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  • Jordan Journal of Chemistry Vol. 1 No.2, 2006, pp. 155-170

    JJC

    Miscibility, Crystallinity and Morphology of Polymer Blends of Polyamide-6/ Poly (-hydroxybutyrate)

    Aiman Eid Al-Rawajfeha*, Hasan A. Al-Salahb, Ismael Al-Rhaelc

    a Tafila Technical Univesity, Department of Chemical Engineering,P.O. Box 179, Tafila 66110, JORDAN, b Mutah University, Department of Chemistry, P.O. Box 7, Al-Karak, JORDAN c Mutah University, Department of Physics., P.O. Box 7, Al-Karak, JORDAN Received on Feb. 26, 2006 Accepted on Nov. 30, 2006

    Abstract

    Polyamide-6 (PA6) with bacterial poly ( -hydroxybutyrate) (PHB) are typical polyamide and polyester, respectively. PA6 is known to be high-strength engineering thermoplastic.

    Although it is ductile at room temperature, it becomes brittle under severe conditions such as

    high strain rates and/or low temperatures. This is due to the low crack propagation resistance of

    polyamides. PHB is a biodegradable and biocompatible thermoplastic polymer of high melting

    temperature (180 o C ) and crystallinity. PHB has attracted much attention as an environmentally degradable resin to be used for agricultural, marine and medical applications. One of the

    limitations of PHB for these applications is its brittleness and narrow processing window.

    Blending of friendly environmental biopolymers with synthetic polymers has proven to be a

    suitable tool to produce novel materials with combined characteristics in having both improved

    application properties and low cost advantages in material performance. In this study, the

    segmental interaction parameters, crystallinity, miscibility and morphology of polymer blends

    (PB) of PA6 and PHB have been studied at different weight fractions and different crystallization

    temperatures. The experimental approaches utilized are Differential Scanning Calorimetry

    (DSC), Fourier Transform Infrared (FTIR) and Polarized Optical Microscopy (POM). The

    interaction parameters were calculated using the Nishi-Wang equation, which is based on the

    Flory-Huggins theory. The values of interaction parameters 12 were negative for all blend

    compositions suggesting that 12 depends on the volume fraction ( ) of the polymer.

    Significant upward shifts of OC= and NH are observed with increasing the voume fraction

    2 of PHB which reflect the miscibility of the blend systems. Polymer blends show spherulitic

    morphology and the spherulites exhibit a banded structure. The band spacing decreases with

    increasing PHB content.

    Keywords: PA6; PHB; Crystallinity; Miscibility; Hydrogen bonding; Interaction parameters; Morphology.

    * Corresponding Author: E-mail: [email protected]

  • 156

    Introduction Polymer Blend (PB) is a mixture of at least two polymers or copolymers.

    Polymer blends are becoming more important in specific sectors of polymer industry [1],

    as they can frequently meet performance requirements that cannot be satisfied by the

    currently available commodity polymers. Consequently, their attractiveness increases

    with the increasing demands for this class of materials. As a logical consequence,

    many studies have been devoted to polymer blends, with special emphasis on their

    mechanical and thermal behavior. It is possible to obtain polymer blends of more

    desirable properties by mixing miscible polymers, and thus it is very important to

    examine the factors affecting the miscibility of polymer mixtures. The miscibility term

    describes the homogeneity of polymer mixtures at some temperatures. Miscibility can

    be influenced by various factors such as morphology, crystalline phase, intermolecular

    interaction, and reduction of surface tension.

    The most common method to establish polymer miscibility is Differential

    Scanning Calorimetry (DSC), with which determination of the glass transition

    temperature (Tg) or the depression of the melting temperature allow one to obtain

    details of the mixing. In some cases, it is necessary to use other experimental

    techniques. The optical microscopy is used to study the spherulitic superstructure of

    polymer crystals from the melt and explain the relationship between morphology and

    crystal growth rate. In addition, Small-angle light scattering (SALS) and Small-angle X-

    ray scattering (SAXS) are used to study the morphology of crystalline/amorphous

    polymer blends.

    The miscibility of homopolymer/copolymer blends has been successfully

    described by the binary interaction model. The most common specific intermolecular

    interactions occuring between two different polymer chains are: hydrogen bond, ionic

    bond and dipole-dipole interactions [2].

