Moulding specimen

ISO 1600 1990 Plastics - Cellulose acetate - Determination of light absorption on moulded specimens produced using different periods of heating ISO 13468-1 1996 Plastics - Determination of the total luminous transmittance of transparent materials - Part 1 Single-beam instrument ISO 13468-2 1999 Plastics - Determination of the total luminous transmittance of transparent materials - Part 2 Double-beam instrument ISO 14782 1999 Plastics - Determination of haze for transparent materials... 

The influence of injection moulding on a preliminary orientation of the ciystallites and their deformation we described recently (Schneider, 2010). It was shown, that injection moulded specimens in injection direction as well as the compression moulded and quickly cooled specimens are highly stretchable. By contrast the specimens transversal to the injection direction fail very soon. Here in some cases even crazing could be observed before failure. 

The influence of the specimen thickness on the E values can be seen in Fig. 3.3. Thinner specimen show slightly higher E values. In order to obtain reliable results from e.g. injection moulded specimen (which have normally a 4 mm thickness) the specimen thickness with 4 mm is a feasible compromise. 

Plastics - Cellulose acetate — Determination of viscosity loss on moulding Plastics - Cellulose acetate — Determination of light absorption on moulded specimens... 

Properties of high-temperature plastics as determined in injection moulded specimens made in our laboratory... 

In order to minimise as far as possible the influence of processing variables, studies have been carried out using tensile creep tests on carefully prepared compression moulded specimens. It must be realised that, vv ith injection moulded articles, the creep properties will also be subject to variation with the amount and direction of residual flow orientation, while, with crystalline polymers such as the polyolefins, the creep effects will also be influenced by variations in density caused by a combination of flow orientation, compressive packing, and cooling effects. Stresses will generally be complex and will often involve compressive and flexural components. However, articles should normally be designed to limit the strains occurring to quite low levels, where a reasonable correlation can be expected between tensile, compressive, and flexural creep data. 

Figure 18.29 Effect of temperature on falling weight impact strength of 0.060 inch compression moulded specimens of various polymers. GMT 61 and KMT 61 = polypropylene copolymer. ABS = acrylonitrile-butadiene-styrene terpolymer, KM 61 polypropylene homopolymer. Source Author s own files)...

Figures 18.29 and 18.42 show the effect of temperature on the falling weight impact strength for compression moulded and injection moulded specimens, respectively, of a range of materials. The reduction in impact strength with decrease in temperature is particularly marked with the injection moulded samples of the two otherwise higher impact resistant types, PP copolymers and ABS terpolymers. The superior impact strength at low temperatures of injection moulded HOPE is clearly illustrated.

The X-ray powder diffraction profiles of melt-crystallized compression moulded specimens of the iPP samples of Table 11.1 are reported in Fig. 11.2a. The samples crystallize from the melt as mixtures of a and y forms (Fig. 11.2b, c, respectively). 

Heat deflection temperature is a single point measurement and does not indicate longterm heat resistance of plastic material. However, it may be used to distinguish between those materials that are able to sustain light loads at high temperatures. The heat deflection temperature of a specimen is affected by the presenee of residual stresses. Warpage of the specimen due to stress relaxation may lead to erroneous results. In addition, injection-moulded specimens tend to give a lower heat defleetion temperature than compression-moulded specimens. This is because compression-moulded speeimens are relatively stress fiee. 

Chain orientation always refers to a particular structural unit (Fig. 9.2). It may be a whole sample or a macroscopic part of a specimen. The core of an injection-moulded specimen is typically unoriented, whereas the material of the same specimen closer to... 

Surface morphology of compression moulded specimens before and after biodegradation were characterized by scanning electron microscopy (SEM) (TM-1000,Hitachi). Samples were coated with gold prior examination. 

Firstly, the two peaks attributed to the third and fourth orders of basal spacing of the layered-silicate seen in the XRD spectra for the injection-moulded specimens and feedstock compounds were absent in the fibre spectra. Because the disappearance of the third and fourth order peaks could be an effect of exfoliation or because of low X-ray beam intensity, it is not possible to distinguish which of the two effects is more prevalent. However, the first and second order peaks of the hsv fibres manifested a more depressed peak shape and exhibited a lower peak intensity compared with the Isv fibres, but, in theory, the Isv fibre should exhibit a greater peak intensity because of the larger circumference and hence area exposed for beam diffraction. It is quite apparent, therefore, that the disappearance of the third and fourth order peaks, and the suppressed peak shape and intensity for the first and second order peaks, are mainly attributed to further exfoliation of the precedently intercalated layered-sihcate through an extensional deformation effect during the melt-spinning process. 

Following the manner of presentation in the previous sections, the subject of viscoelasticity will be explained by reference to experiments familiar to the practitioner of rubber technology. This is a rather unorthodox approach and different from the usual one, which begins with an introduction of the theory. The experiment is tensile stress-strain measurement. In the rubber industry tensile measurements are routinely performed with crosslinked specimens. Here, we are concerned with gum-rubber behaviour. Therefore, we must perform the measurements with uncrosslinked specimens. First, compression-moulded specimens must be prepared they require special attention, which will be described next. 

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