The Structure and Properties of Polymer Composite ... - Springer Link

ISSN 19950780, Nanotechnologies in Russia, 2010, Vol. 5, Nos. 5–6, pp. 340–351. © Pleiades Publishing, Ltd., 2010. Original Russian Text © T.S. Kurkin, A.N. Ozerin, A.S. Kechek`yan, O.T. Gritsenko, L.A. Ozerina, G.G. Alkhanishvili, V.G. Sushchev, V.Yu. Dolmatov, 2010, published in Rossiiskie nanotekhnologii, 2010, Vol. 5, Nos. 5–6.

ARTICLES

The Structure and Properties of Polymer Composite Fibers Based on Poly(vinyl alcohol) and Nanodiamond of Detonation Synthesis T. S. Kurkina, A. N. Ozerina, A. S. Kechek’yana, O. T. Gritsenkoa, L. A. Ozerinaa, G. G. Alkhanishvilia, V. G. Sushchevb, and V. Yu. Dolmatovb a

Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Science, ul. Profsoyuznaya 70, Moscow, 117393 Russia b ZAO Almaznyi Tsentr, Sovetskii pr. 33a, St. Petersburg, 193177 Russia email: [email protected] Received January 24, 2010; in final form, February 10, 2010

Abstract—The structure and properties of the oriented poly(vinyl alcohol) fibers modified with nanodia monds (NDs) and nanodiamond soot (NS) of detonation synthesis were investigated by wideangle and smallangle Xray scattering methods, as well as by electron microscopy and mechanical testing methods. It was shown that the introduced nanodiamond soot particles were dispersed within the polymer matrix while maintaining a high dispersion level without aggregation. The NS treated with ultrasound was found to be a more effective modifier of the mechanical properties of the oriented fibers than untreated soot and NDs. The maximum increase in the longitudinal elastic modulus over nonmodified fibers (from 30 GPa up to 45 GPa) and in the energy stored by oriented fiber modified with NS upon breaking (from 3 up to 6 J/g) was obtained at a small (1% by volume) soot content, which is technologically attractive. The values of the adhesive strength of the soot modified with ND (1%) with volume poly(vinyl alcohol) fibers in the epoxy matrix were measured, and the maximally achieved value (42 MPa) was higher than the adhesive strength of the nonmod ified fibers and comparable with the value of the reference sample (steel wire (57 MPa)). DOI: 10.1134/S1995078010050095

INTRODUCTION The use of polymer composites is important in those fields of industry where high specific values of the mechanical characteristics of materials are required. The mechanical properties of a composite material are determined by the properties of its rein forcing and matrix elements, as well as by the charac ter of their interaction. In recent years, the design of socalled polymer nanocomposites, in which the dispersion level of the reinforced phase is situated in the nanometer range, is a recognized trend in the development of new types of composite materials. This approach makes it possible to control the structure of the material via a transition from simple volumefilled systems to systems with a defined spatial distribution of the reinforcing element (nanofiller) and defined permolecular architecture [1–2]. A particularly clear difference in the properties of “classical” and nanocomposite polymer materials is observed if the characteristic dimensions of the filler particles are close to the radius of gyration of the poly mer chain or to the characteristic dimensions of the macromolecular morphological structural elements (long periods of crystal grain dimensions in the amor phouscrystalline structure, domain dimensions in the structure with microphase separation, the distance

between junctions in the network structures, etc.) [2– 4]. It was shown [5] that the nanosized filler interacts with the polymer matrix in a very complicated man ner, and, for this reason (for example, for the modifi cation of the mechanical properties of the composite material), it is often impossible to fully achieve high values of the anisometric degree for nanofiller particles such as carbon nanotubes and lamellar alumosilicates. Another peculiarity of nanocomposite materials is the high value of the interphase specific area of their superfine filler particles. The surface of nanoparticles usually contains a large amount of different functional groups, and their interaction with the matrix could be controlled to provide, for example, a more effective transfer of external loads from the polymer binder to the filler [6]. Out of all the different fillers currently in use as effective modifiers of the properties of polymer matrixes, nanodiamonds (NDs) obtained in industry by detonation synthesis [7] are the most promising for new types of polymer nanocomposites being designed with improved properties. ND particles have dimen sions on the order of 10–20 nm [8], which corre sponds to the range of characteristic dimensions in the macromolecular systems (see above); they possess a high specific surface area and a large amount of func tional groups of different chemical structures on the surface [9]. NDs are characterized by high sedimenta

