Concentration Of Nucleating Agent Research Articles

Effect of β nucleating agent and rotational shear on morphology and mechanical properties of polypropylene pipes

AbstractHerein, we report a new method of introducing circumferential shear to polypropylene (PP) pipes via a self‐designed rotational shear system (RSS) with the addition of a β‐nucleating agent (TMB‐5). The prepared PP pipes exhibited remarkable enhancement in toughening and tensile strength over conventional PP pipes incorporating 0.025 wt% of the nucleating agent into the sheared sample increased the elongation at break to 243.30%. At 0.05 wt% nucleating agent content, an optimal tensile strength of 40.98 MPa was attained compared to 33.62 MPa for unsheared PP, and the elongation at break also reached 108.09%. In creep tests, the PP pipes prepared with nucleating agents and shear rotation exhibited a minimum displacement of 2.1 mm and the lowest creep rate of 3.23 × 10−5 mm/s. In addition, the samples also showed a high resistance to crack growth compared to conventional PP pipes with a crack initiation time of 24 h and a crack growth rate of 0.08 mm/s.Highlights Reinforced and toughened PP pipes were prepared using a rotational shear system. The shish‐kebab structure and β‐crystals exhibited a synergistic effect. Both short‐term and long‐term mechanical properties were studied.

An efficient β-nucleating agent with high lattice matching rate for plate-like crystallization of polypropylene random copolymer.

It is challenging to naturally produce large amounts of β-crystals by directly adding a commercial β-nucleating agent (β-NA) into polypropylene random copolymer (PPR) at present. In this work, a novel rare earth β-NA WBN-28 was directly introduced into PPR to prepare β-PPR with high β-crystal conversion. The results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) indicated that it is an efficient β-NA for PPR. The β-conversion rate (β-CR) could surpass 85% when the nucleating agent content was mere 0.05%. With the further increment of nucleating agent, the β-CR increased gradually, which could reach 89.5% and 86.9% respectively calculated by DSC and WAXD when the addition amount was 0.4%. The incredible high β-CR delayed the βα-recrystallization in isothermal crystallization. The fusion peak of α-crystal was unobserved below the isothermal crystallization temperature of 122 °C when the addition amount was more than 0.2%. Furthermore, there was a highly ordered structure in WBN-28 with the periodicity of 12.89 Å, which was approximately twice of the unit cell parameter in the c direction of β-PP, indicating a high lattice matching rate between them. Intuitively observed by polarizing optical microscope (POM), the crystal grains of the blends with β-NA were more refined and finally crystallized in a plate-like shape. The forming process of the plate-like β crystalline regions were proposed by scanning electron microscope (SEM) and POM.

Effects of nucleating agent content on the microstructure and macroscopic performances of polypropylene analyzed by non‐isothermal crystallization behaviors and isothermal crystallization morphologies

AbstractDirect attainment of the crystal state corresponding to desired performances in processing can improve the productivity of semi‐crystalline polymer products. This work tried to propose the idea to approach the target by exploring the effects of nucleating agent content on non‐isothermal crystallization kinetics, isothermally crystallization morphologies and macroscopic properties of polypropylene (PP). The nucleating agent content varied from 0 to 0.5 phr, and all samples were prepared by melting blending at 180°C as the antioxidant and lubricant ensured fine stability and processing. The differential scanning calorimetry results and non‐isothermal crystallization kinetics indicated that introducing 0.3 phr nucleating agent advanced both initial crystallization and melting about 10°C and improved crystallization rate and crystallinity. Besides, 145°C was determined as an isothermal crystallization condition by setting temperature gradient, and the crystallization kinetics were described by a power‐law equation well. The average crystal size was refined to 40 μm uniformly and crystallization time was reduced to 1.5 min as loading 0.5 phr nucleating agent, contributing to the significant improvements in tensile and physical properties. Thus, adding such a short‐time heat insulation procedure into the non‐isothermal cooling stage during processing can obtain desired crystal state directly with loading adequate nucleating agent.

