Stearate Groups Research Articles

Crosslinked poly(hydroxyurethane) films from biobased carbonates: Structure-properties relationships and the influence of moisture in the mechanical properties

In this work, crosslinked poly(hydroxyurethane) (PHU) films were prepared by the reaction of biobased cyclic carbonates (BisCC), with different chain lengths, with hyperbranched poly(ethyleneimine) (PEI) under amenable conditions and in the absence of catalysts. Fourier transform infrared (FTIR) spectroscopy revealed that the carbonate groups were completely consumed in the crosslinking reaction and the gel content of the films was about 99 %. It was shown that the thermal and mechanical properties of the PHU films depended on the length of the carbon chain of the BisCC. In the presence of moist environment, the PHU films absorbed moisture (6–8 %) which is ascribed to the presence of hydroxyl groups. This resulted in a deterioration of the mechanical properties, which were not completely recovered after drying. To counteract this effect, a simple procedure was used in which the hydroxyl groups on the surface were modified by stearate groups. Although FTIR and water contact angle measurements demonstrated that the films of PHU became more hydrophobic after modification, the water absorption capacity was similar to that of the unmodified PHU films. This suggests that the modification process may cause some degradation in the bulk of the material that opens spaces for water molecules penetration.In summary, this work has shed light for the first time on the effects of moisture on the mechanical properties of pure PHU films and has shown that surface modifications are not sufficient to prevent moisture absorption.

Aging effect on the magnetic properties of Mn12-stearate single-molecule magnets anchored onto the surface of spherical silica nanoparticles

The effects of structural and magnetic aging in Mn12-stearate single-molecule magnets (SMMs) deposited on the surface of 300 nm spherical silica nanoparticles were investigated. It was pointed out that the molecules attached on the surface preserve its magnetic characteristics (hysteresis in M(H) loops and slow magnetic relaxation). However, the observed magnetic properties evolve over time revealing significant changes. DC susceptibility studies together with Raman spectroscopy were applied to investigate this aging effect. Measurements over 221 days period showed change of magnetic parameters: exponential decrease of coercive field from 4.5 kOe to 150 Oe (with τc = 33 days) and remnant magnetization from 0.072 emu/g to 0.0022 emu/g (with τrem = 46 days). Time-dependent magnetization measurements have indicated the presence of slow magnetic relaxations (Ueff = 33.6 K) for the fresh sample in temperature range 2.0–3.0 K. However, the aged sample (221 days after synthesis) did not show typical relaxations, but a magnetic viscosity behavior was observed. The Raman measurements revealed partial decomposition of stearate groups and possible formation of hydroxyl system over time, which explain the observed magnetic changes.

Polymer composites based on functionalized carbon nanotubes

The present paper considers the efficiency of using carbon nanotubes (CNTs) functionalized by titanium stearate groups for modifying of polyethylene and polypropylene. For this purpose, the strength characteristics, Shore hardness, thermal diffusivity and conductivity of the obtained nanocomposites were determined. The weak effect of the CNTs (0.01-1.5 wt.%) on the values of thermal conductivity coefficients and thermal diffusivity was revealed. It was found that compared to the unmodified matrix, nanocomposites containing 0.01-0.1 wt.% of the titanium stearatefunctionalized CNTs demonstrate, an increase in the Shore hardness by 12.5-14.5%, a decrease in the weight wear by 54.2%, and the daily water absorption - to the values below the threshold of sensitivity of the standardized method of determination. The functionalization by the titanium stearate groups made it possible to reduce the CNTs mass fraction in the composition of polyethylene and polypropylene composites by more than 10 times compared with the pristine nanotubes.

