Construction of hydrated lubricated interfaces on lyocell fabric surfaces and effects on anti-brillation performance

Lyocell �bers are currently claimed as green �ber with a good application prospect, but the major problem of �brillation restricts the further promotion and application. In this study, based on the theory of hydration lubrication at the solid/liquid interface, hexamethylene-diisocyanate trimer (HDIt), polyethylene glycol (PEG), and butanone oxime (MEKO) were used to synthesize a reactive hydrophilic triblock polyurethane (RHT-PU). RHT-PU could construct a water lubrication layer on the lyocell �ber surface via hydrogen bonding between polyoxyethylene ether and water molecular, reducing the coe�cient of friction (COF) of the �ber interface in the water. It was found that PEG molecular weight and grafting density had signi�cant dependence on the COF of modi�ed fabrics, COFs decreased with the increase of PEG molecular weight and grafting density. In water, the COFs of fabrics modi�ed by RHT-PU were reduced from 0.45 to 0.32 and maintained lower COF at higher temperature and higher normal loads. After mechanical friction and household washing test, the surface abrasion of modi�ed fabrics were signi�cantly improved, and color fading grade of fabrics raised from 3 grade to 4–5 grade. Construction of water lubricated interfaces effectively reduced the �brillation.


Introduction
In the textile industry, regenerated cellulose bers are crucial for environmental sustainability and circular economy (Kim et al. 2022).As a new regenerated cellulosic ber, lyocell ber, in addition to the characteristics of natural bers, exhibits many unique properties, such as great gloss and drapability, high wet strength and lower shrinkage (Ke et al. 2021).However, lyocell bers show a distinct propensity to brillate.Fibrillation refers to the longitudinal splitting of a single ber into micro bers of a few microns in diameter when the ber is subject to water and friction (Mak et al. 2006).The production of micro bers greatly affects the luster and color of the fabric and restricts the promotion and application of lyocell ber.
Studies have shown that brillation occurs due to unique high crystalline structure of lyocell bers and a weak lateral cohesion between crystalline sheets in the oriented structure, eventually leading to the result of ber delamination in the axial direction(Mortimer and Péguy 1996; Schurz and Lenz 2011).During water exposure, ber swelling in the radial direction increases, further weakening the radial binding force of the micro brils.At this time, the bril is easily to split along the axial direction, forming micro bers on the surface when subjected to friction(Tomljenović and Čunko 2010).
Cross-linking is a critical process for preventing brillation, because it might improve the lateral cohesion of cellulose chains by physical cross-linking.Currently the most dominating cross-linkers are triazines, amides, and ureas (Dhiman and Chakraborty 2017; Ma et al. 2020; Manian et al. 2017).In the ber production process, dichloro-hydroxytriazine and 1,3,5-triallyl-hexahydrotriazine have generally been used as crosslinking agents (Taylor 2015).In the nishing process, the crosslinking agent, citric acid (CA) and 1,2,3,4-butanetetracarboxylic acid (BTCA), could be used to further improve anti-brillation (Ma et al. 2021).However, all kinds of cross-linker have some limitations in practice.Dichloro-hydroxytriazine is less stable in acidic environments, while, 1,3,5-triacryloyl-hexahydrotriazine is less stable in strong alkali environments, and has also been identi ed as a toxic chemical (Bates et al. 2006).CA and BTCA also cause yellowing and reduce tensile strength (Ma et al. 2021).
It is well known that a biomass hydrophilic layer on the surface of kelp can largely reduce the frictional resistance at solid/liquid interfaces (Dahms and Dobretsov 2017).Thus, the construction of a hydrophilic lubrication interface is a green bionic means for improving the friction properties of solid surfaces (Fang et al. 2019).Water molecules possess a large dipole, such that they can form a hydrated layer surrounding the polar group.In addition, a repulsive effect takes place when hydrated charges approach each other, which avoids the overlap of hydrated layers.In aqueous lubrication, the charged groups on the sliding interfaces can strongly the hydrated oppositely charged groups by electrostatic interaction.Thus, the hydrated layer can bear large normal pressure without being squeezed out during the friction process (Liu et al. 2022a).