Effects of self‐assembled nucleating agent on the crystallization behavior, thermal properties, and mechanical properties of polylactic acid

AbstractPolylactic acid (PLA) is a biodegradable polyester, but its low crystallization rate and excessive embrittlement limit its application. Decanedioic acid 1,10‐bis (2‐benzoylhydrazide) (TMC‐300) as an effective nucleating agent of PLA will induce PLA epitaxial crystallization and improve the crystallization rate of PLA. This article studied the promoting behavior of TMC‐300 with different contents in composite systems on PLA crystallization. The results showed that with the increase of TMC‐300 content, the crystallinity can be significantly increased, up to 22 times, and t1/2 significantly decreases. Meanwhile, with the addition of TMC‐300, the typical spherical crystal morphology of PLA gradually became attached to TMC‐300 fibrous crystal morphology. In terms of mechanical properties, the tensile strength reached its maximum at 0.5 wt% of TMC‐300 content, increasing from 60.60 MPa (PLA) to 74.59 MPa (0.5‐TMC‐300), an increase of 23.09%. At this time, due to the reduction in spherical crystal size, the elongation at break also increased significantly. However, the thermal stability of PLA composites deteriorated with the increase of nucleating agent content due to the low thermal decomposition temperature of TMC‐300 itself, and the Tmax decreased from 372°C (PLA) to 353°C (5‐TMC‐300), a decrease of 19°C.

Optimization of the nucleating agent content for the obtaining of transparent fluormica glass-ceramics

The crystallization behaviours, mechanical and optical properties of fluormica glass-ceramic system without and with P2O5 as nucleating agent are studied. The crystallization mechanism of fluor-phlogopite (KMg3(Si3AlO10)F2) without P2O5 oxide represented one-dimensional surface crystallization with a fixed number of nuclei, and with the addition of P2O5, the mechanism tends to two-dimensional bulk crystallization with a constant nucleation rate being the most predominant phase, forsterite crystals (Mg2SiO4). The base glasses had the spinodal phase separation, which coarsened considerably by increasing P2O5 content. P2O5 had a strong influence on the microstructure and morphology of this type of glass-ceramic. The addition of small amount of P2O5 (1.0 mol%) to these glass-ceramic changed the microstructure from dendritic growth having leaf-like feature to a flower-like morphology of the crystal phase. Glass-ceramic without P2O5 produces yellowish to colourless transparent glass-ceramic, and with the incorporation of the P2O5 (1.0 mol%), which has been found the optimum to obtain transparent glass-ceramics, the transmittance is still about 85%. As the P2O5 content increased to 3.0 mol%, besides fluor-phlogopite mica, forsterite also precipitates, the size of the crystals increase, their distributions turned to be broad due to the change of the crystallization mechanism and the transparency of glass-ceramic consequently decreases.

Enhancing Crystallization and Toughness of Wood Flour/Polypropylene Composites via Matrix Crystalline Modification: A Comparative Study of Two β-Nucleating Agents

Incorporation of short wood fillers such as wood flour (WF) into polypropylene (PP) often results in a marked reduction of toughness, which is one of the main shortcomings for WF/PP composites. This research reports a facile approach to achieve toughening of WF/PP composites via introducing self-assembling β-nucleating agents into PP matrix. The effect of two kinds of nucleating agents, an aryl amide derivative (TMB5) and a rare earth complex (WBG II), at varying concentrations on the crystallization and mechanical properties of WF/PP composites was comparatively investigated. The results showed that both nucleating agents were highly effective in inducing β-crystal for WF/PP, with β-crystal content (kβ) value reaching 0.8 at 0.05 wt% nucleating agent concentration. The incorporation of TMB or WBG significantly decreased the spherulite size, increased the crystallization temperature and accelerated the crystallization process of WF/PP. As a result of PP crystalline modification, the toughness of composites was significantly improved. Through introducing 0.3 wt% TMB or WBG, the notched impact strength and strain at break of WF/PP increased by approximately 28% and 40%, respectively. Comparatively, although WF/PP-WBG had slightly higher Kβ value than WF/PP-TMB at the same concentration, WF/PP/TMB exhibited more uniform crystalline morphology with smaller spherulites. Furthermore, the tensile strength and modulus of WF/PP-TMB were higher than WF/PP-WBG. This matrix crystalline modification strategy provides a promising route to prepare wood filler/thermoplastic composites with improved toughness and accelerated crystallization.

