Crystallization Kinetics Of Isotactic Polypropylene Research Articles

Investigation on crystallization kinetics and solidification behavior of isotactic polypropylene (iPP) using an enthalpy transformation method

ABSTRACT The enthalpy transformation method, a widely accepted way to solve the phase transition related problems, was utilized to investigate the relationship between solidification behavior and crystallization kinetics of isotactic polypropylene (iPP). Our findings suggest that the cooling medium temperature is more effective in controlling the average cooling rate than the melt temperature. A generalized equation, which was obtained by plotting the cooling curves in a double-logarithmic scale, could be adopted to estimate the minimum cooling time (MCT) of the crystalline polymer to optimize the design of an injection molding (IM) cycle. Moreover, the quantitative description of the position dependence of the crystallization rate was also established. The present study will be of practical use to further exploration of the correlation between cooling parameters and the structural evolution of crystalline polymers as well as a better understanding of microstructural formation mechanisms.

Effect of aliphatic chain in dicarboxylic acids on non-isothermal crystallization and mechanical behavior of titanium dioxide/iPP composites

Non-isothermal crystallization kinetics of isotactic polypropylene (iPP) and its composites prepared with functionalized titanium dioxide (TiO2) were investigated by varying both heating rate and dosage of functionalized particles. Jeziorny’s and Mo’s methods were used to describe the non-isothermal crystallization process. The behavior of crystallization activation energy as a function of the crystallinity degree was evaluated by applying an isoconversional method. The modification of the TiO2 surface was done by testing three different carboxylic acids: glutaric, pimelic and azelaic acid and these particles were tested at different concentrations in iPP, 0.1, 0.5 and 1 % w/w; which had a high effect on the crystallization process of the polymer matrix. It was demonstrated the efficiency of the dry basis chemical reaction as a method to modify with dicarboxylic acids the surface of TiO2 particles. Such organic coatings chemically bonded to the surface of the TiO2 promoted a better incorporation of the iPP chains during crystallization and there is a clear effect of the length of dicarboxylic acids since the acids with more carbons, pimelic and azelaic, decreased the time to reach the crystalline state. Besides, the values of Young’s modulus were modified by functionalized TiO2 particles, being the acid with the longest chain (azelaic acid) the one that more increased this parameter.

Isothermal and non-isothermal crystallization of isotactic polypropylene in the presence of an α nucleating agent and zeolite 13X

The isothermal and non-isothermal crystallization kinetics of isotactic polypropylene (iPP) and iPP nucleated with the nucleating agent sodium 2,2′-methylene-bis(4,6-di-tertbutylphenyl)-phosphate (NA11), zeolite 13X (Z13X), and both NA11 and Z13X were investigated. First, isothermal crystallization analyses show that the iPP/NA11/Z13X system provided the smallest half-crystallization time compared with the other three iPP systems even though a smaller amount of NA11 was added in the iPP/NA11/Z13X system (0.08 wt%) relative to that of the iPP/NA11 system (0.2 wt%). Moreover, the fold surface energy of the iPP/NA11/Z13X system was also the least among all samples considered. Then, during non-isothermal crystallization, the iPP/NA11/Z13X system demonstrated the smallest value of F(T), indicating that the required cooling rate to attain a specified relative crystallinity for the system was the lowest among all systems considered. Furthermore, a comparison of the crystallization activation energy shows that the NA11 and NA11/Z13X additives primarily improved the crystallization of iPP through an acceleration of the nucleation process. Finally, polarized optical microscopy results show that the NA11 and Z13X additives affected only the crystallization kinetics of iPP, and did not affect the crystallization morphology.

