Significant Friction Reduction Research Articles

AQUASYN-X: INNOVATIVE SOBM FOR DRILLING IN EXTREME TEMPERATURE AND PRESSURE CONDITIONS

The development of new synthetic oil-based mud (SOBM) is crucial for enhancing drilling operations in extreme environments, such as deepwater and offshore locations, while maintaining environmental sustainability. This paper presents AquaSyn-X, a next-generation SOBM specifically engineered to withstand the harsh conditions encountered during deepwater and high-pressure, high-temperature (HPHT) drilling operations. The primary objectives of developing AquaSyn-X include improving thermal and pressure stability, minimizing toxicity, and enhancing lubricating properties to ensure efficient drilling performance. AquaSyn-X's formulation is based on a unique combination of synthetic oils, emulsifiers, and rheology modifiers, which provide superior stability and functionality in challenging environments. Results from the experiments show that AquaSyn-X exhibits excellent emulsion stability, even under extreme HPHT conditions. The mud also demonstrates a significant reduction in friction, which leads to enhanced wellbore stability and reduced risks of stuck pipe incidents. The findings indicate that this SOBM is compliant with environmental regulations governing offshore drilling, and its use significantly reduces the release of harmful chemicals into marine ecosystems. This innovative SOBM could lead to improved operational efficiency, reduced downtime, and a smaller environmental footprint, thereby setting a new standard for drilling fluids in the oil and gas industry. Keywords: synthetic oil-based mud (SOBM), high-pressure high-temperature (HPHT), deepwater drilling, environmental sustainability, friction reduction, wellbore stability.

Beyond Smoothness: The Art of Surface Texturing Battling against Friction

Abstract Leveraging surface texturing to realize significant friction reduction at contact interfaces has emerged as a preferred technique among tribology experts, boosting tribological energy efficiency and sustainability. This review systematically demonstrates optimization strategies, advanced manufacturing methods, typical applications, and outlooks of technical challenges toward surface texturing for friction reduction. Firstly, the lubricated contact models of microtextures are introduced. Then, we provide a framework of state-of-the-art research on synergistic friction optimization strategies of microtexture structures, surface treatments, liquid lubricants, and external energy fields. A comparative analysis evaluates the strengths and weaknesses of manufacturing techniques commonly employed for microtextured surfaces. The latest research advancements in microtextures in different application scenarios are highlighted. Finally, the challenges and directions of future research on surface texturing technology are briefly addressed. This review aims to elaborate on the worldwide progress in the optimization, manufacturing, and application of microtexture-enabled friction reduction technologies to promote their practical utilizations.

Near-Surface Reconfiguration of Biopolymer Blends by Mechanical Embossment: Creation of Friction-Reduced Foils

Biopolymer blends of polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT) are extruded into flexible monolayer films. These blends are excellent candidates for the realization of environmentally friendly packaging applications. A necessary pre-requisite for that are appropriate tribological properties under mechanical contact. Reasonable wear resistance allows good protection of packed goods, and low friction forces reduce difficulties in stacking. In this research, mechanical embossment under high loads at room temperature was used for the modification of polymer surfaces to exhibit a significant friction reduction under dry conditions. The results particularly show a systematic decrease in the coefficient of friction for biopolymer blends containing 30 wt% and 40 wt% PBAT. FTIR was used to analyze the change in surface composition after mechanical embossing. A sophisticated FTIR calibration method revealed that the blend with 30 wt% PBAT shows a modified distribution of PBAT and PLA at the surface due to mechanical embossment. This leads to a controlled and long-lasting modification of the surface properties without a substantial change in the chemical composition of the polymer in bulk. Without the use of additional coatings, biodegradable packaging foils with improved characteristics are accessible.

