PTT yarn extrusion in the Durbio project for Durable Biobased Plastics
Polytrimethylene terephthalate (PTT) is a linear aromatic polyester derived from the polycondensation of 1,3-propanediol (trimethylene glycol, 3G, or PDO) and, either terephthalic acid (PTA), or dimethyl terephthalate (DMT). The trimethylene glycol monomer derives from a renewable route, resulting in a content of renewable carbon in the polymer of 20 to 37 wt%.
The chemical composition is:
Other acronyms for the same polymer are: PTMT (polytrimethylene terephthalate) and PPT (polypropylene terephthalate).
A PTT grade of Dupont (Sorona 3000 NC010) has been evaluated for yarn extrusion. Compared to PET, the PTT has - because of its zigzagged structure in the polymer chain, an intrinsically higher elasticity and maximum elongation.
Table 1: Basic properties of Sorona 3000 NC010
|Melt enthalpy||54 J/g|
|Melt volume index @ 240°C||15.9 cc/10 min|
|Melt volume index @ 250°C||22.7 cc/10 min|
PTT was transformed in BCF yarns on Centexbel’s semi-industrial pilot-line. PTT is a polyester and hence sensible to hydrolysis at heating above the fusion point. Therefore it was dried below 200 ppm.
Yarns were formed with a titre between 48 and 130 tex (15-40dpf). During the extrusion it was observed that the final line speed had to be limited to obtain a good affinity to spinning. The draw ratio could be high, ranging from 2.4 to 4.
The yarns made from the PTT had a tensile strength between 15 and 23 cN/tex.
Because of their chemical structure, these yarns are characterised by a high elongation rate at break: yarns with a tensile strength of 20 cN/tex or more show a elongation rate at break of at least 45%.
Figure 1: (B)CF extrusion line at Centexbel
The hydrolytic stability of the yarns was evaluated by conditioning the yarns in a climate room at 80°C and a relative humidity of 80% during 7 days. The same set-up was used to determine the hydrolytic stability of PLA yarns. The evolution in tensile strength (figure 2) shows that there is no hydrolysis in the polymer matrix. The tensile strength is maintained. Results of the PLA yarns show that in these test conditions, the strength of non-stabilised PLA based yarns is strongly diminished from day 1 onwards, and that the strength has completely disappeared after 3 days. PTT yarns are thus more stable than PLA yarns versus diminished strength by influences from the environment.
Figure 2: Strength and elongation at break after conditioning at 80°C and 80% RH of PTT yarns
PTT based yarns are submitted to limited shrinkage during heating with a maximum of 5% after heating at 100°C during 30 minutes and a maximum of 1% after heating at 60°C during 15 minutes.
However, standard PTT is sensible to ageing under UV-light. After 1000h in the QUV set-up, the strength is diminished to less than 3 cN/tex. A UV stabilizer masterbatch has to be added to the PTT yarns to obtain a high durability.
Subsequently, a colorant masterbatch was added to the polymer matrix during extrusion. The properties of the coloured yarns were similar to the ones of the yarns without the colorant masterbatch. The coloured yarns were submitted to a colour fastness test: radiation with Xenotest 220+ Atlas with a radiation of 42 W/m² @ 300-400 nm at 47°C and 40% RH. The colour fastness proved excellent with a score of 6-7.
Figure 3: Colour fastness of coloured PTT yarns
More information on the results with PBS during filament extrusion can be obtained on demand:
- Report 7 – PTT yarn extrusion
- Report 7 – PTT yarn extrusion - update June 2014
The above mentioned results have been achieved in the frame of the VIS-trajectory DURBIO
, supported by IWT [IWT 110799].