Maleic Anhydride-grafted Poly Research Articles

Grafting of maleic anhydride on poly(lactic acid)/hydroxyapatite composites augments their ability to support osteogenic differentiation of human mesenchymal stem cells.

Implantation of bone substitutes is the treatment of choice for bone defects exceeding a critical size, when self-healing becomes impossible. The use of 3D printing techniques allows the construction of scaffolds with customized properties. However, there is a lack of suitable materials for bone replacement. In this study, maleic anhydride-grafted poly (lactic acid) (MAPLA) was investigated as a potential compatibilizer agent for 3D-printed polylactic acid (PLA)/hydroxyapatite (HA) composites, in order to enhance the physicochemical and biological properties of the scaffolds. The grafting process was performed by reactive processing in a torque rheometer, with the evaluation of the use of different concentrations of maleic anhydride (MA). The success of the grafting reaction was confirmed by titration of acid groups and spectroscopic analyses, indicating the presence of succinic anhydride groups on the PLA chain. Morphological analysis of the PLA/HA 3D scaffolds, using SEM, revealed that the use of the compatibilizer resulted in a structure free from voids and holes. The compatibilization also increased the degradation process. On the other hand, TGA and DSC analyses revealed that the use of a compatibilizer had little effect on the thermal properties of the composite. Most importantly, the samples with compatibilizer were demonstrated to have a minimal cytotoxic effect on human mesenchymal stem cells (MSCs), promoting the osteogenic differentiation of these cells in a medium without the addition of classical osteogenic factors. Therefore, the grafting of PLA/HA composites improved their physicochemical and biological properties, especially the induction of MSC osteogenic differentiation, demonstrating the potential of these scaffolds for bone tissue replacement.

Role of Maleic Anhydride-Grafted Poly(lactic acid) in Improving Shape Memory Properties of Thermoresponsive Poly(ethylene glycol) and Poly(lactic acid) Blends.

Generally, poly(ethylene glycol) (PEG) is added to poly(lactic acid) (PLA) to reduce brittleness and improve mechanical properties. However, shape memory properties of PEG/PLA blends suffered due to the blend’s incompatibility. To enhance shape memory abilities of the blends, 0.45% maleic anhydride-grafted poly(lactic acid) (PLA-g-MA) was used as a compatibilizer. Thermal and mechanical properties, morphologies, microstructures, and shape memory properties of the blends containing different PLA-g-MA contents were investigated. The compatibilized blend with 2 wt% PLA-g-MA exhibited enhanced tensile modulus, strength, and elongation at break, as well as a lower glass transition temperature and degree of crystallinity than the uncompatibilized blend. Results revealed that PLA-g-MA improved interfacial adhesion between phases and promoted chain entanglement. Shape fixity performance of the compatibilized blends were comparable to that of neat PLA. The compatibilized blend containing 2 wt% PLA-g-MA possessed the best shape fixity and recovery performance. Although a high recovery temperature was expected to enhance the recovery of the PEG/PLA blends, the compatibilized blends can be recovered to their original shape at a lower temperature than the PLA. This study illustrated the possibility of optimizing PLA properties to meet requirements necessary for biomedical applications.

Peroxide-Induced Synthesis of Maleic Anhydride-Grafted Poly(butylene succinate) and Its Compatibilizing Effect on Poly(butylene succinate)/Pistachio Shell Flour Composites.

Framing the Circular Bioeconomy, the use of reactive compatibilizers was applied in order to increase the interfacial adhesion and, hence, the physical properties and applications of green composites based on biopolymers and food waste derived lignocellulosic fillers. In this study, poly(butylene succinate) grafted with maleic anhydride (PBS-g-MAH) was successfully synthetized by a reactive melt-mixing process using poly(butylene succinate) (PBS) and maleic anhydride (MAH) that was induced with dicumyl peroxide (DCP) as a radical initiator and based on the formation of macroradicals derived from the hydrogen abstraction of the biopolymer backbone. Then, PBS-g-MAH was used as reactive compatibilizer for PBS filled with different contents of pistachio shell flour (PSF) during melt extrusion. As confirmed by Fourier transform infrared (FTIR), PBS-g-MAH acted as a bridge between the two composite phases since it was readily soluble in PBS and could successfully form new esters by reaction of its multiple MAH groups with the hydroxyl (–OH) groups present in cellulose or lignin of PSF and the end ones in PBS. The resultant compatibilized green composites were, thereafter, shaped by injection molding into 4-mm thick pieces with a wood-like color. Results showed significant increases in the mechanical and thermomechanical rigidity and hardness, meanwhile variations on the thermal stability were negligible. The enhancement observed was related to the good dispersion and the improved filler-matrix interfacial interactions achieved by PBS-g-MAH and also to the PSF nucleating effect that increased the PBS’s crystallinity. Furthermore, water uptake of the pieces progressively increased as a function of the filler content, whereas the disintegration in controlled compost soil was limited due to their large thickness.

