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The objective of this study was to build an understanding and optimize the secondary drying step of a freeze-drying process using a drug formulation from Fresenius Kabi (FK1) as a case study. For t...

An o-nitrobenzyl-protected precursor was used as a phototrigger for the release of the diamine cadaverine in polyurethane adhesives based on castor oil as a renewable source of polyol and organic diisocyanates. This resulted in formulations with suitably controlled curing by photoactivation. This material shows faster curing when UV light is applied as compared to curing in the absence of irradiation, which was in situ monitored by rheological measurements. In addition, the adhesion performance is superior, reaching lap shear strength values of up to 4600 kPa, which is unprecedented for bio-based adhesives. On one hand, the in-depth chemical characterization with FTIR spectroscopy revealed that the slow release of cadaverine yields a well-balanced urethane/urea composition with direct impact on adhesion properties. The photocured bioadhesive was shown to bond a variety of surfaces, such as polyethylene or even wood. On the other hand, the direct one-time addition of cadaverine yields a material with approximately the same viscoelastic properties, which were achieved almost immediately as a consequence of the favored fast formation of urea bonds in detriment of urethanes, however, lacking adhesion properties., We are grateful for financial support through the project UHU-1252599, financed by the University of Huelva, in the frame of the European Regional Development Fund (ERDF)-Junta de Andalucía 2014−2020 Operational Programme. A.M.B.-L. acknowledges the Spanish Ministerio de Educación, Cultura y Deporte for the award of a doctoral fellowship (FPU16/03697)., Funding for open access charge: Universidad de Huelva / CBUAUniversity of Huelva, in the frame of the European Regional Development Fund (ERDF)-Junta de Andalucía 2014−2020 Operational Programme. Ministerio de Educación, Cultura y Deporte (FPU16/ 03697) Funding for open acess charge: Universidad de Huelva/CBUA

We examined the rheological and tribological behavior of novel formulations based on castor oil and epoxidized cellulose pulp intended for use as biodegradable lubricating greases. Epoxidized cellulose pulp was found to thicken castor oil to a variable extent depending on its modification degree and the epoxide compound. Greases were subjected to small-amplitude oscillatory shear tests, evaluating the temperature-dependence of the plateau modulus. In addition, friction coefficient and wear were determined in a steel–steel ball-on-three-plates tribological configuration, at two different temperatures (25 and 95 °C), generally obtaining smaller values of both parameters when using aromatic diepoxides instead of aliphatic to modify the cellulose pulp.

Nowadays, there is a marked tendency in order to develop new composite fibers based on proteins and polysaccharides due to these materials can exhibit a wide range of tailored functional properties. In this framework, this study has been focused on the development of novel potato protein (PP)-based composite fibers by electrospinning technique using formic acid as solvent media. At the selected electrospinning conditions, PP pure solutions (3–8 wt.%) showed inadequate spinnability. Interestingly, the addition of polyethylene oxide (PEO) as co-blending polymer improved the solutions viscoelasticity and hence, the solutions spinnability. Composite fibers with enhanced properties were obtained at higher PEO concentrations while systems with higher PP protein contents led to electrosprayed separate aggregates of particles. Fourier-transformed infrared spectroscopy and thermogravimetric analysis results showed that the obtained composite fibers were composed of both PP and PEO materials. DSC results show that PP influences on PEO polymer thermal behaviour lowering its melting point, and an increase of the PEO amount produces a decrease of the α-helix denaturation temperature. Due to the properties of PP and PEO, these novel composite fibers could find importance in a diverse range of applications as advanced functional materials in fields like food science and biomedical applications.

To obtain multiple emulsions containing Agnique™ AE 3-2H as oil phase and Atlas™ G-5000 as emulsifier, two formulation variables were studied: the effect of the Atlas™ G-5000 concentration in emulsions containing 15 wt% Agnique™ AE 3-2H and the study of the influence of the solvent concentration maintaining the Agnique™ AE 3-2H/Atlas™ G-5000 ratio equal to 10. To assess microstructure and physical stability of these emulsions different techniques were employed, namely laser diffraction, transmitted light optical microscopy, steady-state measurements, and multiple light scattering. An increase in copolymer concentration and solvent concentration provoked a decrease in Sauter diameter but an increase in volume mean diameter and polydispersion due to droplet coalescence. Regardless of polymer concentration, all emulsions showed Newtonian behavior which led to shear thinning with increasing oil concentration. The main destabilization processes are creaming, when the concentration of polymer or solvent is low, and coalescence, when both concentrations are high.

The overall objective of this work was to study the combined effect of hydrogen peroxide (H2O2) and light emitting diodes (LED) process assisted by titanium dioxide (TiO2) on the photo-oxidation behaviour of polylactic acid (PLA). The photochemical behaviour of PLA in a TiO2 suspensions was studied by irradiation under photo-oxidative conditions (λ > 454 nm, ambient temperature and with or without the presence of H2O2). The chemical and thermal properties induced by LED irradiation process were analyzed using fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that the presence of photoactive TiO2 particles, combined with H2O2 leads to strong impact on the physicochemical properties of the samples during photochemical ageing. A new comprehensive mechanism for the photo-oxidation of PLA for these conditions was discussed.

This paper presents the rheological properties of three types of lime putty, specifying the influence of their origin. The study aims to compare a special lime putty prepared from phosphogypsum with a commercial lime powder and an aged lime putty. The results obtained in terms of chemical composition, crystalline structure, grain size and rheological characterization, (linear viscoelasticity, shear rate and time-dependent flow behaviour) are presented in the study. Putties studied present a similar rheological response, which mainly depends on the particle size and water content. Lower values of the linear viscoelastic functions and viscosity were found for the phosphogypsum lime putty, in agreement with the higher particle size. Transient flow tests reveal a predominant elastic response with no significant shear-induced structural perturbations. However, either a thickening phenomenon over time, i.e. rheopexy, favoured at low shear rates, or a viscosity decrease, i.e. thixotropy, favoured at high shear rates, was observed., The authors would like to thank the aid of CITIUS at the University of Seville for the use of their laboratories for the characterization analyses. A.M.B.-L. has received a Ph.D. Research Grant from the Ministerio de Education, Cultura y Deporte (FPU16/03697).

