Solubility (S) and diffusion (D) of water in low-density polyethylene have been studied by means of desorption experiments. The dependence of S and D on the state of oxidation of the polymers has been measured. A model has been developed to describe the bound-oxygen dependence of S and D. Physically the oxygen groups act as traps that are strong enough to bind the water but not so deep as to remove the water from the diffusion process. Hydroxyl, hydroperoxide, and carboxylic acid groups form the strongest traps, ketone groups are weaker, and ester groups exhibit negligible trapping. Permeation is unaffected by bound oxygen. Trap volumes deduced from the analysis lie in the range of a few cubic angstroms. Some restriction of rotational motion of the trapped water is required by the analysis, and independent NMR evidence is presented to support this result.
he Brabender Plasti-Corder torque rheometer has T been widely used to study the rheological behavior of polymer melts under processing conditions (1, 2, 3 ) . This instrument, however, imparts a very complex shearing motion to the polymer; consequently the manner in which data taken with the Brabender may be related to specific processing operations, such as extrusion or milling, is unknown.The Brabender rheometer, depicted in Figure 1 , consists of a heated sample chamber which fits over two irregularly-shaped rollers. A quantity of polymer which will just fill the sample chamber is charged and melted.The total torque required to turn the rollers in the melt ASSEMBLY VIEW -TOP SAMPLE CHAMBER . ROLLER ASSEMBLY VIEW -FRONT Figure 1. Brabender torque rheometer.
Photopolymers are attractive candidates for high-density holographic data storage because of their high sensitivity and refractive index contrast. We have incorporated several high-index organic monomers into high optical quality acrylate oligomer-based formulations. Using reactivity ratios, reaction kinetics, and component refractive indices as guidelines, a 6-fold increase in Δn has been achieved compared to an initial all-acrylate formulation. Samples prepared from these formulations have been used to write and read >200 high-quality holograms in a given volume of material. This is the first time a photopolymeric medium has successfully been used to multiplex this number of holograms. Using these resins, a protocol for the evaluation of photopolymers as holographic media has been developed.
The capillary flow instability resulting in extrudate distortion has been studied for ethylene polymer melts using a molecular structure approach. It is found that the instability initiates at a critical value of elastic strain energy independent of (average) molecular weight for linear polyethylene. Once the flow breaks down, a slip interface within the melt is formed near the capillary wall, causing an abrupt increase in volumetric throughput. The velocity gradient within the melt remains continuous through the instability, however. Low molecular weight species present in the molecular weight distribution of linear polyethylene tend to suppress slip. Blends of linear and branched polyethylene exhibit instability behavior characteristic of both components throughout the entire range of composition. Results are discussed in terms of specific molecular mechanisms.
synopsisThe influence of hydrogen bonding on the flow behavior of polymer melts a t high shear rates has been investigated using a capillary extrusion rheometer. The systems studied were copolymers of ethylene and acrylic or methacrylic acid. Hydrogen bonding was found to substantially enhance both flow activation energy and viscosity level, as well as the degree of dependence of viscosity on rate of shear. It was also found that hydrogen bonding does not influence the critical shear stress for onset of "melt fracture." The data support the view that hydrogen bonds act effectively as temporary (quasi-) crosslinks during the short time scales of deformation involved in flow a t high shear rates.
Synopsis-111 analysis of the Maxwell orthogonal rheometer for polymer melts is made by using the constitutive equation of White and JIetzner. The results indicate that the shear iieformation involved is oscillatory and that the storage and loss moduli of the melt may be derived from the measured stress response.The rheology of polymer melts is an area of considerable importance both from a practical standpoint and for understanding material behavior. Recently Maxwell and Chartoff' reported on a new device, termed an orthogonal rheometer, for characterizing polymer melt properties. To date, however, its acceptance has been hindered by the need for an analysis of the manner in which the three forces measured by the device are related to the response of the material to the imposed deformation.The molten sample of thickness I is contained between parallel circular plates, the axes of which are not colinear but separated by a distance a along the y axis. The lower plate is driven at a rotational velocity W . The upper plate is allowed to rotate freely a t the same angular velocity. Three orthogonal forces are measured along the 5 , y, and x axes. We have analyzed the rheonieter by formulating the kinenlatics in a nonorthogonal curvilinear coordinate system in which the motion of the fluid can be easily written. This system, depicted in Figure 2, has coordinates (0', r', 2') related to the Cartesian coordinates (2, y , x ) by Figure 1 depicts the rheometer schematically. 8' = tan-' { [ Y -( U / Z ) Z ] / X~
The viscosity of carboxylic-acid-terminated polybutadiene increases markedly upon neutralization with mono-and divalent bases. These viscosity increases are related to apparent molecular weight, considering the association of the terminal salts as "polymerizing" the difunctional prepolymer. For the monovalent alkali-metal salts, simple end-group dimerization seems to occur with an average tJI of ""-25 kcal/mole. Neutralization with ions of higher valency leads to materials with higher viscosities.
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