Friday 3 November 2023

Bio-Polyamides - Part 5: Performance Review of Short- and Long-Chain Aliphatic Homo- and Copolymer Bio-Polyamides

Bio-Polyamides Part 5: performance review. 

Hello and welcome to the fifth part of our Bio-Polyamide series. 

Check out Part 1, Part 2, Part 3, and Part 4 too.

In this post we discuss how to differentiate the performance of Bio-Polyamides in order to support you in your next polymer material selection project

A brief re-cap of Bio-Polyamides

In general we can distinguish between short- and long-chain aliphatic homo- and copolymer Polyamides. The term bio-based covers bio-based, biomass balanced or recycled content. 

PA 5.6 is the main Bio-Polyamide among the short-chain Polyamides and the pentamethylene diamine needed can be derived from biomass or sugar. 

Bio-PA 6 uses starch or sugar as base feedstock and over a fermentation process, caprolactam is obtained. Bio-PA 6 can be also mass-balanced and therefore used as a drop-in solution for replacing fossil based PA 6 allowing to reduce the carbon footprint from 6.7 CO2 eq/kg. to 4.52 kg CO2 eq/kg. 

For aliphatic long-chain homo- and copolymer Bio-Polyamides, castor oil is used to make sebacic acid. In case of PA 6.10 and PA 11, sebacic acid represents the 10 share of PA 6.10. In the case of PA 10.10, the first 10 is based on decamethylene diamine (DMDA) and the second 10 is again from sebacic acid. Obtaining DMDA is achieved by nitrile synthesis of sebacic acid. Standard Polyamides such as PA 6.6 and PA 12 can be replaced with such bio-based materials. 

Table 1 summarises the differences. 

Table 1: Overview differences in chemical structure of Bio-Polyamides [1].

Bio-Polyamide Monomer 1 Monomer 2 Raw material Bio-based carbon content (%)
Polyamide 6 (PA 6) ε-Caprolactam (mass-balanced) ε-Caprolactam (mass-balanced) Tall oil Mass-balanced
Polyamide 6.10 (PA 6.10) Hexamethylendiamine Sebacic acid (bio-feedstock) Castor oil 62 %
Polyamide 5.6 (PA 5.6) Pentamethylendiamine (bio-feedstock) Adipic acid Corn 41 %
Polyamide 11 (PA 11) 11-Aminoundecaoic acid (bio-feedstock) 11-Aminoundecaoic acid (bio-feedstock) Castor oil 92 %

Performance differentiation of Bio-Polyamides
Key chemical element of Polyamides is the amide group which facilitates internal hydrogen bonds between the different chains. Short-chain Polyamides have more amide linkages compared to the long-chain Polyamides and therefore outperform them in terms of thermal and mechanical properties. Downsides of the many amide links is the higher water uptake capability of short-chain Polyamides. The chemical and hydrolysis resistance of long-chain Polyamides is inherently better, combined with lower water uptake. There are many applications where hydrolysis resistance, combined with chemical resistance are more important than thermal and mechanical properties. 

Comparing mid to long chain bio-based Polyamides (PA 6.10, PA 10.10, PA 10.12, and PA 11) to fossil based short chain Polyamides (PA 6, PA 6.6), an outperformance in low water uptake and chemical resistance can be seen (Table 2). Furthermore, since bio-based Polyamides are shorter compared to their long chain fossil based peers such as PA 12, their mechanical strength and heat resistance is better than PA 12. 

Table 2: Performance overview of Bio-Polyamides [4].

Bio-Polyamide Bio-sourcing (% of C-Atom) GWP (kg CO2eq/kg) Glass transition temperature Tg (°C) Tensile strength (MPa) Tensile Modulus (MPa) Water adsorption (%)
Polyamide 6.10 (PA 6.10) 63 4.6 48 61 2100 2.9
Polyamide 10.10 (PA 10.10) 100 4 37 54 1800 1.8
Polyamide 10.12 (PA 10.12) 45 5.2 49 40 1400 1.6
Polyamide 11 (PA 11) 100 4.2 42 34 1100 1.9
Polyamide 10T (PA 10T) 50 6.9 125 73 2700 3
Polyamide 12 (PA 12) 0 6.9 138 45 1400 1.5
Polyamide 6 (PA 6) 0 9.1 47 80 3000 10.5

Amorphous (transparent) bio-based long-chain Polyamides
So far we discussed short- and long chain bio-based Polyamides classified as semi-crystalline. Apart from that, there are transparent long chain Bio-Polyamides based on PA 11 chemistry too. They can be an alternative to PMMA, PC, and PSU. In terms of properties, they offer higher environment stress crack resistance, chemical resistance, and fatigue resistance compared to PC and PMMA [7]. The perecentage of bio-based raw material ranges betwen 45% (Rilsan G850 Rnew; Tg = 150°C) and 62% (Rilsan G820 Rnew; Tg = 105°C) [7].

DMA of short- and long-chain aliphatic Polyamides
Another way to assess performance is to compare the elastic modulus E’ obtained by DMA of short- and long-chain aliphatic Polyamides. Figure 1 shows the elastic modulus E’ (always unfilled and DAm) of PA 6, PA 6.6, PA 12 and PA 6.12 (all fossil based). It can be seen that PA 6 and PA 6.6 are outperforming PA 6.12 and PA 12. PA 6.12 performs between PA 12 and PA 6 and can be a good compromise between thermal, mechanical and water uptake properties. 

Figure 1: elastic modulus E’ obtained by DMA of short- and long-chain aliphatic Polyamides [6].

Altogether we can state that in terms of performance, bio-based Polyamides can be placed between short-chain and long-chain fossil based Polyamides. Depending on the application requirements the bio-based version serves as a drop in solution (f.e. mass-balance PA 6), or is inferior or superior to the fossil-based peer. 

Check out Part 1Part 2Part 3, and Part 4 too.

Thanks for reading and #findoutaboutplastics!


Herwig Juster

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[4] Bio-based plastics materials and applications by Stephan Kabasci 
[6] Dynamic Mechanical Analysis for Plastics Engineering by Sepe, M.P. 

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