This work explores the electrospinnability of low-sulfonate Kraft lignin (LSL)/polyvinylpyrrolidone (PVP) solutions in N,N-dimethylformamide (DMF) and the ability of the different micro- and nano-architectures generated to structure castor oil. LSL/PVP solutionswere prepared at different concentrations (8–15wt%) and LSL:PVP ratios (90:10–0:100) and physico-chemically and rheologically characterized. The morphology of electrospun nanostructures mainly depends on the rheological properties of the solution. Electrosprayed nanoparticles or micro-sized particles connected by thin filamentswere obtained fromsolutionswith lowLSL/PVP concentrations and/or high LSL:PVP ratios,whereas beaded or bead-free nanofibers were produced by increasing concentration and/or decreasing LSL:PVP ratio, due to enhanced extensional viscoelastic properties and non-Newtonian characteristics. Electrospun LSL/PVP nanofibers are able to form oleogels by simply dispersing them into castor oil at concentrations between 10 and 30 wt%. The rheological properties of the oleogels may be tailored bymodifying the LSL:PVP ratio and nanofibers content. The potential application of these oleogels as bio-based lubricants was also explored in a tribological cell. Satisfactory friction and wear results are achieved when using oleogels structured by nanofibers mats with enhanced gel-like properties as lubricants. Overall, electrospinning of lignin/ PVP solutions can be proposed as a simple and effective method to produce nanofibers for oil structuring, Funding for open access charge: Universidad de Huelva / CBUAThis work is part of a research project (RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme

Lignin is demonstrated as an unprecedented reinforcing material that tailors the rheological and cushioning properties of castor oil-based polyurethane elastomers, expanding their viscoelastic moduli by four orders of magnitude. The tensile strain at break was triplicated in the presence of lignin while the Young modulus and the stress at break were enhanced 17- and 7-fold, respectively. Remarkably, in compression tests, lignin addition increased the stresses at break by more than 88-fold, whereas the strain at failure shifted from 50 to 93%. Dynamic mechanical compression tests indicated outstanding cushioning and resistance performance. Overall, the results demonstrate a performance not reached before for biosourced elastomeric materials, fitting the demands of a wide range of applications.

This work presents a comprehensive study on the influence of processing variables (temperature, agitation speed) and type of diisocyanate crosslinker on the rheological properties of liquid and gel-like polyurethane formulations based on lignin and castor oil. With this aim, a green and facile one-step preparation protocol which avoids the use of any harmful catalyst or solvent was proposed. Different processing temperatures (25, 45, 70 °C), stirring speeds (23, 70, 140 rpm) and kinds of diisocyanates (hexamethylene diisocyanate, and toluene diisocyanate) were selected to process the different bio-sourced polyurethane samples. These processing variables have proven to be crucial to modulate and control the rheological (viscous and viscoelastic) properties, and curing kinetics after processing, due to the different chemical structures achieved that were elucidated by means of Fourier-transform infrared spectroscopy and differential scanning calorimetry. In general, a low processing temperature and low stirring speed favour the achievement of gel-like characteristics and/or the formation of highly viscous polyurethanes, as a consequence of a higher number of total hydrogen-bonded carbonyl groups, urethane/urea ratio and ratio of hydrogen-bonded/non-bonded urethane and urea linkages. Besides, the selected one-step process, in comparison with the reported two-step process, provides polyurethanes with similar rheological characteristics by significantly reducing the isocyanate content. Finally, lignin was demonstrated to act as an effective filler agent increasing the values of the viscoelastic moduli.

Freeze-drying, a drying unit operation frequently used in food, pharmaceutical, and biopharmaceutical industries to prolong the shelf life of labile products, is an energy-intensive, time-consuming, and expensive process. Although all three steps (freezing, primary drying, and secondary drying) of freeze-drying are important, primary drying is the longest and most critical one. As sublimation during primary drying is mainly described in terms of heat and mass transfer, the present work provides extensive theoretical and experimental analyses of these processes. First, a detailed review of the current state-of-the art of freeze-drying, focusing on the drying stage, is given, which contributes to a fundamental understanding of the drying process. Second, a detailed experimental study of the drying section of the freeze-drying process is discussed, furnishing information on the relationship between input and output process parameters during the primary drying stage and thus aiding freeze-drying process design and optimization. In this regard, the influence of primary drying input parameters (i.e., shelf temperature and chamber pressure) and vial position on output parameters such as product temperature, sublimation rate, overall vial heat transfer coefficient, and resistance to mass transfer of the dried product are extensively discussed. For all combinations of shelf temperature and chamber pressure studied herein, the highest product temperature, sublimation rate, and overall vial heat transfer coefficient are observed in front edge vials, whereas the lowest values are observed in center vials. In general, the highest sublimation rate, at a given product temperature, is observed for low chamber pressure-high shelf temperature combinations.

The applications of biogenic lubricating greases to machine elements play important roles in the reduction of friction energy and minimizing wear in a tribological contact, as well as the prevention of environmental pollution. The aim of this work was to investigate completely biogenic lubricating greases from a tribological point of view. Model greases were examined using a ball on a disc tribometer at a constant normal force to investigate the friction and wear process according to Fleischer&rsquo, s energetic wear model. Using the energy-based wear model, the friction and wear process could be interpreted as a cause&ndash, effect sequence. Moreover, the influence of the model grease composition on the friction and wear process was analyzed. In addition, rolling bearing tests were performed to investigate the tribological behaviors of some selected biogenic greases during real machine element contact. These tests allowed for the quantification of the friction torque behavior of the full bearing and the evaluation of the wear obtained through lubricant analysis procedures. This experimental work provides useful information regarding the influence that the composition of biogenic model greases has on friction and wear behaviors in a tribological contact.

A method to prepare solvent free castor oil (CO) based polyurethane (PU) adhesives with different ratios of CO and hexamethylene diisocyanate (HMDI) has been developed and the relationships between the microstructure and mechanical properties investigated. Solvent free castor oil-based PU adhesives were synthesized by promoting the reaction between castor oil and HMDI, at room conditions, and by varying the CO/HMDI weight ratio in the range 1:0.032–1:0.32 wt%. The curing of these adhesives did not require any external stimuli such as heat or irradiation treatment and once cured at room temperature they were stable up to 140 °C and water-resistant. A multi-technique approach was used to characterize so-obtained adhesives. The adhesion energy in metal–metal contact was evaluated as a function of the debonding velocity (Vd) through tack experiments. The mechanical properties were influenced by the NCO/ OH ratio, which varies the crosslinking density in the adhesives. Moreover, the structure–mechanical property relationship was explored and the inter-correlation between the storage modulus (G’), adhesion energy (Ead) and correlation length (ξ) detailed, with both G’, Ead increasing while ξ decreased. These solvent-free bio-based adhesives showed capability to adhere different substrates such as wood, paper, textile, and metal, which makes them promising candidates in different industrial and commercial applications.

