Crystallization Of Isotactic Polypropylene Research Articles

Synthesis and Effect of N,N'-Diphenylterephthalamide on Crystallization of Isotactic Polypropylene

A phenyl-substituted terephthalamide β-nucleating agent, N,N'-diphenylterephthalamide (DPTH) was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR). DPTH’s effect on the crystallization and melting behaviors in isotactic polypropylene (iPP) was investigated by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarizing optical microscope (POM). The results illustrated that DPTH was an effective β-nucleating agent for iPP. The relative content of β-crystal (kβ) increased with the rise of the DPTH content and reached a maximum of 0.652 at 0.6% DPTH content. The Avrami and Jeziorny methods were used to describe the nonisothermal crystallization kinetics of iPP. Higher crystallization rate constant Zc and lower halftime of crystallization t1/2 were obtained in iPP containing DPTH.

Investigation on the Roles of β-Nucleating Agents in Crystallization and Polymorphic Behavior of Isotactic Polypropylene

In this study, four types of widely used commercial β-nucleating agents (β-NAs) were used to prepare β-nucleated isotactic polypropylene (β-iPP). Differential scanning calorimetry (DSC), polarizing optical microscopy (PLOM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to comparatively study the roles of β-NA in the β-nucleation efficiency, isothermal crystallization kinetics and crystalline morphology of the samples. Results revealed that the geometric shapes and thermal stabilities of the β-NAs are quite different from each other, moreover, the β-nucleation efficiencies (β-NE) of the β-NAs are quite different. The β-NE of NAB83 and PACA are very high, while those of TMB-5 and WBG‑II are relatively low. The critical concentrations of the β-NAs were obtained as follows: NAB83 = 0.02 wt %, PACA = 0.02 wt %, TMB-5 = 0.15 wt %, WBG = 0.3 wt %. Morphological studies of SEM and PLOM indicated that for different β-NAs, the β-phase fraction, crystalline sizes and morphology of the formed β-phase are quite different. Isothermal crystallization kinetics provided detailed kinetic information on the different β-NAs.

New Insights into Crystallization of Heterophasic Isotactic Polypropylene by Fast Scanning Chip Calorimetry.

The crystallization kinetics of metallocene-catalyzed heterophasic isotactic polypropylene composed of a matrix of isotactic polypropylene (iPP) and rubbery particles made of random ethylene–propylene copolymers (EPC), often denoted as heterophasic iPP copolymers, was analyzed as a function of the cooling rate and supercooling in nonisothermal and isothermal crystallization experiments, respectively. Fast scanning chip calorimetry (FSC) allowed assessing crystallization at processing-relevant conditions, and variation of the content (0–39 wt %) and composition (0–35 wt % propylene counits) of the EPC particles revealed qualitatively new insight about mechanisms of heterogeneous crystal nucleation. For neat iPP homopolymer, the characteristic bimodal temperature dependence of the crystallization rate due to predominance of heterogeneous and homogeneous crystal nucleation at high and low temperatures, respectively, is reconfirmed. At high temperatures, in heterophasic iPP, the here studied ethylene-(C2)-rich EPC particles accelerate crystallization of the iPP-matrix, with the acceleration or nucleation efficacy correlating with the EPC-particle content. The crystallization time reduces by more than half in presence of 39 wt % EPC particles. An additional nucleating effect of the EPC particles on iPP-matrix crystallization is detected after their crystallization, suggesting that liquid/rubbery particles are less effective than solid/semicrystalline particles in affecting crystallization of the surrounding iPP-matrix. At low temperature, homogeneous crystal nucleation in the iPP-matrix outpaces all heterogeneous nucleation effects, and the matrix-crystallization rate is independent of the sample composition. The obtained results lead to the conclusion that the crystallization kinetics of iPP can be affected significantly by the content and composition of EPC particles, even towards superfast crystallizing iPP grades.

