POLYMERS IN SOLID STATE, PHARMACEUTICAL APPLICATIONS OF POLYMERS AND RECENT A...Priyanka Modugu
A description on polymers in solid state, solid state properties of polymers, mechanical properties of polymers, heat of crystallization & fusion, thermodynamics of fusion & crystallization, pharmaceutical applications of polymers and recent advances in the use of polymers for drug delivery system
1. POLYMER by RAVI GOYANI. M.S(pharma) pharmaceutics, NIPER. Raebareli(U.P)
2. Contents of the presentation: Introduction, Classification, Properties of polymer,Characteristics of ideal polymer,Advantages of polymer,Applications of polymer.
3. Introduction of general terminology about the polymer like homopolymer, copolymer and monomer.
4. Figure representation of different monomer which combine to form polymer.
5. Introduction about the copolymer and how its form by one or more monomer.
6. Classification of the polymer on the bases of source, degradability, structure, properties, nature of the polymer and polymerization process.
7.8.9.10.11.12 Example of the polymer according to the class of that polymer.
13. Characteristics of ideal polymer like Should be inert and compatible with environments, Should be nontoxic, Should be easily administered, Should have good mechanical strength, Should be biodegradable, Should have biocompatible.
14. Properties of polymer.
15. Advantages of polymer in to the different area of pharmaceutics.
16. Application of the polymer like as binding agents, coating agents, thickening agents, disintegrants, and also in the formulation of hard and soft gelatin capsules.
17.18. Tables for the examples of different polymer and its specific application.
19. Application of the polymer in to the various drug delivery system in which extended, pulsatiles, controlled release drug delivery systems.
20.21 Other application of polymers in different formulation such as nanocrystals, gels, micro- spheres and also useful for the cancer study or complexation study.
22. List of references.
POLYMERS IN SOLID STATE, PHARMACEUTICAL APPLICATIONS OF POLYMERS AND RECENT A...Priyanka Modugu
A description on polymers in solid state, solid state properties of polymers, mechanical properties of polymers, heat of crystallization & fusion, thermodynamics of fusion & crystallization, pharmaceutical applications of polymers and recent advances in the use of polymers for drug delivery system
1. POLYMER by RAVI GOYANI. M.S(pharma) pharmaceutics, NIPER. Raebareli(U.P)
2. Contents of the presentation: Introduction, Classification, Properties of polymer,Characteristics of ideal polymer,Advantages of polymer,Applications of polymer.
3. Introduction of general terminology about the polymer like homopolymer, copolymer and monomer.
4. Figure representation of different monomer which combine to form polymer.
5. Introduction about the copolymer and how its form by one or more monomer.
6. Classification of the polymer on the bases of source, degradability, structure, properties, nature of the polymer and polymerization process.
7.8.9.10.11.12 Example of the polymer according to the class of that polymer.
13. Characteristics of ideal polymer like Should be inert and compatible with environments, Should be nontoxic, Should be easily administered, Should have good mechanical strength, Should be biodegradable, Should have biocompatible.
14. Properties of polymer.
15. Advantages of polymer in to the different area of pharmaceutics.
16. Application of the polymer like as binding agents, coating agents, thickening agents, disintegrants, and also in the formulation of hard and soft gelatin capsules.
17.18. Tables for the examples of different polymer and its specific application.
19. Application of the polymer in to the various drug delivery system in which extended, pulsatiles, controlled release drug delivery systems.
20.21 Other application of polymers in different formulation such as nanocrystals, gels, micro- spheres and also useful for the cancer study or complexation study.
22. List of references.
WHAT IS COMPRESSION ?
Compression means reduction of bulk volume of material as a result of the removal of gaseous phase (air) by applied pressure
WHAT IS CONSOLIDATION?
Consolidation is an increase in mechanical strength of material resulting from particle - particle interactions.
Physics of Tablet compression is very useful during study of the tablet. It contains the mechanism of tablet compression. It also contains the process of tablet compression.
Polymer - a long chain molecule made up of many small identical units of Monomer is known as Polymer.
Monomer - the smallest repeating unit is known as Monomer.
Polymer is a molecule is obtained by natural and synthetic origin having group of Smallest repeating unit is known as polymer.