In the design of lubricating materials, the use of hydration molecules is a common means.Measurement results have shown that the cyclic structure can provide a super-lubrication surface (Wang et al. 2022).Therefore, it becomes an interesting research to construct a water-based low-friction interface on lyocell fabrics surfaces to reduce its friction and wear in the wet state and improve the antibrillation performance of lyocell fabric.
In this study, reactive hydrophilic triblock polyurethane (RHT-PU) was designed and synthesized using hexamethylene-diisocyanate trimer (HDIt), polyethylene glycol (PEG), and butanone oxime (MEKO).This triblock polyurethane used HDIt as the adhesion block tethered to lyocell ber surfaces, and PEG as a hydrophilic functional block to form the hydration lubrication layer.The hydration lubrication properties of modi ed lyocell fabric with RHT-PU were investigated, examining the effect of hydration lubrication properties on the lyocell fabric anti-brillation performance.This study provided a new method for solving the problem of lyocell fabric anti-brillation.

Materials
Lyocell fabrics (G100, 30S*30S, 160g/m Prior to the experiment, PEG was dehydrated in vacuum at 120°C for 4 h.Acetone, di-n-butylamine and butanone oxime were dewatered by 4Å molecular sieve for two weeks before use.Other reagents were used directly without treatment. Firstly, acetone (40 mL), PEG (0.01 mol), and HDIt (0.021 mol) were added into a four-neck ask equipped with a mechanical stirrer, thermometer, and nitrogen inlet, and heated to 60 ℃ for reaction 3-4 hours.With continued stirring until NCO% reached the theoretical value based on the stoichiometry, at which point MEKO (0.04 mol) was added into the reaction ask to block the isocyanate groups.When the isocyanate groups completely reacted (NCO% less than 0.1%), the reaction was stopped.Acetone in the mixture was removed by vacuum distillation and then the deionized water was added to the synthesis system under a high-speed stirring (1200 rpm) to obtain a stable and homogeneous emulsion with 50% solid content.
The modi cation of lyocell fabric with copolymers Lyocell fabrics were padded two times with nishing bath containing different concentrations of RHT-PU (0.005mol L − 1 , 0.01mol L − 1 and 0.02mol L − 1 ), pick-up was 80%.Then the fabrics were dried at 85°C for 3 min, and cured at 160°C for 4min.Due to the hydrophobic of RHT-PU1000, it was emulsi ed with SDS before treatment.

Characterization methods
The infrared spectra of RHT-PU and fabrics were obtained by Nicolet IS10 Fourier Transform Infrared Spectrometer (Thermo Fisher Scienti c Co., Ltd, USA) with ATR attachment.
The particle size and polydispersity index (PDI) index of RHT-PU emulsions were analyzed by the Nano-ZS nanoparticle size instrument (Malvern Instrument Co., Ltd, UK).The emulsions were diluted to 1 wt% by deionized water.
The Gel permeation chromatography (GPC) analysis was performed on a Waters 1515 instrument (Waters Co., Ltd, USA).Using pure water as solvent, monodisperse polyethylene glycol standard was used to calibrate the instrument.
The surface of lyocell fabrics were observed by TM-3030 scanning electron microscope (Hita-Chi Co., Ltd, Japan).
The KS values of fabrics were measured with Datacolor1000 spectrophotometer (Datacolor Inc., USA).

Friction test of lyocell fabrics
The frictional properties of lyocell fabrics in aqueous solution were tested by the HAAKE MARS rotational rheometer (Thermo Fisher Scienti c Co., Ltd., USA).
Lyocell fabrics were cut into a 25 mm diameter discs, and then xed on the lower plate of the rotational rheometer.Before the friction test, 10 mL of water were added onto the lower plate such that the fabric was completely submerged, and then the test started (Dai et al. 2021).
