Plastics Testing Processing and Flow Properties

49
Md. Mohsin Alam 1

Transcript of Plastics Testing Processing and Flow Properties

Page 1: Plastics Testing Processing and Flow Properties

Md. Mohsin Alam 1

Page 2: Plastics Testing Processing and Flow Properties

Melt Flow IndexMelt Flow Index

Md. Mohsin Alam 2

ASTM D 1238It is defined as the rate of flow of plastic material through a standard die under the specified conditions of temp. & pressure. It is expressed in gms /10 minutes. For different plastic, temp. & pressures are different.

&The amount of thermoplastics resin, measured in grams, which can be forced through a specified orifice within ten minutes when subjected to a specified force. Significance:

It helps o distinguish between different grade of polymerHigh molecular weight polymer is more resistance to flow than low molecular wt.High flow grade material gives better gloss than low MFI.

Page 3: Plastics Testing Processing and Flow Properties

Capillary Type

Melt Flow Index Test (MFI)

Definition: Rate of extrusion of a resin in molten condition under specified temperature and pressure through a specified size of die in 10 min is defined as melt flow index. The unit of MFI is g/10min.

Significance:

•The reported melt index values help to distinguish between the different grades of a polymer.

•A high molecular weight material is more resistant to flow than a low molecular-weight material

•It can also be useful for other purposes like studying the relative thermal effect with respect to barrel residence time on plastics

Md. Mohsin Alam 3

Page 4: Plastics Testing Processing and Flow Properties

Test Methods: ASTM D 1238, ISO 1133, DIN 53735

Test Specimen: The test specimen should be in the form of powder, granules, strips or film or moulded slugs.

Test Apparatus:

Md. Mohsin Alam 4

Page 5: Plastics Testing Processing and Flow Properties

Test Procedure: Place the thermometer on the hold provided. The set temperature stabilizes for 5 min. than charge the material using tool without any air gap. Then apply the load over the piston. Allow some time for material to melt and soften and purge the material upto the lower mark of the piston. Then start the stopwatch and start cutting off the extrudate depending upon the flow.

Calculations: 30 Sec., 1 min, 3 min, or 6 min intervals and tabulate the weight of the extrudate.

Flow rate = (m/t) x 600

Where m = mass of extruded, t = time of piston travel for length L. (sec), 600 = conversion factor to convert in sec.

Md. Mohsin Alam 5

Page 6: Plastics Testing Processing and Flow Properties

Material Temperature Load, Kg Acetal (Homo & Copolymer) 190 2.16/1.05 PMMA 230 1.2/3.8 ABS 200 and 230 5.0 and 3.8 Cellolose esters 190 and 210 0.325/2.16/21.6 Nylon66 275 0.325 Nylon6 235 1.0/2.16/5.0 PCTFE 265 12.5 PE 125 0.325/2.16 190 0.325/2.16/10/2.16 310 12.5 PC 300 1.2 PP 230 2.16 PS or HIPS 190 5.0 200 5.0 230 1.2/3.8 Polyterepthalate 210 2.16 250 2.16 285 2.16 PPS 315 5.0

Table: Temperature and load for MFI test

Md. Mohsin Alam 6

Page 7: Plastics Testing Processing and Flow Properties

Factors Influencing:

1. Preheat Time. If the cylinder is not preheated for a specified length of time. This causes the flow rate to vary considerably.

2. Moisture. Moisture in the material, especially a highly pigmented one, causes bubbles to appear in the extrudate. The weight of the extrudate is significantly influenced by the presence of the moisture bubbles.

3. Packing. The sample resin in the cylinder must be packed properly by Pushing the rod with substantial force to allow the air entrapped between the resins Pellets to escape. Once the piston is lowered, the cylinder is sealed of air can escape. This causes variation in the test results.

