Direct microbial conversion

Applied Biochemistry and Biotechnology - Process development is reviewed for ethanol production from cellulosic biomass via direct microbial conversion (DMC). Experimental data addressing cellulase...     

Weak closure and Oliver’s p-group conjecture

To date almost all verifications of Oliver’s p-group conjecture have proceeded by verifying a stronger conjecture about weakly closed quadratic subgroups. We construct a group of order 3⁴⁹ which refutes the weakly closed conjecture but satisfies Oliver’s conjecture.     

Ketene functionalized polyethylene: control of cross-link density and material properties

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.     

Continuous fermentation of cellulosic biomass to ethanol

Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H₂SO₄) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H₂SO₄). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC. The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time. At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system (77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration in the range of 5–60 g/L cellulose in the feed.     

Morphology re-entry in asymmetric PS-PI-PS' triblock copolymer and PS homopolymer blends

Here, we report the morphology variation in a series of PS-b-PI-b-PS' asymmetric triblock copolymer and PS homopolymer (hPS) blends, where PS' and PS are polystyrene blocks with a molecular weight ratio of approximately 0.11 and PI is poly(isoprene). We find that adding a small amount of hPS results in significant order–order transition (OOT) boundary deflection toward higher PS volume fractions f_PS, which is accompanied by morphology re-entry. For example, the neat triblock copolymer with a PS + PS' volume fraction of f_PS = 0.38 exhibits a lamellar microphase; adding a small amount of hPS reverts the morphology into a hexagonal phase with PS cylinders, while further increasing the hPS fraction leads to normal OOTs from PS cylinders to lamellae, to PI cylinders and finally to spheres. The morphology variation reported here is significantly different from that reported in binary blends of diblock or symmetric triblock copolymer with homopolymer. While the domain features of the LAM structure can be correctly reproduced by self-consistent field theory (SCFT), the observed morphology re-entry is absent in the theoretical SCFT phase diagram. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 169–179     

Perchloroethylene utilization by methanogenic fed-batch cultures

Applied Biochemistry and Biotechnology - Anaerobic sludge granules from two different sources were maintained in serum bottles and fed at 3-d intervals in the presence of 0.2 ppm perchloroethylene...     

Likely features and costs of mature biomass ethanol technology

Applied Biochemistry and Biotechnology - Analysis is undertaken motivated by the question: “What are the likely features and cost of a facility producing ethanol from cellulosic biomass at a...     

A general approach to controlling the surface composition of poly(ethylene oxide)-based block copolymers for antifouling coatings

To control the surface properties of a polystyrene-block-poly(ethylene oxide) diblock copolymer, perfluorinated chemical moieties were specifically incorporated into the block copolymer backbone. A polystyrene-block-poly[(ethylene oxide)-stat-(allyl glycidyl ether)] [PS-b-P(EO-stat-AGE)] statistical diblock terpolymer was synthesized with varying incorporations of allyl glycidyl ether (AGE) in the poly(ethylene oxide) block from 0 to 17 mol %. The pendant alkenes of the AGE repeat units were subsequently functionalized by thiol-ene chemistry with 1H,1H,2H,2H-perfluorooctanethiol, yielding fluorocarbon-functionalized AGE (fAGE) repeat units. (1)H NMR spectroscopy and size-exclusion chromatography indicated well-defined structures with complete functionalization of the pendant alkenes. The surfaces of the polymer films were characterized after spray coating by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), showing that the P(EO-stat-fAGE) block starts to compete with polystyrene to populate the surface after only 1 mol % incorporation of fAGE. Increasing the incorporation of fAGE led to an increased amount of perfluorocarbons on the surface and a decrease in the concentration of PS. At a fAGE incorporation of 8 mol %, PS was not detected at the surface, as measured by NEXAFS spectroscopy. Water contact angles measured by the captive-air-bubble technique showed the underwater surfaces to be dynamic, with advancing and receding contact angles varying by >20°. Protein adsorption studies demonstrated that the fluorinated surfaces effectively prevent nonspecific binding of proteins relative to an unmodified PS-b-PEO diblock copolymer. In biological systems, settlement of spores of the green macroalga Ulva was significantly lower for the fAGE-incorporated polymers compared to the unmodified diblock and a polydimethylsiloxane elastomer standard. Furthermore, the attachment strength of sporelings (young plants) of Ulva was also reduced for the fAGE-containing polymers, affirming their potential as fouling-release coatings.     

A facile synthesis of catechol‐functionalized poly(ethylene oxide) block and random copolymers

Herein we develop a facile synthetic strategy for the functionalization of well‐defined polyether copolymers with control over the number and location of catechol groups. Previously, the functionalization of polyethylene oxide (PEO)‐based polymers with catechols has been limited to functionalization of the chain ends only, hampering the synthesis of adhesive and antifouling materials based on this platform. To address this challenge, we describe an efficient and high‐yielding route to catechol‐functionalized polyethers, which could allow the effects of polymer architecture, molecular weight, and catechol incorporation on the adhesive properties of surface‐anchored PEO to be studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2685–2692