Low Degree Of Substitution Research Articles

Low degree of substitution of cellulose acrylate based green polyelectrolyte: Synthesis, characterization and application to the removal of Cu (II) ions and colloidal Fe(OH)3 turbidity

The uncontrolled radical grafting of acrylamide on cellulose generates a disorderly size distribution of grafted and ungrafted (as a by-product) PAM chains, which required additional purification steps. At this stage, the anionic grafting appears as a well-controlled grafting method of acrylic entities on the cellulosic backbone, using alkali alkoxylation to increase the reactivity of OH-cellulosic groups, and water as transfer agent for hydrogen to stop chain extension and to prevent the formation of polyacrylamide. Based on this mechanism, low Degree of Substitution of cellulose acrylate was elaborated in NaOH/Urea/H2O and used as low-cost, eco-friendly and nontoxic water-soluble polymers. The proposed synthesis were confirmed using (FTIR-ATR) and (1H NMR and 13C NMR). However, SEM-EDX and XRD shows the effect of the incorporation of acrylate entities on the morphology, the surface composition and the crystalline order of cellulose, respectively. Flocculation-coagulation study, according to the effect of various experimental parameters (pH, reaction time, flocculant concentrations, etc.), showed an excellent capacity to heavy metals ions removal (qeCu2+ = 400 mg.g-1) and to cationic colloïdal systems clarification (99% to Fe(OH)3) at neutral conditions (pH7).

Ultrasound-assisted catalyst-free thiol-yne click reaction in chitosan chemistry: Antibacterial and transfection activity of novel cationic chitosan derivatives and their based nanoparticles

In this work, we demonstrate that the thiol-yne click reaction could be efficiently mediated by ultrasonic irradiation and implement the ultrasound-assisted thiol-yne click reaction to chitosan chemistry as a polymer-analogous transformation. We optimize power and frequency of ultrasound to preserve selectivity of the click reaction and avoid ultrasonic degradation of the chitosan polymer chain. Thus, we obtain a new water-soluble betaine. Using ionic gelation of the obtained betaine derivatives of chitosan, we prepare nanoparticles with a unimodal size distribution. Furthermore, we present results of antibacterial and transfection activity tests for the chitosan derivatives and their based nanoparticles. The derivative with a medium molecular weight and a high degree of substitution demonstrated the best antibacterial effect. It derived nanoparticles with a size of ca. 100 nm and ζ-potential of ca. +69 mV revealed even higher antibacterial activity, slightly superior to commercial antibiotics ampicillin and gentamicin. On the contrary, the obtained polymers possess a much more pronounced transfection activity as compared with their based nanoparticles and species with a low degree of substitution acts as the most efficient transfecting agent. Moreover, the obtained betaine chitosan derivatives as well as their derived nanoparticles are non-toxic.

Mechanochemical effect of ultrasound on sweet potato starch and its influence mechanism on the quality of octenyl succinic anhydride modified starch.

The purpose of this study is to reveal the mechanism of preparing high quality modified starch by ultrasonic technology. In this paper, ultrasonic modified starch and octenyl succinic anhydride modified starch with low degree of substitution were prepared under ultrasonic conditions, using sweet potato starch as raw material. The effects of ultrasound on the structure and properties of native sweet potato starch were studied to see whether ultrasound could produce mechanochemical effect on starch. Then the mechanism of ultrasonic effect on quality of octenyl succinic anhydride modified starch was studied by mechanochemical effect. The results showed that after ultrasonic treatment for 1 min, the crystallinity decreased from 37.6 to 33.8% and reaction efficiency increased from 49.43 to 54.39%, while after ultrasonic treatments for 8 and 32-60 min had different changes. These changes showed that ultrasonic treatment produced significant mechanochemical effect on native sweet potato starch. Ultrasound significantly improved the quality of octenyl succinic anhydride modified starch, and its influence mechanism was revealed using the theory of mechanochemistry. This study provides a feasible method for the research of high quality modified starch and lays a theoretical foundation for expanding the application of ultrasound in various fields.

