E.M. Kampouris

Migration of PVC plasticizers into alcohols

Abstract The use of labelled plasticizers and radioactivity measurements in conjunction with weight loss, can give quantitative information on the amount of migrated plasticizer, and on the amount of the liquid medium that diffuses into the polymer during the migration process. In the case of PVC plasticized with dibutyl phthalate and dioctyl phthalate and immersed in alcohols, the specimens soon become heterogeneous due to loss in compatibility between the polymer and the mixtures of plasticizer-alcohol high in alcohol. These mixtures are formed in the polymer as a result of continuous migration and diffusion processes. The following factors affecting the migration process were examined: nature of alcohol, nature of phthalate plasticizer, amount of plasticizer, molecular weight of polymer, thickness of specimens, presence of epoxy plasticizers, plasticization process, presence of stabilizers, temperature, and time.

Solid-state polyamidation of dodecamethylenediammonium adipate

Abstract The solid-state polyamidation of nylon salts comprises an attractive research field. The low sublimation rate of dodecamethylenediamine ensures salt stability and accurate relationships between amine end-group analysis and extent of the reaction. This accuracy is further enhanced by studying the solid-state polyamidation of dodecamethylenediammonium adipate (DMA), a nylon salt with a low melting point. Reaction rate was found to be influenced drastically by temperature, but the temperature range to effect true solid-state reaction is actually limited. Even at temperatures significantly below the melting point of DMA, a transition of the process, from the solid to the melt state, was clearly observed. Kinetic data obtained were tested against well known solid-state and melt reaction models. Nevertheless, none of them can exclusively describe the polyamidation studied, possibly because the true reaction model should take into consideration the process leading to the solid-melt transition observed.

Solid state polyamidation of nylon salts: possible mechanism for the transition solid-melt

Abstract Solid state polyamidation of nylon salts may be accompanied, depending on the reaction conditions, by a typical transition of the process from the solid to the melt state. For an explanation of this phenomenon, dodecamethylenediammonium adipate, a typical salt with such a transitional behaviour, has been chosen for further study. The possibility of the formation of an eutectic system monomer-polymer has been excluded and the role of the water of polycondensation has been taken into account. Water quantitative determinations proved that a significant amount of the water produced, during the course of the reaction, cannot be removed out of the reacting grains. Due to the deliquescent behaviour of the monomer, it is proposed that this water accumulation results in the formation of lower melting point areas. Overlapping of the latter explains the transition observed.

A model recovery process for scrap polystyrene foam by means of solvent systems

A solvent technique is studied for the recovery of polystyrene (PS) foam waste. The model process proposed ensures removal of any impurities present and comprises dissolution of the starting material, filtering, reprecipitation, thorough washing of the polymer grains obtained and drying. The solvent mixtures involved are separated by distillation for re-use. The following criteria are considered: (a) the rheological behaviour of the PS solutions prepared, (b) the yield of the process of polymer of acceptable grain size and (c) sufficient solvent/non-solvent separation. On the basis of these criteria, methyl ethyl ketone/n-hexane or methanol and p-xylene/n-heptane are suggested as effective solvent/non-solvent systems.

Influence of metal catalysts on solid state polyamidation of nylon salts

Abstract Oxides, hydroxides or salts of various metals of Groups IIA, VA and VIII of the periodic table were tested as catalysts for the solid-state polyamidation of dodecamethylenediammonium adipate, chosen as a model nylon salt. The metal compounds were incorporated by coprecipitation or nucleation. Comparative polymerization runs showed that dibasic sodium arsenate heptahydrate (DSAH) was the most effective catalyst so that it was studied in detail: DSAH-containing monomers, prepared by coprecipitation, showed a more consistent behaviour while arsenic concentration seemed to influence the catalytic activity up to a limiting value of about 0.1 wt%.

New solid state polyamidation process

Abstract Solid state polymerization reactions are of considerable scientific and industrial interest. In some cases nylon salts can be converted to polyamides through intermediates of lower melting point, involving a solid-melt-solid sequence which is incompatible with known solid state polyamidation processes. A new solid state polyamidation process is described for use with salts, prepolymers, or amino acids which provides good temperature control and the avoidance of agglomeration of particles. The process comprises: (a) suspension of the particles of raw material (salt, amino acid or prepolymer) in an inert solvent; (b) reaction at the boiling point of the solvent with continuous distillation and feeding of solvent; (c) reactions at higher temperatures by feeding with the correct solvent; (d) separation of the formed granules of polymer by centrifugation, and (e) washing and drying. This process was tested for the solid state polymerization of hexamethylenediammonium maleate, which polymerizes through intermediates of lower melting point, and the following factors were examined: (a) presence and amount of dispersing agents; (b) nature of inert solvent; (c) grain size of salt; (d) distillation rate; (e) the ratio of salt: inert solvent and (f) temperature and time.

Influence of acid catalysts on the solid-state polyamidation of dodecamethylenediammonium adipate

Abstract Solid-state polyamidation is an alternative route for polyamide synthesis. Solid-state polyamidation of dodecamethylenediammonium adipate was studied in the presence of acid catalysts. Boric acid proved to be the most effective catalyst, followed by sulphuric acid, so that—even at high reaction rates—the reaction was maintained in the solid state throughout the process. On the other hand, phosphoric acid showed a clearly weaker action resulting eventually in a transition of the process from the solid to the melt state, in accordance with noncatalysed behaviour. In general, catalyst concentration plays a considerable role in the catalytic effectiveness obtained.

Extractable waxes from Greek lignites

Abstract An investigation on the solvent-extraction yields of Greek lignites has shown that the yields are generally low compared with the yields from certain American and German lignites, and similar to the yields from Czechoslovakian lignites. The highest yields were obtained from lignites of the Psachna deposit. The only extract which resembled rather closely in its nature the Riebeck crude montan wax was obtained by benzene extraction from Ptolemais lignite. The most significant differences between benzene extracts from Greek lignites and Riebeck crude montan wax were the differences in melting points and the greater resin content of the Greek waxes. Extraction with benzene/methanol mixture instead of benzene gave higher yields and extracts characterized by higher melting points, and higher acid and ester values. The compatibility of the extracts with paraffin wax was low; only benzene extract from Ptolemais lignite was completely miscible. No relation was found between the wax yield and the ratio volatile matter/fixed carbon of the coal. We also conclude that extraction of waxes from Greek lignites is not commercially attractive.