The friction force can be calculated using formula (1), and the friction coe cient calculated using formula (2), expressed as: where is the torque, the specimen radius, the friction force, the friction coe cient, and the load.

Anti-brillation evaluation
Fibrillation is related to friction in the swollen state.In this study, household washing method and mechanical wet rubbing method were carried out to form the brillation on the ber surface and evaluate anti-brillation (Abdullah et al. 2006).
Washing methods referred to the brillation evaluation of lyocell fabrics by the Japanese lyocell Association dyeing method.The treated fabrics were washed 15 times using the 4N procedure based on ISO-6330 2012.After washing, the samples were tumble-dried at 40℃.
The mechanical rubbing method was performed using a Y571B friction color fastness tester (Ningbo Textile Instrument Factory, China) at a constant pressure of 9 N.Both testing and rubbing cloths were the modi ed fabrics.Before the test, the cloths were soaked in deionized water for 5 minutes, then xed on the friction color fastness meter, and 10mL deionized water was added onto the testing cloth to ensure the friction experiment was carried out completely in a water environment.The samples were rubbed with 80 cycles and then tumble-dried at 40℃.
After the brillation treatment, brillation was assessed by examining color changes and abrasion of fabric surfaces.The abrasion on the fabric surface was assessed using scanning electron microscope.
Color change was evaluated by KS value change rate and color fading grade.The KS change rate can be calculated by formula (3), expressed as: where is the fabric value before washing (or friction), and is the fabric value after washing (or friction).cm − 1 disappeared, indicating that isocyanate groups completely reacted with hydroxyl groups of PEG and MEKO to form carbamate groups.

Results and discussion
The MW of PEG (Mn = 10000) and RHT-PU10000 were analyzed by GPC, as shown in Fig. 1 (b).RHT-PU10000 performed a MW of 11,364, with a relatively narrow PDI of 1.29.Compared with the MW of PEG, there was a difference of 1291, which was very close to the theoretically calculated difference value of 1308.MW distribution curves of RHT-PU10000 and PEG10000 were also very similar to each other, which indicated that most of the product was triblock polymers without branched structure and chain growth phenomenon.

Properties of RHT-PU emulsion
As amphiphilic block copolymers with hydrophilicity-hydrophobic-hydrophilicity structure, the hydrophilicity of RHT-PU depended on the copolymer structure and the hydrophilicity-hydrophobic interactions.In order to study the effect of hydrophobic chain length and polyoxyethylene ether on hydrophilicity properties and self-emulsi cation, different MW of PEG (MW = 1000, 3500, 6000 and 10000) were used to synthesize RHT-PU, the effects of PEG MW on the properties of the emulsion were investigated.The results are shown in Fig. 2.
As shown in Fig. 2, there was obvious water-oil separation phenomenon for RHT-PU1000.In contrast, RHT-PU3500, RHT-PU6000 and RHT-PU10000 did form stable white emulsion, and the particle sizes gradually increased with the increase of polyoxyethylene ether chain.RHT-PU was the triblock copolymer with hydrophilic-hydrophobic amphiphilic characteristics, in water, the hydrophobic HDIt blocks aggregated to form the inner core, and the hydrophilic PEG block stretched out to present petal-like orientation, forming a ower-like micelle, as shown in Fig. 2 (c).Loop-shaped hydrophilic structure formed a stable hydration layer, which made the emulsion stable for a long time (Ma et al. 2003) RHT-PU10000 with the longest hydrophilic chain was able to form the largest petal diameter, and therefore had the largest particle size.RHT-PU1000 with the shorter hydrophilic chain, had a hydrophilic-lipophilic balance (HLB) value of 8.49 (< 10), indicating that hydrophobicity was stronger than hydrophilicity, and thus the emulsion of RHT-PU1000 showed hydrophobicity in water, which made it di cult for it to produce a selfemulsifying emulsion.
