Extinction Rings Research Articles

Miscibility and crystallization of thermosetting polymer blends of unsaturated polyester resin and poly(ϵ-caprolactone)

Poly(ε-caprolactone) (PCL) was found to be miscible with uncured polyester resin, i.e. oligoester (OER), as shown by the existence of a single glass transition temperature ( T g) in each blend. However, PCL was judged to be partially miscible with crosslinked polyester resin (PER) which was concluded from the results of thermal analysis. Fourier-trarsform infrared (FT-i.r.) studies revealed that intermolecular hydrogen bonding interaction between the components is an important driving force to the miscibility of PCL/OER blends and the partial miscibility of crosslinked PCL/PER blends. The importance of entropy contribution to the miscibility of thermosetting polymer blends is also shown from the FT-i.r. results. The sphetulitic morphology of the blends was remarkably affected by crosslinking. The birefringent spherulites were observed in the uncured PCL/OER blends, whereas a distinct pattern of extinction rings, which was absent either in the pure PCL or in the uncured PCL/OER blends, was apparent in the crosslinked PCL/PER blends.

The formation of ring-banded spherulites of poly(ɛ-caprolactone) in its miscible mixtures with poly(styrene-co-acrylonitrile)

Ring-banded spherulites in polymer blends of poly(ɛ-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) were investigated by optical microscopy equipped with a digital image analysis system. PCL/SAN blends exhibit not only spherulites with a Maltese cross, but also distinct extinction rings. The periodic distance of rings changes with blend ration and crystallization temperature and was plotted as a function of the undercooling and overall mobility of the mixtures, respectively. It was found that the overall mobility of chain segments in the mixtures could be mainly attributed to the origin of the formation of ring-banded spherulites. It was believed that for the first time a quantitative experimental result was obtained about the relationship of periodic distance of rings and the overall mobility of the mixtures. This relationship may be useful to explain the formation mechanism of ring-banded spherulites in polymer blends or even in homopolymers in the future.

The ring-banded spherulite structure of poly(ε-caprolactone) in its miscible mixtures with poly(styrene- co-acrylonitrile)

The structure of the PCL spherulite in poly(ε-caprolactone)/poly(styrene- co-acrylonitrile) (PCL/SAN) blends was investigated by optical microscopy and small angle light scattering. The spherulite structure with a Maltese cross has been observed in pure PCL. Similar PCL/SAN blends exhibited not only spherulites with a Maltese cross, but also distinct extinction rings. The H v light scattering pattern especially caused diffraction rings in PCL/SAN blends but not in pure PCL. The spherical symmetry of spherulite PCL becomes more incomplete and the twist of the lamella becomes more irregular with increasing SAN content. It is found that the spherulite structure of PCL/SAN blends is dependent on the crystallization temperature and the concentration of SAN in PCL/SAN blends.

The phase diagram and morphology of blends of poly(vinylidene fluoride) and poly(ethyl acrylate)

The phase diagram and crystallization behaviour of the polymer blend system consisting of poly(vinylidene fluoride) (PVF 2) and poly(ethyl acrylate) (PEA) have been examined. The melt exhibits phase separation upon heating to 10°C–50°C above the melting point of the PVF 2, depending on the composition. The cloud point and equilibrium melting point curve (for α-PVF 2) intersect at about 180°C and a composition of 50% (by weight) PVF 2. The polymer-polymer interaction parameter, χ, was calculated from the equilibrium melting point depression data and found to be −0.16 (at 170°C). Spherulite growth rate data have been measured as a function of composition and temperature. Assuming regime II crystallization a value of the product of the surface free energies of the α-PVF 2 crystals was calculated to be 4.4 × 10 −4J 2m −4. In blends crystallized from the one phase melt the texture of spherulites becomes more open and the spherulite extinction ring spacing (due to lamaller twist) becomes larger with increasing crystallization temperature. In addition the ring spacing increases with PEA content at constant crystallization temperature.

DEFORMATION BEHAVIOR OF POLYETHYLENE FILMS

The deformation of polyethylene films with spherulites was investigated by electron and polarising microscope. A linear polyethylene, Hizex 5000 was disolved in xylene at above 120°C and films were prepared on a piece of hot glass at 110°C and then cooled slowly to room temperature. (for 2-3 hours). The sperulitic films were drawn with various ratio at 20°C and 60°C. The deformation behaviour of the films at room temperature depends on the crystallization condition.The results obtained are as follows., 1) No deformation of spherulites was observed by polarising microscope in the range within the elastic limits at 20°C and 60°C.2) In the range where the strain is proportional to stress, the deformation of spherulites starts from the center at both temperature.3) In the high stretching the extinction ring was observed in the necking part. This indicates that the crystal lamellae remains without unfolding.4) When cross nicol is set in the direction of 45° to the drawing direction, the angle between the cross extinction lines observed in necking part becomes smaller than 90°.5) In lower stretching the extension of spherulite is of affine deformation.

The superstructure of melt‐crystallized polyethylene. I. Screwlike orientation of unit cell in polyethylene spherulites with periodic extinction rings

AbstractThe ringed structure in polyethylene spherulites was investigated by an x‐ray microdiffraction method. A spherulite with extinction rings whose interval is about 50 μ was observed when viewed under the polarization microscope. An asymmetric x‐ray diffraction fibrous pattern about the b axis was obtained for this specimen. This indicates that in the area of spherulite (several microns in diameter) the unit cells are never randomly oriented around a common b axis but have nearly similar orientations. A series of micro‐diffraction patterns was obtained at intervals of 13 μ (about 1/4 the extinction fringe interval), and it was shown that the unit cells have screwlike orientations with their common b axis along the spherulite radius. The distance corresponding to one‐half the pitch of the screw is just in accordance with the extinction ring interval.