Evaluating the properties and performance of Susterra 1,3-propanediol and Biosuccinium sustainable succinic acid in TPU applications (2013)

Susterra® Propanediol (PDO) and BiosucciniumTM sustainable succinic acid (SA) have been evaluated as potential alternatives for 1,4-butanediol (BDO) and adipic acid (AA) in polyester polyols for thermoplastic polyurethanes (TPU). BiosucciniumTM and Susterra® are unique 100% bio-based offerings from their respective suppliers, Reverdia and DuPont Tate & Lyle Bio Products. The use of BiosucciniumTM and Susterra® makes it possible to yield a final polyester polyol and polyurethane product with a substantial renewable content (up to 100 % and 70 % respectively) and with an improved sustainability characteristic. We found that Susterra® reduces greenhouse gas emissions by more than 56%; BiosucciniumTM has a 90 % carbon footprint reduction potential compared to the conventional short chain petrobased saturated diacid that is mainly used in polyester polyols and polyurethanes. The work presented here is intended to be a reference for a technical evaluation of use of these biobased raw materials in a straightforward standard formulation of polyester polyol and thermoplastic polyurethane. No attempt was made to optimize or to improve the products. PDOSA and BDOSA polyols were synthesized without any problems. Properties are within expectations of standard PDOAA type of polyols. However, the BDOSA polyol exhibited a higher melt temperature – ~100-110°C vs. 46°C and 65°C for PDOSA and BDOSA respectively – which leads to a higher viscosity and requires higher temperatures in the processing of the polyol. Reduction of the melt temperature is possible by adjusting the formulation, e.g. by using a mixture of BDO and ethylene glycol. TPUs were produced via a prepolymer and one shot method at 20-30 % hard segment concentration. BDOSA TPU could only be produced via a one shot method because BDOSA prepolymers could not be processed in available lab equipment. PDOSA TPU is relatively soft and elastomeric at the chosen hard segment concentration. BDOSA TPU is very hard caused by the crystalline morphology of the soft block. That finding is in line with previous work by Sonnenschein et al. and Theunissen et al., who also showed that at higher hard segment concentrations BDOSA TPUs have a hardness more similar to BDOAA TPUs of similar formulation. In general the PDOSA and BDOSA TPUs exhibit very good heat and abrasion resistance. The resilience of these TPUs is low but can be altered somewhat by selection of chain extenders. Both TPUs also showed a very good solvent and moisture resistance. This was a first evaluation of properties of polyurethanes based on BiosucciniumTM and Susterra® using formulations optimized for adipic acid and 1,4-butanediol. The next step in any application will be to improve and optimize the performance portfolio of the polyol and TPU. Suggestions are to consider the evaluation of other types of chain extenders (such as neopentyl glycol, dipropylene glycol or a mixture of PDO and BDO), use of copolymer polyols (mixtures of adipic and succinic acid, or BDO and ethylene glycol) and use of lower molecular weight (e.g. 1000 g/mol) polyester polyols.