PHÂN TÍCH POLYME (POLYMER ANALYSIS)

TRƯỜNG ĐẠI HỌC BÁCH KHOA ĐÀ NẴNG KHOA HOÁ

§ § §

PHÂN TÍCH POLYME

(POLYMER ANALYSIS)

TS. ĐoànTh ị Thu Loan

Polymer analysis

(cid:252)Is a branch of polymer science dealing with analysis and characterisation of

polymers.

(cid:252)The complication of macromolecular chains, the dispersion in molecular

weight, tacticity, crystallinity, orientation, composition of polymers etc. and

complex morphological systems

analysis of polymer „

the small organic materials

(cid:222)

Focus on viscoelasticproperties, dynamic mechanical testing.

(cid:222)

Methods of polymer analysis

Chemical, Molecular and Structural Characterisation Surface Characterisation Mechanical and Physical Properties

-Surface roughness, -Chemical composition, -Interface characetrisation

•-AFM, SEM •-FT-IR •-Pull-out test

•Instronmechanical tester •Vickerhardness tester •DMA •Melt flow indexer •Torsions Rheometer

•

-Molecular weight determination, -Microstructuralcharacterisation and compositional analysis, -Crystallinity, -Investigation of polymer morphology, particle size, -Contact angle and wettability measurements -Tensile, flexural, impact, compression, hardness tests, -Rheologicaland viscoelastic properties, stiffness and modulus, surface tension, permeation and diffusion in polymers, adhesion tests, density

Instruments •FT-IR •IR-microscope •GPC ( size exclusion chromatography SEC) •-Viscosimetry •-X-ray (WAXS and SAXS) •-EM, SEM, TEM, AFM •-Dynamic and static methods for contact angle measurements.

Methods of polymer analysis

Thermal Behaviour Miscellaneous (hontap) Electrical and Optical Properties

Conductivity, electric -Melting point, glass transition Purity and molecular

current in solution, temperature, free rotation temperature, weight of small

light emitting and -Degradation and stability behaviour of molecules, water content

electromagnetic polymers in organic solvents,

surface tension properties

•Thermogravimetricanalyser (TGA)

measurement, pH

•TGA-FTIR coupled technique

•

•Differential scanning calorimetry(DSC)

•GC •pH meter •HPLC •Karl-Fischer titration

•Modulated differential scanning

Instruments Inolabconductivity meter

•Dynamic thermomechanicalanalyser

calorimetry(ADSC)

(DMTA) •Dielectric relaxation

Purpose of polymer analysis

-For quality control

-For predicting service performance

-To generate design data

-To investigate failures

Essential to identify the purpose of testing, because the requirements for each of the purposes are different.

-Precision Balance of these attributes,

-Reproducibility according to the purpose of

-Rapidity the test -Complexity -Automated test -Nondestructive test -Cost

Quality Control Tests

(cid:252)Nondestructive methods are advantageous and indeed essential when

100% of the output is being tested.

(cid:252)The tests should be simple and

inexpensive, and automation will

probably aid the rapidity of testing.

(cid:252)Tests related to product performance are preferred.

Tests Predicting Product Performance

(cid:252)The most important factor is that the tests

relate to service conditions

and to aspects of product performance.

(cid:252)should not be too complex, although rapidity and cheapness are less

important than was the case with quality control.

(cid:252)Nondestructive tests are not always appropriate when predicting product

performance, as it may be necessary to establish the point at which failure

occurs.

Tests for Producing Design Data

(cid:252)Usually test pieces are of a simple shape and a specified size , whereas

the product may be of a different geometry and size

(cid:252)Data must be presented in a form that enables the designer to allow for

changes in geometry, time scale, etc.. which implies

detailed and

comprehensive understanding of material behavior

(cid:252)It follows that data of this type are expensive to produce and that results

are unlikely to be obtained with great rapidity.

(cid:252)However, automation may be advantageous, particularly in the case of

tests running for a long time (creep tests)

Tests for Investigating Failures

(cid:252)Some understanding of the various mechanisms of failure is necessary before

suitable tests can be chosen.

(cid:252) Tests need not be complex but must be relevant

Ex: a simple measurement of product thickness may establish thatthere has

been a departure from the specified design thickness.

