Kutz M. Handbook of materials selection

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588 PLASTICS TESTING

Fig. 22 Typical aluminum exposure racks. (Courtesy Atlas Electric Devices Company)

samples are always utilized and retained at standard conditions of temperature

and humidity. The control samples must also be covered with inert wrapping to

exclude light exposure during the aging period. However, dark storage does not

ensure stability.

Test sites are selected to represent various conditions under which the plastic

product will be used. Arizona is often selected for intense sunlight, wide tem-

perature cycle, and low humidity. Florida, on the other hand, provides high

humidity, intense sunlight, and relatively high temperatures.

Exposure test specimens of suitable shape or size are mounted in a holder

directly applied to the racks. Racks are positioned at a 45

⬚ angle and facing the

equator. Many other variations in the position of the racks are also employed,

depending upon the requirements.

The specimens are removed from the racks after a speciﬁed amount of time

and subjected to various tests such as appearance evaluation, electrical tests, and

mechanical tests. The results are compared with the test results from testing

control specimens. Typical aluminum exposure racks are shown in Fig. 22.

Outdoor Accelerated Weathering

To accelerate the outdoor weathering, a reliable method for predicting long-term

durability in a shorter time frame had to be developed. Outdoor accelerated test

methods were developed some 30 years ago by DSET Laboratories. The method

employs Fresnel-reﬂecting solar concentrators that use 10 ﬂat mirrors to uni-

formly focus natural sunlight onto specimens mounted in the target plane. High-

quality, ﬁrst-surface mirrors provide an intensity of approximately eight suns

with spectral balance of natural sunlight in terms of ultraviolet integrity. The

test method provides an excellent spectral match to sunlight, correlating well to

subtropical conditions such as southern Florida as well as an arid desert envi-

ronment such as Arizona.

BIBLIOGRAPHY 589

Fig. 23 Accelerated outdoor weathering testers. (Courtesy Atlas Electric Devices Company)

The test apparatus is a follow-the-sun rack with mirrors positioned as tangents

to an imaginary parabolic trough. The axis is oriented in a north–south direction,

with the north elevation having the capability for periodic altitude adjustment.

The target board, located at the focal line of the mirrors, lies under a wind

tunnel along which cooling air is deﬂected across the specimens. A nozzle as-

sembly is employed to spray the specimens with deionized water in accordance

with established schedules. Night-time spray cycles can be used to keep speci-

mens moist during the nontracking portion of the test. The entire 3-year real-

time Florida exposure test can be carried out in just 6 months depending on the

program start date. The test is widely used in automotive, agriculture, building,

textile, and packaging industries. Figure 23 illustrates outdoor accelerated weath-

ering test apparatus.

BIBLIOGRAPHY

V. Abolins, ‘‘Gardner Impact Versus Izod, Which is Better for Plastics?’’ Materials Eng., Nov., 52

(1973).

ASTM D1709 (Part 36); ASTM D3029 (Part 35), Annual Book of ASTM Standards, West Consho-

hocken, PA, 1978.

E. Baer, Engineering Design for Plastics, Reinhold, New York, 1964, Chapter 4.

R. L. Bergen, ‘‘Tests for Selecting Plastics,’’ Metal Progress, Nov., 107–108, (1966).

F. W. Billmeyer, Textbook of Polymer Science, Interscience, New York, 1962.

C. G. Bragaw, ‘‘Tensile Impact,’’ Mod. Plast., 33(10), (1956).

R. D. Deanin, Polymer Structure, Properties and Applications, Cahners, Boston, 1972.

O. Delatycki, ‘‘Mechanical Performance and Design in Polymers,’’ Applied Polymer Symposia,

17(134), Interscience, New York, 1971.

‘‘Design Guide,’’ Modern Plastics Encyclopedia, McGraw-Hill, New York, pp. 480–481, 1979–1980.

‘‘Design Guide,’’ Modern Plastics Encyclopedia, McGraw-Hill, New York, p. 49, 1980–1981.

D. R. Dregger, ‘‘How Dependable are Accelerated Weathering Tests for Plastics and Finishes?’’

Machine Design, Nov., 61–67 (1973).

J. H. Dubois and S. Levy, Plastics Product Design Engineering Handbook, Reinhold, New York,

1977.

EMI Shielding, Design Guide, ‘‘Performance of Alternative Conductive Coatings,’’ Enthone-OMI

Inc., New Haven, CT.

GE Plastics ‘‘EMI /RFI Shielding Guide,’’ Pittsﬁeld, MA.

