Heterogeneous Nucleating Agent Research Articles

The influence of in situ synthesized nanoparticles on microstructure and compression properties of polymer foams during supercritical carbon dioxide foaming

ABSTRACTThe influence of in situ synthesized nanoparticles on the microstructure and compression properties of polymer foams during supercritical carbon dioxide foaming has been investigated. The in situ synthesized Ag nanoparticles were chosen to be heterogeneous nucleating agent. For achieving our target, the influence of the nanoparticle size on the cell structure and the nucleation mechanism has been detailed discussed firstly. The results show that the in situ synthesized nanoparticles can be heterogeneous nucleation agent to improve the cell density of the PMMA‐based foams. The particle size is able to reduce to the critical size of heterogeneous nucleation agent and, then, can highly improve the cell density of the foams. The Ag nanoparticles with average size of 2.2 nm led to 85% increase in compressive strength of the foams. The improvement of strength of the polymer matrix and the microstructure of the foams can lead to the remarkable increase in the mechanical properties of the foams. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44629.

Thermal stability and non-isothermal crystallization kinetics of metallocene poly (ethylene-butene-hexene) /high fluid polypropylene copolymer blends

High-fluidity polypropylene (HF-PP) was melt blended with different amount of metallocene poly (ethylene-butene-hexene) copolymer (mEBHC) using a twin-screw extruder. The thermal degradation and non-isothermal crystallization behavior of the blends were investigated using thermo-gravimetric analysis (TGA) and differential scanning calorimeter (DSC). Our investigation revealed that the thermal degradation activation energies of mEBHC/HF-PP blends, calculated from thermo-gravimetric data by Kissinger, Flynn-Wall-Ozawa and Friedman method, increased with the amount of mEBHC added. Therefore, the thermal stability of mEBHC/HF-PP blends was enhanced in comparison to pure HF-PP. Modified Avrami and Mo models and Hoffman-Lauritzen theory were used to evaluate the influence of mEBHC on the non-isothermal crystallization kinetics of HF-PP. The results showed that mEBHC acted as heterogeneous nucleation agent, the non-isothermal crystallization rate of HF-PP matrix was improved by adding mEBHC.

Isothermal crystallization kinetics as a probe of the preferential electroactive phase nucleation in silver-poly(vinylidene fluoride) nanocomposites: Dependence on nanoparticle size and concentration

The effects of the in-situ grown silver nanoparticles on polymorphic crystalline structure and electroactive phase nucleation of isothermally melt crystallized silver-poly(vinylidene fluoride) (Ag-PVDF) nanocomposites have been probed using differential scanning calorimetry and Fourier transformation infrared spectroscopy. Crystallization kinetics data are suitably analyzed using the Avrami theory to evaluate the overall crystallization rate. Ag NPs significantly affect the crystallization rate within the nanocomposites. It is also observed that varying the concentration and size of the nanoparticles, polymorphism in extended chain-crystals can be suitably manipulated. During solution crystallization, Ag nanoparticles act as an effective heterogeneous nucleation agent to induce the formation of β-phase, which increases with both concentration and size of the nanoparticles. Intriguingly, during isothermal melt crystallization, above a certain concentration and size distribution of the nanoparticles, instead of β-phase, significant amount of γ-phase are formed that increases with the crystallization temperature. The observed behavior has been explained in terms of the extent and orientation of the interaction between the negatively charged Ag and the partially positively charge CH2 bonds of PVDF. The equilibrium melting temperatures and the spherulite growth kinetics parameters, estimated from Hoffmen-Week and Lauritzen–Hoffman models also justify the same.

Synergistic Effects of Polyethylene Glycol and Polyhedral Oligomeric Silsesquioxanes on Crystallization Behavior of Poly(L-lactide)

ABSTRACTThe synergistic effects of poly(ethylene glycol) (PEG) and polyhedral oligomeric silsesquioxanes (POSS) on the crystallization behavior of semicrystalline poly(L-lactide) (PLLA) were systemically investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Initially, the influences of PEG and POSS, individually, on PLLA crystallization were studied. The results indicated that PEG, as an efficient plasticizer, enhanced the mobility of the PLLA chains, resulting in decreasing of the glass transition temperature. The enhanced crystallization capacity of PLLA was strongly dependent on the molecular weight and content of the PEG, increasing with decreasing of the molecular weight and increasing of the PEG content. The experimental results also indicated that POSS was a heterogeneous nucleating agent, promoting the crystallization of PLLA. The synergistic effects of PEG and POSS on PLLA crystallization were then analyzed. The results showed that in the presence of PEG and POSS the crystallinity of PLLA was further enhanced due to their synergistic effects.

