Materials and Experimental Techniques

Transcription

1 Chapter 2 Materials and Experimental Techniques - The characteristics of all the materials used in the study and the details of the experimental techniques employed to get final conclusion are presented in this chapter. The methods of preparation of both compatibilised and uncompatibilised blends are discussed in detail. The phase morphology is analysed by scanning electron microscopy where as mechanical and dynamic mechanical tests are used to understand the performance and mechanics of the blends. While therinogravimetry and differential scanning calorimetry are employed to understand the thermal degradation and crystallisation properties of the blends respectively, we depend on dynamic rheometry to elucidate the processing/rnorpholcrgy correlation. --

2 132 Chapter Materials lsotactic polypropylene (PP-Koylene and M3030) having an MFI of 3g/lOmin (at 230"~/2.16kg) and density of 905 kgm3 was kindly supplied by Indian Pet10 Chemicals Limited, Baroda, Gujarat, India. High density polyethylene (HDPE- Relene, M60200) having an MFI 2lgllOmin (at 230'~/2.16k~) and density 958kgm'3 was supplied by Reliance Industries, Hazira, Gujarat, India. Compatibilisers used were ethylene propylene diene terpolymers (EPDM). EPDM rubbers with three diierent ethylenelpropylene (EIP) ratios were kindly supplied by Herdillia Unimers Ltd., Mumbai, India. The characteristics of EPDM random copolymers used in the study are given in Table 2.1. Polyamide 12 (PA12), (Vestamid, L1670) having a mek volume-flow rate (MVR) of 60cm3/10min (at 250"~/2.16k~) and a density of 1010kgm3 was kindly supplied by Degussa, High Performance Polymers, Marl, Germany. PP grafted with rnaleic anhydride (PP-g-MA) (Polytmnd 3200) having MFI 1 l~dgrnin-' and MA content 1.OW/. was obtained by the courtesy of Crompton Corporation, Middlebury, USA. The other important characteristics of PP, HDPE and PA12 are listed in Table Monomer ENB(%) Molecular EPDM - Iati0 fraction (1) (Unsaturation) weight (MV Code ) , E 2 62/ ,10, E 3 74/ ,OOO 0.7E -- Table 2.1: Characteristics of EPDM random copolymers PP (SWW HDPE PA12 Tensile modulus (MPa) Elongation at break (%) Ghsbanslial~ 7d("C) Melting point, T,"("C) Cqsiahtm tenlpenture. T,:"("%) Crystallinity'+ (X) ' 'Frwn OMTA. "From DSC: Table 2.2: Important characteristics of polymers used in the study

3 Materiala andexperiimenla1 Techniques Experimental techniques Blend preparation Preparation of P PWE blends Blends of different compositions of PP (Koylene M3030) and HDPE (Hm, H~o, H30. Ha, HSO. Hw, H70, HBO and Hw, where H denotes HDPE and the subscript denotes the percentage composition by weight of HDPE) were prepared by melt mixing of PP with HDPE in a Brabender Plastograph at 175 C. The rotor speed was 60rev.min.' and the mixing time was optimised as 5 minutes. HzO and H50 have been selected for compatibilisation. Physical compatibilisation method (non-reactive route) has been employed using EPDM with three different E/P ratios. Compatibilised blends were prepared by two-step mixing. In the first step. the compatibiliser was pre-mixed with the minor component and melted for two minutes at 175 C and in the next step, the major component was added and mixing continued for another 5 minutes at a speed of 60 rev.min-' at 175 C. The amount of compatibiliser was varied from 1 to 20wt% to determine the optimum compatibiliser concentration. The melt mixed samples were then compression moulded at 185 C to obtain sheets of 2mm thickness. The coding systems of PPIHDPE blends are presented in Table 2.3. For compatibilised blends each code contains three parts: first reters to the blend, second to the compatibiliser and the third part reters to the amount of compatibiliser in the blend with respect to the minor phase. F.>r example, in Hz00.5E1, H, refers to the blend composition (here 80wP/0 PP and 20Wb HDPE), 0.5E represents the EPDM copolymer and 1 denotes the amount of EPDM copolymer in the blends, i.e., 1wPA of the minor phase. A similar coding was given for compatibilised HsO blends. Wt% ot - Codes compatibiliser E 0.6E 0.7E o Hz0 H20 H20 1 H20-0.5E1 H2~0.6E1 Hz,-0.7E1 3 H2,0.5E3 Hzo-0.6E3 H20-0.7E3 5 HZ,-0.5E5 Hzo-0.6E5 H2L0.7E5 10 H2,0.5E1 0 HzL0.6E10 H2L0.7E10 15 H20-0.5E15 H20-0.6E1 5 HzL0.7E Hm_0.5E20 Hza_0.6E20 Hd.7E20 Table 2.3: The coding system of PPIHDPE compatibilised blends

