Fold Surface Free Energy Research Articles

Melt-crystallization and self-nucleation of UHMWPE/bi-HDPE blends: The combined role of composition and molecular weight

Blends of bi-modal high-density polyethylene (bi-HDPE) and ultra-high molecular weight polyethylene (UHMWPE) with varying content (0–30 wt%.) and different molecular weights (MWs) (2.2, 3.5, and 4.5 M g/mol) of UHMWPE were prepared. The effect of UHMWPE content, MW, and their interplay on the microstructure, nucleation, and crystallization behavior of bi-HDPE was examined through rheology, scanning electron microscopy, and differential scanning calorimetry. The results revealed that UHMWPE serves as a partially miscible nucleating agent, effectively dispersing in the bi-HDPE matrix up to 5 wt%, thereby promoting the transition from randomly dispersed lamellae to a spherulitic morphology. The nucleating effect saturated when the UHMWPE content reached 10 wt%, leading to a diminished spherulitic structure. Beyond 10 wt% of UHMWPE, an anti-nucleation effect with segregated crystalline regions emerged. Isothermal kinetics analysis also revealed the highest crystallization rate at the optimum UHMWPE content of 5 wt%, where the critical nucleation energy barrier and fold-surface free energy were minimized. Apart from the UHMWPE content, signs of nucleation enhancement were slightly more pronounced in the bi-HDPE blend with the lowest molecular weight of UHMWPE. This phenomenon results from increased concentration fluctuations due to the larger interfacial area, as postulated from entanglement density measurements. For the first time, self-nucleation (SN) analysis revealed that the incorporation of 5 wt% of UHMWPE into bi-HDPE resulted in a wider Domain II width, indicating an increased memory effect. Notably, the crystalline memory was more pronounced in the blend containing UHMWPE with the MW of 2.2 M g/mol, exhibiting the super-nucleating effect with the highest nucleation efficiency of 218 %.

Polyvinylidene Fluoride (PVDF) Crystallization Kinetics in an Electric Field

To study the effect of applied electric field on polymer crystallization, the crystallization of polyvinylidene fluoride (PVDF) was observed under modified polarized optical microscopy. The PVDF melts were crystallized based on programmed temperature, changes between two transparent conductive glass electrodes, on which a DC electric field was applied. The observations revealed that without the electric field, crystallizations below 160 °C resulted in only α-form crystals, while, at elevated temperatures, the formation of γ-form crystals also occurred. By applying the electric field at 1.7 kV/cm, γ-form crystals started emerging at the slightly lower temperature of 158 °C. Further examinations showed that both crystals, α-form and γ-form, grew at a greater rate with increasing field strength. A careful calculation of the Avrami parameters supported the data that the electric field enhanced the crystallization kinetics. Careful calculation based on the Laurientz–Hoffmann approach revealed that applying the electric field decreased the required energy for PVDF crystallization. The folding surface free energy of the PVDF crystallization, 1.76 × 10−2 Jm−2, was reduced to 1.57 × 10−2 Jm−2 and 1.43 × 10−2 Jm−2 after applying electric fields of 0.8 and 1.7 kVcm−1, respectively. We suggest that the electric field promoted the polymer chain alignment during the crystallization; as a result, it accelerated the polymer crystallization and lowered the energy requirement for crystallization.

Influence of isotactic polypropylene grafted with styryl-group on the polymer crystallization behavior

4-Furfuryloxymethylstyrene (Sf) grafted isotactic polypropylene (iPP-g-Sf) was prepared by melt grafting reaction. The crystallization temperature of iPP after grafting increased to ∼130 °C. The isothermal and non-isothermal crystallization kinetics of iPP-g-Sf containing up to 1.50 mol% grafted Sf groups were compared with that of virgin iPP, and the isothermal and non-isothermal crystallization kinetics parameters of the polymers, including the fold surface free energy σe, the chain folding work q, and the crystallization activation energy ΔE, were calculated by Lauritzen-Hoffman theory and Kissinger method respectively. The results showed that iPP-g-Sf exhibited a unique self-nucleation phenomenon, which accelerating the crystallization rate of iPP and produced tiny crystal morphology than that for iPP. The introduction of only 0.23–1.50 mol% grafted Sf groups reduced the σe of the crystals by 44–57%. This might provide guidance for the design of polymer crystallization rate by controlling the molecular structures.

