International Plastics News for Asia

High performance plastics from cashew nut shells

New studies in developing bioplastics are getting more interesting and exciting. NEC Corporation recently developed a first-of-its-kind durable new biomass-based plastic produced from non-edible plant resources. The bioplastic is created by bonding cellulose, a main component of plant stems, with cardanol, a primary component of cashew nut shells, which achieves a level of durability that is suitable for electronic equipment.

As an alternative to petroleum-based components, cellulose is the plastic's major ingredient. The cellulose, which is produced in large amounts by plants, including grass stems, etc., is modified by cardanol, an oil-like material that is extracted from cashew nut shells. Most of these stems and nut shells are abundant resources, and are often discarded byproducts of the agricultural process. The use of cellulose and cardanol as the plastic's primary components produces a plastic that features a high plant component ratio of more than 70%. Current cellulose based plastics include large amounts of petroleum-based additives, which results in a low plant component ratio.

After enhancing its reactivity, cardanol is chemically bonded with cellulose, which produces a durable thermoplastic that is strong, heat resistant, water resistant and non-crystalline (short moulding time), due to the bonded cardanol's unique molecular structure consisting of flexible and rigid parts. Comparison to existing bioplastics: polylactic acid resin (PLA) and cellulose acetate (CA) based resin, the new material has superb durability and malleability with twice the strength of existing PLA. Its heat resistance (glass transition temperature) is more than twice the resistance of PLA and approximately 1.3 times more than CA resin, while its water resistance is comparable to PLA and approximately 3 times more than CA resin. Moulding time is half less than that of PLA and comparable to conventional cellulose-based and petroleum-based plastics.

In recent years, bioplastics composed from plant resources attracted much attention as an effective measure to reduce the depletion of petroleum resources and alleviate global warming. However, while current leading bioplastics, such as PLA, primarily use feed grains as a plant resource, the possibility of future food shortages has emphasized the importance of using non-edible plant resources to produce bioplastics. Hence, non-edible plant-based bioplastics have been developed using such resources as cellulose and castor oil. These cellulose-based bioplastics have conventionally been utilised in stationery, toys and household goods. But these modified celluloses require large amounts of petroleum-based additives such as plasticisers, which results in bioplastics with a low plant component ratio and poor durability, including heat resistance and water resistance.

A polyamide resin derived from castor oil, a non-edible plant resource is also being used in electronic parts, however, there is an inadequate supply of this plant resource to expand its use and its characteristics are unsuitable for use in a variety of electronics. However, NEC's newly developed bioplastic resolves each of these issues. Looking forward, the company will continue with research and development towards mass production of this bioplastic and improving its suitability for a wide range of electronic equipment within the 2013 fiscal year.