Effect of Processing Conditions on the Development of Morphological Features of Banded or Nonbanded...

Effect of Processing Conditions on the Development ofMorphological Features of Banded or NonbandedSpherulites of Poly(3-hydroxybutyrate) (PHB) andPolylactic Acid (PLLA) Blends

Ahmed Mohamed El-HadiDepartment of Physics, Faculty of Applied Science, Umm Al-Qura University, Saudi Arabia

Two semicrystalline poly(3-hydroxybutyrate) (PHB) andpolylactic acid (PLLA) blends with and without poly(vinyl acetate) (PVAc) were prepared by dissolving dif-ferent ratios in hot chloroform at 50 8C to obtain prom-ising alternative biodegradable materials for eliminat-ing plastic waste. The miscibility, crystallization, melt-ing behavior and vibration modes of the preparedsamples were characterized by differential scanningcalorimetry (DSC), polarized optical microscopy (POM),Fourier transform infrared spectroscopy (FTIR), andwide angle X-ray diffraction (WAXD) techniques. DSCanalysis showed that only one crystallization tempera-ture for blends with PVAc (single homogeneous phase)and two crystallization temperatures for blends withoutPVAc (immiscible blends) were obtained. The POMresults indicated that the morphological structures ofB381, B551, and B831 samples consist of two types ofspherulites (fibrils and banded) which created at differ-ent crystallization temperatures. The irrelevant interac-tion between PHB and PLLA structures was detectedfrom FTIR spectra. The addition of PVAc caused anobvious decrease in the peak position of the carboxylgroup C¼¼O from 1752 to 1724 cm21 due to dipole-dipole interactions. WAXD indicated that the lattice pa-rameters are changed in blends with PVAc andunchanged without PVAc. Our results indicated that,the PVAc can be used as compatibilizer and improvedthe compatibility between PHB and PLLA. POLYM. ENG.SCI., 51:2191–2202, 2011. ª 2011 Society of Plastics Engineers

INTRODUCTION

The quantities of plastic waste are increasing in all pla-

ces of the world as the production and consumption of

plastic materials. Most of these plastic materials are pro-

duced from raw oil (petrols). However, the excess fabrica-

tion of plastic materials (polymers) resulted in increasing

the price of oil since the oil resources are limited. Alter-

natively, most of plastic materials are formed from petro-

chemicals such as; polyethylene (PE), polypropylene (PP),

polyvinyl chloride, and polystyrene (PS). Plastic materials

are widely used for different practical applications such

as; household, auto parts, building materials, and packag-

ing of food, seeing that their processing, physical proper-

ties and durability are excellent. However, the main disad-

vantage of these materials is its inherent toxicity and pol-

lution of air and groundwater caused by the retention of

nonbiodegradable waste plastic, which prevents its wide

practical applications. Hence, the issue of eliminating

plastic waste is imperative because of the increasing envi-

ronmental concerns, which has invoked extensive studies

on development of recycling of plastics in recent years.

Nowadays, there are several ways to be settled for dis-

posal of waste plastic.

Recycling of plastics again by rearranged according to

their types and colors which are expensive. This requires

cleaning after handling and arrangement according to

their types and colors. Moreover, the physical properties

of recycled plastics are not good as the first use.

Recycling of plastics by chemical decomposition. This

method requires a large amount of thermal and electrical

energy, which leading to remarkable high cost.

Recycling of plastics by burning. This method leads to

raising some toxic gases associated with increasing tem-

perature, such as carbon dioxide. Applying of such meth-

ods brings about big problems, like rising the earth tem-

perature which is known as a global warming.

Recycling of plastics by buried in landfills without bio-

degradation. This waste buried in the earth without any

exploitation leading to pollution of groundwater.

In the recent years, attracted attention has been made by

many scientists to solve this problem and to produce new

biodegradable polymer materials like; PHB, polylactic acid

(PLLA), starch and cellulose. PHB or PLLA are two of the

attractive polymers that can be used to overcome these

problems due to their natural biodegradability. These poly-

mers are produced from renewable natural sources such as;

Ahmed Mohamed El-Hadi is permanently at Department of Basic Sci-

ence, Higher Institute for Engineering and Technology, El Arish, North

Sinai, Egypt.

