Djalal Trache

Physico-chemical properties and thermal stability of microcrystalline cellulose isolated from Alfa fibres.

In this study, microcrystalline cellulose (Alfa-MCC) was extracted from Alfa fibres using acid hydrolysis method. The molecular weight of the cellulose samples was determined by gel permeation chromatography. The crystallinities were studied by means of X-ray diffraction and solid state cross polarization magic angle spinning (13)C nuclear magnetic resonance spectroscopy, revealing that Alfa-MCC was more crystalline than the native cellulose isolated from Alfa fibres. The morphology of the celluloses was investigated using scanning electron microscopy, showing a compact structure and a rough surface. Furthermore, a good thermal stability was shown for Alfa-MCC. Based on these analyses, Alfa-MCC showed tremendous potential use as composites reinforcing agent, foods stabilizer and pharmaceutical additive.

Microcrystalline cellulose: Isolation, characterization and bio-composites application-A review.

Considering its widespread usage in various fields, such as food, pharmaceutical, medical, cosmetic and polymer composites industries, microcrystalline cellulose (MCC) is becoming impellent due to increasing demand of alternatives to non-renewable and scarce fossil materials. Although it still suffers from some drawbacks, MCC has recently gained more interest owing to its renewability, non-toxicity, economic value, biodegradability, high mechanical properties, high surface area and biocompatibility. New sources, new isolation processes, and new treatments are currently under development to satisfy the increasing demand of producing new types of MCC-based materials on an industrial scale. Therefore, this review assembles the current knowledge on the isolation of MCC from different sources using various procedures, its characterization, and its application in bio-composites. Challenges and future opportunities of MCC-based composites are discussed as well as obstacles remaining for their extensive uses.

Experimental determination and prediction of (solid+liquid) phase equilibria for binary mixtures of heavy alkanes and fatty acids

Solid–liquid equilibria for three binary mixtures, n-Eicosane (1) + Lauric acid (2), n-Tetracosane (1) + Stearic acid (2), and n-Octacosane (1) + Palmitic acid (2), were measured using a differential scanning calorimeter. Simple eutectic behaviour was observed for these systems. The experimental results were correlated by means of the modified UNIFAC (Larsen and Gmehling versions), UNIQUAC and ideal models. The root-mean-square deviations of the solubility temperatures for all measured data vary from 0.26 to 3.15 K and depend on the particular model used. The best solubility correlation was obtained with the UNIQUAC model.

Study on the influence of ageing on chemical and mechanical properties of N,N′-dimethyl-N,N′-diphenylcarbamide stabilized propellants

Double-base propellants undergo chemical, physical and mechanical changes upon ageing, leading to changes in ballistic performance and presenting explosive hazards. This report studies the variation of chemical and mechanical properties of aged N,N′-dimethyl-N,N′-diphenylcarbamide (methyl centralite) stabilized propellants in order to simulate and evaluate the natural ageing throughout the artificial one. Therefore, a comparative study of stabilizer depletion, plasticizers content, heat of combustion and mechanical properties such as storage modulus, loss modulus and damping of naturally and artificially aged propellants has been carried out by the following techniques: high-performance liquid chromatography (HPLC), thermogravimetric analyzer (TG), calorimeter of combustion and dynamic mechanical analyzer (DMA), respectively. The results obtained show that all properties are closely connected. In addition, the determination of stabilizer depletion, plasticizers evaporation, decrease of heat of combustion and mechanical properties are very useful for a better understanding of the decomposition and ageing behaviour of propellants. The HPLC investigation of stabilizer has shown good stability of the propellants. The results obtained for DMA have shown that some considerable changes of the mechanical and viscoelastic properties of the propellants occurred during ageing. These results confirm the results obtained by TG for the reduction of the nitroglycerine amount and the decrease of the heat of combustion.

