Chapter 2 Materials and Methods

Transcription

1 Chapter 2 Materials and Methods This chapter deals with the details of materials used, the experimental techniques employed for the preparation of microfibrillar composites from polypropylene/poly (ethylene terephthtalate) and low density polyethylene/poly (ethylene terephthtalate). The various characterization techniques employed are also described.

2 102 Chapter Materials The materials used in this study were Polypropylene, Low density polyethylene, Poly (ethylene terephthtalate). A compatibilizer PE-g-MA was used for the preparation of LDPE/PET MFCs Polypropylene (PP) Polypropylene used was Repol-H110MA, Reliance, India, having an MFI of 11.0 g/10 min.the other properties of PP are given in Table 2.1. Table 2.1. Properties of polypropylene Property Value Specific gravity 0.89 Ultimate Tensile strength * Tensile modulus * 29.2 MPa 1470 MPa Elongation at break * 33.9% Glass transition temperature ** Melting point *** 10.5 C C Crystallization temperature *** 114 C * obtained from tensile test results using ASTM D-638 ** from tan peak obtained from dynamic mechanical thermal analysis *** obtained from differential scanning calorimetry Low density polyethylene (LDPE) LDPE used in this study was Relene-16MA 400, Reliance India, with an MFI of 30 g/10 min. The other properties are listed in Table 2.2.

3 Materials and Methods 103 Table 2.2. Properties of LDPE Property Value Specific gravity 0.91 Ultimate Tensile strength * 7.9 MPa Tensile modulus * MPa Elongation at break * 111 % Melting point C * obtained from tensile test results using ASTM D Poly (ethylene terephthalate) (PET) The PET material used in this study was supplied by Futura Polymers Ltd., Chennai, India. It is a bottle grade material and the relevant properties are given in Table 2.3 Table 2.3. Properties of PET Property Value Bulk density * 0.83g/cc Intrinsic viscosity * 0.81dL/g Acetaldehyde content* 0.87ppm Tensile strength ** 61.7 MPa Tensile modulus ** 3250 MPa Elongation at break ** 24.7 % Melting point *** C * obtained from the brochure of M/s Futura Polymers Ltd.Chennai ** obtained from tensile test results using ASTM D-638 *** obtained from differential scanning calorimetry

4 104 Chapter Compatibilizer LDPE grafted with maleic anhydride (Optim E 126, Pluss Polymers India) was used as the compatibilizer for the preparation of LDPE/PET MFCs. The relevant properties obtained from the technical brochure of M/s Pluss Polymers are given in Table 2.4. Table 2.4. Properties of compatibilizer Property Value Specific gravity 0.92 Melting point 108 C Melt flow index 0.4 g/10min Maleic anhydride content 0.9 to 1.5% 2.2. Preparation of PP/PET microfibrillar composites After drying PET for 12 hours at 100ºC it was tumble mixed with PP at a constant weight ratio of 15/85. The mixture was then melt blended in a single screw extruder (Screw Diameter-20mm, L/D Ratio-30) using a set temperature profile of 225,235,250,255,260ºC and the screw rotating at 30rpm. The scheme of the experimental set up is given in Figure 2.1. The extrudate was in the form of circular strands of diameter 2.5 mm and were taken to a cooling water bath for solidification. Then these strands were passed through a hot air oven maintained at 100ºC. Subsequently these strands were taken to a take up device for continuous drawing. The take up device consists of a pair of nip rolls whose peripheral velocity (V 1 ) is maintained same as the velocity of the extrudate. Beyond the nip

