Polymer processing-2.ppt

8/10/2019 Polymer processing-2.ppt

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Polymer Process Engineering

Introduction

12/24/2014 1Chapter 1. Primer/introduction


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WHAT IS A POLYMER?

Berzelius (1883)Poly (many) + mer (unit)

Polystyrene polymerized in 1938; polyethylene glycol made in 1860sEarly polymer products were based on cellulose- gun cotton = nitrated

cellulose

12/24/2014 Chapter 1. Primer/introduction 3


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A polymer is

Long chain molecule, often based on organicchemical building blocks (monomers)

Long molecules (Mw ~100,000 Da) have solid-

like properties The chain may be amorphous (no regular

structure), crystalline (a regular repeating

structure), crosslinked, Dendrimers and oligomers have different

properties



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HOW DO YOU BUILD A MOLECULE?

Chemical structure

Chain morphologyconstitution, configuration, conformationDegree of polymerization = number of repeating units

Building block sourceshydrocarbons, renewable materials



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Building blocks

5% of petroleum goes

into polymers

Sustainable use is

possible Energy recovery is

possible if solid

polymers are

combusted

Type C H O

gas NG 3 1 0

liquid Crude 6 1 0

solid Coal 14 1 0

Renew-able

cellulose 6 1 5.3

Hemi-

cellulose

6 1 8

lignin 6.8 1 3

protein



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Building methods

Chain (addition)

Examplepolyethylene (PE)

from ethylene

Small number of reactingchains at any one time,

which can grow into long

molecules prior to

termination Long reaction times needed

to achieve high conversions

Step (condensation)

Examplepoly(ethylene

terephthalate) (PET) from

terephthalic acid andethylene glycol

Endgroups react to build the

chain; long reaction times

needed to achieve highpolymer



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Multiple building blocks

Copolymers, terpolymers,

Using multiple building blocks leads to

polymers with intermediate properties or

unique properties compared to the

homopolymers



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Several copolymer configurations



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Chain configurations

Linearrepeating units are aligned

sequentially

Branchedlarge segments branch off the

main chain/carbon backbone

Crosslinked/networkchemical crosslinks

between chains add mechanical strength

EXAMPLES?



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Multiphase systems

Composites

Structural

Random

Other

Nanocomposites

Blends

Dispersed lamellae, cylinders, spheres



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HOW DO WE CLASSIFY POLYMERS?

Structurechemical, configuration

solid performance (mechanical + thermal properties)

other



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Mechanical + Thermal

Thermoplasticsolidified by cooling andreheated by melting

Thermosetsretain their structure when

reheated after polymerization (usuallycrosslinked)

Elastomersrubbers, deform readily with

applied force Thermoplastic elastomers

other



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WHAT IS IN A COMMERCIALPRODUCT?

Very few commercial products are pureMWDmolecular weight distribution

additives



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Polymers vs. metals


Why do we use

polymers?


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Polymeric materials

Compete well on a strength/weight basis

Easy to form into 3D shapes

Creep under load is usually poor; this behavioris usually corrected by adding fillers or fibers

Low corrosion in the environment compared

to metals

Generally good solvent resistance



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Thermoplastics

Commodities: 75% of the polymer volumeused is with 4 polymer families, polyethylene,polystyrene, polypropylene and poly(vinyl

chloride) [low cost] Intermediate: higher heat deflection

temperatures

Engineering plastics: can be used in boilingwater

Advanced thermoplastics: extreme properties



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Thermosets

High moduli, high flex strengths, high heat

deflection temperatures

Shape is retained during thermal cycling

Often made with step/condensation

polymerization systems

Crosslinking is usually used



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HOW DO WE MAKE A PART?