(cid:252)The absolute accuracy of the test may not be important, but it is essential that

it be capable of discriminating between the good and the bad product.

What are our expectations of polymer materials?

•Excellent Characteristics:

Mechanical and Physical Properties

Thermal Behaviour

Electrical and Optical Properties •Safe to use

Surface and interface Characteristics •Light weight

•Reliable, durable

•Low cost

•Less adverse environmental impact

•Good resistance to environmental attacks

Mechanical Testing

of Polymers

Types of MechnicalTests

(h)

(i)

Flexural test (d) (e) (f) Tensile test (a) Impact test (h) (i)

Compression test (b) Shear (g)

Tensile test

Scope:

(cid:252)Measure the force required to break a specimen and the extent to which the

specimen stretches or elongates to that breaking point.

(cid:252)Produce a stress-strain diagram, which is used to determine tensile modulus.

(cid:252)The data is often used to specify a material, to design parts towithstand

application force and as a quality control check of materials.

(cid:252)Since the physical properties of many materials (especially thermoplastics) can

(cid:222) vary depending on ambient temperature test materials at temperatures that

simulate the intended end use environment.

Tensile test

Specimen Size:

(cid:252)The most common specimen for ISO 527 is the ISO 3167 Type 1A

multipurpose specimen.

(cid:252)ASTM D882 uses strips cut from thin sheet or film.

*The multipurpose test specimen:

+150 mm long,

+The centersection: 10 mm wide *4 mm thick *80 mm long.

A tensile dog bone specimen

For the composite samples

Longitudinal test

Transverse test

Tensile test

Test Procedure:

(cid:252)Specimens are placed in the

grips and pulled until failure.

(cid:252)For ASTM D638, the test

speed is determined by the

material specification.

(cid:252)For ISO 527 the test speed

is typically 5 or 50mm/min for

measuring strength and

elongation

+and 1mm/min for measuring

modulus.

(cid:252) An extensometer is used to

Tensile2.wmv

determine elongation and

tensile modulus.

Stress –Strain Behavior

Characteristics of stress-strain behavior:

•

(cid:252) Modulus of elasticity (stiffness, elastic

modulus, Young’s modulus) is the slope of s

, s s e r t

s s the stress-strain curve in the elastic region

y)is the stress applied to a

(cid:252) Yield strength (s

material that just causes permanent

2%0

E deformation e e

y Strain, e

(cid:252) Tensile strength (TS) is defined at the

= d /l

fracture point and can be lower than the

yield strength

(cid:252) Ultimate tensile strength is the stress that

corresponds to the maximum load

(cid:252) Elongation at break (% e ) –the increase in

length of a specimen under tension before

P= Applied load A = Original cross-sectional area it breaks (Strain).

Stress-train behavior of polymers

Stress –Strain Behavior

(cid:252)Moduliof elasticity for polymers are ~ 10MPa-4GPa (compare to metals ~ 50 -

400 GPa)

(cid:252)Tensile strengths are ~ 10 -100MPa (compare to metals, hundreds of MPato

several GPa)

(cid:252)Elongation can be up to 1000 % in some cases (< 100% for metals)

(cid:252)Polymers are also very sensitive to the rate of deformation (strain rate).

Decreasing rate of deformation has the same effect as increasingT.

TENSILE RESPONSE: ELASTOMER CASE

Deformation of Amorphous Polymers

Deformation of Semicrystallineand crosslinkedPolymers

Stress-strain curves

Flexural test

Scope:

(cid:252)Measures the force required to bend a

beam under 3 point loading conditions.

(cid:252)The data is often used to select materials

for parts that will support loads without

flexing.

(cid:252)Flexural modulus is used as an indication

of a material’s stiffness when flexed.

(cid:252)can test materials at temperatures that

simulate the intended end use environment.

Flexural test

(cid:252)A variety of specimen shapes can be used Specimen Size:

(cid:252)The most commonly used specimen size:

+ 3.2mm x 12.7mm x 125mm for ASTM D790

+10mm x 4mm x 80mm for ISO 178

Test Procedure: (cid:252) Most commonly the specimen lies on a span and the load is

applied to the centerby the loading nose producing three point

bending at a specified rate.

