Experimental Study and Optimization of Some of Tribological Characteristics for PMMA-Micro and Nano...

7/30/2019 Experimental Study and Optimization of Some of Tribological Characteristics for PMMA-Micro and Nano Filler Composites

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Experimental study and optimization of some of Tribological characteristics for

PMMA-Micro and Nano filler composites

Mosadaq A. Maleh

Institute of laser for Postgraduate studies

Baghdad University-Iraq

Zainab F. Mahdi

Institute of laser for Postgraduate studies

Baghdad University-Iraq

Abstract

In the present work, polymer micro and Nano filler composite materials were prepared,PMMA/Alumina, PMMA/Titania. The fabrication process of nanocomposite was High-Shear mixingmethod followed by different curing temperatures, (40, 80, and 120 oC). Some of Tribological

characteristics (Hardness, and Wear) were tested for net polymers and composites in all filler sizecategories, with various weighting percentage (0.5, 1, 1.5, and 2%). For micro-filler polymericcomposites, hardness was improved linearly with increasing filler weighting percentage. PMMA-nanocomposites, hardness dropped with increasing weight ratio percentage of nanofiller, indicated ofinduced change of polymeric structure caused by nano Alumina and nano Titania. Wear resistanceincreased with increasing filler percentage in polymeric composites. Nanofiller composites showedbetter results more than microfiller composites. The best wear resistance was for composites of (120oC) curing. Nd-YAG laser of (180 mJ) was used to treat best results specimens which werenanocomposites at (120 oC) curing. Laser improves wear resistance. The effect of aggregation wasshown on the tribological test results. Mathematical modeling of aggregation was built with geneticalgorithm and particle swarm optimization using MatLab programming environment. The model basedon thermodynamics point of view using wear and hardness as main data.

Keywords: PMMA composite, Tribology, Wear, Hardness, Aggregation simulation, Nanocomposite

1- IntroductionEncompassing nanoscale science, engineering,and technology, nanotechnology involves

imaging, measuring, modeling, andmanipulating matter at this length scale. At thislevel, the physical, chemical, and biologicalproperties of materials differ in fundamentaland valuable ways from the properties ofindividual atoms and molecules or bulk matter.Nano materials can be classified intonanostructured materials and

nanophase/'nanoparticle materials. The formerusually refer to condensed bulk materials thatare made of grains (agglomerates), with grainsizes in the nanometer size range, whereas thelatter are usually the dispersive nanoparticles.The nanometer size covers a wide range, from 1nm to as large as 100 to 200 nm. To distinguishNano materials from bulk, it is crucial todemonstrate the unique properties of Nanomaterials and their prospective impacts inscience and technology [1]. Tribologicalproperties of materials play an important role in


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materials selection, even application existence.Wear as an example of tribologicalcharacteristics that cause a lot of industrialslosses due to materials loss, repairing orreplacing parts, and establishing newer designsolution to overcome or less its damage asmuch as possible. Nano technology considerone of the most promising research topics inthis subjects, and there are many application ofits in light weight bearing, and underwaterbearings. Many researchers such as R.W. Siegelet al [2] at 2001 studied the effect of alumina onmechanical properties of PMMA. The influenceof nano alumina was very clear for themechanical properties specially the elasticstability, The change in hardness not inparticular the change of wear in the samedirection, so for this case the hardness isdecrease as the tendency toward ductilityincrease, but worn volume of this system be atminimum. Benjamin J. Ash et al [3], studied theeffect of micro and nano alumina on PMMAmechanical properties. They show that theeffect of nano filler was very effective so itincreases the plastic behavior of PMMA gave ita more endurances but it decrease its hardness.Wear rate been less for Nano filler composite.Amit Chatterjee at [4]2005 studied variousmechanical properties of PMMA TiO2 nanofiller, the researcher use various weight ratiosreach 15% nano filler, he found that thedispersion was crucial in mechanical properties,so for high weight ratio ( bad dispersion) theeffect of added filler was in the lowest region.A. Kashani et al at 2010[5], investigatedPMMAnano Alumina composites mechanicalproperties, including wear and harness. The useof wide range of weight ration of the add fillerwas studied. For higher weight ration than 5%,the behavior of filler change to micro filler inaction. Hardness for drop while wear resistanceimprove.

