Heterogeneous Nucleating Agent Research Articles

Positive Temperature Coefficient and Electrical Conductivity Investigation of Hybrid Nanocomposites Based on High‐Density Polyethylene/Graphene Nanoplatelets/Carbon Black

Hybrid nanocomposites of high‐density polyethylene have been prepared via the melt‐mixing method in the presence of different amounts of graphene nanoplatelets (GNPs) and conductive carbon black (CB). The electrical conductivity, positive temperature coefficient (PTC), and the correlation between crystallinity and electrical conductivity of hybrid nanocomposites are investigated to study the effect of crystallinity on electrical conductivity. The samples are characterized using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X‐ray diffraction (XRD), and electrical resistivity. SEM micrographs reveal good distribution of CB and GNPs in nanocomposites. According to DSC and XRD results, the crystallinity of samples decreases by the addition of CB and GNP. The electrical conductivity of all the samples increases, whereas in the sample 16% of CB and 1% of GNP electrical conductivity decrease due to GNP acting as a heterogeneous nucleating agent and the numerous incomplete and small crystals formation. The highest electrical conductivity (1.46×10−4 S cm−1) is obtained in the sample high‐density polyethylene (HDPE)/CB18/GNP1, which shows high increment in the PTC curve in the range of 105−120 °C. Also, repeatability and reversibility of PTC in this sample show good potential for use in different applications such as thermistors, temperature sensors, and self‐regulating heaters.

Fabrication of Highly Interconnected Poly(ε-caprolactone)/cellulose Nanofiber Composite Foams by Microcellular Foaming and Leaching Processes.

In this study, microcellular polycaprolactone (PCL)/sodium bicarbonate (NaHCO3)/cellulose nanofiber (CNF) composite foams with highly interconnected porous structures were successfully fabricated by microcellular foaming and particle leaching processes. Supercritical CO2 (scCO2) served as a physical foaming agent, NaHCO3 was chosen as a chemical foaming agent and porogen, and CNF acted as a heterogeneous nucleating agent. The effect of scCO2, NaHCO3, and CNF on pore structures and the cofoaming mechanism were investigated. The results indicated that the addition of NaHCO3 and CNF increased the melt strength of the PCL matrix significantly. During the foaming process, the presence of CNF can form a rigid network due to the hydrogen bonding or mechanical entanglement between individual nanofibers, improving the nucleating efficiency but slowing down the cell growth rate. Additionally, due to the interaction of “soft” PCL matrix and “hard” domains in a PCL-based composite during the foaming process, together with the NaHCO3 leaching process, highly interconnected cell structures appeared. The obtained PCL/NaHCO3/CNF composite foams had a cell size of 15.8 μm and cell density of 6.3 × 107 cells/cm3, as well as an open-cell content of 82%. The reported strategy in this paper may provide the guidelines and data supports for the fabrication of a PCL-based porous scaffold.

Polypropylene/graphene nanoplatelets nanocomposites with high conductivity via solid-state shear mixing

Abstract The research on facile, low-cost, and green process for the uniform dispersion of graphene nanoplatelets (GNPs) into polymer matrix has always been a considerable challenge in practical applications. The Van der Waals interaction between graphene layers can easily cause aggregation of the nanofillers. Here, we propose a new method to solve this problem by involving solid-state shear mixing to obtain a well-dispersed nanocomposite. The comprehensive properties of nanocomposite, including antistatic properties, mechanical properties, and thermal stability, can be significantly enhanced by this method. The surface resistivity of the nanocomposite can be up to 2.4 × 107 Ω sq−1 under 1 wt% content of GNPs, which is significantly better than the value obtained by conventional melting compounding and meets the required standard of less than 3 × 108 Ω sq−1 for actual application antistatic materials. The impact strength of the nanocomposite increased by 120.8% when compared with neat PP. At the same time, the heat distortion temperature and initial decomposition temperature of the nanocomposite with only 0.5 wt% content of GNPs are improved by 11.7°C and 110°C, respectively. In addition, GNPs is a heterogeneous nucleating agent that leads PP to emerge β crystal form. This study provides an effective and practical reference for the broad-scale industrial preparation of polymer-based graphene nanocomposites.

