Isothermal Crystallization Process Research Articles

Effect of Tm of blend components on the isothermal melt-crystallization process of PHB/PLLA blends investigated using spectroscopic imaging and DSC

The understanding of morphology and crystallization in biopolymer blends offers the ability to tune these properties for specific uses. In this study, the isothermal melt-crystallization process of poly (3-hydroxybutyrate) (PHB)/poly ( l -lactic acid) (PLLA) blends with different weight loadings and molecular weights was investigated using in-situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopic imaging and differential scanning calorimetry (DSC). When the isothermal crystallization temperature is constant, increasing the fraction of blend component with a lower T m results in the decreasing T m of both blend components, which is indicated in DSC thermograms. The reduced T m delays the crystallization of both blend components and then the restrained crystallization leads to a greater extent of phase separation, which is shown in ATR-FTIR spectroscopic images. Likewise, at a constant isothermal crystallization temperature, with the decreasing molecular weights of blend components, the miscibility of polymer blend should be enhanced because of the shift of the phase boundary in phase diagram to lower temperatures. However, the decreasing overall crystallization rate and the delay of crystallization indicated in the integrated absorbance profiles and the decreasing T m indicated in the DSC thermograms can be used to explain the greater extent of phase separation in the PHB/PLLA blend shown in the spectroscopic images. A phase diagram was prepared to show the effect of polymer molecular weight on the miscibility of PHB/PLLA blends. Thus, increasing the fraction of the blend component with a higher T m , choosing polymers with a higher molecular weight and decreasing the isothermal crystallization temperature have been demonstrated to be effective methods to promote the miscibility of upper critical solution temperature (UCST) crystallizable polymer blends. Moreover, it was concluded that in-situ ATR-FTIR spectroscopic imaging can be combined with integrated absorbance profiles and DSC thermograms to deepen the understanding of multicomponent polymer systems. • A phase diagram was prepared to show the effect of M w on the miscibility of PHB/PLLA blends. • Effective methods are found to promote the miscibility of UCST polymer blends during isothermal crystallization process. • Spectroscopic imaging can be combined with DSC thermograms to deepen the understanding of multicomponent polymer systems.

Melt and nucleation reinforcement for stereocomplex crystallites in poly(ʟ-lactide)/lignin-grafted-poly(ᴅ-lactide) blend

Lignin-grafted-poly (ᴅ-lactide) (LGPD) with two different poly (ᴅ-lactide) (PDLA) block lengths (1100 and 2000 Da), denoted as LGPDL and LGPDH respectively, were synthesized by ring opening polymerization using dodecylated lignin as initiator. They were then blended with poly(ʟ-lactide) (PLLA) to improve its crystallization, mechanical properties and UV-absorbance properties. It was found that stereocomplex (SC) crystallites could be formed in both PLLA/LGPD blends, and the crystallization rate of PLLA/LGPDH was faster than that of PLLA/LGPDL because of the longer PDLA block length. Both in the non-isothermal and isothermal crystallization process, the crystallization of PLLA in the PLLA/LGPDH blend was the fastest when the ratio of LGPDH was 3%. SC crystallites in the PLLA/LGPDH blends also showed broader melting ranges and higher final melting temperatures comparing to the blends of PLLA and 4-armed PDLA (4a-PDLA), whose number of PDLA arms and molecular weight was similar to LGPDH. These results proved that the lignin structure grafted by the PDLA arms could affect the state of SC crystallites and their acceleration effect on the crystallization of PLLA in the blend. The degradation behavior showed that the degradation rate of the LGPDH-5% blend in the final stage of degradation (about 24 h) was the slowest comparing to other blends. Besides, the PLLA/LGPD blends had better tensile strength and UV-absorbance properties than neat PLLA.