Poly(maleic acid-co-acrylic acid) ionomer as nucleating agent on the crystallization behavior and properties of poly(ethylene terephthalate)

Polyethylene terephthalate (PET) generally suffers from low crystallization rate and long molding cycle, which limits its application in injection molding of engineering plastics. To overcome the specific shortcoming, polymaleic acid-co-acrylic acid (PMA-AA) ionomer used as a nucleating agent was added to PET by melt blending, and its effect on the crystallization behavior of PET was investigated in this paper. It is indicated that the modified PET samples (MPET) with the addition of nucleating agents exhibit much higher molecular order and faster crystallization rate. The nucleation mechanism of MPET induced by PMA-AA ionomer was analyzed by means of Avrami equation and Hoffman–Lauritzen theory, revealing that the addition of PMA-AA ionomer provides more nucleation sites and reduces the fold surface free energy of PET. The nucleation and dispersion behavior of PMA-AA ionomer were further observed by SEM and POM morphologies. The results demonstrated that ionomer was dispersed homogeneously in the PET matrix, thus leading to faster crystallization rate of MPET than neat PET. In addition, the thermal stability, mechanical properties, and gas barrier of PET and MPET were characterized.

Transcrystallization of the acetylated bamboo fiber/polypropylene composite under isothermal crystallization

The crystallization behaviors of acetylated bamboo fiber (BF)/polypropylene (PP) composites were assessed using differential scanning calorimetry (DSC) through isothermal crystallization. The transcrystalline (TC) morphologies of composites were observed through polarized optical microscopy (POM), and their surface free energies were calculated based on Hoffman‒Lauritzen theory. Isothermal DSC thermograms demonstrated that acetylated BF with higher weight percentage gains (WPGs, ~ 19%) exhibited a decreased crystallization rate of the PP matrix. POM images indicated that BF as a nucleation agent induced the TC layer on fiber–PP matrix interfaces. However, when WPG reached 19%, the TC layer was not observed on the BF surface and crystal growth was principally observed in the PP matrix bulk. Based on Hoffman‒Lauritzen theory, the folding-surface free energy (σe) and the work of chain folding (q) for acetylated BF/PP composites were estimated to be higher than those for PP composites with unmodified BF. These results indicate that BFs with different WPGs could affect the crystallization behavior of the PP matrix by inducing or hindering TC on BF–PP matrix interfaces.

Effect of Silver Nanoparticles on the Melting Behavior, Isothermal Crystallization Kinetics and Morphology of Polyoxymethylene

In this work, the effects of silver (Ag) nanoparticles on the melting behavior, isothermal crystallization kinetics, and morphology of polyoxymethylene (POM) were studied. It was found that the melting peak temperature (Tm) and the crystallization temperature (TC) of POM/Ag nanocomposites shifted to higher temperature with the content of Ag nanoparticles increased. In addition, the isothermal crystallization kinetics of POM/Ag nanocomposites were determined by Avrami and Lauritzen-Hoffman models. The results of crystallization half-time (t0.5), reciprocal of crystallization half-time (τ0.5), Avrami exponent (n), and Avrami rate constant (k) showed that low loading of Ag nanoparticles (≤1 wt%) accelerated the crystallization rate of POM. However, when the content of Ag nanoparticles reached 2 wt%, they aggregated together and restrained crystallization of POM. Meanwhile, the results of nucleation parameter (Kg) and surface free energy of folding (δe) revealed that Ag nanoparticles reduced the energy need to create a new crystal surface, leading to faster crystallization. Moreover, the crystallization activation energies (∆E) were determined using the Arrhenius model, which suggested that Ag nanoparticles induced the heterogeneous nucleation by lowing the ∆E. Furthermore, polarized light microscopy results indicated Ag nanoparticles generated a great amount of nucleation sites and led to the formation of smaller spherulites.

Crystallization and melting of poly(butylene terephthalate) and poly(ethylene terephthalate) investigated by fast-scan chip calorimetry and small angle X-ray scattering

The crystallization and melting behaviors of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) were examined by Hoffman-Weeks (H–W), Gibbs-Thomson (G-T), and thermal Gibbs-Thomson (t-G-T) plots constructed by using fast-scan calorimetry and small-angle X-ray scattering. With PBT and PET, neither an H–W nor a G-T plot could be utilized for the determination of the equilibrium melting point (TM0) of chain-extended infinite-size crystals. The thermal Gibbs-Thomson plot utilizes the change in the melting point and the heat of fusion of chain-folded crystals during the secondary stage of isothermal crystallization. TM0 was determined from a t-G-T plot, and the results were in good agreement with the literature values for PBT and PET. G-T and t-G-T plots suggested a temperature-dependent folding surface free energy (σe), as has been proposed by Hoffman et al. The σe values obtained with G-T and t-G-T plots support the consistency of the analysis.

