Crystallization Peak Temperature Research Articles

Toughness and crystallization enhancement in wood fiber-reinforced polypropylene composite through controlling matrix nucleation

Wood fiber/polypropylene (WF/PP) composites are commonly used to efficiently utilize natural resources and reduce environmental problems, but the low impact toughness has been a major disadvantage of this composite. Most studies are focused on fiber modification or adding coupling agents to overcome this problem, but few of them paid attention to the microstructure of the matrix and its effect on the interface adhesion. Isotactic polypropylene (PP) is polymorphic with different morphological forms: α-, β- and γ-forms. α-PP is predominated form, while β-PP has received considerable attention due to its promising toughness behavior. This study investigated the effect of adding a highly active β-nucleating agent (TMB) for PP on the mechanical and crystallization properties of PP/WF composite. Specifically, the impact strength, the nucleating effect, content of β-crystal, non-isothermal crystallization behavior and mechanical properties of the composite were investigated. Results showed that the content of the β-form crystal of nucleated PP (K value) reached 87% with the addition of 0.3 wt% TMB. Composites with TMB increased the crystallization peak temperature, accelerated the crystallization process and improved its impact strength by 53.12% with the addition of 0.3 wt% TMB nucleating agent, though tensile and flexural properties were dropped by about 10–20%. Also, the spherulite size of nucleated PP in the composite was dramatically decreased.

Computational alloy design of (Co1-xNix)88Zr7B4Cu1 nanocomposite soft magnets

The dependence of coercivity on composition is an important factor for establishing optimized soft magnetic properties. In this study, we have used the random anisotropy and coherent rotation models to estimate the variation of coercivity with composition in (Co1-xNix)88Zr7B4Cu1 nanocomposite alloys. Our calculations that the magnetoelastic anisotropy contribution to coercivity dominates for Ni rich compositions (x > 0.5). A small range of compositions (0.65 < x < 0.75) is predicted to result in low values of coercivity (<10 A/m). To validate this prediction, (Co1-xNix)88Zr7B4Cu1 nanocomposites in this range were prepared by melt spinning followed by 3600 s isothermal annealing at the primary crystallization peak temperature (∼673 K). Hysteresis loops were measured using vibrating sample magnetometry at room temperature and saturation magnetostriction was measured using a strain gage based magnetostrictometer. Moderately small coercivities (30-40 A/m) and magnetostrictions (3-4 ppm) were measured at for samples with 0.685 < x < 0.725. Our measured coercivity had a minimum value of 32 A/m at x = 0.725, a shift in composition of about 5 at% in the direction of higher Ni content and without the anticipated low value of coercivity. Several reasons for the inaccuracy of this approach are described, including: ignored contributions from amorphous phase (especially in magnetoealstic anisotropy), composition segregation during crystallization leading to unpredictable compositional shifts in prediction, and the general observation that the predictability of minimum coercivity from minimal combined anisotropies has unexplained deviation even in far less complicated materials.

Studies on Se75Te25–xInx chalcogenide glasses; a material for phase change memory

This research paper describes the non-isothermal crystallization during phase transformation in Se75Te25–xInx glasses synthesized by melt quenching method. For crystallization studies in these glasses, non-isothermal differential scanning calorimetry (DSC) measurements was done at constant heating rates of 5, 10, 15, 20 and 25 K min−1 in air atmosphere. The glass transition temperature (Tg), on-set crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperatures (Tm) were derived by DSC thermograms. Using various thermal parameters the activation energy of glass transition and crystallization were determined by using Kissinger, Moynihan and Ozawa approaches and found to be in good agreement. The value of the activation energy of glass transition (ΔEt) was found to be minimum for Se75Te19In6 alloys confirming its maximum probability of transition in a metastable state. Thermal stability parameters of Se75Te25–xInx were determined and found to be increased with indium content. High resolution x-ray diffraction and field emission scanning electron microscopy studies were employed for the study of phase transformation in Se75Te25–xInx glasses. The outcome of these studies shows that the investigated materials may be suitable for phase change memory devices.

Non-isothermal crystallization of lithium germanophosphate glass studied by different kinetic methods

Crystallization kinetics of 22.5Li2O?10Al2O3?30GeO2?37.5P2O5 (mol%) glass was studied under non-isothermal condition using the differential thermal analysis (DTA). The study was performed by using the first crystallization peak temperature (Tp1) which belongs to the precipitation of LiGe2(PO4)3 phase in the glass. The activation energy of glass crystallization (Ea) was determined using different isokinetic methods. The dependence of Ea on the degree of glass-crystal transformation (?) was studied using model-free isoconversional linear integral KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. It was shown that the Ea varies with ? and hence with temperature and consequently the glass/crystal transformation can be described as a complex process involving different mechanisms of nucleation and growth.

