CH62045 Module 1 Polymer Basics 2015

CHEMICAL ENGINEERING PRINCIPLES IN POLYMER PROCESSING

CH 62045

Prof. Swati Neogi

104/18/23

Class Guideline

• Attendance Policy: – 100% attendance is desirable.– No unexcused absence.– Up to four excused absence.

• Guest Lecture & Field Trip: – Guest lecture will be arranged from time to time.– Field trip to industries will be arranged.

• Attendance is mandatory

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Class Guideline

• Assignment and class tests: – Regular homework assignments will be given– Students are expected to maintain a notebook for assignments

and are required to bring the assignment notebooks everyday in the class

– Surprise checking of the assignments will be conducted– Surprise class tests will be taken.

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Grading Policy

Assignments, class tests, teacher’s evaluation: 20%Theory: weightage 0.75

Mid term: 30%Final Exam: 50%------------------------------------------------------------------------Total: 80%

Tutorial: weightage: 0.25Two term paperField trip/Guest lecture

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Text Book

• No single text book will cover the entire subject. Take class notes. Class notes are prepared based on several books. Following is the list of books which can be consulted for the course:

– Principles of Polymer Processing by Tadmor & Gogos– Polymer Processing:Principles and modeling, by

Agassant, Avenas, Sergent, & Carreau.– Plastics Engineering by R. J. Crawford.

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Course Information

• Credit: 3-1-0• Course Objective (Handout)• Course outline (Handout)• Tentative Lecture Schedule (Handout)

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Course Objective

Learn to use ChE principles to describe polymer processing

Polymer basics

1.What are polymers?

2. How do they differ form other materials ?

3. Why are they different ?

4. Properties

5. Applications

Module 1704/18/23

Course Objective

Learn to use CHE. Principles to describe polymer processing

Chemical Engineering principles

(i) Polymer Rheology

(ii) Polymer flow analysis

(iii) Heat transfer & Viscous heat dissipation

(iv) Devolatilisation & Mass transfer

Module 2804/18/23

Course objective

Learn to use CHE. Principles to describe polymer processing

Polymer processing technology (i) Extrusion

(ii) Injection molding (iii) Blow molding (iv) Calendaring

(v) Thermoforming

(vi) Spinning

Module 3

Manufacturing of polymers is beyond the scope & objective

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Course Overview

Module 1: Fundamentals of Polymer (# of Lectures: 10-12)

1.1: Introduction (2)

1.2Molecular characteristics-structure-processing-property relationship (4)

1.3: Polymer properties (3)

1.5: Polymer additives (1)

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Course Overview

Module 2: Chemical Engineering Principles for Polymer Processing (# of lectures: 14)

2.1: Introduction to polymer processing (1)

2.2: Polymer Rheology (3)

2.3: Mass and Momentum equations for isothermal polymer flow analysis (5)

2.4: Heat transfer and viscous heat dissipation in polymer processing (3)

2.5: Mass transfer, diffusivity and devolatilisation during polymer processing (2)

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Course Overview

Module 3: Polymer Processing Technologies ( # of Lectures: 18)

3.1: Extrusion (10)

3.2: Injection Molding(6)

3.3: Calendaring , Thermoforming, Others(2)

1204/18/23

Module 1: Course Outline

– Introduction of polymer (L2)• Definition• Advantages• Classification of polymer• Applications

– Molecular characteristics-structure-property-processing Relationship(L3)• Molecular

• Chemical composition• MW/MWD

• Macroscopic• Topology• Orientation• Phases

- Crystalline

- Amorphous1304/18/23

Module 1: Course Outline

Polymer properties (L4)• Thermal Properties

– Melting point

– Glass transition

• Mechanical Properties– Strength

– Modulus

– Elongation

– Toughness

– Impact

– Creep

– Permeability

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Module 1: Course Outline

• Chemical Properties– Oxidation

– Thermal stability

– Degradability

– Chemical resistance

– Flammability/flame resistance

– UV resistance

• Melt properties– Flow Characteristics

– Viscosity vs. Shear rate

– Shrinkage/cooling

– Polymer swelling/memory effect

Polymer Additives (L0.5) Material selection and design guidelines (L0.5)

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Module 1: Fundamentals of Polymer

Section 1.1: Introduction

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Some Organic Basics

• Name following organic compounds and write down the structure.– CH4, C2H6,C2H2, C3H8, C2H4

• General name of following series of compoundsRCOOH, R-NH2, HO-R, HO-R-OH

write the product of following reaction:

RCOOH +RNH2 ---------

RCOOH +HOR --------------

RCOOH + HO-R-OH ---------

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PolymersProcessing with additives

Finished Product

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Polymer, Resin, and Plastics

• A polymer is any substance made up of many of repeating units, building blocks, called ‘mers’.

• When in form ready for further working, they are called ‘resins’.

• Polymers are seldom used in their neat form, most often compounded with various additives. The resulting material is usually referred to as a ‘plastic’.

• Frequently, polymers, resins, plastics are used interchangeably.

