Photoresponsive Cellulose Nanocrystals

In this communication a method for the creation of fluorescent cellulose nanoparticles using click chemistry and subsequent photodimerization of the installed side‐ chains is demonstrated. In the first step, the primary hydroxyl groups on the surface of the CNCs were converted to carboxylic acids by using TEMPO‐mediated hypohalite oxidation. The alkyne groups, essential for the click reaction, were introduced into the surface of TEMPO‐ oxidized CNCs via carbodiimide‐mediated formation of an amide linkage between monomers carrying an amine functionality and carboxylic acid groups on the surface of the TEMPO‐oxidized CNCs. Finally, the reaction of surface‐modified TEMPO‐oxidized cellulose nanocrystals and azido‐bearing coumarin and anthracene monomers were carried out by means of a click chemistry, i.e., Copper(I)‐catalyzed Azide‐Alkyne Cycloaddition (CuAAC) to produce highly photo‐responsive and fluorescent cellulose nanoparticles. Most significantly, the installed coumarin and/or anthracene side‐chains were shown to undergo UV‐induced [2+2] and [4+4] cycloaddition reactions, bringing and locking the cellulose nanocrystals together. This effort paves the way towards creating, cellulosic photo responsive nano‐arrays with the potential of photo reversibility since these reactions are known to be reversible at varying wavelengths. 

Photoresponsive Cellulose Nanocrystals Regular Paper

In this communication a method for the creation of fluorescent cellulose nanoparticles using click chemistry and subsequent photodimerization of the installed side-chains is demonstrated. In the first step, the primary hydroxyl groups on the surface of the CNCs were converted to carboxylic acids by using TEMPO-mediated hypohalite oxidation. The alkyne groups, essential for the click reaction, were introduced into the surface of TEMPO-oxidized CNCs via carbodiimide-mediated formation of an amide linkage between monomers carrying an amine functionality and carboxylic acid groups on the surface of the TEMPO-oxidized CNCs. Finally, the reaction of surface-modified TEMPO-oxidized cellulose nanocrystals and azido-bearing coumarin and anthracene monomers were carried out by means of a click chemistry, i.e., Copper(I))-catalyzed Azide-Alkyne Cycloaddition (CuAAC) to produce highly photo-responsive and fluorescent cellulose nanoparticles. Most significantly, the installed coumarin and/or anthracene side-chains were shown to undergo UV-induced [2+2] and [4+4] cycloaddition reactions, bringing and locking the cellulose nanocrystals together. This effort paves the way towards creating, cellulosic photo responsive nano-arrays with the potential of photo reversibility since these reactions are known to be reversible at varying wavelengths.Peer reviewe

Lignin as a UV Light Blocker—A Review

Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. Using lignin as a natural ingredient in sunscreen cream, transparent film, paints, varnishes and microorganism protection has been actively investigated. Both in non-modified and modified forms, lignin provides enhancing UV protection of commercial products with less than a 10% blend with other material. In mixtures with other synthetic UV blockers, lignin indicated synergic effects and increased final UV blocking potential in compare with using only synthetic UV blocker or lignin. However, using lignin as a UV blocker is also challenging due to its complex structure, polydispersity in molecular weight, brownish color and some impurities that require more research in order to make it an ideal bio-based UV blocker

Press-fit Femoral Fixation in ACL Reconstruction using Bone-Patellar Tendon-Bone Graft

Bone-patellar tendon auto graft is probably the most widely used graft for ACL reconstruction. Several methods for graft fixation have been described. To avoid intra-articular hardware we adopt biological fixation with a femoral trapezoidal press-fit fixation. A prospective study was performed on 30 consecutive active people who underwent ACL reconstruction with this technique by two surgeons between september2004 and march2007 (mean follow-up 15.2 months). Results were evaluated by an independent examiner using radiography, subjective and objective evaluation. Assessment using the IKDC knee scoring revealed 92% of the patients with a normal or nearly normal knee joint. Lysholm's score was 63.6(40- 86) preoperatively and 91.88(73-100) at the latest follow up (P < 0.005). No patient complained of instability at latest follow up. The quadriceps muscle showed mild atrophy at 3 and 6 months and at final follow-up. Five Patients complained of anterior knee pain and had a positive kneeling test. We found no graft displacement on follow up radiographs. All cases showed radiological evidence of graft osteointegration at last follow up. Our results show that press-fit fixation of trapezoidal bone graft in femoral tunnel is a simple, reliable, and cost-effective alternative for ACL recon-struction using bone-patellar tendon-bone graft

Toward Thermoplastic Lignin Polymers. Part 1. Selective Masking of Phenolic Hydroxyl Groups in Kraft Lignins via Methylation and Oxypropylation Chemistries

