Indian Journal of Fibre & Tex tile Research Vol. 31. March 2006. pp. 15-28

Fibers from polymeric nanocomposites

LA Utracki "

National Research Council Can:Jcl a. Industrial Material s Institute, 75 de M ortagne, 8oucherville. QC, Canada J48 6Y4

The clay-containing polymeric nanocomposites (CPNC) compri se a pol ymeri c matrix and dispersed in it mineral or synthetic clay platelets. The key condition for success is the thermodynamic miscibility of the ingredients at the processing temperature. Toward thi s goal. the clay is usually pre-interca lated •mel/or compatibili zecl w ith the matri x. The role of melt compounding is to accelerate the dispersion process. Adding an extensional flow mi xer to the compounding line acce lerates the dispersion. At the organoclay loading of 1-5 wt%. the CPNC show increased ( in respect to matri x polymer) rigidity. strength. dimensional stability. barrier properties. flame resistance. etc. The main use of CPNC is in the tran sport and packaging industries. Fiber spinning of CPNC started about five years ago. The preliminary work demonstrated several benefi cia l aspects of the technology, e.g. improved spinnability. clyeability. mechanical properties, reduced shrinkage, flame resistance, and others. This rev iew provides a brief outline of the fundamental aspects of CPNC production followed by a summary of publications on the electrospi nning, so lvent spinning. and melt spi nning of CPNC. An effort has been made to focus on the relative effects brought about by incorporation of organoc lay.

Keywords: C lay-containing polymeric nanocomposites. Compounding. Extrusion . Nanocompos ite. Organoclay. Spinning !PC Code: Int. Cl 8 88283/00. COI833/00. DOIH

1 Introduction Polymeric nanocomposite (PNC) is a polymer with

dispersed in it particles, whose at least one dimension is small er than about I 0 nm. The particles may be spherical (e.g. metallic or ceramic, for functional applications), fibrillar (e.g. carbon nanotubes) or lamellar - the only nano-sized particles of interest to polymer industry are layered clays, in particular natural (mineral ) or sy nthetic montmorillonite (MMT) or hectorite (HT). 1 The di cti onary of terms used in the clay-containing polymeric nanocomposite (CPNC) literature is given in Table I .

The global CPNC market is > 20 kton/y or ca. $200 M/y, increasing 18.4%/y and projected to reach 550 kton/y by 2009 (ref. 2). The main application is in the automotive and packaging industries with growing demands for appliances, bui I ding & construction, electrical & electronic, lawn & garden, power tool s, sport equipment, etc. A summary of current CPNC use is given in Table 2.

As shown in Table 2, CPNC has been widely accepted by the industry and its commercialization expands. However, several technological problems still remain and understanding of these systems is superficial. Current industrial production of CPNC is mainl y based on the reactive exfoliation, i. e. polymerization of a given monomcr(s) in the presence

"E-mai I: leszek.utracki @cnrc-nrc.gc.ca

of pre-intercalated clay. 3 This slows clown acceptance of these materials by the plastics industry. Only development of a reliable melt compounding technology that shifts the CPNC manufacture from the resin producers to compounders and fabri cators will change the situation.4 The melt compounding will add flexibility ; nanocomposites with desired performance characteristics will be prepared where and when needed, accelerating CP C penetrati on of the market.

Thi s review di scusses the fundamental s that govern CPNC properties and must be respected when preparing these systems, the type of clays, the methods of CPNC preparation , and the use of CP C in the fiber industry .

2 Fundamentals of CPNC CPNC have been investigated for about 30 years.

At loadings rarely exceeding 4 wt% organoclay, they show significantly improved performance (in comparison to matrix) . The principal advantages are: stiffness , strength. reduction of permeabi I i ty ( I 000-fold at 5 wt% clay loading) and that of flammability. A high degree of dispersion is essential in applications requiring good mechanical and barrier properties, but it is less important. e.g. for the tl ame resistance. Thus , the main goal for the researchers and engineers is to ascertain good and stable di spersion . However, before the engineer can put into practice an

16

Compatibi li zJ ti on

Exfoliated layered materi al

Exfoliat ion

lntercalan t

lntcn.:a latccl mat..: ria l (organoc lay)

l nterca lat ion

La) creel ma terial

l nterlayer >pac ing

lnterl ayer thi ck nc:ss

Misc ible polymeric 'ystem

MMT

Mat ri x polymer

Nanocompos ite ( 1C)

Nanofi be rs

Organoc lay

Platelets

Polymeric nanocompos itc ( I' C)

Shun ' tack or a tactoid

Spaci ng

IN DIA N J. FIBR E T EXT . RES .. MARCH 2006

Table 1- Dicti onary of terms used in the po lymeri c nanocompos ite literature

Process of modifi cati on of the interfacial properti es in CPNC. resulting in fnrm;1tion Df the il/[erp//(/se. creati on and stabili za tion of the des ired morphology .

lncli vicl uJI platelets dispersed in a matri x with the inrer/m·er spacing: drXJI > x.S nm. Dependi ng on concentration. the platelets may be randomly di spersed or or iented, forming shorr swcks or rucroids.

Conve rting il/[ncalare into 1'.>:/iJ/iare.

MateriJI sorbed between plarelt'IS th at binds to their surfaces formi ng an inlen ·,tfare. 1ost inten:Jiants Jre onium (mainl y ammonium) salts.

Lart'red Jn tlferial with inrnca/anr molecules inserted betw..:cn plmelers. thu s increas ing the interlaver spac ing betwee n them to at least 1.5 nm.

Formi ng an inrnca/are.

Synthetic or mineral inorganic compound. such as smectite clay. formed of Jcljacen t lame ll :te w ith a thi ckness or O.:l- 1 nm eJch.

A lso known :1s basal spacing. d-spacing or dw 1 is the minera l platelet thick ness (111 M MT = O.lJ6 nm) + the ga llery thickness. i. e. the thick ness of the repeating layers as seen by the X RD.

A lso J.- now11 as inre rlwnellar .1pacing or inre rgallen· spucing: cl -spacing iess the mineral lamella thi ck ness.

Homogenous clown to the molecu lar leve l. assoc iated w ith the negati ve free energy and heat of

mixing. D.G111 ::: 6 1-!m :S II. and o'tJGjdd>~ > 0. A thennoclynamically stable CPNC. where the clay

platelets :1re well dispersed in a matri x.

M ontmori llon ite: Na- MMT =sodium montmorillonite: 1-1-MMT = protonated MMT.

A polymer in which the inrerm!are is di spersed to form a C PNC.

A materi al (metalli c. ceramic or polymeri c) having dispersed nano-particles. whose at least one dimension docs not exceed 10 nm .

Fibers w ith diameters< I 00 nm. ll'hose material properti es ex hibit size dependence.

lllfe rcalmed elm·.

Clay lamell ae. indi vidual layers of the layered Jllaferia l.

A polymer or copolymer having dispersed in it nano-s izcd parti cles. viz. pl:1 telcts. tibcrs. sphero ids. etc.

lntercalared or exjiJ/iared cl ay plate lets aligned parallel to e~1 c h other.

