Silicone Fluids for Modification of Plastics Peter Stevens Application 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 2 nd most abundant element in earth s crust (~28%). Non-toxic 5 4
Silicon to Silicone C CO 2 sand silicon + methylchloride + Rochow synthesis (Momentive heritage) Methanol water + methylchlorosilanes silicone
Molecular Geometry Hydrolysis of Mono-, Di-, Tri- & Tetramethylchlorosilanes generates M, D, T & Q siloxane units that provide unlimited opportunities for molecular architecture M T D H 3 C Si O Si O Si O H 3 C C H 3 O Si O Si H H 3 C Si O Q Si O Si O Si O H 3 C Si
What is Silicone? Silicone oil = Polydimethylsiloxane (PDMS) H 3 C Si O Si x
Why are Silicones different? -Si-O-Si-O- -C-C-C-C- Silicone Hydrocarbon The silicone backbone is stronger than the carbon-to-carbon chain, making it more resistant to temperature, radiation, oxidation and many chemicals
Why are Silicones different? Silicone Organic 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? Silicone Organic Hydrocarbons are primarily methylene (CH 2 ) Methyl ( ) 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.
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 -100 o C With other things: they are powerful lubricants & release agents
Why add Silicones to Plastics? Silicones are used to modify: 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 Surface properties: Release Improved extrusion Anti-cluster Surface tension Higher molding accuracy Wettability / anti-fog Particle compatibilzation (pigments) Anti-stat via reduced friction & via humectancy Appearance (gloss)
Silicones into Plastics Pure silicones (polydimethylsiloxanes) are poorly soluble in almost everything but can be dispersed into plastics: Silicone 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.
Surface Orientation Organo-modified silicones are surface-active (due to the difference in polarity between the methylated siloxane backbone and the attached organic groups) Silicones added into plastic will therefore tend to migrate to the surface of the plastic 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. Plastic Plastic Silicone Organic (Polyether, Alkyl etc.) Optional reactive group
Silicone Copolymers Marriage of different properties, e.g. Silicone Polyethers -Hydrophobicity -Release -defoaming - Incompatibility Silicone -Hydrophilicity -Adhesion -Foaming - Compatibility Non-Silicone Z Z O O b - Surface affinity - Surface tension reduction -Leveling - Water solubility Si O Si O X a O Si O Si Y
Structural architecture The attachment of organic modifiers can have a geometry as varied as that of the siloxane backbone Silicone Organic (Polyether, Alkyl etc.) Optional reactive group Pendant 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
Other Copolymers 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 Si O Si O Si O Si x R 1 R 2 y Si O Si O Si O Si HO O n Si O Si O Si x O OH n x y
Reactive Silicones R' 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 moldrelease agent and barrier membrane α, ω-silanol α, ω-carbinol α, ω-olefin α, ω-epoxy HO Si O Si O Si O Si OH x R" R' y HO R Si O Si O Si O Si R OH x R' R Si O Si O Si O Si R O x R" R" R' R Si O Si O Si O y y Si R O x R" y
Flame retardancy Mechanism: Plastic just behind the flame front is molten Silicones are surface active and so migrate to the surface of the molten plastic Silicone burns to silica (sand) An effective way to extinguish fires is to pour sand on them! SFR100is a non-toxic FR additive which synergistically enables the replacement of halogenated & antimony FRs in polyolefins and thermoplastics while simultaneously improving processability and mechanical properties.
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