Highly-modified polylactide transparent blends with better heat-resistance,melt strength,toughness and stiffness balance due to the compatibilization and chain extender effects of methacrylate-co-glycidyl methacrylate copolymer

A core-shell modifier with the cross-linked acrylate and silicone copolymer as the core and polymethyl methacrylate (PMMA) as the shell (PASi-g-PMMA) was used to toughen the brittle polylactide (PLA). In addition, the copolymer of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) (MG) was utilized to further enhance the modification efficiency of the PASi-g-PMMA. The MG copolymer played the double roles of compatibilizer and chain extender, which not only improved the interfacial adhesion between the PLA and PASi-g-PMMA particles, but also increased the molecular weight and chain entanglement of the PLA. Compared with the PASi-g-PMMA toughened PLA blend, the PLA/PASi-g-PMMA/MG blends showed much higher heat-resistance, melt strength, transparency, toughness and stiffness balance. When the PASi-g-PMMA content was 20 wt%, 20 wt% MG increased the glass transition temperature (T_g), complex viscosity (η*), transparency, impact and tensile strength of PLA/PASi-g-PMMA blend from 60.1°C, 1.9 × 10³ Pa·s, 76.1%, 748 J/m and 37 MPa to 71.5°C, 0.5 × 10⁴ Pa·s, 78.4%, 860 J/m and 45 MPa for the PLA/PASi-g-PMMA/MG blend. This research provided a facile and practical method to overcome the shortcomings of the PLA and promoted its application in broader fields.     

Optimization of the thermal mending process in epoxy/cyclic olefin copolymer blends

Cyclic olefin copolymer (COC) is utilized as thermoplastic healing agent in an epoxy resin and the effect of mending temperature on the healing of resulting materials is investigated. Blends are prepared by adding 20 and 30 wt% COC powder in the epoxy resin. They are thermo-mechanically characterized and fractured samples are thermally mended at various temperatures to evaluate the healing efficiency of the repaired samples. Optical microscopy reveals a homogenous dispersion of COC domains within epoxy matrix, while thermogravimetric analysis shows improved thermal stability of the samples. The immiscibility of the two phases in the blends lead to a decrease of the mechanical properties under flexural and tensile loading modes with respect to neat epoxy. The fracture toughness increases upon COC addition at elevated amounts. Healing efficiency values up to more than 80% are obtained at the lowest investigated temperature of 145°C for samples with 30 wt% of COC.     

Effect of block copolymer containing ionic liquid moiety on interfacial polarization in PLA/PCL blends

Compared with poly(?‐caprolactone)‐b‐poly(ethylene glycol) block copolymer (BC), a systematic study of the effect of the concentration of the compatibilizer, poly(?‐caprolactone)‐b‐poly(ethylene glycol) BC containing ionic liquid moiety (BCIL), on the interfacial properties of a phase separating blend of poly(l ‐lactic acid)/poly(?‐caprolactone) (PLA/PCL) was performed. BCIL copolymer as a compatibilizer for immiscible PLA/PCL blend can reinforce the interactions between the two polymeric phases by the IL electrostatic interaction at interphase, and the particle size of PCL decreases because of interfacial reinforced‐compatibilization of IL moiety. Ion mobility of IL moiety at interphase and PCL phase for PLA/PCL/BCIL blend can induce interfacial blocking of charge carriers, and IL moiety segregating mainly at the interface can decrease the relaxation rate and increase the dielectric strength of interfacial polarization. Our results provide a methodology to characterize and tune the morphology and blocking of charge carriers with the aim of tailoring the dielectric interfacial properties of blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46161.     

