Silicone Fluids for

Modification of Plastics

Peter StevensApplication Development Manager

Silicon (no E)

Silicon (Si)• Chemical element No. 14 • A ‘half-metal’:

� Metallic like Aluminium (Si is used in semiconductors)� Non-metallic like Carbon (has 4 bonds & likes oxygen)

• Not freely occurring in nature, but a major constituent of rocks, sand, etc. being 2nd most abundant element in earth ’s crust (~28%).

• Non-toxic

5

4

Silicon to Silicone

methylchloride

Methanol

+sand silicon

C

CO2

‘Rochow’ synthesis(Momentive heritage)

+

methylchlorosilaneswater +

silicone

Si

CH3

CH3

CH3 O Si O Si O

CH3

O

CH3

CH3

Si

O

CH3CH3

Si CH3CH3

H

Si O Si

O

O

O

Si

Si

Si

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3CH3

CH3

CH3

DTQ

M

CH3

Hydrolysis of Mono-, Di-, Tri- & Tetra-methylchlorosilanes generates M, D, T & Q siloxane units that provide unlimited opportunities for molecular architecture

Molecular Geometry

Silicone oil = Polydimethylsiloxane (PDMS)

H3C Si O Si CH3

CH3

CH3

CH3

CH3x

What is Silicone ?

Why are Silicones different?

The silicone backbone is stronger than the carbon-to-carbon chain, making it more resistant to temperature, radiation, oxidation and many chemicals

-Si-O-Si-O-

Silicone

-C-C-C-C-

Hydrocarbon

OrganicSilicone

Why are Silicones different?

The free rotation and flexibility of Si-O bonds enables silicones to ‘twist & turn’, making them more resistant to shear than hydrocarbon chains, which tend to break, and enabling them to orientate better at interfaces.

Why are Silicones different?

• Methyl (CH3) is even more apolar, so the high methyl density of silicones makes them literally ‘oilier than oil’ – they can be surface active even in oils and can ‘reach places’ (e.g. surface tension reduction) that hydrocarbons cannot.

Silicone

• Hydrocarbons are primarily methylene (CH2)

Organic

Why are Silicones different?

Silicone

Due to their high methyl density, silicones have very low intermolecular association

• With themselves: they have glass transition temperatures below -100oC

• With other things: they are powerful lubricants & release agents

Why add Silicones to Plastics ?

Silicones are used to modify:

Surface properties:Release

Improved extrusionAnti-cluster

Surface tension Higher molding accuracyWettability / anti-fog

Particle compatibilzation (pigments)Anti-stat via reduced friction & via humectancyAppearance (gloss)

Bulk properties:Impact resistance (especially at low temp.)Injection flow profile Reduced brittleness / higher flexibility (especially at low temp.)Flame retardancy (in combination with other actives)Improved chemical resistance

Silicones into Plastics

• Appropriately organo-modified silicones, e.g. phenyl silicones, can be dissolved into plastic:

• Silicones can be reacted into the polymer chains of plastics

• Silicones can be surface coated onto plastics.

Silicone• ‘Pure’ silicones (polydimethylsiloxanes) are poorly soluble in almost everything but can be dispersed into plastics:

Organo-modified silicones are surface-active (due to the difference in polarity between the methylated siloxane backbone and the attached organic groups)

Surface Orientation

Silicones added into plastic will therefore tend to migrate to the surface of the plastic

Plastic Plastic

SiliconeOrganic (Polyether, Alkyl etc.)Optional reactive group

Whether added into or applied onto plastic, appropriate organo-modifications can be selected for the chemistry of the plastic so that the silicone will orient on the surface either silicone ‘in’ or silicone ‘out’, making the plastic’s surface respectively either more or less polar.

• Marriage of different properties, e.g. Silicone Polyethers

Z

- Surface affinity- Surface tension reduction

- Leveling- Water solubility

Silicone Copolymers

-Hydrophilicity-Adhesion- Foaming

- Compatibility

Non-Silicone

O

O

O

Z

b

a

-Hydrophobicity-Release

- defoaming- Incompatibility

Silicone

X

CH3 S i O S i O

CH3 C H3

CH3 C H3

Si O

CH3

Si

C H3

CH3

C H3

Y

Structural architecture

SiliconeOrganic (Polyether, Alkyl etc.)Optional reactive group

Pendant

The attachment of organic modifiers can have a geometry as varied as that of the siloxane backbone

Linear (ABA)

(AB)n

Silwet* Benefits

Silwet polyether copolymers:

Can be dispersed into an extruder‘s water bath from which they will adsorp onto the surface of the plastic, providing variously (and often simultaneously):

Drainage of extruder bath water via surface tension reduction

Release (anti-clustering, film-separation, improved processability,...) via silicone backbone

Anti-fog via wettability (e.g. for transparent food packaging in refrigerated displays)

Anti-stat via friction reduction & via humectancy

Gloss enhancement via increased refractive index

Wetting & Spreading

Droplets (equal volumes) of aqueous surfactant (with blue dye for visualisation) on polyethylene

SiO

SiO

SiO

Si

R1 R2x y

Other Copolymers

O Si O Si O Si

x

y

Si

HOO

Si O Si O SiO

OH

xn n

Other (non-polyether) copolymers are used in plastics e.g.:

• GPW2233, an alkyl silicone, for the dispersion of pigments into PP

• TSF437, a phenyl silicone, to impart impact resistance and flame retardancy to polycarbonate while maintaining transparency

• Formasil 889, a microemulsified quaternary ammonium (AB)n, as surface-applied anti-stat

Reactive Silicones

– α, ω-Silanol

– α, ω-Carbinol

– α, ω-Olefin

– α, ω-Epoxy

HO Si O Si O Si O

CH3

CH3

CH3

R'

R"

CH3

x

OHSi

CH3

CH3

y

R Si O Si O Si O

CH3

CH3

CH3

R'

R"

CH3

x

RSi

CH3

CH3

y

R Si O Si O Si O

CH3

CH3

CH3

R'

R"

CH3

x

HO R OHSi

CH3

CH3

y

R Si O Si O Si O

CH3

CH3

CH3

R'

R"

CH3

x

RSi

CH3

CH3

y

OO

Silicones may be reacted into the polymer matrix improving the flexibility of plastic and because the silicone, being surface active, tends to be preferentially at the surface of the plastic, acting as an internal mold-release agent and barrier membrane

Flame retardancy

• Silicone burns to silica (sand)

• Silicones are surface active and so migrate to the surface of the molten plastic

• An effective way to extinguish fires is to pour sand on them !

• Plastic just behind the flame front is moltenMechanism:

SFR100 is a non-toxic FR additive which synergistically enables the replacement of halogenated & antimony FRs in polyolefinsand thermoplastics while simultaneously improving processabilityand mechanical properties.

Copyright 2010 Momentive Performance Materials Inc. All rights reserved. CONFIDENTIAL

20

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