Processing Improved
Processing Improved coextrusion Biopolymer extrusion coating with edge encapsulation increases line speed and reduces coat weight SAM North America uses an EDI ® feedblock from Nordson to more than double the line speed in extrusion coating of PLA and reduce coat weight by 40 % Technologies developed by Sam North America (Phoenix, New York, USA) and Nordson Corporation (Chippewa Falls, Wisconsin, USA) have made it possible to increase throughput and reduce coat weight in the extrusion coating of biopolymers such as PLA by encapsulating the edges of the coating with LDPE. While conventional coextrusion yields two or more materials in horizontal layers, special encapsulating inserts developed by Nordson for its coextrusion feedblock make it possible to extrude additional material along either edge of this horizontal structure. Using this technique, Sam North America has found that encapsulating a PLA coextrusion with edges of LDPE makes it possible to offset deficiencies of PLA – in particular, its low melt strength – that have limited its melt curtain stability, draw-down ratio, line speed, and coat weight. “Using LDPE edge encapsulation on our pilot line, we have achieved line speeds in excess of 366 mpm (metre per minute) (1200 fpm) with PLA, as against less than 183 mpm (600 fpm) with PLA alone,” said Ed Lincoln, V.P. Extrusion Sales of Sam North America. “We have seen coat weight reduced from 16 gsm (gram per square metre) to less than 10 gsm.” The high melt strength of LDPE has helped make this polymer by far the most widely used in extrusion coating. “For processors wishing to replace some portion of their LDPE usage with biopolymers, a main obstacle has been that their lower melt strength causes extreme neck-in and edge instability at desirable line speeds,” said Sam Iuliano, Chief Technologist for Nordson’s EDI extrusion die and feedblock business. “By introducing a higher-melt strength material on each edge of the melt curtain, edge encapsulation minimizes the processing limitations posed by many biopolymers.” Neck-in is the tendency of the polymer web to become narrower as tension is applied when it exits the die. The result is a build-up of material along the edges of the web, or edge bead, that must subsequently be trimmed away as scrap. To ensure that this edge bead consists of the lowestcost polymer in the coextruded structure, Nordson has developed customizable feedblock inserts that introduce flow of the low-cost polymer only at the edges of the structure. The combined materials are then distributed to the final target width in the flow channel or manifold of the die. While the encapsulation inserts can be readily retrofitted into existing EDI feedblocks, Nordson offers new EDI dies equipped with the EPC️ deckle system, which can be adjusted to reduce edge bead formation, and a melt flow system in which the edge encapsulation polymer is introduced in the die rather than in the feedblock. The port for introducing the encapsulation polymer moves in concert with the deckle mechanism. “By introducing the encapsulation polymer at this point in the process, the interface between it and the core structure is more defined and the transition overlap between the encapsulation material and the biopolymer material is reduced,” said Sam Iuliano. “The die limits the formation of edge bead and reduces the amount of edge trim.” Sam North America has also developed coextrusion techniques for encapsulating biopolymer structures with LDPE that permit rapid change-over between conventional and biopolymer coatings. The technology addresses the wide differences in processing properties between the two materials. Andy Christie, managing director of Sam North America, will introduce the technology at the Extrusion 2021 Conference, September 21 – 23 at the Donald E. Stephens Convention Center, Rosemont, Illinois, USA. MT www.sam-na.com | www.nordson.com actual die width extruded film width chill roll Schematic above, with upper die and feedblock halves removed, shows encapsulation achieved with Nordson feedblock insert (circled); schematics below show a new EDI EPC die, with encapsulating polymer introduced in the die rather than in the feedblock 52 bioplastics MAGAZINE [04/21] Vol. 16
