Lecture A
A. Revision of Polymer Science

Basic definitions and classifications.

Introduction to polymer chemistry and polymerization techniques (step-growth
and chain polymerization).
B. Polymer Structure

Chain conformations and morphology.

Crystallization in polymers and thermodynamic principles related to
microstructure.
C. Polymer Characterization

Techniques: Viscosity measurement, thermal analysis, mechanical
spectroscopy.
D. Thermomechanical Properties

Viscoelastic behavior and stress-strain response.

Analysis of temperature and moisture effects on material properties.
E. Deformation and Fracture Behavior

Yielding, crazing, and brittle fracture mechanisms.

Impact of environmental factors on polymers.
F. Designing with Polymers

Material selection, design considerations, and cost-efficiency.
G. Design for Manufacture

Injection molding guidelines, shrinkage effects, and modeling software
(Moldflow).
Trends in the New Zealand Plastics Industry

Over 400 plastic companies with a turnover of ~$2 billion annually.

Employment of over 10,000 people in various sectors including packaging and
construction.

Notable trends:

High/Low Density Polyethylene (HDPE/LDPE) dominates production.

Increase in Polypropylene (PP) for curbside recycling efforts.
Summary & Key Takeaways

Polymer Structure-Property Relationship: Critical to material selection.

Assessment components are diversified, promoting practical applications
and theoretical understanding.

Industry Trends: Understanding ongoing developments in plastics vital for
effective engineering decisions.
Lecture B
Macromolecular Structure
Key Concepts

Composition: Involves the atoms present in functional groups of polymers,
which determine various types of chemical bonding.

Configuration: The spatial arrangement of atoms or groups within the
polymer chain.

Conformation: The three-dimensional form of polymer chains based on their
polarity, flexibility, and molecular regularity.
Polymer Structures

Types of Bonds:

Covalent Bonds: Very strong and essential for molecule stability.

Ionic Bonds: Also strong but differ in behavior with temperature and
structure.

Van der Waals Forces: Weaker intermolecular forces impacting
physical properties.
Table of Bonding Forces
Type of Interaction
Strength
Bond Nature
Covalent bond
Very strong
Long-range
Ionic bond
Very strong
Long-range
Ion-dipole
Strong
Short-range
Dipole-dipole
Moderately strong
Short-range
Dispersion (London) forces
Very weak
Extremely short-range
Strength of Plastics

Strength is often low due to weak intermolecular forces compared to primary
bonding forces. This is more evident in thermoplastics compared to
thermosets.

Weak electrostatic ("van der Waals") attractions between polymer chains are
critical for understanding polymer behavior.
Effects of Molecular Temperature and Motion

Chain Separation & Viscosity: As temperature increases, molecular
vibrations rise, leading to greater chain separation and flow.

Crystallinity: Influences properties like tensile strength and toughness.
Higher crystallinity generally increases strength but can lead to brittleness.
Macromolecular Motion and Chain Dynamics

Reptation Theory suggests that chains move within a tube-like constraint due
to entanglements, influencing flow and forming specific mechanical properties.

The effect of molecular weight (Mw) on properties such as strength and
toughness is significant, with an increase in Mw typically resulting in better
performance.
Thermomechanical Properties

Amorphous polymers exhibit substantial changes in properties with
temperature, particularly around the glass transition temperature (Tg),
impacting elasticity and processability.

β-transitions (short-range molecular motions) and α-transitions (significant
chain motions) dictate the mechanical behavior expected in various
temperature ranges.
Summary of Cooling and Heating Effects

The cooling rate impacts crystallinity and the likelihood of defects. Slower
cooling may increase crystal size and regularity but can also lead to
microcracks.

Cooling Rate vs. Crystallinity

Higher cooling rates can lead to less organized structures and
increased defects, while slower rates may enhance structural integrity
at the expense of larger crystal formation.
Summary & Key Takeaways

Composition, configuration, and conformation are critical in
macromolecular structure affecting thermomechanical properties.

The strength of polymers hinges on the nature of bonding (covalent or
intermolecular).

Increased chain length (Mw) improves physical properties, while cooling rates
affect crystallinity and molecular defects.

Thermal transitions play essential roles in the material properties of
amorphous and semi-crystalline polymers.
Lecture C
Polymer Analysis Overview
Key Concepts

Polymer Analysis: A focus on studying the macromolecular structure of
polymers within the nano to mm scales, crucial for understanding physical and
chemical properties.

Molecular Weight Distribution (MWD): The variation of molecular masses in
a polymer sample, usually represented as a bell curve. Evaluation methods
include number average (Mn), weight average (Mw), z-average (Mz), and
viscosity average (Mv).
Characterization Techniques

Size Exclusion Chromatography (SEC): Measures polymer size by passing
a solution through a column with porous beads; larger molecules elute first.