    Polyamides (Nylons) are known to be high-strength engineering thermoplastics.

    Although they are ductile at room temperature, they become brittle under severe

    conditions such as high strain rates and/or low temperatures. This is due to the low

    crack propagation resistance of polyamides. Polyamide-6 (PA6), -[-(CH2)5CONH-]-n is

    prepared by ring-openning polymerization of -caprolactam. Many investigators have studied the blends of polyamide-6, these studies contain; caprolactam /caprolactone

    copolymer [3], aromatic polyamides [4-6], poly(vinyl alcohol) [7], aliphatic polyamides [5, 8,

    9], poly(2-vinyl pyridine) [10], poly(acrylic acid) [11], poly(phenylene oxide) [12],

    poly(ethylene oxide) [13], polycarbonate [14, 15], polycaprolactone (PCL) [16], polyarylate [17], chitosan [18], and liquid crystalline polymer [19, 20].

    Poly ( -hydroxybutyrate) (PHB), -[-CH(CH3)CH2COO-]-n ,is an optically active

    polymer of D- (-) 3-hydroxybutyric acid and produced by a variety of microorganisms

    as an intercellular carbon and energy reserves [21]. PHB is a biodegradable and

    biocompatible thermoplastic polymer of high melting temperature (180 o C ) and

  • 157

    crystallinity. PHB has attracted much attention as an environmentally degradable resin

    to be used for agricultural, marine and medical applications [22]. One of the limitations

    of PHB for these applications is its brittleness and narrow processing window.

    However, a significant number of studies on blending of PHB were reported; with

    poly(methylmethacrylate) (PMMA) [23, 24], poly(epichlorohydrin) [25, 26], poly(ethylene

    oxide) [27, 28], poly(vinyl phenol) [29, 30], poly(vinyl acetate) [31], poly(vinyliden fluoride) [32],

    poly(ethylene succinate) [33], poly(vinyl alcohol) [34], poly(l-lactide) [35], chitin and

    chitosan [36], poly(vinylidene chloride-co-acrylonitrile) copolymer [37], styrene-vinyl

    phenol copolymer [38]. Correlation between degree of crystallinity, morphology, glass

    temperature, mechanical properties and biodegradation of PHB and its blends has

    benn reported [39].

    The purpose of this work is to study the crystallinity, miscibility, melting point

    depression, segmental interaction parameters, and morphology of polymer blends of

    polyamide-6 with Poly (-hydroxybutyrate), (PHB) by using Differential Scanning

    Calorimetry (DSC), Fourier Transform Infrared (FTIR), and Polarized Optical

    Microscopy (POM).

    Theoretical Background Depending on Flory-Huggins theory, the free energy balance of mixing two

    copolymers can be written as [5, 40, 41]:

    ( ) ( ) ( )[ ]ijm fNNRTG

    21222111 ln/ln/ ++=

    , (1)

    where mG is the Gibb's free energy of mixing, 1N and 2N are degree of

    polymerization, T is the absolute temperature and R is the gas constant. The free energy of mixing consists of three main contributions: The combinatorial entropy of

    mixing, the exchange interactions and the free-volume contribution.

    PA6/PHB can be written as y1yx1x CA/BA copolymer blends. Ellis [3-5]

    stated that the net 12 is a summation of individual interaction parameters ij , which is

    affected by the molar fractions x, y and z of the polymer segments A, B, C and D.

    Blend can be written as:

    ( )( ) ( )( ) ( )( ) ACBCABBlend y1yxy1x1x1xy ++= (2)

    This model predicts polymer miscibility, i.e., Blend < 0, even though all

    individual segmentals ij > 0. Alternatively it can be stated that miscibility can result

    between a homopolymer and a copolymer. The simplicity of the model requires a

  • 158

    number of assumptions that are known not to be true and will obviously introduce

    some errors. The most important of these include that is independent of

    composition and that free volume effects are neglected [3, 4].

