R. St. John Manley

Blends of cellulose with polyacrylonitrile prepared from N,N-dimethylacetamide-lithium chloride solutions

Blend films of cellulose with polyacrylonitrile were obtained over the whole composition range from solutions in N,N-dimethylacetamide-lithium chloride by coagulation in a non-solvent. Visual inspection and optical microscopic observation gave no indication of phase separation in any of the blends. Detailed characterization of the state of miscibility was carried out by wide-angle X-ray diffraction, differential scanning calorimetry and dynamic mechanical measurements. The wide-angle X-ray diffraction patterns of the blends were composed of the diffraction rings from the individual polymer crystals, but qualitative estimates showed that the degree of crystallinity was low, especially in the cellulose component. From an estimation of the glass transition temperature by differential scanning calorimetry and dynamic mechanical techniques, it was found that the blends exhibited considerable miscibility at the molecular level in the amorphous regions above 50wt% cellulose content. A possible explanation of the results is presented through consideration of a specific interaction between the hydroxyl groups of cellulose and the nitrile groups of polyacrylonitrile.

Particle motions in sheared suspensions. II. Collisions of uniform spheres

Abstract The interaction of model glass spheres in suspensions subjected to velocity gradients has been studied in detail. Absolute “inelastic” collision frequencies have been measured and found to be in excellent accord with a theory based upon simple geometrical considerations. A doublet so formed rotates as a rigid dumbbell at a known constant angular velocity, and separates at a point which is a mirror image of the initial point of contact. This memory effect persists through interruptions of motion of the suspension, a phenomenon which casts some doubt on the otherwise definite evidence of true contact of the spheres. The details of doublet rotation which have been established experimentally make it possible to calculate the mean and the maximum values of the life of a doublet, and the frequency distribution of doublet lives. Good agreement between various measured and calculated values of doublet lives has been found. Up to the instant of doublet formation, there is no measurable interaction effect upon the translational or rotational velocity of singlets at volume fractions of as high as 1.6%.

Particle motions in sheared suspensions. orientations and interactions of rigid rods

Single rigid cylindrical particles suspended in a fluid which is subjected to laminar shear execute rotations in spherical elliptical orbits in the manner predicted by Jeffery. It could not be established conclusively, however, whether a single undisturbed particle continues to rotate in a fixed orbit or drifts to preferred orbits. The variation in rotational velocity at various positions in the orbit may be expected to yield preferred orientations in various reference planes. Instantaneous particle orientations in the plane of shear, determined after shearing initially isotropic suspensions, yielded a steady-state distribution with a preferred orientation in the direction of flow after about 3000 particle rotations. The steady-state distribution of orbits was also determined and found to lie between those calculated from the assumptions made by Jeffery and Eisenschitz. The effects of two-body interactions upon the period of rotation and rotational orbit were studied. The results strongly suggest that the equilibrium distribution of orientations and of orbit constants is determined by the mechanics of particle interaction.

The morphology of fibrillar polyethylene crystals

Abstract A comparison has been made of the morphology of fibrillar polyethylene crystals prepared by shear-induced crystallization and heterogeneous Ziegler-Natta catalysis under similar solvent and temperature conditions. Both specimens had a shish-kebab superstructure consisting of lamellar overgrowths on a filamentary backbone. For polyethylenes stirrer-crystallized at small supercoolings, the overgrown lamallae were removed by nitric acid oxidation followed by selective dissolution, leaving naked filamentary ribbons. Thermal analysis of these specimens suggested a dual molecular conformation of both folded and extended chains. The fact that these fibrils did not deform easily under uniaxial stress conforms with a core of extended chains. Thermal and oxidative behavior of polyethylenes prepared at lower crystallization temperatures suggested a greater content of chain folds in the central thread as the degree of supercooling increased. The Ziegler-Natta fibrils were degraded into lamellar fragments on ...

Effect of solvent on the polymorphism of poly(4-methylpentene-1): 1. Solution-grown single crystals

Abstract The morphology and structure of poly 4-methylpentene-1 single crystals grown in a variety of solvent systems is studied by electron microscopy, electron and X-ray diffraction. Depending on the solvent, two different crystalline structures are identified. The usual modification I is formed in a xylene-amylacetate mixture. Modification III is grown in decalin and in a xylene-cyclohexane mixture. In a slowly cooled xylene solution, a mixture of single crystals of both structures is obtained. These results confirm earlier work and show that there is a definite dependence of the structure of the solution-grown polymer crystals on the crystallization temperature. Finally, a refined characterization of modification III single crystals is presented.

