Ralph A. Whitney

A biorefinery processing perspective: treatment of lignocellulosic materials for the production of value-added products.

In the last decade, there has been increasing research interest in the value of bio-sourced materials recovered from residual biomass. Research that focuses on the use of extracted, recovered and/or synthesized bioproducts for direct industrial applications is essential for the implementation of sustainable approaches in a forward-looking bio-based economy. The effective use of biomass feedstocks, particularly lignocellulosic materials (plant biomass predominantly comprised of cellulose, hemicellulose, and lignin), in large-scale applications will evolve from innovative research aimed at the development and implementation of biorefineries--multi-step, multi-product facilities established for specific bio-sourced feedstocks. This paper presents recent advances in lignocellulosic biomass processing and analysis from a biorefining perspective. In addition, existing industrial biomass processing applications are discussed and examined within a biorefinery context.

Semisynthesis of a controlled stimuli-responsive alginate hydrogel.

Benefits of the use of natural polymers include biodegradability, biocompatibility, natural abundance, and unique physicochemical/biological properties. Native alginate was used to semisynthesize a new class of biomaterial in which the physical properties such as swelling and pore size can be chemically tailored for desired end use. Semisynthetic network alginate polymer (SNAP) was prepared by reaction with glutaraldehyde, forming an acetal-linked network polymer gel with carboxylate moieties preserved as stimuli-responsive sensors. The molecular structure of the hydrogel was confirmed by cross-polarization magic-angle spinning (13)C solid state NMR, and reaction parameters affecting the polymer synthesis, including reactant, catalyst concentrations, and solvent composition, were characterized by gel equilibrium swelling. The acetalization reaction can be thermodynamically controlled, offering fine-tuned control of gel swelling and pore properties. In addition, SNAP demonstrated pronounced swelling at alkaline pH and contraction in acidic environment with oscillatory response to repeated pH-stimuli, yielding a potential pulsatile, oral drug delivery vehicle. Through selection of reaction conditions, gel swelling, pore size, and stimuli-responsive characteristics can be specifically tailored for applications such as a tissue scaffold in regenerative medicine, as a targeted delivery vehicle, and as a superabsorbent in environmental cleanup.

Polymerization Induced Self-Assembly of Alginate Based Amphiphilic Graft Copolymers Synthesized by Single Electron Transfer Living Radical Polymerization.

Alginate-based amphiphilic graft copolymers were synthesized by single electron transfer living radical polymerization (SET-LRP), forming stable micelles during polymerization induced self-assembly (PISA). First, alginate macroinitiator was prepared by partial depolymerization of native alginate, solubility modification and attachment of initiator. Depolymerized low molecular weight alginate (∼12 000 g/mol) was modified with tetrabutylammonium, enabling miscibility in anhydrous organic solvents, followed by initiator attachment via esterification yielding a macroinitiator with a degree of substitution of 0.02, or 1-2 initiator groups per alginate chain. Then, methyl methacrylate was polymerized from the alginate macroinitiator in mixtures of water and methanol, forming poly(methyl methacrylate) grafts, prior to self-assembly, of ∼75 000 g/mol and polydispersity of 1.2. PISA of the amphiphilic graft-copolymer resulted in the formation of micelles with diameters of 50-300 nm characterized by light scattering and electron microscopy. As the first reported case of LRP from alginate, this work introduces a synthetic route to a preparation of alginate-based hybrid polymers with a precise macromolecular architecture and desired functionalities. The intended application is the preparation of micelles for drug delivery; however, LRP from alginate can also be applied in the field of biomaterials to the improvement of alginate-based hydrogel systems such as nano- and microhydrogel particles, islet encapsulation materials, hydrogel implants, and topical applications. Such modified alginates can also improve the function and application of native alginates in food and agricultural applications.

The effect of substitution on the utility of piperidines and octahydroindoles for reversible hydrogen storage

Substituted piperidines and octahydroindoles are compared in terms of their usability as reversible organic hydrogen storage liquids for hydrogen-powered fuel cells. Theoretical Gaussian calculations indicate which structural features are likely to lower the enthalpy of dehydrogenation. Experimental results show that attaching electron donating or conjugated substituents to the piperidine ring greatly increases the rate of catalytic dehydrogenation, with the greatest rates being observed with 4-aminopiperidine and piperidine-4-carboxamide. Undesired side reactions were observed with some compounds such as alkyl transfer reactions during the dehydrogenation of 4-dimethylaminopiperidine, C–O and C–N cleavage reactions during hydrogenation and/or subsequent dehydrogenation of 4-alkoxy and 4-amino indoles, and disproportionation during the hydrogenation of 4-aminopyridine.