Influence of hydrogen bonding on the crystallization behavior of poly(ethylene oxide)/ionic liquids mixtures

Two types of imidazolium-based ionic liquids (ILs) [BMIM][BF4] and [BMIM][NTf2] and their mixtures were blended with poly(ethylene oxide) (PEO) matrix to tune the strength of intermolecular hydrogen bonding in the system. With the addition of ILs, particularly increasing [BMIM][NTf2] ratio, significantly reduced overall crystallization kinetics in the order of pure PEO > P80B20N0 > P80B16N4 > P80B6N14 > P80B0N20 (P80BxNy represents the mixture containing 80 wt% PEO, x wt% [BMIM][BF4] and y wt% [BMIM][NTf2]) were observed, which is mainly dominated by the enhanced hydrogen bonding. The early stage crystallization is accompanied by the breaking of hydrogen bonds as evidenced by in situ FT-IR, and much slower wavenumber shift of C-O-C groups on PEO backbone in P80B0N20 compared to that of P80B20N0 further demonstrates that the stronger hydrogen bonding between PEO and [BMIM][NTf2] could significantly inhibit the nucleation process. The fold surface free energy estimated from Lauritzen-Hoffman model is about 1.4 times in P80B0N20 than that in P80B20N0 indicating the stronger hydrogen bonding could increase the energy penalty associating to the nucleation and crystal growth. From SAXS, it is seen that hydrogen bonding only functions to the amorphous layer La rather than the lamellar thickness, that is, stronger hydrogen bonding results in larger La and more imperfect lamellar structure.

Reexamination of the equilibrium melting temperature of natural rubber crystals

The equilibrium melting temperature ($$T_{\mathrm{m}}^0$$) of natural rubber crystals was reexamined by the Hoffman–Weeks plot and the Gibbs–Thomson plot using the lamellar thickness obtained from the same sample as the one used for the measurement of melting temperature. The sample was prepared from deproteinized latex. As a result, the $$T_{\mathrm{m}}^0$$ of NR was estimated to be 61 °C. At the same time, the fold-surface free energy was estimated to be 0.046 Jm−2. These values should be more reliable than the previously assumed values. The equilibrium melting temperature ($$T_{\mathrm{m}}^0$$) of natural rubber crystals was reexamined by the Hoffman–Weeks plot and the Gibbs–Thomson plot using the lamellar thickness obtained from the same sample as the one used for the measurement of melting temperature. The sample was prepared from deproteinized latex. As a result, the $$T_{\mathrm{m}}^0$$ of NR was estimated to be 61 °C. At the same time, the fold-surface free energy was estimated to be 0.046 Jm−2. These values should be more reliable than the previously assumed values.

Gibbs–Thomson, Thermal Gibbs–Thomson, and Hoffman–Weeks Plots of Polyethylene Crystals Examined by Fast-Scan Calorimetry and Small-Angle X-ray Scattering

Crystallization and melting behaviors of polyethylene (PE) crystals were examined by fast-scan chip sensor calorimetry (FSC) and small-angle X-ray scattering (SAXS). The melting point TM of chain-folded thin lamellar crystals of PE was determined by utilizing FSC and the crystalline lamellar thickness dc by SAXS. The range of crystallization temperature Tc from SAXS as well as from FSC was extended much more broadly than before by examining those samples prepared on a chip sensor of FSC and applying a deep temperature jump for crystallization at large supercooling ΔTc. While the equilibrium melting point TM0 was reconfirmed with linear relationship of the melting and crystallization lines in the Gibbs–Thomson (G-T) plots of TM and Tc against (dc)−1, respectively, and the Hoffman–Weeks (H-W) plot of TM against Tc at relatively small ΔTc, those G-T and H-W plots seriously deviated from linear straight lines at large ΔTc. The origin of the curved G-T plots was ascribed to the Tc-dependent folding surface free energy σe. The determined values of TM0- and Tc-dependent σe were supported by a newly proposed thermal G-T plot of TM against the inverse of specific heat of fusion Δhfs in terms of the increase during the secondary stage of crystallization on long-term isothermal annealing at Tc of chain-folded PE crystals transforming to more stable states by lamellar thickening and crystal perfecting. The deviation from a linear H-W plot at large ΔTc was then ascribed to the crystal reorganization on heating of those less stable crystals formed at large ΔTc, even with fast heating. Application of fast heating and cooling by FSC plays an essential role in the confirmation of those thermodynamic behaviors of metastable polymer crystals with chain folding.

