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Issue 01/2018

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Automotive Natural fibre

Automotive Natural fibre organic sheets Heating via IR Thermoforming Fig. 1: New and quick processing method for the manufacture of natural fibre reinforced thermoplastic parts Input: NFPP oranic sheet Natural fibre reinforced polymers have been used for decades in particular in the European automotive industry for semi-structural applications like door panels and roof stiffenings [1]. Currently, a European vehicle comprises four to five kg natural or wood fibres on average, whereas long bast fibres like flax and hemp are the most significant due to their low density in conjunction with high stiffness [2, 3]. New trends in the automotive industry In recent years, the usage of thermoplastic based natural fibre reinforced polymers appears to be a general trend, in particular in combination with polypropylene [2]. At first sight, this trend seems to be surprising. The material combination is not new and has never been considered as optimum due to different polarities of fibres and matrix and, thus, insufficient fibre-matrix-adhesion. Moreover, the processing of natural fibre reinforced polypropylene (NFPP) to finished parts is done by using a multi-step compression moulding process with at least two presses and consequently, tremendous floor space and investment. Base material has always been a hybrid nonwoven made of natural fibres and polypropylene melt fibres, which only melt and impregnate the nonwoven by using high temperature and pressure in a contact heating press. Only at a second press, the material is formed to finished parts. However, new trend is the application of already impregnated and pre-compacted NFPP organic sheets. These allow significant processing optimisation by using well-known, highly efficient thermoforming processes derived from manufacturing glass or carbon fibre reinforced composites [4, 5]. NFPP organic sheets are first heated contactless by infrared radiation up to the melting temperature of NFPP and, afterwards, thermoformed by cold pressing to finished parts, Fig. 1. Core processing time takes about one minute. To establish this new process chain, special NFPP organic sheets were developed by J.H. Ziegler GmbH (Achern, Germany), a supplier to the automotive industry. Those sheets are especially suitable for thermoforming processes due to their good impregnation quality and precompaction up to densities around 0.6 g/cm³. A selective infrared heating method has been developed at the Institute for Composite Materials GmbH (Kaiserslautern, Germany), which allows for selective heating of the polymer matrix without thermal load of temperature sensitive natural fibres [6]. This method is based on the selection of a heater temperature which results in the emission of wavelengths maximally absorbed by the polymer. Higher odour due to double thermal load of natural fibres? Obviously, by applying the new processing method, natural fibres are exposed to a double thermal load: first at the manufacture of organic sheets (e.g. in a double belt press) and then at the actual thermoforming process shown in Fig. 1. Previous research on emission and odour of natural fibre composites are limited to a single thermal exposure of natural fibres in a conventional process. Therefore, it is important to investigate whether a double thermal exposure of natural fibres has an impact on olfactory perception and emission values of the final product. For this investigation a natural fibre nonwoven material HACOloft 6106 from J.H. Ziegler with an area weight of 1700 g/m² was used which has a fibre ratio of 50 wt-%. It was pre-compacted to organic sheets (2.5 mm thick, density 0.6 g/cm³) in a hydraulic press at 200 °C (first thermal load). These organic sheets were then heated via infrared ration up to 200 °C (second thermal load) and afterwards thermoformed in a cold press at 25 °C. As reference material, the same NFPP nonwovens from the same batch with the same area weight were heated, impregnated and compacted in a contact heating press up to 200 °C and afterwards thermoformed in a cold press at 25 °C. Hence, the reference material is exposed only to a single thermal load. Processing parameters are shown in Table 1. 18 bioplastics MAGAZINE [01/18] Vol. 13

Automotive Fog value (max. 520µg/g ) Odour grade (max. 4) 100 80 60 40 20 0 Fig. 2: Comparison of odour and emissions of natural fibre reinforced composites exposed to single and double thermal load TVOC (max. 55,8 µgC/ g) Double thermal load (new process) VOC value (max. 193 µg/g) Single thermal load (standard process) All manufactured panels were stored 24 hours after processing, afterwards hermetically packed and examined within the next 48 hours. Odour was investigated according to VDA 270 (variant 3), emissions were tested according to VDA 277 (TVOC) and VDA 278 (VOC and Fog values). Results are shown in Fig. 2 as percentage value of the maximum value for a better comparison. Additionally, maximum numerical values are given with their units. Surprisingly, it can be observed that materials processed with double thermal load have a better odour grade than materials which were exposed to only one thermal load. A reason for this better grade could be the contactless second heating of NFPP organic sheets. This leads to volatilization of odor-forming substances. Also, the sum of total volatile organic compounds (TVOC) is lower for materials with a double thermal load. Only VOC and Fog values are higher for NFPP organic sheets exposed to a double thermal load. This can be attributed to a beginning thermal damage of the material. Conclusion and practical benefit The results of this study indicate that thermoforming NFPP organic sheets offers some opportunities towards optimization of odour perception and reduction of TVOC emissions. However, higher VOC and Fog values must be expected. Depending on the application, a compromise must be found between odour and TVOC as well as VOC and Fog values. Certainly, an optimized organic sheet production (lower first thermal load) offers high potential for reducing both, odour and emission values. Therefore, thermoforming NFPP organic sheets in combination with material selective infrared heating is the basis for a better processing automation of thermoplastic based natural fibre composites. The tests results are a first, but important step towards a higher competitiveness of natural fiber composites compared to glass fiber composites and new areas of application can be established. Material NFPP organic sheet NFPP nonwoven Material thickness By: Jovana Džalto Rhenoflex GmbH Ludwigshafen, Germany Peter Mitschang Institute for Composite Materials GmbH Kaiserslautern, Germany Andreas Wilking J.H. Ziegler Natural Nonwovnes GmbH Lambrecht, Germany Table 1: Parameter for the production of natural fiber reinforced polypropylene First thermal laod in °C Second thermal load in °C Thermoforming temperature in °C 2,5 200 200 25 8 200 – 25 References [1] Bledzki, A.K.; Faruk, O.; Sperver, V.E.: Cars from Bio-Fibres. In: Macromo-lecular Materials and Engineering, Vol. 291, 2006, p. 449-457 [2] Carus, M.: Biocomposites in the Automotive Industry, markets and environ-ment. bio!car – Biobased Materials for Automotive Applications Conference, Stuttgart, 24th-25th September 2015 [3] Carus, M.; Eder, A.; Dammer, L.; Korte, H.; Scholz, L.; Essel, R.; Breitmayer, E.: Wood-Plastic Composteis (WPC) and Natural Fibre Composites (NFC): European and Global Markets 2012 and Future Trends. WPC/NFC Market Study, nova-Institut, Huerth, 2014 [4] Džalto, J.; Medina, L.; Mitschang, P.: Naturfasern sanft erwärmt, Kunststoffe Vol. 10, 2014, p. 194-198 [5] Džalto, J.; Medina, L.; Mitschang, P.: Prozessoptimierung beim Einsatz von Naturfaser-Organoblechen, Lightweight Design Vol. 3, 2014, p. 50- 56 [6] Mitschang, P.; Džalto, J.: Development of an Infrared Heating Method for the Processing of Natural Fiber Reinforced Polypropylene, Processing and Fabrication of Advanced Materials XXV, 22nd-25th January 2017, Auckland, New Zealand | | bioplastics MAGAZINE [01/18] Vol. 13 19

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