POLYETHYLENE-CARBON BLACK NANOCOMPOSITES: MECHANICAL RESPONSE UNDER CREEP AND DYNAMIC LOADING CONDITIONSMatteo Traina, Alessandro Pegoretti and Amabile PenatiUniversity of Trento (DIMTI) and INSTM; Via Mesiano 77, 38050 Trento ItalyE-mail: firstname.lastname@example.org; On web: www.unitn.itINSTM Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei MaterialiUniversit degli Studi di Trento Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali (DIMTI)VI CONVEGNO NAZIONALE SULLA SCIENZA E TECNOLOGIA DEI MATERIALI(June 12th-15th, 2007; Perugia)
INTRODUCTIONCarbon black (CB) Carbon (graphene layers)Combustion or decomposition (CXHY)Microstructure: primary particles (diameter) specific surface area (SSA) measured by the BET (Brunauer EmmettTeller) method (ASTM D 6556-03) TEM analysis aggregates (structure) oil adsorption number (OAN) measured with the dibuthyl phtalate (ASTM D 2414-04) TEM analysis
Other properties ()
INTRODUCTIONCarbon black (CB)
INTRODUCTIONCB FILLED COMPOSITESMatteo Traina, Alessandro Pegoretti and Amabile Penati , Time-temperature dependence of the electrical resistivity of high density polyethylene - carbon black composites. Journal of Applied Polymer Science, in press.Matteo Traina, Alessandro Pegoretti and Amabile Penati , Processing and Electrical Conductivity of High Density Polyethylene Carbon Black Composites. XVII Convegno Nazionale AIM (Napoli, September 11th 15st, 2005)
EXPERIMENTALHDPE-CB compositesVISCOELASTIC BEHAVIOR Creep tests DMTA testsCOMPOSITE MORPHOLOGY constant filler content (1 vol%)MATERIAL (polymeric matrix)
Grade (Supplier)PropertiesHDPEEltex A4009(BP Solvay)MFI = 0.8 g/10min (190C; 2.16kg)Density = 0.958 g/cm3 (23C)
EXPERIMENTALHDPE-CB compositesVISCOELASTIC BEHAVIOR Creep tests DMTA testsCOMPOSITE MORPHOLOGY constant filler content (1 vol%)Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353
Grade (Supplier)OAN[cm3/g]SSA[m2/g]CB105Raven P-FE/B(Columbian Chemicals)0.98105CB226Conductex 975u(Columbian Chemicals)1.69226CB231Cabot XC72(Cabot Corporation)1.78231CB802Ketjenblack EC300J(Akzo Nobel)3.22802CB1353Ketjenblack EC600JD(Akzo Nobel)4.951,353
EXPERIMENTALHDPE-CB compositesVISCOELASTIC BEHAVIOR Creep tests DMTA testsCOMPOSITE MORPHOLOGY constant filler content (1 vol%)Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353PROCESSINGMelt compounding (Extrusion) Twin screw extruder (ThermoHaake PTW16) T = 130-200-210-220-220C n = 12 rpmEffect of the degree of filler dispersion Multiple extrusions (up to 3 times)
FILLER DISPERSIONExtrusions3xHDPE-CB1353500 mHDPE-CB2262x1xHDPE-CB composites >>> thin section (microtome) >>> optical microscopeAs the number of extrusions increases, as the degree of the filler dispersion is better.As the SSA decreases, as the degree of dispersion is better.
FILLER DISPERSIONHDPE-CB226, 1xHDPE-CB composites >>> ultra-thin section (cryo-ultramicrotome) >>> transmission electron microscope>>> PRELIMINARY RESULTSHDPE-CB226, 2xCB226As the number of extrusions increases, as the degree of the filler dispersion is better.
MOLECULAR WEIGTH DISTRIBUTIONHDPE Size Exclusion Chromatography (SEC) 1,2,4 trichlorobenzene (TCB) at 140CIPMWHDPE HDPE-CBThe HDPE undergoes a progressive thermo-mechanical degradation during the extrusion processes.
