Polyethylene product contamination

In the industrial field, this separation technique has been used for purposes as diverse as the analysis of odour and taste problems in high-density polyethylene [93], contaminants in recycled high-impact polystyrene [94], benzene residues in recycled polyethylene terephthalate [95] and denture adhesives [96], residual toluene in medical plasters [97], and lipstick (for assignation of products to manufacturers) [98,99]. 

In addition to molecules diffusing through polyethylene, another important consideration is that of additives diffusing from the polyethylene itself, either contaminating other materials or ehanging the properties of the polyethylene. The latter can be partieularly important when the migrant molecules are antioxidants and the polymer is in an oxidative environment. The loss of antioxidants from polyethylene products exposed to the elements is a major factor in some types of premature failure. Failure of eertain products, such as electrical cables, can be linked to the loss of stabilizer henee diffusion is an important process [40]. 

The problems assoeiated with the recovery of a high grade reeycled polyethylene product start with the quality of the postconsumer waste stream. In addition to polyethylene, the waste stream inevitably contains polymeric and nonpolymeric contaminants. Small amounts of certain thermoplastics can be accommodated in recycled polyethylene, but the presence of even a few tens of parts per million of others ean cause significant problems [2]. Particles of thermosets, such as polyurethanes and cross-linked polyesters, that survive the sorting and washing processes ean plug screenpacks. Those that make it into the final... 

Although each production process yields ash that is essentially chemically equivalent, the various products differ ia physical properties and ia contaminants as shown ia Table 6. Hopper cars, pneumatic tmcks, supersacks, and multiwaH kraft bags with polyethylene liners are the usual shipping containers. 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

Brown Kraft paper is generally used on mineral wool products to give added tensile strength, ease handling, aid positive location between studs or rafters, or prevent contamination when used under concrete screeds. Paper is often laminated with polyethylene to give vapor control layer properties. 

Chemical Hazards. Chemical manufacturers and employees contend with various hazards inherent in production of even commonplace materials. For example, some catalysts used in the manufacture of polyethylene (see Olefin polymers) ignite when exposed to air or explode if allowed to become too warm the basic ingredient in fluorocarbon polymers, eg, Teflon (see Fluorine compounds, organic), can become violendy self-reactive if overheated or contaminated with caustic substances (45,46) one of the raw materials for the manufacture of acrylic fibers (see Fibers, acrylic) is the highly toxic hydrogen cyanide (see Cyanides). 

Removal of cationic impurities from water. Careful analysis of water purified by various methods (see Table 7.10) indicates that the water that is obtained by passing ordinary distilled water through a small monobed deionizer (contained in polyethylene) and a submicrometer filter is equal or superior (with respect to cations) to water obtained by distillation in conventional quartz stills, and is distinctly superior to the product from systems constructed of metal.70 From the data available in the literature, simple distillation clearly does not produce high-purity water. In practice, two effects cause contamination of the distillate. Entrainment is the major factor that prevents the perfect separation of a volatile substance from nonvolatile solids during distillation. Rising bubbles of vapor break through the surface of the liquid with considerable force and throw a fog of droplets (of colloidal dimensions) into the vapor space... 

Five and twenty-three hundredths grams of germanium(IV) oxide (0.05 mol) is dissolved in 15 ml. of a concentrated aqueous solution of hydrofluoric acid (47 %). A platinum evaporating dish or a polyethylene plastic beaker is used to keep silicon contamination to a minimum. A solution of 10.5 g. of barium chloride (0.05 mol) in 50 ml. of water is added. Barium hexafluorogermanate forms as a white, granular precipitate, which is filtered and washed free of chloride. The product is dried by heating to 300° in vacuo and is stored in a desiccator over phosphorus(V) oxide. The yield is 15.24 g. (94%). 

Work Surfaces. All horizontal work surfaces (bench tops, containment cabinets or fume hoods) should be protected with impervious material to prevent contamination of the work surfaces with chemical carcinogens. One of the systems that has proved useful is to use the dry, absorbent polyethylene-backed paper (Benchkote, VWR Scientific Co., Cat. No. 52855 , Continuous Sheet Type, Scientific Products Co., Cat. No. P1180). Following contamination, or upon completion of an experiment, or at the end of the day, this protective cover can be rolled up, packaged for safe removal, and disposed of in an appropriate manner. 

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