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Testing and Quality Control of Plastics Materials and
Products
MD. MOHSIN ALAM
1
With the advent of Science and Technology, the concept of testing is an integral part of research and development, product design and manufacturing.
Why we need testing? • To prove design concepts • To prove a basis for reliability • Safety • Protection against product liability suits • Quality Control • To meet Standards and Specifications • To verify the manufacturing process • To evaluate competitors products • To establish a history for new materials
Testing & Quality Control in Plastics Processing Industry
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Test Method A definitive procedure for the identification, measurement and evaluation of one or more qualities, characteristics or properties of a material, product, system or service that produces a test result.
Fundamental Aspects of Testing
Test Data Helps
• To determine the suitability of plastics for a particular application, for
quality control purposes or to obtain a better understanding of there
behavior under various conditions
• The physical property data obtained by testing is required to
design the product development and failure analysis.
• The testing data are required for to promote the use of plastics.
• Testing feed back helps to aid improved design or quality
control procedures.
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Fundamental Aspects of Testing
Quality Control Test
Quality control datas are useful for finding suitability of a material, design, and
product quality. It carries out the actual test, make use of test planning and
test data processing. The data processing helps In checking reproducibility
and accuracy of the test result.
Standard Method of Test
Standard methods of tests are required for evaluation
• Basic plastics molecule from laboratory level to the resin & the Product
• It helps product reliability.
• Liability registration
4
Fundamental Aspects of Testing
REASONS FOR TESTING
To ensure • Incoming raw material are acceptable and consistent quality. • Product of intermediate stages of manufacture are of an
acceptable and consistent quality. • End product of the overall process is of consistent and
acceptable quality.
To evaluate • New or competitive materials or modifications to a process. The fitness for purpose of a material, process or product.
To obtain • Early evidence of changes taking place in a process.
To prove• Design aspects. • Quality control and Safety
5
Types of Tests
The following are the major types of test:-
Analytical Test.
Material Characterization Test.
Material property test.
Product test.
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Types of Tests
Analytical tests are important for :-
Quality control
Development of new materials.
Product designing.
Process Optimization.
Major analytical tests are :-
Density and specific gravity test.
Water absorption test.
Moisture analysis.
Sieve Analysis.
7
Types of Tests
Material Characterization Test
Material characterization tests are used for:-• To identify the material • To determine chemical composition• To determine Structure • To determine Flow Behavior
Major Characterization Tests are• Melt Flow Test• Viscosity Test• Molecular Weight and Molecular Wt Distribution• Thermal Properties (TGA, DSC, TMA)• Spectroscopy• Microscopy 8
Types of Tests
The property datas of the material are the major resource for selection of material, process optimization and product and mould design.
The various properties of plastics materials are determined by standard test methods, such as ASTM, ISO etc.,
• The most common material property tests are:-• Mechanical properties.• Thermal Properties.• Electrical Properties.• Optical Properties.• Weathering Properties • Chemical Properties
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Types of Tests
Testing of plastics product is important for predicting
product performance.
This test can be carried out from test specimen prepared
by machining the products or the whole product.
Non Destructive Test
• Preferable where the product is very expensive and
which cannot be destruct.
• Ultrasonic and Radiography methods are Advanced
NDT 10
Standard and Specification
Standard and specification helps to develop common language for developers, designers, fabricators, purchasers and suppliers, End users.
Standard:- A technical document based on consolidated results of science, technology and experience approved by a standardizing body for the benefits of the people.
Standardization:- It is the activity giving solutions for repetitive applications to problems, essentially in the sphere of science, technology and economics aimed at the achievement of the optimum degree of order in a given contest.
Technical specification:- A document which lays down characteristics of a product or a service such as levels of quality performance, safety or dimensions
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Types of Standards
•Basic standard :- It contains general provisions for one particular field.
•Terminology standard:- It is concerned with terms, definitions, explanatory notes, illustrations, examples, etc.
•Testing standards:- A standard concerned exclusively with test methods, supplemented with other provisions related to testing such as sampling, statistical methods and sequence of testing.
•Product standard:- A standard specifying some or all the requirements to be met by a product.
•Safety standard:- A standard aimed at the safety of the people and goods.
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Bodies or Organization – Formulating Standards
INTERNATIONAL ORGANIZATION:-
• International Organization for Standardization (ISO):- In plastics field the principle body producing standard is ISO.•International Electrochemical Commission (IEC):- In electrical field IEC producing standards.
NATIONAL ORGANIZATION:-
British Standard Institution (BSI):- BSI was formed in 1901, producing standards in all fields.
American National Standard Institute (ANSI): ANSI is the premier standardization body in USA.
American Society for Testing & Materials (ASTM): ASTM is a Scientific & Technical Organization formed for the development of standards on characteristics and performance of materials, products, systems and services and promotion of related knowledge.
Deutsche Institute Fur Normung (DIN):- The German standard organization was formed in 1917 producing standards in all the fields in German language which published in English, French and Spanish also.
Bureau of Indian Standards (BIS):- BIS is engaged in developing national standards and their revision/review from time to time. 13
Aims of Standardization
Aims of standardization in general :-
• To achieve maximum overall economy in terms of Cost.
• To ensure maximum convenience in use – simplification, rationalization, interchangeability of parts, increased productivity, elimination of unnecessary waste and shortening of inventories.
