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Published on October 15, 2007

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POLYETHYLENE-CARBON BLACK NANOCOMPOSITES: MECHANICAL RESPONSE UNDER CREEP AND DYNAMIC LOADING CONDITIONS:  POLYETHYLENE-CARBON BLACK NANOCOMPOSITES: MECHANICAL RESPONSE UNDER CREEP AND DYNAMIC LOADING CONDITIONS Matteo Traina, Alessandro Pegoretti and Amabile Penati University of Trento (DIMTI) and INSTM; Via Mesiano 77, 38050 Trento – Italy E-mail: matteo.traina@ing.unitn.it; On web: www.unitn.it INSTM Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali Università 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) INTRODUCTION:  INTRODUCTION Carbon black (CB) Carbon (graphene layers) Combustion or decomposition (CXHY) Microstructure:  primary particles (diameter)  specific surface area (SSA) measured by the BET (Brunauer– Emmett–Teller) 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 (…) INTRODUCTION:  INTRODUCTION Carbon black (CB) INTRODUCTION:  INTRODUCTION CB FILLED COMPOSITES Matteo 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) EXPERIMENTAL:  EXPERIMENTAL HDPE-CB composites VISCOELASTIC BEHAVIOR  Creep tests  DMTA tests COMPOSITE MORPHOLOGY constant filler content (1 vol%) MATERIAL (polymeric matrix) EXPERIMENTAL:  EXPERIMENTAL HDPE-CB composites VISCOELASTIC BEHAVIOR  Creep tests  DMTA tests COMPOSITE MORPHOLOGY constant filler content (1 vol%) Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353 EXPERIMENTAL:  EXPERIMENTAL HDPE-CB composites VISCOELASTIC BEHAVIOR  Creep tests  DMTA tests COMPOSITE MORPHOLOGY constant filler content (1 vol%) Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353 PROCESSING Melt compounding (Extrusion) Twin screw extruder (ThermoHaake PTW16) T = 130-200-210-220-220°C n = 12 rpm Effect of the degree of filler dispersion Multiple extrusions (up to 3 times) FILLER DISPERSION:  FILLER DISPERSION Extrusions 3x HDPE-CB1353 500 µm HDPE-CB226 2x 1x HDPE-CB composites >>> thin section (microtome) >>> optical microscope As 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 DISPERSION:  HDPE-CB226, 1x HDPE-CB composites >>> ultra-thin section (cryo-ultramicrotome) >>> transmission electron microscope >>> PRELIMINARY RESULTS HDPE-CB226, 2x CB226 FILLER DISPERSION As the number of extrusions increases, as the degree of the filler dispersion is better. MOLECULAR WEIGTH DISTRIBUTION:  MOLECULAR WEIGTH DISTRIBUTION HDPE Size Exclusion Chromatography (SEC) 1,2,4 trichlorobenzene (TCB) at 140°C IP MW HDPE HDPE-CB The HDPE undergoes a progressive thermo-mechanical degradation during the extrusion processes. CREEP: GENERAL COMPARISON:  EFFECT OF MULTIPLE EXTRUSIONS:  3x > 2x > 1x  HDPE > HDPE-CB226 > HDPE-CB1353 EFFECT OF THE FILLER:  HDPE > HDPE-CB226 > HDPE-CB1353  3x > 2x > 1x CREEP: GENERAL COMPARISON Creep tests: 30°C, 10 MPa extruded 1x extruded 2x extruded 3x Slide12:  HDPE-CB composites VISCOELASTIC BEHAVIOR  Creep tests  DMTA tests COMPOSITE MORPHOLOGY constant filler content (1 vol%) Effect of the SSA of CB matrix HDPE composite HDPE-CB226 composite HDPE-CB1353 Effect 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 3x DEGRADATION PHENOMENA HDPE, 1x HDPE, 3x HDPE 1x HDPE 3x HDPE-CB226 3x HDPE-CB1353 3x FILLER EFFECT HDPE, 3x HDPE-CB226, 3x HDPE-CB1353, 3x CREEP: MASTER CURVES:  CREEP RESISTANCE DEGRADATION: HDPE 3x < HDPE 1x FILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353 These effects are evident at long time, while at short time the curves are almost superimposed. CREEP: MASTER CURVES HDPE-CB @ 30°C HDPE @ 30°C Creep test: temperature = 3090°C stress = 3 MPa (linear