The main aim of this study was to elucidate the influence of an alkali treatment on the rheological and tribological properties, and microstructure, of cellulose pulp-based gel-like dispersions potentially usable as biodegradable lubricating greases. For this purpose, cellulose pulp was treated with sodium hydroxide under different conditions of alkali concentration (20, 30 and 40%), temperature (20, 45 and 75 °C) and contact time (1 and 2 h). Favourable conditions relative to the rheological response of a commercial lithium lubricating grease used as benchmark were found to be 40% NaOH, 20 °C and 2 h. Gel-like dispersions with acceptable lubrication properties in terms of consistency indices, mechanical stability, and frictional and wear performance, were obtained by using a 6–7% (w/w) proportion of cellulose pulp.

This work advances the development and use of sustainable polyurethane elastomers as green adhesives by providing insights into the mechanisms of humidity-induced changes on adhesive performance. Using a model adhesive prepared from equimolar ratios of castor oil and hexamethylene diisocyanate under facile reaction conditions, we show that the subtle changes in the chemical composition which occur with curing under different humidity environments significantly impact the cohesive integrity of the adhesives and, thus, their performances with different substrates. The curing chemistry was evaluated based on the isocyanate consumption, which was followed using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry. Thermal, mechanical and adhesion properties were evaluated from thermogravimetric analysis, differential scanning calorimetry, rheology, tacking and lap shear tests. Moisture-cured adhesives were less covalently crosslinked, harder, more resistant to deformation, and recovered faster upon shear deformation compared to those cured otherwise. These mechanical properties complimented adhesive lap shear performance with substrates which formed covalent bonds during curing. For substrates with which covalent bonds could not form during curing, however, decreased internal cohesive integrity and associated increased hardness by urea formation resulted in poorer adhesive lap shear performance. This is contrary better tack performances obtained for the moisture-cured adhesives, attributed to their increased polarity and the energy dissipating ability.

This work describes the solid-state fermentation(SSF) of wheat straw with Streptomyces sp. MDG147 and further soda-pulping process to obtain wheat straw soda lignins(WSLs). Subsequently, these WSLs were NCO-functionalized with 1,6-hexamethylene diisocyanate and then dispersed in castor oil to achieve stable oleogels. The WSLs were characterized using standard analytical methods, gel permeation chromatography, Fourier transform infrared spectroscopy,differential scanning calorimetry, and thermogravimetric analysis. Rheological properties of oleogels were determinedby means of small-amplitude oscillatory shear and viscous flow measurements. The enzymatic profile and production oflignin−carbohydrate complexes were recorded along the growth time of Streptomyces, whose life cycle was achieved after 7 days. NCO-functionalized WSL was able to chemically interact with castor oil via urethane bonding, providing oleogels with suitable rheological characteristics. Linear viscoelastic functions and viscosity values of oleogels were higher when wheat straw was submitted to SSF using Streptomyces, turning out in stronger oleogels., Ministerio de Economía, Industria y Competitividad

On account of the heavy reliance of the adhesive industry on petrochemical derivatives, there is a particular interest in the development of bio-sourced polyurethane adhesives. In this context, a moisture-curable polyurethane adhesive has been synthesized from cellulose acetate and castor oil, using 1,6-hexamethylene diisocyanate as a crosslinker. In particular, this research delves into the rheological and adhesion properties achieved by bio-inspired polyurethanes cured at 20 °C and under different relative humidity conditions (11, 33, 64, and 90.4%). Green shear and peeling strengths on wood and stainless steel as well as chemical structure variations were monitored over curing time. Moreover, fully cured polyurethane-urea adhesives were thermally (thermogravimetric and differential scanning calorimetric analyses) and rheologically characterized within the linear viscoelastic region. The results corroborated the noteworthy impact of environmental humidity throughout the curing process of the synthesized bio-sourced adhesives, favoring the formation of urea linkages, while sharply reducing the crystalline/amorphous ratio. All the bio-based polyurethane-urea copolymers showed a predominant elastic behavior and the time-Temperature superposition principle was found to be applicable up to around 120 °C, due to the thermal rearrangement of the hard segment units. The crosslinking density of the resulting supramolecular structure depends on the humidity-driven balance between the urethane and urea linkages production. As a consequence of the balance between the establishment of bidentate hydrogen bonds and the curing rate, moisture curable polyurethane adhesive cured at 33% relative humidity exhibited the most appropriate shear adhesion performance on wood, while the debonding shear strength on stainless steel increased with the relative humidity due to the higher urea:urethane ratio and larger proportions of non-bonded urethane and urea groups, thus enhancing secondary interactions. Therefore, on the basis of the present study results, it might be concluded that the synthesis of bio-inspired moisture-curable polyurethane can be tuned according to its end-use application through the control of the environmental conditions, and thereby optimizing their adhesion performance, while meeting the Green Chemistry tenets.

The present work focuses on the development of lignin micro- and nano-structures obtained by means of electrohydrodynamic techniques aimed to be potentially applicable as thickening or structuring agents in vegetable oils. The micro- and nano-structures used were mainly composed of eucalyptus kraft lignin (EKL), which were doped to some extent with polyvinylpyrrolidone (PVP). EKL/PVP solutions were prepared at different concentrations (10–40 wt.%) and EKL:PVP ratios (95:5–100:0) in N, N-dimethylformamide (DMF) and further physico-chemically and rheologically characterized. Electrosprayed micro-sized particles were obtained from solutions with low EKL/PVP concentrations (10 and 20 wt.%) and/or high EKL:PVP ratios, whereas beaded nanofiber mats were produced by increasing the solution concentration and/or decreasing EKL:PVP ratio, as a consequence of improved extensional viscoelastic properties. EKL/PVP electrospun nanofibers were able to form oleogels by simply dispersing them into castor oil at nanofiber concentrations higher than 15 wt.%. The rheological properties of these oleogels were assessed by means of small-amplitude oscillatory shear (SAOS) and viscous flow tests. The values of SAOS functions and viscosity depended on both the nanofiber concentration and the morphology of nanofiber templates and resemble those exhibited by commercial lubricating greases made from traditional metallic soaps and mineral oils, This work is part of a research project (Ref. RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme. The authors gratefully acknowledge their financial support. J.F.R.-V. acknowledges receiving the Ph.D. Research Grant PRE2019-090632 from MICINN (Spain)

