Investigating the relationship between tack and degree of conversion in DGEBA-based epoxy resin cured with dicyandiamide and diuron

The purpose behind this research was to determine the optimum formulation and investigate the cure kinetics of a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin cured by dicyandiamide and diuron for use in prepregs. First, all formulations were examined by the tensile test, and then, the specimens with higher mechanical properties were further investigated by viscometry and tack tests. The cure kinetics of the best formulation (based on tack test) in nonisothermal mode was investigated using differential scanning calorimetry at different heating rates. Kissinger and Ozawa method was used for determining the kinetic parameters of the curing process. The activation energy obtained by this method was 71.43 kJ/mol. The heating rate had no significant effect on the reaction order and the total reaction order was approximately constant ( m + n ≅ 2.1 $m+n\cong 2.1$ ). By comparing the experimental data and the theoretical data obtained by Kissinger and Ozawa method, a good agreement was seen between them. By increasing the degree of conversion, the viscosity decreased; as the degree of conversion increased, so did the slope of viscosity. The results of the tack test also indicated that the highest tack could be obtained with 25% progress of curing.

Non-Isothermal Crystallization Kinetics of Poly(Ethylene Glycol)–Poly(l-Lactide) Diblock Copolymer and Poly(Ethylene Glycol) Homopolymer via Fast-Scan Chip-Calorimeter

The non-isothermal crystallization kinetics of double-crystallizable poly(ethylene glycol)–poly(l-lactide) diblock copolymer (PEG-PLLA) and poly(ethylene glycol) homopolymer (PEG) were studied using the fast cooling rate provided by a Fast-Scan Chip-Calorimeter (FSC). The experimental data were analyzed by the Ozawa method and the Kissinger equation. Additionally, the total crystallization rate was represented by crystallization half time t1/2. The Ozawa method is a perfect success because secondary crystallization is inhibited by using fast cooling rate. The first crystallized PLLA block provides nucleation sites for the crystallization of PEG block and thus promotes the crystallization of the PEG block, which can be regarded as heterogeneous nucleation to a certain extent, while the method of the PEG block and PLLA block crystallized together corresponds to a one-dimensional growth, which reflects that there is a certain separation between the crystallization regions of the PLLA block and PEG block. Although crystallization of the PLLA block provides heterogeneous nucleation conditions for PEG block to a certain extent, it does not shorten the time of the whole crystallization process because of the complexity of the whole crystallization process including nucleation and growth.

Thermogravimetric devolatisation behavior of agricultural residue for generation of syngas

The thermal degradation characteristics of eucalyptus, pearl millet cob, and corncob were investigated using non-isothermal thermogravimetric method. This investigation was performed with the objective of carrying out thermochemical conversion for obtaining syngas. TG and DTG analysis were carried out to understand thermal devolatisation behavior and estimation of various thermophysical properties of the biomasses. The degradation behavior was analysed in the light of lignocellulosic composition that was found to have definitive influence on degradation outcomes. TG analysis has been utilized to obtain proximate analysis of biomass. Activation energy using Flynn-Wall-Ozawa method have been estimated and found to be 201, 150 and 68 kJ mol−1 for eucalyptus, pearl millet cob, and corncob respectively. The TG analysis and activation energy together indicated that corncob is easiest for thermochemical conversion amongst the three biomasses. The TG curve also confirms the same.

Thermo-catalytic degradation of PE and UHMWPE over zeolites with different pore systems and textural properties

The thermo-catalytic degradation of polyethylene (PE) and ultra-high molecular weight polyethylene (UHMWPE) was studied in the presence of zeolites (ZSM-5, ZSM-22, and ferrierite) with different pore systems and textural properties. The zeolites were physically mixed with polymers in the proportion of 30 wt% and submitted to thermogravimetric analysis at heating rates of 5, 10, 20, and 30 °C.min-1. The activation energy of the degradation process was determined using the Flynn-Wall-Ozawa method. The addition of zeolites to polymers has considerably reduced the temperature of degradation. ZSM-22 demonstrated greater efficiency in the degradation of PE because it has a smaller crystallite size, promoting a shorter diffusional path for the polymer fragments coming from the surface. Ferrierite showed a lower energy level in the degradation of UHMWPE, showing the need for synergy between the accessibility of the structure and acidity of the catalyst to promote the cracking of this polymer.