Crystallization mechanism of micro flake Cu particle-filled poly(ethylene glycol) composites

Poly(ethylene glycol) (PEG) is used as phase change materials while the low thermal conductivity restricted the thermal storage efficiency. Incorporation of the metal particles (MPs) into PEG could enhance the thermal conductivity while the crystallization kinetic mechanism of the MP-filled PEG composites is altered. Flake MPs are characterized with layer structure and a large aspect ratio, while there are few research works related to the effect of flake MPs on the crystallization kinetic mechanism of flake MP-filled polymer composites. In this work, different micro flake copper (Cu) particles contents were introduced into the PEG matrix via the physical blending method. The Fourier transform infrared instrument (FT-IR) was used to characterize the chemical compatibility of the PEG/Cu composites. The differential scanning calorimetry (DSC) method was to characterize the crystalline kinetic mechanism of the micro flake Cu particle-filled polymer composites by using the isothermal model and non-isothermal model. It was found that the COC conformation of the confined PEG in the composites was altered, and more helical conformations were transferred from the zigzag conformations. The addition of the Cu particles in the PEG matrix enhanced the heterogeneous nucleation meantime hindered the diffusion of the PEG molecular chains. As a result, the crystallization rate of the PEG/Cu composites was optimized only when there was a middle Cu content in the PEG matrix (14.89 wt% in this work). Additionally, the PEG/Cu composites had 3D PEG crystal growth geometry in the isothermal crystallization process while the stronger dependence of the PEG crystal growth geometry on the temperature was found in the non-isothermal crystallization especially when the Cu amount was higher than 14.89 wt%.

Significantly Enhanced Crystallization of Poly(ethylene succinate-co-1,2-propylene succinate) by Cellulose Nanocrystals as an Efficient Nucleating Agent.

Poly(ethylene succinate-co-1,2-propylene succinate) (PEPS) is a novel aliphatic biodegradable polyester with good mechanical properties. Due to the presence of methyl as a side group, the crystallization rate of PEPS is remarkably slower than that of the poly(ethylene succinate) homopolymer. To promote the potential application of PEPS, the effect of cellulose nanocrystals (CNC) on the crystallization behavior, crystalline morphology, and crystal structure of PEPS was investigated in this research with the aim of increasing the crystallization rate. CNC enhanced both the melt crystallization behavior of PEPS during the cooling process and the overall crystallization rate during the isothermal crystallization process. The crystallization rate of PEPS became faster with an increase in CNC content. The crystalline morphology study directly confirmed the heterogeneous nucleating agent role of CNC. The crystal structure of PEPS remained unchanged in the composites. On the basis of the interfacial energy, the nucleation mechanism of PEPS in the composites was further discussed by taking into consideration the induction of CNC.

Molecular dynamics simulation for polyethylene crystallization: Effect of long chain branches

The influence of long branches on crystallization behavior has been studied by means of molecular dynamics simulations. Using two systems: polyethylene (PE) with long branches (LCB-PE) and PE without long branches (linear-PE) with the same molecular weight, we have examined the crystallization behavior of the two systems by molecular dynamics simulation. This paper explains the influence of long branches on the isothermal crystallization process and the non-isothermal crystallization process with similar initial interchain contact fraction (ICF) in terms of final ICF, crystal regions, crystallinity, concentration of tie chains and energy. It is found that the crystallization process is classified as two stages: the nucleation stage and the crystal growth stage. The existence of long branches is favorable for the first stage while unfavorable for the second stage. Knots that act as crystalline defects are excluded from the lamella, resulting in decreasing in regularity and crystallinity of molecular chains. From the perspective of potential energy and non-bond energy, LCB-PE has lower energy than linear-PE in the nucleation stage while the energy of linear-PE is lower than that of LCB-PE in the second stage. In short, the long branched chains inhibit the crystallization process.