CREEP: GENERAL COMPARISONEFFECT OF MULTIPLE EXTRUSIONS: 3x > 2x > 1x HDPE > HDPE-CB226 > HDPE-CB1353EFFECT OF THE FILLER: HDPE > HDPE-CB226 > HDPE-CB1353 3x > 2x > 1xCreep tests: 30C, 10 MPaextruded 1xextruded 2xextruded 3x
HDPE-CB compositesVISCOELASTIC BEHAVIOR Creep tests DMTA testsCOMPOSITE MORPHOLOGY constant filler content (1 vol%)Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353Effect of the degree of filler dispersion Multiple extrusions (up to 3 times)HDPE 1x HDPE 2x HDPE 3x HDPE-CB226, 1x HDPE-CB226 2x HDPE-CB226 3x HDPE-CB1353 1x HDPE-CB1353 2x HDPE-CB1353 3xDEGRADATION PHENOMENA HDPE, 1x HDPE, 3xHDPE 1x HDPE 3x HDPE-CB226 3x HDPE-CB1353 3xFILLER EFFECT HDPE, 3x HDPE-CB226, 3x HDPE-CB1353, 3x
CREEP: MASTER CURVESCREEP RESISTANCEDEGRADATION: HDPE 3x < HDPE 1xFILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353These effects are evident at long time, while at short time the curves are almost superimposed.HDPE-CB @ 30CHDPE @ 30CCreep test: temperature = 3090C stress = 3 MPa (linear viscoelasticity)ANALYSIS OF THE DATA: Time-Temperature Superposition Principle (temperature spectrum master curve)
CREEP: CREEP RATELOG-linearIN GENERAL: linear decreasing in bi-logarithmic scale the most differences is present at short time (105 s) the curves are superimposedMaster curves linear viscoelasticity Creep tests constant load/stressLOG-LOGLOG-LOGstrain rate:Creep rateAT SHORT TIME:DEGRADATION: HDPE 3x > HDPE 1xFILLER EFFECT: HDPE > HDPE-CB226 > HDPE-CB1353)
CREEP: RETARDATION SPECTRAHDPE-CB @ 30CHDPE @ 30CThe retardation spectrum translates:DEGRADATION: HDPE 3x < HDPE 1xFILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353Linear viscoelasticity: es. Maxwell generalized model retardation time distributionRetardation spectrum (first-order approximation)
CREEP: ISCOCHRONOUS COMPLIANCEThe elastic components dont change in a meaningful way.Comparison of the isochrone compliance (@ 2000s) as a function of the temperatureThe compliance is divided in: elastic component (instantaneous), DE viscoelastic component (time dependent), DVHDPE @ 2000s, DVHDPE-CB @ 2000s, DVD(t=2000) = DE + DVDE = D(t=0s) DV = D(t=2000s) D(t=0s)The viscoelatic components:DEGRADATION: HDPE 3x > HDPE 1x ( HDPE-CB226 > HDPE-CB1353
DMTA: GENERAL COMPARISONGlass transition temperature:DEGRADATION: HDPE 3x < HDPE 1x (-10C)FILLER EFFECT: HDPE < HDPE-CB (+4C)DMTA tests: temperature = -130 130C frequency = 1 HzRelaxation phenomena (, )
MaterialTg=Tg [C]HDPE, 1x-98.8HDPE, 3x-108.9HDPE-CB226, 3x-104.3HDPE-CB1353, 3x-103.8
DMTA: MASTER CURVESHDPE-CB @ 30CHDPE @ 30CDMTA test: temperature = -20130C (a relaxation) frequencies = 0.330 HzANALYSIS OF THE DATA: Time-Temperature Superposition Principle (temperature spectrum master curve)The DMTA results are analogous to the CREEP results.Storage modulus:DEGRADATION: HDPE 3x < HDPE 1xFILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353
DMTA: RELAXATION SPECTRAThe relaxation spectra (DMTA) are consistent with the retardation spectra (CREEP) and very similar to the MWD data for the HDPE.HDPE-CB @ 30CHDPE @ 30CLinear viscoelasticity:Relaxation spectrum (first-order approximation)DEGRADATION: HDPE 3x >narrow> HDPE 1xFILLER EFFECT: longer relaxation times for HDPE-CB
ACTIVATION ENERGYACTIVATION ENERGY of a relaxation [kJ/mol] various method of calculationCREEP shift factor (Arrhenius equation)DMTA shift factor at high temperature (50100C) (Arrhenius equation)DEGRADATION: HDPE 3x < HDPE 1xFILLER EFFECT: HDPE < HDPE-CB
CONCLUSIONSThe creep resistance (in general the viscoelastic behaviour) of the HDPE-CB composites is strictly dependent: on the CB type as the SSA increases as the creep resistance increases >>> The filler-matrix interaction hamper the chain motions elastic/viscoelastic components of compliance activation energy, retardation/relaxation spectra creep rate. on the level of dispersion of the filler in the polymer matrix as the filler dispersion is improved as the creep resistance increases >>> The improved dispersion enhances the filler-matrix interaction, i.e. the effective surface area. on the degradation of the polymer matrix as the matrix degrades as the creep resistance decreases
- DEGRADATION: INFRARED SPECTROSCOPYFT-IR spectra: degradation phenomena (oxidation) carbonyl peak (C=O @ 1720 cm-1) intensity normalized by the peak intensity @ 1300 cm-1 (skeletal C-C vibrations) @ 720 cm-1 (methylene (CH2)n- rockingOXIDATIVE DEGRADATION: the most part of the phenomenon takes place during the first extrusion the oxidative phenomena are more intense for the HDPE-CB composites (HDPE
- DEGRADATION: THERMAL ANALYSESThermal analyses: Differential Scanning Calorymetry (DSC) 0-200C, +10C/min, N2 flux Thermogravimetric Analysis (TGA) 0-600C, +10C/min, N2 fluxThe extrusion induces a meaningful change of crystallinity only after the first extrusion on HDPE. The thermal stability of the composites HDPE-CB increases in comparison with the HDPE of about 5C. In particular: HDPE
DEGRADATION: MOLECULAR WEIGTHMWDFrom the MWD to the CSDF:Canevarolo SV. Chain scission distribution function for polypropylene degradation during multiple extrusions. Polymer Degradation and Stability 709 (2000) 71-76Caceres CA, SV Canevarolo. Calculating the chain scission distribution function (CSDF) using the concentration method. Polymer Degradation and Stability 86 (2004) 437-444Number of chain scissionsChain scission distribution function (CSDF)averagefor each MWThe extrusion induces the scission of the high MW chains and the branching/cross-linking of the low MW chains. The intensity of these phenomena (after each extrusion) decreases (1x>2x>3x).The shape of the CSDF curve gives information on the type and intensity of the degradation.
FRACTURE BEHAVIOUR: EWFEssential Work of Fracture (EWF)Specific total work of fracture wfwf = Wf / LB = we + wpL(under plane stress)DENT samplestensile test to fracturewe = the specific essential