Crystallization and melting behaviors of poly(vinylidene fluoride) examined by fast-scan calorimetry: Hoffman-Weeks, Gibbs-Thomson and thermal Gibbs-Thomson plots

Crystallization and melting behaviors of chain-folded polymer crystals have been examined by fast-scan calorimetry (FSC) combined with small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) for poly(vinylidene fluoride). The melting point of lamellar crystals formed isothermally at Tc was measured by FSC in terms of the heating rate dependence and calibrated on the basis of the modeling of melting kinetics for the determination of the melting point at zero heating rate TM. The Hoffman-Weeks (H-W) plot of TM against Tc was on a linear straight line over Tc range broader than 30 K, and suggested the equilibrium melting point TM0 ≅ 200 °C of chain-extended infinite-size crystals of the α form. On the other hand, utilizing crystalline lamellar thickness dc determined by SAXS, both of the Melting and Crystallization lines in the Gibbs-Thomson (G-T) plots of TM and Tc against (dc)−1, respectively, were found to seriously deviate from linear straight lines. By examining the secondary stage of crystallization on long time isothermal annealing at Tc in terms of the changes in TM and the specific heat of fusion Δhfs by FSC, a newly proposed thermal G-T plot of TM against (Δhfs)−1 has confirmed the reliability of TM0 of the α form determined by the H-Wplot and the Tc dependent folding surface free energy σe, which brings the curved Melting and Crystallization lines in the G-T plots. In addition, on long time isothermal annealing, the changes in dc by SAXS and in crystallite size by WAXD have confirmed the molecular origin of the increase in TM and Δhfs in the secondary stage with thickening and perfecting of metastable chain-folded polymer crystals.

Crystallization and properties of poly(ethylene terephthalate)/layered double hydroxide nanocomposites

Poly(ethylene terephthalate) (PET) generally suffers from low crystallization rate and long molding duration, which as a result limit its application as engineering plastics. To overcome these drawbacks, series of PET/layered double hydroxide (LDH) nanocomposites were prepared by a solution blending process. The effect of metal composition (MgAl and CaAl) and organo-modification (stearic acid intercalated) for LDH fillers on the crystallization behavior of the nanocomposites was investigated. It was revealed that, compared with PET/CaAl-LDH, the PET/MgAl-LDH nanocomposite exhibits a higher crystallization temperature and faster crystallization rate, which is associated with the superior nucleation ability of MgAl-LDH. The nucleation mechanism of PET induced by LDHs was explored by means of Avrami equation and theory of Hoffman-Lauritzen, pointing out that the incorporation of LDHs reduce the free energy of nucleation and the fold surface free energy of PET. In order to improve the compatibility between LDH and PET, stearic acid (SA) intercalated MgAl-LDH was prepared and filled into PET matrix. The resultant PET/MgAl-LDH-SA shows a further enhanced crystallization temperature and accelerated crystallization rate, in comparison with PET/MgAl-LDH nanocomposites. In addition, the thermal stability, gas barrier and mechanical properties of PET/LDH composites were improved upon incorporation of LDH fillers.

Effect of WS₂ Inorganic Nanotubes on Isothermal Crystallization Behavior and Kinetics of Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate).

Nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and tungsten disulfide inorganic nanotubes (INT-WS2) were prepared by blending in solution, and the effects of INT-WS2 on the isothermal crystallization behavior and kinetics of PHBV were investigated for the first time. The isothermal crystallization process was studied in detail using various techniques, with emphasis on the role of INT-WS2 concentration. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) showed that, in the nucleation-controlled regime, crystallization rates of PHBV in the nanocomposites are influenced by the INT-WS2 loading. Our results demonstrated that low loadings of INT-WS2 (0.1–1.0 wt %) increased the crystallization rates of PHBV, reducing the fold surface free energy by up to 24%. This is ascribed to the high nucleation efficiency of INT-WS2 on the crystallization of PHBV. These observations facilitate a deeper understanding of the structure-property relationships in PHBV biopolymer nanocomposites and are useful for their practical applications.

