Flame Retardancy
of Thermoplastic Foams from Biopolymers
—
Robert Schmidt1*, Carl-Christoph Höhne1, Valeria Berner2, Jannik Hallstein2, Elke Metzsch-Zilligen2, Rudolf Pfaendner2, Christoph Mack1
1 Fraunhofer-Institute for Chemical Technology ICT, Joseph-von-Fraunhofer Str. 7, 76327 Pfinztal, Germany
2 Fraunhofer-Institute for Structural Durability and System Reliability LBF, Schloßgartenstr. 6, 64289 Darmstadt, Germany
all Fraunhofer Cluster Circular Plastics Economy CCPE, https://ccpe.fraunhofer.de
*robert.schmidt@ict.fraunhofer.de
1 nova-Institute, European Bioplastics - Bioplastics Market Data; Available from: https://www.european-bioplastics.org/market/.
2 M. Nofar, C. B. Park, Polylactide foams: Fundamentals, manufacturing, and applications. Oxford: Elsevier Ltd; William Andrew; 2018.
3 S. Pilla, S. G. Kim, G. K. Auer, S. Gong, C. B. Park, Polym. Eng. Sci. 2009, 49(8), 1653-60.
4 D. Vadas, T. Igricz, J. Sarazin, S. Bourbigot, G. Marosi, K. Bocz, Polym. Degrad. Stab., 2018, 153, 100-8.
5 C.-C. Höhne, R. Schmidt, V. Berner, E. Metzsch-Zilligen, E. Westphal, R. Pfaendner, C. Mack, J. Appl. Pol. Sci. 2021, 138, 50856.
Steps of the Bead Forming Process.
Bead Foam Preparation
Polylactic acid (PLA), with a global production in 2019 of about 0.29 million tons [1], is currently the commercially most well-developed, inexpensive and readily available biopolymer on the market.[2] In the field of thermoplastic foams,
PLA is able to substitute petro-based polymers like polystyrene (PS), polyethylene terephthalate (PET) and polyethylene (PE), for example in the packaging
industry. [2-4]
Bead foam technologies used to produce products with complex three-
dimensional foam geometry are well-established, for example for expanded polystyrene (EPS). However, the processing of PLA by bead foam technologies is still a challenge. The bead foaming process includes three main steps:
Conclusions
In this study [5], all investigated PLA bead foams show self-extinguishing effects in the DIN 4102-1 B2 test without any addition of a flame retardant. According to the observed LOI results and DIN 4102-1 B2 test the flame retardancy
increases with increasing semi-crystallinity of the used PLA types.
Further information: www.ccpe.fraunhofer.de
Extrusion Pre-foaming Sintering
Table 1 PLA types of this study
# Type Producer MFI (210 °C @2.16 kg)
PLA 1 4032D NatureWorks LLC 7 g / 10 min
PLA 2 4060D NatureWorks LLC 8.5 g / 10 min
PLA 3 6302D NatureWorks LLC 15-20 g / 10 min
PLA 4 7032D NatureWorks LLC 7 g / 10 min
PLA 5 8052D NatureWorks LLC 14 g / 10 min
PLA 6 BF2004 Synbra 35.1 g / 10 min
PLA 7 BF2005 Synbra 31.9 g / 10 min
PLA 8 Luminy L175 Total Corbion 8 g / 10 min
PLA 9 Luminy LX175 Total Corbion 6 g / 10 min
Flammability Characterization
The flammability of a polymeric product is decisive for the application area in which the product is applied. However, little is known about the flammability of PLA particle foam products. The thermal properties of the nine PLA granules are shown in Table 2.
Table 2 Thermal properties of the PLA granulates
# Tg / °C mp / °C Xc / %
1st heating
Xc / %
2nd heating Tonset / °C
PLA 1 61 171 42.8 2.4 340
PLA 2 56 amorphous - - 340
PLA 3 57 amorphous - - 338
PLA 4 61 170 42.6 1.8 338
PLA 5 60 155 34.6 1.3 338
PLA 6 59 155 34.0 0.3 344
PLA 7 59 151 25.8 0.0 345
PLA 8 60 180 51.4 2.4 343
PLA 9 60 158 37.3 0.0 344
For five of the PLA types, bead foam plates with a lower density (26-40 g/L) and a higher density (48-81 g/L) as well as bead foams containing 1.5 wt.-% of the flame retardant Flamestab® NOR116 from BASF were produced. The flame
retardant properties were evaluated using the DIN 4102-1 B2 test and the LOI test according to DIN EN ISO 4589-2:
3
