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A multi-angle spectrophotometer was used to measure the CIELab coordinates L∗, a∗ and b∗ in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a∗ and b∗ decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.

It is well known that the properties of a final polymer product are determined not only by the polymer characteristics but also, via process-related structural changes, by the processing technique and by processing conditions such as cooling rate and machine speed. In this study, the influence of the extrusion coating process on the structure and properties of LDPE-, LLDPE-, and m-LLDPE-grades was evaluated. Process variables such as the melt temperature, the draw ratio, the length of the air gap between the die exit, and the laminating nip and the machine speed were studied. The primary interest was in the influence of the process parameters on the degree of orientation and its corresponding impact on the tensile and barrier properties (water vapor transmission rate) of the polymer films. The degree of orientation of the films, assessed by shrinkage measurements, was found to be directly related to the elongational strain rate imposed on the films during the drawing stage of the coating process. Furtherm...

The finite element method (FEM) is used to calculate the distribution of residual internal stresses in an injection molded plate-shaped polystyrene specimen. The first step of the calculating procedure is the determination of the temperature distributions in the plate and its variation with cooling time. The temperature distribution data are then used for the determination of the corresponding stress distribution. Also this latter step is accomplished using the FEM-technique. The residual stress distribution is obtained when the sample has been cooled to the temperature of the mold. The main result of the calculations is the finding that the surface layer of the plate is subject to compressive stresses, while the interior accommodates stresses of tensile type. The calculations relate to a polystyrene specimen. The results are shown to agree well with earlier data concerning internal stresses in injection molded objects. The possible influence of anisotropy and visco-elastic relaxation has been ne...

When plotting the slope of stress relaxation curves (stress vs. log time) against the initial stress, straight lines are obtained intersecting the axis at a stress value which appears to be associated with the internal stress level of the sample. For injection molded samples, the internal stresses are negative, i.e. frozen-in compressive stresses. They disappear on annealing. Both tensile and compressive stresses can be introduced into stress-free samples by suitable thermal treatment when in a state of compression or tensile strain.

Both native and regenerated (rayon) cellulosic fibers are potential reinforcing elements in rubbers due to their relatively good mechanical properties, suitable aspect ratio, low cost and low density. The properties of the cellulosic fibers can also be changed fairly easily by chemical treatment. The effects of two treatments, mercerization (NaOH-immersion) and benzylation, on the mechanical properties of a rubber-cellulose composite are here reported. The rubber matrix was isoprene and the fiber content 20% by volume (27% by weight). Mercerization of bleached kraft fibers gave a composite with a higher modulus and strength than was attained when untreated kraft fibers were used, whereas benzylation of both kraft fibers and rayon fibers caused a reduction in the strength and stiffness of the rubber composites. This is interpreted as being due to a decrease in the degree of interaction between the cellulose fiber and the matrix due to the benzylation. The effect of these treatments on the mechanic...

It is assumed that, in a system of filler in polymer, an internal stress distribution is associated with a shift in the glass transition temperature of the polymer. Experimental results supporting this theory are presented.