Lattice imaging in polyethylene single crystals

On montre que les images reticulaires de monocristaux de PE peuvent etre aussi enregistrees avec une microscopie electronique en transmission conventionnel si les conditions experimentales sont choisies avec soin

X-ray long periods in bulk crystalline polymers

Abstract Small-angle X-ray diffraction, supplemented by electron microscopy, has been used to probe the morphology of bulk crystallized polyoxymethylene (POM), isotactic polypropylene (PP), isotactic polystyrene (PS), and 1,4-trans-β-polyisoprene (PIP). Samples crystallized isothermally from the melt as well as annealed samples were investigated. The temperature range covered extended from 0[ddot]C to near the melting point. It was found that POM gave rise to three discrete small-angle scattering maxima and that PP gave two, whereas PS and PIP had only one. Attempts at correlating the long spacings corresponding to these maxima with readily identifiable morphological features were not entirely successful. Using the long spacing data in equations based on the Lauritzen and Hoffman theory of polymer crystallization, interfacial free energies were calculated. The values obtained are lower than those reported by other authors using radial spherulitic growth rate data on the same polymers. Various interpretati...

Phase transitions, structure evolution, and mechanical properties of blends of two crystalline polymers: poly(vinylidene fluoride) and poly(butylene adipate)

Abstract The emergence of crystalline structures during phase transitions, involving crystallization and phase separation in blends of poly(vinylidene fluoride) (PVF 2 ) and poly(butylene adipate) (PBA) has been examined by means of time-resolved depolarized light scattering, polarizing optical microscopy, and differential scanning calorimetry. These PVF 2 /PBA blends are known to exhibit various phase transitions including liquid–liquid phase separation, melting of the PVF 2 , melting of the PBA, and a single glass transition, in the order of descending temperature. Several thermal quench experiments were undertaken, from the isotropic melt (200°C) to various crystallization temperatures at several blend compositions, to elucidate the emerging morphology and the crystallization kinetics in competition with phase separation. The development of the crystalline morphology is shown to be strongly dependent on the blend composition and crystallization temperature. Of particular interest is the observation that at PBA-rich compositions, nematic mesophase structures are formed even though the constituents do not contain mesogenic groups. Samples quenched from the isotropic melt (200°C) to low temperatures (e.g., 25°C) develop interconnected spinodal decomposition textures, and this observation is discussed in relation to the possible existence of an upper critical solution temperature (UCST). Tensile properties of high temperature crystallized blends with a spherulitic morphology have been compared with those of the thermal quenched blends having a periodic modulated crystalline structure. It is concluded that the mechanical properties are strongly dependent on the complex interplay of crystalline structure and phase-separated blend morphology.

Cellulose synthesis by Acetobacter xylinum III. Matrix, primer and lipid requirements and heat stability of the cellulose-forming enzymes

The addition of soluble cellodextrins of increasing size to a cell envelope preparation of Acetobacter xylinum stimulated cellulose synthesis from UDPG. This stimulation was attributed to both acceptor and activator effects. Enzymes required for cellulose synthesis were found to be heat-unstable and those required for synthesis of glycosylated lipid components from UDPG, heat-stable. Both heat-inactivated envelope fragments and supernatant fluid from whole cells were necessary for cellulose synthesis from UDPG. Cellulose was not formed from UDPG in the presence of either supernatant fluid alone or heat-inactivated envelopes alone. The combined results of this and previous studies suggest that either the cell envelope is necessary for synthesis of a more immediate precursor to cellulose than UDPG, or that the synthesis from UDPG requires a matrix. The former suggestion and its possible link with lipid intermediate involvement was strengthened by the observation of inefficient glycosylated lipid formation by a celluloseless mutant strain of A. xylinum. The possible locations of various enzyme activities required for the synthesis of the cellulose precursor are indicated and a possible microfibril nucleation process is discussed.

Lattice imaging of poly-4-methyl-pentene-1 single crystals; use and misuse of fourier averaging techniques

Abstract High resolution lattice images of poly-4-methyl-pentene-1 single crystals, obtained at low magnification by using a low-dose technique with a conventional electron microscope, were digitized and computer-processed by Fourier filtration. The molecular image along the chain axis was readily obtained at 4.3 A resolution by using small mask windows so that the averaging extends over a large number of unit cells. On the other hand, attempts to visualize lattice defects gave unreliable results due to the high noise content of the original lattice images. Apparent edge dislocations seen in the reconstructed images were correlated with the noise passing through the large mask windows required to decrease the averaging conditions during Fourier filtration. These results indicate that great care must be exercised in the interpretation of apparent lattice defects in Fourier-filtered images of beam-sensitive specimens such as polymer single crystals.