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21 pages, 1927 KiB

Open AccessArticle

Understanding the Mechanism of Action of Triazine-Phosphonate Derivatives as Flame Retardants for Cotton Fabric

by Monique M. Nguyen, M. Sameer Al-Abdul-Wahid, Krystal R. Fontenot, Elena E. Graves, SeChin Chang, Brian D. Condon, Casey C. Grimm and Gary A. Lorigan

Molecules 2015, 20(6), 11236-11256; https://doi.org/10.3390/molecules200611236 - 18 Jun 2015

Cited by 23 | Viewed by 9379

Abstract

Countless hours of research and studies on triazine, phosphonate, and their combination have provided insightful information into their flame retardant properties on polymeric systems. However, a limited number of studies shed light on the mechanism of flame retardancy of their combination on cotton [...] Read more.

Countless hours of research and studies on triazine, phosphonate, and their combination have provided insightful information into their flame retardant properties on polymeric systems. However, a limited number of studies shed light on the mechanism of flame retardancy of their combination on cotton fabrics. The purpose of this research is to gain an understanding of the thermal degradation process of two triazine-phosphonate derivatives on cotton fabric. The investigation included the preparation of diethyl 4,6-dichloro-1,3,5-triazin-2-ylphosphonate (TPN1) and dimethyl (4,6-dichloro-1,3,5-triazin-2-yloxy) methyl phosphonate (TPN3), their application on fabric materials, and the studies of their thermal degradation mechanism. The studies examined chemical components in both solid and gas phases by using attenuated total reflection infrared (ATR-IR) spectroscopy, thermogravimetric analysis coupled with Fourier transform infrared (TGA-FTIR) spectroscopy, and ³¹P solid state nuclear magnetic resonance (³¹P solid state NMR), in addition to the computational studies of bond dissociation energy (BDE). Despite a few differences in their decomposition, TPN1 and TPN3 produce one common major product that is believed to help reduce the flammability of the fabric. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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16 pages, 3186 KiB

Open AccessArticle

Enhanced Materials from Nature: Nanocellulose from Citrus Waste

by Mayra Mariño, Lucimara Lopes da Silva, Nelson Durán and Ljubica Tasic

Molecules 2015, 20(4), 5908-5923; https://doi.org/10.3390/molecules20045908 - 3 Apr 2015

Cited by 137 | Viewed by 12710

Abstract

Nanocellulose is a relatively inexpensive, highly versatile bio-based renewable material with advantageous properties, including biodegradability and nontoxicity. Numerous potential applications of nanocellulose, such as its use for the preparation of high-performance composites, have attracted much attention from industry. Owing to the low energy [...] Read more.

Nanocellulose is a relatively inexpensive, highly versatile bio-based renewable material with advantageous properties, including biodegradability and nontoxicity. Numerous potential applications of nanocellulose, such as its use for the preparation of high-performance composites, have attracted much attention from industry. Owing to the low energy consumption and the addition of significant value, nanocellulose extraction from agricultural waste is one of the best alternatives for waste treatment. Different techniques for the isolation and purification of nanocellulose have been reported, and combining these techniques influences the morphology of the resultant fibers. Herein, some of the extraction routes for obtaining nanocellulose from citrus waste are addressed. The morphology of nanocellulose was determined by Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM), while cellulose crystallinity indexes (CI) from lyophilized samples were determined using solid-state Nuclear Magnetic Resonance (NMR) and X-Ray Diffraction (XRD) measurements. The resultant nanofibers had 55% crystallinity, an average diameter of 10 nm and a length of 458 nm. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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16 pages, 4376 KiB

Open AccessArticle

Steric Stabilization of “Charge-Free” Cellulose Nanowhiskers by Grafting of Poly(ethylene glycol)

by Jun Araki and Shiho Mishima

Molecules 2015, 20(1), 169-184; https://doi.org/10.3390/molecules20010169 - 24 Dec 2014

Cited by 28 | Viewed by 9907

Abstract

A sterically stabilized aqueous suspension of “charge-free” cellulose nanowhiskers was prepared by hydrochloric acid hydrolysis of cotton powders and subsequent surface grafting of monomethoxy poly(ethylene glycol) (mPEG). The preparation scheme included carboxylation of the terminal hydroxyl groups in mPEG via oxidation with silica [...] Read more.