Effect of N,N'-Dicyclohexyl Terephthalic Dihydrazide on the Crystallization and Properties of Isotactic Polypropylene

Application of nucleating agents is a common way to manipulate the structure and properties of crystalline polymers. Our goal was to synthesize N,N'-dicyclohexyl terephthalic dihydrazide (DCTDH) and study it from the viewpoint of applicability as a nucleating agent for isotactic polypropylene (iPP). We used differential scanning calorimetry to investigate the efficiency of DCTDH in samples containing the nucleating agent in a wide concentration range. We used polarized light microscopy to study the crystalline morphology developed in the presence of this nucleating agent. To characterize the mechanical properties of the nucleated samples, we performed tensile and impact tests on injection molded specimens. DCTDH proved to be a non-soluble α-nucleating agent in iPP, with a saturation concentration around 300 ppm. The nucleating agent has a significant effect on the crystalline structure of iPP, microspherulitic structure forms in its presence. Owing to the different structure, a considerable change in the mechanical properties is observable: with increasing nucleating agent content the tensile modulus increases, while impact resistance has a maximum value around 300 ppm nucleating agent content.

Self-Assembly of Temperature Sensitive Additives in Polypropylene Melt and Its Influence on Viscoelasticity

The use of a temperature-sensitive nucleating agent (NA) for polypropylene (PP), besides its influence on the crystallization characteristic, provides a platform to affect the rheology of molten PP by controlling its self-assembly behavior. In this study, in order to clarify the dependence of the melt rheology properties on the self-assembly behavior of N,N′,N′′-tricyclohexyl-1,3,5-benzenetricarboxylamid, changes in the NA content and final process temperatures (Tf) were used to control the self-assembly behavior of the NA molecules. The morphological and rheological behavior of samples were studied at 180 °C and evaluated by using central composite design-response surface methodology (CCD-RSM). The polarized optical microscopy results showed a fibril shape structure with a length in the range of 26–94 μm and diameter of 3–11 μm. The regression analysis models revealed that the increase in NA wt % and Tf favored the formation of larger fibrils in length and diameter, and the impact of NA wt % was more significant than Tf. Shear rheometry results indicated that the fiber size and its distribution were both directly related to an increase in complex viscosity and storage modulus. The study of the zero shear viscosity, crossover frequency, Cole–Cole plot, and also ANOVA analysis indicated that the optimal value for Tf is 270 °C and for NA is 0.5 wt %.

Comparison of the efficiency of the most effective heterogeneous nucleating agents for Poly(lactic acid)

We selected the thirteen most effective nucleating agents for Poly(lactic acid) (PLA) from the literature, and synthesized and compounded them with two different PLA grades: 3001D (1.4% D-lactide content) and 3100HP (0.5% D-lactide content, considered PLLA). We determined the crystallinity and crystallization of PLA with different nucleating agents in identical conditions (same nucleating agent content, same cooling rate) with the help of differential scanning calorimetry. We compared the efficiency of each nucleating agent and found that for both PLA grades, Zinc PhenylPhosphonate was the most effective. However, even when nucleated PLA was injection molded into a cold mold (25 °C), it still could not fully crystallize during cooling and the heat deflection temperature did not increase significantly. The maximum achieved crystallinity, in this case, was between 32.4 and 35.7%. On the contrary, when a 90 °C “hot mold” and in-mold crystallization together were applied, the specimens achieved full crystallization during the injection molding cycle (crystallinity was between 44.5 and 50.0%), and the heat deflection temperature increased to an average of 88.8 °C. We also examined the mechanical properties of the nucleated PLA and found that the usage of nucleating agents together with a hot mold improved tensile strength, tensile modulus, and Charpy impact strength but decreased elongation at break.

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

The rare earth nucleating agent was used to modify block copolymerized polypropylene (PPB) in foaming process. The results show that the crystallization of PPB and the melting temperature of β-crystal increased gradually with increased β-crystal nucleating agent content. The total crystallinity decreased with amount of addition increasing, and the relative content of β-crystal increased first and then decreased. When β-crystal nucleating agent content was 0.4 wt%, the relative β-crystal content reached the maximum value of 95.27%, and the final crystal grain refinement significantly. The addition of rare earth β-crystal nucleating agent has a good effect on improving the uniformity of foam cells. Under the same content of β-crystal nucleating agent and pressure, the average cell diameter and expansion ratio increased with the saturation temperature increasing. After the foaming temperature reaches 155°C, the expansion ratio began to decrease, which was also consistent with the changed trend of relative β-crystal content. At the same content of temperature and relative β-crystal, as the foaming pressure increased, the cell diameter decreased gradually, and the expansion ratio increased first, and then decreased.

