- - NEC has developed a new production technology which allows it to produce a high-functionality bioplastic using just one-tenth the energy (fewer CO2 emissions) that was previously required for processes using the non-edible plant resource of cellulose and natural oil as raw materials.
Research fellow, Dr. Masatoshi Iji and his research group at the Smart Energy Research Laboratories of NEC Corporation (NEC) have developed a new production technique, the “Two-stage Heterogeneous Synthesis Process,” which can synthesize high-functionality bioplastic using the non-edible plant resource cellulose as its main component (“Cellulose-based High-functionality Bioplastic,” hereafter) while consuming just one-tenth the energy (fewer CO2 emissions) that was previously required.
This Cellulose-based High-functionality Bioplastic developed independently by NEC is synthesized by chemically bonding cellulose*1, a primary component of materials such as wood and straw, with the oily component cardanol*2, which is derived from the agricultural by-product of cashew nut shells. As well as boasting excellent thermoplasticity*3, heat resistance*4 and water resistance*5, 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 (hereafter referred to as “modified cardanol”) 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℃ 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. As a result, this Cellulose-based High-functionality Bioplastic can be produced for about one tenth of the energy (CO2 emissions) when compared with conventional methods, thereby promising a drastic reduction in production costs when the material is mass produced in the future.
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.
Social Background to the Research
The world currently produces around 230 million tons of plastic annually (approximately 13 million tons in Japan), and as most of these plastics are produced by reacting petroleum-based raw materials under high-temperature, high-pressure conditions, the amount of CO2 generated in the plastic production process and the large amount of energy consumption required for production have become issues. In response, progress has been made in the development and use of bioplastics which use renewable plant resources capable of CO2 fixation as raw materials. Traditionally, most bioplastics have used starch derived from the likes of grains, potatoes or sugar as a raw material, but on account of concerns over future food sources, today there is interest in a switch to non-edible plant resources such as cellulose, a principal component of plant stems and wood materials.
History of the Research
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 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 bioplastics*7 (Figure 1), and has since developed a Cellulose-based High-functionality Bioplastic for durable products such as electronic devices.
With these latest advancements, NEC developed technologies for low-energy (low CO2 emission) production with the aim of achieving a practical Cellulose-based High-functionality Bioplastic*6.
NEC developed the Two-stage Heterogeneous Synthesis Process shown in Figure 2 that enables the production of a Cellulose-based High-functionality Bioplastic using approximately one-tenth the energy (CO2 emissions) when compared with conventional production methods. (Figure 3)
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*8 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, 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 Newly Developed Production Process (Two-stage Heterogeneous Synthesis 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.
In the first stage, pulverized cellulose is caused to moderately swell 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℃ or less, they can be separated from the produced resin, and the collected short-chain components and solvent are reused.
The following two points represent the major accomplishments from the research.
- (1) A new production technique (Two-stage Heterogeneous Synthesis Process) that allows a Cellulose-based High-functionality Bioplastic (a cardanol-bonded cellulose-based resin) to be synthesized for approximately one-tenth of the energy used in the conventional production technique (homogeneous process) has been developed.
- (2) The cardanol-bonded cellulose-based resin produced through the process achieves thermoplasticity and water resistance that is of a similar level to the resin produced through the conventional process. Further, if a plant-based polyester resin and glass fibers as additives are used to the resin, the key characteristics of heat resistance and strength could be improved to the practical level for use in durable products such as electronic devices (Table 1).
Table 1: Cellulose-based High-functionality Bioplastic produced with the production technique and properties after additive usage
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℃) 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 also plans to reveal details of this research at the 63rd SPSJ Annual Meeting to be held at the Nagoya Congress Center from May 28 to May 30, 2014.
Reference Figures and Tables
- Figure 1: Cellulose-based High-functionality Bioplastic (cardanol-bonded cellulose-based resin) development (model structures of the raw materials and resin)
- Figure 2: Development of the Two-stage Heterogeneous Synthesis Process Low Energy Production technique
- Figure 3: 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)
- Table 1 : Characteristics of Cellulose-based High-functionality Bioplastic produced with the production technique and the composite after additive usage
Explanation of Terms
- *1 Cellulose
- A polysaccharide which is a major component of plant stems and wood materials, and the most abundant plant resource on earth. While cellulose has a similar structure to starch, as it crystalizes into a solid, it does not dissolve in water or heat and is not suitable for human consumption.
- *2 Cardanol
- An oily ingredient extracted from the shells of cashew nuts when a continuous chain of 15 carbon atoms (long-chain hydrocarbon) and a benzene ring. NEC discovered that as its structure differs from regular natural oils, its addition to cellulose has the effect of improving unique physical properties. (details listed under *6)
- *3 Thermoplasticity
- This refers to the fluidity of a plastic when it is heated. If this property is insufficient, when the plastic is heated and poured into a mold, the molded item may not be completely filled, or the molded surface may suffer from reduced smoothness.
- *4 Heat Resistance
- This refers to the degree to which a plastic resists deformation when heated. While there are several ways to investigate how the properties of a plastic are altered in response to heat, for this research heat resistance was measured according to the glass-transition temperature (the temperature at which properties such as thermal expansion undergo significant change), which indicates resistance to deformation due to heating, and the deflection temperature under load (the temperature at which deformation occurs while under load). The higher these values are, the better the heat resistance of the material.
- *5 Water Resistance
- This refers to the degree to which a plastic resists the absorption of water while immersed (continuous temperature for 24 hours). The higher the absorption rate, the more the dimensions of a plastic compact will increase in a normal environment, and the more prone to deformation the product itself will be.
- *6 August 25, 2010
- “NEC Develops High Performance Bioplastic with a High Plant Ratio by Using Non-edible Plant Resources -- Advanced bioplastic from plant stems and cashew nut shells –“ http://www.nec.co.jp/press/en/1008/2501.html
- *7 Conventional Cellulose-based Bioplastic
- While a cellulose-based bioplastic where a short-chain component such as acetic acid was added to the non-edible raw material cellulose has previously been developed for practical use in regular products, the plant content rate was low (less than 40%, for instance) and its durability in terms of heat and water resistance was inadequate for use in durable products.
- *8 Poor Solvent
- To collect a resin dissolved in an organic solvent containing impurities such as unreacted material, a method where a separate solvent which does not dissolve the resin easily is added and allowed to deposit the resin to separate the impurities is commonly used, and this refers to the solvent added when doing so. As it is necessary to add many times more of the poor solvent than the amount of the initial solvent, after use, large amounts of energy are required to recover the poor solvent for its reuse by separating the initial solvent through means such as distillation.
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