Polymeric Composite Materials with the Strengthened Superficial Properties

7/23/2019 Polymeric Composite Materials with the Strengthened Superficial Properties

http://slidepdf.com/reader/full/polymeric-composite-materials-with-the-strengthened-superficial-properties 1/6

Journal of Materials Science and Engineering A 2 (5) (2012) 385-390

Polymeric Composite Materials with the Strengthened

Superficial Properties

Fakhrutdinova Venera Hafizovna, Islamov Anvar Makhmutovich, Ilyukhin Dmitry Genad’evich and

Abdrahmanova Lyailya Abdullovna

Kazan State University of Architecture and Engineering, Kazan City 420066, Russia

Received: March 21, 2012 / Accepted: April 18, 2012 / Published: May 10, 2012.

Abstract: Polymer composite materials are one of the most important and widely used modern polymeric materials. Surface diffusive

processing of the polymer by the nanomodifying components can receive the gradient materials with high physical and mechanical

properties. In the case of using silica sol as a low-molecular-weight diffusant it is possible to obtain a strengthened gradient layer in thematrix of the base polymer due to a structuring effect of the modifier and enhancement of the polymer macromolecular bonds. As a

result, use of silica sol leads to increased surface microhardness up to 2 times and the flex modulus up to 1.2 times and high resistance

to chemical reagents.

Key words: Polyvinylchloride, nanomodifier, diffusion, swelling, grade.

1. Introduction

Analysis of trends in fundamental studies and new

technologies for the production polymer and composite

materials, including nanosystems, with a set of positive

physical and chemical properties shows that traditional

methods of polymers synthesis, polymerization and

polycondensation, largely exhausted themselves and

the probability of occurrence polymers with

characteristics significantly exceeding the achieved

certain level decreased significantly. During the

operation the polymer products surface is exposed to

various aggressive factors, which are distributed

unevenly in the product volume and concentrated

largely on the surface, containing an increased amountof local stresses and defects associated with the

processing technology. These factors accelerate the

destruction of the surface layer of the real body and

thereby reduce the durability of finished products

during the operation [1-3].

Modification of the polymeric materials and

Corresponding author: Fakhrutdinova Venera Hafizovna,Ph.D., research field: nanomodification of polymers. E-mail:[email protected].

products surface develops rapidly in recent years. It is a

promising area, which allows on the basis of known

polymers to develop technology for the production of

high quality new materials with the set of improved

physical-chemical and performance properties.The surface modification of polymers is carried out

traditionally by mechanical [2, 3], energy [4, 5] and

diffusion [6-10] exposure on the material superficial

layers in the finished product without modifying the

structure and composition of the inner layers. The most

effective way of modification is the surface treatment

by different liquid reagents. As a result of the liquid

diffusion in polymeric material is formed a modified

surface layer with variable structure and properties

over the thickness, that is the gradient layer. This

creates not so much a protective coating as a new layer

of the modified polymer with decreasing concentration

of the modifier into the depth of the base material

volume. By varying the temperature and time

parameters of diffusion impregnation, the depth of

penetration and thus the thickness of surface gradient

layer can be adjusted. The efficiency of the diffusion

method to fill the pores in the structure of the polymer

DAVID PUBLISHING

D



Polymeric Composite Materials with the Strengthened Superficial Properties386

by low-molecular substance is undeniable [1].

Fundamentals of strengthening the surface of the

polymer products by creating gradient structures are

caused by the initial heterogeneity of the polymer on

the supermolecular level. Amorphous polymers, in

particular, the linear PVC, are distinguished by local

heterogeneity of molecular packing and the presence of

dense globular structures. Interglobular regions have a

lower packing density of molecules, large defects,

including defective parts of macromolecules and

impurities. This is a weakened region of the polymer

block; it has a lower strength and hardness than the

closely packed globular or domains, less resistant to

thermal degradation and to attack by corrosive media.There are real microdefects in the polymer due to

localized overtensions that are common to polymer

with spherilitic structure [11-14].

Exactly these weak areas of polymer material should

be strengthened. And because they are more available

to diffusion swelling, it predetermines the modification

of polymers by monomers and oligomers.