Fabrication and Tribology Properties of PTFE-Coated Cemented Carbide Under Dry Friction Conditions

PTFE coatings were deposited on YT15 carbide substrates using spray technology. A series of examinations were conducted, including the use of surface and cross-section micrographs to analyze the structural integrity of the coatings. The surface roughness, the adhesion force between the PTFE coatings and the carbide substrate, and the micro-hardness of the coated carbide were also evaluated. Additionally, the friction and wear behaviors were assessed through dry sliding friction tests against WC/Co balls. The test results indicated that while the PTFE-coated carbide exhibited a rougher surface and reduced micro-hardness, it also demonstrated a significant reduction in surface friction and adhesive wear. These findings suggest that the PTFE coatings enhance the overall wear resistance of the carbides. The lower surface hardness and shear strength of the coatings influenced the friction performance, leading to specific wear failure mechanisms, such as abrasion wear, coating delamination, and flaking. Overall, the deposition of PTFE coatings on carbide substrates presents a promising strategy to enhance their friction and wear performance. This approach not only improves the durability of carbide materials but also offers potential applications in industries where reduced friction and wear are critical for performance.

Measurement of slip length and friction reduction: An experimental study about boundary slip using omniphobic and 2D coatings

There is an intrinsic link between boundary slip and superlubricity. However, due to limitations in experimental techniques, the slip length cannot be precisely measured, leaving the mechanism of boundary slip controversial. This paper aims to accurately measure the slip length at the solid-liquid interface under oil-lubricated elastohydrodynamic lubrication (EHL) conditions using experimental methods, and to explore the friction reduction due to boundary slip. The study reveals that both omniphobic (lotus leaf essence) coatings and two-dimensional (2D) material (MoS2) coatings facilitate boundary slip. The slip length measurement method proposed in this study builds a bridge between oil film thickness and slip length, successfully addressing a key issue in boundary slip research. The findings confirm the significant friction reduction due to boundary slip, representing a major advancement in reducing friction in oil-lubricated EHL contacts through boundary slip. Future research should focus on searching for coating materials with a slip length on the micrometer scale so that superlubricity could be achieved.

Unravelling molecular origins of improved tribological properties of amino acid ionic liquid water-based lubricants

In the quest for sustainable lubrication, this study explores the potential of water-based lubricants (WBLs) with amino acid ionic liquid (AAIL) additives. The research combines experimental and reactive molecular dynamics (MD) simulations to assess the tribological and rheological enhancements provided by AAILs. Specifically, tetrabutylphosphonium (P4444) cations paired with Serine (Ser) and Tryptophan (Trp) anions were mixed into water to create AAIL WBLs. The introduction of AAILs significantly improved the lubricants’ rheological properties and reduced the coefficient of friction by up to 34 %. This reduction is attributed to the formation of hydration shells around the amino acid anions, which create a chemically adsorbed tribofilm on iron oxide surfaces, and P4444 cations that establish a load-bearing layer in the middle regions of the lubricant. This dual-layer structure, supported by hydration lubrication, effectively maintains lubricant fluidity while bearing substantial loads. Among the AAIL WBLs tested, those with a thicker, more stable, hydrated amino acid tribofilm demonstrated more significant friction reduction. These insights into the molecular mechanisms behind AAIL WBLs’ tribological behaviour underscore their promise as eco-friendly lubricants, contributing to advancing a circular economy in industries reliant on lubrication.

Correlation between preparation techniques and frictional properties of cellulose nanocrystals as additives in water-based lubricants

To explore the tribological characteristics of cellulose nanocrystals derived through various preparation techniques when utilized as additives in water-based lubricants, two types of cellulose nanocrystals (S-CNC and C-CNC) were chosen. These were produced via sulfuric acid hydrolysis and oxidation methods. The morphology and structural features were assessed through techniques such as Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), laser confocal Raman spectroscopy, elemental analysis, scanning electron microscopy (SEM), and laser particle size analysis. According to thermogravimetric analysis (TGA), the thermal stability of S-CNC is slightly superior to that of C-CNC. S-CNC exhibits liquid crystallinity when the concentration exceeds 0.5 %, whereas C-CNC does not display liquid crystallinity at any concentration tested. Further investigation was conducted on the frictional properties of the two types of CNCs using a UMT reciprocating friction tester. The results indicate that both types of CNC exhibit significant friction reduction properties at various additive concentrations, provided the addition does not exceed w=1 %. When below their respective liquid crystalline phase concentrations, the friction reduction performance of S-CNC is slightly inferior to that of C-CNC; however, when above the liquid crystalline phase concentration, the friction reduction performance of S-CNC surpasses that of C-CNC. The addition of w=0.5 % S-CNC leads to a relative reduction of 63.4 % in the friction coefficient compared to the base system. Analysis of the steel plate surface contact angle and post-wear surface suggests that the lubrication mechanism of CNC involves the adsorption of polar functional groups such as hydroxyl or carboxyl groups from the CNC structure onto the friction pair surface, forming a lubricating protective film to varying degrees. Additionally, the liquid crystalline structure of S-CNC facilitates the formation of an ordered lubricating film, further enhancing the frictional properties. These findings provide valuable insights into the application of nanocellulose crystals as lubricant additives.