Preparation of acetylated starch by rolling-assisted method and its influence mechanism

Advanced equipment can be used to produce high quality modified starch, but the secrets of these equipment are still unclear. In this study, cassava starch was taken as the research object to produce acetylated starch with low degree of substitution under rolling. Effects of rolling on acetylated starch quality and the changes in structures and properties of native starch were studied. The influence mechanisms of rolling on the quality of acetylated starch was analyzed according to the theory of mechanochemistry. The results indicated that the quality of acetylated starch increased prominently after rolling for 2 h and 12 h, and the reaction efficiency increased to 71.61% and 72.77%, respectively. The changes in structures and properties of native starch indicated that rolling have a significant mechanochemical effect on starch granules. With the increase of rolling time, the interior of starch granules gradually experienced the stress, aggregation and agglomeration stages, consecutively. Therefore, the quality of acetylated starch was improved significantly. In addition, the three stages of mechanochemical effect of starch varied in terms of influence mechanisms, so the mechanism of preparing high quality modified starch by means of advanced equipment was revealed.

Preparation of octenyl succinic anhydride‐modified cassava starch by the ultrasonic‐assisted method and its influence mechanism

As an effective physical method for starch modification, ultrasonic treatment can significantly improve the chemical activity and quality of starch, but its mechanism needs to be further investigated. In this paper, ultrasonic-modified cassava starch and octenyl succinic anhydride (OSA)-modified cassava starch with low degree of substitution were prepared under ultrasonic conditions. The effects of ultrasound on the structure and properties of native cassava starch and the quality of OSA-modified cassava starch were studied. The results showed that the crystallinity decreased from 30.7% to 26.4%, the reaction efficiency increased from 62.28% to 66.20%, and other characteristics also changed after 1 min of ultrasonic treatment. While the structure and properties of cassava starch changed differently after ultrasonic treatments for 8 min and 32–60 min. Consequently, these changes showed that ultrasonic treatment had a significant mechanochemical effect on starch granules. The quality of OSA-modified cassava starch was improved significantly and its influence mechanism was analyzed by the mechanochemistry theory. Practical applications During the esterification of starch, the dense arrangement of crystalline regions limits the reaction of esterifying agents with starch granules. This study showed that ultrasound exerted strong mechanical forces on starch granules, which promoted the production of free radicals and increased the free energy of starch molecules. Besides, the increase of mechanochemical active sites in starch granules was conducive to the homogeneous reaction of octenyl succinic anhydride (OSA) and starch molecules. Therefore, the quality of OSA-modified cassava starch prepared by ultrasonic-assisted treatment was significantly improved. This study provides a reference for the application of ultrasonic technology in other fields and also lays a theoretical basis for the industrial development of high performance-modified starch.

Carbamation of Starch with Amine Using Dimethyl Carbonate as Coupling Agent.

A one-pot coupling of starch with alkyl amine was studied using dimethyl carbonate (DMC) as the coupling agent. Although reaction occurred without a catalyst (24 h, 70 °C), different catalysts, namely, imidazole, tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and combinations thereof were investigated to improve the reaction efficiency. When 20 mol % DBU was used as a catalyst, the degree of substitution (DS) could be improved from 0.05 to 0.15 compared to the noncatalyzed reaction. When the amount of DBU was decreased to 5 mol %, catalytical activity remained, albeit with a slightly lower DS (0.09). Temperature did not have a significant effect on the DS but it could be used to alter the solubility of the product. Based on chemical analysis, the alkyl group was attached to starch by the formation of a carbamate group. As the carbonyl carbon in the carbamate originated from DMC, which, in turn, can be produced from carbon dioxide on an industrial scale, the current study provides a conventional way to utilize carbon dioxide-based chemicals in the functionalization of a natural polymer. DMC is also biodegradable and classified as a nonvolatile organic component, making it an environmentally desirable coupling agent.

Preparation, characterization, and emulsification properties of agarose fatty acid derivatives with different hydrophobic chains

Two types of fatty acid derivatives were used to synthesize agarose fatty acid esters in a heterogeneous medium. Agarose esters with low degree of substitution were synthesized with succinic anhydride, octenyl succinic anhydride, dodecyl succinic anhydride as esterifying agents. Agarose esters with high degree of substitution were synthesized with lauroyl chloride, palmitoyl chloride, and stearoyl chloride as esterifying agents. Scanning electron microscopy revealed that agarose anhydride modification mostly occurred at the surface of the particles, whereas chloride modification occurred at both the surface and interior of the particles. Fourier transform infrared spectroscopy and nuclear magnetic resonance analyses indicated that hydrophobic groups were successfully introduced in agarose, and the hydroxyl group in the C-2 of D-galactose was the preferred location for esterification. The results also showed that agarose esters with long-chain fatty acids and high substitution degree showed higher emulsifying ability and low interfacial tension property than derivatives with short-chain fatty acids and low substitution degree. Compared with commonly used food emulsifiers, such as Tween, sucrose fatty acid ester, and glycerin monostearate, agarose esters were slightly deficient in emulsifying ability but presented high emulsion stability in oil-in-water emulsion.