Investigating the Effect of Aluminum Diethylphosphinate on Thermal Stability, Flame Retardancy, and Mechanical Properties of Poly(butylene succinate)

Poly(butylene succinate) is one of the most promising biodegradable polymers, but its applications are limited by poor flame retardancy. In this work, poly(butylene succinate)/diethylphosphinate (PBS/AlPi) composites were fabricated to investigate the effect of AlPi on their thermal stability, flame retardancy, and mechanical properties. It was found that the high content of AlPi decreased the thermal stability of PBS, and the decrease became stronger under the air atmosphere. When the content of AlPi reached 25wt%, the flame retardancy was improved with limited oxygen index (LOI) of 29.5%, V0 rating in UL-94 vertical burning test, and 49.3% reduction on the peak of heat release rate (PHRR) in cone calorimeter test. Meanwhile, the addition of AlPi could improve the mechanical properties of PBS with high tensile strength and Young’s modulus, which was ascribed to the compatible effect of maleic anhydride-grafted poly(butylene succinate) (PBS-g-MA) with good filler dispersion and strong matrix-particles interaction. Thus, the AlPi was an effective flame retardant to PBS, so that PBS/AlPi composites displayed excellent flame retardancy without seriously sacrificing other comprehensive performances.

Poly (lactic acid)/Spartium junceum fibers biocomposites: effects of the fibers content and surface treatments on the microstructure and thermomechanical properties

ABSTRACTThe aim of this work was to study the effects of alkali and alkali-silane surface treatments on Spartium junceum (Sj) fibers characteristics. Then, untreated and surface treated fibers were incorporated into a poly(lactic acid) matrix and the properties of the composites were studied. To improve the adhesion at the interface between the PLA matrix and alkali-silane treated fibers, maleic anhydride-grafted poly (lactic acid) (PLA-g-MA) was added as a compatibilizer. FTIR and TGA analysis proved the efficiency of the alkali treatment in removing some non-cellulosic components, namely hemicelluloses and lignin. Also, XRD results showed that the applied chemical treatments contribute to the increase in the crystallinity index of the Sj fibers. The incorporation of Sj fibers was found to decrease notably the impact strength of PLA and to affect its thermal behavior by increasing the melting temperature of the composites. However, it has been observed that the treatments increased notably the composites impact properties. These results have been confirmed by scanning electron microscopy (SEM) observations of the composites fractured surfaces which revealed a more intimate contact between the Sj fibers and the PLA matrix after surface modification. Also, the PLA-g-MA acted positively on the adhesion in the interfacial region.

Shape memory effect of three-dimensional printed products based on polypropylene/nylon 6 alloy

Based on the rapid development of three-dimensional (3D) printing, the fabrication of the 3D printed products which can change their shapes over time has been termed as four-dimensional (4D) printing. Since the functionality is generally limited by available materials, especially for fused deposition modeling (FDM, a trendy technology of 3D printing), it has aroused widespread requirements to develop a novel filament with excellent properties and functionalities. In this study, polypropylene/nylon 6 (PP/PA6) alloy was fabricated as a candidate for FDM and maleic anhydride-grafted poly(ethylene–octene) (POE-g-MAH) was used as a modifying agent as well as a compatibilizer. The results showed that the PP/PA6 alloy with 30 wt% of PA6 on the basis of the certain mass ratio of PP and POE-g-MAH (1.5:1) exhibited a high dimensional stability and appropriate mechanical properties in FDM. In addition, the possibility of PP/PA6 alloy as a shape memory polymer blend and the mechanism of shape memory effect (SME) were investigated. The 3D printed product with 30 wt% of PA6 fabricated by the infill orientation of 45°/− 45° and 100% infill density exhibited a great SME with the deformation temperature (Td) of 175 °C. This simple method for preparation of a novel filament with shape memory performance based on PP/PA6 alloy has a vast potential for the development of 4D printing technology.

