaction mechanism of each analyzed system is composed of a couple of parallel phenomena: the fast opening of anhydride ring (corresponding to a first exothermic peak and characterized by "n-th order" kinetics) and resin networking (corresponding to a second exothermic peak and characterized by an "auto-catalytic with zero initial velocity" behavior). The verification of the proposed model was performed by means of a comparison between experimental data (normalized curves derived from DSC thermograms) and theoretical data (derived from a numerical integration-using the second order Runge-Kutta method-of the model-representative equation) and provided very good results. This allows one to apply such a model to any engineering process problem concerning the cure of DGEBA/acid anhydride/phyllosilicate nanocomposite systems. (C) 2004 Wiley Periodicals, Inc.
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Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T(g)s) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsis...
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Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T(g)s) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most useful for the analysis of the derivative of the heat capacity, dC(p)/dt or dC(p)/dT, plots which best highlight overlapping T (g)s. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dC(p)/dt vs. dC(p)/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided for the analysis of bitumen, a complex mixture of natural origin.
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Low density poly(ethylene) (LDPE) was melt functionalized with three different esters namely, thio ester, amino ester, and hydroxy ester under inert atmosphere at 160°C with different experimental conditions. During the functiona...
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Low density poly(ethylene) (LDPE) was melt functionalized with three different esters namely, thio ester, amino ester, and hydroxy ester under inert atmosphere at 160°C with different experimental conditions. During the functionalization reaction, crosslinking (C.L) and C=C formation are the simultaneous competitive reactions. FTIR-RI analysis method was used to determine the % functionalization onto LDPE backbone and the order of functionalization reaction. Thermogravemetric analysis (TGA) and Differential scanning calorimetry (DSC) were used to assess the thermal properties of the functionalized LDPE. Suitable reaction scheme was proposed.
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The crystallization kinetics and crystalline structure of the biodegradable polymorphic polymers, poly(butylene adipate) (PBA) and poly(butylene adipate-co-hexamethylene adipate), in the microparticles and nanoparticles covered by...
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The crystallization kinetics and crystalline structure of the biodegradable polymorphic polymers, poly(butylene adipate) (PBA) and poly(butylene adipate-co-hexamethylene adipate), in the microparticles and nanoparticles covered by poly(vinyl alcohol) (PVA), and those on the PVA substrate were investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and Fourier transform infrared spectroscopy. Both the polymers crystallized in the particle state and on the PVA substrate showed higher crystallization temperatures in the nonisothermal melt crystallization and shorter crystallization times in the isothermal crystallization; this indicated a faster crystallization of the polymer in the particle state and on the PVA substrate than that of the bulk sample. Furthermore, the polymers in the particle state and on the PVA substrate showed the preferential formation of the β-type crystalline form of PBA compared to the bulk one. The mechanism for the effects of the PVA layer or substrate on the crystallization kinetics and crystalline structure of PBA and its copolyesters are discussed.
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We investigated the material properties of different crosslinked sulfonated poly(aryl ether ketone) membranes, focusing on the effect of the degree of sulfonation and crosslinking density on the water uptake, the physical state of...
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We investigated the material properties of different crosslinked sulfonated poly(aryl ether ketone) membranes, focusing on the effect of the degree of sulfonation and crosslinking density on the water uptake, the physical state of the water, and the pore size distribution within the membranes. We observed that the degree of sulfonation and, in particular, the ion-exchange capacity (IEC) had less effect on the control of the extent of water absorbed than the crosslinking density of the membranes. Crosslinking also enabled the membranes to reach a higher water contents without losing mechanical integrity. Moreover, increasing the crosslinking density resulted in the presence of more bound water, without dissolution of the membrane. The crosslinked membranes had lower methanol permeability and electroosmotic drag values. Only at low IEC values and low water uptake in partially crystalline sulphonated poly(ether ether ketone), SPEEK could the presence of nanometer pores in the water-equilibrated crosslinked membranes be confirmed by thermoporometry and the pore size distributions were then comparable to those reported for Nafion membranes. At higher IEC values, the water uptake was extremely high, up to 300%, and then the structure of the swollen membranes was more analogous to that of a dilute aqueous solution of the sulfonated polymer, and no nanopores were present.
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In this work, the nonisothermal and isothermal cold crystallization behaviors of poly(L-lactide) (PLLA)/trisilanolisobutylpolyhedral oligomeric silsesquioxanes (tsib-POSS) nanocomposites with low tsib-POSS contents were fully inve...
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In this work, the nonisothermal and isothermal cold crystallization behaviors of poly(L-lactide) (PLLA)/trisilanolisobutylpolyhedral oligomeric silsesquioxanes (tsib-POSS) nanocomposites with low tsib-POSS contents were fully investigated. For all the samples, the variations of heating rate and the tsib-POSS loading may influence the nonisothermal cold crystallization of PLLA. During the nonisothermal crystallization kinetics study, the Ozawa equation failed to fit the nonisothermal crystallization process of PLLA, while the Tobin equation could fit it well. For the isothermal crystallization kinetics study, the crystallization rates of all the samples increased with increasing crystallization temperature. The cold crystallization activation energy of PLLA was increased with 1 wt % tsib-POSS. Moreover, the addition of tsib-POSS and the increment of tsib-POSS loading could increase the crystallization rate of PLLA, indicating the nucleating agent effect of tsib-POSS. However, the crystallization mechanism and crystal structure of PLLA remained unchanged in the nanocomposites. (C) 2016 Wiley Periodicals, Inc.
