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bioplasticsMAGAZINE_1306

People Consumer

People Consumer Electronics Bioplastics for high-end consumer electronics By: Dr. Chung-Jen (Robin) Wu Chairman Supla Material Technology Co. Ltd. Tainan City, Taiwan olylactic acid (PLA) is a thermoplastic aliphatic polyester derived from renewable resources (mainly starch or sugar, currently). One of the attractive characteristics of the PLA is the nature of crystallinity. With a melting point above 150°C, it opens a wide potential on various applications. However, there are factors affecting the application of PLA. One is the rather low glass transition temperature (Tg) of around 60°C. Another is its low rate of crystallization. These two factors result in a low heat deflection temperature around Tg, which limits PLA’s applications. Based on above facts, the development of PLA used to being focused under ambient environment or none durable usage, say disposable food containers, bags and so on. But even within these applications, there are some critical limitations still affecting the performance of PLA. For example, a traditional PLA copolymer cup can’t hold hot coffee and temperatures above 70°C will result in deformation of products. These factors limit the use of PLA in durable and high-end application. There are many approaches to solve the shortage of PLA mentioned above. To enhance the heat resistance fillers can be added. In the case of semi crystalline plastics, adding nucleating agents is another approach, however for standard PLA copolymer, which crystallizes at a rather slow rate, such treatment does not bring about a significant improvement in heat resistance. In bioplastics MAGAZINE issue 01/2010, SUPLA announced a novel, heat-resistant PLA. By means of novel recipes and process 38 bioplastics MAGAZINE [06/13] Vol. 8

Consumer Electronics equipment, Supla have developed SUPLA C1001 that has a unique crystallization behavior, which results in a high HDT at around 100°C (HDT B 120 K/h, 0.45 MPa). Furthermore, because not much fillers were added, the density was kept at a level almost equivalent to native PLA. This low-density characteristic results in a higher Melt Flow Rate of 31.9 g/10min (190°C, 2.16 kg), which makes Supla C advantageous over other types of modified PLA in injection molding. Supla C1001 with superior heat resistance is a great product for markets such as food wares, stationery, gifts and toys. Furthermore, for most of the 3C (Computer, Consumer, Communication electronics) housings, a PLA blend with flame retardant is a must. Based on the development of a heat resistant PLA blend with 99% by wt content of PLA (Supla C1001) SUPLA developed a flame retardant PLA blend (Supla C1003) which meets the V0 standards of UL-94 Vertical Burning Test in 1/8”, 1/16” and even 1/32”, while its PLA content is kept as high as 90% by weight and its heat resistance (HDT B) is kept to over 100°C. The flame retardant package in Supla C1003 is halogen free. Therefore, this is the greenest flame retardant PLA blend available (bM issue 05/2010). However, for PLA to be a commercially viable alternative, the injection molding cycle time is of critical importance. The cycle time of standard PLA copolymer blends during injection are too long in comparison with current materials like ABS or PC/ABS blends. Moreover, this low crystallization rate might give rise to another drawback on the dimensional stability. A housing often has several parts to be assembled with limited tolerance. Moreover, a very complicated structure in the injection part arose from the need for compromising the needs of placing many electronic parts and the mechanical strength. Meanwhile, the complicated assembling method itself is a very critical to the PLA materials, since there are many fasteners, and screws locations. To solve the above challenges, the choice of the right PLA base materials will be a very important factor. Due to the chiral nature of lactic acid, there are several forms of PLA: poly-L-lactide (PLLA) is the product resulting from polymerization of L,L-lactide (also known as L-lactide), and PDLA (poly-D-lactide), which is the product resulting from polymerization of D,D-lactide. PLLA and PDLA are considered PLA homopolymers. Most currently commercially available PLA’s are PLA copolymers. A percentage of L,D-Lactide (also known as meso-Lactide) is polymerized together with L,L Lactide. This PLA copolymer has limitations. However, if high purity PLLA and PDLA homopolymers are available, the melting temperature of PLLA can be increased by 40-50 °C and its heat deflection temperature can be increased by physically blending the polymer with PDLA (poly-D-lactide). PDLA and PLLA form a highly regular stereo-complex with increased crystallinity. In this case, PDLA or the resulting stereo-complex acts as a nucleating agent to increase the speed of crystallization. By a closed cooperation with Corbion Purac, Supla are able to produce PLLA and PDLA homopolymers. This gives Supla a great opportunity into durable applications. At Corbion Purac’s booth at the K 2013 (Düsseldorf, Germany), Kuender showed an bioplastics MAGAZINE [06/13] Vol. 8 39

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