Bleaching Substances

Chlorination (C) with chlorine, an effective, selective and inexpensive bleaching agent that reacts very fast vidth lignin. For environmental reasons during the last ten years chlorine is being substituted by chlorine dioxide, ozone and/or oxygen all over the world. In Europe substitution is already 100%. In this particular case bleached pulp is called Elementary Chlorine Free - ECF . 

Ozone bleaching (Z) - Because oxygen dehgnification is limited, additional de-Hgnifying agents must be used before final bleaching. Ozone is a possibility, but 

Furthermore peroxide bleaching strongly increases the amount and influences the composition of dissolved colloidal substances (DCS). A high amount of DCS results in a high COD (chemical oxygen demand) load in the process water and in a loss of quality of the mechanical pulp, e.g. strength properties. 

---

Reiser, R. 1949. Peroxidizing and carotene bleaching substances in bacon adipose tissue. J. Am. Oil Chemists Soc. 26, 116. 

Commercial cmde lecithin is a brown to light yeUow fatty substance with a Hquid to plastic consistency. Its density is 0.97 g/mL (Uquid) and 0.5 g/mL (granule). The color is dependent on its origin, process conditions, and whether it is unbleached, bleached, or filtered. Its consistency is deterrnined chiefly by its oil, free fatty acid, and moisture content. Properly refined lecithin has practically no odor and has a bland taste. It is soluble in aflphatic and aromatic hydrocarbons, including the halogenated hydrocarbons however, it is only partially soluble in aflphatic alcohols (Table 5). Pure phosphatidylcholine is soluble in ethanol. 

In wooden tubs, the maintenance of a sanitizer residual becomes compHcated due to the leaching of tannins and other organic matter from the wood into the water. The sanitizer demand of these substances must be overcome in order to maintain proper residual concentrations. As the tub ages, the leaching of these materials decreases, but bleaching of the wood may occur as the lignin (qv) in the wood reacts with sanitizers. 

This is the one example in which metal is not the substrate. Corrosion takes on a new meaning the coating here is required to protect the substrate from direct attack by corrosive substances, from water to more powerful household or industrial chemicals, such as grease, alcohols and bleach. We are concerned with the industrial application of thin protective layers to paper (e.g. labels), card (e.g. playing cards) and many wooden articles, including industrially finished doors, window frames and, particularly, furniture. 

Colored substances contain molecules with chromophores, areas of the molecule that have double bonds between carbon atoms or oxygen atoms. A good example is beta-carotene, and that section goes into more detail on how molecules become colored. Bleaches attack these chromophores in one of two ways. 

Phosphonates are often used in detergents as stabilizers for encymes and bleaching components in a concentration of <0.5%. Dates of acute aquatic toxicity of the most used substances HEDP, aminotrismethylenephosphonic acid (ATMP), and EDTMP are given in Table 14. In a concentration of <2 mg/L no remobilization of heavy metals from sediments was observed [207]. 

The knowledge that allows chemists to describe, interpret, and predict the behavior of chemical substances is gained by making careful experimental measurements. The properties of a sample can be divided into physical properties, which can be measured without observing a chemical reaction, and chemical properties, which are displayed only during a chemical transformation. Physical properties include familiar attributes such as size, color, and mass. Some chemical properties also are familiar to us. As examples, bleach reacts chemically with many colored substances to destroy their colors, and molecular oxygen reacts chemically with many fuels to generate heat. 

As described in Section 4-1. one important class of chemical reactions involves transfers of protons between chemical species. An equally important class of chemical reactions involves transfers of electrons between chemical species. These are oxidation-reduction reactions. Commonplace examples of oxidation-reduction reactions include the msting of iron, the digestion of food, and the burning of gasoline. Paper manufacture, the subject of our Box, employs oxidation-reduction chemishy to bleach wood pulp. All metals used in the chemical industry and manufacturing are extracted and purified through oxidation-reduction chemistry, and many biochemical pathways involve the transfer of electrons from one substance to another. 

A substance added to latex in the preparation of pale crepe rubber sodium bisulphate prevents darkening of the crepe due to the presence of oxidising enzymes, xylyl mercaptan is an effective bleaching agent proper. 

Conversely, vesicants have also been thickened with various substances to enhance deployment, increase their persistency, and increase the risk of percutaneous exposure. Thickeners include polyalkyl methacrylates (methyl, ethyl, butyl, isobutyl), poly(vinyl acetate), polystyrene, plexiglas, alloprene, polychlorinated isoprene, nitrocellulose, as well as bleached montan and lignite waxes. Military thickener K125 is a mixture of methyl, ethyl, and butyl polymethacrylates. When thickened, agents become sticky with a consistency similar to honey. Typically, not enough thickener is added to affect either the color or odor of the agent. 

Azarniouch and Prahacs have patented an electrochemical recovery procedure for NaOH and other valuable substances (lignin, organic compounds, H2S04, H2, 02 or 02/Cl2 mixtures) from spent liquors and bleach plant effluents [282]. 

---