Fiber spinning from the nematic melt. IV. Effect of P oxybenzoate crystallinity on the spinning and fiber properties of the copolyester of polyethylene terephthalate and p-oxybenzoate

We have previously reported two studies of the rheology and fiber properties of one sample of the copolymer of polyethylene terephthalate having 60 mol% of p-oxybenzoate (PHB) units. The DSC curve of that sample exhibited crystalline melting transitions, and the sample appeared to contain PHB blocks. Here we compare those results with observations for a second sample that, although nominally the same polymer, appears to be more random because it exhibits little PHB crystallinity. We had previously reported that the flow of the copolymer containing PHB blocks was non-Newtonian at all temperatures, and that it exhibited a thermal history effect. We find the flow of the more random polymer is Newtonian above the melting temperature, and the melt viscosity of the more random copolymer exhibits no thermal history effect. Fibers were spun from the more random copolymer with a capillary rheometer using a capillary having a length/diameter ratio of 14.1 and a shear rate at the wall of 6.4 sec^?1. Spinning temperatures were 250, 260, and 280°C, and the spin draw ratio was examined as a variable. The initial modulus increased with spin draw ratio but exhibited no dependence upon the spinning temperature. For the copolymer containing PHB blocks, the initial modulus increased as the spinning temperature was raised. These differences are due to the larger amount of PHB crystallinity in the more blocky sample. When chips of the more random sample were heated for 1 h at 235°C, the melt viscosity increased and the initial modulus of the fibers decreased. These changes are due to the crystallization of longer PHB blocks produced by melt interchange.     

Thermotropic homopolyesters. IV. Study of fiber formation

We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun from both the nematic and smectic phases of these semiflexible chain polymers were poor. Increasing the polymer molecular weight or extrusion rate only afforded a modest improvement in fiber properties. Most polymers could not be spun at temperatures corresponding to the existence of the single mesophase. Hence the low viscosity typical of the nematic mesophase is not necessarily an advantage in fiber formation from the melt. It appears from these results that this type of polyester does not possess adequate chain extension to develop ultrahigh-modulus properties. The director, which describes the local orientation of molecules within the mesophase, may undergo more frequent variations than is the case for rigid chain polyesters. Mechanisms relevant to flexible polymers may contribute to the development of orientation for this class of nematogenic melts.     

Fiber spinning from the nematic melt. II. Effect of thermal history on spinning of the copolyester of polyethylene terephthalate and p-oxybenzoate

Fibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % of p-oxybenzoate units. A capillary rheometer was used for spinning with a shear rate at the wall of 6.4 sec^?1, and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250° to 300°C and, at each temperature, the spin-draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin-draw ratio and increased with increasing spinning temperature for a fixed spin-draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280°C for spinning at 250°C, and 300°C for spinning at 280°C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p-hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin-draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PHB in the threadline.     

Structure development of fibers from liquid-crystalline PET/60PHB copolyester

Effect of extrusion conditions, particularly temperature, on the structure development of fibers from poly(ethylene terephthalate) modified with 60 mol% p-hydroxybenzoic acid was investigated. Light microscopy revealed that the structure of the liquid-crystalline fiber was highly dependent on the extrusion temperature: low-temperature-spun fibers exhibited a structure with domains or clusters of crystallites randomly oriented, whereas the fibers spun at high temperatures had a well-developed fibrillar texture. Anisotropy of the fibers, as evidenced by dichroism and by the variation of brightness or darkness of the fibers between crossed polars, was significantly higher for those spun at relatively high temperatures. Scanning electron microscopy revealed that the fibers spun at relatively low temperatures had poorly oriented, nonuniform morphology. Those produced at relatively high temperatures, on the other hand, consisted of well-developed fibrils. X-ray diffraction patterns showed that the molecular orientation increased with increasing extrusion temperature. A model for the development of fiber structure from thermotropic liquid-crystalline polymers is proposed.     

Fiber spinning from the nematic melt. VI. Flow instabilities in the 30:70 copolyester of hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid

The rheological behavior and fiber spinning are investigated for the Celanese liquid crystal copolyester 30 mol% p-hydroxybenzoic acid and 70 mol% 2-hydroxy-6-naphthoic acid (designated as 30HBA/70HNA) with inherent viscosity 7.8 dL/g. Shear thinning viscosity, and yield stress are observed at low shear stress, which probably results from the existence of crystallites in the melt. The crystal-nematic melting point of the copolymer, as measured by differential scanning calorimetry, is around 309°C. Extrudates are collected at four different temperatures ranging from 315 to 345°C. Melt fracture and die swell are observed above 335°C at low shear stress. A wide-angle x-ray diffraction (WAXS) study of an annealed sample indicates that the abnormal phenomenon may be due to crystallites arising from blocky units of HNA. Fiber spinning is performed at high shear rate at 325 and 335°C. Flow is stable under these conditions. The spin draw ratio is the ratio of take-up velocity to the velocity of extrudate existing from the capillary. The initial modulus reaches a maximum at a fairly low spin draw ratio. Instron and wide-angle x-ray (WAXS) studies show that the mechanical properties and orientation are poor for the fiber spun near the crystal-nematic melting point. Also, thermal history is found to affect the rheological behavior. Heat treatment offibers, particularly those which are well oriented, brings an improvement of mechanical properties.     

