Thermoplastic Polyurethane Applications in the Wire and Cable ...

Thermoplastic Polyurethane Applications in the Wire and Cable IndustryRabeh Elleithy 1 and Armando SardanopoliElastollan ® TPU, BASF Corporation, Wyandotte, MI 48192IntroductionThermoplastic polyurethane elastomer (TPU) hasbeen used as a jacketing material for different types ofcables. For example, TPU is used as a jacketing materialfor above ground mining cables due to its high abrasionresistance. TPU also has excellent low temperatureflexibility, high tear resistance, and good insulationproperties. For these reasons and others that will bediscussed in this paper, TPU found its use as a secondaryinsulating material as well as a primary insulatingmaterial in special cases.MaterialTPU belongs to the family of thermoplastic elastomer(TPE). TPE is a two-phase system that could be generallydivided into two categories: [1] block copolymers and [2]elastomer blends. Block copolymers TPE, example ofwhich is TPU, consist of blocks of hard segments andblocks of soft segments within the same molecule. On theother hand, elastomer blends TPE, example of which isthermoplastic vulcanizate TPV, are generally aheterogeneous blend of soft rubbery material in a hardthermoplastic matrix. Figure 1-a shows a schematicpresentation of TPU as an example of block copolymersTPE. Figure 1-b represents TPV as an illustration ofelastomer blends TPE.(a)when the isocyanate reacts with the long chain polyol, asoft segment is formed. The hard segments interacttogether to form local crystals that act as physical crosslinks.Whereas, the long soft segments are tied togetherwith the physical cross-links which give TPU itselastomeric behavior (2) .The material that will be discussed here is PolyetherTPU, namely Elastollan ® produced by BASF Corporation.Several Elastollan ® products that have different hardnessand flame retardancy will be compared and contrasted toeach other. Table I lists the Elastollan® TPU, theirhardness, and their flame retardancy ratings. The flameretardancy ratings are found from tests performed in ourlabs based on UL94 testing procedure at a specificthickness. Similarly, the hardness, shore A or D, is basedon our lab results by following ASTM D2240 as ourguideline.Table I: List of the discussed materials and theirnomenclatures.# Elastollan ® Hardness UL9475W 1175A10W 75A V0-V285A 1185A10 85A HB85W 1185A10W 83A V285F 1185A10F 87A V085FHF 1185A10FHF 89A V054D 1154D 53D --54FHF 1154D-FHF 58D V2-V0T P E - U, E , AFigure 1: Schematic presentations of (a) block copolymerand (b) elastomeric blend of TPE.TPU is formed by the step polyaddition of isocyanatewith a diol and long chain polyol. Depending on the longchain polyol type, TPU could be divided into PolyetherTPU or polyester TPU (1) . In this paper we will befocusing on the Polyether TPU. When the isocyanatereacts with the diol, a hard segment is formed. Similarly,(b)The W indicates a plasticized material; F is a flameretardant material; and FHF is a halogen free flameretardant material.PropertiesThe selection criteria of cable jacketing could bedivided into: [1] mechanical, [2] environmental/chemical,[3] thermal, [4] electrical, and [5] regulations necessities(3) . Here, we will discuss briefly the properties of theElastollan ® TPUs listed in Table I as related to theseselection criteria. We will correlate between theseproperties & the appropriate applications in the wire andcable (W&C) industry.1 Corresponding authorInternational Wire & Cable Symposium 524 Proceedings of the 54th IWCS/Focus

Mechanical PropertiesThe most striking mechanical property of TPU is itsexcellent abrasion resistance. Table II compares theabrasion resistance of TPU to other typical plastics. Thedata of Table II was obtained by performing Taberabrasion using CS17 wheel, 1000 g weight, and 5000revolutions (4) .Table II: Taber abrasion resistance of selected plastics.Plastic materialTPU 0.4 – 3.2HDPE 29PTFE (Teflon) 42Nylon 6/6 58Plasticized PVC 187Butyl Rubber 205Neoprene 280Weight loss, mgThis high abrasion resistance promoted the use of TPU inapplications that require excellent scratch or scraperesistance, e.g. above ground mining cables.Elastollan ® TPU also has high elongation at breakand excellent tear resistance as shown in Table III (2) .Table III: Elongation at break and tear resistance ofdifferent Elastollan ® TPUs.75W 85W 85F 85FHF 54FHFchange in mechanical properties is a factor of theexposure temperature and the duration. For example, itwill take about 30 months at 100°C to reduce theelongation at break of 85FHF from 500% to 300%. Onthe other hand, it will take about 6 months at 120°C toreduce the elongation at break of 85FHF from 500% to300% (2)In the same token, when TPU is immersed in waterfor various periods of time at different temperatures, itsmechanical properties would change. For example,immersing 85FHF in water at 70°C for 41 months wouldreduce its elongation at break from 500% to 300%. Onthe other hand, it will take about 10 months at 80°C toreduce the elongation at break of 85FHF from 500% to300% (2) .In contrast, when 85A was immersed at 100°C for 14Days in ASTM oil-1, 2, and 3, its elongation at break andmaximum strength increased (2) .Thermo-mechanical PropertiesA schematic presentation of the thermo-mechanicalbehavior of 85A and 54D TPU (2) materials is illustrated inFigure 2. The curves of Figure 2 show the change of thematerial modulus as a function of temperature as obtainedby Dynamic Mechanical Analysis (DMA). At very lowtemperatures, both 85A and 54D have similar modulus.However as the temperature increases, 85A shows moreflexibility (lower modulus) than 54D. This is to say thatsoft TPU, like 85A, will be a more suitable jacketingmaterial when low temperature TPU flexibility is themain concern. Whereas, hard TPU, e.g. 54D, will be abetter choice for a jacketing material if high temperatureperformance is required.Elong @Brk, %685 595 505 500 350ModulusTearresistanceKN/m57 88 96 95 11085A54DThe elongation at break was measured using ASTM D412as our guideline, and the tear strength was performed byfollowing the guiding principles of ASTM D624 die C.As the TPU material gets harder, its elongation at breakdecreased and its tear strength increased as seen fromTable III. Even the lowest values shown in Table III arestill better than typical insulating materials, e.g. PVC haselongation at break of 330% and tear strength of 18 KN/m(1) .Environmental EffectsWhen TPU material was exposed to long-term ovenaging at different temperatures for different durations oftime, their mechanical properties were changed. The0.0C25CTemperatureFigure 2: DMA behavior of 85A and 54DA comparison between the low temperaturecharacteristics and high temperature performance ofdifferent TPUs is shown in Figure 3 (2) . The glasstransition temperature, T g , expresses the low temperaturecharacteristic. T g is the temperature at which the polymertransfers from the glassy state to the rubbery state.International Wire & Cable Symposium 525 Proceedings of the 54th IWCS/Focus