    To obtain the individual segmental interaction parameters ij , a modification of

    Equation 2 can be assumed [7, 42] by adding a new term i . Because x and y are

    constant at the volume fraction i of a certain system, a new interaction parameter

    ( 'ij ) can be expressed containing the molar volume fraction of each segment:

    'AC3

    'BC2

    'AB1Blend ++= . (3)

    Where i is a new adjustable parameter that fit the value at each volume fraction i .

    i can be written as:

    22123

    212

    11211

    ==

    =

    . (4)

    Experiments Raw Materials

    Polyamide-6 was obtained from Aldrich Chem. Co. and used as reseived. Poly

    ( -hydroxybutyrate) (PHB) was supplied by Centro De Technologia Copersucar

    (Brazil) and purified by dissolving the polymer in chloroform, precipitated in methanol,

    filtered and dried at room temperature for 12h and then dried under vacuum at

    60 Co for 12h. Blend Preparation

    The binary blends were made by mixing solutions (approximately 3% w/w) of

    each polymer in 98% formic acid. The solutions were stirred for 2h at ambient

    temperature. The films for DSC and FTIR measurements were prepared by casting the

    polymer solutions into shallow soda-glass dishes and allowing the solvent to evaporate

    slowly. The thin films were dried at 60 o C and placed under vacuum at 70-80 o C for at least 3 days to constant weight. Blend compositions of PA6/PHB were 80/20, 60/40,

    50/50, 40/60 and 20/80 by weight.

  • 159

    Characterization Methods

    Differential Scanning Calorimetry (DSC)

    DSC measurements were performed on a DuPont 910 DSC Differential

    Scanning Calorimeter equipped with a Thermal Analysis Data System (TA-2000). The

    samples were first heated from room temperature to 250 o C and maintained for 2

    minutes, and then the samples were quenched cooled to -70 o C to prevent

    crystallization before thermograms were taken. The scanning rate was 10 o C /min. In the isothermal crystallization experiments blends samples of 9-11mg were used.

    Starting at room temperature, the samples were rapidly heated to melting temperature

    to remove any previous crystallinity. The samples were held for 6h at a certain

    crystallization temperature ( CT = 50, 100 and 150o C ), and then were heated to

    250 o C at a rate of 10 o C /min under dry nitrogen atmosphere. Fourier Transform Infrared Spectroscopy (FTIR)

    The FTIR spectra were collected on dry thin film polymer blend samples using a

    UNICAM (Mattson 5000) spectrophotometer by sandwiching the film samples between

    two KBr disks. All of the films were sufficiently thin to be within a range where the

    Beer-Lambert law is obeyed. Films were annealed at 50, 100, and 150 o C for 6h, then

    32 scans were made for each CT at a resolution of 8 cm1 .

    Polarized Optical Microscopy (POM)

    The morphology of polymer and blend samples were performed on thin films

    using a Nikon Polarized Optical Microscope (Optiphot-Pol) equipped with a Mettler hot

    stage (FP82). Samples were sandwiched between microscope cover glasses, melted

    at 225 Co , and then rapidly cooled to the crystallization temperature CT (ambient

    temperature and 100 o C ), and maintained for 6h. Results and Discussions Thermal Behaviour and Miscibility

    Differential Scanning Calorimetry (DSC)

    DSC curves for pure PA6, PHB and PA6/PHB blends are shown in Figure 1.

    The DSC curves show endothermic melting temperature peaks at 221 and 151 Co of

    pure PA6 and PHB, respectively. Melting temperature mT decreases with increase of

    PHB content. In general, a decrease in the melting point in a polymeric blend can be

    due to both morphological effects (decrease in lamellar thickness) and to

    thermodynamic factors (polymer-polymer interactions).

    The results show a slight decrease in the value of fH at ambient conditions. It

    is also observed that the fH values are consistently decreased as the PHB content

    increased at various crystallization temperatures. The most probable reason is the very

  • 160

    slow rate of crystallization one can anticipate at this CT in blend containing small

    quantity of PA6.

    Figure 1: DSC Thermogram of PA6/PHB blends at ambient temperature.

    Crystallinity

    Crystallinity percent of the PA6 and PHB phases (1-)% were calculated by using the

    following Equation [19].

    ( ) 100.

    %1%100

    =

    wHH

    of

    f (5)

    Where fH is the apparent enthalpy of melting of PA6 or PHB, w is the weight

    fraction of PA6 or PHB in the blends, and o %100fH is the extrapolated value of the

    enthalpy corresponding to the melting of 100 % crystalline sample.

