Perfect polymers — polymers that balance physical and environmental properties — do not exist, but polybutylene terephthalate (PBAT) is closer to perfection than many polymers.
For decades, manufacturers of synthetic polymers have failed to prevent their products from eventually entering landfills and oceans, and they are now under pressure to take responsibility. Many people are redoubling their efforts to promote recycling to avoid criticism. Other companies are trying to solve the waste problem by investing in biodegradable bio based plastics, such as polylactic acid (PLA) and polyhydroxyalkanes (PHA), hoping that natural degradation can reduce at least some waste.
However, both recycling and biopolymers face obstacles. For example, despite years of efforts, the plastic recovery rate in the United States is still less than 10%. However, it is difficult for bio based polymers – usually fermentation products – to achieve the same performance and production scale as the mature synthetic polymers they are to replace.
PBAT combines some beneficial properties of synthetic polymers and bio based polymers. It comes from common petrochemical products – purified terephthalic acid (PTA), butanediol and adipic acid, but it is biodegradable. As a synthetic polymer, it can be easily produced on a large scale, and it has the physical properties required to manufacture flexible films, which can be comparable to the films of traditional plastics.
Interest in PBAT is rising. Old brand manufacturers such as BASF in Germany and novamont in Italy have seen an increase in demand after decades of market cultivation. More than half of Asian manufacturers have joined them. With the promotion of sustainable development by regional governments, they expect the business of this polymer to be booming.
Marc Verbruggen, a former CEO of NatureWorks, a PLA manufacturer, is now an independent consultant. He believes that PBAT is “the cheapest and easiest way to manufacture bioplastics products”. He believes that PBAT is becoming an excellent flexible bioplastics, It is ahead of competitors such as polybutylene succinate (PBS) and PHA, and it may become one of the two most important biodegradable plastics as a whole, keeping pace with PLA. He said PLA is becoming the main product for rigid applications.
Ramani Narayan, a professor of chemical engineering at Michigan State University, said that the main selling point of PBAT — its biodegradability — comes from ester bonding rather than carbon carbon bonds like non degradable polymers such as polyethylene. Ester bonds are susceptible to hydrolysis and enzymes.
For example, polylactic acid and PHA are polyesters that degrade when their ester connections are destroyed. But the most common polyester, polyethylene terephthalate (PET), used in fibers and mineral water bottles, is less likely to decompose. This is because the aromatic rings in its backbone come from PTA. According to Narayan, these rings give structural properties and make pet hydrophobic. He said: “water is not easy to enter. It slows down the whole hydrolysis process.”
Some ingenious chemical reactions led scientists to invent PBAT in the 1990s as a bridge between aliphatic and aromatic polyesters.
BASF produces polybutylene terephthalate (PBT), a polyester made of butanediol. The company’s researchers are looking for a biodegradable polymer that they can easily produce. They use aliphatic dibasic acids to replace some PTA in PBT. In this way, the aromatic part of the polymer is separated so that it can be biodegradable. At the same time, enough PTA is left to make the polymer biodegradable Trustworthy physical properties.
Narayan believes that the biodegradability of PBAT is better than that of PLA, which needs industrial compost to decompose. However, it can not be compared with the commercially available PHA, which can be biodegradable under environmental conditions and even in the marine environment.
Experts most often compare the physical properties of PBAT with low-density polyethylene, an elastic polymer used to make films, such as garbage bags.
PBAT is often mixed with polylactic acid, a rigid polymer with polystyrene like properties that provides hardness. BASF’s ecovio brand is based on this mixture. For example, Verbruggen says compostable shopping bags are usually 85% PBAT and 15% PLA.
Novamont added another dimension to the formula. The company mixes PBAT and other biodegradable aliphatic aromatic polyesters with starch to create resins for specific applications.
Stefano facco, the company’s new business development manager, said: “over the past 30 years, novamont has been committed to solving applications where degradability adds value to the product itself.
A big market for PBAT is mulch, which is spread around crops to prevent weeds and help maintain moisture. When polyethylene films are used, they must be pulled up and often buried. However, biodegradable films can be cultivated directly into the soil.