Features of isothermal crystallization of ammonium sulphate

Soil fertility is rapidly decreasing due to irrational land use, erosion and soil pollution and adverse weather conditions. The use of composite granular organic-mineral fertilizers that contain mineral and organic components allows the soil fertility to be increased in the most effective and safe manner for the environment. In the production of granular composite fertilizers in a fluidized bed granulator, the process of isothermal mass crystallization is the main parameter that affects the quality.
 The effect of impurities on the morphological structure of ammonium sulfate microcrystals during mass crystallization on the surface was investigated by means of microscopic analysis. The influence of temperature and pH of the solution on the structure and shape of the microcrystal layer was studied.
 The process of mass crystallization depends on the presence of impurities, pH and temperature. Given the fact that there is no analytical or theoretical dependence describing the influence of impurities on the morphological structure, the influence is determined experimentally. The presence of even a small content of surfactants and other impurities in the ammonium sulfate solution has a significant effect on the morphological structure of ammonium sulfate microcrystals, which is revealed as reduction in the concentration of impurities in ammonium sulfate obtained by coke-chemical method. The pH level of the medium affects the structure and shape of microcrystals: smaller crystals with a layered structure are formed in the case of weakly alkaline medium with pH = 8 and smaller microcrystals with a granular structure are formed in the case of pH = 4. Therefore, it is important to maintain the required pH level of the medium during the mass crystallization of ammonium sulfate.
 In isothermal mass crystallization of saturated aqueous solutions of ammonium sulfate with humic compounds and bone meal proceeding on a surface with temperature 90 °C, small elongated crystals with microcrystal sizes from 10 to 100 μm are formed. Impurities of bone meal and humic compounds in the form of inclusions are placed between the crystals of ammonium sulfate: namely, the endosegregation of impurities in the microcrystalline framework is observed. As the concentration of organic matter in the solution increases, which crystallizes as droplets on the surface, rubble and dendrites are formed outside the initial droplet placement. This phenomenon is explained by the increase of diffusion resistance at the center of the drop; as a result, ammonium sulfate crystallizes in the zone with lower resistance.
 The process of isothermal mass crystallization of saturated aqueous solutions of ammonium sulfate with admixtures of humic compounds, bone meal and other target components in the specified ratios will create new highly effective fertilizers. The obtained results allow formulating theoretical bases for the formation of solid structures based on ammonium sulfate with admixtures of organic and mineral components.

Tuning isothermal crystallization kinetics by minor similar solute element substitution in novel La‐(AlGa)‐C metallic glasses

AbstractIn the present text, the effects of minor similar solute element Ga substitution for Al on the isothermal crystallization kinetics of novel light RE‐based La‐(AlGa)‐C metallic glasses (MGs) were systematically investigated between La60Al26Ga4C10 MG and the precursor La60Al30C10 MG by using phase analysis, Johnson–Mehl–Avrami and Arrhenius using x‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The incubation period, the accomplishment time of the whole process, and the diversity of both the precipitated phases and the varying trend of the local Avrami exponent are elevated by minor similar solute element Ga substitution for Al, respectively. Additionally, the Avrami exponent of different isothermal crystallization temperature changes from g n > 2.5 to a combination of values 1.5 < n < 2.5 and a value n > 2.5 given by minor similar solute element Ga substitution for Al, corresponding to the crystallization characteristics changing from crystallization with promoting nucleation rate to a combination of crystallization with a reducing nucleation rate and crystallization with promoting nucleation rate. Moreover, the isothermal crystallization process becomes more difficult after minor similar solute element Ga substitution for Al, due to the reduced Avrami exponent and the intensified local activation energy.

Crystallization kinetics, crystalline structures and properties of PB/PP blends regulated by poly(butene-block-propylene) copolymers

Blending isotactic polybutene-1 (PB) with isotactic polypropylene (PP) is a facial strategy to improve the mechanical properties and promote polymorphous transformation of PB. As the immiscible polymer pairs with strong crystallizability, the interactions between PP and PB in the melt state influence the subsequent processes like phase separation and crystallization, and then determine the crystalline structures and properties of the blends. Herein, two kinds of poly(butene-block-propylene) (PB-b-PP) copolymers with different sequence structures fractionated from PB/PP in-reactor alloy using temperature rising elution fractionation were utilized to compatibilize the PB/PP (80/20) blend. The phase morphologies, crystallization kinetics of PP and PB phases, and crystalline structures in PB/PP/PB-b-PP blends were characterized by phase contrast optical microscopy (PCOM), differential scanning calorimeter (DSC), and small-angle X-ray scattering (SAXS). The PB-b-PP copolymer with longer PP blocks (A) showed more satisfied compatibilization for PB/PP blends and PB/PP/PB-b-PP-2.5 blend with 2.5 wt% copolymer as compatibilizer exhibited the most stable phase morphology with the smallest PP domains in melt state at 200 °C. During isothermal crystallization processes of the PB/PP/PB-b-PP blends at 135 °C for PP crystallization and then 90 °C for PB crystallization, the crystallization rate including nucleation rate and nucleation density, and crystallinity of PP and PB (form II) increased, and achieved the largest when the copolymer concentration was 2.5 wt% in PB/PP/PB-b-PP blend. The copolymer A significantly accelerated crystallization rate of PP compared with that of copolymer B. The PB/PP/A-2.5 blend with the largest lamellae thickness and highest crystallinity of PB form I, combined with the smallest spherulites, exhibited the highest modulus, tensile strength and toughness. The compatibilizing mechanism and roles of PB-b-PP copolymers for PB/PP blends were discussed to understand the physical and mechanical behaviors of the blends.