Polymerization

Formulation

Fabrication



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Formulation

Additives are used to modify properties

and/or lower costs

Additives: heat stabilizer, light stabilizer,

lubricant, colorant, flame retardant, foaming

agent, plasticizer

Reinforcement: particulate minerals, glass

spheres, activated carbon, fibers

Blends, alloys, laminates



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Additives can change:

Processing properties

Performance properties

Composites: polymers with fiber fillers Packaging: multiple layers often used



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Formulation operations

Thermoplastics: melting or solvent processing

Thermosets: additive addition to monomers

or to prepregs



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Fabrication

Varies by industry sector

Adhesive

Coating

Elastomer

Plastic

fiber



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Overview of the polymer industry

Industry General product requirements

adhesive Strong surface forces; epoxy, superglue

coatings Film-forming; LDPE with good impact

composites Structural materials; epoxy + fibers

elastomers Large deformation and recovery; rubber in tire and seals

fibers High strength/area; polyacrylonitrile

foams Light weight, low thermal conductivity; polyurethane

plastics Stable deformation under static load; HDPE, PP, PVC



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Commodity plastics


Polymer Major uses

LDPE Packaging film, wire and cable insulation, toys, flexible bottles,

housewares, coatings

HDPE Bottles, drums, pipe, conduit, sheet, film, wire and cable

insulation

PP Automobile and appliance parts, rope, cordage, webbing,

carpeting, film

PVC Construction, rigid pipe, flooring, wire and cable insulation,

film, sheet

PS Foam and film packaging, foam insulation, appliances,

housewares, toys


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Film blowing


High strength films are achieved by

orienting the crystallites. The film is

biaxially oriented; the wind-up rolls

stretch the film in the machine direction

and the expansion of the film radially

provides a hoop stress force.


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Wire coating


Wire coating speeds can be high, and process start-up is challenging. Metal wires may need sizing,

or wetting agents in the polymer melt for good adhesion.


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Calendaring


Thin and thick section calendaring is used to make wide sheets (8-12 ft).


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Bottle blowing


The parison is inflated,

developing biaxially

orientation similar to that of

blown film. The sides of the

mold provide cooling, quickly

freezing in the orientation

developed during the

blowing process. When this

process is used to make soda

bottles of PET, the

orientation is critical to

achieving low carbon dioxide

permeation rates (and longbottle shelf life).


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Compression molding



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Thermoset applications


Polymer Major uses

Phenol-

formaldehyde resins

(PF)

Electrical equipment, automobile parts, utensil handles,

plywood adhesives, particleboard binder

Urea-formaldehyde

resins (UF)

Similar to the above; textile coatings and sizings

Unsaturated

polyester (UP)

Construction, vehicle parts, boat hulls, marine accessories,

corrosion-resistant ducts, pipes and tanks, business equipment

Epoxy (EP) Protective coatings, adhesives, electrical parts, industrial

flooring, highway paving materials, composites

Melamine-

formaldehyde resins

(MF)

Similar to UF resins; decorative panels, counter and table tops,

dinnerware


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Elastomers

The polymers used for elastomers usually have

very low heat deflection and melt temperatures

Solids with good mechanical properties are made

by crosslinking polymer chains together

The molecular weight of elastomer parts is the

size of the object

Vulcanization of rubber uses sulfur to providecrosslinks between the C=C bonds of natural

rubber.



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Fibers

Fibers are based on highly crystalline polymers

that can be oriented axially to have great

strength. Orientation (cold drawing) develops

crystal structure in the solid.

Most natural fibers from biomass are based

on cellulose; spider silk has different

compositions and is based on a set ofcopolymers



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Elastomer polymers

Polymer family description

Styrene-butadiene Copolymers with a range of constitutions; SBRstyrene-

butadiene rubber

Polybutadiene Cis-1,4-polymer

Ethylene-propylene EPDethylene-propylene-diene monomer; the small amountsof diene provide unsaturation

Polychloroprene Poly(2-chloro-1,3-butadiene); this polar elastomer has excellent

resistance to non-polar organic solvents (gasoline, diesel)

Polyisoprene Poly(cis-1,4-isoprene); synthetic natural rubber

Nitrile rubber Copolymer of acrylonitrile and butadieneButyl rubber Copolymer of isobutylene and isoprene

Silicon rubber Rubber based on polysiloxanes

Urethane rubber Elastomer with polyethers linked via urethane groups



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Synthetic fibers

Fiber type description

Cellulosic

acetate rayon Cellulose acetate

viscose rayon regenerated cellulose

Non-cellulosic

Polyester Mostly poly(ethylene terephthalate)

Nylon Nylon 6,6; nylon 6, nylon 10; other aliphatic, aromatic

polyamides

Olefin Polypropylene; copolymers of vinyl chloride + acrylonitrile, vinyl

acetate, vinylidene chloride

Acrylic > 80% acrylonitrile; modacrylic = acrylonitrile + vinyl chloride or

vinylidene chloride



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Coatings

Coatings. Major area for expansion; solar cells,

windows, Supplier base is highly

fragmented.