340

THE STRUCTURE AND PROPERTIES OF POLYMER COMPOSITE FIBERS

tion stability in polar solvents, for example, in water and dimethylsulfoxide [10]. A more attractive filler, from the viewpoint of the modification of mechanical properties of large capac ity polymers, is the original product of nanodiamond synthesis (nanodiamond soot (NS)) whose cost of industrial production is essentially lower than the cost of purified and fractionated NDs. It is known that the elemental composition and structure of NS depend on the conditions of the deto nation synthesis. Using an assembly of experimental techniques, it was established that the NS particles are diamond nanoclusters with a cubic lattice covered with carbon shell of complex composition consisting of “onionlike” carbon, graphite, and admixtures of metal compounds [11–13]. The surface of NS, like that of NDs, is saturated with functional groups of dif ferent chemical structures. The properties of nanocomposites based on ND and different polymer matrixes were investigated in [14–23]. It was found that introducing NDs into the polymer matrix leads to a considerable change in the mechanical characteristics of materials [14–20], an increase in their heat capacity [21], or the appearance of proton conductivity [22]. It was also shown that NDbased nanocomposites could serve as the basis for manufacturing selective membranes, sensors, and materials with nonlinear optical properties [23]. Although from the technological viewpoint, the usage of NS is more advantageous than that of NDs, until recently NS use was restricted only by the modi fication of the properties of rubber, elastomers, and thermoelastoplasts [24, 25]. Therefore, the limited field of NS application is connected with the difficul ties of standardization and unification of its properties. In [26] it was shown that this problem could be suc cessfully resolved, for example, by using the method of thermodesorption mass spectrometry. In the above mentioned publication, the methodical approaches to the certification of NDs are discussed; however, the experimental procedure described is fully applicable for the certification of NS. An analysis of publications referring to the design of polymer nanocomposites based on NDs and NS has shown that the structural peculiarities and properties of such materials in the highly oriented condition (for example, microfibers) have not been very well investi gated. This is substantially connected with the difficul ties of retaining the high dispersity level of the filler and the control of the character of its distribution in the matrix at the orientation stretching of the compos ite material. However, the production of highly ori ented nanocomposite materials with improved mechanical properties is undoubtedly the actual task. It has been supposed that a composition based on the poly(vinyl alcohol) (PVA) modified with NS can be used as an interesting and informative system for investigating the peculiarities of the structure and NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

341

properties of polymer nanocomposites at a highly ori ented condition. Indeed, PVA is a largecapacity polymer that has a theoretical elastic modulus with a relatively high value (~80 GPa). Its spinning from the solution with the for mation of highly oriented threads and fibers is a well characterized technological process [27–29]. Also, in the chemical structure of PVA, a lot of polar hydroxyl groups are present, which can be used to adjust the interaction between macromolecules and functional surface of the ND and NS particles, as was recently shown in [30]. Finally, the main industrial solvent for the solution spinning of PVA fibers is a mixture of dim ethylsulfoxide (DMSO) with water. It was found [10] that, in the two particular solvents mentioned, the sed imentation stability of ND particles is the highest of several other organic solvents, which is an advanta geous factor for the successful spinning of PVA fibers with dispersed filler. In this work, the production method and properties of highly oriented PVA fibers modified with NS are described. The structural peculiarities of the nano composyte fibers revealed by wideangle and small angle Xray scattering methods and optical and elec tron microscopy are discussed, and their mechanical and adhesion characteristics are determined. The results are compared with the results from highly ori ented PVA fibers modified with ND. EXPERIMENTAL To prepare nanocomposite fibers, highmolecular weight PVA with M = 220000, the synthesis of which is described in [27–30], was used. NDs (UDASTP by TU 0512144127595 grade) and standard NS (Diamond Center, St. Petersburg) in the form of powders were used as highly disperse fill ers. To remove the residual admixtures of organic compounds, NS was treated with oxylene at 144°C for 1 h, filtered using paper filter, and dried in an exic cator connected with waterjet pump for 30 min at ambient temperature before usage. NDs were used without additional purification. The test portion of NS, calculated using the test portion of the polymer and the concentration of the filler which was leaned in the experiment plan, was redispersed in a DMSOwater mixture (mass ratio 80 : 20) at ambient temperature, and the suspension (vol ume of ~25 ml) was subjected to ultrasonication (the useful power was ~75 W and exposure was 2 min). PVA was added to the stabilized NS suspension at ambient temperature. The mixture obtained was heated during mixing up to 110°C, and the mixing was continued at a constant temperature for 6 h until a uniformly col ored solution was obtained. After degasification to remove air bubbles, the solution was stored until the gel matured for 24 h at ~0°C. The constitutions of the compositions obtained are shown in Table 1. 2010

342

KURKIN et al. 1 2 3

4

Scheme. A schematic representation of the sample prepa ration for the adhesive tests: (1) the fiber, (2) the binding substance, (3) the supporting plate, and (4) the aluminum cup.