Figure 3: Comparison of T g and Vicat temperatures ofdifferent Elastollan ® TPUs.As T g decreases, TPU will stay more flexible at lowertemperatures. Low temperature flexibility of TPU comeswith excellent impact resistance at sub ambienttemperatures. For example, when performing Charpyimpact on un-notched samples per ISO 179, 75W, 85W,85FHF do not break even at –50°C (2) testing temperature.The Vicat softening temperature, ASTM D1525,exemplifies the high temperature performance.Generally, harder TPU will have higher Vicat point, andwill perform better at high temperature as compared tosofter TPU.Electrical PropertiesGenerally speaking, the electrical properties of TPUsuggest its usage for energy cables up to 1000V (5) . Anexception to that would be cables for high frequencytransmission, e.g. antenna cables. Table IV lists someelectrical properties of TPUs material based lab tests atroom temperature by following various IEC standards.As seen from Table IV, as the material gets harder, itsinsulation properties improve.Table IV: List of some electrical properties of 85A and54D.Vol.Resis.,Ω.cmSurf.Resis.,ΩDielec.Strength,KV/mm85A 10 12 10 15 32 0.1054D 10 14 10 15 36 0.06Diss.Factor @1MHzTemperature and environment also affect the insulationproperties (6) . For example, as the temperature increases,the volume resistivity decreases. Similarly, the volumeresistivity measured after immersing the material in waterfor different time duration is lower than the original value.In contrast, as the temperature increases the dielectricstrength increases to a maximum at about 60°C then itstarts to decrease.RegulationsUnder specific temperatures and other favorableconditions, various polymers would burn. There aredifferent regulations that identify the characteristics andsmoke release of polymers during burning. Refer toTable I for one burning characteristic of some TPUs.Table V summarizes the smoke release characteristicsand the limiting Oxygen index, LOI, of 85A and85FHF (6) . The smoke characteristics are measuredaccording to the French standards NF X10-702and NF 16-101. Whereas, the LOI is measured according to ISO4589-1 /-2.Table V: List of some properties of 85A and 85FHF.D m VOF4 Class LOI85A 97 190 F1 23 Vol-%85FHF 253 512 F2 24 Vol-%Where D m is the maximum optical density, VOF4 is thespeed of smoke development in the first four minutes, andthe class is a classification of the material based on itssmoke index.Typical ApplicationsOwing to the previously discussed properties, andothers, TPU found its notable application as a uniqueinsulator in the W&C industry. Some of theseapplications along with the relevant TPU properties aresummarized in Table VI (6) .Table VI: Typical cable applications that use TPU as ajacketing or insulating material.Cable App.IndustrialDragMiningControlOffshoreABSFlat CableSummaryPropertiesSputtering resistance & ToughnessFlexibility & Fatigue resistanceCut & Abrasion resistanceInsulation prop. & Low-temp flex.Hydrolysis & Microbial resistanceReliability & Tear resistanceCrease resistance & FlexibilityBecause of its unique properties, TPU Elastollan ® isconsidered the ideal insulating / sheathing material forspecial cables. Some of these unique properties areexcellent abrasion / wear resistance, flexibility, lowtemperatureflexibility, excellent tear & impact resistance,resistance to Ozone, and resistance to hydrolysis.International Wire & Cable Symposium 526 Proceedings of the 54th IWCS/Focus

Consequently, TPU is used in drag-cables, offshorecables, control bundles, power cables, coiled cables,seismic streamer sleeves, and other cable applications.The data presented here are based on resultsperformed in the lab. The final performance of the cableshould be checked and evaluated as it depends on factorsother than the insulated material.References(1) DeGross, J. L., International wire & cablesymposium proceedings, P. 831, November.1999.(2) Elastollan® technical bulletin, BASFCorporation.(3) Electrical Wire Handbook, the wire associationinternational.(4) Handbook of thermoplastic elastomers, Littoneducational publishing, 1979.(5) Bertels, TPU for high performance cables,Kunststoffe, Feb. 2001.(6) Elastollan® cable sheathing, Elastogran, BASFpublication.BiographyRabeh Elleithy- Author of 25+ papers in the field of polymerapplications and characterization.- Has more than 16 years ofexperience in the polymerfield.- Holds a Ph.D. in PolymersScience and Engineering.- Currently works at BASFCorporation in theTechnical ServiceDepartment of the TPUbusiness.Armando Sardanopoli- Over 35 years ofexperience in the TPUindustry in the area ofproduct and applicationsdevelopment.- Currently works as thetechnical manager of the TPU business at BASFCorporation.International Wire & Cable Symposium 527 Proceedings of the 54th IWCS/Focus