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Development of Plastics

• 1868 Cellulose nitrate• 1909 Phenol-formaldehyde• 1927 Cellulose acetate and polyvinyl chloride• 1929 Urea formaldehyde• 1931 Duprene• 1935 Ethyl cellulose• 1936 Acrylic and polyvinyl acetate• 1938 Nylon• 1942 polyester and polyethylene terephthalate• 1943 silicone• 1947 Epoxy and polypropylene

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Basic Concept

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Basic Concept

• Polymer is large molecule having repeating unit• Repeating structural units joined by covalent bonds• Molecular weight can be up to 10000• Monomers should have reactive functional group or double bond• Basic linear chain is called backbones• Molecular weight can be up to 10000• Extensive formability and ductility• Light weight, low cost• Higher chemical reactivity

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Basic Concepts

• Compound of hydrogen and carbon, and/or O, N, F and Si

• Low strength compared with metals; lower melting point• Properties can be tailor made by choosing different

monomers, by blending different polymers.

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Forces In PolymerForces In Polymer

• Primary force– Covalent bonds within chain

• Secondary Force:– Vander walls force between chains– Hydrogen bonding– Dipole-dipole interactions

• Chemical bonds between chains as in thermoset polymers

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Nomenclature

• Monomer - Molecule with minimum functionality of two

that reacts to form the structural units of the polymer• Oligomer - Short chain synthesized from reaction of

several monomers (dimer, trimer, tetramer . . .)• Polymer - Macromolecule generated through sequential

reaction of a small number of elementary units• Repeating unit - Structure composed of the minimum

number of structural units necessary to generate the polymers. • Degree of polymerization - number of repeating units

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COMMON MONOMERS AND POLYMERSCOMMON MONOMERS AND POLYMERS

• Vinyl and Vinyledene monomer and their polymer• Ester forming monomers and Polyester, Polycarbonate • Amide forming monomers and Polyamide

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Name(s) Formula Monomer Properties Uses

Polyethylene low density (LDPE)

–(CH2-CH2)n– ethylene CH2=CH2

soft, waxy solid film wrap, plastic bags

Polyethylene high density (HDPE)

–(CH2-CH2)n– ethylene CH2=CH2

rigid, translucent solid

electrical insulation bottles, toys

Polypropylene (PP) different grades

–[CH2-CH(CH3)]n–

propylene CH2=CHCH3

atactic: soft, elastic solid isotactic: hard, strong solid

similar to LDPE carpet, upholstery

Poly(vinyl chloride) (PVC)

–(CH2-CHCl)n– vinyl chloride CH2=CHCl

strong rigid solid pipes, siding, flooring

Poly(vinylidene chloride) (Saran A)

–(CH2-CCl2)n– vinylidene chloride CH2=CCl2

dense, high-melting solid seat covers, films

Polystyrene (PS)

–[CH2-CH(C6H5)]n–

styrene CH2=CHC6H5

hard, rigid, clear solid soluble in organic solvents

toys, cabinets packaging (foamed)

Polyacrylonitrile (PAN, Orlon, Acrilan)

–(CH2-CHCN)n– acrylonitrile CH2=CHCN

high-melting solid soluble in organic solvents

rugs, blankets clothing

Polytetrafluoroethylene (PTFE, Teflon)

–(CF2-CF2)n– tetrafluoroethylene CF2=CF2

resistant, smooth solid non-stick surfaces

Common Vinyl and Vinyledene monomers and Polymers

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Common Ester, Carbonate and Amide Polymers

Formula Type Monomers Use

~[CO(CH2)4CO-OCH2CH2O]n~ polyester HO2C-(CH2)4-CO2H HO-CH2CH2-OH

Fiber

polyester Dacron Mylar

para HO2C-C6H4-CO2H HO-CH2CH2-OH

Fiber,moisture Barrier

wrapping

polyester meta HO2C-C6H4-CO2H HO-CH2CH2-OH

bottle

polycarbonate Lexan

(HO-C6H4-)2C(CH3)2 (Bisphenol A)

X2C=O (X = OCH3 or Cl)

electronics

~[CO(CH2)4CO-NH(CH2)6NH]n~

polyamide Nylon 66

HO2C-(CH2)4-CO2H H2N-(CH2)6-NH2

Chemical resistant insulation

~[CO(CH2)5NH]n~

polyamide Nylon 6 Perlon

same

polyamide Kevlar

para HO2C-C6H4-CO2H para H2N-C6H4-NH2

Bullet proof vest, reinforcing element

polyamide Nomex

meta HO2C-C6H4-CO2H meta H2N-C6H4-NH2

FR tape

polyurethane Spandex

HOCH2CH2OH

Garments, medical

bandages

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Applications: Packaging

• Food wrapping• Bottles• Blister packs• Trash bags and grocery sacks• Shrink wrap• Foam packing

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Applications: Medical

• Catheters• Hip joint replacements• Artificial limbs (legs, feet, arms)• Artificial organs (heart, blood vessels, valves)• Dental fillings, bridges, and coatings• Disposable surgical clothes and instruments• Eyeglass frames and lenses

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Applications: Recreational

• Boat hulls, Boat hulls, masts, kayaks, surfboards, and sails

• Rackets, golf clubs, vaulting poles, and oars• Bobsleds, dune buggies, and automobiles• Athletic shoes• Skis, ski poles, ski boots, and ski lift chairs• Golf ball covers and golf club shafts• Bicycle parts, helmets, and pads

