Nonisothermal Crystallization Behavior Research Articles

Non-isothermal crystallization analysis of isotactic polypropylene filled with titanium dioxide particles modified by a dicarboxylic acid

In this work, the non-isothermal crystallization behavior of polypropylene (iPP), induced by a dicarboxilic acid linkage at the surface of commercial titanium dioxide (TiO2), was investigated. The modification of TiO2 particles with pimelic acid (c-TiO2) played an important role in improving the crystallization kinetic parameters, as observed by an increase in the temperature of the crystallization peak during the incubation period (Δtc). Jeziorny analysis suggested that the dominant secondary crystallization process occurs by nucleation on pre-existing crystals and is mainly the two-dimensional extension of the lamellar crystals formed during primary crystallization. As shown by the model of Mo, composites with c-TiO2 particles exhibited a high crystallization rate when the relative crystallinity exceeded the earliest crystallization stage. Activation energies were also determined and higher values were found for the studied composites, compared to neat iPP. These results show how the ability to nucleate into iPP is improved by c-TiO2 particles, which also increase the affinity to iPP chains, minimizing the energy required to reach the crystalline state.

Nano-Cu/Low-Density Polyethylene Composites: Structure and Control Release of Cupric Ions

In recent years a new type of intrauterine device (nanoCu/LDPE composites) has been concerned by a lot of scholars for its short release time, high bioavailability and good biocompatibility. In this study nanoCu/low-density polyethylene composites were prepared by extruding mixtures of pure LDPE and nanoCu using melt-blending method, the release rate of cupric ions (Cu2+) was measured in simulated uterine fluid. The non-isothermal crystallization behavior and thermal stability of the composites before and after immersion were studied by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG). The results showed that Composites effectively shorten the time of the copper ion "burst release" , the burst release phenomenon of Cu2+ occurred during the first five days after immersion , and then tend to stable . By immersion the crystallinity of composites increased, and the thermal stability decreased.

Synthesis and Non-Isothermal Crystallization Behaviors of Maleic Anhydride onto High Density Polyethylene

The grafting reaction for maleic anhydride (MA) onto high density polyethylene (HDPE) was investigated from solution process with initiators. The chemical modification of neat HDPE was carried out with various contents of MA (3-21 wt.%) and initiator (0.2-1 wt.%) at different temperature (80-130℃). The grafting degree was obtained from the titration and the highest grafting degree was 3.1%. The grafting degree increased as the content of MA and initiator increased, however, the highest grafting degree was demonstrated for a particular content of MA and initiator. In the non-isothermal crystallization kinetics, the Ozawa model was unsuitable method to investigate the crystallization behavior of MA onto HDPE, whereas the Avrami and Liu models found effective. The crystallization rate was accelerated as the cooling rate increased, but postponed by combination of MA onto neat HDPE backbone.

Non-isothermal crystallization kinetics of wood-flour/polypropylene composites in the presence of β-nucleating agent

The influence of aryl amide compounds (TMB) as β-nucleating agents, on the non-isothermal crystallization of a wood-flour/polypropylene composite (WF/PP) prepared by compression molding was investigated by wide-angle X-ray diffraction and differential scanning calorimetry. TMB was proved to be an effective β-crystalline nucleating agent for WF/PP. The DSC data showed that the crystallization peak temperature (Tp) increased and the half-time (t1/2) decreased with the addition of TMB. Three theoretical models were used to analyze the non-isothermal crystallization process. The modified Avrami method and Mo method successfully explained the non-isothermal crystallization behavior of PP and its composites. Their activation energies for non-isothermal crystallization were determined basing on the Kissinger method.