Characterization and Properties of Long‐Chain Fatty Acid Starch Esters Prepared with Regenerated Starch by Dry Method

AbstractRegenerated starch (RS) prepared from 14% urea/4% NaOH aqueous solution is used as a raw material to synthesize esterified starch. Starch stearate (SS), a kind of long‐chain fatty acid starch ester, is synthesized through the esterification of RS with stearic acid by a dry method under normal pressure and without an organic solvent or catalyst. Scanning electron microscopy, Laser Particle Sizer, Fourier transform infrared, 1H NMR, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis are used to characterize and analyze the prepared SS. The effect of degree of substitution (DS) on the properties of SS, such as moisture adsorption, transparency, emulsion ability (EA) and emulsion stability (ES), freeze–thaw stability, and retrogradation, is also studied. The results show that the prepared SS has better EA and ES, good freeze–thaw stability, and excellent retrogradation, all of which increase with the increase of DS. The transparency of SS pastes is significantly improved when its DS is under 0.3. The moisture adsorption of SS decreases due to the introduction of stearate groups. All these improved properties make SS a better material for a myriad of industrial applications.

Effect of hydrophobic modification on the structure and rheology of aqueous and brine solutions of scleroglucan polymer

Amphiphilic scleroglucans were synthesized by grafting hydrophobic stearate groups in various densities onto the polysaccharide under its triple-helix conformation. Furthermore, a polyelectrolyte was obtained by attaching ionic-sulfonic groups to the hydrophobically modified scleroglucan. Rheological measurements demonstrated the role of grafted stearates in helix-coil transition of scleroglucan and in reducing the viscosity of scleroglucan in pure aqueous and brine solutions. Nevertheless, grafting the ionic-sulfonic groups caused a substantial recovery of the lost viscosity, especially in brine solution at 90 °C, while keeping the amphiphilic character of the hydrophobically modified scleroglucan. Additionally, the hydrophobic modification altered the adsorption behavior of scleroglucan on oil-reservoir rock surfaces: the higher the grafting density, the greater the adsorption amount. However, the polyelectrolyte sample showed the lowest adsorption among all modified samples. Finally, the modified scleroglucans are promising candidates for enhanced oil recovery applications.

Self-Assembled Dehydro[24]annulene Monolayers at the Liquid/Solid Interface: Toward On-Surface Synthesis of Tubular π-Conjugated Nanowires.

We have studied the self-assembly behavior of dehydro[24]annulene (D24A) derivatives 1, 2a-2d, and 3a-3c at the liquid/solid interface using scanning tunneling microscopy (STM). Both the relative placement and the nature of the four D24A substituents strongly influence the self-assembly pattern. Overall, the eight D24A derivatives examined in this study display seven types of 2D packing patterns. The D24A derivatives 1, 2a, and 3a have either two or four stearate groups and adopt face-on configurations of their macrocyclic cores with respect to the highly oriented pyrolytic graphite (HOPG) surface. Their 2D packing pattern is determined by the interchain spacings and number of stearate substituents. The D24A derivatives 2b-2d and 3b-3c bear hydrogen-bonding carbamate groups to further strengthen intermolecular interactions. Face-on patterns were also observed for most of these compounds, while an unstable edge-on self-assembly was observed in the case of 2b at room temperature. Stable edge-on self-assemblies of D24A derivatives were sought for this work as an important stepping stone to achieving the on-surface topochemical polymerization of these carbon-rich macrocycles into tubular π-conjugated nanowires. The overall factors determining the 2D packing patterns of D24As at the liquid/solid interface are discussed on the basis of theoretical simulations, providing useful guidelines for controlling the self-assembly pattern of future D24A macrocycles.

Salt Dependent Stability of Stearic Acid Langmuir–Blodgett Films Exposed to Aqueous Electrolytes

We use contact angle goniometry, imaging ellipsometry, and atomic force microscopy to study the stability and wettability of Langmuir-Blodgett (LB) monolayers of stearic acid on silica substrates, upon drying and exposure to aqueous solutions of varying salinity. The influences of Ca(2+) and Na(+) ions are compared by varying their concentrations, both in the subphase before the LB transfer, and in the droplets to which the dried LB layers are exposed. Ca(2+) ions in the subphase are found to enhance the stability, leading to contact angles up to 100°, as compared to less than 5° for Na(+). Consistent with the macroscopic wettability, AFM images show almost intact films with few holes exposing bare substrate when prepared in the presence of Ca(2+), while subphases containing Na(+) result in large areas of bare substrate after exposure to aqueous drops. The observations on varying the composition of the droplets corroborate the stabilizing effect of Ca(2+). We attribute these findings to the cation-bridging ability of Ca(2+) ions, which can bind the negatively charged stearate groups to the negatively charged substrates. We discuss the relevance of our findings in the context of enhanced oil recovery.