    The crystallinity levels (1-)% of PA6 and PHB are calculated by using o

    6PA%100fH = 21470 J/mol.monomer [24], and o PHB%100fH = 1268 J/mol.monomer

    [25]

    as shown in Figure 2. The (1-)% values increase with increasing PHB content up to

    50%. Such a result is probably due to the trapped fraction of PA6 in the interlamellar

    amorphous regions of PHB spherulites which is not allowed to crystallize. The

  • 161

    crystallinity percent of PA6 depends on the crystallization temperatures. For example,

    the crystallinity percent of PA6 at 150 oC is doubled compared to ambient conditions.

    Figure 2: Crystallinity percent, ( )1 %, versus 2 of PA6/PHB at ambient and 150 Co .

    Melting Point Depression

    The equilibrium melting points, omBT , values for individual blends can be

    determined by the method of Hoffman and Weeks [43]:

    omB

    CmB T

    TT

    +=11 , (6)

    where is the ratio of the initial and the final lamellar thickness, and CT is the

    isothermal crystallization temperature.

    The mT of PA6, crystallized isothermally from its mixtures with PHB, are plotted

    versus CT (Figure 3) and extrapolated to line where Cm TT = to obtain the equilibrium

    melting points omBT (or omT ) of an infinitely large crystals. A good linear correlation

    between mT and CT was observed. Because only mT values need to be determined,

    this technique has been the method of choice for estimating blend equilibrium melting

  • 162

    point. The values of omT obtained by this method clearly indicate that the addition of

    PHB cause a significant depression in the omT .

    Figure 3: Hoffman-Weeks plot of PA6/PHB blends.

    Flory-Huggins Interaction Parameter

    Thermodynamics predicts that the decrease in chemical potential of the

    crystallizable polymer is due to the presence of the miscible amorphous polymer,

    resulting in a decease in the melting point. This has been modeled by Nishi and Wang [44], which is based on the Flory-Huggins Theory to obtain polymer-polymer interaction

    parameter 12 . Blend melting points are frequently used to estimate the magnitude of

    the polymer-polymer interactions at omBT . When the entropy of mixing is negative:

    2212

    2

    1 )1(11 =

    o

    mo

    mB

    of

    TTRVVH

    , (7)

    where omT and omBT are the equilibrium melting point of the crystallizable component

    in the pure state and the blend, respectively, R is the universal gas constant, iV is

    the molar volume of the respective component, ofH is the heat of fusion per mole of

    repeat unit, and 2 is the volume fraction of second component in the blend. If values

    of omT and omBT are obtained, a suitable graphical procedure using Equation 7

  • 163

    facilitates an estimation of 12 (i.e. Blend ). A plot of the left-hand side of Equation 7

    versus the square of the PHB volume fraction 22 )1( in the blend, Figure 4, can be

    used to estimate the PA6/PHB interaction parameters 12 . This should give a straight

    line passing through the origin if 12 is independent of the composition and the

    melting point depression is not influenced by morphological effects.

    Figure 4: Left-hand side of Equation (7) versus 22 )1( of PA6/PHB blends.

    In order to calculate the Left-Hand Side of Equation 7 the parameter values

    used are as follows: ofH =1268 J/mol.monomer PHB [25], 1V =104.24 cm

    3/mol, 2V =

    75 cm3/mol, and R is the universal gas constant (8.314 J/mol.K). The values Vi are

    calculated by using the amorphous density of PA6 (1.084 gcm-3), and

    PHB (1.15 gcm-3), respectively.

    In Table 1, the values of 12 were found to be negative for all investigated

    compositions, as PHB content increases the 12 become more negative, which

    explains the depression of mT with increasing PHB content. This strongly indicates

    that in the melt, at omT , PA6 and PHB are compatible. The negative values of 12 that

    indicate miscibility, is due to the hydrogen bonding between PA6 segments and PHB.

  • 164

    Table 1: Values of 1 , omT and 12 of the blends.

