Yellowness index

Fig. 2. Yellowness index vs two-roU mill heat stabiUty, where the mercaptide ligands, — SCH2COOR (A), —SCH2CH2COOR ( ), and —SCH2CH2C00R + HSCH2CH2C00R ( )) IT 9, and 6% Sn, respectively. R = CgH. R = H33. ...

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. 

Color/Transparency. Almost all amorphous engineering thermoplastics, except PC and some polyester carbonates, are inherently colored. Even polycarbonates have yellowness indexes (YI) (36) of 0.1 to 5.0. Colorless material is produced from these resins by compounding with complementary blue dyes which reduce transmission. Ha2e in amorphous resins is an indication of particulates. Ha2e reduces optical clarity and transmission. 

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 ... 

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. 

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. 

Figure 8. Formation of 287-nm peak and change in yellowness index in PC film during natural weathering...

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. 

TGA, iodometric, mid-IR, luminescence (fluorescence and phosphorescence) and colour formation (yellowness index according to standard method ASTM 1925) were all employed in a study of aspects of the thermal degradation of EVA copolymers [67], Figure 23 compares a set of spectra from the luminescence analysis reported in this work. In the initial spectra (Figure 23(a)) of the EVA copolymer, two excitation maxima at 237 and 283 nm are observed, which both give rise to one emission spectrum with a maximum at 366 nm weak shoulders... 

PVC resists hydrolysis well but is naturally sensitive to light and UV. It must be protected by addition of anti-UV and other protective agents. In these cases, long warranty periods can be allowed, for example ten years and more. For a white, protected, rigid PVC, after natural weathering for 3 years in Michigan, the retention of impact strength is 68% and the yellowness index increases by 5. 

UV-stabilized grade 87% for transmittance, 15% for the haze, 6 for the yellowing index. 

ASTM D1925-70 (1988, withdrawn 1995) Standard Test Method for Yellowness Index of Plastics. 

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. 

Entry Composition (daltons) (daltons) Tg ( C) Elastic Modulus (Gpa) Hardness (Mpa) Yellowness Index... 

Although the yellowness index, oxygen uptake, and percent weight loss were not valid indicators for evaluating the extent of degradation at... 

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