Thermal stability and crystallization kinetics of Bi doped Si15Te85-xBix (0 ≤ x ≤ 2) chalcogenide glassy alloys

Bulk Si15Te85-xBix (0 ≤ x ≤ 2) chalcogenide glassy alloys were prepared by well-established melt quenching technique. Thermal stability and crystallization kinetics of these alloys were investigated by employing differential scanning calorimetry (DSC) technique at different heating rates, namely, 10, 15, 20 and 25 K/min under non-isothermal condition. Thermal parameters such as glass transition (Tg), onset crystallization (Tc) and peak crystallization (Tp) temperatures were observed. Double crystallization peaks observed in the DSC thermogram refer to the instability and phase separated network in the glasses. Various kinetic parameters such as thermal stability (ΔT), enthalpy (ΔHc), entropy (ΔS), specific heat (ΔCp) and fragility index are deduced. The calculated kinetic parameters suggest that the stability of glassy samples decreases with the increase in Bi addition. The activation energies of glass transition (Eg), and crystallization (Ec) are calculated using relevant kinetic formulae. We further discuss on the kinetics of the synthesized materials relevant for their applications in phase change memory (PCM) material

Control of self-powdering phenomenon in ferroelastic β′-Gd2(MoO4)3 crystallization in boro-tellurite glasses

Glasses with compositions of 21Gd2O3-63MoO3-(16-x)B2O3-xTeO2 (mol%) (x=0, 2, 4, 8) were prepared using a conventional melt quenching technique, and the crystallization behavior of ferroelastic β′-Gd2(MoO4)3 crystals was examined to clarify the mechanism of self-powdering phenomenon and to design bulk crystallized glasses. It was found that the self-powdering phenomenon appeared significantly during the crystallization at temperatures near the crystallization peak temperature, but the phenomenon is suppressed in the crystallization at temperatures much higher than the glass transition temperature. It was also found that the substitution of TeO2 for B2O3 in the base glasses suppresses the self-powdering phenomenon and consequently bulk crystallized glasses were obtained in the glass with x=8mol%. The densities at room temperature of the base glasses are d=4.755–4.906g/cm3, being much higher than the value of d=4.555g/cm3 for β′-Gd2(MoO4)3 crystal. It is proposed that the stresses in the inside of crystals induced by large density differences (i.e., large molar volume differences) between the glassy phase and crystals might be relaxed effectively in the glasses containing TeO2 with weak TeO bonds and fragile character.

Physical properties of pseudo quaternary Na2B4O7 – SiO2 – MoO3 – Dy2O3 glasses

Pseudo quaternary Na2B4O7–SiO2–MoO3–Dy2O3 glasses with various concentrations of Dy2O3 were synthesized and characterized by ultrasound, DTA and X-ray diffraction (XRD). It was found that, the density, the molar volume and the elastic moduli increased while the ultrasonic velocities and the packing density decreased with increasing of Dy2O3 concentration. The lower values of the radii and the bond length of B2O3, compared to those of Dy2O3, decreased the interatomic forces between the reactant glass forming cations and oxygens inside the glassy network. Accordingly, this will increase the molar volume and in the same time will decrease the average cross-link density, the ultrasonic velocities, the glass transition temperature and the thermal stability. Also, this may result in a high density glass sample which will increase the elastic moduli. Based on Lasocka's model, a good correlation between the temperature of both glass transition (Tgl) and crystallization peak (Tpc)was observed.

Crystallization kinetics and phase transformation studies on glassy Se85In15-xSbx system

Our aim in the present research work is to investigate the crystallization kinetics and phase transformation studies in Se85In15-xSbx semiconductor. DSC measurements were done at constant heating rates of 5, 10, 15, 20 and 25 K/min for Se85In15-xSbx alloys. The glass transition (Tg), on-set crystallization (Tc) and peak crystallization (Tp) temperature were found to be increases with heating rate for all samples. The activation energy for glass transition (ΔEg) and crystallization (ΔEc) were calculated by different approaches and found to be nearly identical. Thin films of Se85In15-xSbx alloys were prepared by the thermal evaporation technique and the effect of thermal annealing on optical properties were discussed by means of optical absorption measurements. The optical band gaps were found to decrease with annealing temperature. This decrease in optical band gap can be associated with phase change in Se85In15-xSbx alloys from amorphous to crystalline phase.

