Fibers & Textiles
Fibers & Textiles Technical PLA yarns and ropes creep (%) tenacity [mN/tex] 80 75 70 tenacity [mN/tex] type PLA 9210 PLA 9210 PLA 9210LS count [dtex] 1100 2200 1100 breaking tenacity [mN/tex] 360 340 350 elongation at break [%] 37 40 43 TASE 5% [mN/tex] 96 92 110 HAS @ 130 °C, 2 min, 1 mN/tex [%] 9,1 9,2 1,9 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 65 55 50 45 40 35 30 25 20 15 10 5 0 0 1 500 450 400 350 300 250 200 150 100 50 0 PLA multifilament Figure 2 Tenacity of Senbis PLA yarns 05 10 15 20 25 30 35 40 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 time (hour) viscose / jute viscose / cotton natural fibre 3 PLA fibre 1 PLA fibre 2 Commercial product based on PLA tape PP fibre 2 PP fibre 1 elongation [%] Figure 3 Accelerated creep test of PLA twines wet creep (10N/1000 dtex) at 41°C natural fibre 1 natural fibre 2 Senbis PLA 9210GT PLA compound fibre 1 PLA compound fibre 2 Optimized Senbis PLA multifilament Figure 4 Market comparison of horticulture twines regarding tenacity natural fibre PLA PP 0 5 10 15 20 25 30 elongation at break [%] Senbis Polymer Innovations (Emmen, the Netherlands), formerly known as API, is an independent R&D service provider to the plastic industry, which also develops specific applications on their own account utilizing biopolymers. In June 2018 the company started the first commercial scale production of PLA yarns and ropes destined for the horticulture industry. This a milestone after years of development and field tests. The yarns and ropes are 100% biobased and fully compostable in accordance with the industry standard EN13432. PLA ropes lead to cost reduction for horticulture growers In glass houses (Figure 1), vegetable plants such as tomatoes, bell peppers and cucumbers are supported by twines (ropes). These twines are typically made from polypropylene and lead to high costs for the disposal of plants due to the plastic contamination of the intermingled twine. By utilizing the PLA twines, growers have a sustainable concept that also saves costs as they can compost the plants including the PLA twine. The concept is therefore a perfect example of how biopolymers can be of economic added value next to sustainability. Properties of the PLA yarn The standard type of Senbis PLA yarn is produced in two different counts, 1100f210 and 2200f210. For certain technical yarn applications, such as fabrics, a low shrinkage (LS) yarn is required. Therefore a modified yarn with the commercial name PLA 9210LS is under development. The typical properties of the PLA yarns are shown in the table. Basically higher tenacities of PLA are possible, but more difficult to achieve. Senbis managed to make PLA yarns with higher tenacities with their pilot plant spinning machines but have not upscaled that to a production scale yet, which would require further investments in R&D. In Figure 2 the tensile performance of both the commercially available and the research yarn are shown, which concludes there is still more potential for PLA for technical yarns. Solving creep problems in PLA yarns Senbis concluded that the main challenge for a horticulture twine made from PLA is not reaching a high tenacity but is reducing creep. Creep means that a rope that is subjected to a permanent load will lengthen continuously, up to a point where it will break. This process is taking place at a much lower load than the breaking load as measured on a tensile tester. Polypropylene ropes don’t seem to be strongly affected by creep but PLA surprisingly does so significantly. PLA ropes that have been brought to market earlier have only solved this by 28 bioplastics MAGAZINE [05/18] Vol. 13
Fibers & Textiles making the rope much thicker. Effective, but from an economical point of view unwanted. PLA is most used in packaging and non-wovens, and in these applications creep behaviour does not play a role. As a result it seems that very few people using PLA have been confronted with the creep behaviour. Senbis investigated the physical background of the creep behaviour of PLA, and – more importantly – ways to decrease this behaviour. The standard yarns that are used for the twines for horticulture are produced by a split film process. This means that a film is produced by an extrusion process equipped with a slit. Subsequently the film is drawn and cut into small tapes. These tapes are twisted into a rope. Senbis works with a different route, by spinning multifilament yarn. In this case the polymer is extruded through a plate with holes, and subsequently drawn and wound on bobbins. The advantages of this process are the possibilities to control the physical structure of the resulting yarn to a large extent by using the right settings of the spinning machine. In combination with the right polymer recipe this results in a twine with a reduced creep behaviour. Figure 3 shows the results of an accelerated creep test to help draw conclusions. Market comparison on horticulture twine performance Senbis has compared the mechanical performance of several twines supplied to the horticulture industry, which is visualized in the Figure 4. It concludes that the breaking tenacity of Senbis PLA twine is on a comparable level with conventional PP twines and performs much better than other PLA or natural fibre based twines on the market. Final remark Senbis is interested in finding other applications for which these PLA yarns can be used. Higher sales volumes will help to create a more continuous and economically attractive production, which Senbis executes in cooperation with its neighbour Morssinkhof Sustainable Plastics (MSP). MSP bought the former Diolen/AkzoNobel production spinning machinery to produce yarns of recycled PET. The start of the PLA production can be seen as the second successful spin-off production activity of the R&D company Senbis. In 2014 it started a production company for monofilaments for FDM 3D printing, which was sold in 2017 to BASF 3D printing solutions. Other biopolymer filament applications are already far in the development process and are expected to be launched in 2019. www.senbis.com Figure 1: Tomato hook’ presented in glass house and ... By: Bas Krins, Technical Director and Gerard Nijhoving, Managing Director Senbis Polymer Innovations Emmen, The Netherlands ... by Gerard Nijhoving at the spinning machine bioplastics MAGAZINE [05/18] Vol. 13 29
