Heterogeneous Nucleation Effect Research Articles

Enhanced dielectric, EMI shielding effectiveness, linear and nonlinear optical properties of CdO/SnO2 nanocomposites

In recent days, new advanced nanomaterials are necessary to satisfy the required properties in various electronic and energy applications. This research work concentrates on producing the new nanocomposites with many enhanced electronic and dielectric properties of multifunctional devices. The samples CdO, CdO/SnO2, and PVP capped CdO/SnO2 nanocomposite have been synthesized by microwave irradiation method. The effect of incorporation of SnO2 and PVP with CdO for phase changes, morphological, linear and nonlinear optical properties, LED applications, dielectric properties, and electromagnetic interference shielding efficiency (EMI). XRD phase study confirms that the nanocomposite contains both a cubical structure of CdO and an orthorhombic structure of SnO2. PVP SEM and TEM images show changes in morphology as nanorod in CdO/SnO2/PVP due to heterogeneous nucleation effect and reduction in particle size. PL study reveals that the enrichment of photoluminescence property in CdO/SnO2/PVP nanocomposite due to the incorporation of PVP and SnO2, which produce defects in the lattice. CIE chromaticity diagram represents that the fabricated nanocomposites are suitable in designing a light-emitting diode. Nonlinear refractive index and third-order susceptibility values are more significant in CdO/SnO2/PVP nanocomposite than CdO and CdO/SnO2. The effect of SnO2 and PVP with CdO in dielectric constant, dielectric loss, electrical conductivity, and electromagnetic interference shielding efficiency were discussed. Finally, all present results ensured that the incorporation of SnO2 and PVP with CdO will enhance the optical, electronic and dielectric properties.

Effect of Cd micro-addition on microstructure and mechanical properties in ternary Al-Si-Cu alloy

In present work, Al-7Si-4Cu alloys with/without 0.28 wt % Cd addition were fabricated. Both alloys were solution treated at 500 °C for 10 h, followed by quenching and subsequently ageing at 165 °C for different times of 0.5–20 h. Results showed that hardness, strength and ductility at peak-aged state for Cd-doped alloy were simultaneously enhanced by comparing with Cd-free alloy. Quantitative analysis results of microstructure indicated that with Cd addition a finer and denser microstructure of θ′ can be obtained. Based on microstructure characterization as well as thermodynamics and kinetics calculations, the mechanism for obtaining a finer and denser θ′ was discussed, which was considered as a result of the pre-precipitation and heterogeneous nucleation effect of Cd-rich particles. Improved mechanical properties for Cd-doped alloy were discussed to be ascribed to the precipitation of larger number density and less size of θ′. The increase of yield strength with Cd was quantitatively described by the strengthening models. The results indicated that yield strength increment in alloy B was dominated by strengthening contribution of finer and denser θ′ precipitates.

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.

How colloidal surface additivation of polyamide 12 powders with well-dispersed silver nanoparticles influences the crystallization already at low 0.01 vol%

As Additive Manufacturing (AM) is fast-growing, properties adaption of feedstock materials for AM is becoming more and more relevant due to high quality standards in industrial applications. Compared to traditional manufacturing techniques like injection molding, laser powder bed fusion (PBF-LB) of polymers has a very limited variety of processable materials, which is a major obstacle for future growth. Nanocomposites are an established material class for addressing the limitations in PBF-LB but often show poor dispersion of the nanomaterial in/on the polymer powder. Especially in the context of plasmonic nanomaterials and composites, where the state of aggregation considerably influences the optical properties, dispersion plays an important role. Our study presents a deeper understanding of the colloidal surface additivation of polyamide 12 (PA12) powders with laser-generated plasmonic silver nanoparticles, leading to high dispersion of the nanoparticles on the micropowder surface with good reproducibility. The additivation is ruled by colloidal stability and control of electrostatic forces between particles and resulted in powders that could successfully be processed on a PBF-LB machine to generate plasmonic-functionalized parts. Finally, we introduce the surface specific nanoparticle dose (surf%) as scaling key parameter complementary to the commonly used mass specific dose (wt%) to appropriately describe nanoparticle load, proving the effect of such surface additivation on the recrystallization behavior of PA12. Via flash calorimetry, already at 0.01 vol% silver load, significant nanoparticle-induced heterogeneous nucleation effects are evident, whereas the thermal properties analyzed by conventional calorimetry remain unaffected.