Enhanced energy storage of polyvinylidene fluoride-based nanocomposites induced by high aspect ratio titania nanosheets

To enhance the discharge energy density (U_e ) of polyvinylidene fluoride (PVDF), two-dimensional (2D) titania nanosheets (TNSs) with high aspect ratio were introduced into PVDF. The results show that the TNSs are uniformly dispersed in matrix and the existence of matrix-filler interface is confirmed by small angle X-ray scattering. Introducing of high aspect ratio TNSs is beneficial to enhance the concentration of polar β-phase and interfacial polarization, which can improve the permittivity (ε_r ) of nanocomposites. Meanwhile, the shape of 2D TNSs plays an important role in enhancement of breakdown strength (E_b ). The ε_r and E_b of the nanocomposites are two significant factors of their high energy storage performance. Therefore, the U_e increases to 0.32 J/cm³, which is 28% higher than that of pure PVDF (~0.25 J/cm³). The energy efficiency of this typical nanocomposite is similar as that of pure PVDF (~90%). This work might provide a method of fabricating promising energy storage dielectric materials.     

Effect of chain extender on the morphology,thermal, viscoelastic,and dielectric behavior of soybean polyurethane

The objective of this work was to determine the influence of different chain extenders (CEs) on the morphology, thermal, viscoelastic, and dielectric properties of soybean polyurethane (PU). The PU with ethane-1.2-diol showed a more organized structure, which was attributed to the smaller amount of methylene groups ( CH₂ ) and the shorter distance between the hydrogen bonds. While, PUs with dipropylene glycol, the free volume increased due to the less effective interactions formed between the hard and soft domains. The α, β, and γ transitions dipolar by conductive process, are probably associated with (a) local motions of the main chain, (b) the smaller groups rotation motions in the fatty acid chains in the soft phase, and (c) the  CH₂ group rotation motion in the amorphous region. The phase-separated morphology is most evident at high temperatures due to the Maxwell–Wagner–Sillars interfacial polarization process.     

Effect of solvent on ionic liquid dissolved regenerated antheraea assamensis silk fibroin

We report on the dissolution of semi‐domestic silk type Antheraea assamensis using ionic liquids. We investigated the impact of different coagulating solvents, including isopropanol and water on the structure and the morphology of the regenerated silk. We found that the water regenerated silk film showed a high β‐sheet content and a native silk‐like XRD pattern. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Negative dielectric permittivity of PVDF nanocomposites induced by carbon nanofibers and polymer crystallization

Negative permittivity is a key characteristic of the distinctive metamaterials, a novel class of artificial materials with particular electromagnetic properties. Negative permittivity has been realized in metallic structures with special designs, but rarely achieved in polymer nanocomposites. Our recent studies discover that negative permittivity can be attained from randomly distributed carbon nanofiber (CNF) filled poly(vinylidene fluoride) (PVDF) composites over a wide frequency range, and the negative permittivity values are strongly influenced by CNF and PVDF crystalline structures. The effects of CNF on the crystallization of PVDF, and the resultant negative dielectric permittivity of CNF/PVDF composites influenced by crystallization of PVDF and CNF, are investigated. It is revealed that the introduction of CNF not only affects the dielectric permittivity directly, but also causes indirect effects to the dielectric permittivity through influencing the crystallization of PVDF. In particular, due to addition of more CNF, a α- to β-phase transformation in PVDF is found to affect permittivity of the nanocomposites. Furthermore, the permittivity of CNF/PVDF composites are increased considerably (“more negative”) with more CNF, and is affected noticeably by crystalline structures of PVDF. The lowest negative permittivity achieved is −2,500 for the nanocomposite with 5 wt% CNF at 5 kHz.     

How the biaxially stretching mode influence dielectric and energy storage properties of polypropylene films

The most important polymer film used in commercial capacitors is biaxially oriented polypropylene (BOPP), which could be produced by sequentially or simultaneously biaxial orientation after the melt-extrusion. In order to disclose the influence of the stretching technique on the properties of films, the BOPP films with varied thickness were fabricated by sequential and simultaneous orientation, respectively. Compared to the sequentially biaxially stretched films, the crystal grains in the simultaneously biaxially stretched films are more isotropically dispersed. As temperature increases, all the BOPP films exhibit similar dielectric constant, and the simultaneous films have much lower dielectric loss thanks to the finer blended crystalline and amorphous phases. When the film thickness is smaller than 5 μm, the breakdown field strength, energy density and discharging time of the simultaneous films can be increased by at least 10% comparing to the sequential ones, which is very important for reducing the volume of the film capacitors. All the results suggest the simultaneously biaxial orientation mode shows significant advantages in producing thin BOPP films with better mechanical and electrical properties.     