Differential Scanning Calorimetry (DSC): Monitors heat flow and phase
transitions to assess thermal properties, such as melting and glass transition
temperatures (Tg).

Thermogravimetric Analysis (TGA): Analyzes weight changes with
temperature to identify thermal decomposition and filler content.

Dynamic Mechanical Analysis (DMA): Evaluates viscoelastic properties by
applying oscillating forces and measuring responses related to damping and
modulus.
Molecular Weight Averages
Type
Calculation
Significance
Number
Σ(NiMi) / ΣNi
Average (Mn)
Total weight of all polymer molecules divided by the
number of molecules. Not always accurate with
polydispersity.
Weight
Σ(NiMi²) / Σ(NiMi)
Average (Mw)
Accounts for size contributions; important for
determining mechanical properties.
Z Average
(Mz)
Measures the upper end of distribution; useful for
understanding high molecular weight effects.
Σ(NiMi³) / Σ(NiMi²)
Viscosity
Derived from intrinsic
Average (Mv) viscosity measures
Polymer Properties
Correlates with flow properties in solutions.

Degree of Polymerization (DP): Indicates the number of monomer units in a
polymer chain, calculated by dividing the average molecular weight of the
polymer by that of the monomer.

Polydispersity Index (PDI): PDI = Mw/Mn, a measure of the distribution
range of molecular weights. A value of 1 indicates monodisperse samples.
Thermal Analysis Techniques

Differential Thermal Analysis (DTA): Measures temperature differences
between a sample and a reference to indicate phase transitions.

Thermal Mechanical Analysis (TMA): Measures dimensional changes in
polymers under thermal stress.
Analysis of Viscosity

Viscosity Measures: Involve studies of fluid dynamics in polymer solutions,
determining flow behavior through intrinsic viscosity and utilizing the MarkHouwink equation for polymer-solvent combinations.
Structural Characterization

X-ray Diffraction (XRD): Determines crystallinity, lattice parameters, and
orientation within polymer structures, critical for understanding material
strength.

Mechanical Spectroscopy: Utilizes infrared (IR) spectroscopy to probe
molecular structures and assess polymer behavior under stress.
Summary & Key Takeaways

Polymer analysis encompasses various methods for assessing their
molecular weight, thermal properties, and structural parameters.

Molar mass distribution affects polymer characteristics, with techniques like
SEC, DSC, and TGA being essential for thorough evaluation.

Understanding the thermal and mechanical properties of polymers unlocks
their potential applications in industries such as materials science and
engineering.
Lecture D P1.
Thermomechanical Properties of Polymers
Importance of Thermomechanics

Mechanical Behavior Understanding: Comprehending polymer behavior requires
acknowledgment of thermal properties due to unique molecular structures.

Sensitivity to Temperature: Polymers react significantly to temperature changes,
more so than metals, affecting their mechanical performance.
Viscoelasticity of Polymers

Definition: Polymers exhibit viscoelasticity, meaning they show
both viscous and elastic properties across all temperature ranges.

Key Concepts:

Back Stress: Internal stress builds during deformation, impacting recovery
depending on temperature and time.
Creep Behavior


Creep Definitions: When a constant load is applied, creep results in gradual strain
over time.

Initial loading leads to incremental strain increases (creep).

Unloading allows for recovery, but reloading can show increased strain.
Creep Compliance:

Defined as the strain response to stress over time, seen as straight lines on
graphs for linear viscoelastic behavior.

Applies up to strains of approximately 0.005-0.03.
Non-linear Viscoelastic Creep

Behavior at Higher Stresses:

Deviations from linear creep occur as stress levels rise, resulting in a nonlinear response.

Interpolation for Design: Non-linear data is utilized for practical engineering
predictions.
Examples and Applications

Tensile Creep Measurement:


A polypropylene bar subjected to constant load demonstrates measurable
creep compliance with precise calculations.
Influence of Temperature:

For polymers like HDPE, significant changes in mechanical properties
correlate with specific temperatures (e.g., melting at 413K).
Stress Relaxation

Stress Relaxation Process:

Applying constant strain leads to a change in stress over time.

The relationship is represented by relaxation modulus equations, similar in
concept to creep compliance but defined for stress.
Comparative Behavior

Polymers vs. Metals:

Unlike metals, which exhibit irreversible deformation at high temperatures,
polymers can experience creep even at significantly lower temperatures
(down to ~ -200°C).
Summary & Key Takeaways

Understanding thermomechanical properties is crucial for effective engineering of
polymer materials.

Viscoelasticity reflects the complex relationship between temperature and
mechanical behavior.

Creep and stress relaxation mechanisms are essential for predicting material
response over time under load.