Recent advances in new oxidizers for solid rocket propulsion

Ammonium perchlorate (AP), the workhorse of oxidizers in solid rocket and missile propellants, exhibits various environmental issues resulting from the release of perchlorate into ground water, which have been directly linked to thyroid cancer. Furthermore, the generation of hydrochloric acid causes the depletion of the ozone layer and leads to high concentrations of acid rain. Nowadays, considerable efforts have been devoted to developing solid propellants using green oxidizers which demonstrate less hazards and environmentally friendly chlorine free combustion products. Although many candidates for AP replacement have been identified, most of them are far from being practically employed in real applications because of a number of severe difficulties, including cost. In this review, the potential green chemicals for use as oxidizers are highlighted and these reveal interesting physicochemical properties and performance. After a quick definition of green solid propellants and their main ingredients, the current status of AP propellants issues is discussed in light of possible substitution with potential green ingredients. Particular attention will be paid to the recent advances in the green oxidizers, their production and their characteristic properties. The advantages and shortcomings of various green oxidizers for specific and potential propellant uses are also discussed together with the attempts made to overcome these problems. As a consequence, efforts will certainly continue to seek AP alternatives and efficient green oxidizers for solid rocket propulsion in the near future.

Comments on "thermal degradation behavior of hypochlorite-oxidized starch nanocrystals under different oxidized levels".

This paper intends to discuss the employment of the Coats-Redfern equation to compute the kinetic parameters of the thermal degradation of hypochlorite-oxidized starch nancrystals by Wei et al. [Carbohydrate Polymers 124 (2015) 124-130]. The original paper has shown some fundamental errors when presenting the Coats-Redfern (CR) integral kinetic model. This CR equation is commonly used to calculate the activation energy of the thermal degradation from a single non isothermal thermogravimetric curve. However, the use of a set of experiments recorded under different heating rates is often required to obtain accurate results, as recommended by the International Confederation for Thermal Analysis and Calorimetry (ICTAC) Kinetics Committee. The present comments are focused on these statements giving some arguments and elucidations concerning the Coats-Redfern equation.

The influence of porosity of ammonium perchlorate (AP) on the thermomechanical and thermal properties of the AP/polyvinylchloride (PVC) composite propellants

The influence of porous ammonium perchlorate (POAP) on the thermomechanical and combustion behavior of solid rocket propellants based on polyvinylchloride binder has been investigated. Differential scanning calorimetry, differential thermogravimetry, dynamic mechanical thermal analysis, and scanning electronic microscopy measurements were used for thermomechanical and thermal decomposition properties assessment. The results obtained indicate that lower glass transitions of the propellants and catalytic effect of combustion are obtained with POAP.

Stabilizers for nitrate ester-based energetic materials and their mechanism of action: a state-of-the-art review

Aliphatic nitrate esters are currently the most widely used energetic ingredients in single-, double-, and triple-base propellants. These nitrate esters are unstable at ambient conditions, and stabilizing agents should be incorporated into the energetic compositions to inhibit and slow down the decomposition reactions that can occur. However, the currently used stabilizers present a number of environmental and human health issues. To overcome these shortcomings, many stabilizers have been appeared in the past few decades and continue to be developed. Furthermore, several analytical techniques have been introduced to monitor the stability of nitrate ester-based energetic materials as well, since the existing ones could not be efficiently applied. Therefore, this review paper discusses and summarizes the current and emergent stabilizers as well as their mechanisms of action. A critical and analytical examination of their advantages and drawbacks is made.

Thermal behavior and decomposition kinetics of composite solid propellants in the presence of amide burning rate suppressants

The employment of burning rate suppressants in the solid rocket propellant formulation is long known. Different research activities have been conducted to well understand the mechanism of suppression, but literature about the action of oxamide (OXA) and azodicarbonamide (ADA) on the thermal decomposition of composite propellant is still scarce. The focus of this study is on investigating the effect of burning rate suppressants on the thermal behavior and decomposition kinetics of composite solid propellants. Thermogravimetric analysis (TG) and differential thermal analysis have been used to identify the changes in the thermal and kinetic behaviors of coolant-based propellants. Two main decomposition stages were observed. It was found that OXA played an inhibition effect on both stages, whereas the ADA acts as a catalyst in the first stage and as coolant in the second one. The activation energy dependent on the conversion rate was estimated by two model-free integral methods: Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) based on the TG data obtained at different heating rates. The mechanism of action of coolants on the decomposition of solid propellants was confirmed by the kinetic investigation as well.

Comments on “An experimental investigation on heating rate effect in the thermal behavior of perhydrous bituminous coal during pyrolysis”

This paper has the intension of discussing about the published paper by Wu et al. (J Therm Anal Calorim 119:2195–2203, 2015). The original paper has shown some errors in quoting and using the Coats–Redfern integral kinetic equation. This discussion is focused on the employment of this model, and some arguments and clarifications are also given.