When reactive oligomers are used as a diffusant, it is

possible to create gradient interpenetrating networks

(IPNs) in the matrix of base polymer after the curing of

oligomers. Gradient IPNs are a mixture of

three-dimensional polymers, the concentration of the

components of which varies along section of the

sample. This type of systems can be obtained by the

method of successive curing. The pre-formed first

polymer swelling in the monomers is stopped at a

certain stage, not reach the equilibrium, and

polymerization is carried out to produce second

polymer, which concentration in the matrix polymerchanges from the surface to its depths. The result is a

formation of the systems whose properties differ from

the properties of individual polymers and of IPNs,

obtained in the traditional way. If the matrix polymer is

linear, then semi-IPNs type structures are formed [11].

The method of successive curing in the obtaining of

composite materials is a fundamentally new method of

polymer modification in the products, allowing to solve

the problem of strengthening their surface, in a wide

range to adjust the properties, in particular surface

hardness, wear resistance, resistance to hydroabrasive

wear and diffusion penetration of chemically

aggressive media. The method is much more efficient

and more economical than bulk modification

(consumption of a reactive modifier is reduced in 3-10

times).

Principles for creating the gradient IPNs with high

mechanical and other properties were implemented on

the example of two amorphous polymers, polyvinyl

chloride (PVC) and polymethylmethacrylate (PMMA)

by means of diffusion modification; specific features of

gradient layers formation were found; their structuralmodels that take into account the heterogeneity of the

supermolecular structure of the base polymers were

proposed [15-20].

Polymeric systems by Ivanchev definition [21] are

natural nanostructured systems, they have a complex

supramolecular internal structure (coil, pack, globule

and crystallite) with a different arrangement of the

constituent elements in space and the different nature

of the interaction between them. Note, size of the

polymer crystallite is 10-20 nm (macromolecule may

include a few of the crystallites, because its length is

400 nm). These arguments suggest that

“macromolecular formation and polymer systems due

to the peculiarities of their structure are always

nanostructural formations” [21].

Surface modification of polymeric products, in

accordance with modern concepts of nanostructured

and nanoreactor formations can be represented as a

surface nanomodification (still the question of theformation of “nanostructured” and “nanoreactor”

elements in the surface diffusion modification of

polymers by monomers and oligomers was not

considered in broad terms).

2. Experiment

Following materials were used in the research: block

samples of PVC size 20 mm × 20 mm × 4 mm, silica sol



Polymeric Composite Materials with the Strengthened Superficial Properties 387

Table 1 The main characteristics of silica sol.

Characteristic Value

Density (kg/m3) 1,200

Weight concentration of SiO2 (g/L) 330-340

Weight concentration of Na2O (g/L) 34Viscosity (cSt max) 20.0

Micelle diameter (nm) 5-9.5

рН 10.3

were used as a low molecular weight diffusant. Silica

sol was a lyophilized colloidal system with nanoscale

particles usually spherical (Table 1). To characterize

the particle size distribution of silica sol used laser

particle size analyzer (HORIBA LA950), (Fig. 1). The

surface of the nucleus of the colloidal particle

consisting of silicon dioxide SiO2 is covered by silanol

groups SiOH, which dissociation causes the emergence

of the double electric layer and the negative charge of

the sol particles:

≡ SiOH + ¯ OSi ≡ → OH

¯ + ≡ Si – O – Si ≡

≡ SiOH + ¯ OSi ≡ → H2O + ≡ SiO ¯ .

Samples of PVC were subjected to surface treatment

in a dispersed system of silica sol at 60 °C until the

equilibrium degree of swelling.

To analyze the structure of the gradient polymerused the following methods:

(1) High-resolution scanning electron microscopy

(HR-SEM);

(2) Dynamic mechanical method (DMA);

(3) Microhardness test (HVS-1000).

3. Results and Discussion

Use of nanostructure-forming inorganic modifier

silica sol as the diffusant allows to adjust the character

of nanostructured formations and hence the strength

properties of PVC materials. It should be noted that

only small doses of the sorbed low molecular weight

diffusant (up to 0.5 wt.%) are required to realize this

method of modification.

The first stage of the modification process is the

swelling of PVC in nanomodifying component, silica

sol. Kinetic curves are typical saturation curves (Fig. 2).

