Printer Friendly

Polyacrylonitrile reinforced PVA based-polymeric networks: structural, morphological, and mechanical aspects.


In this era of polymers, when the polymeric materials are replacing most of the conventional materials, there is an increasing demand for new and novel materials with much improved properties in terms of toughness, strength, dimensional stability and permeability. There have been a number of technological developments in materials synthesis to make them worth for use in various fields. Judicious choice of polymeric materials and their proper blending/grafting in a fixed proportion helps to obtain new products of desired property combination. An effective route to develop mechanically strong polymeric matrices has been through the preparation of interpenetrating polymer networks (IPNs) [ l ]. The IPNs have gained much interest in recent past because of the ease of tailoring them to enable for specific applications. In general, an IPN is defined as a combination of at least two polymer chains each in network form and of which at least one is synthesized and/or crosslinked in the immediate presence of the other without formation of any covalent bonds between them [2], These polymers are closely related to other multi-component materials, containing completely entangled chains, such as polymer blends, grafts and blocks. Miscibility of the constituent components of the IPNs is a main factor in determining the IPN's morphology [3].

Polyvinyl alcohol (PVA) based hydrogels have emerged as promising biomaterials for various bioengineering and technological purposes as in paper making and processing, emulsifying and stabilizing agents, construction industry as an addictive to cement, printing, and textile industries. For these applications the mechanical behavior of these materials is one of the prime features to be achieved. One of the major challenges facing the use of PVA based hydrogels is the insufficient mechanical strength that limits their application.

Polyacrylonitrile (PAN), a synthetic vinyl homopolymer, offers quite good resistance [4], thermal stability [5], and mechanical strength [6]. It is regarded as the most preferable precursor material for the production of high strength, high modulus carbon fibers. PAN fibers exhibit a high degree of molecular orientation, higher melting point and tend to decompose before its melting point, ([T.sub.m], 317-330[degrees]C). It becomes plastic at about 180[degrees]C and thus can improve the orientation of molecular segments. It is used in the manufacture of synthetic fibers widely used for clothing. The monomer acrylonitrile is a major component of copolymers such as modacrylics and ABS (acrylonitrile-butadiene-styrene). It is not soluble in its monomer due to strong dipole-dipole interaction between nitrile groups of different polymer chains [7]. It is worth mentioning that although acrylonitrile is reported as mildly toxic monomer, however, its polymer (PAN) is completely non-toxic and recognized as a suitable material for biomedical applications also because of its inherent promising properties. For instance, PAN based membranes find numerous biomedical applications [8-10] as being highly biocompatible in nature [11, 12]. Use of polyacrylonitrile and its copolymers by dental professionals in wearing medical gloves has been frequently reported.

Various researchers have put forward a good deal of efforts for the development of PVA and PAN based network structures in viewpoint of their fair mechanical strength. Blends of polyvinyl alcohol with other polymers, useful in medical fields, have been prepared and mechanically characterized by many workers [13, 14]. Adopting a novel route of hydrogel synthesis, Bajpai et al [15] prepared binary blends of polyvinyl alcohol and polyacrylamide and measured their different mechanical parameters. The specimens were subjected to gamma radiation and their surface microhardness was measured. Mechanical behavior of acrylonitrile-butadiene rubber blends has been largely investigated by various researchers [16, 17]. It was inferred that the mechanical strength of candidate polymer is enhanced by the incorporation of acrylonitrile. For PVA based materials, at significant high loading level, considerable increase in the mechanical properties have been achieved [18]. Thus, various fabrications have been attempted to improve the mechanical and other aspects of PVA as well as PAN based membranes. Realizing a high strength possessed by acrylonitrile gels, high elasticity in PVA based materials and the increasing demand of new materials in terms of improved toughness, strength etc the proposed research work aims at synthesizing a semi-IPN, comprising of PVA and PAN, by redox polymerization in the presence of N,A'-methylene-bri-acrylamide (MBA) as a crosslinking agent. The incorporation of hydrophobic acrylonitrile into the hydrophilic PVA matrix may yield a novel polymer matrix with unusual properties well suited for various applications. The structural, morphological, and mechanical investigations of these synthesized gels would be the focus of study.



