experimental techniques -...
TRANSCRIPT
2.1. Materials
2.1.1. Natural rubber (NR)
N atural rubber, ISNR5, (Indian Standard Natural Rubber-5) was supplied by
the Rubber Research Institute of India, Kottayam. NR, and NR8 are
obtained by mastication of NR for 3 and 8 min, respectively. The physical
characteristics of natural rubber are given in Table 2.1. The rubber from the
same lot has been used in a particular experiment, since the basic properties
such as molecular weight, distribution and the contents of the non-rubber
constituents of NR are affected by clonal variation, season, use of yield stimulants
and methods of preparation [1,2].
2.1.2. Poly(methy1 methacrylate) (PMMA)
Poly(methy1 methactylate) (PMMA1) was synthesised in our laboratoty by
polymerising methyl methactylate using benzoyl peroxide. PMMA2 was supplied
by Gujarat State Fertiiiser Corporation Limited. The characteristics of PMMA
used are given in Table 2.1.
2.1.3. Graft copolymer (NR-g-PMMA)
Graft copolymer of NR and PMMA was prepared in our laboratory by
polymerising methyl methacrylate in the presence of natural rubber latex using a
redox initiator. NR latex particles were swollen with thk.:rqonomer, methyl , %\,,
,<\., methacrylate, which is then polymerised [3]. Cumene &dr+eroxide and 5'' 4 ,
tetraethylene pentammine were the initiator systems which . . pep i t . . the^?^;.' .,. - .- ~ ~
, - . ..
polymerisation to go to completion at room temperature. The NR latex stability
was maintained by the addition of oleic acid with monomer to the ammoniated
NR latex. The graft was purified by fractional precipitation method. Free
PMMA and NR were removed using acetone and petroleum ether respectively.
The purified graft copolymer was dried in vacuum oven for a period of 48 h.
NR-g-PMMA5 and NR-g-PMMAlo were obtained by the mastication of graft
copolymer for 5 and 10 min, respectively. The characteristics of the various graft
copolymers are given in Table 2.1
Table 2.1. Characteristics of the polymers.
Materials -
Density Solubility Molecular ~ w f i n (dcm3) parameter weight
(caycm3)" (Rw)
2.1.4. Solvents
Toluene and chlorobenzene (supplied by the BDH chemicals) distilled and
dried over CaC12 were used. The other solvents acetone, chloroform and
petroleum ether were of analytical grade.
2.1.5. Chemicals
Dicumyl peroxide and tetraethylene pentammine were supplied by RT
Vanderbilt Company, No~walk, USA. Benzoyl peroxide was obtained from BDH
Chemicals Limited.
2.2 Preparation of the blends
2.2.1. Solution cast blends
Binary blends of NR and PMMA with and without graft copolymer were
prepared by solution mixing technique. The polymer components were
dissolved in toluene at a total concentration of 5 % and stirred for about 16 h
using a magnetic stirrer at ambient temperature. The polymer solution was cast
into films and dried at about 1lO"C for several weeks in a vacuum oven to
eliminate the solvent. The solution cast NFUPMMA blends with 0 , 30, 50, 60, 70
and 100% NR are denoted by No, N,, Nw, N,, N,, and Nlm, respectively.
50150 NRPMMA blends with 0, 5, 10 and 1 5 % graft copolymer were denoted by
ON,, 5N50. ION, and 15N,, respectively.
2.2.2. Melt mixed blends
Samples were also prepared by melt mixing the components. Melt mixing
was carried out using a Brabender Plasticorder-PLE 651 at a temperature of
160°C and at a rotor speed of 80 rpm. PMMA was melted for two minutes and
blended with NR for another two minutes. Finally compatibiliser was added and
blended for another four minutes. The molten mixture was removed from the
Brabender mixing bowl, sheeted on a mill and compression moulded into thin
sheets of 2 mm thickness. NFUPMMA melt blends with 0, 50, 70 and 100% of
NR are denoted by No, N',, N'70 and N',oo, respectively. The dynamically
vulcanised blends using DCP and sulphur are denoted by D . The 50150
NRiPMMA melt blends with 0, 5 and 10% graft copolymer are denoted by ON'%,
5N', and ION',, respectively.