For comparative investigations, several composi tions of PVA with NDs and NS without ultrasonica tion and the PVA solution without nanomodifiers were prepared using the same method. By pressing between objectplates, films were pre pared from compositions of PVA with NS and inclu sioned with water for 24 h, followed by being dried in an oven at 70°C. The xerogel films with thicknesses of 100–200 μm that were obtained were used to evaluate the effectiveness of NS introduction into PVA by mea suring the intensity of smallangle Xray scattering. The monofilamentfiber spinning was performed using a SpinLine (DACA Instruments) laboratory device to spin and stretch the fibers. The matured gel was loaded into a camera of the spinning device at ambient temperature and heated to 85°C. After heat setting (1–2 min), the gel was formed by the dryand wet method in two variants: (a) through the round spinneret with a diameter of 1 mm (such fibers will fur ther be referred as “thick” fibers) and (b) through a round spinneret with a diameter of 0.3 mm (“thin” fibers). The spinning rate was 1 m/min; the thread col O CH2 CH CH2O

CH3 C CH3

lection was performed in the deposition tank (isopro panol, ambient temperature). The hardened fiber was subjected to the plasticized stretching (fivefold at ambient temperature) and two phase orientation stretching (2fold at 190°C and then 1.5fold at 218°C) similarly to the procedure described in [20]. The diameter of the maximum ori entated thin and thick fibers was found to be ~90 and ~40 μm, correspondingly. The mechanical characteristics of these orientated fibers were measured using a Shimadzu AGS10 mul tiplepurpose test devise. The tests on monoaxial stretching until it broke were performed using mono fibers at ambient temperature on a gage length (the initial length of the fiber) of 100 mm and a clamp mov ing rate of 10 mm/min. Xray measurements at small angles were per formed using the Bruker NANOSTAR instrument with a doubledimensional coordinate detector on CuKα radiation. The value of the scattering vector modulus s = 4πsin(θ)/λ, where 2θ is the scattering angle and λ = 0.1542 nm is the wavelength of the radi ation, was used as a coordinate of the smallangle scat tering. Photoroentgenograms of the samples in the wide scattering angles for monofilament fibers were obtained using the same devise. The Xray pattern in wide angles were registered on a Bruker D8 diffractometer equipped with a focusing germanium monochromator crystal on the primary beam (CuKα radiation) in transmission mode in a scatteringangle range of 2θ = 10–100°C. The adhesion strength of the nanocomposite fibers in the polymer matrix was measured by the technique of fiber pullout from the matrix of the binding sub stance [35] using the Shimadzu AGS10 multiple purpose test devise at ambient temperature, a gage length of 20 mm, and a clampmoving rate of 0.4 mm/min. A schematic representation of the sam ple preparation for the adhesive tests is shown below. Compositions based on the epoxy resin ED20 were used as a binding substance:

O CH2 CH CH2O OH

In composition 1, the hardener was the aromatic diamine μphenylenediamine (MPDA) and, in com position 2, the hardener was triethanolamine titanate

n

O

CH3 C CH3

OCH2 CH

CH2

(TEAT). To reduce the viscosity of the binding sub stance, diethylenglycoldiglycidyl ether (DEG1) was used:

O CH2 CH CH2 O CH2 CH2 O CH2 CH2 O CH2 CH CH2 OH

O CH2

CH

CH2

n

NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

2010


343

DV, % 13 6 6

22

4

2

0 Fig. 1. Microphotographs of NS prepared by quickly applying the suspension to the support. The mark size is 50 nm.

The adhesion strength of the fibers in the composi tions was compared with the measured adhesion strength of the OVS150 steel wire (with a diameter of 150 μm) in the same compositions. The composition constitutions and the hardening regimes are presented in Table 2. RESULTS AND DISCUSSION It is evident that an important element of conduc tion investigations is determining the quantitative characteristics of the structure of the filler itself. In order to do that, the detailed Xray and electron microscopic studies of NDs and NS for different vari ants of the sample preparations were performed. The main result of investigations obtained by transmit tance electron microscopy is presented in the Fig. 1. Though the NDs and NS dispersed in liquid water, waterorganic, or organic medium are always partially agglomerated, in the case of the their “ideal” disper sion (Fig. 1) only two main structural elements can be found in it: “embrionic” nanoparticles with the size of 5–6 nm (and their “dimers” with the dimensions of 12–13 nm) and larger planar particles with cross dimensions of 20–30 nm (Figs. 1, 2). Functions of the particle size distribution differing little from the one presented in Fig. 2, were also found for the other ND and NS samples obtained by differ ent methods and chemically treated and purified in NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

10 20 The particle diameter, nm

30

Fig. 2. Size distribution of NS particles from Fig. 1.

different ways. This interesting result should be dis cussed in details elsewhere. The question of the dispersion level of ND and NS nanoparticles introduced into the condensed PVA matrix required additional investigation. In order to do that, the method of measuring of the smallangle Xray intensity to evaluate the degree that filling is achieved (the ratio of the net amount dispersed in the polymer matrix in the nanometers size range to the gross amount of the modifier introduced) was used. Since the greatest interest (due to the practical importance of the result) was in the measurements for the samples of PVA filled with NS, the following results will be restricted by an investigation of the structure and properties of PVANS compositions. It is known [36] that, for the scattering particles with dimensions of 1–100 nm (nano range!), the intensity of smallangle Xray scattering i(s) is related to the absolute intensity of the primary beam radiation I0 and the power of the scattering for the sample SV by the Porod ratio (Porod invariant Q): ∞ 2