4. Volume of Sample. In order to achieve the same response curve. Repeatedly, the volume of the sample in the cylinder must be kept constant. Any change in sample volume causes the heat input from the cylinder to the material significantly

Md. Mohsin Alam 7

Page 8: Plastics Testing Processing and Flow Properties

Physical form of test materials Preferably pellets or performs (thermoplastics) samples charges – 2.0 – 8 g

Test equipment Extrusion plastometer Test Condition Dead load on piston varying from polymer

to polymer and Temperature varying from polymer to polymer

Measuring range Test observation are made between two specified scribe marks on the piston

Measurement Extrude cut at uniform time intervals are taken and weighed

Conclusion

Melt flow index as the weight of extrudate (average in 10 min is calculated and reported.

Summary of test specimen for MFI

Md. Mohsin Alam 8

Page 9: Plastics Testing Processing and Flow Properties

Capillary Rheometer (Viscometer) Test

Definition: The flow rates are measured at a single shear stress and a shear rate performed at one set of temperature and geometric conditions.

The capillary rheometer measures apparent viscosities or melt index over an entire range of shear stresses and shear rates encountered in compression molding, calendaring, extrusion, injection molding and other polymer melt processing operation.

Significance and Use: The melt flow index measurements takes accounts of the behavior of polymer at only one point, it is quite possible for two materials with the same melt index values to behave completely different at shear rate and shear stress.

Md. Mohsin Alam 9

Page 10: Plastics Testing Processing and Flow Properties

Molecular characteristics, shear instability, degradation due to mechanical and thermal effects and evaluation of additives (processing aids) on processing of polymer can be studied. Commercially available capillary rheometers are capable of operating at shear rates up to 25000 S-1, which is within the range of shear rates, encountered in actual processing. Rheometers up to a shear range 107 S-l have been developed.Rheological data generated can be very useful in optimizing processing: conditions and improving product quality. Material, output and problems related to processing like die swell, melt fracture etc. can also be studied.Molecular characteristics, shear instability, degradation due to mechanic thermal effects and evaluation of additives (processing aids) on process ability of polymers can be studied.

Md. Mohsin Alam 10

Page 11: Plastics Testing Processing and Flow Properties

The capillary rheometer is consisting of an electrically heated cylinder, a pressure ram, temperature controller, timer and interchangeable capillaries. The plunger can be moved at a constant velocity that translates to a constant shear rate. The forces to move the plunger at this speed is recorded which determines the shear stress.The sample material is placed in the barrel of the extrusion assembly, brought to temperature and force out through a capillary. The forces required moving a load cell detect the plunger at each speed.

Test Method: ASTM D 3835-93a Test specimen:

The specimen may be in any form that can be introduced into the bore of the cylinder such as powder, beds, pellets, strips or film. In case of preformed plugs, any application of heat to the sample must be kept to a minimum and shall be held constant for the entire specimen.

Md. Mohsin Alam 11

Page 12: Plastics Testing Processing and Flow Properties

Table-4: Recommended Test Temperature for different thermoplastics

Material Typical Test Temperature °C Acetal 190 Acrylics 230 Acrylonitrile-butadiene-styrene 200 Cellulose esters 190 Nylon 235 – 275 Polychlorotrifluoroethylene 265 Polyethylene 190 Polycarbonate 300 Polypropylene 230 Polystyrene 190 – 230 Poly (vinyl chloride) 170 – 205 Poly (butylenes terephthalate) 250 Thermoplastic elastomers (Unsaturated) 150 – 210 Thermoplastic elastomers (Saturated) 150 – 210 Test Apparatus: The capillary rheometer is consisting of an electrically heated cylinder, a pressure ram, temperature controller, timer and interchangeable capillaries. The plunger can be moved at a constant velocity that translates to a constant shear rate. The forces to move the plunger at this speed be recorded which determines the shear stress.

Md. Mohsin Alam 12

Page 13: Plastics Testing Processing and Flow Properties

Procedures: Select test temperature shear rates and shear stress accordance with material specification Replace the die and piston in the barrel and allow the assembled apparatus to reach thermal equilibrium.The sample material is placed in the barrel of the extrusion assembly, brought to temperature and force out through a capillary. The charging of materials should be done within 2 min.Place the piston movement until the full melt time reached. Reactivate the piston to start extrusion. After reached steady state operation, record the force and collect the data. The data can be collected by•Run a constant rate test (or a constant shear stress test)•Run a multiple rate of multiple stress level test

Md. Mohsin Alam 13

Page 14: Plastics Testing Processing and Flow Properties

13

4( ) Qsr

Where, = shear rate (sec-1); Q = flow rate (in3/sec.)