(cid:252)The parameters for this test are :

+The support span;

+The speed of the loading

+The maximum deflection for the test.

These parameters are based on the test specimen

thickness, and are defined differently by ASTM and ISO.

Flexural test

m : initial slope of the load vs. deflection curve

=s (cid:252)Flexural strength 3 2

(cid:252)Flexural modulus LF 2 hb 3 Lm 4 hb

Flexural test

For relatively thin samples ﬁ two point loading

For thick samples ﬁ 4 point loading

Izod Impact Testing (Notched Izod)

Scope:

(cid:252)Notched IzodImpact is a single point test that measures

a materials resistance to impact from a swinging

pendulum.

(cid:252) Izodimpact is defined as the kinetic energy needed to

initiate fracture and continue the fracture until the

specimen is broken.

(cid:252)Izodspecimens are notched to prevent deformation of

the specimen upon impact.

(cid:252)This test can be used as a quick and easy quality control

check to determine if a material meets specific impact

properties or to compare materials for general toughness.

Izod Impact Testing (Notched Izod)

Specimen Size:

(cid:252) 64 x 12.7 x 3.2 mm for ASTM D256

(cid:252)The preferred thickness is 6.4 mm because it is not as likely tobend or crush

(cid:252)The depth under the notch of the specimen is 10.2 mm

(cid:252)80 x 10 x 4 mm forISO 180

(cid:252)The depth under the notch of the specimen is 8mm

Izod Impact Testing (Notched Izod)

Test Procedure:

(cid:252)The specimen is clamped into the pendulum impact test

fixture with the notched side facing the striking edge of the

pendulum.

(cid:252)The pendulum is released and allowed to strike through

the specimen.

(cid:252)If breakage does not occur, a heavier hammer is used

izodimpact.wmv

until failure occurs.

(cid:252)Since many materials (especially thermoplastics) exhibit

lower impact strength at reduced temperatures (cid:222) to test

materials at temperatures that simulate the intended end

use environment

Reduced Temperature Test procedure:

(cid:252)The specimens are conditioned at the specified temperature in a freezer

until they reach equilibrium.

(cid:252)The specimens are quickly removed, one at a time, from the freezer and

impacted.

(cid:252)Neither ASTM nor ISO specify a conditioning time or elapsed timefrom

freezer to impact -typical values from other specifications are 6 hours of

conditioning and 5 seconds from freezer to impact.

Data

ASTM

(cid:252)Impact energy is expressed in J/m or ft-lb/in.

(cid:252)Impact strength is calculated by dividing impact energy in J (orft-lb) by the

thickness of the specimen.

(cid:252)The test result is typically the average of 5 specimens.

ISO

(cid:252)Impact strength is expressed in kJ/m2

(cid:252)Impact strength (a cU)is calculated by dividing impact energy in J by the

area under the notch.

3 10

W bh

(cid:252)The test result is typically the average of 10 specimens.

The higher the resulting number, the tougher the material.

W: energy b = width of the sample h = thickness of the sample

Impact Testing

Compression test

Scope:

(cid:252)Compressive properties describe the behaviorof a

material when it is subjected to a compressive load.

(cid:252)Loading is at a relatively low and uniform rate.

(cid:252)Compressive strength and modulus are the two most

common values produced.

Specimen size: (cid:252)Blocks or cylinders

(cid:252)For ASTM D695:

+The typical blocks: 12.7 x 12.7 x 25.4mm

+The cylinders:12.7mm diameter and 25.4mm long

(cid:252)For ISO 604: the preferred specimens:

+50 x 10 x 4mm for modulus

+10 x 10 x 4mm for strength

Compression test

Test Procedure:

(cid:252)The specimen is placed between compressive plates

parallel to the surface.

(cid:252)The specimen is then compressed at a uniform rate.

(cid:252)The maximum load is recorded along with stress-strain

data.

(cid:252)An extensometer attached to the front of the fixture is

used to determine modulus.

maximum compressive load

Compressive strength =

minimum cross-sectional area

change in stress

Compressive modulus =

change in strain

Rockwell Hardness tester

Scope:

(cid:252) A hardness measurement based on the net increase in

depth of impression as a load is applied.

