高分子流變學-聚合物導論

拉伸硬化在炭黑填充橡膠加工中的重要性性能方面：炭黑作為橡膠的補強劑,提高模量,斷裂強度,耐磨性等具有重要作用;加工方面：炭黑對橡膠的熔體剪切粘度,拉伸粘度有重要影響,因此對加工行為有重要影響;不同種類的炭黑具有不同的性質,如比表面積,結構性等,對橡膠的影響各不相同,因此,需要 炭黑對拉伸性能的影響.炭黑生產工藝及其性質炭黑的結構性炭黑的結構性炭黑的結構性是指炭黑粒子連接成長鏈并熔結在一起而成為三度空間的結構，這種體在制造過程中由粒子與粒子間熔合在一起的，這些體（一次結構）也可形成疏松的締合物或者稱“二次結構”，他們很容易破壞，故稱暫時結構。炭黑結構越高，膠料的粘度、定伸應力及硬度就會增加，加工性能改善。炭黑的結構性炭黑用量對丁苯橡膠拉伸流動的影響圖(a)炭黑用量增加，拉伸粘度升高，在較低的伸長率下斷裂。圖(b)拉伸粘度隨炭黑用量減小和拉伸速率增大而降低，同時隨拉伸速率增大，不同炭黑用量的膠料之間，其粘度差別縮小，這與炭黑用量對剪切粘度的影響所得結果相似。這可能與在高應變速率下炭黑網絡受破壞有關。炭黑對丁苯橡膠拉伸硬化的影響從圖可見，該曲線與聚乙烯、聚苯乙烯熔體的拉伸流動曲線有區(qū)別，即使在最低的=

1.8×10-4s-1也沒有穩(wěn)態(tài)粘度的趨勢，反而持續(xù)上升，這是拉伸硬化的結果。不存在穩(wěn)態(tài)粘度,橡膠在外力拉伸作用下發(fā)生結晶,導致拉伸粘度提高.在炭黑用量、結構性相同的條件下，隨著炭黑表面積增大(N234

＞N347

＞N351＞N550)，拉伸粘度增大。在炭黑用量相同，表面積相近的條件下，隨著炭黑結構性增高(N347＞N330＞N326)，拉伸粘度有所提高，但流動曲線形狀不變。炭黑表面積和結構性對丁苯橡膠拉伸流動的影響從上述結果可見，表面積大的炭黑，其膠料在拉伸流動過程中易產生我們需要的應變硬化效應；而結構性的改變，對應變硬化效應影響很小。據(jù)此，

等建議，‘采用結構性較低而表面積較大的炭黑(如低拉伸中超耐磨爐黑N231)較好。因為結構性低，有效體積較小，剪切粘度較低，而表面積較大(粒徑小)則拉伸應變硬化效應較強。這樣的混煉膠對某些加工過程有利．含N330和N23l的丁苯混煉膠與含N330的天然橡膠的拉伸流動曲線當伸長率為300％(即e＝1.4)時，含

N23l的丁苯混煉膠的應力比含N330的高30%，可見N231較好，這是因為N23l的表面積比N330的大。在室溫條件下，天然橡膠混煉膠比丁苯橡膠混煉膠有高得多的扯斷應

(5000kPa)

和扯斷伸長率(e=2.4)。天然膠料在室溫條件下當伸長率超過

300％時，其應力—應變曲線陡然上升，這是應變結晶的結果，而100oC時是沒有強烈應變硬化效應的。中島認為，對于炭黑與橡膠之間的混煉，希望產生應變硬化，以便分

散。為此，耍提高密煉機轉子的轉速，并且轉子凸棱與室壁之間的間隙要小些，采用低溫或分段混煉。粒子團聚體在混煉時所受應力的分析，基體應變硬化有利于將應力傳遞給粒子團

聚體，使之解團聚，從而提高分散性。通過對炭黑/橡膠拉伸流動行為的研究得到以下結論炭黑類型方面：選用結構性較低而表面積較大加工方面：提高密煉機轉子的轉速，減少轉子凸棱與室壁之間的間隙，低溫或分段混煉；目的都是降低剪切黏度以降低加工能耗，同時提高拉伸黏度改善分散效果提高加工效率。拉伸法Stretching

method）紡絲法（Spinning）收縮流法（Converging

flow

method）毛細管斷裂（Capillary

break

up）駐點流（Stagnation

flow

method）拉伸流變行為的研究方法Stretching

methodStretching

techniquesA

Filament Stretching

ExtensionalRheometer

is

used

to measure

thetransient

extensional

viscosity

of

fluidswith

varying

polymerconcentrations.The

diameter

of

the

stretching

filamentis

monitored

using

a

planar

LASERdevice

allowing

a

computer-ontrolledmotor

to

maintain

a

constant

extensionrate

acting

on

the

fluid.An

extremely

sensitive

force

transduceris

attached

to

the

upper

fluid

platesample

holders,

and

is

used

to

measurethe

force

acting

on

the

filament.Advantages:1.