In-situ synthesis and thermal properties of biobased Poly(neopentyl glycol 2,5-furandicarboxylate)/multi-walled carbon nanotubes composites

The in-situ synthesis and thermal properties of biobased poly(neopentyl glycol 2,5-furandicarboxylate) (PNF)/multi-walled carbon nanotubes (MWCNTs) composites were studied in this research. The chemical structure, thermal stability, crystallization behavior, and crystal structure of PNF/MWCNTs composites were extensively investigated and compared with those of PNF. Scanning electron microscopy image revealed that MWCNTs uniformly dispersed in PNF matrix. In the composites, MWCNTs slightly improved the thermal stability of PNF, while the crystallization of PNF was obviously enhanced by MWCNTS under both the nonisothermal and isothermal crystallization conditions as the heterogeneous nucleating agent. Only 0.5 wt% of MWCNTs obviously increased the melt crystallization temperature from 132.9 °C for neat PNF to 141.2 °C for the composite and decreased the crystallization half-time from 3.1 min for neat PNF to 1.9 min for the composite at 165 °C. In addition, MWCNTs did not modify the crystal structure of PNF.

Physical Properties of Biodegradable Poly(L-lactide) Induced by N, N -Bis(Benzoyl) 1, 3-Cyclohexanedicarboxylic Acid Dihydrazide as Crystallinity Additive

This work is aimed at synthesizing an organic compound N, N -bis(benzoyl) 1,3-cyclohexane-dicarboxylic acid dihydrazide (CABH) to focus on its effect on the non-isothermal crystallization of poly(L-lactide) (PLLA), meanwhile the melting behavior, thermal decomposition process and optical property of PLLA/CABH samples in different CABH concentrations were also investigated. It was found that CABH acted as efficient heterogeneous nucleating agent for inducing PLLA�s crystallization through comparative analysis of melt-crystallization process of the virgin PLLA with PLLA/CABH samples, and a high amount of CABH played a much more significant role in promoting PLLA�s crystallization. Additionally, the melt-crystallization processes also showed that both the cooling rate and the final melting temperature affected the crystallization behavior of PLLA, an increase of cooling rate could weaken the crystallization ability of PLLA/CABH samples, and the final melting temperature of 180�C made PLLA/CABH exhibit the best crystallization ability. For the cold-crystallization process, the cold-crystallization peak became flatter and shifted toward the lower temperature with increasing of CABH concentration, but an increase of heating rate could prevent the cold-crystallization peak from moving to low temperature because of the thermal inertia. The melting behaviors of PLLA/CABH depended on the previous crystallization and heating rate in heating, and the difference in melting behavior of PLLA/CABH samples effectively reflected the nucleation role of CABH, as well as the double melting peaks behavior of PLLA/CABH was thought to due to the melting-recrystallization. The introduction of CABH led to a drop in light transmittance, moreover, this negative effect were more obvious with an increase of CABH loading. In contrast, the fluidity of PLLA was significantly enhanced due to the existence of CABH.

Effect of montmorillonite on the oxidative stability of polyphenylene sulfide fibers prepared by melt spinning

Masterbatches of polyphenylene sulfide (PPS)/organic montmorillonite (MMT) composites were produced via melt blending. A self-made spinning equipment was then used to produce the PPS/organic MMT composite fibers by melt spinning directly from the masterbatches. X-ray diffractometer and transmission electron microscope were used to examine the dispersibility of organic MMT. The morphology, tensile property, crystallization behavior, and oxidative stability of PPS fibers were investigated. The results indicated that organic MMT could be uniformly distributed in the PPS matrix to form a mixed dispersion of intercalated and exfoliated structure and influence the longitudinal surface morphology of fibers to become rough. The roughness of composite fibers surface was proportional to the content of organic MMT. The organic MMT nanolayers could act as the heterogeneous nucleating agents to improve the crystallization, and the crystallity of composite fibers increased with the increase of organic MMT content. The breaking strength of composite fibers first increased and then decreased by increasing the amount of organic MMT. After the oxidation treatment, the breaking strength of neat PPS fibers and composite fibers declined, but the degree of breaking strength loss for composite fibers is lower than that of neat PPS fibers. The dynamic oxidation induction temperature of composite fibers also showed a significant increase by adding organic MMT. Moreover, the addition of organic MMT could limit the chemical combination of element sulfur and oxygen, retard the generation of sulfoxide groups, and induce the conversion of sulfur atoms from C-S bond to sulfone for improving oxidative stability.