    PA6/PHB blend composition 1

    omT 12

    100/0 1.0 220.70 - 80/20 0.8 220.38 -0.0004 60/40 0.6 218.00 -0.0066 50/50 0.5 217.04 -0.0125 40/60 0.4 215.22 -0.0301 20/80 0.2 210.87 -0.2179 0/100 0.0 - -

    It can be noticed from Table 1, that the interaction parameter 12 varies with ,

    so that it can be fitted, applying a least-square method, as a function of composition,

    according to Utracki [46]:

    21112 1088.14468.15535.4 += (8)

    Segmental Interaction Parameters

    A method based on the least-square analysis can be used to calculate the

    segmental interaction parameters; BCAB , and AC , for the systems which satisfy

    the highest correlation factor (R2). The values of x=0.7676, and y=0.6580 which are

    calculated using the group contributions to the molar volume of

    polymer )mol/cm(V 3i , CH2 (16.45), CHCH3 (32.65), CONH (24.9) and COO (25.90),

    respectively [4]. The values of ij and 'ij are shown in Table 2. It can be noticed that

    the correlation constants (R2 ) are very high. The physical basis of such a large positive

    interaction between CH2/COO segments can be understood and justified easily within

    the context of the PHB chemical nature which does not include any of possible

    interactions (i.e. no self-association). The positive values of AC and 'AC means that

    there are very good repulsion between PHB segments which is favorable to the net

    interaction parameter 12 . The repulsion effect of each CH2 of PHB and CONH of

    polyamide is very small comparing to its repulsion in the mother polymer which is

    consistent with net interaction of CH2 /CONH segments.

    Negative interactions between CONH of PA6 with COO of PHB can be clearly

    observed. This result supports the net value of 12 (i.e. miscibility), which can be

    attributed to the intermolecular hydrogen bonding of these segments. It can be

    understood within the context of the polymer chemical nature of containing the

    hydrophilic functionality. A supporting result can be obtained by FTIR vibration

    frequency of amide, and hydroxyl units which will be discussed in the next section. The

  • 165

    negative and therefore favorable interaction between the methylene and amide units

    AB means that there is still interaction between them, which is not easy to qualify.

    When a negative value of PA6 methylene and amide units arises, an equal counter

    current effect of negative interaction of PHB methylene segment with the same amide

    segment arises simultaneously, also it is attributable to overcoming this interaction of

    such segments by the effect of the strong interaction of CONH/COO and the repulsion

    of PHB segments (i.e. CH2/COO). The interaction of CH2/CONH of PA6/PHB is nearly

    1/6 of the repulsion of CH2/COO, on the other hand, the interaction of CH2/CONH of 'AB are small and positive which are more logical than the values of AB which mean

    high repulsion between the segments in the blend.

    Table 2: Segmental and corrected interaction parameters ij and 'ij of PA6/PHB

    blends.

    Segment

    ij * 'ij **

    A/B, CH2/CONH -1.9369 0.1174 B/C, CONH/COO -0.4604 -0.03659 A/C, CH2/COO 12.1481 0.4554

    R2 0.9679 0.9679 * Calculated using Ellis equations [3-5]. ** This work

    The value of 12 for any polymer blend is usually small and representative of

    the overall interaction of two different polymer molecules [4]. In this type of assumption,

    where the individual mers are chemically distinct by its molar volume fraction (x and y)

    and the volume fraction from which each segment becomes, the values of ij and

    'ij may be extreme. If the individual mers become less distinct, then the individual

    segmental interaction parameters will be closer to that of the original polymer

    molecule 12 .

    For all these values of ij and 'ij , the qualitative picture does not change at all;

    only the quantitative values change such that the role of 12 in such approach is

    simply to give an idea about the segmental interaction parameter ij of each segment,

    as interaction or repulsion, and to support the FTIR results of affected vibration modes

    of that segment.

    Fourier Transform Infrared (FTIR) Spectroscopy

    Polyamides are self-associating polymers through hydrogen bond, while

    polyester (such as: PHB) is an example of so called adduct or inter-association group

    which associate only with the other component. IR spectroscopy has proved to be an

  • 166

    excellent tool to study the hydrogen-bonding behavior in polyamides and polyamide

    blends. If the blend is immiscible, the absorption spectrum of the blend will be the sum

    of those for the components. If the blend is miscible because of the specific

    interactions, then differences will be noted in the spectrum of the blend relative to the

    sum of those for the components. The FTIR investigation of a miscible blend will not

    only reveal the presence of such an interaction, but will provide information on which

    groups are involved [47]. No detailed information can be derived from the order-

    sensitive absorption band in the 500 to 1200 cm-1 wavenumber region, while significant

    changes can be observed for the intensity, wavenumber position and shape of the

    OC= and NH absorption bands, as consequence of change in the hydrogen

    bonding state (Figure 5). The peak at ca. 1613 cm-1 is due to the free carbonyl, and the

    peak at 1532 cm-1 arises from the carbonyls that are hydrogen bound. As PHB content

    increases the two peaks split to two sharper peaks and lower the area at higher

    frequency, until both disappear. The peaks of free association and bound NH arise at

