A.P. Kharitonov

Practical applications of the direct fluorination of polymers

Abstract Applications are reviewed of direct fluorination to enhance the following commercial properties of polymeric goods: separation factor of polymeric membranes for gas separation and purification, barrier properties, adhesion, wettability, friction, transparency, etc.

Surface modification of polymers by direct fluorination: A convenient approach to improve commercial properties of polymeric articles

The fundamental features and industrial applications of the direct fluorination of polymers are reviewed. Direct fluorination of polymers (i.e., treatment of a polymer surface with gaseous fluorine mixtures) proceeds spontaneously at room temperature and is a surface modification process. More than 25 polymers have been studied with the aid of a variety of analytical and spectroscopic techniques. The fundamental features of the direct fluorination, such as influence of treatment conditions (composition of the fluorinating mixture, fluorine partial pressure, temperature, and fluorination duration) on the rate of formation, chemical composition, density, refraction index, and surface energy of the fluorinated layer, kinetics of formation of radicals during fluorination and their termination, texture of fluorinated layer, etc. were studied. It was demonstrated experimentally that direct fluorination can be effectively used to enhance commercial properties of polymer articles, such as barrier properties of polymer vessels, bottles, and packaging films and envelopes; gas-separation properties of polymer membranes; adhesion and printability properties of polymer articles; and mechanical properties of polymer-based composites.

Improving gas separation properties of polymeric membranes based on glassy polymers by gas phase fluorination

The application area of existing gas separation membranes is limited by commercially available polymers for their preparation. In many cases the separation selectivity of these polymers is not sufficient for effective separation processes. One of the ways to improve the separation effectivity of existing membranes from glassy polymers is gas phase fluorination. It is very important to note that this method can be successfully used for modification of polymeric films, different types of membranes (flat sheet and hollow fiber) and membrane modules. The hollow fibers produced from Matrimid 5218 in Twente University and a flat-sheet membrane from polyvinylthrimethilsilane (PVTMS) produced in Russia were investigated. The treatment of samples by fluorination was carried out in closed reactor at 20–22 °C with gaseous mixtures of F2/He of different composition. A gas mixture of different concentrations (2–10 vol.% of F2) at 1 atm was used The time of fluorination was from 2 min to 265 min. The dependence of the structure of the PVTMS and Matrimid 5218 on gas phase fluorination by IR-spectroscopy and the influence of modification on membrane structure by SEM were studied. The productivity of He, CO2, N2 and CH4 through the membranes modified at different conditions of fluorination was measured, and it was shown that it is possible to achieve a significant increase of He/CH4, CO4/CH4 and He/N2 selectivity at high level He and CO2 productivity by this type of modification. Thus, modified membranes and membrane modules can be successfully used for separation of components of biogas in membrane contactors and selective membrane valves for extraction of He/Ne fraction from waste in the metallurgy industry and separation of natural gas components.

Direct fluorination of polystyrene films

Abstract Kinetics of fluorinated layer formation in polystyrene (PS) were investigated for various fluorine and oxygen partial pressures and temperatures. The PS direct fluorination process was shown to be diffusion-limited, i.e., the rate of the process is limited by fluorine penetration through the fluorinated layer. Dependence of fluorine permeability value and concentration of carbonyl groups in treated polymer on F 2 O 2 mixture composition were investigated. The inhibiting action of oxygen is due to C O groups formation. A scheme of elementary stages of the direct fluorination is proposed.