Correspondence to: Ahmed Mohamed El-Hadi; e-mail: Bioplastics.

[email protected]

DOI 10.1002/pen.21991

Published online in Wiley Online Library (wileyonlinelibrary.com).

VVC 2011 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2011

date syrup, sugar cane, and sugar beet, i.e., fermentation of

micro-organisms with natural fats, oils, molasses, date sy-

rup and some minerals [1–5]. PLLA and PHB could be

totally degraded in aerobic or anaerobic environment throw

2 months up to 3 years [1–3]. After purification, the lactic

acids are polymerized by using extruder and catalysts to

form a high molecular mass of PLLA. PLLA has both a

hydroxyl group and a carboxylic acid group similar to

PHB. Furthermore, both, PLLA and PHB is optically

active [6–8], water and oil resistant and linear aliphatic

polyester. PHB is a partially crystalline material with high

melting temperature and high degree of crystallinity [1–3].

On the other hand, PHB belongs to the family of Polyhy-

droxyalkanoates (PHAs) and has physical and mechanical

properties comparable to those of isotactic polypropylene

(iPP). Moreover, PHB and PLLA blends could be used for

short term packaging in the food industry, in particular for

deep drawing articles and thermoformed products such as;

drink cups, take-away food trays, containers and planter

boxes for surgical materials like; sutures and bone implants

(screws, pins, plates and fixation rods, etc) pharmaceutical,

cosmetic, textiles industries and agricultural films [1–6].

However, there are several problems to be settled for prac-

tical applications in both materials. For instance; brittle-

ness, higher glass transitions, poor mechanical properties

and slower crystallization rate, compared to synthetic poly-

mers such as; polystyrene (PS), polypropylene (PP) and

polyethylene terephthalate (PET). Due to these reasons,

PHB and PLLA blends cannot be used for many practical

applications, especially for food sector as packaging like

depth drawing article. We mixed PHB with highest crystal-

lization kinetics and PLLA with lowest crystallization

kinetics, since the chemical composition of both is similar.

The chemical structure of PHB is:

½�� O��CHðCH3Þ ��CH2��ðC ¼¼ OÞ ��n (1)

and chemical structure of PLLA is:

½�� O��CHðCH3Þ ��ðC ¼¼ OÞ ��n (2)

Polymer blends have more attractive attention in the

last decades. The polymer blending is a good economic

method, which can develop new materials with special

properties such as; greater ductility, stronger moduli and

higher mechanical strength. If two polymers are immisci-

ble with each other, i.e., two glass transition temperatures

or two crystallization temperatures appears in the blends

and the mechanical properties of the materials are weak-

ened. However, (PLLA/PHB) blends are crystalline/crys-

talline polymer. Their properties and miscibility depend

on the polymer molecular weight, blend composition,

chemical or physical cross linked interactions with each

other, morphology and processing conditions. The crystal-

line morphology depends on the crystallization conditions

since their components could be crystalline at a wide

crystallization temperature range. It has been found that

PLLA is immiscible with PHB (higher molecular weight)

[7–11], poly(butadiene-co-acrylonitrile) (NBR) [12],

poly(p-dioxanone) [13], poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-PHV) [14], poly (vinyl alco-

hol) (PVA) [15], poly(butylene succinate) (PBS) [16],

poly(caprolactone) [17], poly(ethylene succinate) [18, 19]

and thermoplastic starch [20]. Conversely, PLLA is misci-

ble with poly(vinyl acetate) (PVAc) [21] and poly(ethyl-

ene oxide) [21]. On the other hand, PHB is immiscible

with ethylene-propylene rubber (EPR) blend [22] and syn-

thetic atactic polyhydroxybutyrate (a-PHB) [8]. Now,

PHB is miscible with PVAc [22] and poly(ethylene oxide)

(PEO) [23]. Both PHB and PLLA are semicrystalline

polymers and consist of two different phases (amorphous

and crystalline). By addition of some polymers to an im-

miscible binary polymer blend, these polymers make as a

simple compatibilizer. Both poly(methyl methacrylate)

(PMMA) and poly(ethyl methacrylate) (PEMA) are im-

miscible, but with the addition of a suitable amount of

polyvinylidene fluoride (PVDF), the miscibility with both

PMMA and PEMA could be improved [24]. PHB is im-

miscible with polyepichlorohydrin (PECH), but polyethyl-

ene oxide (PEO) is miscible with PHB and PECH [25].

