Graded polymer composites using twin-screw extrusion: A combinatorial approach to developing new energetic materials

https://doi.org/10.1016/j.compositesa.2005.03.025Get rights and content

Abstract

The development of new energetic materials is a time-consuming, laborious, and sometimes dangerous process. Batch approaches are most commonly used, especially for energetic materials consisting of polymer composites. Recently, a manufacturing technology known as Twin-Screw Extrusion (TSE), has been demonstrated to increase the safety and affordability for manufacturing composite energetic materials. This technology is also ideally suited to manufacturing graded polymer composites through transient operating and/or feed conditions. In this paper, the TSE process is employed to fabricate graded polymer composites in a combinatorial approach for developing new energetic materials. Graded composite energetic materials with 79–87% solids loading of Ammonium Perchlorate are processed. The dependence of burning rate properties on the variation in composition was determined through strand burning tests. These results were compared with a conventional design of experiments approach using the Kowalski algorithm. The correlation of composition to properties over a range of compositions between the new combinatorial approach and the conventional design of experiments approach validates the use of TSE processing as a combinatorial approach to developing new energetic materials. Because the TSE process is used to manufacture both energetic and non-energetic composite materials, the combinatorial approach can also be applied to the development of new non-energetic polymer composites for applications such as control and sensing.

Introduction

Composite materials are being fabricated for energetic applications using a very high solids loading of energetic particles (≫70 wt%), bound by a polymer. These materials have primarily been processed using batch techniques. By varying the solids content, particle sizes, and particle distributions, combined with smaller volume fractions of additives, it is possible to create a variety of formulations that exhibit a wide range of energy release rates, impact sensitivity, and thermal sensitivity.

Recently, alternative processing techniques that have been conventionally used for inert composite material systems have been pursued for the fabrication of composite energetic materials. In particular, a continuous processing technique known as Twin-Screw Extrusion (TSE) has been particularly attractive for increasing the safety and affordability of manufacturing composite energetic materials. This technology is fairly well understood for the processing of homogeneous energetic composite materials in a steady state and was originally developed in Germany during the mid-1960s and much later adopted by the United States [1], [2].

More recently, it has been shown that the TSE technique can be run in a transient state to produce controlled variations in material distribution resulting in non-energetic graded polymer composites for applications such as control and sensing [3]. The evolution of the gradient architecture was predicted using convolution process models based on residence distributions. A residence distribution is the result of an input disturbance to a continuous process whether it is a screw extruder or series of stirred tank reactors. It is a popular experimental and theoretical tool because it quantitatively reflects the combined effects of the process conditions on the material transport through the process (screw speed and design, throughput rate, temperature, ingredients, etc.). Using the residence distribution data in a novel approach, solutions to the convolution integral were employed in the time and volume domains to predict the one-dimensional structure of graded composite propellant produced using a twin-screw extruder.

Graded materials have been previously employed for combinatorial approaches to advanced materials research & development [4]. The combinatorial approach to developing advanced materials or for high-throughput screening of ingredient combinations and other parameters has been successfully demonstrated for small structures such as thin films and over short distances [4], [5], [6], [7]. Combinatorial and high-throughput experimental methods have also been applied to polymers and nanocomposites in recent years [8], [9], [10]. The experimental processes are quite specific as to material and objective, but the results are similar in that a graded structure, often with a continuous gradient architecture, is made and subjected to a variety of non-destructive testing. The gradients can be effected as compositional and/or processing conditions. From tests at different locations in the graded structures, it is possible to ascertain a number of properties through a range of the parameter space.

In this paper, the TSE technique is pursued as a combinatorial approach to the processing of new composite energetic materials. Using the previously developed convolution process model, it is shown that controlled gradient architectures can be predicted and then produced. The composition of these gradient architectures are then characterized, and then correlated to the combustion properties determined using burning rate testing. These results are compared with a conventional approach to determining the compositional dependence of burning rates using batch processing of formulations determined using a Kowalski–Cornell–Vining (KCV) design-of-experiments algorithm.

Section snippets

Prediction of gradient architectures fabricated using TSE processing

Burning rate is highly dependent upon oxidizer particle size and content among test conditions, etc. The functionally graded rocket motors conceived and developed during this project were linearly graded cylinders measuring 1.25 by 30 inch. Homogeneous compositions with 79 and 87 percent by weight comprised the two ends of the motor. Between the two was a continuous gradient from one fill content to the other measuring approximately 4.5 inch. It is beyond the scope of this paper to describe the

Experimental apparatus

Unique facilities have been assembled at the Naval Surface Warfare Center in Indian Head, MD (NAVSEAIHMD) to address the specific needs for processing energetic polymer composites in a TSE process [11]. One of the extruders employed is a Werner & Pfleiderer ZSK-40 (mm) featuring segmented and cantilevered screws. It has a process length to diameter (L/D) ratio of 28, which is similar to the machine employed at the University of Maryland in a previous investigation on graded polymer composites [3]

