Study of Polystyrene and Acrylonitrile−Styrene Copolymer as Special β-Nucleating Agents To Induce the Crystallization of Isotactic Polypropylene

β-Nucleated Polypropylene: Preparation, Nucleating Efficiency, Composite, and Future Prospects

The β-crystals of polypropylene have a metastable crystal form. The formation of β-crystals can improve the toughness and heat resistance of a material. The introduction of a β-nucleating agent, over many other methods, is undoubtedly the most reliable method through which to obtain β-PP. Furthermore, in this study, certain newly developed β-nucleating agents and their compounds in recent years are listed in detail, including the less-mentioned polymer β-nucleating agents and their nucleation characteristics. In addition, the various influencing factors of β-nucleation efficiency, including the polymer matrix and processing conditions, are analyzed in detail and the corresponding improvement measures are summarized. Finally, the composites and synergistic toughening effects are discussed, and three potential future research directions are speculated upon based on previous research.

Temperature Effects on the Crystalline Structure of iPP Containing Different Solvent-Treated TMB-5 Nucleating Agents

TMB-5 nucleating agent (NA) treated by different solvents were used as the β-NA of iPP. The effects of temperature on the crystalline structure of different iPP/TMB-5, as well as the crystallization and melting behaviors were investigated. It was found that strong polar solvent treated TMB-5 (TMB-5_DMSO and TMB-5_DMF) could induce more β-crystal at high T_c = 140 °C than the other TMB-5 NAs, while the β-crystal inducing efficiency of untreated TMB-5 (TMB-5_UT) and non-polar solvent treated TMB-5 (TMB-5_LP) is seriously reduced at high T_c = 140 °C. TMB-5_DMSO can induce a high and stable content of β-crystal with K_β = 83-94% within T_c = 90-140 °C, and TMB-5_ODCB can induce a high content of β-crystal with K_β > 91.3% within T_c = 90-130 °C. TMB-5_DMF is the most temperature-sensitive one, but can induce a high fraction of β-crystal with K_β > 92% both at low T_c = 90 °C and high T_c = 140 °C. High temperature pre-crystallization at T_pc = 150 °C tremendously reduces the β-crystal inducing efficiency of all TMB-5 NAs. TMB-5_UT and TMB-5_LP exhibit higher nucleating efficiency than TMB-5_DMSO, TMB-5_DMF and TMB-5_ODCB. During the non-isothermal crystallization process, TMB-5_UT induced β-crystal possesses higher structural perfection and stability, while TMB-5_LP is more likely to induce α-crystal with considerable quantity and stability. The structural perfection and stability of TMB-5 induced β-crystal can be enhanced with appropriate increasing of T_c.

Towards a Circular Economy: Study of the Mechanical, Thermal, and Electrical Properties of Recycled Polypropylene and Their Composite Materials

This research focuses on the mechanical properties of polypropylene (PP) blended with recycled PP (rPP) at various concentrations. The rPP can be added at up to 40 wt% into the PP matrix without significantly affecting the mechanical properties. MFI of blended PP increased with increasing rPP content. Modulus and tensile strength of PP slightly decreased with increased rPP content, while the elongation at break increased to up to 30.68% with a 40 wt% increase in rPP content. This is probably caused by the interfacial adhesion of PP and rPP during the blending process. The electrical conductivity of materials was improved by adding carbon black into the rPP matrices. It has a significant effect on the mechanical and electrical properties of the composites. Stress-strain curves of composites changed from ductile to brittle behaviors. This could be caused by the poor interfacial interaction between rPP and carbon black. FTIR spectra indicate that carbon black did not have any chemical reactions with the PP chains. The obtained composites exhibited good performance in the electrical properties tested. Finally, DSC results showed that rPP and carbon black could act as nucleating agents and thus increase the degree of crystallinity of PP.

Phase Transitions in Poly(vinylidene fluoride)/Polymethylene-Based Diblock Copolymers and Blends

The crystallization and morphology of two linear diblock copolymers based on polymethylene (PM) and poly(vinylidene fluoride) (PVDF) with compositions PM23-b-PVDF77 and PM38-b-PVDF62 (where the subscripts indicate the relative compositions in wt%) were compared with blends of neat components with identical compositions. The samples were studied by SAXS (Small Angle X-ray Scattering), WAXS (Wide Angle X-ray Scattering), PLOM (Polarized Light Optical Microscopy), TEM (Transmission Electron Microscopy), DSC (Differential Scanning Calorimetry), BDS (broadband dielectric spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy). The results showed that the blends are immiscible, while the diblock copolymers are miscible in the melt state (or very weakly segregated). The PVDF component crystallization was studied in detail. It was found that the polymorphic structure of PVDF was a strong function of its environment. The number of polymorphs and their amount depended on whether it was on its own as a homopolymer, as a block component in the diblock copolymers or as an immiscible phase in the blends. The cooling rate in non-isothermal crystallization or the crystallization temperature in isothermal tests also induced different polymorphic compositions in the PVDF crystals. As a result, we were able to produce samples with exclusive ferroelectric phases at specific preparation conditions, while others with mixtures of paraelectric and ferroelectric phases.