Crystallization kinetics of ethylene-co-propylene rubber/isotactic polypropylene blend investigated via chip-calorimeter measurement

Differential scanning calorimetry measurement via fast-scan chip-calorimeter Flash DSC1 has been widely applied to investigate the crystallization kinetics of homopolymer and random copolymers. We expanded the measurement to the crystallization kinetics of isotactic polypropylene (iPP) blending with 29.3wt% ethylene-co-propylene rubber (EPR) that contains 39.5wt% ethylene monomers (toughening iPP). The temperature dependence of half-crystallization times of the blend show three regions of deviations from the parallel results of pure iPP, reflecting the effect of interplay between phase separation and crystallization. We attributed faster crystallization in the high-temperature region to crystal nucleation accelerated by the interfaces of two incompatible components, attributed slower crystallization in the middle-temperature region to crystal nucleation retarded by the crystallization of ethylene sequences in the minor EPR component, and attributed faster crystallization in the low-temperature region to crystal nucleation accelerated by the crystallization of propylene sequences in the minor EPR component. The suppression of crystallization on fast cooling as well as the variation of Avrami indexes support the scenario of crystallization competition in the middle temperature region.

Synergistic effect of aryl heterocyclic aluminum phosphate and sodium laurate on non-isothermal crystallization kinetics of isotactic polypropylene

Kinetics of non-isothermal crystallization of isotactic polypropylene (iPP)/nucleating agent blends was studied for the nucleation mechanism. Avrami, Jeziorny, and correctional Friedman methods were applied to analyze the non-isothermal crystallization of the iPP/aryl heterocylic aluminum phosphate/sodium laurate (iPP/AHP-Al/L-Na) blends. For a given cooling rate of 10°C min−1, the onset temperature ( To) and crystallization temperature ( Tc) of the iPP/AHP-Al/L-Na blends increased by 4.19°C and 3.57°C, respectively, compared to iPP/L-Na. The To and Tc of iPP/AHP-Al/L-Na blends increased by 2.13°C and 1.79°C, respectively, compared to iPP/AHP-Al, when the AHP-Al mass fraction reached 1.2‰. The effective activation barrier (Δ E) for non-isothermal crystallization was the least when the AHP-Al mass fraction was 0.8‰. The value of the initial slope of the exotherm increased with the addition of AHP-Al monotonically. All these findings indicated that AHP-Al could improve the initial crystallization rate and also that the addition of AHP-Al/L-Na reduced the Δ E for non-isothermal crystallization. It is speculated that an ion exchange reaction between AHP-Al and L-Na occurs during the mixing process and could be possible that this results in the generation of a more efficient nucleating agent.

More dominant shear flow effect assisted by added carbon nanotubes on crystallization kinetics of isotactic polypropylene in nanocomposites.

More dominant shear flow effect with different shear rates and shear time with assistance of added carbon nanotubes (CNTs) of low amounts on the crystallization kinetics of isotactic polypropylene (iPP) in CNT/iPP nanocomposites was investigated by applying differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheometer. CNTs were chemically modified to improve the dispersity in the iPP matrix. CNT/iPP nanocomposites with different CNT contents were prepared by solution blending method. The crystallization kinetics for CNT/iPP nanocomposites under the quiescent condition studied by DSC indicates that the addition of CNTs of low amounts significantly accelerates crystallization of iPP due to heterogeneous nucleating effect of CNTs, whereas a saturation effect exists at above a critical CNT content. The shear-induced crystallization behaviors for CNT/iPP nanocomposites studied by POM and rheometry demonstrate the continuously accelerated crystallization kinetics with assistance from added CNTs, with increasing CNT content, shear rate, and shear time, without any saturation effect. The changes of nucleation density for CNT/iPP nanocomposites under different shear conditions can be quantified by using a space-filling modeling from the rheological measurements, and the results illustrate that the combined effects of added CNTs and shear flow on the acceleration of crystallization kinetics are not additive, but synergetic. The mechanisms for the synergetic effect of added CNTs and shear flow are provided.

Isothermal and non-isothermal crystallization of isotactic polypropylene nucleated with 1,3,5-benzenetricarboxylic acid tris(cyclohexylamide)

Abstract Isothermal and non-isothermal crystallization kinetics of isotactic polypropylene (iPP) nucleated with 1,3,5-benzenetricarboxylic acid tris(cyclohexylamide) (BTCA-TCHA) were investigated by differential scanning calorimetry (DSC). The classical Avarmi equation and the Mo method were used to analyze the experimental data. The results showed the Avrami equation and the Mo method described the isothermal and non-isothermal crystallization processes of iPP accurately, respectively. During isothermal crystallization, addition of BTCA-TCHA shortened half crystallization time (t1/2) and increased crystallization rate of iPP greatly. In addition, addition of BTCA-TCHA decreased the crystallization activation energy ΔE from 370 kJ/mol of virgin iPP to 312 kJ/mol. During non-isothermal crystallization, half time of the crystallization (t1/2) of virgin iPP was larger than that of nucleated iPP under the same cooling rate and the required cooling rate of virgin iPP to reach the same relative crystallinity was higher than that of nucleated iPP, indicating that addition of BTCA-TCHA increased the crystallization rate obviously.

