Tuesday 28 September 2021

Bio-Based Polyamides – Part 1: PA 5.6 and 5T (Chemical Structure, Production, Properties, Applications, Value Proposition)

Hello and welcome to this three part series on bio-based polyamides. Since biopolymers are among the fastest growing segment in the polymer industry it is worth having a closer look at selected new polymers, such as the PA 5.6. In the first part we will discuss some definitions and then turn the focus towards Polyamide 5.6 and 5T. In part two we have a look at bio-based PA 6.6 and in the third part onto bio-based high performance polyamides.

Definitions and some basics

In this training video I review the chemistry of Polyamide 6 and Polyamide 6.6, discuss the properties and applications of Polyamides and look at their global demand and producers.

In general, Polyamides are semi-crystalline condensation polymers with repeating amide (–CO–NH–) links in their backbone. The number after the prefix ‘PA’ results from the number of carbon atoms between the amide groups. Furthermore, there are Monadic (AB) and Dyadic (AABB) Polyamides. AB-Polyamides have a single repeating lactam with an amine reactive group and as a ‘B’ component a carboxylic acid group. AABB-Polyamides are created by the reaction of diamine and a diacid. For them, the first number after the prefix ‘PA’ is the diamine and the second number describes the diacid. Now back to our bio-based Polyamides

Chemical structure and production of bio-based PA 5.6

Pentamethylene diamine, which is needed for PA 5.6, can be made from biomass or sugar. This is enabled by using microorganisms and in 2013 the company Cathay Industrial Biotech was able to increase the efficiency of amino acid decarboxylase by 100 times during the biological fermentation processes. As an enabler, a gene engineering technique was applied. This can be considered as the breakthrough for industrial up-scale of bio-sourced pentamethylene diamine (commercial name: C-BIO N5). Condensation reaction of the green diamine with a diacid (petrol based or bio-sourced) will lead to a full or partially bio-sourced Polyamide 5.6 (commercial name: Terryl™), depending if the diacid is bio-based too. Cathay claims that 8% less diamine is needed with C-Bio N5.

Cathay and Toray too hold patents on Polyamide PA5T. In general, the melt temperature of 5T is lower compared to PA6T and glass transition temperature of 5T is 141°C and therefore slightly higher (Tg 6T = 138 °C) which results in an improved thermal stability. Due to the high amide group concentration of PA 5.6 and PA5T, water absorption is higher compared to PA6T and PA 6.6.

Properties of PA 5.6 compared to PA 6.6 and PA 6

In the table below major thermal and mechanical properties of PA 5.6, in comparison to PA 6 and PA 6.6 are shown. The comparison indicates that PA 5.6 is more similar to PA 6.6 than to PA6.

Table 1: Property Comparison of Petrol-Based vs. Bio-Based Polyamides

Processing and applications

Processing of bio-based PA 5.6 can be done via the melt fiber spinning route for yarns and textiles as well as injection moulding for engineering parts. Since some internal H and O sites are free (compared to PA 6.6 where all internal H and O sites are bound), an easier dyeing is achieved. Furthermore, the higher moisture absorbance increased the comfort of wearing. Injection moulding compounds reinforced with glass fiber, enter different industries such as automotive, electrical, and industrial.

Environment, Health, Safety and Value Proposition

The bio organism fermentation approach described in the first section represents a safer route to produce monomers and polymers due to lower temperature, low pressure and much less toxic raw materials as well as by-products. This in turn makes the whole process more environmentally friendly, reduces the carbon footprint and also energy requirements. The value proposition of bio-based plastics in general is that by switching the monomer sourcing base from petrol to bio-based plant feedstock an  material with intrinsically zero carbon footprint is obtained. The obtained polymers are not necessarily biodegradable and the optimal end-of-life option (for example circular economy approach) needs to be further developed. 

Also, PA5X (X=6, 10, 12, 13, 16, 18) and PA56T are all already commercially available for global market applications which allows them to be the tomorrow's choice to cover sustainable, renewable and environmental demands.

In this post I discuss the difference between bio-based content vs. bio-based carbon content and in this post helpful standards for composting of biodegradable polymers. In the second part we discuss bio-based Polyamide 6.6 – stay tuned!

Thank you for reading and #findoutaboutplastics



#materialselection #polymerengineering #biobased

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[1] Bio-Based Plastics Materials and Applications, S. Kabasci;

[2] TERRYL™ bio-based nylon, P. Caswell, Cathay Industrial Biotech

[3] Progress in semi crystalline heat-resistant polyamides, C. Zhang

[4] https://matmatch.com/learn/material/biopolymers?utm_content=175746192&utm_medium=social&utm_source=linkedin&hss_channel=lcp-21389968

[5] https://matmatch.com/learn/property/difference-between-biodegradable-compostable-and-degradable?utm_content=176494659&utm_medium=social&utm_source=linkedin&hss_channel=lcp-21389968

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