Non-isothermal crystallization kinetics of TiO2 nanoparticle-filled poly(ethylene terephthalate) with structural and chemical properties

The present research work includes non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET)–titanium dioxide (TiO₂) nanocomposites as well as structural and chemical properties of these nanocomposites. The average grain size of chemically synthesized TiO₂ nanoparticles has been calculated 19.31 nm by TEM and XRD. The morphology and structural analysis of PET–TiO₂ nanocomposites, prepared via solution casting method, has been investigated using SEM and XRD, respectively. The nature of chemical bonds has been discussed on the basis of FTIR spectra. The effect of TiO₂ nanoparticles and cooling rates on non-isothermal crystallization kinetics of PET was examined by differential scanning calorimetry at various heating and cooling rates. It has been observed that TiO₂ nanoparticles accelerate the heterogeneous nucleation in PET matrix. The crystallization kinetics could be explained through Avrami–Ozawa combined theory. TiO₂ nanoparticles cause to make molecular chains of PET easier to crystallize and accelerate the crystallization rates during non-isothermal crystallization process; this conclusion has also been verified by Kissinger model for crystallization activation energy.     

Evaluation of nonisothermal crystallization kinetic models for linear poly(phenylene sulfide)

The nonisothermal crystallization kinetics of linear Poly(phenylene sulfide) (PPS) was studied with differential scanning calorimetry. Ozawa theory, Jeziorny model, and Mo equation were applied to describe the crystallization kinetics and to determine the crystallization parameters and mechanism of the linear PPS resin. The crystallization activation energies were also calculated using Kissinger formula and Flynn‐Wall‐Ozawa equation, respectively. According to the Ozawa model, it is found that instantaneous nucleation takes place during crystallization of PPS; the Ozawa exponent m is 3 in initial stage of crystallization; as the crystallization temperature decreases, the value of m reduces, and the growth rate of crystal almost keeps a constant. The Avrami exponent n obtained from Jeziorny model fluctuate around 1.84. Based on the Jeziorny model, the crystallization rate increases with increasing the cooling rate, but it does not change any longer when the cooling rate rise to a certain value. Mo equation also exhibits great advantages in treating the nonisothermal crystallization kinetics of PPS. The activation energy E of nonisothermal crystallization process of PPS is calculated to be −162.73 kJ/mol by the Kissinger formula, and the mean value of E determined by Flynn‐Wall‐Ozawa equation is −152.40 kJ/mol. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

NONISOTHERMAL CRYSTALLIZATION KINETICS AND MECHANICAL PROPERTIES OF PP/NANO-SiO2 COMPOSITES

The nonisothermal crystallization kinetics of polypropylene (PP)/nano-SiO₂ composites was studied by means of differential scanning calorimetry (DSC). The modified Avrami theories by Jeziorny, Ozawa, and Mo were used to analyze the data of DSC. The results showed that both the Jeziorny and Mo methods could describe this system very well, but the Ozawa analysis failed. The activation energy was evaluated by the Kissinger method. It was found that the crystallization activation energy of PP was higher than that of PP/nano-SiO₂ composites. The determined results of mechanical properties showed that the addition of nano-SiO₂ increased the mechanical properties of the PP. Micrographs of Polarized optical micrograph (POM) further demonstrated that nano-SiO₂ could toughen the PP.     

氧化铁包覆云母对聚对苯二甲酸乙二醇酯非等温结晶动力学的影响

以氧化铁包覆云母为成核剂,对聚对苯二甲酸乙二醇酯（PET）进行成核改性,采用差示扫描量热法分别研究了不同降温速率下PET和PET/氧化铁包覆云母复合材料的非等温结晶行为,用Jeziorny法和莫志深法对非等温结晶过程进行了分析,并用Flynn-Wall-Ozawa法计算其活化能。结果表明：氧化铁包覆云母对PET具有异相成核的作用,可明显提高PET的结晶速率;与Jeziorny法相比,莫志深法可较好描述PET和PET／氧化铁包覆云母复合材料的非等温结晶过程。进一步分析表明,氧化铁包覆云母的加入并没有明显改变PET基体的成核机理和生长方式,但降低了PET的结晶活化能,从而提高了PET的结晶性能。     

Non-isothermal crystallization kinetics and nucleation activity of hyperbranched polyester (HBPET) in recycled PET

The non-isothermal crystallization of pure recycled polyethylene terephthalate (RPET) and its blends with 3 and 5 wt% hyperbranched polyester (HBPET) were investigated by differential scanning calorimetry (DSC). The DSC curves demonstrate that the melt-crystallization temperatures of the blends are always higher than that of pure RPET regardless of the cooling rate. Their non-isothermal crystallization kinetics was further analyzed with modified Avrami equation, Ozawa equation and Mo method. The analysis reveals that the crystallization half-time (t _1/2) of the blends is shorter than pure RPET. The activation energy of crystallization of RPET was also determined according to Kissinger method and it is found to decrease remarkably in RPET-3 and RPET-5 blends. All the results indicate that HBPET serves as an effective nucleating agent for RPET.     