1( . ) Shear stressPa sShear rate

Apparent melt viscosity (poise)

2( )2

rFPaR l

Where, = shear stress (psi); F = Load on the ram (lbs); r = radius of capillary orrifcae (in); R= radius of the barrel (in); l = length of capillary orriface (in).

Calculations:

Md. Mohsin Alam 14

Page 15: Plastics Testing Processing and Flow Properties

Shear stress versus shear rate and melt viscosity versus shear rate curves can be plot for the capillary viscometer as given in Fig

0 1 0 2 0 3 0 4 0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

P c fo r fa te s t sh e a r r a te

F a te s t S h e a r R a te

S lo w e s t S h e a r R a te

L e n g th /D ia m e te r R a t io

Fig. 12: The true graph for capillary viscometer Md. Mohsin Alam 15

Page 16: Plastics Testing Processing and Flow Properties

Factors Influencing and Correction factor:

Capillary Calibration: The apparent viscosity varies with the fourth power of r, it is desirable to know this value within 0.00762 mm.

Piston friction: The frictional force is negligible compared to the pressure drop through the capillary. The frictional force should be subtracted from force reading.

Polymer back flow: The clearance between the plunger and the barrel may permit a small amount of melt to flow along with the piston instead of through the capillary. Due to this the true shear rate to be lower than that calculated from the piston velocity. Melt compressibility: As the hydrostatic pressure diminishes along with the capillary, the fluid density decreases and the flow rate increases. This results in an increase in shear rate. If the compressibility of the material is known can be corrected. Md. Mohsin Alam 16

Page 17: Plastics Testing Processing and Flow Properties

Barrel Pressure Drop: Under isothermal condition, the pressure drop of Newtonian materials varies:

41

2

B

C

P L RP L r

Determining True Shear Stress: To obtain true shear stress, perform the following procedure: using a minimum of two dies having same entrance angle and same diameter (D) of different capillary length (L). At least one L/D ratio should be less than 16 and one should be more than 16. Obtain the true shear stress using the following equation

( ) ( )4 4

c c

B

P P D F F DL LA

Where, = Ture shear stress, P = Melt pressurePc = the intercept between shear rate, D = dia meterL = Die length, Ab = Cross section area, Fc = Bagley plot

Where LB refers to the rheometer barrel length and LC to the capillary length.

Md. Mohsin Alam 17

Page 18: Plastics Testing Processing and Flow Properties

Test Specimen Forms – Granules, powder, strips etc. Important equipment dimensions Barrel diameter 6.350 – 12.700 0.007mm Capillary (Die) (i) Diameter is such that barrel to capillary

diameter ratio is between 3 to 15 (ii) length to diameter ratio of capillary

between 4 to 40 (iii) Piston – 0.02540.007mm clearance

between piston land and barrel Measurements At specified temperature and steady state

operation (constant application of forces; the forces on piston, material output and its times are recorded.

Test run Time ~ 10 min Conclusions Consistency in melt viscosities or viscosity

change with time is calculated and reported.

Summary of test specification for measurement of rheological properties using capillary rheometer

Md. Mohsin Alam 18

Page 19: Plastics Testing Processing and Flow Properties

Rotational Rheometer

Rotational viscometer consists of two basic parts separated by the fluid being tested. The parts may be concentric cylinder (cup and bob), plats, a low angle cone and a plate, or disk, paddle or rotor in a cylinder. Rotation of one part against the other produces a shearing action on the fluid. The torque required to produce a given angular velocities resulting from a given torque is a measure of the velocity. Rotational viscometers are more versatile than capillary viscometers. They can be used with a wide range of materials since opacity, settling and non-Newtonian behavior do not cause difficulties. Cone and Plate Geometry

Parallel Plate Geometry

Co-axial Viscometer

Concentric Cylinder Viscometer Md. Mohsin Alam 19

Page 20: Plastics Testing Processing and Flow Properties

Cone and Plate Geometry 1. The principle of the cone and plate rheometer is, it

consists of flat circular plate and liner concentric cones are rotated relative to each other.