Thermal effects on the percolation behavior of polyvinylidene fluoride/nickel composites

Percolation theory predicts the ideal percolation threshold (P_C) for insulator/conductor composites (ICC) to be at 0.16 of the conductor volume fraction in the composite. In this article, we have investigated the percolation behavior in polyvinylidene fluoride/nickel (Ni) composites by varying the Ni concentration. It is observed that the thermal effect/time of heat treatment play a crucial role in changing the value of P_C in a simple random continuum percolative ICC. The effect is attributed to decrease in: (i) intercluster distance, (ii) viscosity of the polymer, and (iii) wetting of the polymer to metal. The heat energy helps the polymer matrix to be melted as a result the metal particles/clusters come closure, that causes an increase in the cluster size of the metal particles. The overall effect is lowering of P_C mainly due to decrease in intercluster distance. A drastic enhancement in the dielectric permittivity with increase of metal content is explained using boundary layer capacitive effect arising due to Maxwell–Wagner–Sillars interfacial polarization of accumulated charges at the metal–polymer interfaces and blocking of charge carriers at the insulating boundary. The substantial enhancement of ac conductivity at the P_C is attributed to leakage of charge carriers across the insulating barrier. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reversibly highly stretchable and self-healable zwitterion-containing polyelectrolyte hydrogel with high ionic conductivity for high-performance flexible and cold-resistant supercapacitor

It remains challenging to develop stretchable and self-healable polymer electrolytes with improved ion-conductive nature for high-performance multifunctional flexible supercapacitors. Herein, a P(AM-SBMA-AMPS)-SiO₂ zwitterion-containing polyelectrolyte hydrogel is fabricated via copolymerization of acrylamide (AM), sulfobetaine methacrylate (SBMA) zwitterionic monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) anionic monomer grafted from the surface of vinyl silica nanoparticles (VSNPs). The hydrogen bonding among polymer chains and the high-density dynamic ionic interactions between SBMA and AMPS work as reversible “sacrificial bonds” to toughen hydrogel, while the VSNPs function as multifunctional crosslinkers and stress transfer centers, which makes these hydrogels tough (fracture energy 2.7 MJ m⁻³), stretchable (fracture strain 4,016%), and self-healable (fracture strain of healable sample 775%). More importantly, this zwitterion-containing polyelectrolyte hydrogel exhibits high ionic conductivities (3.4 S m⁻¹) owing to the highly hydration capacity of the zwitterionic polyelectrolyte copolymer which produced efficient ion migration channels for ion transport. Accordingly, a flexible supercapacitor based on this multifunctional hydrogel as electrolyte demonstrates a high electric double-layer capacitive capacitance of 60.6 F g⁻¹ at 0.5 A g⁻¹ and excellent capacitance retention of ~98% over 1,000 cycles as well as encouraging electrochemical properties at subzero temperature. This work provides new insights into the synthesis of highly conductive and multifunctional polyelectrolyte hydrogels for high-performance flexible supercapacitors. © 2020 Wiley Periodicals, Inc.     