Analysis of crystallization property of LDPE/Fe3O4 nano-dielectrics based on AFM measurements

In this paper, the microstructure of LDPE/Fe3O4 nano-dielectric and pure LDPE films are respectively measured through AFM, and the influence of Fe3O4 nanoparticles (NPs) and magnetic field processing on the crystallization property of the nano-dielectric films are also analyzed. The result shows that the grown direction of crystal plates in the LDPE matrix is ruleless. While as the doping of the Fe3O4 NPs, thickness the crystal plates decreases, and they are packed tightly, this decreases the amorphous area, free volume, and increases the crystallinity of the nano-dielectric film, which proves that the Fe3O4 NPs work as heterogeneous nucleating agents in the nano-dielectric films. After magnetic field processing at 130 °C, the oriented growth of the crystal plates increases, and all the crystal plates of the nano-dielectrics films and the LDPE matrix are stretched with different level, which result in the decrease of their crystallinity. All the results are all accordant with that of XRD measurement measured before.

Confirmation of a nanohybrid shish‐kebab (NHSK) structure in composites of PET and MWCNTs

ABSTRACTHere, the confirmation of an oriented nanohybrid shish‐kebab (NHSK) crystalline structure in a series of composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNTs) is reported. The combined use of small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and thermal analysis has been used to investigate the morphology development in PET‐MWCNT nanocomposites under hot isothermal crystallization conditions. The MWCNTs act as both heterogeneous nucleating agents and surfaces (oriented shish structures) for the epitaxial growth of PET crystallites (kebabs) giving an oriented crystalline morphology. In contrast, the PET homopolymer does not show any residual oriented crystalline morphology during isothermal crystallization but gave a sporadic nucleation of a classic unoriented lamellar structure with slower crystallization kinetics. The results provide a valuable insight into the role of MWCNTs as nanoparticulate fillers in the morphology development and subsequent modification of physical properties in engineering polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 132–137

Enhancement of crystallinity and toughness of poly (l‐lactic acid) influenced by Ag nanoparticles processed by twin screw extruder

Poly(l‐lactic acid) nanocomposites based on silver nanoparticles (PLA/AgNP) were prepared by melt blending using a twin screw extruder. Nanocomposites at low concentrations were prepared with 0.1, 0.2, and 0.3 wt% of AgNP to enhance the crystallinity and improve the thermal and mechanical properties of PLA. AgNPs smaller than 100 nm which increased the crystallinity of PLA upon the addition were detected by UV–Vis. Crystallinty index of nanocomposites was estimated reaching a maximum of 0.52, where the AgNPs acted as heterogeneous nucleating agent which is correlated with the Ag content. The α and α′ crystals were observed by temperature modulated differential scanning calorimetry and wide angle X‐ray diffraction, thus lattice spacing of more ordered and distorted crystals were corroborated obtaining a higher fraction of α structures when a high content of nanoparticles was added. Moreover, strain at break and toughness of pure PLA were increased from 4.3% to 16.9% and 2.1 to 7.3 MJ/m3, respectively, modifying the inherent brittleness of PLA. Finally, with the obtained results a correlation was established where more disordered crystals show less resistance to deformation that lead to an enhancement of elongation at break observed in the nanocomposites. POLYM. COMPOS., 39:2368–2376, 2018. © 2016 Society of Plastics Engineers

Effect of nanoclay on the nucleation, crystallization and melting behaviour of polypropylene

Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The nanocomposites were prepared using melt intercalation method. It is observed that the crystallization peak temperature of nanocomposite is marginally higher than virgin PP at various cooling rates. The non-isothermal crystallization melt data were analysed using Avrami, Ozawa and Mos models. The half-time for crystallization decreased with incorporation of clay nanoparticles. The values of crystallization rate constant and cooling rate at unit crystallization time showed that the crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization rate of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 196 kJ mol−1, respectively. The polarized micrographs showed that the number of effective nuclei increased in the PP-clay nanocomposite, where the clay acts as a heterogeneous nucleating agent during the crystallization of the nanocomposite.