Polymer is important for increasing the stability of drug molecule, it is important to influencing the solubility of drug molecule, it is important to maintain the Physicochemical properties, it is important to maintain the prolong stability of drug molecule in extended period of time, it is important for influencing the Bioavailability of drug.
Polymer is important for Pharmaceutical industries and research purpose.
WHAT IS COMPRESSION ?
Compression means reduction of bulk volume of material as a result of the removal of gaseous phase (air) by applied pressure
WHAT IS CONSOLIDATION?
Consolidation is an increase in mechanical strength of material resulting from particle - particle interactions.
Physics of Tablet compression is very useful during study of the tablet. It contains the mechanism of tablet compression. It also contains the process of tablet compression.
Polymer - a long chain molecule made up of many small identical units of Monomer is known as Polymer.
Monomer - the smallest repeating unit is known as Monomer.
Polymer is a molecule is obtained by natural and synthetic origin having group of Smallest repeating unit is known as polymer.
Polymer is important for increasing the stability of drug molecule, it is important to influencing the solubility of drug molecule, it is important to maintain the Physicochemical properties, it is important to maintain the prolong stability of drug molecule in extended period of time, it is important for influencing the Bioavailability of drug.
Polymer is important for Pharmaceutical industries and research purpose.
Basic Terms : Macromolecule, Monomer , Repeat Unit, Classification of polymers based on Origin, thermal response Polymerisation , Addition and condensation , Degree of Polymerisation, Polymer Structures - Linear , Branched and Cross-linked. Molecular weight of Polymers: Definition and Formulae of Number Average Molecular Weight , Weight Average Molecular weight, Viscosity Average Molecular Weight , Z-average Molecular Weight. Polydispersity Index
The relationship between stress and deformation will be covered in this section, and some of the important elastic material properties such as Young’s modulus and the modulus of rigidity will be defined.
My name is Paulin O. I am associated with solidworksassignmenthelp.com for the past 10 years and have been helping the engineering students with their assignments I have a Masters in mechanical Engineering from Cornell University, USA.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
5. The slope of the stress-strain
curve in the elastic region.
Hooke’s law: E = σ/ε
A measure of the stiffness of
the material.
Larger the value of E, the
more resistant a material is to
deformation.
Note: ET = Eo – bTe-To/T
where Eo and b are empirical
constants, T and To are
temperatures
Units:
E: [GPa] or [psi]
ε : dimensionless
6. Elastic deformation
Reversible:
( For small strains)
Stress removed material returns to original
size
Plastic deformation
Irreversible:
Stress removed material does not return to
original dimensions.
Yield Strength (σy)
The stress at which plastic deformation
becomes noticeable (0.2% offset).
P the stress that divides the elastic and plastic
behavior of the material.
7. True stress = F/A
True strain =
ln(l/l0) = ln (A0/A)
(A must be used after
necking)
0
0
0
straingEngineerin
stressgEngineerin
l
ll
A
F
−
==
==
ε
σ
Apparent softening
True Strain = ε t =
dl
l
L o
L
∫ = ln
L
Lo
True Stress = σ t =
Load
A
≠
Load
A0
AL = AoLo
εt = ln 1 +ε( )
σt = σ 1 +ε( )
8.
9. The total area under the true stress-strain curve which
measures the energy absorbed by the specimen in the
process of breaking.
Toughness=σdε∫
10. The total elongation of the specimen due to plastic deformation, neglecting
the elastic stretching (the broken ends snap back and separate after failure).
11. Essentials of Materials Science & Engineering
Second Edition
Authors: Donald R. Askeland & Pradeep P. Fulay
Materials Science and Engineering: An Introduction
Sixth Edition, Author: William D. Callister, Jr.
The Science and Engineering of Materials
Fourth Edition, Authors: Askeland and Phule (Fulay ?)
Introduction to Materials Science for Engineers
Sixth Edition, Author: James F. Shackelford
12. • Stress and strain: These are size-independent
measures of load and displacement, respectively.
• Elastic behavior: This reversible behavior often
shows a linear relation between stress and strain.
To minimize deformation, select a material with a
large elastic modulus (E or G).
• Plastic behavior: This permanent deformation
behavior occurs when the tensile (or compressive)
uniaxial stress reaches σy.
• Toughness: The energy needed to break a unit
volume of material.
• Ductility: The plastic strain at failure.
Note: materials selection is critically related to
mechanical behavior for design applications.
