Developing high-molecular materials with low environmental impact

Plastics and Teflon

The word "plastic" is used in Japan as a generic term for synthetic resin products together with the word "vinyl," but originally it meant plasticity that can be shaped at will. Hard resins are often referred to as plastic and soft sheet-like materials as vinyl, but neither of these terms describes the physical or chemical properties of the material.

In English, the word "plastic" is used for all synthetic resin products, regardless of whether they are hard or soft, with plastic bottles being plastic bottles and plastic bags being plastic bags. Plastic bottles are plastic bottles, plastic bags are plastic bags, plastic art is plastic art, and plastic surgery is plastic surgery.

By the way, did you know that Ronald Reagan, the 40th President of the United States, was ridiculed as the Teflon president? The term was coined from the fact that he was able to avoid any accusations without getting hurt, just as a Teflon-coated pot does not burn.

To begin with, Teflon is the trade name for a synthetic resin developed by the U.S.-based DuPont, and it is interesting that the name for a chemical substance was accepted without discomfort by U.S. society in the 1980s. Perhaps this is because in English-speaking countries, words related to chemistry are used relatively close to their original meaning.

In Japanese, "pet" in "PET bottle" is known to be derived from "PET," the English abbreviation for polyethylene terephthalate (PET), the plastic used as a raw material, but its katakana spelling makes it difficult to understand that it is the name of a chemical compound. Polyester, a typical synthetic fiber, is made by processing PET into a fiber form, but it is not called PET fiber.

As described above, there are very few opportunities to come into contact with the official names of chemical substances in our daily lives, and the names of products are used somewhat differently from their original meanings, making it difficult to understand that there are different types of substances called plastics, each with its own unique properties. I believe this is one of the issues that we chemists and the chemical industry need to address.

Green Chemistry and Biodegradable Plastics

Green Chemistry is defined as "the design, development, and implementation of chemicals and manufacturing processes that reduce or eliminate the use or production of hazardous substances," and its philosophy is summarized in the 12 Principles of Green Chemistry. The 12 Principles of Green Chemistry are a set of 12 principles that state the obvious: chemicals produced by human hands should be harmless to human health and the environment, the use of hazardous substances should be avoided in the manufacturing process, waste should be reduced, and limited resources and energy should be conserved. However, the reality is harsh, and environmental pollution is occurring repeatedly in various countries and regions. Recently, the problem of marine plastic debris, which is caused by plastic products that have washed into the ocean, has been gaining attention. In particular, many people are familiar with microplastics, or fine particles, as they have been widely reported.

The root cause of this problem lies in the fact that natural polymers such as wood and synthetic polymers such as plastic have different circulation systems. After death, plants and animals in nature are decomposed by microorganisms in the soil (biodegradation), eventually becoming water and carbon dioxide. The carbon dioxide is then taken up again by plants through photosynthesis ...... This is a cyclical system. On the other hand, many synthetic polymers are not biodegradable and cannot be incorporated into the natural cycle, so they can only be landfilled or incinerated to release the carbon dioxide. (If we wait tens of thousands of years, plants that take in carbon dioxide may become oil, but this is not realistic.)

This is where biodegradable plastics are gaining attention. Its characteristic is that although it is a synthetic polymer derived from petroleum, it is decomposed by microorganisms and incorporated into the circulatory system of the natural world. Therefore, it is expected that the environmental impact of biodegradable plastics will be less than that of non-degradable plastics, even if they are discharged into the natural world. It can be said that these chemicals are close to the philosophy of green chemistry.

However, it is not all good. Most biodegradable plastics are polymer compounds called polyesters, but they do not contain units that are a source of heat resistance and durability like PET, so their applications are limited. Many chemists and chemical manufacturers are working to solve this problem.

Toward the Development of New Polymeric Materials with Less Environmental Impact

My research subject is, without a doubt, "plastics. My first contact with plastic is unknown because plastic products were around me when I was born. However, what I clearly remember is that in the third grade of elementary school, I enjoyed putting a plastic triangular ruler into boiling water for humidification on the classroom stove and transforming it into a squishy shape (although I was scolded by the teacher afterwards). In retrospect, this was my experience of plasticity, but I had no way of knowing that at the time.

More than a decade later, I began to study and research plastics in earnest at university and graduate school. The theme of my doctoral research at the graduate school was the development of new fluorinated polymers. The aforementioned Teflon is the most common example of a fluorinated polymer.

One of my goals was to create a new material that would exhibit water and oil repellency (keep water and oil away) and stain resistance (keep dirt off) better than Teflon, while reducing the amount of fluorine used. As a result, we succeeded in synthesizing a polymer that, while not as durable as Teflon, exhibits excellent water and oil repellency and stain resistance with a small amount of fluorine.

Based on the experience gained from this research, we then successfully introduced about 5% fluorine into biodegradable plastics to develop a material that exhibits excellent water and oil repellency and stain resistance while maintaining 95% biodegradability. Furthermore, we have considered using clean photoreactions to control the molecular mobility of polymers, and are working to develop new materials that simultaneously satisfy the conflicting properties of biodegradability and heat resistance.

(First published in the November/December 2020 issue of the public relations magazine "Hosei")