1、Mechanical Properties of Polyurethane Coated Knitted FabricsIntroductionSamples and working methodResults and discussionConclusionsPart1introductionPolyurethane-coated knittedfabricsareofinterestbecause theyexhibitseveralpositiveproperties,andyet theyare littlestudied,especially those usedinthegarme

2、nt industry. Theadvantages ofpolyurethanecoatingsincomparisontootherpolymersaregreaterresistance toabrasionandsplitting,increasedstrengthanddurability.Polyurethanes areformedbythepolyadditionreactionofapolyisocyanatewith apolyalcohol(polyol)inthepresenceofacatalystandotheradditives.Polyisocyanateisa

3、 molecule withtwoormoreisocyanate functionalgroups,R-(N=C=O)n 2and apolyol is amoleculewith twoormorehydroxylfunctionalgroups, R-(OH)n 2.The reactionproduct is apolymercontaining theurethanelinkage, -RNHCOOR-3.Thereisa chancetodevelop coatedknittedfabrics asprotective clothing,workclothing,sportswea

4、randcasualwearmorecomfortablethan clothesmadeoutofcoatedwovenfabric becausemovementsarelessrestrictedifclothingismade ofelastic knittedmaterial.Coatedknittedfabrics aregenerallymorestretchableandelasticthan woven fabrics.Part2Samples andworking methodSamplesSevenknitted fabricswith differentstructur

5、es (designationsKF1 -KF7)werechosentocoverawide interval of valuesofthecharacteristics of elongationandbreakingforcestested (Tables1& 2).They werecoated underthesameconditions,onthesamecoating line, withthreedifferentpolyurethane coatings(designatedPU1-PU3).Thepolyurethane coatings havenearlyequalav

6、erage thicknesses andweights, butdifferentmechanical properties(Table3).Asdescribedabove, thetotalnumberofcoatedknittedfabrics was21(7knittedfabrics 3polyurethanecoatings).Working methodThis timeweobservedmechanicalpropertiesbeforeand after coating, andformedconclusionsonthepredictionoftheirbehaviou

7、r.Thebehaviour of knittedand coatedknitted fabricsinthelinearapplicationofforcewascomparedwiththat of thesame specimensinthecaseofsphericalforceapplication.Thesampleswere statisticallyanalysed(descriptivestatistics,hypothesis testing- t-test,regression analysis).Part3Results anddiscussionElongation

8、of coatedknitted fabricsinrelationtotheknittedfabricElongation in thewale directionTheknittedfabrics elongatedfrom 46.41%to309.93%,whichisa consequence oftheirdifferentstructures.Thecoated knittedfabrics elongatedinthewaledirectionfrom 44.41%to382.44%.Thecoated knittedfabric hasaconsiderablyhigherav

9、erageelongationinthewale directioninrelationtotheknittedfabric-onaverage about 16%, apart fromtheleaststretchableknitted fabric(KF3),whichwasnotaffectedbythe coating.Namely theKF3sample wasknitted ina power-netstructure(Table1), whereelongation in thewale directiondependsdirectlyonelongation propert

10、iesofthevertically laidyarn(and notformedintoloops).Thet-testshowsthat there isnostatistically considerabledifferencebetween themean valuesofelongation of thegroupsofsamplestested(p=0.92)orthey canbeobservedasthesame typeofpolyester coatingforelongation in thewale direction.Regression analysisindica

11、testherelationshipbetween theelongation of theknitted fabricandthatofthepolyurethane-coatedknitted fabric.cw= 1.2312kw- 8.4717ThecoefficientofdeterminationR2= 0.9915It is possible to usetheregressionmodelobtainedforeasyprediction ofthebehaviour of thecoatedknittedfabricandthe choiceofanappropriatekn

12、ittedfabricsubstrate.Elongation in thecoursedirectionTheknitted fabricselongatedfrom 34.96%to157.93%,whichisa consequence of thedifferentstructures of knittedfabricsandyarnsused. Thecoatedknittedfabricselongatedinthecourse directionfrom 96.15%to358.75%. Thecoatedknittedfabrichasa considerablyhighera

13、verageelongationinthecourse directioninrelationtotheknitted fabric- onaverage about 102%.Thet-test shows thatthereisnostatisticallyconsiderabledifferencebetween themean valuesofelongation of theknittedfabrics coatedwiththreedifferenttypesofPUcoating (p =0.72)forthe elongationinthecourse direction.Re

14、gression analysisshowedthattherelationshipbetween theelongation of theknitted fabricandthe coatedknitted fabricinthecourse directionhave onlyamediumcorrelation(r=0.79).Therelationship betweenvariables isnotlinear.Exponentialregression modelcc= 103.53e0.0064kcwith acoefficientofdetermination R2 =0.62

15、62, is thebest explanation ofelongation varianceinthecourse directionofthesamplesofcoatedknittedfabrics (ecc) studiedwithregardtothe elongationofthe samplesofthesameknitted fabrics(ekc)examined.Itisinterestingtoinvestigatewhichelementstogetherwiththeelongationoftheknitted fabricaffectthe elongationo

16、fthecoatedknittedfabricinthe coursedirection.Thesamplesofcoatedfabric KF3,KF4andKF5show agreaterdifference intheelongationofthecoated fabricanduncoatedfabric(Figure 4, Table 5)andmoresignificantlydeviate fromtheadapted theoretical curve of theexponentialmodel.Theywereproducedfroma lowthicknessknitte