Effect of high content of carbon black on non-isothermal crystallization behavior of poly(ethylene terephthalate)

With the aid of co-rotating twin screw extruder, poly(ethylene terephthalate) (PET)/carbon black (CB) masterbatches were fabricated through melt-compounding using a separate feeding and metering technique and their homogeneous dispersion morphologies were confirmed by scanning electron microscopy and transmission electron microscopy. Moreover, the ultimate content of CB in the masterbatches was verified via thermogravimetric analysis method. The non-isothermal crystallization process of pristine PET and PET/CB masterbatch were investigated by differential scanning calorimetry and the different methods such as Jeziorny modified Avrami equation, Ozawa equation, and the method developed by Mo were employed to analyze their non-isothermal crystallization kinetics. The results show that CB particles uniformly dispersed in PET matrix act as heterogeneous nucleating agents, while crystallization activation energy (ΔE) of PET/CB masterbatch is much greater than that of virgin PET according to Kissinger formula, Takhor model, and Augis-Bennett model. Whereas, the results obtained from the above mentioned three methods simultaneously demonstrate the addition of CB greatly increases crystallization temperature and crystallinity and accelerates crystallization rate. The results reveal that crystal growth has little effect on the crystallization rate and crystal nucleation dominates the crystallization process of PET/CB masterbatch containing very high CB loading (20 wt%).     

Thermal degradation behaviors of phosphorus–silicon synergistic flame‐retardant copolyester

A novel phosphorus‐containing poly (ethylene terephthalate) (PET) copolyester/nano‐SiO₂ composite (PET‐co‐DDP/SiO₂) was synthesized by in situ polycondensation of terephthalic acid (TPA), ethylene glycol (EG), [(6‐oxide‐6H‐dibenz[c,e] [1,2]oxaphosphorin‐6‐yl)‐methyl]‐butanedioic acid (DDP), and nano‐SiO₂. The morphology of PET nanocomposites was observed by using transmission electron microscope and scanning electron microscope. It was found that the SiO₂ nanoparticles were dispersed uniformly at nanoscale in the copolyesters with content 2 wt %. The thermal degradation behavior of PET nanocomposites was investigated by thermogravimetric analysis performed with air and nitrogen ambience. The activation energies of thermal degradation were determined using Kissinger and Flynn–Wall–Ozawa methods, respectively. The results obtained from Kissinger method showed that the activation energy was increased with the introduction of SiO₂. Moreover, the activation energy is decreased for PET‐co‐DDP system in nitrogen and air. The results also indicated that the SiO₂ and DDP had synergic effect on the early decomposition and the late charring in air. Furthermore, in the PET‐co‐DDP/SiO₂ system, the activation energy increased when the DDP component increased. However, the opposite results were obtained when the Flynn–Wall–Ozawa method was used. That was because the Doyle approximation stands correct as the conversion degree is from 5% to 20%. The effects of SiO₂ and DDP on the PET thermal degradation were lower in nitrogen than in air. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization and non-isothermal crystallization behavior of biodegradable poly(ethylene sebacate)/SiO2 nanocomposites

Poly(ethylene sebacate) (PESeb) and PESeb/silica nanocomposites (PESeb/SiO₂) were prepared by in situ polymerization from the direct esterification of ethylene glycol with sebacic acid in the presence of proper amounts of silica nanoparticles. The non-isothermal crystallization behavior of PESeb/SiO₂ nanocomposites has been studied using different theoretical equations such as Avrami, Ozawa and combined Avrami and Ozawa equations. It is found that the addition of nanoparticles of SiO₂ influenced the mechanism of nucleation and the growth of PESeb crystallites. Also, the nanocomposites show a higher Avrami value than the neat PESeb, implying a more complex crystallization configuration. Moreover, the combined Avrami and Ozawa equation can successfully describe the crystallization model under the non-isothermal crystallization. The crystallization activation energies, E _a, calculated from “Kissinger’s equation” have shown that the synthesized PESeb/SiO₂ nanocomposites have lower energy than the neat PESeb, reflecting the much lower energy barrier for the rapid heterogeneous nucleation.     