Polyvinyl alcohol (PVA), (98%, hydrolyzed, molecular weight 14,000 Da) was obtained from Research Lab Chem Industries, Mumbai, India, and used as a preformed polymer without any further purification. Acrylonitrile purchased from Research Lab, Mumbai, India, was freed from inhibitor by successive washing the monomer twice with 5% NaOH, 5% [H.sub.2]S[O.sub.4] and distilled water and finally distilling the washed monomer under vacuum. N,N'-methylene-b/s-acrylamide (MBA; Research Lab Mumbai, India) was used as a crosslinking agent, potassium persulfate (KPS; Loba Chemie, Pvt Ltd. Delhi, India) as an initiator and potassium metabisulfite (KMBS; Qualigens Fine Chemicals, Mumbai, India) as an activator, respectively. Double distilled water was used throughout the experiments.

Synthesis of Hydrogel

Semi-IPNs of various compositions were prepared by redox polymerization method as reported elsewhere [19]. In a typical experiment, into 10 mL of distilled water were added 1 g of PVA, 3.79 mM of acrylonitrile, 0.43 mM of MBA, and 1 mL each of potassium metabisulfite (0.01 M) and potassium persulfate (0.001 M).The reaction mixture taken in a rectangular glass pellet (50 mm X 50 mm X 10 mm) was kept at 35[degrees]C for 3 days. The semi-IPNs so formed were taken out carefully and purified by equilibrating them in distilled water so as to ensure complete leaching of unreacted chemicals, monomer and polymers. The purified semi-IPNs were cut into equal sized square pieces, dried at room temperature for a week and stored in airtight polyethylene bags.

Composition of the IPNs

In order to know the composition of the prepared IPNs, it was allowed to swell in water for purification and the outer aqueous medium was analyzed for the remaining concentrations of unreacted monomer, polymer, and other reactants. It was found that the concentrations obtained were almost negligible in comparison to the feed composition and, therefore, the feed composition was taken as that of the IPNs itself.

It is also worth mentioning here that the specimens with varying amount of PVA, contained AN/MBA in the molar ratio of 9:1, with varying concentration of acrylonitrile, contained PVA/MBA in the molar ratio of 1:6 and the specimens with varying concentration of crosslinker (MBA) contained PVA/AN in the molar ratio 1:54 respectively.


FT-IR Analysis. FT-IR spectrometry is a quantitative approach that helps in understanding the miscibility of the two polymers in the specimen. In the present case, the infrared spectra of the synthesized semi-IPN and that of PVA and polyacrylonitrile were obtained by transmission method on a Perkin-Elmer spectrophotometer (Paragon 1000, FTIR) in the wavelength range of 4000 to 400 [cm.sup.-1].

Atomic Force Microscopy. AFM technique maps the topography with domain formation in the micro and nanoscale, if any, of the synthesized specimens. The drastic differences in the properties of an amorphous and a semicrystalline material may also be judged in the light of AFM topography. The direct visualization of three-dimensional images of the polymer surfaces is helpful for understanding the effects of changes in processing conditions and content matter of the sample. Tapping mode is currently the most successful mode for high-resolution imaging of the samples in order to evaluate and understand their surface. The topography of the synthesized semi-IPNs of varying compositions has been recorded using Atomic Force Microscope (AFM) Nanoscope II in Tapping Mode.

Microhardness Measurements. Microhardness testing is very widely carried out for classifying materials, mainly, because of the ease with which it is accomplished. The most commonly used hardness test is the indentation technique [20] which is a nondestructive test. Completely dried synthesized semi-IPNs of various compositions were indented at room temperature by mhp-160 microhardness tester with a Vickers's diamond pyramidal indenter having a square base and 136[degrees] pyramidal angle, attached to a Carl Zeiss NU2 universal research microscope [21]. The indenting load ranges from 10 to 80 g. The diagonals of indentation were measured by a micrometer eyepiece. The Vickers hardness [H.sub.v] was calculated from the equation:

[H.sub.v] - [1.854 x L/[d.sup.2]]kg/[mm.sup.2]

where L is the load in kg and d is diagonal of indentation in mm. Indentations at each load were obtained in replicate number and average surface hardness was calculated.

