Crystallization Melting Behavior Research Articles

Evaluation of critical process parameter on the production of sustainable bead foams based on polylactic acid

A commercial grade of polylactic acid (PLA) was foamed without using modifiers to obtain expanded polylactic acid bead foams (EPLA). Typically, the foaming process is influenced by both melt properties and crystallization behavior. While factors like water temperature, die structure, and die temperature are known to have effects on bead foam processing, these aspects have not been thoroughly explored in the context of PLA bead foam production. To address this gap, a comprehensive investigation was undertaken, varying water temperature, die structure, and die temperature to discern their impact on PLA processing behavior. Results revealed that water temperature significantly influenced foaming behavior, particularly at elevated temperatures near the glass transition of PLA. Additionally, the study demonstrated that die size wielded a notable influence on all foam properties, dictating process limits. With the selection of an appropriate die size, the die temperature could be manipulated within the range of 190°C to 160°C, revealing a substantial impact on the overall process. Remarkably, the lowest densities achieved were 63 kg/m3 with an average cell size of 36 µm and a cell density of 1.1*107 cells per cm3.

Preparation of a trans-free fat blend to substitute partially hydrogenated oil

Partially hydrogenated oil (PHO) possesses a mild flavor and exceptional processing characteristics, making it historically the primary choice for creamer. The discovery of health problems of trans fatty acids has accelerated the development of alternative fats. This study aimed to develop an optimal PHO alternative fat by physical blending. Based on the correlation between physicochemical properties and sensory attributes, soybean oil, fully hydrogenated palm kernel oil, and fully hydrogenated soybean oil (45/45/10, w/w/w) were selected to make the alternative fat. The fat blend exhibited a solid fat content (SFC) curve identical to PHO, along with similar melting crystallization behavior, crystal nucleation pattern and growth mode, viscosity (705 mPa∙s), and taste profile. Pearson correlation analysis was used to further clarify the correlation between properties and tastes. The result showed that the SFCs and fatty acids compositions have strong correlations with tastes. It provides a reference scheme for preparing fats with ideal tastes.

Comprehensive Investigation into the Impact of Degradation of Recycled Polyethylene and Recycled Polypropylene on the Thermo-Mechanical Characteristics and Thermal Stability of Blends.

The impact of degradation on plastics is a critical factor influencing their properties and behavior, particularly evident in polyethylene (PE) and polypropylene (PP) and their blends. However, the effect of photoaging and thermal degradation, specifically within recycled polyethylene (rPE) and recycled polypropylene (rPP), on the thermo-mechanical and thermostability aspects of these blends remains unexplored. To address this gap, a range of materials, including virgin polyethylene (vPE), recycled polyethylene (rPE), virgin polypropylene (vPP), recycled polypropylene (rPP), and their blends with different ratios, were comprehensively investigated. Through a systematic assessment encompassing variables such as melting flow index (MFI), functional groups, mechanical traits, crystallization behavior, microscopic morphology, and thermostability, it was found that thermo-oxidative degradation generated hydroxyl and carboxyl functional groups in rPE and rPP. Optimal mechanical properties were achieved with a 6:4 mass ratio of rPE to rPP, as validated by FTIR spectroscopy and microscopic morphology. By establishing the chemical model, the changes in the system with an rPE-rPP ratio of 6:4 and 8:2 were monitored by the molecular simulation method. When the rPE-rPP ratio was 6:4, the system's energy was lower, and the number of hydrogen bonds was higher, which also confirmed the above experimental results. Differential scanning calorimetry revealed an increased crystallization temperature in rPE, a reduced crystallization peak area in rPP, and a diminished crystallization capacity in rPE/rPP blends, with rPP exerting a pronounced influence. This study plays a pivotal role in enhancing recycling efficiency and reducing production costs for waste plastics, especially rPE and rPP-the primary components of plastic waste. By uncovering insights into the degradation effects and material behaviors, our research offers practical pathways for more sustainable waste management. This approach facilitates the optimal utilization of the respective performance characteristics of rPE and rPP, enabling the development of highly cost-effective rPE/rPP blend materials and promoting the efficient reuse of waste materials.