2π I 0 S V =

∫ i ( s )s ds = Q . 2

0

The value Q can be determined experimentally from the integral intensity of the smallangle scatter ing. In turn, for the scattering power SV , one can use the ratio 2010

344

KURKIN et al.

during the measurements are constant (which is easily adjusted by the corresponding normalization of the scattering intensity)), for two scattering objects with the registered intensities i1(s) and i2(s),

log(I) 4

1 2 3

∞

∫ i ( s )s ds 2

4

1

2

S V1 Q 〈 Δη 1 〉 0 1 = = = . ∞ 2 Q2 S V2 〈 Δη 2 2〉 i 2 ( s )s ds

5

(1)

∫ 0

2

It is also known [36] that, for a twophase scattering system, 6

2

(2)

where W1 and W2 are the volume fractions of the scat tering phases; W1 = 1 – W2; and η1 and η2 are the elec tron densities of the scattering phases, which are pro portional to their mass densities ρ1 and ρ2. In the case of amorphouscrystalline polymer, W1 and W2 values are the volume fractions of the phases; for the polymer nanocomposite, they are the volume fractions of the filler and polymer, correspondingly.

0

−1

0

log(s)

Fig. 3. Smallangle Xray patterns for PVA films contain ing (1) 3, (2) 2, (3) 1, (4) 0.5, and (6) 0 vol % of NS, (5) scattering of polyethylene. 2

S V = K 〈 Δη 〉 , where 〈Δη2〉 is the meansquare fluctuation of the electron density in the scattering system and K allows the value of the illuminated volume of the sample V and the geometry of the device for the registration of the scattered radiation (the wavelength of the radiation and the distance between the sample and the registra tion plane). In the case of measurements performed on the same instrument (provided that the I0 and V values Table 1. The compositions of solutions for the formation of modified fibers and films The composition of No. of the forming solu tion, compo sition DMSO/water/PV A/NS, mass parts 1 2 3 4 5

2

〈 Δη 〉 = ( η 1 – η 2 ) W 1 W 2 ,

80/20/15 80/20/15/0.21 80/20/15/0.42 80/20/15/0.84 80/20/15/1.26

The composition of the fiber/film PVA 100 vol %/NS 0 vol % PVA 99.5 vol %/NS 0.5 vol % PVA 99 vol %/NS 1 vol % PVA 98 vol %/NS 2 vol % PVA 97 vol %/NS 3 vol %

If the value 〈Δη2〉 is known for any standard scatter ing sample, then by measuring the intensity of small angle Xray scattering for this sample and for the test sample in the same experimental conditions and by determining the invariant Q values by using ratio (1), one can find the value of the meansquare electron density fluctuation 〈Δη2〉 in the test sample; then by using ratio (2), one can determine the volume fraction of the nanofiller using the literary data for the densities of the filler and polymer matrix. The deviation of the values of the filler volume fraction in the polymer matrix determined in such a way from the value deter mined from the initial loading of the components will mean that part of the filler does not disperse in the matrix up to the nanosized level, forming aggregates and agglomerates of submicron and micron sizes, the scattering of which does not hit the registering range of the smallangle Xray scattering. The method described above allows us to characterize the value of the degree of implementation of the polymer matrix filling. In this work, the sample of slowly crystallized poly ethylene with a volume fraction of the crystalline phase of 50% and wellknown values of the densities of the crystalline phase (ρC = 1.00 g/cm3) and amor phous phase (ρA = 0.86 g/cm3) was used as a standard scattering sample for the following calibration. In Figs. 3 and 4, smallangle Xray scattering pat terns from the films of compositions 1–5 (Table 1) and polyethylene, which was used as a standard for the intensity normalization, normalized to the intensity of the primary beam, absorbance, exposure, and the value of the irradiating volume, are presented.


Vol. 5

Nos. 5–6

2010

THE STRUCTURE AND PROPERTIES OF POLYMER COMPOSITE FIBERS I*s2, relative units 1.5

345

The affective NS content, vol % 4 Gross amount of NS, vol %

1 1.0

2 2

k = 0.98

0.5 3

0

4 0

5 6 0

1

2 3 1 Gross amount of NS, vol %

Fig. 5. The degree of implementation of PVA filling, depending on the gross amount of NS introduced.

2

s, nm−1

Fig. 4. Smallangle Xray patterns in the coordinated Is2– s for PVA films containing (1) 3, (2) 2, (3) 1, (4) 0.5, and (6) 0 vol % of NS. (5) Scattering of polyethylene.