Thermal and mechanical properties of poly(L-lactic acid) nucleated with N,N’-bis(phenyl) 1,4-naphthalenedicarboxylic acid dihydrazide

The modified poly(L-lactic acid) (PLLA) with different contents (0.5−3 wt %) of N,N’-bis(phenyl) 1,4-naphthalenedicarboxylic acid dihydrazide (NAPH) were prepared to evaluate effects of NAPH on melt-crystallization behavior (DSC), thermal degradation (TGA) and mechanical properties of PLLA. The melt-crystallization results demonstrated that NAPH as a heterogeneous organic nucleating agent enhanced crystallization ability of PLLA in cooling, and PLLA/1%NAPH had the best crystallization ability because of the highest onset crystallization temperature and the sharpest melt-crystallization peak. However, melt-crystallization behavior also depended on the cooling rate and final melting temperature, overall, a relative slow cooling rate and low final melting temperature were beneficial for crystallization of PLLA. The cold-crystallization results indicated that NAPH had an inhibition for cold-crystallization process of PLLA, and the cold-crystallization peak shifted towards lower temperature and became wider with an increase of NAPH concentration. The different melting behaviors ofPLLA/NAPH after melt-crystallization and isothermal-crystallization efficiently reflected the accelerating role of NAPH for PLLA crystallization; the double melting peaks formed in heating were thought to result from melting-recrystallization, as well as that a higher crystallization temperature could cause melting peak to appear in higher temperature regions and possess larger melting enthalpy. A comparative analysis on thermal degradation in air illustrated that the addition of NAPH accelerated decomposition of PLLA, but a decrease of onset decomposition temperature was inhibited by the probable interaction of PLLA with NAPH. Moreover, the tensile test showed that NAPH decreased tensile modulus and elongation at break of PLLA, whereas PLLA with low concentration of NAPH had higher tensile strength than pure PLLA.

Application of a novel cavity nucleating agent based on cyclodextrin in polymer foaming materials and in situ visual injection moulding study

In this study, β-cyclodextrin nanosponges were synthesized using organic carbonates, namely gelatinous β-cyclodextrin nanosponges (NJ) and vitreous β-cyclodextrin nanosponges (BL). The ‘constructed’ porous structures were characterized by scanning electron microscopy. NJ and BL with different cavity structures as heterogeneous nucleation agents were selected for the polypropylene and polylactic acid foaming injection moulding processes. The obtained experimental results showed that NJ significantly reduced nucleation energy barrier and thus exhibited the highest nucleation efficacy. The nucleation mechanism was explored via a combination of the classical nucleation theory and in situ visual injection moulding analysis. In a word, the current work provided an insight into the structure-nucleating efficiency relationship for porous particles and highlighted the importance of the construction of porous structures in the organic nucleating agents to improve the polymeric foaming performances.

Fiber-induced crystallization in polymer composites: A comparative study on poly(lactic acid) composites filled with basalt fiber and fiber powder

The poly(lactic acid) (PLA) composites with the silane coupling agent treated basalt fiber (SBF) and basalt fiber powder (SBFP) were prepared. The crystalline morphology, mechanical properties, and heat resistance of PLA/SBF/SBFP composites were investigated. The results indicated that SBF or SBFP not only acted as heterogeneous nucleating agents for PLA crystallization but also improved the mechanical properties and heat resistance of PLA. Morphological analyses showed that SBFP could play nucleating role to reduce the spherulites size of PLA, and SBF could restrict the mobility of PLA chains and construct interface crystallization for PLA during isothermal crystallization process. The composites with higher SBF loading, the “Transcrystalline-network” built in the composites significantly improved the heat resistance properties of PLA. Due to the synergistic effect of SBF and SBFP, the PLA/SBF/SBFP composites showed high heat deformation temperature (HDT), especially after isothermal crystallization, the HDT increased to 150.5 °C for the PLA/SBF/SBFP 50/10/40 composite, much higher (about 190%) than that of pure PLA (71.7 °C).