Synergistic effects of nitrogen-containing functionalized copolymer and silicon-doped DLC for friction and wear reduction

We present a strategy to enhance the tribological performances of diamond-like carbon (DLC) films based on synergistic chemical modifications in the polymer lubricant additives and in the carbon film. Our experiments revealed that the polymer functionalization with nitrogen-containing groups and the DLC doping with silicon atoms result in significant friction and wear reduction under severe boundary lubrication conditions. Atomic Force Microscopy revealed the formation of a lubricious tribofilm. Ab initio calculations highlighted the key role of N-Si interactions in promoting the polymer chemisorption on the film, which represents the first, essential step for the tribofilm formation. Our findings suggest that targeted chemical modifications in lubricants and films can substantially advance the tribological performances of DLC films for various industrial applications.

Effect of micro-surface-texturing on the friction between cam/tappet interface of a commercial vehicle engine

Reduced wear and friction are directly related to longer component service lives and increased energy efficiency. The mechanisms used to achieve this goal in mechanical systems include the study of lubricant chemistry, surface coating, and surface modification. Significant research has been conducted on friction reduction of valve trains of internal combustion engines using surface modifications such as coatings and surface texturing. Here, an experimental approach has been adopted to investigate the effect of micro surface texturing on Thermo-Elastohydrodynamically Lubricated cam/tappet contact in a direct-acting valve train. A commercial vehicle valve train has been instrumented to study the effect of varying surface texture area density on friction under realistic engine operating conditions. Fiber laser surface texturing has been used to microtexture three samples of tappet shims with texture densities of 5%, 8%, and 10%. The tests have been run at four engine speeds—300, 500, 700, and 900 RPM—and three temperatures—30 °C, 60 °C, and 90 °C. The experimental results show a significant friction reduction of up to 18.33% for textured shims at the temperature of 90 °C. The friction reduction performance of the 8% textured shim has been optimum for all RPMs at the higher temperatures.

Study on the Tribological Properties of Multilayer Concentric Hexagonal Laser Texturing on Rubber Surfaces of Screw Pumps.

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity.

Characterization of atmospheric pressure plasma deposited (APPD) coatings to improve the friction behavior of thermoplastic surfaces

Achieving a significant friction reduction is crucial for using thermoplastic materials as substrates in tribological applications and presents an eligible alternative to the use of light metals. In this study, previously developed MoS2/graphite/zinc composite coatings, applied by an atmospheric pressure plasma deposition (APPD) process, were investigated to extend the understanding of their characteristics and the influence of the process and environmental parameters on friction behavior. Tribological tests were conducted in ambient conditions and at elevated temperatures (110 °C) to study the friction behavior under application-oriented conditions. The presence of atmospheric oxygen during the deposition process was shown to influence the durability of the coatings, which motivated the application of an inert gas atmosphere for the coating deposition. A novel shrouding plasma nozzle was introduced, which further lowered the friction coefficients. The oxidizing effect of the plasma spray deposition was studied with X-ray photoelectron spectroscopy to investigate the strong impact of the deposition current on the friction behavior and durability of the deposited coatings. Coating composition, morphology, and the effects of the tribological testing were evaluated using optical microscopy, 3D surface measurements, scanning electron microscopy, X-ray diffraction, and nanoindentation. The fabricated coatings with thicknesses in the 10 μm range and good adhesion on the polyamide substrate were stable under extended testing durations and at elevated temperatures and accomplished a significant friction reduction compared to the uncoated polyamide. Thus, APPD-fabricated MoS2/graphite/zinc coatings represent an excellent candidate for low-friction applications of thermoplastic substrates.