Effect of Heterogeneous Nucleation on Removal of Arsenic from Molten Steel by Rare Earth Addition

Cleanliness control is an eternal theme to improve the properties of steel products. With the increasing recycling rates of scrap steel, the removal and stabilization of residual elements have become a vital issue for improving the performance of steel products. Thermodynamic and mismatch calculations plus laboratory experiments were carried out to study the heterogeneous nucleation phenomena of inclusions when lanthanum was employed to remove arsenic from molten steel and stabilize arsenic in solid steel. The effect of heterogeneous nucleation on the mechanism of arsenic removal was discussed. A series of heterogeneous nucleation phenomena of inclusions in the La-O-S-As system were discovered, and the heterogeneous nucleation among the inclusions turned out to be selective. As the vital product of arsenic removal, La-S-As is most likely to generate with LaS as heterogeneous nucleation cores, and its possible chemical formula turned out to be 3LaS⸱LaAs. Sulfur plays an essential role in removing arsenic from molten steel by adding lanthanum. It needs to control the initial sulfur content in an appropriate range, because the high initial content causes too much loss of rare earth, and the low initial content cannot produce LaS and La-S-As.

Functionalized cellulose nanocrystals as the performance regulators of poly(β-hydroxybutyrate-co-valerate) biocomposites

To investigate the relationship between functional groups on cellulose nanocrystals (CNC) and the performance of poly(β-hydroxybutyrate-co-valerate) (PHBV), the surface of CNC was modified by surface graft modification and PHBV/CNC biocomposites were prepared by melt blending. To demonstrate the interfacial adhesion difference between hydrophobic PHBV and hydrophilic CNC, palmitoyl chloride and ε-caprolactone had been used to tailor the oleophilic property of CNC. Results showed that CNC had heterogeneous nucleation effect on the crystallization process of PHBV, while the entanglement of molecular chains weakened the promoting functions of CNC-g-C16 (CNC grafted with palmitoyl chloride) and CNC-g-CL (CNC grafted with ε-caprolactone). Furthermore, CNC-g-CL exhibited better interfacial adhesion with PHBV when compared with CNC-g-C16. And 1 wt% CNC-g-CL improved the tensile strength of PHBV biocomposite to 38.09 MPa, which is 26.25% higher than PHBV.

Fabrication of Poly(vinylidene fluoride)/Multiwalled carbon nanotube nanocomposite foam via supercritical fluid carbon dioxide: Synergistic enhancement of piezoelectric and mechanical properties

The fabrication of poly(vinylidene fluoride) (PVDF) based foam with complicated three-dimensional (3D) geometry and excellent piezoelectric property remains great challenge worldwide. In this study, microcellular PVDF/multiwalled carbon nanotube (MWCNT) nanocomposite foaming part was fabricated by supercritical carbon dioxide (scCO2) bead foaming technology. With the assistance of the ball milling, the good dispersion of MWCNT particles in PVDF matrix was achieved, which promoted the heterogeneous nucleation and enhancement effects of MWCNT on PVDF, resulting in the formation of more unique and denser cells, e.g. from 3.4 × 105 cells/cm3 of pure foam to 1.7 × 106 cells/cm3 of the composite foam when MWCNT content was 1.5%, and high compression strength, i.e. 3.1 MPa with 1.5% MWCNT at 10% compressive strain, about 1.1 MPa higher than that of pure foam. During the bead foaming process, the induced crystallization effect of MWCNT as well as the plasticizing and squeezing effect of scCO2 on PVDF matrix contributed to the increase of the β-phase crystal in PVDF matrix, thus endowing the composite foaming part with good piezoelectric property, i.e. 6.5 V of output voltage under periodic compression, which lightened 4 LEDs and made the foaming part had wide potential application in smart electronic field.

Magnetic Organic-Inorganic Nanohybrid for Efficient Modification of Paraffin Hydrocarbon Crystallization in Model Oil.