Degradability enhancement of poly(lactic acid) by stearate-Zn(3)Al LDH nanolayers.

Recent environmental problems and societal concerns associated with the disposal of petroleum based plastics throughout the world have triggered renewed efforts to develop new biodegradable products compatible with our environment. This article describes the preparation, characterization and biodegradation study of poly(lactic acid)/layered double hydroxide (PLA/LDH) nanocomposites from PLA and stearate-Zn3Al LDH. A solution casting method was used to prepare PLA/stearate-Zn3Al LDH nanocomposites. The anionic clay Zn3Al LDH was firstly prepared by co-precipitation method from a nitrate salt solution at pH 7.0 and then modified by stearate anions through an ion exchange reaction. This modification increased the basal spacing of the synthetic clay from 8.83 Å to 40.10 Å. The morphology and properties of the prepared PLA/stearate-Zn3Al LDH nanocomposites were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TGA), tensile tests as well as biodegradation studies. From the XRD analysis and TEM observation, the stearate-Zn3Al LDH lost its ordered stacking-structure and was greatly exfoliated in the PLA matrix. Tensile test results of PLA/stearate-Zn3Al LDH nanocomposites showed that the presence of around 1.0–3.0 wt % of the stearate-Zn3Al LDH in the PLA drastically improved its elongation at break. The biodegradation studies demonstrated a significant biodegradation rate improvement of PLA in the presence of stearate-Zn3Al LDH nanolayers. This effect can be caused by the catalytic role of the stearate groups in the biodegradation mechanism leading to much faster disintegration of nanocomposites than pure PLA.

Researches on the Properties of Stearate-Carboxymethyl Konjac Glucomannan Ester Prepared by Microwave Method

In this study, microwave heating was used for the preparation of stearate-carboxymethyl konjac glucomannan ester (SCMK), which introduced hydrophilic carboxymethyl and hydrophobic stearate groups on konjac glucomannan (KMG) backbone. The physico-chemical properties and structure of SCMK were investigated. Results show that the viscosity of SCMK is much lower than that of KGM, but larger slightly than the carboxymethyl konjac glucomannan (CMK) and the viscosity is still stable after being placed for 48 h at ambient temperature. Its transmittance decreases and the resistance ability of SCMK solution to salt/sugar as well as base have been significantly promoted. Moreover, SCMK with substitution degree (DS) of 0.02 is proved to be a sound oil/water emulsifier which its HLB value is 13.01. In FTIR spectrum, the absorption peak of SCMK decreases at 2161.84 cm-1 and 2360.74 cm-1. Meanwhile, TGA indicates that SCMK is less thermal stable than KGM and CMK, but is still good.

Variations in the friction coefficients of tablet lubricants and relationship to their physicochemical properties.

A previously described modified annular shear cell (MASC) has been used to measure the friction coefficients of some powdered tablet lubricants on a steel surface. Commonly used lubricants, as well as others belonging to the stearate group, differed in their friction coefficients at equivalent sample sizes and in the degree of their ability to reduce friction with increasing amounts when evaluated by the apparatus. In all comparisons, magnesium stearate had the lowest friction coefficient. Divalent salts of stearic acid appeared to be better than the other lubricants tested, and among themselves differed only in the extent of their ability to decrease friction. The lubricants also differed in their physical and chemical properties. On evaluation by stepwise regression analysis, such physical properties as projected surface area of lubricant particles, Martin's diameter and bulk density accounted for most of the variation in friction coefficients of the lubricants rather than moisture content or melting point. It could therefore be suggested that particle size and/or surface area parameters be incorporated in product specifications to ensure reproducible functionality.