Study on the reactivity of RHT-PU to lyocell fabrics RHT-PU could be grafted on lyocell ber surfaces based on the reaction between isocyanate and hydroxyl.
To verify the successful construction of the block copolymer grafted on lyocell ber, the fabric was treated with 0.02mol L − 1 RHT-PU10000 and then washed ve times according to the 4N procedure in ISO-6330 2012.The untreated fabric, the treated fabric and the treated after-washing fabric were monitored by fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS).The results are shown in Fig. 3.
Figure 3 (a) shows reaction illustrations between RHT-PU and fabrics.There were four isocyanate groups blocked by butanone oxime at individual RHT-PU chain and they could be unblocked during the curing process and releasefree NCO groups.RHT-PU was tethered to the fabric interface by the reaction of four free NCO groups and hydroxyls, forming a loop-shaped brush structure.Two small-spans and one large-span bridge-structure were constructed on the fabric surface by four isocyanate groups in the RHT-PU.Two adjacent NCO groups at the end of RHT-PU chain formed a small-span cross-linking, which strengthened the radial binding force between the cellulose chains and reduced the tendency of the micro bril splitting along the ber's axial direction.The two small-span cross-linked structures together formed a large-span bridge-structure, giving loop-shaped hydrophilic lubrication structure higher laundering durability.

Study on the lubrication properties of modi ed lyocell fabric
The hydrophilic polyoxyethylene ether in RHT-PU could combine with water molecules through hydrogen bonding, forming a hydration lubrication layer on the surface of the fabric to reduce friction.In order to appraise the effects of RHT-PU on the hydration lubrication properties of lyocell fabric surface, four samples (RHT-PU1000, RHT-PU3500, RHT-PU6000 and RHT-PU10000) were employed to investigate the effects of PEG chain length, grafting concentration, temperature and load on lubrication properties.The results were shown in Fig. 4.
Fig. 4 (a) shows that the effect of PEG chain length on the lubrication capability of modi ed fabrics, the treatment concentration was 0.02 mol L -1 and testing load was 1N.
It is seen from Fig. 4 (a) that the COF decline with the increasing PEG chain length.RHT-PU10000 showed the lowest COF with data stabilized at approximately 0.32, a reduction of approximately 28.8% compared to untreated fabric.The COF of RHT-PU1000 was slightly higher than the untreated fabric, which indicated that COF was related to the length of hydrophilic chain, as polyoxyethylene ether, with the longer hydrophilic chain shows a lower COF in water.This because that large numbers of water molecules are adsorbed by the hydrophilic groups through hydrogen bonding, forming a hydration layer on the fabric surface.The thickness and uniformity of the hydration layer on the ber surface increases with the growth of polyoxyethylene ether chain, which could better segregate the two friction interfaces and create a lower COF.While, the short length ether hydrophilic chains in RHT-PU 1000 might have been insu cient to form a lubricious water lm, resulting in a higher COF (Røn et al. 2021).
Figure 4 (b) shows the comparison of COFs of modi ed fabrics in dry and water conditions.In dry conditions, COF of modi ed fabrics was lower than that of untreated fabrics, the mean COFs decreasing by 5.1%, 6.2%, 11.7% and 13.5% respectively with the polyoxyethylene ether chain growth.This indicated exible macromolecules grafted on the fabric are well ordered and rmly attached on the fabric surfaces, forming a solid-like layer segregating the friction interface, appearing boundary lubrication regime (Ma and Luo 2016).Under water conditions, the COFs of the untreated fabric increased by 4.3%, which was related to the increased roughness caused by swelling.In contrast, the COFs of the fabrics modi ed by hydrophilic RHT-PU3500, RHT-PU6000 and RHT-PU10000 were signi cantly lower than the COFs in dry condition, decreasing by 3.6%, 5.8% and 13.7%, respectively.That was because the strong interaction of RHT-PU and water molecules formed an effective strongly bound water layer between the sliding surfaces, thus obtaining excellent lubrication performance.Comparing COFs in dry and water conditions, fully demonstrated the effective effect of the hydration layer in reducing COF.