Tensile Tests

The tensile tests of the synthesized semi-IPNs, of various compositions, were carried out on the ASTM D638 Hounsfield Tensometer at room temperature. The dumb-bell shaped samples with initial dimensions of 20 mm in length, 6 mm in width and nearly 1.0 mm in thickness were stretched at a speed of 5 mm/min. Different specimens having, different concentrations of PVA, acrylonitrile and MBA were tested. The tensile strength and the elongation at break were recorded directly from the digital displays at the end of each test. In each case, five specimens of nearly equal dimensions were used in and the final mechanical parameters were evaluated from the average of four independent measurements in each case.

Statistical Analysis

All the presented mechanical results have been expressed as mean [+ or -] SD by conducting the tests in replicate numbers for each composition and calculating their respective mean value and SD.


FT-IR Spectral Analysis

The IR spectra of native polyvinyl alcohol (PVA), polyacrylonitrile (PAN) and grafted gel are shown in Fig. la to c, respectively. A comparison of the spectra "a" and "c" clearly suggests, not only the presence of PVA in the grafted gel, but also provides evidences for the shifting of spectral peaks due to the formation of hydrogen bonding between the hydroxyls of PVA and nitriles of PAN. For example, the peak observed at 3440 [cm.sup.-1] (O-H stretching) in the spectra "a" shifts to 3468 [cm.sup.-1] in the spectra "c," 1110 [cm.sup.-1] (CO stretching) in the spectra "a" shifts to spectra 1120 [cm.sup.-l] in the spectra "c," 600 [cm.sup.-1] (O-H stretching) in the spectra "a" shifts to 630 [cm.sup.-1] in the spectra "a," 1440 [cm.sup.-1] (C[H.sub.2] bending) in the spectra "a" shifts to 1460 [cm.sup.-1] in the spectra "c," 800 [cm.sup.-1] (C-H out of plane bending) in the spectra "a" shifts to 820 [cm.sup.-1] in the spectra "c" and 2920 [cm.sup.-1] (C[H.sub.2] stretching) in the spectra "a" shifts to 2940 [cm.sup.-1] in the spectra "c" of the grafted gel.

It is also clear from the spectra "c" that a sharp peak appears at 2260 [cm.sup.-1] which could be assigned to C [equivalent to] N stretching of nitrile groups. It is remarkable to see that the same peak appears at 2240 [cm.sup.-1] in the spectra "b" of PAN. Thus, the observed shift in C[equivalent to] N peak from 2240 [cm.sup.-1] to 2260 [cm.sup.-1] could again be due to hydrogen bonding between nitrile group of PAN and hydroxyl of PVA. Furthermore, the spectral peak appearing at 1580 [cm.sup.-1] in the spectra "c" may be assigned to N-H bending vibration of the crosslinker MBA. It is also worth to mention that the spectral peak at 2180 [cm.sup.-1] of the spectra "a" could be due to combination frequency of C-C and C-H groups of PVA.

AFM Analysis

When the amount of PVA is varied in the range of 0.07 to 0.21 mM in the feed composition of the semi-IPN, the observed AFM images are shown in Figs. 2 to 4. It is clear from the image that at the lowest PVA content, the network surface appears loose and separated (Fig. 2). A specific interaction between the PVA macromolecular chains and PAN molecules decreases the surface energy, promoting voids and empty space. A significant difference in the morphology is observed with increasing PVA content; the network surface appears quite compact and porous. The topographical features further show that surface morphology with highly ordered cylindrical pores reflecting height image ranges from 38 to 52 nm. The presence of disc shaped objects, in the AFM image of specimen with 0.21 mM PVA content, can be attributed to the acrylonitrile particles, while the linear parts may be related to the PVA polymer chains. However, structural heterogeneity is a common feature for most of the crystalline specimens in which amorphous material is one of the components. In the AFM imaging, as the tip indents, a stiffer region (crystalline regions) appears darker, whereas the amorphous part appears lighter.

This compactness tends to reduce, and a very different topography is observed on varying the concentration of PAN in the feed mixture. A spherical nano phase all over the surface suggests for the amorphous nature of acrylonitrile (Fig. 3a,b). This fact is in correlation with the results of XRD analysis as well [22], In addition to the organization, a specific uniaxial orientation of PAN molecules separated in nanometer scale is clearly evident in a wide area of the sample. The larger stacks in the micrographs may correspond to the PAN, as it is in majority. These organized regions may be due to the existence of PAN and may not be representative of the whole sample. Thus, the AFM morphology reveals that the increased PVA-PAN interactions lead to formation of desired grafted gel. The obtained results are in good agreement with SEM observations [23].