Crystal nucleation in random l/d-lactide copolymers

Poly (l-lactic acid) (PLLA) and its random copolymers with small amount of d-isomer co-units but identical mass-average molar mass of 120kDa were analyzed regarding the non-isothermal and isothermal crystallization and nucleation behaviors. First, it was confirmed that the gross crystallization rate and crystal growth rate decrease with increasing d-isomer content in the chains. In extension to earlier work, the isothermal analysis of the crystallization rate was completed by determination of critical cooling rates to suppress ordering of the melt. While in case of the PLLA homopolymer the melt needs to be cooled faster than 0.5Ks−1 in order to suppress crystallization, the critical cooling rate is lowered by about one order of magnitude to 0.05Ks−1 in case of a copolymer with 4% d-isomer co-units. However, even if the melt is cooled faster than the critical cooling rate to suppress crystallization, nuclei formation still occurs in a specific cooling-rate range depending on the d-isomer content, ceasing only on cooling about two orders of magnitude faster than the critical cooling rate to suppress crystallization. The observation of slower nuclei formation at non-isothermal conditions in PLLA containing d-isomer co-units is confirmed by isothermal nucleation experiments.

Nonisothermal and isothermal crystallization behavior of isotactic polypropylene/chemically reduced graphene nanocomposites

Graphene oxide was firstly prepared by a modified Hummers method and then reduced via hydrazine reduction method to obtain chemically reduced graphene (CRG). The morphology of CRG dispersed in the isotactic polypropylene (iPP) matrix was observed using transmission electron microscope and rheological measurement methods. Nonisothermal and isothermal crystallization behaviors of iPP/CRG nanocomposites were investigated by differential scanning calorimetry and polarizing optical microscopy methods, respectively. Nonisothermal crystallization measurement revealed that CRG elevated the crystallization temperature of iPP due to the nucleating effect of CRG. And during isothermal crystallization process, the half time crystallization of nanocomposites was significantly reduced. Furthermore, the images of polarized optical microscopy also exhibited that the nucleation density of nanocomposites was much higher than that of neat iPP due to the heterogeneous nucleation of CRG even at a loading of 0.5%. POLYM. COMPOS., 38:E342–E350, 2017. © 2016 Society of Plastics Engineers

Effect of different nanofillers on non-isothermal crystallization kinetics and electric conductivity of dynamically-vulcanized PP-EPDM Blends

In this study, nanofillers composed of hydroxylated carbon nanotubes (h-CNT), carbon nanotubes (CNT) and graphene (GR) were separately added into the dynamically-vulcanized polypropylene (PP)/ethylene-propylenediene monomer (EPDM) blend. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and electrical resistivity measurements were employed to study the effect of nanofillers on the melt behavior, non-isothermal crystallization behavior and electrical conductivity of the prepared composites. WAXD results showed that h-CNT had a better induction effect of β-PP in the nanocomposites. The sequence of the activity in inducing the formation of β-PP was h-CNT>GR>CNT. However, the total crystallinity of the nanocomposites nearly remained constant. Non-isothermal crystallization kinetic analysis indicated that the presence of nanofillers improved the crystallization rate of the nanocomposites. The consequence of nucleation activity was as follows: CNT>GR>h-CNT. Although EPDM hindered the macromolecular motion of PP, interestingly it could increase the crystallization rate to an extent. Besides, the influence of nanofillers on enhancing the conductive property of the nanocomposites can be ranked as follow: CNT>GR>h-CNT.

Non-Isothermal Crystallization Behavior of Rice Husk Powder/HDPE Composites

Non-Isothermal Crystallization Behavior of Rice Husk Powder/HDPE Composites

Morphology and thermal properties of biodegradable poly(hydroxybutyrate-co-hydroxyvalerate)/tungsten disulphide inorganic nanotube nanocomposites

