Date of Award

Spring 4-29-2020

Degree Type

Dissertation

Degree Name

PhD. Chemistry

Department

Chemistry and Biochemistry

Advisor

Alexander Y. Fadeev, Ph.D.

Committee Member

Sergiu M. Gorun, Ph.D.

Committee Member

Yuri Kazakevich, Ph.D.

Keywords

Nitrocellulose, Surface Chemistry, Silane, Contact Angle

Abstract

This research describes an investigation into the wettability of nitrocellulose (NC), most importantly to nitroglycerin (NG), which are key components of formulations used to propel military ammunition. NG demonstrates complete wetting of NC and, overtime, NG sweats on the NC surface and leaks out. The leaking out of NG from the solid formulation is a known cause of fires and explosions resulting from storage. The origin of this research is inspired by the need to engineer a solution to leakage problems of energetic plasticizer in NC based propellant. While searching for a viable material for a specific application, we journeyed into the very specific details of the properties of NC, and the chemical structures used for surface functionalization. In Chapter 1, we discuss the properties of nitrocellulose and the classes of propellant that contain NC and NG. We discuss the significance of the contact angle and how it’s measured. Experimental data showing the surface tension of nitroglycerin and its use as a probe fluid is described.

In Chapter 2, silane surface chemistry and its applications are discussed. We described reactions from previous work involving cellulose that assisted us with work with NC. We discuss our results from reacting alpha cellulose and silyl isocyanate that provided conformation for further applications with NC. We explain experiments for functionalizing NC using acyl chlorides and isocyanate chemistry. We then proceed with our findings that allowed us to establish chemical designs described in the following chapter. We describe approaches for producing a ‘tunable’ NC surface that is derived from a two-step process using the reaction of 3-(triethoxysilyl-propyl) isocyanate followed by reactions with alkyl-, fluoroalkyl-, or phenyl-silane, producing NC surfaces ranging in lyophobicity. Each functional group allows various degrees of reduced wettability of NC with NG. We demonstrate surface preparation using tetramethoxysilane and polydimethysilane vapor reactions on solid state NC. We further functionalized the silanol rich solid state NC with alkyl and fluoroalkyl functionalities. In Chapter 3, the progress of reactions is demonstrated by chemical analysis. SEM analysis of modified NC materials suggests bulk properties of NC were not affected by silane. DSC demonstrated consistent decomposition of bare and treated NC. XPS provided evidence of chemically modified fibers. Increased lyophobicity of modified NC demonstrate thermal stability and equivalent energetic properties compared to bare NC. NC was characterized by dynamic contact angles using water, hexadecane, and NG as probe fluids. Wettability of modified NC demonstrated significant variations in surface energy in accordance with the nature of surface functionalities. In Chapter 4, we discuss the methods of measuring contact angles. The contact angles of modified NC demonstrated surfaces with “tunable” wetting. NC grafted with fluoroalkyl-groups showed the most NG-repelling properties (θAdv/θRec~90o/50o). Estimation of contact angles on nitrocellulose treated fibers allowed insight of the surface properties showing an increase in curvature and reduced capillary effect. Surface energy was estimated using contact angle measurements. In Chapter 5, nitrogen gas adsorption gives insight on textural properties of bare and treated NC.

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