1

CHM 585 /490

Chapter 12

Additives

2

Chapter 12Additives

• Antioxidants

• UV stabilizers

• Antistatic Agents

• Peroxides

• Lubricants

• FR

• Heat stabilizers

3

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

4

Antioxidants

• $160 million in U.S.

• Hindered phenols

• Phosphites

• Thioesters

5

Hindered Phenols

• BHT has FDA approval and is relatively inexpensive

• But volatile and may cause discoloration

OH

BHT

R.

O.

+ RH

6

Less Volatile Hindered Phenols

OH

CH2CH2CO2C18H37

OH

CH2CH2CO2CH2

() C

4

7

Phosphites

• Often used as costabilizers with hindered phenols

O PC9H19( )3

(ArO)3 P O

8

Thioesters

• S(CH2CH2CO2R)2

• Often used with hindered phenols

9

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

10

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

11

Preferential UV absorbers

O OH

OR NN

N

HO

Cl

Tinuvin 326

12

Hindered Amine Light Stabilizers

HALS

N

H

R

13

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

14

Antistatic Agents

• Typically hygroscopic chemicals such as ethoxylated amines

RN CH2CH2OH

CH2CH2OH

15

Peroxides

• For polymerization of – PVC– LDPE– ABS

For crosslinking resins

As hardeners for unsaturated polyester resins(thermoset polyester)

O O RR

16

Lubricants

• Internal lubricants to improve flow

• External to enhance mold release

• Typically long hydrocarbon chain with a polar end

17

Lubricants

• Fatty acid amides

• Fatty acid esters

• Fatty acids

• Fatty acid salts

• Waxes

RCONH2RCO2H

RCO2M+

18

FR

•

                               

19

20

21

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

22

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

23

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. Dupont’s Corian), thermoset polyester resins, polyolefins and PVC

24

Forming an insulating char on the substrate which starves the fire

• Phosphorous flame retardants

• Phosphate esters (RO)3PO

• PVC, Polyurethanes, PPO

25

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

26

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.

27

1 + 1 = 3 !

Synergy

28

Heat Stabilizers

• Used for PVC

• > $200 M business in U.S.

• Various barium, cadmium, tin compounds that scavenge reactive organic chlorine bonds thereby preventing catastrophic dehydrochlorination

29

Fillers

• Glass fibers

• Nickel

• Clay – Prevent shrinkage

• Mica

• Pigments

30

Other Additives

• Nucleating agents

• Clarifiers

• Impact Modifiers

• Antimicrobial agents