Effect of lanthanum‐modified magnesium silicate on isotactic polypropylene crystallization in composite materials during shear flow

AbstractThe activity of isotactic polypropylene (iPP) nucleating additives during shear flow of composite materials is still not entirely explained. In current work the sol‐gel method was employed to synthesize MgO·SiO2 filler, surface‐modified with trivalent lanthanum. The crystallization of commercial iPP in the presence of 0.5% by weight La3+ modified or unmodified silicates was analyzed. The wide angle X‐ray scattering analysis proved that the presence of even small amount of filler influences significantly on supermolecular structure of iPP. The results of microscope observations confirmed that the lanthanum‐modified filler shows the nucleating ability for iPP. In that case a significant reduction of crystallization induction time was noticed. The investigation of iPP crystallization in composites after shear treatment confirmed that the increase of shear rate reduces the nucleating ability of additives. Moreover, the flow of filler particles during shearing may impede the shear‐induced crystallization phenomenon.

Rheology of crystallizing polymers: The role of spherulitic superstructures, gap height, and nucleation densities

A longstanding goal in polymer rheology is to develop a physical picture that relates the growth of mechanical moduli during polymer crystallization to that of a structure. Here, we utilize simultaneous mechanical rheology and optical microscopy, with augmentation by deterministic reconstruction and stochastic simulations, to study isothermal crystallization in isotactic polypropylene. We observe the nucleation and growth of the surface and bulk spherulites, which are initially isolated and then impinge to form clusters and superstructures that eventually span the gap. We find that spherulitic superstructures play a critical role in the rheology, especially in the characteristic sharp upturn in moduli. Both the rheology and the spherulitic superstructures show pronounced gap dependencies, which we explain via finite-size effects in percolation phenomena and via surface-induced nucleation. The modulus-crystallinity relationship can be described through a general effective medium theory. It indicates that for thicker gaps, the viscoelastic liquid to solid transition can be described via percolation, whereas for our thinnest gap, it is best described by the linear mixing rule. We describe our results in terms of dimensionless nucleation rates and spherulite size, which enable the estimation of when gap-dependent superstructure effects can be anticipated.

Estimating the Nucleation Ability of Various Surfaces Towards Isotactic Polypropylene via Light Intensity Induction Time Measurements

Crystallization of isotactic polypropylene (iPP) at the interface with crystalline films of two commercially employed nucleating agents (sodium benzoate (NaBz) and sodium 2,2’-methylene bis-(4,6-di-tert-butylphenyl)phosphate (NA-11)) and with a glass fiber (GF) was investigated using a polarized optical microscope. The analysis of the light intensity evolution during the crystallization process enabled the successful estimation of the time at which the crystal growth began, i.e., the induction time (ti), at various crystallization temperatures. Meaningful differences in the ti values were observed between the investigated systems. Moreover, the ti data have been analyzed according to different nucleation models proposed in the literature, which consider either the time to form the first crystalline layer in contact with the substrate or the time required to grow a cluster of critical size. It has been found that the two models are applicable in different temperature ranges depending on the efficiency of the given substrate. Therefore, in order to obtain the value of the surface free energy difference function, Δσ, which is directly related to the nucleation energy barrier and useful for the definition of a universal nucleating efficiency scale, a model that considers both the above-mentioned times was fitted to the overall data. The values of Δσ for the nucleation of iPP on the surface of the different substrates are thus obtained and discussed in the framework of the literature results.

Evolution of chain entanglements under large amplitude oscillatory shear flow and its effect on crystallization of isotactic polypropylene

The effect of large amplitude oscillatory shear (LAOS) flow on isotactic polypropylene (i-PP) chain entanglement-disentanglement transition and on the subsequent crystallization behavior was studied by dynamic rheology and polarized optical microscope (POM). i-PP with reduced entanglement density was generated through the application of LAOS flow at 180 °C. The re-entanglement process of disentangled chains was in-situ monitored by time-sweep rheological measurements. Interestingly, the re-entanglement kinetics was substantially slower than expectations based on the linear viscoelastic relaxation time of the fully entangled melt. Moreover, with the adjustment of shear conditions (strain amplitude, frequency and temperature), the entanglement density could be effectively modified. Disentangled chains exhibiting less topological constraints played a distinct role in the subsequent crystallization process. The nucleation density and growth rate of spherulites increased with reducing the entanglement density, resulting in a faster overall crystallization kinetics, compared to that in the fully entangled melt. It is worth to note that LAOS flow could produce a less disentangled melt state, and has a correspondingly weaker influence on the subsequent crystallization behavior, with respect to steady shear flow.