Another example, PHB is immiscible with PMMA, but

PEO is miscible with PHB and PMMA. Therefore, the

completely miscible blend is formed by adding PEO to

PHB and PMMA [26]. Since the blend of PHB and PLLA

is immiscible [7–9], the addition of PVAc to (PLLA and

PHB) blends makes it miscible. Therefore, the purpose of

this study is to prepare different types of blends from two

semi crystalline polymers; PLLA and PHB with and with-

out PVAc to develop of new biodegradable polymer

blends, used for different short term packaging in the food

and surgical industry, as a replacement of the nonbiode-

gradable petrochemicals. The structure, morphology, crys-

tallization, melting behavior and miscibility of blends

have been investigated by polarized optical microscopy

(POM), differential scanning calorimeter (DSC), wide

angle X-ray diffraction (WAXD) and FTIR spectroscopy.

Furthermore, correlations between the evolution of the

microstructure (morphology) and miscibility of blends are

studied.

EXPERIMENTAL

Materials

PHB crystallinity 60% (Mw ¼ 2.3 3 105 g/mol) and

PLLA crystallinity 40% (Mw ¼ 2.2 3 105 g/mol) were

supplied from Biomer1, Germany. PVAc (Mw ¼ 0.51 3105 g/mol) was purchased from Sigma-Aldrich Chemicals.

Preparation of Blends

The compositions of PHB/ PLLA/ PVAc blends were

prepared with different weight ratios as follows: (25/75/

0), (50/50/0), (75/25/0), (22.7/68.1/9.1), (45.4/45.4/9.1),

2192 POLYMER ENGINEERING AND SCIENCE—-2011 DOI 10.1002/pen

(68.1/22.7/9.1). The sample codes and compositions of

these composites was given in Table 1. All blends were

prepared by dissolving components together in hot chloro-

form at 508C, and then the solution was cast in a Petri

dish to prepare the casting films. The samples were dried

at 608C for 24 h to remove any residual solvent com-

pletely. The chemicals structures of PHB and PLLA were

shown at Scheme 1.

Measurements

Differential Scanning Calorimetry. DSC is an impor-

tant technique to study melting and crystallization behav-

ior of polymers. A thermal analysis was carried out with

a differential scanning calorimeter (Schimadzu-DSC 50,

Japan). All samples of 5 6 0.1 mg were sealed in an alu-

minum sample pan for DSC. Samples were kept under a

dry nitrogen atmosphere. DSC analysis was carried out

from room temperature to 2008C at heating and cooling

rates of 108C min21. Besides, the analysis of DSC curves

was carried out for the second heating run data to exam-

ine the melting temperature (Tm) and the cold crystalliza-

tion temperature (Tcc).

Polarized Optical Microscopy. The evolution of micro-

structure for all studied blends was examined using Nikon

polarizing microscope (Nikon Eclipse E600) equipped

with hot-stage (Instec STC200). Small amount of polymer

is placed between two microscopy glass slides as a sand-

wich and inserted to hot stage and melted at 2008C. Aftermelting, thin film was obtained by applied small pressing

on top glass slide (the thin film was approximately 0.05–

0.1 mm in thickness). The blends samples were heated on

the hot-stage from room temperature to 2008C and then

kept at 2008C for 3 min to erase their thermal history and

finally cooled from 2008C to a temperature where the

growing of spherulites are started.