Paints. Major area for expansion; vehicles,

Materials supplier base is clustered; painting

systems base is clustered; user base is

fragmented



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Adhesives

Highly fragmented market.



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Foams

Major area: insulation

for housing, sound

control,

Materials:

polystyrene,

polyurethanes,

Reaction injectionmolding example



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Composites

Thermosets and thermoplastics

Sheet molding compounds

Filament winding



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HOW DO WE NAME POLYMERS?

Polymer nomenclature is widely varied.

Trademarks and common names may be industry-sector specific.

Nomenclature: Polymer Handbook. Chapter 1.



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Source-based names

Source-based name when the polymer is derivedfrom a single (original or hypothetical) monomer;or random co-/ter-polymers Poly(vinyl alcohola)

Poly(styrene-co-butadiene) Polyformaldehyde (not polyoxymethylene)b

Poly(ethylene oxide) (not poly(ethylene glycol)b

a

when the name is long, parentheses are used toseparate the name from poly

b - actually the second name is quite common



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Structure-based names

Structure-based name when the

constitutional repeating unit (CRU) has several

components

The CRU is independent of the monomers and

polymerization methods

Poly(hexamethylene adipamide)

Poly(ethylene terephthalate)



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copolymers

Type Connective Example

unspecified -co- Poly(A-co-B)

statistical -stat- Poly(A-stat-B)

random -ran- Poly(A-ran-B)

alternating -alt- Poly(A-alt-B)periodic -per- Poly(A-per-B-per-C)

block -block- (-b-) Poly(A-b-B) or Poly A-block-poly B

graft -graft- (-g-) Poly(A-g-B) or Poly A-graft-poly B



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Source-based name Structure-based name Trade name, abbreviation

polyethylene polymethylene PE, LDPE, HDPE, LLDPE

polypropylene Poly(propylene) PP

polyisobutylene Poly(1,1-dmethylethylene) PIB

polystyrene Poly(1-phenylethylene) Styron, Styrofoam

Poly(vinyl chloride) Poly(1-chloroethylene) PVC

Poly(vinylidene chloride) Poly(1,1-dichlorethylene) Saran

polytetrafluoroethylene Poly(difluoromethylene) Teflon

Poly(vinyl acetate) Poly(1-acetoxyethylene) PVAC

Poly(vinyl alcohol) Poly(1-hydroxyethylene) PVAL

Poly(methyl methacrylate) Poly(1-methoxycarbonyl-1-

methylethylene)

PMMA; Lucite, Plexiglass

polyacrylonitrile Poly(1-cyanoethylene) PAN; Orlon, Acrilan fibers

polybutadiene Poly(1-butenylene) BR rubber

polyisoprene Poly(1-methyl-1-butenylene) NR rubber

polychloroprene Poly(1-chloro-butenylene) Neoprene



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Polymers with other backbones

Source-based name Structure-based name Trade name, abbreviation

polyformaldehyde Poly(oxymethylene) POM

Poly(ethylene oxide) Poly(oxyethylene) PEO

Poly(ethylene glycol adipate) Poly(oxyethylene oxyadipoyl) Polyester 2,6

Poly(ethylene terephthalate) Poly(oxyethylene oxy-terephthaloyl) PET; Dacron

Poly(hexamethylene

adipamide)

Poly(iminoadipoyl imino-hexamethylene) Nylon 6,6

Poly(e-caprolactam) Poly(imino[1-oxohexamethylene]) Nylon 6

polyglycine Poly(imino[1-oxoethylene]) Nylon 2



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WHY ARE LONG CHAIN MOLECULESSOLIDS?

Bonding along the backbone is not extraordinary.

With long chains, secondary valence forces, integrated over the entirechain, provide considerable bonding forces.

Chain entanglements provide physical linkages.



