Degradable materials natural polymers

As a partial solution to the global issue of plastic waste, in recent years much interest has been devoted to the formulation of environmentally degradable plastic materials. In particular the use of natural polymers presents several advantages such as biodegradability, utilizing of renewable resources, recyclability. At the same time water sensitivity and degradability of natural polymers limit their possible applications. Consequently bioplastics cannot replace synthetic plastics in every application but they can result appropriate in specific products especially for those applications in which recovery of plastics is not economically feasible, viable and... 

The objective of this chapter is to review degradable materials, including polymers, and the resulting delivery systems fabricated from them that are usefid for the delivery of proteins and peptides. Owing to the diverse nature of the subject area, we have chosen to divide the chapter into sections on hydrophobic synthetic polymers, hydrophilic polymeric biomaterials, and hydrophobic nonpolymeric biomaterials. Each section seeks to briefly highlight ftie chemist and characteristics of the polymer or matrix and provide recent examples of their use in the delivery of proteins. 

In addition to natural materials, synthetic polymers might also be present in works of art. Since the end of the nineteenth century, synthetic polymers have been produced and used in the field of cultural heritage, to restore works of art [3], but also as paint binders, such as alkyd resins and acrylic water dispersions. Most synthetic polymers can be detected by GC/MS only through thermal degradation followed by GC/MS [4,5] (Chapter 12 deals with the characterisation of synthetic resins in detail). 

The ability of a degradable plastic to decay depends on the structure of its polymer chain. Biodegradable plastics are often manufactured from natural polymers, such as cornstarch and wheat gluten. Micro-organisms in the soil can break down these natural polymers. Ideally, a biodegradable plastic would break down completely into carbon dioxide, water, and biomass within six months, just like a natural material. 

Starch-plastic composites contain a mixture of two very different types of materials (/) hydrophobic, petrochemical-derived polymers (PE, EAA) known to be highly resistant to degradation by living organisms, and (i7) a hydrophilic, natural polymer (starch) that is easily broken down by a wide array of organisms. In the process developed by Otey (3), these fundamentally incompatible materials are forced into an intimate mixture during production of the plastic film. Since... 

Solid waste discharges from chemical plants can represent very large problems, especially from paper mills, plastics plants, and food processing plants. Some materials do not decompose in the environment, and can become burdens when they accumulate. Some polymers have backbones that degrade in nature, such as aliphatic polyesters and polyvinyl alcohols others do not, such as polyethylene and polystyrene. 

Hydrolytic degradation is especially important in polymers with hydrolyzable links between the CRUs. Thus, polyesters can be saponified to yield the starting materials from which they were formed. Acetal links in synthetic polymers such as polyoxymethylene, or in natural polymers such as cellulose, can be hydrolyzed with acids. However, the resistance to hydrolysis depends very much on the structure of the polymer for example, polyesters of terephthalic acid are very difficult to hydrolyze while aliphatic polyesters are generally easily hydro-... 

Grinding or milling causes degradation of many polymers. The process of mastication of natural rubber involves a mechanically initiated, autoxidative degradation which lowers the molecular weight to a level where the material is easier to process on a commercial scale. 

Natural rubber, chemically speaking poly(W.v-1,4-isoprene), is a natural polymer derived from Hevea brasiliensis and various other tropical plants like Castilloa elastica [147]. This natural polymer is mainly produced in Asia and the tropics in high, industrially relevant, amounts (e.g., 9.7 Mio mto in 2007). Apart from its usual use as an elastomeric material, some research was devoted onto the metathesis degradation (depolymerization) of natural rubber with ethylene in a CM fashion. It was believed that metathesis of natural rubber is impossible, until a pioneering... 

Polymers are very soft materials which are not easily milled under normal conditions. The mastication of natural rubber is the reduction of molecular weight by milling or cutting, the process being invented by Thomas Hancock as early as 1820. Even today this is a major industrial process in the tire and rubber industry. Other polymers are milled under reduced temperature or even in liquid nitrogen to achieve a controlled molecular mass. The degradation of several polymers has been investigated by Dimitrov et al. [104]. 

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