• To adopt the best possible solution to recurring problems by use of scientific knowledge and technological developments.
• Standardization of sampling procedures, test methods, grading schemes and quality specification.
14
Quality & Standardization
•Quality is “ the totality of features & characteristics of a
product or service that bear on its ability to satisfy a given
need in an economical manner.”
• The objective of standardization is to ensure maximum
convenience in use by simplification, rationalization and
interchangeability of parts, increased productivity,
elimination of waste, shortening of inventories, etc.
15
Specimen Preparation
Manufacturing process
Orientation of the molecule chains, as they are created
in, e.g. an injection operation or during stretching (films, deep drawing), has
significant effect on the various characteristics. Other things which effect the
characteristics of the specimen are;
1.cooling speeds
2.Tool temperatures
3.injection speeds
4.curing temperatures
5.and times.
The manufacturing process of a test specimen can be standardized only for
molding materials. Tests on finished components always show the status of the
material at the location the specimen 16
Mechanical Properties
Fundamental to the understanding of a material’s performance is a knowledge of how the material will respond to any load.The important mechanical properties are
Tensile tests Flexural properties Compressive properties Creep properties Stress relaxation Impact properties Shear strength Abrasion Hardness tests
17
Tensile Strength
18
Tensile Strength
19
Tensile Strength
20
By knowing the amount of deformation (strain) introduced by a given load (stress), the designer can predict the response of the application under its working conditions.
Standard Test Method for Tensile Properties of Plastics (ASTM D 638),
IS-8453, JIS-7113, ISO-1184, BS-2782
Tensile Strength
21
Tensile Strength
22
Formula and Calculations
Force (load) (N)
(1) Tensile strength = --------------------------------------------------------- Cross-section area of the specimen (mm²)
Maximum load recorded (N)(2) Tensile strength at yield (N/mm²) = ----------------------------------------- Cross section area (mm²)
Load recorded at break (N)(3) Tensile strength at break (N/mm²) = ---------------------------------------- Cross section area (mm²)
Difference in stress(4) Tensile Modulus = ---------------------------------------------------
Difference in corresponding strain
Change in length (elongation) (5) Elongation at yield, Strain (ε) = ---------------------------------------------
Original length (gauge length)
(6) Percent Elongation = ε x 100
NOTE: If the specimen gives a yield load that is larger than the load at break, calculate “percent elongation at yield” otherwise; calculate “percent elongation at break”.
23
Factors Affecting Tensile Results
24
Flexural Strength
1. Flexural strength is the measure of how well a material resists bending, or
‘what is the stiffness of the material’.
2. Unlike tensile loading, in flexural testing all force is applied in one direction.
3. The stress induced due to flexural load are a combination of compressive
and tensile stresses.
4. Useful in selection of suitable plastic material for designing a part required
for structural application.
Two test methods are describes are as follows:
(i) Test method 1: A three point leading system utilizing central leading on a
simply Supported beam
(ii) Test method 2: A four point leading system utilizing two load equally
spaced from their adjacent support points with a distance between
load points of either 1/3 or 1/2 of the support span. 25
Flexural Strength
The stress induced due to flexural load are a combination of compressive and tensile
stress
26
Flexural Strength
Test Method: ASTM D 790, ISO-R-178, DIN-53452, BS-2782 Method 302 D, JIS-K 7203
Flexural Strength
Flexural strength is the ability of the material to withstand
bending forces applied perpendicular to its longitudinal axis. The stresses
induced due to the flexural load are a combination of compressive and
tensile stresses.
Flexural Modulus
Within the elastic limit, the ratio of the applied stress on a test
specimen in flexure to the corresponding strain in the outermost fiber of
the specimen. Flexural modulus is the measure of relative stiffness.
Unit-Kg/cm2
27
Flexural Strength
FORMULA AND CALCULATION
1) Calculate the rate of cross-head motion as follows and set the machine for the calculated rate, or as near as possible to it,
R = Z l2 / 6dWhere, R = rate of cross-head motion (mm/min) l = support span (mm) d = depth of beam (mm) Z = rate of straining of entire fiber (mm/min)
2) Terminate the test in the maximum strain in the outer fiber has reached 0.05 mm/min. The deflection at which distortion occurs are calculated by ‘r’ equal to 0.05 mm/min as follows D= rl2 / 6d Where, D = midspan deflection (mm) r = strain (mm/mm) l = support span d = depth of beam (mm)
28
Flexural Strength
FORMULA AND CALCULATION
1) Calculate the rate of cross-head motion as follows and set the machine for the calculated rate, or as near as possible to it,
R = Z l2 / 6dWhere, R = rate of cross-head motion (mm/min) l = support span (mm) d = depth of beam (mm) Z = rate of straining of entire fiber (mm/min)
2) Terminate the test in the maximum strain in the outer fiber has reached 0.05 mm/min. The deflection at which distortion occurs are calculated by ‘r’ equal to 0.05 mm/min as follows D= rl2 / 6d Where, D = midspan deflection (mm) r = strain (mm/mm) l = support span d = depth of beam (mm)
29
Flexural Strength
3) Max.fiber stress- test method ‘1’ S = 3PL / 2 bd2
Where, S = stress in the outer fiber at midspan (Mpa) p = load at given point on the load deflection curve(v) L= support beam (mm) b= width of beam tested (mm) d = depth of beam tested in (mm) 4) Maximum fiber stress for beam tested at large support spans-test method ‘1’,
S = (3PL / 2 bd2 ) 1+ 6(D/L)2 – 4(d/l) (D/L) 5) Max.fiber stress-test method ‘2’ S = PL / bd2
For a load span of ½ of the support span S = 3PL / 4 bd2
6) Maximum fiber stress test method ‘2’ for beam tested at large support span:- S = (PL / bd2 ) 1 + (4.70 D2 / L2 – (7.04 Dd / L2 )]For a span of one-half of the support Span: S = (3PL / 4bd2 ) * [ 1- (10.91 Dd / L2 ) ] 30
Factors Affecting Flexural Results
31
Impact Properties
1. Tensile and flexural testing, the material absorbs energy slowly. materials
often absorb applied forces very quickly: falling objects, blows, collisions,
drops etc. The purpose of impact testing is to simulate these conditions.
