Influence of molecular weight and free NCO content on the rheological properties of lithium lubricating greases modified with NCO-terminated prepolymers

In this work, the use of reactive diisocyanate-terminated polymeric materials as rheology modifiers of lubricating greases has been studied. Particularly, the influences that free NCO content, molecular weight and functionality of the reactive prepolymers exert on the rheological response and microstructure of lubricating greases were analyzed. With this aim, NCO-terminated prepolymers were prepared from several di and trifunctional polyols and polymeric MDI. Afterwards, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap, used as thickener, was promoted during processing of lubricating greases. Polymeric materials used as additives and final lubricating greases were characterized by FTIR, DSC and GPC techniques. The effectiveness of these reactive additives was tested by performing small-amplitude oscillatory shear (SAOS), as well as standardized mechanical stability tests, on final greases. The rheological response was related to the microstructure of these greases, characterized by means of atomic force microscopy (AFM). From the experimental results obtained, it may be concluded that the effectiveness of these polymeric additives to modify the rheology of greases is due to the progress of the reaction between terminal isocyanate groups and the hydroxy group of lithium soap. However, a large dependence on both free NCO content and prepolymer molecular weight was found. Experimental results confirm that a balance between prepolymer molecular weight and NCO content is necessary to reach an optimal rheological modification of lithium greases. Moreover, this balance is a function of grease ageing, due to the progress of the reaction promoted.     

Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil

Hydrophobic cellulose nanocrystals (CNs) have been prepared by grafting isocyanate-terminated castor oil, a kind of natural vegetable oil, onto their surface. The existence of castor oil component in the modified cellulose nanocrystals was verified by Fourier transform infrared spectroscopy, solid-state ¹³C NMR spectra and X-ray photoelectron spectroscopy. At the same time, X-ray diffraction and transmission electron micrographs further proved that the crystalline structure and large aspect ratio of cellulose nanocrystals were essentially preserved after chemical grafting. Furthermore, the surface of modified cellulose nanocrystals appeared to be hydrophobic as indicated by contact angle measurements. The value of the polar component of surface energy decreased from 21.5 mJ/m² to almost zero via grafting castor oil. These novel hydrophobic castor oil-grafted cellulose nanocrystals appear as valuable alternatives to formulate bionanocomposites with non-polar polymers for optimized performances.     

Nuclear magnetic resonance/magnetic resonance imaging on lubricating greases: Observation of bleeding and aging

Lubricating greases were investigated by nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) to get insight into their structure and into their response to mechanical forces, which is related to bleeding and aging. The investigated greases are based on metallic soaps of fatty acids and oils, whereby LiOH is often used. These organic soaps act as thickeners and provide a network in which oils and their additives are embedded. Lubricating greases can thus be considered as a class of substances similar to oleogels or even hydrogels. Questions arise about translational mobility of guest molecules, mainly base oil, in these networks. Molecular structuring and interactions within the network of thickeners are of interest as they are related to macroscopic stability. Apart from NMR spectroscopy (¹H-, ⁷Li- and ³¹P-NMR), spectrally resolved relaxation and diffusion measurements are used for characterization. In addition, magic angle spinning (MAS)-NMR was combined with ¹H-MRI to investigate the impact of mechanical stress and swelling of lubricating greases.     

Development of biobased polyurethane‐imides from maleinized cottonseed oil and castor oil

An eco‐friendly coating system, which is largely biobased, has been developed from castor and cottonseed oil. Cottonseed oil was functionalized with maleic anhydride by “ene” reaction to give maleinized cottonseed oil (MACSO); the anhydride groups were reacted with isocyanates to yield –NCO terminated polyurethane prepolymer. The prepolymer was further chain extended with hydroxyl groups of castor oil to give polyurethane‐imides (PUIs). The cross‐linked films thus obtained had good mechanical properties, and the imide groups in the backbone improved the corrosion resistance of PUIs as revealed by potentiodynamic polarization study. With increasing content of MACSO, thermal stability, glass transition temperatures (T_g), tensile strength, and corrosion resistance of resulting PUIs significantly increased.     

Interpenetrating polymer network from castor oil-based polyurethanes and poly(methyl methacrylate). XV

The polyurethanes have been prepared from 2.12 functional ? OH containing castor oil and diphenyl methane diisocyanate under identical experimental conditions with a varying NCO/OH ratio. These polyurethanes were swollen in methyl methacrylate and subsequently interpenetrated by free radical polymerization using benzoyl peroxide and crosslinker ethylene glycol dimethacrylate. A series of interpenetrating polymer network (IPN) PU/PMMA IPNs were obtained as films by a transfer moulding technique. These IPNs were characterized by their resistance to chemical reagents, thermal behavior, and mechanical properties. The morphology was shown by SEM and dielectric properties at different temperatures were measured.     

