Polymer Process Engineering Introduction 8/7/20151Chapter 1. Primer/introduction

Polymer Process Engineering

Introduction

04/19/23 1Chapter 1. Primer/introduction

PRIMER

Fundamental concepts + languageNomenclatureChemical bonding, chemical interactions, entanglementsMolecular weightThermal transitions

04/19/23 Chapter 1. Primer/introduction 2

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


A polymer is…

• Long chain molecule, often based on organic chemical 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


HOW DO YOU BUILD A MOLECULE?

Chemical structureChain morphology – constitution, configuration, conformationDegree of polymerization = number of repeating unitsBuilding block sources – hydrocarbons, renewable materials


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


‘Building’ methods

Chain (addition)• Example – polyethylene

(PE) from ethylene• Small number of reacting

chains at any one time, which can grow into long molecules prior to termination

• Long reaction times needed to achieve high conversions

Step (condensation)• Example – poly(ethylene

terephthalate) (PET) from terephthalic acid and ethylene glycol

• Endgroups react to build the chain; long reaction times needed to achieve high polymer


Multiple building blocks

• Copolymers, terpolymers, …• Using multiple building blocks leads to

polymers with intermediate properties or unique properties compared to the homopolymers


Several copolymer configurations


Chain configurations

• Linear – repeating units are aligned sequentially

• Branched – large segments ‘branch’ off the main chain/carbon backbone

• Crosslinked/network – chemical crosslinks between chains add mechanical strength

• EXAMPLES?


Multiphase systems

• Composites– Structural– Random– Other– Nanocomposites

• Blends– Dispersed lamellae, cylinders, spheres


HOW DO WE CLASSIFY POLYMERS?

Structure – chemical, configurationsolid performance (mechanical + thermal properties)other


Mechanical + Thermal

• Thermoplastic – solidified by cooling and reheated by melting

• Thermosets – retain their structure when reheated after polymerization (usually crosslinked)

• Elastomers – rubbers, deform readily with applied force

• Thermoplastic elastomers• other


WHAT IS IN A COMMERCIAL PRODUCT?

Very few commercial products are ‘pure’MWD – molecular weight distributionadditives


Polymers vs. metals


Why do we use polymers?

Polymeric materials

• Compete well on a strength/weight basis• Easy to form into 3D shapes• Creep under load is usually poor; this behavior

is usually corrected by adding fillers or fibers• Low corrosion in the environment compared

to metals• Generally good solvent resistance


Thermoplastics

• Commodities: 75% of the polymer volume used 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 boiling water

• Advanced thermoplastics: extreme properties


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



HOW DO WE MAKE A PART?

PolymerizationFormulationFabrication


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


Additives can change:

• Processing properties• Performance properties• Composites: polymers with fiber fillers• Packaging: multiple layers often used


Formulation operations

• Thermoplastics: melting or solvent processing• Thermosets: additive addition to monomers

or to prepregs


Fabrication

• Varies by industry sector– Adhesive– Coating– Elastomer– Plastic– fiber


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


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

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.

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.

Calendaring


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

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 long bottle shelf life).

Compression molding


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

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 provide crosslinks between the C=C bonds of natural rubber.


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 of copolymers


Elastomer polymersPolymer family description

Styrene-butadiene Copolymers with a range of constitutions; SBR – styrene-butadiene rubber

Polybutadiene Cis-1,4-polymer

Ethylene-propylene EPD – ethylene-propylene-diene monomer; the small amounts of 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 butadiene

Butyl rubber Copolymer of isobutylene and isoprene

Silicon rubber Rubber based on polysiloxanes

Urethane rubber Elastomer with polyethers linked via urethane groups


Synthetic fibersFiber 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


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


Adhesives

• Highly fragmented market.


Foams

• Major area: insulation for housing, sound control,…

• Materials: polystyrene, polyurethanes, …

• Reaction injection molding example


Composites

• Thermosets and thermoplastics• Sheet molding compounds• Filament winding


HOW DO WE NAME POLYMERS?

Polymer nomenclature is widely varied.Trademarks and common names may be industry-sector specific.Nomenclature: Polymer Handbook. Chapter 1.


Source-based names• Source-based name when the polymer is derived

from 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 to separate the name from ‘poly’

b - actually the second name is quite common


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)


copolymersType 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


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) Neoprene04/19/23 Chapter 1. Primer/introduction 45

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

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


WHY ARE LONG CHAIN MOLECULES SOLIDS?

Bonding along the backbone is not extraordinary.With long chains, secondary valence forces, integrated over the entire chain, provide considerable ‘bonding’ forces.Chain entanglements provide physical linkages.


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


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)

WHAT ARE TYPICAL CHAIN LENGTH DISTRIBUTIONS?

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 properties in the melt and solid states.


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 fuel

5-11 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

MWD - oligomer• Poly(-olefin); PAO6• Synthetic base oil –

vehicle use• Trimer, tetramer,

pentamer, hexamer, heptamer

• Based on 1-decene• Ionic polymerization• Differential distribution

by size exclusion chromatography

• PeakFit™ used for curve deconvolution


Two polyethylenes• Weight frequency, differential

distributions• Number-average molecular

weights are the same• Weight-average molecular

weights are different• Narrow MWD – PD ~ 5.7• Broad MWD – PD ~ 15• Differences in flow, tensile and

appearance properties


€

Mn =

ni ⋅M i

i

∑

nii

∑

€

Mw =

wi ⋅M i

i

∑

wii

∑=

ni ⋅M i2

i

∑

ni ⋅M i

i

∑

€

PD =Mw

Mn

HOW DOES CHAIN LENGTH AFFECT PROCESSING?

In-class exercise


HOW DOES CHAIN LENGTH AFFECT PERFORMANCE?

In-class exercise


WHAT ARE IMPORTANT THERMAL TRANSITIONS?

Thermal properties are often key criteria used to select polymers for specific applications.Five regions of viscoelastic behavior (many polymers have all five): < glass transition, power law region, rubbery plateau, rubbery flow, fluid flowOther – crystalline solids, crosslinked elastomers


Five regions of viscoelasticity• Use amorphous polymers below Tg• Use crystalline polymers below Tm• Crosslinked elastomers at G• Melt processing between B and C


Typical G vs T plots


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 < 0.1%; PS is brittle and fails at low elongations. PE yields, and then undergoes cold drawing to > 300% elongation.


BUILDING A GLOSSARY


POLYMER SCIENCE DIRECTIONS

Medical applications are a rich applications area for polymers.Local variations in surface roughness at the nanoscale can induce strains in cell membranes, leading to the growth of F-actin stress fibers that span the length of the cell.W.E. Thomas, D. E. Discher, V. P. Shastri, Mechanical regulation of cells by materials and tissues, MRS Bulletin, 35 (2010), 578-583.


Cells feel their environment

• Tissues are hydrated natural polymers with controlled elasticity

• Most animals cells require adhesion to a solid to be viable

• Tissue elasticity (~ kPa’s) is important for regulating cell growth, maturation and differentiation. Brain – 0.2 < E < 1 kPa; fat – 2 < E < 4 kPa; muscle – 9 < E < 15 kPa; cartilage – 20 < E < 25; bone – 30 < E < 40 kPa

• Nanoroughness seems to affect a number of cell processes

• 3D scaffolding is important• Mechanotransduction: cells adhere to surfaces via

adhesive proteins attached to adaptor proteins, to the actomyosin cytoskeleton.


Documents

Polymer Process Engineering Introduction 8/7/20151Chapter 1. Primer/introduction