From the data presented in Figs. 3 and 4, one can conclude that the smallangle Xray diffraction of the tested samples is caused mainly by the contrast between PVA (ρPVA ~ 1.22 g/cm3) and NS particles, the pycnometric specific gravity of which is close to the density of NS and is equal to ρNS ~ 3.2 g/cm3 [37]. The dependence of the filling by NS (calculated from the smallangle scattering intensity degree of implementation of the polymer matrix) on its intro duced gross amount is shown in Fig. 5. The dependence obtained within the experimental error is straight line with a slope coefficient equal to 1. This means that, under the introduction of NS into PVA, it dispenses in the matrix in a highly dispersed condition. This result is nontrivial, since usually the degree of implementation of filling is less than 1 (for example, due to the formation of nanoparticle aggre gates of submicron and micromicron size ranges) and it depends mostly on the filler type (on the structure of its surface) but not on its dispersion in the original state. Let us point out that the prior ultrasonication of fillers, as was expected, led to additional dispersion in NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

the optical size range both in the liquid phase and in the polymer matrix (Fig. 6). At the same time, at the level of nanometer sizes, ultrasonication does not influence the dispersion of the filler, which follows from the data of smallangle Xray scattering (Fig. 7). It is obvious that the data of optic microscopy and smallangle Xray scattering will not contradict with each other if one assumes that visible (in the optic range of sizes) creations are spongy agglomerates of highly disperse NS particles. A more detailed investi gation of this problem should be performed in future studies. The introduction of ND and NS nanoparticles into the PVA matrix led to a change in the mechanical characteristics of the oriented fibers (Figs. 8a–8d). The results presented in Fig. 8 evidence that the most considerable effect of modifying mechanical properties of oriented PVA fibers is achieved when the filler is NS previously treated with ultrasound. For the same type of filler, the maximum increase in the values of longitudinal elastic modulus and the deformation energy upon breaking are achieved at the minimal among the tested fillertype content of the filler (1 vol %), which is a technologically attractive result. It was found that the considerable increase in the longitudinal elastic modulus value (~40%) upon filling with NS (1 vol %) observed in Fig. 8a does not corre 2010

346

KURKIN et al.

10 μm

(а)

(b)

10 μm

Fig. 6. Optical photomicrograps of PVA films with NS: (a) previous ultrasonication of the suspension (composition 3 from Table 1) and (b) NS without additional treatment.

late with the change in the mean molecule orientation in it. Indeed, the halfwide Δ of the azimuth distribu tion of intensity of the most powerful equatorial reflex of PVAhaving indexes 101 (Fig. 9), which represents the degree of the function of the fiber’s molecular ori entation and the decrease of which corresponds to an increase in the macromolecules orientation in the direction of the oriented stretch, is 7.5° and 8.0° for the nonmodified PVA fiber and for the fiber with 1 vol % of NS, correspondingly.

I, relative units 10000

1000

100

10 1, 2 1

0.5

1.0 s, nm−1

1.5

2.0

Fig. 7. Smallangle Xray patterns of the NS water suspen sion (1 vol %) (1) without ultrasonication and (2) after treatment for 8 min.

Since the longitudinal elastic modulus of the non filled oriented polymers is unambiguously deter mined by the orientation of the molecules along the direction of stretching [38], the pointed effect of the increase of the modulus is caused only by the interac tion of NS with the polymer matrix, but not with the difference in the orientation degree of the macro molecules in the fiber, which was practically unchanged for all other constitutions of the PVANS compositions tested. This is the most simple way to explain the result obtained, if one supposes the existence of a specific interaction between hydroxyl groups of PVA mole cules (similarly to the formation of weak hydrogen bonds or cooperative dipoledipole interactions) with the polar functional groups on the surface of NS parti cles (carboxylic, carbonyl, etc.), which are revealed by thermodesorption mass spectrometry and IR spec troscopy not only in NDs [26], but also in the NS, as our previous studies have shown. NS particles in this case will act as an active filler of polymer matrix, lead ing to it reinforcement. It is important for such inter action to have a dynamic character (a “sliding joint” on the meshing network) and to not obstruct the rein forcement of the fiber at the orientation stretching, since otherwise we will see, as is observed for other polymer crosslinked systems, a significant decrease in the relative strain and energy of fiber deformation at break values. In principle, developing the specific interaction of NS with polymer molecules is possible not only in the fiber volume, but also on its surface, for example, upon the placement of the polymer fiber into the polymer matrix of binder, which should lead to changes in the adhesion characteristics of the modified PVA fiber. Indeed, in Figs. 10 and 11, the stressstrain curves for the original PVA fibers and thick and thin ones modified with NS, obtained while changing their adhesion to the binding systems based on the ED20 epoxy resin (Table 2) using the “pullout” method, are presented. The data presented in Figs. 10 and 11 show that a break in the contact between the fiber and the binder not only has an adhesive character, but it happens


Vol. 5

Nos. 5–6

2010

THE STRUCTURE AND PROPERTIES OF POLYMER COMPOSITE FIBERS E, GPa

Strength, MPa 1800

(a)

347

(b)

45 1

2

1600

3

40 1400

3

2 35 1200 1

0

1000

4 6 2 Degree of filling, vol %

(c) Breaking extension, %


(d) Specific energy at break, J/g

5

6 2 3

5

1

4 4 1

2 3

0


4 6 8 2 Degree of filling, vol %

Fig. 8. The dependence of (a) the longitudinal elastic modulus, (b) the break strength, (c) break stretch, and (d) the specific energy stored in the thin fiber upon breaking on the degree of filling for different nanomodifiers: (1) NS with ultrasonication of suspension, (2) nanodiamonds ([20]), and (3) NS without previous ultrasonication.