A similar nanodomain and microphase separation is characterized in the AFM imaging of the specimens with varying concentration of the crosslinker and PVA/AN in a fixed ratio of 1:54 (Fig. 4). The surface morphology appears to be smooth for samples with 0.43 mM MBA concentration and thereafter, the surface texture tends to appear like wave with increase in the concentration of MBA as revealed by the three-dimensional images of the micrographs. The heights of the hills are observed to be in the nanometer range illustrating the nano domain structure in the surface morphology. The AFM measurements with increasing crosslinker content show an increasing height profile from 38 nm to 58.5 nm but with heterogeneity. With the increasing degree of crosslinking, the semi-IPNs tends to become more and more compact which may further lead to the formation of segregations in the nano domain range, as also observed in the topography. The presence of nano domains further reveals the fact that the film morphology strongly depends on the chemical composition leading to the formation of nonporous structures.

Microhardness Measurements

Variation of Hv with Load for Various Compositions of semi-IPNs. Microhardness of a material greatly depends on the chemical and morphological nature of the material and, therefore, by a proper selection of the components of the material, the hardness of the material may desirably be altered. The forthcoming paragraph discusses the impact of chemical composition of the semi-IPN on the microhardness at different values of applied load (10-80 g).

Figures 5 to 7 illustrate the variation of Vickers hardness number ([H.sub.v]) as a function of applied load (L) for varying concentration of PVA, acrylonitrile and crosslinker MBA. All the curves in these figures exhibit almost similair profile; initially the microhardness increases with increase in load and thereafter, beyond certain load, [H.sub.v] tends to attain a saturation value. It is also evident from the graphs that the microhardness increases at a faster rate up to the load of 30 g, and thereafter up to 60 g, this rate of increase slows down. However, beyond 60 g, [H.sub.v] tends to saturate as no appreciable change in the [H.sub.v] values are observed with. The increase in the [H.sub.v] with increasing load can be explained on the basis of strain hardening phenomenon [24], In the polymer chains, there is a spectrum of micromodes of deformation. Every micromode is achieved by its characteristic temperature and stress conditions. When sufficient number of micromodes becomes active, large scale plastic deformation begins. As the load increases, the specimen is subjected to greater and greater strain hardening and consequently, the increase in the value of [H.sub.v] is observed.

Effect of PVA. The effect of PVA content of the semi-lPN on their microhardness has been investigated by varying the concentration of PVA from 0.07 to 0.28 mM while keeping the molar ration of AN/MBA as 9:1. The results, as shown in Fig. 5, reveal that the microhardness of semi-IPNs increases with increase in PVA content from 0.07 to 0.28 mM in the specimen. It is also clear from the figure that the value of [H.sub.v] increases with increasing load up to 60 g and tends to saturate beyond this load, on the sample. The increase in [H.sub.v] with load is due to strain hardening in the specimens. It is noticed that the rate of strain hardening is greater at lower loads and at higher PVA content. [H.sub.v] value tends to be independent of the applied load and attains a limiting value beyond the load of 60 g. It is observed that pure PVA is soft in comparison to the pure acrylonitrile and when these two polymers are developed as IPN, then hardened IPNs are obtained with increasing content of PVA in the IPN. The observed increase may also be attributed to the fact that PVA is a crystallizable polymer and its increasing amount in the gel matrix introduces some crystallinity, which further hardens the specimen. This feature is also confirmed from the DSC study [25] where the increase in the glass transition temperature with the increase in the content of PVA is observed.

