2018 constitution of Aromatic heterocyclic polyamide is

 

2018

 

Dr.Munir Ashraf Sb
 

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Mr. Shehbaz Ali
 
 
 

 
 
 

Russian Aromatic Fibres (KEP)

 

 

Russian
Aromatic Fibres (KEP)

 

 

Introduction

To produced aromatic fibres
with high modulus and strength. In 1970s, Russian Professor (Prof. Georgy I.
Kudryavtsev, All-Russia Research Institute of Polymeric Fibres) began it. SVM
is the first Russian p-polyamide fibre. Terlon and Armos were synthesized after
it. It replaced Kevlar. The investigation focused on:

 

                                                           

Figure 01

The research led to the production
of the following fibres 

 

Terlon®

PPTA
copolymer including diamines selected from the left column of Fig. 1. Terlon is
an aramid copolymer fibre, based on PPTA with up to 10–15% comonomer content.
Its manufacture, structure and properties are similar to other aramid fibres,
although the Terlon copolymer is not the same as the copolymer in Technora.

 

 

SVM®
(formerly Vnivlon®)

Principal
of chemical constitution of Aromatic heterocyclic polyamide is that

 

                               

 NH

Ar1

NH

CO

Ar2

CO

 

 

Armos®

Armos is a higher tenacity fibre and
yarn that retains the high thermal and fire-resistant properties of SVM. Creation of Armos was the principal step after the elaboration of SVM fibres. The high thermal properties
of aramids are the result of their wholly aromatic structure, but heterocyclic
units, such as those in Heterocyclic para-polyamides and para-copolyamides
(PHA) polymers, lead to increased thermal and fire resistance.Aromatic
heterocyclic copolyamide of principal chemical constitution

 

 

 

 

 

NH

 

Ar1

 

 

 

 

NH

 

 

 

 

 

 

 

 

 

 

 

It is the heterocyclic diamine.

 

 

 

 

CO

 

Ar2

 

 

 

 

CO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It is the residue of terephthalic
acid shown at the top of the right column in Fig.1

 

 

 

 

NH

 

Ar3

 

 

 

 

NH

 

 

 

 

 

 

 

 

 

 

It is the residue of p-phenylenediamine shown at the top of
the left column in Fig.1

 

NOW in complete structure

Fiber Structure

The
fibre structures differ on all three levels (molecular, super-molecular and
micro) from the usual fibre structure of flexible and semi rigid polymers. The
main structural features are shown in Table 1

SVM and Armos fibres contain heterocyclic links and two kinds of polar
group, amide links and tertiary nitrogen atoms. The structure of these
poly-mers and copolymers is characterised by less regularity and less rigidity
than PPTA. The absence of liquid crystalline domains in solution makes it
possible to regulate structure building at the fibre forming and thermal
treatment stages to give maximal orientation order. Owing to the lack of a
plane of symmetry in the heterocyclic groups and to the mixed linking of
monomers (head-to-head, tail-to-tail and head-to-tail), the extended chain
conformations are irregular and lead to minimal crystalline order, with a
consequent reduction in the possibility of axial movement. The less regular
molecular chain structure leads to a higher proportion of stress-holding
molecular chains and therefore to mechanical properties that are superior in SVM and especially in Armos fibre to those of aramid fibres
such as Terlon, which is similar to Kevlar and Twaron.

                                                                        Table
1

Structural
levels

     Terlon

SVM

Armos

Molecular

PPTA and co- polymers;

statistical
segment

30–50 nm;

main polar group:

—CONH—

Heterocyclic
 para-aramid;
statistical
Segment
20–40 nm;
polar groups:
—CONH—; ==N—

Heterocyclic
 para-aramid copolymer; statistical
segment
20–40 nm;
polar groups:
—CONH—;
==N—

Super
molecular

Extended
chain
3D
crystalline order
fibrillar;
Highly
oriented.

Extended
chain
3D
crystalline order
fibrillar;
Highly
oriented.