2. The test material is placed in the space between the plate and cone. The major advantage of the instrument is constant shear rate application on the test fluid, requirement of small sample size and hence less heat built up at high shear rates than with a concentric cylinder apparatus.

3. The disadvantage other than low shear rate range of the test is the tendency for the development of secondary flows in the polymer, which affects the accuracy of the measurement.

Md. Mohsin Alam 20

Page 21: Plastics Testing Processing and Flow Properties

9.3.1.2.1 Cone and Plate Geometry

For Newtonian fluid, the basic equations for the cone and plate rheometer are:

3

32MR

dvdr

3

32MR

R = Radius distance of the sample in cone and plate

= Angle in radian which cone makes with the flat plate

M = Torque required to rotate the cone relative to the plate of an angular frequency of

Md. Mohsin Alam 21

Page 22: Plastics Testing Processing and Flow Properties

Parallel Plate Geometry 1. Parallel plate geometry consists of a stationary and a

rotating flat circular plate wherein a thin layer of the sample is placed between them for the test.

2. The gap width can be varied in this viscometer. This is an advantage when suspension or dispersion with large particles or with a tendency to fly out the gap.

3. However, the velocity, the shear rate, varies with the distance from the center of the plate. This makes viscosity data more difficult to evaluate.

4. Maximum shear rate at plate rim) is given by

mRh

Where, R is the radius of the plate and h the distance between the two plats. The velocity given by:

3

3 ln1 32 ln

M d M

R d

Md. Mohsin Alam 22

Page 23: Plastics Testing Processing and Flow Properties

9.3.1.2.3 Co-axial Viscometer It consists of two cylinders, one within the other (cup and bob) with the sample between them.

2 2

1 14 i o

M kMh R R

Where, M is the torque on the inner cylinder, h is the length of the inner cylinder, is the relative angular velocity of the cylinder in radius per seconds Ri the radius of the inner cylinder wall, Ro the radius of the outer cylinder wall and k an instrument constant.The shear rate can be given by

2 22

2 2

2 / i o

o i

r R R

R R

Md. Mohsin Alam 23

Page 24: Plastics Testing Processing and Flow Properties

Where r is any given radius. The shear stress is given by:

22Mr h

Co-axial Viscometer

The viscosity of Newtonian liquid may be determined from the above equation or from slope of a shear stress –shear rate plot. Non-Newtonian fluid gives intercepts and curves with such plots.

Md. Mohsin Alam 24

Page 25: Plastics Testing Processing and Flow Properties

Concentric Cylinder Viscometer

1. The test material (fluid state) is placed in the annular spaces between two cylinders.

2. The cylinder is rotated at a constant speed, while a transducer measures the torque acting on it.

3. The major advantage of concentric cylinder geometry is that a nearly constant shear rate is maintained throughout the entire volume of fluid being tested.

4. This is important in the case of non-Newtonian fluid since viscosity may be strongly dependent upon the rate of shear. The relationship of viscosity () to the ratio of ‘’ and ‘’ is shown below:

Where K is the instrument constant. k

Md. Mohsin Alam 25

Page 26: Plastics Testing Processing and Flow Properties

Brookfield Viscometer Definition:

The viscosity defines the flow behaviour of plastisol under low shear. This viscosity relates to the conditions encountered in pouring, casting, molding and dipping process. The Brookfield instrument is a commercially used rotating spindle type viscometer.

Significance:

The suitability of a dispersion resin for given application process is dependent upon its viscosity characteristics. The test standard for viscosity measurement of plastisols / organosols, epoxy resin and emulsion etc.

Test Methods:

ASTM D-2393, ASTM D 1824 and ISO 2555. Md. Mohsin Alam 26

Page 27: Plastics Testing Processing and Flow Properties

Procedure:

1. Select the spindle in middle or upper portion of viscometer dial at the highest rotational speed to be used. Insert the spindle approximately at 45° angle. Move the sample so as to center the spindle, adjust the depth to the immersion mark.