A sterically stabilized aqueous suspension of “charge-free” cellulose nanowhiskers was prepared by hydrochloric acid hydrolysis of cotton powders and subsequent surface grafting of monomethoxy poly(ethylene glycol) (mPEG). The preparation scheme included carboxylation of the terminal hydroxyl groups in mPEG via oxidation with silica gel particles carrying 2,2,6,6-tetramethyl-1-pyperidinyloxyl (TEMPO) moieties and subsequent esterification between terminal carboxyls in mPEG and surface hydroxyl groups of cellulose nanowhiskers, mediated by 1,1'-carbonyldiimidazole (CDI) in dimethyl sulfoxide or dimethylacetamide. Some of the prepared PEG-grafted samples showed remarkable flow birefringence and enhanced stability after 24 h, even in 0.1 M NaCl, suggesting successful steric stabilization by efficient mPEG grafting. Actual PEG grafting via ester linkages was confirmed by attenuated total reflectance-Fourier transform infrared spectrometry. In a typical example, the amount of grafted mPEG was estimated as ca. 0.3 g/g cellulose by two measurements, i.e., weight increase after grafting and weight loss after alkali cleavage of ester linkages. Transmission electron microscopy indicated unchanged nanowhisker morphology after mPEG grafting. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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16 pages, 1359 KiB

Open AccessArticle

Sulfated Chitosan Oligosaccharides Suppress LPS-Induced NO Production via JNK and NF-κB Inactivation

by Jung-Hyun Kim, Yon-Suk Kim, Jin-Woo Hwang, Young-Ki Han, Jung-Suck Lee, Se-Kwon Kim, You-Jin Jeon, Sang-Ho Moon, Byong-Tae Jeon, Young Yil Bahk and Pyo-Jam Park

Molecules 2014, 19(11), 18232-18247; https://doi.org/10.3390/molecules191118232 - 7 Nov 2014

Cited by 50 | Viewed by 9197

Abstract

Various biological effects have been reported for sulfated chitosan oligosaccharides, but the molecular mechanisms of action of their anti-inflammatory effects are still unknown. This study aimed to evaluate the anti-inflammatory effects of sulfated chitosan oligosaccharides and to elucidate the possible mechanisms of action. [...] Read more.

Various biological effects have been reported for sulfated chitosan oligosaccharides, but the molecular mechanisms of action of their anti-inflammatory effects are still unknown. This study aimed to evaluate the anti-inflammatory effects of sulfated chitosan oligosaccharides and to elucidate the possible mechanisms of action. The results showed that pretreated low molecular weight sulfated chitosan oligosaccharides inhibited the production of nitric oxide (NO) and inflammatory cytokines such as IL-6 and TNF-α in lipopolysaccharide (LPS)-activated RAW264.7 cells. The sulfated chitosan oligosaccharides also suppressed inducible nitric oxide synthase (iNOS), phosphorylation of JNK and translocation of p65, a subunit of NF-κB, into the nucleus by inhibiting degradation of IκB-α. Our investigation suggests sulfated chitosan oligosaccharides inhibit IL-6/TNF-α in LPS-induced macrophages, regulated by mitogen-activated protein kinases (MAPKs) pathways dependent on NF-κB activation. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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15 pages, 910 KiB

Open AccessArticle

ESI(+)-MS and GC-MS Study of the Hydrolysis of N-Azobenzyl Derivatives of Chitosan

by Fernanda S. Pereira, Heliara D. L. Nascimento, Alviclér Magalhães, Martin G. Peter, Giovana Anceski Bataglion, Marcos N. Eberlin and Eduardo R. P. González