Comparison of the freezing behavior of two liverwort species – Conocephalum salebrosum and Marchantia polymorpha subsp. ruderalis

Extracellular ice formation as a dehydrating agent is generally acknowledged as an important element of freezing avoidance in frost hardy plants, preventing the development of lethal ice crystals within living cells. While many reports on extracellular ice formation do exist for vascular plants, not much is known on ice formation for liverworts. In this study, ice formation was studied for two liverwort species occurring in climate zones with winter freezing, Conocephalum salebrosum and Marchanthia polymorpha L. subsp. ruderalis, together with taxon-specific ice nucleating temperature and seasonal concentration of ice nucleating agents. Samples were collected in late autumn from various sites in south west Germany. Afterwards the collected liverwort specimen were cultivated and acclimated in pots in the inner courtyard of the State Museum of Natural History Stuttgart, Germany. Ice formation was observed in the environmental scanning electron microscope (ESEM) within the air chambers of both species, with ice crystals growing out of the air chamber pores, as well as random ice crystal formation on various sites on the ventral side for both taxa. The growing ice sheets led to dehydration particularly of the parenchymatous cells. For both taxa, the observations support the relevance of extracellular ice formation for surviving freezing conditions but the experiments also indicate a better adaptation of C. salebrosum to frost.

A Comparison of CO2 and N2 Foaming Behaviors of PP in a Visualization System

Abstract Understanding of polypropylene (PP) foaming is critically important to reduce the weight of automotive parts. In this study, we used a batch foaming simulation system with visualization cell, to observe the foaming behaviors of PP that is blown with CO2 and N2 under various experimental conditions. We found that the nucleating agent content, initial temperature, pressure (i. e., gas content), and pressure drop rate during foaming have a significant effect on cell nucleation and cell growth. The cell density and the void fraction of PP foamed with CO2 and N2, respectively, were separately observed and compared. It was found that under the same experimental conditions, the maximum cell density of PP foamed with CO2 was higher than that of PP foamed with N2. However, the maximum cell density of PP foamed with CO2 was determined to be lower than that of PP foamed with N2, when the same gas mole numbers were employed. Based on the experimental results, optimum foaming conditions and effective processing strategies for PP-CO2 system are suggested.

An approach for prediction optimum crystallization conditions for formation of beta polypropylene by response surface methodology (RSM)

In this work beta nucleating agent is synthesized and mixed with various grades of polypropylene (PP). The beta nucleating agent (β-NA) content, melt flow rate (MFR) of PP and cooling rate as independent variables are correlated to the beta crystal content (β-PP) by using Response Surface Methodology (RSM) models. Central cubic design was employed for experimental design. The crystallization behavior of various grades of PP at different percentage of beta nucleating agents is analyzed by differential scanning calorimetry (DSC) at three different cooling rates. The results showed that the enthalpy of fusion of beta crystals (△Hβ) are directly related to the amount of β-NA. The sensitivity of the alpha polymorph to beta nucleating agent concentration increased with increasing the cooling rate. The optimal condition to achieve to a maximum Kβ are obtained for the resin with MFR of 21 g/10min containing 0.59 %wt β-NA and cooling rate of 8 °C/min.

Influence of talc in polypropylene foam cores of sandwich structures with skins made of thermoplastic prepregs

Properties of sandwich structures with a core of thermoplastic foam depends on cell size and cell density (cell number). Nucleating agents have a benefit to generate cell nucleation, which affects an increase in the cell density. In this study, sandwich structures composed of a polypropylene (PP) foam core and organic sheet skins in-situ produced by injection moulding process. A chemical blowing agent was employed to generate cellular structure in the core. The influence of the varying nucleating agent content with the same chemical blowing agent content on density, cellular structure and mechanical properties of the sandwich structures were investigated. The talc contents had a slight influence on the density of the sandwich structures. Moreover, flexural modulus and flexural strength of the sandwich structures consisting of the foam core with 4 wt% of talc were higher than the foam core without talc. However, the utilization of these talc contents with PP and the chemical blowing agent had no significant effect on the reduction of the cell size and the increase of the cell density.

