Morphological studies of plastic deformation of single crystals, thin layers, and bulk samples together with mechanical, X-ray and infra-red data revealed the existence of three stages in cold drawing of crystalline polymer: the plastic deformation of the original spherulitic structure, the discontinuous transformation of the spherulitic into fibre structure by micronecking, and the plastic deformation of the fibre structure The initial material, which has low strength and high ductility, consist of stacks of parallel lamellae with few interlamella links It deforms plastically by stack rotation, sliding of lamellae, phase change and twinning of crystal lattice, chain slip and tilt until the predeformed lamellae reach the position of maximum compliance for fracture by micronecking The micronecks transform every single lamella into microfibrils of between one and three hundred angstroms in width, consisting of folded chain blocks broken off the lamella primarily by chain slip in the boundary layers between adjacent mosaic blocks The chains bridging the crack are partially unfolded during the micronecking process They connect in axial direction the blocks in the microfibril as intrafibrillar tie molecules The number of microfibrils per cm of crack length increases with molecular weight The draw ratio of the microfibrils and the axial separation in the microfibril of the originally adjacent crystal blocks increase with the average distance between microfibrils and, hence, decrease with increasing molecular weight The concentration of micronecks in every stack of lamellae in a thin destruction zone produces a bundle of microfibrils of rather uniform draw ratio Such a fibril measuring a few thousand angstroms in width includes the interlamella ties of the original sample as interfibrillar tie molecules connecting adjacent microfibrils The concentration of micronecks also provides the conditions for a nearly adiabatic heating of the generated fibril by the transformation work in the destruction zone The local temperature rise imparts so much mobility to the chains in the crystal blocks that during subsequent cooling to ambient temperature, the long period becomes adjusted to this temperature The more or less random distribution of destruction zones in the neck makes the transformation from spherulitic to fibre structure appear to be a gradual process in spite of the discontinuous transformation in the micronecks The plastic deformation of the new fibre structure can proceed only by longitudinal sliding of microfibrils past each other, a process limited by interfibrillar tie molecules Hence, high molecular weight samples with many interlamella links exhibit a smaller draw ratio than lower molecular weight material The three stages are to some extent intermixed in the neck In the initial neck characterised by a low draw ratio and rather gentle constriction, the transformation into the fibre structure is not complete, so that some of the remains of the original microspherulitic structure are still present in the necked portion They are destroyed during subsequent drawing which completes the transformation and also deforms the fibre structure The sharply constricted mature neck, however, yields a high draw ratio which is composed of the draw ratio of microfibrils and of subsequent sliding motion of the microfibrils The technically important natural draw ratio is the maximum draw ratio obtained with the sample under the conditions of the experiment It seems to be higher than the draw ratio of the microfibrils

Molecular model of drawing polyethylene and polypropylene.

ZusammenfassungSpezielle Rotationsisomere — Kinkisomere — werden am Beispiel des Polyäthylens zunächst für das freie Kettenmolekül geometrisch und energetisch diskutiert. Unter Verwendung der Ergebnisse einer Schmelztheorie (14) läßt sich damit eine quantitative Mikrostruktur — kooperative Kinkisomerie — in Molekülbündeln aus nahezu parallelen Ketten postulieren. Schließt man darin noch Molekülfalten ein, so entsteht ein Zustandsbild (Defekt-Kristall-Modell), das die Grundlage für eine quantitative Beschreibung der Eigenschaften polymerer Festkörper und Schmelzen darstellt. Mit Hilfe der irreversiblen Thermodynamik werden die Paraelastizität von Kinkblockstrukturen, Theorien der Relaxationserscheinungen im Festkörper (γ,α-Prozeß), der Gummielastizität, Viskosität und des Glasübergangs entwickelt. Dem Kettensegment der Molekülknäuelvorstellung entspricht das 2gl-Kinksegment im Bündelmodell, der Kettenverschlaufung die Molekülverhakung (2g2-, 2g3-, 3g2-Kinken).SummarySpecial rotational isomers — kink-isomers — are first discussed geometrically and energetically for the isolated (polyethylene-)chain-molecule. Accounting for the results of a theory of melting (14) a quantitative microstructure (cooperative kink-isomerism) in bundles of nearly parallel chains can be asserted. Considering further chain-folds one gets a molecular model (defectcrystal-model) which is the basis for the quantitative treatment of the properties of polymer solids and melts. With the formalism of irreversible thermodynamics, theories of relaxations in the solid (γ,α-process), paraelasticity of kinkbloc-structures, rubber-elasticity, viscosity and of the glass transition are derived. The chain-segment in the coiled-molecule-concept corresponds to the 2g 1-kink-segment in a bundle of chains, the entanglements compare with the jogs in a molecule (2g2-, 2g3-, 3g2-kinks).

