A simple method for the preparation of stable chitooligomers

The chitosan was degraded by the cheap, efficient, and commercially available enzymes in hydrochloric acid solution. The effect of molar ratio of added HCl to ? NH₂ of chitosan on the degradation was investigated, and the favorable ratio was between 0.50 and 0.95. The chitooligomer hydrochlorides were directly prepared by this simple method. The chitooligomer hydrochlorides were characterized by thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared. These results show that the obtained chitooligomer hydrochlorides were much more stable than the chitooligomer acetates. This preparation procedure of chitooligomer hydrochlorides was simple and cheap, and helpful for the preservation of chitooligomers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal stability and thermal oxidation kinetics of PU/CA-MMT composites

In this work, we prepared three composites polyurethane (PU)/chlorhexidine acetate (CA), PU/montmorillonite (MMT), and PU/CA-MMT, and investigated their kinetics of thermal degradation at different heating rates at atmosphere. These materials had good thermal stability and aging resistance. The thermal stability of PU/CA (T_onset: 237.3°C) was not obviously enhanced by the addition of only CA when compared with that of PU (T_onset: 232.3°C), while the thermal stability of PU/MMT (T_onset: 273.4°C) was considerably enhanced by the addition of MMT due to the high thermal stability of MMT. CA-MMT filler was dispersed and exfoliated in PU more easily than CA or MMT in PU, so the composite PU/CA-MMT possessed the best thermal stability (T_onset: 285.8°C). In addition, PU/CA-MMT also had the best resistance to bacterial adhesion and antibacterial ability. The analysis with Flynn-Wall-Ozawa method showed that the activation energy of thermal oxidation of PU increased when CA-MMT was added and thus its anti-aging ability was enhanced, and the thermal oxidation of these four materials was first-order reaction. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47002.     

Changes of oxygen-containing groups during thermal treatment and their influences on moisture readsorption of lignite

The changes in oxygen-containing groups in the thermal treatment process of lignite were analyzed and the moisture readsorption amounts of upgraded coals were related in this study. A chemical titration method was applied to determine the types and contents of oxygen-containing groups in raw lignite and upgraded coals obtained in the temperature range of 353–633 K under atmospheres of argon, air, and carbon dioxide. Experimental results showed that the oxygen-containing groups mainly involved carbonyl, phenolic hydroxyl, and carboxylic groups (including carboxyl and carboxylate), among which phenolic groups were dominant. These different oxygen-containing groups decomposed discriminatingly with temperature according to thermal stability. The removal of oxygen-containing groups proceeded more easily in a CO₂ atmosphere compared to in Ar. The oxidation reaction occurring on the surface of lignite exposed to air led to an increase in oxygen-containing groups. The different types of oxygen-containing groups possessed various combining abilities with water, among which carboxyl was considered the most important group for the moisture readsorption. Decomposition of oxygen-containing groups in the thermal treatment process of lignite mainly caused a reduction in monolayer water adsorption and further decreased the multilayer water.     

海藻酸钠TEMPO改性及其在造纸中的应用初探

钙离子对实现造纸白水封闭循环有关键性的制约作用。通过对天然海藻酸钠进行改性来制备高羧基含量的化学助剂用于造纸湿部,可以起到控制钙离子影响的效果。通过测定2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)改性海藻酸钠羧基含量和螯合值,分析研究了NaClO用量、pH值和温度对反应过程的影响。选取氧化后羧基含量为2.14%、3.61%和未氧化(1.96%)的三组海藻酸钠添加到造纸湿部中进行应用实验,结果表明在一定的添加量下海藻酸钠能提高纸料的留着、滤水性能,并同时提高纸张强度。海藻酸钠加入量0.02%时最佳,并且羧基含量为3.61%的改性海藻酸钠作用效果最好。     

羧基化改性纤维素凝胶球的制备和表征

以微晶纤维素为原料,利用NaOH/尿素体系对微晶纤维素进行溶解,得到再生纤维素溶液。采用滴定悬浮的方法制备纤维素水凝胶球,采用2,2,6,6-四甲基哌啶-1-氧基自由基（TEMPO）/NaBr/NaClO选择性氧化体系对纤维素水凝胶球进行氧化处理,获得羧基化改性纤维素水凝胶球,冷冻干燥得到羧基化改性纤维素气凝胶球。研究结果表明：羧基化改性纤维素水凝胶球的含水量为95.64%,吸附4h,亚甲基蓝的吸附量达到6.97mg/g。对羧基化改性纤维素气凝胶球进行傅里叶变换红外光谱（FT-IR）和扫描电子显微镜（SEM）表征分析,在1600cm^-1处出现了CO的伸缩振动峰,TEMPO的选择性氧化对样品起到羧基化改性作用,羧基化改性纤维素气凝胶增加了球形气凝胶的表面通透性,内部仍呈现网络结构,羧基化改性纤维素气凝胶球的密度为0.038g/cm³。     

