The influence of temperature on the plastic deformation of polyethylene

Abstract

Temperature iduences the attainable draw ratio, the transparency of the drawn material, the long period and the intensity distribution in the small angle X-ray diffraction pattern. Drawing a t or below 80' C yields a first order small angle maximum with relatively large lateral width indicating a variation of lamellar surface orientation between 90' and 45' to the draw direction. Drawing above 80' C reduces the lateral width of the first order maximum and leads to the appearance of the second order. The thermal history of the starting material, quenched, slowly cooled, or annealed, affects the draw behavior. The long period, however, seems to be independent of the physical conditions of the initial sample. At 6OoC, for instance, the drawing of polyethylene samples with a long period of 195, 250,290, 310, and 380 tf yields a material with long periods between 170 and 180 8.Annealing drawn samples produces observahle changes even a t 90'C. At temperatures below 120'C annealing for 100 min yields long periods slightly below those for samples drawn a t the same temperature. At 120'C and above the drawing and annealing show nearly the same long period. Annealing also greatly increases the intensity of the X-ray small angle reflections, but a t temperatures below 120'C causes only minor changes in the lateral width of the same reflections. ZUSAMMENFASSUNG: Die Temperatur beeidufit das beim Ziehen erreichbare Dehnungsverhaltnis, die Durchsichtigkeit der gezogenen Probe, die Langperiode und die Intensitatsverteilung der Rontgenkleinwinkelstreuung. Ziehversuche bei oder unterhalb 80 ' C ergeben ein verhdtnismafiig breites Streumaximum erster Ordnung, das a d eine Schwankung des Normalenwinkels der Kristall-Lamellen mit der Dehnungsrichtung zwischen 0 und 45' schlieBen liil3t. Oberhalb 80' C wird die transversale Verbreiterung des Maximums erster Ordnung geringer, und das Maximum zweiter Ordnung wird gut sichtbar. Die Warmevorbehandlung des Ausgangsmaterials, d. h. Abschrecken, langsames Kiihlen der Schmelze oder Tempern, beeinflufit das Ziehverhalten, doch nicht die Langperiode der gezogenen Probe. So erhdt man, 2.B. im Ziehversuch bei 6OoC, immer eine Langperiode zwischen 170 und 180% obwohl als Folge von verschiedener Wirmebehandlung die Ausgangsproben eine Langperiode von 195, 250, 290, 310 und 380 A gehabt hahen.Das Tempern von gezogenen Proben erzeugt schon bei 9OoC mefibare hderungen. Durch ein 100-Minuten-Tempern unterhalb 120'C erhiilt man Langperioden, die nur sehr wenig unterhalb der Werte von den Proben zu liegen kommen, die bei der Tempertemperatur gezogen wurden. Oberhalb 120'C stimmen die beiden Werte ungefihr iiberein. Durch das Tempern wird auch die lntensitat der Kleinwinkelreflexe stark erhoht. Doch treten unterhalb 120'C nur kleinere Anderungen in der transversalen Verbreiterung derselben auf.

Drawing and extrusion of semi-crystalline polymers

“…In the former case no loops are formed and in the latter case L of the fibrous structure is identical with L of the undrawn material and not dependent on Td. Both effects are in disagreement with experiments [235][236][237].…”

“…The long period of the microfibrillar structure is a function of the temperature of drawing, L(Ta), [226,236,237] as if the crystals were formed at Ta from the melt at rest. The new L is completely independent of L1 of the starting material.…”

Structural heterogeneity and dynamic mechanical relaxations of ethylene ?-olefin copolymers

“…It can be seen that the long period decreases sharply on drawing at room temperature, which is consistent with previous work on LDPE 16 and with measurements on unbranched polyethylene. 17,18 Also shown in Table II are values for the crystal size, calculated from measurements of crystallinity and long peiod. The use of mass crystallinity introduces an additional error of several percent, but considering the large uncertainty in the crystallinity and the fact that the lamellar size obtained from the melting peaks relates to the largest lamellae, the results from the two approaches are quite consistent.…”

A structural study on solid state drawing of solution-crystallized ultra-high molecular weight polyethylene

“…Some of them have proposed a temporary melting during the first stages of drawing [19][20][21][22]. The strongest and often-cited evidence for melting and recrystallization on drawing is the correlation between the long period (measured via small angle X-ray scattering (SAXS)) and the drawing temperature, which is independent of the initial lamellar thickness [23]. However, as long as high randomization of molecules is prevented by applied stress, no significant influence of possible partial melting on the deformation phenomena is to be expected.…”