Nonisothermal crystallization of isotactic polypropylene in carbon nanotube networks

Isotactic polypropylene (iPP) composites with carbon nanotube (CNT) networks at relatively high loadings could have various applications such as electromagnetic interference shielding and thermal conductivity. The crystallization behavior of iPP inside CNT networks could be very much related to the above properties, which was found to be quite different from that of neat iPP in this work. In CNT networks, CNTs not only act as effective heterogeneous nucleating agents to noticeably increase the onset temperature (more than 18°C) of iPP crystallization but also bring strong confinement on the mobility of iPP chains and then reduce the overall crystallization rate of iPP matrix. It is interesting to find that CNT networks, especially in the case of ultrahigh loading (90 wt%), have remarkable confinement effect on crystallization of iPP, overcoming the heterogeneous nucleation of CNTs, resulting in a decline of crystallization rate of iPP. The nonisothermal crystallization kinetics of iPP in the dense CNT network quite fits to the modified Avrami mode by Jeziorny, even more satisfactorily than the case of neat iPP. When confinement effect is dominated during crystallization, we found that the perfection and size of crystallites are extremely decreased at ultrahigh loading, leading to a very low melting point of iPP (approximately 140°C).

Characteristics and Biodegradation Properties of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Functionalized Graphene (PHBV/FGO) Blends

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/functionalized graphene blends were prepared by solution blend method. The structure, thermal properties, thermal degradation and crystalline morphology were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG), and polarizing optical microscopy (POM) analyses. Experimental results indicated that FGO increase the intensity of diffraction peak. Small-sized PHBV spherulites were formed. FGO affects the crystallization behavior of PHBV as heterogeneous nucleation agent. FGO acts as an effective thermal barrier due to its large aspect ratio and thereby hinders the degradtion of PHBV.

Effect of foam processing parameters on bubble nucleation and growth dynamics in high-pressure foam injection molding

We used an innovative visualization mold to investigate the effect of foam processing parameters on bubble nucleation and growth. This was also done to uncover the mechanisms responsible for cellular structural development in the high-pressure foam injection molding process. The effects of the injection speed, the injection gate geometry, the blowing agent content, the melt flow rate and the use of talc as a heterogeneous nucleating agent on the formation and dynamics of cell bubbles were all explored. In the high-pressure foam injection molding process with a proper packing pressure, the overall cell density did not change with the injection speed nor with the injection gate resistance. However, the cell density increased significantly with the blowing agent's concentration and with a nucleating agent. We also observed the growth mechanism of the bubbles in a confined mold cavity, and concluded that the bubble growth rate decreased as the cell density increased. In addition, the satelliting phenomenon, i.e. bubble nucleation around the previously nucleated cells, was observed. This was due to the induced stress fluctuations in the surrounding melt, which could eventually affect the final cellular structure.

Nonisothermal crystallization kinetics of polyphenylene sulfide composites based on organic clay modified by benzimidazolium salt

Polyphenylene sulfide (PPS)/organic clay nanocomposites were prepared by simple melt blending. A synthesized benzimidazolium salt was used to modify the sodium montmorillonite in order to improve the compatibility with the PPS. The nonisothermal crystallization kinetics of PPS/organic clay composites were investigated by differerntial scanning calorimetry(DSC). It was observed that the crystallization peak temperature of PPS/organic clay composites was higher than pure PPS at various cooling rates. Several models such as the Ozawa and Mo equation were used to characterize the nonisothermal cooling crystallization kinetics of the PPS/organic clay composites. The results indicated that the Ozawa equation was not successful, while the Mo equation was successful to describe the nanoisothermal ctystallization kinetics of PPS/organic clay nanocomposites. The results also indicated that organic clay not only served as heterogeneous nucleating agents for PPS crystallization at lower content but also restricted the mobility and diffusion of PPS chains at higher content. These results were further supported by the crystallization activation energy of the samples determined by the Kissinger method.