In this work, alkali lignin together with different diisocyanates (hexamethylene diisocyanate (HDI), isophorone diisocyanate (IDI), toluene diisocyanate (TDI) and 4,4′-methylenebis (phenyl isocyanate) (MDI)) have been tested as gelling agents in a castor oil medium. A two-step process comprising first lignin functionalization with a diisocyanate and then the formation of a bio-based polyurethane with gel-like characteristics by combining the functionalized lignin with castor was followed. FTIR and thermogravimetry analysis were carried out on both the gelling agents and resulting oleogels. Moreover, oleogel rheological properties were evaluated by means of small-amplitude oscillatory shear (SAOS) tests and viscous flow measurements. The influences of time-temperature processing conditions during oleogel formation, lignin/diisocyanate ratio and functionalized lignin concentration on the rheological properties of oleogels were analyzed using HDI as crosslinker. 30% (w/w) thickener concentration and room temperature processing were selected to prepare oleogels with the rest of diisocyanates considered. Under the same conditions, HDI-functionalized lignin-based oleogels showed the strongest gel-like behavior whereas TDI-, IDI- and especially MDI-functionalized lignin-based oleogels displayed weak gel-like, or even a liquid-like, behaviors as a consequence of the respective chemical structures, which guide to higher steric hindrance, diminishing the formation of urethane linkages and/or Van der Waals forces. In general, oleogels exhibited an internal curing process due to the progressive formation of urethane linkages, which is closely related to the evolving rheological properties. The kinetics of this curing process was studied and an empirical model has been proposed to predict the evolution of the rheological properties with time., This work is a part of two research projects (CTQ2014-56038-C3-1R and TEP-1499) sponsored by the MINECO-FEDER and Junta de Andalucía programmes, respectively.

As well known, cellulose fibers, defibrillated/activated in different degrees or even chemically modified, can be employed as additives in matrixes of different nature with the aim of modulating some properties such as the mechanical resistance, rheological behavior or hydrophobicity of the product. Consequently, there is an increasing interest in the incorporation of these materials in a wide variety of products, being necessary the development of green methodologies for their chemical modification. The objective of this work is the use of the ball milling technology as tool for the activation and chemical modification of cellulose fibers, specifically of cellulosic material from jute. The traditional method used to date for the NCO-functionalization of cellulose fibers requires a solvent as reaction medium, the action of a catalyst and a previous stage of mercerization to boost the reactivity of the fibers. Accordingly to the former, jute fibers were NCO-functionalized, on one side, evading previous mercerization and, on other side, applying two different alkali-based activation pre-treatments that lead to materials with different crystallinity index. In addition to this, and after having optimized milling conditions, both activation and NCO-functionalization were successfully carried out in a planetary ball mill avoiding solvent, catalyst and previous alkalization. Cellulose fibers esterification was successfully implemented over already ball milled cellulosic material, showing that activation and chemical modification do not need to be performed at the same time. Fourier transform infrared spectroscopy provided the follow-up of each reaction and the impact of ball milling on the fibers was analyzed by hydrodynamic diameter measurements. Thus, it is demonstrated that ball milling can be proposed as an efficient and environmentally friendly methodology for the activation and/or functionalization of cellulose fibers. ispartof: Cellulose vol:27 issue:2 pages:643-656 status: Published online

This work addresses the reuse of waste products as a raw material for lime putties, which are one of the components of mortar. 1:3 Lime/sand mortars very similar to conventional construction mortars were prepared using a lime putty obtained from the treatment of phosphogypsum with sodium hydroxide. The physical, rheological and mechanical properties of this phosphogypsum-derived mortar have been studied, as well as the mineralogical composition, microstructure by scanning electron microscope (SEM) and curing process by monitoring carbonation and ultrasonic propagation velocity. Considering the negative influence of sulphates on the hardened material, the behaviour of the material after sulphates precipitation by adding barium sulphate was additionally tested. Carbonation progressed from the outside to the inside of the specimen through the porous system by Liesegang rings patterns for mortars with soluble sulphates, while the carbonation with precipitated sulphates was controlled by diffusion-precipitation. Overall, the negative influence of low-sulphate contents on the mechanical properties of mortars was verified. It must be highlighted the importance of their precipitation to obtain adequate performance., This research was funded by Programa Estatal I+D+i Retos de la Sociedad of the Ministry of Science and Innovation (Spain), which supported this research (MAT2017-84228-R research project).

This work has been focused on the preparation and characterization of gel-like dispersions based on sepiolite and castor oil potentially suitable as eco-friendly lubricating greases. Particularity, the effect of sepiolite content exerted on rheological, chemical, thermal and tribological properties was studied. The system exhibited a gel-like behaviour for all the concentrations considered (20–40 wt%) related to the development of a sepiolite three-dimensional colloidal network due to its characteristic nanoscale structure formed by fibers, laths and bundles. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increased with sepiolite content, as a consequence of a strengthening of the gel network. An empirical correlation between viscoelastic modulus and sepiolite concentration was proposed. From tribological point of view, the friction coefficient values and wear marks obtained after the frictional tests became lower when sepiolite concentrations decrease. Gel-like dispersion formulated with 30 wt% sepiolite showed appropriate rheological and tribological behaviour to be used as biolubricating greases.

The stability of the thickener microstructure in lubricating greases influences their ability to reduce friction and protect the lubricated surfaces in a tribological system. Shear-induced degradation of the thickener network in lubricating greases that occurs as a result of reduced particle interactions can be considered a process associated with exceeding a critical energy level, i.e. the activation energy. The aim of this experimental study was to investigate the relationship between the activation energy, which represents the amount of energy required to produce shear-induced structural degradation, and the extent of the structural degradation that occurs under different shearing conditions. To this end, rotational transient flow tests were carried out in a rheometer at varying temperatures (25–70 °C) and a constant shear rate to quantify the activation energy of six model greases. The model greases differed in the nature and concentration of the thickener used, and the activation energy was calculated by fitting the rheological energy density to the Arrhenius equation. The activation energy was found to depend on the nature and concentration of the thickener in the greases; higher thickener concentrations resulted in lower activation energies. In addition, oscillation amplitude sweep tests were performed to obtain information about the early stages of shear-induced structural degradation. Lower activation energies were found to result in an earlier onset of shear-induced structural degradation. Finally, correlations between the activation energy and structural degradation of the model greases under different shear situations were presented and discussed. This enhanced understanding of the shear-induced degradation will facilitate the improvement of the service life of lubricating greases.