Two measures are used: inrerlm·er spacing and inrerlwnella r spacing. The form r comprises the latter plus the platelet thickness. ror exampl e. for MMT. d001 = fnrerlalll ellar spacing+ 0.96 (nm).

ef f icient and commerciall y successful technology he or she must understand the factors involved - the fundamental s.

similar size - excellent description o f the observed behavior validated the concept fo r CPNC with PA-67

.

polys ty rene (PS )8.'1, or PP 10 as the matri x. These

computations make obvious th key role of thermodynamics fo r dispersing cb y platelets 111

molten poly mer - only when the thermodynamic conditions are sati sfied the mechanical exfo liati on may be achieved. i .e. the negati ve free energy or mi x ing is required:

Phys ics is marvelous - its l::iws have uni versal va lidity. For exampl e, th e ru les governing misci bi I i ty or water and alcohol are the same for cl ay and water or clay and polymer. The bes t way to regard exfoliated CPNC is to threa t it as a so lution of 'clay molecules' in molten polymer. In thi s concept, the ·clay molecules · are equated with indi v idual platelets. charac teri zed by their size and the thermodynamic propert ies. Similarl y like macromolecules, these 'clay molecu les' may be treated as composed of a number or statis tical segments each w ith a se t or characteri sti c parameters. Th is concept has been explored in molecu lar dynamics (MD) computa ti ons, e.g. using the se l f-consiste nt fi eld (SCF)5

.h or a ce ll -hole latt ice mode l. where segmen ts of the "c lay molecule" and that or a po lymer arc pl aced in the latti ce ce ll s or

D.G11, =M-f - TD.S < O .. . ( I )

Since polymer diffusion inro the gallery decreases the en tropy. D.S < 0, the on ly way to sa ti sfy the conditi on is fo r the enthalpy to be ;;tro ngly ncgati\·e. D. H < 0. Thus. interacti ons that resul t in exothermic reacti ons arc needed.

Ow ing :o hydrophi lic char~tct r or clay. the preparation of CPNC with water- so lub le polymers i"

General

A kzo Nobel

BASF

Bayer

Clariant

Dow Chem.

Eastman Ch<.:m.

Gitto & Nanocor

GM

l-l onevwe ll

M itsubishi

Nanocor and partners

PolyOne

RT P

Toray Incl.

Toyota

Ube

Unit ika

Wil son Sport s

UTRACKI: Fll3 ERS FROM POLYM ERIC N A NOCOMPOSITES 17

Table 2- Usc of CPNC in 2004/5

Nanocomposite concentrates are being evaluated in films not only for enhancing barri er, but also to control the release and migration of additi ves such as biocides and dyes.

Several car manufacturers use PP-based CPNC. e.g. for seat backs (2004 Acura TL) or interior consoles (2006 li ght trucks and van s).

Semi -aromati c PA-bascd CPNC (e.g. PA-mX D6) are used as barrier layers in PET bottles and films. e.g. in Europe for alcoholi c beve rage bott les. carbonated so ft -drink bottles and thermoformed meat and chee'e conta i ncrs.

De ve loped PNC for coa ting. pi gmenting and health care products.

Uses nanoparticks in scratch res istant paints. filtrati on :111d thermoplasti c PNC.

O ilers polyamide (PA) based CPNC for film barri er applications.

Manufactu res polypropy lene (PP) based nanocompos ites for pack::tg ing.

Appli es nanoparti cles in filtrati on and is acti ve ly deve loping CPNC w ith thermoplasti c matri ces.

DeYc lopccl multi -layer polyethy lene tncphthalate (PET ) containers and films for food packag ing w ith high ba rri er properties. The central layer is a PA- 111X D6-hasccl CPNC.

Deve loped polyo lclln (PO) nanocompos ites for low flammabilit y appli cati ons.

Since 2002 used CP 1C for "step-ass i>t .. in GM C Safari and Chevro let A stro vans. In 2004. introduced side mo lding (Impala ) and in 200.'i load ll oor (e.g. in Hummer H2) .

Deve loped CPNC for food packag ing ( films. containers and bottles).

Uses CPNC for the manufacture of thermoplastic membranes.

Oiler sevc r~il types of CPNC for di ve rse appli cati ons. e.g. based on PA (a liphatic or semi -aromati c). po lyo lefins (PO). etc. to be ex truded. injec ti on or blow molded.

Has commerciali zed CPNC mastcrbatchcs with high impact strength. stiffness. and chemical res istance. The formulations reduce cyc le time.

O tTers several CP C for di verse applica ti ons. including electri cal cabl es and w ires.

Deve loped advanced CPNC.

Deve lops poly lacti c ac id (PLA) based C1'1 C to replace PP composit es in it s automobiles.

Produces PA-based CPNC for the transportati on and packaging markets.

Co rmncrciali zed PA- or PLA-based CP C using synthetic clay.

Introduced long- life tenni s ball s w ith intern :1 l CPNC coatings Ill reduce permc:J bility . The technology is 10

be used for the manufacture of di verse ha lls and tires.

the easies t. ' The problems increase as the polymer becomes less po lar and more hydrophobi c. Two non-exclusive methods have been used to solve this problem: (i) clay intercalati on and ( ii ) compatibili zati on of the system.

At the polymer processing temperatures. the quaternary ammonium ions are notoriously unstable­the onset o f degradation at T = 1 50- 1 80°C has been reported .'" Tl~c degradation o f CPNC with polymethy lmethacry late (PMMA) 13

, polye thy lene (PE) 14 or PP 15 as the matrix foll owed the Hoffmann cl i mi nation mechanism 16

:

Historicall y, the organoclays were deve loped as thi ckeners for lubri cating o il s and greases, thu s even today the most common intercalant is a quaternary ammontum ion w ith paraffinic substituent s, e.g. di-methy l eli-h ydrogenated tall ow ammonium chloride (2M2HT. Quoremillln- 18 , C1(,-1 H7(,s Cl MW = 567-573 g/mol). Clay intercalated with such a compound becomes miscibl e (or di spersible) in hydrocarbons, but se ldom in po lymers. intercalant s w ith benzy l or ethoxy groups are known and respecti ve organoc lays arc commerciall y avai lable. However, the presence of these groups does not provide suf fi cient thermodynami c miscibili ty . e.g. C l oi~ ilcQ<J 1 OA (el i ­methy l benzy 1 hydrogenated ta l low am mon t urn chloride. 2M BHT) in spi te o f i ts ben;yl group is tmmi scible wi th PS.x.tt

+

As the ~c h e mati c indicates, th e longest paraffin ic substituen t (R-C H2-C H2- ) is converted into viny l­terminat ed compound that in the presence or oxygen rorms perox ides. which, in turn . attack the matrix po lymer causing a loss of performance. Thus. CPNC must be compoumled under blan ke t or 2 !