Effect of Acrylonitrile. The effect of variation of acrylonitrile in the semi-IPN shows quite different result for the Vickers micro-hardness [H.sub.v]. The results have been studied by varying the concentration of acrylonitrile from 3.79 mM to 15.17 mM while keeping the molar ration of PVA/MBA at a fixed value 1:6 in the semi-IPN. Figure 6 illustrates the influence of various content of acrylonitrile on the microhardness at various loads ranging from 10 to 80 g. The value of [H.sub.v] increases with increasing load (10-80 g) for all the variations and attains a limiting value beyond the load of 50 g and tends to be independent of the applied load as the IPNs are fully hardened. The increase in microhardness with the increasing load can be explained by the phenomenon of strain hardening and the observed results are most expected as PAN being a hydrophobic polymer brings about an increase in hydrophobicity of the IPN which directly results in increased hardness. For the varying concentrations, it is observed that the value of [H.sub.v] increases with a lower acrylonitrile content (3.79 mM and 5.06 mM), but, a further increase in the concentration of acrylonitrile in the semi-IPN (7.59 mM and 15.17 mM) decreases the microhardness of the specimen and more plasticized gels are obtained. Extensive formation of hydrogen bonds between the nitrile and hydroxyl functional groups of polyacrylonitrile and PVA macromolecules may make the specimen harder; also attributed to the hydrophobic nature of PAN. But as the concentration of PAN increases, plasticization effect is observed. PAN fibers get coagulated within the PVA matrix; the crosslinking density in PVA thus, decreases and the specimen gets softened.

Effect of MBA. The number of crosslinks in an IPN is one of the decisive factors to produce hardness in the specimen. The effect of crosslink density of the semi-IPN on Vickers hardness number [H.sub.v] has been investigated by varying the concentration of crosslinker MBA in the range 0.43 mM to 1.72 mM and keeping the molar ration of PVA/AN at a fixed value of 1:54, respectively. The results are shown in Figure 7 which indicates that the microhardness of the IPN increases with an initial increasing concentration of MBA from 0.43 to 0.86 mM. Also, the profile for increase in microhardness with increasing load indicates that [H.sub.v] increases up to 50 g load for the lowest concentration of MBA in the IPN. However, this saturation load value is 60 g for the higher concentration of MBA. Beyond the load of 60 g, microhardness is independent of the applied load. The results further reveal that the microhardness of the semi-IPN decreases with a further increase in the concentration of MBA (1.29 mM and 1.72 mM). Decrease in microhardness value with increasing MBA content is likely to be probable due to copolymerization of MBA into PVA chains making the copolymer more ductile. Further, Due to crosslinking, the network chains come much closer to each other and, therefore, a dense and compact network is obtained. But the hydrophobic amide group of this bifunctional monomer brings amorphousness in the specimen and thus, decreasing the hardness value.

Strain Hardening Index

The strain hardening index (n) helps in understanding the stress-strain behavior [26]. One may use it to characterize the elastic and non elastic deformations occurring in a specimen as a result of increased stress [27]. The dependence of microhardness on the load can be studied with the help of Meyer's law which indicates that the value of [H.sub.v] increases continuously with load, when n is greater than 2 and the value of n approaches to 2 in the saturation load region when [H.sub.v] becomes independent of load. Meyer related the load and the size of indentation as:

L = a.d"


log L = log a + n log d

where L is load (kg), d is the diameter of recovered indentation, a is load for unit dimension and n is the Meyer's constant, usually known as logarithmic index. Hence, the logarithmic index number, n, can be considered as a measure of strain hardening in different specimens and may be determined by the slope of the line by plotting log d versus log L.

The different values of n for different specimens reflect the varying degree of strain hardening which indicates the changing morphology and crosslinking in the pure polymers and semi-IPNs. In fact, the different values of n in the different load regions reflect the elastic and plastic characteristics of deformation. In most of the specimens of the semi-IPN, the value of strain hardening index tends to be nearly 2 in the high load region. The different values of n for various semi-IPN specimens in two regions are shown in the Table 1.

Mechanical Tests (Tensile Strength Measurements and Stress-Strain Behavior of Semi-IPNs)

The tensile testing provides an indication of the strength and elasticity of the films, which can be reflected by strength and strain-at-break. Physical crosslinking using an appropriate crosslinker leads to an intermolecular interaction between the component polymers, resulting in an improvement in the mechanical strength of the synthesized gel. The tensile strength and percentage elongation values (as given in Table 2) were obtained from the load-displacement behavior of semi-IPNs having different composition of PVA, PAN and MBA. Their profiles showed a distinct behavior in comparison to the stress-strain behavior of pure PVA [28] and PAN [29-32],

The effect of chemical composition on load-displacement behavior, tensile strength and percentage elongation of semi-IPNs have been discussed in the forthcoming paragraphs:

