Efficient Nucleating Agent Research Articles

Synthesis of POSS-based star-shaped poly(ionic liquid)s and its application in supercritical CO2 microcellular foaming of polystyrene

Developing new and highly efficient nucleating agent becomes more and more important for the preparation of polymeric microcellular foams. Here, a “soft” star-sharp nucleating agent with in which poly(ionic liquid)s (PILs) are the arms and polyhedral oligomeric silsesquioxane (POSS) is a core, respectively, was synthesized via atom transfer radical polymerization (ATRP). This nucleating agent was applied in microcellular foaming of polystyrene using supercritical carbon dioxide (scCO2) as blowing agent, which showed that it can be dispersed as particles with size of ~200 nm, can increasing the CO2 solubility in polymer, and in turn can significantly improve the cell morphology of the foams. Our results demonstrate that the combinations of POSS and PILs with novel structure show somehow higher efficiency in manipulating cell morphology, and help to design new and high efficient nucleating agent for polymer microcellular foams.

Preparation and characterization of high-performance wood polymer nanocomposites using multi-walled carbon nanotubes

Effect of industrial grade multi-walled carbon nanotubes on mechanical, decay, and thermal properties of wood polymer nanocomposites was investigated. To meet this objective, pine wood flour, polypropylene with and without coupling agent (maleic anhydride grafted polypropylene), and multi-walled carbon nanotube (0, 1, 3, 5 wt%) were compounded in a twin screw co-rotating extruder. The mass ratio of the wood flour to polypropylene was 50/50 (w/w) in all compounds. Test specimens were produced using injection molding machine from the pellets. The flexural and tensile properties, biological durability, and thermal analysis (thermogravimetric analysis and differential scanning calorimetry) of the nanocomposites were investigated. The flexural and tensile properties of the wood polymer nanocomposites increased with increasing content of the industrial grade multi-walled carbon nanotubes (from 1 to 5 wt%) and maleic anhydride grafted polypropylene (3 wt%). The mass loss rates of the wood polymer nanocomposites decreased with increasing amounts of the maleic anhydride grafted polypropylene and industrial grade multi-walled carbon nanotube. The differential scanning calorimetry analysis showed that the melt crystallization enthalpies of the wood polymer nanocomposites increased with increasing amount of the industrial grade multi-walled carbon nanotubes. The increase in the Tc indicated that the industrial grade multi-walled carbon nanotubes were the efficient nucleating agent for the wood polymer nanocomposites.

Nanocellular polymer foams nucleated by core-shell nanoparticles

The synthesis of low surface energy polymer grafted silica nanoparticles is reported for the utilization as highly efficient cell nucleation agents to obtain nanocellular, CO2 blown polystyrene (PS) and poly(methyl methacrylate) (PMMA) films in a batch process. For nanoparticle surface functionalization hydroxyl-terminated perfluoropolyether and poly(dimethylsiloxane) (PDMS) were used. Their successful grafting to silica nanoparticles was confirmed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Following melt blending of the modified silica nanoparticles with PS or PMMA their dispersions were evaluated by scanning electron microscopy (SEM) analyses. We demonstrate that proper selection of the polymer grafts results in nucleation efficiencies of up to approximately 0.5 (i.e. 1 foam cell per 2 particles on average), which is the highest value reported so far for nanofillers as nucleation agents. This number was confirmed by the presence of only 2 to 4 nanoparticles per cell in nanocellular PS and PMMA foams containing SiO2 nanoparticles with a PDMS shell as was observed in cross sectional SEM images. The lowest density foam we obtained (∼0.32 g cm−3) had a nanocellular morphology with a cell size and cell density of ∼440 nm and 1.85 × 1013 cells cm−3, respectively. It is shown that the use of a low surface energy thin shell around silica nanoparticles is beneficial for cell nucleation compared to untreated particles.

Effect of wood flour as nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of wood flour (WF) as an efficient nucleating agent on the isothermal melt crystallization and isothermal cold crystallization behavior of poly(lactic acid) (PLA) was investigated by differential scanning calorimeter and polarized optical microscopy. It was found that the incorporation of 4 wt% WF promoted the crystallization of PLA about 4.2%. Polarized optical microscopy results showed the Maltese cross of the samples. The presence of the 4 wt% WF may increase the nucleation density, leading to the increase of the spherulites; however, the size of the spherulites decreased, and the structure became incomplete. The Avrami model was applied to analyze the isothermal crystallization kinetics. It is concluded that the addition of WF modified the crystallization process of PLA (the value of Avrami exponent changed). Various parameters, such as the crystallization half time and crystallization rate constant, reflect that 4 wt% WF significantly improves the crystallization process. The observations in this article indicate that WF is an efficient nucleating agent of PLA. Copyright © 2016 John Wiley & Sons, Ltd.