The mathematical modeling leads to the conclusion that macromolecular intercal an ts (espec iall y

18 INDIAN J. FIBRE TEXT RES .. MARCI-l 2006

chemi call y identi cal to the matri x, but with a terminal group abl e to interact with the cl ay surface) should

l h b I d .. •b'l' 17JS(\ engenc er t e es t t 1crmo ynam1c mi SCI 1 1ty. · · MD of PA-based CPNC indicates that the presence of paraffini c-type interca lants is detrimental to the thermodynamic mi sc ibility of clay with the matri x. 19·

20 The i ntercal ant ' s hydrocarbon chains form a low- mobili ty, immiscible, isolating layer between clay and PA. Only the loca l absence of intercalant molecul es might lead to thermodynamically favorable condition for clay di spersion. A simil ar mechanism migh t also be valid fo r the enhancement of properti es in systems co mposed of PP/organoclay compatibili zed with maleated-PP (PP-MA)21

, in whi ch the maleic anhydride groups are to interact with clay surface. These interacti ons were indeed detected by FriR.22

However, the method of exfoli ation that relies on the thermal eliminati on of intercalant is precari ous. The des ired interac tions between bare clay surface and the matri x or compatibili zer must compete with re-aggregation of pl atelets - the relative rates decide on the outcome. The crys talline solids have hi gh surface energy and their polar/i oni c interacti ons are long range. For example, the specifi c surface energy of freshl y cleaved mica is v 1 = 4500 mN/m. decreas ing in air to 375 mN/m (ref. 23); corresponding values for polymers at 20°C range fro m 10 to 49 mN/m (ref. 24).

One of the conseq uences of hi gh surface energy of crys talline solids is adsorption of liquid or gas molecules and their immobili za tion on the surface. The surface fo rce apparatus was used to study rheology of polybutad iene (PBD) within nano-size gap between two mi ca fl akes. 25 The results demonstrated the presence of an incompress ible 'hard wall ' at z1,,. = 5 nm of solid-like PBD adsorbed on the mica surface, and a second layer, about l 00 nm thi ck, where the melt viscosity ex ponenti ally decreased fro m infinity to the bulk value. Only at larger distances from the clay surface, the bulk viscosity of PBD was observed. Similar behavior has been reported for low molecular weight organi c solvents.

l k .I I. 26-28 Tl e.g. a anes. SI oxanes, o 1gomers, etc. 1ese resul ts were confirmed by mathemati cal modeling.29

The conseq uences of the adsorpti on-&-solidi fication on the clay surface signi ficantly affec t the CPNC behav ior. The MMT lamell ae are 0.96 nm thi ck, but since the thi ckness of each solidifi ed organic layer is 5-6 nm, the solidi ficati on augments

the volume of each exfoli ated platelet by a factor of about 12 ! However, when the system is only intercalated (hence, hav ing the interl ayer spacing. d001

< 8.8 nm), the adsorprion-&-so lidif;cati on turns the in te rcalated stack into a solid block , making delamination difficult.

The polymer so lidificati on on the clay su rface leads to decrease of segmental mobility, and thus a loss of free volume. As shown in Fig. l , the loss is proportional to the avai I able surface - the largest loss was found fo r full y exfo li ated CPNC hav ing PA-6 as the matri x, the small est for poorly dispersed organoclay in PS matri x.7'

8'10 Th us, at constant

organoclay load ing of 2 wt% the loss of free volume (i. e. the rein fo rcing ability) is a linear fun cti on of the interlayer spacing (c/001 , as measured by the X-ray diffracti on), i.e. of the clay surface area avail able fo r adsorption.

The large multipli cation factor of the adsorbed so lid offers explanati on for the disproportionate enhancement of performance by add iti on of small amount of clay. For example, CPNC from Ube. PA IOISC2 is reacti vely exfolia ted PA-6 with </> = 0.64 vol% of clay, but such a small amount of

rein fo rcement causes'0: tensile modu lus to increase by 26%, strength by 14%, HOT by 65°C and permeabi I i ty to decrease by a facto r of two.

The enl argement of clay platelet vol ume by matri x solidifi cation also affects the fl ow properti es. From the rheological point of view one must dist ingui sh several types of CPNC, e.g. with : # 1 intercalated stacks, #2 ex fo li ated organoclay pbtelets not bonded

r-=--·~-------PA-6 ~ 14 1 .. . . .. .

i 10

f 0 > Q)

~ I :: 6 - .

o I <ll I (/) I ..3 IPS

2 ---~---~------~ 0 17. 16

lnterlayer spacing (d001 ), nm

Fig. 1- Loss of free vo lume determined for CPNC containing 2 wt% of organoc lay dispersed in (from topJ PA-6. PP. and PS matri x7

·8

·10 T he empir ica l dependences shown as straight l ine is:

!'J.h = 2.50 + 0.833d01 1• wi th the corn: lation coe fficient r = 1.00.

UTRACKI: FIBERS FROM POLYMERIC NANOCOMPOSITES 19

to the matrix (intercalant is miscible with polymer), and #3 exfo li ated platelets bonded to the matri x. System # I follows the pattern of viscoelastic suspensions of anisometri c particles. At low clay loading it may show a red uction of viscos ity, but when the concentration of stacks exceeds the criti cal packing volume fraction the system may show a yield stress and high plateau modulus. System #3 displays the distinctive CPNC behav ior. For example, the stress growth function in steady shear experiment shows that relaxation of platelet orien tation requires about one hour' 1 - the system is unusuall y sluggish. The effect ong1nates in the adsorpti on-&­solidification of the matrix , as we ll as direct bonding of thousands macromolecules to each clay platelet. The entanglements of macromolecules attached to eli fferent platele ts engender fo rmat ion of tri­dimensiona l struct ures at the clay vol ume fraction as low as cp = 0.00 16. Furthermore, the large clay platelets behave si milarly to mesogenic groups in liquid crystal polymers (LCP). 1 The flow closely resembles that of LCP, but with the relaxat ion times three orders of magnitude larger. Good processability requires low clay conten t, 1.0- 1.5 wt%. The effects of fl ow-imposed orientation and sluggishness of its eradication profound ly affect the performance. Sys tem #2 displays an intermed iate behavior between #1 and#~.

Another e\ iclence of the adsorpti on-&-solidifi cation is more recent and more direct. The tensile strength. CJ,. of CPNC with PA-6 and PP matri x was measured21

. Assuming that clay platelets are perfectly aligned in the stress direct ion and that they perrectly ad here to the matri x, the vo lumetri c rule of mixtures was applied 12

:

CJ R = CJ, I cr, = I + cp 1 ( cr,. - I) ; CJ ,. = CJ 1 I CJ, . .. . (2)

In Eq. (2), cp IS the volume fra·~ tion, and th e subscripts c, 111 and .f stand for compos ite, matrix, and fill er, respectively. Ev identl y, the assumptions used in deri ving Eq. (2) lead to predic ti on of the maximum poss ible val ue of relative strength , a u.

To calculate rJ11 from Eq. (2) for PP and PA-6 systems. the clay tensi lc strength of mica was used, rJr = 240 MPa'). wh il e that of matrix, a 111 , was measured. The clay vo lume frac ti on in PP and PA-6 systems was: C/J .t = 0.0042 and 0.0053 respectively. With these va lue., Eq. (2) high ly underesti mated a11 •

Si nce the relation shou ld predict the max11n um. the

on ly ex planation is that there is a larger volume or reinforci ng particles in the samples than that of bare inorganic clay platelets. The value of ¢1 req uired for Eq . (2) to predict the correct value of a11 was found to be about 5 and 9 times larger (for PP- and PA-6 CPNC respectively) than that calculated for bare MMT platelets. These numbers are quite reasonable. cons idering solidi fication of the matri x in these partially exfol iated systems.

