Thermoplastische vezels zijn synthetische (man-made) vezels, gemaakt door het extruderen van polymeren doorheen de gaten van een spinplaat, waardoor een filament wordt gevormd. Smeltspinnen is hierbij het vaakst toegepaste procedé. Centexbel-VKC's onderzoek is gericht op:
- hernieuwbare, biogebaseerde, duurzame alternatieven voor oliegebaseerde thermoplastics
- verbeteren van de eigenschappen van biomaterialen om die van de conventionele materialen te evenaren en indien mogelijk te overschrijden
- functionaliseren van thermoplastische vezels (chemisch, fysisch, via nano-technologie)
- creatie van biogebaseerde prepregs en high-end vezelversterkte of zelfversterkte composieten die beantwoorden aan de strengste mechanische vereisten
- implementatie van nieuwe technologieën (zoals Additive Manufacturing) in traditionele productieprocessen
- recyclage en gesloten kringloop, Life Cycle Analyse
Om de intrinsieke eigenschappen van de nieuwe types biopolymeren, zoals PLA (Polymelkzuur), PHA (PolyHydroxyAlkanoates), PHB (PolyHydroxyButerate), PBS (Poly-butyleensuccinaat), TPS (ThermoPlastic Starches) en PEF (PolyEthyleneFuranoat) ten volle te exploiteren en te optimaliseren, zoeken we naar de geschikte verwerkingscondities en additieven.
Enkele resultaten van ons onderzoek:
Agrotextiles from renewable resources with tailored biodegradability
"BIOAGROTEX” was one of the first large-scale projects on biopolymers, coordinated by Centexbel. The project aimed at developing fully biobased agrotextiles, exploiting the specific properties of biopolymers such as PLA to be composted after its normal lifetime. To those agrotextiles requiring a guaranteed lifetime of several years, but preferentially have to be composted after reaching its end-of-life, this polymer can offer an attractive solution. In the project we succeeded in defining appropriate grades and processing conditions for production of fibres, monofilaments and tapes, which fulfilled the requirements of the specific applications.
Based on the positive results, several industrial partners launched specific new biobased Agrotextiles into the market; amongst others:
• DURACOVER® – Bonar Technical fabrics: Woven groundcovers from PLA tapes.
• HORTAFLEX® – DS Textiles: needlefelt groundcovers from PLA fibre
• FILBIO®PLA –Texinov: Knitted insect screens from PLA monofil
The products have been successfully implemented in the market and a market growth is expected in those countries where public procurement rules define the use of biodegradable or more ecologic, sustainable products, especially in the case of large public projects (railways, highways, public green space, … ).
Biobased PLA yarns with high mechanical properties
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. To that purpose, Centexbel has defined an adapted set of extrusion conditions and PLA grades resulting in yarns with similar mechanical properties as e.g. PP yarns.
The figure on the left 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%.
Recycled biopolymers with good mechanical properties
Melt recycling, in which waste fraction is applied in a new extrusion step is the most obvious recycling option. Centexbel has proved that it is possible to mix PLA-based monofilaments after pelletizing in a concentration of minimum 10% with virgin PLA without the need of adapting the extrusion conditions. The slightly lower viscosity of the PLA recyclate has no influence on the processing. There is no influence on the mechanical properties of the yarns either.
Even when the PLA recyclate belongs to a different PLA grade than the matrix to which it is added, the mechanical properties are similar to the ones of yarns without recyclates.
The practical application of the test results has been demonstrated by dosing several biopolymer-based textiles in a concentration of 10% during a second extrusion step. The effects on the mechanical properties of the new fibres were minimal: similar resistance to tear (at most -10%) and a similar elongation at break.
Centexbel also demonstrated the valorisation of these textile products as recycled matter for injection moulded products.