Method purifies polyolefins

Images: United States Patent and Trademark Office

Procter & Gamble Co. (P&G), Cincinnati, has received a patent for a method to purify postconsumer and postindustrial plastics using solvents, heat and pressure. The method is suitable for polyolefins, such as polyethylene and polypropylene, resulting in a colorless, odor-free, virgin-like polymer.

In conventional recycling methods that involve washing and mechanically reprocessing the plastic, the resulting pellets can remain contaminated with impurities, such as food residue and perfume. Additionally, they can have a dark color because of the mixture of pigments. Existing solvent-based methods do not produce virgin-like polymer, according to the patent.

The invention “uses a solvent that is readily and economically removed from the polymer,” the patent states.

The patent lists multiple embodiments of the invention, using a variety of solvents, including olefinic hydrocarbons, aliphatic hydrocarbons and mixtures of the two.

The patent states: “Surprisingly, it has been found that certain fluid solvents … when used in a relatively simple process can be used to purify contaminated polymers, especially reclaimed or recycled polymers, to a near virgin-like quality.”

Patent 9,982,066; issued May 29, 2018

Recycling method. Two inventors in Houston are seeking to patent an apparatus and method for recycling plastics that involve using a molten aluminum compound to break plastic materials down into their basic components.

The method, invented by Ronald G. Presswood Jr. and Ian C. Bishop, is applicable to any plastic, including polyvinyl chloride, high-density polyethylene (HDPE), low-density polyethylene and acrylonitrile butadiene styrene. The invention includes a reaction vessel for holding the aluminum bath and at least one separator for removing particulate matter.

In the process, the ground plastic is introduced into a bath of molten aluminum. As the plastic or other material passes through the bath, the bath reacts, breaking the material into its elemental parts. Those elements are removed from the bath using gravimetric and gas-capture processes. The elemental materials, such as carbon and sulfur, can be recovered and sold or, in the case of hydrocarbons, burned. Excess heat generated by the process can be used for power generation.

According to the patent application, additional uses for the invention include recycling electronics, munitions and propellants. It also is capable of separating out rare earth metals and heavy metals.

Patent application 20180050372; published Feb. 22, 2018

Flake washing. Plastic Revolutions Inc., Reidsville, North Carolina, has patented a friction washer for cleaning recycled plastic flakes or chips. Its design improves on previous equipment, which can leave debris from labels and glue on the flakes while using a large quantity of hot water and electricity.

In the device, a motor drives a rotor with staggered blades that agitate the flakes against one another and the inside of the machine’s housing to remove debris via friction. Water and the debris pass through mesh to a discharge port, while the plastic flakes exit through a separate discharge port. The system can use unheated or room-temperature water.

The patent states, “This configuration has been found to be energy- and water-efficient yet yield[s] excellent cleaning results. … It has been found that the water needed can be reduced to about 20 gallons of water to about 6,000 pounds of plastic chips. The reduced water need reduces the contaminated-water cleanup costs.”

The system works well with HDPE but is applicable to other types of plastic, according to the patent.

Patent 9,968,971; issued May 15, 2018

Correction: The patent column in the spring issue of Plastics Recycling provided an incorrect patent application number and date for a Unisensor Sensorsysteme GmbH sorting device. Patent 20180038793 was issued Feb. 8, 2018.