3 Mineral vs . Synthetic Clay While the mineral clays still dominate the market.

the sy nthetic ones constitute a valuable alternative for CPNC. For example, Unitika produces CPNC with syntheti c fluorohectorite (FH) dispersed in PA (and in PLA) matrix34

·35

• whi le Ube uses mineral MMT. The properties of these two commerc ial CPNC are li sted in Table 3.

Synthet ic layered silicates are prepared using several methods and might be classified as:

(i) Semi-synthetic-Prepared by modification of such mineral s as talc or obsidi an. partiall y rep lacing Mg+2 by Na+ or Li+ in the octahedral layer. For thi s purpose Li 2C03 and a2SiF, may be used . In the fluoro mica (FM), the fluorin e partially replaces the - OH groups and thus modifies reactivity.

(i i) Fu ll y synthetic- Here, formation of layered silicate starts with a variety of metal oxides that provide suitable composition, e.g. (Si -1 0toH Mg6_, Li x)(0H)4-y Fy. for crys talli zable layered silicates. Two sub-categories are known: • The low temperature. hydrothermal process starts with aqueous sa lt solutions. fo ll owed by co-

Tab le 3- Mechanical properti es of CPNC with PA-6 as the matrix

Property

Ten~ i le strength . kg/em2

Tensi le elongati on. %

Flex ural strength. kg/em~

Flexural modulus. Mg/cm2

! mpaet strength . kg em/em

I lTD ( 18.56 kg/em\ "C

I-lTD (4.6 kg/em\ "C

1-1 ~0 permeability g/m2 24 h

Density. kg/m1

CP C from Ube

PA-6 CP C

800 9 10

100 75

1100 1390

28.5 35.9

6.5 5

75 140

180 197

203 106

11 40 1150

CPNC from Uniti k:J

PA-6 CP C

810 930

100 4

1080 1580

29 .0 45.0

4.9 4.5

70 172

175 193

11 40 1150

20 I DI A N J. FIBR E TEXT. RES .. M A RCI-l 2006

precipitation into slurry, whi ch. in turn is boiled under reflu x for J0-20 h to induce crystalli zation. • The high temperature process starts with fine powder of suitable salts (e.g. Li 20 , M gO, Si02

and M gF2), mixed in proper proporti on, heated at 1300°C for 3 h and then allowed to coo l for I 0 h. The reaction mass is placed into water, and the solid contaminants sedimented, y ielding syntheti c hectori te. ' 6

(i ii ) Templated syntheti c (non-commerciai)-Based on organic templates . which after synthes is may be pyrolysed, or left in as intercalants. 37

The advantages and di sadvantages of mineral and syntheti c clays are summari zed in T able 4. Owing to non-tox icity. lack of co lor. reproducible compos ition and a wide range of avail able aspect rati os, the synthetic clays may be particularl y attractive for the producti on of CPNC-type nano-fibers.

4 Compounding CPNC CPNC belong to the ca tegory of multi -phase

systems (M PS : blends, compos ites and foams) that require contro lled compounding, ori entation of the dispersed phase, stabili zati on of dispersion and ori entation as well as optimi zati on of interacti ons in the solid state. The dispersive mixing is responsible for breaking the minor component domains to des ired size, which than are homogeneously di stributed within the matri x. Microrheology may be used to describe the dispersive process in the shear or extensional llow f ield, while distri buti ve mixing may be treated in terms of the laminar flow theory or that of chaoti c mixing. Both , the microrheology and laminar mi xing, point out the superi ority of the ex tensional tl ow field. 4

M ost pl astics compounders employ shear. while theori es reveal superi ority of extensional flow for mi xing.38 For example, elongational mi ing:

(i) is orders of magnitude more energy-efficient (th an shear),

(i i) generates better dispersive unci di stri butive mi XIng,

(iii ) generates low temperature increases : ca. I-3°C (vs. 70°C in shear),

(i v) does not cause re-aggregation of solid panicles (reported in shear), and

(v) may be generated using convergent-di vergen t (C-D) llow geometry, either in motionless or dynamic mi xing devices.

These reasons motivated the development of the ex tensional fl ow mi xer (EFM) and its dynamic version, DEFM .w EFM has been des igned as an inexpensive mixer to be attached to a single-screw ex truder (SS E) fo r dispersing one molten polymer in another40

, i .e. fo r alloy ing and bl nding polymers. homogenizati on of reaction products, etc. 41

A lternati ve ly, a tw in-screw ex truder (TSE) could be used with EFM. However, th is compounder is not only much more expensive than SSE, bu t al so a gear pump (GP) must be used to prov ide the dri ving pressure for EFM. 42 Addition of GP to the compounding line increases cosl and induces additional process ing and performance problems.

The blends prepared in SSE + EFM often outperformed those from TSE. These results were expected on the basis of theoret ical analys is of mi xing. and indeed for melt homogenizati on and blending, EFM performs well. However, since the principles of dispersing one molten polymer into another are di f ferent than those for dispersing solid

Table 4- Advantages nnd disadvantages of mineral and syn thetic clays'

Mineral c lny Montmorill onite (MMT)

Advantages D isndvnnwges

Wc ll -es tabli shecl technology Variabili ty of compos ition and color

Ava il ability Crysta llographic de fec ts that prevent to tal exfoliati on

Lower cost than synthetic Poor reproducibi l ity of PNC performance

D i fficult remova l of contaminants

Synthetic clay Fluoro mica (FM )

Advantages Disadvantnges

Stable composition and shape Developi11g technology

W ide range of platelets aspect rati o: Li mited and uncertain p = 20-6.000 sourcing

Reproducible PNC performance Higher co>t th an mineral

Absence of co lor and non-tox icity

UTRACK l: FIBERS FROM POL YMERlC NANOCOMPOSlTES 2 1

aggregates. it came as a surpri se that the co mmercia l EFM-3 (Fig. 2a) success full y di spersed organoc lay in thermoplastic matrices (polyethylene terephthalat e or PET. PA-6. PP. PS , etc.).r .n--tr, The theory of mi xing suggests that the di spersion or solid particles should be four times more efficient in the extens iona l fl ow than in a shear field .-1 7 PET compounded wi th organoclay in a TSE + EFM-3 showed the tensil e modulus increased by 67 7c. tens il e strength by 70% and impact strength by 80% as compared to the prod uct compounded without EFM . The resu lts encouraged redesigning the EFM.

The new unit (EFM-N) was designed cons idering deduced mechani sm of clay di spersion. In principle. the ll ow profile between co nvergent-divergent (C-D) plates was modified. The material has to pass through a series of C-D elemen ts. each or them havi ng three flow zones: (i) a hyperbolic converge nce that ori en t organoclay aggregates in the now directi on. (ii ) controllable gap were the top and bottom clay platelets are peeled orr from the aggregate. and (iii ) a divergen t part that random izes the fl ow. The most critical is the balance of the extens iona l to shear st resses wi thin each C-D clement.

