Biopolymers cellulose esters

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. 

Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) are thermoplastic materials produced through esterification of cellulose and are used for many packaging applications. Different raw materials such as cotton, recycled paper, wood cellulose, and sugarcane are used in the production of cellulose ester biopolymers in powder form. Such cellulose ester powders in the presence of different plasticizers and additives are extruded to produce various grades of commercial cellulose plastics. Recently, Misra et al. successfully used melt intercalation technique for the fabrication of cellulose nanocomposites and studied the effect of C30B on its performance characteristics [44]. From the study, the... 

G. Toriz, P. Gatenholm, B.D. Seiler, and D. Tindall, Cellulose fiber-reinforced cellulose Esters Biocomposites for the future. Nat. Fibers Biopolym. Biocompos. (2005). 

A composite material is a two-phase or multiphase compact material with its components (phases) separated by interfaces which can be formed naturally or be manmade. One of the composite material phases is the matrix (phase I). It exists in the solid (crystalline or amorphous) state of aggregation. Within the matrix, particles are distributed discretely. This is phase II or disperse phase [23]. Biocomposites are composite materials made from natural fiber and petroleum-derived nonbiodegradable polymers like PP, PE, and epoxies or biopolymers like poly lactic acid (PLA), cellulose esters. Composite materials derived from biopolymer and synthetic fibers such as glass and carbon come under biocomposites. Biocomposites derived from plant-derived fiber (natural/biofi-ber) and crop/bioderived plastics (biopolymer/bioplastic) are likely more ecofriendly, and such biocomposites are sometimes termed green composites [24]. 

Edible coatings are thin layers of edible biopolymers applied on the surface of foods as protective coatings. One of the benefits of using cellulose esters in coating is the control of viscosity properties. 

The use of traditional composites made by glass, aramid, or carbon fiber-reinforced plastics has recently been discussed critically because of increasing environmental consciousness [8]. Thus, the recent research and development (R D) efforts have led to new products based on natural resources. Some of these are biodegradable polymers like PLA, cellulose esters, polyhydroxyalkan-otes (PHAs), and starch polymers. Furthermore, natural fiber-reinforced plastics made of natural fibers like flax, hemp, kenaf, jute, and cotton fibers are important R D achievements. Composites made of natural fibers and biopolymers... 

Cellulose (see Table 11.9 for its structure) cannot be processed by means of techniques used for thermoplastics, but esterification can yield materials suited for thermoplastic processing. A variety of raw materials, such as cotton, recycled paper, wood cellulose, and sugarcane, are used in making cellulose ester biopolymers in powder form. Cellulose esters are easy to extrude and injection mold. Through plasticization of cellulose acetate with environmentally friendly triethyl citrate, they are processable at 170-180 °C, which is below their melting point of 233 °C. 

Microwave heating has also been applied in the solvent-free phosphorylation of microcrystalline cellulose (Gospodinova et al., 2002). In the isolation step of this procedure, only water and ethanol were used as additional solvents. Wax esters have been produced from vegetable oils using a solvent-free enzymatic process (Petersson et al, 2005) this is particularly noteworthy as enzymes are often intolerant to high concentrations of substrates. The examples of solvent-free procedures described here show that solvents are not always required in the transformation of naturally sourced biopolymers and also in the chemistry of small molecules that can be obtained from a biorefinery. 

In addition to lignin, certain components of the leaf cuticles of vascular plants are also selectively preserved. Cutin, a polyester-like biopolymer that is a major component of modem cuticles, is apparently biodegraded during peatification (Nip et al., 1986 Tegelaar, 1990), but cutan, a minor component of the leaf cuticle, is more readily preserved in peats (Tegelaar et al., 1989). The chemical stmcture of cutan is still subject to debate, but may consist of polymethy-lenic stmctures ester-bonded to cellulose or to an aromatic core (Tegelaar et al., 1989 Nip et al., 1989 McKinney et al., 1996). Whatever its chemical stmcture, cutan is sufficiently resistant to survive peatification. 

Approximately 2% of the 5 x 1011 metric tons of cellulose generated yearly by biosynthesis throughout the world is recovered industrially and of these 108 tons, about 2% is transformed into various esters (3/4) and ethers (1/4). Historically, cellulose nitrate is the oldest (inorganic) ester synthetized, but it has found almost no applications as a biopolymer. The first organic ester and which remains widely used in the field of life sciences is cellulose acetate (1865). Ethers are more recent, since methylation was first described in 1905. 

Emulsification of cellulose or starch with water or ethanol, soap and a fatty acid is a performing method to allow the grafting of fatty chains onto the biopolymer backbone. An experimental design allowed to determine the best conditions to synthesize starch fatty esters with DS < 0,5 using natural raw materials as reagents. 

The cellulose fibers in paper are the starting material for regenerated fibers such as rayon and cellulose acetate, which, together, form the historical bridge from biopolymers to completely synthetic fibers. Synthetic rubber was created in Germany in 1917, but from the forensic perspective, a much more important advance was the S5mthesis of nylon (specifically, nylon 6,6) in 1935. The discovery of nylon is credited to Dr. Wallace Carothers, who worked at DuPont Chemical Corp. Initially, his work had been with esters and phenols, but he became interest in amides for possible use in the then-infant world of polymer science. What would become known as nylon was developed in 1935 and commercialized in 1939, initially for women s hosiery. World War n jump-started the polymer indu.stry, and many advances quickly followed. The emphasis here will be on fibers, with later sections in the chapter examining other applications of synthetic polymers. 

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