Injection Moulding
Injection Moulding Injection moulding of PTT Combining the benefits of renewability with processing and performance advantages As the demand for bio-based polymers with renewable materials content, smaller carbon footprint and reduced dependence on fossil fuels continues to grow, the challenge for advanced polymer producers is to offer these environmentally friendly attributes without compromising processing and end-use performance. DuPont took up the challenge in developing a new biobased engineering thermoplastic —Sorona ® EP PTT (poly trimethylene terephthalate) — working closely with plastics processors and parts manufacturers to prove several key processing and finished part benefits versus PBT (polybutylene terephthalate), PET (polyethylene terephthalate) and PC/ ABS (polycarbonate/acrylonitrile butadiene styrene) in developmental and commercial programs. With Sorona EP, DuPont achieved a new combination of advantages in one product – a renewably sourced engineering plastic that can be processed in the same way as PBT and PET, and also offers very low shrinkage and warpage, plus enhanced surface finish, gloss, and scratch resistance in finished parts. The DuPont PTT contains 20% to 37% renewable content made from starch, using proprietary fermentation and chemical processes, resulting in high-performance resins suitable for engineering applications. A DuPont cradle-to-gate study indicates that the bio-based Sorona EP has a smaller carbon footprint than the traditional fossil route used to make the same polymer. Using bio-feedstock makes Sorona EP less dependent on fossil fuels, yet the performance of these products more than competes with conventional PBT, PET and PC/ABS. Renewably sourced Sorona was one of the bio-based polymers independently certified to meet the United States Department of Agriculture (USDA) BioPreferred program standards for biobased content. In addition to replacing petrochemical based ingredients with those made with renewable resources, the DuPont PTT also provides a 30% reduction in energy use and a 63% reduction in carbon dioxide emissions compared to incumbent materials such as nylon 6. Grades and properties Sorona EP is currently available in a selection of grades including unreinforced, medium toughened, and15%, 30% and 45% glass-fiber reinforced grades. Table 1. shows grade properties, and comparison with equivalent glass-reinforced PBT and PET polymers. Toyota chose DuPont Sorona EP for instrument panel vent louvre vanes on the Prius hybrid electric car to ensure scratch resistance and excellent surface appearance Diagram 1: Drying curve of 15% glassreinforced Sorona EP at 120°C Moisture Content (%) 0 0.05 0.10 0.15 0.20 0 1 2 2 2 5 During at 120 °C, -40 °C Dew Point DuPont Sorona 3015G NC010 [Melt Temperature / Residence Time] 10 bioplastics MAGAZINE [03/14] Vol. 9
ISO Sorona 3301 Unreinforces Sorona 3015G PBT-GF15 Sorona 3030G PBT-GF30 PET-GF30 Sorona 2045G Stress at Break, MPa 60* 125 109 165 140 158 180 Strain at Break, % 15 3 3.5 2.5 2.7 2.5 1.6 Tensile Modulus, MPa 2,400 6,500 5,800 11,000 10,000 11,000 16,000 Notched Charpy, kJ/m 2 4 5.5 7 9 11 11 9 Melting Temperature, °C 228 227 225 227 225 252 227 Density, g/cm 3 1.3 1.4 1.4 1.56 1.53 1.56 1.7 Parallel 1.3 0.2 0.4 0.2 0.3 0.2 0.2 Mold Shrinkage, 2 mm, % Normal 1.4 0.7 1.1 0.7 1.1 0.8 0.5 Table 1: Properties of currently available Sorona EP grades, and comparison with equivalent glass-reinforced PBT and PET polymers * Stress at Yield Commercial successes “The end-use advantages of Sorona EP — higher strength and stiffness at elevated temperatures, lower warpage and shrinkage, and improved scratch resistance and surface appearance — are already being seen in successful commercial programs,” said Thomas Werner, Business Development Manager, DuPont Performance Polymers. “These attributes make Sorona EP an excellent choice for many precision molded industrial and consumer products, including automotive parts such as instrument panel air conditioning vent louvers — chosen by Toyota for the Prius — electrical/electronic components like connectors, switches, plugs, mobile phone housings, and for furniture.” In its renewably sourced fiber form, Sorona is already widely used in residential and commercial carpets, apparel and automotive mats and carpets. Mohawk Group, the worlds largest flooring manufacturer, HBC Bulckaert and Godfrey Hirst Carpets, specify the DuPont biopolymer for durability and stain resistance. In automotive, the Toyota SAI ® has ceiling surface skin, sun visor and pillar garnish of Sorona, complementing the car’s eco-friendly design. Processing characteristics and recommendations Material preparation Like PET polyester, pellets of Sorona EP must be dried to a moisture content below 0.02%, using a dehumidifier drier with direct material transfer in a closed hopper, to ensure that optimum mechanical properties are achieved. The dew point of the drier must remain below -20°C. A drying temperature of 120°C is recommended, allowing 4 hours drying for a newly opened bag, and 6-8 hours for a bag that has been opened for more than 1 week. Flow length Sorona EP exhibits good flow properties, allowing parts with long flow paths and narrow wall thicknesses to be molded easily. Good flow also contributes to generating a high surface finish and glossy appearance, even with glass-fiber reinforced grades. Using a standard 1mm thickness spiral flow test, Sorona EP exhibited 20% greater flow than standard PBT, allowing: Diagram 2: Strain at break of Sorona EP as a function of melt temperature and residence time Diagram 3: Recommended cylinder temperature setting as a function of residence time ain at Bre 5 10 15 20 25 0 10 20 250 °C / 6 min 250 °C / 10 min 250 °C / 15 min 270 °C / 6 min 275 °C / 10 min Temperat ture 230 240 250 260 270 280 270 °C 250 °C 235 °C 90 °C 5 min Residence Time Molding Settings [Melt Temperature / Residence Time] Front Center Rear bioplastics MAGAZINE [03/14] Vol. 9 11