Rheology of poly(lactic acid)/poly(trimethylene terephthalate) blends compatibilized by clay or maleic anhydride-grafted poly(ethylene-octene) elastomer

Abstract Blends of two biobased polymers, poly(lactic acid) and poly(trimethylene terephthalate) (PTT), were compatibilized with either maleic anhydride-grafted poly(ethylene-octene) (mPOE) or organically modified clay (Cloisite 30B). Dynamic rheological measurements revealed that the mPOE inclusion resulted in a four-fold increase in viscosity relative to the noncompatibilized blends. By loading 3 wt% Cloisite 30B, the storage moduli of the blends showed a distinct solid-like behavior and high complex viscosity in the low-frequency region, which can be interpreted by the reduced sizes of the PTT phase evidenced from the scanning electron microscopy (SEM) micrography. A temperature sweep of the viscosity of the blends starting from 180°C revealed that the existence of an unmelted PTT dispersed phase might impede the decline in viscosity with increasing temperature near the melting point of PTT. The introduced compatibilizers can restrict the temperature-dependent morphology evolution, and the use of the 3 wt% 30B clay can prohibit the morphology evolution during the temperature sweep.

Effect of SEBS-MA and MAPP as coupling agent on the thermal and mechanical properties in highly filled composites of oil palm fiber/PP

ABSTRACTThis paper reports on a study of highly filled composites of polypropylene (PP) and 75 and 85% by weight of oil palm mesocarp fiber (OPF) with and without coupling agent, maleic anhydride-grafted poly (styrene-ethylene/butadiene styrene) (SEBS-MA) and a maleated polypropylene (MAPP). Composites were prepared using a thermokinetic mixer for blending followed by hot pressing. The thermal and mechanical behavior of these composites was investigated by flexural and impact testing and scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA) was also used to study the properties. The MAPP improve the flexural modulus and flexural strength of the composites with 75 and 85wt% of oil palm fiber while SEBS-MA improved the impact strength of the composites. By SEM it was possible to observe some voids, pull out and debonding in the polypropylene, and allowing the observation of level of adhesion between the fiber and matrix. DMTA showed a decrease in storage modulus when high amounts of fiber were added to polypropylene, however, the presence of the SEBS-MA and MAPP increased the storage modulus. This study looks into the effect of MAH modification on the compatibility of OPF and PP, gives a broad overview of an initial study of these new materials.

Styrene-Assisted Maleic Anhydride Grafted Poly(lactic acid) as an Effective Compatibilizer for Wood Flour/Poly(lactic acid) Bio-Composites.

This study aimed to evaluate the effect of styrene-assisted maleic anhydride-grafted poly(lactic acid) (PLA-g-St/MAH) on the interfacial properties of wood flour/poly(lactic acid) (PLA) bio-composites. PLA-g-St/MAH was synthesized by free-radical melt grafting using styrene as a comonomer and dicumyl peroxide as an initiator. The structure of PLA-g-St/MAH was characterized by Fourier transform infrared spectroscopy. Wood flour/PLA composites were prepared by compression molding using PLA-g-St/MAH as a compatibilizer. The effects of PLA-g-St/MAH on the rheological and mechanical properties, as well as on the fractured surface morphology of the composites were investigated. Results indicated that storage modulus, complex viscosity, equilibrium torque, and shear heat were significantly increased. The mechanical properties of the wood flour/PLA composites were also significantly increased after the addition of PLA-g-St/MAH. The maximum values were achieved at the loading rate of 3 wt % because of the improved interfacial adhesion between the wood flour and the PLA matrix.

