Material Combinations
Material Combinations Starch Blends with Enhanced Performance A process for blending starch with other polymers while retaining the key properties of the host resin is now operating commercially in North America. The first products on the market are ‘hybrids’ of thermoplastic starch (TPS) with petrochemical plastics, but soon to follow will be blends of thermoplastic starch with other biopolymers, such as polylactic acid (PLA) or polyhydroxy alkanoate (PHA). Manufactured by the Bioplastics Division of Teknor Apex Company, the new blends are among the first products in a broad family of compounds tradenamed Terraloy. In 2008, Teknor Apex obtained an exclusive global license for the patented starch blending process, which was developed at Cerestech (Montreal, Canada), a spin-off company of Ecole Polytechnique. The process represents an advance from conventional methods of preparing starch-based bioplastics, which typically involve mixing starch with a plasticizer like glycerol, sorbitol, or a citrate ester. These conventional processes, in the presence of heat and shear, soften the starch, so that it behaves like a thermoplastic, but they also cause breakage in its polymer structure. The destructured starch behaves as a filler, reducing the physical properties of the base polymer. Micrographs of such blends show large starch granules poorly adhered to the host polymer phase. In contrast, the Cerestech process melt-mixes starch with the host polymer during the compounding operation, producing a co-continuous phase of thermoplastic starch (TPS) and the host polymer. Small domains of TPS, approximately 1 to 10 microns, are dispersed in the continuous host polymer phase. Such morphology produces bioplastic compounds with outstanding mechanical properties. Teknor Apex will use this process to produce three bioplastic product ranges: 1) 100% biodegradable or compostable bioplastic compounds; 2) hybrid compounds that contain up to 50% renewable content with petroleum-based resin; and 3) blends with recycled content. Number 2) and 3) are of course not biodegradable. The Terraloy bioplastic compounds introduced so far include: • A Biodegradable grade for blown film or injection molding. This is a blend of TPS and biodegradable copolyester, available with varying levels of TPS. • Polypropylene / TPS blend for injection molding, incorporating 25 to 35 % renewable content in the finished product. • LLDPE or LDPE / TPS blend for blown film with 25 to 35% renewable content in the finished product. • High-impact polystyrene / TPS blend for injection molding. With a TPS content of up to 35% . In addition to these standard products, Teknor Apex develops formulations on a custom basis. The Bioplastics Division also offers non-starch bioplastic compounds under the Terraloy brand. One such compound to be introduced will be a biodegradable compound as a replacement for HDPE in blown film applications such as carrier bags. www.teknorapex.com/division/bioplastics. 22 bioplastics MAGAZINE [02/10] Vol. 5
Materials Biobased Flame Retardant Polymers Injection molded end manufactured using deTerra biobased FR polymers. (Courtesy of Alpar Architectural Products, LLC) For many years specialty polymer compounds have existed that meet various industry standards for flame retardant (FR) performance. These materials include polymers that are inherently flame retardant as well as a variety of common polymers that are combined with FR additives to produce specialty compounds that meet the required flame resistance tests put forth by various industries. However, changes stemming from agency mandates as well as increased focus on environmental stewardship in some industries have driven the need for revised formulations in FR materials to provide more green alternatives. In response to this, Interfacial Solutions, LLC of River Falls, Wisconsin, USA, has developed and introduced the deTerra line of biobased non-halogenated flame retardant products. In development of the new product line of FR compounds, several objectives were reached including 1) a very high biobased content, 2) the use of only non-halogenated flame retardants, 3) improved toughness as compared to common lower cost biopolymers, 4) high FR performance level, and 5) custom formulations to meet the needs of sheet and profile extrusion as well as injection molding. “Our first set of deTerra products are PLA based, but we anticipate future grades to be based on other biopolymers as well” as stated by Jim Howard, New Business Development Manager at Interfacial Solutions. The initial grade of deTerra, targeted for commercial building and construction components, receives a class 1/A rating under UL 723 (ASTM E84-08) Test for Surface Burning Characteristics of Building Materials. This is the highest rating a plastic material can receive under that test. The material’s test results showed a Flame Spread Index (FSI) value of 0.0 and a Smoke Developed Index value of 75. Additional grades of deTerra have been developed that are targeted for injection molded and profile extruded parts requiring a V-0 rating under the UL-94 flame test. These grades have variation in melt flow and impact strength custom designed to meet a variety of end use applications. The material is also easily colorable to match a variety of custom colors. Mechanical properties for the initial deTerra FR grades include approximate values of tensile strength of 41 MPa (6,000 psi), modulus of 3,440 MPa (500,000 psi), elongation of 4.0%, notched izod impact strength of 5.5 kJ/m 2 (1.05 ftlbs/in) and a specific gravity of 1.30. MT www.interfacialsolutions.com bioplastics MAGAZINE [02/10] Vol. 5 23