Phase transition of syndiotactic polypropylene in electrospun nanofibers during progressive heating

By means of high-temperature electrospinning process, syndiotactic polypropylene (sPP) nanofibers with an average diameter of 127 nm were obtained using a rotating disc as a collector. The aligned fibers were subjected to progressive heating for fiber melting. During heating, structural evolution of the sPP nanofibers was investigated in situ by means of two-dimensional wide-angle and small-angle X-ray scattering with synchrotron radiation sources. It was found that the as-spun fibers consist of the antichiral form I (9 %), mesophase (31 %), and amorphous phase (60 %), in the absence of isochiral form II. Upon heating, the mesophase started to melt and completely disappeared at 90 °C. The melting of the mesophase directly produced amorphous chains at 35–60 °C, and brought up the isochiral form II at low temperatures (60–70 °C), as well as the antichiral form I at high temperatures (70–110 °C). These events were in accordance with the DSC heating curve, which exhibited a small endotherm centered at 52 °C for the mesophase melting, followed by a shallow and broad exotherm associated with two phase-transition events, i.e., the crystal reorganization and the crystallization of supercooled liquid. The former is likely due to the solid–solid transition of meso→II phase as suggested by Lotz et al. (Macromolecules 31:9253, 1998), and the latter is relevant with crystallization of amorphous chains to develop the thermodynamic stable form I phase at high temperatures.     

Dynamic mechanical properties of extruded rods of poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl‐n‐propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene‐co‐methyl‐n‐propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide‐angle X‐ray diffraction (WAXD) to clarify the structure–mechanical‐property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 698–706, 2000     

Fiber spinning from the nematic melt. I. Copolyester of poly(ethylene terephthalate) and p-oxybenzoate

The Tennessee Eastman copolyester of poly(ethylene terephthalate) with 60 mol % p-oxybenzoate units was spun with various capillaries using a constant shear rate at the wall. Variables examined were the length-to-diameter ratio L/D of the capillary, the spin draw ratio V_f/V₀, and the spinning temperature. Fibers spun at 260°C showed improved homogeneity of orientation through the cross section, better crystallite orientation, and higher initial moduli as L/D was increased. The spin draw ratio required to optimize these fiber properties decreases as L/D is increased. For example, when L/D = 49.44, the initial modulus has nearly reached its plateau value at a spin draw ratio of 10. However, in contrast to the results of Sugiyama, Lewis, White, and Fellers, we find that some spin draw is always required to optimize fiber properties. Fibers spun with a spin draw ratio of approximately unity showed very poor crystallite orientation and initial moduli. It is suggested that loss of orientation under these conditions may be due to the different velocity profiles in the spinneret and in the solidifed fiber. Fibers were also spun at five temperatures using a capillary having L/D = 49.44. Shear in the capillary is more effective in introducing orientation when the spinning temperature is 260°C or above. At spinning temperatures of 240 and 250°C, the initial modulus increases more slowly with spin draw ratio, and appears to have a lower plateau value. Acierno, La Mantia, Polizzotti, Ciferri, and Valenti spun the same polymer under conditions in which essentially all the orientation was introduced by spin draw. They used a very low extrusion velocity at the spinneret, a small L/D, and spin draw ratios up to 3000. They reported that the initial modulus increased with decreasing spinning temperature, in contrast to our results. Thus the optimum spinning conditions may depend upon whether most of the orientation is introduced by shear in the capillary, or by a high spin draw ratio.     

A temperature window of extrudability and reduced flow resistance in high-molecular weight polyethylene; interpretation in terms of flow-induced mobile hexagonal phase

An unexpected feature of melt flow behavior has been identified in high-molecular weight (≥ 4.10⁵) polyethylenes such as are being considered unprocessable at conventional temperatures (> 160°C) and at practicable extrusion rates (> 1 cm/min). In addition to a lower temperature window of smooth extrudability, lying in the range of 138–155°C already observed in previous works, we now discovered within this window a narrow temperature interval (150–152°C) of minimum flow resistance (viscosity). The new effect has the attributes of being associated with a new phase of increased fluidity. This, in turn, we attribute to a transient mesophase arising through the chain-orienting effect of the elongational flow within the extrusion orifice; from the experiments presented here, this mesophase depends critically on both molecular weight and strain rate. The hexagonal form of polyethylene, known to exist under other circumstances, is suggested as this mesophase. The relevance of the new findings for applications (extrusion, melt rheology) and for fundamentals (orientation-induced phase transformations, liquid crystals from flexible chains in particular) should be obvious and are accordingly highlighted.     