The effect of polymer-substrate interaction on the nucleation property: Comparing study of graphene and hexagonal boron nitride Nanosheets

Hexagonal boron nitride nanosheets (BNNSs) can work as a more efficient nucleating agent for two polyesters compared to graphene. Studies on the crystallization and dewetting processes of two polyesters, poly(butylene succinate) and poly(butylene adipate), on the two substrate surfaces prove that the interaction between BNNSs and the polyesters is stronger than that between graphene and the polyesters. This strong interaction induces the pre-ordered conformation of molten PBA which has been identified by the in situ FTIR spectra. Thus BNNSs possess higher nucleation property than graphene. Finally, a new polymer-substrate interaction induced nucleation mechanism was proposed to explain the nucleation efficiency difference between graphene and BNNSs.

New Understanding on Regulating the Crystallization and Morphology of the β-Polymorph of Isotactic Polypropylene Based on Carboxylate–Alumoxane Nucleating Agents

Carboxylate–alumoxane derived from p-n-alkylbenzoic acids, where n-alkyl group changes from 2 to 8 carbon atoms, exhibits dual nucleating ability and nucleates isotactic polypropylene (iPP) into predominantly in the β-phase under specific conditions. The selectivity of the β-phase nucleation depends on the concentration of the nucleating agent, end melting temperature and cooling rate. The β-phase obtained from p-n-alkylbenzoate–alumoxanes is compared with the β-phase obtained from calcium pimelate (CaP), an efficient β-phase selective nucleating agent, using the results from DSC, WAXS, and SAXS analysis. The lamellar morphology of iPP nucleated with different nucleating agents crystallized at different crystallization temperatures (TC) under controlled nonisothermal conditions are evaluated using SAXS analysis. The long period increases with increasing crystallization temperature and the long period of the β-phase is always larger than that of the α-phase for a given crystallization temperature. Furthermore, the variation of long period with crystallization temperature clearly brings out two crystallization temperature ranges; the low temperature range and the high temperature range. However, the β-phase shows a lower changeover temperature compared to that of the α-phase. The one-dimensional correlation analysis of the β-phase shows that the thickness of the crystal lamellae (lc) increases with TC and exhibits the low and high crystallization temperature ranges, while the thickness of the amorphous layer (la) more or less remains constant. In-situ high temperature WAXS studies capture the β-phase to the α-phase transition and the transformed material correlates well with the lamellar thickness of the β-phase. The morphological difference between the α- and the β-phases are discussed and attributed to the differences in the impact properties and the melting temperature. This study clearly demonstrates that the lamellar morphology mainly depends on the TC and not on the nature of the nucleating agents.

The effect of the grafted chains on the crystallization of PLLA/PLLA-grafted SiO2 nanocomposites

Two types of homemade poly(l-lactide) (PLLA)-grafted SiO2 nanoparticles with totally different topological structures are introduced into PLLA to prepare PLLA nanocomposites with different interface interactions and study the effect of the topology of polymer grafted nanoparticle on crystallization of PLLA. Differential scanning calorimetry (DSC) and polarized optical photomicrographs (POM) results show that the crystallization rate of PLLA has been greatly improved by the introduction of grafted SiO2, due to the improved heterogeneous nucleating effect. The nucleation constant of the two modified nanoparticles is evaluated by Hoffman–Lauritzen analysis; it is suggested that by introducing modified nanoparticles with long grafted chains, the interaction between the nanofiller and PLLA matrix will be enhanced, leading to the improved nucleation effective (the larger nucleation constant Kg), and the changed crystalline morphology, from large spherocrystals to tiny crystals. These observations are explained on the basis of different nucleation mechanism caused by the different surface structures of grafted SiO2, through the application of time-resolved Fourier transform infrared (FTIR) spectroscopy in the molecular level. The special long grafted PLLA chains can be acted as a more efficient nucleating agent for PLLA, and the conformational ordering of PLLA during the crystallization is significantly influenced by the topology of modified nanoparticles.

Investigating the crystallization behavior of poly(lactic acid) using CdSe/ZnS quantum dots as heterogeneous nucleating agents

Abstract Heterogeneous nucleation is a frequently encountered phenomenon in the crystallization of inorganic nanoparticle/polymer systems, and has a great influence on the morphology and properties (such as optical, mechanical and degradable properties) of the nanocomposites. In this study, a solution casting method was adopted to fabricate CdSe–ZnS quantum dots (QDs)/poly(lactic acid) (PLA) nanocomposites films of various QDs concentrations by using chloroform as the solvent. Fourier transform infrared (FT-IR) spectroscopy, polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffractometry (XRD) were used to characterize the crystallization behavior of the nanocomposites films that had been thermally treated differently from the as-cast state. The FT-IR and POM results showed that the nucleation density and the crystallization ability of PLA are greatly enhanced with addition of the QDs in the processes of isothermal crystallization at 403 K. The results of DSC revealed that the glass transition temperature of PLA has no obvious change with the addition of QDs. For the QDs/PLA samples which were isothermally annealed at 403 K for 30 min, the degree of (melt) crystallinity increased with increase of QD concentrations in the PLA matrix. All the results obtained from FT-IR spectroscopy, POM, DSC, and XRD were consistent, suggesting that the CdSe–ZnS QDs can serve as an efficient heterogeneous nucleating agent for the acceleration and enhancement of the melt crystallization of PLA at the optimized condition.