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Applications: Entertainment

• Stereo and television components• VCR tapes and housings• Cases for radios, tape players, tapes, and CDs• Toys

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Applications: Textile

• Clothing• Carpets• Non-woven fabrics• Diapers and other disposables• Upholstered fabrics for furniture• Draperies and wall paper material

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Applications: Construction and Home

• Mouldings• Sprinklers and pipes• Counter tops• Sinks, shower stalls, and plumbing fixtures• Flooring (vinyl and carpeting)• Paint

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Applications: Transportation

• Automotive bodies, body panels, trim, and seats• Aerospace components• Train, monorail, and light rail cars• Seat covers and dashboard covers• Truck bed liners• Gas tanks

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Applications: Industrial

• Pipes, valves, and tanks• Gears and housings• Adhesives and coatings• Vibration damping pads• Electrical circuit boards• Wire insulation and connector devices• Gaskets and sealants

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Applications: Information Technology

• Photo resists for microprocessor fabrication• Interlayer dielectrics for microprocessor• Fabrication• Alignment layers for liquid crystal displays• Lubricants for computer hard disks

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Class Assignment

• Write at least two more application of polymer for each sector from your own observation.

• Write structures indication monomer for:– PP– PE– Nylon

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Review of Lecture 1

• What are polymers and plastics?• Characteristics of polymer• Characteristics of monomer required to undergo

polymerization• Types of monomer.• Examples of polymers using each type of monomers.• Application of polymers in different areas.

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Classification of Polymer

1. Based on availability

Synthetic – Adhesives – Fibres – Coatings – Plastics – Rubbers

Natural Polysaccharides

– Adhesives – Fibres

Proteins – Adhesives – Fibres

Polyisoprene – Rubbers

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Classification of Polymer

2. Based on reaction MechanismAddition (Chain) Polymer

– Break a double bond

• PE,PP

Condensation (Step) Polymer– Elimination of by product (except epoxies and polyurethanes)

• PET, PBT, Nylon

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Classification of Polymer

3. Based on molecular Structure– Linear Chain

– Branched Chain

– Network or gel Polymer

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Classification of Polymer

4. Based on Morphology– Amorphous– Crystalline/semicrystalline

5. Based on molecular composition– Homopolymer– Copolymer

• Alternate Copolymer: ABABAB• Block Copolymer:AAAAAABBBBBBBAAAAAAABBBBB

– SBS (styrene-Butadiene-Styrene)

• Graft Copolymer: AAAAAAAAAAAAABBB

-High Impact Polystyrene, HIPS(Polystyrene with grafted polybutadiene)

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Classification of Polymer

6. Based on processing and response to temperature

– Thermoplastic: Melts/softens with temperature and can be reprocessed

– Thermoset: Does not melt/soften with heat

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Classification by Application

• Plastics• Fibers• Elastomers• Coatings• Adhesives

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Lessons learned in Section 1.1

• What is polymer?• Different monomer and their polymer.• Unique characteristics of polymer.• Terms related to polymer such as monomer, oligomer,

polymer, plastics, resins.• Applications of polymers.• Classification of polymers: different scheme of

classification.

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Assignment: Section 1.1

1. Write down the abbreviation, chemical structure of monomer and chemical Structure of polymer formed. Classify these polymers based on reaction mechanism.i. Polystyrene

ii. Polyethylene

iii. Polymethylacrylate

iv. Polymethylmethacrylate

v. Polypropylene

vi. Polyethylene terepthalate

vii. Polyvinyledene fluoride

viii.Polycarbonate

ix. Nylon 6,6

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Assignment: Section 1.1

2. Write the classification scheme of polymers with examples.

3. Name three common vinyl polymer and write down their

structure

4. Find at least 10 polymers from your surroundings and

everyday use and write the name of polymer and chemical

structure and classification and basis of classification.

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Assignment: section 1.1

5. Name three common vinyl polymer and write down their

structure

6. Find at least 10 polymers from your surroundings and

everyday use and write the name of polymer and chemical

structure and classification and basis of classification

7. Write the differences between polymer, resin and plastics

8. Write different applications of polymer listing some specific

polymers for specific applications4904/18/23

Module 1: Fundamentals of Polymer

Section 1.2 Molecular characteristics-structure-property-processing Relationship

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•Thermal•Mechanical•Rheological•Chemical•Other

•Thermal•Mechanical•Rheological•Chemical•Other

•Chemistry (mer composition)•Size (molecular weight distribution)

•Chemistry (mer composition)•Size (molecular weight distribution)

•Shape•Topology•Orientation•Phases

•Shape•Topology•Orientation•Phases

Molecular Characteristics

Structure

Properties Processes

Molecular characteristics-structure-property-processing Relationship

Intermolecular and Intramolecular forces

•Thermal properties•Rheology

•Thermal properties•Rheology

Chemical Composition• Chemical composition:

– Chemical nature of the monomers and the resulting nature of backbones.

• Chemical Composition Determines

– Strength of the covalent bond.