Flocculation of silica nanoparticles by natural, wood-based polyelectrolytes

Wood-based polyelectrolytes, produced from renewable and biodegradable sources, can be considered as more environmentally friendly flocculation agents for the wastewater treatment compared to the traditional synthetic flocculants.The aim of this study was to produce new natural-based polyelectrolytes (bio-PELs), water-soluble, cationic cellulose-based polymers derived from Eucalyptus bleached fibres (CDACf) and to evaluate their effectiveness as flocculation agents by studying their interaction with model particles and the associated particle flocculation and accelerated sedimentation. Three different CDACf with varying cationicity index/degree of substitution and molecular weight were synthesized by a two-step reaction. Firstly, by periodate oxidation of the surplus bleached fibres, the introduction of reactive aldehyde groups into the cellulose backbone can be achieved. This is followed by modification of the resulting polymers by introducing alkylammonium positively charged groups in the cellulosic chain, thus resulting in the formation of bio-derived, water-soluble, bio-PELs. The final products were characterized by several analytical techniques: FTIR-ATR, 1H NMR, elemental analysis, dynamic light scattering, and electrophoretic light scattering. The CDACf with the highest and the lowest degree of substitution (DS) of cationic groups were evaluated for their performance in solid/liquid separation of silica suspensions. The CDACf with the highest cationicity performed better at lower dosages while higher bio-PEL dosages for the same apparent sedimentation efficiency were needed for the bio-PEL with lower charge density.

Homogenous synthesis of sodium cellulose sulfates with regulable low and high degree of substitutions with SO3/Py in N,N-dimethylacetamide/LiCl

Synthesis possibility of cellulose sulfates with a low and high degree of substitution (DS) by direct homogenous sulfation of cotton cellulose in N,N-dimethylacetamide/lithium chloride (DMA/LiCl) using SO3/pyridine (Py) complex was studied comprehensively. The sulfation reactions were carried at different temperatures, time durations, amount of the sulfating reagent and celluloses with varying weight average degree of polymerization (DPw). It was found that the method is very appropriate to prepare sodium cellulose sulfate (SCS) with low and high DS from celluloses having wide range DPw. Completely water-soluble SCS samples with regulable DS values from 0.23 to 2.56 were obtained. Suitable conditions were proposed to gain high sulfate content and the samples with DS values of 2.16–2.32, and yield of 69.4–77.8% could be prepared in these conditions. Celluloses with low and high DPw values exhibited similar reactivity for sulfation. Precipitation of the product and drastic depolymerization in the polymer chain have not occurred during the reaction.

Carboxymethyl Cellulose Nanofibrils with a Treelike Matrix: Preparation and Behavior of Pickering Emulsions Stabilization

Carboxymethyl cellulose nanofibrils (CMCNFs) are of great importance in the fields of sustainable chemistry and energy materials but challenging in preparation, e.g., low yield, pollution, and morphology control. In this work, CMCNFs with a quantitative yield (95%) and good morphology control were successfully achieved using a simple, low-cost, and relatively ecofriendly protocol. Water-insoluble carboxymethyl cellulose (CMC) with a low degree of substitution (DS ≤ 0.35) was obtained via moderate alkalization and etherification of cellulose raw materials and then was mechanically fibrillated to prepare CMCNFs using a microfluidizer. As the DS of the CMCNFs was increased from 0.05 to 0.35, the diameter was obviously decreased from 100 to 35 nm without changing the treelike matrix that was confirmed by TEM characterization. More importantly, there is no obvious difference in the final performance of the CMCNFs derived from different cellulose raw materials (i.e., cotton and wood) through this approach. Additionally, compared with the commercial CNFs, high stabilization of Pickering emulsions stabilized by the CMCNFs (DS = 0.23) could be achieved because of its novel morphology with a network structure, implying that the CMCNFs could potentially serve as a biofunctional stabilizer.