Polylactide/nano‐ and micro‐scale silica composite films. II. Melting behavior and cold crystallization

Nonisothermal crystallization of polylactide (PLA)/silica composites prepared by (i) directly blending the PLA with nanoscale colloidal silica sol and by (ii) a sol–gel process are studied by differential scanning calorimeter (DSC) at various heating rates. Samples quenched from the molten state exhibited two melting endotherms (T_ml and T_mh) due to melt‐recrystallization during the DSC scans. Lower heating rate and the presence of silica particles generate a lower peak intensity ratio of T_ml /T_mh. The nonisothermal crystallization kinetics is analyzed by modified Avrami model, Ozawa model, and Liu‐Mo models. The modified Avrami and Liu‐Mo models successfully described the nonisothermal cold crystallization processes, but Ozawa is inapplicable. The nucleation constant (K_g) is calculated by modified Lauritzen‐Hoffman equation and the activation energy by Augis‐Bennett, Kissinger, and Takhor models. These calculated parameters indicate consistently that the nanoscale silica particles seem to form more heterogeneous nucleation to increase crystallization, but microscale one form hindrance to retard crystallization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nonisothermal crystallization kinetics of high‐density polyethylene/barium sulfate nanocomposites

The high‐density polyethylene (HDPE)/barium sulfate (BaSO₄) nanocomposites had been successfully prepared by melt‐blending. Nonisothermal melt‐crystallization kinetics of neat HDPE and HDPE/BaSO₄ nanocomposites was investigated with differential scanning calorimetry under different cooling rates. The nonisothermal crystallization behavior was analyzed by Ozawa, Avrami, and combined Ozawa–Avrami methods. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of neat HDPE and HDPE/BaSO₄ nanocomposites. The modified Avrami method by Jeziorny was only valid for describing the middle stage of crystallization but was not able to describe the later stage of neat HDPE and HDPE/BaSO₄ nanocomposites crystallization. The value of Avrami exponent n for neat HDPE ranged from 3.3 to 5.7 and for HDPE/BaSO₄ nanocomposites ranged from 1.8 to 2.5. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation, whereas simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n. The combined Ozawa–Avrami method by Mo and coworkers (Polym. Eng. Sci., 37(3) , 568 (1997)) was able to satisfactorily describe the crystallization behavior of neat HDPE and HDPE/BaSO₄ nanocomposites. In addition, the activation energy of nonisothermal crystallization was determined using the Kissinger (J. Res. Natl. Bur. Stand., 57(4) , 217 (1956)) method, showing that the crystallization activation energy of HDPE/BaSO₄ nanocomposites was lower than that of neat HDPE. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Non-isothermal Crystallization Kinetics of Poly (Ethylene Terephthalate)/Grafted Carbon Black Composite

Summary The grafted carbon black (GCB) was prepared by in-situ grafting low molecular weight compound on the surface of carbon black (CB) using a new technique. Poly(ethylene terephthalate)/grafted carbon black (PET/GCB) and poly(ethylene terephthalate)/ carbon black (PET/CB) composites were prepared by melt blending. The non-isothermal crystallization process of virgin Poly(ethylene terephthalate)(PET), PET/CB, and PET/GCB composites were investigated by differential scanning calorimetry (DSC), and the non-isothermal crystallization kinetics was analyzed using different approaches, i.e. modified Avrami equation, Ozawa equation and the method developed by Liu. The effective energy barrier ΔE of virgin PET, PET/CB, and PET/GCB composites were calculated using the differential iso-conversional method. All of the results showed that GCB and CB acted as nucleating agents and increased the crystallization rate of PET. Compared with CB, GCB was a more effective nucleator for PET.     

PE-LLD/纳米Al2O3复合材料非等温结晶动力学研究

采用差示扫描量热法研究了线形低密度聚乙烯（PE-LLD）/纳米氧化铝（Al2O3）复合材料的非等温结晶行为,分别利用Avrami方程和莫志深方程对结晶动力学进行了分析,运用Kissinger方程计算了结晶过程中的活化能。结果表明,添加5 %（质量分数,下同）和10 %的纳米Al2O3,在PE-LLD的非等温结晶过程中起到的异相成核作用较为微弱,PE-LLD/纳米Al2O3复合材料的结晶起始温度、峰值温度和结晶速率均较PE-LLD略有提高,但结晶活化能有所降低。     

Crystallization behavior of polyhydroxybutyrate in model composites with kenaf fibers

The kinetics of the nonisothermal crystallization process of polyhydroxybutyrate in polyhydroxybutyrate/kenaf fiber model composites (with 80/20 and 70/30 w/w matrix/kenaf fibers) were investigated with differential scanning calorimetry. An analysis of the data was carried out with the Avrami, Ozawa, and modified Avrami and Ozawa models, as well as the Kissinger approach, for the determination of the crystallization activation energy. The Ozawa model was unsuitable for analyzing the nonisothermal data, whereas the other models described these systems very well. By the analysis of all the relevant parameters, the nucleation activity of the kenaf fibers was confirmed. The activation energies from the Kissinger method were evaluated to be 41.2, 32.6, and 26.3 kJ/mol for the pure polymer resin and 80/20 and 70/30 (w/w) polyhydroxybutyrate/kenaf fiber composites, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 804–809, 2006     

