CHM 585 /490

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CHM 585 /490

• Chapter 12
• Additives

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Chapter 12Additives

• Antioxidants
• UV stabilizers
• Antistatic Agents
• Peroxides
• Lubricants
• FR
• Heat stabilizers

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Antioxidants

• Antioxidants retard the oxidative degradation of
  plastics which is initiated when free radicals
  are created in the polymer by heat, UV,
  mechanical shear, or metallic impurities

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Antioxidants

• 160 million in U.S.
• Hindered phenols
• Phosphites
• Thioesters

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Hindered Phenols

• BHT has FDA approval and is relatively
  inexpensive
• But volatile and may cause discoloration

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Less Volatile Hindered Phenols
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Phosphites

• Often used as costabilizers with hindered phenols

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Thioesters

• S(CH2CH2CO2R)2
• Often used with hindered phenols

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UV Stabilizers

• 130 Million in U.S.
• Preferential UV absorbers
• Absorb preferentially to the polymer and
  dissipate the absorbed energy without harm to the
  polymer
• Quenching Agents
• Metal chelates that convert the excess energy
  absorbed to heat

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UV Stabilizers

• Free Radical Terminators
• Radical scavengers that both inhibit the
  propagation of free radicals and act as a
  scavenger
• Hydroperoxide Decomposers
• Metal chelates and hindered amines that prevent
  the formation of free radicals by stabilizing
  hydroperoxides

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Preferential UV absorbers
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Hindered Amine Light StabilizersHALS
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Antistatic Agents

• Static electricity can build up on the surface of
  polymers and needs to be dispersed to avoid the
  possibility of sparking, the accumulation of dust
  and other complications

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Antistatic Agents

• Typically hygroscopic chemicals such as
  ethoxylated amines

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Peroxides

• For polymerization of
• PVC
• LDPE
• ABS
• For crosslinking resins
• As hardeners for unsaturated polyester
  resins(thermoset polyester)

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Lubricants

• Internal lubricants to improve flow
• External to enhance mold release
• Typically long hydrocarbon chain with a polar end

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Lubricants

• Fatty acid amides
• Fatty acid esters
• Fatty acids
• Fatty acid salts
• Waxes

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FR

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Flame Retardants

• Chemicals used to retard ignition and burning of
  plastics
• Worldwide market 2.5 Billion
• FR additives enable plastics to meet various fire
  safety and performance standards imposed upon
  them.
• UL

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FR Mechanisms

• Absorbing heat by the release of water
• Forming an insulating char on the substrate which
  starves the fire
• Interfering with the chemical reactions that
  maintain the fire and promote the spread of flame

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Absorbing heat by the release of water

• Alumina Trihydrate Al2O3.3H20
• Largest volume FR in the U.S.
• 240,000 metric tons
• ATH used in polyacrylates ( e.g. Duponts
  Corian), thermoset polyester resins, polyolefins
  and PVC

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Forming an insulating char on the substrate which
starves the fire

• Phosphorous flame retardants
• Phosphate esters (RO)3PO
• PVC, Polyurethanes, PPO

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Interfering with the chemical reactions that
maintain the fire and promote the spread of flame

• Halogenated compounds
• Brominated aromatics most common
• Nylons, polyesters, styrenics, polyolefins

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Halogenated FR

• Free radical capture" process - takes place in
  the vapor phase. On combustion at a temperature
  of over 600 F, the halogen forms hydrochloric or
  hydrobromic acid that reacts with the antimony
  oxide to form antimony trihalide or antimony
  oxyhalide.
• The flame retarding action takes place in the
  vapor stage above the burning material. It is
  thought that "free radicals propagate" the flame.
• Antimony trihalides or antimony oxyhalides act as
  "free radical traps", and take up free radicals.

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1 1 3 !

• Synergy

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Heat Stabilizers

• Used for PVC
• gt 200 M business in U.S.
• Various barium, cadmium, tin compounds that
  scavenge reactive organic chlorine bonds thereby
  preventing catastrophic dehydrochlorination

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Fillers

• Glass fibers
• Nickel
• Clay
• Prevent shrinkage
• Mica
• Pigments

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Other Additives

• Nucleating agents
• Clarifiers
• Impact Modifiers
• Antimicrobial agents