2. Start the viscometer at its lowest speed. Allow it to run 2 min. record the scale reading during the next rotation.

3. Placing it in a constant temperature bath at the specified test temperature preconditions the sample. The proper size spindle is allowed to rotate in the sample for 30 sec. The instrument is stopped through the use of a clutch and the reading is taken from the dial. The test is repeated until a constant reading is obtained. Record the sample temperature at the conclusion of viscosity reading. Md. Mohsin Alam 27

Page 28: Plastics Testing Processing and Flow Properties

Range (cP) Spindle Speed (rpm) Factor 100-400 1 20 5 400-800 1 10 10

800-1600 2 20 20 1600-3200 2 10 40 3200-4000 3 20 50 4000-8000 4 20 100 8000-16000 4 10 200 16000-20000 3 4 250 20000-40000 4 4 500 40000-80000 4 2 1000

80000-160000 5 2 2000 160000-200000 6 4 2500 200000-400000 6 2 5000 400000-800000 7 4 10000 800000-2000000 7 2 20000

Conversion table from centipoises to factor

Md. Mohsin Alam 28

Page 29: Plastics Testing Processing and Flow Properties

Torque Rheometer (ASTM D-2396 ) Definition:

A torque rheometer measures flow properties of materials in a miniature form of typical processing equipment. The capabilities of the sensors used with a torque rheometer are as follows:

1. (i) An internal mixer with roller blades measures flow properties of resin

2. (ii) A single-screw extruder with different types of dies providing a measures of the absolute viscosity of the material

3. (iii) A twin-screw extruder, which provides information on compounding characteristics of resins.

Md. Mohsin Alam 29

Page 30: Plastics Testing Processing and Flow Properties

Significance:

The ability of PVC granules to accept a plasticizer and become a dry free flowing powder is related to the internal pore structure of the resin, resin temperature, plasticizer temperature and the plasticizer used. The abs option of plasticizer in PVC can be detect using this method.

Test Method: ASTM: D2396-94

Test Specimen: The specimen should be in powder form and plasticizer will be liquid form.

Conditioning: Maintain the PVC and plasticizer at 23 1°C and 50 5% relative humidity for all time after mixing and throughout the period of determination.

Md. Mohsin Alam 30

Page 31: Plastics Testing Processing and Flow Properties

Test Apparatus:

A torque rheometer is a device consisting of a drive, a torque (viscosity) measuring system, a sensor, a temperature control unit and a data recorder. The sensors available are batch mixers, single/twin-screw extrusion sensor with post-extrusion line and continuous mixing, compounding and extrusion sensors with post extrusion systems. The sigma Mixture is shown in Figure

Md. Mohsin Alam 31

Page 32: Plastics Testing Processing and Flow Properties

Procedure:

• A sample of material to be tested is placed in the mixing head where it is subjected to shear by means of two rotating blades.

• These methods determine the powder mixing characteristics of the polyvinyl chloride. The test requires the use of a torque rheometer measuring head as shown in fig. The mixture is heated either electrically or oil circulating heat transfer jacket. In order to obtain consistency, a standard formulation is established as follows:

PVC resin : 225 g 0.1g

Filler : 15.75 g 0.1g

Basic Lead carbonate : 22.50 g 0.1g

DOP plasticizer : 117.00g 0.1gMd. Mohsin Alam 32

Page 33: Plastics Testing Processing and Flow Properties

• Because of lot-to-lot variations in the quality of plasticizer, and basic lead carbonate, it is recommended that the laboratory maintain a large enough inven tory of these additives to establish control standards. A standard powder-mix curve should also be generated using standard additives and kept on file for com parison purposes.

Temperature : 88 1°C

Mixer Speed : 63 1 rpm

Material Weight : 380g 10g

• The sample material is also subjected to high temperatures. The dynamometer is suspended freely between two bearing blocks.