Extended
chain
non-crystalline
fibrillar;
Highly
oriented.

Micro
level (fibre)

Stress-holding   molecular chains proportion 0.6–0.75

Round
cross-section, low heterogeneity

 

 

Principal scheme for fibre production based on
heterocyclic polyamides and co polyamides.

 

Figure
2

 

 

Mechanical properties

Stress–strain plots for Terlon yarns

1 at 220 °C;  2 at 180 °C;  3
at 140 °C;  4 at 100 °C;  5 at 80 °C;  6
at 60 °C;  7 at 40 °C;  8
at 20 °C

Figure
3

Stress–strain plots for SVM yarns

1at 220 °C; 2 at 180 °C; 3 at 140 °C; 4 at 100 °C; 5 at 60 °C;
6 at 20 °C.

Figure
4

 

 

 

 

Stress–strain for Armos yarns      

1 at 220 °C;    2 at 180 °C;   3
at 140 °C;  4 at 100 °C; 5 at 60
°C;  6
at 20 °C.

Figure 5

SVM and Armos fibres have mechanical properties
superior to those of Terlon as shown by the data in Table 2

Table
2

 Stress–strain curves at different temperatures
for Terlon, SVM and Armos yarns are presented in Figs.3, 4&5. An
interesting feature is that the high strength of SVM and Armos fibres is due to
a higher breaking elongation, not to a higher modulus. The energy to break is
therefore greater.

Fibre tenacity depends on
moisture content owing to two influences, the plasticization effect and the
intermolecular interactions caused by hydrogen bond bridges, which are created
by water molecules. These two influences lead to tenacity increasing to some
extent with increasing moisture content up to a maximum value and then falling
when wet to 90–95% of the dry value.

High orientational, structural
and energy anisotropy of the fibres lead to anisotropy of their mechanical
properties

                                                          Table
3

Thermal properties

All
three para-aramide types are characterized by high glass transition temperatures,
high thermal and thermal-oxidative resistance, high ignition and self-ignition
temperatures, and high limiting oxygen indexes. All three, especially SVM and
Armos, are dimensionally stable on long heating. The tendency to spontaneous
elongation in technological heat treatment (‘self-ordering effect’) leads to
the same effect in the first stage of heating slight elongation or very small
shrinkage with rise in temperature. The data show that change in dimensions is
practically absent up to 300°C. There is a small shrinkage of SVM and Armos
yarns by 350°C; the shrinkage at 400–450 °C is not more than 2–3%.

 

It is known theoretically and
practically that thermo-oxidative degradation includes three main reactions

ü  separation
of substances with low molecular weight

ü  molecular
chain destruction by oxidation or hydrolysis

ü  intermolecular
bridge creation

From this point of view, carbocyclic aromatic polyamides
are more stable than heterocyclic ones.If chain degradation leads to loss of
mechanical properties, on the other hand, the intermolecular bridges lead to
tenacity preservation. Therefore the resultant effect of all three kinds of
reaction is indefinite in terms of change in mechanical properties.

 

Effect of ageing on mechanical properties

Table 4

 

Fire resistance and thermal characteristics

Table
5

 

The comparative thermal-ageing
characteristics of Terlon and Armos fibres at 200–300°C are presented in Table
4.At higher temperatures, the loss of strength is greater. For Armos, the
retention of tensile properties (strength and elongation at break) is slightly
higher than for Terlon.

The
high glass transition temperature and practically zero shrinkage for para-aromatic
fibres give thermo resistant goods made from them important advantages in high
temperature media, in comparison with meta-aramid fibres. SVM and Armos fibres are
highly fire resistant and superior to PPTA fibres, owing to the nitrogen containing
heterocyclic structure and the presence of hydrogen chloride, which is a good
fireproofing compound. The main thermal characteristics and fire resistance
indices are shown in Table 5.

Armos fibres and its types

At
present, Armos fibres and yarns have
the highest mechanical properties among aramids and related fibres. Armos yarns are produced by the
Tver-chimvolokno Joint-Stock Company in Tver city.