T. D. Goldman, and J. T. Lutz, ‘‘Developing Low Temperature Impact Resistance PVC: A New

Testing Approach,’’ ANTEC, 25, 354–357 (1979).

590 PLASTICS TESTING

C. A. Harper, ‘‘Short Course in Electrical Properties,’’ Plast. World, April, 73 (1979).

R. D. Heap and R. H. Norman, Flexural Testing of Plastics, The Plastics Institute, London, England,

1969.

G. C. Ives, J. A. Mead, and M. M. Riley, Handbook of Plastics Test Methods, Iliffe Books, London,

England, 1971.

M. R. Kamal, ‘‘Weatherability of Plastic Materials,’’ Appl. Poly. Symp., No. 4, Interscience, New

York, 1967.

G. F. Kinney, Engineering Properties and Applications, Wiley, 1957.

R. A. Kinmonth, R. Saxon, and R. M. King, ‘‘Sources of Variability in Laboratory Weathering,’’

Polym. Eng. Sci., 10(5), 309–313 (1970).

S. Levy and H. Dubois, Plastics Product Design Engineering Handbook, Reinhold, New York, 1977.

LNP Corporation, ‘‘Predict Shrinkage and Warpage of Reinforced and Filled Thermoplastics,’’ Tech.

Bulletin, Malvern, PA, 1978.

G. Lubin, Handbook of Fiberglass and Advanced Plastics Composites, Reinhold, New York, 1969.

L. Mascia, The Role of Additives in Plastics, Edward Arnold, London, 1974.

B. Maxwell, and J. P. Harrington, ‘‘Effect of Velocity on Tensile Impact Properties of PMMA,’’

Trans. ASME, 74, 579 (1952).

S. McMichael and S. Fischer, ‘‘Understanding Materials with Instrumented Impact,’’ Materials Engr.,

April, 47 (1989).

R. Milby, Plastics Technology, McGraw-Hill, New York, 1973.

R. W. Miller, ‘‘Considerations in the Evaluation of Plastics in Electrical Equipment,’’ Plast. Design

Processing, July, 25–30 (1980).

L. E. Nielsen, Mechanical Properties of Polymers, Reinhold, New York, 1962.

J. L. O’Toole, ‘‘Creep Properties of Plastics,’’ in Modern Plastics Encyclopedia, McGraw-Hill, New

York, 1969–1970.

‘‘The Perils of Izod—Part 1,’’ Plast. Design Forum, May / June, (1980).

H. Reymers, ‘‘A New Temperature Index, Who Needs It, What does it Tell,’’ Modern Plastics, March,

79 (1970).

F. Rodriguez, Principles of Polymer Systems, McGraw-Hill, New York, 1970, Chapter 8.

W. Spath, Impact Testing of Materials, Gordon and Breach, New York, 1961.

J. M. Starita, ‘‘Impact Testing,’’ Plast. World, April, 58 (1977).

Symp. on Plastics Testing—Present and Future, ASTM Publication No. 132, American Society for

Testing and Materials, West Conshohocken, PA, 1953.

J. D. Tanzillo, ‘‘Development of an Impact Test for Evaluation of Toughness of Rigid Plastic Building

Components,’’ ANTEC, 15, 346–349 (1969).

H. P. Tardif and H. Marquis, ‘‘Impact Testing with an Instrumented Machine,’’ Metal Progress, Feb.,

58 (1964).

G. R. Tryson, M. T. Takemori, and A. F. Yee, ‘‘Puncture Testing of Plastics: Effects of Test Geom-

etry,’’ ANTEC, 25 (1979).

Underwriters Laboratories Publication, ‘‘Polymeric Materials—Long Term Property Evaluations,’’

UL 746B, U.L. Inc., Melville, New York, 1997.

Underwriters Laboratories Standards for Safety, UL 746 A-B-C-D, U.L. Inc. Melville, New York,

1997.

P. I. Vincent, Impact Tests and Service Performance of Thermoplastics, The Plastics Institute, London,

England, 1971.

R. F. Westover, ‘‘The Thirty Years of Plastics Impact Testing,’’ Plastics Tech, 4, 223–228, 348–352

(1958).

R. F. Westover and W. C. Warner, ‘‘Tensile Impact Test for Plastic Materials,’’ Res. and Stand., 1(11)

867–871 (1961).

J. G. Williams, Stress Analysis of Polymers, Longman Group Limited, London, 1973, Chapter 3.

R. M. Winolow, W. Matreyek, and A. M. Trozzolo, ‘‘Polymers Under Weather,’’ S.P.E.J. 28(7), 19–

24 (1972).

