Foreign contamination

Foreign contamination is typically first discovered by quality control checks of the finished product or by the loss of the web for film processes. If a melt filtration system is installed downstream of the extruder, the larger size particles will be collected. After the contaminants are collected they must be analyzed for composition. Some types of contaminants are easily identified using a microscope or hand lens and include paper and cloth fibers, dirt, and metal fragments. Other contaminants such as gels or foreign resins are not as easily identified, and their identification often requires advanced analytical procedures. Many resin manufacturers offer these types of services to their customers. After the contaminant is identified, the source must be determined and then eliminated. Elimination of the source can be simple for common contaminants but can be a challenge for contaminants that exist at a very low level. 

Figure 11.2 Photographs for several common gel types found in PE films a) a highly oxidized and crosslinked gel, b) a gel with a small particle of carbonized PE, c) a foreign contaminant, and d) a gel caused by a fiber contaminant. Photographs were provided by B. Vastenhout of The Dow Chemical Company...

Figure 11.6 Photographs of foreign contamination in pellets of a re-pelletized reclaim stream a) photomicrograph of discolored PE pellets containing dark defects, and b) transmitted polarized light micrograph of a pellet cross section containing a defect. Photographs were provided by E. Garcia-Meitin of The Dow Chemical Company...

The 200-liter (55-gal) drums are the most common and work very well with bulk distribution equipment. Drums have two 2-in. openings that mate via threaded fittings with sealed dispense heads and sealed stirrer connections that minimize loss of water or other volatile components and minimize entry of foreign contaminants. All connections, including the drum hole caps, should be thoroughly cleaned to prevent dried slurry from falling into the drum. The need for stirring is very dependent on the type of slurry and will be covered later. 

Given the sensitivity of colligative methods to the presence of low molecular weight impurities, particular care was taken to isolate lignin samples free of such foreign contaminants. Thus, for example, the extraction... 

Other components in the Echinacea products may contribute to many of the adverse reactions reported, not only Australian, but also the United States, United Kingdom, Canada and New Zealand. Additional studies are needed to further support the IgE-mediated hypersensitivity reported in Echinacea-containing products. Studies could include growing and processing of Echinacea under environmentally controlled conditions, with the intent to minimize foreign contaminants, and administration of extracts to patients under supervision. Although this would not represent real-world conditions, it may further support or refute the IgE-mediated hypersensitivity observed in subjects taking commercial Echinacea products. Additional work is also needed to identify the component responsible for the IgE-mediated hypersensitivity. 

Clarification. The raw washed sugar hquor from the melter contains particulate matter coming from all sources, for example, field soil and fiber, yeast, molds, gums, colloids, and foreign contaminants. The object of clarification is the complete removal of these undesirables. The raw liquor is also acidic. One of three processes is then used carbonation, phosphatation, or filtration. 

Presence of foreign contaminants such as cleaning solvents and... 

Regarding the workability the common constituents in ambient air are aerosols composed mainly of solid and liquid particulate matter which can cause serious contamination problems at trace and ultra trace levels. The values in Table 5 demonstrate the significance of clean room conditions for precise and accurate determinations at these levels.Thus, for prevention of foreign contamination through Pb, Cu, Zn the clean room technology is a must. ... 

The variation of the work function and the Fermi level in metals and semiconductors is illustrated in Fig. 5.2. In the metal (Fig. 5.2a), the Fermi level is fixed at the energy where the N lowest-lying electron states are filled with the N electrons in the (uppermost) band of valence electrons. There are many additional empty electron states above p, but these remain empty regardless of the presence of small amounts of foreign contaminants. The position of p and the value of (j) in metals are thus rigorous materials constants. 

No oxygen was detected on the uncoated substrate. Within the sensitivity of RBS, the films were free from foreign contaminants. 

All products are shipped free from bark, dirt, metal and other foreign contamination. 

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