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Rheometry: Examples From Industry -Steve Brenno- RTP Company 9 March 2012. Lecture Outline. • General/Material Background Torque Rheometer (Process Development) Capillary Rheometer (Effect of Additive) Dynamic Rheometer (Material Design). RTP?.

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Rheometry: Examples From Industry

-Steve Brenno-

RTP Company

9 March 2012

Lecture outline
Lecture Outline

• General/Material Background

  • Torque Rheometer (Process Development)

  • Capillary Rheometer (Effect of Additive)

  • Dynamic Rheometer (Material Design)


  • Independent custom thermoplastics compounder

  • Established 1982; additional 20 year history

  • 500+ employees

  • 10 Global manufacturing locations

    • 5 in US

    • 2 in Europe

    • 1 in Singapore

    • 1 in China

    • 1 in Mexico

  • Worldwide sales rep. and distribution system

ThermoPlastic Elastomer (TPE)?

“…Having the property of softening or fusing when heated and of hardening again when cooled…”

“…Any of various elastic substances resembling rubber…”

Int. Institute of Synthetic Rubber Producers (IISRP) definition:

“Polymers, polymer blends or compounds which, above their melt temperatures, exhibit thermoplastic character that enables them to be shaped into fabricated articles and which, within their design temperature range, possess elastomeric behavior without cross-linking during fabrication. This process is reversible and the product can be reprocessed and remoulded.”

TPE Industry Overview

  • TPE’s are a 3.5 billion pound global market (by comparison, thermoset rubber for tires is a 5 billion pound market)

  • Thermoplastic market is 300 billion pounds

  • North American consumption in 2003 was 1.8 billion pounds

  • TPE market has grown at 6-8% rate through 2003 and is projected to continue @ a 6% pace

How TPEs “Work”

TPEs are composed of hard and soft domains. They are dualphase materials at the nano- or micro-scale in their solid state.

- Hard phase contributes “plastic” properties such as:

tensile strength

tear strength

chemical resistance

high-temperature performance

- Soft phase contributes “elastomeric” properties such as:


compression & tension set


low-temperature performance



But Why Are TPEs “Rubbery”?



At usage temperature, the TPE’s elastomeric/softphase is above its glass transition temperature region (Tg).

So how can tpes be melt processible

“Heat fugitive” crosslinks

So How Can TPEs Be Melt Processible?


By raising the temperature of the TPE above the glass transition or melting temperature (Tm) of the plastic/hardphase.

So how can tpes be melt processible1

“Heat fugitive” crosslinks


+ Shear

So How Can TPEs Be Melt Processible?

…and applying shear forces typical of thermoplastic processes.

*** For comparison, thermoset rubbers (TSRs) are singlephase materials with non-reversible chemical (covalent) bond cross-links***

A tpe morphology nano scale i
A TPE Morphology (Nano-scale)- I

Tri-block copolymers develop a “nanocomposite-like” material


A tpe morphology nano scale ii
A TPE Morphology (Nano-scale) - II

Multi-block copolymers with polymer crystallinity creating the hard phase and physical x-link.


A tpe morphology micro scale
A TPE Morphology (Micro-scale)

…Processdependent, two-phase morphology on the micro-scale

Lecture outline1
Lecture Outline

• General/Material Background

  • Torque Rheometer (Process Development)

  • Capillary Rheometer (Effect of Additive)

  • Dynamic Rheometer (Material Design)

Instrument Background / Theory

  • Concentric cylinder-style “rheometer”

    • Non-uniform temperature and strain rate!

  • Mean shear rate = C1* Rpm

    Mean shear stress = C2 * Torque

    • Efforts made to obtain viscosity data from instrument output

      (Example: Journal of Rheology43, 415 (1999))

  • Unique ability to study rheology (transient events) during polymer mixing/compounding (reactions, stability/degradation, morphology changes, etc.)

Industrial Uses

  • Thermal stability studies (additives)

  • Vulcanization/Cross-linking studies

  • Quality control and failure analysis

  • Melt blending studies

    • Order-of-addition of fillers, extenders, etc.

    • Additive incorporation (will it mix?)

    • Screening experimentation

Case Study: Process Development

  • Technical problem: Develop manufacturing process for a flame retardant thermoplastic elastomer used in a cellular phone network infrastructure device

  • Tool: C.W. Brabender Prep-Mixer (roller rotors)

  • Technique: Conduct order-of-addition and additive incorporation experiments using a torque rheometer prior to scale-up to a continuous mixing device (twin screw extruder)





Experimental Data

Instrument Background / Theory

  • Pressure-driven flow through a tube

    • Shear stress and shear rate at wall easily derived

  • Instrument is “simple” mathematically and mechanically

    • Ability to switch load cell, transducer(s), and die to optimize performance

  • High shear rate in measurement region similar to levels of shear found in industrial processing equipment and tooling (molds/dies)

Industrial Uses

  • Processibility studies/ranking

    • Ease-of-flow

    • Degradation/residence time

    • Extrudate swell

  • Development of process models (“moldflow”)

  • Quality control

  • Fiber science and engineering

    • Polymer chain/crystallite orientation

Case study effect of additive
Case Study: Effect of Additive

  • Technical problem: Will the presence of a small amount of a polymeric modifier improve the processibility of an optically clear SBC compound used in an injection-molded medical mask

  • Tool: Dynisco LCR 7000 Capillary Rheometer

  • Technique: Prepare two compounds and analyze at expected processing temperature (being careful to utilize good experimental technique…predry samples, cleaning between runs, etc.)

Instrument background theory
Instrument Background / Theory

  • Ability to measure viscoelastic properties of polymer melts (η*) and solids (E*, G*) using a small oscillatory stress or strain

  • Superposition (time/frequency vs. temperature and Boltzmann) are powerful concepts to extend usefulness of rheometer, but can be misused

    • Same mechanisms of “change” at all test temperatures!

  • Multiple instrument deformation modes (tension, compression, torsional shear) relate directly to loadings applied in numerous dynamic applications (shock mounts, aircraft structures, tires)

Industrial Uses

  • Polymer blend development (miscibility)

  • Thermoset curing studies

  • Polymer science and physics

    • Molecular weight, MWD, branching, filler interaction, plasticization…

  • Mechanical design

    • Creep and stress relaxation

    • Dynamic response

Case study material design
Case Study: Material Design

  • Technical problem: Develop an injection-moldable TPE compound to replace a thermoset rubber compound in an automotive speaker surround component

  • Tool: TA Inst. ARES dynamic rheometer (shear mode)

  • Technique: Perform temperature sweep at 1 Hz to obtain G* vs. temperature curves for various TPE samples. Compare to existing thermoset rubber compound tested under similar conditions. Use data for initial screening of TPE candidates prior to dynamic testing in actual speaker assemblies.

Exper data tan vs temp @ 1 hz


Exper. Data: tan δvs. Temp. @ 1 Hz

tan δ


Lecture outline2
Lecture Outline

• General/Material Background

  • Torque Rheometer (Process Development)

  • Capillary Rheometer (Effect of Additive)

  • Dynamic Rheometer (Material Design)