查看更多>>摘要：A peculiar thermochemical phenomenon of coexistence of chemical decomposition and material softening, observed in cellulose acetate butyrate (CAB) and named glass chemical transition is further scrutinized. It is demonstrated that cellulose acetate (CA), also, exhibits a thermo-chemical transition and that mixed esters like CAB, may exhibit more than one thermo-chemical transitions. The DSC intense endotherm below 100 degrees C, common in cellulose esters, is shown to arise, mainly, from esterification. The variation of the stability of the acetyl bond in CAB and CA is also analyzed. A critical discussion of these findings along with corroborating experimental data for poly(vinyl alcohol) (PVA) and literature data for vinyl polymers is presented, suggesting that the thermo-chemical transition is not a phenomenon exhibited, exclusively, by cellulose esters. Instead, it is an often-encountered phenomenon encompassing physicochemical changes and material softening at temperatures erroneously attributed to glass transitions or melting points.
查看更多>>摘要：Thermal characteristics and kinetics of the curing reaction of natural rubber latex foam (NRLF) incorporated with 0-3 phr (parts per hundred rubber) nano-alumina (NA) were comprehensively investigated. The kinetics of thermal degradation reaction of the vulcanized NRLF-NA was also modeled through a suitable kinetic mechanism, according to the Coats-Redfern (CR) model. Moreover, the foam crosslinking degree was determined via using the swelling method and the Flory-Rehner (FR) equation to create a deep insight into the impact of NA and its content on the foam network structure. The results showed that the filler of NA led to increasing the heat distribution within the compound and followed by the significant effects on the characteristics and kinetics of the vulcanization reaction, and as well as the foam crosslink density. This phenomenon caused the variation of the thermal stability, secondary crosslinking of the cured NRLF-NA and the thermal degradation mechanism. The resultant data indicated that the addition of 1 phr NA to the compound led to the highest thermal distribution which resulted in the latex foam with unfavorable thermal stability and degradation. Whereas, the NRLF-NA thermal properties were improved with increasing the loading content of NA, after 1 phr NA.
查看更多>>摘要：Polymeric solid-solid phase change materials (PSSPCMs) can essentially solve the leakage problem of physically composited solid-solid phase change materials, but the phase change enthalpies, which are usually far lower than the theoretical values, limit their applications. In this work, three PSSPCMs were prepared by co-esterification and polymerization with different amount of stearic acid (SA). The PSSPCMs suffered from lower crystallinities and activation energies at transition than pure SA, indicating that confinement of polymeric network on crystalline domains may lead to the decrease of enthalpy. According to analysis from generalized two-dimensional correlation Fourier transform infrared, the polymer network confinement in PSSPCMs mainly restricted the vibrations of nu asCH3, nu CH, and nu sCH3. In-depth understanding of the interaction between the crystalline chains and the polymeric networks would be beneficial for molecule design of novel PSSPCMs with high enthalpy.
查看更多>>摘要：Improving flame retardancy of silk fabric will expand its potential application fields. Herein, a novel P/N/S-containing flame retardant (FR) named glutaraldehyde ammonium sulfamate diethyl phosphate salt (GASDP) was prepared by one-pot reaction among glutaraldehyde, ammonium sulfamate and diethyl phosphite. We further explored its potential applications in durable FR modification of silk fabric through textile exhaustion approach. The grafting mechanism, thermal stability, flame retardancy and washing durability, and FR mechanism of the coated silk fabrics were studied. GASDP coating showed high FR functional efficiency due to the synergism among P, N and S. The coated silk fabric covalently grafted by GASDP had a high LOI of about 30.0%; it still reached B-1 classification after 25 washing cycles. GASDP coating exerted good flame retardancy to silk fabric through the intumescent FR mechanism. GASDP coating displays great potential to functional as efficient and durable approach to improve flame retardancy of silk fabric.
Uwaoma, R. C.Seheri, M. P.Strydom, C. A.Bunt, J. R....
9页
查看更多>>摘要：Amorphous calcium lignosulphonate (CaLS), a by-product of the paper industry, was evaluated as an adhesive to bind demineralised bituminous coal fines in various weight percentage ratios. Sequential acid (HCl, HF, HCl) leaching was used to reduce mineral matter content in the coal fines. The pyrolysis and gasification of the samples were investigated in laboratory-scale experiments to determine the effect of the CaLS addition on the pyrolysis and gasification reactivities. Coal-CaLS blends consisting of 5, 10, and 15% calcium lignosulphonate were prepared, compressed into pellets, and characterised using proximate, X-ray diffraction, and X-ray fluorescence analyses. An increase in binder concentration increases the mechanical strength of the pellets due to the increased interparticle contact area. The relative coal gasification reaction reactivity (1/T-max and 0.5/T-50), which was determined from the derivative thermogravimetry curves, increases with CaLS addition. The experimental results revealed that these wastes (coal fines and calcium lignosulphonate) could be utilised in thermochemical processes. Utilising these wastes will reduce the environmentally unfriendly volumes of amorphous calcium lignosulphonate and coal fines particles.