Maximizing the yield of water-soluble cellouronic acid sodium salt with high carboxyl content by 4-acetamide-TEMPO mediated oxidation of parenchyma cellulose from bagasse pith

Parenchyma cellulose, isolated from bagasse pith BP, was utilized as an alternative resource for preparation of soluble cellouronic acid sodium salt (SCA) by selective oxidation with the catalytic amounts of 4-acetamide-TEMPO and NaClO, in which NaClO₂ was used as a primary oxidant in an aqueous condition. The yield and carboxyl content of SCA were measured as a function of NaClO₂ content, 4-acetamide-TEMPO loading, oxidation temperature, initial pH, and reaction time, and optimized by an orthogonal test with the objective of achieving a maximum yield with high carboxyl content. An optimal SCA yield of 71.0 % with 32.92 % carboxyl content was found under the conditions of NaClO₂ dosage of 16 mmol/g, 4-acetamide-TEMPO loading of 0.20 mmol/g, and oxidation temperature of 50 °C in acetate buffer at pH 5.5 for 72 h. The structure and morphology of both parenchyma cellulose and its oxidized product were further characterized by means of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectronic spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). These techniques confirmed that parenchyma cellulose from bagasse pith was successively modified by an effective TEMPO-derivative-catalyzed oxidation process. The finding of this study might provide guidance in maximizing the yield of SCA from parenchyma cells utilizing the 4-acetamide-TEMPO/NaClO/NaClO₂ system. Considering the simple preparation process and favorable SCA property, this BP parenchyma cellulose showed unique characteristics with a great promise for high-valued modification and application in the areas of advanced and functional materials.     

New electromagnetic shielding materials based on viscose‐carbon nanotubes composites

A convenient approach for the preparation of cellulose ‐ carbon nanotubes (CNT) hybrid materials owning electromagnetic shielding properties, based on viscose (V) and TEMPO‐oxidized viscose fibers (VO) is proposed. Viscose ‐ carbon nanotubes (V‐CNT) and TEMPO‐oxidized viscose ‐ carbon nanotubes (VO‐CNT) composites were prepared by embedding carbon nanotubes on the surface of two types of cellulose fibers, that is, viscose and its C₆‐oxidized derivative. The chemical composition, morphology, and thermal stability of the prepared hybrid materials were thoroughly investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analyses. Moreover, electrical properties of the original and composite fibers were assessed. POLYM. ENG. SCI., 59:1499–1506 2019. © 2019 Society of Plastics Engineers     

Effect of nitrogen content on high-temperature stability of hard and optically transparent amorphous Hf-Y-Si-B-C-N coatings

We study the effect of nitrogen content on functional properties, thermal stability and oxidation resistance of hard and optically transparent amorphous Hf-Y-Si-B-C-N coatings prepared by pulsed magnetron sputtering. Ab-initio simulations are performed to link the experimentally obtained properties with the atomic and electronic structures of the fabricated materials. It is shown that the content of N in the material, varied from subsaturation 46 at.% to saturation 51 at.%, is of significant importance for the optimization of thermal stability and tuning the refractive index and extinction coefficient. We identify an optimum N₂ content in the plasma and in turn N content in the coatings which outperform the previously introduced high-temperature material Hf₆Y₂Si₂₉B₁₂C₂N₄₅. The results constitute a progress in the efforts to combine multiple functional properties with exceptional (above 1300 °C) thermal stability and oxidation resistance.     