(cid:252)Hardness numbers have no units and are commonly

given in the R, L, M, E and K scales.

(cid:252)The higher the number in each of the scales, the harder

the material

ﬁ (cid:252)The harder the material better resistance to plastic

deformation or cracking in compression, better wear

properties

Specimen size:

(cid:252)Standardspecimen of 6.4mm thickness

(cid:252) is moldedor cut from a sheet.

DurometerHardness -Shore Hardness

Scope:

(cid:252)Determine the relative hardness of soft materials,

usually plastic or rubber.

(cid:252)The test measures the penetration of a specified

indentorinto the material under specified conditions of

force and time.

(cid:252)The hardness value is often used to identify or

specify a particular hardness of elastomersor as a

quality control measure on lots of material.

DurometerHardness -Shore Hardness

Specimen size:

(cid:252)Generally 6.4mm (¼in) thick for ASTM D 2240.

Test Procedure:

(cid:252)The specimen is first placed on a hard flat surface.

(cid:252)The indentorfor the instrument is then pressed into the specimen making sure

that it is parallel to the surface.

(cid:252)The hardness is read within one second (or as specified by the customer) of firm

contact with the specimen.

Data:

(cid:252)The hardness numbers are derived from a scale.

(cid:252)Shore A and Shore D hardness scales are common, with the A scalebeing used

for softer and the D scale being used for harder materials.

Density and Specific Gravity ASTM D792, ISO 1183

Scope:

(cid:252) Density is the mass per unit volume of a material.

(cid:252) Specific gravity is a measure of the ratio of mass of a given volume of

material at 23°C to the same volume of deionizedwater.

(cid:252)Specific gravity and density are especially relevant because plastic is

sold on a cost per pound basis and a lower density or specific gravity

means more material per pound or varied part weight.

Test procedures:

(cid:252) For sheet, rod, tube and moldedarticles.

(cid:252)The specimen is weighed in air then weighed when immersed in distilled water at

23°C using a sinker and wire to hold the specimen completely submerged as

required.Density and Specific Gravity are calculated.

(cid:252)Any convenient size

+Specific gravity = a/[(a + w)-b]

a = mass of specimen in air.

b = mass of specimen and sinker (if used) in water.

W = mass of totally immersed sinker if used and partially immersed wire.

+Density, kg/m3= (specific gravity) x (997.6)

Bulk Density ASTM D1895B

(cid:252)Bulk density is defined as the weight per unit volume of material.

(cid:252)Bulk density is primarily used for powders or pellets.

(cid:252)The test can provide a gross measure of particle size and dispersion which can affect

material flow consistency and reflect packaging quantity.

(cid:252)A funnel is suspended above a measuring cylinder.

(cid:252)The funnel is filled with the sample and allowed to freely flow into the measuring

cylinder.

(cid:252)The excess material on top of the measuring cylinder is scraped off with a straight

edge.

(cid:252)The sample and the cylinder is then weighed and the weight / volume (Bulk Density) is

determined.

(cid:252)Apparent density value is recorded as g/cm3

Thermal Analysis

(cid:252)Thermal analysis (TA) is frequently used to describe analytical experimental

techniques which investigate the behaviourof a sample as a function of temperature.

TA refers to conventional TA techniques such as:

+Differential thermal analysis (DTA)

+Differential scanning calorimetry(DSC)

+Dynamic mechanical analysis (DMA)

+Thermogravimetry(TG/TGA)

Representative TA curves

Thermal Analysis

The advantages of TA over other analytical methods can be summarized as follows:

(i)the sample can be studied over a wide temperature range using various temperature

programmes

(ii)almost any physical form of sample (solid, liquid or gel) can beaccommodated using

a variety of sample vessels or attachments

(iii)a small amount of sample (0.1 µg-10 mg) is required

(iv)the atmosphere in the vicinity of the sample can be standardized

(v)the time required to complete an experiment ranges from several minutes to several

hours

(vi)TA instruments are reasonably priced

Differential thermal analysis (DTA)

Scope:

(cid:252)Measure the differential temperature between a sample and a reference pan

ﬁ to determine the temperature of the transitions

Test procedures:

(cid:252)As the sample goes through the programmed temperature change, there is no

temperature difference until the sample undergoes an exothermic or endothermic

chemical reaction or change of physical state.