Effects of posttreatment on the properties of modified PLLA/PDLA fibers

Poly(L ‐lactic acid)/poly(D ‐lactic acid) (PLLA/PDLA) blended with plasticizer poly(ethylene glycol) and nucleation agent TMC‐306 as‐spun fibers were prepared by melt spinning. The posttreatment was applied by hot drawing at 70°C and then heat‐treating at different temperatures for 30 minutes. In the process of hot drawing, orientation induced the further formation of the sc crystals and increased the degree of crystallinity of drawn fibers. When the hot drawing ratio reached 3 times, the properties of the fibers were relatively better. The highly oriented fibers containing pure sc crystals with high crystallinity were obtained by heat‐treating at a temperature above the melting point of α crystals. The posttreated PLLA/PDLA fibers with poly(ethylene glycol) and TMC‐306 (LDTP) obtained by hot drawing to 3 times at 70°C and then annealing at 170°C for 30 minutes exhibited the best antioxidative degradation and heat resistance properties. The initial decomposition temperature (T_5%) and heat resistance of posttreated LDTP fiber were about 94°C and 20°C higher than those of the commercial PLLA fiber, respectively.     

Oriented noncrystalline structure in PET fibers prepared with threadline modification process

The development of an oriented noncrystalline phase in a semicrystalline polymer filament has been studied via X-ray scattering. These unique PET fibers contain a relatively high noncrystalline content and also have high tenacity, high modulus, and low breaking elongation. Fiber properties were found to be very responsive to the oriented amorphous phase content. This phase was utilized for interpreting noncrystalline orientation in PET fibers produced by a new extrusion technique. Here, the oriented noncrystalline regions in a series of PET fibers varies from 6% to 63%, depending strongly on the production conditions. In particular, samples produced with a newly developed threadline modification process possess a high content of oriented noncrystalline polymer. Measurements such as dynamic and static mechanical properties have been performed on various samples, and these properties are related to the oriented noncrystalline phase. The results provide direct evidence for the existence of highly oriented noncrystalline material in these unique PET fibers spun with a threadline modification process. © 1996 John Wiley & Sons, Inc.     

Microstructure and mechanical properties of hot‐air drawn poly(ethylene terephthalate) fibers

Hot‐air drawing method has been applied to poly(ethylene terephthalate) (PET) fibers in order to investigate the effect of strain rate on their microstructure and mechanical properties and produce high‐performance PET fibers. The hot‐air drawing was carried out by blowing hot air controlled at a constant temperature against an as‐spun PET fiber connected to a weight. As the hot air blew against the fibers weighted variously at a flow rate of about 90 ℓ/min, the fibers elongated instantaneously at a strain rate in the range of 2.3–18.7 s⁻¹. The strain rate in the hot‐air drawing increased with increasing drawing temperature and applied tension. When the hot‐air drawing was carried out at a drawing temperature of 220°C under an applied tension of 27.6 MPa, the strain rate was the highest value of 18.7 s⁻¹. A draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest stain rate had a birefringence of 0.231, degree of crystallinity of 44%, tensile modulus of 18 GPa, and dynamic storage modulus of 19 GPa at 25°C. The mechanical properties of fiber obtained had almost the same values as those of the zone‐annealed PET fiber reported previously. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1703–1713, 1999     

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters

High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole-% p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39–40) and heat deflection temperatures (150–220°C) were obtained with 80–90 mole-% PHB.     

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters

High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole- % p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39-40) and heat deflection temperatures (150-220°C) were obtained with 80–90 mole-% PHB.     