according to the mixed adhesioncohesion mecha nism, which usually evidences the penetration of a binder into the fiber on some depth. It was also found that the effect of PVA fiber modi fication develops on the adhesion characteristics in an unusual fashion. Thick and thin fibers of the same NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

composition obtained at the same conditions interact with the binder matrix in different fashions. The thick fibers containing 1 vol % of NS by the adhesion strength, according to the ED20/MPDA system, practically do not differ from nonmodified fibers; the thin fibers of the same composition, according to their 2010

348

KURKIN et al. Stress, MPa 5 Δ 2

30 4

1

–20

–10 0 10 Azimuth angle ψ, degrees

20

20

Fig. 9. Roentgenogram of the thin PVANS fibers (the direction of the oriented stretching is vertical) and the functions of the azimuth distribution of the intensity of the most powerful equatorial reflex of PVA having indexes 101. NS content: 0 vol % is shown by a solid line on the left and 1 vol % is shown by a dotted line at right.

adhesion strength, exceed the thin nonmodified fiber almost by 50% (Fig. 10). For adhesion in the ED20/TEAT system (Fig. 11), the abovementioned tendency remains, but the effect of modification in this case is expressed more weakly. The adhesion strength of the thin fiber with 1 vol % of NS exceeds the adhesion strength of the nonmodified fiber by 16%. In the both cases, the adhesion strength of the modified thin fibers is compatible to the adhesion strength of the etalon sample (the steel wire). One possible reason for the different behavior of thick and thin modified fibers in the adhesion experi ments could be the different structure of their surface layer, through which it interacts with the binder matrix. We can suppose that this difference is intro duced by the fiberspinning stage. It is known that loading the gel into a collecting bath is accompanied with the microphase separation Table 2. The constitution of the binder composition and hardening regimes No. of compo The constitution of Hardening regime sition the binder, mass parts 1

ED20: 100 MPDA: 20 DEG1: 15

50°C, 45 min 70°C, 45 min 100°C, 45 min 150°C, 45 min

2

ED20: 100 TEAT: 11 DEG1: 10

50°C, 45 min 70°C, 45 min 100°C, 45 min 150°C, 45 min

2

3 1

10

0

2

4

6

Strain, % Fig. 10. Stressstrain curves of the thick (1, 2) and thin (3, 4) PVA fibers upon determining their adhesion to the ED 20/MPDA system (composition 1, Table 2). NS content in the composition: (1, 3) 0 vol % and (2, 4) 1 vol %. The curve (5) was obtained for the OVS150 steel wire under the same conditions.

process (swollen polymer/polymer solution) with the diffusion of the precipitant into the fibers volume. Upon being in the precipitation bath for an equal amount of time, the thin fibers turned out to be fully hardened and, in the thick fibers, the hardening pro cess could proceed not in the full volume of the fiber but only in a certain level on its surface (“the shell”). Here, the density of the fiber shell as a rule is higher then the density of the fiber “core.” As a result of the structure of the fiber crosssection of the coreshell type forming, NS particles could be displaced from the hardened shell into the core, thereby the NS concen tration in the shell decreases and, according to its adhesion characteristics, the thick modified fiber becomes closer to the nonmodified fiber. In the thin fiber, NS is not displaced from its surface because of the uniformity of the volume hardening (the cross sec tion is uniform), no decrease of the NS concentration in the surface level occurs, and the adhesion strength of the fiber caused by the specific interaction of NS particles with the binder matrix increases. The strength of NS interaction with the matrix will be determined by the functional composition of the NSparticle surface and the chemical structure of the


Vol. 5

Nos. 5–6

2010


349

Stress, MPa b

5

4 40 3

2 1 a

20

380 um Fig. 12. Microphotographs of (a) thick fiber (composition 3, Table 2) with a cut shell and (b) core.

0

2

4

6

Strain, % Fig. 11. Stressstrain curves of the (1, 2) thick and (3, 4) thin PVA fibers upon determining their adhesion to the ED20/TEAT system (composition 2, Table 2). NS con tent in the composition: (1, 3) 0 vol % and (2, 4) 1 vol %. The curve (5) was obtained for the steel wire OVS150 under the same conditions.