Correlation Between Solidification Behavior and Melt Crystallization Kinetics of Isotactic Polypropylene (iPP) during Injection Molding

The relationship between solidification behavior and crystallization kinetics, during the injection molding process of isotactic polypropylene (iPP) was investigated. It was found that the crystallization rate was in proportion to the cooling rate. The existence of a turning point (TP) in the dimensionless temperature (θ) vs. ln t curve, which is potentially applicable for the estimation of cooling time, was experimentally verified for iPP. The present study is expected to be useful for the optimization of the processing conditions during injection molding of crystalline polymers, and also supplies a good insight into further study of the “processing-structure-property” relationship of polymeric materials.

Nonisothermal Crystallization Kinetics of Isotactic Polypropylene Filled with a Novel Nucleating Agent

The nonisothermal crystallization kinetics of isotactic polypropylene (iPP) filled with a novel nucleating agent (TMC328) was studied by using differential scanning calorimetric. The commonly used Arami, Ozawa, and Mo models were used to model the crystallization kinetics, and it appears that Arami and Mo models can well describe the nonisothermal crystallization behaviors of iPP/TMC328 blends. The results indicate that a small amount of TMC328 can obviously enhance the kinetic crystallizability of iPP due to its heterogeneous nucleation effect.

Critical Content of Ultrahigh-Molecular-Weight Polyethylene To Induce the Highest Nucleation Rate for Isotactic Polypropylene in Blends

The influence of the addition of low amounts of ultrahigh-molecular-weight polyethylene (UHMWPE) on the crystallization kinetics of isotactic polypropylene (iPP) in iPP/UHMWPE blends has been inves...

Effect of Hyperbranched Polymer on Crystallization Kinetics of Isotactic Polypropylene

In this paper, the isothermal crystallization kinetics of isotactic polypropylene (iPP) and iPP with 5% hyperbranched polymer (HBP) added had been investigated by differential scanning calorimetry (DSC). The results show that a small addition of HBP affects the crystallization behavior of iPP. During isothermal crystallization, the crystallization rate of the blend is higher than those of iPP remarkably. An increase in the Avrami exponent may be attributed to the fractal structure of hyperbranched polymer. The crystallization activation energy is estimated by the Friedman equation, the results show that the activation energy decreases remarkably by addition of HBP and the crystallization rate of the blend is more sensitive to temperature than that of iPP.

Influence of Thermo-degradation on the Crystallization Kinetics of Isotactic Polypropylene with a β-Nucleating Agent

Isotactic polypropylene (i-PP) with a β-nucleating agent (β-NA) was degraded isothermally at 190°C for periods up to 60 min, causing a reduction in molecular weight and a buildup of carbonyl groups. The effect of the thermo-degradation on the kinetics of subsequent crystallization was investigated using a polarizing optical microscope (POM). Kinetic studies revealed that the rates of nucleation and spherulite growth were affected differently by the thermo-degradation. No difference was found in the spherulite growth rate between pristine polypropylene and somewhat degraded samples, while spherulite growth was slightly depressed in the highly degraded sample. However, the thermo-oxidation of the polypropylene caused a gradual reduction in nucleation probability. It is suggested the extra carbonyl groups are mainly concentrated in the oligomeric products of chain scission, which are then excluded during the solidification process. Consequently, the impurity-rich phase acts as a barrier and hinders the diffusion of polymer chains, led to an increase of free energy for formation of a critical nucleus. The decrease of nucleation probability leaded to lower overall crystallization rate at a fixed temperature of 130°C, but the Avrami exponent n (n = 2.5 ± 1) was independent of the thermo-degradation, which was consistent with a three-dimensional growth habit by heterogeneous nucleation.