591

CHAPTER 21

CHARACTERIZATION AND

IDENTIFICATION OF PLASTICS

Vishu Shah

Consultek

Brea, California

1 MATERIAL

CHARACTERIZATION TESTS 591

1.1 Melt Index Test (ASTM D1238,

ISO 1133) 592

1.2 Rheology 595

1.3 Viscosity Tests 599

1.4 Gel Permeation Chromatography 599

1.5 Thermal Analysis Techniques 602

1.6 Spectroscopy 607

2 IDENTIFICATION ANALYSIS OF

PLASTIC MATERIALS 607

2.1 Melting Point Determination 610

2.2 Solubility Test 612

2.3 Copper Wire Test 613

2.4 Speciﬁc Gravity Test 613

2.5 Chemical and Thermal Analysis

for Identiﬁcation of Polymers 613

BIBLIOGRAPHY 614

1 MATERIAL CHARACTERIZATION TESTS

The plastics industry has grown phenomenally in the past two decades. Plastic

material consumption has quadrupled. Today there are countless numbers of

processors consuming in excess of 100 million pounds of material every year.

An increasing number of processors are looking into various techniques for

characterizing the incoming plastic resin to guard against batch-to-batch varia-

tions. Such variation in the properties and the processability of the polymer have

been very costly.

To understand the phenomenon of batch-to-batch variation, one must under-

stand the polymerization process. The polymerization mechanism can often be

very complex. Basically, it involves adding a monomer or a mixture of mono-

mers into a reaction kettle along with several other ingredients such as a catalyst,

an initiator, and water, depending on the type of polymerization process. The

contents are agitated at a speciﬁc speed. The time, temperature, and pressure are

carefully controlled. During this process, the monomer is converted into a poly-

mer. The properties of the ﬁnal product depend on several factors such as the

monomer-to-water ratio, if water is present, the degree of agitation, the removal

of exothermic heat generated during the polymerization, and the ability of the

polymer to dissolve in monomer. This is further complicated by the fact that

different polymerization techniques are used to form the same chemical type of

polymer. Since it is difﬁcult to manufacture a monodispersed polymer (a polymer

HandbookofMaterialsSelection.EditedbyMyerKutz

592 CHARACTERIZATION AND IDENTIFICATION OF PLASTICS

in which all molecules have the same size) commercially, we are forced to live

with variations in the size and weight of molecules in a polymer. Such variations

in the size and the weight of the polymer molecules are also extremely difﬁcult

to control. The relative proportions of molecules of different weights within a

polymer comprise its molecular weight distribution. Depending on the range of

distribution (narrow or broad), the processibility and the properties of a polymer

vary signiﬁcantly. This basic nature of the polymerization process creates a need

for material characterization tests that can be used as an insurance against var-

iations in the characteristics of the polymer.

Table 1 lists various applications using rheometry and thermal analysis tech-

niques.

There are numerous ways of characterizing a polymer. Some are very basic

and simple, others are more sophisticated and complex. The ﬁve most common

and widely accepted tests are:

Melt index (melt ﬂowrate) test, rheological tests

Viscosity tests

Gel permeation chromatography

Thermal analysis [thermogravimetric analysis (TGA), thermomechanical anal-

ysis (TMA), and differential scanning calorimetry (DSC)]

Spectroscopy

1.1 Melt Index Test (ASTM D1238, ISO 1133)

The melt index, also known as melt ﬂow rate (MFR), test measures the rate of

extrusion of a thermoplastic material through an oriﬁce of speciﬁc length and

diameter under prescribed conditions of temperature and pressure. This test is

primarily used as a means of measuring the uniformity of the ﬂowrate of the

material. 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. However, the data obtained from this test

does not necessarily correlate with the processibility of the polymer. This is due

to the fact that plastic materials are seldom manufactured without incorporating

additives that affect the processing characteristics of a material such as stability

and ﬂowability. The effect of these additives is not readily observed via the melt

index test. The rheological characteristics of polymer melts depend on a number

of variables. Since the values of these variables may differ substantially from

those in large-scale processes, the test results may not correlate directly with

processing behavior.

The melt index apparatus (Fig. 1) is preheated to a speciﬁed temperature. The

material is loaded into the cylinder from the top and a speciﬁed weight is placed

on a piston. The material is allowed to ﬂow through the die. The initial extrudate

is discarded since it may contain some air bubbles and contaminants. Depending

on the material or its ﬂowrate, cuts for the test are taken at different time inter-

vals. The extrudate is weighed and melt index values are calculated in g/10 min.

A commercial melt indexer is shown in Fig. 2.