The freeze-drying process is a combination of 2 equally important processes, freezing, and drying. In the past, the effort was mainly focused on optimizing the drying process without considering the possible effects of the freezing step. During freezing, a solution undergoes several physical changes, including a supercooling state. The degree of supercooling of a solution dictates the ice habit (size, number, and morphology) during freezing, which impacts the subsequent drying process, such as the resistance to water vapor flow. Therefore, heterogeneous degree of supercooling leads to heterogeneous ice habits and, in turn, to heterogeneous drying behavior. This poses significant challenges during freeze-drying process development, optimization, and scale up. Hence, controlling the degree of supercooling significantly improves freeze-drying process design. The aim of the current review is to gather existing information on the physicochemical phenomena involved in the freezing process and how these phenomena impact the subsequent drying step of the freeze-drying process. In addition, modification of the freezing process and different techniques used to actively control the degree of supercooling during freezing will be reviewed and discussed. Their impact on freeze-drying process performance will be also addressed.

Considerable efforts are currently being made by the academic community and industry, aiming to develop environmentally friendly lubricants with suitable technical features for their performance. In this context, lignin could be considered a promising candidate to be used as a bio-sourced thickening agent to formulate eco-friendly lubricating greases. In this work, alkali lignin (AL) was chemically modified with poly(ethylene glycol) diglycidyl ether (PEGDE). Afterwards, the epoxidized lignin was properly dispersed in castor oil (CO) in order to obtain an oleogel for lubricant applications. The epoxidized lignins were characterized by means of epoxy index determination, thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The epoxide-functionalized lignin-based oleogels were analyzed from both rheological and tribological points of view. It was found that the viscosity, consistency and viscoelastic functions of these oleogels clearly increased with the epoxy index of the epoxide-modified lignin compound. Thermo-rheological characterization of these oleogels revealed a slight thermal dependence of the viscoelastic moduli below 100 &deg, C, but a significant softening above that critical temperature. In general, these oleogels showed low values of the friction coefficient under the mixed lubrication regime as compared to the neat castor oil.

The scope of this study is to elucidate the physical mechanisms influencing the transient flow behavior of lubricating greases based on biogenic oleochemicals from a polarity point of view. This includes the mutually interacting influence of base oil polarity and thickening agents on the rheologically-measured mechanical structural degradation in transient shear flow. Due to the high temperature dependence of Keesom forces in the background of polar-active bond mechanisms, the analysis of the transient flow response as a function of temperature allows to attribute the observed influences to differences in base oil polarity. In general, clay-thickened greases show a greater tendency to be rheologically influenced by base oil polarities than soap-thickened lubricating greases.

In this work, several lignocellulose pulps from different origins and/or submitted to different treatments were cross-linked with hexamethylene diisocyanate (HMDI) and further dispersed in castor oil in order to obtain gel-like formulations based on renewable resources, which can be potentially applicable as semisolid lubricants. The rheological and tribological properties attained as well as physical and mechanical stability were suitable to consider these gel-like dispersions as efficient alternatives to traditional lubricating greases. The rheological behavior was evaluated by means of both small-amplitude oscillatory shear tests (SAOS) and viscous flow measurements, at different temperatures. The HMDI/cellulose pulp weight ratio applied in the cross-linking reaction can be used to modify and modulate the consistency and the values of rheological functions of these gel-like dispersions. However, the rheological behavior is not qualitatively affected by the amount of HMDI used as coupling agent. The the...

The overall objective of this work was to study the effect of reprocessing cycles of isotactic polypropylene (PP) on the rheological behavior and microstructure of gel-like dispersions in mineral oil. PP was subjected to 10 reprocessing cycles and oleogel samples were further prepared by using the mixing rheometry technique and characterized from a rheological point of view and polarized light optical microscopy (PLOM). Recycled polymer samples were also characterized by means of rheological measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to evaluate the property changes induced by reprocessing. The values of different linear viscoelastic functions (elastic modulus and complex viscosity) of recycled PP decrease with the number of reprocessing cycles, which influences oleogel rheological response. An empirical exponential correlation between the storage modulus (G′) of PP samples and the plateau modulus ( G N o ) of oleogels has been proposed to predict the rheological behavior of oleogels. Results were explained considering the scission of PP chains induced by the thermomechanical reprocessing treatment applied.

New oleogel formulations based on high-oleic sunflower oil (HOSO) and ethylene vinyl acetate copolymer (EVA)/polypropylene (PP) blends were prepared using the mixing rheometry technique and further characterized. The effects of PP tacticity and EVA vinyl acetate (VAc) content on the rheological, morphological, and thermal behavior of derived oleogels were investigated. Differential scanning calorimetry (DSC) and polarized-light optical microscopy (PLOM) observations indicated that VAc segments markedly influence the crystalline structure of polymeric fractions and phase morphology of oleogels. The normalized crystallinity of isotactic polypropylene (iPP) phase increased linearly with its concentration whereas syndiotactic polypropylene (sPP) content does not exert a significant influence. PLOM observations showed that VAc content plays an important role in the phase morphology of PP frictions (size and shape of crystals). The viscoelastic response of oleogels depended on PP tacticity and VAc content, which may be explained attending to the different microstructures attained. POLYM. ENG. SCI., 55:1429–1440, 2015. © 2015 Society of Plastics Engineers

Nowadays, different types of natural carbohydrates such as sugars, starch, cellulose and their derivatives are widely used as renewable raw materials. Vegetable oils are also considered as promising raw materials to be used in the synthesis of high quality products in different applications, including in the adhesive field. According to this, several bio-based formulations with adhesion properties were synthesized first by inducing the functionalization of cellulose acetate with 1,6-hexamethylene diisocyanate and then mixing the resulting biopolymer with a variable amount of castor oil, from 20% to 70% (wt). These bio-based adhesives were mechanically characterized by means of small-amplitude oscillatory torsion measurements, at different temperatures, and standardized tests to evaluate tension loading (ASTM-D906) and peel strength (ASTM-D903). In addition, thermal properties and stability of the synthesized bio-polyurethane formulations were also analyzed through differential scanning calorimetry and thermal gravimetric analysis. As a result, the performance of these bio-polyurethane products as wood adhesives were compared and analyzed. Bio-polyurethane formulations exhibited a simple thermo-rheological behavior below a critical temperature of around 80–100 °C depending on the castor oil/cellulose acetate weight ratio. Formulation with medium castor oil/biopolymer weight ratio (50:50 % wt) showed the most suitable mechanical properties and adhesion performance for bonding wood., This work is part of two research projects (CTQ2014-56038-C3-1R and TEP-1499) sponsored by MINECO-FEDER and Junta de Andalucía programmes, respectively. One of the authors (Adri án Tenorio) has also received a PhD. Research Grant from ‘Ministerio de Educación’ (FPU13/01114). The authors gratefully acknowledge the financial support.