The

process

allowsthe

extensionalviscosity

to

be

measured in

anearly

shear-

free

flow.2.

Experiments

can

be

run

at

a

variety

ofextension

rates

and

can

reach

relativelylarge

Hencky

strainsStretching

techniques(1)恒拉伸速率測定法，即給定e

，測de

。例如Ide—WhiteextensionaI,測單絲，單絲長約21.5cm，其一端由夾持器夾緊，另一端固定在卷繞

Roller上，并置于硅油浴槽內，用加熱裝置將絲條熔化，卷繞Roller以恒速轉動將絲牽引，熔體張力記錄在記錄儀上，主要用于測定膠料的拉伸粘度。恒拉伸速率測定法，即給定，測e。恒拉伸應力測定法，即給定e,測。這要求外加拉力隨拉仲斷面積的減少而自動減小。..Trouton

ratioextensional

viscositythe

shear

viscosityTo

describe

strain

hardeningThe

material

initially

look

like

a

Newtonian

sample,

then

look

more

andmore

elastic

as

the

polymer

chains

begin

to

align

and

stretch

out

in

theflow.

Termed

"strain

hardening,"

the

extensional

viscosity

will

begin

toincrease.

The

extensional

viscosity

isoften

non-dimensionalized

withthe

shear

viscosity.

This

ratio

is

called

the

Trouton

Ratio

.

For

aNewtonian

fluid,

the

Trouton

ratio

Tr=3.絲條半徑保持不變Tr=1000Tr=3As

the

plot

shows

below,

the

non-Newtonian

fluidinitially

reaches

a

Tr=3,

then

increases

by

3orders

of

magnitude.

After

the

deformation

halts,

the

polymer

chains

relax,

cause

the

stressand

hence

the

Trouton

ratio

to

decrease.

Because

the

material

has

strain-hardened,

thefilament

radius

remains

constant

for

several

seconds

after

cessation

of

stretching.恒應力法測定法，即給定e,

測。這要求外加拉力隨拉伸斷面積的減少而自動減小。通過光學裝置測量樣品的橫截面積，自動降低拉伸應力(2)

恒拉伸應力.eA(t)

(t)

F

(t)

const用旋轉流變儀實現(xiàn)拉伸流動的測量Fiber

Spinning:

Spinning

Viscosity1.

The

principle

of

the

fibre

spinning

method

is

to

measurethe

force

required

when

stretching

an

extrudate

underspecified

haul-off

conditions.

From

the

response

of

thematerial

to

the

stretching

deformation

and

the

forcemeasured,

approximate

extensional

viscosities

can

bedetermined.

As

indicated

in

anresults

obtained

are

dependent

onoperation

of

the

instrument

and

subsequentparison

thethe

preciseysis

ofthe

raw

data.

Furthermore,

the

"melt

strength"

can

bedetermined

-

a

measure

of

the

extensional

response

ofthe

material

at

high

strains

-

and

is

suitable

for

qualitycontrol

type

applications.2.

Data

derived

from

the

draw-down

of

the

extrudate

in

amelt

flow

rate

test

has

recently

beencorrelatedsuccessfully

with

tensile

stress

growth

coefficient

dataobtained

from

stretching

measurements.

The

benefitsof

this

simple

technique

have

been

demonstrated

in

anindustrial

case

study

indicating

that

it

has

considerablepotential

for

quality

control

type

applications.The

Rheotensmeasures

theproperties of

polymerdrawing

a vertical

meltextensionalmelts

bystrandonstant

pull-off

speedor

with

a

linear

or

exponentiallyaccelerating

velocity.The

Rheotens

measures

the

forcesneeded

to

elongate

the

strand

andcalculates

elongational

stress,

drawratios,

rate

of

elongation

andelongational

viscosity.The

polymer

melt

is

drawn

downward

from

the

die

by

a

pair

of

counter

rotating

wheelsmounted

on

a

balance

beam.

The

tensile

force

applied

on

the

strand

during

extension

isplotted

against

time

or

velocity

of

the

wheels.

The

velocity

of

the

wheels

accelerates

until

thepolymer

strand

breaks

and

the

force

at

which

the

polymer

melt

breaks

is

defined

as

themelt

strength.Fiber

Spinning:G?ttfert

melt

strength

(熔體強度)tester拉伸流變測試中易出現(xiàn)的問題Converging

flow

methods:用類似于毛細管流變儀(剪切流變儀)測量拉伸流動Extensional

viscosity

might

be

obtained

from

themeasurement

of

pressure

drop

and

flow

rate

in

a

convergingflow.實驗簡單,數(shù)據(jù)處理麻煩,不能研究拉伸硬化行為.用零長毛細管流變儀測量拉伸流動兩種聚合物兩種聚合物加工行為有很大差異。拉伸粘度的測量以上介紹的是聚合物熔體或橡膠的拉伸流變實驗,聚合物溶液,懸浮液,膠體的拉伸流變行為較難研究Capillary