Nucleating agents based on graphene and graphene oxide for crystallization of the \u03b2-form of isotactic polypropylene

During the investigations, functionalization of graphene oxide synthesized using modified Hummers’ method and its reduced form was performed. Mixtures of graphene oxide and reduced graphene oxide with pimelic acid and calcium hydroxide were prepared for functionalization. During the reaction, the molecules of pimelic acid were attached to the surface of graphene sheets. By forming links between the carboxylic groups of pimelic acid and graphene oxide, the durable connection was achieved. The functionalized graphene oxide and the reduced graphene oxide were used as additives in isotactic polypropylene crystallization. The influence of additives on crystallisation in non-isothermal conditions was examined using polarized optical microscopy and differential scanning calorimetry. The effect of the additives on the polypropylene structure was analysed using wide-angle X-ray scattering. For both functionalized compounds, the nucleating ability towards β-form of polypropylene was detected. Both additives showed the increase in the nucleation rate and promotion of growth of the β-form crystals. Nucleation efficiency similar to other nucleating agents used in the crystallization of the β-form of polypropylene was revealed.

Precursor assisted crystallization in cross-linked isotactic polypropylene

Combining the extension rheometry and simultaneous in-situ synchrotron radiation small/wide angle X-ray scattering (SAXS/WAXS) measurement, extension induced crystallization of cross-linked isotactic polypropylene (CL-iPP) is studied at different temperature from 130 to 160 °C. After extension at strain of 1.5, precursor is generated before crystallization and the relative stability increases with temperature. Precursor growth is confined due to limited chain diffusion, resulting in a periodic two-dimensional distribution. Crystallization takes place later with the existence of precursor, accompanied with the slowdown of precursor dynamics. Based on the results, a model of precursor assisted crystallization is proposed to illustrate this unique phase behavior.

Modification of illite with calcium pimelate and its influence on the crystallization and mechanical property of isotactic polypropylene

A novel illite with β-nucleation ability toward iPP has been prepared through decoration the pristine illite with CaHA, i.e. CaHA-illite. The crystallization behavior and mechanical property of the iPP/CaHA-illite composite were studied. For comparison, the composites were also made simply by adding different components simultaneously into iPP matrix during mixing in a mini-extruder. The results show that, due to the opposite nucleation ability of illite and CaHA, the illite inhibits the β crystallization whereas the CaHA promotes the β crystallization of iPP. The CaHA-illite is very efficient for inducing the β crystallization of iPP. Its efficiency is higher than any of the other samples. Due to the high crystallinity and β iPP crystal fraction, the iPP/CaHA-illite exhibits the best mechanical properties with an increase of 36% in tensile modulus, 163% in maximum strain, and 69% in non-notched impact strength. Meanwhile, the tensile strength of pure iPP has been well maintained.

Non-isothermal crystallization kinetics and nucleation behavior of isotactic polypropylene composites with micro-talc

The non-isothermal crystallization (NIC) of isotactic polypropylene (iPP) and its composites with submicronic talc particles (μ-talc) was investigated by differential scanning calorimetry. The modeling of the NIC kinetics of the iPP matrix was performed using Jeziorny-modified Avrami’s model, Ozawa’s and Mo’s theoretical approaches. The Jeziorny’s and Ozawa’s theories allowed us to confirm that the μ-talc filler particles significantly promote the NIC kinetics of the iPP matrix which noticeably manifests itself via a change in the nucleation mechanism. However, Mo’s model proved to be the more relevant model to account for the NIC of the present materials. In parallel, the activation energy and nucleation activity of NIC were calculated by Kissinger’s and Dobreva’s methods, respectively. Both approaches reveal that a maximum nucleation activity of μ-talc takes place for 20% filler content. This finding is discussed in relation to the μ-talc content thresholds of mechanical percolation and crystallinity saturation that were reported in previous studies for these composites, about 10 and 30% μ-talc, respectively. An endeavor of physical explanation for these phenomena is put forward.