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Chemical bonding in polymers

Most primary bonds along the

backbone are covalent

Secondary valence bonds

Much smaller forces than the

covalent bonds, but become

significant when integrated over the

entire chain

Consider the forces acting on this

macromolecule as it is pulled

through the tube surrounding its

structure in three dimensional space

As each chain segment moves, it

must overcome the local

interactions at the tube surface Longer chains will have more

resistance to motion



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Secondary valence forces

Secondary valence forces affect the glass transition, the

melting temperature, crystallinity, melt flow,

They include: nonpolar dispersion, polar dipoles, polar

induction, and hydrogen bonds


Secondary bond Bond energy,

kcal/mol

Range of action,

Angstrom

Dispersion 0.1-5.0 3-5 (r-6)

Dipole-dipole 0.5-5.0 1-2 (r-3)

Dipole-induced

dipole

0.05-0.5 1-2 (r-6)

Hydrogen bond 1.0-12 2-3 (r-2)


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WHAT ARE TYPICAL CHAIN LENGTHDISTRIBUTIONS?

Few synthetic polymers are monodisperse, i.e., have one chain length.

Many biological polymers do have specific molecular weights, e.g., proteins,DNA,

The molecular weight distribution has critical effects on polymer propertiesin the melt and solid states.


T i l ff t f l l i ht


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Typical effects of molecular weight

distributions Homopolymers with different molecular weight distributions may be

insoluble in each other


# carbon atoms State Use

1-4 Gas Gaseous fuel5-11 Low viscosity liquid gasoline

9-16 Medium viscosity

liquid

kerosene

16-25 High viscosity liquid Oil, grease

25-50 Crystalline solid Paraffin wax

1000-3000 Plastic solid

(crystalline +

amorphous)

polyethylene

Linear

alkane

properties


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MWD - oligomer

Poly(a-olefin); PAO6

Synthetic base oil

vehicle use

Trimer, tetramer,

pentamer, hexamer,

heptamer

Based on 1-decene

Ionic polymerization

Differential distribution

by size exclusionchromatography

PeakFit used for curve

deconvolution



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Two polyethylenes

Weight frequency, differential

distributions

Number-average molecular

weights are the same

Weight-average molecular

weights are different Narrow MWDPD ~ 5.7

Broad MWDPD ~ 15

Differences in flow, tensile and

appearance properties


Mn

ni Mii

ni

i

Mw

wi Mii

wi

i

ni Mi2

i

ni M

i

i

PD

Mw

Mn


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HOW DOES CHAIN LENGTH AFFECTPROCESSING?

In-class exercise



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HOW DOES CHAIN LENGTH AFFECTPERFORMANCE?

In-class exercise



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WHAT ARE IMPORTANT THERMALTRANSITIONS?

Thermal properties are often key criteria used to select polymers for specificapplications.

Five regions of viscoelastic behavior (many polymers have all five): < glasstransition, power law region, rubbery plateau, rubbery flow, fluid flow

Othercrystalline solids, crosslinked elastomers



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Five regions of viscoelasticity

Use amorphous polymers below Tg

Use crystalline polymers below Tm

Crosslinked elastomers at G

Melt processing between B and C



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Typical G vs T plots



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regions

Viscoelasticity: most polymers creep(slow flow) under long-term stress.Creep may not be recoverable, i.e., the sample may not recoil to its

original dimensions. Over short periods of time, polymers are elastic.

Solid yield and fracture: elasticity for e< 0.1%; PS is brittle and fails at low

elongations. PE yields, and then undergoes cold drawing to > 300%

elongation.



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BUILDING A GLOSSARY



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POLYMER SCIENCE DIRECTIONS

Medical applications are arich applications area forpolymers.

Local variations in surfaceroughness at the nanoscalecan induce strains in cellmembranes, leading to thegrowth of F-actin stress

fibers that span the lengthof the cell.W.E. Thomas, D. E. Discher, V. P. Shastri,Mechanical regulation of cells by materialsand tissues, MRS Bulletin, 35(2010), 578-583.



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Cells feel their environment

Tissues are hydrated natural polymers with controlledelasticity

Most animals cells require adhesion to a solid to beviable

Tissue elasticity (~ kPas) is important for regulating cell

growth, maturation and differentiation. Brain0.2 < E

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