The effect of H2O2dip pretreatment on the oxidative stability of unblanched salted roasted peanut: the effects of moisture content and temperature

The samples were dipped into 0.9%, 1.3% or 1.7% H₂O₂solution prior to salting and roasting and stored at 25°C to see the effects on fat oxidation in the production of commercial unblanched salted and roasted peanuts. It was found that the H₂ O₂ dip improved the oxidative stability of peanuts at all concentrations, a maximum stability was obtained with 1.7% H₂O₂dip pretreatment. The effects of temperature and moisture content were investigated by storing samples pretreated with 1% H₂O₂solution at different moisture levels, i.e. 1.8%, 2.7% and 3.2% and at two temperatures, 35°C and 45°C. Finally, the stability of the pretreated samples was compared to that of the commercial sample by storing in glass jars and in regular polypropylene (PP) packages at 25°C. Pretreated samples were more stable than the control and the airtight packages (glass jars) were found better than PP packages in which the moisture content of the samples increased continuously because of their permeable nature. By selecting suitable packages and moisture levels, H₂O₂dip proved to be effective in retarding the peroxide formation during storage of unblanched salted and roasted peanuts.     

Comparative studies of three redox shuttle molecule classes for overcharge protection of LiFePO4-based Li-ion cells

Three classes of molecules have been shown to be successful for protecting lithium-ion cells during overcharge. These three classes are, the molecule 2,5-di-tert-butyl-1,4-dimethoxybenzene (DDB), molecules based on a phenothiazine core, such as 10-methylphenothiazine (MPT) and molecules based on a 2,2,6,6-tetramethylpiperidinyl-oxide (TEMPO) core, such as TEMPO and 4-cyano-TEMPO. These molecules were examined using Li-ion coin cells, three-electrode cyclic voltammetry and four-electrode cyclic voltammetry. Three-electrode cyclic voltammetry was used to measure the diffusion coefficients and the stability of the shuttle molecules at high and low potentials. The transport of electrons through the solid-electrolyte interface on the negative electrode to the oxidized shuttle molecule was studied using the four-electrode cell for electrolytes containing both LiPF₆ and lithium bis(oxalato)borate salts. The rate of charge transfer to the oxidized TEMPO and MPT molecules is significantly reduced on glassy carbon below 1.7 V (versus Li/Li⁺) in electrolytes containing LiBOB, but not in electrolytes containing LiPF₆. Charge transfer to oxidized DDB seems facile at all potentials above 0.2 V in both LiPF₆ and LiBOB electrolytes.     

A novel route for well‐defined polystyrene‐grafted multiwalled carbon nanotubes via the radical coupling reaction

Multiwalled carbon nanotubes‐graft‐polystyrene (MWNTs‐g‐PS) was synthesized by atom transfer nitroxide radical coupling chemistry. MWNTs with 2,2,6,6‐tetramethylpiperidine‐1‐oxy (MWNTs‐TEMPO) groups was prepared first by esterification of 4‐hydroxy (HO)‐TEMPO and carboxylic acid group on the surface of MWNTs (MWNTs‐COOH); PS with bromide end group (PS‐Br) were then obtained by atom transfer radical polymerization using ethyl 2‐bromoisobutyrate as initiator and CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst. The MWNTs‐TEMPO was mixed with PS‐Br and heated to 90°C in the presence of CuBr/PMDETA to form MWNTs‐g‐PS. The product was characterized by FTIR, NMR, TGA, and TEM. TEM indicates that the MWNTs are enveloped by the polymer molecules. The content of grafted polymers is 46.7% by TGA measurements when the number‐average molecular weight (M_n) of PS‐Br is 10,200 g/mol. The as‐prepared nanocomposites exhibit relatively good dispersibility in solvents such as CH₂Cl₂, THF, and toluene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of Starch Oxidization and Modification on Interfacial Interaction,Rheological Behavior,and Properties of Poly(Propylene Carbonate)/Starch Blends

The enhanced maleic anhydride-end-capped poly(propylene carbonate)/starch blends were prepared through starch oxidization and modification with a coupling agent, aluminic ester. The interfacial interaction, rheological behavior, and properties of blends were investigated through Fourier transform infrared spectroscopy, rheological measurement, mechanical property test, differential scanning calorimetric, thermogravimetric analysis, and moisture absorption test. The results show that hydrogen-bonding interaction is formed between poly(propylene carbonate) and starch, which makes the tensile strength of maleic anhydride-end-capped poly(propylene carbonate)/starch blends improved significantly. The glass transition temperature (T_g) of blends is increased when coupling agent is induced into polymer system. When increasing the content of starch modified with coupling agent from 10 to 30%, T_g values for composites increased from 30.5 to 32.8°C. Thermogravimetric analysis results show that oxidation of starch can improve the thermal stability and modification of starch through aluminic ester that can further increase the thermal stability of maleic anhydride-end-capped poly(propylene carbonate)/starch blends. Oxidation of starch has no significant effect on moisture absorption for poly(propylene carbonate)/starch blends.     

