Additions of chemicals

Several more recent variations of the film-to-fiber approach result in direct conversion of film to fabric. The film may be embossed in a controlled pattern and subsequently drawn uniaxiaHy or biaxiaHy to produce a variety of nonwoven products (47). Addition of chemical blowing agents to the film causes fibrillation upon extmsion. Nonwovens can be formed directly from blown film using a unique radial die and control of the biaxial draw ratio (48)... 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Further Modifications. There have been attempts to improve the pulp strength and decrease the energy requirement of the groundwood process by the addition of chemicals, eg, sodium carbonate or sodium sulfite. Although some benefits can be obtained, the additional costs and chemical disposal problems have not been justified. Presteaming of wood is practiced in Europe to add moisture and to soften the lignin, which is especially advantageous for certain hardwoods. 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

The bulk density of powdered diatomite varies from 112 to 320 kg/m. The tme specific gravity of diatomite is 2.1 to 2.2, the same as for opaline sihca, or opal (1). The thermal conductivity of bulk quantities of diatomite is low but increases with higher percentages of impurities and a higher density. The fusion point depends on the purity but averages about 1430°C for pure material, which is slightly less than for pure siUca. The addition of chemical agents, such as soda ash, reduces the fusion point. 

Technology Description Hydrolysis is the process of breaking a bond in a molecule (which is ordinarily not water-soluble) so that it will go into ionic solution with water. Hydrolysis can be achieved by the addition of chemicals (e.g., acid hydrolysis), by irradiation (e.g., photolysis) or by biological action (e.g., enzymatic bond cleavage). The cloven molecule can then be further treated by other means to reduce toxicity. 

Coagulation involves the addition of chemicals to alter the physical state of dissolved and suspended solids. This facilitates their removal by sedimentation and filtration. The most common primary coagulants are alum ferric sulfate and ferric chloride. Additional chemicals that may be added to enhance coagulation include activate silica, a complex silicate made from sodium silicate, and charged organic molecules called polyelectrolytes, which include large-molecular-weight polyacrylamides, dimethyl-diallylammonium chloride, polyamines, and starch. 

Chemical precipitation Precipitation induced by addition of chemicals the process of softening water by the addition of lime and soda ash as the precipitants. Chloramines Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia. 

Chemical filters are used to collect gases these are mainly adsorption filters based on activated carbon. By the addition of chemical substances, impregnation ), gases which are difficult to adsorb are adsorbed and retained by-means of a chemical reaction. 

The addition of chemicals to the receptacle must be done outside the balance case. It is good practice to weigh the chosen receptacle on the analytical balance, to transfer it to a rough balance, to add approximately the required amount of the necessary chemical, and then to return the receptacle to the analytical balance for re-weighing, thus giving the exact weight of substance taken. 

When steam in the cycle is lost or used in a process, the reduced volume of returning condensate is compensated for by introducing some level of MU water. The loss of water or steam from a steam system cycle may vary from 1 to 100%. The supply of MU (and to a lesser degree the addition of chemical treatments) provides a source of dissolved solid contaminants that can concentrate in the boiler until some predefined limit is reached. At this point, BD is required, the loss of which is also compensated for by the addition of further MU water. 

When systems are poorly designed, with unlagged condensate receiver and FW tanks open to the atmosphere, thus permitting loss of heat (colder water holds more oxygen) and permanent contact with air. (This vent point is commonly employed for the addition of chemical treatment.)... 

Addition of chemicals, rapid mixing, then flocculation. 

Chemical treatment programs based on the direct addition of chemicals to FW or BW in order to prevent subsequent deposition, corrosion, or other problems from occurring. With precipitating types of internal treatments, the boiler waterside space is employed as a reaction vessel and, where a particular boiler design is unsuitable, inadvertent problems of fouling may occur. 

The intermittent addition of chemical treatments by hand rather than continuous addition by use of a feed pump. 

Performance requirements, environmental issues, and avaUabUity/cost of the material will mainly drive material requirement in the future. In order to face the huge tire wastage problem causing major hazards to the environment, future development in mbbery materials will be focused on development of thermoplastic polymer so that used polymer could be recovered by thermal treatment and separation, biological degradation by radiation/addition of chemical into the mbber compound that could be activated by exposure to radiation and development of biopolymer. 

The emulsion must be separated by the addition of chemical demulsifiers before the crude oil can be accepted for transportation. The quality criteria for a delivered crude oil are the residual salt content and the water content. For the oil to have a pipeline quality, it is necessary to reduce the water content to less than approximately 1.0%. 

Chemical, semichemical, or mechanical breakdown of pulping material into fibers Removal of pulp impurities, cleaning and thickening of pulp fiber mixture Addition of chemicals in a staged process of reaction and washing increases whiteness and brightness of pulp, if necessary At nonintegrated pulp mills, pulp is dried and bundled into bales for transport to a paper mill... 

These reactions are slowed by addition of chemically inert organic solvents to water and are generally slower in micelles than in water, although the effect is often small. The micellar inhibition has been discussed in terms of water activity, or more likely polarity, being somewhat lower at the micellar surface than in water (Menger et al., 1981). 

The methods outlined in Table 6.4 will often require the addition of chemicals. As a general concern, whether or not such methods give negative effects, e.g., on the successive wastewater treatment processes or in the receiving waters, must be considered. 

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