Production of Potash and N‐Mg Compound Fertilizer via Mineral Shoenite from Kunteyi Salt Lake: Phase Diagrams of Quaternary System (NH4)2SO4‐MgSO4‐K2SO4‐H2O in the Isothermal Evaporation and Crystallization Process

AbstractBased on the requirement of the new technology for producing potassium sulfate and N‐Mg compound fertilizer, boussingaultite, by the reaction of the mineral shoenite from Kunteyi Salt Lake, Qinghai province, and the industrial byproduct ammonium sulfate, the solubilities of the quaternary system (NH4)2SO4‐MgSO4‐K2SO4‐H2O at 25.0°C in the isothermal evaporation and crystallization process were measured using the isothermal evaporation method, and the corresponding phase diagrams were plotted. According to the diagram, this system contains six saturation points and six solid phase fields of crystallization, which correspond to (K1‐m,(NH4)m)2SO4, (NH4)2SO4·MgSO4·6H2O, K2SO4·MgSO4·6H2O, MgSO4·6H2O, (K1‐n,(NH4)n)2SO4·MgSO4·6H2O and MgSO4·7H2O, respectively. By analyzing and calculating the isothermal evaporation and dissolution phase diagram of this quaternary system at 25.0°C, K2SO4 and (NH4) 2SO4·MgSO4·6H2O can be separated via K2SO4·MgSO4·6H2O and (NH4)2SO4 as raw materials. Theoretical calculations about the proposed process were carried out and verified by experiment, which indicated that the yield of potassium sulfate was improved and the magnesium resources were fully utilized.

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).

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 1 – Crystallization kinetics and crystal growth

The initial stage processes of nucleation and growth of crystalline phases in Co-based amorphous microwires in a glass shell were studied by processing kinetic curves using various theoretical models. The results of X-ray diffraction for research of the microstructure evolution at Synchrotron Radiation Source and High Resolution Transmission Electron Microscopy were considered. The study of the crystallization process kinetics was carried out by a non-conventional method, in particular based on data of sample magnetization changes over time and with temperature at a unique in situ vibromagnetometer. The analysis of the kinetic curves for isothermal and non-isothermal crystallization process led to the similar conclusions and made it possible to establish the values of the Avrami exponent for the initial stage of surface and bulk crystallization, to establish the dimensionality of crystal growth, and to conclude that there was no nucleation in the process of crystal growth. Based on the analysis of kinetic curves by three methods, the activation energy of the primary crystallization process was determined, its high value is associated with the presence of chromium in the alloy, which determines its nanocrystallization. The microstructure and shape of crystals were analyzed.

Study on crystallization behavior of Tibet butter

Tibetan butter (TB), generally called butter, is a solid oil product extracted from yak milk in the Qinghai-Tibet plateau area. However, due to the limitations of raw material sources and production technology, there is a shortage of TB, so it is important to find substitutes of TB. This paper studied the crystallization behavior of six kinds of commercial TB products in Tibet to provide the theoretical basis for the development of TB substitutes for the production of TB lamps and flowers. This study assessed the crystallization behaviors of the TB samples, including isothermal crystallization process and non-isothermal crystallization process. The microstructure, isothermal crystallization of TB were evaluated by polarized light microscopy and low-pulse NMR spectrometry, respectively. The non-isothermal crystallization process of TB under temperature scanning were investigated using Rheometer, and the crystallization behavior under different cooling rates were determined by differential scanning calorimetry (DSC) procedures. The results showed that the TB was crystallized at a higher supercooling (−10, 0 and 10 °C). Dimensional growth is dominant; at 20 °C, spiral growth dominates. The TB has complex crystallization nucleation behavior. The crystal types of TB are mainly β '-crystal form and β '-like crystal form. The lower the cooling rate, the shorter the crystallization induction time, and the more the number of crystal nuclei. Therefore, during producing TB substitutes in the factory, the cooling rate can be controlled at 10 °C/min to reduce energy consumption and production costs.