Acetylated Nanocellulose for Single-Component Bioinks and Cell Proliferation on 3D-Printed Scaffolds.

Nanocellulose has been demonstrated as a suitable material for cell culturing, given its similarity to extracellular matrices. Taking advantage of the shear thinning behavior, nanocellulose suits three-dimensional (3D) printing into scaffolds that support cell attachment and proliferation. Here, we propose aqueous suspensions of acetylated nanocellulose of a low degree of substitution for direct ink writing (DIW). This benefits from the heterogeneous acetylation of precursor cellulosic fibers, which eases their deconstruction and confers the characteristics required for extrusion in DIW. Accordingly, the morphology of related 3D-printed architectures and their performance during drying and rewetting as well as interactions with living cells are compared with those produced from typical unmodified and TEMPO-oxidized nanocelluloses. We find that a significantly lower concentration of acetylated nanofibrils is needed to obtain bioinks of similar performance, affording more porous structures. Together with their high surface charge and axial aspect, acetylated nanocellulose produces dimensionally stable monolithic scaffolds that support drying and rewetting, required for packaging and sterilization. Considering their potential uses in cardiac devices, we discuss the interactions of the scaffolds with cardiac myoblast cells. Attachment, proliferation, and viability for 21 days are demonstrated. Overall, the performance of acetylated nanocellulose bioinks opens the possibility for reliable and scale-up fabrication of scaffolds appropriate for studies on cellular processes and for tissue engineering.

Influences of grinding on structures and properties of mung bean starch and quality of acetylated starch

The aim of this study was to reveal the mechanism of preparing high quality modified starch by grinding. Modified starch and acetylated starch with low degree of substitution were prepared under grinding. The influences of grinding on structures and properties of mung bean starch and quality of acetylated starch were investigated. The influence mechanisms were analyzed using the theory of mechanochemistry and the models of starch granules and molecules. The results indicated that there were pores and umbilical points with loose structure in mung bean starch granules. During the grinding treatment, starch granules were constantly deformed like elastic balls, and starch molecules could keep moving and rearrange, resulting in changes in structures and properties of starch. It could be seen that grinding had a marked mechanochemical effect on starch granules. As a result, the reaction efficiency of the starch rose to 81.61% at 12 h of grinding, and other qualities (solubility and swelling power) were also improved.

Effects of carboxymethyl cellulose grafting on stability and reactivity of zerovalent iron in water systems

The present study investigated the effects of degree of substitution (DS) and grafting method (pre-grafting or post-grafting) of carboxymethyl cellulose (CMC) on particle size, surface chemistry, colloidal and oxidative stability and reactivity of zerovalent iron (ZVI) particles. CMC with different DS were systematically synthesized by etherification of cellulose using monochloroacetic acid (MCA) in alcoholic medium. Structural Identity and purity of CMC was confirmed using NMR, FTIR and XRD analyses. It was found that DS of CMC can regulate the particle size, stability, dispersibility and reactivity of stabilized ZVI particles. CMC stabilized ZVI particles had smaller particle size, higher surface area and high dispersibility as compared to bare ZVI particles. Further, less aggregation was observed in higher DS CMC stabilized ZVI samples compared to lower DS CMC stabilized ZVI samples due to the better shielding ability for van der waals attractive forces. Also, the reactivity of stabilized ZVI particles was better than bare ZVI particles as the complete degradation of naphthenic acid was achieved in 180 min (>95% in 60 min). The colloidal stability and reactivity of stabilized ZVI particles remained intact even after 6 months of storage. Overall, CMC was found most efficient in colloidal stabilization of ZVI particles both in pre-grafting as well as post-grafting mode.

