Basics Table 1:
Basics Table 1: Properties of PLA Types Type T m T g σ n E b PLLA 160-180 °C 55-65 °C 45-55 Mpa 3-5 % PL / DLA 55 °C 50-200 % sc PLA 220-230 °C 60 °C 3-5 % sbc PLA 185-195 °C 55 °C 5-10 % T m - melting temperature T g - glass transition temperature E b - elongation at break σ n - tensile strength at break lactide with small contents of meso-lactide a co-polymer is formed. Increasing meso-lactide leads to decreasing crystallinity. With more than 10-15% meso-lactide the polymer is amorphous. By varying the amount of meso-lactide the properties of the polymer can be adjusted for specific applications. One of the reasons for the limited consumption of PLA up to now is the low thermal resistance. The Tg (glass transition temperature) is about 55°C depending on comonomer content to a small extent (Table 1). Methods of improving thermal resistance are to prepare a stereo complex (sc PLA) or a stereo-block copolymer (sbc PLA). Melting point and heat distortion temperature (HDT) will increase significantly. Improving the thermal properties can extend the applications of PLA considerably in the future. There are also various additives that improve the properties of PLA with respect to impact strength, melt viscosity, HDT, crystallinity etc. Perspective PLA combines all prerequisites of sustainability with important properties of well established polymers. Applications have already been found in many niches of packaging and textile products. Within those niches fast growth of consumption is expected to continue depending on the availability of PLA polymer. High research activity is dedicated to overcome typical weaknesses of PLA – low impact strength and low heat distortion temperature – and to develop tailor-made PLA grades in order to serve special applications. These activities will conquer new niches for PLA and will help to increase PLA consumption at high velocity. Other growth factors are the availability and prices of crude oil, agricultural products and production plants and technology. Within the foreseeable future PLA will not become a commodity polymer like PE, PP, PS – this is considered to be an advantage both for PLA producers and converters. However, this could change in the long term. www.thyssenkrupp.com *: The article is based on a contribution to a book, submitted for publication in T. Haas, M. Kircher, T. Köhler, G. Wich, U. Schörken, R. Hagen, White Biotechnology, in R. Höfer, Ed., Sustainable solutions for modern economies, The Royal Society of Chemistry, Cambridge, forthcoming 2009, ISBN 9781847559050. 40 bioplastics MAGAZINE [01/09] Vol. 4
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