Perf'ormance of the new EFM-N was examined by preparing a series of CPNC compos iti ons with PA-6 or PP as the matrix. ~ 1 The organoc lay was used at 0, 2

and 4 wt% load ings. The PP-based CPNC were compatibili zed with a mixture or two PP-M A's. The material characteri stics are given in Table 5.

The compounding was carri ed out using a TSE. TSE + GP, TSE + GP + EFM or a SSE with or without EFM. For compari son. EFM-3 and EFM- N were used with at least four different gap settings between the C-D plates . To ascertain homogeneity of compos iti on, a master-batch (MB) was prepared in a TSE. Dry blending MB with homopolymer, and then mi xing in the aforementioned compounding lines resulted in CPNC. The degree of clay di spersion was de term ined using the X-ray diffraction (X RD) and hi gh-resolution transmi ss ion electron m1croscopy (HRTEM). The performance was assessed measuring the tens ile, fl exural and impact properties.

As shown in Fig. 3, the use of the new EFM­rcsu lted in good dispersio n of C 15 A in PA-6. The exfo li ati on (97.1 %) was higher than that determined for Ube PA I 0 15C2. (80.7%) - the material used as a reference. The XRD data were confirmed by HRTEM (Fig. 4).

The result s for PP-based CPNC were less spectacular than those for PA. Here, the thermal

instability of C I5 A dominated. TS E caused the greates t red ucti on or door as a functi on or decreasin g gap, while in SSE + EFM degrada ti on was ev ident onl y at the smallest C-D gap of 15 f.lm. However. in all three compounding lines the red ucti on of C-D gap was paralleled by progress ive ex foli at ion. The best di spersion was obtained using SSE + EFM -N with gap or about 30 ~llll .

5 Use of CPNC in Fiber Industry The first modern use of clays in a pol ymeri c matri x

is cred ited to Fujiwara and Sakamoto, who in 1976 applied for Japanese patent on the 'Method j(Jr

lllm llt/'acturing a c/ay-p olvwnide COIIIfHJsite' -ts . It took addit ional 2.0 years before PA-based CPNC became commerciall y available. The exp loratory fiber spinning of CPNC started about five years ago. Three

Melt flow from extruder

Flange onto extruder -~..,;t

End cap

Outer wall

Extensional flow zone

Flange to die To die

(a )

(b)

channel

Fig. 2-The commercial ex tensional !low mi xer EFM-:l (a). and the dynamic ex tensional fl ow mixer DEFM (b). whi ch may be used as a torpedo attac hed to SSE or as a "stand-alone" un it ~ 11

I DIAN J. FI8RE TEXT. RES .. MARCH 200(1

Tabil: 5- Material characteri stics

M;Hcri;il Trade name·' M,. kg/mol

PA-6 Ubc-PA 10158 21.7

PI' PROf AX -I'DC I 274 250

PI'-MAI Epo lene -~0 15 47

I'P-Mi\ 2 Po lybond 3150 330

Orga noclay (C 15A ) Cloisite .

15A

Density J:, g/mL oc 1. 14 2 16

0.902 161

0.91 162

0.91 164

MAll Supplier wt"k

Ube JnJu <ari <.:s

Uascll Polyolerins

1.31 Eastman Chemical!,

0.5 Crom pton

South . Clay Prod.

·' C 15 i-; MMT interca lated \\'ith cxce" ( 1.25 meq/g or 0. 78 mmo l/g) or eli -methyl eli -hydrogenated tallow ammonium chl oride (f\rquad ::!JJT }: it COillains 43 \\'tri o r the organic phase and 2 wt rk or water

E c

0 'bo

OJ c

' (3 ro a. IJ)

55,-----~,---------------------

1

"' ··3 · TSE + GP + EFM-3

\ ./\ • SSE + EFM-3 UBE -SSE+ EFM-N

5 r5_33 ....... \ / \ , : ~

,:. \. ,./ \

TSE

0 -- \~- --.. ~.; __ ~ ... rr::__; -....._.; ----....

'---'

4 -··· TSE + GP -

I SSE

10' 10' 10~ 10'

EFM gap (h) , pm

:§?. 0

-... >< ~ c 0 -~

0 x w

100

90 luBE ~- ' s~\ J - . ,J!t~ I 81 %

/ BO I

70 -

r:- • . .. -...............

-.- ·'· '· · .. -~.\

,h . ..._: .. _

··. 60

. ::: • TSE+GP+EFM-3 .. SSE+ EFM-3 *SSE+ EFM-N

EFM gap (h) , 1-lm 10'

l·ig. 3- lntcr layc r spac ing ;1nd the degree or c:-.ro liation for l't\ -6 naiHlCOinpmites co mpoumkcl in a TSE + GP + EF\1. and in SSE \\ ith either EFM-3 or EFM - 1. for comparison. the \' a lues for Uhc PI\ I 0 1.'\C::! arc abo , JHn\ 11 ~ 1

ha~ ic methods or fiber spinning have been used: (i) elec trospinning. (ii ) so luti on sp inning and (iii) melt ~p1n n1ng. The discuss ion bel ow follows the same ~cquence.

lncorporat ion of organoclay into matrix polymer i ~

C'\ pectccl [() modi ry the ri berltcx ti lc perrormance. The

main crrccts should be in ph y~ i cal properties. e.g. enhanced tensile modulus and streng th. reducti on ur :-.hrinkage. contro llccl elec trostati c behavior. enhanced a bra~ ion resi stance. etc. In a deli tion. the presence or

hydrophilic clay might enhance moisture absorption (but at a slower rate). dyeability . biodegradability and

chemical resistance . Since clay platelets block the UV irradiation. the CP C textiles should have better weatherability. Furthermore. the inherent tendency or clay to reduce the burning rate and rorm char is expected to enhance applicabil ity or these fibers in the

domestic and transport appli ca ti ons.

The mineral MMT clay pla telets used in most commerc ial organoc lays have th e as pect rat io31,

Fi g.4- II RTEM of PA-6 wit h 2-wl'h C 15 ! c.>mpnundcd in SSE + ErM - wilh 30 pm gap bciw..:cn iht' C- D platc, 21

p :::::: 286, wh ich means that the average 'd iameter· I S

d :::::: 300 nm. However, the clay platelets fracture

mainl y along strai ght lines, thus d=2Ja1o

2/n,

UTRACKI : FIBERS FROM POLYMERIC NANOCOMPOSITES ...,, _ , )

where a 1 and a" are the width and length of rec tangular flak e. If the rectangle has sides whose length rati o is I :3. the width and length of such a rlake wou ld be about 150 and 450 nm respecti ve ly. Thus. for smooth surface. the fiber diameter (longitudinally elongated flake) should be > 150 nm. However. when polymers are end-tethered to the clay platelet. on stretching the latter gets oriented in the transverse to stress (or fiber) direc tion. In consequence, the surface of sub-micron fibers might be rough. especiall y when the organoc lay is not full y exfoliated. Alternatively . one may mill the organoc lays or use synthetic clays with low aspect rati o, viz. p = 20-50. These clays offer additi onal advantages, e.g. selection of chemical composition to contro l conclucti vity, clyeabi I ity, etc. Furthermore, since synthetic clays are colorless, they allow generating bright and consistent colors (the mineral MMT is contaminated with Fe+' , coloring the CPNC from light ye llow to brown reel).