In order to acquire further insight into effects of the RHT-PU grafting density on lubrication properties, different concentrations of RHT-PU10000 were grafted on the fabric, testing the average COFs within 180s under 1N load and 600/s shear rate, the results are shown in Fig. 4(c).As grafting density of RHT-PU10000 on fabric surfaces increased, COF showed a signi cant downward trend.The fabric with a high grafting density of 0.02 mol L − 1 show a decreased COF of 22.3% compared to a low grafting density of 0.001 mol L − 1 .This was due to the fact that at lower grafting density, polyoxyethylene ether chains were far away from each other and steric repulsion between monomers was weaker, so that the conformation of RHT-PU10000 tended to atten rather than stretch upward at the fabric interface.The attened conformation resulted in a thin hydration layer in which, when subjected to mechanical force, the loadbearing capacity of the hydration layer was poor and easily destroyed.As grafting density increased, polyoxyethylene ether chains were closer to each other, so that steric repulsion between the monomers forced the chains to stretch perpendicular from the surface (Divandari et al. 2019).High-density grafting increased the thickness and density of the hydration layer on the fabric interface and improved the stability and load-bearing capacity, resulting in a highly lubricated surface.Figure 4 (d) shows the relationship between temperature and lubrication performance.The COFs of modi ed fabrics and untreated fabrics were tested under a 1 N load and a 600/s shear rate.CoFs were seen to increase with increased ambient temperature.For untreated fabric, friction properties were mainly in uenced by the roughness of the material itself.Under high temperature condition, wet swelling of ber was aggravated and roughness increased, resulting in increased COFs.COFs of untreated showed a signi cant increasing with time at 40°C and 60°C, this was because brous fuzz gradually formed hairballs on the fabric surface during the friction process, further increasing COFs.That suggested higher temperature accelerated the wear of untreated fabrics.For modi ed fabric, the hydrogen bonding between the polyether chain and the water molecule is weakened with the increase of temperature, which resulted in a thinner hydration layer at the fabric interface and an increase in COFs.However the results showed there was less COFs change with temperature, with only 4.95% increase at 60 ℃, and the change over time was not too much.We inferred that the hydrogen bonding between the polyether chain and water molecule may be less affected by temperature in the experimental temperature range.In addition, the COFs of modi ed fabrics increased slightly with time at 40℃ and 60℃.On one hand, because of the presence of a hydration layer, friction actually occurred between the upper plate of the rotational rheometer and hydration layer, as the increase in roughness on the fabrics produced little effect.On the other hand, due to the lower COF, brous fuzz and hairballs were hardly produced on fabric surfaces during rubbing and thus there was no further increase in roughness.It is indicated that hydration layers effectively separated direct contact of the two solid surfaces, weakening the in uence of fabric swelling and roughness increasing on COFs.
In general, COFs were related to the roughness of the material surface and is independent of applied load between the friction surfaces.However, for the polymers and their composites, when the load was higher, the load affected COF by changing the surface contact state.In order to investigate the relationship between normal load and COF on the fabric surface, the COFs of untreated and modi ed fabrics were tested under different loads.As shown in Fig. 4 (e), the COFs of the untreated fabric decreased with increased load, at a rate of 20.6%.Also COFs of the modi ed fabrics rstly decreased with an increase of load and then tended to be stable, decreasing by 13.6%.This was mainly because the effect of load on COFs was related to the surface deformation state of the material.The micro-bumps with certain elasticity existed on the fabric surface.When the load was lower, the contact between the fabric surface and upper plate of rotational rheometer was in an elastic or viscoelastic state, where the fabric surface had elastic resistance, so the friction coe cient was larger.With the increase of load, the micro-bumps on the fabric surface tended to atten and the contact between fabric surface and plate changed from elastic or viscoelastic state to plastic or viscoplastic state.Thus, the elastic resistance decreased, resulting in a reduction of the COFs (Tian et al. 2023).At different loads, COFs of modi ed fabrics were signi cantly lower than the untreated fabric, and stayed stable after 7N, which indicated that the hydration layer formed on the fabric surface could bear huge loads.Thus low COFs surfaces were still obtained at higher load.In addition, micro-bumps on the modi ed fabric surface were covered by hydration layers, reducing the roughness.Applying a certain load could make the micro-bumps on the fabric surface tended to atten, from elastic state to plastic state, COFs stayed stable.However, higher pressure was required for untreated fabric surfaces to change from elastic state to plastic state.At a pressure of 9N, the COF of untreated fabric was still not stabilized.