Micropitting performance and friction behaviour of DLC coated bearing steel surfaces : On the influence of Glycerol-based lubricants

A better understanding about the rolling contact fatigue and micropitting performance of machine component surfaces lubricated with environmentally friendly lubricants is critical to designing and further formulating new lubricants intended to be used in rolling–sliding contacts such as those found in gear and bearing applications. In this work, the frictional behaviour and rolling contact fatigue (RCF) performance of DLC, Cr/a-WC:H/a-C:H and a-C:Cr coatings under glycerol-based lubrication in rolling sliding contact conditions have been investigated. Traction maps, Stribeck curves, and fatigue plots have been generated by using a micropitting test rig (MPR). The initiation and progression of micropitting was monitored by means of white light optical interferometry and scanning electron microscopy (SEM). Results indicated that glycerol-based lubricants exhibited a significant friction reduction as the hydrodynamic effect is enhanced at higher rolling-speeds. Under boundary lubrication the friction coefficient was significantly higher compared to the values obtained with a commercial mineral-based transmission oil. Compared to uncoated steel surfaces, DLC coatings effectively reduced the volume loss and micropitting progression. Irrespective of the coating thickness, DLC showed an excellent tribological behaviour when the base lubricant favours the onset of mild-wear, over micropitting. When the lubricant formulation favoured the onset of micropitting, the coatings tended to prematurely fail due to debonding from the substrate, and local micro-spallation. The experiments demonstrated that friction reduction does not necessarily correspond with a reduction of micropitting.

Generation method and antifriction performance evaluation of discrete micro-pit surface texture based on high speed ball-end milling process

Benefiting from the structural characteristics of the ball-end milling cutter and the tool motion characteristics during the cutting process, the high speed ball-end milling process can be directly used to manufacture discrete surface micro-pits texture with different sizes and distributions. The influencing mechanism of the interval and distribution of the micro-pit texture on the antifriction performance was investigated by combining Fluent fluid simulation and reciprocating sliding friction test under oil immersion lubrication condition. Results show that the textured surface with micro-pit features shows obvious antifriction ability. The friction coefficient of textured surface was reduced by 61.5 % compared with that of polished specimens. The interval can influence the oil film bearing capacity and then the antifriction ability. The most significant friction reduction effect was achieved when the micro-pit interval was 900 μm. Additionally, the friction coefficient can be further reduced by optimizing the distribution of the micro-pits. The friction coefficient decreased to 0.121 for the orientation angle 70° condition.

Effect of Cu content on the wear resistant behavior of arc-sprayed laminated-structured Cu–TiN/TiO2 composite coating

The wear and corrosion effects in marine or coastal environments are critical issues that seriously deteriorate the service performance of marine infrastructure. Thus, development of an effective and long-lasting wear-resistant and corrosion-resistant protective coating is highly desirable. By controlling the diameter ratio of different heterogeneous metal wires during the supersonic arc spraying process, a laminated-structured Cu-TiN/TiO2 metal-ceramic composite coating with a Cu content of 8.3 % -66.6 % was fabricated. The effects of Cu loading on the microstructure, morphology, mechanical properties, and wear resistance of composite coating were analyzed. The results of scanning electron microscopy and nanoindentation tests indicated that the composite coating exhibited a dense microstructure, with tight interlayer bonding, and a gradient change in hardness and Young's modulus with Cu loading. The friction and wear tests under different loads and wear environments shown that the composite coating had excellent wear resistance. The composite coating with 8.3 % Cu loading had stronger resistance to plastic deformation and abrasive wear under dry sliding friction with 5 N and 10 N loads. The composite coating with 35.8 % Cu loading shown the most significant lubrication and friction reduction effect of Cu under dry sliding friction at a larger load of 20 N, showing the best wear resistance. The wear test under 10 N load with 3.5 wt% NaCl corrosion solution shown that the composite coating with 8.3 % Cu load had a more prominent role in resisting corrosion wear. These results may guide the preparation of high hardness, wear and corrosion resistant Cu-TiN/TiO2 metal-ceramic composite coating with appropriate Cu loading capacity through simple and effective preparation methods and easily customized raw materials, according to different wear and corrosion conditions.

