Renewable resources, biodegradable polymers from

BIODEGRADABLE POLYMERS FROM RENEWABLE RESOURCES 2.1.1 Poly(lacHc acid) - PLA 

The molecular structure of polylactic acid (PLA) is schematically presented in Fig. 2.2. PLA, linear aliphatic thermoplastic polyester, is prepared from lactic acid. Lactic acid (2-hydroxy propionic acid) is one of the simplest chiral molecitles and exists as two stereo isomers, L- and D-lactic acid (Fig. 2.3). 

Each of the process steps is free of organic solvent water is used in the fermentation while molten lactide and polymer serve as the reaction media in monomer and pofymer production. The essential novelty of the process lies in the ability to go from lactic acid to a low molecular weight potylactic acid, followed by controlled depolymerization to produce the cyclic 

Lactic acid used in the preparation of PLA is derived from annually renewable resources. Cargill Dow uses sugar from maize as feedstock, due to its low cost and abundance, but it is envisaged to use local plant sources containing starch, or sugar, such as wheat, sugar beets or agricultural waste (Fig. 2.5). 

In contrast, Mitsui Toatsu (presently Mitsui Chemicals) utilizes a solvent-based process, in which a high molecular weight PLA is produced by direct condensation using azeotropic distillation to remove the water of condensation continuously (Fig. 2.6). 

Performance, processability, and price comprise the typical requirements for biodegradable polymers. Performance is based on the ability to perform Ihe necessary functions during the service life as well as the disposal performance, biodegradability. Mechanical strength, processability, moisture and oxygen barrier properties, interactions with the product, printability, sterilizability, transparency, and inert to environmental exposures are a few of the properties necessary to evaluate for the service performance. Due to the variety of applications, it is expected that numerous polymers or formulations will be required to best serve each application. 

The materials that make up the renewable resources are agricultural based and based on biosynthesis. 

Regenerated cellulose film, cellophane, can be cast from the solution of cellulose xanthate formed through the viscose process after which the film is subsequently hydrolyzed back to cellulose. Since the end product is essentially cellulose, it is readily biodegradable [11], Cellophane is typically plasticized with ethylene glycol, propylene glycol, or glycerol. To improve the barrier properties, cellophane is often coated with polyvinylidene chloride, which would hinder the biodegradability. 

Modified cellulose of commercial significance involves primarily the cellulose esters and ethers. The cellulose esters include cellulose acetate, cellulose propionate, cellulose acetate-butyrate, cellulose nitrate. Cellulose ethers include ethyl cellulose as a melt, processable-grade and water-soluble derivatives. Historically, it was accepted that cellulose derivatives that had a degree of substitution above 1.0 were not biodegradable [18-20]. However, cellulose acetate has been found to be biodegradable in both aerobic compost and anaerobic bioreactor environments [21-23]. The potential for additional, biodegradable, cellulose derivatives is currently being explored. 

Konjac Konjac is a natural polysaccharide found in plant tubers from Amor-phophallus konjac and produced commercially by FMC (Philadephia, PA). Konjac is a copolymer of glucose and mannose (1 1.6) linked /i-1.4 with random acetylation of approximately monomer units. The polymer is water soluble and as such the applications are limited. Chemical modifications of the konjac as well as liquid crystalline properties have been reported [32]. 

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This paper is a summary of new biodegradable polymers from renewable resources. 

ACQ Preserve A Dramatic Pollution Prevention Advancement An Efficient Process for the Production of Cytovene , A Potent Antiviral Agent ULTIMER A Water-Soluble Polyelectrolyte for Wastewater Treatment Manufacturing a Biodegradable Polymer from Renewable Resources ... 

A potentially important industrial extension of the production of naturally biodegradable polymers from renewable resources is the utilisation of biological processes to synthesise biodegradable polymers. 

M.J.-L. Tschan, E. Brule, P. Haquette, C.M. Thomas, Synthesis of biodegradable polymers from renewable resources. Polym. Chem. 3 (2012) 836, doi 10.1039/c2py00452f. 

Biodegradable polymers from renewable resources include ... 

With the desire to reduce the amount of waste remaining in landfills, there is a need to use biodegradable (sometimes also referred to as compostable) polymers in parts of the world where the infrastructure to capture the gases formed exists. Biodegradable polymers come from either renewable resources or petroleum sources. The primary biodegradable polymers from renewable resources are PLA, PHA, TPS, cellulose, chitin, and proteins. The basic structures of these polymers along with some key thermal characteristics are shown in Table 11.9 and will be discussed in more detail in the following section. 

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