13. Polymers have unique mechanical properties vs. metals & ceramics.
Why?
Bonding, structure, configurations
Polymers and inorganic glasses exhibit viscoelastic behavior
(time and temperature dependant behavior)
Polymers may act as an elastic solid or a viscous liquid
i.e. Silly Putty (silicon rubber)
- bounces, stretches, will flatten over long times
Low Strain Rate
High extension - failure
resilient rubber ball
Elastic behavior rapid deformation
Very low Strain rate - Flatten
Flow like a viscous fluid
14. Polymers
Polymer : Materials are made up of many (poly) identical chemical units
(mers) that are joined together to construct giant molecules.
Plastics - deformable, composed of polymers plus additives. E.g. a variety
of films, coatings, fibers, adhesives, and foams. Most are distinguished by
their chemical form and composition.
The properties of polymers is related to their structures, which in turn,
depend upon the chemical composition. Many of these molecules contain
backbones of carbon atoms, they are usually called "organic" molecules
and the chemistry of their formation is taught as organic chemistry.
The most common types of polymers are lightweight, disposable, materials
for use at low temperatures. Many of these are recyclable. But polymers are
also used in textile fibers, non-stick or chemically resistant coatings,
adhesive fastenings, bulletproof windows and vests, and so on.
15. Polymers
Polymer : Materials are made up of many (poly) identical chemical
units (mers) that are joined together to construct giant molecules.
Carbon – 1s2
2s2
2p2
It has four electrons in its outermost shell, and needs four more to make a
complete stable orbital. It does this by forming covalent bonds, up to 4 of which
can be formed.
The bonds can be either single bonds, ie one electron donated by each
participating element, or double bonds (2 e-
from each), or triple bonds (3 from
each)
C X1
X2
X4
X4
Xi can be any entity ex H, O, another C, or even a similar monomer
C X1
X2
X4
X4
16. Polymers – many repeating units
C X1
X2
X4
X4 + C X1
X2
X4
X4
+…
CCCC C
And so on… if the bonds can keep getting formed, entire string-like structures
(strands, or chains) of the repeating units are created. C is the most common
element in polymers. Occasionally, Si may also participate in such bonding.
17. Classes of Polymers
Thermoplastics:
Consist of flexible linear molecular chains that are
tangled together like a plate of spaghetti or bucket
of worms. They soften when heated.
Thermosets:
Remain rigid when heated & usually consist of a
highly cross-linked, 3D network.
Elastomers:
Consist of linear polymer chains that are lightly
cross-linked. Stretching an elastomer causes chains
to partially untangle but not deform permanently
(like the thermoplastics).
Of all the materials, polymers are perhaps the most versatile, not only because the
properties can be drastically modified by simple chemistry, but the behavior is also
dependent on the architecture of the chains themselves.
From proteins to bullet-proof jackets to bottles, polymers are INDISPENSIBLE to life
as we know it
20. Polymer Synthesis - I
Addition
in which one “mer” is added to
the structure at a time.
This process is begun by an
initiator that "opens up" a C=C
double bond, attaches itself to
one of the resulting single
bonds, & leaves the second
one dangling to repeat the
process
21. Polymer Synthesis - II
Condensation
in which the ends of the
precursor molecules lose
atoms to form water or
alcohol, leaving bonds that
join with each other to
form bits of the final large
molecules. An example is
shown in the Detail - the
formation of nylon.
22.
23. Molecular weight distribution
The degree of polymerization (DP) = no. of monomers per polymer. It is
determined from the ratio of the average molecular weight Mw of the polymer
to the molecular weight of the repeat unit (MRP
).
DP = Mw / MRP
where
Mw = Σ fi Mi : Mw = weight average molecular weight
Mn = Σ xi Mi : Mn = number average molecular weight
Mi = mean molecular weight of each range
fi = weight fraction of polymer having chains within that range
xi = fraction of total number of chains within each range
24. Mn = xiMi
i
∑
Mw = wiMi
i
∑ = xiMi
2
i
∑
xi =
ni
ni
i
∑
= number fraction
Degreeof Polymerization
nn =
Mn
m
; nw =
Mw
m
m= "mer" molecular weight
25. Degree of polymerization (DP)- number of monomers per polymer chain, ie no. of
repeat units.