Non-isothermal crystallization kinetics of isotactic polypropylene nucleated with nucleating agent bicyclic [2,2,1] heptane di-carboxylate

AbstractBicyclic [2,2,1] heptane di-carboxylate (commercial product name: HPN- 68) is a novel nucleating agent with high nucleation efficiency for isotactic polypropylene (iPP). In this paper, the non-isothermal crystallization kinetics of virgin iPP and iPP nucleated with HPN-68 were investigated by means of a differential scanning calorimeter (DSC).The Caze method was used to analyze the non-isothermal crystallization kinetics. The results show that addition of HPN-68 can increase the crystallization peak temperature (Tp) of iPP greatly under the same cooling rate. Under non-isothermal conditions, the addition of HPN-68 changes the spherulite growth pattern of iPP. For virgin iPP, the growth pattern is mainly spontaneous nucleation followed by three-dimensional spherulite growth, while for iPP nucleated with HPN-68, the growth pattern is mainly heterogeneous nucleation followed by three-dimensional spherulite growth.

Prediction of non-isothermal crystallization parameters for isotactic polypropylene

Non-isothermal crystallization kinetics of isotactic polypropylene (iPP) was simulated with the assumption that the non-isothermal crystallization process was composed of some finite isothermal crystallization processes, while each isothermal crystallization process consists of three main steps—induction, nucleation and crystal growth. In the simulation, induction time was taken into account, allowing one to make predictions on the start of the non-isothermal crystallization of iPP; nuclei density was treated as a function of temperature; the Hoffman–Lauritzen theory was employed to describe the spherulite growth rate varied with temperature, and the relative crystallinity was determined by the equation of Kolmogorov. Finally, model prediction was verified by quantitative comparison between the theoretical results with the experimental results.

Effect of nano-nucleating agent addition on the isothermal and nonisothermal crystallization kinetics of isotactic polypropylene

Using differential scanning calorimetry (DSC) technique, a comparative study has been made of the isothermal and nonisothermal crystallization kinetics of nonnucleated isotactic polypropylene (iPP) and of nucleated iPP with 0.5 wt% of single-walled carbon nanotubes (SWCNTs) as a nucleating agent. The Avrami exponents (n) of iPP and nucleated iPP are close to 3.0 for isothermal crystallization. These results indicate that the addition of nucleating agents did not change the crystallization growth patterns of the neat polymer and that crystal growth was heterogeneous three-dimensional spherulitic. The results show that the addition of SWCNTs can shorten the crystallization half-time (t 1/2) and increase the crystallization rate of iPP. In the nonisothermal crystallization process, the Ozawa model failed to describe the crystallization behavior of nucleated iPP. The Caze–Chuah model successfully described the nonisothermal crystallization process of iPP and its nanocomposite. A kinetic treatment based on the Ziabicki theory is presented to describe the kinetic crystallizability, in order to characterize the nonisothermal crystallization kinetics of iPP and nucleated iPP. Polarized light microscopy (PLM) experiments reveal that SWCNTs served as nucleating sites, resulting in a decrease of the spherulite size.

Isothermal Crystallization Behaviors of Isotactic Polypropylene Nucleated with Nucleating Agent Bicyclic [2,2,1] heptane di-carboxylate

Bicyclic [2,2,1] heptane di-carboxylate (commercial product name: HPN-68) is a novel nucleating agent with high nucleation efficiency for α-iPP. In this article, differential scanning calorimetry (DSC) was adopted to investigate the isothermal crystallization kinetics of isotactic polypropylene (iPP) nucleated with HPN-68. The Avrami equation well described the isothermal crystallization kinetics of iPP nucleated with HPN-68. The results showed that addition of HPN-68 could shorten half crystallization time (t1/2) and increase the crystallization rate of iPP significantly. The Avrami exponents of both virgin iPP and iPP nucleated with HPN-68 were close to 3.0, which indicated that the addition of nucleating agent HPN-68 didn't change the crystallization growth patterns of iPP under isothermal conditions and the crystal growth was heterogeneously nucleated three-dimensional spherulitic growth. In addition, incorporation of nucleating agent HPN-68 obviously decreased the crystallization activation energy ΔE of iPP, from 368 kJ/mol for virgin iPP to 306 kJ/mol.