2- Molecular Kinetic Theory ofcontact surfaces

To deals with Nano point of view oftribological behavior of the contacted surfacesthe acts on asperities size must be consider.

There are many approaches to interpretingtribological behavior in mathematicallanguages. For polymers the earlier works ofMolecularKinetic concept of contact surfacesby the theory of Bartneve-Schallamach[6,7],was inspire the work of many researchers suchas Yukisaburo and V. V. LAVRENTEV et al.the present work stand of G.M. BARTENEV etal , point of view, so the active surface energyfor rub surfaces was found. To adapt the workthat done in early years of the 80 th of the lastcentury there are some assumption the workwithot them may be questionable. First thesystem will work after some time good enoughto expose reinforcement fillers. The secondassumption was stand on the asperities are thereinforcement filler, so the action of polymerpolymer (which represent with active surfaceenergy). The third assumption was built onperfection, which was the dispersion ofreinforcement filler, therefor; separationdistance of every particle is the same, as shownin figure (1).

Figure (1) ideal dispersion

First the active energy is

( ) .. (1) is separation distancekis Boltzmann constant

Tis absolute temperature

is sliding velocity


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is sound velocity in matrix material is the real are of contact which is . (3)

. (2) . (3) . (4)Where

Pis normal load

His hardness of the softer of the two contactingsurfaces.

L is sliding distance

is the roughness coefficient

Eis youngs modulus for the softer material.

is worn volumeFis sliding force

is statistical distribution of asperities alongthe surface, which is . (5)The free energy of a cluster formation followsthe equilibrium between forces of atomiccohesion in the condensate phase and theenergy barrier caused by forces of a surfacetension. In terms of the nucleus radius r. thisGibbs free energy variation can be expressed

as: . (6)Where

is the difference of potentials between thecondensed and the non-condensed atoms, and

. (7) is the atomic density.

3- Material in usedThe PMMA used in the present work was used

from the local market. The hardener is added tothe powder in order of polymerization. Thepreparing method was the standard that used indental laboratories .There are two maincategories were used in this research, Micro andNano Alumina and Titania particles. MicroAlumina was bought from the local Iraqimarket and tested with x-ray diffraction todetermine the purity and the quality. Titaniumdioxide Micro particles was also bought fromthe local market and also tested with x-ray

diffraction to determine purity and quality.Alumina and Titania Nano powder werepurchased from laboratory Reagent LTD,SIGMA-ALDRICH, Germany, was used. ForAlumina the particle size was around 50 nm,and for Titanium Dioxide was 25 nm.

4- Specimens PreparationThe first step for preparing the specimen was tocalculate the exact amount of epoxy (resin andhardener according to the manufacture

instructions) for the molds as, so the amount ofthe filler was determine according to thisformula:

Weight of filler to be added = epoxy weight

(resin and hardener)* wetting percentage of the

filler/100 (8)

The amount of epoxy was calculated accordingto the mold capacity, so there were two types of

molds, wear specimen (ASTM G99) mold.Wear specimen mold was prepare from aplastic sheet warped to be a cylinder of 1 cmdiameter with 2 cm height. A domestic shearmixer was used to achieve good mix of epoxyingredients (resin and hardener), then thespecific amount of filler was weighted using asensitive laboratory balance. The added to themixer with amount of sodium silicate (0.1-0.2)


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wt. % as a dispersion agent, then mix thematerials about 10 minutes, then purring it inthe specific molds. After casting the curingcondition was done using domestic electricoven. For Poly methyl methacrylate, the sameprinciples were used.

