Synthesis of Bio-based Polytrimethylene Terephthalate

Polytrimethylene terephthalate (PTT) is a newly commercialized aromatic polyester generally made by the melt polycondensation of 1,3-propanediol and terephthalic acid (figure 1). Bio-based polytrimethylene terephthalate is produced from the renewable sources such as sugarcane or corn rather than being derived from the petrochemical feedstocks. Bio-based polytrimethylene terephthalate has better environmental credentials as compared to the petroleum based polytrimethylene terephthalates because it does not generate carbon emissions, greenhouse gases or air pollutants during its production process.

Synthesis of Bio-based Polytrimethylene Terephthalate

There are two main methods for the preparation of bio-based polytrimethylene terephthalate: transesterification and direct esterification, as shown in figure 2. The difference between the two methods mainly lies in the first step. As for former method, the oligomer intermediate is obtained by using the transesterification of dimethyl terephthalate (DMT) and with 1,3-propanediol. While in direct esterification, terephthalic acid (TPA) reacts with 1,3-propanediol to form the oligomer intermediate. Polytrimethylene terephthalate is then synthesized by polycondensation reaction of the oligomer intermediate. Due to the high cost of transesterification reactions (both the material and the production process), the direct esterification is absolutely dominant in industrial production. As a result, the bio-based terephthalic acid and 1,3-propanediol are of particular importance.

• Synthesis of bio-based terephthalic acid

Bio-based terephthalic acid can be synthetized through different methods: the iso-butanol method, the muconic acid method, the limonene method or the furfural method. For instance, furfural is an ideal biomass resource, as it is traditionally produced from cellulosic and waste biomass such as corncob, corn stock and rice hull. Another advantage of using furfural is that it can be readily converted to other useful chemicals due to its high reactivity. 

• Synthesis of bio-based 1,3-propanediol

The first description of the fermentation of glycerol to 1,3-propanediol dates back to the end of the 19th century. Essentially, there are two enzymatic activities directly involved in the conversion of glycerol to 1,3-propanediol: glycerol dehydratase and 1,3-propanediol oxidoreductase. 

Applications

Because of its lightweight and degradability, bio-based polyethylene terephthalate is used in the packaging of food products, soft drinks, alcoholic beverages, cosmetics, pharmaceutical products, and edible oils. Besides, it can be used in textile, automotive, film and coating, consumer goods, industrial electrical & electronics, etc.