Non-isothermal crystallization kinetics of isotactic polypropylene nucleated with 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol

Non-isothermal crystallization kinetics of isotactic polypropylene (iPP) nucleated with 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) was studied by using differential scanning calorimetry (DSC). The modified Avrami theory of Jeziorny and the Mo method were used to analyze the DSC data. The results suggested that the two methods were both suitable for crystallization kinetics of iPP nucleated with DMDBS. Half time of the crystallisation (t1/2) of virgin iPP was larger than that of nucleated iPP under the same cooling rate. Meanwhile, the required cooling rate of virgin iPP was higher than that of iPP nucleated with DMDBS in order to reach the same relative crystallinity, both of which showed that the addition of nucleating agent DMDBS could increase the crystallization rate of iPP. In addition, incorporation of DMDBS changed the manner of nucleation and development.

Saturation of Pointlike Nuclei and the Transition to Oriented Structures in Flow-Induced Crystallization of Isotactic Polypropylene

The influence of molecular weight and processing conditions on the crystallization kinetics of isotactic polypropylene is studied using rheometry. Flow-induced crystallization experiments are performed with shear rates at which molecular stretch of the longest chains is expected. Depending on the molecular weight, a saturation of pointlike nuclei is observed with increasing shear time. In most cases, the process accelerates after sufficient flow time, and this change in kinetics is due to the occurrence of fibrillar nucleation resulting in the formation of row structures and/or shishes. The number of pointlike nuclei is derived from the rheometry experiments by modeling the system as a suspension. This method has some important advantages, i.e., (1) it is applicable to systems where optical microscopy does not work (i.e., colored systems) and (2) it is much easier, faster, and more accurate than optical methods.

Crystallization behavior and crystallization kinetic studies of isotactic polypropylene modified by long‐chain branching polypropylene

AbstractIn this article, we discuss the crystallization behavior and crystallization kinetics of isotactic polypropylene (iPP) modified by long‐chain‐branching (LCB) high‐melt‐strength iPP over a wide composition range, that is, LCB‐iPP from 10 to 50 wt %. Over the entire range we investigated, the presence of LCB‐iPP accelerated crystallization in both the isothermal crystallization process and nonisothermal crystallization process, even when the LCB‐iPP content was as low as 10%, and both crystallization processes were enhanced more significantly as the LCB‐iPP content increased. Hoffman–Lauritzen theory analysis revealed that the fold‐free energy decreased effectively with the occurrence of the LCB structure, although the growth rate of spherulites was depressed, as shown by polarized optical microscopy. Meanwhile, the regime III–regime II transition temperature was about 15° higher for all of the LCB‐iPP compositions than that of iPP because the LCB structure reduced the mobility of the polypropylene chains. Furthermore, the γ‐form crystal structure was favored by LCB compared to the β form, which was supported by wide‐angle X‐ray diffraction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Crystallization kinetics of isotactic polypropylene nucleated with organic dicarboxylic acid salts

AbstractBicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylate salts (BCHED) were synthesized by hydrothermal method. The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with BCHED were investigated by differential scanning calorimeter (DSC) under isothermal and nonisothermal conditions. Isothermal crystallization kinetics was described by Avrami equation and the fold surface free energy (σe) of iPP was calculated by Hoffman theory. The results showed Avrami exponents of nucleated iPP become smaller, the values of t1/2 dramatically decrease, the crystallization rate constants Z(T) greatly increase and the fold surface free energy (σe) of iPP decrease with the addition of the nucleating agents. Under nonisothermal condition the Caze method was applied to deal with the crystallization kinetics of iPP and the crystallization active energy of iPP was determined by Kissinger method. The results showed the crystallization peak temperatures (Tcp) of nucleated iPP greatly increase, but Avrami exponents of iPP were slightly influenced and the crystallization active energy of iPP increases by the addition of BCHED. It can be concluded that BCHED act as nucleating agents and BCHE11 shows the best nucleating effect. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009