5- Mechanical tests5-1 Wear Test

A compatible ASTM apparatus was used tomeasure weight method wear. Wear specimenwas ASTM G99. Wear rate was calculatedusing weighting method, and it couldsummarize as follow:

1- Weight the specimen before the testusing sensitive balance (W1).2- Run the test with facing the specimen tothe steel disc of the apparatus with desireweight.3- Weight the specimen after test (W2).For fixed time test time (t) 10 minute, rotationspeed (n) 500 rpm and circle path diameter (dD)of 8 cm respectively, the following relation wasused . (9)Where . (10) . (11)

5-2Hardness testA D type shore durometer compatible hardnesstesting device was used. It was equiped withinterface system, so the reading was taking inexel form, and to do so click on begin/ continue

after calibrate the Durometer to start reading ,after every reading press zero button on thedevice and it will be ready to the next readinguntil you finish. The hand should be steady andpressing perpendicular as possible.

The software has the ability to save reading asan excel sheet, as well as graphic chart, gives

the basic statistical information such as meanvalue, and standard deviation.

To do so, click pauses/ stop button and proceed,or else it will not respond giving you an errormessage.

6- Nd-YAG LaserIn the present work, a home built Q-

switched Nd:YAG laser was used. The pulseduration is 30 ns. Table (2-1) shows thecharacteristics of Nd:YAG laser. The Q-swicthed is a dye shutter type (DFQS 233).

The power supply of the laser consist oftransformer with a transforming ratio of (1:10).The transformer was connected with a triggercircuit to provide high trigger voltage (about20kV) to the xenon flash lamp.

Table 1 Characterization of Nd:YAG laser

Main Specifications

Nd dopantconcentration

0.7---1.3atm%

Damagethreshold

over 15 J/cm2 (rodswithout coating)

over 700 MW/cm2(coating)

Physical and Chemical Properties

ChemicalFormula Nd:Y3A15O12

Melting Point 1970C (2240K)Density 4.56 g/cm3Refractive Index 1.82ThermalExpansionCoefficient

7.8 x 10-6 /K 0 - 250 C

ThermalConductivity

14 W/m /K @20 C,10.5 W /m /K @100C.

Physical and Optical propertiesLasingWavelength

1064 nm

RadiativeLifetime

550 ms

SpontaneousFluorescence

230 ms

PumpWavelength

807.5 nm

Linewidth 0.6 nm

7- Beam Divergence Measurement


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The beam divergence measurement isimportant to calculate the minimum spot size ofthe laser beam. The measurement was donepractically at two points using a piece of carbonpaper, the first point -1- was taken point to thelaser source, and the second point -2- was takenfar away from the laser source as shown inFigure (2).

Fig. (2) Schematic drawing of the beam

divergence measurement of Nd-YAG laser.

The full angle beam divergence is given by

o (d2 - d1) /(l2 - l1) (12)

Where d1, d2:- the beam diameter at the twoselected points

l1, l2:- the distance between the laserand the two selected points.

8- OverlappingTo scan large areas by pulsed laser beam,partial overlapping method can be used.Overlapping percentage can be calculatedaccording to the relation.

. (13)where (rf) is radius of spot, (dc) center to centerspacing, as shown in figure (3)

Fig. (3) Percent overlap defined

geometrically

The overlapping percent has been used in this

work 25%.

9- SimulationDesigning optimized Composite Structures

is a difficult task because of the numerousdesign variables which have to besimultaneously taken into account. Particlediameter and concentration can be adjusted toachieve some requirements or given propertieswhich optimize the mechanical response of

structures.The first operation of optimization lead by

GA programs written in MATLAB R2008a (32bit) environment, and with computer itshardware are: AMD Turion X2 Ultra Dual-Core Mobile ZM-85, ~2.3GHz processor,3072MB DDR3 , bus 1333 ram, and 320gigabyte, 7200 RPM hard, as said before,Genetic algorithms is class of evolutionaryalgorithms inspires some techniques from theevolutionary biology. The optimizationvariables , so they the generals variables duringGA programming. In order to increase theconvergence rate of GA, the followingimprovements were included in the presentstudy:

1- Real string coding was used to replacethe binary encoding and decoding


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operations. This reduces computingtime.

2- Multi-point of crossover and that alsoreduce time besides increasing solutionefficiency.

Fig. (4) Flow chart of GA programs

Particle swarm optimization was used withsame hardware and software equibments, to dothe same task as GA.