Acoustic strand burner test description

The best measure of a propellant's combustion properties is to test it in a motor; however, this is costly and inefficient during development. Instead, a good alternative is to conduct strand burning tests under a range of conditions (e.g. chamber pressure and temperature). Testing at different pressures allows determination of the burning rate exponent. The common method of strand burning is to test six-inch long strands 1/4 inch in thickness and report the average burning rate for

Comparison of compositional dependence between the combinatorial approach with the experimental response surface analysis (RSA)

It was desirable to compare the compositional dependence of properties obtained from the combinatorial approach with the most optimal mixture experiment approach for ascertaining the effects of the individual ingredients on the burning rates as produced over the range of feeding and extruding capability for the process. Response surface methods can quantify the contribution of individual ingredients and more importantly the combined effects of two or more ingredients. Most mixture designs are

Conclusions

A combinatorial approach based on Twin-Screw Extrusion (TSE) has been developed for evaluating new composite energetic materials. Materials with gradient architectures are produced by the TSE process. The combinatorial approach uses a convolution process model to predict the variation of composition in the gradient architecture. Experiments were developed for characterizing the variation in burning rate through the gradient architecture using strand burning tests. Comparisons of the burning

References (18)

  • D. Fair

    Application of screw processors to the manufacture of energetic materials

    (1987)
  • F.M. Gallant et al.

    Twin-screw processing of plastic bonded explosives at naval surface warfare center

    (1988)
  • F.M. Gallant et al.

    Fabrication of particle-reinforced polymers with continuous gradient architectures using twin-screw extrusion processing

    J Compos Mater

    (2004)
  • R. Cremer et al.

    Combinatorial methods for advanced materials research & development

    Z Metallkunde

    (2001)
  • F. Tsui et al.

    The combinatorial approach: a useful tool for studying epitaxial processes in doped magnetic semiconductors

    Macromol Rapid Commun

    (2004)
  • D. Godovsky et al.

    Use of combinatorial materials development for polymer solar cells

    Adv Mater Opt Electron

    (2000)
  • N. Eidelman et al.

    Combinatorial approach to characterizing epoxy curing

    Macromol Rapid Commun

    (2004)
  • J.C. Meredith

    A current perspective on high-throughput polymer science

    J Mater Sci

    (2003)
  • J.W. Gilman et al.

    High throughput methods for nanocomposites materials research. Extrusion and visible optical probes

    Polymeric Mater: Sci Eng

    (2004)
There are more references available in the full text version of this article.

Cited by (25)

  • Mechanism of microwave-initiated ignition of sensitized energetic nanocomposites

    2021, Chemical Engineering Journal
    Citation Excerpt :

    An ongoing challenge in the tailoring of energetic materials is enabling the ability to modulate energy release rates. One way that this can be accomplished is by using additively manufactured graded materials [1–4] which enable electromagnetic radiation to locally stimulate materials to moderate burn rate or initiate reactions at specified locations or times. Infrared, visible (400–700 nm), and ultraviolet (UV, 10–400 nm) wavelength light sources are readily available and considerable effort has been expended on exploring these wavelengths (e.g. laser ignition) [5–9].

  • MULTI-MATERIAL ADDITIVELY MANUFACTURED COMPOSITE REACTIVE MATERIALS VIA CONTINUOUS FILAMENT DIRECT INK WRITING

    2020, Additive Manufacturing
    Citation Excerpt :

    Similarly, Truby et al. created soft actuators via embedded 3d printing to emulate the human somatosensory system [16]. Composite energetics have been created using twin screw extrusion processes allowing for composite or graded energetics [17–19] This work explores the natural overlap of these two topics: using multi-material additive manufacturing to create composite energetics.

  • Kinetic diffusion multiple: A high throughput approach to screening the composition-microstructure-micromechanical properties relationships

    2018, Calphad: Computer Coupling of Phase Diagrams and Thermochemistry
    Citation Excerpt :

    This complicates determination of the outcomes from different experimental runs as functions of both compositions and microstructures, because associated effecting factors are difficult and/or costly to control. Innovative high throughput work to tackle these difficulties include: Gallant et al., via introducing thermo-mechanical gradients and surveying the processing parameters that influence bulk energy materials [18], in situ screening that acquired the evolution of phases associated with gas-solid reactions in combinatorial catalyst libraries [19], and the process-property linkage of structural Al-6061 alloy [20]. Meanwhile, promising high throughput diffusion studies have focused on materials subjected to either diffusion annealing or processing by a single stage that essentially generates a single array, either continuous or discrete, of compositions or processing of materials without further treatments, thus rendering it a one-array-at-a-time approach.

  • Electric field assisted gradient structure formation of glass microsphere columns in polymer films

    2017, Composites Science and Technology
    Citation Excerpt :

    Over the past few decades, various technologies have been developed to create spatial gradients. For the inorganic particles/polymer system, these fabrication methods generally are classified into two groups [9,10]. In the first group, the particles are first dispersed in polymer to form uniform suspension or solution, and then driven by gravity force [11] or centrifugal force [12] or external magnetic field [13,14] to produce gradient distribution along a specific direction.

View all citing articles on Scopus
View full text