Largely restricted nucleation effect of carbon nanotubes in a miscible poly(vinylidene fluoride)/poly(butylene succinate) blend

AbstractThe crystallization behaviors of miscible poly(vinylidene fluoride)/poly(butylene succinate) (PVDF/PBS) and its blend composites with carbon nanotubes (CNTs) during non‐isothermal and isothermal processes were investigated. The results showed that CNTs acted as heterogeneous nucleation agents and further improved the nucleation ability of PBS and PVDF in blends. However, compared with the nucleation effects of CNTs in PBS/CNT or PVDF/CNT binary composites, the nucleation effect of CNTs in miscible PVDF/PBS was largely restricted and nucleation efficiency was lowered. A reasonable explanation about the restricted nucleation ability of CNTs was studied from the viewpoint of interfacial interactions between polymer components and CNTs, in which a preferential affinity of CNTs to PBS was found. Further combined with the preparation method, it is proposed that PVDF chains adsorbed on the CNT surface in the master batch were peeled off from the CNTs by incorporated PBS chains, due to the better interaction between PBS and CNTs. Finally, the PVDF chains at the interface were diluted by PBS, and most of the CNT surface was covered by PBS chains, giving rise to the nucleation of PBS on the CNTs. On the other hand, unremoved PVDF still adsorbed on the CNT surface and crystallized. Compared with PVDF/CNT and PBS/CNT binary composites, the nucleation density in the ternary composites was greatly lowered, resulting in restricted nucleation effects of CNTs. On the other hand, the preferable adsorption of PBS on CNTs induced an apparent phase fluctuation in the PVDF/PBS blend composites, which also reflected the selective adsorption of PBS on the CNT surface. © 2016 Society of Chemical Industry

Morphology and interaction of nanocomposite foams formed with organo-palygorskite and ethylene-vinyl acetate copolymers

To obtain excellent mechanical properties of polymer nanocomposite foams without sacrificing the lower density through popular and friendly means. Organically modified palygorskite (OPal) was prepared with γ-aminopropyltriethoxysilane on the surface of rod-shaped Pal particles, and nanocomposite foams based on ethylene-vinyl acetate (EVA) copolymer was prepared by melt-blending EVA with OPal. Fourier transform infrared spectroscopy (FTIR) was used to investigate the interaction between OPal and EVA matrix, and the OPal/EVA nanocomposites were also characterized by X-ray photoelectron spectra (XPS), X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). The dispersivity of OPal in the EVA matrix and the morphology of the foams were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the OPal/EVA nanocomposite foams were also characterized by thermogravimetric analysis (TGA). The effect of OPal content in the foam samples on the cellular structure and mechanical properties was investigated. Our studies indicate that the OPal nanofibers could be used as a heterogeneous nucleation agent to reduce the average cell diameter. The uniformity of cell structure of the foams was improved, and the physical properties of OPal/EVA nanocomposite foams were enhanced by the addition of OPal. The density of OPal/EVA nanocomposite foams was decreased to 0.133 g/cm3. Also, the best tear strength, peel strength and compression set values of nanocomposite foams were 4.65, 2.65 N/mm and 25.5 %, which were improved by 36.0, 54.3 and 12.0 %, respectively, compared with those of the initial foam.

SiC sedimentation and carbon migration in mc-Si by election beam melting with slow cooling pattern

The development of photovoltaic industry demands great amount of multicrystalline silicon. Carbon and SiC in silicon need to be contained in a limited amount since they can cause great adverse affect to solar cells. The behavior of carbon and its precipitation SiC in silicon by electron beam melting (EBM) with a slow cooling pattern was investigated in this study. SiC is found to sedimentate to ingot bottom after EBM. The presence of Si3N4 can be heterogeneous nucleation agent for SiC to nucleate continually and both of them precipitate to the ingot bottom. The comprehensive effect of slow solidification condition, temperature gradient and melt convection causes the sedimentation of SiC. It is also found that oxygen plays an important role on the migration of the dissolved carbon. The formation of carbon-oxygen complexes tend to migrate to ingot top since oxygen can transfer from silicon melt to vacuum environment during EBM.