Breakup

RheometryCapillary

BreakupA

MFR

that

can

be

used

toreadily

differentiate

between

theresponseof

different

fluid

formulations.The

device

relies

on

a

detailed

observation

of

the

rate

of

extensional

thinning

of

a

Newtonian

or

aviscoelastic

fluid

filament

and

provides

a

direct

measurement

of

the

ultimate

time

to

break-up

of

thefluid

filament.Measurements

are

performed

in

a

controlled

temperatureand

environmental

conditions.We

consider

four

different

classes

of

entangled

polymer

liquids

that

are

of

importance

commerciallyincluding(i)pressure

sensitiveadhesives(PSA，壓敏膠),(ii)branched

and

linear

polymer

melts,(iii)concentrated

polymer

solutions

and(iv)aqueous

solutions

of

associating

polymers

such

as

HEUR(Hydrophobically

modified

urethane-ethoxylate).We

observed

that

the

breakup

dynamics

in

theseliquids

depend

on

the

extensional

viscosity,on

molecular

parameters

such

as

the

chain-length,entanglement

density

or

degree

of

chain

branching,and

on

external

factors

such

as

solvent

volatility.Varying

these

factors

changes

the

dominant

time

scales

in

the

extensional

flow.For

example,

PSA

are

elastically

stabilized

against

break

up

and

are

'tacky'

if

the

solventevaporation

rate

-1evap=

h/R0

(where

h

is

the

mass

transfer

coefficient

for

thesolvent

and

R0

is

the

initialradiusof

the

filament)

is

significantly

larger

than

the

stress

relaxation

ra

-1whereas

they

are

'non-tacky'and

undergo

capillary

breakup

if

theevaporation

rate

is

much

slower

than

thecapillary

necking

rate

-1neck

0

0

0=

/

R

)(

where

is

the

surface

tension

and

is

the

zero

shear

viscosity).In

the

case

of

associativepolymers,

the

breakup

mechanism

also

depends

on

the

concentration

of

micelles

and

the

ionicsurfactant

strength.Elasto-Capillary

Thining

in

a

Microfilament

Rheometer,Test

Fluid:

Glycerinentov

glycerin.avi(1.6

MB)Elasto-Capillary

Thiningin

a

MicrofilamentRheometer,

Test

Fluid:

HEUR

(Associative

Polymer)entov

heur.avi(1.6MB)Elasto-Capillary

Thining

in

a

Microfilament

Rheometer,

Test

Fluid:

Pressure

Sensitive

Adhesive

(PSA)entov

psa.avi(2.3

MB)Stretching

and

Breakup

of

Polymeric

Liquids

in

a

MicrofilamentRheometer

(MFR)Polystryene

with

Clay

Particles0%

Clay3%

Clay10%

ClayApplication

in

Food

industry

---

Dannon

YogurtOpen

Stretch

BreakThe

difference

in

fluid

property

of

regular

and

non-fat

yogurt

is

evaluated

to

understand

the

effect

of

milkfat

suspended

in

yogurt.Example：Optimization

of

the

filling

process

of

shampoo

sachetsThe

HAAKE

CaBER

1

extensional

rheometer

iscapable

of

an

easy-tohandle

and

quick

way

ofdistinguishing

between

different

shampoos

and

ofpredicting

filament

life

times

for

production

andquality

control.

Shampoos

3

-

5

will

need

to

bereformulated

to

solve

the

serious

filling

problems.In

this

way

it

is

possible

to

optimize

the

quality

ofthe

shampoos

and

the

production

process.With

certain

shampoo

formulations,

‘strings’

of

shampoo

are

formed

when

filling

the

sachets,

whichcauses

the

product

to

spill

across

the

seam

area.

As

a

consequence,

the

sachet

cannot

be

properlysealed.

This

failure

is

expensive

as

it

will

result

in

the

disposal

of

many

improperly

sealed

sachets.(剝離)The

experiment

shown

was

done

using

apolystyreneBoger

fluid

('SM3')

at

De=43.4.

Theendplate

diameteris

5mm

and

the

initialendplateseparation

is

0.1mm.研究peeling的意義對粘合劑的性質進行研究:

研究剝離現(xiàn)象;必須避免拉伸實驗中出現(xiàn)類似的問題:一旦出現(xiàn),無法判斷實際受力面積.The

buckling

instability,

which

occurs

on

the

platesof

the

lament

stretching

device,

can

seriouslycompromise

the

utility

of

the

device

unless

measuresare

taken

to

prevent

it.Development

of

the

buckling

instability,

after

Spiegelberg

and

McKinley'sgure.Thedash-dot

curves

represent

streamlines.Fluid

is

drained

from

the

'foot'

of

the

column

to

feed

the

extending

column.The

reservoir

next

to

the

column

is

depleted,

at

which

time

the

foot

begins

tobreak

up

into

fibrils.

As

the

reservoir

at

the

foot

of

the

column

is

drained,

thestreamlines e

increasingly

more

c