Wide Angle X-Ray Diffraction (WAXD). The crystal-

line phases were analyzed by wide-angle X-ray diffraction

(WAXD) measured with Analytical PRO X’Pert -Holland,

Cu-Ka radiations (k ¼ 1.54178 A) in the range of 5–358at 40 kV. The WAXD data for PHB/PLLA blends were

obtained at room temperature (�258C), with the scan rate

of (28) 2 y min21. Film samples were cut into rectangular

pieces (4 cm2) and mounted on the matrix before analy-

sis.

FTIR Spectrometer. Infrared spectra were recorded

with a Fourier Transform FTIR 6100 Jasco spectrometer

in the wavenumber range 550–4000 cm21. All spectra are

recorded at room temperature. The films of the samples

are cut into rectangular pieces (4 cm2).

RESULTS AND DISCUSSION

Differential Scanning Calorimeter Analysis

DSC analyze used to identify the fundamental thermal

reactions of blends. Figure 1 shows the relation between

temperature and heat flow. One can seen the glass transi-

tion temperature (Tg) of pure PLLA appears at 708C. Inour previous work [1–3], we find that pure PHB has glass

transition temperature of 58C. Increasing the weight per-

centage of PHB results in a gradual decrease of Tg to

638C for B130 sample, 628C for B110 sample and 618C for

B310 sample. The second heating of all blends shows exo-

thermic peaks related to the cold crystallization tempera-

ture (Tcc). The decrease of PLLA content in the blend

provided an increase in Tcc. According to the DSC results,

the cold crystallization temperature (Tcc) of the samples

B130 and B310 are 108 and 1108C, respectively. In case of

B110 there are two values for Tcc, which are 108 and

1218C. The first peak is related to the PHB phase,

whereas the second peak is to the PLLA phase. When the

amount of PHB and PLLA are less than 25%, the blend

TABLE 1. The samples and composition of blends.

Sample code Composition (wt %)

PLLA PLLA (100)

B130 PHB/PLLA/PVAc (25/75/0)



B381 PHB/PLLA/PVAc (22.7/68.1/9.1)

B551 PHB/PLLA/PVAc (45.4/45.4/9.1)

B831 PHB/PLLA/PVAc (68.1/22.7/9.1)

SCHEME 1. Chemical structures of PHB and PLLA.

FIG. 1. DSC, second heating of PLLA and PHB/PLLA/PVAc blend

with different compositions (B130, B110, and B310).

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2011 2193

is homogeneous and becomes immiscible at 50% PLLA.

These results agree well with the previously reported

results by Ozaki and coworkers [8] and Zhang et al. [27].

It is interesting to note that both PHB/PLLA (25/75) and

(75/25) samples exhibit two melting peaks (Tm) at 172,

180 and 174, 1808C, respectively. These peaks are attrib-

uted to recrystallization or two different lamella thicken-

ing. The melting peak (Tm) appears brooding 1808C and

shoulder at 1728C in case of B110 due to the crystalliza-

tion process form the two types of lamella. These results

are in agreement with the results of Wasantha et al. [28].

Figure 2 shows the DSC results of the samples B381, B551,

and B831 with 9.1% of PVAc. The figure reveals that, the

glass transition temperature appears at 60, 56, and 558C,cold crystallization (Tcc) at 108, 112, and 1138C and melt-

ing point (Tm) at 174, 175, and 1758C. Also, the cold crys-

tallization peak temperature (Tcc) moves to a higher tem-

perature and becomes broader when PHB content is

increased. The presence of one crystallization temperature

suggests that PHB/PLLA blends significant single homoge-

neous phase throughout the heating process. By comparing

the data of Figs. 1 and 2, it was noted that, the melting

point becomes one peak and shifts to a lower temperature

by addition of PVAc. This is due to the increase in the

amorphous phase in both component.

Morphology of the Spherulites

The miscibility of blends was studied by POM. It is

known that, large spherulitic material is more brittle than

fine spherulite with the same percentage of crystallinity.

Figure 3 shows the surface morphology of sample B110.