Effects of glycidyl methacrylate content and addition sequence on the acrylic latexes with carboxyl groups

Acrylic latexes with epoxy and carboxyl groups have been synthesized via a two-stage emulsion polymerization process. Different contents of glycidyl methacrylate (GMA) were introduced by three addition modes to copolymerize with methyl methacrylate, butyl acrylate, acrylic acid (AA) in the presence of K₂S₂O₈. To obtain stable latexes, NaHCO₃ was employed as a buffer to compensate for the acidity from the thermal dissociation of K₂S₂O₈, and triethylamine was used to neutralize the carboxyl acid from AA. The results showed that the stable latexes with core/shell structure were synthesized by this method, and higher GMA content or addition at earlier stage led to forming the latexes with higher content of coagulum and bigger sized particles. During the formation of films, the polymer epoxy groups underwent the crosslinking reaction with carboxyl acid. When the GMA content increased or GMA was introduced at a later stage, high crosslinking extent was formed in the films. As a result, the crosslinking provided the films with improved water resistance, chemical resistance, tensile strength, hardness, abrasion resistance, and thermal stability.     

TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展

2,2,6,6-四甲基哌啶氧自由基(TEMPO)共氧化剂体系被广泛应用于选择性氧化纤维素的C6位伯醇羟基。在氧化过程中,纤维素的聚合度大幅度降低,因此被应用于制备纳米纤维素。随着TEMPO/NaClO/NaBr氧化技术的发展成熟,TEMPO/NaClO/NaClO2和4-乙酰胺基-TEMPO/NaClO/NaClO2体系都得到了广泛关注。随着研究的深入,TEMPO及其衍生物氧化体系已经成为一种高效且全pH范围适用的选择性氧化体系。TEMPO/NaClO/NaBr氧化体系在pH范围9～11活性最高,TEMPO/NaClO/NaClO2体系能够应用于pH中性的条件下,4-乙酰胺基-TEMPO/NaClO/NaClO2体系一般的pH使用范围为3.5～6.8。传统的TEMPO氧化过程需要持续手动控制pH恒定,操作繁琐,可控性差,应用缓冲溶液可控制TEMPO氧化过程中pH在一定范围内恒定,从而实现了TEMPO氧化体系的智能控制。文章综述了TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展。     

Stability of Tocopherol Homologs in Bulk Oils at 60°C Oxidation and Chlorophyll Photosensitization by the Action of Moisture

The effects of deuterium oxide (D₂O) on the stability of tocopherol homologs were evaluated in corn oil stored at 60°C or in the process of chlorophyll photosensitization. The degree of oxidation, changes in moisture, and the levels of tocopherol homologs were analyzed. The moisture content in corn oil incubated with deuterium-free water (H₂O) was significantly (P < 0.05) higher than that in corn oil incubated with D₂O. The presence of D₂O accelerated the rate of lipid oxidation in corn oil, irrespective of whether it has been oxidized at 60°C or has been photosensitized by chlorophyll. After exposure to either of the oxidative stresses, the stability of β + γ-tocopherols present in corn oil was enhanced in the presence of D₂O compared to corn oil incubated in the presence of H₂O, or control corn oil without the addition of moisture. However, the stability of α-tocopherol in corn oil incubated with D₂O was significantly lower after oxidation at 60°C compared to the other conditions (P < 0.05), whereas it was significantly higher than under the other conditions after chlorophyll photosensitization (P < 0.05). The moisture and type of oxidative stress, therefore, play important roles in the stability of tocopherol homologs in bulk oils.     

Processing characteristics of poly(ethylene terephthalate): hydrolytic and thermal degradation

The effects of poly(ethylene terephthalate) (PET) resin moisture content and temperature exposure have been investigated in terms of material changes resulting from the injection moulding process. Two resins with initial carboxyl contents of 10 µeq/g PET and 20 µeq/g PET have been analysed. Preforms processed at different resin moisture contents and processing temperatures of 280, 290 and 300 °C were evaluated in terms of carboxyl end‐group concentration using a titration method. Intrinsic viscosities of the performs were also measured by solution viscosity. Mathematical models describing the relationships of carboxyl end‐group concentration and intrinsic viscosity to the processing conditions were generated from the experimental data. Carboxyl end‐groups formed were compared for both resins and shown to be dependent on initial carboxyl content in the resin. Reducing the initial carboxyl content in the resin has been shown to increase its hydrolytic stability. The hydrolytic effect on the overall molecular weight drop was separated from the thermal/thermal‐oxidative degradation and shown to be dependent on both the processing temperature and the resin moisture content. © 2002 Society of Chemical Industry     