5.1 Elcctwspinning

In most reports where electrospinning was used, the fibers were produced from so lutions containing ca. 10-wt% of pol ymer or CPNC. The method resulted in the production of neat polymer fibers with diameters ranging from about 70 nm to 1000 nm (refs 49.50). The CPNC technology adds ex tra dimension to the range of applications of fibers and nanofibers. Ev identl y. suitab le CP C for the fiber manufacturing must possess several criteria , including the type, geometry. and concentration of nanoparti cle •. high degree of clay dispersion, miscibility of polymeric matrix and organoclay in se lected solvent(s). During electrospinning. fibers are formed from an electricall y charged po lymer liquid jet in the presence of elec tric potential. Accordingly, the electrospinnability may be defined as the ability of forming stable and continuous jet in the presence of an electric fi eld.

Fong et a/.51 are cred ited to demonstrate elcctrosp innability of CPNC first. The authors prepared CP C by melt compounding of PA-6 with Cloisite® 308 (C30B ; MMT intercalated with methy l tall ow di-ethoxy ammonium chloride. MT2ETOH)­the system known to y ield well -dispersed nanocomposite. For electrospinning, the compound was dissol vecl in hexafluoro-iso-propanol (H Fl P). Addition of di -methy l formamide (DMF) was found to aggregate C30B. pointing out the need for se lecti on of so lvent (s) misc ible with al l CPNC components. Hi ghly ori ented f ibers were produced with diameter

ranging from about 100 to 500 nm. but in additi on 100-200 nm thick and 10.000 nm wide ribbon s were obtained. The ori entation of MMT platelets was perpendicular to the fiber axi s. Thus, since the fi be r surface was smooth , one must infer that the longest dimension of MMT platelets in the product was less th an 100 nm, which may indicate attrition eiiher before or during processing. Unfortunately. the authors did not comment on the relati ve merits or C30B presence in the electrospun polymer.

Similarly , poly lactic acid (PLA) and PLA with 3-5 wt% C30B were electrospun from CHCh solution. 5c Again, smooth fibers with uniform diameter ranging from I 00 to 500 nm were reported. Incorporation of organoc lay resulted in formation of /)-PLA. reduction of the melting point by 10°C (to 140°C) and signifi cant decrease of PLA crysta llinity . The plast ica ting effects of C30B intercalant might be responsible for these changes.

M ore recentl y, electrospun fibers were prepared from DMF solutions of emulsion polymeri zed poly(methyl methacrylate-co-methacry li c acid) copolymers (PMMA-MA) or their nanocomposi t es. :i .~ In the latter case, Na-MMT (Cloisite®- a) or sodium tluorohectorite (Na-FH; a magnes ium silicate with aspect ratio: p :::; 6,000) was dispersed in emulsion of the monomers. After polymeri zati on, the M MT platelets were wel l dispersed. whereas FH formed ti ghtl y packed (c/0(11 = 1.04-1.1 9 nm). randomly dispersed stacks. Several observations were made: ( i) The presence of clays improved the electrospinnabi I ity through increased ex tensional viscosi ty and strain hardening (S H); (ii ) Additi on of clay resulted in reduction of fiber diameter. viz. 550. 350 and 320 nm for neat PMMA-MA, that with MMT, and that with FH respectively; (iii ) MMT was well di spersed and fiber surface was smooth: (i v) FH platelets were poorl y dispersed and protruded from fibers: (v) The ex foliated MMT clays increased the glass tran sition temperature and thermal stabi I i ty as well as reduced llammahi I ity and improved sel !'­ex tinguishing properti es through char formation.

These preliminary reports on CP C electro­spinnability point out that organoclay must be well dispersed (preferably ex foliated) and mi scible (internall y and w ith the solvent). Additi on or organoc lay that interacts with the matri x is expected to increase the elong.ati onal viscos ity and SH 1 -both des irable for improved spinnability and elimination or polymeric beads (observed on fibers from neat

I DIAN J. FIBRE TEXT. RES .. M ARCH 2006

po l yme rs). 5~ However, when organoc lay is immiscib le w ith matrix. the effect on flow is small . and the strain hardening is absent. For clec trospinnabi lity . the source of layered silicate migh t be important. Owing to vari ability of natural clay composition (from different geographic locations as we ll as from local strata). the MMT dielectric properti es vary, wh ich, in turn , may affect the CPNC electrospi nnabi I i ty.

5.2 Solution Spinning

These days the conventional so lution spinning method is se ldom used. However. for CPNC w ith water- so luble polymers the method may be attractive as it is non- tox ic, non-polluting and inexpensive. Water-soluble polymers include: polyv iny l py rrol idone (PVP), polyvinyl alcohol (PYA! ), poly ­glycols (e.g. ethy lene or propy lene: PEG or PPG), polyacrylic acid (PAA), etc. Additiona l advantage is th at in water, the clay (e.g. Na-MMT) may be full y exfo liated by adjusting pK and pH, and thus avo iding the cumbersome and expensi ve pre­intercalation 1. Evidently, these comments are al so va lid for electrospinning - the small est diameter nanofibers (ca. 70 nm) were obtained from aqueous sol utions 5~

The so lution sp inning was used to prepare fibers of PV AI with Na-MMT. The latter compound was f irst dispersed in water at room temperature and then PV A I was dissolved. The nano-suspension was filtered and spun.55 Fibers cou ld be obta ined only when MMT concentration was < 2wt% (on the total mass of CP C). While the degree of clay dispersion is not given. the reported properti es were improved. However, drawing (to unknown rati o) reduced the re lat ive va lues. viz. tensile modulus from 1.95 (as spun) to 1. 11 (drawn). strength from 1.11 to 1.10 and elongation-a t-break from 0.8 1 to 0.66. The CP C fibers showed improved thermal stability.

5.J 1\lclt Spinning

Melt spinning 1s the most common method. However, ow ing to large number of parameters invo lved, it is the most difficu lt to draw conc lusions from. The CPNC for spinning may be prepared by different methods: in many cases the vital informat ion (e.g. the clay concen trati on. level of clay dispersion. spinning parameters. the draw rati o) is not prov ided. The melt spinning is carried out at different temperatures and speeds using diversity of equipment and procedures .

The most consistent set of information originating from a single laboratory is available for fibers melt spun from CPNC w ith thermoplastic polyester (PEST) matrix. The early '-"Ork in volved thermoplastic LCP5

(' compounded with 2-6 wt% of Clo isite® 25A (C25A; MMT pre- intercalated w i th di -methy l hydrogenated tallow octy l ammonium sal t.

2MHTL8) in internal mi xer at 190°C, i .e. within the nematic zone. The fibers were produced using a capillary rheometer w ith 0.75 mm diameter die. Even at 2 wt% loading, T EM showed presence or clay stacks. In spite or poor di spersion, there was a significant enhancement of the tens i le modulus and strength .