5 Materials and Methods 105 rolls there was a pair of stretch rolls of the same diameter as that of the nip rolls, but whose speed (V 2 ) can be varied to attain different draw ratios and thereby reduction in the cross sectional dimensions of the strands. The ratio of the speeds of the stretch rolls to the nip rolls (V 2 / V 1 ) was taken as the draw (stretch) ratio. PP +PET V 1 V 2 Extruder Cooling water bath Nip rolls Oven Draw rolls Grinder Drawn Blend Injection moulding machine Figure 2.1. Scheme of the experimental set up for PP/PET microfibrillar in-situ composites preparation. The experiment was carried out for draw ratios 1, 2, 5, 8, 10 and the specimens were named as NS, MS2, MS5, MS8, and MS10 respectively. Downstream the stretching unit, the strands were granulated to approximately 3mm length. The granules thus produced were injection moulded into tensile test and impact test samples in a Ferromatic Milacron-Sigma 50T machine. The extruded neat blend was injection moulded at a temperature profile of 185,225,245,270ºC from the feed

6 106 Chapter 2 zone to the nozzle and it was designated as NB. All the drawn blends were injection moulded at a set temperature profile of 160,170,190,205ºC, from the feed zone to the nozzle. The low temperature was maintained to preserve the fibrillar morphology of PET. The samples taken were designated as MC2, MC5, MC8, MC10 corresponding to the stretch ratios Preparation of LDPE/PET microfibrillar composites The PET material was dried for 12 hours at 100 C. LDPE was tumble mixed with dried PET at weight ratios of 95/5, 85/15 75/25, 65/35 and 55/45 w/w %. For preparing compatibilized blends and microfibrillar composites, 2, 4, 6, 8 wt% of LDPE was replaced by PE-g-MAH in 75/25 w/w %blends. Figure 2.2. Scheme of the experimental set up for LDPE/PET microfibrillar in-situ composites preparation.

7 Materials and Methods 107 The prepared mixture was then melt blended in a single screw extruder (Screw Diameter-35mm, L/D Ratio-30) provided with a strand die of diameter 2 mm at a set temperature profile of 185, 205, 245, 255, 260 ºC from feed to die zone. The normal blends were extruded without any draw down applied beyond the die. They were designated as NS95, NS85, NS75, NS65 and NS55 corresponding to the LDPE wt% in the blend. In the case of microfibrillar blends, the speed of the rolls was adjusted to achieve a draw ratio (Area of cross section of die/area of cross section of strand) between 6 and 8. The final diameter of the strands was in the range of 0.7 to 0.85mm. The take up rolls were nor used in this case as the oven need not be used to raise the temperature of the strands after cooling in the water bath. The microfibrillar blends thus obtained were designated as MS95, MS85, MS75, MS65 and MS55. Downstream the rolls the strands were granulated to approximately 3mm length. The granules thus produced were injection moulded in a Ferromatik Milacron-Sigma 50T machine. The extruded normal blends (obtained without drawing) were injection moulded at a temperature profile of 160, 220, 245, 265ºC from the feed zone to the nozzle. The scheme of the experimental set up is given in Figure 2.2. The injection moulded normal neat blends were designated as N95, N 85, N75, N65 and N55. The normal compatibilized blends after injection moulding were designated as N75-2, N75-4, N75-6 and N75-8. All the drawn blends were injection moulded at a set temperature profile of 130, 160, 180, 200 ºC from the feed zone to the nozzle to preserve the fibrillar nature of PET. The samples obtained were designated as M95, M85, M75, M65 and M55.The compatibilized drawn blends were designated as MS75-