The kinetics and mechanism of the direct fluorination of polyethylenes

SummariesTwo types of low-density polyethylene (LDPE), five types of high-density polyethylene (HDPE), poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVDF) were studied. The fluorination of LDPE and HDPE is a diffusion-controlled process and proceeds via a branched chain mechanism following an induction period. Initiation of the reaction takes place via the reaction of molecular fluorine with the C-H bond. The rate of fluorination of HDPE exceeds that of LDPE. PVDF cannot be fluorinated even at temperatures as high as 430K and/or under UV irradiation. The kinetics associated with the formation and termination of peroxy RO2• and fluorocarbon long-lifetime radicals was studied. It is mainly middle peroxy radicals that are formed at treatment conditions close to those used in industrial processes.RésuméDeux types de polyéthylène de basse densité (LDPE), cinq types de polyéthylène de haute densité (HDPE), le poly(vinyle fluoride) (PVF) et le poly(vinylidène fluoride) (PVDF) ont été étudiés. La fluorisation du LDPE et du HDPE est un procédé à diffusion contrôlée et se déroule au moyen d’un mécanisme à chaîne branchée qui se produit après une période d’induction. L’initiation de l’action se produit au moyen de la réaction du fluor moléculaire avec la liaison C-H. Le taux de la fluorisation des HDPE excède celui des LDPE. Le PVDF ne peut pas être fluoré même à des températures aussi élevées que 430K et/ou sous irradiation UV. On a étudié la cinétique associée à la formation et à la terminaison du peroxy RO2• et des radicaux fluorocarbone à longue durée de vie. Ce sont pour la plupart des radicaux peroxy centraux qui sont formés sous des conditions de traitement qui sont proches de celles des procédés industriels.ZusammenfassungZwei Arten von Polyethylen mit niedriger Dichte (LDPE), fünf Arten mit hoher Dichte (HDPE), sowie Polyvinyl-Fluorid (PVF) und Polyvinylidene-Fluorid (PVDF) wurden untersucht. Die Fluorinierung von LDPE und HDPE ist ein diffusionskontrollierter Prozeß, der durch eine verzweigte Kettenreaktion nach einer Induktionsperiode abläuft. Der Prozeß wird durch die Reaktion von molekularem Fluorin mit der C-H Verbindung in Gang gesetzt. Die Fluorinierungsrate von HDPE ist größer, als die von LDPE. PVDF kann selbst bei hohen Temperaturen (430 °K) und/oder UV-Licht nicht fluoriniert werden. Wir erforschten auch die Kinetik der Formation und Terminierung von Peroxy RO2• und die langlebigen Fluorkarbonradikale. Unter den in Industrieprozessen üblichen Operationsbedingungen werden vor Allem die mittleren Peroxyradikale gebildet.

DIRECT FLUORINATION OF POLY(VINYL TRIMETHYLSILANE) AND POLY(PHENYLENE OXIDE)

Abstract Fundamental features of the direct fluorination of poly(vinyl trimethylsilane) (PVTMS) and poly(phenylene oxide) (PPO) have been investigated. The influence of the fluorination conditions (fluorinating mixture composition, treatment duration) and polymer molecular weight on the rate of formation of the fluorinated layer and on physical–chemical properties (chemical composition, density, refractive index, absorption spectra in the visible and UV, surface energy) was investigated.

Formation of free radicals in the low-temperature fluorination of polymers

The formation of free radicals in the process of direct fluorination of natural and synthetic polymers at temperatures close to 77 K was studied by ESR. The maximum concentrations of radicals, (1017–5·1018 spin g−1) and their complete oxidation were observed in the temperature interval from 77 to 250 K at a fluorine pressure of 30 Torr. The initiation of chain halogenation, which consists of homolytic breaking of chemical bonds to yield free-radical intermediates. was examined in the framework of the multi-center synchronous transitions model.

Fabrication and characterization of fluorinated single-walled carbon nanotubes

The optimum conditions for the fluorination of single-walled carbon nanotubes (SWCNT) in the atmosphere of gaseous fluorine with the nanotube structure remaining intact up to a stoichiometry of CFx, x ∼ 0.5 were determined. The kinetics of fluorination was examined. The fluorinated SWCNTs were characterized by various methods, including transmission electron microscopy, measurements of specific surface area and accessible internal volume, NMR spectroscopy, IR spectroscopy, X-ray absorption and photoelectron spectroscopies, thermal stability, and analysis of gaseous products by mass-spectrometry. The structure of fluorinated SWCNT was preserved up to brutto-composition CF0.5 but degree of fluorination of SWCNT bundles was decreased with distance from the SWCNT surface to its core. Such a decrease becomes evident at ∼1.5 nm distance. It means that the degree of fluorination depends on the degree of its dispersion.

Direct Fluorination of Polymer Final Products: From Fundamental Study to Practical Application

The results of study of the fundamental features of the direct fluoridation of polymers, physical and chemical properties of the fluorinated layer at the surface and possible application areas of the direct fluoridation are reviewed. The influence of the composition of fluorinating mixture, the process pressure, temperature and duration on the kinetics of formation of the fluorinated layer was investigated. The fluorinated layer composition, density, refraction index and surface energy were measured at the different conditions of the surface treatment. Kinetics of termination of long-lived radicals formed inside the fluorinated layer was studied. The methods of enhancing the barrier properties of fluorinated polyethylene with respect to alcohol-containing fuel, enhancing the gas separation properties of flat membranes and hollow-fiber membrane modules and improving chemical stability of polymer pipes were developed. Possibility to use direct fluorination for reinforcement of polymer composites was demonstrated.

Application of interference spectroscopy for studying kinetics of chemical reactions in optically transparent films

Abstract It is proposed to use interference spectroscopy for studying kinetics of various processes of modification of the surface layer in optically transparent polymer films. These methods are mathematically explained and a system was recommended for experimental use. It was found possible to apply the method proposed for studying direct fluorination of PE, PETP, PS, PMMA and PVA films using gaseous fluorine.