Nucleation barrier, growth kinetics in ternary polymer blend filled with preferentially distributed carbon nanotubes

Structural properties, evolution of morphology and crystallization kinetics in immiscible polymer blends filled with multiwall carbon nanotubes (MWNTs) in the droplet phase were systematically investigated in this study. By grafting suitable macromolecules (here SAN, styrene acrylonitrile), that can drive the MWNTs to the droplet phase, allowed the understanding of the rate of nucleation and growth of the semicrystalline matrix in droplet-filled blends in contrast to matrix-filled blends. By blending 90 wt% of PVDF with 10 wt% ABS, matrix-droplet morphologies were generated and by grafting SAN onto MWNTs, the localization of the nanotubes was tuned to fill the droplet phase which otherwise prefers the matrix phase (here PVDF); driven by thermodynamics. The evolution of morphology under quiescent annealing conditions was assessed by SEM. The blends with SAN-g-MWNTs also coarsened as a function of time similar to neat blends however, to a lesser extent. Although, droplet laden MWNTs did not suppress coarsening in the blends but it still improved the tensile properties when compared with the neat blends. The fold surface free energy (as evaluated from isothermal crystallization kinetics) was estimated to be less in case of blends with only MWNTs in contrast to blends with SAN-g-MWNTs. This was attributed to the fact that matrix (here PVDF) filled with MWNTs experiences faster crystallization rate due to heterogeneous dispersion of nucleating agents (here MWNTs) in the matrix. However, when the SAN-g-MWNTs were mostly localized in the amorphous droplet phase (here ABS), PVDF experienced similar crystallization behavior like the neat PVDF/ABS blends. Taken together, our study demonstrates that lower amount of energy is required for the arrangement of PVDF chains into the crystal lattice upon cooling from the melt state and accelerate the crystallization process when the heteronucleating agents are localized in the matrix phase than when they are localized in the amorphous droplet phase.

Influence of Graphene Oxide on Crystallization Behavior and Chain Folding Surface Free Energy of Poly(vinylidenefluoride‐co‐hexafluoropropylene)

Graphene oxide (GO) filled poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HPF) copolymer nanocomposites as promising piezoelectric materials are developed, and their crystallization behavior and chain folding free energy are examined. Appropriate distribution of GO nanoparticles in the copolymer is confirmed by transmission electron microscopic analysis. The crystalline structure of nanocomposites is analyzed by wide‐angle X‐ray scattering and Fourier transform infrared spectroscopy. The results show an increase in the β‐phase content of PVDF‐HPF copolymer in the presence of GO. Non‐isothermal crystallization kinetics of the neat polymer and corresponding nanocomposites are studied by a multiple heating rate differential scanning calorimetry using modified Avrami–Jeziorny and Liu models. Moreover, barrier energy of crystallization is calculated by Friedman and Kissinger models. It is found that addition of GO to the copolymer increases nucleation activity of the nanocomposites. Investigation on linear crystal growth via Hoffman's theorem indicates an enhanced nucleation activity upon increasing GO content. The surface folding free energy of the neat polymer is changed from 5.79 × 10−2 to 7.27 × 10−2 J m−2 upon addition of 5 wt% of GO. A bundle‐like mechanism is proposed, which can explain the crystallite growth. Analysis based on Vyazovkin theorem reveals that the crystallization activation energy is independent of GO at elevated temperatures.

Relationship between melting behavior and morphological changes of semicrystalline polymers

The present study on the case of poly(hexamethylene succinate) is to provide a basis for a better understanding of the subtle relationship between melting behavior and morphological changes of semicrystalline polymers. The melting behavior and morphological changes of poly(hexamethylene succinate) during both isothermal secondary crystallization and annealing processes were investigated by DSC and SAXS. DSC results showed that, with increasing crystallization time or annealing time, the melting endotherm continuously shifted to higher temperature, which suggested that some minor structural or morphological changes must occur. However, almost no changes at all on the crystal thickness were observed from SAXS measurements. The observed evidence confirmed that the increase in the melting temperature is not attributed to crystal thickening but crystal perfection. More exactly, the rearrangement and smoothing of tie molecules at the folding surface result in the reduction of the fold surface free energy, which dominantly contributes to the increase in the melting peak temperature. The origin of the new endothermic peak observed after annealing at elevated temperature was also discussed. TMDSC results indicated that the annealing peak resulted from the enthalpy relaxation and devitrification transition of rigid amorphous fraction formed by the driving force of thermodynamic nonequilibrium, rather than usually regarded as the melting of thin lamellae or imperfect crystals formed by annealing secondary crystallization.