Promising biodegradable and renewable poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites based on tungsten disulphide inorganic nanotubes (INT-WS2) were efficiently prepared by a simple solution blending method. The structure, morphology, thermal stability and crystallization behavior of the nanocomposites were investigated by ultra-high field-emission scanning electron microscope (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and polarized optical microscopy (POM) techniques. As previously observed in poly(3-hydroxybutyrate) (PHB) hybrid systems, the dispersion, morphology and thermal properties of PHBV/INT-WS2 nanocomposites could be tuned by the introduction of small amounts of INT-WS2. The results revealed that a good dispersion of INT-WS2 in the PHBV matrix influenced the morphology and non-isothermal crystallization behavior of PHBV that depends on both the INT-WS2 concentration and the cooling rate. A significant enhancement in thermal stability of PHBV and a highly efficient nucleating effect of the INT-WS2 comparable to specific nucleating agents or other nano-sized fillers was observed. These observations are of importance for extending the practical applications of these biopolymer nanocomposites towards eco-friendly (e.g. sustainable packaging) and biomedical (e.g. bone tissue engineering) applications.

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.

Role of N,N'-bis(1H-benzotriazole) adipic acid acethydrazide in crystallization nucleating effect and melting behavior of poly(L-lactic acid)

The enhancement of crystallization performance is very important in semicrystalline polymers for broadening their practical application. In this study, N,N'-bis(1H-benzotriazole) adipic acid acethydrazide (BA) was synthesized from 1H-benzotriazole and adipic acid in order to evaluate the heterogeneous nucleating performance of poly(L-lactic acid) (PLLA). Through the investigation of non-isothermal crystallization behavior of PLLA containing different BA content using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), it was clear that BA was able to significantly promote the crystallization of PLLA compared to pristine PLLA, and the addition of BA resulted in an increase in the onset and peak crystallization temperatures and in the non-isothermal crystallization enthalpy. Furthermore, 1 wt% BA was found to be the optimal concentration, achieving the best nucleating effect for PLLA. The cooling rate was a key factor affecting the non-isothermal crystallization peak. The set final melting temperature also affected crystallization, as a result of the solubility of BA in the PLLA matrix and the thermal decomposition of PLLA at the set temperature. Comparative study of the melting behavior of PLLA and PLLA/BA further confirmed the nucleating interaction of BA with PLLA. Differences in melting behavior were largely dependent on the competition between the crystallization rate and the relevant heating or cooling rate.

Non-isothermal Crystallization Kinetics of Waterborne Polyurethane/functionalized Graphene Nanocomposites

The non-isothermal crystallization behavior of waterborne polyurethane / functionalized graphene nanocomposites( WPU / FGNs) was studied by differential scanning calorimetry( DSC). The non-isothermal crystallization kinetics of WPU / FGNs was investigated by Ozawa and Mo equations,and the crystallization activation energies were calculated by Kissinger equation. The results show that FGNs can be used as heterogeneous nucleation agent to increase the onset of crystallization temperature,peak temperature and crystallization rate of WPU during non-isothermal crystallization process of WPU / FGNs. Crystallization dimension of the composites increases with the increase of the mass fraction of FGNs. When the mass fraction of FGNs increases to 0. 3%,crystallization activation energy of the composite decreases from- 47. 74 k J / mol to- 53. 60 k J / mol. When the mass fraction of FGNs is 1. 0%,the crystallization activation energy of the composite increases to- 41. 74 k J / mol.

Effects of POSS addition on Non-isothermal crystallization and morphology of PVDF

The influence of polyhedral oligomericsilsesquioxane (POSS) content on the rheological behavior, non-isothermal crystallization behavior, and on crystal morphology of the poly(vinylidene fluoride) nanocomposites prepared through melt blending were investigated in this work. Rheological analysis showed that the POSS additiondecreased viscosity as compared to pure PVDF and induced a deviation in the liquid-like behavior predict by Einstein Suspension Sphere Law. The addition of POSS into PVDF promoted chances in the crystallization behavior. The crystallization was slower in the nanocomposite with higher POSS content due to the diluent effect of POSS in this system. Small angle X-ray scattering (SAXS) patterns showed a small increasing in the lamellar region of PVDF. The amorphous region increases significantly with POSS addition. The interface between the crystalline and amorphous region remains practically unchanged.

