Biobased PLA yarns with high mechanical properties
The production volume of biobased polymers increases year after year. In the product group of biobased polymers, polylactic acid or PLA offers the best application perspectives to the textile industry in the medium term. Its increasing implementation goes hand in hand with both adapted polymer formulations for specific applications and adjusted processing conditions.
Since petrol-based polymers have been perfected over several decennia to suit the most divergent applications, developments in biobased end products are needed to equal the properties of e.g. PP or PA products. In the meantime, Centexbel has already defined an adapted set of extrusion conditions and PLA grades resulting in yarns with similar mechanical properties as e.g. PP yarns.
The figure below summarises the mechanical properties of PLA yarns (strength and elongation at break) that have been produced on Centexbel’s pilot extrusion line. PLA grades and settings that were the original reference, show a maximum strength of about 26 cN/tex. From 25 cN/tex onward, the elongation at break was limited to less than 20%, due to the higher draw ratio.
The newly defined settings result in significantly stronger yarns (up to 38 cN/tex) and the possibility to set a higher elongation at break (up to 35%). Both the grades by Natureworks and by Corbion are suited to this purpose.
By means of an adapted process setup it is even possible to obtain strengths of more than 50 cN/tex, introducing PLA yarns in the range of high tenacity PET yarns. The high strength is not limited to a specific PLA grade. However, to obtain this strength, a very specific extrusion process needs to be used that is not available in most Belgian fibre extrusion companies.
The static shrinkage of PLA yarns has also been reported as being rather high. Adapted process settings can limit this feature. A higher temperature of the stabilisation roller (around 135-150°C) is an important factor. Centexbel succeeded in limiting the static shrinkage (measured after pre-treatment at 100°C) to 4.5% . In the Spun Eco Yarn project, we will study this further to obtain a still lower shrinkage percentage.
Related research projects:
Contact: Raf Van Olmen