According to the experimental data and analysis presented above, the lubrication mechanism of fabric modi ed by RHT-PU was described as Fig. 4 (f).In dry conditions, RHT-PU was anchored to the ber and polyoxyethylene ether chains curled on the fabric surface, forming a solid layer.When the upper plate of the rotational rheometer contacted with fabrics, the solid layer prevented the fabric from directly contacting with the upper plate, thus reducing friction.In water, large numbers of water molecules were adsorbed by the hydrophilic polyoxyethylene ether groups through hydrogen bonding, forming a hydration layer on fabric surfaces.As the upper plate of the rotational rheometer rotated, friction actually occurred between the hydration layers formed on the fabric.Meanwhile, as the increase of modi ed concentration and polyoxyethylene ether molecular weight, the number of bound water molecules increased, which formed more dense and stable hydration layers at friction interfaces, resulting in a lower friction interface.Because of strong interaction between polyoxyethylene ether and water molecules, water molecular were adsorbed strongly to provide a high load bearing capacity.
The effects of lubrication properties on anti-brillation performance of modi ed lyocell fabrics When lyocell bers are subject to wet abrasion, micro brils can split along their axis, producing brillation tendency, imparting a 'frosty-white' appearance, especially for dark hues fabrics.Reducing abrasion during wet friction is an effective way to improve brillation.In order to investigate the dependence between lubrication properties and brillation, two methods, mechanical rubbing and household washing, were performed to generate brillation.The effects of RHT-PU with different molecular weight on antibrillation has been analyzed by abrasion and color fading.Figure 5 shows the SEM image of the fabric surface after mechanical friction test.
As shown in Fig. 5, for the untreated fabric, fracture of multiple bers were visible on surface after wet rubbing.In the 500x magni ed image, it is clearly seen that the rupture caused by multiple splitting of lyocell bers, which suggested that the surface of the untreated fabric was severely abraded after 80 times rubbing.In Fig. 5 (a), fabrics modi ed with RHT-PU1000 presented less abrasion than the untreated fabric.Although the COF of the fabric modi ed by RHT-PU1000 was a little higher than the untreated fabric, brillation was improved to a certain extent.This indicated that the cross-linking between the NCO in the RHT-PU and the OH in the ber improve the lateral cohesion of cellulose chains, thus, reduce the splitting of bers along the axial direction.Comparing Fig. 5 (a) to Fig. 5 (d), the brillation was reduced with increased hydrophilic chains length in RHT-PU and the modi ed concentration.For fabrics modi ed with RHT-PU6000, rupture of bers was signi cantly improved and the damage mainly micro ber splitting.When modi ed with RHT-PU10000 at 0.01mol L − 1 and 0.02mol L − 1 , there was no obvious brillation phenomenon on fabrics surface and the appearance of fabrics were clean, without the "frostwhite" phenomenon.This was consistent with lubricating properties of the fabrics, indicating that the construction of water lubricated interface effectively reduced brillation.In addition, from SEM images, splitting of micro bers on the modi ed fabrics adhered to the ber surface rather than protruding on the ber surface.This might have been because, in water, polyoxyethylene ether chains stretched and, after drying, the chains curled and were pulled by the anchored isocyanate groups at both ends to form a solid lm.The solid lm adhered micro bers on the fabric surface, reducing light scattering caused by protruding micro bers on the surface, in turn reducing the "frost-white" appearance.