• The shear rate, measured by the angular velocity of the rotors, is set according to a tachometer.Md. Mohsin Alam 33

Page 34: Plastics Testing Processing and Flow Properties

• All ingredients except the plasticizer are weighed into the container and mix thoroughly. The mixer is preheated and allowed to run at a specified speed for 30 min to obtain equilibrium conditions. All dry additives are added to the mixer and allowed to mix for 5 min. next, the plasticizer is poured quickly into the mixer and mixing is continued for 10 min. beyond the dry point. • The torque rheometer serves dual purpose of providing constant torques drive for the extruder screw and simultaneously recording the torque on the screw. The instrument responds to the reaction torque encountered by rotating the extruder screw. The instrument accommodates a number of interchangeable mixer and extruder attachments.• The measuring head rotors encounter a resistance torque from the test material that causes the dynamometer to rotate in the opposite direction. • The measuring head is either electrically or oil heated.

Md. Mohsin Alam 34

Page 35: Plastics Testing Processing and Flow Properties

Case Study for PVCTest Condition

Speed : 60 rpm, Mix Temperature : 180°C-195°C, Start Temperature :180°C, Test Time : 55 Min, Sample Weight : 60 gm

Md. Mohsin Alam 35

Page 36: Plastics Testing Processing and Flow Properties

9.3.2 Flow Properties of Thermosetting Materials

Factor Affecting Flow:

1.    Resin Type: All resin flow differently because of basic differences in the structure of the polymer e.g. melamine formaldehyde exhibit longer flow than urea formaldehyde.

2.       Type of filler: The small particle size filler e.g. wood floor, mica, and minerals creates less turbulence and less frictional drag during mold filling. The size of the glass fibre and long fibre can adversely affect the flow.

3.   Storage Time: All resins have a natural tendency to polymerize in storage, causing partial precure, which reduces flow.

36Md. Mohsin Alam

Page 37: Plastics Testing Processing and Flow Properties

9.3.2.1 Cup Flow (ASTM D 731)

9.3.2.1.1 Definition: The measurement of the molding index of thermosetting plastics ranging in flow from soft to stiff by selection of appropriate molding pressure within the range from 4.1 to 31.9 MPa

9.3.2.1.2 Significance: This test is specifically designed for thermosetting molding compounds. This test is primarily useful for determining the minimum pressure required to mold a standard cup and the time required to close the mold fully. The material is molded using a mould of specified cup-shaped cavity dimensions. The method provides the guide for evaluating the mold ability of thermosetting powders.

9.3.2.1.3 Test Methods: ASTM D 731

37Md. Mohsin Alam

Page 38: Plastics Testing Processing and Flow Properties

9.3.2.1.6 Test Apparatus: The test apparatus shown in Figure

38Md. Mohsin Alam

Page 39: Plastics Testing Processing and Flow Properties

9.3.2.1.7 Procedure:

1.       The rate of flow is sensitive to the condition of the mold surface. First two reading has to be discarded and after two successive reading the mold flow can be accepted. The preferred mold temperature is given below:

Phenolics: 165 1 °C

Melamine: 155 1 °C

Urea: 150 1 °C

Epoxy: 150 1 °C

Diallyl phthalates: 150 1 °C

Alkyd: 150 1 °C

39Md. Mohsin Alam

Page 40: Plastics Testing Processing and Flow Properties

# Take the weight and begin the test with proper load to close the mold to the fin thickness specified for the type of material. The load can be applied to the mold is as given below:

Total Load Molding Pressure (MPa)

1112 4.6

1601 6.6

1124 9.0

1686 13.6

2248 18.0

3372 21.2

4496 36.3

11120 45.4

40Md. Mohsin Alam

Page 41: Plastics Testing Processing and Flow Properties

# If a 2248 N load applied to make initial cup and required fin thickness is obtained, the next lower load 1686N is applied as indicated above. If the mold close to the required thickness again then next 1124 N load applied. If the mold then does not close, the ‘molding index’ is close to 1686 N load.

# The time of flow in seconds shell be measured from that the hydraulic gage indicates an applied load of 454 kg to the instant that the fin has reached 0.20 mm I thickness for material with an izod impact strength of 27 J/m of notch.

41Md. Mohsin Alam

Page 42: Plastics Testing Processing and Flow Properties

9.3.2.2 Spiral Flow

9.3.2.2.1 Definition: The spiral flow of a thermosetting molding compounds is a measure of the combined characteristics of fusion under pressure, melt viscosity and gelation rate under specific condition.