An increase in temperature leads to a decrease in time

Fig. 1 The silica sol particles distribution in sizes.

Fig. 2 Kinetic curves of swelling of PVC in silica sol at

room temperature (1) and at 60 °C (2).

required to reach an appropriate degree of swelling.

The obtained samples by diffusion impregnationduring different periods of time with varying degrees of

swelling (mass and volume) change the actual

concentration of modifier in the surface layer. The

maximum degree of impregnation (up to 1.4 wt.%)

corresponds the modifier concentration more than 6%.

The modifier concentration gradient in the surface

layers causes the changes in the properties over the

thickness of the samples. There is a definite relation

[15-18] between the concentration of the diffusant and

parameters such as the microhardness of the sample. So

the change in microhardness can indirectly determine

the nature of the modifier distribution in the surface

layer of the polymer sample. Fig. 3 shows the curves of

the distribution of microhardness over the thickness of

the flat sample (plate 4 mm thick). In studying the

processes of surface nanomodification, the authors are

dealing with a complex system, which involves several

components: the dissolved nanomodifier, the solvent




Fig. 3 Distribution of microhardness over the thickness of

the PVC samples containing (1) 0%, (2) 1.4%, (3) 1.4%

silica sol (2) before and (3) after solvent removal.

(water) and the surface layer of the polymer block. The

penetration diffusion layer of the solvent in the

polymer block is always greater than of nanomodifier.

Diffusion modification is not only loading of

modifying component in the most critical surface layer,

but also improving the structure and physical state of

the surface layers of polymer products, firstly, due to

the formation of hydrogen bonds and the ordering of

water structure in the polar groups of PVC [22, 23];secondly, due to the structuring effect of free d -orbitals

of silicon and unshared electron pairs of chlorine and

oxygen of the polymer; thirdly, due to the formation of

bonds of the donor-acceptor character. After removal

of physically bound water (free) there is a further

increase in the microhardness on the surface because of

structural changes that lead to transformation of both

the molecular and supramolecular nature. The most

thermodynamically equilibrium structure is formed.

The chemical compositions of gradient layers at

different depths were analyzed by high-resolution

scanning electron microscopy to estimate the changes

in the silica sol concentration in the surface layers. The

content of the modifier was identified by the lines of

the spectra of Si and O. Quantitative surface analysis

based on the proportionality of the intensity of spectral

lines of atomic concentration of the test element.

Decreased the silica sol concentration with the

deepening into the sample was estimated by the content

of Si and O, whose presence is due to not only its

content in silica sol, but the presence in the content of

ketogroups of PVC macromolecules. Chemical state of

the raw PVC surface was almost identical to the

characteristic of gradient PVC at a depth of 250 µm

(Figs. 4-6).

Fig. 4 The chemical composition of the modified PVC at adepth of 50 µm.

Fig. 5 The chemical composition of the modified PVC at a

depth of 150 µm.



Polymeric Composite Materials with the Strengthened Superficial Properties 389

Fig. 6 The chemical composition of the modified PVC at a

depth of 250 µm.

Fig. 7 Temperature dependence of the elastic modulus for

(1) pure and (2) the modified PVC.

The state of the surface layer affects the

macro-properties of polymer material which

significantly altered by changing the packing density.

For example, the elastic modulus of surface-modified

samples were higher (Fig. 7). This can be explained by

the fact that the action of nanomodifier causes the

unique physical “crosslinking” of the polymer which

leads to its compaction and, consequently, to an

increase in strength and elastic modulus of the polymer

system.

4. Conclusions

Specifics of the formation of specific nanostructures

in the polymer and the realization of their

nanostructural characteristics were observed.Improving the complex of physical and mechanical

characteristics and changes in the structure was

achieved with the loading of fine nanoscale inorganic

particles into the surface layer of polymer block, and to

implement the desired effect only small amounts of

additives (0.5 wt.%) are required. Polymer system in

the surface layers is transformed into organic-inorganic

polymer composite material by means of the formation

of nanoscale structured zones, a hybrid system based

on the incompatible by nature components [21].

The principles of nanochemistry and

nanotechnology in the polymer materials can greatly

increase the efficiency of polymer systems, to improve

their properties and operational characteristics.