– Intermolecular forces. Determines strengths .

• Dipole-dipole force as in PVC, Polyester.

• Hydrogen Bonding when polymer contains –OH and NH groups.

– How closely they are packed. Determines morphology.

• Pendant groups such as Benzene ring, bulky side chains.

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Chemical Composition(contd.)– How much flexibility

• Presence of non flexible groups in the backbone such as amide, p-phenylene,sulfone, Carbonyl.

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Think!!!!!!

• How chemical composition will affect following properties?– Melting point?– Crystallinity?– Degradation/durability?– Chemical resistance?– Moisture absorption?– Reactivity?– Density?

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Molecular Weight and Distribution

Molecular weight:– Polymer = (mer)n

– n is not a single number. It has a range. Theoretically, n can vary from zero to Infinity

– Single polymer contains number of molecules with varying weights.

– Usually the molecular weight of a polymer is characterized by average molecular weight and a range of distribution

– The molecular weights of polymers are much larger than the molecules usually encountered in organic chemistry

– Molecular weight and its distribution affects the properties significantly

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Molecular Weight Distribution in Polymer

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Average Molecular Weights

• Different average values can be defined depending on the statistical method that is applied. The weighted mean can be taken with the weight fraction, the mole fraction or the volume fraction:– Weight average molar mass or Mw

– Number average molar mass or Mn

– Viscosity average molar mass or Mv

– Z average molar mass or Mz

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Average Molecular Weights

• Average Molecular weight based on Degree of Polymerization(DP) – DP is the number, n, of repeating units in the polymer chain. – The molecular weight of a particular polymer molecule is a

product of the degree of polymerization and the molecular weight of the repeating unit.

– DP based on average molecular weight– DP based on number average molecular weight

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Number Average Molecular Weight

Number-Average Molecular Weight

• The number average is the simple arithmetic mean, representing the total weight of the molecules present divided by the total number of molecules.

• Ni: number of molecules with mass Mi

• Pi: number average probablity of Ni

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Weight Average Molecular Weight       

• Weight-average emphasizes the mass of the molecules so that the heavier molecules are more important.    

•  Pi : weight average probability of molecule Ni with mass Mi

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Viscosity Average Molecular Weight

• One of the oldest methods of measuring the average molecular weight of polymers is by solution viscosity. The viscosity-average molecular weight lies somewhere between the number average and the weight average

a is constant that depends on the polymer-solvent pair and on temperature

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Z Average Molecular Weight

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Comparison of Average Molecular Weights

Mn < Mv < Mw < Mz 6304/18/23

MWD: Polydispersity Index

• Molecular weight distribution also plays important role in determining the properties along with the average molecular weight.

• The weight-average molecular weight is larger than or equal to the number-average molecular weight.

• The ratio of the weight-average and number-average molecular weights, is a measure of the polydispersity of a polymer mixture.

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MWD: Polydispersity Index

• Polydispersity Index indicates how widely distributed the range of molecular weights are in the mixture.

• A ratio that is around 1.0 indicates that the range of molecular weights in the mixture is narrow; a high ratio indicates that the range is wide. With rare exceptions, all synthetic polymers are polydisperse

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Polydispersity Index

Mi

Ni

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Number Average Molecular Weight: Example

Example :

Size exclusion chromatographic data of a new polymer shows the

following molecular weight distribution.

Number of Molecules Mass of each molecule

5 10,000

3 30,000

2 60,000

Calculate the number average (Mn) and the weight average (Mw)

molecular weights of this polymer.

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Number Average Molecular Weight: Example

Multiply the weight of the polymer molecule by the number of polymer molecules of that weight– ΣNiMi would be: 5(1000) + 3(30,000)+ 2(60,000) = 260,000

– ΣNi would be: 5+3+2 = 10

– Therefore, Number Average Molecular Weight Mn

– = 260,000 / 10 = 26,000

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Number Average Molecular Weight: Example

Weight Average Molecular Weight is ΣWiMi = 39,960

ΣNiMi = 260,000

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Practice Question

• Calculate average Molecular weight of PE with DP of 1000 

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Number Average Molecular Weight: Experimental Measurement Technique

• The number average molecular weight may be

determined by colligative property measurements:– Osmometry– Vapor pressure change– Freezing point depression (rare)– Boiling point elevation (rare)

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MW/MWD

• The weight average molecular weight may be determined experimentally by:– Scattering measurements

• Light• X-rays• Neutrons

– Sedimentation equilibrium (ultracentrifuge)

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Molecular Weight and Properties

• MW ----> Viscosity ----> Processing hardness ---->Part property• Performance properties of finished product and processing

parameters affected by MW• Tensile strength• Impact strength• Toughness• Creep resistance• Stress-crack resistance• Elongation to break• Reversible elasticity• Melting temperature• Melt viscosity• Difficulty of processing

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Threshold and Working Molecular Weight

• Below a certain molecular weight, known as threshold molecular weight, polymer does not exhibit its properties for a particular application.

• Threshold MW depends on the Application. – For adhesive, threshold MW is relatively low– For high strength shaped plastic products, Threshold MW is quite

high

• With MW strength and other properties increases but Viscosity increases due to chain entanglement.

