Materials O O O H O H
Materials O O O H O H PBS production The energy-saving, resource-efficient production of PBS using the 2-reactor process Uhde Inventa-Fischer, based in Berlin, Germany and Domat/Ems, Switzerland, can look back on over 50 years of history serving the polymer industry. During this time more than 400 plants for the production of polyesters such as PET and PBT, as well as polyamides like PA 6 and PA 6.6, have been successfully built and commissioned worldwide. Years of experience and intensive research and development work have enabled the company to launch and successfully establish a multitude of innovative technologies and concepts on the market. As well as technologies based on the processing of monomers obtained from fossil raw materials, Uhde Inventa-Fischer has greatly extended its commitment to the development of processes for producing biopolymers and has expanded its product portfolio to include the PLAneo ® polylactic acid technology and the process for producing polybutylene succinate (PBS). The PBS here is purely aliphatic polyester created from the polycondensation of succinic acid and butanediol. PBS is usually produced in a two-stage process. In the first stage the succinic acid is esterified with an excess of butanediol with the water removed. The second stage comprises the polycondensation of the esterification product with the butanediol removed (see Figure 1). Production of succinic acid and butanediol from renewable resources Even as recently as just a few years ago succinic acid was produced exclusively by petrochemical means. Due to the fact that succinic acid is found as an intermediate in the metabolic chain of a variety of organisms such as bacteria or yeast, however, the potential for biochemical production was identified early on and research into this aspect was promoted across the world. Today many companies are already producing succinic acid from renewable resources (see recent issues of bioplastics MAGAZINE). Furthermore, intensive research is being carried out on processes which enable the production of butanediol on the basis of renewable resources such as, for example, the hydrogenation of biobased succinic acid. 2-reactor technology – for the continuous production of ultra-high-quality PBS granulate While developing a continuous process for the production of PBS a series of important outline conditions had to be taken into consideration. Based on a variety of laboratory Figure 1: 2-stage PBS production process 2 step reaction: A) Esterification of succinic acid with butanediol: O H O O O H + 2 H O O H H O O O + 2 H 2 O succinc acid butanediol B) Polycondensation of bis-hydroxybutylenesuccinate H O O O H O O O O bis-hydroxybutylenesuccinate - approx. 170 – 200°C, mole ratio approx. ca. 1.1 – 2.0 BDO/SAC O O n O H +(n-1) O H O H bis-hydroxybutylenesuccinate PBS butanediol - approx. 200 – 240°C - approx. 0.1 – 1 mbar 24 bioplastics MAGAZINE [05/12] Vol. 7
Materials Table 1: Comparison of the properties of PBS with polypropylene and polyethylene PBS PP PE (LDPE / HDPE) By Christopher Hess Vice President Research and Development Uhde Inventa-Fischer Berlin, Germany Heat Distortion temperature (HDT-B) °C 97 145 88 - 110 Melting temperature °C 115 - 118 164 108 - 130 Glass transition temperature °C -32 +5 -120 Crystallization temperature °C 75 120 80 - 104 Tensile strength at break MPa 57 44 35 - 39 Elongation at break % 700 800 400 - 650 Crystallinity % 35 - 45 56 49 - 69 Density g/cm³ 1.26 0.90 0.92 - 0.95 Data source: Biodegradable Plastic, Product Data, SHOWA HIGHPOLYMER CO.. LTD., 2009 tests, the most important parameters for the PBS process, e.g. the mole ratio of succinic acid to butanediol, the optimum quantity, appropriate type and ideal catalyst feed point, were set out first. Moreover, the ideal residence times during the individual process stages as well as the required temperature and pressure conditions had to be defined. The results that were achieved showed that the 2R process, which was developed and patented by Uhde Inventa-Fischer and includes both the ESPREE ® and DISCAGE ® reactors, was perfectly suited for the production of PBS. With this process the succinic acid can react and the polymer can be produced at very low temperatures and low thermal loads. High surface renewal rates mean that the chain can be quickly and gently built up to high molar masses (see Figure 2). Following technical modifications to the 2-reactor pilot plant at Uhde Inventa-Fischer, PBS granulate is being successfully produced at a capacity of around 40 kg/h. The material produced is of a very high quality and therefore ideally suited for commercial use. This was borne out in a multitude of tests which demonstrated that the PBS granulate produced on the 2-reactor plant, or even compounds made from it, were perfect for processing in various applications. Thanks to its high degree of flexibility, low energy and raw material consumption, and the low quantity of by-products formed, the 2R process is the ideal choice for producing costeffective, high-quality polyester. With the new continuous PBS technology Uhde Inventa-Fischer is gearing up its plans to establish other bio-based materials on the market. Impressive material qualities are what make PBS stand out The thermal and mechanical properties of PBS are very similar to those of polyolefins such as polyethylene (PE) and polypropylene (PP) (see Table 1). PBS can be easily processed on standard machinery into films, extrusions and injection-moulded parts. A major advantage of PBS, in addition to its good mechanical properties, is primarily its biodegradability, making it the ideal choice of material to be processed into films for use in agriculture, as well as into food packaging or biodegradable hygiene products. What‘s more, PBS is perfect for processing into compounds or blends with PLA, among other materials. The properties of PLA materials can be customized and modified, for example if greater elasticity is required. www.uhde-inventa-fischer.com Figure 2: 2-stage PBS production process ESPREE ® Reactor DISCAGE ® HV Reactor PBS Succinc acid + Butanediol bioplastics MAGAZINE [05/12] Vol. 7 25
