Structured particles in the thermoplastics

1
Structured particles in the thermoplastics
Joong-In Kim Bayer Corporation Plastics,
Technology Oct. 6th, 2000
Emulsion Short Course Yonsei University
2
Contents

• Role of structured particles in thermoplastics
• Toughening mechanism
• ABS / HIPS
• Structure property relationship
• Role of emulsion
• Structured particles

C. Bucknall in Polymer blends, edited by D. Paul
et al.
3
Measuring ductility of thermoplastics
C. Bucknall in Polymer blends, edited by D. Paul
et al.
4
Role of structured particles

• Impact strength drop of PC
• Thick specimen
• Sharp notch

Continuous Mass
Emulsion
B.S. Lomabardo et al., J. Appl. Polym. Sci., 54,
1697 (1994)
5
Toughening mechanisms - ABS/HIPS

• Crazing
• Cavitation
• Shear yielding
• Wus theoretical model

C. Bucknall in Polymer blends, edited by D. Paul
et al.
6
Fracture Mechanisms

• How do we know the mechanisms?

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Fracture Mechanisms
Lets break it !!!
Are you CRAZ... ?
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Fracture Mechanisms
9
TEM of the fractured surface (HIPS)

• Crazing (large rubber particles)

J. Stabenow and F. Haaf, Die Ange. Makro.
Chemie, 29, 1 (1973)
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Optimum RPS on HIPS Toughening

• D. Cook et al. J. App. Polym. Sci., 48, 75 (1993)
• J. App. Polym. Sci., 44, 505 (1992)

11
TEM of the fractured surface (ABS)

• Crazing / Cavitation

J. Stabenow and F. Haaf, Die Ange. Makro. Chemie,
29, 1 (1973)
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Cavitation, not crazing

• Stress whitening due to cavitation, not crazing

H. Breuer, F. Haaf, and J. Stabenow, J. Macromol.
Sci., Phys., B14(3), 387 (1977)
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Optimum RPS on ABS Toughening
D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ.
(1993)
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Fracture mechanisms on ABS Toughening

• Cavitation / Shear strain dominant
• No shear at large RPS (0.5 micron)
• Little crazing at small RPS

D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ.
(1993)
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Rubber toughening mechanism

• Wu et al. Interparticle distance model
• Critical rubber particle size for the
  brittle-tough transition at different rubber
  volume.

S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model
tc Critical matrix ligament thickness Inde
pendent of rubber volume and size Characteristic
of the matrix Brittle-tough transition at
tc
S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model

• Toughness Matrix property
• t lt tc Shear yield, toughen
• t gt tc Brittle failure

S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model

• Change in stress state and stress field overlap

S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model

• Critical rubber particle diameter for toughness
• dc tc (p / 6 f r)1/3 - 1
• dc Max. diameter of the rubber particles for
  toughness
• tc Critical ligament thickness
• f r Volume fraction of the rubber particles

S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model

• Connectivity of liagments (Rubber clustering)

S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Interparticle distance model
As the polydispersity, sg , increases the
number of particles, n(sg), decreases the
average ligament thickness, t, increases toughnes
s decreases.
S. Wu, J. Appl. Polym. Sci., 35, 549 (1988)
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Degree of dispersion on toughness

• F. Haaf et al., J. Sci. Ind. Res., 40, 659 (1980)

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Degree of dispersion on toughness
J. Qian, Ph. D. Thesis, Lehigh University (1994)
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Degree of Grafting on Dispersability
25 40 65
H. Breuer et al., J. Macromol. Sci., Phys.,
B14(3), 387 (1977)
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Improved toughness with clustering
H. Keskkula et al., Poly. Eng. Sci., 30, 21, 1373
(1990)
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No sharp transition in ABS

• No abrupt change due to increased crazing above
  tc.
• Cavitation/Shear yielding and Crazing should be
  considered together

D.J. Buckley Jr., Ph.D. Thesis, Cornell Univ.
(1993)
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ABS toughening mechanisms

• Toughening mechanisms Wus model
• Critical RPS for ductility
• Not dependent on rubber type
• Dependent on matrix characteristic (Inherent
  ductility)
• Uniform dispersion of small particles
• Toughening mechanisms for ABS
• Rubber cavitation by small particles
• Crazing by large particles
• Optimum RPS
• Non uniform dispersion (Network structure)

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Gloss and gloss thermal stability

• Gloss Surface appearance
• light reflected from the sample surface
• light reflected from a mirror surface
• Gloss decreases with
• increasing particle size
• increasing rubber clustering
• thermal history (time and temp)
• decreasing graft level

F. Lednicky et al., Ange. Makro. Chemie, 141, 151
(1986)
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Rubber particle size and Gloss

• ln G ln Gm - D/Do
• Gm matrix gloss

F. Lednicky et al., Ange. Makro. Chemie, 141, 151
(1986)
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Gloss vs Toughness

• Max. toughness at intermediate gloss (graft
  level)