Figure 6 shows abrasion SEM images of fabrics after household washing, which is closer to the fabric abrasion in the practical application.Comparing the two methods, the wear degree of the fabric surfaces after washing were lighter than the mechanical friction.This might have been related to the normal load and contact area.During mechanical friction test, the fabric was subjected to higher normal load and the two friction surfaces were closer to each other.There were clearly ber fractures observed on the untreated lyocell fabric, while the surface wear of the other modi ed fabrics were mainly ber splitting, except for fabrics modi ed with RHT-PU1000.This indicated that reducing the wet COF of fabrics effectively improved anti-brillation, which was consistent with mechanical friction results.However, from Fig. 6 (b) to (d), it is found that the fabrics modi ed with 0.02 mol L − 1 RHT-PU3500 and 0.01 mol L − 1 RHT-PU6000 shows the best anti-brillation performance, while fabrics modi ed with RHT-PU10000 presented the worse.This indicated that higher molecular weight and larger grafting density had a negative impact on the anti-brillation performance during household washing.This result was contrary to the lubrication performance of the fabrics studied above.In contrast to the at state of fabrics in mechanical friction test, the fabrics would be creased and bent, during tumbling in the household washing process.The creases formed were more susceptible to abrasion, which in turn generated brillation.We found that when the higher molecular weight and higher grafting density would cause fabrics to stiffen, which increased slipping resistance between yarn.If the forces were su cient magnitude, the yarns will be forced out of the fabric plane and a crease developed, resulting more serious abrasion.This meant the lubrication properties of fabrics could improve brillation, such that it is equally important to maintain a softness handle.
Fibrillation of lyocell bers caused micro bers protruding from the ber surface, which increased light scattering, making the fabric colors lighter and appearing "frost-white" appearance.Thus, from a macro perspective, the performances of anti-brillation could be evaluated by K/S.Color fading grades are shown in Table 1, along with the KS values and its change rate of fabrics before and after anti-brillation tests.As shown in Table 1, the KS values of modi ed fabrics slightly increased, indicating a darkening effect of RHT-PU.The K/S change tendency was consistent with abrasion.In mechanical friction, the KS value change rate of RHT-PU10000-0.02molL − 1 was the lowest, only 0.51%, with a color fading grade was 5 almost no color difference.And, in household washing test, the K/S changes of fabrics modi ed with RHT-PU3500-0.02molL − 1 , RHT-PU6000-0.01molL − 1 and RHT-PU10000-0.005molL − 1 showed smaller changes of 4.41%, 5.93%, 7.29% respectively, with a color fading grade can be increased by 1 to 1.5 levels.

Conclusion
This study was the rst attempt to solve lyocell fabrics brillation from the perspective of hydration lubrication.A reactive hydrophilic triblock polyurethane (RHT-PU) using hexamethylene-diisocyanate trimer (HDIt), polyethylene glycol (PEG) and butanone oxime (MEKO)was successfully prepared and its structure and molecular weight were demonstrated by the FTIR and GPC.RHT-PU was then grafted onto lyocell ber surfaces by a pad-cure process, and evaluated the dependence between hydration lubricity and anti-brillation performance.The results showed that the COF of fabric modi ed by RHT-PU decreased from 0.45 to 0.32.The low friction interface was mainly due to the hydration layer formed by hydrogen bond interaction between polyoxyethylene ether chain in RHT-PU and water molecules, which effectively separated the solid-solid friction interface.The COF of the constructed polymer hydration lubrication interface increased with the increase of the molecular weight and grafting density of the polyether, and remained stable under high temperature and high load conditions.The effects of water lubricity on lyocell fabric brillation were evaluated by mechanical friction and household washing tests.