Δ 1

binder. This is probably the reason why the adhesion strength of the modified fibers measured in the present work depends on the structure of the binder. This makes it possible to optimize the adhesion interaction of the fibers with the matrix for the following practical applications, both by changing the functional compo sition of the NSparticle surface and through a change in the chemical structure of the binder. To confirm the correctness our assumptions, the sur face level (shell) of the thick fiber containing 1 vol % NS was cut (Fig. 12). The fiber passing only one stage of the orientation stretching at 190°C was investigated, because the attempt to cut the fully oriented fiber was not successful. A comparison of the wideangle photoroentgeno grams for the cut shell and core of the fiber presented in Fig. 13 shows that the shell is more oriented than the core. The halfwide Δ of the azimuth distribution intensity of the PVA reflex having indexes 101 was found to be 19.0° and 16.5° for the core and shell, cor respondingly. As was expected, the displacement of NS particles from the hardened shell of the thick fiber into the non NANOTECHNOLOGIES IN RUSSIA

Vol. 5

Nos. 5–6

2

–20

–10 0 10 Azimuth angle ψ, degrees

20

Fig. 13. Roentgenogram of the core and shell of a thick fiber from Fig. 12 (the direction of the oriented stretching is vertical) and the functions of the azimuth distribution of the intensity of the most powerful equatorial reflex of PVA with indexes 101. The core is shown by the solid line on the left and the shell is shown by the dotted line on the right.

hardened core should result in a decrease in the NS concentration in the shell and to an increase in the NS content in the core. We suppose that this is the reason for the improvement of the shell orientation observed by Xray analysis (facilitated shear and nonhampered orientation of the macromolecules at stretching) over the orientation of the core (shear and orientation are complicated by the “dynamical crosslinkages” inter acting with PVA NS particles). 2010

350

KURKIN et al.

CONCLUSIONS Let us point out that the values of the physico mechanical characteristics of PVA fibers modified with a small amount of NS (one of the cheapest nano modifiers) confirm the economical appropriateness of using modified PVA fibers as a perspective reinforced element of the constructional composite materials. Thus, in this work, the following was found: (1) ND and NS are effective modifiers of the phys icomechanical properties of the oriented PVA fibers. (2) Nanosized NS particles in the PVA matrix retain a high level of dispersion without aggregation up to a filling degree of 3 vol %. (3) The previous ultrasonication of NS induced into the fiber promotes a more significant change in the mechanical characteristics of the oriented PVA fibers when compared to nontreated ND and NS. Maximum values of the longitudinal elastic modulus and the energy stored by the modified PVA fiber upon stretching it until it breaks is achieved at a small (1 vol %) NS filling value, which is technologically attrac tive. (4) The adhesion strength of the oriented PVA fibers modified by NS in the epoxy matrix substan tially exceeds the adhesion strength of the nonmodi fied fibers, and it is comparable with the adhesion strength of the etalon sample (steel wire). REFERENCES 1. R. A. Vaia and J. F. Maguire, Chem. Mater. 19, 2736– 2751 (2007). 2. A. C. Balazs, T. Emrick, and T. P. Russell, Science (Washington) 314 (5802), 1107–1110 (2006). 3. F. M. Erguney and W. L. Mattice, Polymer 49, 2621– 2623 (2008). 4. M. Vacatello, Macromol. Theory Simul. 12, 86–91 (2003). 5. D. W. Schaefer and R. S. Justice, Macromolecules 40 (24), 8501–8517 (2007). 6. P. Ajayan, L. Schadler, and P. Braun, Nanocomposites Science and Technology (Wiley, Weinheim, 2003). 7. V. Yu. Dolmatov, M. V. Veretennikova, V. A. Mar chukov, and V. G. Sushchev, Fiz. Tverd. Tela (St. Peters burg) 46 (4), 596–600 (2004) [Phys. Solid State 46 (4), 611–615 (2004)]. 8. A. N. Ozerin, T. S. Kurkin, L. A. Ozerina, and V. Yu. Dolmatov, Kristallografiya 53 (1), 80–87 (2008) [Crystallogr. Rep. 53 (1), 60–67 (2008)]. 9. V. Yu. Dolmatov, Usp. Khim. 70 (7), 687–708 (2001). 10. M. Ozawa, M. Inaguma, M. Takahashi, F. Kataoka, A. Kruger, and E. Osawa, Adv. Mater. (Weinheim) 19 (9), 1201–1206 (2007).