viscoelasticity) ANALYSIS OF THE DATA: Time-Temperature Superposition Principle (temperature spectrum  master curve) CREEP: CREEP RATE:  LOG-linear IN GENERAL:  linear decreasing in bi-logarithmic scale  the most differences is present at short time (<105 s)  at long time (>105 s) the curves are superimposed CREEP: CREEP RATE Master curves  linear viscoelasticity Creep tests  constant load/stress LOG-LOG LOG-LOG strain rate: Creep rate AT SHORT TIME: DEGRADATION:  HDPE 3x > HDPE 1x FILLER EFFECT:  HDPE > HDPE-CB226 > HDPE-CB1353) CREEP: RETARDATION SPECTRA:  CREEP: RETARDATION SPECTRA HDPE-CB @ 30°C HDPE @ 30°C The retardation spectrum translates: DEGRADATION: HDPE 3x < HDPE 1x FILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353 Linear viscoelasticity: es. Maxwell generalized model retardation time distribution Retardation spectrum (first-order approximation) CREEP: ISCOCHRONOUS COMPLIANCE:  The elastic components don’t change in a meaningful way. CREEP: ISCOCHRONOUS COMPLIANCE Comparison of the isochrone compliance (@ 2000s) as a function of the temperature The compliance is divided in:  elastic component (instantaneous), DE  viscoelastic component (time dependent), DV HDPE @ 2000s, DV HDPE-CB @ 2000s, DV D(t=2000) = DE + DV DE = D(t=0s) DV = D(t=2000s) – D(t=0s) The viscoelatic components: DEGRADATION: HDPE 3x > HDPE 1x (<70°C) FILLER EFFECT: HDPE > HDPE-CB226 > HDPE-CB1353 DMTA: GENERAL COMPARISON:  Glass transition temperature: DEGRADATION: HDPE 3x < HDPE 1x (-10°C) FILLER EFFECT: HDPE < HDPE-CB (+4°C) DMTA: GENERAL COMPARISON DMTA tests: temperature = -130  130°C frequency = 1 Hz Relaxation phenomena (, )     DMTA: MASTER CURVES:  DMTA: MASTER CURVES HDPE-CB @ 30°C HDPE @ 30°C DMTA test: temperature = -20130°C (a relaxation) frequencies = 0.330 Hz ANALYSIS 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 1x FILLER EFFECT: HDPE < HDPE-CB226 < HDPE-CB1353 DMTA: RELAXATION SPECTRA:  The relaxation spectra (DMTA) are consistent with the retardation spectra (CREEP) and very similar to the MWD data for the HDPE. DMTA: RELAXATION SPECTRA HDPE-CB @ 30°C HDPE @ 30°C Linear viscoelasticity: Relaxation spectrum (first-order approximation) DEGRADATION: HDPE 3x >narrow> HDPE 1x FILLER EFFECT: longer relaxation times for HDPE-CB ACTIVATION ENERGY:  ACTIVATION ENERGY ACTIVATION ENERGY of “a” relaxation [kJ/mol]  various method of calculation CREEP shift factor (Arrhenius equation) DMTA shift factor at high temperature (50100°C) (Arrhenius equation) DEGRADATION: HDPE 3x < HDPE 1x FILLER EFFECT: HDPE < HDPE-CB CONCLUSIONS:  CONCLUSIONS The 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 ADDITIONAL MATERIAL:  ADDITIONAL MATERIAL DEGRADATION: INFRARED SPECTROSCOPY:  FT-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- rocking OXIDATIVE 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<HDPE-CB226<HDPE-CB1353) C=O DEGRADATION: INFRARED SPECTROSCOPY DEGRADATION: THERMAL ANALYSES:  DEGRADATION: THERMAL ANALYSES Thermal analyses: Differential Scanning Calorymetry (DSC) 0-200°C, +10°C/min, N2 flux Thermogravimetric Analysis (TGA) 0-600°C, +10°C/min, N2 flux The 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 5°C. In particular: HDPE<HDPE-CB226<HDPE-CB1353. DEGRADATION: MOLECULAR WEIGTH:  MWD DEGRADATION: MOLECULAR WEIGTH From the MWD to the CSDF: Canevarolo SV. Chain scission distribution function for polypropylene degradation during multiple extrusions. Polymer Degradation and Stability 709 (2000) 71-76 Caceres CA, SV Canevarolo. Calculating the chain scission distribution function (CSDF) using the concentration method. Polymer Degradation and Stability 86 (2004) 437-444 