Exam 2 - Ingredients of Plastics

Question 0

Additives

Answer 0

Chemicals added to plastics to alter properties, appearance, or performance/cost
Usually added prior to final processing

Question 1

Antioxidants

Answer 1

prevent the oxidation of plastic material

Question 2

Antioxidant package

Answer 2

– prevents oxidations by stopping reaction and neutralizing materials that cause it

Question 3

additives used to prevent oxidation

Answer 3

Phenolics and amines

Question 4

Oxidation

Answer 4

the breakdown of polymer chains due to reaction with oxygen
• Cause material weakness and at extreme, disintegration
– Occurs more at higher temperatures

Question 5

Two materials particularly susceptible to oxidation

Answer 5

Polypropylene and polyethylene

Question 6

used to neutralize oxidizers

Answer 6

Phosphites and thioesters

Question 7

Antistatic Agents –

Answer 7

assist in the dissipation of static charge

Question 9

Antistatic agent applications

Answer 9

These agents can be mixed in or applied to the surface
– Attract moisture from the air to make material more conductive
– Computer and automotive uses due to static electricity considerations

Question 9

Flame Retardants definition

Answer 9

– prevent material from sustaining a flame

Question 10

Anti static agent materials

Answer 10

Amines, quaternary ammonium compounds, organic phosphates used as antistatic agents
– Concentrations can be up to 2% of materials

Question 11

UV Stabilizers

Answer 11

reduce damage done by UV light (sunlight)
– UV light can cause crazing, color changes, and loss of chemical/physical properties

Question 12

UV Stabilizers – materials

Answer 12

– Polyolefins (PP, PE), Polystyrene, PVC, ABS, polyesters, and polyurethanes are susceptible to UV radiation
– Carbon black, hindered-amine light stabilizers

Question 13

Preservatives

Answer 13

– prevent micro-organisms, insects or rodents from attacking material

Question 14

Preservative types

Answer 14

– Antimicrobials, fungicides, mildewicides, and rodenticides – Heavily regulated by EPA and FDA

Question 15

Heat Stabilizers –

Answer 15

retard decomposition of polymer by heat, light, oxidation, or mechanical shear

Question 16

Colorants

Answer 16

– allow plastics to come in a wide array of colors and with various effects

Question 17

Heat stabilizers (materials)

Answer 17

– Previously based on lead or cadmium, But now other materials tried due to health concerns
– Other materials (zinc, barium, organotin)
– Sometimes lead still used in multilayer systems

Question 18

Colorants can be delivered in different ways (4)

Answer 18

– Precolor – material that is ready for processing that is the desired color
– Dry color – powder; hard to handle, dust problems
– Liquid color – liquid base that requires special processing equipment
– Color concentrate – high levels of color that come in a base resin

Question 19

Coupling agents (materials)

Answer 19

– Silane and Titanate widely used

Question 20

Coupling Agents

Answer 20

– used to promote bonding with reinforcements, filler, or laminates
– Polymers tend not to adhere to other materials without coupling agent
– very bad outcome for composites

Question 21

Polymerization Additives

Answer 21

– chemicals that speed up, promote or inhibit polymerization and cross-linking

Question 22

4 Basic Types of Colorants

Answer 22

1. Dyes
   –organic colorants
   –form chemical links with molecules
   – Bright and strong
   – Work in transparent products
   – Poor thermal and light stability
   – Can migrate/move into in parts
2. Organic pigments
   – not soluble in resin
   – Must be thoroughly mixed into plastic
   – Colors can be duller than those produced with dyes
   – Can agglomerate and form specs
3. Inorganic Pigments
   – based on metal oxides and sulfides
   – Have to be dispersed into resin (insoluble)
   – Resistant to heat and light
   – Heavy metals cause of health concern
   – Not as brilliant as organic pigments and dyes
   – Carbon black, iron oxide red, cobalt oxide blue
4. Special Effect Pigments
   – addition of materials to produce reflective or “jewel/metal like” look
   – Clear or colored glass added to increase reflectivity
   – Flakes of metal used to produce metallic sheen– Pearl essence used for luster
   – Luminescent material
   – emit light when excited electrically, chemically, or with light
   • Fluorescent materials
   – reflect light in the presence of excitation
   • Phosphorescent materials
   – continue to emit light after excitation removed

Question 23

Foaming or Blowing Agents

Answer 23

– assist in forming plastics with cellular structure

Question 25

Polymerization additives (types)