A Comparative Study on the Melt Crystallization of Biodegradable Poly(butylene succinate-co-terephthalate) and Poly(butylene adipate-co-terephthalate) Copolyesters.

As an important biodegradable and partially biobased copolyester, poly(butylene succinate-co-terephthalate) (PBST) possesses comparable thermal and mechanical properties and superior gas barrier performance when compared with poly(butylene adipate-co-terephthalate) (PBAT), but it was found to display poorer melt processability during pelletizing and injection molding. To make clear its melt crystallization behavior under rapid cooling, PBST48 and PBST44 were synthesized, and their melt crystallization was investigated comparatively with PBAT48. PBST48 showed a PBAT48-comparable melt crystallization performance at a cooling rate of 10 °C/min or at isothermal conditions, but it showed a melt crystallization ability at a cooling rate of 40 °C/min which was clearly poorer. PBST44, which has the same mass composition as PBAT48, completely lost its melt crystallization ability under the rapid cooling. The weaker chain mobility of PBST, resulting from its shorter succinate moiety, is responsible for its inferior melt crystallization ability and processability. In comparison with PBAT48, PBST48 displayed higher tensile modulus, and both PBST48 and PBST44 showed higher light transmittance. The findings in this study deepen the understanding of PBST's properties and will be of guiding significance for improving PBST's processability and application development.

The effect of tetra‐needle‐like zinc oxide whisker as additive on the crystallization kinetics of polybutylene adipate terephthalate/polylactic acid blend

AbstractHerein, we investigate the effect of the addition of tetra‐needle‐like zinc oxide whisker (T‐ZnOw), a novel reinforcing additive, on the melt crystallization behavior of biodegradable polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA) polymer blends. PBAT and PLA were blended in a Haake mixer at a fixed weight ratio of 70/30, and the contents of T‐ZnOw varied from 0 to 7 wt%. The melt thermal properties and crystallization behavior of PBAT/PLA blends and PBAT/PLA/T‐ZnOw composites were studied using differential scanning calorimetry. The kinetics of melt crystallization have been quantitatively explained using a range of mathematical formalisms. The Avrami equation is adopted to analyze the isothermal crystallization process and kinetics of PBAT/PLA/T‐ZnOw composites. For its nonisothermal crystallization process and kinetics, the Ozawa equation cannot describe the entire process, while the Jeziomy‐modified Avrami equation can only describe the initial stage of its nonisothermal crystallization. Using Mo‐analysis, the impact of T‐ZnOw contents on the composite's nonisothermal crystallization kinetic has been thoroughly examined. Given that the PBAT/PLA blend system's crystal formation may be inhibited by T‐ZnOw, the observation demonstrates that T‐ZnOw only marginally alters this process. The work is of significant scientific value and adds a new concept to the development of sustainable thin film for packaging.Highlights T‐ZnOw is used as a novel additive for PBAT/PLA polymer blends. The crystallization of PBAT/PLA/T‐ZnOw composite systems is thoroughly examined. T‐ZnOw marginally reduces the kinetics of the crystallization process of PBAT/PLA blends. PBAT/PLA/T‐ZnOw composites follow volume nucleation with mixed 2D/1D growth. The nonisothermal crystallization of PBAT/PLA/T‐ZnOw composites is validated by Mo‐analysis.

Preparation and Properties of PA10T/PPO Blends Compatibilized with SEBS-g-MAH.

