SynopsisInvestigations were undertaken of the structure and rheological properties of mixtures consisting of one crystallizing and one amorphous polymers. It was established that mixtures of poly(ethylene adipate) and poly(vinyl acetate); of poly(ethylene adipate) and poly(methyl methacrylate); and of poly(ethylene sebacinate) and poly(methyl methacrylate) can form amorphous solid solutions with one another or can crystallize without any apparent division of the two components. The phase condition of the mixture is determined by the nature of the two polymers, by the ratio between them, and by their molecular weights. The melting point of these mixtures drops in proportion to the content of the amorphous component. The assumption is made on the basis of the results obtained that the amorphous component occupies the defective areas in the crystal grating. The fluidity of the mixtures was measured by means of a capillary viscosimeter. I t was established in all cases that there appear deviations from the proportional change of the effective viscosity between the viscosities of the components. These deviations are explained by the change in the energy of activation of the viscous flow of the melts which was also subject to determination.In recent years there has been a steadily growing interest in polymer mixtures. This interest is due to the fact that there is no simpler, more accessible, and sometimes more effective way of modifying the properties of polymers than by mixing two or more of them. The properties of the mixture change slowly within certain limits, depending on the composition of the solid dispersion system. Sometimes, however, the mixtures reveal properties which none of the components possesses. The wide application of polymer mixtures has been achieved so far along practical lines. It is still not known what connection there is among the properties, structure, and composition of the mixtures. Furthermore, an investigation of polymer mixtures should permit us to broaden and supplement the data we have on individual polymers. They are highly convenient models for the purpose.Of greatest interest are the systems composed of amorphous and crystallizing polymers. These are characterized by two opposing trends: the crystal formation of the crystallizing components, on the one hand, and the formation of an amorphous solution between the components, on the 4197
Der Phasenzustand des aus Hochdruckpolyäthylen und isotaktischem Polypropylen bestchenden Polymerengemisches wurde in Abhängigkeit von der prozentualen Zusammensetzung und von den Molekulargewichten der Komponenten untersucht. Es zeigte sich, daß der Phasenzustand von der Temperatur, dem Gewichtsverhältnis der Komponenten und dem Molekulargewicht der Polymeren abhängt. Feste Lösugen bilden sich bei einem hohen Polypropylengehalt des Gemisches. Das Molekulargewicht des Polyäthylens wirkt sich nicht merklich aus, dasjenige des Polypropylens hingegen beeinflußt den Phasenzustand des Gemisches. Das Zustandsdiagramm des Polymerengemisches wird am besten in einem räumlichen Koordinatensystem mit Temperatur, Zusammensetzung und Molekulargewicht des Polypropylens als Koordinaten dargestellt.
SynopsisThe influence of certain factors on the kinetics of styrene mass transfer from polystyrene in air at elevated temperature is investigated. It is established that this process can be simulated by a model including molecular diffusion of styrene to the surface of the solid material and evaporation from that surface. The effective coefficients of molecular diffusion at different temperatures and the evaporation coefficients under different hydrodynamic conditions are determined. The data obtained can be used for estimation of the monomer removal by thermal treatment of the polymer. INTRODUCTIONFrom theoretical and practical points of view, the kinetics of monomer mass transfer from polystyrene in air at elevated temperature is of great interest. Such transfer is expected to take place both in the polymer granulation and in the granulate processing into products. Depending on the rate of the process, on one hand, the monomer contents in the product will change, which is of great importance when it is used for food packaging, and on the other hand, the surroundings will be polluted with styrene to different extents.Studies on this matter carried out so far'-3 are insufficient to predict the rate of the process, since the monomer in them is removed by a liquid with undefined hydrodynamics.Under these circumstances we set ourselves the task of studying the kinetics of styrene transfer from polystyrene in air at elevated temperature. THEORYMonomer transfer in the gas phase around the polystyrene is expected to comprise two stages: diffusion of styrene to the surface of the polymer, and evaporation of the monomer from the surface into the gas phase. Should this mechanism be assumed, the process of transfer from an infinite plane sheet of polystyrene will be described by the differential equation If the styrene initial distribution in the sheet is uniform, the total amount of the monomer leaving the sheet up to time t of contact with the gas phase will be expressed by the equation which results from the mathematical solution of Eq. ( 1 ) at the boundary condition (2).4In the above expression /In are the positive roots of the equationThe evaporation coefficient a depends mainly on the hydrodynamic conditions in the surrounding fluid.5 At suf?iciently large gas flow rates a > > D and L -, 00. Then the mass transfer rate will be determined entirely by the diffusion in the sheet and Eq. (3) In-=In, --tUsing the above equations and appropriate experiments makes possible the determination of the molecular diffusion coefficient and the coefficient of evaporation, needed for estimation of the process. EXPERIMENTALIn order to study the process, plates of impact-resistant polystyrene Bustrene with length 40 111171, width 20 pm, and thickness 1.7 mm were utilized. They were put into a glass tube with regulated external heating. The flow rate of the air passing through it was measured with a rotameter. The desired temperature of the air before and behind the sheet was obtained by varying the voltage applied to the heater coil...
Empirical relationships, describing the change in mechanical properties of polyolefins at natural ageing in a seaside climate at middle geographic latitudes are derived on the basis of experimental data collected in a long exposure periodmore than 10 years. The empirical equations describe the experimental data with a good accuracy. A constant is introduced accounting for the period in which the properties remain unchanged (induction period). The empirical equations derived may be used in predicting the change in mechanical properties of the investigated polymers in outdoor applications. ZUSAMMENFASSUNG:Empirische Beziehungen, die die Anderung der mechanischen Eigenschaften von Polyolefinen bei natiirlicher Alterung in einem Meeresklima in mittleren geographischen Breiten beschreiben, wurden aus wtihrend eines Bewitterungszeitraumes von mehr als zehn Jahren gewonnenen experimentellen Daten erhalten. Die empirische Gleichung beschreibt die experimentellen Daten mit guter Genauigkeit . Zur Beriicksichtigung des Zeitraumes, in dem sich die Eigenschaften nicht vertindern (Induktionsperiode), wurde eine Konstante eingefiihrt. Die erhaltenen empirischen Gleichungen k h n e n zur Vorhersage der Anderung von mechanischen Eigenschaften der untersuchten Polymeren bei Anwendung im Freien dienen.
Nach der abgeleiteten Phasenregel sind die Zustandsdiagramme, namentlich die der binären Polymerensysteme, in einem vierdimensionalen Raum mit folgenden Koordinaten darzustellen: Zusammensetzung, Temperatur, Molekulargewicht für die eine, und Molekulargewicht für die andere Komponente. Mit Hilfe der Differentialthermoanalyse werden die Phasenübergänge bei unterschiedlicher Zusammensetzung des Systems und unterschiedlichem Molekulargewicht der Komponenten bestimmt. Anhand der Phasenübergänge sind die Flächendiagramme bei konstantem Molekulargewicht der Komponenten sowie dreidimensionale Diagramme bei unveränderlichem Molekulargewicht der einen Komponente aufgezeichnet. Das Molekulargewicht der beiden Polymerenarten beeinflußt ihre Kongruenz. Die Zustandsdiagramme des Systems erklären in zufriedenstellender Weise die nichtadditive änderung der mechanischen Eigenschaften beim Wechsel der Zusammensetzung.
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