The Three-Phase Structure of Random Butene-1/Ethylene Copolymers

Abstract The three-phase arrangement of random copolymers of butene-1 with ethylene was investigated and compared with isotactic poly(butene-1) homopolymer (iPB-1). In all the analyzed compositions, isothermal crystallization leads to a three-phase structure, made of one crystal phase and two amorphous fractions that differ in mobility: the mobile amorphous fraction (MAF), made of the polymer chains that relax at the glass transition, and a rigid amorphous fraction (RAF) made of the amorphous segments coupled with the crystal phase. Copolymerization with ethylene leads to a drop in crystal fraction and to a sizable increase of both the RAF, and of the specific RAF, i.e. of the RAF normalized to crystallinity. Analysis of crystal growth rate allowed quantifying the fold surface free energy, which increases of about 50 to 100% in the copolymers, compared to iPB-1 homopolymer. In the butene-1/ethylene random copolymers, ethylene units are mostly excluded from the crystals and accumulate at the crystal/amorphous interphase, thus affecting the rigid amorphous area. The varied composition and higher mobility of the rigid amorphous fraction of the copolymers affects also the Form II to Form I transformation of poly(butene-1) crystals, which occurs with enhanced kinetics in the copolymers, compared to iPB-1 homopolymer.

Crystallization behaviour of syndiotactic polystyrene and benzoylated syndiotactic polystyrene

The crystallization behaviour of syndiotactic polystyrene (sPS) and benzoylated sPS (BzsPS) was investigated by POM, DSC and XRD. The results suggest β form of sPS has higher equilibrium melting temperature Tm0 and the fold surface free energy σe than α form. With increasing benzoylation degree the growth rates and Tm0 of two forms decrease, but their Tm0 decrement is very close; the σe of β form more increases than that of α form, the formation of α is more favourable. Upon loading trace amount of α nucleating agent PTBBNa in samples the growth rate of two forms can be strictly compared in the same melting and crystallization temperature condition, the results reveal that the growth rate of β form is faster than that of α form in sPS and BzsPS-2%. Using supercooling degree ΔT and σe two parameters has explained the formation competition mechanism of α and β forms.

Effect of graphene nanoplatelets diameter on non-isothermal crystallization kinetics and melting behavior of high density polyethylene nanocomposites

In the present study the effect of different size of graphene nanoparticles 5, 15 and 25μm in diameter, on melting behavior and crystallization kinetics of high density polyethylene (HDPE) was investigated. Crystallization of HDPE and its graphene nanocomposites in non-isothermal conditions was studied at several constant cooling rates from 1 to 20K/min by means of differential scanning calorimetry. The results showed that the Avrami analysis modified by Jeziorny and a method developed by Mo could describe the non-isothermal crystallization of nanocomposites very well. Kinetics data analysis showed that the overall crystallization rate, the activation energy and the fold surface-free energy of the HDPE polymer were apparently changed due to the addition of graphene filler in different diameter size. Particularly, the incorporation of all graphene nanoparticles resulted in a greater crystallization temperature of HDPE, but graphene nanoparticles M5 with the smaller diameter increase more the number of heterogeneous crystallization nuclei and this resulted in a higher crystallization rate.

Enhanced crystallization behaviour and impact toughness of poly(ethylene terephthalate) with a phenyl phosphonic acid salts compound

Low crystallization rate and inherent brittleness characteristics limit the wide application of PET. In this paper, it was found that a low molecular weight Phenyl phosphonic acid salts compound (TMC-210) is a very effective nucleator and can enhance the impact strength very much. So, the effect of TMC-210 on the crystallization behaviour and mechanical properties of poly(ethylene terephthalate) were systematically evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), scanning electron microscope (SEM) and mechanical properties test. The results show that TMC-210 obviously improves the crystallization temperature and accelerates the crystallization rate of PET and reflects a significant heterogeneous nucleating effect with a nucleation efficiency of 99.8 % when introducing a low content of 0.6 wt% TMC-210. The spherulites size and number of blended PET are greater than pure PET. The crystal structure of PET does not change but the blends with high TMC-210 content appears new diffraction peaks in x-ray diffraction spectrogram and it may attribute to the agglomeration of TMC-210 particles, which is verified by SEM observation. The impact fracture surface of PET develops a brittle ductile transition and thus the impact strength of PET improves significantly. Additionally, Lauritzen–Hoffman equation was used to discuss the effect of TMC-210 on the fold surface free energy (σ e) of PET in the crystallization process and found that the σ e values of PET/TMC-210 blends is smaller than that of pure PET.