Polylactic acid nanocomposite films with spherical nanocelluloses as efficient nucleation agents: effects on crystallization, mechanical and thermal properties

An important industrial problem (low crystallization rate) for commercial polylactic acid (PLA) is addressed by incorporating SCNFs as efficient nucleation agents.

ZnO as an efficient nucleating agent and morphology template for rapid, facile and scalable synthesis of MOF-46 and ZnO@MOF-46 with selective sensing properties and enhanced photocatalytic ability

MOF-46 and a novel core–shell heterostructure containing ZnO@MOF-46 rods have been successfully synthesized via a simple, versatile and economic method.

In situ rapid preparation of homochiral metal-organic framework coated column for open tubular capillary electrochromatography

Fabricating metal-organic frameworks (MOFs) with the use of nucleating agents in the microenvironment have attracted increasing attention recently. Herein, a simple and rapid synthesis method was developed to in situ fabricate homochiral MOF [Zn(s-nip)2]n in the capillary inner wall by using ZnO nanoparticles as efficient nucleating agents for open tubular capillary electrochromatography (OT-CEC) separation of monoamine neurotransmitters enantiomers of epinephrine, isoprenaline and synephrine, the diastereoisomers of ephedrine and pseudoephedrine, the isomers of nitrophenols and analogues of bisphenols with good resolution. The relative standard deviations (RSDs) for the analytes migration time of intra-day, inter-day and column-to-column were in the range of 0.8–2.1% (n=10), 0.3–3.2% (n=3) and 3.2–9.3% (n=3), respectively. Additionally, the homochiral MOF [Zn(s-nip)2]n coated capillary column could be successively used over 260 runs without observable change in the separation efficiency.

Effect of cerium on the as-cast microstructure and tensile ductility of the twin-roll casting Fe–6.5 wt% Si alloy

Fe–6.5wt% Si alloy doped with cerium is fabricated by twin-roll casting. Ce2O2S precipitates in the melt and acts as the efficient nucleation agent, leading to a refined solidification microstructure. The tensile ductility of this as-cast strip significantly reaches up to 56.8% at 600°C, which is superior to the 22.8% of the as-cast strip undoped with cerium. The much more uniform and finer solidification microstructure along with the strengthened grain boundary is inferred to result in the dramatic improvement in tensile ductility.

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.

Crystallization Behavior of Poly(lactic acid)/Titanium Dioxide Nanocomposites

In this study, a poly(lactic acid) (PLA) with various titanium dioxide (TiO 2 ) nanoparticles loading were prepared by a manual laboratory mixing method. The effect of TiO 2 nanoparticles on the non-isothermal and the isothermal crystallization behavior of PLA were investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The presence of TiO 2 nanoparticles decreased the spherulite growth rate of PLA, whereas it initiated faster crystallization through the heterogeneous nucleation process as observed by optical microscopy. The results of DSC analyses confirmed that the TiO 2 nanoparticles act as an efficient nucleating agent for PLA crystallization. The cold crystallization temperature and crystallization half-time of PLA decreased, while degree of crystallinity of PLA increased in relation to increases of TiO 2 nanoparticles.

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.

Macromol. Chem. Phys. 17/2015

Front Cover: Polymer carbon nanotube nanocomposites are prepared by melt-mixing a poly(oxymethylene)/poly(l-lactic acid) (POM/PLLA) blend and multiwalled carbon nanotubes (MWCNTs). Investigation of the crystallization behaviour shows that the MWCNTs first selectively nucleate POM to yield novel “mace-like” hybrid structure crystals, which then serve as efficient polymeric nucleating agents of PLLA. The crystallization rate and crystallinity are remarkably enhanced. Further details can be found in the article by Lijun Ye, Cuicui Ye, Xianchun Shi, Hengti Wang, Hongyan Zhao, Xiaojun Cao, Jichun You, Yongjin Li,* and Yuanyuan Liang on page 1801.