Core/shell morphologies in recycled poly(ethylene terephthalate)/linear low-density polyethylene/poly(styrene-b-(ethylene-co-butylene)-b-styrene) ternary blends

Compatibilizer plays very important roles in preparing high performance polymer composites, not only for the ternary immiscible polymer blends, but also for the recycled and reused of waste plastics mixture. Generally, the compatibilizers can be used as the toughening agent in blending polymer materials. In the present work, the poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) or maleic anhydride-grafted poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS-g-MA) acts as the compatibilizer and toughening agent for the preparation of R-PET/LDPE/SEBS (70/20/10) ternary blends. It must be pointed that the ternary blends are costlessly and conveniently prepared from the recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) through a melt blending in a co-rotating twin-screw extruder and injection moulded. The morphologies of the ternary blends are characterized by scanning electron microscopy (SEM). It was found that the blends contains reactive or non-reactive compatibilizer, the morphology originates from the LLDPE particles encapsulated by both SEBS and SEBS-g-MA. So, it results to the reduced interfacial tension between of the R-PET and SEBS-g-MA, in which the grafted chains of PET-g-SEBS-g-MA formed through in situ reaction between R-PET and SEBS-g-MA phases. Therefore, core–shell particles with smaller diameter disperse uniformly in the blends. Moreover, the good compatibilization and corresponding morphologies induce in balanced mechanical and thermal properties. DSC analysis show the dispersed phase particles could act as nucleating agent in the R-PET matrix, which results the improvement of the crystallization temperature. And it was also observed the decreased nucleation activity in graft copolymers in the R-PET/LLDPE/SEBS-g-MA blends. Notched Charpy impact strength and elongation at break are improved by the addition of compatibilizer.

Maleic anhydride-grafted poly(lactic acid) as a compatibilizer in poly(lactic acid)/graphene oxide nanocomposites

The goal of this work is to study the influence of maleic anhydride-grafted poly(lactic acid) compatibilizer (PLAgMA) on morphology, thermal and barrier properties of poly(lactic acid) (PLA)/graphene oxide (GO) nanocomposites. Graphene oxide was synthesized from graphite flakes using modified Hummers method. The nanocomposites were prepared by the incorporation of graphene oxide into PLA via solution casting. The formation of nanolayers of graphene oxide was confirmed by Fourier transform infrared spectroscopic analysis, scanning electron microscopy and atomic force microscopy measurements. A maximum in elastic modulus G′ measured at low frequencies was identified for the PLA containing 3 wt% GO and 3 wt% PLAgMA, which indicates a better dispersion of GO in the presence of compatibilizer and, therefore, yield better thermal and barrier properties of the nanocomposites.

Biodegradable composition of poly(lactic acid) from renewable wood flour

Maleic anhydride-grafted poly(lactic acid) (PLA-g-MAH) was prepared by blending with wood flour (WF). The effect of MAH and WF inclusion on the mechanical and thermal properties of the composites was examined. PLA-g-MAH/WF had optimum tensile properties compared with PLA/WF. Scanning electron microscopic images indicated poor interfacial adhesion of the PLA/WF. It was enhanced after MAH was grafted onto PLA; the PLA-g-MAH/WF showed excellent compatible morphology. Results also revealed that the biodegradation of PLA and PLA-g-MAH was improved with increasing of WF content.

Physical properties of maleated poly(lactic acid) composites containing different functionalized multiwalled carbon nanotubes.

In the current study, maleic anhydride-grafted poly(lactic acid) (MA-g-PLA) was prepared by using a reactive blending method to improve interfacial interaction and compatibilization in PLA/functionalized multiwalled carbon nanotube nanocomposites. Concentrations of maleic anhydride and initiator were varied at 3, 5 wt% and 0-0.7 wt%, respectively. The maleation content was determined by using a titration method, in which MA-g-PLA containing the optimum degree of grafting was subsequently chosen to prepare the nanocomposites containing hydroxyl and carboxylic functionalized multiwalled carbon nanotubes at various contents (0-5 wt%) and compared with the ones prepared with non-functionalized type. Dispersion morphology, thermal and mechanical properties of the resultant nanocomposites were investigated by means of transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and tensile measurement. It was shown that the compatibility between the nanotubes and MA-g-PLA was improved where the functionalized nanotubes exhibited a better dispersion and mechanical property than the nonfunctionalized nanotubes. With increasing concentration of carbon nanotubes, tensile strength and Young's modulus of the nanocomposites were correspondingly enhanced, in which at 5 wt% addition yielded the highest values at 90 MPa and 10 GPa, respectively.