The microstructure was characterized by a Maltese cross-

birefringent pattern spherulites. A sharp banded spherulite

of PHB with the fibrils spherulite of PLLA was seen in

the isothermally crystallized at 1008C. It is clear from the

image that, the PLLA spherulites are darker than the PHB

spherulites, which suggested that PHB was crystallized

faster than PLLA due to the higher crystallization rate of

PHB. Two phase separations was found in the sample

B110 and this indicated that PLLA was not miscible with

PHB. These results were discussed from DSC analysis in

Refs. 29–33.

The Spherulitic morphology of blends, at various crys-

tallization temperatures for the investigated samples B381

(a) 1208C, (a0) 1408C, sample B551 (b) 1208C, (b0) 1408C,sample B831 (c) 1208C, and (c0) 1408C that formed as the

nonbanded spherulite are shown in Fig. 4. By increasing

the crystallization temperature, the number of spherulites

was found to be reduces, whereas their size increases.

The results also show that the blends were miscible after

addition of 9.1% PVAc. Figure 5 shows spherulitic mor-

phology of samples blends after annealed at 1608C for

180 min and different crystallization temperatures, sample

B381 (a) 1208C, (a0) 1308C, sample B551 (b) 1208C, (b0)1308C, sample B831 (c) 1208C and (c0) 1308C. The shape

of the spherulite is ring with twisting lamellae, like PE

FIG. 2. DSC, second heating of PLLA and PHB/PLLA/PVAc blend

with different compositions (B381, B551, and B831).

FIG. 3. Spherulitic morphology of sample B110 at crystallization temperatures 1008C: (a) with optical polar-

izer, (a0) without optical polarizer. [Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]


and PVDF. One can seen from Fig. 5c0 that a sharp

banded spherulite structure growing radially with a large

radius from initiate (primary) nucleation site with closed

circles. Figure 6 shows fibrils spherulite (nonbanded) of

sample B551 after melting and at different isothermal crys-

tallization temperatures (a) 1008C, (b) 1108C, (c) 1208C,(d) 1308C with optical polarizer and (a0) 1008C (b0)1108C, (c0) 1208C, (d0) 1308C without optical polarizer.

POM without optical polarizer was used to illustrate the

appearance of spherulite. In contrast, Fig. 7 shows POM

graphs of sample B551 with banded spherulites (ring). The

sample of this blend was annealed at 1608C for 180 min

and isothermal crystallization temperature at 1008C and

1208C. The POM images (a) and (b) are measured with

optical polarizer while the images (a0) and (b0) are meas-

ured without optical polarizer. The images without optical

polarizer reveal ring spherulite. The morphology of sam-

ple B551 prepared at isothermal crystallization temperature

of 1608C (600 min) and cooled to 1208C was shown in

Fig. 8. In the begin, the sample was melted and annealed

at crystallization temperature of 1608C (600 min) until

the fibrils spherulite is not completely grow and presence

FIG. 4. Spherulitic morphology of PHB/PLLA/PVAc blend, at various crystallization temperatures: sample

B381 (a) 1208C and (a0) 1408C, sample B551 (b) 1208C and (b0) 1408C, sample B831 (c) 1208C, and (c0)1408C. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


of space between spherulites (as in Fig. 8a and b). By

reducing the temperature of crystallization to 1208C and

1108C, the banded (ring) spherulites are started to form.

One can see the variation between fibrils spherulite and

the ring (banded) spherulite. The POM image was meas-

ured with optical polarizer (a) while the image without

optical polarizer (a0). This means that the two types of

crystals depend on the crystallization process. The reason

for this spiral is the tilting of the lamella by longer

annealing time. Such twist on the sheaf leads to the for-

mation of spiral, which can be observed in helicoidally

twisted crystallites with a perfect spherulite around them.