Naturally derived green bio-additives

During the last few years, special attention has been paid by the lubricant industry towards vegetable oil-based lubricants due to their biodegradability, renewability and excellent tribological properties. But to maintain the biodegradability of the final lubricants, the additive in the lubricants must also be biodegradable. Hence, in our present work, multifunctional lubricating oil additive based on castor oil has been investigated as a less toxic, feasible alternative to traditional petroleum based additives. Homopolymer of castor oil and its copolymer with α-pinene were synthesized by a thermal method using azobisisobutyronitrile as a radical initiator. Characterization of the prepared polymers was performed by spectral analysis and gel permeation chromatography (GPC). Additive performances of each of the prepared polymers as viscosity index improvers/viscosity modifiers and pour point depressants were carefully evaluated. Photo micrographic image was used to study the effectiveness of the additives as pour point depressants. Thermogravimetric analysis (TGA) was conducted to investigate the thermal response of the additives at high temperature. Finally, biodegradability of all the polymers was tested against fungal pathogen by the disc diffusion method and soil burial test. The study illuminated excellent additive performances of the polymers and thus their potential for acting as entirely naturally derived green bio-additives for lube oil.     

不同异氰酸酯固化的蓖麻油／酚氧树脂聚氨酯的力学性能

以ＢＦ３·ＯＥｔ２为催化剂，４，４－二羟基二苯基丙烷与环氧氯丙烷反应，生成端羟基的酚氧树脂（Ａ），Ａ与蓖麻油（Ｂ）混合，用３种异氰酸酯（ＴＤＩ、ＩＰＤＩ和ＨＤＩ）作为固化剂，制得交联聚氨酯。研究了这３种聚氨酯的力学性能及形态与组成和二异氰酸酯结构的关系；改变ＮＣＯ／ＯＨ摩尔比及Ｂ与Ａ的质量比，可以制得具有较好力学性能的聚氨酯材料。蓖麻油，酚氧树脂，聚氨酯，力学性能     

STUDY ON CASTOR OIL POLYURETHANE/POLY (METHYL METHACRYLATE) AB CROSSLINKED POLYMERS

Castor oil polyurethane/poly(methyl methacrylate) AB crosslinked polymers (ABCP) were synthesized by free radical copolymerization of MMA and vinyl-terminated castor oil polyurethane which was obtained from isocyanate-terminated castor oil polyurethane and hydroxyethyl methacrylate The mechanical properties, transition and relaxation, as well as compatibility and morphology of the ABCP were investigated by changing the component. The results show that the ABCP is a semicompatible system and the compatibility of the two components decreases with increasing content of the hard segment. The mechanical and damping properties of the ABCP are obviously superior to that of their homopolymers. The damping value is mainly controlled by cross[ink density of the ABCP but the T-g value by component.     

Grafting onto carbon black by the reaction of reactive carbon black having masked isocyanate or acyl azide group with functional polymers

Although isocyanate group (NCO) introduced onto carbon black surface was inactivated rapidly upon storage, it could be stabilized by masking the NCO group with active hydrogen compounds such as acetylacetone, diethyl malonate, and sodium hydrogensulfite. Upon heating these carbon blacks having masked NCO group at 150°C, the NCO group was regenerated on carbon black by the decomposition of the masked NCO group. On the other hand, acyl azide (CON₃) group introduced onto carbon black was stable at below 20°C, but readily decomposed to NCO group by heating. By means of the reaction of NCO group on carbon black with functional polymers having hydroxyl, amino, and carboxyl group, these polymers were effectively grafted onto carbon black surface. When carbon black having CON₃ group was used as reactive carbon black, the grafting ratio of diol-type polyethylene glycol (M_n = 8.2 × 10³), polyethyleneimine (M_n = 2.0 × 10⁴), polyvinyl alcohol (M_n = 2.2 × 10⁴), and bifunctional carboxyl-terminated polystyrene (M_n = 1.1 × 10⁵) was determined to be 29.7, 81.7, 32.2, and 50.4%, respectively. The number of grafted polymer chain decreases with an increase in molecular weight of the polymers, because the shielding effect of NCO group by grafted polymer chain is enhanced with an increase in molecular weight of the polymer.     

