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Cellulosics

Basics Virgin CA has a

Basics Virgin CA has a high glass transition with a degree of polymerization (DP) around 300, a high transparency, stiffness and chemical resistance. These properties are favourable for solvent-resistant and grease-resistant coatings (paper products, wires or fabrics), fibres, lacquers (electrical insulation or capacitors) or filter tows [12;13]. In 2002, the total consumption of CA flakes in the United States, Western Europe, Japan, and China was 655,000 tonnes [13]. Raw CAB is used as binders in protective and decorative coatings for instance for. textiles, paper, plastics or metals because of its excellent colour, toughness, flexibility, flow control and weather resistance [12]. Pure CAP exhibits properties between CA and CAB that make it useful for inks, varnishes or coatings [12]. Furthermore CAP is highly effective to disperse pigments since it is stable to UV-light and does not react with metallic pigments or fluorescent substances. Plastics made of CA, CAB or CAP can be used for different processing technologies including injection moulding or extrusion, to manufacture a wide range of products such as cosmetic or personal care containers, tool or toothbrush handles, displays, optical safety frames and profiles (Fig. 4). The most important producers of cellulose ester compounds are Albis Plastic GmbH (Cellidor CP, Cellidor CB), Eastman (Tenite Acetate, Tenite Butyrate, Tenite Propionate), FKuR GmbH (BIOGRADE), Mazzucchelli (Sethilithe, Plastiloid, Bioceta) and Rotuba (Auracell, Naturacell). Further applications of cellulose esters are liquid crystalline solutions [11]. CTA dissolved in a mixture of trifluoroacetic acid and dichloroacetic acid or trifluoroacetic acid and dichloromethane exhibits brilliant iridescence, high optical rotation and viscosity-temperature profiles characteristic of a typical anisotropic phase containing liquid crystalline solutions [13]. Wet spinning of these solutions results in fibres with significantly higher strength than conventional cellulose ester based fibres. Fig. 4: Example products made of BIOGRADE (FKuR GmbH) Nitrocellulose Nitrocellulose (NC) is the most important inorganic cellulose ester. It has been produced for more than 150 years by nitrating cellulose through exposure to nitric acid or other nitrating agent (often a mixture of nitric and sulphuric acid). The density of NC increases with the DS (DS is between 1.8 and 2.8) and ranges from 1.5 to 1.7 g/cm³ [14]. In general, cellulose nitrates are white, transparent and non-toxic but show high flammability or even deflagration due to friction or shock. Because of its flammability this inorganic cellulose ester is used in military explosives [14]. With a dielectric constant of about 7 and a specific resistance of 10 11 to 10 12 Ω/cm, industrial NC is considered to be a good insulator. The mixture with camphor as plasticizer was the first thermoplastic compound to produce flexible films for X-ray or photo applications (Eastman Kodak). They show excellent filmforming properties with an elongation at break from 3 to 70% and a tensile strength from 50 to 100 N/mm² [14]. Today cellulose nitrate is often used in lacquer, coating or printing ink applications because of its good adhesive and mechanical properties. NC is compatible with many other raw materials including plasticizers (e.g. phthalates), polymers (e.g. polyesters), pigments or additives. The total annual production of NC amounts to approximately 150.000 tonnes [14]. DOW Chemical (DOW Wolff), Hagedorn NC and Nobel Nitrocellulose are major suppliers of NC. Cellulose Ethers Cellulose ethers are derived from alkylation of pure cellulose by the reaction with alkylating reagents usually in presence of a base (generally sodium hydroxide) and an inert diluent (Fig. 5). The base, in combination with water, activates the cellulose matrix by destroying hydrogen-bonded 46 bioplastics MAGAZINE [01/10] Vol. 5