Molecules 2014, 19(11), 17604-17618; https://doi.org/10.3390/molecules191117604 - 30 Oct 2014

Cited by 2 | Viewed by 7753

Abstract

New N-p-chloro-, N-p-bromo-, and N-p-nitrophenylazobenzylchitosan derivatives, as well as the corresponding azophenyl and azophenyl-p-sulfonic acids, were synthesized by coupling N-benzylvchitosan with aryl diazonium salts. The synthesized molecules were analyzed by UV-Vis, [...] Read more.

New N-p-chloro-, N-p-bromo-, and N-p-nitrophenylazobenzylchitosan derivatives, as well as the corresponding azophenyl and azophenyl-p-sulfonic acids, were synthesized by coupling N-benzylvchitosan with aryl diazonium salts. The synthesized molecules were analyzed by UV-Vis, FT-IR, ¹H-NMR and ¹⁵N-NMR spectroscopy. The capacity of copper chelation by these materials was studied by AAS. Chitosan and the derivatives were subjected to hydrolysis and the products were analyzed by ESI(+)-MS and GC-MS, confirming the formation of N-benzyl chitosan. Furthermore, the MS results indicate that a nucleophilic aromatic substitution (S_nAr) reaction occurs under hydrolysis conditions, yielding chloroaniline from N-p-bromo-, and N-p-nitrophenylazo-benzylchitosan as well as bromoaniline from N-p-chloro-, and N-p-nitrophenylazobenzyl-chitosan. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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32 pages, 906 KiB

Open AccessArticle

Radiation-Induced High-Temperature Conversion of Cellulose

by Alexander V. Ponomarev and Boris G. Ershov

Molecules 2014, 19(10), 16877-16908; https://doi.org/10.3390/molecules191016877 - 21 Oct 2014

Cited by 31 | Viewed by 8687

Abstract

Thermal decomposition of cellulose can be upgraded by means of an electron-beam irradiation to produce valuable organic products via chain mechanisms. The samples being irradiated decompose effectively at temperatures below the threshold of pyrolysis inception. Cellulose decomposition resembles local “explosion” of the glucopyranose [...] Read more.

Thermal decomposition of cellulose can be upgraded by means of an electron-beam irradiation to produce valuable organic products via chain mechanisms. The samples being irradiated decompose effectively at temperatures below the threshold of pyrolysis inception. Cellulose decomposition resembles local “explosion” of the glucopyranose unit when fast elimination of carbon dioxide and water precede formation of residual carbonyl or carboxyl compounds. The dry distillation being performed during an irradiation gives a liquid condensate where furfural and its derivatives are dominant components. Excessively fast heating is adverse, as it results in a decrease of the yield of key organic products because pyrolysis predominates over the radiolytic-controlled decomposition of feedstock. Most likely, conversion of cellulose starts via radiolytic formation of macroradicals do not conform with each other, resulting in instability of the macroradical. As a consequence, glucosidic bond cleavage, elimination of light fragments (water, carbon oxides, formaldehyde, etc.) and formation of furfural take place. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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8 pages, 886 KiB

Open AccessCommunication

Photoregeneration of Trimethylsilyl Cellulose as a Tool for Microstructuring Ultrathin Cellulose Supports

by Archim Wolfberger, Rupert Kargl, Thomas Griesser and Stefan Spirk

Molecules 2014, 19(10), 16266-16273; https://doi.org/10.3390/molecules191016266 - 10 Oct 2014

Cited by 12 | Viewed by 7285

Abstract

Microstructured thin films based on cellulose, the most abundant biopolymer on Earth, have been obtained by UV-irradiation of acid-labile trimethylsilyl cellulose thin films in the presence of N-hydroxynaphtalimide triflate as photoacid generator. We demonstrate that this photoregeneration process can be exploited for [...] Read more.

