Biopolymers cellulose

Pyrolysis of biomass is defined as the chemical degradation of the biopolymers (cellulose, lignin and hemicellulose) constituting the wood fuel which initially requires heat. As can be seen in Figure 51, all reaction pathways making up the pyrolysis are not endothermic, which implies that some of the pyrolysis reactions generate heat. However, overall the pyrolysis process is endothermic. 

Lignocellulose denotes the mixture of the carbohydrate biopolymers cellulose and hemicellulose with the aromatic polymer lignin that is found in plants. Wooden raw materials consist mainly of cellulose (30-50 wt%), hemicellulose (10-40 wt%), and lignin (15-30 wt%). As the structure of cellulose (C6 carbohydrates) and hemicellulose (C5 carbohydrates) is quite similar, they will be discussed together in Section 2.2.2.1.1, followed by lignin, which has a very different composition (Section 2.2.2.1.2). 

Pyrolysis in inert atmosphere between 400 and yOO C produces water vapour, CO2, combustible gases CO, H2, CH and a multitude of organic vapours from the biopolymers cellulose (C6(H 0)s), hemicellulose (Cj(H20)4) and lignin. An impression of the complex product spectrum especially of the condensable organic vapours is given in Fig. 6. The remainder is a black char, mainly consisting of carbon and inorganic ash oxides. 

As biopolymers, cellulosics soluble in organic solvents are essentially used as semipermeable membranes (e.g. reverse osmosis separation), and for drug delivery in coating materials for reservoir or osmotic systems and excipients for matrix systems (e.g. films, compressed tablets). Recent advances in the latter fields will be reviewed. 

Carbohydrates (many of them being at the same time polyhydric alcohols) and those of their derivatives that are of interest in the above context are usually water soluble (notable exceptions, the biopolymers cellulose and chitin). Good water solubility has allowed to study the radiation chemistry of their aqueous solutions without the difficulties that are encountered in the case of poorly soluble substrates. Difficulties are mainly of a product-analytical nature. It is relatively easy to determine the low-molecular weight carbohydrate products that are formed via the unimolecular transformation of the starting radical, while it is very difficult to analyse completely the complex mixtures of the dehydro dimers which arise from the substrates under anoxic conditions as several different primary radicals intercombine and, in addition, different stereochemical options exist for each combination. 

Keywords Drug delivery, biopolymers, cellulose derivates, polysaccharides, polyhydroxyalcanoates, proteins... 

Figure 2, Basic scheme for environmentally friendly bleaching of wood - a new and catalytic bleaching technology for paper manufacture. No chlorinating agents are used. Wood is composed of two principal biopolymers cellulose and lignin whose structures (representative repeating units) are illustrated.

Keywords Biocomposites Biodegradation Biopolymers Cellulose Photodegradation... 

Keywords Biodegradation Biopolymer Cellulose Composites Nanocomposites Renewable resources... 

Johansson, LS Campbell, JM. Reproducible XPS on biopolymers cellulose studies. 

Polymer fibres are woven to make fabrics, so we are literally covered in them The most common fibres encountered are those produced by nature. Cell walls in plants contain the biopolymer cellulose. Many plants contain fibres, but only some of these are exploited by man, especially cotton, flax and hemp. Other natnral fibres include wool and silk. Wool is made from polymers of the protein keratin (also found in our hair and fingernails) and silk contains biopolymers of fibrion. 

All these polymers are electrically neutral. If chains are built up of monomers that contain an ionizable group, i.e., a group that can dissociate into a chain-fixed kation or anion and a mobile counter-ion bearing the opposite charge, a polyelectrolyte is obtained. Table 1.2 collects a few typical examples. The first three compounds are synthetic polymers, the other two samples are biopolymers cellulose and starch in the form of derivatives which include ionizable substitutes. 

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