Synthesis and spectrum stability of high quality CdTe quantum dots capped with stearate groups in N-oleoylmorpholine solvent

The stearate-capped CdTe quantum dots (QDs) have been first prepared via direct reaction of cadmium stearate with Te powder in N-oleoylmorpholine solvent, which was a kind of clean, air-stable and conveniently synthesized acylamide, and can readily dissolve precursors cadmium stearate and Te powder at a relative low temperature. The as-prepared CdTe QDs exhibited size-dependent optical properties, steep absorbance edge and narrow photoluminescence full width at half maximum. The high-resolution transmission electron microscopy images and X-ray diffraction revealed that the highly monodisperse CdTe QDs were of regular spherical morphology with zinc blende crystal structure displaying mean sizes of about 4 nm. The energy dispersed spectrometry measurement indicated the presence of Cd and Te, with the Cd:Te ratio being close to 1:1. Fourier transform infrared transmission spectra confirmed the existence of stearate on the CdTe QDs surfaces. The experimental results also demonstrated that the stearate-capped CdTe QDs had an unexpected good stability.

Abstract 1885: Dietary stearate reduces abdominal fat, serum leptin and glucose and increases MCP-1

Abstract Stearate is a dietary, long-chain saturated fatty acid (C18:0) that has been shown to decrease breast cancer cell proliferation, migration, and invasion in vitro and reduce tumor growth and metastasis in vivo. Obesity, or excess adipose tissue, is a risk factor for breast cancer. Our overall hypothesis is that dietary stearate inhibits breast cancer by decreasing body fat. Our goal was to determine whether there was an association between dietary stearate and adipose tissue. Four groups of 10 athymic nude mice each were each fed one of four different diets for 18 weeks (6% corn oil - low fat diet, 17% stearate diet, 17% corn oil diet, or 17% safflower oil diet). Body composition was assessed by nuclear magnetic resonance (NMR) and dual energy X-ray absorptionmetry (DXA). Serum concentrations of glucose, insulin, leptin, adiponectin, interleukin-6, and monocyte chemoattractant protein-1 (MCP-1) were also determined. In a repeated measures model assessing the relationship between groups, for fat and lean mass over time the following differences were found: the stearate group had significantly reduced body fat compared to the low fat and the corn oil groups (p<0.001); mice on the high fat diets (stearate, corn oil, and safflower oil) had a significantly increased lean body mass compared to the low fat group (p=0.009, 0.012, and 0.022 respectively). Postmortem measurement revealed no significant changes in organ weight (brain, heart/lungs, liver, and kidney) among the four diet groups. However dietary stearate had less abdominal fat than the other diets although only the low fat - stearate difference was significant (low fat-stearate *p= 0.0043. corn oil-stearate p= 0.0565, and safflower-stearate p= 0.0636). Serum glucose and leptin concentrations were significantly reduced in the stearate diet mice (glucose, p<0.039, stearate vs all other diets, leptin, p<0.015, stearate vs low fat and corn oil diets). Serum MCP-1 was increased in stearate diet mice compared to either the low fat or safflower oil mice (p<0.019). Significant differences were not observed with the other analytes. Studies have suggested that glucose and leptin have cancer promoting effects, while MCP-1 may promote or inhibit breast cancer. Overall these data support our hypothesis that dietary stearate decreases body fat and that this decrease in body fat may be related to stearate inhibition of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1885.

Abstract 2878: Dietary stearate inhibits tumor development and tumor burden in the N-nitroso-N-methylurea (NMU) rat breast cancer carcinogen model