Preparation and oxidation resistance of polyphenylene sulfide modified by high-temperature antioxidants

Two types of high-temperature antioxidants (Revonox 608 and GA-80) were used to improve the oxidation resistance of polyphenylene sulfide (PPS) through melt blending, and the resistance against oxidation and other properties were characterized. The results showed that GA-80 exhibited better dispersibility and compatibility with the PPS matrix than did Revonox 608. Revonox 608 could act as a heterogeneous nucleation agent that can promote crystallization and improve the crystallinity of PPS, whereas GA-80 could delay the movement of chain segments and limit crystallization. The thermal-oxidative stability of PPS can be improved by adding antioxidants due to prior oxidative decomposition. The dynamic oxidation induction temperature of PPS increased by more than 10 °C because of the capture of free radicals and the decomposition of hydroperoxides by antioxidants. The XPS results showed that both GA-80 and Revonox 608 could retard the oxidative cleavage of the C-S-C bond in the PPS macromolecular chains and protect the S atoms from oxidizing to sulfone groups.

Designer Core-Shell Nanoparticles as Polymer Foam Cell Nucleating Agents: The Impact of Molecularly Engineered Interfaces.

The interface between nucleating agents and polymers plays a pivotal role in heterogeneous cell nucleation in polymer foaming. We describe how interfacial engineering of nucleating particles by polymer shells impacts cell nucleation efficiency in CO2 blown polymer foams. Core–shell nanoparticles (NPs) with a 80 nm silica core and various polymer shells including polystyrene (PS), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and poly(acrylonitrile) (PAN) are prepared and used as heterogeneous nucleation agents to obtain CO2 blown PMMA and PS micro- and nanocellular foams. Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy are employed to confirm the successful synthesis of core–shell NPs. The cell size and cell density are determined by scanning electron microscopy. Silica NPs grafted with a thin PDMS shell layer exhibit the highest nucleation efficiency values, followed by PAN. The nucleation efficiency of PS- and PMMA-grafted NPs are comparable with the untreated particles and are significantly lower when compared to PDMS and PAN shells. Molecular dynamics simulations (MDS) are employed to better understand CO2 absorption and nucleation, in particular to study the impact of interfacial properties and CO2-philicity. The MDS results show that the incompatibility between particle shell layers and the polymer matrix results in immiscibility at the interface area, which leads to a local accumulation of CO2 at the interfaces. Elevated CO2 concentrations at the interfaces combined with the high interfacial tension (caused by the immiscibility) induce an energetically favorable cell nucleation process. These findings emphasize the importance of interfacial effects on cell nucleation and provide guidance for designing new, highly efficient nucleation agents in nanocellular polymer foaming.

Effect of 1,2,3-triazolium-functionalized PEG-b-PCL block copolymer on crystallization behavior of poly(L‑lactic acid) as nucleation agent and mobility promoter

The effect of 1,2,3-triazolium-functionalized PCL-b-PEG block copolymer (PCL-b-PEG(IL)) on crystallization behavior and kinetics of PLA was systematically studied by DSC, POM and XRD. A small amount of micelle of aggregated PCL-b-PEG(IL) containing ionic clusters and a large number of disaggregated PCL-b-PEG(IL) can significantly improve the chain segment mobility of PLA. The glass transition temperature and cold crystallization temperature of PLA gradually decreased with the increase in PCL-b-PEG(IL) or PCL-b-PEG content. Compared with PCL-b-PEG, PCL-b-PEG(IL) decreases the Tg of PLA more obviously because of the strong plasticizing effect of PCL-b-PEG(IL). More importantly, the isothermal crystallization kinetics results manifested that the synergistic effect of heterogeneous nucleation agent of ionic clusters of PCL-b-PEG(IL) and chain mobility promoter of PEG chain segment can enhance the crystallization ability of PLA at all crystallization temperature. The 5 mass% PCL-b-PEG(IL) can induce high amount of stable α-form crystal of PLA after annealing treatment.

