Natural materials monomer sources

The non-biodegradable and non-renewable nature of plastic packaging has led to a renewed interest in packaging materials based on biopolymers derived from renewable sources. Such biopolymers include naturally occurring proteins, cellulose, starches, and other polysaccharides and those synthesized chemically from naturally derived monomers such as lactic acid. Commercialization of these bio-based polymers has already begun. Naturewoiks, LLC (Minnetonka, MN) manufactures polylactide from... 

The properties of PHAs are dependent on their monomer composition and therefore it is of great interest that recent research has revealed that, in addition to PHB, a large variety of PHAs can be synthesized microbially. The monomer composition of PHAs depends on the nature of the carbon source and microorganism used. PHB is a typical highly crystalline thermoplastic whereas medium chain length PHAs are elastomers with low melting points and a relatively lower degree of crystallinity. By (chemical) modification of the PHAs, the ultimate properties of the materials can be adjusted even further, when necessary. 

Since the chemical structure and monomer composition of a specific polymer are the most important factors in determining the polymer s physical and material properties, a short recapitulation of typical representatives of microbially synthesized poly(hydroxyalkanoates) is presented in this section. A more detailed overview on this issue is available from References [19-21], but is not within our scope here. The monomer composition of PHAs depends on the nature of the carbon source and the microorganisms used. This way, numerous monomers have been introduced into PH A chains [3-9]. PHAs have been divided roughly into two classes [19]. 

Introducing chirality into polymers has distinctive advantages over the use of nonchiral or atactic polymers because it adds a higher level of complexity, allowing for the formation of hierarchically organized materials. This may have benefits in high-end applications such as nanostructured materials, biomaterials, and electronic materials. Synthetically, chiral polymers are typically accessed by two methods. Firstly, optically active monomers - often obtained from natural sources - are polymerized to afford chiral polymers. Secondly, chiral catalysts are applied that induce a preferred helicity or tacticity into the polymer backbone or activate preferably one of the enantiomers [59-64]. 

Most active principles and pharmaceutical forms are processed in the presence of organic solvents or reagents. The current regulations on products generally restrict to a few p.p.m. the amount of residual solvent. This very low concentration level could favour the CO2 utilization when non-polar compounds have to be eliminated. On the other hand, the elimination of residual solvents from tablets, films or other pharmaceutical preparations in which organic solvent are involved has been addressed [15]. Another application is related to the removal of residues from medical materials such as monomers, additives or polymerization residues from polymers or elastomers. Purification of active principles includes elimination of other undesired molecules pesticides from some vegetal extracts, and antibacterials suspected of toxic co-extracts from natural sources. 

In many freshwater systems, humic substances account for most of the DOM pool (Thurman, 1986). This material provides a reservoir of slowly metabolized nutrients that coexist and interact with a labile pool of rapidly consumed monomers and polymers (Tranvik, 1992, 1998 Sondergaard and Middleboe, 1995 Munster and De Haan, 1998 see Chapter 19). The literature clearly illustrates the amphitrophic nature of humic DOM it acts variously as a significant energy source for bacteria (Tranvik and Hofle, 1987 Tulonen et al., 1992 Moran and Hodson, 1994 Volk et al., 1997 Jannson, 1998) and as an inhibiter of growth and metabolic activity (Moran and Hodson, 1990 Tranvik, 1992 Foreman et al., 1998). This range of... 

A large fraction of the chemical industry worldwide is devoted to polymer manufacture, which is very important in the area of hazardous wastes, as a source of environmental pollutants, in toxicology, and in the manufacture of materials used to alleviate environmental and waste problems. Synthetic polymers are produced when small molecules called monomers bond together to form a much smaller number of very large molecules. Many natural products are polymers for example, cellulose in wood, paper, and many other materials is a polymer of the sugar glucose. Synthetic polymers form the basis of many industries, such as rubber, plastics, and textiles manufacture. 

The most important monomers for the production of polyolefins, in terms of industrial capacity, are ethylene, propylene and butene, followed by isobutene and 4-methyl-1-pentene. Higher a-olefins, such as 1-hexene, and cyclic monomers, such as norbornene, are used together with the monomers mentioned above, to produce copolymer materials. Another monomer with wide application in the polymer industry is styrene. The main sources presently used and conceivably usable for olefin monomer production are petroleum (see also Chapters 1 and 3), natural gas (largely methane plus some ethane, etc.), coal (a composite of polymerized and cross-linked hydrocarbons containing many impurities), biomass (organic wastes from plants or animals), and vegetable oils (see Chapter 3). 

Polymers, in the form of plastics, are used in making articles of daily use, such as knobs, handles, switches, pipes, heart valves, and so on. An overwhelming percentage of the polymers to make these commodities are synthesized from petroleum sources or natural gas raw materials. The key petrochemicals for polymer synthesis (ethylene, propylene, styrene, vinyl chloride monomer, and others) are produced largely from naphtha, one of the distillation fractions of crude oil or from natural gas. Once synthesized, the polymer materials, such as polyethylene, polypropylene. 

Natural rubber is utilized mainly as an isolation material in CRFMs in HVAC components. Natural rubber is tapped from the Hevea brasilienis tree in the form of latex or a colloidal suspension. These trees produce more rubber when they are wounded, thereby providing a renewable source of rubber. Figure 8.10 shows the two base components present in natural and synthetic rubbers. The repeating units consist of isoprene and some diene monomer such as butadiene shown in the figure and natural impurities. Synthetic rubber is typically made with isoprene and butadiene. 

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