The melt index values obtained from the test can be interpreted in several

different ways. First of all, a slight variation (up to 10% in the case of polyeth-

1 MATERIAL CHARACTERIZATION TESTS 593

Table 1 Characterization through Rheology and Thermal Analysis: Applications ⴙ

Instruments ⴝ Solutions

Rheometry Thermal Analysis

Application

Torque

Rheometer

Rotational

Rheometer

Capillary

Rheometer DMA DSC TG / DTA TMA DES

Bubble stability-

blown ﬁlm

⻬⻬

Compositional

analysis

⻬⻬

Compounding ⻬⻬

Creep and stress

relaxation

⻬⻬⻬

Curing studies ⻬⻬⻬⻬

Degree of cross-

linking

⻬⻬

Dielectric prop-

erties

⻬

Die swell ⻬⻬

Electrorheology ⻬

Elongational vis-

cosity

⻬

Gamma, beta

transitions

⻬⻬

Gel point ⻬⻬⻬

Glass transition ⻬⻬⻬⻬⻬

Haze and gloss

of ﬁlms

⻬⻬

Heat capacities ⻬

Impact resistance ⻬⻬⻬

Lifetime predic-

tions

⻬⻬

Measure degree

of dispersion

⻬⻬⻬⻬

Measure rheo-

logical proper-

ties

⻬⻬⻬⻬⻬

Melt strength ⻬⻬

Melting tempera-

tures

⻬⻬⻬⻬⻬

Molecular weight ⻬⻬⻬⻬

Molecular weight

distribution

⻬⻬⻬⻬

Oxidative stabil-

ity

⻬⻬

Processibility ⻬⻬⻬⻬

Sample prepara-

tion

⻬

Shear viscosity ⻬⻬⻬

Shrinkage forces ⻬

Tack and peel of

pressure-

sensitive addi-

tives

⻬⻬⻬

Thermal stability ⻬⻬⻬⻬⻬⻬

Viscoelastic

properties

⻬⻬⻬

594 CHARACTERIZATION AND IDENTIFICATION OF PLASTICS

Table 1 (Continued )

Information Process

Data obtainable

Composition

Resins, polymers

modiﬁers

DSC Types present, plus ratio if copolymer, blend or mixture

GC Polymers, oligomers, and residual monomer; amounts

present

Additives DSC Deduce presence and amount from thermal effects

(stabilizers, antioxidants, blowing agents, plasticizers,

etc.)

GC Detect any organic additive (by MW)

Reinforcement, ﬁllers TG Amount (from weight of ash)

Moisture, volatiles TG Amounts (from weight loss)

DSC Amounts (if sufﬁcient heat absorbed)

Regrind level DSC Deduce amount from melting-point shift

GC Deduce amount from shift in MW distribution

Processability

Melting behavior DSC Melt point and range (each resin, if blend); melt-energy

requirements

Flow characteristics GC Deduce from balance of high and low MW polymer in

MW distribution

Physical, Mechanical

Glass transition temper-

ature

DSC Shown by step-up in energy absorption as resin heats

(marginal for some semicrystalline resins)

TM Detected by sample’s expansion

Crystallinity DSC Calculate percentage from heat of fusion during melt-

ing; also can ﬁnd time–temperature conditions for

desired percent crystallinity

Temsile, ﬂexibility, im-

pact

GC Deduce from balance of high and low MW polymer in

MW distribution

DSC Deduce from overall composition

Cure Characteristics, Thermosets

Reactive systems DSC Shows gel time, cure temperature, and cure time

Prepreg DSC Measures unreacted resin in B-stage prepreg or after

cure (by volatiles)

GC As above, but checks by MW analysis of composite

residue

DSC ⫽ differential scanning calorimeter; GC ⫽ gel chromatography; TM ⫽ thermomechanical

analysis.

These techniques do not speciﬁcally identify materials. Materials can be identiﬁed by matching the

instrument’s test curves with those of known polymers or compounds. Otherwise other analytical

procedures must be used. MW

⫽ molecular weight.

(Courtesy Haake-USA)

ylene) in the melt index value should not be interpreted as indicating a suspect

material. The material supplier should be consulted to determine the expected

reproducibility for a particular grade of plastic material. A signiﬁcantly different

melt index value than the control standard may indicate several different things.

The material may be of a different grade with a different ﬂow characteristic. It

also means that the average molecular weight or the molecular weight distri-

bution of the material is different than the control standard and may have dif-

ferent properties.

1 MATERIAL CHARACTERIZATION TESTS 595

Fig. 1 Schematic of melt indexer. (Reprinted by permission of ASTM.)

