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NEC reduces production energy for cellulose-based bioplastic by 90%

NEC Corporation (NEC) has developed a new production technology which allows it to produce a high-functionality bioplastic using just one-tenth the energy (i.e., fewer CO2 emissions) that was previously required for processes using the non-edible plant resource of cellulose and natural oil as raw materials.

This cellulose-based high-functionality bioplastic is synthesized by chemically bonding cellulose, a primary component of materials such as wood and straw, with the oily component cardanol, which is derived from the agricultural by-product of cashew nut shells. As well as boasting excellent thermoplasticity, heat resistance and water resistance, this bioplastic features a characteristically high plant content (approximately 70%), and there are plans for it to be commercialized in durable products such as electronic devices.

The cardanol used in the process was chemically modified into a reactive structure in collaboration with Tohoku Chemical Industries Ltd.

In the new two-stage heterogeneous synthesis process developed by NEC, instead of dissolving the raw material cellulose into an organic solvent (homogenous system) as before, after being swollen into a gel-like substance with an organic solvent (heterogeneous system), it is bonded with the modified cardanol (long-chain component) and acetic acid (short-chain component) in two stages to synthesize a resin.

This resin can be easily collected from a liquid solution through solid-liquid separation methods such as precipitation and filtration. As this process achieves the reaction conditions at almost ordinary pressure and medium temperature (100 ˚C or less), and does not require a solvent for separation of the produced resin, as was required with the conventional homogeneous process, a significant reduction in the amount of solvent needed for synthesis (a roughly 90% decrease from the conventional process) is achieved.

NEC aims to use this technology to start mass production of a cellulose-based high-functionality bioplastic during fiscal 2016 and seeks to deploy the material in electronic devices and various other durable products.

Background. The research and development work was conducted as a part of “Research and Development of Bioplastics Using Non-edible Polysaccharides” (Representative: Research fellow, Dr. Masatoshi Iji, NEC Smart Energy Research Laboratories) under the Advanced Low Carbon Technology Research and Development Program run by the Japan Science and Technology Agency (JST). The research aims to develop an innovative bioplastic that achieves reduced CO2 emissions using non-edible plant-derived polysaccharides such as cellulose, which enjoys a stable supply.

In 2010, NEC bonded cellulose with the modified cardanol as a long-chain component along with a short-chain component, for the first time achieving a high plant content (approximately 70%) and excellent thermoplasticity, heat resistance and water resistance, an accomplishment that until then had not been possible with conventional cellulose-based bioplastic, and has since developed a cellulose-based high-functionality bioplastic for durable products such as electronic devices.

This Cellulose-based High-functionality Bioplastic was produced using methods similar to conventional cellulose-based bioplastics through a homogeneous process where cellulose was dissolved in an organic solvent and reacted with other ingredients to produce a resin. Large amounts of poor solvent were needed to recover the resin that was produced in the solution, which gave rise to the issues of large production energy (CO2 emissions) and difficulties in reducing costs.

As an alternative to this homogeneous process, a heterogeneous process can be carried out where the cellulose is not dissolved in an organic solvent. Instead, an organic solvent is used to swell the cellulose gel-like substance in order to produce a resin, and since the produced resin can be easily collected through precipitation and filtration when stirring is stopped after the reaction, a significant amount of energy savings can be realized.

However, when proceeding with the production of a resin after the addition of a long-chain component, such as the modified cardanol, which is effective in improving the physical properties of the resin, precipitation separation becomes more difficult due to the increased affinity with the solvent. On the other hand, simply adding short-chain components like acetic acid improves precipitation separability but produces undesirable physical properties in the resin, such as insufficient thermoplasticity and water resistance.

Due to these issues, NEC faced difficulties in striking a balance between the precipitation separability of the produced resin (the productivity of the cellulose-based bioplastic) and the physical properties of the resin.

The new process. NEC developed a two-stage heterogeneous synthesis process that strikes a balance between the productivity and physical properties of its cellulose-based high-functionality bioplastic.

Development of the Two-stage Heterogeneous Synthesis Process Low Energy Production technique. Source: NEC. Click to enlarge.

In the first stage, pulverized cellulose is caused to swell moderately into a gel-like substance in an appropriate organic solvent, and then a long-chain component (modified cardanol) and a short-chain component (acetic acid) are added. At this stage, by restricting the addition of the long-chain and short-chain components to a limited amount, resinification is kept in an incomplete state, and the product (cellulose bonded with cardanol and acetic acid) is efficiently recovered through precipitation separation (+filtration under reduced pressure). The supernatant solution including unreacted material consisting of long-chain and short-chain components is reused by adding the insufficient components.

In the second stage, the product collected in the first stage (partially resinified substance) is caused to develop affinity in an appropriate organic solvent (partially-dissolved heterogeneous system) and a resin (cardanol and acetic acid-bonded cellulose: cardanol-bonded cellulose based resin) is made to form with the addition of sufficient short-chain components. As the unreacted short-chain components and the solvent are prone to volatility, through distillation at a relatively low temperature of 100 ˚C or less, they can be separated from the produced resin, and the collected short-chain components and solvent are reused.

Comparison of the amount of solvent used and production energy (CO2 emissions) for the production technique (Two-stage Heterogeneous Synthesis Process) and the conventional technique (homogeneous process). (Measured during laboratory-scale synthesis. Energy for solvent distillation collection calculated as amount of solvent x latent heat.) Source: NEC. Click to enlarge.

Future development. Moving forward, NEC plans to complete techniques for mass production while expanding the current scale of production (laboratory level) based on the newly-developed production technique in stages, with the aim to commence mass production during fiscal 2016.

To coincide with the start of full-scale mass production in the future, NEC also aims to reduce the production energy (CO2 emissions) for petroleum-based high-functionality plastics such as polyethylene terephthalate (PET, produced under high pressure + vacuum at more than 200 ˚C) by around 50% (In terms of CO2 emissions: approximately 1.3kg per 1.0 kg resin). Moreover, there are also plans to expand usage of the plastic beyond electronic devices to other high-added value durable products and new products subject to growth in the future.

NEC will reveal details of this research at the 63rd SPSJ Annual Meeting to be held at the Nagoya Congress Center from 28-30 May 2014.



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