    3337 and 3250 cm-1, respectively, they remain unchanged up to (60/40) PA6/PHB, and

    then become shifted and sharper at 50/50, 40/80, and 20/80 fractions, and the sharp

    peak of PHB at 3438 cm-1 appears and does not change.

    Figure 5: FTIR spectra of PA6/PHB blend system: (A) NH stretching band, (B) shifts in C=O frequency.

    The vibration of IR spectra at the NH and C=O stretching band reflect the

    hydrogen bonding condition of amide groups [48] and the hydrogen bond formation

    generally shifts to lower frequently due to the N-H and C=O stretching modes. This is

    an important source of information, since hydrogen bonding is a strong intermolecular

    interaction and should affect the miscibility. In the presence of PHB slight downward

  • 167

    frequency shift of N-H and significant upward frequency shift of C=O stretching

    absorptions had occurred on blending. The chemical structure of the polymers

    supports the possibility of formation hydrogen bonds between amide group with each

    of the ester and hydroxyl groups that should lead to miscible blends. The occurrence of

    a hydrogen bonding interaction perturbs the C=O, NH and OH groups by changing its

    electronic environment, and provide a favorable enthalpic contribution to mixing. The

    enthalpy of hydrogen bond formation is always negative when a self-associating

    polymer molecule is a component of a mixture; a positive contribution to the change in

    enthalpy arises from the breaking of the hydrogen bonds of the self-associating

    molecules [47].

    In the presence of PHB, the maximum peaks positions of OC= and NH have

    shifted toward lower wavenumbers as shown in Figure 5. The NH stretching band are

    shown in Figure 5A and shifts in the C=O ( OC= ) are shown in Figure 5B. Shifts in

    OC= and NH indicate the miscibility of the blend system [7, 47, 49]. It can be

    proposed that the formation of hydrogen bonding between C=O and NH groups is the

    predominant, since the formation of hydrogen bonding is always favorable to the

    miscibility. It was claimed [48] that non-combinatorial entropy change involves in the

    strongly associating polymer blends, and that the favorable contribution of the entropy

    can overcome the unfavorable enthalpy increase accompanied by the dissociation of

    the hydrogen bonding. This non-combinatorial entropy mechanism of miscibility also

    explains phase separation observed in the high-PA6-content blend systems.

    Morphology

    Polarized optical microscopy observations of the crystallization processes at

    ambient temperature and 80C, indicate that PA6 and PHB are able to crystallize

    according to spherulitic morphology even in case of the 80/20 PA6/PHB blend (Figure

    6). The spherulites exhibit a typical banded structure. In 80/20 blend the banded

    spherulite of PHB superimposed on the spherulitic structure of PA6. Two phases are

    observed in 60/40 blend, the bright region is PHB and the dark region is PA6. The

    same observation is observed in 50/50 blend. In 40/60 and 20/80 blend systems,

    miscible regions are observed, characterized by ringed spherulites and the band

    spacing decreases with the composition as PHB content is increased.

    The preliminary results at these crystallization temperatures show the existence

    of wide variety of morphologies. These complicated morphologies will result from

    competitive nucleation and growth processing for PA6 and PHB as expressed

    previously. Beside that, which is consistent with depression of the equilibrium melting

    temperature, the blend composition will also control the nature of the interlamellar

    amorphous material and its composition. It is observed that each spherulite exhibits

    extinction cross (a Maltese cross). The Maltese cross occurs when the principal

    directions of the radial units fall parallel to those of the polarizing microscope.

  • 168

    Nucleation rate together with growth determine the size and number of spherulites:

    slow nucleation and fast growth result in a small number of large spherulites, whereas

    fast nucleation and slow growth result in a large number of small spherulites [50].

