Cellulose acetate, renewable resources

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. 

While this reaction is substantially exothermic (6), it provides an intriguing approach to the production of fuels from renewable resources, as the required acids (including acetic acid, butyric acid, and a variety of other simple aliphatic carboxylic acids) can be produced in abundant yields by the enzymatic fermentation of simple sugars which are, in turn, available from the microbiological hydrolysis of cellulosic biomass materials ( ] ) These considerations have led us to suggest the concept of a "tandem" photoelectrolysis system, in which a solar photoelectrolysis device for the production of fuels via the photo-Kolbe reaction might derive its acid-rich aqueous feedstock from a biomass conversion plant for the hydrolysis and fermentation of crop wastes or other cellulosic materials (4). 

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)... 

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... 

Presently, PLA and other biopolyesters suffer from two important deficiencies that limit their use, of which the first is the low heat distortion temperature. The second is their relatively high permeabilities toward a number of substances, pmticularly water. Recently, copolymerization of cellulose acetate with PLA, both originating from renewable resources, resulted in a material with increased heat distortion temperature (200). In addition, nanocomposite technologies hold promise for improving both temperature distortion and permeation characteristics, as they have in conventional plastics. 

So far, various bio-based polymers have been developed, e.g., cellulose acetate, poly(alkylene succinate)s, starch-based blends, poly(3-hydroxy alkanoate)s (PHA) [1], poly(lactic acid) (PLA) [2], etc. Nowadays, some typical commodity plastics have also been S5mthesized from biomass, for example, polyethylene, polypropylene, poly(methyl methacrylate) [3], polyamide-4 [4], and polycarbonate [5]. If plastic materials are synthesized from renewable resources and circularly utilized with precise control of their depolymerization, an ideal recycling system could be constructed for plastic products, in which the resources and production energy could be minimized. Thus, the development of bio-based recyclable polymers is significant. In Scheme 9.1, t5 ical... 

The development and use of materials from renewable sources is not a new concept. Besides providing food, feed, clothes, shelter, and energy, biomass has been employed since ancient times to extract valuable products such as medicinal drugs, flavors, and fragrances. With the development of civilization of human society, in the nineteenth century various biomass resources were employed for the large-scale industrial production of chemicals and durable materials, such as cellulose esters (nitrate and acetate), oxidized linseed oil (linoleum), vulcanized rubber, adhesives from starches, and so on. However, the widespread use of such renewable materials diminished in the twentieth century since the development of fossil fuel derivatives, leading to the polymer renaissance. Today commodity polymers such as polyolefins are ubiquitous in our societies because they represent the optimal choice based on several factors, including monomer cost and... 

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