4 Preparation of PA 12/PP blends Both uncompatibilised and compatibilised blends were prepared by melt mixing process in a Brabender Plastograph. Before mixing PA12 was dried in a vacuum oven at 80 C for 12 hours in order to remove the absorbed water. Appropriate amounts of PA12 and PP (Koflene S3030) were mixed at 185 C and 60 rev.min-' for 6min to obtain blend:; of different compositions (PAlZPP = 90110, 80120, 70130, 60140, 50150, 40160, 30170, and 10190). These blends are represented as Nw, Nm and so on where subscripts represent the wt% of PA12. N, N, and N, blends were selected for compatibilisation. Reactive compatibilisation technique has been adopted using PP-g-MA as reactive compatibiliser precursor (Note that for simplicity, PP-g-MA itself was referred to as compatibiliser some times). Compatibilised blends were obtained in two-step mixing process. In the first step, the compatibiliser was premixed with PP for 2min at 185 C and 60rev.min.' and in the second step PA12 was added to this mixture and mixing was continued for further 6min. The amount of compatibiliser was varied from 1 to 20wt% to determine the optimum compatibiliser concentration (for N-, blends up to 15wt%). Both uncompatibilised and compatibilised blends were compression moulded at 190 C to obtain sheets of 2mm thickness for mechanical testing Phase morphology studies Scanning electron microscope was used to analyse the phase morphology of the blends. The specimens for phase morphology studies were cryogenically fractured in liquid nitrogen. In the case of PAlZPP system, in PP rich blends, the dispersed PA phase was etched with formic acid at ambient temperature for 48 hours. In PA rich blends boiling xylene was used (for 72 hours) to extract the PP dispersed phase preferentially. Fracture surface was sputter coated with AuIPd alloy in a sputter coating machine (Balzers SCD 050) for 150s. A minimum of 5 photographs were taker1 for each sample using a scanning electron microscope (SEM; Jeol 5400, Tokyo, Japan). About 200 particles were considered to determine the droplet d~ameter of the dispersed phase. The number (D,) and weight (D,) average diameters were determined using the following equations:

5 Material8 and Experimental Techniques 135 The number average diameter, NiDi D" = x~i The weight average diameter, C N;D? D" =- NiDi From the dispersed droplet type morphology, morphological parameters such as polydispersity index (pdi), interfacial are per unit volume (Ai) and interparticle distance (IPD) were calculated using the following expressions: is the volume fraction and R the average radius of the dispersed particles. In order to analyse the morphology stability against static coalescence, SEM micrographs oj' cryogenically fractured annealed samples (both PPlHDPE and PA12IPP blends) have been taken. For PA12/PP blends, extracted samples have been used. The samples were annealed in a vacuum oven at 190 C for 10, 30 and 60 minutes Mechanical property testing Tensile testing Tensile properties of the blends were determined at room temperature (RT) using a Zwick universal testing machine (Zwick Ulm, Germany) with extensometer at a cross-head speed of 50mmlmin as per ASTM standards. Five dumbbell specimens were used for each blend to determine the Young's modulus (E), tensile strength (cr,) and elongation at break values (Ed High speed izod impact testing Impact tests were performed on notched izod specimens. The specimens were notched by a Notchvis device of Ceast (Piannezza, Italy) for an ami ratio of ca. 0.5, where a is the notch length (W-a is the free ligament of the specimens). The

6 136 Chapter 2 specimens were subjected to instrumented impact testing at room temperature (RT). The instrumented impact pendulum of Ceast (DAS 8000) records the force during impact as a function of time. The primary data stored can be convetted in other representation of the fractograms (force-deflection, energy-deflection, etc.) using the DAS 8 WIN (2.10) software of the device from which impact energy was obtained directly. Parameters of the impact tests were: striker speed: 3.7rn/s, striker energy: 15J. load range: up to 650 N, sampling time: up to Ems Dynamic mechanical thermal analysis The dynamic mechanical properties of the blends were analysed using a dynamic mechanical thermal analyzer (Eplexor 150N, Gabo Qualimeter, Ahlden, Germany) in tension mode. The static force and dynamic force were taken as 10 and + 5N, respectively. The dynamic frequency was kept constant at lohz and the heating rate was selected as 1"CImin from -100 to +10O0C (from -140 C to 100 C for PPIHDPE blends). From the dynamic mechanical thermal analysis, storage modulus (E'), loss modulus (E") and tan 6 values have been obtained Differential scanning calorimetry The melting and crystallization behaviour of the blends were determined using a Mettler 820 DSC thermal analyser. The first heating was done from RT to 200 C at a rate of 4O0C/min followed by isothermal heating for 3min and first cooling and second heating were performed at 1O0C/m~n in nitrogen atmosphere. The melting and crystallisation characteristics were determined fmm the DSC heating and cooling curves, respectively. The following characteristics have been computed: (i) the onsets of crystallisation (T,) and melting (T,,o,) (ii) the crystallisation temperature (T, ) and melting point (T,) (iii) the normalised enthalpy of crystallisation (AH,,norm) (iv) the normalised enthalpy of fusion (AH,,norm) and (v) the percentage crystallinity (X%) The normalised values have been calculated by normalising the enthalpy values (AH) obtained from the instrument with respect the weight fraction of the

7 Materials andexpn'mental Techniques 137 correspondiny component. The X% was estimated from the Aff,,norm using the following equation: where m,,,ls the enthalpy of fusion of 100% crystalline polymer. MI,, of HDPE, PP and PA12 were taken as 290,209 and respectively Thermogravimetric analysis The thermal degradation studies of the blends were done in a Mettler TG 50. The samples were scanned from RT to 600 C at a heating rate of 20 C per min. From the TG curves, the thermal degradation characteristics such as onset of degradation (T,), temperature at nlaximum rate of degradation (T,.), temperatures at different weight losses and integral procedural decomposition temperature (IPDT) have been calculated. In addition, Horowitz-Metzger (HM), equation was used k ~r computing the activation energy (E,) for degradation Dynamic rheology The rheoiogical properties of the blends were evaluated on a Rheometric Scientific ARES rheometer in platelplate geometry. Spherical samples of 25mm diameter and lmm thickness were punched out from injection moulded plaques and the soak time was carefully adjusted as 3 min. A temperatureflrequency sweep method was selected and the frequency range was taken as 0.1 to 100rad/sec at three different temperatures 190, 210 and 230 C. The strain rate was taken as lo?". From the rheological measurements, the shear modulus (G'), Loss modulus (G"), Complex viscosity (E'), tan& etc. have been obtained from the instruments.