Mitsubishi Electric Corp plans to separate and recover polypropylene (PP), polystyrene (PS) and acrylonitrile butadiene styrene (ABS) with a purity of 99% or higher from the plastic mixture produced during the recycling of household appliances. The recovered plastics will be used to make new products. A total of about 6,400 tons of PP, PS and ABS can be recovered yearly.
In the new business, Mitsubishi will separate PP from PS and ABS based on the difference in specific gravity, and then separates PS and ABS from each other based on the difference in charging characteristic. The company also developed a proprietary technology to separate and recover PP, which is lighter than water, based on the specific gravity. To evaluate the mass-production technique, the company is using of tons of PP every year for water trays of refrigerators, lower covers of dishwashers and so on.
The company developed and adopted the "electrostatic separation technology" to separate PS and ABS from each other with a high purity based on the difference in charging characteristic. In the electrostatic separation, a plastic mixture containing granular ABS and PS is first put into a cylindrical triboelectric charger. Then, the charger is rotated so that ABS and PS are rubbed against each other for charging. PS plastic is charged negatively (-), while ABS plastic is charged positively (+). Next, they descend between electrodes to which a voltage is applied so that PS is collected on the positive electrode and ABS is attracted on the negative electrode. During this process, the separation accuracy lowers if the granular plastics are attracted and agglomerate by the electric force. The company maximized the amount of triboelectric charge to prevent deterioration of accuracy. As a result, PS and ABS can be recovered with a purity of 99% or higher.
The total amount of plastics recovered by Mitsubishi's closed-loop recycle system is expected to increase to 7,000 ton pa. Closed-loop recycling of PP, PS and ABS from plastic mixture is likely to reduce the total amount of these plastics used in the company's household appliances business by approximately 18%. In addition, CO2 emissions can be reduced by 6,700 ton.