Yellowness index measurements

UV spectra were recorded using a Perkin-Elmer Coleman 575 spectrometer. Yellowness index measurements (ASTM-D-1925) of film samples were made using a Colormaster Model V colorimeter. 

Another test method appHcable to textiles is ASTM E313, Indexes of Whiteness and Yellowness of Near-White, Opaque Materials. The method is based on obtaining G, ie, green reflectance, and B, ie, blue reflectance, from X, Y, and Z tristimulus values. Whiteness and yellowness index are then calculated from the G and B values. This method has particular appHcability to measurement of whiteness of bleached textiles. AATCC test method 110 also addresses measurement of the whiteness of textiles. 

By contrast, the coated PVC plate was found to be little affected by QUV aging (figure 9) even after 1000h of exposure, it still remained essentially uncolored and perfectly transparent in the visible range. By measuring the light-transmission of the sample at 420, 580 and 680 nm, one can evaluate the yellow index (YI) from the following equation ... 

The formation of the major UV degradation peak at about 287 nm in the weathered PC appears to correlate well with the formation of the yellow color in the weathered sample. In Figure 8 the formation of both the peak at 287 nm and the yellow color have been assumed to be products of a first order reaction. This figure shows a plot of the log of the percentage of a scaling constant minus the yellowness index divided by the constant, versus a measurement of the exposure. In this case, the exposure is expressed as cal/cm2, obtained from ENC0N data. 

The author thanks the General Electric Research and Development Center for permission to publish this work and thanks Mr. S. T. Rice for many of the yellowness index and UV spectral measurements. Mr. William Delaware of the New York State Department of Environmental Conservation is also thanked for his data. 

High Density Polyethylene - [Both regular and high molecular weight (HMW)]. The time to increase in torque at 220°C. by the Brabender Plasticorder was determined as a measure of crosslinking. Yellowness Index after the Brabender test at 220°C. and after the first extrusion at 260°C. were also performed. 

On the basis of melt flow rate measurements after 1, 3 and 5 extrusions, compounds 1, 2 and 2 when used alone at 0.1 in the polypropylene base resin provide superior stabilization to BHT, 7 and 8. Under these conditions compound J2 provides the lowest Yellowness Index (Y.I.) color over other compounds evaluated. 

Yellowness Index. The yellowness of the 50-mil plaques used for stabilization studies was measured directly from a Hunter D-25 color difference meter equipped with a 90° sphere attachment. The samples were placed in the reflectance port of the sphere using a standard white ceramic as backing. The instrument is designed to give direct yellowness index values as described in ASTM D-1925. 

Yellowing - Developing of yellow color in near-white or near-transparent materials such as plastics or coatings as a result of degradation on exposure to light, heat aging, weathering, etc. Usually is measured in terms of yellow index. 

The stability of PVC formulations is tested, for instance, according to ISO 305 by static heat tests, where test specimens are aged at constant temperature and mainly color changes (e.g.. Yellowness Index) are recorded. Alternatively, to assess the performance of heat stabilizers, the time until the dehydrochlorination reaction takes place can be measured, for example, through pH change (ISO 182). Combined thermal and shear stress is analyzed via dynamic tests such as two-roll mill processing or multiple extrusion. 

Color Measurement. The color (expresssed In x, y, Y co-ordinates) and color differences (CIELAB) between dyed and undyed untreated, formaldehyde-treated samples before and after weathering were measured using a MacBeth MS2000 color spectrophotometer using lllumlnant C. The Yellowness Index for undyed samples and the color of and color differences between face and back of weathered samples were also determined. The color properties of the fabrics are found In Tables III-VI. 

Solution color refers to the yellowness of the cellulose acetate solution. The most meaningful measurement is the yellowness index (YI) for an 18% solution of cellulose acetate in 9/1 methylene chloride methanol (by weight). Measurement is made by the Hunter colorimeter described above. Hemicelluloses in the pulp affect the color of the solution of cellulose acetate, but there are other factors that relate to solution color including brightness of the wood pulp and cellulose acetate processing conditions. 