Effect of Hf addition on the glass forming ability, thermal and magnetic properties in the (Fe86B13Cu1)100 − xHfx alloys

In this study, the effect of Hf addition on the glass formation ability (GFA), micro structural, thermal and magnetic properties were investigated in the Fe-B-Cu alloy with high saturation magnetization (Ms). It is found that the addition of Hf is beneficial for improving GFA of (Fe86B13Cu1)100−xHfx Alloys. The melt-spun ribbons at x=0.75 and x=1.0 show an entirely amorphous structure by x-ray diffraction and have two obvious separated exothermic peaks on DSC curves, Hf element plays a positive role on postponing the first crystallization and improved the thermal stability of the amorphous Fe-B-Cu-Hf alloys. As x=0.75, the melt-spun ribbon has a higher apparent activation energy of Fe3B phase than of the ribbon at x=1.0, and the first crystallization is easier than the second crystallization. Therefore it was easy to obtain an α-Fe/amorphous dual phases structure alloy ribbons with few or without Fe3B phase by a suitable annealing process near peak temperature of the first crystallization. After annealing, the saturation magnetization (Ms) was tested by vibrating sample magnetometer, and the value of x=0.75 changes slightly first, then increase obviously and reach the maximum 220emu/g at 750K higher Tp2. This alloy shows a good glass forming ability and a high saturation magnetization.

Effect of Sorbitol Plasticizer on the Structure and Properties of Melt Processed Polyvinyl Alcohol Films.

Poly (vinyl alcohol) (PVA) possesses wide applications as food packaging materials, but is difficult to melt process for its strong inter/intra hydrogen bonding. In this work, flexible PVA films with different content of sorbitol plasticizers were prepared by melt processing with the assistance of water. And the influence of sorbitol plasticizer content on the crystallinity, optical transparency, water-retaining capability, mechanical properties, thermal stability and oxygen and water permeability were investigated. The results indicated that sorbitol dramatically improved the melt processing ability of PVA. Sorbitol could interact with PVA to form strong hydrogen bonding interactions, which would decrease the original hydrogen bonding of the matrix, resulting in the decrease of crystallinity degrees. The glass transition, melting and crystallization peak temperatures decreased with the increase of sorbitol. All the films exhibited fine optical transparency. The water retaining capability were improved with the increase of sorbitol. Especially, an increase in elongation at break and decrease in Young's modulus and tensile strength were observed indicating good plasticizing effect of sorbitol on PVA films. In addition, the PVA films prepared in this work exhibited fine barrier properties against oxygen and water, suggesting wide application potential as packaging materials.

Supernucleation and Orientation of Poly(butylene terephthalate) Crystals in Nanocomposites Containing Highly Reduced Graphene Oxide.

The ring-opening polymerization of cyclic butylene terephthalate into poly(butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a supernucleating effect caused by RGO, which is maximized by highly reduced graphene oxide. Furthermore, combined analyses by differential scanning calorimetry (DSC) experiments and wide-angle X-ray diffraction (WAXS) showed the formation of a thick α-crystalline form pCBT lamellae with a melting point of ∼250 °C, close to the equilibrium melting temperature of pCBT. WAXS also demonstrated the pair orientation of pCBT crystals with RGO nanoflakes, indicating a strong interfacial interaction between the aromatic rings of pCBT and RGO planes, especially with highly reduced graphene oxide.

An in-depth study on crystallization kinetics of PET/PLA blends

The crystallization behavior and mechanical properties of PET/PLA blends with various amounts of PLA were investigated using a wide angle X-ray diffraction (WAXD), differential scanning calorimeter (DSC) and tensile analyses. The crystallization rate and relative crystallinity of the PET/PLA blends were studied by theoretical models of Kissinger, Avrami, Ziabicki and Ozawa. The WAXD analysis showed that the PLA phase was wholly amorphous in all blends after cooling from the melt to ambient temperature. Crystallization behavior assessments on PET/PLA blends suggest that PLA acts as a nucleating agent for PET phase leading to an increase in the initial and peak crystallization temperatures. Kissinger’s model showed a rise in activation energy up to 72% for the PET/PLA blends containing 30 wt% PLA. Ziabicki’s model gave a minimum value for kinetic parameter in PET/PLA (70/30 w/w) due to the nucleating action of PLA. On the other hand, PLA acted as a retarder for chain segments of PET tending to diffuse through the surface of growing crystals. Therefore, at an optimal composition of PET/PLA, crystallization occurs appropriately. However, an increase in PET content leads to fall in ductility, tensile strength, modulus, elongation-at-break, and fracture toughness of PET/PLA blends.