(cid:252)The thermal event (a temperature difference between the sample and the

D reference (D T)) will be recordedﬁ Tversus time or temperature plot

Differential thermal analysis (DTA)

Schematic of a DTA apparatus

A DTA curve

The subscripts represent: s-sample, r-reference, i-initial,f-final.

Differential Scanning Calorimeter(DSC)

Scope: DSC measures:

Tg = Glass Transition Temperature = The temperature (°C) at which an amorphous

polymer or an amorphous part of a crystalline polymer goes from a hard, brittle state to

a soft, rubbery state.

Tm = melting point = The temperature (°C) at which a crystalline polymer melts.

DHm = the amount of energy in (joules/gram) a sample absorbs while melting.

Tc = crystallization point = is the temperature at which a polymercrystallizes upon

heating.

DHc = the amount of energy (joules/gram) a sample releases while crystallizing.

The data can be used to identify materials, differentiate homopolymersfrom

copolymers or to characterize materials for their thermal performance.

Test Procedure:

(cid:252)A sample of 10 to 20 mg in an aluminum

sample pan is placed into the differential

scanning calorimeter.

(cid:252)The sample is heated at a controlled

rate (usually 10°/min)

(cid:252)a plot of heat flow versus temperature

is produced.

(cid:252)The resulting thermogram

is then

Dsc3.wmv

analyzed.

DSC

Some factors influence on DSC resultsc

Does the sample contain volatile components? 1.

g) by up to

(cid:252) 2 to 3% water/solvent can lower the glass transition temperature(T

100oC

(cid:252) Evaporation creates endothermic peaks in standard (non-hermetic) DSC pans and

can be suppressed with use of hermetic DSC pans.

2. At what temperature does the sample decompose?

(cid:252) Set the upper limit of the DSC experiment based on decompositiontemperature

(TGA). No meaningful DSC data can be obtained once decompositionresults in a

5% weight loss

(cid:252) Decomposition affect: the quality of the baseline due to both endothermic and

exothermic heat flow, the quality of the baseline for future experiments and can affect

the useful lifetime of the DSC cell due to corrosion.

Some factors influence on DSC results

3. How does thermal history (temperature and time) affect DSC results on the sample?

4. Identical materials can look totally different based on:

- Storage temperature and time.

- Cooling rate from a temperature above Tgor above the melting point.

- Heating rate.

- Different kinds of experiments may need to be performed in orderto measure the

current structure vs. comparing samples to see if the materials are the same.

5. How is the Influence of the atmosphere (air or inert gases (N2, argon,..))

Tgsensitivity

Use >10oC/min heating rates

Thermogravimetry(TG)

(cid:252)To characterize the decomposition and the thermal stability of materials.

(cid:252)To provide an indication of the composition of the sample, including volatiles and

inert filler

(cid:252)The change of mass as function of temperature (scanning mode) ortime

(isothermal mode)

(cid:252)To get information about the following processes:

vDecomposition

vDesorption

vAbsorption

vVaporization

vOxidation

vReduction

Tma.wmv

Block diagramofa thermobalance

Test procedure:

(cid:252)Set the inert (usually N2) and oxidative (air, O2) gas flow rates to provide the

appropriate environments for the test.

(cid:252)Place the test material in the specimen holder and raise the furnace.

(cid:252)Set the initial weight reading to 100%, then initiate the heating program.

(cid:252)The gas environment is preselectedfor :

veither a thermal decomposition (inert -nitrogen gas), an oxidative decomposition

(air or oxygen)

vor a thermal-oxidative combination.

vSample amount: 10 to 15 milligrams

TG curve

TG and DTG curves for the thermal decomposition of calcium oxalate (CaC2O4. H2O in argon at 20oC/min(3).