2.3. Morphology of the blends
Scanning electron microscopy has been found to be a valuable tool in
studying the phase morphology of high impact strength of blends PP and EPDM
[41.
The morphology of the sample was examined under optical (Inco
Ambala) and scanning electron microscopies (Joel 35 CF). For SEM studies,
samples were fractured under liquid nitrogen and examined under the
microscope. Thin films of 1 0 pm thickness were used for optical microscopy
studies.
2.4. Viscosity measurements
Interactions in binary polymer systems by viscomehy have been reported
by Kulshreshtha et al. [5 ] . The relative viscosities of the polymer solution of
different concentrations and their mixtures were determined by Ubbelodhe type
viscometer (Schott Gerate AVS 400 viscometer). The measurements were
carried out at constant temperature of 28.9 +. 0.010C and was achieved in a
water bath with a thermostat (Schott Gerate CT 145012 thermostat). Blends of
NR and PMMA having 100, 70, 50, 30 and 0% PMMA at maximum
concentration of 0.1 g/dm3 in toluene were prepared for viscometric
experiments.
2.5. Phase separation experiments
Phase separation experiments were carried out by preparing the solution
of 50150, 60140 and 70130 W M M A in toluene with and without the addition
of graft copolymer. The blend solution was stirred for 12 h and kept standing.
The sample was examined for phase separation as a function of time and graft
copolymer concentration. The volume fraction of the phase separated PMMA
layer was measured at different time intervals and graft copolymer concentration.
The experiment was repeated with chlorobenzene solvent, with graft and
homopolymers of various molecular weights and also by changing the mode of
addition of the graft copolymer. Similar phase separation experiments have been
reported by Molau et al. [6,7]
2.6. Mechanical properties
2.6.1. Tensile strength
Tensile strength and elongation at break of the samples were measured at
25°C according to ASTM D6.38 specification using dumb-bell shaped test pieces
at a cross head speed of 500 m d m i n using a Zwick U n i v e ~ l testing machine.
The Young's modulus were determined from the linear portion of the stress-
strain curve.
2.6.2. Tear strength
The tear strength of the sample was determined according to ASTM
D624-81 using 90" angle test pieces. The temperature and cross head speed
used are the same as that for tensile strength measurements.
2.6.3. lzod impact strength
The izod impact strength of samples was measured according to the
ASTM D256 test method. The dimensions of the specimen used were 6.13 x
1.20 x 1.23 cm. The impad energy was obtained by the difference in the
potential energy of the falling hammer before and after impact.
2.6.4. Morphology of the failure surface
Scanning electron microscopy (SEM) has been successi~ib used for
studying the failure surface of rubber composites 18). The SEM observations of
the tensile and tear failure surface were made using scanning electron
microscope. The failure surfaces of the test sampler were carefully cut and
sputter coated with gold and then examined under the microscope.
2.7. Rheological properties
2.7.1. Measurements
The rheological studies were carried out using a capillay rheometer
attached to a Zwick Universal Testing machine model 1474. The capillay used
was made of tungsten carbide and has an Vd ratio 40 and an angle of entry 180".
The sample for testing was placed inside the barrel of the extmsion assembly and
forced down to the capillay with a plunger attached to the moving cross head.
The studies were carried out in the shear range of 1.6 to 833 s-'. The
temperature controller provided the facility to increase the temperature
gradually across the length of the barrel. W~th a single charge of the material the
machine was operated to give nine dierent plunger speed. A warm up period
of 3 min was given to the sample before starting the experiment. The melt was
extruded through the capillary at preselected speed of the cross head. The
forces corresponding to specific plunger speed were recorded using a strip chart
assembly. The force and the cross head speed were converted into shear stres
(T,) and shear rate (f,) at wall, respectively using the following equations
involving the geometry of the capillary and the plunger
where F = force applied a t a particular shear rate
A, = cross sectional area of the plunger (mm2)
6 = length of the capillary (mm)
dc = diameter of the capillary (mm)
Q = the volume flow rate (mrn3/s)
Q is calculated from the velocity of the cross-head and the diameter of the
plunger. The flow behaviour index n' is defined by
and was determined by regression analysis of the values of rw and Y,, obtained
from the experimental data. The apparent wall shear rate (yw,) was calculated as
32Q/nd;. The shear viscosity q was calculated using the equation
Rheological measurements were carried out at temperatures of 130, 140 and
150°C.