A study on the effects of organoclay content and compatibilizer addition on the properties of biodegradable poly(butylene succinate) nanocomposites under natural weathering

Biodegradable poly(butylene succinate)/organo-montmorillonite nanocomposites were prepared at different organo-montmorillonite loadings, using maleic anhydride-grafted poly(butylene succinate) as compatibilizer. Poly(butylene succinate) nanocomposites were exposed to outdoor natural weathering for 180 days. Weight loss and decrease in mechanical properties after weathering revealed the degradation of poly(butylene succinate). Natural weathering caused photo-oxidation on poly(butylene succinate), leading to the formation of degraded products, as manifested in Fourier transform infrared spectroscopy. Gel permeation chromatography showed a significant reduction in molecular weight after weathering. It was noted that poly(butylene succinate) nanocomposite exhibited lower degradability as compared to neat poly(butylene succinate), due to the enhanced barrier properties after the addition of organo-montmorillonite. However, the incorporation of maleic anhydride-grafted poly(butylene succinate) increased the degradability. Degree of crystallinity of poly(butylene succinate) reduced after weathering, as shown in differential scanning calorimetry. Scanning electron microscopy analysis revealed fungal and bacterial colonization on the sample surface. In addition, the isolation and identification of bacterial strain were also performed.

Preparation, characterization and biodegradability of crosslinked tea plant-fibre-reinforced polyhydroxyalkanoate composites

The biodegradability, morphology, and mechanical properties of composite materials made from maleic anhydride-grafted poly(hydroxyalkanoate) (PHA-g-MA) and treated (crosslinked) tea plant fibre (t-TPF) were evaluated. Composites containing PHA-g-MA (PHA-g-MA/t-TPF) had noticeably superior mechanical properties compared with those of PHA/TPF because of greater compatibility with TPF. The dispersion of t-TPF in the PHA-g-MA matrix was more homogeneous because of ester formation and the consequent creation of branched and crosslinked macromolecules between the anhydride carboxyl groups of PHA-g-MA and hydroxyl groups in t-TPF. Additionally, the PHA-g-MA/t-TPF composites were more easily processed because of their lower melt viscosities. The water resistance of PHA-g-MA/t-TPF was higher than that of PHA/TPF, although the weight loss of composites buried in soil compost indicated that both were biodegradable, especially at high levels of TPF substitution. The PHA/TPF and PHA-g-MA/t-TPF composites were more biodegradable than pure PHA, which implied a strong connection between TPF content and biodegradability.

Reactive processing of maleic anhydride-grafted poly(butylene succinate) and the compatibilizing effect on poly(butylene succinate) nanocomposites

In this study, maleic anhydride-grafted poly(butylene succinate) (PBS-g-MA) was synthesized via reactive melt- grafting process using different initiator contents. The grafting efficiency was increased with the initiator content, mani- fested by the higher degree of grafting in PBS-g-MA. The grafting reaction was confirmed through Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Then, PBS-g-MA was incorporated into organo-montmorillonite (OMMT) filled poly(butylene succinate) (PBS) nanocomposites as compatibilizer. Mechani- cal properties of PBS nanocomposites were enhanced after compatibilized with PBS-g-MA, due to the better dispersion of OMMT in PBS matrix and the improved filler-matrix interfacial interactions. This was verifiable through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) showed that the degree of crystallinity and melting temperature increased after addition of PBS-g-MA. However, the presence of PBS-g-MA did not favor the thermal stability of the nanocomposites, as reported in the thermo- gravimetry (TGA).

Assessing feasibility of promoting fertilizer utilization facilitated by controlled release of bacteria-encapsulated film bag

The feasibility of using maleic anhydride-grafted poly(ethylene succinate) (PESU-g-MA)/starch as a film bag material to facilitate the controlled release of an encapsulated phosphate-solubilizing bacterium (PSB) as fertilizer utilization promoter was evaluated. For the purposes of comparison and accurate characterization, a polyethylene succinate (PESU) film bag was also assessed. The PSB was an indigenous Bacillus sp. PG01 isolate, and the results showed that the bacterium completely degraded both the PESU and the PESU-g-MA/starch composite film bags, resulting in cell release. The PESU-g-MA/starch (20 wt.%) film bags were more biodegradable than those made of PESU and also suffered a more severe decrease in molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability. On the other hand, the PG01 strain can degrade the particle of fertilizer into slight ones and make fertilizer easier to be absorbed by plants. Based on the results of this work, the controlled release of bacteria-encapsulated film bag for fertilizer utilization promotion appears achievable.