Ultratough and recoverable ionogels based on multiple interpolymer hydrogen bonding as durable electrolytes for flexible solid-state supercapacitor

The emerging application of ionogels in flexible devices require it enough durable under repeated mechanical deformation while maintaining their superior electrochemical properties. In this work, ultratough and recoverable ionogels, where ionic liquids are confined in chemically and interpolymer hydrogen-bonding hybrid crosslinked network, were fabricated by in situ copolymerization of acrylic acid and 1-vinylimidazole monomer within 1-buty-3-methylimidazolium chloride ionic liquid. The reversible hydrogen bonds between imidazole and carboxylic acid groups of polymer chains in the network work as reversible “sacrificial bonds” to toughen ionogel, which makes the ionogels tough (tensile strength 1.62 MPa, toughness 8.7 MJ m⁻³), stretchable (elongation at break 1090%), and recoverable (91% recovery resting for 30 min, at 534 kPa stress and 500% strain). Moreover, the hydrogen-bonded ionogels exhibit high ionic conductivity of 2.3 S m⁻¹ at 80°C to 3.2 S m⁻¹ at 150°C. Furthermore, the ionogel-based flexible electrical double-layer capacitor can be operated up to 1.5 V with a capacitance of 341.47 F g⁻¹ at 0.5 A·g⁻¹ and exhibits excellent capacitance retention after 1000 cycles as well as superior electrochemical performance over a wide range of temperature. This work provides new insights into the synthesis of tough and recoverable ionogels for high-performance flexible supercapacitors.     

Improvement of mechanical properties of polylactide by equal channel multiple angular extrusion

The combination of high strength and toughness is always the goal of high-performance polymer materials for industrial use. This study addresses the potentialities of a solid state equal-channel multiple-angular extrusion (ECMAE) in production of polylactide (PLA) with simultaneous improvement in toughness, strength, and thermal stability. Chain extender Joncryl was used to form PLA with different chain length and morphology (linear or branched PLA). It is demonstrated that simple shear deformation implemented in ECMAE results in formation of an orientation order, an increase in the degree of crystallinity, and the creation of α crystals with an increased degree of perfection. The value of the effects achieved depends on the type of PLA morphology. The best result is observed in the case of linear PLA. ECMAE-modified linear PLA possess the better combination of strength, modulus, and ductility than the branched one. Compared with neat linear PLA, ECMAE-modified linear PLA shows 12%, 26%, 217%, and 40% increase in tensile strength, Young's modulus, strain at break and impact strength, respectively. Additionally, the storage modulus shows an improved thermal stability of ECMAE-modified PLA.     

New Epoxy/Jeffamine networks modified with ionic liquids

Diglycidyl ether of Bisphenol A/Jeffamine D400 system was modified with 2.5 and 5.0 phr of ionic liquids based on imidazolium and phosphonium cations denoted N,N ′‐dioctadecyl‐imidazolium iodide, or octadecyl‐triphenylphosphonium iodide, [OdTPP][I], aiming to develop new networked materials with enhanced performance particularly in terms of mechanical properties and conductivity. The curing behavior was investigated by differential scanning calorimetry, suggesting that the presence of ionic liquids (ILs) accelerates the curing process of the epoxy system. Then, the networked materials were analyzed by dynamic mechanical analysis, and mechanical testing. The presence of the ILs did not affect the glass transition temperature but resulted in a decrease on the storage modulus. By transmission electron microscopy, we have highlighted that the ILs are not miscible inside the epoxy matrix. In fact, a phase separation in nanometric scale has been observed. Measurements of conductivity revealed that the system modified with [OdTPP][I] presented higher dielectric constant and higher electrical conductivity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39834.     

Phase morphology evolution and thermally conductive networks of immiscible polymer blends

The selective distribution of fillers in multi-phase polymer blends was dramatically studied to deal with thermal management fields issues. Concerning thermodynamic and kinetic effects of fillers on immiscible polymer blends, the compatibilization of fillers on phase morphology evolution and final construction of thermal conductive pathways were rarely discussed. In this work, BN fillers and polar dispersed phase were introduced into PE through various processing methods. The result showed that filler-coated shell was formed around the larger-sized dispersed phase, thereby forming more thermal conductivity network with other fillers in the two-step processing composites. When the BN content was 20 phr, the thermal conductivity was 0.8271 W/(m·K) for PE/PA6/BN-two steps composites, which was 95.48% higher than that of PE/PA6 composites. From the perspective of the regulation of the morphological structure of the dispersed phase, this study can provide methods and basic data for improving the thermal conductivity of incompatible polymer blends.     