• High viscosities create processing problems.• Working Molecular Weight is defined as the MW

optimized for processing and properties.

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Molecular Weight and Properties

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Assignment:6. Calculate number average molecular weight, weight average molecular weight and

polydispersity index from the following size exclusion chromatography data.

Number of molecules Molecular weight

50 1000

45 2000

30 3000

40 5000

80 6000

25 7000

30 8000

20 9000

10 100007604/18/23

Assignment 3: Molecular characterization and molecular weight

1. Why polymer characterization is so important for a polymer engineer? List characterization parameters.

2. What is pendant group? Name and write the formula of two polymers which has the pendant group identifying pendant groups.

3. Write the formula for number average molecular weight, weight average molecular weight and polydispersity index.

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Calculate number average, weight average, and polydispersity index

Number of Molecules Mass of each Molecule

1 800,000

3 750,000

5 700,000

8 650,000

10 600,000

13 550,000

20 500,000

13 450,000

10 400,000

8 350,000

5 300,000

3 250,000

1 200,000 7804/18/23

Number Average Molecular Weight

Number of Molecules, Ni Mass of Each Molecule, Mi Total Mass of Each Type of Molecule, NiMi

1 800,000 800,000

3 750,000 2,250,000

5 700,000 3,500,000

8 650,000 5,200,000

10 600,000 6,000,000

13 550,000 7,150,000

20 500,000 10,000,000

13 450,000 5,850,000

10 400,000 4,000,000

8 350,000 2,800,000

5 300,000 1,500,000

3 250,000 750,000

1 200,000 200,000

∑Ni = 100 

∑NiMi = 50,000,000

Number average Molecular weight=5,00,0007904/18/23

Weight Average MW & PDI

Number of MoleculesMass of Each

MoleculeTotal Mass of Each Type of Molecule

Weight Fraction Type of Molecule

(Ni) (Mi) (NiMi) (NiMi)/∑(NiMi) (WiMi)

1 800,000 800,000 0.016 12,800

3 750,000 2,250,000 0.045 33,750

5 700,000 3,500,000 0.070 49,000

8 650,000 5,200,000 0.104 67,600

10 600,000 6,000,000 0.120 72,000

13 550,000 7,150,000 0.143 78,650

20 500,000 10,000,000 0.200 100,000

13 450,000 5,850,000 0.117 52,650

10 400,000 4,000,000 0.080 32,000

8 350,000 2,800,000 0.056 19,600

5 300,000 1,500,000 0.030 9,000

3 250,000 750,000 0.015 3,750

1 200,000 200,000 0.004 800

  ∑WiMi = 531,600

PDI=531600/500000=1.063 8004/18/23

Problem Statement 4.6

• Molecular weight data for some polymer are tabulated here. Compute:-

1. The number-average molecular weight, and the weight-average

molecular weight.

2. If it is known that this material’s number-average degree of

polymerization is 477, which one of the polymers listed in Table 4.3

is this polymer? Why?

3. What is this material’s weight-average degree of polymerization?

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Problem Statement 4.6

Molecular Weight Range (g/mol) xi wi

8,000-20,000 0.05 0.02

20,000-32,000 0.15 0.08

32,000-44,000 0.21 0.17

44,000-56,000 0.28 0.29

56,000-68,000 0.18 0.23

68,000-80,000 0.10 0.16

80,000-92,000 0.03 0.05

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xi versus wi

• xi – the number fraction– The number of polymer chains that fall within a certain molecular

weight range divided by the total number of polymer chains.

• wi – the weight fraction– The mass of polymer chains that fall within a certain molecular

weight range divided by the total mass.

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1. Number-average molecular weight.

Mi (g/mol) xi xi*Mi (g/mol)

14,000 0.05 700

26,000 0.15 3900

38,000 0.21 7980

50,000 0.28 14000

62,000 0.18 11160

74,000 0.10 7400

86,000 0.03 2580

Mn=ΣxiMi =47720 g/mol

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1. Weight-average molecular weight

Mi (g/mol) wi wi*Mi (g/mol)

14,000 0.02 280

26,000 0.08 2080

38,000 0.17 6460

50,000 0.29 14500

62,000 0.23 14260

74,000 0.16 11840

86,000 0.05 4300

Mw=ΣwiMi =53720 g/mol

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2. Identify polymer using number-average degree of polymerization

• nn = number-average degree of polymerization– Average number of mer units per polymer chain

– nn = Mn / m, where m is the molecular weight of a mer unit

– nn = 477 and Mn = 47720 g/mol, therefore m = 100.042 g/mol

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3. Identify polymer using number-average degree of polymerization

• Molecular weight of each mer unit can be found by summing molecular weights of constituent atoms

• In this case we’ll ignore the molecular weight contributions of the terminal groups

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Polymer Atoms in Mer Mer Unit MW

PE 4H+2C 28.054 g/mol

PVC 3H+2C+Cl 62.499 g/mol

PTFE 4F+2C 100.014 g/mol

PP 5H+2C 29.062 g/mol

PS 8H+8C 104.152 g/mol

PMMA 8H+5C+2O 100.117 g/mol

Bakelite 9H+9C+1O 133.17 g/mol

Nylon 6,6 6H+4C+2O+2N 114.104 g/mol

PET 8H+10C+4O 192.17 g/mol

Polycarbonate 14H+16C+3O 254.285 g/mol

Mer Unit Molecular Weights

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Identify polymer using number-average degree of polymerization

• Most likely PTFE (Teflon) or PMMA (Plexiglass)• Differentiate by color

– Teflon – white– PMMA – clear

• Unlikely to use this procedure to identify a polymer in real life.

