Migration stain

Migration stain - A discoloration of a surface by a rubber article which is adjacent to but not touching the discolored surface. 

A variety of test procedures have been in fairly widespread use for many years, virtually all of them being subjective in that visual assessment of the degree of staining is used. There has also been considerable confusion over the use of such terms as migration staining, which has been used differently in different commercial standards, so that it was particularly helpful when an international standard was published. 

Migration stain is the stain which occurs on the surface surrounding the contact area. 

It must be noted that the stain on the surface directly in contact with the rubber is always contact stain even if the stain has to be intensified by exposure to light after removal of the rubber, whilst any stain outside the area of contact is always migration stain. 

At the time of writing, a revision of ISO 3865 is almost complete which in most respects should be relatively little changed technically. The option to only expose to light for contact and migration staining is being deleted as it is a somewhat pointless exercise. If the panel discoloured without any rubber it would do so all over. 

BS 903 Part A3384 is identical to ISO 3865. ASTM D92585 has methods for contact, migration and diffusion (equivalent to penetration) staining. The contact stain method is similar to ISO 3865 except that there is no provision for developing the stain by exposure to light. Migration stain is not measured at the same time. 

Santoflex 77PD is used as an antiozonant in natural and synthetic elastomer compounds that can tolerate discoloration (it will discolor compounds and cause severe contact and migration staining). It also protects against catalytic degradation by copper and other heavy metals. 

Some of these early materials found acceptabiUty, but often had to be discarded when it was found that they were incompatible with the rubber or caused staining of fight-coloured compounds or migration stains to other materials coming into contact with the vulcanized rubber component containing them. 

Outstanding properties fast fusion, higher filler loading, low migration, stain abrasion resistance ... 

Sihcone polymer plasticizers have historically been used in many formulations. These plasticizers (qv) are of the same Si—O backbone as the functional polymers but generally are terrninated with trimethyl groups which are unreactive to the cure system. This nonreactivity means that, if improperly used, the plasticizer can migrate from the sealant and stain certain substrates. Staining has been a widely pubHcized flaw of sihcone sealants, but the potential of a formulation to stain a substrate can be minimized or eliminated with proper formulation work. In general, this is accompHshed by not using plasticizers for formulations developed for stain-sensitive substrates. 

Under certain conditions the sample is clearly visible throughout the process. Other times it is necessary to stain the matrix to visualize the components. In cases where a final staining procedure is required, a small amount of dye is often added to the sample before the analysis. The dye typically migrates faster than any sample component. The position of the dye in the matrix indicates the speed of the resolution of the components of the sample. Typically, the electrophoretic medium is discarded after use. Good resolution can be obtained from 1 to 20 hours, using applied voltages of 10 to 2000 V and currents of 5 to 100 m A. 

Corrosion products are almost always absent in stainless steel crevices. Areas just outside stainless crevices are stained brown and orange with oxides (Figs. 2.20 and 2.21). Metal ions migrate out of the crevice. Precipitation occurs by reactions similar to Reactions 2.3 and 2.4. Crevice interiors remain relatively free of rust (Figs. 2.16 and 2.17). 

The commonest staining trouble is iron stain —the blue-black stain caused by the interaction of soluble iron corrosion products and the natural tannins in wood. Hardwoods are generally more susceptible than softwoods. Steel wool should not be used for smoothing wood surfaces. Iron stains, if not too severe, can be removed with oxalic acid. Heavy contamination with soluble iron corrosion products usually results in migration and conversion to rust deposits in the wood. 

Tests were carried out as designated in ASTM Method D-925-83 related to staining of surfaces by contact, migration, or by diffusion. Hunter color values were measured on the L-scale. On this scale 100 is white and 0 is black. 

The band number refers to the position of migration on SDS-PAGE (see Figure 52-3). The glycophorins are detected by staining with the periodic acid-Schiff reagent. A number of other components (eg, 42 and 4.9) are not listed. Native spectrin is... 

Migration studies (compliance with regulations, blooming, staining medical)... 

Fig. 6.2. Caco-2 epithelial cell monolayers cultured with T. spiralis L1 larvae in (A) the absence or (B) presence of 1 mg ml 1 rat monoclonal, tyvelose-specific antibody 9D4 (McVay etal., 2000). Monolayers were fixed and stained with trypan blue as described in ManWarren etal. (1997). (A) Serpentine trails of nuclei in dead cells are evident, revealing the paths travelled by larvae. (B) Tyvelose-specific antibody has inhibited the migration of the larva such that it is encumbered in cell debris and has pulled up a large area of the monolayer, creating a plaque (P). Bar = 50 urn. Photomicrograph prepared by C. McVay, TTUHSC, Lubbock, Texas. 

Figure 7.1 Separation of proteins by SDS-PAGE. Protein samples are incubated with SDS (as well as reducing agents, which disrupt disulfide linkages). The electric field is applied across the gel after the protein samples to be analysed are loaded into the gel wells. The rate of protein migration towards the anode is dependent upon protein size. After electrophoresis is complete, individual protein bands may be visualized by staining with a protein-binding dye (a). If one well is loaded with a mixture of proteins, each of known molecular mass, a standard curve relating distance migrated to molecular mass can be constructed (b). This allows estimation of the molecular mass of the purified protein...

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