Nickel‐multiwalled carbon nanotubes/polyvinylidene fluoride composites with high dielectric permittivity

Composites with nickel particles coated multiwalled carbon nanotubes (Ni‐MWNTs) embedded into polyvinylidene fluoride (PVDF) were prepared by solution blending and hot‐press processing. The morphology, structure, crystallization behavior, and dielectric properties of composites were studied. The results showed that the crystallization of PVDF was affected by Ni‐MWNTs. With the increment of Ni‐MWNTs, the content of β‐phase in PVDF increased. The dielectric permittivity was as high as 290 at 10³ Hz when the weight fraction of Ni‐MWNTs was 10%. The results can be explained by the space charge polarization at the interfaces between the insulator and the conductor, and the formation of microcapacitance structure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3746–3752, 2013     

Effect of starch ratio and compatibilization on the viscoelastic behavior of POE/starch blends

In this research, polyolefin elastomers (POE)/starch blends were prepared using an internal mixer with 0 to 55 wt% starch content, and MAH was added into POE/starch blend to prepare a composite that improves its biodegradation, while tuning the viscoelastic behavior and morphology. The effect of the composition and the compatibilizer addition on properties, such as morphology, rheology, and the creep behavior, was investigated. The observations of microstructures through thescanning electron microscope (SEM) showed that in the incompatibilized blends, the interfacial adhesion of the phases was very weak. In contrast, in compatibilized samples, the broken surface of starch was observed confirming the enhanced interfacial tension. Additionally, the increase in the starch content led to the rise in the relaxation times. The creep test results revealed that with the increment of starch content, the creep of the blends increased. The compatibilizer improved the creep recovery of the blends. Moreover, by addition of the compatibilizer, the values of the creep parameters including η, E₁, E_2, and τ_R obtained from the standard linear solid model (SLS), was higher than those for the incompatibilized blends. The addition of POE-MA compatibilizer can improve the properties of POE/starch blends, while keeping their biocompatibility. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48877.     

Phase transformation and dielectric properties of polyvinylidene fluoride/organic-montmorillonite nanocomposites fabricated under elongational flow field

Compounding montmorillonite (MMT) with polymorphic polyvinylidene fluoride (PVDF) by melt intercalation method can induce the crystal phase transformation of PVDF, which is of great significance to obtain the electroactive PVDF. In this research, PVDF/Organic-Montmorillonite (OMMT) nanocomposites were prepared by a novel vane mixer, which was dominated by the elongational flow field in the whole plasticizing. The dispersion of OMMT, the crystal phase transformation of PVDF, and the resulting properties of nanocomposites were experimentally studied. The results of TEM and WAXD evidenced that homogeneous dispersion and desirable intercalation structure of OMMT were formed in the PVDF matrix under the effect of the elongational flow field. WAXD, FTIR, and DSC tests demonstrated that large amounts of β-phase of PVDF was formed due to the introduction of OMMT. The intercalation structure of OMMT and the crystal transformation of PVDF increased the dielectric constant and piezoelectric properties of nanocomposites, while the dielectric loss still maintained at a very low level. Finally, the effect of unique ''double-layer peeling'' mechanism of OMMT on the properties of nanocomposites was discussed.     

Epoxy/imidazolium-based ionic liquid systems: The effect of the hardener on the curing behavior,thermal stability,and microwave absorbing properties

