Weathering, chalking

In a special weathering device we constructed ourselves (4), we later carried out chalking tests in which great care was taken to exclude water while allowing air to enter unhindered. This and the... 

The effect of chalking is rapid and marked even after a short weathering time. There appears to be no clear distinction between chalking in the broader sense of the word and plate-out the two phenomena are very much related. As in plate-out and unlike in blooming, the particles that adhere to the polymer surface through chalking can be removed comparatively easily without reappearing. 

Full shades and similar deep shades exhibit excellent weatherfastness, but rapidly decrease in tints made by adding TiOz. The cleanness of full shades increases noticeably by exposure to weather. There are certain binders in which P.Y.138 tends to chalk if employed at high concentration. 

LCPs are slightly altered by one year of outdoor exposure, with a light surface chalking, but after a 2000 h exposure in a Weather-Ometer, retention of mechanical properties is superior to 90%. 

Linzon reported snb symptoms on white pine after several days of wet weather followed by a continuous sunny period. Symptoms were noted several times during the 1957-1964 growing seasons at Chalk River, Ontario, but time of occurrence did not correlate well with peak oxidant concentrations. Berry and Ripperton observed emergence tipbum on susceptible trees in West Virginia several days after oxidant peaks of 0.065 ppm. They found that container-grown susceptible pine clones were protected from injury if placed in a chamber supplied with charcoal-filtered air. 

The empirical tests described below determine the chalking and weathering differences between two pigments, but do not always give the true differences. Other test methods have therefore been developed, e.g., determination of mass losses on weathering (gravimetric test) [1.51]. 

Cycloaliphatic and heterocyclic epoxy have better weather resistance and less tendency to yellow and chalk than do aromatic epoxy resins. These resins possess excellent electrical properties and are often used in electrical and electronic applications. They are generally formulated into casting and filament winding compounds. 

Accelerated weathering test was carried out by the exposure of the films to a Sunshine weather meter with Xenon arc type accelerated weathering machine. HS-polymer s fihn does not chalk nor yellow. However under the conditions employed, polyimide (PI) is led to chalking and polyethylenenaphtalate (PEN), polycarbonate (PC) and polyethylenetelephtalate (PET) are led to yellowing (Table 1). 

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