F. Lednicky et al., Ange. Makro. Chemie, 141, 151
(1986)
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Rubber Particle Clustering

• Changes in physical properties
• Molding time and temperature

A. Casale et al., Polym. Eng. Sci., 15, 286
(1975)
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Rubber Particle Clustering

• Rubber particle size measurement
• Stable rubber dispersion in a solvent
• Joyce Loebl disk type centrifuge
• Agglomeration Index
• Np (Dw,c)3/(Dw,p )3
• Dw,c Clustered rubber particle size measured
  from the molded chip
• Dw,p Primary rubber particle size measured
  from the pellet

O.M. Chang et al., PMSE, ACS 71, Washington D.C.,
739 (1994)
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Rubber Particle Clustering by Np
O.M. Chang et al., J. Appl. Polym. Sci., 61, 1003
(1996)
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Effect of graft level on melt dispersion
M. Huguet et al., Colloidal and Morphological
Behavior of Block and Graft Copolymer, Plenum,
NY, 183, (1971)
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What kind of Thermoplastics ?
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Structure property relationships

• Matrix structure
• Interparticle spacing
• Rubber particle size and size distribution
• Rubber matrix compatibility
• Large rubber particles and internal occlusions
• Cross-linking of the rubber phase
• Graft level
• Structure of the graft latex

C. Bucknall in Polymer blends, edited by D. Paul
et al.
37
Rubber matrix compatibility - thermal expansion
C. Bucknall in Polymer blends, edited by D. Paul
et al.
38
AN mismatch on Dispersability

• 2.5 11.5
• 17.5 22.5

H. Kim et al., Polymer, 31, 5, 869 (1990)
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Toughness of ABS (Fixed SAN graft)

• H. Kim et al., Polymer, 32, 8, 1447 (1991)

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Bimode rubber particles

• Optimum properties balance

C.R. Bernal et al, J. Appl. Polym. Sci., 58, 1
(1995)
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Bimode rubber particles

• Synergistic increase of toughness

L. Morbitzer et al., J. Appl. Polym. Sci., 20,
2691 (1976) F. Fowler et al., Polymer, 28, 1703
(1987) J. Appl. Polym. Sci., 35, 1563 (1988)
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Role of Emulsion Technology

• What you want is what you get !!!
• Adjust the process parameters
• to control the structures
• for the optimum properties

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Morphologies of Graft Latex Particles
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Graft Morphology Control

• Thermodynamic Process parameters
• Rubber composition
• Rubber particle size
• Rubber level
• Surfactant (Interfacial tension)
• Kinetic Process parameters
• Initiator type, level, and charging method
• Cross-link density of rubber
• Monomer metering time
• Reaction Temperature
• Chain transfer agent

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Graft Degree and Graft Density
Graft Degree (gd) Ratio between the weight of
grafted polymers and the weight of the
particles Graft density (s) Number of polymer
per unit area of the particles s gd D rp
NA/6Mg D Diameter of the particles rp
Density of the particles NA Avogadros
number Mg Molecular weight of the grafted
polymer Thickness of the grafted polymer
t (D/2) (1 gd rp / rg) 1/3 - 1
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Critical Degree of Grafting
Aoki, Macromolecules, 20, 2208 (1987) Aoki et al,
Macromolecules, 29, 6656 (1996)
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Grafting Degree and chain conformation
Under grafting (gd lt gd,c) Mushroom
conformation, The particle surface is not well
covered. Agglomeration of the particles Optimum
grafting (gd ? gd,c) The thickness of graft
layer equivalent to two radius of
gyration. The particles are just well covered
and protected Over grafting (gd gt
gd,c) Brush conformation, The particle surface
is well covered. Matrix chains are expelled from
the grafted layer and causes agglomeration
Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)
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Effect of particle size on Critical Grafting
Bimodal particle size case Minimum modulus at
the same as the small particles Dominated by the
small particles
Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)
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Effect of matrix properties on Critical Grafting
Critical Degree of Grafting Independent of
rubber content and matrix properties Controlled
mainly by the particle size and size distribution
Bertin et al, Polym Eng. Sci., 35, 17, 1394 (1995)
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Optimum graft shell thickness
M. Huguet et al., Colloidal and Morphological
Behavior of Block and Graft Copolymer, Plenum,
NY, 183, (1971)
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Cross-linking of Graft Shell
Swelling morphology in the uncured
epoxy Cross-linked shell No change in the
particle size and morphology between water and
epoxy medium Uncross-linked shell Increased
particle size and brush-like morphology in epoxy
J. Qian, Ph D thesis, Lehigh Univ., (1994 )
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Effect of X-linked Graft Shell on Dispersion
J. Qian, EPI GRPR 42, 145 ( )
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Multilayer Grafting
Hard core/hard shell, with an intermediate rubber
layer Provides an optimum balance between
stiffness and impact. Modulus depends only on
rubbery part, not on the sequence of hard and
soft layers
N. Shah, J. Mater. Sci., 23, 3623 (1988)