The three steps in Figure are: (1)The loss of H2O to form anhydrous oxalate (2)The loss of CO to form the carbonate ,and (3)The loss of CO to form CaO

120

100

As received_J3 NaOH_J3 NaOH/(APS+XB)_J3 NaOH/Y9669_J3

)

( t h g i e

D e v i a t i o n

-20

100

200

500

600

300

400

Temperature(°C)

TG and DTG curves of jute fibrewith different treatments

Dynamic Mechanical Analysis (DMA)

Scope:

(cid:252)Determines elastic modulus (or storage modulus, G'),

viscous modulus (or loss modulus, G'') and damping

coefficient (Tan D) as a function of temperature, frequency

or time.

(cid:252)Results are typically provided as a graphical plot of G',

G'', and Tan Dversus temperature.

(cid:252)Identifies transition regions in plastics, such as the glass

transition, and may be used for quality control or product

development.

(cid:252) Can recognize small transition regions that are beyond

the resolution of DSC (Differential Scanning Calorimetry).

Dynamic Mechanical Analysis (DMA)

Specimen size:

-Typically 56 x 13 x 3 mm, cut from the centersection of an ASTM Type I tensile bar,

or an ISO multipurpose test specimen.

Test Procedure:

(cid:252)The test specimen is clamped between the movable and stationary fixtures, and

then enclosed in the thermal chamber.

(cid:252)Frequency, amplitude, and a temperature range appropriate for the material being

tested are input.

(cid:252)The Analyzer applies torsionaloscillation to the test sample while slowly moving

through the specified temperature range.

Is DMA Thermal Analysis or Rheology

(cid:216) Definitions

(cid:216) Thermal Analysis is the measurement of some characteristic of a

substance as a function of temperature or time.

(cid:216) Rheology is the science of flow and deformation of matter.

(cid:216) DMA is the general name given to an instrument that mechanically deforms

a sample and measures the sample response. The deformation can be

applied sinusoidally, in a constant (or step) fashion, or under a fixed rate.

The response to the deformation can be monitored as a function of

temperature or time.

Dynamic Mechanical Testing

Deformation

l An oscillatory (sinusoidal) deformation (stress or strain) is applied to a sample.

Response

lThe material response (strain or stress) is measured.

Phase angle d

lThe phase angle d , or phase shift, between the deformation and response is measured.

Dynamic Mechanical Testing

Purely Elastic Response (HookeanSolid)

Purely Viscous Response (Newtonian Liquid)

d = 90

d = 0

Stress

Strain

Dynamic Mechanical Testing: ViscoelasticMaterial Response

Phase angle 0 < d < 90

Strain

Stress

DMA ViscoelasticParameters

G = Stress/Strain

G' = (stress/strain)cosd

The Modulus: Measure of materials overall resistance to deformation.

G" = (stress/strain)sind

The Elastic (Storage) Modulus: Measure of elasticity of material. The ability of the material to store energy.

The Viscous (loss) Modulus: The ability of the material to dissipate energy. Energy lost as heat.

Tan d = G"/G'

Tan Delta: Measure of material damping -such as vibration or sound damping.

Storage and Loss of a ViscoelasticMaterial

SUPER BALL

LOSS

TENNIS BALL

STORAGE

DMA ViscoelasticParameters: Damping, tan d

Dynamic measurement represented as a vector

Phase angle d

lThe tangent of the phase angle is the ratio of the loss modulus to the storage modulus.

tan d = G"/G' l"TAN DELTA" (tan d ) is a measure of the damping ability of the material.

DMA 2980 : Schematic

BIFILAR-WOUND FURNACE

SAMPLE

CLAMPS

LOW MASS, HIGH STIFFNESS CLAMPING FIXTURES

AIR BEARING SLIDE

AIR BEARING

OPTICAL ENCODER

DRIVE MOTOR

UNIQUE PATENT-PENDING DESIGN

DMA : Dual Cantilever Mode

Sample

Movable clamp Stationary Clamp

DMA : Single Cantilever Mode

Sample

Stationary Clamp

Movable clamp

DMA : 3-Point Bend Mode

Sample

Stationary Fulcrum

Force

Moveable Clamp

DMA : Tension Mode

Stationary Clamp

Sample (film, fiber,orthin sheet)

Movable clamp

DMA : Shear Sandwich Mode

Sample

Movable Clamp

Stationary Clamp

DMA : Compression Mode

Movable Clamp

Sample

Stationary clamp

PSA: Glass Transition Measurement

INTERFACES IN COMPOSITES

• Questions that need to be answered:

–Are interfacial properties important at all?