On the other hand, the banded or nonbanded spherulites

morphology detected in samples B381, B551, and B831 are

strongly depending on the crystallization conditions. In

general, there are several crystal polymorphs in the poly-

mers. Some of these crystalline polymers take the form of

various banded spherulites and nonbanded (fibrils spheru-

lites) such as; isotactic polypropylene (PP) [34] and

PVDF [35]. Figure 9 shows other image of the morphol-

ogy of B551 prepared at isothermal crystallization temper-

ature of 1608C (600 min) with different scale. From this

image it can be observed that the lamella begin to form

fibrils branches and splay apart from each other. As a

result of continual splaying and branching of the lamellae,

the initial lamella gradually developed into a lamella

sheaf (Fig. 5c0). L. J. Ping et al. [36] found two kinds of

banded spherulites in PHB, which are formed at 100 and

1158C. Many scientists also tried to interpret the crystal

growth mechanisms of banded and fibril spherulites. So

FIG. 5. Spherulitic morphology of samples PHB/PLLA/PVAc blend after annealed at 1608C for 180 minute

and then different crystallization temperatures: sample B381 (a) 1208C and (a0) 1308C, sample B551 (b) 1208Cand (b0) 1308C, sample B831 (c) 1208C and (c0) 1308C. [Color figure can be viewed in the online issue, which

is available at wileyonlinelibrary.com.]


far, there are some models that have been accepted

widely. One of these models proposed by Keller [37],

Keith et al. [38], and Bassett et al. [39] that depends on

the stress of twisting (rotation) lamellar crystal. Gan et al.

[40] proposed two types of crystals with different struc-

tures formed in the banded spherulites. In addition, Owen

FIG. 6. Spherulitic morphology of sample B551, fibrils spherulite at isothermal crystallization temperature at

(a) 1008C, (b) 1108C, (c) 1208C, (d) 1308C with optical polarizer and (a0) 1008C (b0) 1108C, (c0) 1208C, (d0)1308C without optical polarizer. [Color figure can be viewed in the online issue, which is available at



FIG. 7. Spherulitic morphology of sample B551, banded spherulite at crystallization temperature 1008C and

1208C, after annealed at 1608C for 180 min, (a) and (b) with optical polarizer (a0) and (b0) without opticalpolarizer. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

FIG. 8. The morphology of sample B551 prepared at isothermal crystallization temperature at 1608C (600

min.) and cooled to 1208C, (a) with optical polarizer and (a0) without optical polarizer, (b) cooled to 1108C,with optical polarizer. [Color figure can be viewed in the online issue, which is available at



et al [41] proposed a mechanism for twist banding, which

could be due to the flexibility of bending and torsion

twisted lamella as helix. These models could explain the

mechanism of spiral twist and therefore, it should be suita-

ble for many polymers especially for chiral polymers.

Nevertheless, these models cannot explain all the phenom-

ena that occur in the experiments generally, but only

explain some special cases. It is known that spherulites of

chiral polymers are banded polymers such as; polyepichlo-

rhydrin (PECH) [42], PE [42] and PHB [3]. In addition,

there are chiral polyesters that it make helical conforma-

tions, i.e., the helices are left-handed like PHB and poly(3-

hydroxybutyrate-co-3-hydroxyvalerate) PHB-co-PHV.

