Exam 2 - Ingredients of Plastics Flashcards
Additives
Chemicals added to plastics to alter properties, appearance, or performance/cost
Usually added prior to final processing
Antioxidants
prevent the oxidation of plastic material
Antioxidant package
– prevents oxidations by stopping reaction and neutralizing materials that cause it
additives used to prevent oxidation
Phenolics and amines
Oxidation
the breakdown of polymer chains due to reaction with oxygen
• Cause material weakness and at extreme, disintegration
– Occurs more at higher temperatures
Two materials particularly susceptible to oxidation
Polypropylene and polyethylene
used to neutralize oxidizers
Phosphites and thioesters
Antistatic Agents –
assist in the dissipation of static charge
Antistatic agent applications
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
Flame Retardants definition
– prevent material from sustaining a flame
Anti static agent materials
Amines, quaternary ammonium compounds, organic phosphates used as antistatic agents
– Concentrations can be up to 2% of materials
UV Stabilizers
reduce damage done by UV light (sunlight)
– UV light can cause crazing, color changes, and loss of chemical/physical properties
UV Stabilizers – materials
– Polyolefins (PP, PE), Polystyrene, PVC, ABS, polyesters, and polyurethanes are susceptible to UV radiation
– Carbon black, hindered-amine light stabilizers
Preservatives
– prevent micro-organisms, insects or rodents from attacking material
Preservative types
– Antimicrobials, fungicides, mildewicides, and rodenticides – Heavily regulated by EPA and FDA
Heat Stabilizers –
retard decomposition of polymer by heat, light, oxidation, or mechanical shear
Colorants
– allow plastics to come in a wide array of colors and with various effects
Heat stabilizers (materials)
– 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
Colorants can be delivered in different ways (4)
– 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
Coupling agents (materials)
– Silane and Titanate widely used
Coupling Agents
– 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
Polymerization Additives
– chemicals that speed up, promote or inhibit polymerization and cross-linking
4 Basic Types of Colorants
- 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 - 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 - 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 - 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
Foaming or Blowing Agents
– assist in forming plastics with cellular structure
Polymerization additives (types)
– 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
Foaming agents (types)
– 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)
Lubricants –
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
Lubricants (materials)
– Flourocarbons (Scotchgard), polyamides, silicone plastics
Nucleating Agents
– increase crystallinity
– Decrease time for material to solidify during processing and increase cycle time
– Inert mineral fillers widely used (chalk, clay, talc)
Plasticizers
– 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
Reinforcements
– Immiscible ingredients added to resins or polymer
– Usually to improve physical performance
Two main types of reinforcement
– laminar and fibrous
Performance of reinforcements determined by six variables
- Interface bond
– the adhesion between the matrix and the reinforcement
– Tug of war – you have to hold onto the rope - 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 - 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
- Laminar reinforcement
– composite divided into separate layers
– Alignment of reinforcement is key when putting together composite
Fibrous reinforcements
– fibers in a polymer matrix
Fillers
– 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
Flame Retardant Materials
– bromine (health concerns), chlorine, antimony, boron, or phosphorus (form char barriers)
– Either produce extinguishing gas or some other barrier to the flame
Fiber Reinforcements (types)
– 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
