Davis-Standard Technical Expertise at NPE/ANTEC
March 18, 2009 - (Pawcatuck, Conn.)--Davis-Standard, LLC will be well represented in the technical arena during NPE with two ANTEC paper presentations and results from an in-house extruder efficiency study. The papers, outlined below, are entitled "An Extrusion Study: Examination of the Improved Processing Characteristics of a PLA Modified Blend" and "Single Screw Extrusion of Bio-based and Biodegradable Poly (Hydroxyl Butanoic Acid) Copolymers." The Extruder Energy Efficiency study, currently underway at Davis-Standard's lab is aimed at improving the energy efficiency of single screw extruder platforms. The studies examine different extruder drive and motor systems, comparing the performance to gearless alternatives using AC torque motor technology. New barrel heater/cooler configurations are also being tested to determine the most efficient configurations for specific applications. The results will be available at NPE.
Paper #1: "An Extrusion Study: Examination of the Improved Processing Characteristics of a PLA Impact Modified Blend"
This paper, written by Dr. Jason Baird and John Christiano of Davis-Standard and Barry Morris of DuPont, investigates the processing characteristics of PLA (polylactic acid) with and without the impact modifier (IM) Biomax®Strong. PLA is a biorenewable and compostable polymer derived from corn. It is most commonly used for sheet and thermoformed applications, but is becoming more viable for packaging applications due to its clarity. In some cases it has replaced PET and PS in transparent bottles and bags, and has also been converted into films. The only downside is that PLA is challenging to process because of its stiff and brittle physical properties.
Additives such as Biomax® Strong from DuPont have been introduced to make PLA more conducive to processing. Biomax is a petroleum-based ethylene acrylate copolymer
that is compatible with PLA. It can be blended directly with PLA in the feed hopper of a sheet line and has proven to significantly improve toughness without substantially decreasing
transparency. Previous studies have also shown a reduction in extruder drive power, lower melt
temperature and lower extruder head pressure as well as improved energy efficiency.
The study outlined in this paper investigates the mechanisms behind the reduction in extruder drive torque requirements when processing Impact-Modified Blends (IMBs) as well as the quantifiable energy savings. Among the several conclusions presented, adding 2% IM to PLA resulted in a net energy savings ranging from 21.5% at 50 RPM to 16% at 125 RPM.
Paper #2: "Single Screw Extrusion of Bio-based and Biodegradable Poly (Hydroxy Butanoic Acid) Copolymers"
Coauthored by Dr. Jason Baird and John Christiano of Davis-Standard, and Rajendra K. Krishnaswamy of Metabolix, Inc., this paper investigates the single screw extrusion characteristics of PHB copolymers, including screw design recommendations, for stable processing and optimal performance. Process stability, output rate, melt temperature, melt pressure and molecular weight retention were examined as a function of screw type, process temperature settings and screw rpm. All research was done on 63.5mm Davis-Standard 24:1 and 30:1 L/D water-cooled extruders using high-speed data acquisition with dual thermocouples.
The presence of thermoplastic polyesters within bacterial cells has been documented as far back as 1926. The basic polyester isolated and characterized was poly (3-hydroxybutanoic acid) or P(3HB). In 2006, a new company called Metabolix formed a 50-50 joint venture with Archer Daniels Midland (ADM) to commercialize the production of a new family of PHB copolymers under the trade name Mirel(TM). These polymers are made by microbial fermentation of sugars such as corn sugar, cane sugar or vegetable oils. Since P(3HB) is stored by bacteria for eventual breakdown and consumption, these polyesters are biodegradable in a variety of environments. Mirel(TM) polymers and their products are known to biodegrade in soil, home compost, and industrial compost sites as well as in fresh water and sea water environments.
The research revealed that when proper screw designs and appropriate temperature profiles were used, the extrusion characteristics of PHB copolymers are similar to those of metallocene-based polyethylene. A few of the findings using smooth-bore feed sections include a preference for a "reverse" temperature profile (higher temperature settings early in the extruder followed by continuous lowering of the temperature); the use of barrier screws in lieu of standard metering screws to improve stability; and shorter L/D extruders for better molecular weight and preservation. In general, the specific output rate for PHB copolymers was also similar to polyethylene extrusion.
For more detailed information about these papers and the findings before NPE/ANTEC, contact John Christiano at jchristiano@davis-standard.com.
CONTACT
Luann Kupka
Marketing & Sales Administration Manager
Extrusion Systems
860-599-6262