Plant-derived PA10T is regarded as one of the most promising semi-aromatic polyamides; however, shortcomings, including low dimensional accuracy, high moisture absorption, and relatively high dielectric constant and loss, have impeded its extensive utilization. Polymer blending is a versatile and cost-effective method to fabricate new polymeric materials with excellent comprehensive performance. In this study, various ratios of PA10T/PPO blends were fabricated via melt blending with the addition of a SEBS-g-MAH compatibilizer. Molau test and scanning electron microscopy (SEM) were employed to study the influence of SEBS-g-MAH on the compatibility of PA10T and PPO. These studies indicated that SEBS-g-MAH effectively refines the domain size of the dispersed PPO phase and improves the dispersion stability of PPO particles within a hexafluoroisopropanol solvent. This result was attributed to the in situ formation of the SEBS-g-PA10T copolymer, which serves as a compatibilizer. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results showed that the melting-crystallization behavior and thermal stability of blends closely resembled that of pure PA10T. Dynamic mechanical analysis (DMA) revealed that as the PPO content increased, there was a decrease in the glass transition temperature and storage modulus of PA10T. The water absorption rate, injection molding shrinkage, dielectric properties, and mechanical strength of blends were also systematically investigated. As the PPO content increased from 10% to 40%, the dielectric loss at 2.5 GHz decreased significantly from 0.00866 to 0.00572, while the notched Izod impact strength increased from 7.9 kJ/m2 to 13.7 kJ/m2.

Eco-friendly zinc-metal-organic framework as a nucleating agent for poly (lactic acid)

Eco-friendly poly(L-lactic acid) (PLA) can be made more versatile, and its crystallization rate is accelerated by adding Zinc-based metal-organic framework (Zn-MOF) particles. Using differential scanning calorimetry (DSC), the non-isothermal melt crystallization behavior of biodegradable PLA nucleated by 0.3 to 3 wt% of Zn-MOF was examined. The non-isothermal melt crystallization kinetics parameters were determined using a modified Avrami model and Mo approach. Zn-MOF dramatically accelerated the crystallization process, as evidenced by several non-isothermal crystallization metrics, including the crystallization half-time and crystallization rate constant. The melt crystallization temperatures of the PLA-Zn-MOF composites, with contents of 0.7 and 1 wt%, were increased by 21 °C compared to the neat PLA. Using the Friedman isoconversional kinetic method, the neat PLA and PLA-Zn-MOF composites' effective activation energy values, ∆E, were determined. The ∆E values of PLA-Zn-MOF from 0.3 to 1 wt% Zn-MOF composites were lower than that of neat PLA. Moreover, polarized optical microscopy revealed the formation of numerous small-sized PLA spherulites upon Zn-MOF addition. The results indicate that the Zn-MOF (at concentrations of 0.7 to 1.0 wt%) can be used as an efficient nucleating agent for PLA, where it increases the melt crystallization temperature, nucleation density, and crystallinity without changing the crystalline structure, while also significantly reduces the effective activation energy and the size of spherulites. Additionally, scanning electron microscopy confirms good dispersion of Zn-MOF (0.3 to 1 wt%) within the PLA matrix.

Strength-plasticity synergetic CF/PEEK composites obtained by adjusting melt flow rate

Short carbon fiber reinforced PEEK (CF/PEEK) composite materials with the advantages of excellent mechanical properties and easy processing, have been widely applied in the fields of aeronautics and astronautics, automotive engineering, and so on. However, their development in microinjection molding is hindered by the incompatibility between excellent plasticity and high mechanical properties. Herein, strength-plasticity synergetic CF/PEEK composites are prepared by adjusting the melt fluidity and crystallization behaviors, based on PEEK with different melt flow rate (MFR) and T800 carbon fiber. The rheological results showed that the melt viscosity of CF/PEEK composite was negatively related to the MFR of PEEK. Moreover, the mechanical properties of composites were increased by the crystallinity of PEEKs with high MFR. This work presents strength-plasticity synergetic CF/PEEK composites suitable for microinjection molding thin-walled and intricate components, offering new opportunities for next-generation portable electronic.