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Crosslinking of amorphous poly (ether ether ketone) films was carried out by means of thermal annealing at 400 degrees C as well as by irradiation with 11.0 MeV proton beam at different dose rate ranging from 1.75 to 15.5 kW g(-1)...
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Crosslinking of amorphous poly (ether ether ketone) films was carried out by means of thermal annealing at 400 degrees C as well as by irradiation with 11.0 MeV proton beam at different dose rate ranging from 1.75 to 15.5 kW g(-1). The materials properties of the resulting films were investigated by mean of light microscopy, sol-gel analysis, two-dimensional infra-red correlation spectroscopy, 2DCOS-IR, and differential scanning calorimetry (DSC). It was found that both chain scission and crosslinking yields were decreased by an increase of dose rate and the ratio of crosslinks to chain scission was increased from 0.9 to 1.4. The 2DCOS-IR analysis in the region 1400-1800 cm(-1) showed progressive development of new bands at 1470 and 1740 cm(-1), which have been used to support the presence of crosslinking and chain scission reactions. The glass transition temperature also increased in line with increasing crosslinking density, but the results showed a limiting plateau value for the glass transition Tg, which depended only on the absorbed dose. This suggests that crosslinking was limited and did not increase after a specific value of the dose rate. Crosslinking by irradiation has many advantages over thermal annealing; in particular it is a one step rapid process producing a variety of homogeneously crosslinked, good quality films available for chemical modification. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41999.
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A series of 1,3,5-trialkyl-benzenetricarboxylamides (BTA-Rs) with different side-chain lengths of n-alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed i...
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A series of 1,3,5-trialkyl-benzenetricarboxylamides (BTA-Rs) with different side-chain lengths of n-alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt-crystallization with addition of the synthesized nucleating agents. Among these BTA-Rs, BTA-n-butyl (BTA-nBu) shows the most excellent nucleation ability for PLA. The influences of BTA-nBu on the nonisothermal melt-crystallization and cold-crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA-nBu to improve the crystallization of PLA. In the case of isothermal melt-crystallization from melt, the addition of BTA-nBu shortens the crystallization half-time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA-nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA.
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The effects of melt-spinning and cold-drawing parameters on the formation of beta-phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were melt-spun with fo...
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The effects of melt-spinning and cold-drawing parameters on the formation of beta-phase crystallinity in poly(vinylidene fluoride) (PVDF) fibers and ways of increasing such crystallinity were studied. Fibers were melt-spun with four different melt draw ratios (MDRs) and were subsequently cold-drawn at different draw ratios (lambda). The maximum lambda value in cold drawing was dependent on the MDR used in melt spinning. The crystalline structure of the fibers was studied mainly with differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the degree of crystallinity in the fibers was determined by the MDR and that before cold drawing the crystalline structure of the fibers was predominantly in the alpha form. By cold drawing, alpha-phase crystallites could be transformed into the beta phase. It was established that, under certain conditions of melt spinning and cold drawing, PVDF fibers of up to 80% crystallinity, mainly in the beta form, could be prepared. It was further proposed that fibers spun at a sufficiently high MDR consist to a large extent of extended-chain crystals, and this greatly affects the melting point of PVDF. Thus, DSC melting-point data were shown to be insufficient for determining the crystalline phase of PVDF.
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The influence of magnesium sulfate (MgSO4) whiskers on the structure and properties of polypropylene cast films and stretched microporous membranes was investigated. We found that for the cast films, MgSO4 showed some nucleation e...
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The influence of magnesium sulfate (MgSO4) whiskers on the structure and properties of polypropylene cast films and stretched microporous membranes was investigated. We found that for the cast films, MgSO4 showed some nucleation effects, and the introduction of MgSO4 led to the decrease of the orientation degree along the machine direction (MD), whereas that along the transverse direction (TD) was improved; this indicated that MgSO4 whiskers were mainly arranged along the TD. The introduction of MgSO4 up to 10 wt % did not induce apparent changes in the pore structure and air permeability properties of the stretched microporous membranes but improved the electrolyte absorption ability. The most pronounced change for the stretched microporous membranes was the strength along the TD. It was increased by 110% when the MgSO4 content was 2 wt %. During the fabrication of microporous membranes, only stretching along the MD was carried out to initiate pore formation; this resulted in a lower strength along the TD. This study gave us a method for improving the mechanical properties of stretched microporous membranes along the TD. The obtained microporous membranes with better electrolyte absorption and higher mechanical strength along the TD could be used in lithium-ion batteries as separators. (C) 2016 Wiley Periodicals, Inc.
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