Effect of PVA. Incorporation of PVA in different wt% in the semi-IPN significantly affects the tensile properties, although tensile strength is found to be greater for pure PVA, which shows the influence of semi-crystalline nature of PVA. Semi-IPNs with different wt% of PVA show an increase in tensile strength (Table 2). As strain increases, the specimen is observed to deviate from its linearity. This nonlinearity is usually associated with stress-induced "plastic" flow in the specimen. Here the specimen is undergoing a rearrangement of its internal molecular or microscopic structure, in which atoms are being moved to new equilibrium positions. This plasticity requires a mechanism for molecular mobility, which in crystalline materials can arise from dislocation motion. Materials lacking this mobility are usually brittle rather than ductile. Increasing percentage of PVA content in the semi-IPN yields an increase in percentage elongation and specimen becomes ductile in nature, whereas specimen with pure PVA shows maximum percentage elongation (45.7 %) and confirms the soft and rubbery nature of PVA. Further, on increasing the PVA content in the semi-IPN the stress needed to increase the strain beyond the proportional limit continues to rise due to mechanism of strain hardening. In such cases the microstructural rearrangements associated with plastic flow are usually not reversed. For specimen with 0.14 mM PVA content, the value of maximum stress is 235.33 N; while on the other hand for IPN with 0.21 mM PVA content the value of maximum stress is 300.16 N. In case of crosslinked networks, increase in the free volume with increasing the content of soft segment influences the mechanical properties [33]. The IPN specimen having 0.21 mM PVA content is more ductile.

Effect of Acrylonitrile. It is clear from Table 2 that the tensile strength increases initially with increase in acrylonitrile content in the semi-IPN (i.e. from 3.79 mM to 7.59 mM; however, the strength decreases for a further increase in acrylonitrile content (15.17 mM). This variation corresponds to the brittle nature of acrylonitrile which is also confirmed from the microhardness studies. The relative increase in percent elongation for 7.59 mM content of acrylonitrile may be attributed to the fact that acrylonitrile is a well known plasticizer, leading to a greater mobility of both; the PAN, and the PVA, macromolecular chains in the specimen. On increasing the content of acrylonitrile form 7.59 mM to 15.17 mM in the semi-IPN, the percentage elongation increases. The specimen with 7.59 mM acrylonitrile content shows maximum tensile strength (25.2 MPa) and the value of maximum stress for this specimen is 237.3 N, whereas specimen with 15.17 mM acrylonitrile content shows quite good ductility with a maximum stress value 157.7 N.

Effect of MBA. In general, the stress-strain curves for brittle materials are typically linear over their full range of strain, eventually terminating in fracture without appreciable plastic flow or necking. Increase in MBA content in the semi-IPN makes the specimen brittle but with an increasing percentage elongation and tensile strength. Although, there is less difference between the respective values of percentage elongation and tensile strength for semi-IPNs having 0.86 and 1.29 mM MBA content, but the value of ultimate stress is different; whereas the stress is 212.4 N for 0.86 mM and increases to 393.5 N for 1.29 mM MBA content. For specimen with higher MBA content no well-defined plastic deformation region is observed before the ultimate failure. This feature is related to high degree of crosslinking with increase in the content of MBA which yields greater degree of brittleness in the semi-IPNs. This phenomenon is due to the change in crosslink density and compact morphology of the semi-IPN with increasing crosslinker content. More elongation for specimen arises due to the segmental motion of uncrosslinked chains. On increasing the content of crosslinker, network becomes compact which increases its brittleness.


PVA based semi-IPNs, with acrylonitrile as the second network, were successfully synthesized. The FTIR spectra of the semi -IPN not only confirm the presence of PVA and crosslinked PAN but also provide significant information about the nature of the network formed. The changes in topography of semi-IPNs with various contents of PVA, PAN and crosslinker suggest a good compatibility of the two polymeric phases having spherical nanodomain regularity. The formation of nanostructure within the gel attributes to the improved mechanical properties. The synthesized semi-IPNs of varying chemical compositions exert a remarkable influence on their microhardness and mechanical strength. The microhardness measurements of the semi-IPNs, investigated by means of the micro-indentation technique, shows that microhardness increases with increase in PVA content. A detailed analysis of their stress-strain behavior shows that presence of crosslinked chains of PAN imparts strength and crosslinker (MBA) imparts brittleness. Percent elongation of the specimens is higher with a high PVA and PAN content. Tensile strength and elasticity of specimens with higher PVA content was the largest. The plots for log L versus log d reveal that strain hardening index has two values--at low load region and at high load region; thus reflecting the elastic and plastic characteristics of deformation.