Optimal radiation shielding capacity and thermal properties of poly(methyl methacrylate) films enhanced with different metal complexes

Samples of pure poly(methyl methacrylate) (PMMA) and PMMA enhanced with metal complexes of Zn, Cd, and Hg were synthesized via catalytic chain transfer polymerization. Structural analysis, by means of XRD, showed the amorphous nature of the studied samples which meant high homogenous dissolution of the metals (Zn, Cd and Hg) into the polymer matrix. Density values increased linearly with respect to atomic radius of the incorporated metals. Addition of such elements causes an increase in mass attenuation coefficients and a remarkable decrease in the Half Value Layer (HVL) values, in comparison to existing standard shielding materials. Thermal studies by DSC indicated highly homogenous internal structure of the studied samples, with slight decrease in the Tg value when introducing metals due to heterogeneous nucleation agent role of the Cd, Zn and Hg. All observations and results suggest the studied materials to be used as promising and proper aprons for medical radiation shielding applications.

The effect of cooling rate on resistance-welded CF/PEEK joints

The influence of cooling rate on the mechanical properties of resistance-welded continuous carbon fiber/poly-ether-ether-ketone (CF/PEEK) joints and crystallization behavior of PEEK in the heating elements (HEs) was investigated. 6 kinds of joints with different cooling rates were designed and prepared in resistance welding processes. A lap shear strength (LSS) improvement of 28% was reported for joints with lower cooling rates relative to joints without controlled cooling process, and the crystallinity degrees measured by differential scanning calorimetry (DSC) of lower-cooling-rate joints were also higher. The fatigue performances showed the same trend. The polarized optical microscope (POM) images showed that stainless steel (SS) wires in the HEs acted as heterogeneous nucleating agents, promoting high-density nucleation sites and accelerating formation of transcrystallinity at a cooling rate lower than 80 °C/min, and the transcrystallinity was hardly observed at higher cooling rates. The results of crystallization kinetics also showed that the Avrami exponent n reduced with cooling rate increasing, indicating that a two-dimensional growth of transcrystallinity dominated at lower cooling rates. It was suggested that qualities of resistance-welded joints were significantly affected by crystallinity and morphology which were both controlled by the cooling rate.

Synthesis and Performances of Hydrocinnamic Acid Derivatives Containing Alkyl Dihydrazide

In this work, four hydrocinnamic acid derivatives including N, N’-succinic bis(hydrocinnamic acid) dihydrazide (HASUD), N, N’-adipic bis(hydrocinnamic acid) dihydrazide (HAADD), N, N’-sebacic bis(hydrocinnamic acid) dihydrazide (HASED) and N, N’-dodecanedioic bis(hydrocinnamic acid) dihydrazide (HADOD) were synthesized via two liquid reactions. And then fourier transform infrared spectrometer and 1H nuclear magnetic resonance were used to characterize molecular structures of four hydrocinnamic acid derivatives. Additionally, the orthogonal experiment obtained the optimum synthesis process of four hydrocinnamic acid derivatives, and the maximum yield of HASUD, HAADD, HASED and HADOD were 33.3%, 43.2%, 43.5% and 51.9%, respectively. DMol3 was used to optimize geometric structure and obtain frontier orbital energy. Finally, hydrocinnamic acid derivatives and poly(L-lactide) (PLLA) were blended using the torque rheometer to investigate these role in PLLA resin. The resultant from the melt-crystallization process showed that hydrocinnamic acid derivatives as heterogeneous nucleating agents could significantly enhance PLLA’s crystallization.

Effect of sucrose ester S370 on interfacial layers and fat crystals network of whipped cream

The effect of sucrose ester S370 on the interfacial layers and fat crystals network of whipped cream has been studied in this work. The addition of S370 showed a little effect on the droplets size, interfacial protein concentration and viscosity of emulsion samples before whipping. However, the addition of S370, as a heterogeneous nucleating agent, could induce nucleation and lead to the formation of more small crystals in the bulk mixture and emulsions. These small crystals, which were not able to pierce the interface of fat droplets effectively, would retard fat coalescence during whipping process. The addition of S370 resulted in lower degree of fat coalescence, lower interfacial protein concentration, shorter optimum whipping time (top) and lower overrun of whipped cream. At lower S370 concentration (<0.05 wt%), large-size crystals and inhomogeneous fat crystals network led to lower firmness and less bubbles stability of whipped cream samples. At 0.05 wt% S370 concentration, homogeneous crystals network, resulted in whipped cream with high firmness and bubbles stability. However, lower interfacial protein concentration and small-size crystals were observed at higher concentration of S370 (>0.05 wt%). As a result, the aerated structure was not strong enough to stabilize whipped cream.