The Nucleated Poly(L-lactic acid): The Role of a Phenylacetic Hydrazide Derivative

The melt-crystallization, cold-crystallization, melting behaviors, thermal stability, and optical properties of poly(L-lactic acid) (PLLA) nucleated by a phenylacetic hydrazide derivative (DAPH) were investigated. The melt-crystallization confirmed DAPH’s heterogeneous nucleation role in improving PLLA’s poor crystallization capability, concurrently DAPH loading, cooling rate and final melting temperature were three key factors affecting PLLA’s melt-crystallization behaviors. The results from cold-crystallization indicated that the addition of DAPH could accelerate PLLA’s cold-crystallization via cold-crystallization peak’s shift toward the lower temperature side as DAPH loading increased. Through analysis of PLLA/DAPH’s multiple melting behaviors after melt-crystallization, it was found that DAPH loading, the previous melt-crystallization and heating rate determined PLLA/DAPH’s melting processes after melt-crystallization; and PLLA/DAPH’s melting processes after isothermal crystallization depended on the previous crystallization temperature. A drop in thermal decomposition temperature for 5 wt.% mass loss suggested that pure PLLA has better thermal stability compared with PLLA/DAPH. Additionally, the introduction of DAPH could not improve PLLA’s transparency, in contrast, the haze of PLLA was increased greatly owing to the existence of DAPH.

Research progress of direct contact heat storage based on phase change heat storage

AbstractPhase change heat storage presents a promising solution to address challenges related to new energy intermittency and waste heat recovery. However, for it to function as an effective energy hub, heat storage becomes crucial. Among the available options, the direct contact heat accumulator stands out due to its simple structure, substantial heat transfer area, and minimal heat transfer resistance, making it a favorable choice for enhancing energy storage rates. Although a great deal of research has been done on phase change materials and heat accumulators over the years, a systematic review of direct‐contact heat accumulators is lacking. This article reviews the related research on direct contact heat storage, aiming to summarize the research work on direct contact phase change heat storage systems. Various phase change materials (PCMs) for direct contact systems are analyzed, and the study of PCM melting crystallization behavior, heat transfer coefficients and system performance in direct contact systems is summarized, as well as the improvement methods for direct contact vessels and PCMs. It provides a useful reference for future research on direct‐contact heat storage systems.

3D printed sequence-controlled copolyimides with high thermal and mechanical performance

Inadequate heat resistance and mechanical property limited the application of 3D printed polymer parts in aerospace industry. To address this restriction, a kind of sequence-controlled copolyimides with both amorphous segment and crystalline segment, suitable for fused deposition modeling 3D printing technique were designed and synthesized. The effect of content and distribution of crystalline segment on melt fluidity and crystallization behavior was disclosed. It was found that copolyimide with crystalline segment only distributed in the end of backbone exhibited good melt fluidity and slow crystallization rate. Microstructure change of the corresponding copolyimide during 3D printing and thermal annealing was revealed. Due to slow crystallization rate of copolyimide, no crystals formed during 3D printing. Thus, the diffusion and entanglement of polymer chain at interface were guaranteed. Thermal annealing at 350 °C facilitated diffusion and arrangement of polymer chain, leading to the enhancement of interfacial bonding and crystallization of copolyimide at interface and in filament. Therefore, the printed copolyimide specimens exhibited high heat resistance, high mechanical property and excellent interfacial bonding performance. The tensile strength of specimens printed in XY plane with 0° infill direction (XY-0), XY plane with 90° infill direction (XY-90) and XZ plane with 90° infill direction (XZ-90) were 110 MPa, 96 MPa and 57 MPa, respectively. The tensile strength of XY-0 printed specimen at 200 °C was 186 % higher than that of XY-0 printed amorphous polyimide specimen, reaching 40 MPa. This study expanded the kinds of polymeric materials suitable for fused deposition modeling, and provided the possibility of printing high performance engineering parts.

