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

JJC

Miscibility, Crystallinity and Morphology of Polymer Blends of Polyamide-6/ Poly (β-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 Mu’tah University, Department of Chemistry, P.O. Box 7, Al-Karak, JORDAN c Mu’tah 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 ( β -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 12χ were negative for all blend

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

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

2Φ 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: aimanr@yahoo.com

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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 ε -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 (β -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

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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 (β-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 fNN

RTG

χ21222111 ln/ln/ ΦΦ+ΦΦ+ΦΦ=∆

, (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 12χ is a summation of individual interaction parameters ijχ , which is

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

Blendχ can be written as:

( )( ) ( )( ) ( )( ) ACBCABBlend y1yxy1x1x1xy χ−−+χ−−+χ−−=χ (2)

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

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

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

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

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

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

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

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

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

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

'AC3

'BC2

'AB1Blend χα+χα+χα=χ . (3)

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

iα can be written as:

22123

212

11211

ΦΦ−ΦΦ=ΦΦ=

ΦΦ−ΦΦ=

ααα

. (4)

Experiments Raw Materials

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

(β -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.

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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 150 o 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 cm−1 .

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

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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-λ)% were calculated by using the

following Equation [19].

( ) 100.

%1%100

×∆

∆=−

wHH

of

fλ (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-λ)% of PA6 and PHB are calculated by using o

6PA%100fH∆ = 21470 J/mol.monomer [24], and oPHB%100fH∆ = 1268 J/mol.monomer [25]

as shown in Figure 2. The (1-λ)% 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

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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, ( )λ−1 %, versus Φ2 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 •

−+=γγ11 , (6)

where γ 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 o

mT ) 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

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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 12χ . 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(11Φ−=

−

∆− χo

mo

mB

of

TTRVVH

, (7)

where omT and o

mBT 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 2Φ is the volume fraction of second component in the blend. If values

of omT and o

mBT are obtained, a suitable graphical procedure using Equation 7

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

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

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

line passing through the origin if 12χ 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( Φ− 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 cm3/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 12χ were found to be negative for all investigated

compositions, as PHB content increases the 12χ 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 12χ that

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

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

PA6/PHB blend composition 1Φ o

mT 12χ

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 12χ varies with Φ ,

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 Φ−Φ+−=χ (8)

Segmental Interaction Parameters

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

segmental interaction parameters; BCAB ,χχ and ACχ , 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 ijχ and 'ijχ 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 ACχ and 'ACχ means that

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

interaction parameter 12χ . 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 12χ (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

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negative and therefore favorable interaction between the methylene and amide units

ABχ 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 'ABχ are small and positive which are more logical than the values of ABχ which mean

high repulsion between the segments in the blend.

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

blends.

Segment

ijχ * 'ijχ **

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 12χ 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 Φ from which each segment becomes, the values of ijχ and

'ijχ 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 12χ .

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

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

simply to give an idea about the segmental interaction parameter ijχ 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

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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=ν and NHν 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

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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=ν and NHν 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=∆ν ) are shown in Figure 5B. Shifts in

OC=ν and NHν 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 80°C, 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.

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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

( β -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 12χ at each composition. The values of

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

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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 ijχ

and 'ijχ are evaluated by fitting 12χ with iα and found to be consistent with the net

12χ . 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.

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