Development of a Temperature-Responsive Water-Soluble Polymer that Makes Recycling Easy

Polymer and Recycling

Owing to mass production and mass consumption, so many people can now live affluent lives in today’s society. On the other hand, as this has caused environmental problems due to huge volumes of waste on a global scale, there are widespread calls to promote recycling and shift to a recycle-oriented society.
Plastic packaging containers have different designs printed in different colors, and have various multi-layered structures made of different materials to protect products. However, if plastic packaging containers are recycled directly, the ink components, their combustion products, or the coexistence of various materials may affect the strength or safety of the recycled materials.

Kao is developing a temperature-responsive water-soluble polymer as an approach to separating these various materials and making plastic recycling easy. Our temperature-responsive water-soluble polymer is designed not to dissolve in water at room temperature but to dissolve only in hot water, by controlling its water-attracting and water-repelling properties. We believe that if this polymer is used between ink layers or layers that comprise a multi-layered structure, the product can be kept free of any influence from water or humidity when it is used, and the ink or multi-layered structure can then be easily separated by using hot water when the product is recycled.
We are working to apply this temperature-responsive water-soluble polymer when developing technologies that make recycling easy, and spread them throughout society.

A graph is shown that compares the solution rates of a commercial water-soluble polymer and of the developed temperature-responsive water-soluble polymer at different temperatures. The commercial water-soluble polymer starts to gradually dissolve in water at 30°C. On the other hand, Kao’s developed temperature-responsive water-soluble polymer does not dissolve in water at 30°C but starts to gradually dissolve in water at around 50°C, and starts to rapidly dissolve in water at 60°C.

Comparison of solubility behavior between two polymers at different water temperatures

Application of the Temperature-Responsive Water-Soluble Polymer

The following video does not include audio, and a text transcription of its visual content is available.

A transcript is available here.

This video, in which samples with a design printed by using our temperature-responsive water-soluble polymer are soaked in water at 30°C and water at 70°C, compares how the print ink is removed from the two samples.

A figure shows the structure of the sample film using our temperature-responsive water-soluble polymer. The polymer is applied to a PET film, and a print ink is further applied in a way that covers the polymer.

Two glass bottles containing water are shown side by side. The temperatures of the left bottle and right bottle are 30°C and 70°C, respectively. The sample films are soaked in the left and right bottles at the same time.

00:04
In the right bottle at 70°C, the print ink is quickly removed from the film immediately after the film was soaked.

00:09
In the left bottle at 30°C, the print ink remains unchanged 10 minutes after the film was soaked.

00:24
The samples are taken out of the left and right water bottles, and the prints on these samples are shown.
The print remains on the film that had been soaked in the left bottle at 30°C. On the other hand, no print remains on the film that had been soaked in the right bottle at 70°C, and the film is transparent.

Industrial Chemicals

Industrial Chemicals

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