Wolfgang G. Glasser

Recent Industrial Applications of Lignin: A Sustainable Alternative to Nonrenewable Materials

Lignin represents a vastly under-utilized natural polymer co-generated during papermaking and biomass fractionation. Different types of lignin exist, and these differ with regard to isolation protocol and plant resource (i.e., wood type or agricultural harvesting residue). The incorporation of lignin into polymeric systems has been demonstrated, and this depends on solubility and reactivity characteristics. Several industrial utilization examples are presented for sulfur-free, water-insoluble lignins. These include materials for automotive brakes, wood panel products, biodispersants, polyurethane foams, and epoxy resins for printed circuit boards.

Separation, characterization and hydrogel-formation of hemicellulose from aspen wood.

Abstract Hemicellulose from aspen (Populus tremula) was isolated by an alkali extraction method, which was followed by hydrogen peroxide treatment, ultrafiltration and recovery by spray drying. The sugar composition and lignin content were monitored with HPLC at each step of the separation procedure. Size-exclusion chromatography showed a polymeric hemicellulose of relatively high molar mass. The product was characterized by 1H and 13C NMR spectroscopy and was found to be composed of a linear (1→4)-β-linked d -xylose main chain with a 4-O-methyl-α- d -glucuronic acid substituting the 2-position of approximately every eighth xylose unit. Lignin and O-acetyl groups had largely been removed in the separation process. The xylan was soluble in hot water, and the film forming properties were examined at various mixtures of the hemicellulose and chitosan. These films formed hydrogels with a high swelling capacity at certain compositions. The morphologies of the films were examined with wide angle X-ray spectroscopy, and a pure xylan film was found to be crystalline, which was suggested to be a consequence of the lack of O-acetyl groups. The crystallinity of the films was found to decrease with an increasing amount of chitosan, and the film of chitosan alone showed no crystallinity. The cohesive forces of the hydrogels are suggested to be the result of the crystalline arrangement of the polymers and of electrostatic interactions between acidic groups in the hemicellulose and amine groups in the chitosan.

Relaxation behaviour of the amorphous components of wood

The viscoelastic properties of mod were investigated using dynamic mechanical thermal analysis and differential scanning calorimetry. Under a limited set of conditions, two separate glass transitions (Tg) could be identified with both techniques. These two transitions were identified as arising from the amorphous lignin and hernicellulose matrix in the wood cell wall. Moisture dramatically affected the temperature at which the two dispersions occurred and, consequently, the ability to resolve their independent responses. The relationship betweenTg and moisture for both components could be modelled with the Kwei equation, which accounts for the presence of secondary interactions. Annealing and specific interactions of a series of organic diluents were wed in an attempt to enhance the resolution of the two components values ofTg. Time-temperature superposition was shown to be applicable to wood plasticized with ethyl formamide, following Williams-Landel-Ferry behaviour over the temperature rangeTg toTg + 85° C. These observations allow certain conclusions to be drawn concerning the applicability of existing models of the wood cell walls supermolecular morphology. Most notably, models of thein situ morphology of the three wood components can be limited to those which consider the amorphous matrix of lignin and hemicellulose to be immiscible.

Novel cellulose derivatives. iv. Preparation and thermal analysis of waxy esters of cellulose

Cellulose esters with linear aliphatic acyl substituents ranging in size from C12 (lauric acid) to C20 (eicosanoic acid) were prepared in homogeneous solution (DMAc/LiCl) using a novel synthetic method based on the use of a mixed p-toluenesulfonic/carboxylic acid anhydride. The resulting waxy cellulose esters had a high degree of substitution (DS), between 2.8 and 2.9, and showed little degradation. Thermal analysis of these cellulose derivatives by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) revealed a series of transitions that represented motion by both ester substituents and cellulosic main chain. Broad crystallization and melting transitions attributed to side-chain crystallinity were observed in the range between −19 and +55°C; these side-chain Tm and Tc transition temperatures increased by 10°C per carbon atom of the ester substituent. The Tg of these derivatives increased linearly with increasing substituent size from 94°C for C12 (cellulose laurate) to 134°C for C20 (cellulose eicosanoate). Evidence of “main-chain” crystallization was not observed for these samples, except in the case of peracetylated C12 and C14 esters, which had Tm values of 96°C and 107°C, respectively.

About the structure of cellulose: debating the Lindman hypothesis

The hypothesis advanced in this issue of CELLULOSE [Springer] by Bjorn Lindman, which asserts that the solubility or insolubility characteristics of cellulose are significantly based upon amphiphilic and hydrophobic molecular interactions, is debated by cellulose scientists with a wide range of experiences representing a variety of scientific disciplines. The hypothesis is based on the consideration of some fundamental polymer physicochemical principles and some widely recognized inconsistencies in behavior. The assertion that little-recognized (or under-estimated) hydrophobic interactions have been the reason for a tardy development of cellulose solvents provides the platform for a debate in the hope that new scientific endeavors are stimulated on this important topic.

Fiber-reinforced cellulosic thermoplastic composites

Steam-exploded fibers from Yellow poplar (Liriodendron tulipifera) wood were assessed in terms of their thermal stability characteristics, their impact on torque during melt processing of a thermoplastic cellulose ester (plasticized CAB) matrix, their fiber–matrix adhesion and dispersion in composites, and their mechanical properties under tension. Fibers included water-extracted steam-exploded fibers (WEF), alkali extracted fibers (AEF), acetylated fibers (AAEF), and a commercial milled oat fiber sample (COF) (i.e., untreated control). The results indicate that the thermal stability of steam-exploded fibers increases progressively as the fibers are extracted with water and alkali and following acetylation. The greatest improvement resulted from the removal of water-soluble hemicelluloses. The modification by acetylation contributed to improved interfacial wetting that was revealed by increased torque during melt processing. Whereas modulus increased by between 0 and 100% with the incorporation of 40% fibers by weight, tensile strength either declined by ⅓ to ½ or it increased by a maximum of 10%, depending on fiber type. AAEF composites produced the best mechanical properties. Fiber–aspect ratio was reduced to an average of 25–50 from ≫ 200 during compounding. The superior reinforcing characteristics of AAEF fibers were also reflected by SEM, which revealed better fiber–matrix adhesion and failure by fiber fibrillation rather than by fiber pullout.

Steam-assisted biomass fractionation. I. Process considerations and economic evaluation

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

Steam-assisted biomass fractionation. II. fractionation behavior of various biomass resources

0.077 kg−1, dry basis. A water washed steam-exploded biomass fiber along with water-soluble solids (WSS) can be produced for

Molecular Weight Distribution of (Semi-) Commercial Lignin Derivatives

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

Lignin derivatives. I: Alkanoates

0.222 and