8 108 Chapter 2 2, MS 75-4, MS75-6 and MS 75-8.The microfibrillar composites prepared from them were denoted as M75-2, M75-4, M75-6 and M Various stages of MFC preparation The photographs of the blends during the various stages of the MFC preparation are presented below. In the Figure 2.3a the pellets of LDPE (left side) and PET (right side) are shown. Figure 2.3b indicates the strands obtained without the application of any draw down i.e. corresponding to the normal blends. The sectional dimensions of these strands were in the range of 2.2 to 2.6mm, which is slightly larger than the die opening due to the die swell characteristics. These strands were used to prepare injection moulded specimens of normal blends. Figure 2.3c represents the bunch of strands of microfibrillar blends, which are obtained by the continuous drawing of the extruded blends. The drawing process causes a reduction in the diameter of the strands. They are hereafter referred to as microfibrillar blends (MFB). The cross sectional dimensions are in the range of 0.7 to 0.85 mm. Figure 2.3d gives a comparison of the size of the strand of the normal blend (top) and the microfibrillar blend (bottom). In the Figure 2.3e the granulated microfibrillar blends obtained by shear cutting to be used for injection moulding is shown. The bunch of continuous strands of microfibrillar blends were first sheared to approximately 150mm length. Subsequently they were introduced into a standard granulator to reduce the length to approximately 7-12 mm. Figure 2.3f shows the injection moulded test specimens (with feed system) prepared from the granulated microfibrillar blends to complete the preparation of microfibrillar composites. A family

9 Materials and Methods 109 mould was employed to obtain tensile and flexural test specimens in a single shot of moulding. (a) (b) (c) (d) (e) (f) Figure 2.3. Photographs of raw material and blends during the various stages of MFC preparation a) granules b) after extrusion c) after drawing d) comparison of as extruded and drawn blend e) granulated drawn blend and f) after injection moulding

10 110 Chapter Characterization methods Scanning electron microscopy (SEM) A JEOL JSM 840 SEM with an acceleration voltage of 20 kv was used for studying the morphology of the specimens. To extract the PET phase from the specimens, a mixture of phenol/1, 1, 2, 2, tetra chloroethane in 60/40 w/w % was used as the solvent. Similarly, to remove PP or LDPE and retain the PET fibrils the specimens were treated with hot xylene. All the specimens were coated with a thin gold layer prior to SEM analysis. The diameter of about 100 fibrils was measured from the micrographs of stretched samples using image analysis software The number-average diameter D n was calculated as follows: NiDi D n (2.1) Ni where Ni is the number of particles or microfibrils of size i Wide angle X-ray diffraction The morphology/crystallization characteristics of PP, PET, NB, MFBs and MFCs was analyzed on a wide angle X-ray diffractometer - Bruker AXS D8 Advanced using X- ray source of Cu (1.542A ) in the 2θ range 3 to 70 at a scanning speed of 10 /min Infrared spectroscopy FT-IR spectra of blends and MFCs based on LDPE/PET MFCs were obtained using a Nicolet-510 FT-IR spectrometer. The analysis was aimed to understand the effect of the compatibilizer PE-g-MA on the blends of LDPE and PET. The samples for infrared analysis were thin films prepared by hot pressing, and the resolution of the spectrum was 0.4 cm -1.

11 Materials and Methods Mechanical properties measurements The tensile properties of the microfibrillar in-situ composites at different stretch ratios were measured at room temperature according to ASTM D-638 using the injection moulded dumbbell specimens. All the tests were conducted at a constant crosshead speed of 50 mm/min. Impact Strength was measured using an Izod impact tester using notched specimens according to ASTM D-256. The flexural properties of the samples were measured according to ASTM D-790 using injection moulded rectangular specimens. Five specimens were tested in each case and the average values were reported Dynamic mechanical thermal analysis Rectangular specimens having size 60 mm X 13 mm X 3.3 mm were used for the dynamic mechanical experiments. Dynamic mechanical thermal analyzer NETZSCH DMA 242 was used for the evaluation of storage modulus (E ), loss modulus (E ) and mechanical damping factor (Tan ). Three point bending modes were used. The temperature range over which properties were measured was -20 to +150 C at a heating rate of 5 C/min for PP based blends and MFCs. The tests were carried for frequencies 1Hz and 10 Hz. In the case of LDPE based MFCs the temperature range used was -150 to 100 C. The tests were carried out at frequencies 0.1, 1 and 10Hz. The storage modulus and tan max values obtained experimentally were compared with those obtained from theoretical equations Dynamic rheology The dynamic rheology of PP, neat blend and MFCs was studied using rotational rheometer (Haake RT 10, Germany), employing parallel

