Fibers & Textiles International engineering companies, such as Uhde Inventa-Fischer, offer PLA polymerization technologies, which are independent from LA (lactic acid) and PLA producers. Integrated LA-PLA production plants with capacities up to 100,000 tonnes per year (see Fig. 4) can be constructed within a few years after contract award. This is definitely no growth limiting factor. However, the price of textile grade PLA is still higher compared to PET and cotton. Nevertheless, it is to be expected that the price will come down to a similar level as a result of upcoming world-scale production plants and increasing competition between producers. PLA can be processed on existing spinning equipment for PET staple fibers, filaments and spunbond nonwovens, therefore no new developments or technologies are required. Melt spinning technology of PET has achieved a high standard with respect to product quality, process efficiency, operability and automation. Modifications related to the lower PLA operating temperature are almost negligible. Dyeing of fibers and textiles made from PLA presents a major challenge. The PET dispersion dyeing process can also be used for PLA. However, because of the limited hydrolysis resistance in aqueous dispersions, dyeing temperatures must not exceed 100°C. Still a certain amount of shrinkage has to be taken into account as well as a loss of molecular mass which entails a loss of tenacity and elongation. Also problems such as low dye saturation and exhaustion need to be solved. If the PLA fiber market is to grow, it is worthwhile to look for other dyeing methods which involve a milder treatment of PLA fibers. Spin dyeing (addition of pigment dyes in the melt spinning process) can be used for large volume PLA applications, such as carpet yarn. Yet, for small lots this method does not offer the required flexibility. A very recent method is dyeing with supercritical carbon dioxide. This process operates at moderate temperatures and – even more importantly – without consuming water and generating waste water. Pressurized carbon dioxide promotes dyestuff migration into the fiber. A broad range of dispersion dyes available on the market have been tested successfully with PET (Fig. 5 [2]). Tests conducted with PLA have only covered a limited number of dyestuffs [3] so far, but showed the method‘s potential and the need for optimization. Polymer production, spinning and dyeing are just a few processing steps on the long way to PLA textiles. Many more steps are required to obtain a finished textile product, such as mixing with fibers of other origin, texturizing, weaving, knitting and sewing. Fig. 4 Uhde Inventa-Fischer’s Integrated LA-PLA-Process Source: Uhde Inventa-Fischer GmbH, Germany, 2013 Biomass for NH 3 composting or biogas H 2 SO 4 (NH 4 ) 2 SO 4 for fertiliser production Glucose/ sucrose water fermentation centrifuge Ultrafiltration Salt/acidseparation Polishing Dewatering complex N source Thermophilic bacteria PLA waste Hydrolysis Lactic Acid Demonomerisation/ stabilisation Ring opening polymerisation Lactide purification Lactide formation Precondensation PLA pellets 14 bioplastics MAGAZINE [05/13] Vol. 8
Fibers & Textiles The textile industry is extremely segmented. Almost every processing step is performed by a different company. Therefore, very few textile producers have established test production of a finished textile article made from PLA. The entire production chain will have to be optimized, if weaknesses of PLA textiles are detected. They have to be improved by cooperation of all stakeholders involved up to the polymer producer. Fig. 5 Dyed Polyester Fabrics Source: Uhde High Pressure Technologies GmbH, Germany, 2013 For example, insufficient durability of a textile article might be caused by partial polymer degradation during the dyeing process. Therefore, improvements have to be made either by optimizing the dyeing process or by changing the polymer recipe. Up to now, PLA has played a limited role in the textile market, because of relatively high prices and some processing sensitivity of PLA in the textile production chain. However, solutions already exist to overcome these deficiencies and various efforts are ongoing to meet these challenges. Given the attractive properties of PLA and its huge growth potential, the combined know-how of technology companies, producers, processing equipment manufacturers as well as downstream converters will make PLA a very attractive polymer for the textile market. www.uhde-inventa-fischer.com [1] Viju, S.; Thilagavathi, G; Chem. Fibers Int. 2/2009 [2] Courtesy of Uhde High Pressure Technology 2013 [3] Bach, E.; Knittel, D.; Schollmeyer, E; Color. Technol. 122, 252-258 2006 COUNTDOWN TO THE NEW DIMENSION K 2013 / 16-23 October 2013 Düsseldorf / Germany / Hall 09, Booth C05 CHOOSE THE NUMBER ONE. bioplastics MAGAZINE [05/13] Vol. 8 15