    Figure 6: POM (X 100) of PA6/PHB blends at ambient temperature and 80oC.

    The other significant observation of the blends is the appearing of cracks. It was

    inferred that those cracks might contribute to the embrittlement of PHB. Two types of

    cracks were identified, one running circumferentially around spherulites and the other

    running radially through them. Barham et al [51] suggested that the circumferential

    cracks may be caused by thermal stresses that occur during the cooling of the

    spherulites from the high crystallization temperatures down to room temperature. They

    show that the cracks are, in fact, due to differences in thermal expansion between the

    PHB film and the constraining glass slides.

    Conclusion Blending of friendly environmental biopolymers with synthetic polymers has

    proven to be a suitable tool to produce novel materials with combined characteristics in

    having both improved application properties and low cost advantages in material

    performance. The melting and crystallization of Polyamide-6 (PA6) with bacterial poly

    ( -hydroxybutyrate) (PHB) were studied at different weight fractions. In this blend

    system clear depression of the omT was observed. The blend systems are found

    miscible because of the negative values of 12 at each composition. The values of

    PA6/PHB interaction parameters up to 50/50 are slightly negative; so that those blend

  • 169

    systems can be considered as partially miscible such a result is strongly supported by

    POM in which two phases are observed. The segmental interaction parameters ij

    and 'ij are evaluated by fitting 12 with i and found to be consistent with the net

    12 . FTIR results strongly support the DSC results that give an idea about

    intermolecular hydrogen bonding which is favorable to the free energy of mixing.

    Ringed spherulites are formed in the mixture crystallized from the melt suggesting a

    strong effect of PHB and PVA on the melting and crystallization of PA6.

    Acknowledgement:

    This work has partially been supported by the Ministry of Higher Education and

    Scientific Research, Jordan. The valuable discussions with Prof. S. Khalil, Mu'tah

    University, are greatly acknowledged.

    References [1] Miles, I. S.; Rostami, S., Multicomponent Polymer Systems, Longman Scientific and

    Technical, 1992. [2] Landry, M. R.; Massa, D. J.; Landry, C. J. T.; Teegarden, D. M.; Colby, R. H.; Long, T. E.;

    Henrichs, R. M., J. Appl. Polym. Sci., 1994, 54, 991. [3] Ellis, T. E., J. Polym. Sci., Polym. Phys., 1993, 31, 1109. [4] Ellis, T. S., Macromolecules, 1989, 22, 742. [5] Ellis, T. E., Polymer,1992, 33, 1469. [6] Shibayama, M.; Uenoyama, K.; Oura, Jun-ichi; Nomura, S.; Iwamoto, T., Polymer, 1995,

    36, 4811. [7] Al-Rawajfeh, A. E., Desalination, 2005, 179, 209. [8] Majumdar, B.; Keskkula, H. and Paul, D. R., Polymer, 1994, 35, 1399. [9] Davis, C. R., J. Appl. Polym. Sci., 1996, 62, 2237. [10] Skrovanek, D. J.; Coleman, M. M., Polym. Eng. Sci., 1987, 27, 857. [11] Jin, Y.; Huang, R. Y. M., J. Appl. Polym. Sci., 1988, 36, 1799. [12] Laverty, J. J., Polym. Eng. Sci., 1988, 28, 360. [13] Kodama, M.; Kuramoto, K.; Karino, I., J. Appl. Polym. Sci., 1987, 34, 1889. [14] Gattiglia, E.; La Mantia, F. P.; Turturro, A.; Valenza, A., Polym. Bull., 1989, 21, 47 [15] Gattiglia, E.; Turturro, A.; Pedemonte, E.; Dandero, G., J. Appl. Polym. Sci., 1990, 41,

    1411. [16] Kim, W.; Park, Ch.; Burns, C. M., J. Appl. Polym. Sci., 1993, 49, 1003. [17] Ahn, T.O.; Lee, S.; Jeong, H. M.; Lee, S. W.; Polymer, 1996, 37, 3559. [18] Dufresne, A.; Cavaill, J. Y.; Dupeyre, D.; Garcia-Ramirez, M.; Polym. J., 1999, 40,