Thus, the synthesized gels are observed to possess a combinational property: the strength and rigidity of the acrylonitrile, toughness and elasticity of PVA. With such a special feature, the synthesized specimens with a desired content ratio of PVA and PAN are expected to be suitably used for various bioengineering and other applications. The present investigation, thus, offers a novel synthesis strategy and broad spectrum of properties to obtain hard IPNs of PVA and PAN.


The authors acknowledge 1UC-DAE, Indore, and CIPET, Bhopal, (M.P.), India for providing AFM, XRD, and UTS measurements facilities.


[1.] L.H. Sperling, Polym. Eng. Sci., 25, 517 (1985).

[2.] A.P. Rokhade, S.A. Patil, and T.M. Aminabhavi, Carbohydr. Polym., 67, 605 (2007).

[3.] G.A. Domrachev, W.E. Douglas, B. Henner, L.G. Klapshina, V.V. Semenov, and A.A. Sorokin, Polym. Adv. Techno!., 10, 215 (1999).

[4.] D.A. Musale and A. Kumar, J. Appl. Polym. Sci., 77, 1782 (2000).

[5.] Y. Aoki and M. Watanabe, Polym. Eng. Sci., 32, 878 (1992).

[6.] Q. Xu, L. Xu, W. Cao, and S. Wu, Poly. Adv. Techno!., 16, 642 (2005).

[7.] M. Wu, Acrylonitrile and Acrylonitrile Polymers, Encylopedia of Polymer Science and Technology, Wiley Interscience, Hoboken, NJ (2003).

[8.] E. Jain, A. Srivastava, and A. Kumar, J. Mater. Sci. Mater. Med., 20, 173 (2009).

[9.] L.S. Wan, Z.K. Xu, X.J. Huang, Z.G. Wang, and P. Ye, Macromo!. Biosci., 5, 229 (2005).

[10.] Z.G. Wang, L.S. Wan, and Z.K. Xu, J. Membr. Sci., 304, 8 (2007).

[11.] A.D. Martino, A.R. Vaccaro, J.Y. Lee, V. Denaro, and M.R. Lim, Spine, 30, 16 (2005).

[12.] R. Bajpai, A.K. Bajpai, and S. Rajvaidya, J. Macromol. Sci. A Pure Appl. Chem., 42, 1271 (2005).

[13.] P. Zahedi, I. Rezaeian, S.O.R. Siadat, S.H. Jafari, and P. Supaphol, Polym. Adv. Techno!., 21, (2010).

[14.] V. Leung and F. Ko, Polym. Adv. Techno!., 22, (2011).

[15.] R. Bajpai, S. Mishra, R. Katare, and A.K. Bajpai, J. Mater. Sci. Mater. Med., 17, 1305 (2006).

[16.] M.A. Abdeen and I. Elamer, Mater. Design, 31, 808 (2009).

[17.] F.D. Jestin, N.B. Oudin, C. Cardinet, J. Lacoste, and J. Lemaire, Polym. Degrad. Stab., 70, 1 (2000).

[18.] W. Chen, X. Tao, P. Xue, and X. Cheng, Appl. Surf. Sci., 252, 1404 (2005).

[19.] A.K. Bajpai and M. Shrivastava, J. Biomater. Sci. Polym., 13, 237 (2002).

[20.] S.R. Choi and J.A. Salem, J. Mater. Res., 8, 3210 (1993).

[21.] S.K. Awasthi and R. Bajpai, Ind. Pure. Appl. Phys., 39, 795 (2001).

[22.] D.S. Deshpande, R. Bajpai, and A.K. Bajpai, Soft Material, Taylor Francis, 11 (2013).

[23.] D.S. Deshpande, R. Bajpai, and A.K. Bajpai, Int. J. Chem. Res., 3, 74 (2011).

[24.] R.P. Kambour, J. Polym. Sci. Macromol. Rev., 7, 1 (1973).

[25.] D.S. Deshpande, R. Bajpai, A.K. Bajpai, J. Polym. Res., 19, 9938 (2012).

[26.] P.O. Kettunen and V.T. Kuokkala, Plastic Deformation and Strain Hardening, Materials Science Foundations (Monograph Series), 420 Trans Tech Publications Inc., Springer, Netherlands 116 (2003).

