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.

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.

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.

Non-crystalline polylactic acid starts to soften above 60°C. In crystalline form, however, it resists softening even above 60°C. For this reason, the material must undergo crystallization before it can be used in electrical appliances. Unfortunately, the crystallization of polylactic acid is a time-consuming process that also reduces moldability and productivity. However, Sony discovered that the crystallization process could be dramatically accelerated through the addition of pigments, such as copper phthalocyanine. By adding these substances as crystallization accelerants, Sony was able to achieve a molding cycle of around 30 seconds, which is the same as conventional plastics. This discovery dramatically enhanced the suitability of Sony's vegetable-based plastics for mass-production, since it meant that they could be molded in the same injection molding systems used for conventional plastics.

The carbon materials used in vegetable-based materials are derived from plants, which absorb carbon dioxide from the atmosphere. This means that even if vegetable-based plastics are burned, only atmospheric carbon dioxide that had been fixed by plants is released, and there is no increase in carbon dioxide in terms of the total cycle. In that sense, vegetable-based plastics are an ideal renewable material. Increased use of vegetable-based plastics will help to reduce oil consumption and lower total greenhouse gas emissions.

The aluminum hydroxide added to vegetable-based plastics is safe for humans. In fact it is used in toothpaste. The other additives of vegetable-based plastics are mainly derived from vegetable-based materials. Vegetable-based plastics currently account for 55% of plastics used in Sony products. Sony plans to take the initiative in further research and development relating to vegetable-based plastics. It also intends to use these materials in its products.