Subject natural polymers

Besides the previously mentioned collagen, a wide variety of natural polymers have been involved in the synthesis of bio-nanohybrid materials with potential application in bone repair and dental prostheses. For instance, some recent examples refer to bionanocomposites based on the combination of HAP with alginate [96,97], chitosan [98,99], bovine serum albumin (BSA) [100], sodium caseinate [101], hyaluronic acid [102], silk fibroin [103,104], silk sericin [105], or polylactic add (PLA) [106,107]. These examples illustrate the increasing interest in the subject of HAP-based biohybrid materials, which has led to almost 400 articles appeared in scientific journals in 2006 alone. 

Polymers are large molecules (macromolecules) that consist of one or two small molecules (monomers) joined to each other in long, often highly branched, chains in a process called polymerization. Both natural and synthetic polymers exist. Some examples of natural polymers are starch, cellulose, chitin (the material of which shells are made), nucleic acids, and proteins. Synthetic polymers, the subject of this chapter, include polyethylene, polypropylene, polystyrene, polyesters, polycarbonates, and polyurethanes. In their raw, unprocessed form, synthetic polymers are sometimes referred to as resins. Polymers are formed in two general ways by addition or by condensation. 

Polymers with unsaturated carbon chain backbone form another important class of macromolecules, many of the compounds from this class having properties of elastomers. The most common polymers from this class are obtained from 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene) and their derivatives. Natural rubber, which is poly(c/s-isoprene), as well as the natural polymers gutta-percha and balata also have an unsaturated carbon chain backbone. For many practical applications, the polymers from this class are subject to a process known as vulcanization, which consists of a reaction with sulfur or S2CI2, and leads to the formation of bridges between the molecular chains of the polymer. This process significantly improves certain physical properties of practical interest. A separate subclass of polymers with unsaturated carbon chain backbone is formed by polyacetylene. 

Tyrosinase (polyphenol oxidase, a copper-containing monooxygenation enzyme) was used as catalyst for the modification of natural polymers. Phenol moiety-incorporated chitosan derivatives were subjected to tyrosinase-catalyzed cross-linking, yielding stable and self-sustaining gels.90 Tyrosinase also catalyzed the hybrid production between the modified chitosan and proteins. 

Biomedical polymer material is an important component of biological material and is a remarkable functional polymer. It involves in physics, chemistry, biochemistry, medicine, pathology subjects. The synthetic polymer materials and the organisms (natural polymer) have a very similar chemical structure, which determines their similarity in performance and enables high molecular polymer to meet the many complicate and rigorous functional requirements for medical products. Most metal and inorganic materials are incapable in this respect. Presently, high molecular polymers are widely used in medical products. 

Indonesia is a tropical country with about 144 million Ha of tropical forest, producing a large amount of natural polymers, mainly natural rubber and wood products. In 1991 the total production of natural rubber was about 1.36 million tonnes while the production of log was about 40 million. Such large amount and various kinds of natural polymers were subject to investigation by a number of research centers since before the second WW. Center for the Application of Isotopes and Radiation, using radiation technique as a tool to modify the property of various natural polymers in order to meet the industries. Several Cobalt-60 sources and electron beam machine (EBM) from a small scale to a pilot scale are available. Other polymers such as synthetic fibers also becoming a subject of investigation. 

Natural rubber (NR) is one of natural polymers produced by a number of tropical countries Indonesia, Malaysia, Thailand, Sri Lanka etc. Indonesia, with about 2.6 Million Ha of rubber plantation, producing about 1.3 Million tonnes of NR annually. It was a subject of investigation long before the second WW,from the process of producing a raw NR which should meet a standard of quality to the process of producing rubber goods. 

There has been considerable controversy on the subject of polymer crystallinity. Many questions still remain. When macromolecules possess a certain amount of symmetry, there is a strong accompanying tendency to form ordered domains, or crystalline regions. Crystallinity in polymers, however, differs in nature from that of small molecules. When the small molecules crystallize, each crystal that forms is made up of molecules that totally participate in its makeup. Crystallinity in polymers, on the other hand, means that certain elements of the polymeric system or segments of the polymeric chains have attained a form of a three-dimensional order. This order resembles orderly arrangement of small molecules in crystals. The crystalline domains, however, are much smaller than the crystals of small molecules and possess many more imperfections. 

As mentioned above, most polymers are characterized by a distribution of molar masses of the individual polymer chains that is, almost every polymer sample is a mixture of polymers with different molar masses, an effect which is referred to as polydispersity. In the past, significant attempts have been made to produce polymers with a narrow molar mass distribution, and to prepare polymers with precisely identical molar masses. This is a consequence of the inherent desire of the synthetic chemist to produce a compound that is as well defined as possible - in just the way that Nature teaches us. Yet, only natural polymers such as DNA are really 100% monodisperse. In the following case study, it should be noted that even the absolute counterpoint to these longlasting attempts can open the way to a successful polymer in a highly competitive market. The subject here is probably the most competitive landscape in polymer chemistry over all, the polyolefins. 

Starch in its native or modified form, has been subjected to extensive study over the past 50 years. Early interest in starch was associated with the food and paper industry, textile manufacture, and pharmacolog) . With the increased interest of biomedical and pharmaceutical research in biodegradable polymers as matrices for controlled drug delivery systems, impressive activities on the modification of natural polymers to meet growing needs have been reported (Hag et al, 1990 Kost and Shefer, 1990 Shefer et al, 1992 Trimnell et al, 1982 Vandenbossche et al, 1992 Visavarungroj et al, 1990). 

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