Melt index is an inverse measure of molecular weight. Since ﬂow character-

istics are inversely proportional to the molecular weight, a low-molecular-weight

polymer will have a high melt index value and vice versa.

1.2 Rheology

Rheology is deﬁned as study of ﬂow. Viscosity is the measure of resistance to

ﬂow due to internal friction when one layer of ﬂuid is caused to move in rela-

tionship to another layer. The greater the friction, the greater the amount of force

required to cause this movement, which is called shear. Shearing occurs when-

ever the ﬂuid is physically moved or disturbed as in pouring, mixing, and spray-

ing. Highly viscous ﬂuids, therefore, require more force to move then less

viscous materials. The velocity gradient is a measure of the speed at which the

intermediate layers move with respect to each other. It describes the shearing

the liquid experiences and is thus called shear rate. Shear stress is the stress

596 CHARACTERIZATION AND IDENTIFICATION OF PLASTICS

Fig. 2 Melt indexer. (Courtesy Dynisco-Kayeness Polymer Test Systems)

developing in the polymer melt when the layers in a cross section are gliding

along each other. When the ratio of shearing stress to the rate of shear is con-

stant, as in case of water, the ﬂuid is called a Newtonian ﬂuid. In the case of

non-Newtonian ﬂuids, the ratio varies with shearing stress or stated another way,

when shear rate is varied, the shear stress does not vary in the same proportion.

The viscosity of such ﬂuids will change with the change in shear rate. All

polymeric materials exhibit non-Newtonian ﬂow behavior. This information con-

cerning the ﬂow of polymeric material is very useful in identiﬁcation and char-

acterization of the polymers. Rheological measurements are very useful in the

determination of molecular, elastic, physical properties of polymers, simulation,

determination of large-scale processing conditions, and basic research and de-

velopment. Instruments developed for measuring the ﬂow properties of polymers

are known as rheometers. Many different types of rheometers have been devel-

oped. Data analysis and interpretation has been simpliﬁed with newly developed

Windows-based software.

1 MATERIAL CHARACTERIZATION TESTS 597

The following describes three major types of rheometers, most commonly

used in the industry.

Torque Rheometer

Torque rheometry is used extensively for measuring the rheological properties

as well as determining melt ﬂow values, thermal stability of polymers, degra-

dation time, and characterization of different formulations.

Rotational Rheometers

Many types of rotational rheometers have been developed over the years. Cone

and plate, couette, torsional, and disc are most common.

The Spindle Viscometer (ASTM D2393) is one of the simplest instruments

to use of all the rheometers used today. It measures torque required to rotate an

immersed element (the spindle) in a ﬂuid. The spindle is driven by a synchronous

motor through a calibrated spring; the deﬂection of the spring is indicated by a

pointer and a dial or a digital display. By utilizing a multiple speed transmission

and interchangeable spindles, a variety of viscosity ranges can be measured. The

sample is preconditioned by placing it in a constant temperature bath at the

speciﬁed test temperature. The proper sized spindle is allowed to rotate in the

sample for 2 min. The instrument is stopped through the use of a clutch, and

the reading is taken from the dial or read directly from the digital display. The

test is repeated until a constant reading is obtained. Viscosity is calculated using

the factors provided with the viscometer. Data can be formatted to a printer or

can be linked to a computer using a special software package. The newer model

viscometers are programmable and have the capability of measuring and dis-

playing viscosity and temperature simultaneously. Figure 3 shows a digital pro-

grammable viscometer.

Cone-and-plate viscometer is ideal for determining absolute viscosity of ﬂuids

in a small sample volume. The commercially available cone-and-plate viscom-

eter (Wells-Brookﬁeld), a precise torque measuring system, which consists of a

calibrated beryllium–copper spring connecting the drive mechanism to a rotating

cone, senses the resistance to rotation caused by a presence of sample ﬂuid

between the cone and a stationary ﬂat plate. The resistance to the rotation of the

cone produces a torque that is proportional to the shear stress in the ﬂuid. The

amount of torque is indicated on a dial or displayed digitally.

Capillary Rheometer

Quite often, the melt index test results simply do not provide sufﬁcient infor-

mation. This is because the melt index is a single-point test. The ﬂowrates are

measured at a single shear stress and shear rate performed at one set of tem-

peratures and geometric conditions. Furthermore, since the melt index measure-

ment takes account of the behavior of the polymer at only one point, it is quite

possible for two materials with the same melt index values to behave completely

different at shear stresses that are different from the ones used during the melt

index measurements. The capillary rheometer measures apparent viscosity or

melt index over an entire range of shear stresses and shear rates encountered in

compression molding, calendering, extrusion, injection molding, and other