Basics Cellulose Sodium hydroxide Water Organic diluent Alkylating reagent(s) Aqueous diluents or water Reaction Purification Drying Grinding Packout By-products, organic diluent, water Organic diluent, water Fig. 5: General operation scheme for the production of cellulose ethers [15]. crystalline domains and increasing accessibility to the alkylating reagent. The activated matrix is often defined as alkali cellulose. [15]. The most important cellulose ethers are watersoluble and therefore a key additive in many water-based formulations to control the rheology (e.g. thickening or flow behaviour). Water-binding (absorbency, retention), colloid and suspension stabilization, film formation, lubrication and gelation are further valuable properties. Therefore cellulose ethers still have a broad range of applications including coatings, cosmetics, pharmaceuticals, adhesives, printings, ceramics, textiles or papers [15]. In 2000 the total worldwide consumption of cellulose ethers was around 371,000 tonnes. Methyl, ethyl and benzyl cellulose have been available since the mid-1930s and are soluble in organic solvents. Water-soluble cellulose ethers like sodium carboxymethyl cellulose or hydroxyethyl cellulose have grown rapidly in the past decades since their investigation. In addition to dry powders, cellulose ethers are also supplied in liquid forms such as fluidized suspensions or water solutions. Most types of ethers contain mixed substituents (e.g. hydroxylethyl cellulose) to enhance or adjust the properties of monosubstituted derivatives. In general, cellulose ethers are non-toxic and no adverse environmental factors are reported. Ethyl cellulose (EC) is a nonionic, water-insoluble but organo-soluble polymer with a specific gravity of 1.12 to 1.15 g/cm³ [15]. Furthermore it is colourless, odorless and tasteless with a melting point around 160°C. Typical tensile strength lies between 46 and 72 MPa, whereas the elongation at break ranges from 7 to 30 % [15]. It is manufactured by the reaction of alkali cellulose with a large amount of ethylene chloride and sodium hydroxide. EC has a wide range of applications from food through pharmaceutical to personal care including water barriers, rheology modifiers, binders, flexible film formers, masking or time-release agents. Moreover EC provides excellent thermoplasticity and modification behaviour by using plasticizers, waxes or other polymers. Therefore, the polymer is available for conventional thermoplastic processing technologies such as extrusion, laminating or moulding. The major producers of EC are DOW Chemical (DOW Wolff) and Hercules. Methyl cellulose (MC) is a nonionic, surface-active and water-soluble polymer with a high melting point around 290°C [15]. The tensile strength runs from 58 to 79 MPa and the elongation at break ranges from 10 to 15 % [15]. MC is produced through reaction of alkali cellulose with methylene chloride. Major suppliers of MC as well as mixed methyl cellulose ethers (e.g. hydroxylpropyl methyl cellulose) are Clariant, Cognis, DOW Chemical (DOW Wolff), Hercules, or Shin-Etsu Chemical. MC and its derivatives are used as thickeners, binder, adhesive, coatings or stabilizer [15]. Sodium carboxylmethyl cellulose (CMC), also known as cellulose gum, is an anionic mixed cellulose ether with a wide range of substitution. CMC is soluble in hot and cold water whereas it is not soluble in organic solvents. Solutions of CMC tend to be pseudoplastic or thixotropic depending on the molecular weight [16]. It is produced by reaction of sodium chloroacetate with alkali cellulose. The molecular weight of CMC ranges from 9 x 10 4 to 7 x 10 5 and has a high water binding capacity. In general, CMC is an extremely versatile polymer for food applications, as adhesives, in pharmaceuticals, cosmetics, ceramics or paper products [15]. CMC is produced by a large number of suppliers worldwide, e.g. Daicel, DOW Chemical (DOW Wolff), Hercules, Lamberti, Penn Carbose. www.umsicht.fraunhofer.de References [1] T. Heinze, et al.: Esterification of Polysaccharides, Springer, 2006. [2] D. Klemm, et al.: Comprehensive Cellulose Chemistry – Volume 1: Fundamentals and Analytical Methods, WILEY- VCH, 1998. [3] E. Ott, et al.: Cellulose and Cellulose Derivatives, 2nd Edition, Interscience Publishers, 1954. [4] H. Krässig, et al.: Cellulose, in: Ullmann‘s Encyclopedia of Industrial Chemistry, WILEY Interscience, 2004. [5] http://en.wikipedia.org/wiki/Rayon [04.12.2009]. [6] http://www.swicofil.com/viscose.html [30.11.2009]. [7] http://idw-online.de/de/news2591 [04.12.2009]. [8] http://www.innoviafilms.com/ [04.12.2009]. [9] K. Balser, et al.: Cellulose esters, in: Ullmann‘s Encyclopedia of Industrial Chemistry, WILEY Interscience, 2004. [10] http://www.ides.com/generics/CA/CA_typical_properties.htm [06.12.2009]. [11] L. B. Bottenbruch: 3. Technische Thermoplaste: Polycarbonate, Polyacetale, Polyester, Celluloseester, in G. W. Becker, D. Braun: Kunststoff-Handbuch, Hanser Verlag, 1992. [12] Eastman cellulose-based speciality polymers, Eastman Chemical Company, www.eastman.com [06.12.2009]. [13] K. J. Edgar: Cellulose esters, organic, Vol. 9, in H. F. Mark: Encyclopedia of Polymer Science and Technology, Part III, Vol. 9-12, 3rd edition, WILEY Interscience, 2004, pp 129-158. [14] D. Klemm et al.: Comprehensive Cellulose Chemistry – Volume 2: Functionalization of Cellulose, WILEY-VCH, 1998. [15] T. G. Majewicz, et al.: Cellulose ethers, Vol. 5, in H. F. Mark: Encyclopedia of Polymer Science and Technology, Part II, Vol. 5-8, 3rd edition, WILEY Interscience, 2004, pp 507-532. [16] Ethocel – Ethylcellulose Polymers: Technical Handbook, DOW Cellulosics, 2005, www.dow.com [11.12.2009]. bioplastics MAGAZINE [01/10] Vol. 5 47

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