In the mechanical friction method, the wear degree and color fading of the fabric were positively correlated with its hydration lubrication performance, that was, the wear degree decreasing with the increase of the grafting density and the molecular weight of RHT-PU.In the household washing method, due to creases formed during washing and the in uence of surface COF, the softness of the fabric was also a key factor affecting the wear degree.The higher molecular weight and higher grafting density caused the fabric to stiffen, which then easily formed creases during washing.The creases were more susceptible to abrasion, in turn generating brillation.Thus, fabric treated with RHT-PU3500-0.02mol L − 1 , RHT-PU10000-0.005 mol L − 1 , and RHT-PU6000-0.01mol L − 1 presented the better anti-brillation performance in household washing experiments.This study explored the relationship between friction and brillation from the perspective of hydration lubrication, and provided a new idea for anti-brillation nishing.

Declarations Figures
Structural characterization of RHT-PUReactive hydrophilic triblock polyurethane was synthesized from HDIt, PEG (Mn = 10000) and MEKO, according to the method shown in Scheme 1.The chemical structures of raw materials, HDIt, MEKO, PEG (Mn = 10000) and nal products RHT-PU10000 were analyzed by FT-IR, and the molecular weight (MW) distributions of RHT-PU10000 (10000 represent the molecular weight of PEG in RHT-PU) and PEG (Mn = 10000) were measured by GPC.The results are shown in Fig.1.As shown in Fig.1 (a), in the FTIR spectrum of HDIt, the absorption peak at 2260 cm − 1 and 1680 cm − 1 were ascribed to NCO and C = O stretching vibration(Hu et al. 2016).For the FT-IR spectrum of MEKO, the peaks around 3220cm − 1 and 1670cm − 1 were attributed to the stretching vibration of OH and C = N respectively(Hierso et al. 2000).And the peak around 1110 cm − 1 was due to the stretching vibration of C-O-C groups in PEG spectra(Naz et al. 2018).The spectrum of RHT-PU showed two new peaks at 3350 cm − 1 and 1720 cm − 1 corresponding to the N-H and C = O stretching vibrations of the carbamate structure, respectively (Li et al. 2022).The peak located at 1110cm − 1 represented C-O-C stretching vibration in polyoxyethylene ether structures.Meanwhile the NCO characteristic absorption peak at 2260

Figure 3 (
Figure 3 (b)  shows the FT-IR of fabrics, in the treated fabrics FT-IR, there were two new absorption peaks located at 1680cm − 1 and 1720cm − 1 , corresponding to keto carbonyl stretching vibration in HDIt and the ester carbonyl stretching vibration in the carbamate group, respectively, which indicated that RHT-PU has been successfully grafted onto the fabric.After ve times washing, these two absorption peaks were also detected at 1680 cm − 1 and 1720 cm − 1 , and the intensity of the absorption peaks did not change signi cantly, indicating that covalent bonds between RHT-PU and lyocell ber were stable and had a certain laundering durability.Figure3 (c) is the XPS survey spectra of fabrics.Compared with the untreated fabric, the intensity of the signal for N 1s increased in treated fabrics before and after washing, which is related to RHT-PU grafted on the fabric.In order to further determine the chemical bonding type, a high-resolution C 1s scan was performed, shown in Fig.3 (d).For the untreated fabric, the C 1s signal was separated into three peaks located at 284.6 eV (C-C), 286.5 eV (C-O), 288.2 eV (C = O), which were characteristic peaks of cellulosic structure(Chen et al. 2020).For the treated fabric, a new signal at 289.6 eV corresponded to the N (C = O) O group appeared, which was from the reaction of RHT-PU with OH in the fabric during the curing process and the carbamate groups in RHT-PU(Canteri et al. 2003).After ve washings, the peak at 289.6 eV still presented on the fabric, which further veri ed the good washing fastness of the grafted copolymer, which was consistent with the FI-IR results.

Table 1
Color fading grade, KS value and its change rate of fabrics before and after anti-brillation tests.