Polyether Single and Double Crystalline Blends and the Effect of Lithium Salt on Their Crystallinity and Ionic Conductivity

In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10⁻³ S cm⁻¹, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.

Concepts of Nucleation in Polymer Crystallization

Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. In this viewpoint, we attempt to discuss some of the remaining open questions and corresponding concepts: non-equilibrated polymers, self-induced nucleation, microscopic kinetics of different processes, metastability of polymer lamellar crystals, hierarchical order and cooperativity involved in nucleation, etc. Addressing these open questions through a combination of novel concepts, new theories and advanced approaches provides a deeper understanding of the multifaceted process of crystal nucleation of polymers.

Poly(Acrylonitrile-Butadiene-Styrene) as a Special β-Nucleating Agent on the Toughness of Isotactic Polypropylene

The influence of poly(acrylonitrile–butadiene–styrene) (ABS) as a special β-nucleating agent on the impact and tensile properties of isotactic polypropylene (iPP) were investigated by dynamic rheological measurements, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and mechanical properties tests. It is found that the β nucleation efficiency of ABS is closely related to its concentration, dispersibility, and molding method for the iPP/ABS blends. The content of β-crystal (K_β) rises with the incorporation of ABS and shows a maximum with the introduction of 1% ABS for compression-molded blends and 2% ABS for injection-molded blends, respectively, which is followed by a decrease in K_β. The addition of a small amount of ABS has a significant reinforcing and toughening effect on iPP. Compared with the compression-molded samples, the ABS dispersed phase in injection-molded samples has a smaller particle size and a larger specific surface area, which are favorable for stress transmission and higher β nucleation efficiency, and therefore, better tensile and impact properties can be expected.

Enhancing the mechanical and thermal properties of polypropylene composite by encapsulating styrene acrylonitrile with ammonium polyphosphate

Backgrounds

In recent decades, incorporating polypropylene (PP) within flame retardants has proved to be an effective method of improving the thermal stabilities of PP, but too much adversely affects the mechanical properties of this polymer materials. Herein we report a novel multifunctional flame retardant, (styrene acrylonitrile)-(titanate-modified ammonium polyphosphate) (SAN-TAPP), to simultaneously improve the mechanical properties and thermal stability of PP composites.

Methods

SAN-TAPP was synthesized by encapsulating SAN resins with functional titanate-modified APP (TAPP) and subsequently was incorporated into PP by a melt-blending process. The phase characteristics and morphology of SAN-TAPP were investigated, and the mechanical properties and thermal stability of different content of PP/SAN-TAPP composites were studied.

Results

The results showed that the TAPP was almost entirely wrapped in the SAN resins and PP/SAN-TAPP composites exhibited the sea-island morphology. For the mechanical properties, the impact strength of PP/SAN-TAPP composite was significantly improved, especially 15 wt% SAN-TAPP filled PP/SAN-TAPP composite exhibiting 2.17 times higher than that of pure PP. And the tensile strength and modulus also increased by addition of SAN-TAPP. For the thermal stabilities, melting temperatures (T_m) and residual char yield were improved. Furthermore, the LOI value of PP/SAN-TAPP composites increased from 19.8 to 27.5%; The 15 and 20 wt% SAN-TAPP filled in PP/SAN-TAPP composites passed the V-2 test of UL-94, and exerted the similar effect on the flame retardancy to TAPP with the same loading.

Conclusions

These results revealed that a novel PP/SAN-TAPP composites with synthetically enhancement on the mechanical properties, thermal stabilities and flame retardancy, suggesting a strong correlation between the phase structure, mechanical and thermal properties.

An Effective α/β Nucleating Agent Compoundfor the Preparation of Polypropylene

The crystallization behavior and mechanical properties were investigated by mixing the traditional α-form nucleating agent (sodium benzoate, SB) and commercialized β-form nucleating agent (TMB-5) in isotactic polypropylene (iPP). Mechanical properties were evaluated by universal testing machines. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were conducted to illustrate the crystallization behavior. Polarized optical microscopy (POM) was adopted to observe the crystal morphologies. The experimental results show that the weight ratio of two types of nucleating agents determines the final crystal structure and mechanical properties of iPP. When the weight ratio of [SB] : [TMB-5] is 4 : 1, the impact strength and flexural modulus of iPP reach a maximum value. Compared with the single component β-form nucleating agent, the compound nucleating agent exhibits significant synergistic effect and shows better mechanical properties. It is expected that this new nucleation system will have potential industrial applications.

Modeling of polystyrenic nanoparticles driven β-trans-crystalline efficiency in isotactic polypropylene

Addition of four styrenic soft nano-particles induced relative β-polymorphism as much as 20, 27, 34 and 10% during 10 minutes annealing of iPP at 116 °C. The kinetic and thermodynamic aspects of the phenomenon rationalized by a bi-exponential function

Melt recrystallization behavior of carbon-coated melt-drawn oriented isotactic polypropylene thin films

The melt recrystallization of vacuum carbon evaporated melt-drawn iPP thin films at varying melting temperature, melting time and recrystallization temperature was studied by means of transmission electron microscopy combined with electron diffraction.