Crystallization modification has been applied in many fields, such as materials science, petroleum engineering, and chemical engineering. The modification of organic-inorganic hybrids via paraffin hydrocarbon crystallization has been significantly important for the exploration of undersea oil and gas resources. In this work, a metal oxide organic-inorganic hybrid pour point depressant (MOIH-PPD) is provided along with an analysis of the microscopic structure of the paraffin hydrocarbon crystal employing small-angle X-ray scattering and X-ray diffraction. The MOIH-PPD modified crystal grain exhibited a decrease in the long period and in the radius of gyration of the crystal grain and an increase in the thickness of the interface layer compared with those of the unmodified paraffin crystal. In addition, the synergistic effect of heterogeneous nucleation and the magnetic response of MOIH-PPD on the paraffin hydrocarbon system was also investigated, revealing that the synergism modification yields stress superior to that of MOIH-PPD or magnetic field alone, which provides insight into the possibility of the modification of paraffin hydrocarbon crystallization.

Poly(lactic acid)/opal-methacryloylpropyltrimethoxysilane-polystyrene graft polymer composites: preparation, characterization, and performance

Opal-methacryloylpropyltrimethoxysilane-polystyrene graft polymer (opal-MPS-PS) was synthesized using coupling method and solution polymerization. The results of orthogonal experiments showed optimum reaction conditions including: polymerization time of 4 h, catalyst at 0.03 g, reaction temperature of 80 °C, and styrene volume of 4 mL. Moreover, the structure of opal-MPS-PS was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results demonstrated that PS was grafted onto opal-MPS. Furthermore, poly(lactic acid) composites (PLA/opal-MPS-PS) were prepared using opal-MPS-PS as filler by melt blending. The results of mechanical testing showed that the impact toughness of PLA/opal-MPS-PS composites was increased by 50.5%. The rheological behavior and morphological analysis showed that PLA displayed high interfacial compatibility with opal-MPS-PS. The polarized optical microscopic and differential scanning calorimetric results showed that opal-MPS-PS with heterogeneous nucleation effect improved the crystallization properties of PLA, and enhanced toughness of PLA. The flame retardancy test showed that the thermal stability and flame retardancy of the PLA composites material were improved compared with PLA. Enzymatic degradation tests showed that opal-MPS-PS had an inhibitory effect on the degradation of PLA. In all, this study provides a promising method to improve the comprehensive performance of PLA through organic modification using opal as filler.

Enhanced mechanical properties of poly(lactic acid) composites with ultrathin nanosheets of MXene modified by stearic acid

ABSTRACTMXene modified by stearic acid (Ti3C2Tx‐g‐SA) is incorporated into poly(lactic acid) (PLA) matrix to prepare Ti3C2Tx‐g‐SA/PLA composites. The effects of Ti3C2Tx‐g‐SA to pure PLA are investigated, including crystallization, mechanical, and thermal properties. Fourier transform infrared spectroscopy and X‐ray diffraction analyses confirm that Ti3C2Tx interlayer is successfully intercalated by SA, and the interlayer spacing of Ti3C2Tx is increased. Differential scanning calorimetry illustrates that the cold crystallization enthalpy (ΔHcc), melting enthalpy (ΔHm), and crystallinity (Xc) of Ti3C2Tx‐g‐SA/PLA composites are improved by the plasticization and heterogeneous nucleation effect of Ti3C2Tx‐g‐SA. Specially, the Ti3C2Tx‐g‐SA/PLA composites exhibit excellent mechanical properties at an appropriate content of the Ti3C2Tx‐g‐SA. Compared with pure PLA, the elongation at break of the Ti3C2Tx‐g‐SA/PLA composite is increased 5.9‐fold (up to 131.6%) when only containing 0.5 wt % Ti3C2Tx‐g‐SA. Besides, the Ti3C2Tx‐g‐SA/PLA composites exhibit good thermal stability in the low loading (lower than 1 wt %) of Ti3C2Tx‐g‐SA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48621.

Synergistic effect of polylactic acid(PLA) and Poly(butylene succinate-co-adipate) (PBSA) based sustainable, reactive, super toughened eco-composite blown films for flexible packaging applications

Polylactic acid (PLA)/poly (butylene succinate-co-adipate) (PBSA) based blend films at variable compositions and fixed weight percentage of Epoxy functionalized styrene acrylate (ESA) were prepared using a single step blending process, followed by blown film extrusion process. The morphological studies revealed proper interaction between polymers by the interaction of chain extender (ESA) subsequently improved the mechanical properties of the prepared blown films. Similarly, the blend films showed a decrease in oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) in the order of 60% and 14% as compared with VPLA film. The optical and antislip properties of the blend films also increased considerably. The thermal analysis of the blend films depicted marginal enhancement in the stability of PLA along with heterogeneous nucleation effect in PLA matrix due to the presence of ESA and PBSA.