 

ü
High-modulus reinforcement yarns and
roving (Armos HMR)

 

ü
High-modulus yarns for technical
textiles (Armos HMT)

 

ü
Highly thermally stable yarns for
textiles (Armos HTS).

 

All values were measured by Russian standard methods

Properties of high-modulus reinforcement and
technical yarns

Table
6

Properties of highly thermally stable yarns

Table 7

Modified Fibres

New
chemically and physically modified fibres based on heterocyclic polymers and
copolymers have been produced with properties depending on the modification
method:

 

ü
use of different monomers for new
polymer or copolymer synthesis at the stage of polycondensation

 

ü
polymeric mixtures

 

ü
additives to polymer solution

 

ü
Surface modification.

 

One
way is to include meta-links or other non-para-links in polymeric chains. This
leads to increased chain flexibility and therefore lower fibre modulus. These
copolymers have better solubility and their solutions are isotropic.

 The principles of fibre formation are
approximately the same as for traditional flexible chain polymer processing –
wet-spinning, stretching for orientation, and additional thermal treatment to
fix fibre structure. The fibre properties are characterised by modulus and
tenacity, which are similar to general purpose fibres, of the type required for
some kinds of technical textiles and reinforcement of rubber goods.

 Togilen®

Changing
up to 50% of the terephthalic links in the heterocyclic polymer to isophthalic
links at the polycondensation stage leads to decrease of fibre rigidity and
increase of elongation to normal textile values. This kind of fibre has good
thermal and fire resistance (high oxygen index), but it has the disadvantage of
water action on mechanical properties,the tenacity in the wet state is only 70%
of that in the conditioned state.

Tverlana®

Changing
up to 30% of heterocyclic diamine to m-phenylenediamine
in the polycondensation stage.This polymer also gives fibres with good thermal properties. The properties of these two
fibres are presented in Table 8 in comparison with the ‘mother-fibres’ – SVM and Armos

 

Table 8

Therefore the production technology
of these fibres is similar to Terlon
and other aramid fibres.

Modified
aramid fibres, created by adding different polymers in the spinning solution,
lead to new application possibilities. The best result was obtained by adding
flexible chain polymers to the solution of PPTA in sulphuric acid.A modified Terlon yarn with 10% addition of polycaproamide
(nylon 6) had improved adhesion to rubber in tyres or other elastomeric
manufactured goods.At the same time this polymer addition led to an increase in
mechanical properties. These practically important effects may be due to
formation of intermolecular bonds and increase in super molecular structural
order. Addition of rigid chain polymers did not have a positive effect.

Surface
modification is useful for barrier creation against water and protection
against external influences. Surface treatment of SVM and other fibres by silicon organic substances as emulsions in
water leads to higher moisture resistance.Surface grafting of
polytetrafluorethylene decreases wettability and water sorption.

Conclusion

Tenacity
of Armos yarn is 20–50% higher than that of other aramid and related yarns and
glass yarns. The thermal characteristics show the advantages of heterocyclic
polymers (SVM, Armos, Togilen, Tverlana) in comparison with aramid fibres based
on PPTA (Terlon, Twaron, Kevlar) and meta-aramid fibres (Fenilon, Nomex),
especially to open fire resistance.

Table 9

For glass
yarn S-type are following:

ü  Density 2.52–2.55 g/cm3

ü  Elasticity modulus 85–90 GPa

ü  Tenacity 4–4.6 GPa.

Comparison of tenacity and fire
resistance of various aramid and other fibres.

Figure
6

Sequence
of fire resistance with respect to tenacity

Armos>SVM>Terlon,Kevlar>togilen>Fenilion>tverla>nomex

Application

The applications found for the
Russian aromatic HM-HT fibres are similar,high-strength and high-stiffness
technical textiles loaded in the axial direction. This includes

ü  high-strength composites,

ü  ropes,

ü  conveyor belts,

ü  hoses,

ü  protective clothing

ü  a host of similar uses