Obviously, the weight (either in AMU, or in g/mol) is the same for each repeat
unit. Then, the total weight of the polymer chain, ie its molecular weight is :-
mol. Wt. = N.Mm
where N is the number of monomers in that chain, ie the DP;
Mm is the weight of the monomer.
In a polymer sample synthesized from monomers by either condensation or
addition polymerization, one always has a distribution of DPs amongst the
resulting chains.
So let us consider that we have 100 monomers. Let the weight of each monomer
be 1g/mol (in reality, this is Hydrogen !) Let us see some ways in which we can
arrange this:
1)1 chain of N=100, ie mol. Wt. = 100
2)2 chains of N=50 each, ie mol. Wt. = 50
3)10 chains of N=10 each, ie mol. Wt. = 10
4)3 chains, 2 of N=25, and 1 of N=50
26. 3 chains, 2 of N=25, and 1 of N=50.
Now, to calculate the average molecular weight, we have two methods:
1) Take the simple numerical average, ie
(25+25+50)/3.0 = (2x25 + 1x50)/3.0 = 33.33. This value is according to the
number fraction of each type of chain (1/3 of the chains are of N=50, and 2/3
have N = 25)
2) Take the average according to the weight fraction of each chain. What is the
total weight ?
Mtotal=100
Wfraction
50
= 50/100, ie ½ , Wfraction
25
=2*25/100 = 1/2
So, taking weight fractions, we get the average molecular weight as
Mw = 50*1/2 + 25*1/2 = 25+12.5 = 37.5
So, numerical fractions, and weight fractions for mol. Wt. give different answers!
Mn = SUM(niMi)/Sum(ni) , where ni = no. of chains of length Mi
Mw = SUM(wiMi), where wi = weight fraction of chains of length Mi.
But, wi = niMi/SUM(niMi) ie the weight of that polymer (i), divided by total
weight.
50 25 25
27. Suppose we want to find out the average population of each state.*
We can go to each senator of each state and find out what the population of
their state is, and then divide that number by 100.
This number is the number-average population for each state. This is exactly
similar to the Mn that we calculated earlier, ie no. av. Mol. wt.. Problem ?
Yes, of course. What do we do about say, CA and AK ?
Now, senators are busy, so we ask congressmen from each state. Then, we take
the value that each congressman/congresswoman gives us, and then divide
by the number of congresscritters. What value do we get ? Certainly one
different from our earlier attempt ! Problem ?
Now the value is much higher than before. This is exactly similar to the Mw that
we calculated earlier, ie to weight av. mol. Wt.
Is this value MUCH more representative (eh eh !) of the average population of
each state ? Well, not really. But at least, it is an average.
We learn about these differences, because different measurement techniques
measure different averages, and the ratio of Mw to Mn, called the Poly
Dispersity Index (PDI) often determines properties.
* taken from “Polymer Physics” by M. Rubinstein & R. H. Colby, 1st
edition, OUP
28. • Polymer = many mers
• Covalent chain configurations and strength:
Direction of increasing strength
Branched Cross-Linked NetworkLinear
secondary
bonding
C C C C C C
HHHHHH
HHHHHH
Polyethylene (PE)
mer
ClCl Cl
C C C C C C
HHH
HHHHHH
Polyvinyl chloride (PVC)
mer
Polypropylene (PP)
CH3
C C C C C C
HHH
HHHHHH
CH3 CH3
mer
29. Structure of polymers strongly affects their properties; e.g., the ability of chains to slide past
each other (breaking Van der Waals bonds) or to arrange themselves in regular crystalline
patterns.
Some of the parameters are: the extent of branching of the linear polymers;
the arrangement of side groups. A regular arrangement (isotactic) permits the greatest
regularity of packing and bonding, while an alternating pattern (syndiotactic) or a random
pattern (atactic) produces poorer packing which lowers strength & melting temperature.
30. C
C
HH
R H
C
C
HH
R H
C
C
HH
R H
C
C
HH
R H
C
C
HH
R H
C
C
HH
R H
C
C
HH
H R
C
C
HH
R H
C
C
HH
H R
C
C
HH
R H
C
C
HH
R H
C
C
HH
H R
C
C
HH
R H
C
C
HH
R H
C
C
HH
R H
Isotactic
Syndiotactic
Atactic
Can’t Crystallize
Isomerism – different structures, but same chemical
composition
32. We have discussed polymers comprised of a single kind of a monomer,
ie just one repeating entity. However, this is not unique: we can
synthesize polymers that consist of different repeating units, and such
polymers are called copolymers
The combination of different mers allows flexibility in selecting
properties, but the way in which the mers are combined is also
important. Two different mers can be alternating, random, or in blocks
along the backbone or grafted on as branches.