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Weight-average degree of polymerization

• nw = weight-average degree of polymerization

– Average number of mer units per polymer chain

– nw = Mw / m, where m is the molecular weight of a mer unit

– m = 100.042 g/mol and Mw = 53720 g/mol, therefore nw = 537

• Different from nn because calculated using different average molecular weight, Mw vs Mn

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Topology

• Molecular topology is a description of molecules which includes their stereo-chemical arrangement, branching, formation of helices and network/looping/entanglement characteristics.

• Physical properties of chain depends on interactions between its chains.

• Interactions between chains depend on the shape of the chain making up the backbone .

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Topology

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Topology

• Linear Polymers:– Can form close packed structure

• Nonlinear (Branched) Polymers – Some polymers, such as low density polyethylene

(LDPE), have branches of different sizes irregularly spaced along the chain. Such polymers are said to be nonlinear.

– Polymers with pendant groups, such as the methyl group in polypropylene, are considered to be linear.

– The branches prevent the nonlinear molecules from packing as closely as the linear, reducing their density.

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Topology

• Cross linked and Network Polymers – Some polymers have cross-links between polymer chains creating

three-dimensional networks.– A high density of cross-linking restricts the motion of the chains and

leads to a rigid material.• Different structure give rise to very different properties• linear polyethylene has a melting point 20⁰C higher than branched

polyethylene. Unlike linear and branched polymers, network polymers do not melt and will not dissolve in solvents.

• The effect of structure on polymer properties is called the “Structure-Property Relationship“.

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Isomerism

• Regularity of polymer chains decides the morphology. • Highly irregular chains form amorphous polymer.• Highly regular structure promotes crystalline growth.• Some isomeric forms of polymer chains decrease the

regularity of chains reducing the probability of forming crystalline structure.

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Isomerism

• Isomers are molecules– with same molecular formula.– Different arrangement of the atoms in space.

• Different arrangements which are simply due to the molecule rotating as a whole, or rotating about particular bonds is not considered as isomers.

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Isomerism

• Three forms of isomerism in polymers– Monomer orientation

• Head-to-tail• Head-to-head

– Geometric • Cis isomerism• trans isomerism

– Stereoisomerism or tacticity• Isotactic• Syndiotactic• Atactic

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Monomer Orientation

• Monomers with pendant groups can attach in two ways.– head-to-tail – head-to-head

• The usual arrangement is head-to-tail with the pendant groups on every other carbon atom in the chain.

Head to tail Head to head

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Geometric Isomerism

• Double bonds in the polymer chain can show cis- or trans-isomerism. When a monomer with two conjugated double bonds, such as isoprene, undergoes chain polymerization one double bond can remain in the chain.

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Stereoisomerism

• Three different form– Atactic (Random configuration)– Isotactic (Same configuration)– Syndiotactic (Alternating configuration)

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Stereoisomerism

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Stereoisomerism• The physical properties of a polymer can have a strong

dependence on tacticity.• Isotactic and Syndiotactic polypropylene have regular

structures, which allow favourable polymer-polymer packing

• Atactic polyprop. has an irregular structure and poor packing

• Isotactic and Syndiotactic forms have higher melting temperatures (~165° and 130° C) and are poorly soluble in many solvents.

• Atactic has lower melting temp (< 0° C), is soft, rubbery, and can be moulded. It is also more soluble in most solvents.

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Morphology• Polymer morphology is the overall description of polymer

structure including phases

• Morphology is determined by – Topology

o linear, branched, cross-linked– Molecular Weight

• Phases of polymer– Crystalline phase– Amorphous phase

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Amorphous Phase

• Polymer chains with branches or irregular pendant groups cannot pack together regularly enough to form crystals. These polymers are said to be amorphous.

• Amorphous polymers are – softer– have lower melting points– penetrated more by solvents

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Crystalline Phase• Polymer chains without branches or bulkier pendant groups can

pack together regularly enough to form crystals. These polymers are called crystalline polymers

• Polymers are semi crystalline

• Highly crystalline polymers – rigid– high melting,– less affected by solvent penetration– strong but with low impact resistance

• Polymer Molecules form lamella

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Crystalline Phase

• Regular polymers forms plate like structure called lamellar

• Usual thickness of the lamella is about 10 to 20 nm

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Semi-Crystalline Polymers Semi-crystalline polymers have both

crystalline and amorphous regions

When crystals are formed from the melt, chain entanglements are extremely important. Polymer chains meandering in and out of ordered crystalline portions

The crystalline portion is in the lamellae; the amorphous portion is outside the lamella

Percentage of the polymer that is crystalline is called the percent crystallinity. The percent crystallinity has an important influence on the properties of the polymer.