Melt spinning of thermotropic liquid-crystal polyesters to form ultrahigh-modulus filaments

The properties and structure of ultrahigh-modulus filaments were investigated for wholly aromatic copolyesters (WACPs) containing 60 and 70 mol% p-oxybenzoate, based on p-hydroxybenzoic acid, p,p′-biphenol, terephthalic acid, and isophthalic acid and for poly(ethylene terephthalate co-p-oxybenzoate) containing 60 mol% p-oxybenzoate. As-spun filaments with varying degrees of molecular orientation were spun from melts by taking the spin-extension ratio as a variable at given temperatures. The as-spun filaments were further subjected to thermal annealing. Changes in the structural ordering with the extension ratio were monitored by wide-angle x-ray scattering, scanning electron microscopy, viscoelastic properties, and measurements of the thermal expansion coefficient. The increase in modulus is correlated well with the crystallite orientation at a relatively low extension ratio. However, for extension ratios above 10, the modulus of as-spun filaments is almost independent of the crystallite orientation. Modulus values as high as 100 GPa are obtained for WACP filaments spun at extension ratios above 500. It is suggested that ultrahigh-modulus values can be reached in highly oriented noncrystalline chains. Furthermore, the results for annealed filaments indicated that the relaxation of molecular orientation occurs partially in the oriented noncrystalline regions during the stage of long-time annealing above T_g, leading to depression of the modulus.     

Effect of Polycondensation Reaction Conditions on the Properties of Thermotropic Liquid‐Crystalline Copolyester

In this study a range of wholly aromatic copolyesters based on kink m‐acetoxybenzoic acid (m‐ABA) monomer (33 mol%) and equimolar‐linear p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280°C and 260°C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide–angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), hot‐stage polarized light microscopy, proton‐nuclear magnetic resonance analysis (¹H‐NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280°C in 5 h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5–15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160°C and 165°C) in the nematic mesophase. The T_g values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93–126°C. Fibers prepared by a hand‐spinning technique from the polymer melt exhibit well‐developed fibrillar structure parallel to the fiber axis.     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

Transverse heterogeneity in PET fibers

X-ray scattering from a series of poly(ethylene terephthalate) (PET) fibers spun at differet speeds is analyzed to probe the morphology in the direction transverse to the fiber axis. Both the apparent crystal modulus, determined from the change in wide-angle X-ray scattering angle with fiber stretching, and the transverse degree of crystallinity indicate there is a substantial interfiberillar amorphous content. In the PET fiber spun at conventional speeds, only roughly one-quarter of the fiber cross-section is actually occupied by fibrils. The transverse crystallinity increases for fibers spun at speeds sufficient to cause crystallization in the spin line. The X-ray moduli and fibril diameters are correspondingly larger in these high speed spun fibers. © 1993 John Wiley & Sons, Inc.     

Transformation of isotactic polypropylene droplets from the mesophase into the α‐phase

The structural transformation of homogeneously nucleated metastable mesophase of polypropylene (PP) particles was investigated in this study. We demonstrated the formation of heterogeneity‐free mesophase by slow cooling of the droplets unlike mesophase formation by quenching of the PP melt, which contained large number of bulk nuclei. Submicron size PP droplets were produced by thermal break up of PP and polystyrene layered film assembly. When cooled from melt, the PP droplets crystallized into mesophase at 44 °C revealing granular morphology. Subsequent heating thermogram of the PP particles showed a broad exotherm, which was attributed to the transformation of mesophase into α‐phase. This transformation was investigated during heating by annealing the PP particles at different temperatures. Annealed PP particles were analyzed by means of thermal, morphological and structural properties measurements. Results revealed a two step process for the transformation process. In the first step, the internal rearrangement of PP chains, as against melting and recrystallization of the mesophase, was observed. Since granular morphology was not affected significantly up to 120 °C, it was suggested that translational and rotational motions of PP helices produced ordered α‐phase. In the second step, increment in grain size distribution was observed, when the droplets were annealed at 140 °C. The results were attributed to enhanced chain mobility and merging of the grain boundaries. Annealing at 160 °C revealed the formation of short lamellar structures. Crystal thickening, melting and recrystallization of α‐phase were suggested at high temperature annealing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Influence of microcrystalline cellulose fiber (MCCF) on the morphology of poly(3-hydroxybutyrate) (PHB)

Biopolymer composites were prepared from poly(3-hydroxybutyrate) (PHB)/microcrystalline cellulose fiber (MCCF)/plastiziers/poly(vinyl acetate) by melt extrusion. The morphology, crystal structure, and non-isothermal crystallization of these composites were investigated by polarized optical microscopy (POM), differential scanning calorimetry, Fourier transform infrared spectrometer, and wide-angle X-ray diffraction. The results of DSC indicate that the addition of small amount of MCCF improved the crystallization rate. Non-isothermal crystallization shows that the composites 1 and 2 have lower crystallization half time (t _{0 .5}) than that of pure PHB. Higher MCCF contents in PHB (composite 4) lead to a decrease in the crystallization rate. POM micrographs show that the MCCF were well dispersed in the PHB matrix and served as a nucleating agent with a strong change in PHB morphology. Increasing the isothermal crystallization temperature above 120 °C, leads to the formation of banded spherulites with large regular band spacing. Decreasing the isothermal crystallization temperature below 100 °C produces more and small spherulites.