–What is the role/effect of interfaces with respect to overall

mechanical properties of composites?

–How can we measure interfacial adhesion in composites?

–Can we develop analytical models that are useful for design

purposes?

–Is it possible to tailor interfacial adhesion?

EXAMPLES OF PRACTICAL RELEVANCE (VARIOUS FIELDS)

• Thin coatings on critical surfaces (reflective coatings on optical components, plating for corrosion protection, magnetic films for data storage…)

• Interfaces in composites (carbon-epoxy, glass-PP, SiC-SiC, PE-

PE…)

• Interaction of biological systems or media with engineering materials (tissue bonding of prostheses, dental implants, artificial hips, cell adhesion [cells remain alive only if they adhere to a substrate]…)

Wetting and adhesive strength

• Adequate wetting is a necessary (but not sufficient!) condition for

good adhesion between a liquid and a solid surface.

• The contact angle between a liquid droplet and a surface is an

indication of compatibility between these.

q

If q < 90°, the liquid ‘wets’the solid surface. If q = 0°, the liquid ‘spreads’on the surface (complete wetting). If q = 180°, the liquid ‘does not wet’the surface

• • •

In terms of surface energies:

•

Surface energies (g)

vapor

liquid

gLV q

gSV

gSL

solid

(S = Solid, V = Vapor, L = Liquid)

The equilibrium wetting or contact angle q is dictated by the Young equation, obtained by a balance of horizontal forces:

gSV = gLV cosq+ g SL

Thus, good wetting (q = 0 or small) arises when the surface energy of the solid is equal to or greater than the sum of the liquid surface energy and the solid-liquid interface surface energy.

gSV ≥ gLV + gSL

[Interface surface energies are difficult to measure (and may be influenced by chemical reactions) but are often smaller than thevalues for the phases in air]

The lower the contact angle, the greater the wettability:

Liquid is attracted to itself, not to solid

Liquid is attracted to solid, less to itself

Indirect measurement can be made by immersing the fiber into the liquid

of interest and measuring the force of immersion or emersion (= Wilhelmy

microbalance technique). A force balance permits the calculationof the

contact angle if the fiber perimeter and surface energy of the liquid are

known (see Bascom).

Mic robalanc e

Krüs s tensiomete r

Comp ute r

Fibr e

Liq uid

Glass containe r

Drive system

Capillary-rise method

Sessile drop method

Wilhelmymethod

Fiber-matrix interfacial adhesion

• Two general methodologies:

–Indirect (or macromechanical) testing -

focuses on the collective

behavior of fibers in a polymer matrix [interfacial strength is

interpreted via simplistic approximations; fast but questionable

data collection]

–Direct (or micromechanical) testing –probes interfacial behavior

of individual fibers interacting with a polymer matrix [more

fundamental information; variability within and between

techniques; issue of relevance to real-life composites (scaling-

up)]

Indirect (or macromechanical) testing

1.The transverse tensile test

2. The short-beam shear (or interlaminarshear

strength -ILSS) test

3. Asymetrical4-point (Iosipescu) bend test

CONCLUSION – They are simple to perform, but yield

ambiguous, inaccurate data.

(And other macroscopic tests… )

Direct (or micromechanical) testing

a) b)

Fibre

Indentor Microscope Objective

Matrix

Composite

c) F d) F Knife edge Fibre

Matrix Sustrate le le

Micromichanicaltests : (a)fragmentation, (b) microindentation, (c) pull-out and (d) microbondtest

Single fiber pull-out test

Load cell

Mesurement object

Greszczuk’smodel for pull-out

A small single fiber is embedded in a resin and the debondingload for the

pull-out of the fiber from the resin is measured and calculated for the

F lf 2 r p

interfacial shear strength (IFSS, t) using the following equation:

where F is the debondingload, r f the fiber radius, and ℓ the embedded length. This technique has been successfully studied in carbon and boronfibers in

an epoxy resin.