Number of chain scissions Chain scission distribution function (CSDF) average for each MW The 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: EWF:  FRACTURE BEHAVIOUR: EWF Essential Work of Fracture (EWF) Specific total work of fracture wf wf = Wf / LB = we + wpL (under plane stress) DENT samples tensile test to fracture we = the specific essential work of fracture, i.e. the work dissipated in the process zone close to the crack tip (██); wp = the specific non-essential work of fracture, i.e. the work responsible for the plastic deforma- tion outside the fracture-process zone (██). we calculation Wf FRACTURE BEHAVIOUR: EWF:  FRACTURE BEHAVIOUR: EWF HDPE-CB HDPE HDPE as the number of extrusions increases, as the fracture toughness decreases (we) HDPE-CB as the number of extrusions increases, as the fracture toughness of the HDPE-CB composites in comparison to the HDPE toughness (with the same number of extrusion) increases (we/we,HDPE). This phenomenon has a different dynamic with different CB (i.e. different SSA). Essential Work of Fracture (EWF): DENT specimens (L = 515 mm; H = 6 mm) crosshead speed = 12 mm/min at room temperature (23°C) Fracture toughness (plane stress) Matteo Traina, Alessandro Pegoretti and Amabile Penati , Fracture behaviour of high density polyethylene – carbon black composites evaluated by Essential Work of Fracture approach. 8° Convegno Nazionale AIMAT (Palermo, June 27th – July 1st, 2006) CREEP: MASTER CURVES:  Creep test: temperature = 3090°C stress = 3 MPa (linear viscoelasticity) ANALYSIS OF THE DATA: Time-Temperature Superposition Principle (temperature spectrum  master curve) CREEP: MASTER CURVES PRELIMINARY TEST: Creep tests: 30 and 75°C, 310MPa Isochronous curves: 2000 s  deviation from linearity over 6 MPa  increasing creep resistance for HDPE 1x  increasing creep resistance for the compo- sites at all the tested stresses (HDPE<HDPE-CB226<HDPE-CB1353) HDPE 1x @ 30°C CREEP: TEMPERATURE SPECTRA:  CREEP: TEMPERATURE SPECTRA HDPE, 1x HDPE, 3x HDPE-CB226, 3x HDPE-CB1353, 3x temperature temperature temperature temperature CREEP: MASTER CURVES:  CREEP: MASTER CURVES HDPE, 1x @ 30°C HDPE, 3x @ 30°C HDPE-CB226, 3x @ 30°C HDPE-CB1353, 3x @ 30°C CREEP: ISCOCHRONOUS COMPLIANCE:  CREEP: ISCOCHRONOUS COMPLIANCE HDPE @ 0s, DE HDPE-CB @ 0s, DE HDPE @ 2000s, DV HDPE-CB @ 2000s, DV DMTA: POLYETHYLENE RELAXATIONS:  DMTA: POLYETHYLENE RELAXATIONS storage and dissipative modulus loss factor “” transition 30  60°C Relaxation phenomena in the crystalline regions of the polymer “” transition -30  20°C Relaxation phenomena in the side-branching of the polymer (if present) YES: LDPE NO: HDPE; LLDPE “” transition (glass transition) -120  -110°C Micro-Brownian motion of long chain segments in the amorphous regions of the polymer ACTIVATION ENERGY:  The activation energy decreases after 3 extrusions for the HDPE. The activation energy generally increases for the HDPE-CB composites in comparison to the HDPE (shift factor). Only in the case of the E’’ method the activation energy clearly decrease. ACTIVATION ENERGY ACTIVATION ENERGY [kJ/mol]  various method of calculation CREEP shift factor (Arrhenius equation) DMTA peak of E’’ (Arrhenius equation) DMTA shift factor high temperature (50100°C) (Arrhenius equation) DMTA shift factor low temperature (025°C) (Arrhenius equation) An increase of the activation energy from the shift factor (under/over the relaxation temperature) is related to a reduced mobility of the polymer chains. A change of the activation energy from the Arrhenius plot is directly related to the relaxation.

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