This paper reports a physical characterization of multiple emulsions formulated with a green solvent (2-ethylhexyl lactate) and different HLB amphiphilic block copolymers (Atlas™ G-5000 and Atlox™ 4912), as emulsifiers. 15 wt% 2-ethylhexyl lactate emulsions stabilized by a 1:1 mass ratio of both copolymers were prepared with different copolymer concentrations in one single emulsification step, using a rotor-stator emulsification device. Multiple emulsions were characterized by means of electrolytic conductivity measurements, viscosity, optical microscopy, laser diffraction and multiple light scattering techniques. W/O/W emulsions were obtained in all cases, regardless of the copolymer composition used. All emulsions showed Newtonian behaviour and relatively low viscosity values (2–2.6 times the viscosity of water at 20 °C). Viscosity hardly increased with the overall copolymer concentration. The mean Sauter diameter of O/W globules increased with copolymer concentration, while the evolution of the volumetric mean diameter depended on the occurrence of some recoalescence. The onset of different simultaneous destabilization mechanisms was detected by multiple light scattering. Even though creaming was the predominant destabilization mechanism, a separated layer of oil phase due to coalescence was also observed in most cases after a long aging time. The destabilization kinetics was slowed down by increasing the total copolymer concentration when both types of copolymers were used.

The overall objective of this work was to study the influence of vinyl acetate (VAc) content on the rheological properties and microstructure of polymer gels based on conventional and high-oleic sunflower vegetable oils and ethylene-vinyl acetate copolymer (EVA). The mechanical properties during gel preparation can be in situ monitored through the evolution of torque with processing time by using the mixing rheometry technique. Linear viscoelastic measurements, as well as differential scanning calorimetry (DSC) tests and morphological observations, were performed on the resulting gels. From the experimental results, it can be concluded that VAc content and melt flow index of the EVA copolymer significantly affect the rheological and thermal responses of polymer gels. VAc content, mainly affecting EVA degree of crystallinity, and melt flow index influence the linear viscoelastic behaviour in opposite directions. On the contrary, the extension of the linear viscoelastic regime and gel-like to liquid-like response transition temperatures are mainly dominated by EVA degree of crystallinity, as confirmed through calorimetry tests and microscopy observations. The different fatty acid profile in sunflower oils tested does not exert an important influence on process rheokinetics and rheological behaviour.

This work deals with the influence of functionalization degree on the thermogravimetric and rheological behaviour of NCO-functionalized chitosan- and chitin-based oleogels. Chitosan and chitin were functionalized using different proportions of 1,6-hexamethylene diisocyanate (HMDI) and subsequently dispersed in castor oil to promote the chemical reaction between the –NCO group of the modified biopolymer and the –OH group located in the ricinoleic fatty acid chain of castor oil, thus resulting in different oleogels with specific thermogravimetric and rheological characteristics. Biopolymers and oleogels were characterized through Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Small-amplitude oscillatory shear (SAOS) measurements were performed on the oleogels. Oleogels presented suitable thermal resistance, despite the fact that the inclusion of HMDI moieties in the polymer structure led to a reduction in the onset temperature of thermal degradation. The insertion of low amounts of HMDI in both chitin and chitosan produces a drastic reduction in the values of oleogel viscoelastic functions but, above a critical threshold, they increase with the functionalization degree so that isocyanate functionalization results in a chemical tool to modulate oleogel rheological response. Several NCO-functionalized chitosan- and chitin-based oleogel formulations present suitable thermal resistance and rheological characteristics to be proposed as bio-based alternatives to traditional lubricating greases., This work is part of two research projects (CTQ2010-15338 and TEP-1499) sponsored by MINECO-FEDER (70% European cofunding rate) and Junta de Andalucia programmes, respectively. One of the authors (Rocio Gallego) has received a Ph.D. Research Grant from DIGICyT (MINECO). The authors gratefully acknowledge the financial support.

This work compares the thermal, rheological, and tribological properties of a new gel-like biodegradable formulation, prepared using an acylated chitosan thickener and castor oil, with properties exhibited by two conventional greases thickened with lithium and calcium soaps, respectively, taken as benchmarks. Thermogravimetric (TGA), rheological (small-amplitude oscillatory shear [SAOS], rheodestruction, and viscous flow) and tribological (friction and wear analysis) tests, as well as roll-stability measurements were carried out to characterize the three grease samples. In addition, infrared spectroscopy and differential scanning calorimetry (DSC) were used to chemically characterize the acylated chitosan thickener agent. From a thermogravimetric point of view, the new formulation displayed better thermal resistance than the calcium and lithium lubricating greases. The evolution of the linear viscoelasticity functions with frequency and viscosity values in the shear rate and temperature ranges studied wer...

This work deals with the development and rheological characterization of a variety of green lubricating grease formulations based on different combinations of vegetable oil-derived basestocks and biopolymers obtained from renewable resources. Castor oil, high-oleic sunflower acid oil (HOS-AO) and a ricinoleic acid-derived estolide were tested as basestocks, whereas chitosan and Kraft cellulose pulp, apart from traditional lithium soap, were selected as thickener agents. Rheological behaviour was characterized by means of small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, some standard mechanical tests were carried out in order to evaluate the suitability of these formulations for lubricant applications. The rheological response depends on the type of vegetable oil-derived basestocks and thickener agent. Higher values of the SAOS functions were obtained for chitosan-based formulations. High viscosity and consistency were particularly achieved by combining the estolide sample and lithium hydroxide. On the contrary, soft greases and generally higher flow indexes were found in cellulose pulp-based formulations. The effect of the different basestocks on the rheological response was explained attending to the influence exerted by oil viscosity and basestock-thickener polar interactions, as well as the chemical reaction between the basestock carboxylic moieties and lithium hydroxide to form different thickener structures.