Glass transition and thermal degradation of rigid polyurethane foams derived from castor oil–molasses polyols

Rigid polyurethane (PU) foams having saccharide and castor oil structures in the molecular chain were prepared by reaction between reactive alcoholic hydroxyl group and isocyanate. The apparent density of PU foams was in a range from 0.05 to 0.15 g cm^?3. Thermal properties of the above polyurethane foams were studied by differential scanning calorimetry, thermogravimetry and thermal conductivity measurement. Glass transitions were observed in two steps. The low-temperature side glass transition was observed at around 220 K, regardless of castor oil content. This transition is attributed to the molecular motion of alkyl chain groups of castor oil. The high-temperature side glass transition observed in the temperature range from 350 to 390 K depends on the amount of molasses polyol content. The high-temperature side glass transition is attributed to the molecular motion of saccharides, such as sucrose, glucose, fructose as well as isocyanate phenyl rings, which act as rigid components. Thermal decomposition was observed in two steps at 570 and 620–670 K. Thermal conductivity was observed at around 0.032 J sec^?1 m^?1 K^?1. Compression strength and modulus of PU foams were obtained by mechanical test. It was confirmed that the thermal and mechanical properties of PU foams could be controlled by changing the mixing ratio of castor oil and molasses for suitable practical applications.     

Polymers from Renewable Resources. Xiv. Interpenetrating Polymer Networks Derived from Castor Oil—Isophorone Diisocyanate-Polyacrylamide: Thermal,Scanning Electron Microscopy,and Xrd Studies

Abstract

A large number of castor oil based polyurethanes were prepared using various diisocyanates such as isophorone diisocyanate varying the NCO/OH ratio. All the polyurethanes were reacted with acrylamide and methacrylamide using ethylene glycol dimethacrylate as crosslinker and benzoyl peroxide as initiator. Thermogravimetric analysis of the polymers were followed using computer analysis method for assigning the kinetic mechanism. The degradation steps have been discussed in the light of kinetic parameters. The SEM of some of the IPNs has been studied and the morphology has been examined. The samples were subjected to wide angle X-ray diffraction analysis. Ruland and Vonk method was used to calculate the degree of crystallinity (X_cr).     

Kinetics of the Production of Castor Oil Maleate through the Autocatalyzed Thermal Reaction and the Free Radical Reaction

Castor oil maleate is used in drying oils, water‐soluble paints, healthcare products, synthetic lubricants, and as a monomer in several polymers. This maleate can be produced by a direct autocatalyzed reaction between castor oil and maleic anhydride. However, the reaction rate can be increased using a free radical catalyst. In this work, the influence of the concentration of benzoyl peroxide (BPO) and temperature in the kinetics and productivity of castor oil maleate was studied. The optimal operating condition was found at 120°C, 1 mol of maleic anhydride/mol of castor oil, and 0.003 mol of BPO/mol of castor oil, yielding 90.0% of castor oil maleate in 90 min. A kinetic model was developed, and the model parameters were estimated both for the thermal autocatalyzed reaction and the free radical reaction.     

Epoxidation of unsaturated FAMEs obtained from vegetable source over Ti(IV)-grafted silica catalysts: A comparison between ordered and non-ordered mesoporous materials

The liquid-phase epoxidation of mixtures of fatty acid methyl esters (FAMEs) over titanium-containing silica materials, using tert-butylhydroperoxide (TBHP) as oxidant, is here reported. The mixtures were obtained from vegetable renewable source, i.e. from high-oleic sunflower oil, coriander oil, castor oil and soya-bean oil. The influence of the nature and the position of functional groups on the C-18 chain of the FAMEs was studied. Very high activity and selectivity were obtained in the epoxidation of castor and soya-bean oil methyl esters in a reaction medium free from organic acids. Ti–MCM-41 (an ordered mesoporous titanium-grafted silica) displayed in this case, for the first time, superior performances, from a synthetic point of view, with respect to non-ordered mesoporous titanosilicates.     

A Diels‐Alder/retro Diels‐Alder strategy to synthesize polymers bearing maleimide side chains

Polymers containing thiol‐reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels‐Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels‐Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and ¹H and ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545–4551, 2007     

Thermal stability of polyurethane materials based on castor oil as polyol component

Preparation of the series of polyurethane elastomers and its nanocomposites from castor oil (a vegetable triglyceride) and different isocyanates (aromatic: toluene diisocyanate, TDI and aliphatic: isophorone diisocyanate, IPDI) is described. The synthesis was carried out in bulk and without catalyst by a one-step reactive process. Different elastomers were prepared by using several stoichiometric imbalances. For polyurethane nanocomposites based on TDI, titanium(IV) oxide nanoparticles was used. The thermal properties of the materials are discussed on the basis of simultaneous TG-DSC measurements results and TMDSC data. TMDSC results show that T _g increases with increasing r = NCO/OH ratio. Namely, with increasing NCO/OH ratio the cross-linkage density increases and as a consequence, the chain mobility decreases, resulting in a higher T _g. It was estimated that the T _g of the samples decreased as the nanofiller content increased due to the changes in the segmental mobility in polyurethane materials. Thermal data refers to increased stability of nanocomposites compared with that of the unfilled elastomers.     

