Materials Innovative
Materials Innovative partnership approach for PLA production PURAC from Gorinchem, The Netherlands, a pioneer in the field of lactic acid and lactide, team up with Sulzer Chemtech and other plastics industry-partners to offer a unique approach that lowers the entry barrier and development time for the production of PLA. Purac has been producing lactic acid and derivatives for a variety of applications for more than 70 years. “It is the innovative capabilities that enable us to offer products in a very high purity so that our qualities have set the standards” says Ruud Reichert, Business Manager of Purac. Today Purac is the market leader with over 65% market share in lactic acid. In addition, Purac has been producing lactide and PLA for bio-medical applications for 18 years. These PLA types stand out due to their high molecular weight, controlled microstructure, crystallinity and the high purity, resulting in superior mechanical and thermal properties, as Ruud points out. PLA production partnership About two years ago, Purac decided to make a major shift in the company’s strategy to extend the portfolio from lactic acid into D- and L-lactides for the production of PLA for industrial use. This should make it easier for potential customers to produce their own PLA. Lactides are cyclic lactic acid dimers (ring-molecules consisting of two lactic acid molecules), or better PLA monomers, which can be polymerized to PLA by ring-opening-polymerization. Purac’s process for lactide production allows to keep racemization low1 and therefore the amount of mesolactide formed in the process low. “Compared to the process of direct polycondensation of lactic acid to PLA, this intermediate step via lactide allows us to create significantly higher quality of PLA,” explains Hans van der Pol, Purac’s Marketing Manager. Knowing about the PLA-quality and the high purity of L and D lactides 1 customers started to ask if Purac could supply a process to make PLA from their lactide. The fit of technologies from the Swiss company Sulzer Chemtech with the Purac concepts promted both companies to start a partnership for PLA technology development based on Purac lactides. One of the drivers was the proven static mixer technology of Sulzer Chemtech. Based on this technology and the experience with lactide, the two companies together developed a new cost effective process. 18 bioplastics MAGAZINE [01/09] Vol. 4
Materials SULZER “The process consists of two steps:” says Hans van der Pol, “the polymerization and the devolatilization, where residual monomers are removed from the polymer. The Sulzer Chemtech’s system offers a very mild process with a good temperature control and a very efficient high vacuum devolatilization process. “The process allows for flexibility in the end-product architecture and allows for high molecular weight, controllable polydispersity and a low color,“ as Hans points out. “This allows our partners the flexibility to produce relatively pure and high quality PLLA and PDLA with superior physical properties, or amorphous grades of PLA.” Unique business model “Due to its strong technology position in lactic acid production and processing, it is a logical step for Purac to extend its position one step further in the value-chain, thereby facilitating polymers and plastics producers to make the step into bio-plastics production. Because the economy of scale effect of lactide production is much higher than the scale effect of the polymerization, polymer producers can invest in smaller plants. Step by step integration as the market grows allows for a phased approach and reduced risks.” says Ruud Reichert. In order to be able to offer a complete solution for polymerization to its lactide customers, Purac and Sulzer Chemtech in close collaboration have developed a polymerization process that works uniquely with Purac lactides. “By combining these Lactides in new and creative ways, the improvement of the PLA heat-stability through stereocomplexation concepts– one of its key issues – can become a reality,” Hans van der Pol says. “Purac’s Innovation center has recently demonstrated the ability to produce cups with a heat-stability of over 100°C by injection moulding using less than 5% of PDLA.” PLA production partners are ideally companies that are already active in the field of polymerization, compounding and processing of plastic materials. Based on the use of lactides from Purac, clients can licence the polymerization process from Sulzer Chemtech Hans Keist, General Manager Sales EMA, Sulzer Chemtech adds: “This business model creates something new with a high user value. Especially because the entry barrier into the PLA market for smaller producers of plastics has come down. We received a lot of interest from potential PLA producers.” PLA Quality Within the framework of this new business model, customers can obtain the equipment, raw materials and know-how to produce high quality PLA in different grades for different applications. “Most PLA grades that are currently available on the market are what we call amorphous types (A-PLA), says Hans van der Pol. “These grades have relatively high amounts of random D-lactic acid units in the chains and their HDT is relatively low.” High temperature PLA A better PLA grade that can be produced with almost 100% pure L(+) lactic acid (PLLA with less than 2 % D(-)) shows a melting point of about 180°C. “If we now produce pure PLLA chains and pure PDLA chains and eventually can combine these to stereo-block- Lactide and PLA technogogy PURAC The total PLA solution scPLA Stereo-block PLA PLLA PLA A-PLA sc-PLA High pure PLA Lactides Stereo-complex Technology PLA Process Technology D-Lactic Unit PLA is actually a family of (co-)polymers of D- and L-lactic units % D 14 12 10 8 6 4 2 0 2 Coating film Injection moulding Fiber Bottle Fiberfill Fiber PLA grades and applications Plant design Polymerization technology L-Lactic Unit PLA Producers crystalline 230°C 200°C 180°C 130°C amorphous No T m increasing T m 2.5 3 3.5 4 4.5 5 Relative viscosity Foam Thermoforming Pharma Biax film bioplastics MAGAZINE [01/09] Vol. 4 19