2. The impact properties of the polymeric materials are directly related to the
overall toughness of the material
3. Toughness is defined as the ability of the polymer to absorb applied
energy.
4. The area under the stress-strain curve is directly proportional to the
toughness of a material.
5. The impact resistance is the ability of a material to resist breaking under a
shock loading.
32
Impact Properties
There are basically four types of failures encountered due to impact
load.
Brittle Fracture -The product fractures extensively without yielding
Slight Cracking -The product shows evidence of slight cracking
and yielding without losing its shape.
Yielding -The product yields showing formation and stress
whitening.
Ductile Failure -A definite yielding of material along with cracking
33
Impact Properties
TEST METHODTest Method for Impact Resistance of Plastics & Electrical Insulating Material (ASTM D 256 A & B), ASTMD1822, JISK-7111 &7112 The impact test methods are as following:(1) Pendulum impact tests
(i) Izod impact test (ii) Charpy impact test(iii) Chip impact test(iv) Tensile impact test
(2) High-rate tension test(3) Falling weight impact test
(a) Drop weight (top) impact test(4) Instrumented impact tests(5) High- rate impact testers.
(a) High speed ball impact tester(b) High speed plunger impact tester
(6) Miscellaneous impact test.34
Impact Properties
ASTM D 256, ISO-R-180, BS-2782 Method 306 A, DIN 53453, JIS-K 7110
IMPACT TEST
Impact test is a method of determining the behavior of
material subjected to shock loading in bending or tension. The
quantity usually measured is the energy absorbed in fracturing in a
single blow.
IMPACT STRENGTH
Energy required fracturing a specimen subjected to shock
loading.
Unit : J/m
35
Impact Properties
SIGNIFICANCE
(1) The excess energy pendulum impact test indicates the energy to break std. Test specimen of specified size under stipulated conditions of specimen mounting, notching and pendulum velocity at impact.
(2) The energy lost by the pendulum during the breakage of the specimen is the sum of energy required,
(i) To initiate fracture of the specimen(ii) To propagate the fracture across the specimen(iii) To through the free end of the broken specimen(iv) To bend the specimen(v) To produced vibration in the pendulum arm (vi) To produced vibration ‘or’ horizontal movement of the machine frame ‘or’
base(vii) To overcome friction in the pendulum bearing and in the excess energy
indicating mechanism and to overcome pendulum air drag (wind age).(viii) To indent ‘or’ deformed plastically the specimen at the line of impact.
36
Impact Properties
37
Impact Properties
1. Impact properties can be very sensitive to test specimen thickness and molecular orientation. The differences in specimen thickness as used in ASTM and ISO methods may affect impact values strongly.
2. A change from 3 to 4 mm thickness can even provide a transition in the failure mode from ductile to brittle behaviour - through the influence of molecular weight and specimen thickness on Izod notched impact.
3. Materials already showinga brittle fracture mode in 3 mm thickness – such as mineral and glass filled grades - will not be affected. Neither will impact modified materials.
38
Impact Properties
CHARPY IMPACT STRENGTH
Test Method: ASTM D 6110, ISO-R-179, BS-2782 Method 306 B & 307
Charpy impact is less common in US but is widely used in Europe. The test is identical to Izod test except that the specimen is a simply supported beam that is impacted, midlong between the supports.
Specimen Size: 12.7 x 6.4 x 127.0 mm
39
Impact Properties
The main difference between Charpy and Izod tests is the way the test bar is held. In Charpy testing the specimen is not clamped, but lies freely on the support in a horizontal position.
40
Impact Properties
FORMULA AND CALCULATIONS
Energy required breaking the sample (J) Impact strength (J/m) = ---------------------------------------------------------------------------------------------
(Izod / Charpy) Thickness (m)
Dart Impact Test=
Calculate Wf = WL - [ ΔW (S/100 – ½)]
Where,
Wf = impact failure weight, gms,
ΔW = uniform weight increment used, gms,
WL = lowest missile weight, gms, according to the particular ΔW used,
at which 100% failure occurred and
S = sum of the percentages of breaks at each missile weight (from a
weight corresponding to no failures upto and including WL )41
Factors Affecting Impact Results
42
Falling-Weight Impact Test
Impact Properties
1. The falling impact test, also known as the drop impact test or the variable-height impact
test, employs a falling weight.
2. This falling weight is a tip with a conical nose, a ball, or a ball-end dart.
3. The energy required to fail the specimen is measured by dropping a known weight from a
known height onto a test specimen.