Non-linear behaviors require careful consideration in design and application due to
their potential unpredictability.
Lecture D P1
Long-Term Loading of Polymers
Key Concepts

Viscoelastic Behavior: Polymers exhibit both elastic (instant recovery)
and viscous (time-dependent deformation) properties.

Stress Relaxation: A phenomenon where applied strain leads to a gradual decrease
in stress over time. Quantified through stress relaxation moduli E(t).

Creep Behavior: Occurs when a constant stress leads to increased strain over time.
Comprised of two components:

Primary Creep: Immediate strain response.

Secondary Creep: Continual strain increase at a decreasing rate.
Mechanical Phenomena
1. Stress Relaxation:

Stress decreases as a function of time under constant strain.

Less commonly published data.
2. Creep:

Recorded under constant stress with strains observed over time.

Noted for the creep modulus, calculated as stress/strain at specified
temperature and time.
Factors Affecting Behavior

Temperature and Time Interchange: Increasing temperature can lead to increased
creep or stress relaxation, illustrating a potential interchange between time and
temperature.
Data Presentation

Creep data often represented in 3D plots, illustrating the relationship between stress,
strain, and time, capturing the dynamics of polymer response under varying
conditions.
Modeling Approaches

Various models, including the Maxwell (good for stress relaxation) and KelvinVoigt (better for creep), though no single model perfectly predicts both phenomena.

Standard Linear Solid Model combines elements for improved accuracy in both
creep and relaxation predictions.
Time-Temperature Superposition (TTS)

Used to predict long-term behaviors by adjusting short-term results at various
temperatures through scaling, advantageous for plastics due to their temperature
sensitivity.
Dynamic Mechanical Properties

Dynamic Mechanical Analysis (DMA) measures how materials respond to
oscillatory stress, yielding valuable insights into mechanical damping and storage
modulus, revealing temperature-dependence in viscoelastic materials.
Short-Term Mechanical Behavior

Dependent on strain rate, suggesting increased rates lead to higher moduli and
strengths.

Various moduli (elastic, tangent, and secant) are defined to assess material behavior.
Summary & Key Takeaways

Viscoelasticity combines both immediate and time-dependent responses, important
for understanding long-term polymer behavior.

Stress relaxation and creep are critical phenomena influencing polymer durability
under load.

Models help predict behaviors, but practical applications benefit from TTS to extend
data applicability.

Dynamic mechanical properties are vital in assessing damping characteristics and
material suitability for various applications.
Lecture E
Key Concepts
Polymer Mechanics

Yield and Fracture Behavior: Analysis of how polymers behave under stress,
including yielding (ductile fracture) and cracking (brittle fracture).

Brittle-Ductile Transitions: Changes in failure modes of polymers based on stress
and environmental conditions.
Boltzmann Superposition Principle (BSP)

Definition: Principle stating that the response of a material to a given load is
independent of prior loads; pivotal in linear viscoelasticity.

Application: Used to calculate total strain from multiple applied stresses over time.
Yield Predictions for Plastics

Eyring Model: Predicts the yield stress of plastics as a function of strain rate and
temperature. Yield stress increases with strain rate and decreases with temperature.
Fracture Mechanics

Basic Fracture Mechanics: Concepts based on Griffith's theory that governs crack
propagation, including equations for determining fracture stress in different loading
conditions (plane stress vs. plane strain).

Stress Intensity Factor (K): Key measure of stress state near a crack tip; governs
conditions for crack propagation.
Creep Behavior

Creep: Time-dependent strain under constant stress, illustrated through compliance
functions.

Stress Relaxation: The gradual decrease of stress in a material under constant
strain.
Practical Applications and Examples

Creep Calculation: Sample problems demonstrating strain calculations over time
given specific stress scenarios.
Time
(s)
Applied Stress
(MPa)
Creep Strain Calculation
1500
1.5
ϵ(1500)=1.2×(1500)+0.5
0
Complex calculation involves cumulative strains over applied
stresses.
2500
Material Selection

Yielding Behavior: Variability in yield stress affected by material composition,
demonstrated through comparisons between ductile and brittle materials.
Crazing and Its Effects

Crazing: Formation of microvoids leading to failure; impacts mechanical properties
and stress distribution.

Effect of Crazing on Properties: Analysis of how the density of crazes affects
residual mechanical properties of plastics.
Toughened Polymers

Toughening Mechanisms: Use of rubber particles to improve fracture toughness
and reduce notch sensitivity.
Summary & Key Takeaways

Boltzmann Superposition Principle is critical for understanding elastic behavior in
polymers.

Eyring Model effectively predicts yielding behavior based on strain rates and
temperatures.

Fracture mechanics is crucial for assessing failure in polymers, with distinct methods
for brittle and ductile materials.

Crazing impacts the mechanical performance of polymers significantly and should be
factored into material selection and application.