Simi I ar resu Its were obtai ned for C PN C based on pol ybuty lene terephthalate (PBT)57

, PET58 or poly­trimethy l terephthalate (PTT).5

<J The re lative modulus, Efi, and relati ve strength. afi, was found to depend on the clay con tent, 1v, and draw ratio, D R:

... (3)

As the data in Fig. 5 demonstrate. the incorporati on o f C25A enhanced performance of LCP. However, the dependencies in Fig. 6 are more interes ting. They show that as DR increases, the performance of CPNC fibers fall s below that observed ror neat matri x (relative va lues < I ). Draw ing usua lly enhances crys tallinity of the polymer. However, in the case of PBT with organoclay, it resulted in CPNC softening and reducti on of tensile strength. T he most likely reason is the immisc ibility of intcrca lant w ith the matrix, which provides a stress releas ing interphase­the phenomenon we ll -known for poly mer blends. ~

en :J :J "0 0

,.. --. ~oR =1 .01+0 . 19w-0 . 0 1 7w 2 • r=0.989 ;

E 1.8 ~--------------------~

• - ER = 1.01 + 0.15w; r= 0.978

' LCP + C25A f J"'~ '""~ en c

./

/ /

/

... ... ··r ,

T 2 Q)

> :;:J

Ill a> IY 1(·-~------.L----------------~ lY 2 4 6

C25A organoclay (w) , wt%

f ig. 5--Rclative tensi!t: strength, a11 • and rcln tive tensile modulus. EH. o f LCP as a functi on of Cloisite® 25.A. -.:on tcnt at draw ralio: DR = t (ref. 56) .

UTRACK I: FII3ERS FROM POLYMERIC NANOCOM POS ITES 25

(/) 1.5 r-::---------,-----=--~ -?-aR = 0.355 + 1.10/DR

-g · - ER = 0.836 + 0.448/DR E

ol:! ..c OJ c ~ u:; Q)

(/)

c 2 Q) >

I 1 -

i l I I

·~ PBT with 3-wt% organoclayl Qj

0.5

_ Chang el a/., 2003 ~ 0 ---~------~~~~

0.4 0.8 1.2

1/DR

Fi g. 6- R..: Iati vc tensil e strength . rTfi. and relati ve tensile mod ulus. L'K. of PBT wi th 3 wt'.k orga noc lay as a functi on of in ve rse draw ratio. 1/DR (ref. 57).

A better mi scibi lity of organoc lay with PET or PTT matrices was ach ieved using an aromatic phosphine intercalant: dodecyl tri -phenyl phosphonium. DD3PhP. In add it ion to improved miscibility the organoclay (MMT-DD3PhP) was more thermall y stable - an important aspec t when the process ing temperature is 280°C.

Eq uati on (3) fit ted to the relati ve modulus, ER, of CP C with PTT as the matrix oave the followino 0 c parameters: a11 = 1.006 ± 0.05 1; a 1 = 0.133 ± 0.016: a 2 = 0: and a 3 = 0. 198 ± 0.036. The good ness of fit can be judged by the standard deviation, rr = 0.044 and the correlatio n coefficient squared, / = 0.9993. Since all parameters of Eq. (3) are non-negati ve, the relative modu lus ts always larger then an = 1.006 ± 0.05 1. thus £(C PNC) > £( PTT). For the relati ve strength. rr1( a0 = 1.24 ± 0.33: a, = -0.12 ± 0.23 : a2 = 0.026 ± 0.038 ; and o 3 = 0.300 ± 0.051: rr = 0.063 and / = 0.998. Thus. here the clay concentrati on has a secondary dfect to drawing, which red uces the CP C tensil e strength .

However, the reason for incorporating clay is not limited to tensil e properti es . For industrial appli cati ons, e.g. hot rinsin g in the pulp-&-papcr industry. the heat shrinkage of a PET filter is . t I d60 I I . . f. tmpor ant. t was repone t1at t1e Incorporation o 1.5 wt% MMT (pre-intercalated with PVP) into pre­polycondensation reactants reduced the heat shrinkage of PET-based CP C by ca. 12%.

Owing to a wide use of polyamides in the fiber industry , several research groups inves ti gated the effect of organoc lay addition on PA fiber

· . (•t -('5 I PA 6 I b . p10pert1es . n most cases - 1as een the matn x

(PA- 12 in ref. 62). The CPNC were prepared by melt co mpounding PA-6 with a variety of pre-intercalated MMT and probably by reactive intercalation (refs 61.62). The concentration of organoc lay ranged from I to 5 wt ~"/n . At the hi gh limit. the fibers showed surface roughness and irregular variati on of diameter. indi cating the presence of organoc lay aggregates or different size and properties r'2 Most organoc lays had i ntcrcalants with paraffinic groups, thus i mmisc iblc vvith PA matrix. As one of the conseq uences, the PA-6 crys tallin ity either was un affected or reduced by organoc lay. In spite of that , the tensil e mod ul us was enhanced, e.g. at 3 wt % of organoc lay by 40 % (DR

. f" I) (> I not spec1 tee .

Sim il arly as it was the case for CPNC with PEST matrix. the absolute and relative values of ten. ik modulus and strength of CP C fibers with PA matri x changed with DR . PA macromolecules can be bonded to clay platelets either covalentl y or by virtue of strong polar-po lar bonds 1

• When such bonding takes place, drawing is ex pected to be more benefici al !'or CP C than neat polymer fibers.

For example, PA-6 was compounded with I wt 7c or organoclay (MMT pre-intercalated with 2M20D A = di -meth yl di -octadecy l ammonium) in a TSE and then spun at 260°C, i.e. well above the limit of thermal stabilit y of 2M20DAf'' At DR = I , 1.5 and about 3. the relati ve modu lus (£~<) was respectively 0.90. 1.02 and 1.1 3. Furthermore. incorporati on of organoc lay i ncreascd the flame retardance and thermal stabi I ity (over that of PA)rl-l Thi s encouraging information notwith standing, the relati ve merit or cl ay incorporation into PA matri x awai ts the systematic. we ll -planned studies.

PP-based nanoco mpos ites also have been melt-1'6.h7 Tl CPNC spun. 1e was prepared by melt

interca lation in a TSE, fo ll owed by mel t spinning from a SSE. The compos iti on co mpri sed PP (MFR = 44 dg/min), 2 wt% PP-MA. 5 wt% unknown organoc lay and I wt % PS .66 Good spinnability was reported. The XRD and TEM indicated the presence of organoclay stacks (intercalation). The organoclay was found to nucleate crystallization of PP, increasing the crystallization rate and total crystallinity. but without affecting the crystal form . Considering the hi gh clay content, it was not surpri sing that the CP IC fiber surface was rough with many fl aws and grooves. However. thi s. in turn, improved the moisture absorpti on as well as dyeability of the PP fibers. The latter aspect is of particular importance, considering

26 INDIAN J. FIBRE TEXT. RES .. MARCH :2006

the wel l-known problems associated with clycability and printability or PP. Recentl y . it was round th at the presence or organoc lay (C ioisiteQi) 15 A = MMT-2M2 HTA : C l5 A) racilita tes boncli n!! of acidic and di<>persecl dyes.67 The dye adsorpti OJ; increased wi th the amount or organoclay in the system as well as \\'ith the degree of dispersion. However. the latter term refers mainly to ball milling C l5A prior to dispersing it in xy lene solution of PP by means of ultrasonication. Two reel mono-azo dyes (both having amino groups). Acid Reel 266 and Disperse Reel 65 . were used. Milling C 15A improved color uniformit y or dyed specimens.