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Spherulites

When a molten crystallizable polymer cools, the crystals grow from individual nuclei and radiate out like the spokes of a bicycle wheel

The crystalline portions actually radiate out in in three dimensions, forming spheres that are called spherulites

In a sample of a crystalline polymer there are billions of spherulites 

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Spherulite

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Factors Affecting Crystallinity

Structural Regularity Degree of Polymerization Intermolecular Forces Pendant Groups Processing

Rate of Cooling Orientation

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Structural Regularity

• Structural regularity promotes crystallization

• Crystallization is favoured by– Linear structure– High degree of symmetry

o Syndiotactic and or isotactic isomers

• Limited crystallization can take place if a small number of branches are present.

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Degree of Polymerization

Relatively short polymer chains form crystals more readily than long chains, because the long chains tend to be more tangled.

High crystallinity generally means a stronger material, but low molecular weight polymers usually are weaker in strength even if they are highly crystalline

Low molecular weight polymers have a low degree of chain entanglement, so the polymer chains can slide by each other and cause a break in the material.

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Intermolecular Forces

Crystallinity is favoured by strong inter backbone forces

The presence of polar and hydrogen bonding groups favours crystallinity because they make possible dipole-dipole and hydrogen bonding intermolecular forces

Polyethylene Terephthalate, contains polar ester groups. Dipole-dipole forces between the polar groups hold the PET molecules in strong crystals.

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Pendant Groups Regular polymers with small pendant groups crystallize

more readily than do polymers with large, bulky pendant groups

Poly vinyl alcohol (PVA) is made by the hydrolysis of poly vinyl acetate ) (PVAc). PVA crystallizes more readily than PVAc because of the bulky acetate groups in PVAc. The -OH groups in PVA also form strong hydrogen bonds.

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Processing : Cooling Rate Major difference between small molecules and polymers is that the

morphology of a polymer is dependent on its thermal history

The crystallinity of a polymer can be changed by cooling the polymer melt slowly or quickly, and by "pulling" the bulk material either during its synthesis or during its processing

When they are processed industrially, polymers often are cooled rapidly from the melt. In this situation, crystallization is controlled by kinetics rather than thermodynamics

There may not be time for the chains, which are entangled in the melt, to separate enough to form crystals, so the amorphous nature of the melt is "frozen into" the solid

A polymer is more likely to have a higher percent crystallinity if it is cooled slowly from the melt.

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Processing: Orientation Crystallinity can be enhanced by stretching the bulk material either

when it is synthesized or during its processing

Induced crystallization due to orientation is common for both films and fibres

When a film is formed the small crystallites tend to be randomly oriented relative to each other. Drawing (stretching) the film pulls the individual chains into a roughly parallel organization

Films can either be uniaxially oriented (oriented in only one direction) or biaxially oriented (oriented in two directions).

Fibers normally are drawn so that they are oriented in one direction. Unstretched nylon fibers are brittle, for example.. When the fibers are stretched the oriented fibers are strong and tough.

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Effect of Crystallinity on Properties

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Module 1: Fundamentals of Polymer

Section 1.3: Polymer Properties

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Polymer Properties

• Thermal Properties– Melting point

– Glass transition

– Thermal stability

• Mechanical Properties– Strength

– Modulus

– Elongation

– Toughness

– Impact

– Creep

– Stress Relaxation

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Polymer Properties• Chemical Properties

– Oxidation

– Thermooxidative stability

– Degradability

– Chemical resistance

– Flammability/flame resistance

– UV resistance

• Melt properties

– Polymer Rheologyo Flow Characteristics o Viscosity vs. Shear rate

– Shrinkage/cooling

– Polymer swelling/memory effect

• Other

– Electrical properties

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Thermal Properties

Semicrystalline polymer

Heat, Tm

Molten polymer

Heat, Tg

Glassy State

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Glass Transition Temperature

• Above Tg polymers are rubbery whereas below Tg, polymers are glassy

• Rubbery behavior due to polymers ability to change its conformation at high temperature

• Glassy behaviour due to lack of ability to change conformation at low temperature

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Change in modulus with Tg

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Factors Affecting Tg

•Backbone-Polar groups increases Tg

•Molecular Weight•Pendant Group•Cross linking

–-Tg in creases with cross link density

•Plasticizer

-Plasticizer decreases Tg

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Backbone Flexibility

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Tg and Molecular Weight

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Pendant Group

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Cross Linking

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Effect of Plasticizer

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Factors Affecting Melting point

Melting temperature depends on % Crystallinity

Chemical composition

Chain entanglement

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Melting Temperature and Chemical Composition

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Melting Temperature and Crystallinity

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Mechanical Properties Tensile strength: Resistance to stretching

Compressive strength: Resistance to compression

Flexural strength: Resistance to bending (flexing)

Impact strength: Resistance to sudden stress, like a hammer blow

Fatigue: Resistance to repeated applications of tensile, flexural, or compressive stress

Creep: Increase in strain when a polymer sample is subjected to a constant stress (typical Viscoelastic Properties): time dependent

Stress relaxation: Decrease in stress when a sample is elongated rapidly to constant strain (typical Viscoelastic Properties): time dependent