Hierarchically built hyaluronan nano-platelets have symmetrical hexagonal shape, flattened surfaces and controlled size

Most of nanomaterials composed of hyaluronic acid (HA) used for drug targeting are spherical. In this investigation, we suggest that the morphology of HA nanomaterials could be considered as a new parameter to control their interactions with cells. However, designing nanomaterials with elongated morphology and controlled size is still challenging. The aim of this study was to design and to characterize non-spherical HA nanomaterials with flat surfaces and to highlight main parameters controlling the size. Nanoparticles were formed by mixing HA hydrophobically-modified with palmitoyl groups (PA-HA) and α-cyclodextrin in water. These particles, called nano-platelets, had symmetrical hexagonal shape, flattened surfaces and were 9-fold larger than thick. Small nano-platelets with well-defined shape were obtained with low PA-HA degree of substitution, by adding 5 wt% of α-cyclodextrin solution for a fixed concentration of PA-HA (1 wt%) (569 nm) and for long stirring periods (735–538 nm for 72–168 h). PA-HA was successfully conjugated to a near-infrared fluorescent probe suitable for in vitro and in vivo experiments without nano-platelet size and surface charge modification. This is the first report showing the design of non-spherical and flattened HA nano-platelets that could be used to study the impact of nanomaterial shape on molecular interactions with cells.

Synthesis of novel 1H-tetrazole derivatives of chitosan via metal-catalyzed 1,3-dipolar cycloaddition. Catalytic and antibacterial properties of [3-(1H-tetrazole-5-yl)ethyl]chitosan and its nanoparticles.

New tetrazole derivatives of chitosan with low, moderate, and high degrees of substitution were obtained using a novel approach, i.e. metal-catalyzed 1,3-dipolar cycloaddition of azide ion to cyanoethyl chitosan in water - the most straightforward, selective and preparatively convenient route to tetrazole chitosan derivatives. Ionic gelation of these tetrazole derivatives with sodium tripolyphosphate resulted in nanoparticles with an apparent hydrodynamic diameter of 100-800 nm and ζ-potential of 22-57 mV. The tetrazole derivatives of chitosan and their nanoparticles were tested as catalysts of the aldol reaction between p-chlorobenzaldehyde and acetone. The tetrazole derivatives have been found to possess better catalytic properties than the corresponding nanoparticles. The obtained data indicate that the tetrazole-chitosan polymers exhibit high catalytic activity in aldol reaction, and these catalysts are among the best studied so far. Tetrazole derivatives and their nanoparticles were also tested as antibacterial agents. The in vitro antibacterial activity against S. aureus and E. coli of the tetrazole-chitosan-based nanoparticles is much more than the activity of the corresponding tetrazole-chitosan polymers, and their activity is comparable with that of antibiotics ampicillin and gentamicin.

An injectable and self‐healing novel chitosan hydrogel with low adamantane substitution degree

AbstractChitosan (CS) is a semi‐natural polymer with supreme biological function, while the strong interchain hydrogen bonds cause poor water solubility and limit its broader use. To break the semi‐rigid structure of CS, a kind of CS modified by adamantane (AD‐CS) was successfully synthesized by amidation reaction with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride as catalyst. The chemical structure of AD‐CS was characterized by Fourier transform infrared spectroscopy and 1H NMR. The AD substitution degree of CS is around 2%, calculated by 1H NMR. A soft and transparent hydrogel composed of hydrogen bonds was obtained directly by simply adding a certain amount of water under mild conditions. Rheological measurements were carried out to research the mechanism of hydrogel formation by measuring the influence of different additives and conditions on the AD‐CS hydrogel. Reinforced hydrogels were prepared by freezing and thawing. The mechanical strength and self‐healing property of reinforced and pristine hydrogels were assessed with an oscillatory rheometer. The modulus of the reinforced hydrogel was obviously enhanced without much loss of self‐healing property. Other properties such as adhesion, injectability and temperature response were also studied. These injectable and self‐healing hydrogels show potential value in medical care. Additionally, this is a new method to design CS hydrogels with their original interchain hydrogen bonds. © 2019 Society of Chemical Industry

Ion substitution induced formation of spherical ceramic particles

How to precipitate ceramic nano- and microspheres in water based solutions only using inorganic ions is a challenge. In this study, spherical particles of alkaline earth phosphates and fluorides were synthesized using a precipitation reaction. Substituting ions, through inhibition of crystal growth, was used to induce sphere formation and to alter the morphology, size and composition of the spheres. The difference in ionic radius between the substituting ion (Mg, Ca and Sr) and the main cation (Sr and Ba) influenced the critical concentration to allow for sphere formation as well as the crystallinity. The larger difference, the lower was the concentration needed to form spheres. Low concentrations of Mg was enough to generate amorphous spheres of Sr- and Ba-phosphates whereas higher concentrations were needed if the radius difference were smaller. An increasing degree of substitution leads to a decrease in crystallinity of precipitated particles. The degree of substitution was determined to 16–55% where a low degree of ion substitution in the phosphates resulted in the formation of spheres (500–800 nm) with rough surfaces composed of apatite like phases. A higher degree of substitution resulted in amorphous spheres (500 nm- 1 μm) with smooth surfaces.