References

[1] A.N. Machulis, E.E. Tornau, Diffusion Stabilization of

Polymers, MINTIS, Vilnius, 1974, p. 256.

[2]

A.S. Hoffman, Surface modification of polymers, Chinese

Journal of Polymer Science 13 (1995) 105-203.[3] T.J. Carry, Organic chemistry at chemically resistant

polymer surfaces: Modification of surface reactivity

and surface properties, Chemia. 44 (90) (1990)

316-318.

[4] M. Dror, M.L. Elsable, G.C. Berry, Gradient

interprenetrating polymer networks, 1 Pbly (ether urethane)

and polyacrylamide IPN, J. Appl. Polym. Sci. 26 (1981)

1741-1757.

[5]

G. Akovali, A. Labban, Gradient polymers: Some futher

studies with systems of hard matrices contania hard

gradients, In: IUPAC morco, Florence 1980, Int. Symp.

Macromol, Preprints Pisa, 1980, pp. 264-267.[6] A.E. Chalyh, Diffusion in the polymer systems, М.,

Chemistry, 1987, p. 312.

[7] A.A. Tager, L.V. Adamova, N.T. Herush, The influence

of pre-swelling in methanol on the sorption and diffusion

of water in cross-linked copolymers of methyl

methacrylate, Highmolecular Comp. (1991) 176-179.

[8] I.I. Zlotnikov, V.V. Lisovskiy, V.G. Savkin, Methods of

diffusion modification of phenolic, STC abstracts:

Modification of polymeric materials during their

processing and modification of the molded products from




them, Izhevsk, 1988, p. 42.

[9] A.A. Shturman, Strengthening of details from the

secondary plastic, Plast. Masses (1991) 53-54.

[10]

V.G. Nazarov, Surface modification of polymers:

Monograph, М., Msuee, 2008, p. 474.

[11]

U.S. Lipatov, Physical chemistry of multicomponent

polymer systems, Nauk. Dumka, Kiev, 1988, p. 384.

[12] L.R. Strelkova, G.T. Fedoseeva, K.S. Minsker,

Photochemical ageing of rigid PVC, Plast. Masses7 (1976)

2-73.

[13] L.R. Strelkova, G.T. Fedoseeva, K.S. Minsker,

Photochemical degradation of PVC, Highmolec. Comp.

(1976) 2064-2066.

[14]

G.T. Fedoseeva, L.R. Strelkova, E.O. Krats,

Photo-oxidative degradation of polyvinylchloride under

atmospheric ageing, Plast. Masses 7 (1980) 28-29.

[15] L.A. Abdrahmanova, V.H. Fakhrutdinova, V.G. Khozin,

Surface modifications of products of PVC by furan

oligomers, Plast. Masses 1 (1993) 17-18.


Processing of PVC-products by reactive oligomers, Plast.

Masses 4 (1995) 30-31.

[17] L.A. Abdrahmanova, V.G. Khozin, Thermodynamics of

binary systems of PVC-furan plasticizer, Journal of

Applied Chemistry 69 (1996) 486-489.

[18]

L.A. Abdrahmanova, V.H. Fakhrutdinova, V.G. Khozin,

Chemical transformations of furan compounds in the

matrix of PVC, Journal of Applied Chemistry 72 (1998)

1003-1006.


Prospects for enhancing the surface of polymeric building

materials using the diffusion modification, Building

Materials 11 (2005) 11-14.

[20]

L.A. Abdrahmanova, V.H. Fakhrutdinova, V.G. Khozin,

Diffusion modification of polymethylmethacrylate

oligoester akrilates, Journal of Applied Chemistry 76

(2003) 1883-1885.

[21] S.S. Ivanchev, A.N. Ozerin, Nanostructures in polymer

materials, Highmolec. Comp. B 48 (2006) 1531-1544.

[22]

I.V. Kozlov, S.P. Papkov, Physico-chemical basis of

plasticization of polymers,М. Chemistry (1982) 223.

[23] V.N. Gud, B.S. Kolupaev, IR spectroscopic study of

adsorbed by polymers water of different polarity, Plast.

Masses 3 (2011) 44-47.

Documents

Polymeric Composite Materials with the Strengthened Superficial Properties