Microstructured thin films based on cellulose, the most abundant biopolymer on Earth, have been obtained by UV-irradiation of acid-labile trimethylsilyl cellulose thin films in the presence of N-hydroxynaphtalimide triflate as photoacid generator. We demonstrate that this photoregeneration process can be exploited for the manufacture of cellulose patterns having feature sizes down to 1 μm, with potential applications in life sciences. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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Review

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29 pages, 946 KiB

Open AccessReview

Overview of Methods for the Direct Molar Mass Determination of Cellulose

by Josua Timotheus Oberlerchner, Thomas Rosenau and Antje Potthast

Molecules 2015, 20(6), 10313-10341; https://doi.org/10.3390/molecules200610313 - 4 Jun 2015

Cited by 93 | Viewed by 16288

Abstract

The purpose of this article is to provide the reader with an overview of the methods used to determine the molecular weights of cellulose. Methods that employ direct dissolution of the cellulose polymer are described; hence methods for investigating the molecular weight of [...] Read more.

The purpose of this article is to provide the reader with an overview of the methods used to determine the molecular weights of cellulose. Methods that employ direct dissolution of the cellulose polymer are described; hence methods for investigating the molecular weight of cellulose in derivatized states, such as ethers or esters, only form a minor part of this review. Many of the methods described are primarily of historical interest since they have no use in modern cellulose chemistry. However, older methods, such as osmometry or ultracentrifuge experiments, were the first analytical methods used in polymer chemistry and continue to serve as sources of fundamental information (such as the cellulose structure in solution). The first part of the paper reviews methods, either absolute or relative, for the estimation of average molecular weights. Regardless of an absolute or relative approach, the outcome is a molecular weight average (MWA). In the final section, coupling methods are described. The primary benefit of performing a pre-separation step on the molecules is the discovery of the molecular weight distribution (MWD). Here, size exclusion chromatography (SEC) is unquestionably the most powerful and most commonly-applied method in modern laboratories and industrial settings. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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16 pages, 1634 KiB

Open AccessReview

Nanofibers of Cellulose and Its Derivatives Fabricated Using Direct Electrospinning

by Kousaku Ohkawa

Molecules 2015, 20(5), 9139-9154; https://doi.org/10.3390/molecules20059139 - 19 May 2015

Cited by 70 | Viewed by 9850

Abstract

A short review with 49 references describes the electrospinninng (ES) process for polysaccharides, cellulose and chitosan, and their derivatives, including cellulose acetate and hydroxypropyl cellulose. A majority of applied studies adopted a two step-process, in which the cellulose acetate was used for the [...] Read more.

A short review with 49 references describes the electrospinninng (ES) process for polysaccharides, cellulose and chitosan, and their derivatives, including cellulose acetate and hydroxypropyl cellulose. A majority of applied studies adopted a two step-process, in which the cellulose acetate was used for the first ES process, followed by acetyl group removal to regenerate cellulose thin fibers. The electrospun nonwoven fabrics (ESNW) of regenerated cellulose can be modified by introduction of aldehyde groups by oxidative cleavage of vicinal diols using periodates, and these aldehyde groups serve as acceptors of foreign substances, with various chemical/biological functions, to be immobilized on the fiber surfaces in the ESNW matrices. Direct electrospinning of cellulose from trifluroacetic acid solution was also developed and the applied studies were summarized to conclude the current trends of interests in the ES and related technologies. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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41 pages, 7419 KiB

Open AccessReview

Functional Thermoplastic Materials from Derivatives of Cellulose and Related Structural Polysaccharides

by Yoshikuni Teramoto

Molecules 2015, 20(4), 5487-5527; https://doi.org/10.3390/molecules20045487 - 27 Mar 2015

Cited by 59 | Viewed by 14974

Abstract

This review surveys advances in the development of various material functionalities based on thermoplastic cellulose and related structural polysaccharide derivatives. First, the dependence of thermal (phase) transition behavior on the molecular composition of simple derivatives is rationalized. Next, approaches enabling effective thermoplasticization and [...] Read more.