9.3.2.2.2 Significance: This is a high shear-rate test for thermoplastics and is widely accepted in the molding industry and quality control test. The test is performed on an injection-molding machine under specified condition and using a spiral-flow mould.

9.3.2.2.3 Test Method: ASTM D 3123-98

42Md. Mohsin Alam

Page 43: Plastics Testing Processing and Flow Properties

9.3.2.2.4 Procedure

Molding condition:

1. Temperature: A temperature of 1503°C shall be maintained on the mold and transfer plunger.

2. Transfer Pressure: The actual pressure applied to the compounds at the base of the pot shall be 6.900.17MPa.

3. Charges Mass: The mass of the compounds shall be determined empirically so that the thickness of the molded compounded on the top of the sprue plate of the mold.

4.  Transfer plunger speed: The transfer plunger speed without load shall be controlled between 25 and 100 mm/s.

5. Pressure Cure Time: sufficient cure time shall be used to facilitate easy removal of spiral from the mold.

43Md. Mohsin Alam

Page 44: Plastics Testing Processing and Flow Properties

MFI of polypropylene (g/10min at 230°C and 2.16 Kg load

Spiral flow (cm3) at 260°C barrel temperature, 700 kg/cm2 injection

pressure 1.7 25.0 3.0 32.0 5.6 36.0 10.0 46.25

9.3.2.3 Disc Flow Test

Resin Temperature (°C 5°C) Pressure (MPa 10%) Polyester 120 1.4

Epoxy 160 1.4 Silicones 175 1.4 – 6.9

1 2

1

( )100 w wFlow percentw

1 3

1

( 4 )100 w wFlow percentw

Spiral flow data of polypropylene.

44Md. Mohsin Alam

Page 45: Plastics Testing Processing and Flow Properties

9.3.3 For Elastomer

For vulcanisable compound a measure of the time to the incipient vulcanisation and rate of curing can be determined for elastomeric material using Mooney viscosity.

9.3.3.1 Mooney Viscosity

9.3.3.1.1 Definition:

Mooney viscosity is defined as the shearing torque resisting rotation of a cylindrical metal disk (or rotor) embedded in rubber within a cylindrical cavity.

9.3.3.1.3 Test Method: ASTM D 1646, ISO 289

45Md. Mohsin Alam

Page 46: Plastics Testing Processing and Flow Properties

9.3.3.1.2 Significance:

1.       By this method molecular mass and viscosity can be determined because rubber is non-newtonian fluid.

2. These mooney viscosities of polymers will normally relate to how they will be processed. Lower Mooney viscosity materials (30 to 50) will be used in injection molding, while higher Mooney products (60 to 80) can be more highly extended and used in extrusion and compression molding.

3. The onset for vulcanization can be detected by increase in viscosity. The curing rate also can be detected for rubbers.

4. Test Apparatus:

46Md. Mohsin Alam

Page 47: Plastics Testing Processing and Flow Properties

Type Rubber Test Temperature °C Running Time (Min) NBS 388 1000.5 or 1250.5 8 NR, BR, CR, IR, NBR, SBR 1000.5 4

BIIR, CIIR, IIR 1000.5 or 1250.5 8 EPDM, EPM 1250.5 4 Synthetic Rubber black master batches 1000.5 4

Compounded stock reclaimed material 1000.5 4

9.3.3.1.6 Procedure:

1. Select the rotor to be used and select the test temperature table given below:

1. Adjust the torque indicator to the zero reading while viscometer running in the unloaded condition with the rotor in place.

2. Remove the hot rotor and place the test piece and replace the viscometer and start the viscometer and recorder.

47Md. Mohsin Alam

Page 48: Plastics Testing Processing and Flow Properties

Scorch assessed by plasticity test on rubber sample when sample heated and an increase in stiffness with heating time was observed (The results shown in Fig.). Rate of cure is still assessed by vulcanising samples for various times and following the change in tensile properties, hardness, set, swelling etc

Determinations of scorch and cure characteristics

48Md. Mohsin Alam

Page 49: Plastics Testing Processing and Flow Properties

Md. Mohsin Alam 49