From Science & Research
From Science & Research Bio-Plastics and Bio-Composites for Household Appliances Fig. 5: BIONA TM products by Efbe GmbH Müller, K.; Reußmann, T.; Lützkendorf, R. Thüringisches Institut für Textil- und Kunststoff- Forschung e.V. (Thuringian Institute for Textile and Plastics Research), Rudolstadt, Germany Heinze, O.; Heyder, J.; Kämpf, B. Efbe GmbH, Bad Blankenburg, Germany While the biodegradable properties of some bio-plastics are the main argument for their use in packaging, more recently bio-plastics have become interesting for use in durable products such as in cars or as housings for electrical appliances. There are already some products in the electronic entertainment area (e.g. MP3 players, Walkman ® , cell phones) in the market [1, 2]. There is however so far not much expert knowledge for electrical household appliances. For that reason the Efbe GmbH in conjunction with the Thüringisches Institut für Textil- und Kunststoff-Forschung e.V. (TITK) has researched the suitability of different bio-plastics for the production of housings for household appliances. Requirements for the Use in Household Appliances The demands placed on materials that are to be used in household appliances are very different from those placed on packaging materials. Barrier properties or biodegradability in this case are of secondary interest. Thermal and chemical durability, long-term behaviour and flammability are the important criteria (table 1). The materials and appliances have to meet the requirements of DIN EN 60335. Food contact Performance Temperature Glow-wire characteristics Specifics Hair dryer No 50-60 °C 550 °C - Water kettle Yes > 100 °C 850 °C Contact with boiling water Coffee maker Yes > 100 °C 850 °C Table 1: Material Requirements for the use in household appliances Especially critical are the demands on the materials for appliances such as water kettles or coffee makers. Hot runner moulds are frequently used in the production of the components for these appliances, limiting the number of usable bio-plastics. Material Choice and Technical Implementation Fig. 4: Sample housing made of a bio-composite In the meantime a multitude of materials are available in the marketplace, and from these diverse material categories various bio-polymers were chosen. Important criteria were the smallest possible percentage of nonrenewable additives, the standard specification and the state of development 38 bioplastics MAGAZINE [02/10] Vol. 5
From Science & Research of the materials (sufficient material bases/capacity available) as well as the price. Based on these criteria the following materials were included in the research: • PLA-based plastics (PLA1 and PLA2) • Plastics based on Cellulose (Cell1 and Cell2) • Plastics made of Polyhydroxyalkanoates (PHA1) In addition to the plastics available on the market, biocomposites (BC1 and BC2) made of PLA and different natural fibres were experimentally produced and tested, based on a granulate technology developed at TITK. To better judge the results a standard polypropylene (PP) was used in the research for comparison purposes. The different materials were tested for the usual material parameters (MFI, glass temperature, melt temperature, melt rheological behaviour) and afterwards processed on a standard injection-moulding machine type Allrounder 520C (Arburg Co.). Subsequently tests were made to determine the mechanical and thermal properties, the fire hazard and processing shrinkage. Tensile Modulus in N/mm² PP PLA1 Tensile Modulus PLA2 Cell1 no break Cell2 Impact Strenght PHA1 BC1 BC2 Figure 1: Tensile E-Modulus and impact strength of bio-polymers and bio-composites 100 Impact Strength in kJ/m² Processing and Characteristics In the changeover from petrochemical to bio-based plastics adjustments to the processing parameters have to be made. Usually the lower processing temperatures of bio-polymers prove to be advantageous, but a disadvantage is in longer cycle times due to longer cooling times. Another factor to be taken into account is the close proximity of the melt and decomposition temperatures, which means that destruction of the polymer may occur during processing. Hence shear and temperature stress have to be adjusted accordingly. Depending on the type of polymer used the various degrees of stiffness (tensile strength test according to DIN EN ISO 527) are approximately those of PP or higher (figure 1). The materials with a particularly high E-modulus however show low notched impact strength (Charpy notched impact strength test according to DIN EN ISO 179). Beside the mechanical properties of a material, for the use in household appliances heat resistance and fire hazard or flammability are of particular interest. For that reason the heat deflection temperatures (HDT A) according to DIN EN ISO 75/A, the Vicat Temperature according to DIN EN ISO 306/B as well as the glow wire flammability index (GWFI) according to IEC 60695-2-12 were determined. The HDT and Vicat values may also be seen as borderline values for long duration usage temperatures. This demonstrated that some of the bio-plastics are only marginally usable for household appliances (compare figure 2 and table 1). For instance, only the PHA based material fulfilled the thermal demands of coffee makers and water kettles. However the fire behaviour would need to be improved, for instance through appropriate flame retardant additives (figure 3). In contrast, PLA2 shows a very high GWFI value but is not usable for coffee makers because of its low heat resistance. Temperature in °C GWFI in °C 0 PP PLA1 Tensile Modulus PLA2 Cell1 Cell2 Impact Strenght PHA1 Figure 2: Heat resistance of bio-polymers and bio-composites PP PLA1 PLA2 Cell1 Figure 3: GWFI of bio-polymers and bio-composites no test Cell2 PHA1 BC1 BC1 BC2 BC2 bioplastics MAGAZINE [02/10] Vol. 5 39