Acrylic fibers discolor and decompose rather than melt when heated. Acrylic fibers, however, have very good color and heat stability at temperatures less than 230°C. In a study by American Cyanamid (using Federal Test Specification TT-P-141a Method 425.2), the yellowness of acrylic fabric was measured as a function of temperature [365]. Compared with a value of 0.00 for a pure-white body, the original fiber had a yellowness index of 0.04-0.10. After 30 min of exposure at 115°C, the yellowness increased only slightly from 0.11 to 0.17. After 6h at 130°C, however, the yellowness increased from 0.38 to 0.41. 

Objective color measurement is based on tristimulus colorimetry. " This instrumental method measures tristimulus values of light transmitted by a sample and compares the results to the values transmitted by distilled water. The results can be recalculated to the platinum-cobalt scale referred to in the previous standards. The results can also be interpreted by normal methods of color measurement to yellowness index, color, color depth, etc. 

Chow et al. (2011) determined numerous properties of the laser-treated cotton fabrics such as fabric weight loss yellowness index breaking strength tearing strength dyeing and colour measurement and fastness. Figure 2.12 shows a selection of the properties determined. 

See color measurement and control for a discussion on applying color quality standards (color evaluation, comparison, matching, and specification). However, a case of special interest is assoicated with the tendency for many initial colorless or white, transparent, or translucent polymers to develop undesirable yellowish color, with aging in particular. A standard method (ASTM D1925), based on the use of a recording spectrophotometer for transmittance and reflectance measurement, permits the determination of a yellowness index (YI). 

The practical characterization of the optical properties of polymeric solids is a complex subject. It involves the definitions and measurement of quantities such as index of refraction, transparency, gloss, haze, and yellowness index. 

The stability of HPMCAS at higher temperatures for shorter periods of time has been examined to understand its behavior while considering processes such as HME (Shin-Etsu Chemicals Co., Ltd). In this study, the stability was tested at 150-180 °C, for 15-30 min. A powder sample was stored in an oven, and the tests were carried out according to Japanese Pharmaceutical Excipients (JPE), with the exception of the yellowness index, which was measured using a color computer. The observed changes were a decrease in viscosity (due to a decrease in the molecular weight of the polymer), an increase in free acid, and discoloration. From the results, it is suggested that the polymer itself will be fairly stable up to about 150 °C when subjected to this temperature for a short period of 15 min. The results are shown in Table 4.3. 

The colour of most polymers is restricted to a yellow tinge. This is usually reported in terms of the yellowness index (ASTM E313-05, 2005 ISO 4582, 2007), which is calculated from reflection or transmission measurements. In comparing two materials, a difference of about two points in the index is just visible under good conditions of viewing (Tennent and Townsend, 1984b). 

Allen and co-workers [29] degraded EVA polymer films containing 17% and 28% vinyl acetate for various times in a hot air oven at 180 "C, and then examined the products by TGA, Fourier-transform infrared (E llR), spectroscopy, luminescence analysis, and carried out measurements of the yellowness index and hydroperoxide content. 

The method relies on the instrumental measurement of the degree of yellowness under daylight illumination of close to colorless or close to white translucent or opaque plastics. The measurement is made on pellets and is based on the tristimulus values that are obtained with a colorimeter. Methods are provided to determine the color measurements, such as yellowness index, CIE X, Y, Z, and Hunter L, a, b, or CIE L, a, b. A series of specimens that is compared should have similar gloss, texture, etc. 

Standard test method for polyurethane raw materials Instrumental measurement of tristimulus CIELAB color and yellowness index of liquids, ASTM Standard, Book of Standards, Vol. 08.03 ASTM D7133-05, ASTM International, West Conshohocken, PA, 2005. 

Some optical properties of films were also measured. These include standard methods of yellowness index and haze determination, as well as the see-through method developed for experimental studies of the effect of antiblocks on optical properties of films.The see-through test assigns a measurable value (distance in inches) to observable clarity differences seen by the human eye. A single layer of film is mounted to an 8-inch diameter embroidery hoop or solid frame. The distance between the eye chart and the observer eye is 48 inches. The film is moved toward the letter chart until all letters are clearly visible. The distance between the film and chart is recorded. The greater the distance, the better the film clarity. ... 

Yellowness index A measure of the tendency of plastics to turn yellow upon long-term... 

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