查看更多>>摘要：This study aims to analyze the thermal decomposition through pyrolysis process of coconut fiber and its thermodynamic properties by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). Three decomposition stages were identified: dehydration, volatile release (characterized by two exothermic events), and carbonization. Regarding the thermodynamic properties, the specific heat capacities, c(p), were obtained using three methods: ASTM E1269-11, modified ASTM E1269-11, and method of total solids. We observed that the main differences in the c(p) profiles as a function of the temperature occurred above 538 K, due to the particularities of each method regarding the mass loss. The method of total solids proved to be more suitable for the determination of c(p). Besides that, three linear equations were proposed to predict the c(p) for each pseudocomponent and char of the biomass. The enthalpy of reaction (H-R) was estimated, 564.45 kJ/kg, from integration of the heat flow of reaction (Q(R)). The knowledge of these thermodynamic properties is useful for heat transfer modeling and reactor design.
查看更多>>摘要：Correct sensible heat curve (virtual baseline) during phase change is a must for accurate evaluation of latent heat. In this article, the dynamically moving interface (DMI) model for any phase change material (PCM) measured with a differential scanning calorimeter (DSC) is devised not only for elucidating the complex mechanisms of transient heat transfer in the five stages from solid phase to liquid phase, but also for constructing a correct sensible heat curve during phase change. We derive all the governing relations in exact or analytic form to describe the corresponding heat currents in the five stages of transient heat transfer together with the correct sensible heat curve during phase change inside any tiny PCM sample. The error budget analysis for the expanded uncertainty of specific latent heat about the tiny indium sample is detailed after the full assessment to specific latent heats of several PCMs.
查看更多>>摘要：We present VITRIFAST, a high throughput optimization procedure to characterize the vitrification kinetics based on calorimetric measurements. By analyzing the temperature dependence of specific heat capacity, the method determines the fictive temperature, T-f, and the enthalpy change during physical aging, Delta H, within only a few seconds. We tested VITRIFAST on the low molecular weight glass-former o - terphenyl (OTP) and on an archetypal glass forming polymer, polystyrene (PS), by analyzing the outcome of two classical sets of experiments. By means of fast scanning calorimetry (FSC), we characterized the vitrification kinetics in a wide range of cooling rates and the isothermal physical aging after vitrification at a given rate. In less than 3 minutes, our method could process 18 different calorimetric scans and provided values of T-f and Delta H in excellent agreement with those reported in the literature. VITRIFAST can be employed in the analysis of the temperature dependence of any type of second order derivative of free energy and represents a tremendous advance in the data analysis of calorimetric scans. The method is particularly helpful for fast scanning calorimetry users, considering the extremely large number of heat capacity scans recorded by this technique within a few minutes.
查看更多>>摘要：To understand the thermal decomposition mechanism and performance of nitroimidazoles, 1,4-dinitroimidazole (1,4-DNI), 2,4-dinitroimidazole (2,4-DNI) and 4,5-dinitroimidazole (4,5-DNI) were synthesized by 4-nitroimidazole firstly and all of them were studied using Differential Scanning Calorimetry (DSC), Accelerating Rate Calorimetry (ARC) and Density Functional Theory (DFT). The experiments show that among the four nitroimidazoles, the decomposition temperature and apparent activation energy of 1,4-DNI are relatively low. Theoretical calculations show that compared with C-NO2, N-NO2 is easier to break from the imidazole ring, and the detonation performance of 1,4-DNI is the best among the four nitroimidazoles. Dinitroimidazoles all contain two nitro groups, resulting in their sensitivity and energy much greater than 4-NI. Since 1,4-DNI is the only substance containing N-NO2, the chemical activity of 1,4-DNI is further improved. In addition, 1,4-DNI has relatively excellent detonation performance, which can be used as the research direction of new energetic materials.
查看更多>>摘要：The thermal behavior of propyl (PG), octyl (OG) and dodecyl (DG) gallates, three antioxidants widely used in fuel and food industries, was evaluated by thermoanalytical techniques (TG, DTA, DSC and hot stage microscopy), and complementary techniques, such as FTIR-ATR and XRD. All of them presented melting in characteristic temperatures during heating. The resulting liquid phases crystallized in different solid forms when cooled just after melting. However, when the samples were heated beyond melting temperature, they decomposed. Although thermal studies were conducted at higher temperature than those in which they are regularly used, this work provided relevant information regarding their thermal behavior at higher temperatures. Data from XRD, FTIR-ATR and hot stage microscopy were used to confirm the presence of new polymorphs. Finally, based on these results mechanisms describing the thermal behavior of PG, OG and DG were proposed.
NSTL
Elsevier