4. This test is also very suitable for determining the impact resistance of plastic films, sheets
and laminated materials.
Three basic ASTM tests are commonly used depending upon the application:
ASTMD 3029 Impact resistance of rigid plastics sheeting
ASTMD 1709 Impact resistance of poly ethylene film by the free falling dart method
ASTMD 244 Test for impact resistance of thermoplastics pipe and fittings by
means of a tip.43
DROP IMPACT TEST
Impact Properties
1. The test is carried out by raising the weight to a desired height manually or automatically
with the use of motor-driven mechanism & allowing it to fall freely on to the others side of
the round- nosed punch.
2. The punch transfers the impact energy to the flat test specimen, which is positioned, on a
cylindrical die or a part lying on the base of the machine.
3. The kinetic energy is possessed by the falling weight at the instant of impact is equal to the
energy used to raise to the height of drop and is the potential energy possessed by the
weight as it is released.
4. Since the potential energy is expressed as the product of weight and height, the guide tube
is marked with a linear scale representing the impact range of the instrument in in-lb.
5. Thus, the toughness or the impact strength of a specimen or a part is read directly off the
calibrated scale in in-lb.
6. The energy loss due to the friction in the tube or due to the momentary acceleration of the
punch is negligible 44
Compressive Properties
1. Compressive properties describe the behaviour of a material when it is
subjected to a compressive load at a relatively low and uniform rate of loading.
2. Compressive properties include modulus of elasticity; yield stress, deformation
beyond yield point, compressive strength, compressive strain and slenderness
ratio. Material processing a low order of ductility may not exhibit yield point.
3. Compressive strength is a value that shows how much force is needed to
rupture or crush a material.
4. Compression tests provide a standard method of obtaining data for research and
development, quality control, acceptance or rejection under specifications and
special purposes
5. COMPRESSIVE STRENGTH The maximum load sustained by a test specimen
in a compressive test divide by the original cross section area of the
specimen. 45
Compressive Properties
COMPRESSIVE DEFORMATION: - The decrease in length produced in the gauge length of
the test specimen by a compressive load. It is expressed in unit of length.
COMPRESSIVE STRAIN: - The ratio of compressive deformation to the gauge length of the
test specimen, i.e., the change in length per unit of original length along the longitudinal axis. It
is expressed as dimension ratio.
SLENDERNESS RATIO:- The ratio of the length of a column of uniform cross section to its
least radius of gyration known as slenderness ratio.
MODULUS OF ELASTICITY:- The ratio of stress to corresponding strain below the
proportional limit of a material. It is expressed as force per unit area, based on the average
initial cross- sectional area.
COMPRESSIVE YIELD POINT:- The fist point of stress-strain diagram at which an increase in
strain occurs without an increase in stress.
Unit :- kg/cm2
Test Method: ASTM D 695, ISO-R-604, BS-2782 Method 303, DIN-53454, JIS-K 7208 46
Compressive Properties
FORMULA E AND CALCULATION
Compressive strength: Calculate the compressive strength by dividing the max. Compressive load
carried by the specimen during the test by the original minimum cross sectional area of the
specimens. Express the result in MPa. Load (kg)(1) Compressive strength = ---------------------------------------------------- Original cross sectional area (cm2) Maximum load recorded (N)(2) Compressive strength at yield (N/mm²) = ---------------------------------------------- Cross-section area (mm²) Load recorded at break (N) (3) Compressive strength at break (N/mm²) = -------------------------------------------- Cross-section area (mm²) Difference in stress (4) Compressive Modulus = -------------------------------------------------- Difference in corresponding strain Change in length (Deformation) (5) Deformation at yield, Strain (ε) = ------------------------------------------------------- Original length (gauge length) (6) Percent Deformation = ε x 100
If the specimen gives a yield load that is larger than the load at break, calculate “percent Deformation at
yield” otherwise; calculate “percent Deformation at break”. 47
Factors Affecting Compressive Strength
48
Hardness Test
1. Hardness is defined as the resistance of a material to deformation, particularly permanent
deformation by indentation or scratching.
2. Two most commonly used hardness tests for plastics are the Rockwell hardness test and
the Durometer hardness test
3. Rockwell ASTM D 785, ISO-2039, JIS-K7202, DIN-53426 hardness for relatively hard
plastics such as acetals, nylons, acrylics and polystyrenes
4. Durometer ASTM D 2240, ISO-868, JIS-K 7215, BS2782 Method 307 A and DIN 53505
hardness for flexible PVC, rubbers, polyethylene & polyurethane.
49
Hardness Test
Comparison of Ball, Rockwell and Shore hardness
1. The Rockwell hardness test determines the hardness of plastics after allowing
for elastic recovery of the test specimen.
2. This is different from both Ball and Shore hardness: in these tests, hardness is
derived from the depth of penetration under load - thus excluding any elastic
recovery of the material.
3. Rockwell values CANNOT, therefore, be directly related to Ball or Shore values.
4. Ranges for Shore A and D values can be compared to ranges for Ball
indentation hardness values. A linear correlation, however, does not exist.