Oral tribology of dairy protein-rich emulsions and emulsion-filled gels affected by colloidal processing and composition

Designing nutritious food for the elderly population often requires significant quantities of leucine-rich whey proteins to combat malnutrition, yet high-protein formulations can cause mouth dryness and increased oral friction. This study investigated how various colloidal processing methods and compositions impact the in vitro oral tribological properties of protein-rich emulsions and emulsion-filled gels. Oil-in-water emulsions with oil fractions from 1 wt% to 20 wt% were prepared, alongside emulsion-filled gels containing whey protein isolate (WPI), hydrolysed whey protein (HWP), or a blend of both (10 wt% protein content). Two processing approaches were employed: creating emulsions with an initial 10 w% protein content (M1) and initially forming emulsions with 0.1 wt% protein content, then enriching to a final 10 wt% concentration (M2). The hypothesis was that formulations with HWP or method 2 (M2) would offer lubrication benefits by inducing droplet coalescence, aiding in the formation of a lubricating boundary tribofilm. Surprisingly, the tribological behavior of high-protein emulsions showed minimal dependence on oil droplet volume fraction. However, both HWP-based emulsions and those processed with M2 for WPI exhibited significant friction reduction, which may be attributed to the presence of coalesced oil droplets, supporting our hypothesis. Substituting 50 wt% of WPI with HWP in emulsion-filled gel boli resulted in very low friction coefficients in the boundary lubrication regime, suggesting oil droplet release from the gel matrix. These findings provide insights into designing high-protein foods with improved mouthfeel for the elderly population, necessitating further validation through sensory studies.

Experimental study of viscous oil-water core-annular flow in horizontal pipe

Transporting viscous oils through pipelines is usually challenging due to their very high viscosity. Significant friction reduction in the transportation of viscous oils through pipelines using an ecologically friendly way is the most appealing feature of the core annular Flow (CAF) technique. An experimental study has been conducted to investigate the flow patterns and pressure gradient of viscous oil-water two-phase flow in a horizontal acrylic pipe with a 50 mm inner diameter. The test section was equipped with a fluid lubrication injector element to artificially provide CAF. The pressure gradient measurements were focused on the CAF pattern. The prediction models of the CAF pressure gradient were reviewed and evaluated. An empirical prediction model of CAF pressure gradient was developed, relying on both the present and previously published experimental results. The flow patterns were classified into five patterns. It was observed that the CAF occupied a large region in the constructed flow pattern map and its frictional pressure gradient closely resembles that of water flowing alone. It was found that the developed empirical model provided quite good predictions of the experimental pressure gradients and significantly outperformed the original model. The reviewed prediction models in this area for CAF either overpredicted or underpredicted the experimental pressure gradients. Some of these models considered the extensive effect of viscous oil adhered to the inner wall of the pipe, while others neglected the effect entirely.

Tribological considerations of threaded fastener friction and the importance of lubrication

The torque-tension relationship of threaded fasteners affects almost all engineering disciplines. Tribological processes at fastener interfaces manifest as the system's friction coefficient. Lubrication-related influences are usually described empirically using K or μ. The drive towards lightweight fastener materials in engineering systems and lubricants with reduced environmental impact is challenging existing knowledge and industrial practice in a range of applications, many safety critical. More comprehensive understanding is needed to achieve repeatable friction during assembly and re-assembly, resistance to loosening and fretting during operation, and effective anti-seize for disassembly with a growing range of materials and lubricants. The lubricants considered showed three predominant lubrication mechanisms: plastic deformation of metal powders; burnishing/alignment of molybdenum disulphide, MoS2; and adhering/embedding of non-metal particles. Multivariate analysis identified key sensitivities for these mechanisms. Assembly generated changes at fastener surfaces and in the lubricating materials. Re-assembly exhibited significant reductions in friction.