Abstract The goal of the present study was to test the effectiveness of dietary stearate at inhibiting breast cancer development in a carcinogen induced breast cancer model. Three diets were used; a 17% stearate diet, the key being that highly purified stearate was added directly to the diet, a linoleate diet (SF) containing 17% safflower oil as the source of linoleate and a low fat control diet (LF) with a reduced amount of fat (5%) from corn oil. All three diets had adequate essential fatty acids. These 3 diets were initiated 1 week prior to the rats receiving NMU and followed out 100 days. There was no difference in the weight of the rats among groups throughout the study. Approximately 40% fewer animals on the stearate and safflower diets developed palpable tumors compared to the LF (n=30-35 animals/diet; p<0.05). No difference was observed among the three diets as to the time for first tumor appearance. Stearate decreased the average number of tumors per rat compared to the LF (n=30-35 animals per diet; p<0.05) and had less tumors per rat than the SF although this was not statistically significant. Stearate also significantly reduced tumor burden as defined by tumor weight by ∼50% compared to LF and SF (p<0.001) and large tumors compared to the LF (∼47% reduction in tumors over 0.25 g, p= 0.02). In those rats that did develop tumors, the stearate diet group had a similar number of adenocarcinomas compared to other diets; however the stearate and SF groups had lower numbers of DCIS/microinvasive disease as compared to the LF. The dietary groups tended to have similar numbers of the other precursor lesions classified although the dietary stearate group had the least number of “tubular adenomas”. Dietary stearate may be useful as an alternative/complementary therapy or preventative agent against breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2878.

Super-Stable, High-Quality Fe3 O4 Dendron-Nanocrystals Dispersible in Both Organic and Aqueous Solutions.

High-quality Fe3 O4 nanocrystals coated with stearate groups are successfully converted to dendron-coated nanocrystals (dendron-nanocrystals). Poly(ethylene glycol) oligomers are used as major terminal groups for the dendron ligands, which afford excellent dispersibility of the dendron-nanocrystals in a broad spectrum of solvents, ranging from dichloromethane to water.

Investigation of thermal stabilization of poly(vinyl chloride) by lead stearate and its combination with synthetic hydrotalcite

The effect of lead stearate on the stability of PVC during its heat treatment was examined. In the presence of lead stearate, the rate of elimination of HCl is halved as compared to non-stabilized PVC. During the degradation, lead stearate is reacted completely mainly in the neutralization of the released HCl, irrespective of the initial concentration of the former. The results indicate that the stabilization reaction is also associated with a reversible bonding of the stearate group to the polymer chain. Replacement of a fraction of the stabilizer by synthetic hydrotalcite increases the thermal and colour stability of the PVC.

Neutron Reflectivity of Linear−Dendritic Diblock Copolymer Monolayers

Specular neutron reflectivity has been used to investigate the structure of monolayers formed from linear-dendritic diblock copolymers at an air-water interface. The dendritic block copolymers consist of a linear poly(ethylene oxide) (PEO) block of 2000 molecular weight linked to a third or fourth generation polyamidoamine (PAMAM) dendron. The dendritic end groups were functionalized with deuterated stearic acid to make the dendritic block hydrophobic, resulting in a macroamphiphile. Results indicate that stable monolayers are formed with PEO resting on the subphase and stearate groups extending into the air. In general, at low surface concentrations the PEO block intermixes with the PAMAM dendron, whereas at high surface concentrations the PAMAM forms a distinct layer above the PEO. The ordering of the stearate groups functionalized on the dendrimer was dependent on generation. Stearate groups form a distinct ordered layer which is separate from the third generation PAMAM dendron, whereas the stearate groups are intermixed with fourth generation PAMAM segments due to the curvature of the higher generation dendron. The PEO block becomes intermixed with the water subphase if the monolayer is held at constant area for at least 10 h. These finding are consistent with earlier published studies of pressure-area isotherms of these systems on the Langmuir-Blodgett trough.