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene

The influences of α/β compound nucleating agents based on octamethylenedicarboxylic dibenzoylhydrazide on crystallization and melting behavior of isotactic polypropylene (iPP) were analyzed. It is found that the crystallization temperatures of nucleated iPP were increased by above 11.0°C and the relative contents of β‐crystals (Kβ) in iPP reached above 0.40 after addition of compound nucleating agents. The Kβ values depend on cooling rate, crystallization temperature in isothermal crystallization, and the difference between the crystallization temperatures of iPP nucleated by two individual nucleating agents. The nonisothermal crystallization kinetics were studied by Caze method and Mo method, respectively. The effective activation energy was calculated by the Friedman's method. The results illustrate that the half crystallization time was shortened and the crystallization rate was increased obviously after addition of nucleating agents, and the effective activation energy was increased with the relative crystallinity.

Experimental analysis of lateral thermal inhomogeneity of a specific chip-calorimeter sensor

Fast scanning calorimetry (FSC) requires reliable temperature measurements and knowledge about the temperature distribution in the chip calorimeter sensor. Analysis of the melting temperature of indium placed at different positions on the sensor and thermo-optical analysis of the isotropization of 4,4′-octyloxy cyanobiphenyl (8OCB) liquid crystal allow estimation of the lateral temperature distribution of chip calorimeter sensors. The chip sensor UFS 1 (Flash DSC1™, Mettler Toledo, Switzerland) was chosen as an example but the procedures described also hold for other sensors. The data revealed on one side existence of distinct hot- and cold-spots and on the other side an area with a rather homogeneous temperature distribution. The latter, central area of the sensor is recommended for placing samples if precise measurement of transition temperatures are anticipated. The observed inhomogeneous temperature distribution over the total sensor area is confirmed by thermo-optical analysis of melting of poly (l-lactic acid) and crystallization of isotactic polypropylene, emphasizing the need for careful sample preparation/positioning in typical fast scanning chip calorimeter analyses.

The influence of illite on the crystallization and properties of isotactic polypropylene

The influence of illite on the crystallization and properties of isotactic polypropylene

Effect of the Metal Phenylphosphonates on the Nonisothermal Crystallization and Performance of Isotactic Polypropylene

ABSTRACTThe use of metal phenylphosphonates as efficient nucleating agents (NAs) for isotactic polypropylene (iPP) is reported and a possible structural correlation to the nucleation efficiency is studied. First, three kinds of metal phenylphosphonates are synthesized via reflux method: Ca(C6H5PO3)•2H2O (CaPPA), Ca(C6H5PO3H)2 (CaPPA2), and Al(HO3PC6H5)(O3PC6H5)•H2O (AlPPA2). Then, the nonisothermal crystallization behaviors, mechanical, and optical properties of iPP composites are investigated. Compared to CaPPA2 and AlPPA2, CaPPA exhibits more effective heterogeneous nucleation effect during iPP crystallization. Furthermore, the nucleation efficiency of CaPPA is similar to industrial standard NAs NA‐21 and NA‐11. With the addition of 0.1 wt % CaPPA, the crystallization temperature is enhanced and the parameter F(T) of Mo method is decreased appreciably. Moreover, the flexural modulus, impact strength, and haze values of iPP composites are improved remarkably by introducing CaPPA. The CH/π interaction between polymer and aromatic cleft of CaPPA is considered to facilitate the attachment of iPP chains and subsequent nucleation and crystallization, which is verified by the viscoelastic properties of pure iPP and composites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 161–173

Effects of β-nucleating agent and graphene oxide on the crystallization and polymorphic composition of isotactic polypropylene / graphene oxide composites for bridge pavement

To control the polymorphic and crystallization behavior of β-nucleated isotactic polypropylene / graphene oxide (β-iPP/GO) composites for bridge pavement, the roles of β-nucleating agent (β-NA) concentration and GO content in the polymorphic crystallization behavior, morphology and crystallization kinetics were studied by means of differential scanning calorimentry (DSC), wide-angle X-ray diffraction (WAXD), scanning electronic microscopy (SEM). Results revealed that with the increase of β-NA concentration, the crystallization temperature, the percentage of β-phase βc and relative degree of crystallinity Xc increased evidently. Moreover, the crystallite sizes decreased, and the crystallization activation energy △E decreased, reflecting the strong nucleation effect of the β-NA to the composites; On the other hand, as the GO content increased, the crystallization temperatures and relative degree of crystallinity Xc also increased slightly. Interestingly, GO exhibited strong α-nucleation effect, which was not favorable for formation of β-phase. When the GO content was 2.0 wt%, unusual small banding patterned crystals were observed. In general, to control the polymorphic behavior and morphology of the β-iPP/GO composites, both β-NA concentration and GO content were very important factors.

