2018   Dr.Munir Ashraf Sb   17-NTU-6011 Mr. Shehbaz Ali             Russian Aromatic Fibres (KEP)    RussianAromatic Fibres (KEP)  Introduction To produced aromatic fibreswith high modulus and strength. In 1970s, Russian Professor (Prof.

Georgy I.Kudryavtsev, All-Russia Research Institute of Polymeric Fibres) began it. SVMis the first Russian p-polyamide fibre. Terlon and Armos were synthesized afterit. It replaced Kevlar. The investigation focused on:                                                              Figure 01The research led to the productionof the following fibres   Terlon®PPTAcopolymer including diamines selected from the left column of Fig. 1.

Terlon isan 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®) Principalof chemical constitution of Aromatic heterocyclic polyamide is that                                    NH Ar1 NH CO Ar2 CO   Armos®Armos is a higher tenacity fibre andyarn 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 propertiesof aramids are the result of their wholly aromatic structure, but heterocyclicunits, such as those in Heterocyclic para-polyamides and para-copolyamides(PHA) polymers, lead to increased thermal and fire resistance.Aromaticheterocyclic copolyamide of principal chemical constitution          NH   Ar1         NH                       It is the heterocyclic diamine.         CO   Ar2         CO                             It is the residue of terephthalicacid 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 ofthe left column in Fig.1 NOW in complete structure Fiber StructureThefibre structures differ on all three levels (molecular, super-molecular andmicro) from the usual fibre structure of flexible and semi rigid polymers. Themain structural features are shown in Table 1SVM and Armos fibres contain heterocyclic links and two kinds of polargroup, amide links and tertiary nitrogen atoms. The structure of thesepoly-mers and copolymers is characterised by less regularity and less rigiditythan PPTA. The absence of liquid crystalline domains in solution makes itpossible to regulate structure building at the fibre forming and thermaltreatment stages to give maximal orientation order. Owing to the lack of aplane of symmetry in the heterocyclic groups and to the mixed linking ofmonomers (head-to-head, tail-to-tail and head-to-tail), the extended chainconformations are irregular and lead to minimal crystalline order, with aconsequent reduction in the possibility of axial movement. The less regularmolecular chain structure leads to a higher proportion of stress-holdingmolecular chains and therefore to mechanical properties that are superior in SVM and especially in Armos fibre to those of aramid fibressuch as Terlon, which is similar to Kevlar and Twaron.                                                                        Table1 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 onheterocyclic polyamides and co polyamides. Figure2  Mechanical propertiesStress–strain plots for Terlon yarns 1 at 220 °C;  2 at 180 °C;  3at 140 °C;  4 at 100 °C;  5 at 80 °C;  6at 60 °C;  7 at 40 °C;  8at 20 °CFigure3Stress–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.

Figure4    Stress–strain for Armos yarns       1 at 220 °C;    2 at 180 °C;   3at 140 °C;  4 at 100 °C; 5 at 60°C;  6at 20 °C.Figure 5SVM and Armos fibres have mechanical propertiessuperior to those of Terlon as shown by the data in Table 2Table2  Stress–strain curves at different temperaturesfor Terlon, SVM and Armos yarns are presented in Figs.3, 4&5.

Aninteresting feature is that the high strength of SVM and Armos fibres is due toa higher breaking elongation, not to a higher modulus. The energy to break istherefore greater.Fibre tenacity depends onmoisture content owing to two influences, the plasticization effect and theintermolecular interactions caused by hydrogen bond bridges, which are createdby water molecules. These two influences lead to tenacity increasing to someextent with increasing moisture content up to a maximum value and then fallingwhen wet to 90–95% of the dry value.

High orientational, structuraland energy anisotropy of the fibres lead to anisotropy of their mechanicalproperties                                                          Table3 Thermal propertiesAllthree para-aramide types are characterized by high glass transition temperatures,high thermal and thermal-oxidative resistance, high ignition and self-ignitiontemperatures, and high limiting oxygen indexes. All three, especially SVM andArmos, are dimensionally stable on long heating. The tendency to spontaneouselongation in technological heat treatment (‘self-ordering effect’) leads tothe same effect in the first stage of heating slight elongation or very smallshrinkage with rise in temperature. The data show that change in dimensions ispractically absent up to 300°C. There is a small shrinkage of SVM and Armosyarns by 350°C; the shrinkage at 400–450 °C is not more than 2–3%. It is known theoretically andpractically that thermo-oxidative degradation includes three main reactions ü  separationof substances with low molecular weightü  molecularchain destruction by oxidation or hydrolysisü  intermolecularbridge creationFrom this point of view, carbocyclic aromatic polyamidesare more stable than heterocyclic ones.