Space Charge Characteristics of Polypropylene Modified by Rare Earth Nucleating Agent for β Crystallization.

Compared to cross-linked polyethylene, polypropylene has a thermoplastic property and the advantage of recycling. However, the poor impact resistance at low temperature and the corresponding space charge problem restrict the application of polypropylene with the extruded high voltage direct current (HVDC) cable. Sufficient introduction of the β form of the polypropylene crystal can significantly improve impact resistance at low temperatures. Although it has been widely applied in insulation engineering, the effect of β-crystal on the space charge characteristics of polypropylene has rarely been researched until now. In this paper, a rare earth nucleating agent of β-crystal is employed to modify the performance of polypropylene to investigate the effects of nucleating agent content on β-crystalline, mechanical relaxation, trap, and space charge characteristics of polypropylene. The results of differential scanning calorimeter (DSC) and X-ray diffraction (XRD) tests indicate that the relative content of β-crystal in modified polypropylene increases gradually with the increasing concentration of the nucleating agent, approaching 43.5% when the nucleating agent content has been raised to 0.2 wt %, suggesting appreciable efficiency of the nucleating agent utilized in our research. Scanning electron microscopy (SEM) is utilized to characterize the morphology of β-crystal spherulites, which illustrates that the β-spherulites are in bunchy shape, and the lamellar crystals are parallel to each other without an obvious boundary between them. The results of the space charge test demonstrate that the modified polypropylene can substantially suppress space charge accumulation, which is attributed to an increment of β-crystal content by adopting a rare earth nucleating agent. It is indicated from dynamic mechanical analysis (DMA) measurements that the enhancement of β-crystalline in modified polypropylene can distinctly increase and decrease the β and α relaxation losses, respectively, which proves that the defects in β-crystal and amorphous regions are reduced and increased respectively. Thermally stimulated depolarization current tests further confirm that the number of traps caused by defects in the β-form of polypropylene crystal declines definitely, which dominantly accounts for the suppression of space charge accumulation.

A biaxial stretched β‐isotactic polypropylene microporous membrane for lithium‐ion batteries

ABSTRACTIn this article, microporous polypropylene (PP) membranes were produced with TMB‐5 as β‐crystal nucleating agent by biaxial stretching. Influences of different concentration of TMB‐5 were studied using differential scanning calorimetry and X‐ray diffraction. It was found that the highest crystallinity was reached when the nucleating agent content was 0.5 wt %. The effect of stretching temperature and stretching ratio on pore size distribution and porosity of the membranes were investigated by scanning electron microscopy and mercury porosimeter, respectively. And physical properties, such as tensile strength, permeability, and puncture resistance of the microporous membrane prepared at the optimized conditions, were evaluated. Compared with commercial PP separator membrane, the as‐prepared microporous membrane shows similar uniform pore size distribution and exhibits slightly higher porosity and ionic conductivities. When used as lithium‐ion separator, the experimental film shows more stable cycling performance than the commercial one. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45825.

Supercooling-dependent morphology evolution of an organic nucleating agent in poly(l-lactide)/poly(d-lactide) blends