Poly(propylene)–poly(propylene)‐grafted maleic anhydride–organic montmorillonite (PP–PP‐g‐MAH–Org‐MMT) nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of poly(propylene) (PP), PP–organic‐montmorillonite (Org‐MMT) composite, and PP–PP‐grafted maleic anhydride (PP‐g‐MAH)–Org‐MMT nanocomposites were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny and a method developed by Mo well‐described the nonisothermal crystallization process of these samples. The difference in the exponent n between PP and composite (either PP–Org‐MMT or PP–PP‐g‐MAH–Org‐MMT) indicated that nonisothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half‐time, Z_c; and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PP and composites, but the crystallization rate of composites was faster than that of PP at a given cooling rate. The method developed by Ozawa can also be applied to describe the nonisothermal crystallization process of PP, but did not describe that of composites. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PP–Org‐MMT was much greater than that of PP, but the activation energy of PP–PP‐g‐MAH–Org‐MMT was close to that of pure PP. Overall, the results indicate that the addition of Org‐MMT and PP‐g‐MAH may accelerate the overall nonisothermal crystallization process of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3093–3099, 2003     

Nonisothermal crystallization kinetics of kenaf fiber/polypropylene composites

Nonisothermal crystallization behavior of model ecocomposites based on polypropylene (PP), maleic anhydride modified polypropylene (PP_m), and kenaf fibers were extensively studied. Melting and crystallization behavior of the composites with 20 wt/wt% kenaf fibers were analyzed by differential scanning calorimetry (DSC) in dynamic regime (with heating rate of 10 K/min, and cooling rates of 5, 10, 15, 20, and 40 K/min). It was shown that the kenaf fiber surface acts as a nucleating agent during nonisothermal crystallization of both PP matrices, shifting the onset and peak crystallization temperatures toward higher values. Crystallization behavior was analyzed by Avrami, Jeziorny, Ozawa, Mo, and Kissinger methods. The results confirmed the applicability of the used models, with exception of the Ozawa approach that was rather inapplicable for these composites. POLYM. ENG. SCI., 47:745–749, 2007. © 2007 Society of Plastics Engineers.     

Isothermal and nonisothermal crystallization kinetics of nylon-11

Analysis of the isothermal, and nonisothermal crystallization kinetics of Nylon-11 is carried out using differential scanning calorimetry. The Avrami equation and that modified by Jeziorny can describe the primary stage of isothermal and nonisothermal crystallization of Nylon-11. In the isothermal crystallization process, the mechanism of spherulitic nucleation and growth are discussed; the lateral and folding surface free energies determined from the Lauritzen–Hoffman equation are ς = 10.68 erg/cm² and ς_e = 110.62 erg/cm²; and the work of chain folding q = 7.61 Kcal/mol. In the nonisothermal crystallization process, Ozawa analysis failed to describe the crystallization behavior of Nylon-11. Combining the Avrami and Ozawa equations, we obtain a new and convenient method to analyze the nonisothermal crystallization kinetics of Nylon-11; in the meantime, the activation energies are determined to be −394.56 and 328.37 KJ/mol in isothermal and nonisothermal crystallization process from the Arrhonius form and the Kissinger method. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2371–2380, 1998     

A different approach for the study of the crystallization kinetics in polymers. Key study: poly(ethylene terephthalate)/ SiO2 nanocomposites

Polymer crystallization is complex and difficult to model, especially when it is non‐isothermal and even more so when describing cold crystallization. In most cases, two different processes occur, so‐called primary and secondary crystallization. In the literature, two assumptions are generally made. Firstly, the validity of the Avrami model is assumed a priori. Secondly, for calculations of the kinetic parameters and activation energy, data from a single differential scanning calorimetry scan at a given heating rate are used. The other popular model, that of Ozawa, is also based on similar assumptions. In the study reported here, a different approach was adopted, which uses multiple scans at various heating rates simultaneously. Here the experimental data of the non‐isothermal cold crystallization of an in situ‐prepared poly(ethylene terephthalate)/1% SiO₂ nanocomposite were used. Data were analysed following both the ordinary procedure and the method proposed in this work. Findings showed that when the Avrami model is a priori supposed to hold and the data of different heating rates are analysed separately, results are not acceptable. The new approach involves calculation of the activation energy through use of the isoconversional methods of Ozawa–Flynn–Wall and Friedman over the whole range of the crystallization conversion. The reaction model f(a) was determined after the evaluation of 16 different models. The best fitting was achieved for the Prout–Tompkins model or for a mechanism involving two steps described by respective Avrami equations with different activation energies. Copyright © 2010 Society of Chemical Industry