M.Stephan, S.Große:

Micophotometric Control of Particles and Inhomogeneities

in Flowing Polymer Melts during Extrusion Processing

WorkshopJanuary, 28th - 29th 2005, Dresden

Particulate Heterogeneities in Polymer Melts

unmolten granulesprocessing conditions

black spotsdegraded polymerextrusion start-up’s

gels / fisheyescrosslinked + ultra high molecular

gas bubblesoverheating, humidity

additive agglomerates, environmental dust, insects

sample

?Quality?bufferstore

final productinjection molding

!Quality!

Extrusion

offline analysis• lab-extruder + film observation• microscopy

• dead-times between taking a sample and getting a quality result• large low quality batches possible• generation of plastics waste• time and cost consuming procedure

State of the Art - Determination of Melt Homogeneity

!Quality!

Extrusion

inline/online analysis• micro-photometric sensors

final productinjection molding

• continuous real-time data on melt quality• low quality batches can be detected immediately • application at processing conditions (p, T)• technological and economical benefits

increased level of process-/quality control(new applications of high performance polymers)

Objective - Real-time Determination of Melt Homogeneity

light source detector

Measuring Principle Photometry - Light Extinction

Extinction E = absorption + scattering (reflection, deflection, refraction)

particle

refraction

deflection

reflection

absorption

inci

dent

ligh

t bea

m

dete

ctor

setup parameters (Lambert-Beers-Law):

• size d, concentration cV, shape of the particles• refractive indices particles/polymer matrix m• optical path length L• laser wavelength λ

limitations (Lambert-Beers-Law):• acceptance of spherical particles• no multiple scattering appears

LcAT

E VV ⋅⋅==1lnLambert Beer:

),,( mdfAV λ=Mie:

2 Modes of Signal Evaluation

• by variation of time resolution of data recording (min .. ms-range)

• integral signal analysis: - shift of mean signal level- for nm-scaled particles (>300nm)- limitation on low concentrations (< 5Vol.%)

(multiple scattering effects)- determination of mean particle sizes or

particle concentrations (Lambert Beer)

• single particle counting: - single particle impulses

- for µm-scaled particles (>20µm)

- limitation on lowest particle concentrations - determination of mean particle sizes and

particle concentrations (calibration needed)

t [min]

U [V

]

U

t [ms]

U [V

]

∆U

Sensor Setup

beam splitterBackscatter-

DetectorExtinction-

Detector

melt flowLaser660nm

beam splitterBackscatter-

DetectorExtinction-

Detector

melt flowLaser660nm

• sensors can be adapted to various positions of different extruders inline or online

• different sensor types are available

inlinemain melt flow

EXTRUDERsingle screw / twin screw

inlinescrew-in

onlinebypass melt flow

Sensor Adaptation to Extrusion Processing

Laser

Extinction

online mode - extinction

bypass melt flow

LaserExtinction

main melt flow

inline mode - extinction

extruder barrel

inline mode backscattering

Sensor Adaptation to Extrusion Processing

Laser

AnimationAnimation

Sensor Adaptation to Extrusion Processing

• integral signal analysis - classical turbidimetry • light extinction by nm-particles - decrease of signal level by turbid melt• applicable to polymer blending and control of batch changes

pure polymer polymer-blend(nm-particles)

tran

smis

sion

sig

nal

10001100120013001400150016001700180019002000

0 100 200 300 400 500 600time [ms]10001100120013001400150016001700180019002000

0 100 200 300 400 500 600

Transparency Control in Molten State

• limitation on maximum blend concentrations of about 5 wt.% • also applicable to low concentrated composites

Determination of Mean Blend Particle Diameters

0,83

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 wt.% PS / PA6 1 wt.% PMMA / PS

x 5

0,3

[µm

]

0,79

0,34

0,25

PMP SEM

part

icle

size

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5cV [%]

Extin

ktio

n [/]

PMMA / PS m=1,0578

PS / PA6 m=0,9638

Lambert-Beer multiple scattering

extin

ctio

n

• integral signal analysis (Lambert Beer calculation)

• first step of extrusion processing, detection of unmolten granules• optimization of extrusion parameters (energy costs - melt quality)• improved pellets melting with an increasing screw speed

Real-Time Monitoring of Pellets Melting

n=50 min-1 Tmelt =252°C n=100 min-1 Tmelt =256°C n=200 min-1 Tmelt = 261°C

500

700

900

1100

1300

0 200 400 600 800500

700

900

1100

1300

0 200 400 600 800

Time [ms]

500

700

900

1100

1300

0 200 400 600 800

Time [ms]

tran

smis

sion

sig

nal

Time [ms]

tran

smis

sion

sig

nal

tran

smis

sion

sig

nal

Sensor 1 Sensor 2 Sensor 3

Real-Time Observation of Additive Dispersion during Extrusion Processing

dispersion process

single particle analysis>20µm, lowest concentrations

particle size and particle concentration

integral particle analysis>300nm, low concentrations (<5 vol.-%)

particle size or particle concentration

• inline measurements at various extruder position • changes in particle situation can be observed (disagglomeration of nanoparticle agglomerates)

additive-agglomerates(µm-range)

inline backscatter or online extinction sensors can be applied

dispersed additives(nm-range)

Application PMPxyz sensors on nanocomposites extrusion processing may be usefull applicable to

•a direct monitoring of nanoparticle agglomerates in a flowing polymer melt from inside a twin screw extruder

• get in-process realtime informations about dispersion progress of nanoparticle agglomerates (µm-range observation by single particle counting)

• get in-process realtime informations about primary nanoparticle size (nm-range observation by turbitity analysis)

• get both particle informations simultaneously

Summary

our partners:

TOPAS

Dresden Universityof Technology

Leibniz - Institute of Polymer Researchstephan@ipfdd.de

Contact

APPENDIX

• particle type (gels, black spots, unmolten granules, gas bubbles)

• particle size

• particle concentration

• access to extruder (inline, bypass)

Users Input:

Sensor Setup:• extinction / backscatter measurement

• optical setup (measuring volume, layer thickness, focus)

• signal processing

Sensor Output:• particle size detection limit

• sampling statistics

Sensor Configuration

• several sensors with different setups for various applications developed + tested• optimization of a sensor for each special application necessary

Sensor Overview

Co-Operating Partners

cellulosic fibers

melt filters

multilayer pipes

colored masterbatches

plastics recycling machines

industrial extruderslabscale extruders

polymer producer

high performance polymers