Think big, build small Sulzer’s processing technologies enable effective small-scale bioplastic manufacturing Processing T he demand for sustainable bioplastics is booming, offering unique opportunities to manufacturers entering this market. Small-scale facilities are ideal for new players in the industry as they represent low capital investments with quick returns. When a business in China wanted to develop one of the first fully integrated sugar-to- PLA (polylactic acid) plants in the country, Sulzer (Winterthur, Switzerland) delivered a customized project. This allowed the manufacturer to swiftly begin producing 30,000 tonnes of biobased, recyclable, compostable, and biodegradable PLA bioplastic annually. PLA can be obtained from sugar-rich crops, such as corn and cassava. More precisely, these are used to produce lactic acid and raw lactide, which are then purified and polymerized to obtain high-quality plastics. Thanks to its characteristics, the demand for innovative sustainable bioplastics, such as PLA, has skyrocketed in recent years with the global market size expected to register a double-digit compound annual growth rate (CAGR) of 16 % from 2020 to 2027. The expansion of this sector is also shaping manufacturing activities in China, the world’s leading producer of plastic, which is responsible for 31 % of the global production of plastic materials. Businesses interested in manufacturing PLA bioplastics and entering this growing market can benefit from a product with applications in a wide range of industries. To quickly enter this sector, while minimizing any capital risk, smallscale facilities and infrastructures are ideal. Moreover, these can be built closer to where raw materials are sourced, supporting the creation of localized manufacturing and supply centres. When good things come in small … plants! These are some of the reasons why a company interested in building one of the first fully-integrated sugar-to-PLA plants in China took this approach. To quickly create an infrastructure with an annual PLA capacity of 30,000 tonnes, the company selected Sulzer as its partner. With over 25 years of experience in lactic acid and PLA-related processes, Sulzer was responsible for the design, basic engineering packages, supply, commissioning, and start-up. The customer appreciated Sulzer’s ability to provide a comprehensive solution for the purification of crude lactide, polymerization into high-quality PLA and downstream processing. In addition to the creation of a commercial small-scale plant, the producer was interested in setting up a flexible and scalable system that could provide highquality materials at a competitive price for a wide range of downstream applications, including food packaging and textiles. Optimizing capital investments To address these requirements, Sulzer proposed both stickbuilt or skid-mounted, modular, fully-integrated designs. This comprised distillation and crystallization units, static mixer reactors (SMRs) for polymerization as well as degassing (devolatilization) and pelletizing technologies. More precisely, the combination of distillation and crystallization methods allowed the manufacturer to achieve high purity levels while preserving the chemical, physical, and mechanical properties of lactide as well as optimizing energy usage. The use of Sulzer’s SMRs created a highly homogeneous melt to obtain high-quality, consistent PLA polymer products while cutting the volume of waste and off-spec materials. Moreover, as they do not have any moving parts, the SMRs consume less energy and require less maintenance than alternative solutions, considerably reducing operational expenses. The system design also supported the mixing of additives in the melt for pre-compounding PLA prior to the pelletization stage. This further lowered energy utilization and reduced the risk of thermal degradation while limiting the number of processing units on the line, minimizing capital and operational expenses. Sulzer collaborated with MAAG Group (Oberglatt, Switzerland), which provided its specialist, state-of-the-art vacorex ® x6 class extraction gear pump technology for the polymerization and devolatilization stages. In the degassing units, the melt pumps were used to create the necessary pressure to process the melt through the downstream equipment up to the underwater pelletizer. In addition to fulfilling the key system requirements, Maag Group’s technology helped Sulzer and therefore the customer to further reduce energy consumption and carbon dioxide emissions. As a result, the plant could leverage an extremely sustainable setup to produce PLA bioplastic. The power of a leading technology partner In less than two years, Sulzer’s specialized teams were able to complete the entire project from design to the start-up of the crude lactide to PLA and downstream line. One of the main advantages of the partnership with Sulzer reported by the Chinese company was the ability of the process technology specialist to act as a full-service provider and take care of the entire project, allowing the manufacturer to focus on other areas of its business. This streamlined the development of a highly effective fully integrated PLA plant and enabled the company to quickly enter the bioplastic market. While the current setup allows the PLA manufacturer to produce 30,000 tonnes of bioplastic per year, the modular system that was developed by Sulzer can be easily scaled up, supporting future expansion projects. As a result, the bioplastic manufacturer can adapt to future market demands and grow its business effectively as well as sustainably. Details about the Chinese customer were not disclosed. MT www.sulzer.com www.maag.com bioplastics MAGAZINE [04/21] Vol. 16 53