Significant reduction in friction and wear of an ultrafine-grained single-phase FeCoNi alloy through the formation of nanolaminated structure

Reducing friction and wear has long posed a challenge for metallic components under dry sliding conditions. This study unveils a significant reduction in friction and wear of a single-phase ultrafine-grained FeCoNi multi-principal element alloy (MPEA). Through a comparative analysis of the sliding wear behaviors of single-phase ultrafine-grained CoCrFeMnNi and FeCoNi alloys with different stacking fault energies and detailed microstructure characterization, we found that despite having a similar initial microstructure and even a 20% lower hardness, the FeCoNi alloy exhibited a remarkable 52% reduction in coefficient of friction, and more notably, a wear rate three orders of magnitude lower than that of CoCrFeMnNi. The significantly reduced friction and wear can be attributed to the remarkable disparities in wear-induced surface microstructures between the two alloys during repetitive sliding. The sliding wear of FeCoNi alloy triggers the formation of a nanolaminated structure with excellent strain-hardening capacity and substantial deformation plasticity, as evidenced by micropillar compression tests. Conversely, the twinning-active CoCrFeMnNi alloy induces the formation of an equiaxed nanograin layer which exhibits a high compressive strength but catastrophic failure behavior after the onset of yielding, and thus deteriorates the wear resistance. The findings provide significant insights into fundamental understanding of the plastic deformation of single-phase MPEAs during wear and guide the design of wear-resistant alloys.

Efficient lubrication of alkylated reduced graphene oxide based on tribochemistry

Graphene has been applied to the research of new lubricant additives in the field of tribology because of its excellent properties. However, during the mixing process of graphene and base oil, agglomerated structures are formed due to their incompatibility, and this phenomenon limits the full play of its advantages. In the face of this challenge, this paper designs a simple and efficient octadecyltriethoxysilane modified reduced graphene oxide (rGOOES) nanolubricant through a three-step process, including the synthesis, functionalization, and chemical reduction of GO, to meet the future needs of oil-based interface lubrication. The morphological and structural characteristics of rGOOES nanosheets were studied by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier infrared spectroscopy and thermal weight loss analyzer, and the dispersion stability and tribological properties of rGOOES nanofluids were investigated by particle size distribution method and four-sphere method, respectively. According to the findings, the outcomes demonstrated that the procedure had the ability to augment the stability of rGOOES nanosheets’ dispersion and ensured their uninterrupted delivery to the contact interfaces of the steel ball friction pairs. Macro tribological experiments confirmed that the blend with rGOOES (0.01 wt%) exhibited significant friction and wear reduction compared to the base oil, reducing the coefficient of friction by 22.1% and the wear scar diameter by 24.8% of the steel ball friction pairs. The mechanism analysis indicated that this improvement in lubrication properties was attributed to the high dispersion of rGOOES nanosheets and the reorganization of the sliding interfaces, as well as the protective film formed on the friction interfaces of the steel balls. Thus, this work provides a practical application of two-dimensional nanomaterials in the field of lubrication.

Effect of soy peptides with different hydrolysis degrees on the rheological, tribological, and textural properties of soy protein isolate gels.

This study was performed to examine the effect of two soy peptides addition with hydrolysis degrees of 90% and 30% (hydrolysis degree (DH)90, DH30) at various concentrations (1-10mg/mL) on soy protein isolate (SPI) gel behavior and pure SPI gel was set as control. SPI gels with adding peptides were prepared, and their rheological, textural, and tribological properties, as well as water-holding capacity, zeta potential, and particle size, were determined. During the rheological measurement, adding peptides reduced storage modulus (G') compared to the control, with larger particles formed. However, peptide addition could significantly reduce gelation time, showing a more significant effect with DH30. The gels' firmness, adhesiveness, and water-holding capacity decreased as peptide concentration increased. Syneresis was observed in gels with peptides, whereas the control sample showed no syneresis. Based on the rheological results, the shear stress in the control sample was higher than in the gels containing peptides indicating more resistance to shear. The gels with DH30 showed greater G' and G″ than DH90 at all studied concentrations. Nevertheless, there was an improvement in the lubrication behavior of SPI gels with peptide addition. DH30 showed a relatively more significant friction reduction than DH90, indicating their slightly better lubrication properties.