From the fundame ntal point of view, the basic condi ti ons for ascertaining th at composi tes have hi gh modulus and st rength are: good adhesion between the reinforcing particles and the matri x. as well as filler orientation in the stress direction. Translating these to CPNC fibers. the desi red clements are: ex foliation. miscibility of the clay intercalant with the matrix and platelets orientation in the fiber direction. To sati "fy all three criteria is difficult. and the difficulti es increase with the processi ng temperature. For example. melt spinning of polyctherimide (PE l )

requires 345°C. At this temperature. even the high temperature organoclay is not stab le. The latter was prepared by interca lating Na-MMT wi th HCI salt of amino phenoxy benzene (APB):

Cl Cl . .

H3N. ~ 0 -~ 0 ~ NH3 l ~~-- -r J- --c. ~r '-../ ~ /

In the produced CP C. the clay dispersion was poor and the mechanica l properti es of CPNC fibers (with 3 wt% organoclay) were not improvcd68

: the modulus slightl y increased at a cost of loss of strength and elongation.

6 Conclusions The main reasons for incorporating organoc lay into

polymeric fibers are: i mprovcd spi nnabi I ity , stiffness. strength , heat deflection temperature, weatherability, biodegradability, moisture and dye absorpti on as well as reduced shrinkage, electrostatic charge, and flammability. These enhancemen ts are achieved with ~~ small increase of density and cost. At present, the use of CPNC for fiber spinning is in a preliminary, exploratory stage. Electrospinning, so lution spinning

and melt spinning of a vari ety of CP C were reported. Most work was carried out on nanocomposi tes wi th polymeric matrix or interest to fiber indu~try, viz. polyamides and thermoplastic polyesters.

It is imperative to recognize that for good performance of CPNC fibers. the bas1c material mu st be prepared observ ing the fundamental rule<. of CPNC manufacture. The key to CPNC performance is a high degree of clay dispersion, governed b) the th ermodynamics and clay concent rari,)n-cxfoliation i on ly possible ' hen the platelets can freely rotate in the matri X. e.g. be low abOUt 1.2 WtCJr Of clay with aspect ratio of 300. Incorporation or organoclay \\'<IS

found to improve spinnability. via tile increase or elongat ional viscosity and strain hardening. SH. The mechani sm for generating SH itwolvcs enhanced chai n en tanglements engendered by strong interacti ons between clay and the matrix.

The role or melt mixing or compounding is to accelerate the thermodynamically driven prOCl'<;S of 'd isso lu tion' of organoclay into a matri x. Recent progress in the ex tensional flow mixing offers a new technology for rapid clay dispersion.

In addition to natural clays, there arc se\·eral sy nthetic clay manufacturers offering layered silicates with well-controlled and reproduci ble geometry and composition. Their usc in the CPNC f iber application should be explored.

2M2 liT

2M20DA 2M B! IT

:2M HTLS

APB C 15A C25 /\ ClOB C-D CPNC DD3PilP DEFM DMF DR EFM EFM-N Fll FM Ff!R GP

Abbt·eviations and symbols used

di -methy l di-llydrogcnatccl tall'' "" ammonium chloride di-methyl cli -oc taclecy l arn rnuni um chloride di-methyl bcnzylllyclrogcnatcJ tall ow arnrnoniurn chlori de di-methy l hydrogenated tallow Pcty l ammonium sail amino phenoxy benzene Cloisitc~> I5A Cloi,ilc@ 25 A Cloisite(•> 30B convergenl-clivergent (plates. flow geomclry. etc.) c!Jy-eoniaining po lymeric tW tHlcomposiles cloclccy l tri -phcnyl phosphoni um. dynamic ex ten sional fl o" llli\cr di -methy l formarnicle (fiber) draw rati o ex tensional !low mixe r new EFM for dispersing nanopanicles synthetic fluorollectorite flu oro rnica Fourier transform infrared sp-:ctroscopy gear pump

Ill' II' II- IMT HRTEM liT !lTD ILl' MAll t--Ill MD

11-R MMT MPS

MT2E.TOII a- MMT

PA I'A- 12 i'J\ -6 PAA PA-111XD6

i>r\RA I'BD 1'13T I'E PEC I'EI PEST PET pll

pK !'LA Pt--lMA PM MA-MA

I'NC PO PI' pp(j

1'1'-1\ l i\ PI'T

PS PlT

PVAI 1'\'P scr SSE TI :M TSE

\ '

XRD

i'.G,"

"'" i'. /1111

,I.S"' E,,

UTRACK I: FIBERS f-ROM POLYMERI C NA OCOMPOSITES

h..:xarluoro-i 1o-propanol protonatccl MMT high-re,olution tr~msmi ss ion electron microscopy hectorit c heal deflection temperature liq uid crystal pol ymer maleic anhydride ma-, ter-batch molecular dynamic melt rlm1 rate llH lnlmnri llonite multi -pha.,e sy.,tems (bknds. composites and foam~ )

methy l tallow di -e thoxy ammonium chloride: sodium monunorillonite pol yamide polyamide- !:?.. or poly(clodecano-amide) pol yamicl..:-6. or poly-e-caprolactam pol yacrylic acid semi -aromatic poly( 111-X)' Ien..: eli -amine and adipic acid -< ·o-caprolactam) aromatic pol yamide p< llybutadicne pol yhuty lene tercph thalate pol ye t h) lcne polycth) lenc glycol pol:ctherimide thcnnop la~ ti c polyester pol ye thylene tercphth~tlatc negative logarithm of the effective H+ ion concentration ncg;11i1·e logarithm of the ionic constant K pol: lactic ~1cicl pol ymethy !methacry late pol) (methy l methacrylate-m-methacrylic acid) copolymer poly meric nanocompnsitcs pol yo lefin pol ) propylene polypropylene glycol maleatcd -PP polypropy lene terephthalate (also. poly- trim..:thy l tcreph thalate PTT) pol) ., tyrem: pol y- trimeth y l tcrcphthalatc (al so pol ypropylene tc:rephthalat e. PPT) pol yvinyl alcohol polyv in) I pyrrolidnne sci f-consistent fi eld single-screw ex truder transmi ssion electron micro,copy twin -screw ex truder ultr:11·iolct irradiation X -ray di !Tracti on

free energy of mixing

In's of matrix free vo lume

enthalpy o f mi xing

entropy of mi x ing relati ve tensile modulus 1nelting point

a 1. a2

tl d,H/1

1', ,.-\\ "

rJ,.

(Jill

width. length of rectangular clay flake c lay platelet average "diameter· interlayer spacing aspect ratio correlation coefficient squared clay content in wt% thickness of so lidi lice! polymer on clay surfacc volume fraction fillcr (clay) vo lume fracti on

surface energy per unit area. or ; urfacc tension standard deviation CPNC ten sile strength filler (clay) teJbile strength matri x tensile strength

cr,. = utf a ... erN =cr, /cr..,

ratio or tiller-to-matrix tensi!t: strcngth

relative tensile strengt h of CPNC

Rcfe•·ences I Utracki L A. Clar-Conwining Pol\'n/eric Nanocon/f!Oiiln

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