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Effect of T on E

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Factors affecting stiffness

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Toughness

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Comparison of Toughness

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Creep and Stress Relaxation

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Chemical Properties

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Chemical Properties

• Oxidation• Thermal stability• Chemical resistance• UV resistance• Flammability/flame resistance• Degradability

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Resistance to Oxidation and Thermal Degradation

• Oxygen in the atmosphere and high heat can cause the can polymer degradation

• Tertiary carbon atoms are more vulnerable for this type of degradation

• Usually Antioxidants(polymer additives) are added to improve the oxidaive properties of polymers

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Resistance to Oxidation and Thermal Degradation

Polymer degrades at high temperature. Two things happen when polymer is heated to a very high temperature:

Processing temperature is well below than the degradation temperature

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Resistance to Oxidation and Thermal Degradation

Thermo-oxidative Stability

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Chemical Resistance Chemicals can break the bond Can extract additives and antioxidants Can fill up of void and cause for swelling. Swelling

reduces mechanical strength Chemical resistance varies among polymers Chemical resistance of polymers can be increased by

modifying the polymers Crystalline polymers are more resistant than

Amorphous polymers Crosslinking increases chemical resistance Most of the polymers are better chemical resistant than

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Resistance to UV Light

UV light can cause the degradation of Polymer

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Resistance to UV Light

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Resistance to UV Light

• UV stabilizer can be added to improve the UV resistance of polymer

• Carbon Black is an excellent UV stabilizer

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Ozonolysis

• Ozone in atmosphere can cause the degradation of polymers by breaking the bond

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Resistance to Burning

Polymer mostly being carbon and hydrogen is flammable

Additives can be added to improve the flame retardant properties of polymer

Halogens are excellent flame retardants. Most of the flame retardant additives are halogen based

European countries does not allow halogen because of the toxicity of the halogen based additives

Aluminium Trihydroxide (ATH) and Magnesium Dihydroxides (MDH) are non-halogeneted flame retardant additives

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Resistance to Burning

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Resistance to Burning

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Retarding Combustion Process

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Char Formation

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Decomposing Material

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Durability

• How long polymer will last in service condition?

• Durability usually is determined by the combined effect of environments and chemicals

• To predict the service lifetime usually accelerated aging test is conducted in a simulated service condition such as heat, chemicals, moisture and mechanical tension

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Flow/Melt Properties

• To process the polymer, polymer needs to be melted

• Viscosity of molten polymer is an important parameter for processing

• Polymer is highly non Newtonian fluid and polymer rheology is very complex

• Thermal history and memory effect also very important for process engineers and to determine how the polymer will respond to processing condition

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Material Selection-DesignRequirements

• Structural/load constraints– Load– Frequency– Worst case scenarios– During manufacturing/shipping/use

• Environmental constraints– Temperature– Humidity– Chemical– Radiation

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Material Selection-DesignRequirements

• Regulation/standards constraints– Trade groups– Governmental– Need to identify all– Range from materials to design

• Marketing constraints– Costs– Esthetic– Use models

• Durability

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Additives

• The reason to add additives, reinforcements, and fillers

– To improve process ability– To reduce costs– To reduce shrinkage– To improve surface finish– To change thermal & electrical properties– To prevent degradation– To provide desirable color– To improve mechanical properties– To lower the coefficient of friction

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Additives

• Increase properties of plastics

– Strength– Glass fibers– Graphite fibers– Kevlar fibers– Wood fibers– Impact strength– Particles– Talc

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Additives• Increase properties of plastics

– Flame retardants– Stability (UV and chemical)– Mold release

• Antioxidants– Oxidation of plastics – breaking of bonds in polymers– Effects on plastics: chain scission– How to overcome: Add antioxidants

• Primary antioxidant: stop oxidative reactions

• Secondary antioxidant: neutralize reactive materials

• Examples:– Plastics: PP & PE– Primary: Phenolic, Amine– Secondary: Phosphite, Thioesters

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Plastisizers

• Increase flexibility• Reduce melt temperature• Lower viscosity

– Water– Mild solvents– Commercial– Dioctyl phthalate

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UV stabilizers (Carbon black)

• UV can break/weaken C-C backbone and many side groups– Brittle– Weaken

• Other additives;– 2-hydrocybenzophenone

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Flame retardant

• Ammonium phosphate

• Chlorinated hydrocarbons

• Chemicals of Bromine, Chlorine, Antimony

• Effects:– Emit fire-extinguishing gas (CO2 +N2)

– Form an insulation barrier against heat and flame.

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Foaming Agents

• Foaming agents– Physical: decompose at specific temperatures,

releasing gases– Chemical: release gases due to a chemical reaction

• Uses: – polyurethane pads– seats for cars, trucks– sofas

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Internal Lubricants

• Lubricants1. Lower external and internal friction

2. No-sticking to the mould

3. Prevent products from adhering to each other

• Examples:– Waxes– Metallic soaps

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Antistatic Agents

• Attract moisture from the air making the surface more conductive and then dissipating static charges

• Examples:– Amines – Quaternary ammonium compounds– Organic phosphates – Polyethylene glycol– Esters

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