50
Hardness Test
51
Shear Strength
1. Shear strength of plastic material is defined as the ability to withstand the
maximum load required to shear the specimen so that the moving portion
completely clears the stationary portion. Forcing a standardized punch at a
specified rate through a sheet of plastics until the two portions of the specimen
completely separate carries out shear strength test
2. Shear strength data is of great importance to a designer of film and sheet
products that tends to be subjected to such shear loads. Most large molded
and extruded products are usually not subjected to shear loads
SHEAR STRENGTH: The maximum load required to shear a specimen in such a
manner that the resulting pieces are completely clear of each other.
Unit is lb / inch².
TEST METHOD
Test Method for shear strength of plastics by punch tool (ASTM D 732) 52
Shear Strength
A shear tool of the punch type, which is so, constructed that the specimen is rigidly clamped both to the stationary block and movable block so that it cannot be deflected during the test.
Shear strength is calculated as follows: Force required to shear the specimen Shear strength (psi) = ---------------------------------------------------------------- Area of sheared edge Area of sheared edge = (circumference of punch) x (thickness of specimen)
Calculate shear strength in MPa determined by dividing the load required to shear the specimen by
the area of the sheared edge, which shall be taken as the product of the thickness of the specimen by the
circumference of the punch.
53
Taber Abrasion Resistance
1. This test measures the quantity of abrasion loss by abrading a test specimen with a
Taber machine. As per the standard ISO 3537, DIN 52347 and ASTM D1044
2. The specimen is mounted on a rotating disc, turning with a speed of 60 r.p.m. Loads, by
means of weights, are applied.
3. pushing the abrasive wheels onto the specimen. After a specified number of cycles, the
test is stopped.
4. The mass of abrasion loss is defined as the mass of test piece fragments which have
dropped off: reported in mg/1000 cycles.
54
THERMAL PROPERTIES
o Melt flow index (MFI)
o Heat deflection temperature (HDT)
o Vicat softening temperature (VSP)
o Flammability
o Thermal conductivity
o Low temperature Brittleness
o Oxygen Index
55
Melt Flow Index (MFI)
Test Method: ASTM D 1238, ISO-1133, JIS-K 7210, BS-2782 Method 105 C
Sample size: Minimum 50 gm. of granules
Definition: The quality of material extruded through a standard orifice under
specified temperature and load, measured for 10 minutes.
M Where,
MFI = ------ x 600 M = Mass of the extrudate (gm)
t t = Cut off time (sec.)
Significance:
To measure the uniformity of the flow rate of the material.
This values help to distinguish between the different grades of a polymer.
MFI is indirectly proportional to Molecular Weight.
56
Melt Flow Index (MFI)
57
Factors Affecting MFI
58
Heat Deflection Temperature
1. HDT is a relative measure of a material’s ability to perform for a short time at
elevated temperatures while supporting a load.
2. The test measures the effect of temperature on stiffness: a standard test specimen is
given a defined surface stress and the temperature is raised at a uniform rate.
3. Defined as the temperature at which a standard test bar (5 x ½ x ¼ in ) deflects 0.010
inch under a stated load of either 66 or 264 psi.
4. HDT values are used to compare the elevated temperature performance of the
materials under load at the stated conditions.59
Heat Deflection Temperature
Test Method: • ASTMD 648, ISO 75 -1 and 75-2
Test Specimen: • 127mm (5 in.) in length, 13mm (½ in.) in depth by any width from 3mm (⅛
in.) to 13mm ((½ in.) Conditioning: • 23 ± 2oC and 50 ± 5% RH for not less than 40 hrs prior to test.
Test Method • Specimen Supports: Metal supports for the specimen of 100 ±
2mm
• Immersion Bath
• Deflection Measurement Device
• Weights: 0.455 MPa (66 psi) ± 2.5% or 1.82 MPa (264 psi) ± 2.5%.
• Temperature Measurement SystemTwo replicate specimens are used for each test
60
Heat Deflection Temperature
The weight of the rod used to transfer the force on the test specimen is included as part of the total load. The load (P) is calculated as:
P = 2Sbd2 / 3L
Where,
S = Max. Fibre stress in the specimen of 66 Psi / 264 Psib = Width of specimend = Depth of specimenL = Width of span between support (4 in)
61
Heat Deflection Temperature
HDT and Amorphous & Semi-Crystalline plastics
1. In amorphous polymers, HDT is nearly the same as the glass transition temperature Tg of
the material.
2. Because amorphous polymers have no defined melting temperature, they are processed
in their rubbery state above Tg.
3. Crystalline polymers may show low HDT values and still have structural utility at higher
4. Temperatures.
5. HDT test method is more reproducible with amorphous plastics than with crystalline.
6. With some polymers it may be necessary to anneal the test specimens to obtain reliable
results.
7. Addition of glass fibres to the polymer will increase its modulus. Since the HDT represents
a temperature where the material exhibits a defined modulus, increasing the modulus will
also increase the HDT.
62
Heat Deflection Temperature
9. The results obtained by this test method do NOT represent maximum use
temperatures, because in real life essential factors such as time, loading and
nominal surface stress may differ from the testing conditions.
10. Glass fibres have a more significant effect on the HDT of crystalline polymers
than on amorphous polymers.
11.The data are not intended for use in design or predicting endurance at elevated
temperatures.
12.Used for screening and ranking materials for short-term heat resistance.
63
Heat Deflection Temperature
Factors Influencing HDT
64
Vicat Softening Point (VSP)
1. This test gives a measure of the temperature at which a plastic starts to soften
rapidly.
2. A round, flat-ended needle of 1 mm2 cross section penetrates, the surface of a
plastic test specimen under a predefined load, and the temperature is raised at a
uniform rate.
3. The Vicat softening temperature, or VST, is the temperature at which the
penetration reaches 1 mm.
4. Useful in quality control, development and to characterise the material. Also
useful in comparing heat softening qualities of thermoplastics.
5. Test Method: ASTM D 1525, ISO-306, JIS-K7206, BS-2782 Method 102 D & J65
Vicat Softening Point (VSP)
Test Specimens : • The specimen shall be flat, between 3 and 6.5mm thick and at least 10 by
10mm in area or 10mm in diameter.
Conditioning: • 23 ± 2oC and at 50 ± 5% relative humidity of not less than 40 hrs 66
Limiting Oxygen Index
Oxygen index is defined as the minimum concentration of oxygen in a mixture of oxygen and nitrogen that will just support combustion.
Test method : ASTM D 2863, ISO 4589
specimen size : 150 x 6 x 4mm
the specimen is ignited and the
concentration of oxygen is adjusted
to burn for 3 minutes or 50 mm length.
100 x o2
percentage oxygen index = ------------
o2 + n2
significance: the results allows to rate the material on numerical basis and simplifies the selection in terms of flammability.
67
Limiting Oxygen Index
• The purpose of the oxygen index test is to measure the relative flammability of materials by burning them in a controlled environment.
• The oxygen index represents the minimum level of oxygen in the atmosphere which
• can sustain flame on a thermoplastic material.• The test atmosphere is an externally controlled mixture of nitrogen and oxygen.
68
Thermal Conductivity
• Rate at which heat is transferred by conduction through a unit cross sectional area of a material when a temperature gradient exists perpendicular to the area.
• `• The coefficient of thermal conductivity (K factor), is defined as the quantity of
heat that passes through a unit cube of the substance in a given unit time when the difference in temperature of the two faces is 10C.
• Mathematically, thermal conductivity is expressed as K = Qt/A(T1-T2)
• Q = amount of heat passing through a cross section, A causing a temperature difference, ∆T (T1-T2), t = thickness of the specimen.
• K is the thermal conductivity, typically measured as BTU in / (hr.ft2 . 0F) indicates the materials ability to conduct heat energy.
69
Thermal Conductivity
Guarded Hot plate Apparatus Courtesy: Bayer Material Data Sheet
• Test method: Guarded hot plate test ASTM 177, ISO 2582• Test Specimen: two identical specimens having plane surface of such size as to
completely cover the heating unit surface• The thickness should be greater than that for which the apparent thermal resistivity
does not change by more than 2% with further increase in thickness 70
Thermal Conductivity
• Thermal conductivity is calculated by using the value of rate of flow at a fixed temperature gradient.
• Data are obtained in the steady state.• Crystallites have higher conductivity.• As the density of the cellular plastic decreases, the conductivity also decreases up to a
minimum value and rises again due to increased convection effects caused by a higher proportion of open cells.
The relationship between the quantity of heat flow and thermal conductivity is defined as
Q ~ K x
Q = Quantity of heat flowK = Thermal ConductivityX = The distance the heat must flow
Thermal conductivity is calculated as :
K = Qt / A (T1 – T2)
Q = Rate of heat flow (w)T = Thickness of specimen (m)A = Area under test (m2)T1 = Temperature of hot surface of specimen (k)T2 = Temperature of cold surface of specimen (k)
71
Coefficient of Linear Thermal ExpansionASTM D696, DIN 53752
1.Any material will expand when heated. Injection moulded polymer parts will
expand and change dimensions in proportion to the increase in temperature.
2.To characterise this expansion, designers rely on the Coefficient of Linear
Thermal Expansion or CLTE to describe the changes in length, width, or
thickness of a molded part.
3.Amorphous polymers will generally show consistent expansion rates over
their useful temperature range.
4.Crystalline polymers generally have increased rates of expansion above
their glass transition temperature.
5.Addition of fillers, causing anisotropy, significantly alters the CLTE of a
polymer.
6.Glass fibers will generally align in the direction of the flow front: when the
polymer is heated, the fibers restrict expansion along their axis and reduce
the CLTE.
7.In directions perpendicular to flow direction and thickness, the CLTE will be
higher.
72
Coefficient of Linear Thermal Expansion
• Measures the change in length per unit length of a material, per unit change in temperature.
• Expressed as in/in/°F or cm/cm/°C
• Mathematically, CLTE (α), between temperatures T1 and T2 for a specimen of length L0 at the reference temperature, is given by :
• α = (L2 – L1)/[L0(T2 – T1 )] = L/L0ΔT .
• The thermal expansion difference develops internal stresses and stress concentrations in the polymer, which allows premature failure to occur. 73
Flammability
• Plastics are carbon-based materials and burn and give off gases and smoke when subjected to a flame.
• Plastics are excellent fuels but are generally classed as ordinary combustibles
• For combustion to take place, three components form the 'fire triangle’
74
Flammability
UL 94Method of classifying a material’s tendency to either extinguish or spread a flame once it has been ignited.
Significance
• 12 flame classifications specified in UL 94.
• Describes materials burning characteristics after test specimens have been exposed to a specific test flame under controlled laboratory conditions.