Influence of Two Different Nanofillers on the Crystallization Behavior and Dynamic Mechanical Properties of Biodegradable Poly(ethylene adipate)

In this work two biodegradable poly(ethylene adipate) (PEA) based nanocomposites containing the same low loading of cellulose nanocrystals (CNC) and carboxyl-functionalized multi-walled carbon nanotubes (f-MWCNT) were prepared through a solution and casting method, respectively. The crystallization behavior and dynamic mechanical properties of neat PEA and the nanocomposites were studied in detail and compared with each other. Both CNC and f-MWCNT finely dispersed in PEA matrix. The addition of CNC or f-MWCNT not only increased the melt crystallization peak temperature but also decreased the crystallization half-time of PEA, suggesting that the crystallization of PEA was apparently enhanced by CNC or f-MWCNT due to the heterogeneous nucleating agent effect. Both CNC and f-MWCNT increased the storage modulus and glass transition temperature of PEA matrix in the nanocomposites. As a nucleating agent, f-MWCNT was more efficient than CNC, while CNC was stronger than f-MWCNT as a reinforcer.

Effects of Ultrasonic Treatment on the Microstructure and Mechanical Properties of Mg-3Y-3.5Sm-2Zn-0.6Zr (wt %) Alloy.

Ultrasonic treatment (UST) was applied in the smelting process of Mg-3Y-3.5Sm-2Zn-0.6Zr (wt %) alloy and the microstructure as well as mechanical properties of the experimental alloy were investigated. Results showed that the effect of UST on grain refinement was obvious, and the distribution of the second phases along grain boundary became discontinuous. The width of the grain boundary precipitates decreased after UST. The contents of solute elements within grains increased, and the morphologies of Zr-rich compounds and Y-rich compounds both at grain boundaries and within grains changed after UST. The mechanical properties of the experimental alloy after UST were significantly improved. The ultimate tensile strength (UTS) was 265 MPa, the tensile yield strength (TYS) was 171 MPa, and the elongation (EL) was 11%. The mechanism of UST of the alloy can be attributed to the combined effects of cavitation-induced heterogeneous nucleation and melt convection induced by acoustic streaming, resulting in the refinement of grains and the grain boundary precipitates, which promoted the improvement of mechanical properties.

Effect of Doping Microcapsules on Typical Electrical Performances of Self-Healing Polyethylene Insulating Composite

Polyethylene cables, as important transmission equipment of modern power grid, would inevitably be slightly damaged, which seriously threatens the safety of the power supply. This paper has pioneered the preparation and typical performances of a self-healing polyethylene insulating composite. The self-healing performance to structural damage was verified by tests of electrical and mechanical damage. The effect mechanism of doping microcapsules on the electrical performance of polyethylene was emphatically analyzed. The results show that in appropriate conditions (such as 60 °C/30 min), the composite can not only repair the electrical tree and scratches, but also restore the insulation strength of damaged area. The effect of doping microcapsules on the electrical performances of polyethylene, such as breakdown strength, volumetric resistivity, dielectric properties, and space charge characteristics, are mainly related to impurity and the interface of microcapsule. Polarization and ionization of impurities can reduce the electrical performance of polyethylene. The interface not only improves the microstructure of polyethylene (such as how the heterogeneous nucleation effect increases the number of crystal regions, and the anchoring effect enhances the stability of amorphous regions), but also increases the charge traps. Moreover, the microstructure and charge trap can affect the characteristics of carrier transport, material polarization, and space charge accumulation, thus improving the electrical performance of polyethylene. In addition, the important electrical performance of the composite can meet the basic application requirements of polyethylene insulating material, which has good application prospects.