Synthesis, Crystal Structure and Thermal Decomposition of a New Energetic Potassium Salt of dihydridobis(3-nitro-1,2,4-triazolyl) Borate

A new energetic organic potassium salt of dihydridobis (3-nitro-1,2,4-triazolyl) borate was synthesized from 3-nitro-1,2,4-triazole and potassium borohydride at 110 °C, and structurally characterized by elemental analysis, IR spectra, 13C NMR and singlecrystal X-ray diffraction. Results show that the crystal belongs to monoclinic system with space group of p21 / C and cell parameters of a = 10.335 (8) Å, B = 10.812 (8) Å, C = 9.821 (8) Å, α = 90 ˚, β = 106.470 (13), γ = 90 °, z = 4. Its crystal density is 1.755g/cm3. Thermal properties were studied with TG-DTA and DSC. There was only one sharp decomposition peak temperature of 270 °C at the heating rate of 10 °C/ min-1. The activation energies EK = 48.0kJ/mol-1 and EO = 49.8kJ/mol-1 were calculated by the Kissinger method and Ozawa method respectively (CCDC: 1975139).

A Novel Zirconium Modified Arylacetylene Resin: Preparation, Thermal Properties and Ceramifiable Mechanism

With the rapid development of thermal protection systems for the aerospace industry and power electronics, polyarylacetylene (PAA) resin plays an important role because of its good mechanical properties, high glass transition temperature (Tg), low water absorption, high char yield (Yc), and the fact that there is no byproduct released in the curing process. In order to further improve the thermal property of PAA based FRP for the thermal protection field, the introduction of a zirconium element into arylacetylene is promising. In this paper, zirconium modified arylacetylene (ZAA) resin was prepared by two-step synthesis. The FTIR analysis characterized its molecular structure and confirmed the products. The viscosity of ZAA was about 6.5 Pa·s when the temperature was above 120 °C. The DSC analysis showed that the ZAA had a low curing temperature, and its apparent activation energy was 103.86 kJ/mol in the Kissinger method and 106.46 kJ/mol in the Ozawa method. The dielectric constant at 1 MHz of poly(zirconium modified arylacetylene) (PZAA) was 3.4. The TG analysis showed that the temperatures of a weight loss of 5% (Td5) and char yield (Yc) at 800 °C of PZAA were 407.5 °C and 61.4%, respectively. The XRD results showed the presence of SiO2 and ZrO2 in the PZAA residue after ablation. The XRF results showed that the contents of SiO2 and ZrO2 in PZAA residual after ablation were, respectively, 15.3% and 12.4%. The SEM showed that the surface of PZAA after ablation had been covered with a dense and rigid ceramic phase composed of ZrO2 and SiO2. Therefore, the introduction of Zr into arylacetylene greatly improved the densification of the surface after ablation, and improved the heat resistant property.

Kinetic studies on the pyrolysis of plastic waste using a combination of model-fitting and model-free methods

In this work, the pyrolysis behavior of plastic waste—TV plastic shell—was investigated, based on thermogravimetric analysis and using a combination of model-fitting and model-free methods. The possible reaction mechanism and kinetic compensation effects were also examined. Thermogravimetric analysis indicated that the decomposition of plastic waste in a helium atmosphere can be divided into three stages: the minor loss stage (20–300°C), the major loss stage (300–500°C) and the stable loss stage (500–1000°C). The corresponding weight loss at three different heating rates of 15, 25 and 35 K/min were determined to be 2.80–3.02%, 94.45–95.11% and 0.04–0.16%, respectively. The activation energy ( Ea) and correlation coefficient ( R2) profiles revealed that the kinetic parameters calculated using the Friedman and Kissinger–Akahira–Sunose method displayed a similar trend. The values from the Flynn–Wall–Ozawa and Starink methods were comparable, although the former gave higher R2 values. The Eα values gradually decreased from 269.75 kJ/mol to 184.18 kJ/mol as the degree of conversion ( α) increased from 0.1 to 0.8. Beyond this range, the Eα slightly increased to 211.31 kJ/mol. The model-fitting method of Coats–Redfern was used to predict the possible reaction mechanism, for which the first-order model resulted in higher R2 values than and comparable Eα values to those obtained from the Flynn–Wall–Ozawa method. The pre-exponential factors (ln A) were calculated based on the F1 reaction model and the Flynn–Wall–Ozawa method, and fell in the range 59.34–48.05. The study of the kinetic compensation effect confirmed that a compensation effect existed between Ea and ln A during the plastic waste pyrolysis.