Fig. (5) Flow chart of PSO programs

10-Results9-1 FTIR test

The FTIR test was done for Epoxy matrixcomposite systems as shown in Figures (6), and(7).

Fig. (6) FTIR absorption of PMMA-Nano

Alumina.

Input data

Start

Evaluate each

chromosome in the

Select good

Initialize a population of

chromosomes

GA operation (crossover

and mutation)

Select good

Yes

Is fitness

criterion

Stop

Reproduction of

Chromosomes

No

Input DATA

Start

Evaluate Each Particle

Select the Best Local &

Global

Initialize Swarm &

Particle Velocity

Update Particle Position

Evaluate Each New

Yes

No

Is fitness

criterion

Stop

Reproduction of

Chromosomes


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Fig. (7) FTIR absorption of PMMA-Nano

Titania9-2 Hardness test

D-type shore durometer compatible hardnesstesting device was used to find hardnessmeasurement for the PMMA based matrixcomposite, for micro and Nano fillers oftitanium oxide and alumina. There are three

curing temperature used which are 40, 80, 120oC held for two hours. The results of PMMAMicro fillrs are shown in the figures (8) to (9).

Figure. (8) Shor Hardness (D) for PMMA

Micro fillers system at 40oC Curing

Figure (9) Shor Hardness (D) for PMMA




The results of PMMA Nano fillrs are shownbelow (Fig (11) to (13))

Fig. (11) Shor Hardness (D) for PMMA

Nano fillers system at 40oC Curing.


Nano fillers system at 80oC Curing


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Nano fillers system at 120oC Curing

9-3 Wear test

9-3-1 Wear results without laser

There are three curing temperature used whichare 40, 80, 120 oC held for two hours. The

results of wear for micro filler PMMAcomposite are shown in the figures (14), (15),and (16).

Figure (14) wear rate for PMMA based

composite at 40oC curing temperature.





The results of wear for Nano fillerPMMAcomposite are shown in the figures (17), (18),and (19).

Figure (17) wear rate for PMMA basedcomposite at 40oC curing temperature.




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9-3-2 Wear with laser effect

Nd-YAG laser effect on Wear of fillercomposites systems was done. The sampleswere placed at 25 cm from laser head, the spotdiameter was 4 mm, and pulse duration was 30nanosecond of (180 m J) energy. To ensuregood surface exposure of laser, the overlappingtechnique was used with 25%. Figure (20)showed wear results of PMMA Nano fillercomposites. In order to focus on laser effect ofwear resistance, the selection was done for bestwear resistance cases which were for 120 oCcuring of PMMA matrix based composites.

Figure (20) Wear rate for Laser treated

PMMA based composite at 120 oC curingtemperature.

11- Theoretical resultsEvolutionary based information was used inthis work as a quicker solution of programming,so programs built with genetic algorithm andparticle swarm technique using MATLAB as a

programming environment. The idea behindthat was to avoid unnecessary running loopsthrough running progress to limit calculationtime using the ability of newer modifiedoptimization methods adaptation for solving setof mathematical equations in selected progressfor wide controlled random range ofpossibilities. The word controlled lying in thesame sentence with the word random gives apretty good amount of questions, therefore; it isneed more expression. The search domain ofthe evolutionary algorithms based on randomexpression gives a random domain every timeand every process cycle, and the naturalselection will determine the prevailed set ofoutputs or in other word solution string.However this randomness may take the solutionto a wrong direction and may be the initial set isnot right. For these problems the randomness isunder a little bit boundaries and conditions thatensure walking in the correct path as they say.The reaction happened in the filler matrixsystem between two particles. For each particlethere is two major energies that shape itsrelation with other filler community, first one isthe force that hold it in its place and it is basedon surface active energy between the host (inthis research is the polymer) and the other forcethat affect particles is the tendency to coincidewith other similar kind particles, or in otherwords, the tendency to form a local communityor cluster. The results of these forces are asystem struggled to be in equilibrium state. Anychange of force balance change the probabilityof equilibrium earthier toward preserve thesituation or change to clustering phenomenon.

