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Automotive Biodegradable

Automotive Biodegradable PLA/PC Copolymers for Automotive Applications Article contributed by Maurizio Penco, Arifur Rahman University of Brescia Steven Verstichel, Bruno De Wilde Organic Waste Systems Patrizia Cinelli, Andrea Lazzeri University of Pisa Figure 3: Micrographs showing morphology of pure PLA/PC (20wt%PC) copolymer (a) and fibre (30wt%) containing composites (b). (a) (b) With environmentally-friendly products becoming the norm, research and development of biopolymers, in addition to their versatile applications in durables - particularly automotives, invoke high expectations from the industry as well as consumers. However, we are yet to witness a scenario where the production of biopolymers is appropriate to the demand and their prices are competitive with the petrochemical-based polymers. For instance, the application of Poly(lactic acid) PLA and other biopolymers in the automotive sector (especially interiors) requires the products to meet the high quality standards of mechanical strength, a low degree of degradation by sunlight, resistance to abrasion, a high durability and a high thermal resistance. Although PLA has certain limitations new materials and modifying agents are expanding both its reach and applications. Efforts are focused on boosting mechanical and thermal properties so biopolymers can be effective alternatives to less costly commodity materials. Especially for automotive application a new biodegradable copolymer has recently been patented: The copolymer is based on Poly(lactic acid) and Polycarbonate (PC) and has been developed within the Forbioplast project (No. KBBE- 212239), funded by the 7th Framework Programme of the European Commission. The objective of the development was to find a material for automotive applications that has not only high thermal stability and high durability but is also biodegradable. PLA is a well-known biodegradable polymer that can be produced from renewable resources such as corn. The other component, PC, is a lightweight, high-performance material that possesses a unique balance of toughness, dimensional stability, optical clarity, high heat resistance and excellent electrical resistance. The new material, having a segmented copolymer structure (PLA-b-PC) has been prepared by reactive melt mixing in the presence of a specific catalyst. The presence of a segmented copolymer structure has been observed by analysing the molar mass distribution in sizeexclusion chromatography (Fig. 1). A significant maintenance of mechanical strength across the glass transition temperature (T g ) is an important concern 20 bioplastics MAGAZINE [01/11] Vol. 6

Automotive Figure 1: Molar mass distribution of PLA, PC and the copolymer. for automotive materials. The PLA/PC copolymer indeed showed good maintenance (in terms of storage modulus) at high temperatures (Fig. 2a). Moreover, the addition of wood fibres to the PLA/PC copolymer significantly improved the mechanical properties (Fig. 2b). It is important to note here that, among the different range of compositions, the 20 wt% PC containing PLA/PC copolymer exhibited significant improvement in overall mechanical properties and 30 wt% fibre was incorporated into PLA/PC copolymer to further improve its mechanical properties. The morphology analysis (Fig. 3) shows a homogenous structure in the PLA/PC copolymer and good interfacial adhesion between PLA/PC copolymer matrix and wood fibres. dw/cLog (M) 1.8 PC (Brabender 250°C) PLA (Brabender 250°C) 1.6 PCcoPLA (50/50) PLAcoPLA (50/50) 5% Cat 1.2 0.9 0.6 0.3 0.0 1.0E+03 1.0E+04 1.0E+05 1.0E+06 Molecular Weight (g/mol) The PLA/PC copolymer has a multi-phase structure with two glassy phases and one crystalline phase. Thermal analysis reveals a higher melting point (170 °C) for the PLA/ PC copolymer in comparison with pure PLA (150 °C). The presence of a second high T g glassy phase increases the heat distortion resistance in comparison with standard PLA. The decrease of storage modulus above the glass transition temperature of PLA is compensated by the PC segment in the copolymer. Due to the presence of shorter PLA segments with respect to the molar mass it is expected that the copolymer produces high crystallization rates. The crystallization kinetics of the PLA/PC copolymer is in fact much faster than for PLA (copolymer: half time of crystallization t 1/2 = 5.5 min; PLA: t 1/2 = 105 min). This can play a significant role in the processing of this new material. Storage Modulus (GPa) 3,5 3 2,5 2 1,5 1 0,5 0 Figure 2: Variation in storage modulus for different PC content (wt%) in PLA/PC copolymer (a) and improved modulus for fibre containing PLA/PC copolymer (20wt% of PC) (b). (a) 0 10 20 30 40 45 50 60 PC Content (%) Modulus at 60°C modulus at room temperature One of the most interesting characteristics of the new PLA/ PC copolymer is its degradability in composting facilities. Preliminary results for PLA80/PC20 copolymer and PLA80/ PC20 with additional 20% fibre show complete degradation after 110 days of controlled composting (ISO 14855). After a phase lag of 20 days (typical for PLA) the biodegradation began and reached an absolute biodegradation at a level of 96.6% and 92.7%, respectively (Fig. 4). According to the European standard EN 13432 on compostability of packaging, a material fulfils the requirement on biodegradation when the percentage of biodegradation is at least 90% in total or 90% of the maximum degradation of a suitable reference item (e.g. cellulose) after a plateau has been reached for both reference and test item within a test duration of 180 days. Since pure PC is not biodegradable, copolymer blending with PLA might provide a useful method for biodegrading postconsumer recycled PC, when, after several reuses, material degradation prevents further recycling. The new class of biodegradable PLA/PC copolymer blends, originally developed for lightweight components in automotive applications and construction materials, may - as a result of the findings - be used in a wide range of other applications such as cell phones, portable electronics, medical devices, sporting goods, toys and multiple use packaging, to name just a few. Storage Modulus (GPa) Biodegradation (%) 6 5 4 3 2 1 0 110 100 90 80 70 60 50 40 30 20 10 0 (b) 0 20 30 40 50 60 70 Fibre Content (wt%) Figure 4: Evolution of biodegradation of PLA80/PC20 and PLA80/PC20 reinforced with additional 20% fibre, in comparison with pure cellulose and lignocellulose fibres. Cellulose PLA/PC (80/20) PLA/PC (80/20) + 20% fibres Fibre -10 0 10 20 30 40 50 60 70 80 90 100 110 Time (days) bioplastics MAGAZINE [01/11] Vol. 6 21

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