Thermal analysis of cadmium addition on the glass transition and crystallization kinetics of Se–Te–Sn glassy network

Calorimetric measurements have been performed in quaternary glassy system Se78−xTe20Sn2Cdx (x = 0, 2, 4, and 6) to study the thermally induced glass transition and crystallization phenomena. The characteristics kinetic temperatures (glass transition temperature $$T_{\text{g}}$$ , onset crystallization temperature $$T_{\text{o}}$$ , peak crystallization temperature $$T_{\text{c}}$$ ) and static melting temperature $$T_{\text{m}}$$ of the quaternary glassy series have been determined using their non-isothermal DSC curves. These temperatures were utilized to calculate the thermal stability $$S$$ and the Hruby parameter $$H_{\text{R}}$$ for the studied glasses. Both the activation energy of glass transition $$E_{\text{t}}$$ and the activation energy of crystallization $$E_{\text{c}}$$ for all compositions were evaluated using the well-known Kissinger's relation and the method of Augis–Bennett. Values of the fragility index $$m$$ and the crystallization rate factor $$K_{\text{p}}$$ were estimated using the activation energy values $$E_{\text{t}}$$ and $$E_{\text{c}}$$ , respectively. The compositional dependence of the above-mentioned parameters was discussed on the basis of rigidity models and according to the formation of iono-covalent bonds when our glassy Se–Te–Sn system is doped with a heavy element as Cd.

Unique crystallization behavior of isotactic polypropylene in the presence of l‐isoleucine and its inhibition and promotion mechanism of nucleation

ABSTRACTl‐Isoleucine (l‐Ile) was identified as an efficient anti‐nucleating agent for isotactic polypropylene (iPP). At 0.08 wt %, l‐Ile could significantly decrease the peak crystallization temperature (Tcp) of iPP by up to 8 °C at a cooling rate of 20 °C/min. Furthermore, l‐Ile exhibited both anti‐nucleation and pro‐nucleation abilities; i.e., a low content of l‐Ile inhibited iPP crystallization, whereas a high content promoted iPP crystallization. The unique crystallization behavior of iPP in the presence of l‐Ile was investigated by differential scanning calorimetry, polarized optical microscopy (POM), and rheological measurement. According to POM, a low content of l‐Ile completely dissolved in the iPP melt, whereas a high content of l‐Ile did not. Therefore, a mechanism by which l‐Ile inhibits and promotes the nucleation of iPP was proposed. Dissolving l‐Ile molecules in the iPP melt hindered the homogeneous nucleation of iPP as a “dilution effect”; however, as the content increases, l‐Ile could not be completely dissolved in molten iPP, and the residual crystals of l‐Ile thus provided heterogeneous nucleation sites for iPP and further promoted its crystallization. Experimental evidence from rheology and POM supported this mechanism. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45956.

Enhanced crystallization kinetics of symmetric poly(l-lactide)/poly(d-lactide) stereocomplex in the presence of nanocrystalline cellulose

In this work, poly(l-lactide)/poly(d-lactide)/nanocrystalline cellulose (PLLA/PDLA/NCC) stereocomplex blends were prepared using a solution blending method. The effect of NCC on the crystallization kinetics of symmetric PLLA/PDLA blend was systematically investigated. The incorporation of NCC significantly enhanced the formation of stereocomplex crystal (sc), as indicated by increasing the crystallization peak temperature and crystallinity of sc from approx. 143 °C and 24% to around 160 °C and 40%, respectively, during the non-isothermal crystallizing upon cooling at 10 °C/min. Meanwhile, the addition of NCC caused no influence on the crystal morphology and crystal form of sc in the PLLA/PDLA blend, as evidenced by the POM and WAXD results. The crystallization kinetics of the PLLA/PDLA/NCC blends was studied in detail by using the Dobreva and Gutzow model, the Avrami-Jeziorny equation and the well-known Avrami model. It was found that NCC showed high nucleating activity in the PLLA/PDLA blend. The half-life time of crystallization of the PLLA/PDLA blend was decreased by ca. 78% at 180 °C after the addition of 0.5 wt% NCC. In addition, POM tests showed that the nuclei density in the PLLA/PDLA blend during isothermally crystallizing at 180 °C was largely increased by the addition of NCC.