Comparative study on matrix resins in two low‐density polyethylene based cable insulation materials with different voltage grades

AbstractIn industry, crosslinked polyethylene (XLPE) cable insulation is usually produced from crosslinkable compounds consisting of low‐density polyethylene (LDPE) and additives, which known as “cable materials”. Considering that in addition to additives, the structure of matrix resin is a key factor in determining the property of XLPE, it is worthy to study the structure requirements of matrix resin for the development of cable materials with different voltage grades. In this work, the structure of matrix resins of a high voltage grade and an extra high voltage grade cable material were comparatively investigated. Interestingly, it was found that the matrix resins have no significant difference in chain structure parameters including molecular weight and its distribution and vinyl content between two samples, and their crystalline structure as well as the melt rheology and melting crystallization behavior are also very similar. These results suggest that these matrix resins may not substantially differ. Our work shows that cable materials with different voltage grades are not necessarily diverge in terms of matrix resin structure, and it could be possible to develop higher grade cable materials using the same matrix resin as lower grade counterparts.

Preparation of polylactic acid (PLA) films plasticized with a renewable and natural Liquidambar Orientalis oil

Polylactic acid (PLA) is a brittle biodegradable thermoplastic due to its relatively high glass transition temperature (Tg ∼ 60 °C). This Tg limits the using of PLA in flexible applications, for example packaging films. In this study, it has been shown for the first time that the Liquidambar Orientalis (LO) oil as a nontoxic, environmentally friendly, and green additive can be successfully used as a natural, renewable, and sustainable plasticizer to produce flexible PLA parts and improve its thermal and physical properties and application potential. Natural oil obtained from Liquidambar Orientalis tree was introduced into PLA (as 10, 20, and 30 phr) by melt compounding (MC) and solution mixing (SM) methods. Effect of LO oil amount on the glass transition temperature, melt and cold crystallization behaviors, and degree of crystallinity values of samples were determined with differential scanning calorimetry (DSC). In addition, solid state viscoelastic properties of PLA films were also characterized with dynamic mechanical analysis (DMA) tests. Results showed that LO oil significantly reduced the Tg and storage modulus (E') value of PLA and LO oil showed an excellent plasticizing effect for PLA due to reducing strong hydrogen bonds and secondary interactions between PLA chains.

On the Effect of Non-Thermal Atmospheric Pressure Plasma Treatment on the Properties of PET Film.

The aim of the work was to investigate the effect of non-thermal plasma treatment of an ultra-thin polyethylene terephthalate (PET) film on changes in its physicochemical properties and biodegradability. Plasma treatment using a dielectric barrier discharge plasma reactor was carried out in air at room temperature and atmospheric pressure twice for 5 and 15 min, respectively. It has been shown that pre-treatment of the PET surface with non-thermal atmospheric plasma leads to changes in the physicochemical properties of this polymer. After plasma modification, the films showed a more developed surface compared to the control samples, which may be related to the surface etching and oxidation processes. After a 5-min plasma exposure, PET films were characterized by the highest wettability, i.e., the contact angle decreased by more than twice compared to the untreated samples. The differential scanning calorimetry analysis revealed the influence of plasma pretreatment on crystallinity content and the melt crystallization behavior of PET after soil degradation. The main novelty of the work is the fact that the combined action of two factors (i.e., physical and biological) led to a reduction in the content of the crystalline phase in the tested polymeric material.

Microstructure and Tensile Properties of Melt-Spun Filaments of Polybutene-1 and Butene-1/Ethylene Copolymer.