Figure (21) show the results of the forecastprogram that build with MATLAB 2010a usingparticle swarm evolutionary technique. It

predicts the suitable amount of Alumina Nanofiller weight percent.


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Figure (21) data prediction curve for

PMMA-Alumina composite system

For PMMA Titania the results was shown in

fig. (22)

Figure (22) data prediction curve for

PMMA-Titania composite system

Figure (23) show the results of the forecastprogram that build with MATLAB 2010a usinggenetic algorithm technique. It predicts thesuitable amount of Alumina Nano filler weight

percent.

Figure (23) Data prediction curve for

PMMA-Alumina composite system

For PMMA Titania the results was shown in

figure (24)

Figure (24) data prediction curve for Epoxy-

Titania composite system

12- DiscussionPMMA micro filler composites hardness resultsshow good enhancement of hardness for the use

of Titanium dioxide together but little less withthe use of Alumina. Hardness was drop, andthat result agree with Amit Chatterjee andZhong Cao et al. this phenomenon caused byinfluenced crosslinking across polymer. Thedelicate balance between Filler amount andproperties were notice clearly in wear tests, soresults Curve go down linearly then it change


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with high order function. Usually wearbehavior could be concluded from hardnessbehavior, therefore; for high hardness materials,wear resistance increase. Thats true for pure

materials, but for composite materials (which isin general lie under this general observation)that consist of two or more materials that reacttogether physically to give improve materialstheir properties combined of ingredientsproperties as their existence quantity. In specialcases, reinforcement materials do change thechemical entity of the holding matrix, as inPMMA based Nano composites. The effect ofNano filler on hardness which is a guidelineindicator of mechanical stiffness was soobvious. The hardness decrease with increasingfiller amounts. That was an indication ofmolecular level changes, or in other words,Nano filler triggered a chemical changes in thematrix itself. At quick first look wear results forthis case is more surprising, but with a secondlook it is be reasonable, even expected, becauseNano filler is so hard, so when wear happenedhard Nano fillers face the other worn surfacethey stretched as the stiffness matrix allows it,scratching hardly with minimum loss. PMMAbased composites showed a slightly enhance intribological properties with changing curingtemperature.Laser treating of samples improvein wear resistance. This is due to post curing ofpolymer.

13-Conclusions1-Adding Metallic oxides fillers to polymersimprove their tribological properties. Curingincreasing also tribological properties as well.

2- Nano filler impressively increase tribologicalproperties in general.

4-Nd-YAG laser increase all propertiesslightly according to its thermal post curingeffect.

5- Hardness decrease for PMMA- Nanofillerbecause of crosslinking that the fillerinduced and as shown in FTIR results, butwear resistance highly increased.

6- The clustering increase with decreasing ofparticle size for the same weight ratio, and withincreasing weight ratio for the same particlesize.

References

[1] Enrico Gnecco, and ErnstMeyer,Fundamentals of Friction and Wear,

Springer, 2007, Germany.

[2] R. W. Siegel, S. K. Chang, B. J. Ash, J.Stone, P. M. Ajayan, R. W. Doremus, L. S.Schadler, "Mechanical behavior of polymer andceramic matrix nanocomposites", Scr.Mater.vol.44 , pp. 2061-2064, 2001

[3] BENJAMIN J. ASH, DIANA F. ROGERS,CHRISTOPHER J. WIEGAND, LINDA S.SCHADLER, RICHARD W. SIEGEL, BRIANC. BENICEWICZ, and TOM APPLE, "Mechanical Properties of Al2O3/Polymethylmethacrylate Nanocomposites",POLYMER COMPOSITES, Vol. 23, pp. 1014-1025, 2002.

[4] Amit Chatterjee, " Properties improvementof PMMA using nano TiO2", Journal ofApplied Polymer Science, Vol. 118, pp.28902897, 2005.

[5] A. Kashani, and S. Moradian," Effects ofNano Alumina on Some Physical andMechanical Properties of an Acrylic WaterBased Clear Coat ", Journal of Color Scienceand Technology, vol.4, pp.169-174, Iran, 2010.

[6] G.M. BARTENEV, and U. U.LAVRENTEV, Friction and Wear of

Polymers, ELSEVIER, 1981.