11. A. E. Aleksenskii, M. V. Baidakova, A. Ya. Vul’, and V. I. Siklitskii, Fiz. Tverd. Tela (St. Petersburg) 41 (4), 740–743 (1999) [Phys. Solid State 41 (4), 668–671 (1999)]. 12. P. Chen, F. Huang, and S. Yun, Carbon 41 (11), 2093– 2099 (2003). 13. X. Tao, X. Kang, and Z. Jiazheng, Mater. Sci. Eng. 38 (1–2), L1–L4 (1996). 14. A. P. Korobko, Yu. M. Milekhin, S. V. Krasheninnikov, N. I. Shishov, I. V. Levakova, S. N. Chvalun, L. A. Oze rina, T. A. Bestuzheva, S. N. Drozd, and E. A. Butenko, Vysokomol. Soedin., Ser. A 46 (9), 1558–1569 (2004) [Polym. Sci., Ser. A 46 (9), 965–973 (2004)]. 15. A. P. Korobko, N. P. Bessonova, S. V. Krasheninnikov, E. V. Konyukhova, S. N. Drozd, and S. N. Chvalun, Diamond Relat. Mater. 16 (12), 2141–2144 (2007). 16. O. Shenderova, T. Tyler, G. Cunningham, M. Ray, J. Walsh, M. Casulli, S. Hens, G. McGuire, V. Kuz netsov, and S. Lipa, Diamond Relat. Mater. 16 (4–7), 1213–1217 (2007). 17. K. Behler, A. Stravato, V. Mochalin, G. Korneva, G. Yushin, and Y. Gogotsi, Am. Chem. Soc. Nano 3 (2), 363–369 (2009). 18. C. Silvestre, S. Cimmino, M. Raimo, C. Carfagna, V. Capuano, and R. Kotsilkova, Macromol. Symp. 228, 99–114 (2005). 19. V. Bershtein, L. Karabanova, T. Sukhanova, P. Yaku shev, L. Egorova, E. Lutsyk, A. Svyatyna, and M. Vylegzhanina, Polymer 49 (4), 836–842 (2008). 20. T. S. Kurkin, A. N. Ozerin, A. S. Kechek’yan, L. A. Ozerina, E. S. Obolonkova, M. A. Beshenko, and V. Yu. Dolmatov, Vysokomol. Soedin., Ser. A 50 (1), 54–62 (2008) [Polym. Sci., Ser. A 50 (1), 43–50 (2008)]. 21. V. V. Shilov, Y. P. Gomza, O. A. Shilova, V. I. Padalko, L. N. Efimova, and S. D. Nesin, Synthesis, Properties, and Applications of Ultrananocrystalline Diamond, Ed. by D. M. Gruen, O. A. Shenderova, and A. Ya. Vul' (Springer, Amsterdam, 2005), pp. 373–383. 22. O. Williams, T. Zimmermann, M. Kubovic, A. Denisenko, E. Kohn, and R. Jackman, Synthesis, Properties, and Applications of Ultrananocrystalline Dia mond, Ed. by D. M. Gruen, O. A. Shenderova, and A. Ya. Vul’ (Springer, Amsterdam, 2005), pp. 299–311. 23. J. L. Davidson and W. P. Kang, Synthesis, Properties, and Applications of Ultrananocrystalline Diamond, Ed. by D. M. Gruen, O. A. Shenderova, and A. Ya. Vul’ (Springer, Amsterdam, 2005), pp. 357–373. 24. A. N. Ozerin, T. S. Kurkin, G. G. Alkhanishvili, A. S. Kechek’yan, O. T. Gritsenko, N. S. Perov, L. A. Oze rina, M. A. Beshenko, and V. Yu. Dolmatov, Ross. Nan otekhnol. 4 (7–8), 114–121 (2009) [Nanotechnol. Russ. 4 (7–8), 480–488 (2009)].


Vol. 5

Nos. 5–6

2010


351

25. V. Yu. Dolmatov, Ross. Nanotekhnol. 2 (7–8), 19–37 (2007).

33. RF Patent 2 234 518 (2004).

26. A. P. Koshcheev, Ross. Khim. Zh. 52 (5), 88–96 (2008).

34. V. V. Boiko, A. A. Kuznetsov, G. K. Semenova, M. S. Tsar’kova, V. G. Krasovskii, and A. N. Ozerin, Plastmassy, No. 4, 22 (2003).

27. W. I. Cha, S. H. Hyon, and Y. Ikada, J. Polym. Sci., Part B: Polym. Phys. 32 (2), 297 (1994). 28. T. Tanigami, Y. Nakashima, K. Murase, H. Suzuki, K. Yamaura, and S. Matsuzawa, J. Mater. Sci. 30 (20), 5110–5120 (1995). 29. T. Tanigami, H. Suzuki, K. Yamaura, and S. Mat suzawa, J. Mater. Sci. 33 (9), 2331–2338 (1998). 30. Urmimala Maitra, K. Eswar Prasad, U. Ramamurty, and C. N. R. Rao, Solid State Commun. 149 (39–40), 1693–1697 (2009). 31. V. V. Boiko, A. A. Kuznetsov, G. K. Semenova, and A. N. Ozerin, Izv. Akad. Nauk, Ser. Khim., No. 3, 735 (2003) [Russ. Chem. Bull. 52 (3), 771 (2003)]. 32. RF Patent 2 205 191 (2003).


Vol. 5

Nos. 5–6

35. Yu. A. Gorbatkina, Adhesive Strength in Polymer–Fibre Systems (Khimiya, Moscow, 1987) [in Russian]. 36. G. Porod, KolloidZ. 125, 109–122 (1952). 37. P. Y. Detkov, V. A. Popov, V. G. Kulichikhin, and S. I. Chukhaeva, “Development of Composite Materi als Based on Improved Nanodiamonds,” in Molecular Building Blocks for Nanotechnology, Ed. by G. Ali Man soori, T. F. George, L. Assoufid, and G. Zhang (Springer, New York, 2007), pp. 29–43. 38. G. Capaccio, T. A. Crompton, and I. M. Ward, J. Polym. Sci., Polym. Phys. Ed. 14 (9), 1641–1658 (1976).

2010