A comparative safety and efficacy study of clarithromycin and erythromycin stearate in community-acquired pneumonia

The efficacy and tolerance of clarithromycin and erythromycin stearate in the treatment of community-acquired pneumonia were compared in a multicentre, double-blind randomized trial. Two hundred and eight adult patients were randomized to receive either clarithromycin 250 mg 12-hourly (96 patients) or erythromycin stearate 500 mg 6-hourly (112 patients), each for 14 days. One hundred and eight patients were evaluable for efficacy, 64 receiving clarithromycin and 44 erythromycin stearate. There was no significant difference between the two groups in terms of clinical cure (52% for clarithromycin, 40% for erythromycin) or clinical success (clinical cure and improvement; 89% for clarithromycin, 98% for erythromycin stearate), or radiological response (90% for both groups). An intention-to-treat analysis, including all patients entering the study revealed significant differences in favour of clarithromycin. The clinical cure rate after two weeks of treatment was 45% in those who received clarithromycin compared with 25% in the erythromycin stearate group (P = 0.003), whilst improvement in cough was observed in 97% and 80% of patients receiving clarithromycin and erythromycin stearate, respectively (P = 0.07). Adverse effects, mainly gastrointestinal, caused discontinuation of treatment in 4% (4/96) patients in the clarithromycin group in comparison with 19% (21/112) treated with erythromycin stearate (P less than 0.01). These results demonstrate that clarithromycin twice daily is at least as effective as four times daily erythromycin stearate for the treatment of community-acquired pneumonia and is better tolerated.

Thermal dehydrochlorination and stabilization of poly(vinylchloride) in solution: Part IV—Synergistic effects of β-diketone compounds and metal soap stabilizers

Thermal degradation of poly(vinylchloride) (PVC) has been carried out in trichlorobenzene (TCB) solution at 187°C in the presence of zinc and calcium stearates and β-diketone compounds (BDCs). BDCs are able to react alone with PVC through C alkylation, but the reaction is strongly enhanced by the metal soap system. In the initial stages of the reaction, both BDC residues and stearate groups are grafted onto the PVC backbone and some crosslinking may occur due to the double reaction of BDC compounds. The initial dehydrochlorination of PVC, as well as the development of polyene sequences are strongly inhibited in the presence of the total system, but later, the degradation of the polymer is accelerated. The rates of all the processes are strongly dependent on the concentration of structural defects initially present in the polymer. Coordination complexes between BDC and zinc compounds and re-equilibrium keto-enol forms of the BDC are observed in the presence of Ca compounds.

Thermal dehydrochlorination and stabilization of poly(vinyl chloride) in solution: Part III—Zn-Ca stearates as stabilizers

The thermal degradation of poly(vinyl chloride) (PVC) in trichlorobenzene (TCB) solution at 187°C has been studied in the presence of various mixtures of zinc and calcium stearates, using coulometric titration of chloride ions, HCl evolution measurements and spectroscopic analysis (FTIR and UV) of the degraded polymer at various times. The substitution reaction, initially suggested by Frye and Horst 1,2 is clearly demonstrated, although the very small amount of stearate groups involved with respect to the number of vinyl chloride units makes it difficult and requires the use of high performance equipment and careful recording conditions. Many of the known features of the stabilization of PVC with mixed metal soaps are also observed. In addition, a transient complex between the metal stearates is observed which cannot be separated from the polymer because it shows the same solubility behavior. Evidence for secondary reactions between metal chlorides and stearic acid is given. Finally, the rates of the processes are very dependent on the amounts of structural defects in the initial polymer.

The use of i.r. spectroscopy for gaining insight into the mechanism of stabilization of PVC by cadmium stearate

Infrated spectra (1800-1500 cm −1) of polyvinyl chloride films stabilized with cadmium stearate, prepared by pressing at 180°C, are studied. The spectral changes are investigated in relation to the thermal treatment, interaction of cadmium stearate with water or with stearic acid, as well as to the degree of association of stearic acid in the polyvinyl chloride matrix. The fraction of cadmium stearate engaged in the reaction with the labile chlorine atoms of the PVC chain on a ca 7 min thermal treatment at 180°C, is estimated as approximately 2.4% of the initial stearate group content of the sample, which was 5 mmol/100 g PVC. As in PVC, the formation of stearic acid is found to be the dominant feature ofa model reaction of cadmium stearate with 4-chloro-2-nonene. It is concluded that if ester groups are formed, their concentration is too low for detection by i.r. spectroscopy, hence this technique is not able to give unambiguous evidence for the mechanism proposed.