Molekülbewegung in Polymeren: I. Teil: Konzept einer Festkörperphysik makromolekularer Stoffe

The plastic deformation of fibrous material occurs primarily by a sliding motion of fibrils. To a first approximation, the displacement of their centers of mass can be well described by an affine transformation corresponding to the deformation of the bulk sample. Such a sliding motion of fibrils does not affect the morphology of the microfibrils. But by chain unfolding, it smoothes the surface inhomogeneities of the fibrils caused by microfibril ends which act as point defects of the microfibrillar lattice. This makes possible a more perfect lateral contact between adjacent fibrils and results in a steadily increasing resistance to plastic deformation. The sliding motion of fibrils produces a shear stress on skewed fibrils and this causes a slight shear displacement of microfibrils. But in spite of its smallness, this shear displacement enormously extends the interfibrillar tie molecules by chain unfolding and thus increases their fraction in the amorphous layers.

Plastic deformation of polymers with fibrous structure

ZusammenfassungAuf der Grundlage des Bündelmodells und mit streng molekularen Parametern wird im ersten Teil die Mikrostruktur von Polymerschmelzen und teilkristallinen Festkörpern behandelt. Die mäanderartige Anordnung der Bündel im amorphen Zustand läßt sich thermodynamisch begründen und führt zu einem Mäanderradius von 50 Å. Auf dieser Grundlage wird eine molekulare Theorie der Relaxationserscheinungen (α, β, γ) am Beispiel des linearen Polyäthylens vorgelegt und experimentall geprüft. Im letzten Teil werden die beiden Grenzfälle des Deformationsverhaltens molekular quantitativ beschrieben: die reine Plastizität am Beispiel der Streckgrenze (yield-stress) des linearen Polyäthylens und die reine Paraelastizität am Beispiel der Spannungs-Dehnungskurve des verstreckten Polyamidfadens.SummaryIn the first part the microstructure of polymer melts and semicrystalline bulk material is treated on the basis of the bundle model and with molecular parameters. The meander-shaped arrangement of the bundles in the amorphous phase can be founded thermodynamically and leads to a radius of the meander of 50 Å. Based on this model a molecular theory of the relaxation processes (α, β, γ) is given and experimentally proved for linear polyethylene. In the last part both limiting cases of the deformation behavior are quantitatively derived in a molecular picture: the ideal plasticity illustrated by the yield stress of linear polyethylene and the ideal paraelasticity illustrated by the stress-strain curve of the drawn polyamide fiber.

Molekülbewegung in Polymeren: III. Teil: Mikrostruktur und mechanische Eigenschaften

The stress-strain curves of MDPE samples show strong evidence that yielding of MDPE involves two thermally activated rate processes operating co-operatively, but having different activation parameters relative to both the temperature dependence and the strain-rate dependence

Double yield point in polyethylene under tensile loading

Tei lchenzahl 152 t 32 Dank dem Entgegenkommen der zust~indigen NASABeh6rden konnten wir auch an einigen Staubsammlungen im Rahmen der bemannten GEMINI-Fliige teilnehmen. Die Untersuchungen der erhaltenen Sammelfl~ichen sind im Gange. Ftir das Jahr t 967 planen wir in Zusammenarbeit mit der europ~tischen RaumforschungsbehSrde (ESRO) Raketen-Sammelfliige in Nordschweden. Vier Raketen werden zur Sammlung yon kosmisehem Staub aus Meteorschauern und den dort in den Sommermonaten bisweilen sichtbaren Leuchtenden Nachtwolken geflogen werden. Aus umfangreichen optischen Messungen [71 und den Ergebnissen eines Sammel-Raketenfluges im Jahre 1962 I8~ ist bekannt, dab in diesen Wolken zahlreiche submikroskopisch kleine Teilchen vorhanden sind. Fiir diese Teilchen wird eine kosmische Herkunft angenommen.

Die sogenannten einkristalle in hochpolymeren

Aus den (h00)- und (hh0)-Weitwinkelreflexen von bei 125° C getemperten Bundeln orientierter, aus Losung gezuchteter, Polyathylen-Einkristalle findet man, das diese aus im Durchschnitt 260 A breiten und 830 A langen, von (310)-Seitenflachen begrenzten Mosaikblockchen bestehen. Das zusatzliche Studium der Langperiode mittels Kleinwinkelstreuung zeigt, das sie sich jeweils nach 104 min Temperzeit in allen 3 Dimensionen um jeweils etwa 30% vergrosert haben.

H. Čačković

Papers

Die sogenannten einkristalle in hochpolymeren

Mosaikstruktur und Korngrenzen in Polyäthylen-Einkristallen

OrdnungszustÄnde und diamagnetische SuszeptibilitÄt in PolyÄthylen