If chain degradation leads to loss ofmechanical properties, on the other hand, the intermolecular bridges lead totenacity preservation. Therefore the resultant effect of all three kinds ofreaction is indefinite in terms of change in mechanical properties. Effect of ageing on mechanical properties Table 4 Fire resistance and thermal characteristics Table5 The comparative thermal-ageingcharacteristics of Terlon and Armos fibres at 200–300°C are presented in Table4.At higher temperatures, the loss of strength is greater. For Armos, theretention of tensile properties (strength and elongation at break) is slightlyhigher than for Terlon.Thehigh glass transition temperature and practically zero shrinkage for para-aromaticfibres give thermo resistant goods made from them important advantages in hightemperature media, in comparison with meta-aramid fibres.

SVM and Armos fibres arehighly fire resistant and superior to PPTA fibres, owing to the nitrogen containingheterocyclic structure and the presence of hydrogen chloride, which is a goodfireproofing compound. The main thermal characteristics and fire resistanceindices are shown in Table 5.Armos fibres and its typesAtpresent, Armos fibres and yarns havethe highest mechanical properties among aramids and related fibres. Armos yarns are produced by theTver-chimvolokno Joint-Stock Company in Tver city. üHigh-modulus reinforcement yarns androving (Armos HMR) üHigh-modulus yarns for technicaltextiles (Armos HMT) üHighly thermally stable yarns fortextiles (Armos HTS). All values were measured by Russian standard methodsProperties of high-modulus reinforcement andtechnical yarnsTable6 Properties of highly thermally stable yarns Table 7Modified FibresNewchemically and physically modified fibres based on heterocyclic polymers andcopolymers have been produced with properties depending on the modificationmethod: üuse of different monomers for newpolymer or copolymer synthesis at the stage of polycondensation  üpolymeric mixtures üadditives to polymer solution üSurface modification.

 Oneway is to include meta-links or other non-para-links in polymeric chains. Thisleads to increased chain flexibility and therefore lower fibre modulus. Thesecopolymers have better solubility and their solutions are isotropic. The principles of fibre formation areapproximately the same as for traditional flexible chain polymer processing –wet-spinning, stretching for orientation, and additional thermal treatment tofix fibre structure. The fibre properties are characterised by modulus andtenacity, which are similar to general purpose fibres, of the type required forsome kinds of technical textiles and reinforcement of rubber goods. Togilen®Changingup to 50% of the terephthalic links in the heterocyclic polymer to isophthaliclinks at the polycondensation stage leads to decrease of fibre rigidity andincrease of elongation to normal textile values. This kind of fibre has goodthermal and fire resistance (high oxygen index), but it has the disadvantage ofwater action on mechanical properties,the tenacity in the wet state is only 70%of that in the conditioned state.

Tverlana®Changingup to 30% of heterocyclic diamine to m-phenylenediaminein the polycondensation stage.This polymer also gives fibres with good thermal properties. The properties of these twofibres are presented in Table 8 in comparison with the ‘mother-fibres’ – SVM and Armos  Table 8Therefore the production technologyof these fibres is similar to Terlonand other aramid fibres.Modifiedaramid fibres, created by adding different polymers in the spinning solution,lead to new application possibilities. The best result was obtained by addingflexible 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 elastomericmanufactured goods.At the same time this polymer addition led to an increase inmechanical properties.

These practically important effects may be due toformation of intermolecular bonds and increase in super molecular structuralorder. Addition of rigid chain polymers did not have a positive effect.Surfacemodification is useful for barrier creation against water and protectionagainst external influences. Surface treatment of SVM and other fibres by silicon organic substances as emulsions inwater leads to higher moisture resistance.Surface grafting ofpolytetrafluorethylene decreases wettability and water sorption.

ConclusionTenacityof Armos yarn is 20–50% higher than that of other aramid and related yarns andglass yarns. The thermal characteristics show the advantages of heterocyclicpolymers (SVM, Armos, Togilen, Tverlana) in comparison with aramid fibres basedon PPTA (Terlon, Twaron, Kevlar) and meta-aramid fibres (Fenilon, Nomex),especially to open fire resistance.Table 9 For glassyarn S-type are following:ü  Density 2.

52–2.55 g/cm3ü  Elasticity modulus 85–90 GPaü  Tenacity 4–4.6 GPa.

Comparison of tenacity and fireresistance of various aramid and other fibres.Figure6Sequenceof fire resistance with respect to tenacityArmos>SVM>Terlon,Kevlar>togilen>Fenilion>tverla>nomexApplicationThe applications found for theRussian aromatic HM-HT fibres are similar,high-strength and high-stiffnesstechnical textiles loaded in the axial direction. This includesü  high-strength composites,ü  ropes,ü  conveyor belts, ü  hoses,ü  protective clothing ü  a host of similar uses 

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