The morphology evolution of an organic nucleating agent (NA) in poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blends was investigated under a series of multi-step isothermal and nonisothermal processes at identical NA solubility achieved via the same NA concentration and final molten temperature of heating (Tf). It was found that the morphology of NA frameworks depended on the supercooling determined by the recrystallization temperature of the NA in the polymer melt, except for NA solubility. When the NA partly dissolved in the matrix, the residuum of the original flat-plate NA acting as a nucleus induced recrystallization at a low degree of supercooling, and small sheet-like NA particles formed in the melt. When the NA dissolved in the matrix absolutely, NA aggregation increased in the melt due to the low nucleation density of the NA itself. The shape of the NA aggregation depended on the recrystallization temperature. With the increase in the supercooling, the large aggregated sheet-like NA transformed into a dendritic-like framework accompanied by a decrease in the stem size of the NA frameworks. Moreover, the stereocomplex efficiency of the blend was influenced by the effective nucleation surface induced by the shape of the NA aggregation. For PLLA/PDLA blends with 1.0 wt% NA, the crystallization half time (t1/2) of stereocomplex (sc) crystallites at the crystallization temperature of 180 °C is as long as 79.8 min for the sample with a large aggregated sheet-like NA, with 1 order of magnitude reduction for that with a dendritic-like NA framework, leading to a t1/2 of 7.9 min. The morphological control of NA frameworks is of great significance to guide the formation of various crystal morphologies of sc crystallites. The established relationship between the self-assembled morphology of NA and NA concentration, NA solubility and supercooling affords guidance in practical processing to control the crystal morphology and polymorphic crystalline morphology of PLLA/PDLA blends via tuning the crystal morphology of NA in the polymer matrix.

Effect of Processing Conditions on the Cellular Morphology of Polypropylene Foamed Films for Piezoelectric Applications

In this work, continuous extrusion-calendering was used to produce polypropylene (PP) foam films for piezoelectric applications. The setup is based on physical foaming using supercritical nitrogen (SC-N2) and calcium carbonate (CaCO3) as nucleating agent. In particular, the extrusion parameters (screw design, temperature profile, blowing agent and nucleating agent content) and post-extrusion conditions (calendaring temperature and speed) were optimized to achieve a specific stretched eye-like cellular structure with uniform cell size distribution. The morphology in both machine and transverse directions, as well as tensile properties were characterized. The results show that a cellular structure with a higher cell aspect ratio has a lower Young's modulus, which is appropriate for piezoelectric cellular films. Generally, the developed foam morphology presents high potential for the production of ferroelectret PP films used in different piezoelectric applications.

Melt-Miscible Oxalamide Based Nucleating Agents and Their Nucleation Efficiency in Isotactic Polypropylene

In this study, the performance of three aliphatic oxalamide based compounds as nucleating agent (NA) for isotactic polypropylene (iPP) has been evaluated. The NAs evaluated in this study contain two oxalamide motifs that are connected through linking spacers with 2, 3, or 4 methylene units in between the oxalamide groups, while containing flexible hexyl end-groups on the outside. It is demonstrated that the onset of crystallization in the presence of these NAs under quiescent conditions, generally observed around 120–125 °C, is strongly dependent on both the crystallization conditions and NA concentration. Although these oxalamide compounds are only moderately effective under quiescent conditions, they show promise for use under industrially relevant processing conditions that require high cooling and shear rates: When the NA is forced to undergo shear-induced self-assembly and shear-alignment during cooling, the onset of crystallization of the iPP phase is observed in SAXS at temperatures up to 140 °C.

Polymer ferroelectret based on polypropylene foam: piezoelectric properties prediction using dynamic mechanical analysis

Thin polypropylene (PP) foam films were produced by continuous extrusion using supercritical nitrogen (N2) and then charged via corona discharge. The samples were characterized by dynamic mechanical analysis as a simple method to predict the piezoelectric properties of the cellular PP obtained. The results were then related to morphological analysis based on scanning electron microscopy and mechanical properties in tension. The results showed that the presence of a nucleating agent (CaCO3) substantially improved the morphology (in terms of cell size and cell density) of the produced foam. Also, an optimization of the extrusion (screw design, temperature profile, blowing agent, and nucleating agent content) and post‐extrusion (calendering temperature and speed) conditions led to the development of a stretched eye‐like cellular structure with uniform cell size distribution. This morphology produced higher storage and loss moduli in the machine (longitudinal) direction than for the transverse direction, as well as higher piezoelectric properties. The morphological and mechanical results showed that higher cell aspect ratio led to lower Young's modulus, which is suitable to achieve higher piezoelectric properties. Finally, the best quasi‐static piezoelectric d33 coefficient was 550 pC/N for a cellular PP ferroelectret having a uniform eye‐like cellular structure using N2 as the ionizing gas inside the cells, while the highest value was only 250 pC/N when air was used. Hence, the value of d33 can be improved by more than 100% just by replacing air with N2 as the ionizing gas. Copyright © 2016 John Wiley & Sons, Ltd.