Structure and property of propellant based on nitroglycerine/glycerol triacetate mixed plasticizers: molecular dynamics simulation and experimental study

Molecular dynamics simulation has been used to investigate the influence of nitroglycerine (NG)/glycerol triacetate (GTA) mixed plasticizers on the plasticizing ability of nitrocellulose (NC) binder in solid propellant. The radial distribution function and binding energy indicated that NC/plasticizers blends showed stronger intermolecular interaction of van der Waals and hydrogen bonds. The mean-squared displacements of plasticizers and volume distribution revealed that the mobility of plasticizer GTA in the NC polymer binder was higher than that of NG. Then, the mechanical properties of the propellant based on NG/GTA mixed plasticizers were investigated systematically using experimental and simulation calculation method. The results suggested that the ductility of propellant based on NG/GTA mixed plasticizers was improved, implying that NG/GTA mixed plasticizers have a higher plasticizing efficiency for NC. Furthermore, we conducted experimental studies on the effects of NG/GTA mixed plasticizers on the energy and combustion properties of propellants. It was shown that NG/GTA mixed plasticizers could enhance the combustion efficiency of propellants effectively at low pressures. These computational and experimental studies provided guidance for the application of NG/GTA mixed plasticizers in high-performance propellants.

An Eco-Friendly Approach to Low-Temperature and Near-Neutral Bleaching of Cotton Knitted Fabrics Using Glycerol Triacetate as an Activator

Near-neutral bleaching of cotton fabrics at low temperature is of great importance for saving energy and ecological friendliness in textile industry. In this work, glycerol triacetate (GT) was investigated as an activator of hydrogen peroxide (H2O2) for low temperature bleaching of cotton knitted fabrics, and satisfactory whiteness was obtained. The bleaching properties of H2O2/GT system for cotton was assessed by the CIE whiteness index, H2O2 decomposition rate, concentration of generated peracetic acid (PAA) and bursting strength. Possible factors affecting the performance of H2O2/GT bleaching system were discussed in detail. Adding only 10 mmol/L GT to the hydrogen peroxide solution (60 mmol/L) to bleach cotton knitted fabrics at 60 ℃ for 60 min, the WI was significantly increased from 52.09 to 68.92. By using benzenepentacarboxylic acid as a fluorescent probe for hydroxyl radical (HO·) detection, it was found that GT could clearly promote HO· generation and the concentration of HO· closely related to the WI of cotton fabric. Furthermore, the bleaching mechanism of H2O2/GT system to cotton was proposed by exploring the relationship between WI and HO· concentration. As a bleach activator, GT has more economical benefits and better solubility in water than that of TAED. The H2O2/GT system may provide a cost-effective and environmentally friendly approach as alternative to conventional alkaline high-temperature bleaching of cotton.

A confocal Raman microscopic visualization of small penetrants in cellulose acetate using a deuterium-labeling technique

The purpose of the present study was to visualize the sorption dynamics of small compounds, such as propylene glycol (PG) in cellulose acetate (CA) film, by deuterium (d) labeling-aided confocal Raman spectroscopy (CRM). Substitution of hydrogen atoms in the target molecule with deuterium caused a marked shift of C-H bond-related Raman bands to low wavenumbers, while the number of deuterium did not affect the magnitude of the shift. Raman bands derived from the stretching vibration of C–H near 2900 cm−1 for PG and ethanol were shifted to approximately 2100 cm−1 for PG-d6 and ethanol-d5 in the silent region of the CA Raman spectrum. When PG-d6 was dissolved in glycerol triacetate (GTA), the observed Raman intensity ratio at 2123 cm−1 of PG-d6 against 1739 cm−1 of GTA (C=O bond-related) showed a linear relationship between the molar and intensity ratios, indicating that the observed Raman intensity can be used for quantitative assay of the target in polymer film. The depth profiling experiments by CRM revealed that the distribution (or sorption) of PG-d6 in CA film was successfully visualized as a function of Raman band at the characteristic 2123 cm−1 intensity ratio.

Scalable Green Approach Toward Fragrant Acetates

The advantageous properties of ethylene glycol diacetate (EGDA) qualify it as a useful substitute for glycerol triacetate (GTA) for various green applications. We scrutinised the lipase-mediated acetylation of structurally diverse alcohols in neat EGDA furnishing the range of naturally occurring fragrant acetates. We found that such enzymatic system exhibits high reactivity and selectivity towards activated (homo) allylic and non-activated primary/secondary alcohols. This feature was utilised in the scalable multigram synthesis of fragrant (Z)-hex-3-en-1-yl acetate in 70% yield. In addition, the Lipozyme 435/EGDA system was also found to be applicable for the chemo-selective acetylation of (hydroxyalkyl) phenols as well as for the kinetic resolution of chiral secondary alcohols. Lastly, its discrimination power was demonstrated in competitive experiments of equimolar mixtures of two isomeric alcohols. This enabled the practical synthesis of 1-pentyl acetate isolated as a single product in 68% yield from the equimolar mixture of 1-pentanol and 3-pentanol.

Application of bio-based solvents for biocatalysed synthesis of amides with Pseudomonas stutzeri lipase (PSL)

Bio-based solvents were investigated for the biocatalysed amidation reactions of various ester-amine combinations by Pseudomonas stutzeri lipase (PSL). Reactions were undertaken in a range of green and potentially bio-based solvents including terpinolene, p-cymene, limonene, 2-methyl THF, ɣ-valerolactone, propylene carbonate, dimethyl isosorbide, glycerol triacetate and water. Solvent screenings demonstrated the importance and potential of using non-polar bio-based solvents for favouring aminolysis over hydrolysis; whilst substrate screenings highlighted the unfavourable impact of reactants bearing bulky para- or 4-substituents. Renewable terpene-based solvents (terpinolene, p-cymene, D-limonene) were demonstrated to be suitable bio-based media for PSL amidation reactions. Such solvents could provide a greener and more sustainable alternative to traditional petrochemical derived non-polar solvents. Importantly, once the enzyme (either PSL or CALB) binds with a bulky para-substituted substrate, only small reagents are able to access the active site. This therefore limits the possibility for aminolysis to take place, thereby promoting the hydrolysis. This mechanism of binding supports the widely accepted ‘Ping Pong – Bi Bi’ mechanism used to describe enzyme kinetics. The work highlights the need to further investigate enzyme activity in relation to para- or 4-substituted substrates. A priority in PSL chemistry remains a methodology to tackle the competing hydrolysis reaction.

Fabrication and Optimization of a Lipase Immobilized Enzymatic Membrane Bioreactor based on Polysulfone Gradient-Pore Hollow Fiber Membrane

Enzymatic membrane bioreactors (EMBRs) possess the characteristic of combining catalysis with separation, and therefore have promising application potentials. In order to achieve a high-performance EMBR, membrane property, as well as operating parameters, should give special cause for concerns. In this work, an EMBR based on hollow fiber polysulfone microfiltration membranes with radial gradient pore structure was fabricated and enzyme immobilization was achieved through pressure-driven filtration. Lipase from Candida rugosa was used for immobilization and EMBR performance was studied with the enzymatic hydrolysis of glycerol triacetate as a model reaction. The influences of membrane pore diameter, substrate feed direction as well as operational parameters of operation pressure, substrate concentration, and temperature on the EMBR activity were investigated with the production of hydrolysates kinetically fitted. The complete EMBR system showed the highest activity of 1.07 × 104 U⋅g−1. The results in this work indicate future efforts for improvement in EMBR.