Effect of rare earth oxide on the crystallization behavior of CaO-Al2O3-based mold flux for rare earth heat-resistant steel continuous casting

New CaO-Al2O3-based mold flux for rare earth steel continuous casting was devised to restrain the slag-steel interface reaction. The effect of Ce2O3 on the crystallization behavior were investigated. The continuous cooling transformation tests show that the addition of Ce2O3 not only reduces the critical cooling rate of the mold flux but also reduces the initial crystallization temperature. Besides, the distribution of the initial crystallization temperature became more stable. The temperature time transformation tests show that the crystallization incubation time is slightly increased, the addition of Ce2O3 inhibit the isothermal crystallization process to a certain extent. The crystalline phases changed from LiAlO2+CaO to LiAlO2+CaCeAlO4. The precipitation of CaO was restrained by adding Ce2O3. With the combination of Ca2+, Ce3+, and [AlO69−]-octahedron units, CaCeAlO4 formed and precipitated in the crystallization process. Besides inhibiting the crystallization of CaO-Al2O3-based mold flux, adding rare earth oxide also can reduce the viscosity and the breaking temperature.

Thermal degradation and isothermal crystallization behavior of curdlan propionate and its melt-spinning fiber

The thermal properties and crystallization kinetics of Curdlan propionate, a type of bio-based plastic and β-1,3-glucan derivative, were investigated. Melt-spun fibers were also prepared, and the fiber formation mechanism and internal structure were analyzed. The decrease curve in molecular weight suggests that the thermal degradation of Curdlan propionate likely proceeds by random scission. Polarized light microscopy of the isothermal crystallization process showed Curdlan propionate forms a spherulite-like morphology, which is unusual among polysaccharides with a rigid backbone chain. By optimizing the melt spinning conditions, it was found that it is possible to spin with good spinnability using a no plasticizer. The crystallization rate of Curdlan propionate was significantly different between the isothermal crystallization process and the melt spinning process. There was a positive correlation between the take-up speed, crystallinity, and the tensile strength of the fiber. A highly ordered structural model of the fiber was suggested from wide-angle x-ray diffraction results and other measurements.

Kinetic Regularities of Crystallization of Nanocomposites Based on Clinoptilolite and Ethylene-Hexene Copolymer

The paper presents the results of experimental studies of the crystallization process of nanocomposites based on clinoptilolite and an ethylene-hexene copolymer. The temperature dependence of the specific volume and free volume was investigated by the method of dilatometric measurements. In accordance with the theory of Avrami, the kinetic regularity of the isothermal crystallization process at the temperature of the first-order phase transition has been studied. The mechanism and type of crystal growth for the initial polymer matrix and nanocomposites are determined.

Detailed thermal analysis of crystallization kinetics and band morphology for future blending of absorbable poly(p‐dioxanone) monofilament surgical suture with poly(ε‐caprolactone)

AbstractThe thermal effects on crystallization kinetics and the band morphology of absorbable poly(p‐dioxanone) (PDS) were studied in detail with TGA, AFM, DSC and polarized optical microscopy techniques. The polymer film was crystallized with isothermal and non‐isothermal conditions over a wide temperature range, cooling from the melt at 140 °C (beyond the equilibrium melting temperature but below the degradation temperature). With the isothermal crystallization process, a well‐defined spherulitic morphology of the PDS polymer, linearly growing in all directions with time, was observed. A microstructure analysis by polarized optical microscopy and AFM revealed that the crystallized PDS shows large spherulites with band morphology, the nucleation density decreases and the spacing between the band increases with crystallization temperature. The periodic band morphology of the spherulites is related to edge‐on and flat‐on lamella orientation. The crystallization temperature dependent spherulite growth rate displayed a bell‐shaped curve, showing a highest spherulite growth rate at 60 °C, explained by classical nucleation theory. These results allowed a good understanding of the thermal and morphological properties of the PDS polymer over a wide temperatures range in both isothermal and non‐isothermal conditions. Additionally, the crystallization and melting behaviors of the PDS polymer were studied and compared for the future application of blending with other compatible polymers, e.g. poly(ε‐caprolactone). © 2020 Society of Industrial Chemistry