Morphology and Thermal Property of Poly(L-Lactide)/Layered Double Hydroxides Nanocomposites via Melt Intercalation

In this work, sodium dodecyl sulfate (SDS) was used to obtain organically-modified layered double hydroxide (OMgAl-LDH) by anion-exchange reaction. The PLLA/LDH nanocomposites were prepared via direct melt intercalation. The results from both XRD patterns and FTIR spectra showed that SDS entered into the layers of LDH successfully and the layer space was increased from 0.756 to 1.64 nm. For the PLLA/LDH nanocomposites, the increase of the layer space was verified by the good dispersion of LDH in the PLLA matrix from the SEM images. The rheological analysis showed that the typical Newtonian behaviour shifted to shear-thinning behaviour with the addition of LDH. In addition, DSC data illustrated that the glass transition temperature of the PLLA/LDH nanocomposites decreased and the crystallinity of PLLA increased due to the addition of LDH, which indicates that LDH acts as a heterogeneous nucleating agent and induces the crystallization of PLLA. The modified LDH provided a better nucleating effect than the unmodified LDH. TGA results showed that OMgAl-LDH in the PLLA matrix caused earlier initial decomposition, suggesting that the presence of LDH decreased the thermal stability of the PLLA matrix.

Solid-state polyetherimide (PEI) nanofoams: the influence of the compatibility of nucleation agent on the cellular morphology

The introduction of polyhedral oligomeric silsesquioxane (POSS) particles which act as heterogeneous nucleation agent was applied to improve the cellular morphology of nanocellular polyetherimide (PEI) foams. The loading of POSS particles increases the solubility and diffusivity characteristics of gases in nanocomposite sheets by changing the distribution of the free volume and enlarging the unoccupied volume in polymer matrix. When the range of content of POSS particles is 0.2 ~ 1.0 wt. %, the range of the calculated surface tension of PEI/scCO2 (γ mix ) and radius of the critical nucleus (r*) are 30.98 ~ 28.14 mN/m, and 6.88 ~ 6.25 nm, respectively. However, the small aggregated POSS particles are favour of heterogeneous nucleation bacause the actual diameter of the aggregated POSS particles is approximate to twice r*, so the addtion of 0.5 wt. % POSS to PEI matrix presents excellent heterogeneous nucleation performance for foaming. The average cell size of 0.5 wt. % POSS/PEI nanofoams compared with neat PEI decreases from 108 to 66 nm and the cell density increses from 5.96 × 1014 to 3.34 × 1015 cells/cm3.

In situ polymerization of poly(styrene-alt-maleic anhydride)/organic montmorillonite nanocomposites and their ionomers as crystallization nucleating agents for poly(ethylene terephthalate)

The poly(styrene-alt-maleic anhydride)/organic montmorillonite (SMA/OMMT) nanocomposites are obtained through in situ polymerization of styrene and maleic anhydride. The OMMT is exfoliated into small platelets and dispersed well in SMA copolymers, which is thus easily made into ionomers/OMMT (IM) nanocomposites. The IMs are employed as nucleating agents for poly(ethylene terephthalate) (PET) and the crystallization behavior is investigated by DSC isothermally and non-isothermally, respectively. The crystallization rate of PET is significantly accelerated and melt-crystallization temperature is increased with the addition of IMs which acted as heterogeneous nucleating agent due to good miscibility between anhydride and PET, and large interfaces provided by exfoliated OMMT.

Effect of silver nanoparticles on the morphology, crystallization, and melting behavior of polypropylene: A study on non-isothermal crystallization kinetics

The nanocomposites were prepared using melt intercalation method and the effects of the processing conditions on silver nanoparticles dispersion were investigated by transmission electron microscopy. Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The non-isothermal crystallization melt data were analyzed using macro kinetics equation with the help of Avrami, Malkin, and Mo’s models. The crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 211 kJ/mol, respectively. Transmission electron microscopy analysis reveals balanced dispersion and presence of some silver nanoparticles aggregates, which act as a heterogeneous nucleating agent during the crystallization of the nanocomposite.

Dy3+‐Doped Selenide Chalcogenide Glasses: Influence of Dy3+ Dopant‐Additive and Containment

This work reports on process‐induced impurities in rare‐earth ion: Dy3+‐doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid‐infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat‐treating Dy‐foil‐only, and DyCl3‐only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare‐earth additives. The presence of [Ga2Se3] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy3+‐doped Ge16.5As9Ga10Se64.5 glasses show that Dy‐foil is better than DyCl3 as the Dy3+ additive in Ge‐As‐Ga‐Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy‐foil‐doped chalcogenide glasses, as found for DyCl3‐doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy2O3 and/or [≡Si‐O‐Dy=]‐containing particles during chalcogenide glass melting, which are potential light‐scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α‐Ga2Se3 crystals.