The synergistic effect of zinc oxide and phenylphosphonic acid zinc salt on the crystallization behavior of poly (lactic acid)

In order to improve the crystallinity and crystallization rate of poly (lactic acid) (PLA), a method for the preparation of a composite nucleating agent (CNA) consisting of zinc oxide and phenylphosphonic acid zinc salt was proposed. Zinc oxide, phenylphosphonic acid zinc salt and CNA were mixed into PLA through the melt blending method, respectively. The resultant PLA samples were characterized by differential scan calorimeter (DSC) and polarized optical microscope (POM). The DSC results showed that the crystallinity and crystallization temperature of the PLA samples with CNA were higher than those of the other PLA samples. The phenomena of crystallization nucleation and growth of various PLA samples were observed by means of POM. Isothermal and non-isothermal crystallization behavior of various PLA samples with different addition of CNA was studied, the corresponding result showed that the overall crystallinity, crystallization rate, nucleation density, and spherulite number increased obviously, as well as the crystallization time decreased, indicating the heterogeneous nucleating effect of CNA on the crystallization of PLA. For each of the component of CNA, the phenylphosphonic acid zinc salt could be used as an effective site of heterogeneous nucleation, resulting in the increasing nucleation density of PLA, and the zinc oxide could be acted as a good crystallization promoter for promoting the crystal growth of PLA. At the CNA content of 1 phr, CNA had a significant impact on crystallization behavior of PLA with a little negative influence on the molecular weight of PLA.

Study on Thermal Stability and Non-Isothermal Crystallization Behaviour of Polyethylene/Clay Nanocomposites

In this work, thermal stability and non-isothermal crystallization behaviour of polyethylene/clay nanocomposites prepared by in-situ polymerization were studied. The thermal degradation kinetics of polyethylene/clay nanocomposites in nitrogen was investigated by a pseudo-first order method indicating that the addition of clay filler in polyethylene matrix could improve the thermal stability of nanocomposites. The Ozawa, Avrami, and modified Avrami-Ozawa methods were applied to study the non-isothermal crystallization behaviour of polyethylene/clay nanocomposite. It was found that the clay filler not only acted as a heterogeneous nucleation for the crystallization of polyethylene but also hindered the transport of the polyethylene molecule chains at the same time, resulting in a decrease of the crystallization growth rate of polyethylene with clay loading. In addition, the nucleation activity and the activation energy for the crystallization of polyethylene/clay nanocomposites were also estimated.

Non-isothermal crystallization behavior of dynamically vulcanized long chain branched polypropylene/ethylene-propylene-diene monomer blends

The non-isothermal crystallization behaviors of long chain branched isotactic polypropylene (LCB PP), dynamically vulcanized LCB PP/ethylene-propylene-diene monomer (EPDM) blends at various weight ratios were investigated by DSC, rheology and optical microscopy. LCB PP/EPDM blends were found to show a different crystallization behavior in comparison with linear PP/EPDM blends, showing a minimum in the peak temperature of crystallization with increasing the content of EPDM while the latter showing a maximum. The nucleation and the crystallization kinetics of PP were induced and accelerated by long chain branches and EPDM. The acceleration of crystallization kinetics of LCB PP induced by LCB structures was attributed to the grafted efficient nucleation agent. The influence of EDPM on the crystallization combines the effects of enhancement and retardation, depending on its content in the blends. Based on the thermodynamics theory of crystallization, a modified crystallization model was developed to reveal the crystallization mechanism of LCB PP/EPDM blends.

Non-isothermal melting and crystallization behavior of UHMWPE/SCF/nano-SiO2 hybrid composites

The non-isothermal crystallization and melting behavior of ultrahigh molecular weight polyethylene reinforced with short carbon fibers (SCFs) and nano-SiO2 particles were investigated using differential scanning calorimetry. The melting tests were conducted at the cooling rates of 10, 20 and 30 °C min−1 prior to heating at the rate of 10 °C min−1. Melting peak temperatures increased by the incorporation of SCFs and remained almost constant by adding nano-SiO2 particles. The crystallization tests were performed at the cooling rates of 10, 20, 30 and 40 °C min−1. Ozawa–Avrami model was proved the best model to describe the kinetics of the composites. SCFs increased the absolute crystallinity of the neat polymer; however, adding various amounts of nano-SiO2 leaded to a decrease in the absolute crystallinity.