Arabinose substitution effect on xylan rigidity and self-aggregation

Substituted xylans play an important role in the structure and mechanics of the primary cell wall of plants. Arabinoxylans (AX) consist of a xylose backbone substituted with arabinose, while glucuronoarabinoxylans (GAX) also contain glucuronic acid substitutions and ferulic acid esters on some of the arabinoses. We provide a molecular-level description on the dependence of xylan conformational, self-aggregation properties and binding to cellulose on the degree of arabinose substitution. Molecular dynamics simulations reveal fully solubilized xylans with a low degree of arabinose substitution (lsAX) to be stiffer than their highly substituted (hsAX) counterparts. Small-angle neutron scattering experiments indicate that both wild-type hsAX and debranched lsAX form macromolecular networks that are penetrated by water. In those networks, lsAX are more folded and entangled than hsAX chains. Increased conformational entropy upon network formation for hsAX contributes to AX loss of solubility upon debranching. Furthermore, simulations show the intermolecular contacts to cellulose are not affected by arabinose substitution (within the margin of error). Ferulic acid is the GAX moiety found here to bind to cellulose most strongly, suggesting it may play an anchoring role to strengthen GAX-cellulose interactions. The above results suggest highly substituted GAX acts as a spacer, keeping cellulose microfibrils apart, whereas low substitution GAX is more localized in plant cell walls and promotes cellulose bundling.

Influence of the chemical structure of different carboxymethylcelluloses on the performance of clay dispersions

Abstract The aim of this work was to evaluate the influence of the chemical structure of carboxymethylcellulose (CMC) on the rheological performance and fluid loss of clay dispersions. The dispersions were prepared with a fixed content of bentonite clay (15 g/350 mL of water) and different concentrations of CMCs (0.5, 1.0, 2.0 g/350 mL of water). After aging for 24 h in ambient and static conditions, the dispersions were tested in a viscometer. Apparent and plastic viscosities, yield point and gel strength were obtained using the viscometer, according to Petrobras’ standard (EP-1EP-00011-A). The filtrate volume was determined using the API filter press. The results showed that the addition of long chain, low degree of substitution and lower substitution uniformity of CMC contribute to the flocculation phenomenon. In addition, the different chemical characteristics of CMC only influence fluid loss when the ionic strength of the dispersion is set to any other value than zero.

Structural characterization and mechanical properties of dextrin-graft-poly(butyl acrylate-co-styrene) copolymers

Dextrin/starch-graft-poly(butyl acrylate-co-styrene) copolymers have been synthesized by radical graft copoly-merization and their structure and mechanical properties are reported. High molecular weight grafted chains formation isfavored, leading to a low degree of substitution of starch hydroxyl groups. Wide-Angle-X-ray Scattering (WAXS) analysisindicates that all materials are amorphous and Transmission Electron Microscopy (TEM) investigations reveal a two-phasemorphology. This is further confirmed by the presence of two glass transitions, one related to the starch/dextrin macromol-ecules and sensitive to water content, and one assigned to the grafted polymers that is composition dependent. Water uptakeis controlled by dextrin/starch content but diffusivity increases with the butyl acrylate ratio. The mechanical behavior is de-pendent on monomer ratio, and water content. Increasing butyl acrylate ratio improves the ductility of the sample while ma-terials become brittle as soon as styrene ratio is predominant in the grafted chains. While no effect of molecular weight ofstarch substrate on structure and thermal behavior is evidenced, dextrin-based materials are slightly more ductile than starch-based ones. The interest of using dextrin instead of starch is further highlighted by a lower viscosity of the reactive medium,together with an improved processability, as structural materials can be obtained over a wider range of composition thanwith native starch.