A new transparent microwave absorbing coating was developed by compounding 1-butyl-3-methyl imidazolium tetrafluoroborate (bmim.BF₄) ionic liquid (IL) with diglycidyl ether of bisphenol A-type epoxy resin. The systems were crosslinked with the IL alone or combined with conventional hardeners, as anhydride or aromatic amine. The curing behavior was investigated by thermal and spectroscopic analysis performed at high temperatures. Neat bmim.BF₄ was able to cure epoxy resin, giving rise to networks with outstanding thermal stability compared with the systems cured with anhydride or aromatic amine. bmim.BF₄ accelerated the curing process in the presence of aromatic amine but retarded this event when anhydride was used as an external curing agent. The glass-transition temperature evaluated by dynamic mechanical analysis decreased when the amount of IL increased, which can be attributed to side reactions during the curing process, as well as the plasticizing effect of IL. The epoxy networks cured with bmim.BF₄ alone or in combination with anhydride or aromatic amine were transparent and presented considerable microwave absorbing properties in the X-band frequency range (8–12 GHz), being the best performance observed for the systems cured with bmim.BF4/anhydride curing system, with reflection loss value around −16 dB at 11.3 GHz. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48326.     

Preparation and characterization of low environmental humidity sensitive ionic liquid polymer electrolytes

Methyl 3‐(3‐(2‐hydroxyethyl)imidazole‐1‐yl)propanoate chloride salt (IL‐Cl), methyl 3‐(3‐(2‐hydroxyethyl)imidazole‐1‐yl)propanoate bromate salt (IL‐Br), and their derivatives modified by polyethylene glycol (PEG) through ester‐exchange reaction (IL‐PEGs) were synthesized. First, the properties of those materials, especially their conductivity, have been extensively studied. Second, using the IL‐PEG with the highest conductivity as a plasticizer and electrolyte, a series of gel polymer electrolytes were successfully fabricated from polyurethane, poly‐1,4‐butylene adipate glycol 2000, and IL‐PEGs by melting blends with different mass ratios in a Haake torque rheometer. The surface morphology, thermal properties, and the surface resistivity of gel polymer electrolytes were studied by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and surface resistivity test, respectively. Scanning electron microscopy pictures showed that the surface of polymer electrolyte is smoother than that without added IL‐PEGs. Thermogravimetric analysis results revealed that the polymer electrolytes will not decompose when the processing temperature is below 275°C. It was found that the surface resistivity of polymer electrolytes can be below 10⁹ Ω, showing a good antistatic property, and it changes slightly as the relative humidity decreases from 40% to 0.1%, indicting that the material has low humidity sensitivity. This study is a new demonstration and development in ionic liquid based polymer electrolyte. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40675.     

In situ compatibilization of polylactide/thermoplastic polyester elastomer blends using a multifunctional epoxide compound as a processing agent

In situ compatibilized poly(lactic acid)/thermoplastic polyester elastomer (PLA/TPEE) (80/20) blends are prepared by using multifunctional epoxide oligomer (coded as ADR) as a reactive modifier. Experiments such as torque, melt mass flow rate (MFR), SEM, DSC and tensile test were conducted to characterize properties of the PLA/TPEE/ADR blends. In situ reactions between PLA, TPEE and ADR were researched using a lab torque rheometer. It was proposed that ADR may initiate a variety of chain extension/branching reactions between PLA and TPEE under mixing process. In particular, the formed copolymer PLA‐ADR‐TPEE could be viewed as an in situ compatibilizer to improve the compatibility of PLA and TPEE. As expected, the value of MFR decreased greatly with increasing the ADR addition. The morphology reveals that interface adhesion of PLA/TPEE blend was enhanced with the incorporation of ADR, which led to a reduction in TPEE domain size. Moreover, tensile ductility of PLA/TPEE (80/20) blend was improved greatly by addition of the reactive modifier, e.g. the elongation at break was increased from 53% to the maximum value of 213% with addition of 1.2 phr ADR. The toughening effect can be explained by crazing with shear yielding mechanism. Attempts were made to produce ductile films from these PLA/TPEE/ADR blends by using extrusion blowing method. Effect of ADR on blowing stability and tensile property of these blends was investigated. Improvement on blowing stability and tensile ductility of PLA/TPEE/ADR films also shows that ADR is an efficiently reactive compatibilizer, as well as a viscosity enhancer for PLA/TPEE blends. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43424.