Color and Antioxidant Changes in Various Natural Rubber Processes

Fresh field natural rubber was coagulated by acetic acid, soaked in water at room temperature (WRT) or 70°C (W70) for 1 hr, and then dried in an oven at 40°C. Non-soaked natural rubber samples (NoW) served as a control. Two grades of natural rubber, namely air-dry sheet (ADS) and ribbed smoked sheet No.3 (RSS3) derived from the same latex, were also investigated. All dry rubber samples were characterized with Lovibond colorimeter according to ASTM D3157, as well as with a HunterLab spectrophotometer. Furthermore, all the dry rubber samples were dissolved in a chloroform:methanol mixture (4:1 v:v). The rubber was then precipitated out of the solution with methanol, and the remaining solution was quantitatively analyzed for total phenolic content (TPC). The plasticity retention index (PRI) was determined for all the dried rubber samples according to ASTM D3194. It was found that WRT, W70 and ADS were similar in lightness L*, while RSS3 had the lowest L*. W70 had the lowest redness a*, which increased in the order WRT, NoW, RSS3 and ADS. W70 also had the lowest yellowness b*, which increased in the order RSS3, NoW and WRT and ADS. Moreover, TPC was the lowest for the W70 sample, increasing in the order ADS, WRT, NoW and RSS3. The PRI was highest for W70, and decreased in the order WRT, RSS3, NoW and ADS. All of the PRI values observed were comparatively high relative to blocked standard Thai rubber 20 (STR20).

Digital Design and Implementation of Measuring Oil Color

This paper introduces an automatic Lovibond colorimeter, which is a system of color measuring, the TCS2300D color sensor and STC12C5A60S2 microcontroller are the cores of the system. The color sensor got the data of samples, and sent to microcontroller, by the bilinear interpolation algorithm, data for RGB color space was converted to the Lovibond color space [1], and last displayed on the tubes. The experimental results showed that automatic Lovibond colorimeter had good correlation with the Lovibond visual method, and the data read from the tubes was stable. With the advantages of low cost, simple operation, short measurement period that the colorimeter will be widely applied to the determination of oil color.

Color Measurements of Latices and of Rubber Films Prepared from Them

In the introduction to the present work, reasons for latex becoming discolored are reviewed, and the importance of color measurements are discussed. In addition, methods which have been developed for measuring the colors of various socalled white products, such as sugar, flour, paper, and the like, and methods for measuring the color of latex, are reviewed. Some of these methods are subjective; on the contrary, others utilize photocells so that subjective observations are eliminated. Measurements of the colors of different samples of latices were carried out with a Lovibond colorimeter, as a result of which it was found that this instrument is wholly unsuitable for this purpose. Measurements of the colors of both latices and films prepared from these latices were then made with a Hilger blancometer. The method of measuring and of calculating the intensity of the reflected light of a definite color is explained. The results obtained in measurements of the reflection of white light and of blue light from different samples of latex, using a Hilger blancometer, are compared with the results obtained with the same samples of latex estimated by simple visual examination. It was found that latices of good color reflect 80 or more per cent of white light and 78 or more per cent of blue light. The reflection of a yellow latex is considerably less in blue light than in white light. The reflection of a gray latex in white light does not differ much from that in blue light; in each case it is less than 80 per cent. It is proved conclusively that, judged by measurements of the colors of films, there is a close relationship between the color of a latex and the color of white-pigmented films made from the particular latex.