[27.] J.M. Lefebvre, C. Bultel, and B. Escaig, J. Mater. Sci., 19, 2415 (1984).

[28.] X. Wang, and M. Nie, Adv. Mater. Res., 284, 253 (2011).

[29.] J. Yang, C.X. Wang, Z.S.Yu, Y. Li, K.K. Yang, and Y.Z. Wang, J. Appl. Polym. Sci., 121, 458 (2011).

[30.] F.L. Jin, S.L. Lu, Z.B. Song, J.X. Pang, L. Zhang, J.D. Sun, and X.P. Cai, Mater. Sci. Eng., 527, 3438 (2010).

[31.] A.M. Donald and E.J. Kramer, J. Mater. Sci., 17, 1765 (1982).

[32.] X.Y. Xu, and X.F. Xu, Polym. Eng. Sci., 51, 902 (2011).

[33.] V. Sriram, S. Subramani, and G. Radhakrishnan, Polym. Int., 50, 1124 (2001).

Deepti S. Desphande, (1) Rakesh Bajpai, (1) Anil K. Bajpai (2)

(1) Department of Physics, Rani Durgavati University, Jabalpur 482001, Madhya Pradesh, India

(2) Department of Chemistry, Bose Memorial Research Laboratory, Government Autonomous Science College, Jabalpur 482001, Madhya Pradesh, India

Correspondence to: R. Bajpai; e-mail:

DOI 10.1002/pen.23803

Published online in Wiley Online Library (

TABLE 1. Values of strain hardening index number n for semi-IPNs of
different compositions.

                                               Slope n

                                       Low load   High load
S.No.   PVA (g)   AN (mM)   MBA (mM)    region     region

1.         1       3.79       0.43       2.7        1.67
2.         2       3.79       0.43       2.5         1.2
3.         3       3.79       0.43       2.4         2.0
4.         4       3.79       0.43       2.2         2.1
5.         1       5.06       0.43       3.1        1.97
6.         1       7.59       0.43       3.0        2.04
7.         1       15.17      0.43       2.9        2.11
8.         1       3.79       0.86       2.9        2.12
9.         1       3.79       1.29       3.4         1.9
10.        1       3.79       1.72       3.6         1.7

TABLE 2. Tensile strength and percentage elongation of the semi-IPNs
of various compositions.

S.No.   PVA (g)   AN (mM)   MBA (mM)   Load (N)

1         2.0       --         --        91.2
2.        1.0      3.79       0.43      230.72
3.        2.0      3.79       0.43      235.33
4.        3.0      3.79       0.43      300.16
5.        1.0      3.79       0.43      230.72
6.        1.0      7.59       0.43      237.3
7.        1.0      15.17      0.43      157.7
8.        1.0      3.79       0.43      230.72
9.        1.0      3.79       0.86      212.4
10.       1.0      3.79       1.29      393.5

S.No.   Tensile strength (M Pa)   Percentage elongation

1          83.6 [+ or -] 4.2        45.7 [+ or -] 2.3
2.         23.4 [+ or -] 1.2       13.72 [+ or -] 0.69
3.        32.47 [+ or -] 1.6       19.5 [+ or -] 0.97
4.         32.3 [+ or -] 1.6        23.6 [+ or -] 1.2
5.         23.4 [+ or -] 1.2       13.72 [+ or -] 0.69
6.         25.2 [+ or -] 1.3       15.95 [+ or -] 0.8
7.         19.1 [+ or -] 0.5       16.72 [+ or -] 0.84
8.         23.4 [+ or -] 1.2       13.72 [+ or -] 0.69
9.         25.5 [+ or -] 1.3        9.1 [+ or -] 0.5
10.        29.6 [+ or -] 1.5        11.2 [+ or -] 0.6
COPYRIGHT 2014 Society of Plastics Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2014 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Desphande, Deepti S.; Bajpai, Rakesh; Bajpai, Anil K.
Publication:Polymer Engineering and Science
Article Type:Report
Date:Nov 1, 2014
Previous Article:In vitro degradation of PLLA/nHA composite scaffolds.
Next Article:Integrin [alpha]5[beta]1-mediated attachment of NIH/3T3 fibroblasts to fibronectin adsorbed onto electrospun polymer scaffolds.

Terms of use | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters