S M Diwan

Reliance Industries Ltd. Product Application & Research Centre

Chemical compounds formed when many small chemical units (monomers) combine to form large

molecules with a regular repeating structure.

Monomer Polymer

Heat

Catalyst

H H H CH3 H H H CH3 \ / l l l l l l C = C – C – C – C – C – C– C – / \ l l l l l l H CH3 H H H CH3 H H Propylene Polypropylene (PP)

O HO– C – ll O

– C –OH ll O

+ Terephthalic Acid

H H l l HO – C – C – OH l l H H

Ethylene Glycol

O – C – ll O

H H l l – C – O – C – C – O – ll l l O H H

Polyethylene Terephthalate (PET)

n

n

Heat

Heat

Catalyst (Condensation Polymerization)

Catalyst (Addition Polymerization)

Chemical Composition

Methane = CH4 Gas

Octane = C8H18 Liquid

Paraffin Wax = C50H102 Solid

Polyethylene = C2000H4002 Polymer

Size of the Molecules

log Molecular Size (Weight)

log

Num

ber o

f Mol

ecul

es

Range of Sizes of the Molecules

As a result of the polymerization process:

Almost all polymers contain a Range of Molecular Sizes.

Linear

Branched

Long-Chain Short-Chain

Cross-Linked

Shape of the Molecules

Solid State Structure of Thermoplastics

Organization of the Molecules

Amorphous

No polymer structure.

Examples: Poly Vinyl Chloride Polystyrene

Polycarbonate PMMA

Semi-Crystalline

Contains both crystalline (ordered)and amorphous

polymer.

Examples: Polyethylene Polypropylene

PET Polyamides (nylon)

Why & When

The Quality of a product is determined by analysing the product for critical parameters. Any material before being utilized or processed further has to be checked for different Properties. Various instances where testing has to be carried out are :

• Testing of raw materials, • Process monitoring and control, • Quality Assurance : Meeting the specified requirements • Sales promotion data, • Comparison with competitors’ products, • Evaluating quality complaints and product failures.

Sources of Errors

Errors in testing come about from four main areas :

• From the basic test itself, • From the operator conducting the test, • From the variation in the test specimen, • From the variation in testing environment

Standard Test Methods

Official Definition of a Standard -

“ A technical specification or document available to the public, drawn-up with the co-operation and consensus of all interests affected by it, based on the consolidated results of science, technology and experience, aimed at the promotion of optimum community benefits and approved by a body recognized on the regional, national or international level.”

Contents of a Typical Standard

1. Scope and Field of Application, 2. Principle, 3. Reagents specified for the subject testing, 4. Apparatus specified for the subject testing, 5. Procedure a) Preparation of Specimens b) Conditioning of the Specimens c) Standard Operating Procedure 6. Expression of Results, 7. Test Report, 8. Schematic Diagrams, 9. Notes & Warnings.

The Most Common Tests

Various Tests carried out on plastics can be broadly categorized as :

1. Processability 2. Mechanical Tests 3. Thermal Tests 4. Optical Tests

5. Electrical Tests

6. Permanence Tests

Processability

• The Processability of a polymer depends mainly on its molecular weight. • Molecular weight affects the viscosity, which in turn controls the flow behavior of the polymer. • Thus determination of flow behavior or solution viscosity are two major routes to assess the Processability of the polymer.

Capillary (D =2.0955 mm, L = 8.000 mm)

Barrel (D = 9.55 04 mm)

Piston

Temperature

Thermometer

Load

Method most frequently used to measure melt flow in the plastics industry.

Standardized test (ASTM, ISO). Constant load test.

(Rate varies with viscosity.)

Fixed die diameter. Fixed die L/D ratio. Mass / time measured. (g/10 min.) Higher MFR = Easy processabilty Lower MFR = Better Mechanicals

Melt Flow Rate

Viscosity Number / K Value

Determination of solution viscosity of polymers..

Fixed capillary dia.. and length. Fixed solution concentration Flow times measured. (t0/tc)

Lower K value = Easy processability Higher K Value = Better mechanical

Tensile Properties

The most important single indication of strength of a material.

The force necessary to pull the specimen apart is determined along with prebreak

stretch. Specimens can be injection molded/

compression molded/machined. Both ends of the specimen are firmly clamped in the jaws of the testing machine.The jaws move apart at specified rates, pulling the samples from both the ends.