Nanohybrid Polymeric Nucleating Agents: In Situ Decorated Carbon Nanotubes and Serial Nucleation Behaviors in a Melt‐Miscible Crystalline/Crystalline Blend

Polymer carbon nanotube (PCN) nanocomposites based on a melt‐miscible poly(oxymethylene)/poly(l‐lactic acid) (POM/PLLA) blend and a trace of multiwalled carbon nanotubes (MWCNTs) have been prepared by simple melt‐mixing. The crystallization behaviors of the ternary poly­mer–CNT nanocomposites (t‐PCNs) have been investigated. It is found that MWCNTs first nucleate POM selectively to yield novel “mace‐like” hybrid structure crystals. The “mace‐like” hybrid POM crystals subsequently serve as highly efficient polymeric nucleating agents (PNAs) for the crystallization of PLLA, leading to the remarkable enhancement of crystallization rate (vc) and crystallinity (Xc) of PLLA. image

Determination of Nucleus Density in Semicrystalline Polymers from Nonisothermal Crystallization Curves

The present study introduces a new calculation method for obtaining nucleus density formed during nonisothermal crystallization of semicrystalline polymers. Isotactic polypropylene homopolymer (iPP) was used as a semicrystalline model polymer, and its crystalline structure was modified using highly efficient nucleating agents or different cooling rates in order to manipulate the nucleus density (N) within a wide range. The melting and crystallization characteristics were studied by calorimetry (DSC), and the nucleus density was calculated from the crystallization curves recorded under nonisothermal conditions at a constant cooling rate. The nucleus density was correlated to the optical property, in fact to the haze index of injection-molded plaques in order to qualify the calculated values of N. It was found that N increases more orders of magnitude in nucleated samples and correlates strongly to the optical properties. These observations are according to our expectations and indicate clearly the reliability of the proposed calculation approach.

Enhancing Thermomechanical Properties and Heat Distortion Resistance of Poly(l-lactide) with High Crystallinity under High Cooling Rate

In this work, a novel, effective and simple approach to largely improve the thermomechanical properties and heat distortion resistance of biodegradable poly(l-lactide) (PLLA) by using a new nucleating agent (NA), i.e., itself high-melting-point homocrystallites (hPLLA crystallites) is reported. Specially, hPLLA crystallites with a melting temperature (Tm) of 187 °C were introduced into the PLLA matrix with a lower Tm, i.e., 168 °C via simply melt blending at 170 °C which is between the Tms of the two PLLAs. Nonisothermal and isothermal crystallization results reveal that hPLLA crystallite is an efficient nucleating agent for PLLA. Also, hPLLA crystallites show much more prominently promoting effect on the crystallization rate of PLLA in comparison with two widely reported NAs for PLLA, talc and stereocomplex crystallites. Most importantly, this promoting effect is still efficient at very high cooling rate, leading to a crystallinity of 39.1% at a cooling rate of 100 °C/min, which can help to obtain high-crystallinity PLLA products in conventional manufacturing processes. The optical microscopic observation reveals that the remarkable crystallization promotion can be attributed to the outstanding heterogeneous nucleation effect, as a result of both identical chemical constitution and lattice constitution between hPLLA crystallites and PLLA matrix. Further characterizations indicate that the enhancement of PLLA crystallinity by using such a new efficient NA can enhance the thermomechanical properties and heat distortion resistance of PLLA remarkably. For instance, at 80 °C (above Tg of PLLA), the elastic modulus increases by 60 times from 8 to 477 MPa with the incorporation of 5 wt % hPLLA.

Non‐isothermal crystallization kinetics and spherulitic morphology of nucleated poly(lactic acid): effect of dilithium cis‐4‐cyclohexene‐1,2‐dicarboxylate as a novel and efficient nucleating agent

The effect of dilithium cis‐4‐cyclohexene‐1,2‐dicarboxylate (CHDA‐Li) as a novel and efficient nucleating agent on the crystallization behaviors and spherulitic morphology of poly(lactic acid) (PLA) as well as non‐isothermal crystallization kinetics of the nucleated PLA was studied by means of differential scanning calorimetry and polarized light microscopy. The results show that CHDA‐Li serves as a good nucleating agent to accelerate the crystallization rate of PLA. The nucleation ability of CHDA‐Li is superior to octamethylenedicarboxylic dibenzoylhydrazide. With the incorporation of CHDA‐Li, the number of the spherulites increases, and the size decreases significantly. The non‐isothermal crystallization kinetics of the nucleated PLA can be well described by Jeziorny's and Mo's models. The activation energies (ΔE) of non‐isothermal crystallization were calculated by Kissinger's and Friedman's methods. The crystallization rate of PLA/0.5 wt% CHDA‐Li sample is faster than that of PLA/0.2 wt% CHDA‐Li sample, while the ΔE of the former is lower than that of the latter. Copyright © 2015 John Wiley & Sons, Ltd.