    1657. [19] Campoy, I.; Gomez, M. A.; Marco, C.; Polymer, 1998, 39, 6279 [20] Seo, Y.; Kim, B.; Kwak, S.; Kim, K. U.; Kim, J., Polymer, 1999, 40, 4441. [21] Sharma, R.; Ray, R. A., J. Macromol. Sci.-Rev., 1995, C 35(2), 327. [22] King, P. P., J. Chem. Tech. Biotechnol., 1982, 32, 2. [23] Lotti, N.; Pizzoli, M.; Ceccorulli, G.; Scandola, M., Polymer, 1993, 34, 35. [24] Cannetti, M.; Sadocco, P.; Siciliano, A.; Seves, A., Polymer, 1993, 35, 2884. [25] (a) Peglia, E. D.; Beltrame, P. L.; Canetti, M.; Seves, A.; Marcandalli, B.; Martuscelli, E.,

    Polymer, 1993, 34,996. (b) Saddoca, P.; Caneti, M.; Seves, A.; Martuscelli, E., Polymer, 1993, 34, 336. [26] (a) Miguel, O.; Eguiburu, J.; Iruin J.J., Polymer, 2001, 42, 953. (b) Gonzalez, A.; Iriarte, M.; Iriondo, P.J.; Iruin, J.J., Polymer, 2003, 44, 7701. [27] Wang, J. H.; Schertz, D. M., US Patent 6890989, 2005. [28] Avella, M.; Martuscelli, E.; Raimo, M., Polymer, 1993, 34, 3234. [29] Iriondo, P.; Iruin, J. J.; Fernandez J. Berridi, Polymer, 1995, 36, 3235. [30] Xing, P.; Dong, L.; An, Y.; Feng, Z.; Avella, M.; Martuscelli, E., Macromolecules,1997, 30,

    2726. [31] Greco, P.; Martuscelli, E.; Polymer, 1989, 30, 1475. [32] Marand, H.; Collins, M., Polym. Prep. Am. Chem. Soc., 1990, 31, 552.

  • 170

    [33] Al-Salah, H. A., Polym. Bull., 1998, 41, 593. [34] Azuma, Y.; Yoshie, N.; Sakurai, M.; Inoue, Y.; Chujo, R., Polymer, 1992, 33, 4763. [35] Zhang, L.; Xiong, C.; Deng, X., Polymer, 1996, 37, 235. [36] Ikejima, T.; Inoue, Y., Carbohydrat Polymers, 2000, 41, 351. [37] Gonzalez, A.; Irirte, M.; Iriondo, P.J. ; Iruin, J.J., Polymer, 2002, 43, 6205. [38] Gonzalez A.; Irusta L.; Fernandez-Berridi M. J.; Iriarte, M.; Iruin, J.J., Polymer, 2004, 45,

    1477. [39] El-Hadi, A.; Schnabel, R.; Straube, E.; Mller, G.; Henning, S., Polymer Testing, 2002,

    21, 665. [40] Paul, D. R.; Newmans, S., Polymer Blends, Academic: New York, 1978. [41] Ten Brinke, G.; Karasz, F.E; Macknight, W. J., Macromolecules, 1983, 16, 1827. [42] Al-Rawajfeh, A. E.; Al-Salah, H. A., Proc. PPS-20, 20th annual meeting of the Polymer

    Processing Society, Akron, June 20-24, 2004. [43] Hoffman, J. D.; Week, J. J., J. Res. Natt. Bur. Stand. USA, 1962, 66, 13. [44] Nishi, T.; Wang T. T., Macromolecules, 1975, 8, 909. [45] Zhu, S.; Hamidec, E., Macromolecules, 1993, 26, 3131. [46] Utracki, L. A., Polymer Alloys and Blends, Hanser Publisher, Munich Vienna New York

    1990. [47] Siesler, H. W.; Holland-Moritz, K., Infrared and Raman Spectroscopy of Polymers,

    Marcel Dekker, Inc., 1980. [48] Nakata, S.; Kakimota, M.; Imai, Y., Polymer J., 1993, 25, 569. [49] Flory, P. J., Principle of Polymer Chemistry, Cornel University Press, New York NY,

    1956. [50] Bassett, D. C., Principles of polymer Morphology, Cambridge University Press,

    Cambridge, 1981. [51] Hobbs, J. K.; McMaster, T. J.; Miles, M. J.; Barham, P. J., Polymer, 1996, 37, 3241.