Twin-Screw Extrusion of Nano-Alumina–Based Simulants of Energetic Formulations Involving Gel-Based Binders

Abstract

A 7.5-mm twin-screw extruder was developed specifically for the processing of energetic formulations involving nanoparticles. Prior to extrusion of energetic formulations, simulants of CMC, water, and alumina nanoparticle gels were extruded. Quantitative measures of degree of mixedness (statistics of concentration distributions) were obtained on samples processed with the twin-screw extruder and with conventional processing methods using wide-angle X-ray diffraction (WAXD) and thermo-gravimetric analysis (TGA) and were corroborated with microscopy. Twin-screw extrusion process generated more homogeneous mixtures of nanoparticles than conventional (intensive batch) mixing technologies and the use of surfactants further improved the homogeneity. With increasing homogeneity the suspension exhibited lower elasticity and shear viscosity. Overall, the results of this study emphasize the important roles played by the surface properties of rigid particles, the interfacial tension between the particles and the binder, and the rheological behavior of the binder. In the absence of properly selected binder and surfactant(s), the processing of nanoparticles, without agglomeration, is difficult to achieve. This finding may be relevant to the evaluation of past efforts, which have aimed to improve the ultimate properties of energetic formulations by incorporating nanoparticles.

Coupling of solvent-free synthesis and reactive extrusion of alumina: an ecologically efficient integration for heterogenous catalyst synthesis

“…that can be handled easily and loaded in flow reactors without causing excessive pressure-drop. [35][36][37][38] This kneadingextrusion process includes the peptization of the powder in a liquid, usually an acid or base, and potentially with an organic or mineral additive before extrusion. Peptization leads to deagglomeration of particles due to electrostatic repulsion of the charged surface after the adsorption of protons or hydroxyl ions.…”

“…39,40 The final textural properties of the support are mainly set during boehmite synthesis, but it can be modulated to a certain degree during the shaping process. 35 As shown in Fig. 1, before calcination, at least six elementary steps are necessary to obtain γ-Al 2 O 3 shaped extrudates via the conventional precipitation methods.…”

“…39,40 The final textural properties of the support are mainly set during boehmite synthesis, but it can be modulated to a certain degree during the shaping process. 35…”

Non-Isothermal Simulation and Safety Analysis of Twin-Screw Extrusion Process for Synthetizing Glycidyl Azide Polymer-Based Energetic Thermoplastic Elastomer

“…In order to investigate the effects of operating parameters and screw geometry on the mixing performance during the reactive extrusion process in the TSE, many experimental and numerical simulation studies have been carried out in recent years [ 23 , 24 , 25 ]. Ozkan, S. et al [ 26 ] developed a 7.5 mm twin-screw extruder to process high-energy formulations containing nanoparticles. The twin-screw extrusion process has been shown to have several inherent advantages.…”

Distributive mixing of carbon nanotubes in poly(caprolactone) via solution and melt processing: Viscoelasticity and crystallization behavior versus mixing indices

“…Generally commercially available CNTs are offered dry in agglomerated states, i.e., in bundles of several thousands of individual tubes held together via physical entanglements and attractive van der Waals forces. Mixing of the CNTs with the polymeric binder/s requires the breakup of the agglomerates via the disentanglement and separation of nanotubes from each other and their spatial distribution within the polymeric matrix (distributive mixing) . Even if the nanotube agglomerates can be broken down and the nanotubes separated from each other during the earlier stages of mixing and processing, the nanotubes can again demix into various agglomerate shapes and sizes during subsequent deformation and processing .…”