Effect of clay on melt crystallization, crystallization kinetics and spherulitic morphology of poly(trimethylene terephthalate) nanocomposites

Poly(trimethylene terephthalate) (PTT)/clay nanocomposite films have been prepared via a novel two-step approach. The resulting nanocomposites have been characterized by Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized light microscopy (PLM). XRD results showed this two-step process of preparation forms predominantly exfoliated structures. The effect of nanoclay on the isothermal and nonisothermal melt crystallization behaviors of PTT has been investigated and shown that the incorporation of clay accelerates the rate of crystallization and increases the total crystallinity of PTT nanocomposites compared to neat PTT. Nonisothermal melt crystallization kinetics of neat PTT and PTT nanocomposites was analyzed using crystallization isotherm. The Avrami analysis modified by Jeziorny was successfully used to describe the non-isothermal crystallization kinetics of neat PTT and PTT nanocomposites, shown by the decrease in half time (t1/2) of crystallization and increase in rate constant (Zc) as organoclay content increased up to 10%. FTIR spectroscopy has been utilized for the first time to monitor conformational changes during the melt crystallization of PTT nanocomposites. It was demonstrated that the amorphous trans conformation transforms into the crystalline gauche conformation with increasing clay content, which suggests that nanoclay accelerates the polymer chain conformational transition from trans to gauche conformation. No significant change in amorphous gauche conformation was observed either with crystallization temperature or clay content.

Non-Isothermal Crystallization Behaviour and Kinetics of LLDPE/REDMUD Blends

The non-isothermal crystallization behaviour of pure LLDPE and LLDPE/REDMUD blends was investigated by differential scanning calorimetry (DSC), and the crystallization kinetics was analyzed by three methods, namely the Jeziorny, the Mo and the Ozawa. The results show that an optimal content of REDMUD (lower than10 wt.%) can enhance the kinetic crystallizability of the system because of heterogeneous nucleation, but excessive REDMUD, by physical hindrance, would impair the kinetic crystallizability. In non-isothermal crystallization kinetics, the Ozawa model did not fit well with the crystallization behaviour of these systems, while the Jeziorny and Mo models were found to be applicable. Furthermore, the activation energy ΔE calculated by the Kissinger method for the transport of macromolecular segments to the growing surface of crystal nucleus indicates that REDMUD could significantly reduce the crystallization migration activation energy of these blends.

Melting and non-isothermal crystallization behaviors of polypropylene and polypropylene/montmorillonite nanocomposites under pressurized carbon dioxide

Both the melting and non-isothermal crystallization behaviors of polypropylene (PP) and PP/montmorillonite (MMT) nanocomposites under atmospheric N2 and pressurized CO2 were carefully studied by using high-pressure differential scanning calorimeter (DSC). Jeziorny modified Avrami and Mo's methods were applied to analyze the non-isothermal crystallization kinetics, respectively. The Avrami exponent decreased with CO2 pressure while increased with the addition of nano-MMT. The Mo's methods demonstrated a success for the systems investigated. The cooling rate needed to reach a certain crystallinity (FT) showed that the crystallization rates fluctuated with increasing CO2. This trend was flattened after introducing nano-MMT because of its heterogeneous effects. The activation energy, Ea, decreased with increasing CO2 pressure while increased in the presence of nano-MMT. The overall crystallization rate characterized by the crystallization half-time, t1/2, showed an decrease in PP/MMT nanocomposites, indicating that MMT had significant heterogeneous nucleation effect on enhancing the crystallization rate despite hindering the polymer chain movement.