Polymers, Natural Organic types

Thickeners. Thickeners are added to remover formulas to increase the viscosity which allows the remover to cling to vertical surfaces. Natural and synthetic polymers are used as thickeners. They are generally dispersed and then caused to swell by the addition of a protic solvent or by adjusting the pH of the remover. When the polymer swells, it causes the viscosity of the mixture to increase. Viscosity is controlled by the amount of thickener added. Common thickeners used in organic removers include hydroxypropylmethylceUulose [9004-65-3], hydroxypropylceUulose [9004-64-2], hydroxyethyl cellulose, and poly(acryHc acid) [9003-01-4]. Thickeners used in aqueous removers include acryHc polymers and latex-type polymers. Some thickeners are not stable in very acidic or very basic environments, so careful selection is important. 

Different types of hydroxy and carboxylic groups present in natural organic substances, exemplified in a hypothetical complex polymer from Thurman (1985). 

Figure 1 illustrates the different phases available for organic chemicals in the environment. These may include the original HWM, as well as water, air, soil, and other organic chemicals present in liquid or solid phases. As previously mentioned, the HWM may be recycled-asphalt pavement or shredded tires. Both the HWM and soil can be very complex. HWM may consist of different polymers, rocks and mineral fragments, and various HOPs. Soils consist of different types and amounts of natural organic matter, black carbon, and minerals. As discussed below, carbonaceous materials typically have the greatest affinity for HOPs. 

Eliminations and other reactions do not necessarily take place only on the polymeric chain or only on the side groups. Combined reactions may take place, either with a cyclic transition state or with free radical formation. The free radicals formed during polymeric chain scission or during the side chain reactions can certainly interact with any other part of the molecule. Particularly in the case of natural organic polymers, the products of pyrolysis and the reactions that occur can be of extreme diversity. A common result in the pyrolysis of polymers is, for example, the carbonization. The carbonization is the result of a sequence of reactions of different types. This type of process occurs frequently, mainly for natural polymers. An example of combined reactions is shown below for an idealized structure of pectin. Only three units of monosaccharide are shown for idealized pectin, two of galacturonic acid and one of methylated galacturonic acid ... 

The classification of polymers previously described has been used in this book for the discussion of pyrolysis results. An important class of polymers that is not discussed here is that of chemically modified natural polymers (or semisynthetic polymers). Examples of such polymers are the modified celluloses (carboxymethyl cellulose, ethyl cellulose, etc ), modified starches, casein plastics (Galalith), etc. These types of compounds were discussed in the book on pyrolysis of natural organic polymers [2]. 

Consolidation generally can be divided into two types of methods inorganic or organic consolidants. The latter may be natural organic polymers or even synthetic polymers. Both types of treatment may cause longer-term drastic alterations although acceptable results may have been obtained directly after application. 

In this section, examples of self-assembled systems formed by simple mixing of multiple components are discussed. These components can be mixed either in the monomeric state or after supramolecular homopolymers have been formed. This type of preparation relies heavily on the thermodynamic interactions between the different components as well as on the dynamic nature of the supramolecular polymer. For each type of organization, these two features are discussed followed by representative examples from the literature. 

There are several types of biodegradable polymers. A common classification is based on the distinction between natural and synthetic biodegradable polymers. Natural biodegradable polymers are typically produced directly by living organisms, and they are extracted from them a posteriori. The most common biodegradable natural polymers are collagen, elastin, fibrin, and several polysaccharide derivatives, such as... 

PC nanocomposites are an emerging class of organic-inorganic hybrids that contain a relatively low wt% of nanometer-sized clay. These were first developed in the late 1980s. The dispersion of the nanometer-sized clay in the polymer matrix significantly improves the mechanical, thermal, barrier properties and flame retardancy of the base polymer. Three main types of nanocomposites can be obtained when clay is dispersed in a polymer matrix. This depends on the nature of the components used, including polymer matrix, clay and organic cation. If the polymer cannot intercalate between the silicate sheets, a microcomposite is obtained. The phase-separated composite that is obtained has the same properties as traditional microcomposites. 

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