Cellulose acetate, renewable

A rather impressive Hst of materials and products are made from renewable resources. For example, per capita consumption of wood is twice that of all metals combined. The ceUulosic fibers, rayon and cellulose acetate, are among the oldest and stiU relatively popular textile fibers and plastics. Soy and other oilseeds, including the cereals, are refined into important commodities such as starch, protein, oil, and their derivatives. The naval stores, turpentine, pine oil, and resin, are stiU important although their sources are changing from the traditional gum and pine stumps to tall oil recovered from pulping. 

Narayan, R. and Shay, M. (1986). Graft polymerization onto cellulose acetate and wood using anionic polymerisation. In Renewable Resource Materials, Carraher, E. and Springer, L.H. (Eds.). Plenum Publishing Corporation, pp. 137-146. 

Cellulose and its derivatives - cellulose acetate - are renewed polymers, that, together with the whole complex of valuable and indispensable properties, defines continuous growth of their production. 

Cellulose is the most abundant natural biopolymer and is readily available from renewable resources. Esterified cellulose is a highly flexible material as its properties can be varied by controlling the type and amount of the ester substituents during the chemical manufacturing process. Some cellulose esters have been applied as optical films for decades by virtue of their excellent properties such as high transparency and heat resistance. The cellulose ester used is mainly cellulose acetate, while the applications are rather limited to photographic films and protective films. 

The progress of chemistry, associated with the industrial revolution, created a new scope for the preparation of novel polymeric materials based on renewable resources, first through the chemical modification of natural polymers from the mid-nineteenth century, which gave rise to the first commercial thermoplastic materials, like cellulose acetate and nitrate and the first elastomers, through the vulcanization of natural rubber. Later, these processes were complemented by approaches based on the controlled polymerization of a variety of natural monomers and oligomers, including terpenes, polyphenols and rosins. A further development called upon chemical technologies which transformed renewable resources to produce novel monomeric species like furfuryl alcohol. 

The incessant biological activities that the earth sustains thanks to solar energy provide not only the means of our survival, but also a variety of complementary substances and materials which have been exploited by mankind since its inception, albeit with a growing degree of sophistication. Suffice it to mention, as an example, wood as a source of shelter and, later, of paper. In modem times, the exploitation of renewable resources to prepare useful products and plastics was indeed quite prominent between about 1870 and 1940 (natural rabber for tyres, cellulose acetate and nitrate, plant-based dyes, drying oils, etc ). As already pointed out, however, a major shift in industrial chemistry took place, starting from the second quarter of the last century, which led to the supremacy of first coal and then petrol as the basis of its output in terms of most intermediates, commodities and polymers. 

Rhone-Poulenc indicates that cellulose acetate with a degree of substitution of about 2 is biodegradable, in agreement with its earlier reference [176]. Cellulose has been discussed as a renewable resource [177], A recent publication [178] on chitosan reacted with citric acid indicates that the ampholytic product is biodegradable. Chitosan acetate liquid crystals [179], hydrophobic amide derivatives [180], and crossUnked chitosan [181] are also claimed to be biodegradable. 

To summarize, cellulose applications in the packaging industry can be organized into three main topics. The first one is to extract cellulose from plants and use it directly to prepare composites. The second one is to produce cellulosic plastics like cellulose acetate, which are the best examples of biopolymers derived from renewable resources. The third one is to prepare cellulose coating materials, edible and non-edible films. Therefore, detailed discussions about each of these topics and processes are presented in this chapter along with many related subjects based on cellulose and its derivatives. 

Mohanty, A.K., Wibowo, A., Misra, M., Drzal, L.T. Development of renewable resource-based cellulose acetate bioplastic Effect of process engineering on the performance of cellulosic plastics. Polym. Eng. Sci. 43, 1151-1161 (2003)... 

Biodegradation indicates degradation of a polymer in natural environment. This implies loss of mechanical properties, changing in the chemical structure, and into other eco-friendly compounds (Jamshidian et al. 2010). Degradable polymers from natural sources (such as lignin, cellulose acetate, starch, polylactic acid (PLA), polyhydroxylaUcanoates, polyhydroxylbutyrate (PHB)), and some synthetic sources (polyvinyl alcohol, modified polyolefins, etc.) are classified as biopolymers (John and Thomas 2008). It is noticeable that the nanocomposite from nonrenewable synthetic sources is neither wholly degradable nor renewable. 

Bacterial cellulose has been used as a material in combination with many others to develop composites. It has been used with materials such as xmsaturated polyester [185], the conducting polymer polyaniline [158-162, 186], as well as various acrylic and phenolic resins [178, 187-189]. It has also been used with several biodegradable materials such as cellulose acetate butyrate (CAB) [146,190], PLA [167,174,191,192], PHB [193-195], PVA [196,197], and thermoplastic starch [198,199], to produce completely biodegradable composites. Though renewable and biodegradable composites are the focus of this review, techniques and resulting composites from non-renewable sources are also mentioned. 

That means that biopolymers do not have to come exclusively from renewable resources. Bio-degradable biopolymers can also be manufactured from petrochemical raw materials, such as polyvinyl alcohols, polycaprolactone, copolyester, polyester amide. On the other hand, not all biopolymers based on renewable resources are necessarily bio-degradable, e.g., highly substituted cellulose acetate, vulcanized rubber, casein plastics, or linoleum. 

This does not mean we will see a mega-ton return to the old style polymers, such as casein plastics, cellulose nitrate and cellulose acetate. Many of these older polymers have severe deficits. For example, wool is eaten by moths and other insects cotton shrinks and does not hold a crease, unless treated with another polymer cellulose acetate is not solvent resistant, and cellulose nitrate is highly flammable. However, these older polymers come from renewable resources, which are also biodegradable, and this is a virtue in today s throw-away society. This alone should resurrect interest in natural polymers. Additionally, we have learned many vital things in the past century which will enable us to develop new and better polymers from biotechnology - polymers which... 

---