Surface plasmon resonance studies showed pullulan cinnamates (PCs) with varying degrees of substitution (DS) adsorbed onto regenerated cellulose surfaces from aqueous solutions below their critical ...aggregation concentrations. Results on cellulose were compared to PC adsorption onto hydrophilic and hydrophobic self-assembled thiol monolayers (SAMs) on gold to probe how different interactions affected PC adsorption. PC adsorbed onto methyl-terminated SAMs (SAM-CH3) > cellulose > hydroxyl-terminated SAMs (SAM-OH) for high DS and increased with DS for each surface. Data for PC adsorption onto cellulose and SAM-OH surfaces were effectively fit by Langmuir isotherms; however, Freundlich isotherms were required to fit PC adsorption isotherms for SAM-CH3 surfaces. Atomic force microscopy images from the solid/liquid interfaces revealed PC coatings were uniform with surface roughnesses <2 nm for all surfaces. This study revealed hydrogen bonding alone could not explain PC adsorption onto cellulose and hydrophobic modification of water-soluble polysaccharides was a facile strategy for their conversion into surface modifying agents.
The random wetlay process was used to fabricate thermoplastic composite sheets reinforced with chopped lyocell (regenerated cellulose from the
N-methylmorpholine-
N-oxide process) fibers, and with ...blends of lyocell and steam-exploded hardwood (SEW) fibers. Polypropylene (PP) served as matrix material in compression-molded composites reinforced with 25–65
wt.% fiber. Tensile and flexural properties of the resulting composites were compared with those reported for melt-processed (injection-molded) rayon fiber-reinforced PP composites. Association between fiber and matrix was also observed using scanning electron microscopy (SEM). Mechanical properties of wetlaid composites were found to be generally comparable with those of melt-processed composites over similar ranges of fiber loading. The fiber length-preserving advantage of the wetlay process was found to produce superior composite flexural properties. Tensile properties on the other hand, were found to require the presence of an interfacial binding agent. Results of hybrid composite studies revealed surprisingly high strength and modulus retention when as much as 60% of lyocell fibers were replaced with SEW fibers. The addition of wood fibers may potentially result in substantial savings in fiber cost.
A series of process design and economics models have been created which calculate the process cost for several scenarios in steam-explosion/fractionation of wood. Steam-explosion/fractionation ...technology offers the opportunity to produce chemicals and materials from such biomass resources as wood processing residues, agricultural crop residues and waste paper. The models comprise a series of modular computer simulations, where each module summarizes a particular group of unit operations with respect to mass balance, energy requirements, and process cost including utilities, capital, labor, and other related costs. These modules are compiled into three groups of scenarios: (1) unprocessed steam-exploded biomass, (2) water extracted steam-exploded biomass, and (3) water and aqueous solvent (alkali or ethanol) extracted steam-exploded biomass. For the base case evaluated, the cost of producing a 50% moisture content (based on total weight) steam-exploded fiber amounts to the raw material cost plus $0.077 kg
−1, dry basis. A water washed steam-exploded biomass fiber along with water-soluble solids (WSS) can be produced for $0.165 kg
−1, plus raw material, if the WSS are recovered by evaporative concentration. A more delignified, steam-exploded fiber with recovery of WSS and an aqueous alkali soluble lignin can be produced for between $0.222 and $0.246 kg
−1 of raw material processed, dry basis, depending on the lignin recovery option employed (i.e. evaporative concentration; precipitation from alkaline solution; or spray drying).
The isolation of non-cellulosic heteropolysaccharides (HetPS) from barley husks (Hordeum spp.) and yellow poplar wood chips (Liriodendron tulipifera) was accomplished using mild steam explosion ...followed by extraction with water and ultrafiltration. The generally low yields, low purity, and low degree of polymerization (DP) improved when the HetPS were isolated following either alkali extraction of hammermilled or disk-refined biomass, or from holocellulose preparations generated by the conventional chlorite method or by organosolv delignification. Several purification methods were examined including precipitation using methanol; treatment with hydrogen peroxide (H2O2) or activated carbon (C) followed by precipitation with methanol; and H2O2-treatment followed by ultrafiltration. The isolation protocols were judged based on product yield, xylan content, and DP. The results indicate that, although steam explosion is effective in removing HetPS from the fiber source, virtually none remain in polymeric form. By contrast, alkali extraction succeeds in separating polymeric HetPS from the fiber source; and HetPS purity increases and polydispersity decreases with fiber prehydrolysis and delignification. Significant processing difficulties were attributed to the intimate association of HetPS with lignin which was effectively disrupted by acid-catalyzed pretreatment and treatment with H2O2. Ultrafiltration of H2O2-treated HetPS solutions represents the best procedure for isolating a xylan-rich polymer in high yield, with high DP and with high purity. Aqueous HetPS solutions can be spray- or freeze-dried into powderous products.
Polymeric xylan can be reacted with propylene oxide (PO) in aqueous alkali homogeneously. Since xylan is isolated from biomass in aqueous alkaline solution, an ‘in-line’ modification with PO as part ...of the isolation protocol, is most practical. Hydroxypropyl xylan (HPX) is a low molecular weight, branched, water-soluble polysaccharide with low intrinsic viscosity and thermoplasticity. Following peracetylation of HPX in formamide solution, water-insoluble acetoxypropyl xylan (APX) is formed that is also thermoplastic but no longer water soluble. The glass transition temperature (T g) of APX varies in relation to degree of substitution with hydroxypropyl groups (DSPO), and this is found to decline from 160 to 70°C as DSPO rises from 0.2 to 2.0. At a temperature above the T g of HPX a molecular reorganization is noted, and a faint transition due to melting (T ₘ) is observed at 205°C. HPX thermally degrades with a weight loss maximum at 317°C, or approximately 60°C below that of a corresponding cellulose derivative. HPX forms clear films when solvent cast from aqueous solution. Films are higher in ultimate tensile strength and lower in toughness than corresponding cellulose derivative films. The properties of HPX and APX derivatives qualify this material as a potential biodegradable and thermoplastic additive to melt-processed plastics. Blend characteristics with polystyrene reveal a shear-thinning effect in melt and a plasticization effect in solid state.
The fractionation behavior following steam explosion of three biomass resources, yellow poplar (
Liriodendron tulipifera) wood chips, peanut hulls (
Arachis hypogaea), and sugar cane (
Saccharum ...officinarum) bagasse (three separate fractions, leaf, pith, and whole bagasse) were examined following steam explosion using a Stake II reactor. Component separation was evaluated using a range of different severity factors. Water solubles, alkali solubles, and an insoluble fraction were collected separately and subjected to component analysis. The latter addressed both chemical (component analysis by NMR and UV spectroscopy) and molecular structure (molecular weight determinations). The water soluble fraction consisted primarily of xylose (mono and oligo-saccharides) and water soluble lignin; the alkali soluble fraction contained most of the lignin and unidentified alkali-soluble polysaccharides; and the residual fiber was mostly cellulose. Whereas the hemi-celluloses could not be preserved as polymers, lignin had molecular weights (M
n) in excess of 3000 and dispersities in excess of 10, except for highly severe reaction conditions which produced lignins with lower molecular weight. The molecular weight of the cellulose declined steadily with reaction severity; that of lignin dropped abruptly at a severity of log
R
0 4.25 where homolytic depolymerization was indicated. Fraction behavior and fraction character were found to be highly dependent on the severity of the steam explosion treatment.
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