Another big market is compostable garbage bags, which are used for catering services and household collection of food and yard waste. Bags from companies such as biobag, which novamont recently acquired, have been sold at retailers for many years.
Joerg auffermann, head of the global business development team of BASF biopolymers, said: “the main ecological benefits of Compostable Plastics come from their service life, because these products help transfer food waste from landfills or incinerators to organic recycling.
Over the years, biodegradable polyester industry has entered applications other than film. For example, in 2013, the Swiss coffee company launched a coffee capsule made of BASF’s ecovio resin.
An emerging market for novamont materials is biodegradable tableware, which can be composted with other organics. Facco said the tableware has started in Europe and other places that have passed regulations restricting the use of disposable plastics.
As more environment driven growth is expected, new Asian PBAT participants are entering the market. In Korea, LG Chemical is building a PBAT plant with an annual output of 50000 tons, which will open in 2024 as part of the $2.2 billion sustainable investment plan of Ruishan city. Sk geo centric (formerly known as SK global chemistry) and Kolon industries are cooperating to build a 50000 ton PBAT plant in Seoul. Kolon industries, a nylon and polyester manufacturer, provides production technology, while SK provides raw materials.
PBAT in the Chinese market is the most popular. Okchem, a Chinese chemical distributor, predicts that China’s PBAT production will rise from 150000 tons in 2020 to about 400000 tons in 2022.
Some Chinese enterprises are increasing their investment in PBAT. Hengli Petrochemical’s new biodegradable material project with an annual output of 450000 tons, with a total investment of 1.8 billion yuan, is located in Hengli (Changxing Island, Dalian) Industrial Park. Using independently developed process technology and formula, relying on the raw materials and supporting advantages of the industrial park, it mainly constructs two major projects: 150000 T / a PBS biodegradable plastics and 300000 t / a PBAT biodegradable plastics.
Verbruggen believes that there are many driving forces for investment. First, all types of biopolymers have recently experienced an increase in demand. The supply is tight, so the prices of PBAT and PLA are very high.
In addition, Verbruggen said that the Chinese government has been promoting China’s “great development” in bioplastics. Earlier this year, the Chinese government passed a law banning the use of non degradable shopping bags, straws and tableware.
Verbruggen said that the PBAT market is attractive to Chinese chemical manufacturers. This technology is not complicated, especially for companies with experience in polyester.
In contrast, polylactic acid is capital intensive. Before manufacturing this polymer, the company needs to ferment lactic acid from an adequate sugar source. Verbruggen pointed out that China has a “sugar deficit” and needs to import carbohydrates. “China is not necessarily a good place to build a lot of capacity,” he said.
Existing PBDE manufacturers have been keeping up with new players in Asia. In 2018, novamont completed a project to transform a PET plant in patrica, Italy, to produce degradable polyester. The project doubled the output of biodegradable polyester to 100000 tons per year.
In 2016, novamont opened a plant to produce butanediol from sugar using the fermentation technology developed by genomatica. The plant with an annual output of 30000 tons is located in Italy and is the only similar plant in the world.
According to facco, the new Asian PBAT manufacturers may produce a limited number of commercial polymer grades for large-scale applications. “It’s not complicated.” He said. In contrast, novamont will maintain its strategy of serving the professional market. “This is where we have some knowledge and are good for the market,” he said
BASF is responding to the trend of PBAT construction in Asia and participating in the construction of a new factory in China. The company licensed its PBAT technology to Tongcheng Xincai, a Chinese company, which plans to build a production plant with a capacity of 60000 tons / year in Shanghai by 2022.
Auffermann said: “with the upcoming new laws and regulations guiding the application of bioplastic materials in packaging, mulching and bags, it is expected that the positive market development will continue. The new plant will enable BASF to meet the growing demand in the region locally.”
In other words, BASF, which started producing PBAT 25 years ago, is now keeping up with the upsurge of new business because this polymer is becoming a mainstream material.