Polybutene-1 with form I crystals exhibits excellent creep resistance and environmental stress crack resistance. The filaments of polybutene-1 and its random copolymer with 4 mol% ethylene co-units were produced via extrusion melt spinning, which are expected to be in form I states and show outstanding mechanical properties. The variances in microstructure, crystallization-melting behavior, and mechanical properties between homopolymer and copolymer filaments were analyzed using SEM, SAXS/WAXD, DSC, and tensile tests. The crystallization of form II and subsequent phase transition into form I finished after the melt-spinning process in the copolymer sample while small amounts of form II crystals remained in homopolymer filaments. Surprisingly, copolymer filaments exhibited higher tensile strength and Young's modulus than homopolymer filaments, while the homopolymer films showed better mechanical properties than copolymer films. The high degree of orientation and long fibrous crystals play a critical role in the superior properties of copolymer filaments. The results indicate that the existence of ethylene increases the chain flexibility and benefits the formation of intercrystalline links during spinning, which contributes to an enhancement of mechanical properties. The structure-property correlation of melt-spun PB-1 filaments provides a reference for the development of polymer fibers with excellent creep resistance.

Designing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) films with tailored mechanical properties

Increasing the 3HV molar fraction up to 45 mol% in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) monomeric composition is assumed to improve the ductility of P(3HB-co-3HV)-based materials. The objective of the paper was to assess how the polymer recovery treatment and the melt processing temperature could counterbalance this effect. For that purpose, copolymers with different 3HV contents (18, 28 and 40 mol%) and recovered both using a solvent free high-pressure homogenization (HPH) based treatment and a chloroform-based treatment were used to produce non-formulated and self-supported films by thermopressing. The improvement of ductility with increased 3HV content was confirmed whatever the recovery treatment. Lower elongation at break values were obtained for HHP-based extracted copoplymers, due to the presence of impurities, including non-PHAs cell mass, that favored thermal degradation during the film shaping process. An in-depth study by differential scanning calorimetry (DSC) analysis of the melt crystallization behavior, coupled to observations in polarized optical microscopy (POM), allowed to predict the optimal processing temperature, i.e. the temperature allowing the formation of microstructures in favor of improved ductility. Tensile properties were discussed in relation to the thermal properties and crystalline structure of copolymers evaluated by wide-angle and small-angle X-ray scattering analyses (WAXS/SAXS).

Nucleating Agents to Enhance Poly(L-lactide) Crystallization and Melting Behavior of Modified Poly(L-lactide)

Melt processing poly(L-lactide) (PLLA) with a nucleating agent has been thought to be one of the most effective route to enhance PLLA s crystallization and heat resistance. In the current work, a newly-developed organic nucleating agent named N, N -bis(2-picolinyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NCAPH) was synthesized to investigate its effects on PLLA�s crystallization and melting behaviors. It is proved that NCAPH as an organic crystallization nucleating agent could provide large number of crystallization nucleation sites to improve PLLA�s crystallization, as observed from DSC and POM measurements. The result from melt-crystallization processes further showed that the final melting temperature and cooling rate were two important factors for affecting PLLA�s melt-crystallization behaviors in cooling, and the theoretical calculation result of frontier orbital energy indicated there existed probable intermolecular interaction between N-H of NCAPH and C=O of PLLA, which was proposed as nucleation mechanism of NCAPH for promoting PLLA�s crystallization. The melting behaviors of PLLA/NCAPH after non-isothermal crystallization or isothermal crystallization further confirmed the positive effects of NCAPH and NCAPH�s loading for the crystallization of PLLA, meantime, the melting behaviors depended on the heating rate, crystallization temperature, crystallization time, etc.