17、d fabric(Table1).Theratiobetweenknitted fabricthicknessand coatingthicknessincomparison withotherknitted fabricsislower(Table 5)There is relativelymore coating,makingagreater contributiontoelongation in suchcoatedfabrics.Therelationship betweentheratioofthicknesses(Tr)andthatofelongation(er)clearly

18、shows (r =0.89)r =5.9156 Tr-0.8882theelongationdecreasesifthereisrelativelyless coatingonthe coatedfabric.Byusingmultiplelinearregression, amuch betterrelationshipbetweentheelongation of thecoatedfabricinthecoursedirection andboth variables(elongationoftheknittedfabricand ratio ofknitted fabricthick

19、nessand coating)cc=149.3042+2.032309kc- 44.866TrThecoefficientofmultiplecorrelation(R= 0.91)indicatesa strongrelationshipbetween theelongation of thecoatedknittedfabricinthecourse directionandthe twovariablesobserved.Inadditiontotheelongationoftheknittedfabric,theratioofthe knittedfabricthickness an

20、dcoatingshouldbeconsidered.Technologicallythesefindingsshow howextremelysensitiveitistopredictthebehaviour of coatedknitted fabricswitha verythinsubstrate(thickness0.4 mm).Comparison of theelongationoftheknittedfabricand coatedknittedfabricduring sphericalelongationTheknitted fabricselongatedfrom 26

21、 to 68 mmuntilballbursting.Thecoatedknittedfabricselongatedfrom 25 to 66 mm.Thet-testshowsagainthat there isnostatistically significantdifferencebetween thearithmeticmeansofthethreetypes(PU1- PU3)ofsamplestested(p= 0.8372), andthey canbeobservedasonegroupofsamples.Thelowerelongationofthecoatedknitte

22、dfabricduringsphericalelongation, onaverage 8%.Itispossibletoconcludethatcoating fixes theyarn andtheknittedfabricstructure, i.e.the polyurethaneadhesivegluestheyarnwhichformsloops,henceitcannotmovefreelyand deformthefabric structurenoradapttospherical elongation, causinganearlyburstofthecoated knit

23、tedfabric.Thesame coatedknitted fabric,whichwillshow bettercharacteristicsthantheknitted fabricitselfduringelongationinthecourse or waledirection, exposedtosphericalelongationwill showpoorercharacteristics.Themodeloflinear regressioncb= 0.7468kb+ 6.1557with coefficientofdetermination R2 =0.9292Break

24、ingforceofthecoated anduncoatedknitted fabricsBreakingforceinthewaledirectionBreakingforcesfrom104.6N to907.5Nwere measured in theknittedfabricofdifferent structures. Breakingforcesfrom136.7N to 1053Nweremeasuredinthecoated knittedfabrics.Thecoatingcausedslightlyhigherbreakingforcesonaverage 24%.The

25、t-testshowsagainthat there isnostatistically significant differencebetweenbetweenthebreakingforces ofthethreepolyurethane-coatedgroupsofsamplestested(p= 0.93).Linearregressionmodel Fcw=1.098Fkw+48.736,with thecoefficientofdeterminationR2= 0.9802Breakingforceinthecourse directionoftheknittedfabricBre

26、akingforcesfrom 66.27 Nto501.8Nwere measured in theknitted fabric.Theburstingofthecoatedknittedfabricsinthecourse directionoccurredatbreakingforcesfrom 108.1 Nto672.2N. Thecoating causedanincreaseinbreakingforcesinthecourse directionoftheknittedfabric-onaverage about 27%.Thet-test shows again thatth

27、ereisnostatistically significant differencebetweenthebreakingforces of thethreepolyurethane-coatedgroupsofsamplestested(p= 0.88).Regression modelFcc=99.511,0039Fkc,with thecoefficientofdeterminationR2= 0.9367Breakingforceofthespherical burstoftheknittedfabricand coatedknittedfabricBreakingforcesfrom

28、 73 Nto1058Nwere measuredintheknittedfabrics andfrom 91 Nto1228 Ninthecoated knittedfabricsCoating causedanincreaseintheresistance to sphericalbursting- on averageabout13%.thet-test showsagainthat thereisnostatistically significant differencebetween thebreakingforcesofthethreepolyurethane-coatedgrou

29、psofsamplestested(p= 0.989).LinearregressionmodelFcb=1,1214Fkb +4,0992explainstherelationship betweentheoccurrencesobserved(Figure 13).ThecoefficientofdeterminationR2= 0.9956Part4ConclusionsAlthoughcoatingsignificantly changesthemechanical propertiesofknittedfabrics, theproperties of coatedknittedfa

30、brics areprimarilydeterminedbytheproperties of theknitted substrate.Elongation in thecoursedirectionoftheknitted fabricsignificantlyincreasesaftercoating -onaveragebyabout102%,whiletheincreaseinelongationbycoating in thewale directionislower,amountingtoabout16%.Elongation in thewale directionofcoatedknittedfabrics canbepredictedwith great certaintyknowing thatoftheknitted fabric.A linearregression modelexplains99.15%ofthe relationshipbetweentheelongationoftheknittedfabricandcoated knittedfabric.Elongation in thecoursedirectionofcoatedknittedfabrics canbepredictedwith great certaintyknowing th