In this work, the capability of organo-bentonite (OBent)/recycled polypropylene (PP) and mineral oil blends to form gel-like dispersions potentially applicable as lubricating greases was explored. Specifically, the effect of both thickener concentration ratios on the rheology, thermal and some lubricant performance properties of the resulting gel-like dispersions was studied. The rheological response was qualitatively similar for all the samples studied and also similar to that found in standard lubricating greases. The plateau modulus G°N, of OBent/PP dispersions in mineral oil showed negative deviation from the additivity line and minimum values were observed for intermediate OBent/PP concentration ratios, excepting at the highest temperature studied (150 °C), where a continuous increase of this viscoelastic parameter with OBent content was found. The degree of crystallinity of recycled PP in the sample was influenced by the presence of OBent. Samples formulated with lower values of OBent/PP concentration ratio yield gel-like formulations with appropriate mechanical stabilities to be used as lubricating greases. The friction coefficient evaluated in a ball-on-plate tribological contact decreased with OBent content.

In this study, cellulose acetate and castor oil have been used to synthesize new eco-friendly alternatives to traditional polyurethane adhesives. First, cellulose acetate (CA) was modified with diphenylmethane-4,4′-diisocyanate (MDI) at different NCO:OH molar ratios, ranging from 2 to 4.53, and then the resulting biopolymers were mixed with castor oil (CO) at 1:1 wt ratio. The fully cured bio-sourced adhesives were rheologically characterized by applying dynamic oscillatory torsional tests at different temperatures (from −30 up to 200 °C). Furthermore, their adhesion performance on stainless steel and poplar wood substrates was analyzed, by conducting standardized mechanical tests, namely single-lap shear and 180° peel strengths, at room temperature and 100 °C. Fourier transform infrared spectroscopy-attenuated total reflectance along with differential scanning calorimetry and thermogravimetric analysis were also performed. Above a critical NCO:OH ratio, a thermo-rheological simplicity was found within the whole temperature range considered, being able to apply the t-T superposition principle. However, an increase in the temperature led to a depletion in their mechanical performance, thus reducing their temperature range of application. Thermal and spectroscopic analysis corroborated the complete disappearance of free isocyanate during the first few days of curing, and a segmented structure, typical of polyurethanes. Optimum thermo-rheological behaviour and adhesion performance on wood and stainless steel of the bio-sourced polyurethanes studied were found for NCO:OH molar ratios higher than 3.5, which was related to the higher compatibility between hard and soft microdomains.

Practical steady-state flow curves were obtained from different rheological tests and protocols for five lubricating greases, containing thickeners of a rather different nature, i.e., aluminum complex, lithium, lithium complex, and calcium complex soaps and polyurea. The experimental results demonstrated the difficulty to reach &ldquo, real&rdquo, steady-state flow conditions for these colloidal suspensions as a consequence of the strong time dependence and marked yielding behavior in a wide range of shear rates, resulting in flow instabilities such as shear banding and fracture. In order to better understand these phenomena, transient flow experiments, at constant shear rates, and creep tests, at constant shear stresses, were also carried out using controlled-strain and controlled-stress rheometers, respectively. The main objective of this work was to study the steady-state flow behaviour of lubricating greases, analyzing how the microstructural characteristics may affect the yielding flow behaviour.

This work focuses on the development of gel-like formulations for use as lubricating greases. These dispersions were formulated using mineral oil and recycled/amorphous polypropylene blends. In particular, the influence of the polypropylene concentration ratio (Wi) on the rheology, thermal and some lubricant performance properties of polymer/oil blends were studied. The rheological responses of these systems were quite different, influenced mainly by the concentration of amorphous polypropylene. At intermediate temperatures (25 °C, 50 °C) and high recycled polypropylene concentrations (Wi > 0.5), the evolution of small-amplitude oscillatory shear (SAOS) functions was very similar to those found with other commercial lubricating greases. Samples with lower concentrations of amorphous polypropylene (12.5%) present maximum G N ° values in the temperature range studied. An Arrhenius-type equation can be used to quantify the thermal dependence of the linear viscoelastic functions of these gel-like dispersions. In general, sample formulations studied exhibited values of the friction coefficient comparable to those found for traditional lithium lubricating greases.

This work has been focused on the development of polyolefins/oil blends potentially suitable as lubricating greases by studying the effect that some thermo-mechanical processing variables exert on their rheological properties and microstructure. Polyolefin/oil blends have been prepared by dispersing recycled and virgin polyolefins such as high-density polyethylenes (HDPEs) and polypropylenes (PPs) in mineral lubricating oil. Linear viscoelasticity functions have been significantly influenced by processing conditions. The nature of polymers used, specially the content of HDPE, has been found to modify the microstructure of blends yielding lower mechanical stability but, on the other hand, higher values of linear viscoelastic functions.

This work deals with the selective incorporation of reactive isocyanate groups into methyl cellulose in order to be used as reactive thickening agent in castor oil. Resulting gel-like dispersions may have potential applications as green lubricating greases formulated from renewable resources. Two different isocyanate-functionalized methyl cellulose-based polymers were obtained by reaction of methyl cellulose with 1,6-hexamethylene diisocyanate. The functionalization degree, from fully functionalized to a certain number of free hydroxyl groups (58:36:6 ratio between –OMe, –NCO and free –OH groups), was controlled by modifying the reagents molar ratio. These polymers were characterized through nuclear magnetic resonance of protons (1H-NMR), Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA). Thermal and rheological responses of oleogels prepared by dispersing these polymers in castor oil were studied by means of TGA analysis and small-amplitude oscillatory shear measurements. The evolution of linear viscoelasticity functions with frequency of the oleogel containing isocyanate-functionalized methyl cellulose with lower –NCO content is quite similar to that found for traditional lithium lubricating greases. In relation to long-term stability of these oleogels, the values of viscoelastic functions significantly increase during the first 7 days of ageing and then remain almost constant.