Effect of Ce Addition on Inclusions and Grain Structure in Gear Steel 20CrNiMo

Through laboratory experiments and thermodynamic calculation, the chemical composition and morphology of inclusion and grain size in the cast melt are comprehensively characterized herein. The results show the evolution of Al2O3 inclusion formed by Al deoxidation in the gear steel 20CrNiMo follows the route of Al2O3 → CeAlO3 → Ce2O2S → Ce2O2S + CeS, and thus the nucleation core of complex CemnS sulfides changes from CeAlO inclusion to CeOS inclusion with the increase in Ce addition. Moreover, grain size of gear steel 20CrNiMo treated by Ce addition decreases from 491.4 to 164.0 μm, because both the Ce2O2S and CeS form with Ce addition and have potential to be effective heterogeneous nucleation agents for the primary δ‐ferrite during the solidification process of gear steel 20CrNiMo. And statistical results show that the percentage of small inclusion with a diameter less than 3 μm are, respectively, 64.4%, 86.5%, 96.4%, 93.6%, and 75.6% in the steel samples with Ce content of 0, 13, 31, 77, and 203 ppm. Thus, the recommended Ce content to achieve fine inclusions and solidification structure of gear steel 20CrNiMo is 31 ppm.

Thermal and rheological properties of fully biodegradable Poly(ethylene succinate)/Cellulose nanocrystals composites

The effect of low contents of cellulose nanocrystals (CNC) on the thermal and rheological properties of poly(ethylene succinate) (PES) was studied in this work in their fully biodegradable composites. Regardless of CNC content, the incorporation of CNC slightly improved the thermal stability and obviously enhanced the melt crystallization as an efficient heterogeneous nucleating agent as well as the complex viscosity, storage modulus, and loss modulus of PES as a rigid reinforcing nanofiller in the composites; however, the crystal structures of PES/CNC composites were not modified. The rheological behavior study indirectly revealed the content dependence of the dispersion of CNC in PES matrix, i.e., fine dispersion at low CNC contents of 0.5 wt% and below and aggregation at 1 wt% of CNC. Depending on CNC content, the external surfaces available for the nucleation of PES crystals were different due to the different dispersion states of CNC in polymer matrix. The morphology study confirmed that the melt crystallization of PES was apparently affected by the content and dispersion of CNC in the composites.

Solid–solid phase‐change materials cross‐linked by carbon quantum dots: Address leakage and high super‐cooling degree simultaneously

AbstractLeakage and super‐cooling are two main disadvantages of polyethylene glycol (PEG) when used as phase‐change materials (PCMs) for thermal energy storage, which seriously restrict the practical applications of the materials. In this study, we employ carbon quantum dots (CQDs) as cross‐linkers to fabricate PEG‐based solid–solid PCMs, which not only address the leakage issue of PEG during melting process, but also have much lower super‐cooling degree compared with PEG, exhibiting extraordinary thermal energy storage performance. CQDs serve as a heterogeneous nucleating agent in the crystal domains of these PEG‐based PCMs according to the characterizations. Additionally, CQDs are also beneficial to the thermal stability of the PCMs. And these PEG‐based PCMs have high phase‐change enthalpies (94.4 J/g) and applicable phase‐change temperatures (25–37°C), showing potential for thermal energy storage.

Non-isothermal crystallization behavior of PP/EVA/basalt/carbon fiber composites

The surface treatment of basalt and carbon fiber was carried out by sulfuric acid etching and coupling. Combined fiber was prepared by melt mixing. Polarizing optical microscope (POM) and differential scanning calorimetry (DSC) were employed to investigate the effect of combined fiber on crystallization behavior. To be specific, POM indicated that the addition of combined fiber reduced the crystal size. DSC observations illustrated that the combined fiber accelerated the crystallization rate and increased the crystallization temperature from 112-122 °C to 122-133 °C. It means that combined fiber can make the composites crystallize rapidly at high temperature in production. Modified Avrami models were used to evaluate the influence of combined fiber on the non-isothermal crystallization kinetics of PP. The presence of combined fiber reduced the Avrami exponent (n) from 2.16-3.13 to 1.54-2.49. The results showed that the combined fiber acted as heterogeneous nucleation agent, which changed crystal nucleation mechanism and growth mode.