This work offers a comprehensive understanding of the conditions required for the selective masking of the phenolic hydroxyl groups in technical kraft lignins, which is pivotal in determining their subsequent chemical and thermal reactivity. To this effect, we have examined the chemistry and developed the conditions for the facile, mild, and selective masking of the phenolic hydroxyl groups in softwood and hardwood kraft lignins. We have compared two series of methylated softwood kraft lignins synthesized using different methylation chemistries. Our data show that (when used as specified) dimethyl sulfate in aqueous NaOH selectively converts the phenolic hydroxyl groups of kraft lignin to its methylated derivatives without apparent side reactions. In contrast, methyl iodide (in the presence of excess K₂CO₃ in <i>N</i>,<i>N</i>-dimethylformamide) was found to be rather ineffective and unselective. Various milder methylation conditions were also examined for both softwood and hardwood kraft lignins using dimethyl sulfate, and the details of this work are documented. In addition, a series of oxypropylation reactions were also carried out using propylene oxide in aqueous NaOH. Propylene oxide was shown to selectively add (at room temperature, 0.5 M NaOH, 18 h) less than two units on average per phenolic hydroxyl group without significant additional polymerization or other side reactions

Kraft Lignin Chain Extension Chemistry via Propargylation, Oxidative Coupling, and Claisen Rearrangement

Despite its aromatic and polymeric nature, the heterogeneous, stochastic, and reactive characteristics of softwood kraft lignin seriously limit its potential for thermoplastic applications. Our continuing efforts toward creating thermoplastic lignin polymers are now focused at exploring propargylation derivatization chemistry and its potential as a versatile novel route for the eventual utilization of technical lignins with a significant amount of molecular control. To do this, we initially report the systematic propargylation of softwood kraft lignin. The synthesized derivatives were extensively characterized with thermal methods (DSC, TGA), ¹H, ¹³C, and quantitative ³¹P NMR and IR spectroscopies. Further on, we explore the versatile nature of the lignin pendant propargyl groups by demonstrating two distinct chain extension chemistries; the solution-based, copper-mediated, oxidative coupling and the thermally induced, solid-state, Claissen rearrangement polymerization chemistries. Overall, we show that it is possible to modulate the reactivity of softwood kraft lignin via a combination of methylation and chain extension providing a rational means for the creation of higher molecular weight polymers with the potential for thermoplastic materials and carbon fibers with the desired control of structure–property relations

Synthesis and Characterization of Poly(arylene ether sulfone) Kraft Lignin Heat Stable Copolymers

In this effort we aim at documenting our understanding of using the phenolic hydroxyl groups of technical softwood kraft lignin in replacing the multifunctional phenolic component required for the synthesis of poly­(arylene ether) sulfones. To do this we use a two-pronged approach that uses fractionated softwood kraft lignin whose phenolic hydroxyl groups have been systematically protected in order to avoid gelation when copolymerized with 4, 4′-diflourodiphenyl sulfone (DFDPS). This has been done by careful ³¹P NMR profiling of the various hydroxyl groups present in the lignin as a function of the degree of phenolic hydroxyl group protection. For all copolymers, weight average molecular weights (<i>M</i>_w), polydispersity indices (PDI), glass transition temperatures (<i>T</i>_g), and thermal stability profiles (TGA) were obtained, providing an integrated picture of the scientific and technological ramifications of this work. Overall, this effort provides the foundations for creating lignin copolymers of controlled and modulated characteristics exhibiting augmented thermal stability. Such thermal properties and uniform molecular weight distributions of lignins and copolymers produced from commercial lignins provides a means for beneficially modulating the properties of an otherwise intractable biopolymer

A review of the combined torrefaction and densification technology as a source of renewable energy

Densification techniques allow biomass to be used in the energy mix with coal or as a direct replacement for coal as it is a renewable resource. Typically, biomass is bulky, so thermochemical methods, like torrefaction, reduce volatiles and moisture, leaving a higher composition of fixed carbon. After the torrefaction process, the torrefied biomass poses problems during handling, transportation, and storage because it consists of small (<100 μm) disintegrated particles. Densification minimizes these problems through thermal compaction which produces integrated and larger (4 mm – 200 mm diameter) solid particles. This process can be done naturally (without any additives) or by adding binders which improve the torrefied biomass’s physical, chemical, mechanical, and heating properties. This in turn reduces any costs associated with handling/transportation and storage of the biomass before it is used for energy generation. Densification increases the biomass’s energy content per unit volume thereby enabling coal substitution. Recent reviews on densification have mainly focused on the binding of coal fines, raw biomass, and some torrefied biomass. Reviews on the binding theories are also available. This current review focuses solely on the aspect of torrefied biomass densification and the factors associated with the process. Insights and recommendations for the possible application of an integrated biomass torrefaction and densification process were provided herein. In addition, the gaps in literature were identified to enable future research on the application of the process to realize innovative renewable energy production in industry