Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology in Germany have developed a process for manufacturing high-quality plastics from terpenes, a waste stream of cellulose production.¹ The synthesis of polyamides from terpenes was developed at BioCat – Bio, Electro and Chemocataysis — the Straubing branch of Fraunhofer IGB, under the direction of Professor Volker Sieber.

Terpenes are a renewable resource that is generated in large quantities as a side stream of pulp production as well as in the fruit industry. As a waste stream, the application of terpenes for the production of new bioplastics is not in conflict with the need of food production for humans and animals.

Today, significant amounts of terpenes are not used as a bio-based raw material, but incinerated to aid the energy supply of pulp mills. But because of the complex structure of the terpenes, a much higher value application is desirable.

Researchers expect to be able to manufacture products like coatings, textiles and adhesives from the bio-based polyamides. Up to now, these bio-based plastics have been manufactured only in the laboratory, but the plan is to develop a synthetic route which allows future production on an industrial scale.

Elsewhere, another novel high-performance bio-based polyamide, poly(pentamethylene oxamide), exhibits excellent mechanical, thermal, and water absorption properties, and is suitable for the fabrication of plastic parts for the automobile and electronics industries.

1,5-pentanediamine (also known as cadaverine) is a potential renewable candidate to replace hexamethylenediamine in the production of polyamide (an important polymer in the plastic and textile industries). To date, however, yields of 1,5-pentanediamine have been too low for commercialisation and only recently has cadaverine been produced on a mass scale.

Cadaverine can be used to produce a variety of polyoxamides — a class of polyamides that include the shortest possible diacid link (an oxalyl unit) in their parent chain. These have recently attracted attention because they exhibit high chemical resistance, melting temperature, modulus, and UV light stability, as well as low water absorption and solubility properties. They include:

• poly(pentamethylene succinamide) (PA54)
• poly(pentamethylene hexanediamide) (PA56)
• poly(pentamethylene decanediamide) (PA510)
• poly(pentamethylene eicosanediamide) (PA520)

In particular, it has been shown that PA510 has a low water uptake compared with nylon 6 and 66 (PA6 and PA66). This means that PA510 has good dimensional stability and mechanical properties, and it is well-suited for energy-friendly transportation (because of its low density). It has also been demonstrated that PA56 exhibits good thermal properties and a special crystallisation behaviour.

Despite these attractive engineering properties, polyoxamides have not yet been widely commercialised. Ube Industries Ltd (Japan), however, has recently initiated pilot commercial runs for poly(nonamethylene oxamide) - PA92 - which has been intensely studied for many years and has been shown to have good properties.

Another novel bio-based polyoxamide is poly(pentamethylene oxamide) or PA52. This can be synthesised from dibutyl oxalate and 1,5-pentanediamine with the use of a conventional two-step polymerization technique (pre-condensation in solution and post-condensation in the solid state).

Compared with commercially available polyamides — PA6, PA66 and PA46 — PA52 exhibits a high melting temperature, good mechanical properties, low water absorption, and excellent crystallisation characteristics (see Table 1 below). PA52 is thus well suited for high-temperature, high-performance parts in the automobile and electronics industries. PA52 thus has great potential to compete with and replace fossil-fuel-based polyamides.

Table 1. Summary of the properties of PA52, compared with those of three commercially available polyamides, i.e., PA46,14,15 PA6, and PA6614).4PA46: Poly(tetramethylene adipamide). PA66: Poly(hexamethylene adipamide).

At the 10th International Conference on Bio-based Materials in May 2017, Kado announced it was focusing on the production of novel specialty chemicals by biological techniques and replacing incumbent product by a bio-based equivalent with similar characteristics.