Regulating performance of poly(L-lactic acid) by Addition of N, N′-Bis(Salicyloyl) p-phthalic acid dihydrazide

Within this work, the influence of a crystallization accelerator N, N′-bis(salicyloyl) p-phthalic acid dihydrazide (PAS) on the non-isothermal crystallization behavior, melting behavior, thermal stability, and light transmittance of poly(L-lactic acid) (PLLA) was investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), thermogravimetric analysis (TGA), and light transmittance meter. Comparative analysis of the non-isothermal crystallization behavior of the primary PLLA and PLLA/PAS samples revealed an important role of PAS in promoting the crystallization of PLLA in cooling. Additionally, the concentration of PAS and cooling rate also exhibited significant effect on the non-isothermal crystallization process, and the 3 wt% PAS causes the PLLA to have the highest the onset crystallization temperature and the crystallization peak temperature, and the largest non-isothermal crystallization enthalpy. However, the increase of cooling rate resulted in the decrease of crystal growth ability, weakening the crystallization of PLLA. The investigating on the melting behavior under different conditions further confirmed the crystallization promoting effect of PAS for PLLA, and the crystallization temperature, resulting from the different crystal growth rate, affected remarkably the melting behavior of PLLA/3%PAS sample. The addition of PAS could not change the thermal decomposition behavior of the primary PLLA, but decreased the onset decomposition temperature with an increase of PAS concentration in PLLA matrix. Similarly, the incorporation of PAS is unfavourable to the light transmittance of the primary PLLA.

Effect of Thermoplastic Polyurethane-Modified Silica on Melt-Blended Poly(Lactic Acid) (PLA) Nanocomposites

3-aminopropyltriethoxysilane (APTES) was used as a coupling agent to graft thermoplastic polyurethane (TPU) onto a nanosilica surface. The modification of TPU on the surface of silica nanoparticles was confirmed by FTIR, NMR, ESCA and TGA assessment. The grafting degree of TPU onto the silica was about 7.3%. The incorporation of surface-modified silica (TAS50) into poly(lactic acid) (PLA) induced the nucleation of PLA, giving a higher crystallisation peak temperature, which would be advantageous for fast processing cycles in the commercial moulding process. With pristine silica incorporated into PLA, the variation in the cold crystallisation and melting temperatures was limited. However, for the surface-modified silica filled PLA, a lower cold crystallisation temperature at 112.1 °C and a shift of melting temperature from Tm1 to Tm2 at 167.7 °C were observed. The cooling rate also played an essential role in the derived crystalline forms. The tensile strength of the composite containing modified silica was slightly higher than that with the pristine silica, even though both showed similar degrees of silica dispersion from the morphology observation. For the surface-modified silica composite, the optical transmittance was higher than that of unmodified silica case. This finding implies the significance of the surface modification.

Effect of Si addition on crystallization behavior, thermal ability and magnetic properties in high Fe content Fe-Si-B-P-Cu-C alloy

Dependence on the crystallization behavior, thermal ability and soft magnetic properties of the Fe84.7SixB10.5-xP4Cu0.5C0.3 (x=0–2.0at.%) alloys with high Fe content were investigated. The results show that the addition of minor Si significantly weakens the crystallization peaks and increases the amorphous forming ability of the alloys. With the increase of Si content, it improves the second crystallization peak temperature and greatly enlarges the temperature interval between the two crystallization peaks, which broadens the annealing range. When Si content is up to 1.5at.%, the alloy can effectively inhibit the precipitation of Fe-B compounds during the process of annealing. The addition of Si contributes to the formation of stable nano-structure, leading to a good soft magnetic properties for the amorphous alloy. Through the optimum annealing treatments, the nanocrystalline alloy exhibits the high Ms of 206.5emu/g (Bs≈1.92T) and low Hc of 12.5A/m.

Enhanced crystallization rate of biodegradable poly(ε-caprolactone) by cyanuric acid as an efficient nucleating agent

The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(e-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.

Effects of Process Temperatures on the Flow-Induced Crystallization of Isotactic Polypropylene/Poly(ethylene terephthalate) Blends in Microinjection Molding

In this work, the effects of mold and melt temperatures on microstructures and properties of micropart were systematically investigated. Results showed that the remarkably enhanced flow field generated during microinjection molding process proved to be beneficial in forming highly oriented self-fibrillating structures. In addition, especially in blends, changing the process temperatures from 200 °C to 270 °C significantly enhanced the onset crystallization temperature To (Δt = 4.8 °C), peak crystallization temperature (Δt = 1.5 °C), and the crystallization half-time (∼18.6 s). Interestingly, because of the orientation maintenance and shear amplification effects of in situ poly(ethylene terephthalate) (PET) microfibrils, the branching of lamella and the formation of hybrid-oriented structures (fan-shaped β-crystals and trans-crystals) were accelerated. Furthermore, relative content of the β crystal (increments of ∼14.1%) and the degree of orientation were also significantly improved as the process temperat...