Characterization of Polyhydroxybutyrate Biosynthesized from Crude Glycerol Waste Using Mixed Microbial Consortia Shengjun Hu, 1 Armando Gabriel McDonald, 1 Erik Robert Coats 2 1 Department of Forest, Rangeland and Fire Science, Renewable Materials Program, University of Idaho, Moscow, Idaho 83844-1132 2 Department of Civil Engineering, University of Idaho, Moscow, Idaho 83844-1022 Correspondence to: A. G. McDonald (E-mail: armandm@uidaho.edu) ABSTRACT: This study focused on the characterization of polyhydroxybutyrate (PHB) produced from crude glycerol (CG) using mixed microbial consortia (MMC). PHB recovered from two biomass drying treatments (65  C oven drying and lyophilization) was characterized comparatively along with a commercially sourced PHB (PHB-C). Characterization results showed that oven- drying method caused PHB partial hydrolysis, as indicated by its lower molecular weight (M w ) (PHB-O, 144,000 g mol 1 ), which further affected its physical and chemical properties. Lyophilization helped alleviate PHB hydrolysis during drying process, leading to PHB (PHB-L) of higher M w (309,000 g mol 1 ) and material properties comparable with commercial PHB. Further- more, crystallization and morphological studies showed that PHB-L featured faster crystallization rates and smaller spherulites as compared with PHB-C, probably due to its lower M w . In general, the results from this study suggested that CG-MMC-derived PHB-L possessed material properties comparable with those of pure substrate/culture produced PHB. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 129: 1314–1321, 2013 KEYWORDS: biopolymers and renewable polymers; crystallization; mechanical properties; thermal properties; thermoplastics Received 11 September 2012; accepted 9 November 2012; published online 3 December 2012 DOI: 10.1002/app.38820 INTRODUCTION Polyhydroxyalkanoates (PHAs) are a family of polyesters that are naturally biosynthesized by a variety of bacteria. To date more than 300 different PHA-producing bacterial species have been isolated. 1,2 PHAs are accumulated as granules within the bacterial cytoplasm as carbon and energy reserves, analogous to starch in plants and to glycogen in bacterial and mammalian systems, under nutrient limited or unbalanced growth condi- tions. 3,4 PHAs have received extensive research attention because of their similar material properties to and potential replacement of conventional petro-plastics; plus, they are biodegradable, biocompatible, and renewable. 2 The material properties of PHAs are quite versatile, ranging from rigid plastics to elasto- mers, due to their large number of monomeric constituents. 5 For example, PHAs with monomers containing 3-5 carbon atoms are referred as short-chain-length (SCL) PHAs and include poly (3-hydroxybutyrate) (PHB) and poly (3-hydroxy- butyrate-co-3-hydroxyvalerate) (PHBV). PHB is generally con- sidered to be rigid and brittle unless they were processed by such special techniques as annealing and drawing. 6 Compared with PHB, PHBV showed more favorable mechanical properties such as improved flexibility and reduced brittleness, although the exact material properties of PHBV largely depend on the content of hydroxyvalerate units in its molecular chains. 7 While PHA is an attractive renewable alternative to petroleum- based thermoplastics, current commercial production practices exhibit higher production costs than conventional plastics; their higher production costs are largely associated with substrate production and bioreactor operations. 8,9 Research to minimize these impacts has been focusing on the use of pure cultures with waste streams rich in organic carbon 10–13 or mixed micro- bial consortia (MMC) grown on synthetic feedstocks. 14–16 The use of MMC has great potentials in reducing PHA production costs, principally due to the elimination of requirement to maintain axenic conditions for bioreactor operations. 15,17 Depending on different substrates and feeding conditions, PHA contents in MMC synthesized biomass vary widely from approximately 40–89% dry cell weight, while pure culture synthesized biomass generally shows PHA contents from 75 to 90%. 15,17–22 Generally, the material properties of MMC-derived PHA such as molecular weight and thermal transitions have been shown to be similar to those derived from pure cultures. 20 V C 2012 Wiley Periodicals, Inc. 1314 J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38820 WILEYONLINELIBRARY.COM/APP