Effect of copolymerization on the thermal characteristics and behavior of crystallization of biobased semi‐aromatic PA10T/10I

AbstractThis work synthesized the pure poly (decamethylene terephthalamide) acid (PA10T) and a series of PA10T/10I through an efficient one‐pot melt polymerization method. The structures, thermal behavior, crystallization performance, and mechanical properties of PA10T and PA10T/10I were investigated by FT‐IR, DSC, TGA, POM, XRD, and mechanics performance testing, respectively. The thermal analysis demonstrates that the melting temperature of PA10T/10I gradually decreased with the increase of isophthalic acid (IPA) copolymerization proportions. Specifically, it was observed that, the Tm1 of pure PA10T was 299.5°C, while the Tm1 of PA10T/10I‐4 with a linear downward trend was 284.7°C. And the introduction of IPA copolymerization has an obvious beneficial effect on the thermal stability of PA10T/10I (Td,5 varied from 429.5 to 434.5°C) with a wider temperature range of processing, which could potentially be applied in high‐temperature scenes. POM and XRD were used to characterize the crystallization behavior of all samples further. It was discovered that although adding IPA did not alter the crystal structure of PA10T, it dramatically reduced the size of crystalline grains and increased the number of crystal nuclei. In addition, the copolyamides possess excellent mechanical properties, and the tensile strength of PA10T/10I varied between 42.91 and 46.89 MPa, the bending strength varied between 76.69 and 85.83 MPa, and the izod impact strength varied between 25.41 and 29.82 kJ m−2. Moreover, the influence of the IPA comonomer of copolyamides PA10T/10I on melting points, thermal stability, crystallization behavior, and mechanical characteristics was investigated. This work provides a reference for preparing biobased semi‐aromatic copolyamides PA10T/10I with outstanding processing performance, excellent thermal characteristics, and adjustable mechanical properties.

Using PCL oligomers to study the differences in melting behavior between polymers and small molecules crystals

Polymer crystals usually show a completely different melting behavior than small molecules. Instead of starting from the crystal growth front, the lamellar crystals within polymer spherulites always experience a successive thickening process upon heating before they simultaneously melt. However, a systematic comparative study of the different melting behavior of crystals formed by small and large polymer chains is still scarce. In this work, two PCL oligomers with similar molecular weight are selected to study their crystallization and melting behavior. The defect-free oligomer (PCL2.4) exhibits a similar melting behavior as polymeric crystals (where spherulites melt simultaneously). In contrast, the other oligomer (PCL2.0) with a mid-chain defect shows prominent surface melting starting at the spherulite growth front. SAXS, SSA thermal fractionation, and flash DSC results confirm that an extended chain-like crystal structure could form at relatively high crystallization temperatures. According to the Gibbs-Thomson equation, the melting temperature of PCL2.0 crystals at the spherulite growth front is relatively lower than in the inner part due to different surface free energies. On the other hand, the thermal stability of PCL2.4 is enhanced due to melting and recrystallization during heating, and the spherulites show identical melting points and lamellar thicknesses at their growth front centers.

Realizing simultaneous high‐temperature strength and low‐temperature elongation in polyolefin elastomer toughened polypropylene via controlling the dispersed phase size

AbstractThe properties of modified polypropylene (PP) materials are closely related to their phase structure. In this work, polyolefin elastomer (POE)‐toughened PP materials with different phase structures were designed by using various types of POEs (ethylene‐butene 710, 110, ethylene‐propylene 6202, ethylene‐octene 8200). Then, the effects of phase separation in PP/POE blends on both thermal and tensile properties as well as ultraviolet (UV) resistance were investigated. The results revealed that the POE type hardly affected the melt flow rate, melting or crystallization behavior of the modified PP samples. Moreover, scanning electron microscopy results showed that POE6202 had a smaller dispersed phase size in PP (0.1–0.5 μm), which improved the low‐temperature elongation at break. PP/POE110 blends with a larger microdomain (1–5 μm) had better high‐temperature tensile strength. Further, when toughened with POE110 and POE6202 simultaneously, modified PP had excellent low‐temperature elongation (272%@ −40°C) without sacrificing as much of its high‐temperature tensile strength (10.4 MPa@70°C). Finally, Electron Paramagnetic Resonance tests showed that the addition of amorphous POE decreased the intensity of free radicals generated in PP during irradiation and promoted their attenuation during decay. This indicated that the introduction of POE improved the UV resistance of PP.