2.7.2. Extrudate swell
The extrudates were collected from the capillary die and care was taken
to avoid any deformation. The diameter of the extrudate was measured after
24 h. of extrusion using a travelling microscope. The ratios of the diameter of
the extrudate to that of the capillary was calculated as the die swell (ddd,). The
distortion of the extrudate was studied by taking the photograph of the extrudate
at different shear rates.
2.7.3. Melt flow indices
The melt flow indices (MR) were determined using a Ceast melt flow
indexer model 6542 using 49.05 N load as per ASTM D 123873. The
measurements were made at 200, 210, 220 and 230°C for 50150, 60140 and
70130 W M M A blends with and without the addition of graft copolymer.
2.7.4. Morphology of the extrudate
Morphological characterisation of the extrudate was performed using
scanning electron microscope. The blends with 0, 10 and 15% of graft
copolymer was fractured under liquid nitrogen and examined under scanning
electron microscope. The influence of annealing on the morphology of the
blends has been studied. The blends with 0 and 10% graft copolymer were
annealed by keeping it inside the barrel of the MFl apparatus for 1 h at 220°C
and then extruded. The extrudates before and after annealing were fractured
under liquid nitrogen and the morphology was examined by scanning electron
microscope.
2.8. Thermal analysis
2.8.1. Dynamic mechanical analysis
The dynamic mechanical properties of the NR, PMMA and NRIPMMA
blends were measured using a Rheovibron DDV-IIIC. Moulded samples of
dimensions 7 x 1 x 0.5 cm were used for testing. The samples were tested at a
strain amplitude of 0.0025 cm and at a frequency of 35 Hz. The heating rate of
the sample was 1°C rise in temperature per minute. The complex modulus E"
was calculated with a microcomputer using the following equation.
(L + AL) 1$ E* - - dy nes/cm2
8 x S x A ( D - K )
where F = dynamic complex modulus
L = length of the sample between the clamps
AL = oscillating displacement
S = cross sectional area of the sample
A = amplitude factor
D = value of dynamic force dial
K - - error constant.
The storage modulus E' and loss modulus E are obtained from EH and F
using the following equations.
E - - F S i n 6
E' = F C o s 6
The loss tangent
tan 6 = F I E '
2.8.2. Differential scanning calorimetry
Perkin-Elmer differential scanning calorimeter was used to study the
thermal behaviour of NR. PMMA and W M M A blends with 0, 5 and i C % graft
copolymer. The samples were inserted into the apparatus at room temperature
and immediately heated to 200°C at a rate of WCImin and kept for 1 min at thii
temperature. The samples were quenched to 80°C at a rate of 320"C/min. The
DSC scan was made from -80 to 1lO"C at a heating rate of 1O0C/rnin in the
presence of helium atmosphere.
2.8.3. Thermogravimetry (TG)
Therrnogravimety and derivative thermogravimeby (DTG) were carried
out in a Schirnadzu D T 4 , thermal analyser in nitrogen at a heating rate of
1O0Urnin.
References
1. Subramanyam, A. Rubber Chem. Technol. 1972,15,346.
2. Subramanyam, A. Proc. of the RRIM Planters Conference, Kualumpur, 1971, p. 225.
3. Bloomfield, G. F. and McL Swift, P. J. Appl. Chem. 1955,5, 609.
4 . N. M. Mathew and S. K. De Polymer 1982,23,632.
5 . Kulshreshtha, A. K.; Singh, B. P. and Sharma, Y. N. Polym. J. 1988,24,29.
6 . Molau, G. E. J. Polym. Sci. Part A 1965, 3, 1267.
7 . Molau, G. E. J. Polym. Sci. Part A 1%5, 3,4235.
8. Bas.com, W . D. Rubber Chem. Technol. 1977,50,327.