• The classifications relate to rate of burning time to extinguish ability to resist dripping and whether or not the drips are burning.
75
Flammability
UL94 Horizontal Burning (HB)• Where flammability is a safety requirement, HB materials are normally not
permitted. In general, HB classified materials are not recommended for electrical applications except for mechanical and/or decorative purposes.
• Specimen is supported in a horizontal position, tilted at 45°.
• Flame applied to the end of the specimen for 30 seconds or until the flame reaches the 1 inch mark.
• If the specimen continues to burn after the removal of the flame, the time for the specimen to burn between the 1 and 4 inch marks are recorded.
• If the specimen stops burning before the flame spreads to the 4 inch mark, the time of combustion and damaged length between the two marks is recorded. Three specimens are tested for each thickness.
HBslow burning on a horizontal specimenburning rate < 76 mm/min for thickness < 3 mmburning rate < 38 mm/min for thickness > 3 mm 76
Flammability
Vertical Testing (V-0, V-1, V-2)
• A specimen is supported in a vertical position and a flame is applied to the bottom of the specimen.
• The flame is applied for 10 secs & then removed until flaming stops at which time the flame is reapplied for another 10 secs and then removed.
• Two sets of five specimens are tested.
• The two sets are conditioned under different conditions.
77
Flammability
Vertical Testing (V-0, V-1, V-2)
V-0burning stops within 10 seconds on a vertical specimen; no drips allowedV- lburning stops within 30 seconds on a vertical specimen; no drips allowedV-2burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed
UL94-5VUL94-5V is the most severe of all UL classifications. It involves two steps:
Step 1A standard flammability bar is mounted vertically and subjected to each of five applications of a 127 mm flame, five seconds duration. To pass, no bar specimen may burn with flaming or glowing combustion for more than 60 seconds after the fifth flame application. Also, no burning drips are allowed that ignite cotton placed beneath the samples. The totalprocedure is repeated with five bars. 78
Flammability
Step 2
A plaque - with the same thickness as the bars - is
tested in a horizontal position with the same flame.
The total procedure is repeated with three plaques.
Two classifications result from this
horizontal test:
5VB and 5VA.
· 5VB allows holes (burn-through)
· 5VA does not allow holes
UL94-5VA is the most stringent of all UL tests,
specified for fire enclosures on larger office
machines. For those applications with expected wall
thickness of less than 1.5 mm, glass
filled material grades should be used.
79
Electrical Properties
Insulation resistance
Volume and Surface resistivity
Dielectric strength
Arc resistance
INSULATION RESISTANCE
The most desirable characteristic of an insulator is its ability to resist the leakage of the electrical current.
The higher the insulation resistance, the better the insulator.
The insulation resistance can be divided into- Volume resistance- Surface resistance
80
VOLUME RESISTIVITY
Test Methods: ASTM D 257, ISO-3915, BS-2782 Method 202
Test specimen size: 110 mm dia disc with 3 mm thickness
The volume resistance is defined as the ratio of direct voltage applied to two
electrodes that are in contact with a specimen to that portion of the current
between them that is distributed through the volume of the specimen.
Volume resistivity(ohm-cm) = RvA/t
Where,
Rv = Volume resistance (ohms)
A = Area of the electrode contact
with the test specimen (cm²)
t = Thickness of the test specimen (cm)
81
VOLUME RESISTIVITY
o When an electric potential is applied across an insulator, the current
flow will be limited by the resistance capabilities of the material.
o Volume resistivity is the electrical resistance when an electric
potential is applied
o between opposite faces of a unit cube.
o Volume resistivity will be affected by environmental conditions
imposed upon the material. It varies inversely with temperature, and
decreases slightly in moist environments.
o Materials with volume resistivity values above 108 Ohm·cm are
considered insulators. Partial conductors have values of 103 to 108
Ohm·cm
82
VOLUME RESISTIVITY
Volume Resistivity (ohm-cm)1014 -1016
1016 -1018
1016
1012 - 1016
1015 -1017
1014 - 1017
1014 - 1017
1015 - 1017
1015 - 1017
1016
1016 - 1017
1015
PlasticsACETAL ACRLYICABSNYLONPOLYCARBONATETP POLYESTERPOLYPROPYLENEPOLYSULFONEMODIFIED PPO/PPEPOLYPHENYLENE SULFIDEPOLYARYLATELIQUID CRYSTAL POLYMER
83
SURFACE RESISTIVITY
Test Method: ASTM D 257, ISO-3915, BS 2782 Method 203Test specimen size: 110 mm dia disc with 3.0 mm thickness
This test measures the ability of current to flow over the surface of a material.Surface resistance is the ratio of the direct voltage applied to the electrodes to the portion of the current between them which is primarily in thin layer of moisture or other semi-conducting material that may be deposited on the surface.Volume resistivity is a property of the material.Surface resistivity is a measure of the susceptibility of the material to surface contamination. Particularly moisture.Data from this test are best used when material are being evaluated and selected for applications in which surface leakage may be a problem.
84
DIELECTRIC STRENGTH
Test Method:: ASTM D 149, ISO-1325, BS-2782 Method 201 A, DIN-53483
Test specimen size: 50 mm or 100 mm dia disc with 3.0 mm thickness
When an insulator is subjected to increasingly high voltage, it eventually breaks down and allows a current to pass. The voltage reached just before it breaks down divided by the thickness of the sample is known as the Dielectric strength of the material measured in volts/mil.