FTIR Analysis

In our previous work, the vibration structure of the

neat PHB were examined [1–3]. In the present study,

PLLA and PLLA with PHB blends were analyzed using

FTIR spectroscopy (see Fig. 10). The neat PLLA and

PHB were used for comparison [3, 7, 8]. It is known that

the C¼¼O stretching bands for PHB appeared at 1723

cm21 [3, 7, 8]. Figure 10 shows that the C¼¼O stretching

band occurs at 1752 cm21 for PLLA. Besides, the C¼¼O

stretching band of samples B130, B110, and B310 appears

at 1750 cm21 with small change of wave number. On the

other hand, the C¼¼O stretching band for samples B381,

B551, and B831 appears at 1744, 1726, and 1724 cm21

with a change of its position, respectively. Since the

peaks at 1272 and 1226 cm21 are crystalline-sensitive

bands for PHB and PLLA [7, 30], they are assigned to

the C��O��C stretching bands of the crystalline parts and

may be due to the helical structures. These peaks are

appears as shoulder for PLLA as well as samples B130,

B110, B310, B381, and B551. In contrast, the peak appears

at 1272 cm21 in sample B831 is a board peak similar to

stretching band of PHB, since its peak intensity become

stronger with the increase PHB content. i.e., the crystal-

linity increased with increasing PHB content. It has been

reported [7, 30] that the bands at 1180 cm21 are assigned

to the amorphous of C��O��C stretching bands for PHB,

PLLA and their blends. Also, the C��O��C stretching

band of PLLA and samples B130, B110, B310, B381 appears

at 1083 cm21. Besides, the C��O��C stretching band

appears at 1097, 1093, and 1096 cm21 for PHB [3, 7, 8],

B551 and B831, respectively. Additionally, the bands at

1048 cm21 are assigned to the C��CH3 stretching for

PLLA, PHB and their blends [7, 30]. What’s more the

peaks located at 1130 cm21 of PLLA, PHB and their

blends were assigned to the stretching vibration of CH3

rocking [29]. Figure 11 shows the FTIR spectra. It can be

seen that the CH3 asymmetric deformation band at 1455

cm21 of PLLA, PHB [30], and their blends and CH3 sym-

metric deformation band at 1366 for PLLA, and samples

B130, B110, B310, and B381. It also appears at 1376 cm21

for PHB [7, 30] and samples B551 and B831. The peaks at

FIG. 9. Spherulitic morphology of sample B551, nonband spherulite at isothermal crystallization temperature

1608C (600 min.) at different scale. [Color figure can be viewed in the online issue, which is available at


FIG. 10. FTIR spectra of PLLA and different compositions PHB/

PLLA/PVAc blend from 550 to 1850 cm21.


755 and 867 cm21 are distinguish between the crystalline

and the amorphous phases of PLLA, and samples B130,

B110, B310, and B381. These peaks are shifted for samples

B551 and B831 from 867 to 897 cm21. It is also found that

the intensity of both peaks is decreased. These results

indicate that samples B130, B110, and B310 are immiscible

since no changes in the peaks positions of blends were

observed. These means that there are no strong molecular

interactions between PHB and PLLA were noted. It is

interesting to note that the addition of PVAc to PLLA

and PHB leads to shift the C¼¼O band and make dipole-

dipole interactions between the C¼¼O group and the CH3

group in PHB and PLLA. The spectra of samples B551

and B831 are similar to that of pure PHB [3]. All spectra

of the samples B130, B110, B310, and B381 are very similar

to the neat PLLA spectra.

Wide Angle X-Ray Diffraction Analysis

It is known that the crystalline structure of PHB is

orthorhombic. The lattice parameters of PHB are: a ¼0.572 nm and b ¼ 1.312 nm with its chain conformation

in the left-handed 21 helix [1–3]. PLLA can be crystal-

lized from melting or solution as orthorhombic unit cell

with a lattice parameters of a ¼ 1.037 nm, b ¼ 0.598 nm

[43]. It is acknowledged that neat PLLA was usually

formed from the a-type a helix 103. PLLA can be form

two-crystals clearly, depending on the crystallization con-

ditions of a form with a 103 helical shape [43–46] and bform with a spiral shape 31 [30, 45–47]. In our previous

studies [1–3], the WAXD of neat PHB has reflection

peaks at 13.58 and 16.78 corresponding to (020) and (110)

planes [1–3]. Figures 11 and 12 show the WAXD analysis

of all the samples. There are two sharp strong crystalline

reflection peaks at 13.58 and 16.78 corresponded to the

(020), and (110) planes and three other weakly peaks at

19.18, 228, and 25.48. The two first peaks characteristics

of typical a-form orthorhombic structure of PHB [1–3].

The PLLA with only one broad diffraction peak (major

peak) appeared at 2y of 16.78 corresponding the (110/

200) reflections (d ¼ 0.536) and smaller peaks at 19.18and 328 corresponding to (010) and (203) respectively. In

Fig. 11, the maximum intensity of samples B130, B110,

and B310 (a-form crystal) occurs approximately at 2y ¼13.58, which corresponding to the basal spacing (d ¼0.655, 0.655, 0.654 nm) of the (020) plane along with 2y¼ 16.68, which corresponded to the basal spacing (d ¼0.531, 0.532, 0.532 nm) of the (110) plane. Figure 12 also

shows that the maximum intensity of samples B381, B551,

and B831 (a-form crystal) occurs at 2y ¼ 13.58, corre-

sponds to the basal spacing (d ¼ 0.660, 0.658, 0.657 nm)

of the (020) plane and 2y ¼ 16.68, corresponds to basal

spacing (d ¼ 0.534, 0.533, 0.529 nm) of the (110) plane.

