POLYMERS
1.Fundamentals of Polymer Technology
2.Thermoplastic Polymers
3.Thermosetting Polymers
4.Processing of Plastics
Polymer
A compound consisting of long-chain molecules, each molecule made up of repeating units connected together
•There may be thousands, even millions of units in a single polymer molecule
•The word polymer is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part
•Most polymers are based on carbon and are therefore considered organic chemicals
Types of Polymers
•As engineering materials, it is appropriate to divide them into the following two categories:
1.Thermoplastic polymers
2.Thermosetting polymers
Thermoplastic Polymers - Thermoplastics
Solid materials at room temperature but viscous liquids when heated to temperatures of only a few hundred degrees
•This characteristic allows them to be easily and economically shaped into products
•They can be subjected to heating and cooling cycles repeatedly without significant degradation
•Symbolized by TP
Thermosetting Polymers - Thermosets
•Cannot tolerate repeated heating cycles as thermoplastics can
•When initially heated, they soften and flow for molding
•Elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid
•If reheated, thermosets degrade and char rather than soften
•Symbolized by TS
•TS polymers are distinguished by their highly cross-linked three-dimensional, covalently-bonded structure
•In effect, the formed part (e.g., pot handle, electrical switch cover, etc.) becomes one large macromolecule
•Always amorphous and exhibits no glass transition temperature
Examples of Polymers
•Thermoplastics:
•Polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylon
•Thermosets:
•Phenolics, epoxies, and certain polyesters
Reasons Why Polymers are Important:
•Plastics can be molded into intricate part shapes, usually with no further processing
•Very compatible with net shape processing
•On a volumetric basis, polymers:
•Are cost competitive with metals
•Generally require less energy to produce than metals
•Certain plastics are translucent and/or transparent, which makes them competitive with glass in some applications
General Properties of Polymers
•Low density relative to metals and ceramics
•Good strength-to-weight ratios for certain (but not all) polymers
•High corrosion resistance
•Low electrical and thermal conductivity
Limitations of Polymers
•Low strength relative to metals and ceramics
•Low modulus of elasticity (stiffness)
•Service temperatures are limited to only a few hundred degrees
•Viscoelastic properties, which can be a distinct limitation in load bearing applications
•Some polymers degrade when subjected to sunlight and other forms of radiation
Additives
•Properties of a polymer can often be beneficially changed by combining it with additives
•Additives either alter the molecular structure or
•Add a second phase, in effect transforming the polymer into a composite material
Types of Additives by Function
Fillers – to strengthen polymer or reduce cost- wood flour, quartz, talc
Plasticizers – to soften polymer and improve flow- di-iso-octyl is mixed with PVC
Colorants – pigments or dyes- Organic and Inorganic dyes
Flame retardants – to reduce flammability of polymer- boron, nitrogen, chlorine, antimony and phosphorous
Reinforcing agents – to increase mechanical properties- glass fibers
Stabilizers– to stabilize the properties of the plastic
Lubricant- to reduce friction- Mineral oil and Waxes
Mechanical Properties of Thermoplastics
•Low modulus of elasticity (stiffness)
•E is two or three orders of magnitude lower than metals and ceramics
•Low tensile strength
•TS is about 10% of the metal
•Much lower hardness than metals or ceramics
•Greater ductility on average
•Tremendous range of values, from 1% elongation for polystyrene to 500% or more for polypropylene
General Properties of Thermosets
•Rigid - modulus of elasticity is two to three times greater than thermoplastics
•Brittle, virtually no ductility
•Less soluble in common solvents than thermoplastics
•Capable of higher service temperatures than thermoplastics
•Cannot be remelted - instead they degrade or burn
1.Fundamentals of Polymer Technology
2.Thermoplastic Polymers
3.Thermosetting Polymers
4.Processing of Plastics
Polymer
A compound consisting of long-chain molecules, each molecule made up of repeating units connected together
•There may be thousands, even millions of units in a single polymer molecule
•The word polymer is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part
•Most polymers are based on carbon and are therefore considered organic chemicals
Types of Polymers
•As engineering materials, it is appropriate to divide them into the following two categories:
1.Thermoplastic polymers
2.Thermosetting polymers
Thermoplastic Polymers - Thermoplastics
Solid materials at room temperature but viscous liquids when heated to temperatures of only a few hundred degrees
•This characteristic allows them to be easily and economically shaped into products
•They can be subjected to heating and cooling cycles repeatedly without significant degradation
•Symbolized by TP
Thermosetting Polymers - Thermosets
•Cannot tolerate repeated heating cycles as thermoplastics can
•When initially heated, they soften and flow for molding
•Elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid
•If reheated, thermosets degrade and char rather than soften
•Symbolized by TS
•TS polymers are distinguished by their highly cross-linked three-dimensional, covalently-bonded structure
•In effect, the formed part (e.g., pot handle, electrical switch cover, etc.) becomes one large macromolecule
•Always amorphous and exhibits no glass transition temperature
Examples of Polymers
•Thermoplastics:
•Polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylon
•Thermosets:
•Phenolics, epoxies, and certain polyesters
Reasons Why Polymers are Important:
•Plastics can be molded into intricate part shapes, usually with no further processing
•Very compatible with net shape processing
•On a volumetric basis, polymers:
•Are cost competitive with metals
•Generally require less energy to produce than metals
•Certain plastics are translucent and/or transparent, which makes them competitive with glass in some applications
General Properties of Polymers
•Low density relative to metals and ceramics
•Good strength-to-weight ratios for certain (but not all) polymers
•High corrosion resistance
•Low electrical and thermal conductivity
Limitations of Polymers
•Low strength relative to metals and ceramics
•Low modulus of elasticity (stiffness)
•Service temperatures are limited to only a few hundred degrees
•Viscoelastic properties, which can be a distinct limitation in load bearing applications
•Some polymers degrade when subjected to sunlight and other forms of radiation
Additives
•Properties of a polymer can often be beneficially changed by combining it with additives
•Additives either alter the molecular structure or
•Add a second phase, in effect transforming the polymer into a composite material
Types of Additives by Function
Fillers – to strengthen polymer or reduce cost- wood flour, quartz, talc
Plasticizers – to soften polymer and improve flow- di-iso-octyl is mixed with PVC
Colorants – pigments or dyes- Organic and Inorganic dyes
Flame retardants – to reduce flammability of polymer- boron, nitrogen, chlorine, antimony and phosphorous
Reinforcing agents – to increase mechanical properties- glass fibers
Stabilizers– to stabilize the properties of the plastic
Lubricant- to reduce friction- Mineral oil and Waxes
Mechanical Properties of Thermoplastics
•Low modulus of elasticity (stiffness)
•E is two or three orders of magnitude lower than metals and ceramics
•Low tensile strength
•TS is about 10% of the metal
•Much lower hardness than metals or ceramics
•Greater ductility on average
•Tremendous range of values, from 1% elongation for polystyrene to 500% or more for polypropylene
General Properties of Thermosets
•Rigid - modulus of elasticity is two to three times greater than thermoplastics
•Brittle, virtually no ductility
•Less soluble in common solvents than thermoplastics
•Capable of higher service temperatures than thermoplastics
•Cannot be remelted - instead they degrade or burn