A comparison of thermal degradation kinetic mechanisms between elongational and shearing flow fields for nano-silica/IFR synergistic fire retardant polypropylene nanocomposites

In this work, the same formulations of Nano-Silica/intumescent fire retardant polypropylene nanocomposites were prepared via a novel vane extruder and a tri-screw extruder, which represented elongational flow field and shearing flow field, respectively. Not only the synergistic combustion mechanisms of Kissinger method and Flynn-Wall-Ozawa method were revealed, but also the combustion effect and efficiency were compared. Both two methods proved specimens that processed by TE exhibited higher thermal stability. The smaller aggregates of physical initial Nano-Silica, the better dispersivity of aggregates in specimens that processed by VE. Such property broke the compactness degree of char layer.

Thermal Degradation and Water Uptake of Biodegradable Resin Prepared from Millet Flour and Wheat Gluten Crosslinked with Epoxydized Vegetable Oils

The degradation temperatures (DTs), heat stability (IPDT), degradation kinetics, and water uptake of epoxy resin were investigated using thermogravimetric analysis. Epoxy resins were prepared by crosslinking epoxydized oils with vital wheat gluten (VG) and millet flour. The reactions included three oils (cottonseed, sesame, and sunflower) and three levels of zinc chloride (ZC) (1, 2, and 3%). The apparent activation energy (Ea) was calculated using the Flynn–Wall–Ozawa method. The DT increased at higher heating rates within the same ZC level of the same oil type. Cottonseed oil exhibited the highest DT. The highest IPDT was 637°C of the sunflower oil/millet resin (3% ZC), and the least was the cottonseed/millet (1% ZC) at 479°C. The sesame-millet resin exhibited the highest Ea (622 KJ/mol) followed by sunflower-gluten (496 KJ/mol) and sesame-gluten (454 KJ/mol). The profiles of all resins point to a multistep degradation, but some of the profiles display two dominant kinetic processes, and the remaining resins showed three processes. The variation in crosslinking density between the oils is attributable to the different amounts of oxirane rings which are associated with the double bonds of the fatty acid of the oils. Like other parameters, the water uptake was affected by the ZC content, where most of the resins did not reach water uptake equilibrium. Nonetheless, the 3% ZC resin reached equilibrium after 5 days of immersion.

Comparative study on the pyrolysis kinetics of polyurethane foam from waste refrigerators

Thermal treatment offers advantages of significant volume reduction and energy recovery for the polyurethane foam from waste refrigerators. In this work, the pyrolysis kinetics of polyurethane foam was investigated using the model-fitting, model-free and distributed activation energy model methods. The thermogravimetric analysis indicated that the polyurethane foam decomposition could be divided into three stages with temperatures of 38°C–400°C, 400°C–550°C and 550°C–1000°C. Peak temperatures for the major decomposition stage (<400°C) were determined as 324°C, 342°C and 344°C for heating rates of 5, 15 and 25 K min-1, respectively. The activation energy ( Eα) from the Friedman, Flynn–Wall–Ozawa and Tang methods increased with degree of conversion ( α) in the range of 0.05 to 0.5. The coefficients from the Flynn–Wall–Ozawa method were larger and the resulted Eα values fell into the range of 163.980–328.190 kJ mol-1 with an average of 206.099 kJ mol-1. For the Coats–Redfern method, the diffusion models offered higher coefficients, but the E values were smaller than that from the Flynn–Wall–Ozawa method. The Eα values derived from the distributed activation energy model method were determined as 163.536–334.231 kJ mol-1, with an average of 206.799 kJ mol-1. The peak of activation energy distribution curve was located at 205.929 kJ mol-1, consistent with the thermogravimetric results. The Flynn–Wall–Ozawa and distributed activation energy model methods were more reliable for describing the polyurethane foam pyrolysis process.