Izod Impact Test

It indicates the energy required to break notched specimens under standard conditions. The data is useful in comparing various types or grades of plastics. Specimens can be injection molded /

compression molded/machined. The sample is clamped in the base of a pendulum clamping machine. The pendulum is released, and the force consumed in breaking the sample is calculated.

Falling Dart Impact Test

It indicates the energy required to break clamped specimens under standard conditions. The data is useful in understanding the behavior of the material under conditions of impact. Several types of falling dart tests : for films, for pipes, for rigid sheets. A weight is dropped from a tower on to the specimen. The amount of weight and the drop height are varied. The total energy absorbed to cause failure is calculated.

Flexural Properties

Flexural strength is the measure of how well a material resists bending. Specimens can be injection molded/

compression molded/machined. The specimen is placed on two supports spaced by a specified distance. A load is applied in the centre at a specified rate and the loading at failure is noted. For materials which do not break, the flexural property is usually given at 5% deflection.

Deflection Temperature It shows the temperature at which an arbitrary amount of deflection occurs under specific load. The data is useful in comparing relative behaviors of different materials under the test conditions. Specimens can be injection molded/

compression molded/machined. The specimen is placed on support at specified distance and a specified load is placed on the centre. The temperature in the chamber is raised at a specified rate. The temperature at which the bar deflects by 0.25 mm is the deflection temperature at the specific load.

Vicat Softening Point It is a good way of comparing the heat softening characteristics of thermoplastics materials.. Specimens can be injection molded/

compression molded/machined. The apparatus consists of a temperature-regulated oil bath with a flat ended needle penetrated to register degree of penetration on a gauge. A specimen is placed with the needle resting on it. The temperature of the bath is raised at a specified rate. The temperature at which the needle penetrates 1 mm is the vicat softening point.

Flammability Test

It distinguishes between the ‘burning’, ‘non-burning and ‘self-extinguishing’ type of materials.

The specimen is clamped at one end on a ring stand so that the longitudinal axis is horizontal. A piece of 20 mesh Bubson burner gauze is clamped horizontally 9.5 mm below the specimen. A Bunson burner, placed so the flame contacts the end of the specimen, is held there 30 sec. And then removed. Extent of burning is measured on the specimen’s lower edge.

If the specimen does not ignite, it is ‘non-burning’, if it ignites but does not continue to burn, it is ‘self-extinguishing’ and when it continues to burn, it is ‘burning’ type.

Brittleness temperature

This test is of use in judging the relative merits of various materials for low-temperature flexing or impact. The specimens are cantilevered from the sample holder in the test apparatus, which has been brought to specified low temperature. When the specimens have been at the conditions for 3 minutes, a single impact is administered and the samples are examined for failure.

Gloss

This test measures how well a material reflects light. In a glossmeter, a bright light is reflected off a specimen at an angle and the brightness of the reflected beam is measured by a photo detector.

Haze This test measures how well a material absorbs, transmits and deflects light. A 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 photo detector. Here the total strength of the light beam and the amount of light scattered by more than 2.5 deg. From the original beam are determined. Haze is the % of incident light scattered more than 2.5 deg., and luminous transmittance is the % of incident light which transmitted through the specimen.

Volume Resistivity

This test measures the resistance to leakage of current through the body of the material.

Volume resistivity mainly depends on the material. In cases where additives are incorporated, even the small quantities of them affect the property noticeably.

Both temperature and humidity affect the resistivity of the material appreciably.

Knowing the volume resitivity of an insulation material makes it possible to design an insulator for specific application.

Environmental Stress Crack Resistance

The cracking obtained in this test is indicative of what may be expected from a wide variety of other stress-cracking agents.

The notched specimens are bent into a “U” shape in a channel and inserted into a test tube which is then filled with fresh reagent. The tube is stoppered and is placed in a constant temperature bath at 50 ded C. The specimens are inspected periodically and any visible crack is considered as failure. The duration of the test is reported together with the % failure obtained.

Accelerated Weathering Test

This test gives an indication of life of the product in variety of selected conditions. The exposure involves changes in temperature, relative humidity and UV radiation energy with or without water spray.

Hydrostatic Pressure Test on Pipes

Installations of plastics pipes may be expected to give many years of service. This test, by using relatively higher pressures, indicates whether the material will hold up in normal services.