Effects of Multiwalled Carbon Nanotubes on Phase Transformation and Dielectric Properties in Poly(Vinylidene Fluoride-Hexafluoropropylene) Nanocomposites

Poly(Vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] nanocomposites filled with multiwalled carbon nanotubes (MWCNTs) were successfully fabricated by solution casting. The influence of MWCNTs on the phase structure, dielectric and mechanical properties of MWCNTs/P(VDF-HFP) nanocomposites were evaluated. FTIR spectra and X-ray diffraction show that the incorporation of MWNTs promoted the formation of γ phase crystal. The DSC curves demonstrated that the nanocomposites possess higher Tm and Tc than neat P(VDF-HFP), which can be explained by the increasing of the γ phase crystal and the heterogeneous nucleation effect respectively. In addition, the dielectric constant of the nanocomposites is enhanced remarkably with the increasing content of the MWNTs. The highest dielectric constant of the MWCNTs/P(VDF-HFP) nanocomposites was about 106 when the content of fillers was 1.3 vol% at 1 kHz. The percolation threshold of the nanocomposites was predicted at about 1.2 vol%. Moreover, The tensile strength and Young’s modulus of 1.2 vol% MWCNTs/P(VDF-HFP) nanocomposites reach to maximum.

Isolation and characterisation of nanofibrillated cellulose from waste cotton: effects on thermo-mechanical properties of polylactic acid/MA-g-SEBS blends

In garment industry, cotton waste is the major threat for disposal or waste management due to environmental issues. Nanofibrillated cellulose (NFC) from waste cotton was isolated by steam explosion technique, an eco-friendly method in comparison with chemical methods. Nanocellulose was characterised by different analysis techniques like TEM, SEM and XRD. The crystallinity index of nanocellulose was found to be 66% based on Seigel’s empirical method. SEM micrographs showed highly entangled nanofibrils with diameters ranging from 67 to 70 nm. TEM results revealed reduction in the size of fiber from micro to nano upon mild acid treatment along with steam explosion. Bionanocomposites of maleated styrene ethylene butylene styrene (MA-g-SEBS) toughened polylactic acid (PLA) reinforced with nanocellulose were fabricated by twin screw extruder and tested for thermo-mechanical behaviour using injection molded specimen. Mechanical property evaluation showed that the composites containing nanocellulose exhibited higher modulus compared to virgin PLA and PLA binary blend system containing SEBS or MA-g-SEBS. The elongations of bionanocomposites were substantially increased, possibly due to good dispersion of nanocellulose and its plasticizing effect. Morphological studies were also carried out to investigate the effect of nanocellulose on toughened PLA. The impact strength was also found to be higher compared to virgin PLA by the incorporation of nanocellulose to SEBS toughened PLA. Differential scanning calorimetry measurements observed an increase in crystallization of PLA by heterogeneous nucleation effect of NFC.

Heterogeneous Nucleation Effect of N, N'-Adipic Bis(4-phenylbutyric Acid) Dihydrazide on Crystallization Process of Poly(L-lactic Acid)

Enhancing crystallization ability is a fundamental challenges in Poly(L-lactic acid) (PLLA) industry, therefore, the goal of this work was to synthesis a new organic nucleating agent N, N'-adipic bis(4-phenylbutyric acid) dihydrazide (APAD), and investigate its effect on non-isothermal crystallization, isothermal crystallization, melting behavior, thermal stability, and optical property of PLLA. Non-isothermal melt crystallization results showed that APAD acted as more effective nucleating and accelerating agent for the crystallization of PLLA, as a result, upon cooling at 1 °C/min, PLLA/0.5 %APAD had the highest onset crystallization temperature 136.4 °C and the crystallization peak temperature 132.0 °C, as well as the largest non-isothermal crystallization enthalpy 48.1 J/g. However, with increasing of APAD concentration from 0.5 wt.% to 3 wt.%, the crystallization peak shifted to the lower temperature. In contrast, for the non-isothermal cold crystallization process, the effect of APAD concentration on the crystallization behavior of PLLA was negligible. Additionally, the non-isothermal crystallization process was also depended on the cooling rates and the final melting temperature. In isothermal crystallization section, to compare with the primary PLLA, the crystallization half-time of PLLA/APAD could decrease from 254.3 s to the minimum value 29.4 s, with 0.5 wt.% APAD contents at 125 °C. Melting behavior of PLLA/APAD samples under different conditions further confirmed the heterogeneous nucleation effect of APAD for PLLA, and the appearance of the double melting peaks was attributed to the melting-recrystallization. Finally, the addition of APAD decreased the thermal stability to some extent, although APAD could not change the thermal decomposition profile of PLLA. And a drop of PLLA/APAD samples in light transmittance resulted from the double influence of the enhancement of crystallization and the opaqueness of APAD.