[7] D.A. Dillard, and A.V. Pocius, THE

MECHANICS OF ADHESION, ELSEVIER,2002.

[8] R. W. Siegel, S. K. Chang, B. J. Ash, J.Stone, P. M. Ajayan, R. W. Doremus, L. S.Schadler, "Mechanical behavior of polymer andceramic matrix nanocomposites", Scr.Mater.vol.44 , pp. 2061-2064, 2001


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[9] Ming Qiu Zhang, Min Zhi Rong, Shu LiYu, Bernd Wetzel, Klaus Friedrich, " Effect ofparticle surface treatment on the tribologicalperformance of epoxy based nanocomposites",wear, vol. 235, pp. 10861093, 2002.

[10] Guang Shia, Ming Qiu Zhangb, Min Zhi

Ronga, Bernd Wetzelc, Klaus Friedrich,"Sliding wear behavior of epoxy containingnano-Al2O3 particles with differentpretreatments", Vol. 256, pp. 10721081, wear,2004.

[11] H. Couderc, M. F. Frchette, S. Savoie,E. David, " Nanofiller effect during post-heattreatmentof micro-loaded epoxy", IEEE, vol.15,pp. 1-4, 2010.

[12] Zafer Gurdal, "Design and Optimization ofLaminated Composite Materials", John Wiley& Sons, INC., 1999.

[13] A.V. Pocius, and, D.A. Dillard THEMECHANICS OF ADHESION, Elsevier,

2002.

[14] Joseph H. Koo. Polymer NanocompositesProcessing, Characterization, andApplications, McGraw-Hill, USA, 2006.

[15] I. Capek. Nanocomposite Structures andDispersions Science and Nanotechnology Fundamental Principles and ColloidalParticles, ELSEVIER, USA, 2006.

[16] F. Hussain, M. Hojjati, M. Okamoto andR. E. Gorga , " Review article: Polymer-matrix NanocompositesOverview ", J. of

Composite Matr., 40, 1511, 2006.

[17] C. Chen , Jian-Yuan Jian and Fu-Su Yen ,"Preparation and Characterization of

epoxy/-aluminum oxide nanocomposites",Composites: Part A, 40, 463468, 2009.

[18] Bharat Bhushan, MODERNTRIBOLOGY HANDBOOK Volume OnePrinciples of Tribology, CRC Press LLC,

USA, 2001.

[19] Wendell T. Hill and Chi H. Lee, Light-Matter Interaction, WILEY-VCH VerlagGmbH & Co. KGaA, Germany, 2007.

[20] William M. Steen. Laser Materialprocessing, Springer, Germany, 1991.

[21] JACQUES PERRIRE, ERIC MILLON,and ERIC FOGARASSY, RECENT

ADVANCES IN LASER PROCESSING OFMATERIALS, Elsevier, UK, 2006.

[22] John S. Eckersley, Laser Applications inMaterials Surface Hardening, Advances in

Surface Treatment vol. I, 1982.

[23] Hans-Jrgen Butt and Michael Kappl,Surface and Interfacial Forces, WILEY-VCHVerlag GmbH & Co. KGaA, Germany, 2010

[24] Anders Nilsson, Lars G.M. Pettersson, andJens K. Nrskov, Chemical Bonding atSurfaces and Interfaces, ELSEVIER,2008.

[25] Vladimir B. Gantovnik, "An ImprovedGenetic Algorithm for the Optimization ofComposite Structures "Doctoral Thesis,Virginia Polytechnic Institute and StateUniversity, 2005.

[26] Lion A. Costa et al., "ComplianceMinimization of a Composite Laminated Platesby Genetic Algorithms", Project ofRAXIS/P/MAT/38/96 populations, Ministry ofScience and Technology of Portugal, 2005.

[27] Maurice Clerc, Particle SwarmOptimization, ISTE Ltd, UK, 2006.

[28] Aleksandar Lazinica, Particle SwarmOptimization, In-tech, Croatia, 2009.

Experimental Study and Optimization of Some of Tribological Characteristics for PMMA-Micro and Nano...

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