Dielectric strength = Breakdown voltage/Thickness (mil)It is generally measured by putting electrodes on either side of the test specimen and increasing the voltage at a controlled rate.Factors that affect the results are:1. Temperature & relative humidity2. Rate of increase in voltage3. Sample thickness & electrode area4. Conditioning of sample5. Any contamination or internal voids in the 6. Sample may cause for premature failure.
85
DIELECTRIC STRENGTH
PFA (fluorocarbon)
CPVC
Rigid PVC
Ionomer
Polyester(thermoplastic)
Polypropylene
Polystyrene (high impact)
FEP(fluorocarbon)
Nylons
Polystyrene(General purpose)
Acetals
PTFE fluorocarbon
PPO
Polyphenylene sulfide
Polyethylene
Polycarbonate
ABS
Phenolics
PVC2 (fluorocarbon)
Dielectric strength (V/mil)
2000
1200-1500
800-1400
1000
600-750
650
650
600
350-560
500
500
500
500
490
480
450
415
240-340
26086
ARC RESISTANCE
Test Method: ASTM D 495Test specimen size: 50 mm dia disc with 3.00 mm thickness
It is defined on the time required for a given electrical current to render the surface of a material conductive because of contamination by arcing.This test is more applicable for thermoset plastics, since a conductive path can be formed from the decomposition products by this kind of localized heating.This test results is affected by temperature, moisture contaminations in the plastic materialsHigh values would be advantageous in electrical applications where the possibility of arcing exists. e.g.: Switches, Circuit breakers, Automotive ignition components and High voltage apparatus
87
ARC RESISTANCE
PlasticsPolycarbonate (10-40%G.F)PolycarbonatePolystyrene(high impact)ABSPolystyrene (general
purpose)Rigid PVCPolysulfoneUrea FormaldehydeIonomerSANEpoxyAcetal (Homopolymer)Polyethylene (low density)PolypropylenePTFEAcrylics
Arc Resistance (sec.)5-12010-12020-10050-8560-8060-8075-19080-15090-140100-150120-150130135-160135-180>200No track
88
Comparative Tracking Index (CTI)
1. The tracking index is the relative resistance of electrical insulating materials to tracking when the surface is exposed - under electrical stress - to contaminants containing water.
2. Comparative Tracking Index, or CTI, and CTI-M tests are undertaken to evaluate the safety of components carrying live parts: insulating material between live parts must be resistant to tracking.
3. CTI is defined as the maximum voltage at which no failure occurs at 50 drops of ammonium chloride in water.
89
Comparative Tracking Index (CTI)
1. Materials meeting the CTI requirements at 600 Volts are called ‘high
tracking’ resins.
2. The CTI test procedure is complex. Influencing factors are the
condition of the electrodes, electrolyte and sample surface, and of the
applied voltage. Values can be lowered by
3. additives such as
· pigments - in particular carbon black
· flame retardants
· glass fibres
4. Thus black, FR and GF materials in general, are not recommended
when tracking resistance is a key requirement. Minerals (TiO2) tend to
raise CTI values.
90
Optical Properties
Haze and Light transmission ASTM D1003oHaze is caused by the scattering of light within a material, and can be affected by molecular
structure, degree of crystallinity or impurities at the surface or interior of the polymer.oHaze is only appropriate for translucent or transparent materials, not for opaque ones.oHaze isosometimes thought of as the opposite of gloss, which would properly be absorption of an
incident beam.oHowever, the haze test method actually measures absorption, transmittance and deviation of
a direct beam by a translucent material.oA specimen is placed in the path of a narrow beam of bright light so that some of the light
passes through the specimen and some continues unimpeded. Both parts of the beam pass
into a sphere equipped with a photodetector. Two quantities can be determined:
· the total strength of the light beam
· the amount of light deviated by moreothan 2.5° from the original beam. From these two quantities, two values are calculated:
· haze, or the percentage of incident (light scattered more than 2.5°)
· luminous transmittance, or the (percentage of incident light which is transmitted through
the specimen.) 91
Optical Properties
Gloss
1. Gloss is associated with the capacity of a surface to reflect more light in some
directions than in others. Gloss can be measured in a glossmeter.
2. A bright light is reflected off a specimen at an angle and the luminance or
brightness of the reflected beam is measured by a photodetector.
3. Most commonly, a 60° angle is used. Shinier materials can be measured at 20°
and matt surfaces at 85°.
4. The glossmeter is calibrated by using a black glass standard with a gloss value
of 100. Plastics show lower values - they strongly depend on the way of
moulding.
92
Optical Properties
Haze and Gloss
1. Haze and gloss test methods measure how well a material reflects and transmits
light.
2. They quantify qualifications such as ‘clear’ and ‘shiny’.
3. While haze is only appropriate for transparent or translucent materials, gloss can
be measured for any material.
4. Both gloss and haze tests are precise. But they are often used to measure
appearance, which is more subjective.
5. The correlation between haze and gloss values and how people rate the ‘clarity’
6. or ‘shininess’ of a plastic is uncertain.
Refractive index DIN 53491, ASTM D542
A light beam is transmitted through a transparent specimen under a certain angle. The deviation from the beam - caused by the material when passing the specimen - is the index of refraction, found by dividing sin by sin . 93
Optical Properties
94
