Starch chemical structure

Biodegradable plastics have been used on an industrial scale since the end of the 1990s when BASF launched Ecoflex . This is a fossil-based, man-made polyester but yet is completely biodegradable due to its chemical structure. This structure is also the reason why Ecoflex combines excellent mechanical properties with the good processability of synthetic thermoplastics. Ecoflex is the preferred blend partner for bio-based and biodegradable polymers, which typically do not exhibit good mechanics and processability for film applications by themselves. Ecoflex therefore is a synthetic polymer that enables the extensive use of renewable raw materials (e.g., starch). 

As an example the characterization of surface grafting onto an ethylene-vinyl alcohol (33 67) random copolymer (EVA) film33 is described here. Since this water-insoluble film has hydroxyl groups on the surface, surface grafting may occur, for instance, with the so-called dialdehyde starch (DAS), whose chemical structure is given by... 

While biodegradable polymers may be similar to petrochemical-based thermoplastics in terms of their structure, their chemical structure imbues them with technical properties that make them perform in different ways. For example, starch blends can produce film with better moisture barrier protection and higher clarity than some conventional plastics. PLA has a high water vapour transmission rate, which is beneficial for fresh food applications where it is important that the water vapour escapes quickly from the packaging. PLA also reduces fogging on the lid of the packaging. 

A condensation polymer is one in which the repeating unit lacks certain atoms which were present in the monomer(s) from which the polymer was formed or to which it can be degraded by chemical means. Condensation polymers are formed from bi- or polyfunctional monomers by reactions which involve elimination of some smaller molecule. Polyesters (e.g., 1-5) and polyamides like 1-6 are examples of such thermoplastic polymers. Phenol-formaldehyde resins (Fig. 5-1) are thermosetting condensation polymers. All these polymers are directly synthesized by condensation reactions. Other condensation polymers like cellulose (1-11) or starches can be hydrolyzed to glucose units. Their chemical structure indicates that their repealing units consist of linked glucose entities which lack the elements of water. They are also considered to be condensation polymers although they have not been synthesized yet in the laboratory. 

Unique to Organic Chemistry are the micro-to-macro illustrations, where line art and photos are combined with chemical structures. These micro-to-macro illustrations reveal the underlying molecular structures that give rise to macroscopic properties of common phenomena. Examples include starch and cellulose (Chapter 5), adrenaline (Chapter 7), and dopamine (Chapter 25). 

Similar analyses of moisture uptake data available in the literature for other cellulose and starch derivatives used as pharmaceutical excipients are presented in Table 5. Considering the uncertainties associated with the estimated moisture uptake values from published graphs, the values of are all quite consistent with each other and with a stoichiometry of one water molecule per anhydroglucose unit. It is interesting to note that the two samples derived from cellulose, sodium carboxymethylcellulose and sodium croscar-mellose, did not require any correction for degree of crystallinity to conform to close to a 1 1 stoichiometry. It appears quite likely, therefore, that the change in chemical structure and the processing of these materials essentially eliminates the crystallinity of cellulose. 

Fractionation of various starches. A wide variety of starches should be separated by Pentasol precipitation, to determine the distribution of the fractions. Comparison of the physical properties of the purified fractions from typical starches (especially corn, wheat, rice, potato, tapioca, canna, lily and arrowroot) should clarify specific differences in chemical structure. 

Most starches are composed of two kinds of polysaccharides, a linear o -(1 4) linked glucan, called amylose, and an o -(1 4) linked glucan with 4.2 to 5.9% a-(l 6) branch linkages, called amylopectin. See O Fig, 1 for the chemical structure of a segment of amylose and a segment of amylopectin and O Table 1 for the percent branching in amylopectin for several different starches. 

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