12 112 Chapter 2 plate sensor of diameter of 35mm. The samples used were square type (20mm X 20mm) punched out from the injection moulded specimens of thickness approximately 3mm. Dynamic complex viscosity (η*), storage and loss modulii (G and G ) and mechanical loss factor (tan ) were investigated as function of angular frequency (ω) ranging from 0.6 to 200 rad/s at 205 C Differential scanning calorimetry Thermal properties of PP, neat blend; drawn (microfibrillar) blends and MFCs were studied using a Mettler Toledo DSC 822 e at a heating and cooling rate of 5 C/min. The samples were heated up to a maximum temperature of 200 C, held there for 3 min and then allowed to cool to room temperature to analyze the non isothermal crystallization behaviour of PP phase. In order to avoid the influence of thermal history, the melting behaviour and percentage crystallinity of PP phase were determined during second heating of the samples to 200 C. The melting and crystallization behaviour of PP, neat blend, MFB and MFC were recorded. The thermal properties such as, melting temperature (T m ), heat of crystallization (ΔH f ), percentage of crystallinity (X c ), onset and peak crystallization rate temperatures (T o and T p, respectively), undercooling temperature (ΔT c, difference between melting and crystallization temperature), maximum crystallization time (t max, time required to crystallize from T o to T p ) and half crystallization time (t 1/2 ) were obtained from the DSC scans for describing the non isothermal crystallization behaviour of these four samples. The crystallinity of the PP component was determined using the relationship,

13 Materials and Methods 113 H f Xc H 100 w 0 f (2.2) ΔH f is the heat of fusion of the PP phase in the sample. The value 0 of ΔH f which is the heat of fusion of 100% crystalline PP was taken as 207J/g [1, 2] and w is the mass fraction of PP in the blend/composite Thermogravimetric analysis The thermal degradation studies of the samples from PP/PET system and LDPE/PET system were carried out in Perkin - Elmer TGA analyzer. The samples were degraded under nitrogen flow (30 cm 3 /min) in the thermobalance under dynamic condition at the heating rate of 10 C/min.The samples were scanned from room temperature (28 C) to 700 C. The thermal degradation kinetics of the MFBs and MFCs was analyzed using the Horowitz and Metzger [3] method to estimate the activation energy required. In this method the activation energy was calculated using the equation 1 Ea ln [(ln(1 ) ] = Ea 2 RT max (2.3) where, is the decomposed fraction of the sample, Ea is the activation energy, T max is the temperature at which the rate of weight loss is maximum. R is the universal gas constant J/mol K, and given by (T-T max ) in K Solvent sorption experiments For solvent sorption studies, rectangular samples of size 10 mm X10 mm were cut from the moulded samples of LDPE, neat blends and

14 114 Chapter 2 MFCs. The edges of the samples are slightly curved to obtain uniform absorption. The thickness of each samples were measured. The samples were fully immersed in xylene and kept at different temperatures 30, 50 and 70 C respectively. At specific time intervals the specimens were removed from the solvent one at a time. The excess solvent on the surface was removed using tissue paper and then weighed. The process was continued until the increase in weight of the solvent reaches equilibrium. The mole percent uptake Q t for solvent was determined using the formula Q t Mass of solvent sorbed Molar mass of solvent Mass of polymer % X 100 (2.4) The molar mass of xylene was taken as 106. The sorption data was evaluated by plotting the mole percentage uptake of the blends and composites versus square root time. The diffusion and permeability coefficients were then calculated. Reference 1. Jose S, Aprem AS, Francis B, Chandy MC, Werner P, Alstaedt V, Thomas S. Eur. Polym.J. 2004: 40; Zhang G, Fu Q, Shen K, Jian L, Wang Y. J Appl. Polym. Sci. 2002: 86; Horowitz HH, Metzger G. Anal.Chem. 1963:35; 1463.