2. The single-fiber microcompression(or MIT) test

Tricky test, difficult to perform, fiber-matrix interfacial fracture is often

only partial due to slight off-axis moments, loading must be exactly

parallel to the fiber axis.

3. The single-fiber fragmentation test

Single fiber embedded in matrix

Fragmented fiber

Pre-conditions for successful test : (a) failure strain of the fiber is much

smaller than that of matrix; (b) Interfacial bonding must be fair to good.

Mapping NanomechanicalProperties by AFM Nanoindentation

Stiffness contrast

Glass fibre

Interp hase E pox y

Fmax

2.6

)

Unloading

dF dh

( e c r o f n o i t a t n e d n I

hmax

Penetration depth(nm)

Cyclic Loading-AFM-TopographyatFailure

• APS

Virginfiber

Aftercyclic loading

Pulloutaps.000

Pulloutaps.001

Ra= 3.5 nm, Rmax= 151 nm Ra= 4.2 nm, Rmax= 48 nm

Scanning Electron Microscopy (SEM)

(cid:252) Examine surface irregularities or fracture areas in a part for plastics applications.

(cid:252) Measure the thickness (in cross section) of thin coatings.

(cid:252)Study surface topography and failure analysis

(cid:252)Test specimens are sputter coated with gold, then placed in a vacuum chamber for

viewing on the computer monitor at up to 10,000x magnification.

(cid:252) Polaroid photos are taken for a permanent record. Approximately 0.25" x 0.25"

Polaroid photos can be scanned into electronic documents.

Untreated jute NaOH-treated jute

NaOH/PAPS-jute

PP/jute composite without treatment

PP/jute composite with treatment

Fourier Transform Infrared Spectrometry (FTIR)

-ASTM E1252

-Identify of polymer

-Detect organic layers or fiberglass

-Detect surface coatings

-Also examine contaminants and some fillers within the polymers

-A small amount (few grams) of sample is needed.

Fourier Transform Infrared Spectrometry (FTIR)

Simplified optical layout of a typical FTIR spectrometer

-Three basic spectrometer components: -The sample is inserted into a detector

and the amount of Infrared Light absorbed

at each frequency is determined. +Radiation source +Interferometer (giaothoa k ế), +and detector

Fourier Transform Infrared Spectrometry (FTIR)

The most commonly used interferometer is a Michelson interferometer.

(cid:252)Consists of 3 active components: a moving mirror, a fixed mirror, and a beamsplitter

(cid:252)The two mirrors are perpendicular to each other.

(cid:252)The beamsplitteris often made by depositing a thin film of germanium onto a flat KBr

substrate

(cid:252)Radiation from the broadband IR source impinges on the beamsplitter

(cid:252) At the beamsplitter, half the IR beam is transmitted to the fixed mirror and the

remaining half is reflected to the moving mirror

(cid:252)After the divided beams are reflected from the two mirrors, theyare recombined at the

beamsplitter. Due to changes in the relative position of the moving mirror to the fixed

mirror, an interference pattern is generated.

(cid:252)The resulting beam then passes through the sample and is eventually focused on the

detector.

Infrared Region(IR)

FTIR

['gæmə]

['reidiou]

ultraviolet

electromagnetic spectrum

The energy of the wave (E):

hν

Wavenumber( ): =1 / l

• ch λ

n: frequency l :wavelength

The infrared region (14,000 cm-1 to 10 cm-1): near, mid and far-infrared region (cid:252)Mid-infrared region (4,000 cm-1 to 400 cm-1):

ﬁ themost interest region

ﬁ corresponds to changes in vibrational energies within molecules

(cid:252)The far infrared region (400 cm-1 to 10 cm-1): ﬁ useful for molecules containing heavy atoms such as inorganic compounds

ﬁ requires rather specialisedexperimental techniques.

FTIR

Molecular Vibrations

Stretching vibration

Asymmetrical stretching Symmetrical stretching

Out-of -plane bend

Bending vibration

In-plane bending Out-of-plane bending

Major vibrationalmodes for a nonlinear group, CH 2 (When a compound absorbs the energy of Infrared radiation)

FTIR

Single Bonds to Hydrogen

PHÂN TÍCH POLYME (POLYMER ANALYSIS)

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