Lignin, the second most abundant biopolymer on the planet, serves land-plants as bonding agent in juvenile cell tissues and as stiffening (modulus-building) agent in mature cell walls. The chemical ...structure analysis of cell wall lignins from two partially delignified wood species representing between 6 and 65% of total wood lignin has revealed that cell wall-bound lignins are virtually invariable in terms of inter-unit linkages, and resemble the native state. Variability is recognized as the result of isolation procedure. In native state, lignin has a low glass-to-rubber transition temperature and is part of a block copolymer with non-crystalline polysaccharides. This molecular architecture determines all of lignin's properties, foremost of all its failure to undergo interfacial failure by separation from (semi-) crystalline cellulose under a wide range of environmental conditions. This seemingly unexpected compatibility (on the nano-level) between a carbohydrate component and the highly aromatic lignin represents a lesson by nature that human technology is only now beginning to mimic. Since the isolation of lignin from lignocellulosic biomass (i.e., by pulping or biorefining) necessitates significant molecular alteration of lignin, isolated lignins are highly variable in structure and reflect the isolation method. While numerous procedures exist for converting isolated (carbon-rich) lignins into well-defined commodity chemicals by various liquefaction techniques (such as pyrolysis, hydrogenolysis, etc.), the use of lignin in man-made thermosetting and thermoplastic structural materials appears to offer greatest value. The well-recognized variabilities of isolated lignins can in large part be remedied by targeted chemical modification, and by adopting nature's principles of functionalization leading to inter-molecular compatibility. Lignins isolated from large-scale industrial delignification processes operating under invariable isolation conditions produce polymers of virtually invariable character. This makes lignin from pulp mills a potentially valuable biopolymeric resource. The restoration of molecular character resembling that in native plants is illustrated in this review via the demonstrated (and in part commercially-implemented) use of pulp lignins in bio-degradable (or compostable) polymeric materials.
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.
Amidation and ionic complexation were evaluated as surface modification treatments for TEMPO-oxidized nanocelluloses (TONc), using octadecylamine (ODA) as the modifying compound. Effects of the two ...treatments on TONc with respect to degree of ODA substitution, surface hydrophobicity, crystalline characteristics, and thermal decomposition properties were investigated, respectively, with elemental analysis, contact angle measurements, X-ray diffraction spectroscopy, and thermogravimetric analysis. Both treatments resulted in complete substitution of TONc surface carboxyl groups with ODA, transforming TONc surfaces from hydrophilic to hydrophobic. A slightly greater than one-to-one ODA-to-carboxyl ratio was found for the ionic complexation product, giving it a more hydrophobic character than the amidation product. Furthermore, the ionic complexation product was found to be surprisingly stable in acidic environment and was able to resist dissociation at fairly low pH. TONc from both treatments could be readily dispersed in organic solvents of wide-ranging polarities, making ionic complexation an equally effective surface modification approach as amidation for the hydrophobization of TONc surfaces. It was also found, through X-ray diffraction results that the crystalline structure of TONc was preserved even after the surface modification treatments. Finally, the thermal stability of TONc was slightly increased as a result of the surface modification treatments as evidenced by slight shifts to higher values of TONc thermal decomposition temperature.
Utilization of TEMPO-oxidized celluloses in bio-based nanocomposites is reported for the first time. TEMPO-oxidized wood pulps (net carboxylate content 1.1 mmol/g cellulose) were fibrillated to ...varying degrees using a high intensity ultrasonic processor. The degree of fibrillation was controlled by varying sonication time from 1 to 20 min. The sonication products were then characterized independently and as fillers (5 wt% loading) in hydroxypropyl cellulose nanocomposite films. Nanofibril yields ranging from 11 to 98 wt% (on fiber weight basis) were obtained over the range of sonication times used. Suspension viscosities increased initially with sonication time, peaked with gel-like behavior at 10 min of sonication and then decreased with further sonication. The thermal degradation temperature of unfibrillated oxidized pulps was only minimally affected (6 °C decrease) by the fibrillation process. Dynamic mechanical analysis of the nanocomposites revealed strong fibril-matrix interactions as evidenced by remarkable storage modulus retention at high temperatures and a suppression of matrix glass transition at “high” (~5 wt%) nanofibril loadings. Creep properties likewise exhibited significant (order of magnitude) suppression of matrix flow at high temperatures. It was also believed, based on morphologies of freeze-fracture surfaces that the nanocomposites may be characterized by high fracture toughness. Direct fracture testing will however be necessary to verify this suspicion.
Condensed tannins (CTs) are high molar mass polyphenolic bio-polymers based on flavonol units. CTs have been well-studied due to their respective biological activity. However, the application of CTs ...in several areas is limited because of their physicochemical properties. The objective of this review is to investigate the state of the art regarding the chemical modification of CTs, and to outline recent and potential applications of tannin derivatives. An overview of the most important reactions is given, and a comprehensive summary of the experimental parameters for modification (chemicals, time, temperature, solvent type, and yield) is presented. The impact of the modification on the physicochemical properties of derivatives in comparison to native tannin behavior is discussed. Finally, the applicability of modified or unmodified CTs is described, referring to academic articles and patents. Future research in terms of modification reaction type, as well as derivatizing agents, is discussed.
Condensed tannins (CTs) are high molar mass polyphenolic bio-polymers based on flavonol units.
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.
This work highlights a real-time and label-free method to monitor the dehydrogenative polymerization of monolignols initiated by horseradish peroxidase (HRP) physically immobilized on surfaces using ...a quartz crystal microbalance with dissipation monitoring (QCM-D). The dehydrogenative polymer (DHP) films are expected to provide good model substrates for studying ligninolytic enzymes. The HRP was adsorbed onto gold or silica surfaces or onto and within porous desulfated nanocrystalline cellulose films from an aqueous solution. Surface-immobilized HRP retained its activity and selectivity for monolignols as coniferyl and p-coumaryl alcohol underwent dehydrogenative polymerization in the presence of hydrogen peroxide, whereas sinapyl alcohol polymerization required the addition of a nucleophile. The morphologies of the DHP layers on the surfaces were investigated via atomic force microscopy (AFM). Data from QCM-D and AFM showed that the surface-immobilized HRP-initiated dehydrogenative polymerization of monolignols was greatly affected by the support surface, monolignol concentration, hydrogen peroxide concentration, and temperature.
•We modified Pinus pinaster bark tannin with propylene oxide.•We synthetized derivatives with monosubstituted phenolic functionalities.•The polyphenolic derivatives were characterized by FT-IR, ...UV–vis, 1H NMR and bidimensional spectroscopies.•The integration of the aromatic proton signals in the 1H NMR spectra of acetylated HPT allowed for an easy quantitative determination of DS.•We expected to enhance their role as new oligomeric building-blocks.
Tannins from Pinus pinaster bark were modified with propylene oxide (PO) in aqueous alkali at room temperature (∼22°C) for the first time. The hydroxypropylation to four different degrees of substitution (DS) produced derivatives (HPT) with monosubstituted phenolic functionalities in yields in excess of 80%. The isolated HPTs were characterized by FT-IR, UV–vis, 1H NMR and bidimensional spectroscopies (HMBC, HSQC and COSY). The integration of the aromatic proton signals in the 1H NMR spectra of acetylated HPT allowed for an easy quantitative determination of DS. HPTs possess properties that are expected to enhance their role in new oligomeric building-blocks for the synthesis of engineered plastics and tannin-based bio-foams.
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