A. Búcsi

A theoretical approach to understanding the connection between ignitability and flammability parameters of organic polymers

Abstract For a postulated model, the theoretical dependencies of LOI and time to ignition on parameters of polymer decomposition and heat transfer and oxygen and fuel flows were determined and compared with experimental curves. The model provides a tool to understanding the effect of various parameters, each taken separately, on the flammability parameters of different polymers. Several experimental aspects of polymer flammability are discussed within the proposed model.

Kinetics of radical generation in PVC with dibenzoyl peroxide utilizing high-pressure technique

Full Paper: The radical concentration generated in poly-(vinyl chloride) (PVC) by dibenzoyl peroxide (DBP) was investigated by means of electron paramagnetic resonance (EPR). High-pressure technique was utilized to stabilize the radicals during the experiments. The radical concentration as a function of time and temperature of annealing was studied. Different peaks, corresponding to reactive intermediate radicals were observed on the curves. The kinetics of stable radicals formed on the polyene system is governed by an associated exponential function.

Ignitability of Polymers Related to Polymer Properties and Different Steady States of Combustion Theoretical Approach

A mathematical model of ignition and burning of organic polymers was used for evaluation and quantification of the tendency of polymers to ignition. The model permits investigation of the influence of one parameter of the polymer on the others. It was found that the model could be used for the verification of the ignitability method developed by Miller et al. [1].Different steady states of combustion were found when using the model proposed. There is a characteristic steady state for normal flaming combustion, another for non-flaming combustion, and there are also unstable steady states that have no real physical meaning.

DOPE–oleic acid–Ca2+ as DNA condensing agent

Abstract Phospholipid-based non-viral carriers composed of neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) and the binary mixture DOPE–oleic acid (OA) are examined as potential DNA delivery vectors. The process of DNA condensation in the presence of Ca2+ ions has been monitored through changes in emmision intensity of fluorescent probe ethidium bromide. The decline in fluorescence intensity with increasing Ca2+ concentration at two different time intervals was correlated with the binding capacity of complexes and possible release of DNA from the complex. The microstructure of DOPE–OA mixtures at different OA/DOPE molar ratios and that of DOPE–OA–DNA–Ca2+ complexes were determined using synchrotron small angle X-ray diffraction (SAXD). We identified inverted hexagonal phase HII as the dominant structure. OA affects the lattice parameter of HII formed by DOPE. With the increasing OA/DOPE molar ratio, the lattice parameter decreases, which results in significantly lower fraction of DNA bound to the OA-enriched complexes.

Kinetics of DNA condensation with DPPC: effect of calcium and sodium cations

Kinetics of DNA condensation with zwitterionic lipid, dipalmitoylphosphatidylcholine, in the presence of calcium and sodium cations was investigated using fluorescence stopped-flow technique. The process was followed from two points of view: the changes on DNA were monitored with ethidium bromide, and fluorescently labelled phospholipid was used to follow the changes in the lipid bilayer. The measurements showed different reaction kinetics. In the case of the DNA side, a consecutive reaction mechanism was found, while two-step first-order reaction mechanism described well the processes on the lipid side. Both, sodium and calcium cations influence significantly the reaction mechanism. Calcium is necessary to condensate DNA with lipid, while sodium modulates the kinetics of the reactions considerably.

Lipid based drug delivery systems: Kinetics by SANS

N,N-dimethyldodecylamine-N-oxide (C12NO) is a surfactant that may exist either in a neutral or protonated form depending on the pH of aqueous solutions. Using small angle X-ray diffraction (SAXD) we demonstrate structural responsivity of C12NO/dioleoylphospha-tidylethanolamine (DOPE)/DNA complexes designed as pH sensitive gene delivery vectors. Small angle neutron scattering (SANS) was employed to follow kinetics of C12NO protonization and DNA binding into C12NO/DOPE/DNA complexes in solution of 150 mM NaCl at acidic condition. SANS data analyzed using paracrystal lamellar model show the formation of complexes with stacking up to ~32 bilayers, spacing ~ 62 A, and lipid bilayer thickness ~37 A in 3 minutes after changing pH from 7 to 4. Subsequent structural reorganization of the complexes was observed along 90 minutes of SANS mesurements.

Experimental and theoretical study of free radicals of L-(+)-ascorbic acid in PMMA matrix, generated under high pressure

Free radicals of L-(+)-ascorbic acid were generated with dibenzoyl-peroxide in poly-methylmetacrylate matrix by a high-pressure technique at 600 MPa. The radical concentration was followed as a function of annealing time. On the basis of quantum chemical calculations we chose the three most stable radical structures. The calculatedg-values of these radicals provide lines that are in the range of the experimental spectrum. Vitamin C kept its antioxidative properties despite the high temperature used during the experiments.