In this work, model renewable and biodegradable lubricating greases based on castor oil and chemically modified biopolymers (methylcellulose, chitin and cellulosic pulp) were tribologically characterized in a steel–steel ball-on-plates tribological cell coupled to a controlled-stress rheometer, and the results were compared to those provided by conventional lithium and calcium soap-based greases. Viscous flow, sliding velocity sweep and transient friction tests were carried out and resulting wear scars in the steel plates were evaluated by means of scanning electron microscopy (SEM). Different frictional responses were found depending on the thickener, especially at high temperature. Excepting for most severe conditions, wear is negligible when using chemically modified chitin and methylcellulose-based greases as lubricants., This work is part of two research projects (CTQ2014-56038-C3-1R and TEP-1499) sponsored by MINECO-FEDER and Junta de Andalucia programmes, respectively. One of the authors (Rocio Gallego) has received a Ph.D. Research Grant (BES-2011-045029) from DIGICyT (MINECO). The authors gratefully acknowledge the financial support. Maria Teresa Cidade acknowledges the support of the Portuguese Foundation for Science and Technology through Project PEst-C/CTM/LA0025/2013 and The Portuguese Society of Rheology (SPR) for her stay in University of Huelva.

The microstructure of lubricating greases greatly conditions their in-service performance. In that sense, optimal testing protocols are required in order to accomplish their correct morphological characterization. This study explores and compares the suitability of atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques for imaging six different commercial metallic soap-based greases and two novel biopolymer-based formulations. Pros and cons of both techniques and the effect of sample preparation protocol were analysed. The results revealed a wide variety of morphological characteristics depending on composition. Thus, the four anhydrous calcium-based greases demonstrated two clearly distinct microstructures (fibrous and granular) determined by the type of base oil employed. With regard to the lithium complex greases, the typically reported microstructure characterized by well-defined entangled and fibrous network was observed in both AFM and SEM techniques. As for the two biopolymer-based greases, fibre networks were also encountered. Besides this, selected greases were subjected to different tribological tests, and the effect of high-shear frictional working treatments on their microstructure was also analysed. As a result of the friction and internal wear, the AFM results evidenced microstructural changes which depended on grease composition. Overall, the combined use of AFM and SEM techniques was demonstrated to be a powerful approach to microstructurally characterize lubricating greases., This work is part of two research projects (CTQ2014-56038-C3-1R and TEP-1499) sponsored by MINECO-FEDER and Junta de Andalucia programmes, respectively. The authors gratefully acknowledge the financial support. Authors also acknowledge Castrol (Germany) and Verkol S.A. (Spain) for kindly providing commercial samples.

This work deals with the manufacture of oil-in-water food emulsions stabilised by tuna proteins. The influence of protein and oil concentrations on the linear viscoelastic properties and microstructure of these emulsions was analysed. Stable emulsions with suitable linear viscoelastic response and microstructural characteristics were formulated with 70 wt.% oil and, at least, 0.25 wt.% tuna protein. Similarly, emulsions with oil concentrations between 45 and 70 wt.% were prepared using 0.50 wt.% protein. All these emulsions showed a predominantly elastic response in the linear viscoelastic region and a well-developed plateau region in its mechanical spectrum. Rheological and droplet size distribution results pointed out an extensive droplet flocculation, due to interactions among emulsifier molecules located at the oil–water interface of adjacent droplets. As a result, the linear viscoelastic behaviour was controlled by protein–protein interactions, allowing the use of the plateau modulus to successfully normalise both the storage and loss moduli as a function of frequency onto a master curve, irrespective of the selected emulsion formulation.

This article deals with the influence of temperature on the rheological behavior of lithium lubricating greases modified with three different types of recycled polymers, high-density polyethylene (HDPE), low-density polyethylene, and polypropylene (PP), all deriving from waste plastic recycling plants. Grease formulations containing diverse polymers were manufactured and rheologically characterized. Small-amplitude oscillatory shear and viscous flow measurements over a temperature range of 25–175°C were carried out. The experimental results obtained suggest that a blend of HDPE and PP could be considered a suitable potential viscosity modifier for lithium lubricating greases in a wide range of in-service temperature. Thus, the lubricating greases studied modified by HDPE or PP show quite promising results at low or high temperature, respectively. In addition, thermomechanical reversibility has been studied by applying different combined stress–temperature protocols. Lubricating greases containing any of the recycled polymers studied show a significant irreversible structural breakdown when the sample is submitted to temperatures and stresses higher than 75°C and 200 Pa, respectively. Regarding lubricating grease viscous flow behavior, a minimum in the shear stress versus shear rate plots appeared at temperatures above 50°C, more pronounced as temperature increased, resulting from material flow instabilities. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.

Different biodegradable lubricating greases formulated with esters of fatty acids, as base oils, and bentonite and highly dispersed silica acid, as thickener agents, were tribologically investigated in a nanotribometer and compared with polyalpha olefin greases with equal thickeners. Material combinations of steel ball on steel disc and sapphire ball on steel disc were used with different normal loads. Several friction and wear effects were found depending on the thickener and the base oil. The influence of grease components is also different in both material combinations evaluated. On the one hand, the base oil exerts a much higher impact on friction and wear in grease systems thickened with highly dispersed silica acid than in those thickened with bentonite. On the other hand, the latter reacts more sensitively to a change in material combination. Results were discussed and explained on the basis of polarity influences of the base oils and solid surfaces. Copyright © 2012 John Wiley & Sons, Ltd.

This work deals with the incorporation of reactive isocyanate groups into polymer additives, which could be potentially used to modify the rheological properties of lubricating greases by reinforcing the role of traditional thickening agents. Thus, a batch of partially protected poly(vinylalcohol) (PVA) copolymers was successfully synthesized. Some of their OH groups were blocked as tetrahydropyranyl (THP) ethers (PVA–THP), while the spare hydroxyl groups were further functionalized with NCO pendant groups by reaction with 1,6-hexamethylene diisocyanate, leading to several isocyanate-functionalized PVA-based polymers (PVA–THP–NCO), which were tested as rheology modifiers of lithium lubricating greases. The highest protection degree of hydroxyl groups achieved as THP-ether was 58.5% and the recovered polymers were isolated with excellent yields (close to 90% in most cases). NCO-functionalized PVA-based polymers (PVA–THP–NCO) exerted a significant rheological modification in lithium 12-hydroxystearate lubricating greases, increasing the values of the linear viscoelastic functions. The influence of the degree of protection and later functionalization of PVA on the rheological properties of PVA–THP–NCO-additivated lubricating greases is discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012