Trempe de couches minces dans l'azote liquide, la glace et l'eau a temperature ambiante; formation de cristaux β

A number of years ago the morphology of amorphous polyethylene terephthalate (PET) quenched from the melt at 280°C into ice water and cast from solution was reported [1]. A nodular structure ca. 75 Å in diameter was described, the electron diffraction pattern consisting of a single diffuse ring. Based on brightfield and dark-field diffraction contrast micrographs, which showed the presence of ordered domains of similar size, it was proposed that the molecules in amorphous PET both above and below Tg are locally aligned and have a nematic liquid-crystal-like arrangment, in domains of the size of the nodules. The proposal of order in the amorphous material above Tg was based on the assumption that the quenching was sufficiently rapid that the morphology observed in the glass reflected that present above Tg at the instant of quenching; in the melt itself the ordered domains were presumed to undergo continuous fluctuation.

Abstract Several electron microscope techniques have been used to characterize the microdomain morphology of plasticized PVC. The plasticizer was found to be heterogeneously distributed in samples processed at low temperatures. The 100—200-Å microdomains, which are essentially unplasticized, do not fuse at temperatures up to 165°C. However, at 180°C they begin to fuse, resulting in a more homogeneous distribution of the plasticizer. With increasing plasticizer level, the additional plasticizer was found to favor regions where it was already present, the unplasticized regions being almost unaffected. Milling time at 165°C was found to have little effect on the plasticizer distribution.

AbstractCold Compaction Molding and Sintering of Ultra High Molecular Weight Polyethylene (UHMWPE) has been examined as a function of particle size, sintering time and temperature, and cooling rate. Properties nearly equivalent to those obtained by compression molding can be obtained from samples with a fibrous particle morphology, sintered just above the melting point, with further improvement possible by control of particle size and addition of fine particles of normal molecular weight linear polyethylene. UHMWPE with a nodular particle morphology sintered poorly.

Ultrastructure deformation studies of reconstituted and native rat tail tendon collagen revealed that deformation occurs primarily in the non-staining and presumably non-polar proline rich regions for all ages examined. At low deformation (tension and compression) the deformation occurs somewhat more between the a2 and b1 and b2 and c2 bands than within the rest of the d period. At moderate elongations (greater than 40%), the deformation becomes localized between the c2 and d bands, with subfibrils on the order of 3-15 nm being drawn across the openings between the c2 and d bands. At high elongations (100% or greater) d period splitting occur on a regular basis between the c2 and d bands, along with a retraction of the 64 nm repeat period into 60 nm segments. It is in this deformation region that the effects of molecular slip and the apparent association of the acid mucopolysaccharides can be noted. These results suggest that crosslinking, if increasing as a function of age, does not affect the deformation characteristics of the individual fibrils and that changes with age in mechanical properties should be sought in changes in the fibril size and their interaction with the surrounding matrix.

Following the conclusion of the Characterization Section on Tuesday, at the request of the Chairman, Prof. P. H. Geil, approximately 25 symposium attendees remained to discuss the general problem of morphology terminology for PVC. As a result the list of terms given in Table 1 was developed. It is strongly recommended that future papers discussing PVC use these terms to permit common understanding of the morphological units being described.

Dr. Berens (B. F. Goodrich Co., Brecksville, Ohio, U. S.): I will ask Dr. Geil to start the discussion because his area of expertise is polymer morphology. A suitable subject on which to start is the relationship between morphology, as formed during polymerization, and some of the morphological features observed in solid PVC during and after processing.

Electron microscopy indicates that PVC contains aggregates on three size scales: 100 to 500 Å, 0.1 to 0.5 μm, and 1 to 10 μm. The effects of plasticizers and processing conditions on this morphology and its effect on mechanical properties are discussed.