Aliphatic Polyester-Based Green Renewable Eco-composites from Agricultural Residues: Characterization and Assessment of Mechanical Properties

The biodegradability, morphology, and mechanical properties of composite materials consisting of maleic anhydride-grafted poly(butylene succinate adipate) (PBSA-g-MA) and agricultural residues (wheat bran, WB) were evaluated. Composites containing maleic anhydride-grafted PBSA (PBSA-g-MA/WB) exhibited noticeably superior mechanical properties compared with those of PBSA/WB because of greater compatibility with WB. PBSA/WB exhibited a tensile strength at break of approximately 2–15 MPa more than PBSA-g-MA/WB. The dispersion of WB in the PBSA-g-MA matrix was highly homogeneous as a result of ester formation and the subsequent creation of branched and cross-linked macromolecules between the anhydride carboxyl groups of PBSA-g-MA and hydroxyl groups in WB. Additionally, the PBSA-g-MA/WB composites were more easily processed due to their lower melt viscosity. Water resistance of PBSA-g-MA/WB was higher than that of PBSA/WB, although weight loss of composites buried in Azospirillum brasilense BCRC 12270 liquid culture medium compost indicated that both were biodegradable, especially at high levels of WB substitution. After 60 days, the weight loss of the PBSA-g-MA/WB (40 wt%) composite was greater than 90 %. PBSA/WB exhibited a weight loss of approximately 4–8 wt% more than PBSA-g-MA/WB. The PBSA/WB and PBSA-g-MA/WB composites were more biodegradable than pure PBSA, which implies a strong connection between WB content and biodegradability.

Evaluation of toughening mechanisms of polypropylene/ethylene-octene copolymer/maleic anhydride-grafted poly(ethylene-co -octene)/clay nanocomposite

The toughness of a polypropylene (PP)/ethylene-octene copolymer (EOC)/maleic anhydride-grafted poly(ethylene-co-octene) (EOC-g-MA)/clay nanocomposite and blends of PP/EOC and PP/EOC/EOC-g-MA was investigated using Charpy impact and single-edge-notch tensile (SENT) tests. In order to understand the toughening mechanisms, impact fracture surfaces and damage zones of single-edge-notch samples were studied with scanning electron microscopy and transmission optical microscopy, respectively. It was observed that the addition of EOC-g-MA to PP/EOC blend led to improvements in both impact strength and fracture energy of SENT tests because of the enhanced compatibility of the blend, which resulted from reduced EOC particle size and improved interfacial adhesion, and the decreased crystallinity of PP. The incorporation of clay to PP/EOC/EOC-g-MA blend caused a further increase of the toughness, owing to the greater decrease in the size of elastomer particles, to the presence of clay tactoids inside the elastomer phase and presumably to debonding of clay layers during the low-speed SENT tests. The results of microscopic observations showed that the main toughening mechanism in PP/EOC/EOC-g-MA blend and PP/EOC/EOC-g-MA/clay nanocomposite is crazing. Copyright © 2012 Society of Chemical Industry

Effect of Organoclay Platelets on Crystallization of Polytrimethylene Terephthalate/Polyethylene-octene-g-maleic Anhydride Blends: Isothermal Crystallization

The blends of poly(trimethylene terephthalate) (PTT) with maleic anhydride-grafted poly(ethylene-octene) (POE-g-MA) and organoclay (OMMT) were prepared by melt-blending. The effects of organoclay platelets on the isothermal crystallization behaviors of PTT/POE-g-MA blend were examined using differential scanning calorimetry. The crystallization kinetics of the primary stage under isothermal conditions could be described by the Avrami equation, with values of the Avrami exponent between 2.01 and 2.81 for all samples. The crystallization rate parameter, K, decreased with increase of melt-crystallization temperature for all samples. The activation energies for isothermal crystallization were determined by the Arrhenius equation.