Mesomorphic and dynamic properties of 3F5BFBiHex antiferroelectric liquid crystal as reflected by polarized optical microscopy, differential scanning calorimetry and broadband dielectric spectroscopy

This paper presents studies of the influence of various thermal treatments on molecular dynamics and phase behavior of 3F5BFBiHex antiferroelectric liquid crystal by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). Three liquid crystalline phases: the paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmC*A phases, and vitrification of SmC*A were found upon cooling. The cold crystallization of phase Cr was observed only upon heating at the rate lower than 1.5 K/min. During heating faster than 1.5 K/min 3F5BFBiHex shows the same phase sequence as on cooling. Two relaxation processes in the SmC*A phase obey the Vogel−Fulcher−Tammann (VFT) relation when approaching the glass transition temperature (Tg). An unusual finding that relaxation processes are preserved upon the SmC*A – Cr transition on heating is presented in detail. Finally, the time evolution of relaxation parameters during isothermal cold crystallization process in SmC*A is discussed.

Crystallization of UHMWPE nanocomposites filled by multi-wall carbon nanotubes

In order to study the effect of MWCNTs on the crystallization of UHMWPE, the UHMWPE nanocomposites filled by MWCNTs with high content were prepared by solution method. The non-isothermal and isothermal crystallization of MWCNTs/UHMWPE nanocomposites were studied by differential scanning calorimetry and X-ray diffraction. The results showed that the heterogeneous nucleation of MWCNTs increases the crystallization temperature and crystallinity of UHMWPE filled by MWCNTs below 40 mass% with the increase in MWCNTs content in the non-isothermal crystallization process. However, addition of MWCNTs above 40 mass% reduces the crystallization temperature and crystallinity of UHMWPE with the increase in MWCNTs content. The crystallization kinetics of UHMWPE nanocomposites filled by high MWCNTs content can be described by Jeziorny, Mo and Avrami model. The increase in MWCNTs content decreases the crystallization rate of UHMWPE in the non-isothermal crystallization process. For the isothermal crystallization process, although addition of MWCNTs increases the crystallization rate of UHMWPE, the crystallization rate of UHMWPE also decreases with the increase in MWCNTs content. Above results are discussed based on the combined action of heterogeneous nucleation of MWCNTs and the macromolecular chains of UHMWPE confined on the surface of MWCNTs.

Study of the effect of crystallization conditions on the structure of polyurethane block copolymer based on poly-ε-caprolactone diol and isophoron diisocyanate

In the paper a study of isothermal crystallization kinetics of polyurethane on the basis of poly-ε-caprolactone diol, isopforon diisocyanate and 1, 4-butanediol is presented. The process of isothermal crystallization in the temperatures range from -15 to 30ºC was studied by DSC method. Analysis of total melting enthalpy and degree of crystallinity of the polyurethane allows to obtain material with one or two melting points of polyester block at desired temperature. These results will help in design of new thermoplastic elastomers with one- or two-stage shape memory effect.

Effects of sepiolite on crystallization behaviors and properties of sepiolite/polyoxymethylene composites

For filler-polymer systems, the ultimate importance of interfacial interactions between fillers and polymers lies in improving morphological developments and properties of composites. In this work, sepiolite fiber (SEP)/polyoxymethylene (POM) is formulated through melt extrusion processing, with the aim of promoting the crystallization and overall performance of POM. Results show that hydrogen bonding prevails between SEP hydroxyls and POM C-O-C groups. Thus SEP fibers are dispersed uniformly in the POM matrix due to interfacial interactions between these two components. During the isothermal crystallization process, POM nuclei originate and grow on the SEP surface, resulting in decreasing spherulite sizes and facilitating the POM crystallization. Meanwhile, the crystallinity of POM is increased from 48.3% to 54.1% by the addition of 5 wt% SEP. Noteworthily, mechanical and thermostability performances of SEP/POM composites have been improved considerably by means of sufficient interfacial interactions, enhanced crystallization, and favorable physical properties of SEP. Maximum values of the tensile strength and modulus at 3.0 wt% SEP loading can reach 66 MPa and 2022 MPa, respectively higher than those of neat POM.