33. • Thermoplastics:
--little cross-linking
--ductile
--soften w/heating
Ex: grocery bags, bottles
• Thermosets:
--large cross-linking
(10 to 50% of mers)
--hard and brittle
--do NOT soften w/heating
--vulcanized rubber, epoxies,
polyester resin, phenolic resin
Ex: car tyres, structural plastics
cross-linking
34. In thermoset, the network is inter-connnected in a non-regular fashion. Elastomers
belong to the first category. Polyisoprene, the hydrocarbon that constitutes raw natural
rubber, is an example. It contains unsaturated C=C bonds, and when vulcanizing
rubber, sulfur is added to promote crosslinks. Two S atoms are required to fully saturate
a pair of –C=C— bonds and link a pair of adjacent molecules (mers) as indicated in the
reaction.
Without vulcanization, rubber is soft and sticky and flows viscously even at room
temperature. By crosslinking about 10% of the sites, the rubber attains mechanical
stability while preserving its flexibility. Hard rubber materials contain even greater sulfur
additions.
35.
36. • Molecular weight Mw: Mass of a mole of chains.
• Tensile strength (TS):
--often increases with Mw.
--Why? Longer chains are entangled (anchored) better.
• % Crystallinity: % of material that is crystalline.
--TS and E often increase
with % crystallinity.
--Annealing causes
crystalline regions
to grow. % crystallinity
increases.
crystalline
region
amorphous
region
smaller Mw larger Mw
Molecular weight, Crystallinity
and Properties
37. ~10 nm spacing
Oriented chains with long-range order
Amorphous disordered polymer chains in
the “intercrystalline” region
38.
39. Random arrangement = High Entropy Stretched = Low Entropy
Entropy is a measure of randomness: The more ordered the chains are, the lower
is the entropy. Spontaneous processes always tend to increase the entropy, which
means that after stretching, the chains will tend to return to a high-entropy state
42. Temperature & Strain Dependence:
Low T & high strain rates = rigid solids
High T & low strain rates = viscous
Rubber-like Elastic
Deformation
Slow
relaxation
Glassy (Elastic-high modulus)
Leathery
(Elastic-low modulus)
Thermoplastic (uncrosslinked)
Tg Tm
Modulusofelasticity
Temp.
Rubbery Plateau
Elastic at high strain rate
Viscous at low strain rate
medium times
Long times
43. Crosslinked Branched
Effect of crosslinking
Thermoset
Heavy Crosslinking
Elastomer
Light crosslinking
Effect of crystallinity
Tg Tm
LogMod.OfElasticity
amorphous
50 % Crystalline
100 % crystalline
Tm
LogMod.OfElasticity
Thermoplastic
No crosslinking
Tg
Branched polymer
Crystals act like crosslinks
Strain Induced Crystallization in NR
44. • Compare to responses of other polymers:
--brittle response (aligned, cross linked & networked case)
--plastic response (semi-crystalline case)
initial: amorphous chains are
kinked, heavily cross-linked.
final: chains
are straight,
still
cross-linked
0
20
40
60
0 2 4 6
σ(MPa)
ε 8
x
x
x
elastomer
plastic failure
brittle failure
Deformation
is reversible!
45. • Decreasing T...
--increases E
--increases TS
--decreases %EL
• Increasing
strain rate...
--same effects
as decreasing T.
20
40
60
80
0
0 0.1 0.2 0.3
4°C
20°C
40°C
60°C
to 1.3
σ(MPa)
ε
Data for the
semicrystalline
polymer: PMMA
(Plexiglas)
46. • Stress relaxation test:
Er (t) =
σ(t)
εo
--strain to εο and hold.
--observe decrease in
stress with time.
• Relaxation modulus:
• Data: Large drop in Er
for T > Tg.
(amorphous
polystyrene)
103
101
10-1
10-3
105
60 100 140 180
rigid solid
(small relax)
viscous liquid
(large relax)
transition
region
T(°C)
Tg
Er(10s)
in MPa
time
strain
tensile test
εo
tσ( )