Additionally, the maximum diffraction of the B831 occurs

at 2y ¼ 13.58. In this case, the intensity was increased

due to the increasing of crystallinity. Moreover, diffrac-

tion peak at 2y ¼16.68 was shifted to higher angle of

16.88 and its maximum intensity was increased, because

the crystal structure was changed. Furthermore, the peak

diffraction at 2y ¼ 25.48 and 22.18 increased in compari-

son to those of the samples B381 and B551. The b-formcrystal was observed at 2y ¼ 19.68 for all samples, which

corresponds to (110) plane and d ¼ 0.465, 0.464, 0.464,

0.464, 0.469, and 0.448 nm (see Figs. 11 and 12). It can

also be observed in Fig. 12 that the intensity of a-formdiffraction at 2y ¼ 13.68 is increased, while the intensity

of (020) diffraction of b-form at 2y ¼ 19.48 remains

unchanged. However, with increasing PHB content in

blends, the intensities of large peak a-form at 2y ¼ 13.58(020) and 2y ¼ 16.78 (110) are increased. This result

means that some traces of a-form and b-form crystalline

structures of PHB and PLLA could be exist in blends.FIG. 11. WAXS diffraction curves of PLLA and different compositions

of PHB/PLLA/PVAc blend (samples B130, B110, and B310).

FIG. 12. WAXS diffraction curves of PLLA and different compositions

of PHB/PLLA/PVAc blend (samples B381, B551, and B831).


The lattice parameters are unchanged in samples B130,

B110, and B310. This result suggests that each component

of the blends forms its crystalline structure independently

of the second component. In conclusion, the lattice pa-

rameters are changed in samples B381, B551, and B831.

Furthermore, the WAXD results revealed that all (PHB/

PLLA) blends without PVAc are immiscible whereas, the

(PHB/PLLA) blends with PVAc are miscible.

CONCLUSION

The effect of processing conditions on the development

of morphological features of banded or nonbanded spher-

ulites of PHB/PLLA blends (with and without PVAc addi-

tion) has been studied. The structure, morphology, crystal-

lization, melting behavior and miscibility of PHB/PLLA

blends have been investigated and analyzed using POM,

DSC, WAXD and FTIR spectroscopy. The results show

that, the blends with PVAc have two types of spherulites,

produced at different crystallization temperatures. One of

these spherulites is ring and occurs after annealing at high

temperature (1608C) and long annealing time (180 min),

which results in tilting of the lamella consequence lamel-

lar twisting. The second is fibrils, which is directly pro-

duced after melting and isothermal crystallization without

annealing. This depends on the crystallization conditions

and thermal treatment. Further structural analyses revealed

that no miscibility and phase separation were observed in

the sample B110.

DSC examination indicated that all blends are misci-

ble, except the B110, which is immiscible with having two

cold crystallization temperatures.

FTIR analysis indicated that the PHB/PLLA blends

without PVAc were immiscible, but the addition of PVAc

to PLLA and PHB (in B381, B551, and B831) leads to shift

the C¼¼O band and makes dipole-dipole interactions

between the C¼¼O group and the CH3 group in both of

PHB and PLLA.

The diffraction analysis showed four a crystal diffrac-

tion peaks at {(020), (110), (121), and (040)} planes and

one b crystal diffraction peak at (021) plane. The lattice

parameters are unchanged in samples B130, B110, and

B310. This result suggests immiscible blends, but the lat-

tice parameters are changed in samples B381, B551, and

B831. This result suggests miscible blends.

ACKNOWLEDGMENTS

The author thanks SABIC company for petrochemicals

(Research & Consulting Center) and Institute of Scientific

Research for part supporting this Project.

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