酚氧树脂／蓖麻油交联聚氨酯

使2.2-(4’-羟基苯基)丙烷(双酚A)与环氧氯丙烷反应制得了带端羟基的酚氧树脂(HBA),将其与蓖麻油共混,用2.4-甲苯二异氰酸酯(TDI)作固化剂,制得了一系列交联聚氨酯。DSC和DMA测试结果表明,这种聚氨酯只有一个T_g。改变NCO/OH摩尔比及HBA/(HBA 蓖麻油)比可制得具有较好阻尼性能的聚氨酯材料。     

Interpenetrating polymer networks from castor oil-based polyurethanes and poly(methyl methacrylate). V

Castor oil is reacted with hexamethylene diisocyanate under different experimental conditions varying the NCO/OH ratio to yield liquid prepolyurethanes (PPU's). All these polyurethanes were interpenetrated with methyl methacrylate (MMA) and a crosslinker EGDM by radical polymerization initiated by benzoyl peroxide. The novel PPU/MMA interpenetrating polymer networks (IPN's) were obtained as tough films by transfer molding. The characterization of these IPN's includes resistance to chemical reagents, thermal behavior (DSC, TGA), and the mechanical properties, namely, tensile strength, modulus of elasticity, elongation at break (%), and hardness. The morphological behavior (SEM) and dielectrical properties such as electrical conductivity, dielectric constant (ε′), dielectric loss (ε″), and loss tangent (tan δ) were estimated.     

Development of new lubricating grease formulations using recycled LDPE as rheology modifier additive

The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate lubricating greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium lubricating greases and its relationship with grease microstructure are discussed in this work. In this way, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these greases resulting greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases.     

Boronated (co)polystyrene: monomer reactivity ratios,thermal behavior and flammability

Chemical modification based on incorporation of flame retardants (FR) into the polymer backbone was used in order to reduce polystyrene flammability. Boronated styrenes such as 4‐vinylphenylboronic acid (StB(OH)₂) and 6‐methyl‐2‐(4‐vinylphenyl)‐1,3,6,2‐dioxazaborocane‐4,8‐dione (StBcyclo) were applied as reactive FR. Homo‐ and copolymers of boronated styrenes and styrene (St) were synthesized with different feed ratios using free radical polymerization. It yielded in series of (co)polymers with various amounts of StB(OH)₂ and StBcyclo (5–20% mol/mol of St). Copolymer compositions were determined by ¹H NMR. The relative reactivity ratios of system St‐StBcyclo were determined by applying the Jaacks method. Glass transition temperature and thermal stability of obtained (co)polymers were determined from DSC and TGA analysis, respectively. The pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and characterization of biodegradable poly(lactic acid)‐ block‐poly(ε‐caprolactone) multiblock copolymer

Biodegradable copolymers of poly(lactic acid)‐block‐poly(ε‐caprolactone) (PLA‐b‐PCL) were successfully prepared by two steps. In the first step, lactic acid monomer is oligomerized to low molecular weight prepolymer and copolymerized with the (ε‐caprolactone) diol to prepolymer, and then the molecular weight is raised by joining prepolymer chains together using 1,6‐hexamethylene diisocyanate (HDI) as the chain extender. The polymer was carefully characterized by using ¹H‐NMR analysis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The results of ¹H‐NMR and TGA indicate PLA‐b‐PCL prepolymer with number average molecular weights (M_n) of 4000–6000 were obtained. When PCL‐diols are 10 wt%, copolymer is better for chain extension reaction to obtain the polymer with high molecular weight. After chain extension, the weight average molecular weight can reach 250,000 g/mol, as determined by GPC, when the molar ratio of –NCO to –OH was 3:1. DSC curve showed that the degree of crystallization of PLA–PCL copolymer was low, even became amorphous after chain extended reaction. The product exhibits superior mechanical properties with elongation at break above 297% that is much higher than that of PLA chain extended products. Copyright © 2009 John Wiley & Sons, Ltd.