Kinetics of the Surface Degradation of Polymethylmethacrylate

Chaiken, Robert F.; Andersen, W. H.; Barsh, Max K.; Mishuck, E.; Moe, Geir; Schultz, Robert D.

doi:10.1063/1.1700888

Cited by 53 publications

(13 citation statements)

References 9 publications

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“…Of particular importance to this discussion is the fact that the rate controlling mechanism of surface decomposition of certain solids has been found experimentally to be different from that of decomposition in the bulk phase under isothermal conditions. This duality of thermal decomposition has been demonstrated with ammonium nitrate (11) and typical polymeric binders (8,12), where it was shown that at high surface temperatures endothermic surface vaporization or dissociative sublimation is apparently rate determining. The duality of the reaction mechanism (bulk and surface) in ammonium nitrate is related to the manner in which thermal energy is supplied to the solid.…”

Section: Grain Burningmentioning

confidence: 92%

Detonability of Solid Composite Propellants

Andersen¹

1961

ARS Journal

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The thin film platinum resistance thermometer (heat flux gage) has been successfully applied to measurement of heat fluxes from initiators for solid propellants. Heat fluxes measured were as high as 1000 Btu/ft 2 -sec from hot, particleladen reaction products of pyrotechnic igniters. Results of heat flux studies and ignition of propellants by these igniters show good agreement with independent propellant ignition studies in shock tubes and radiation furnaces. Nomenclature H = heat or energy} = time \ T L rrii Dimensions = temperature = length .."» = slope of the ith. straight line segment, T6~l q(t) = heat flux at time t from start of igniter action, HL~26~l t = time from start of igniter action, B = temperature at the terminus of the ^'th straight line segment, T -temperature at zero time, T = thermal responsitivity (square root of the product of Ti To r density, heat capacity, and thermal conductivity) = time at terminus of the ith. straight line segment, 0 = time at the terminus of last straight line segment # (0 n = t), 6 = time variable of integration, 6A theoretical model of propagation of detonation in propellants is presented. This model is based on the hypothesis that detonation is propagated by the same rate controlling chemical reactions that occur during normal burning of the propellant. In particular, it is assumed that a grain burning of the oxidizer occurs and that the rate of linear-surface decomposition (pyrolysis) of the oxidizer can be used to describe the rate of detonation reaction. Kinetic data on the surface decomposition of ammonium perchlorate, which were obtained by the hot plate-linear pyrolysis technique, suggests that sublimation of ammonium perchlorate (with an apparent activation energy of ^22 kcal/mole) is the rate controlling step in the surface decomposition of this oxidizer. A discussion is presented on how these data can be used in conjunction with the detonation model to calculate the minimum (critical) diameters at which detonation can propagate in a cylindrical charge of solid propellant. The possible effect of various propellant parameters, i.e., oxidizer binder ratio, oxidizer particle size, confinement, etc., on the detonation process is discussed. The role of ignition, diffusion and heat conduction processes in the detonation and rapid deflagration of solid composite propellants is discussed. A preliminary theoretical approach to accelerating burning in porous propellant is also presented. This approach indicates that porous burning in rocket motors containing solid composite propellants can lead to very rapid chamber pressure build-up, so that an explosion could occur within several milliseconds after porous burning begins.

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Section: Grain Burningmentioning

confidence: 92%

Detonability of Solid Composite Propellants

Andersen¹

1961

ARS Journal

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“…However, such assumptions might not hold. Previous works showed [39] that for surface temperatures below 714 K (typical PMMA burning surface temperatures are about 650 K), the polymer surface is not saturated with monomer. The formation of monomers and diffusion to the surface are the rate-controlling processes of gasification.…”

Section: Discussionmentioning

confidence: 99%

Improving Fire Suppression of Water Mist by Chemical Additives

Chow

Jiang

et al. 2007

Polymer-Plastics Technology and Engineering

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Although water mist fire suppression system (WMFSS) is very common, there are concerns that the system is not efficient in controlling some fires. Additives are proposed to use in a WMFSS for better fire protection. In this paper, different groups of additives for WMFSS will be briefly reviewed. Experimental studies on the surface physical and chemical characteristic of polymethylmethacrylate (PMMA) under four groups of original polymer surface without treatment, self-extinguishment, suppressed by water mist and by water mist with sodium chloride NaCl, are reviewed. The surface profiles, element constitutions, binding energies and functional groups of PMMA surfaces were analyzed with scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrometer (FTIR).The near surface molten polymer and bubble layers in burning polymethylmethacrylate (PMMA) are found to be very complicated. The melted surface of burning PMMA is not saturated with pure MMA. Results also demonstrated that chemical reactions do occur while applying water mist. Water mist with NaCl can penetrate deeper on the burning surface of PMMA, suggesting that NaCl might be involved in the extinguishment reactions. The chloride ion from NaCl might be responsible for the interaction with the melting surface of PMMA.

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“…Thermal decomposition of PMMA involves a depolymerization and desorption of MMA towards the evolved gas-phase plume. The mechanism for PMMA surface degradation according to Chaiken et al [43] occurs in three stages with: (a) monomer forming near the surface, (b) diffusion of monomer to the surface, and (c) desorption of the monomer from the surface. Zeroth and first-order kinetics have been considered for the thermal decomposition of PMMA, effective activation energies for the desorption of MMA have been reported between 29 and 84 kJ/mol [6,43,44].…”

Section: Kineticsmentioning

confidence: 99%

“…Zeroth and first-order kinetics have been considered for the thermal decomposition of PMMA, effective activation energies for the desorption of MMA have been reported between 29 and 84 kJ/mol [6,43,44]. Chaiken et al [43] reported activation energies for: desorption (E ds ) of MMA from the polymer, chain propagation (E p ), chain depropagation (E d ), and diffusion of monomer (E D ) in the polymer with respective values of 46, 23, 89 and 145 kJ/mol. Fig.…”

Section: Kineticsmentioning

confidence: 99%