Answer 25

– Curing Agents – chemicals that cause cross-linking – Inhibitors – used to inhibit the polymerization of material and prolong storage – Catalysts – speed up or help polymerization and cross-linking – Promoters – aid in polymerization • Only work in presence of catalyst • Reducematerialshelflife– All tend to be rather nasty chemicals

Question 25

Foaming agents (types)

Answer 25

– Physical foaming agents decompose at certain temperatures and release gases which cause voids – Chemical foaming agents release gases to cause voids as the result of a chemical reaction – Polyurethanes foams widely used as cushions – Chlorinated flouro-carbons widely used physical foaming agent until late 1980’s • Now hydrochlorofluorocarbons used – don’t work as well – Azodicarbonamide widely used as a chemical foaming agent – also used as a food additive (oxidizing agent)

Question 26

Lubricants –

Answer 26

reduce friction in processing – Can be used to reduce friction in processing equipment or assist in part ejection from mold – Can be used to prevent products from sticking to each other – Waxes and metallic soaps used as lubricants – Too much lubrication can reduce polymerization or cause cloudy patches

Question 27

Lubricants (materials)

Answer 27

– Flourocarbons (Scotchgard), polyamides, silicone plastics

Question 29

Nucleating Agents

Answer 29

– increase crystallinity – Decrease time for material to solidify during processing and increase cycle time – Inert mineral fillers widely used (chalk, clay, talc)

Question 30

Plasticizers

Answer 30

– additive that increases flexibility, reduces melt temperature, and decreases viscosity – Increase the processibility of the material – Can leach out of material, not good for food/drugs; materials then become brittle – Some are toxic

Question 31

Reinforcements

Answer 31

– Immiscible ingredients added to resins or polymer | – Usually to improve physical performance

Question 31

Two main types of reinforcement

Answer 31

– laminar and fibrous

Question 32

Performance of reinforcements determined by six variables

Answer 32

1. Interface bond – the adhesion between the matrix and the reinforcement – Tug of war – you have to hold onto the rope 2. Properties of reinforcement – how strong is the material you have added to the plastic – Reinforcement usually much stronger than matrix3. Size and shape of reinforcement– Short vs. continuous fiber; fiber vs. cloth vs. particulate 4. Loading of reinforcement – the amount you have in the compound – The more of one material, the more the composite behaves like that material5. Processing technique – the manner in which the composite is “put together” – Must be careful to maintain reinforcement’s shape, size, orientation6. Alignment and distribution of reinforcement – The way the reinforcement is aligned affects the behavior of the composite – Reinforcement must be properly dispersed

Question 33

1. Laminar reinforcement

Answer 33

– composite divided into separate layers – Alignment of reinforcement is key when putting together composite

Question 34

Fibrous reinforcements

Answer 34

– fibers in a polymer matrix

Question 36

Fillers

Answer 36

– inert material added to modify material or reduce cost • Fillers can be organic or inorganic • Fillerscandecreasethermalexpansion,decrease shrinkage • Filler effect on bulk material dependent on material and aspect ratio • Nanocomposites – materials at submicron scale – widely used to reduce thermal expansion and shrinkage (fillings) • Sometimes filler material is the bulk of product – 80%+ for particle boards • A large amount of filler used to reduce expensive material usage and thus cost

Question 36

Flame Retardant Materials

Answer 36

– bromine (health concerns), chlorine, antimony, boron, or phosphorus (form char barriers) – Either produce extinguishing gas or some other barrier to the flame

Question 37

Fiber Reinforcements (types)

Answer 37

– Glass – very common and widely used – several fiberglass products • Glass is very strong (tensile strength of 3-5 GPa) depending on type • Rovings are loosely twisted strands of glass fiber • Yarns of twisted glass rope available • Chopped fibers (3-50 mm) and milled fibers (<1.5mm) also widely used • Mats – non-directional chopped strands held together in resin binder or stitching • Woven cloth of glass available – very expensive Carbonaceous Fibers – organic fiber that has been carbonized or oxidized • High strength, high modulus, low density– Polymer Fibers – usually high strength fibers like aramids (Kevlar) • Have the benefit of being electrically non-conductive – Inorganic Fibers – crystalline, usually ceramics • Very high tensile strengths (40 GPa); low thermal expansion • Includes carbon/graphite fibers • Expensive to make – Metal Fibers – common metals such as aluminum or steel • Not as high strength or low density as other • Add heat transfer and conductivity improvement– Hybrid Fibers – combination of two materials for better reinforcement • Glass and carbon sometimes used together to decrease cost and improve impact toughness