Influence of Ca adsorption on the heterogeneous nucleation of α-Mg on Al4C3 particles: First-principles calculation and experiment

Abstract The addition of Ca in magnesium melt has a significant influence on the heterogeneous nucleation effect of Al4C3 particles with open question for the mechanism. We have conducted first-principles calculations of the adsorption of Ca and Mg atoms on Al4C3 surfaces to study the initial nucleation and growth of Mg atoms on Al4C3 surfaces. The single Ca or Mg adsorption, as well as Ca Mg co-adsorption on a 28-layer slab (A-type) of Al-terminated Al4C3(0001) surface has been simulated. We demonstrate that both Ca and Mg atoms tend to stabilize at the H2 site of Al-terminated Al4C3(0001) surface. Meanwhile, a comparative experiment is conducted to study the influence of Ca on the grain refining effect, showing that Ca atoms promotes the adsorption and nucleation growth of Mg atoms on Al4C3 surfaces.

Thermal and rheological properties of polyamide 6/layered double hydroxide clay composites

Thermal and rheological properties of polyamide 6/layered double hydroxide (PA6/LDH) composites were studied. Pristine (U-LDH) and organically modified (M-LDH) clays were used in this study. Some evidence of intercalation was observed on the microstructure of PA6/M-LDH samples, while PA6/U-LDH was characterised by microcomposite morphology as shown by the transmission electron microscopy results. The scanning electron microscopy results showed a complete delamination of the M-LDH in the PA6 matrix while U-LDH was evenly dispersed as immiscible tactoids. In the melt state, the M-LDH had a significant influence on the melt microstructure of PA6 matrix when compared to U-LDH. Differential scanning calorimetry results, both dynamic and isothermal experiments, showed that LDH had a heterogeneous nucleating effect on the PA6 matrix, with the U-LDH showing better nucleating effect when compared to M-LDH. The thermogravimetric analysis results showed that M-LDH had a negative influence on the thermal stability of the composites, while U-LDH improved their thermal stability. The X-ray diffraction and dynamic mechanical analysis results showed that the presence of M-LDH promoted the formation of γ-crystallites in the PA6 matrix, while U-LDH composites were dominated by the α-crystallites. This phenomenon had a positive correlation with increasing content of both LDH clays. An overall improved dynamic mechanical properties were observed for PA6/U-LDH when compared to PA6/M-LDH composites.

Physical properties of Poly(L-lactic acid) fabricated using salicylic hydrazide derivative with tetraamide structure

ABSTRACTWith the aim of overcoming the slow crystallization rate of Poly(L-lactic acid) (PLLA), a heterogeneous nucleating agent, N, N, N, N’-salicylic tetra(1, 2, 4, 5-benzenetetracarboxylic acid) hydrazide (BAS), was synthesized to accelerate the crystallization of PLLA in this work. The effects of BAS on the non-isothermal crystallization, melting behavior, thermal stability, the fluidity and optical property of PLLA were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), melt index instrument and light transmittance meter. DSC results from the non-isothermal crystallization behavior revealed that BAS acted as an excellent crystallization promoter for promoting the nuclear of PLLA. Upon the cooling of 1°C/min from the melt of 190°C, 3 wt% exhibited the best accelerating effect on the melt-crystallization of PLLA. Even the BAS as a high-efficient nucleating agent could significantly promote the crystallization of PLLA upon fast cooling at 20°C/min. Additionally, the final melting temperature was another important factor for the crystallization process, and the 200°C is the best melting temperature for melt-crystallization of PLLA. The studies on the cold-crystallization process and melting behavior of PLLA/BAS samples under different conditions further confirmed the heterogeneous nucleating effect of BAS. And for the melting behavior of PLLA/BAS, both the crystallization temperatures and heating rates affected the melting behavior, and the double-melting peaks were assigned to melting-recrystallization. Overall, the addition of BAS could effectively improve the thermal stability and fluidity comparing with the primary PLLA, but decrease the light transmittance of PLLA.