An early focus of Sony's efforts to address environmental issues was the development of vegetable-based plastics. Sony's work in this field resulted in the development of a durable, fire-resistant vegetable-based plastic suitable for use in durable consumer goods. The environmental advantages of this material compared with conventional plastics include reductions in the use of petroleum resources and greenhouse gas emissions. In addition, vegetable-based plastics can be reprocessed in various ways after use.
What are Vegetable-based Plastics?
Vegetable-based plastics are plastics made from corn, potatoes, and other vegetable-based raw materials. The first major applications of this technology were biodegradable plastics made from polylactic acid, a polymer derived from starch in corn and other plants. The biodegradability of this material made it ideal for a variety of uses, including surgical sutures. Unfortunately, the material was also flammable and brittle, which meant that it could not be used in durable consumer goods. However, Sony was able to develop vegetable-based plastics that equaled or surpassed the fire-resistance and durability of petroleum-based plastics by combining polylactic acid with inorganic chemicals and other substances developed through in-house research. Vegetable-based materials were used for the first time 2002 in Walkman cases (WM-FX202/WM-EC1). Since then these materials have been used in a wide variety of products, including AIBO Entertainment Robots, DVD players, VAIO devices, mobile telephones, non-contact IC cards and transparent blister packaging.
Fire-Resistance
Vegetable-based plastics are made from polylactic acid, which is an extremely flammable substance. When polylactic acid is heated, thermal decomposition releases a combustible gas that can easily react with oxygen in the air to cause combustion. To make polylactic acid materials fire-resistant, it is necessary to use a fire-retardant. However, some fire-retardants cause significant environmental risks and may also be hazardous to human health. Sony therefore decided to use aluminum hydroxide, a fire-retardant that is safer for the environment and human health.
Figure 2 illustrates the flame-retardant mechanism that is created when aluminum hydroxide is added to polylactic acid.
As an inorganic filler, aluminum hydroxide suppresses the emission of combustible gas when the material is heated.
When heated above 200°C, aluminum hydroxide undergoes hydrolytic decomposition while also absorbing heat. This process produces alumina (aluminum oxide), an extremely heat-resistant material, which coats the material and seals out oxygen.
The addition of aluminum hydroxide suppresses the production of combustible gas. Hydrolytic decomposition of aluminum hydroxide absorbs heat, releases water, and produces an alumina coating that seals out oxygen. These three effects produce excellent fire-resistance.
Rubber Additive Provides Durability
The addition of aluminum hydroxide to polylactic acid enhances fire-resistance. However, it also reduces the strength of the material, causing a loss of durability. By adding rubber to the raw materials, it is possible to increase the strength of vegetable-based plastics. Rubber is an extremely elastic material that gives the polylactic acid the toughness needed to withstand impact. Rubber is a relatively flammable substance. However, by carefully balancing the rubber against the fire-resistant ingredient and selecting the type of rubber used, Sony was able to increase strength without compromising fire-resistance. For the sake of the environment, Sony also decided to use a vegetable-based rubber material.