Laccase/TEMPO-modified lignin improved soy-protein-based adhesives: Adhesion performance and properties

The aim of this study was to enhance the water resistance of soy protein (SP) adhesives using laccase/TEMPO-modified lignin. Kraft lignin was depolymerized by laccase enzyme in the presence of TEMPO to expand the oxidation reaction of both phenolic and non-phenolic compounds. This simplified process has the distinct advantage of enhancing lignin-protein interaction. Compared with SP adhesives, lignin-protein adhesives showed a stronger elastic modulus, higher thermal stability, and increased wet adhesion performance. Wet shear strength increased by 106% from 0.693 to 1.429 MPa, and partial wood failure was observed after the test. Better performance was also observed in the three-cycle soaking test. At the same time, the stronger interactions between -COO^- and -NH₂ groups of protein and lignin led to a decrease in flowability and spreadability.     

Synthesis and catalytic performance of gold-loaded TiO2 nanofibers

Organic modification of sol–gel catalytic glassy electrodes made of a thin layer of organosilica doped with nitroxyl radical TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) crucially enhances stability in the waste-free oxidation of alcohols to carbonyls in water. Structural comparison between analogous films made of organosilica and unmodified SiO₂ shows that the origin of the pronounced stable activity of the ORMOSIL film lies in high hydrophobic and also in the pronounced low degree of hydrophilicity. This article is dedicated to the memory of professor Angelo Patricolo, great Italian neurosurgerist and fine gentleman from Sicily     

Novel polyhydrazides and polyoxadiazoles based on 1,3,4-thiadiazole moiety in the main chain with high thermal stability,good solubility,and notable antimicrobial activity

Polyoxadiazoles (PODs) and polyhydrazides (PHs) have wide potential applications; however, PODs are normally insoluble in organic solvents, do not melt, and do not express glass-transition temperature (T_g), and also PHs do not have high-temperature resistance. In this work, novel PHs based on 1,3,4-thiadiazole in the polymer main chain were synthesized by low-temperature polycondensation. New PODs were then obtained by cyclodehydration of the PHs. The thermal behavior, surface morphology, and crystalline structure were studied using differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. In addition, the viscosity, solubility, UV–visible absorption, and antimicrobial activity were examined. The new polymers showed melting, T_g, high thermal stability, good solubility in polar aprotic solvents, and significant antimicrobial activities. The enhanced solubility may be attributed to the ability of thiadiazole moiety to form hydrogen bonding with the solvent molecules. Also, it can be concluded that introducing 1,3,4-thiadiazole and other bulky moieties like the oxadiazole ring into the polymer main chain encouraged more free volumes and weakened the chains packing; hence, the solubility was enhanced and T_g decreased without affecting the thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47770.     

Enhancement of water barrier properties of cassava starch-based biodegradable films using silica particles

Biodegradable films are used in a variety of applications, including packaging. However, their use is limited due to their high moisture and water sensitivity. In this work, cassava starch (CS) was blended with poly(vinyl alcohol) (PVA). Silica particles (SiO₂) were incorporated to increase the hydrophobicity of the blend by intermolecular interaction through hydrogen bonding between the three components. Instead of a plasticizer or crosslinker, a small amount of triethylamine was added to eliminate residual acetate groups in PVA. The miscibility of CS and PVA phases was confirmed by smooth fracture surfaces and a single glass transition temperature. When SiO₂ content was below 5% (wt), the particles were well dispersed in a continuous phase of polymer matrix. At this loading of SiO₂, the increase in tensile strength was as high as 170% and in elongation-at-break, 250%. All loadings of SiO₂ increased thermal stability of the blend films because silanol groups on the surface of SiO₂ particles formed effective interfacial interactions with hydroxyl groups of the polymers. These interactions also prevented the ingress of water molecules, significantly increasing the hydrophobicity of the films. The water contact angle increased as high as 113° and moisture absorbency and water solubility were low. These highly hydrophobic, photodegradable, biodegradable CS/PVA/SiO₂ films show great potential as a low-cost, eco-friendly material.