This review surveys advances in the development of various material functionalities based on thermoplastic cellulose and related structural polysaccharide derivatives. First, the dependence of thermal (phase) transition behavior on the molecular composition of simple derivatives is rationalized. Next, approaches enabling effective thermoplasticization and further incorporation of material functionalities into structural polysaccharides are discussed. These approaches include: (a) single-substituent derivatization, (b) derivatization with multi-substituents, (c) blending of simple derivatives with synthetic polymers, and (d) graft copolymerization. Some examples addressing the control of supramolecular structures and the regulation of molecular and segmental orientations for functional materials fabrication, which have especially progressed over the past decade, are also addressed. Attractive material functions include improved mechanical performance, controlled biodegradability, cytocompatiblity, and optical functions. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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14 pages, 1888 KiB

Open AccessReview

Chemically-Modified Cellulose Paper as a Microstructured Catalytic Reactor

by Hirotaka Koga, Takuya Kitaoka and Akira Isogai

Molecules 2015, 20(1), 1495-1508; https://doi.org/10.3390/molecules20011495 - 15 Jan 2015

Cited by 28 | Viewed by 10269

Abstract

We discuss the successful use of chemically-modified cellulose paper as a microstructured catalytic reactor for the production of useful chemicals. The chemical modification of cellulose paper was achieved using a silane-coupling technique. Amine-modified paper was directly used as a base catalyst for the [...] Read more.

We discuss the successful use of chemically-modified cellulose paper as a microstructured catalytic reactor for the production of useful chemicals. The chemical modification of cellulose paper was achieved using a silane-coupling technique. Amine-modified paper was directly used as a base catalyst for the Knoevenagel condensation reaction. Methacrylate-modified paper was used for the immobilization of lipase and then in nonaqueous transesterification processes. These catalytic paper materials offer high reaction efficiencies and have excellent practical properties. We suggest that the paper-specific interconnected microstructure with pulp fiber networks provides fast mixing of the reactants and efficient transport of the reactants to the catalytically-active sites. This concept is expected to be a promising route to green and sustainable chemistry. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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14 pages, 1819 KiB

Open AccessReview

Chitin and Chitosan Nanofibers: Preparation and Chemical Modifications

by Shinsuke Ifuku

Molecules 2014, 19(11), 18367-18380; https://doi.org/10.3390/molecules191118367 - 11 Nov 2014

Cited by 224 | Viewed by 21951

Abstract

Chitin nanofibers are prepared from the exoskeletons of crabs and prawns, squid pens and mushrooms by a simple mechanical treatment after a series of purification steps. The nanofibers have fine nanofiber networks with a uniform width of approximately 10 nm. The method used [...] Read more.

Chitin nanofibers are prepared from the exoskeletons of crabs and prawns, squid pens and mushrooms by a simple mechanical treatment after a series of purification steps. The nanofibers have fine nanofiber networks with a uniform width of approximately 10 nm. The method used for chitin-nanofiber isolation is also successfully applied to the cell walls of mushrooms. Commercial chitin and chitosan powders are also easily converted into nanofibers by mechanical treatment, since these powders consist of nanofiber aggregates. Grinders and high-pressure waterjet systems are effective for disintegrating chitin into nanofibers. Acidic conditions are the key factor to facilitate mechanical fibrillation. Surface modification is an effective way to change the surface property and to endow nanofiber surface with other properties. Several modifications to the chitin NF surface are achieved, including acetylation, deacetylation, phthaloylation, naphthaloylation, maleylation, chlorination, TEMPO-mediated oxidation, and graft polymerization. Those derivatives and their properties are characterized. Full article

(This article belongs to the Special Issue New Trends in Cellulose and Chitin Chemistry)

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