Fiber, contaminants processing wastes

Polyester can be recovered from contaminated polyester waste which contains non-polyester components. The waste may be polyester blended with cotton or other fibers, polyester magnetic tapes, or coated polyester films and engineering resins. The waste is dissolved in dimethylterephthalate, methyl-p-toluate or dimethylisophthalate. The eon-taminants are filtered from solution and polyester is reeovered by erystallization or used as a feedstock in a methanolysis process which forms dimethylterephthalate and alkylene glycol. 

Injection molding of samples containing more than 40% cellulose is limited by the high viscosity of the filled melt. This limit is reached at about 60% by hydrolyzing the fibers. Prehydrolytic treatment has been further optimized in our laboratory and has been applied in a pilot plant for the processing of paper-contaminated plastics waste collected from a municipal solid waste stream. The application of this method to the waste stream not only contributes to a decrease in the amount of of waste but at the same time creates novel composite materials at a very attractive price. Table II demonstrates the differences between the mechanical properties of composites manufactured by treatment of paper-contaminated plastics waste collected fi om different sources and illustrates the benefits of prehydrolytical treatment. 

Contaminant removal processes depend on the type and source of secondary fiber to be pulped. Mill paper waste can be easily repulped with minimal contaminant removal. Recycled postconsumer newspaper, on the other hand, may require extensive contaminant removal, including deinking, prior to reuse. Secondary fiber is typically used in lower-quality applications such as multiply paper-board or corrugating paper. 

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

Waste Disposal. All processes must include some form of washing step to remove impurities from the bottles. If the adhesive, poly(vinylacetate), PVA, is to be separated through dissolution or hydrolysis to poly(vinyl alcohol), the waste stream will contain PVA and/or dissolved polyvinyl alcohol in addition to the other contaminants which must be removed. Paper fibers are another major source of impurities. For a lOMM Ib/yr plant about 75,(XX) Ib/yr PVA will be removed via the effluent. Environmental regulations probably require that this problem be addressed, especially since polyvinyl alcohol is an excellent foaming agent. 

Any additive or contaminant that is part of a fiber is likely to be liberated to the environment during subsequent processing. Therefore, it is worthwhile to examine the nonflber content of raw textile fibers. These contaminants, even if present in trace concentrations, can contribute significantly due to the massive amount of fibers that are typically used by manufacturers. The environmental aspects of these contaminants are discussed under fabric preparation, where they are typically liberated into the air or wastewater. Contaminants include natural waxes and oils, metals, agricultural residues, added lubricants, tints, unreacted monomer, catalyst residues, colorants, tines, brighteners, delusterants, fiber finishes, and antistatic additives. Ultimately the fibers themselves also become waste when the textile end-use products are discarded. 

As the first step in the wet processing sequence, substrates are typically cleansed of contaminants that inhibit sorption or interfere with reaction of the processing solutions used for dyeing, printing, and finishing. A wide variety of contaminants are present in raw fibers [48], As the fiber is heated or scoured, these contaminants are liberated into water and air as pollutants. Due to the massive amounts of fibers used, impurities present even in trace quantities can be important pollutants. The total polyester/cotton fiber wastes (from all sources in the United States) is estimated to be 4.5 x 10 lb annually [31]. 

In addition to supercritical fluid extraction and supercritical fluid chromatography, supercritical and near-critical fluids are of increasing interest for other applications. These include their use as processing fluids for dyeing of fibers, production of finely dispersed particles (RESS, PGSS, SAS, GAS, etc.), as promising solvents for syntheses and kinetic studies, for the destructive oxidation of wastes with supercritical water (SCWO), for the purification of filters, catalysts, contaminated soils, for drying and sterilization processes, and others [13,19,20]. 

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