Peroxide‐initiated grafting of maleic anhydride onto linear and branched hydrocarbons

The structural features of the grafting of maleic anhydride onto low-molecular-weight compounds have been elucidated using several spectroscopic and analytical techniques. Conclusive evidence for the occurrence of singly grafted anhydride residues in multiply grafted products has been established using 2,3-13C2 labeled maleic anhydride. In homogeneous solution, at the low concentrations of maleic anhydride employed, there is little evidence for oligomeric or polymeric grafts to dodecane, pristane, or squalane. The results suggest that isothermal grafting of maleic anhydride to hydrocarbon polymers should also lead to a predominance of single grafts.

Kinetic controlled synthesis of pH-responsive network alginate.

Alginates are of considerable interest in the fields of biotechnology and biomedical engineering. To enable the control of properties generally not possible with the native polymer, we have chemically modified alginate with dialdehyde via acid-catalyzed acetalization. The kinetics of acetalization measured through equilibrium swelling of the networked polymer were found to undergo a zero- and second-order reaction with respect to alginate and dialdehyde, respectively. With the determined rate constant of 19.06 microL x mole(-1) x s(-1) at 40 degrees C and activation energy of 78.58 kJ x mol(-1), a proposed predictive reaction model may be used a priori to select reaction conditions providing specific polymer properties. Gel swelling and average pore size were then able to be controlled between 80-1000-fold and 35-840 nm, respectively, by predictive estimation of reagent concentration and formulation conditions. This semisynthetic but natural polymer is stimuli-responsive exhibiting high water absorbency and may potentially be used as drug delivery vehicle for protein therapeutics.

Composition distribution in poly(ethylene-graft-vinyltrimethoxysilane)

Abstract Insight into the composition distribution created by free-radical mediated addition of vinyltrimethoxysilane (VTMS) to high-density polyethylene (HDPE) has been gained using physical methods of polymer characterization as well as detailed structural studies of a model hydrocarbon system. Analysis of poly(ethylene- graft -vinyltrimethoxysilane), or HDPE- g -VTMS, by moisture curing and by differential scanning calorimetry–successive self-nucleation and annealing (DSC–SSA) indicated that the distribution of pendant alkoxysilane grafts amongst polymer chains was non-uniform. Fractionation and characterization of a graft-modified model compound, tetradecane- g -VTMS, showed that composition distributions were influenced strongly by intramolecular hydrogen atom abstraction, yielding multiple grafts per chain in the form of single pendant units as opposed to oligomeric grafts. Chain transfer to the methoxy substituent of bound VTMS was found to contribute significantly to the product distribution.

Furoxans as nitrile oxide precursors: Cycloaddition reactions of bis(benzenesulfonyl)furoxan.

Abstract Bis(benzenesulfonyl)furoxan has been shown to undergo cycloaddition reactions with dipolarophiles in refluxing xylene to give benzenesulfonylnitrile oxide cycloadducts.

Peroxide‐initiated comonomer grafting of styrene and maleic anhydride onto polyethylene: Effect of polyethylene microstructure

Maleic anhydride has been grafted onto various polyethylenes (PEs) using 2,5-dimethyl-2,5-(di-t-butylperoxy)hexane as a free radical initiator in the presence of styrene as a comonomer. Three polyethylenes, differing systematically in their levels of terminal unsaturation and branching, were selected to investigate the effect of these microstructural characteristics on the course of both grafting and crosslinking. It was observed that when polyethylenes containing high levels of terminal unsaturation were reacted in the presence of peroxide or peroxide–maleic anhydride, crosslinking events were enhanced. When styrene was added as comonomer to the reaction medium to eliminate these undesirable side reactions, crosslinking was still observed with those polyethylenes that contained a high concentration of terminal unsaturation. This is attributed to a low reactivity between styrene and the allylic radical generated on the polyethylene backbone, which is believed to be responsible for the increased crosslinking. However, in the presence of high concentrations of styrene, crosslinking was eliminated for PEs containing high degrees of branching.

Silane‐modified poly(ethylene‐co‐vinyl acetate): influence of comonomers on peroxide‐initiated vinylsilane grafting

Functionalization of poly(ethylene-co-vinyl acetate) (EVA) with vinyltriethoxysilane (VTEOS) has been carried out by a free-radical melt-grafting procedure in the presence of added comonomers. The influence of comonomers on silane graft yield and crosslink density has been assessed. Experiments were performed on masterbatches of EVA, VTEOS (5 wt %), peroxide initiator (L-231, 0.05 wt %), and comonomer (0–1 comonomer : VTEOS mole ratio) prepared at 90°C. Melt-grafting experiments were carried out at 145°C in an oscillating disk rheometer (ODR), which measured crosslink density during the grafting process. Silane graft yields were determined by proton NMR spectroscopy. Comonomers evaluated were maleic anhydride (MAn), 1-vinyl-2-pyrrolidone (VP), and 1-dodecene (DD). At the comonomer ratios examined, MAn suppressed both silane grafting and peroxide-initiated crosslinking. Both VP and DD, however, exhibited greater selectivity in suppressing crosslinking than silane grafting; optimum performance was found at a comonomer : vinylsilane mole ratio of 0.2. None of the comonomers studied enhanced the level of silane grafting.