Characterization of maleic anhydride/styrene melt-grafted random copolypropylene and its impact on crystallization and mechanical properties of isotactic polypropylene

Maleic anhydride/styrene-grafted random copolypropylene (MPP) was prepared by multi-monomer melt grafting. Fourier transform infrared spectroscopy verified that maleic anhydride and styrene were successfully grafted onto the polypropylene random copolymer (PPR) backbones. Dynamic rheological tests indicated the existence of long branched chains on MPP. The influence of grafting degree of maleic anhydride on the crystallization behavior of MPP was investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy. The results showed that the crystallization rate of MPP was higher than that of PPR, and it increased with the increase in grafting degree. The long-chain branched structure could promote heterogeneous nucleation formation of MPP, resulting in the increase in crystallization rate and the decrease in spherulite size. Moreover, the effect of MPP content on crystallization and mechanical properties of isotactic polypropylene (PP)/MPP blends was further investigated. It was found that the interfacial interaction in the blends with 1–10 wt% of MPP was higher than PP/MPP-15% blend. Introducing MPP into PP could induce the formation of β-crystal. Consequently, the incorporation of MPP into PP increased the tensile strength and impact strength and maximum values were obtained for PP/MPP-10% blend.

In situ optical microscope studies at isotactic polypropylene crystallization induced by shear forces – A review

A lot of mechanisms and phenomena associated with the polymers crystallization, are not explained presently. For this reason, new methods of isotactic polypropylene (iPP) crystallization phenomena analysis are still sought. One of them are the investigations with use of Linkam CSS450 shear stage. In this work, a short review of the world literature data prepared with use of Linkam shear stage, has been made. Mentioned equipment can be successfully used in: investigations at iPP crystallization mechanisms, describing crystallization kinetics, observations of iPP crystallization in polymers blends and multi-component systems. Several mechanism of shear induced crystallization, which have not been known so far, have been proposed in analyzed publications. Moreover, the known mathematical models and equations, which describe the iPP crystallization kinetics, have been modified for melts crystalized in shear conditions. The experimental data, obtained with use of Linkam CSS450 have been successfully used in mentioned modifications. Furthermore, a few theories regarding the iPP crystallization in heterogeneous compositions, namely: polymer melts with β-nucleating agents, polymer blends and polymer composites, have been presented in the papers reviewed in this work.

Effect of Self-Assembly of Oxalamide Based Organic Compounds on Melt Behavior, Nucleation, and Crystallization of Isotactic Polypropylene.

We report on the effect of an aliphatic oxalamide based nucleating agent (OXA3,6) on the melt and crystallization behavior of isotactic polypropylene (iPP) under defined shear conditions. Through polarized optical microscopy, we demonstrate that OXA3,6 self-assembles from the iPP melt into rhombic crystals whereas their size and distribution proved highly dependent on the employed cooling rates. The presence of 0.5 wt % of OXA3,6 in iPP results in a significant suppression in iPP melt viscosity, which could not be explained via molecular modeling. A possible cause for the drop in viscosity in the presence of OXA3,6 is attributed to the interaction (absorption) of high molecular weight iPP chains with the nucleating agent, thereby suppressing their contribution to the viscoelastic response of the melt. This proposed mechanism for the suppression in melt viscosity appears similar to that encountered by the homogeneous distribution of nanoparticles such as CNTs, graphene, and silica. Shear experiments, performed using a slit flow device combined with small-angle X-ray diffraction measurements, indicate that crystallization is significantly enhanced in the presence of OXA3,6 at relatively low shear rates despite its lowered sensitivity to shear. This enhancement in crystallization is attributed to the shear alignment of the rhombic OXA3,6 crystals that provide surface for iPP kebab growth upon cooling. Overall, the suppression in melt viscosity in combination with enhanced nucleation efficiency at low as well as high shear rates makes this self-assembling oxalamide based nucleating agent a promising candidate for fast processing.

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.