Highly efficient electrically conductive networks in carbon‐black‐filled ternary blends through the formation of thermodynamically induced self‐assembled hierarchical structures

Highly efficient electrical conductive networks were constructed in carbon‐black (CB)‐filled polyoxymethylene (POM)–thermoplastic polyurethane (TPU)–polyamide 6 (PA6) ternary blends through the formation of a hierarchical structure composed of a minor PA6 phase as droplets inside one major phase (TPU) and CB particles localized at the TPU–PA6 interface by thermodynamically induced self‐assembly. The hierarchical structure was thermodynamically predicted on the basis of the minimization of total interfacial energies and confirmed by electron microscopy. The degrees of the TPU phase continuity before and after the addition of PA6 were determined by solvent‐extraction experiments. The percolation threshold of CB decreased by 50% compared to that in the POM–TPU binary blend because of the more efficient formation of a CB conductive network through CB‐covered PA6 domains inside the TPU phase. The hierarchical structure not only increased the electrical conductivity of the composites but also improved their thermal stability in comparison with the simple structure formed by the homogeneously dispersed CB particles in POM. The method reported in this article can offer possibilities for improving the comprehensive properties of the conductive composites and the widening of their applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45877.     

Super‐Tough and Highly‐Ductile Poly(l‐lactic acid)/Thermoplastic Polyurethane/Epoxide‐Containing Ethylene Copolymer Blends Prepared by Reactive Blending

Ethylene‐methyl acrylate‐glycidyl methacrylate copolymer (E‐MA‐GMA) is employed to improve the impact toughness of poly(l ‐lactic acid) (PLLA)/thermoplastic polyurethane (TPU) blends by reactive melt‐blending. The reaction and miscibility between the components are confirmed by Fourier transform infrared spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry. A super‐tough PLLA/TPU/E‐MA‐GMA multiphase blend (75/10/15) exhibits a significantly improved impact strength of 77.77 kJ m^?2, which is more than 17 times higher than that of PLLA/TPU (90/10) blend. A co‐continuous‐like TPU phase structure involving E‐MA‐GMA phase at the etched cryo‐fractured surface and the high‐orientated matrix deformation at the impact‐fractured surface are observed by scanning electron microscopy. The high‐orientated matrix deformation induced by the co‐continuous TPU phase structure is responsible for the super toughness of PLLA/TPU/E‐MA‐GMA blends.     

Triple‐shape memory properties of polyurethane/polylactide–polytetramethylene ether blends

A facile method to prepare triple‐shape memory polymers was developed by blending polyurethane and polylactide–polytetramethylene with well‐separated glass transition temperatures. The thermal properties of the blends were characterized using modulated differential scanning calorimetry and differential scanning calorimetry. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction were used to characterize the microstructures and crystal structures of the blends. The mechanical properties were also evaluated. The versatile triple‐shape memory effect and quantitative shape memory response were evaluated by consecutive thermal mechanical experiments based on a two‐step programming process and subsequent progressive thermal recovery. The results show that the blends have phase‐separated microstructures resulting in an ability to fix two temporary shapes independently and can recover to their original shapes sequentially. The blends have excellent triple‐shape memory properties and may have some applications in multi‐shape coatings, adhesives, films and temperature sensing or actuating elements. © 2015 Society of Chemical Industry     

Synthesis and characterization of epoxy with improved thermal remendability based on Diels‐Alder reaction

To produce an epoxy resin with high intrinsic self‐healing efficiency, furfurylglycidyl ether (FGE) was synthesized following a two‐step route. It carried one furan and one epoxide on each of its molecules. Having been cured using N,N′‐(4,4′‐diphenylmethane)bismaleimide and methylhexahydrophthalic anhydride, FGE was then polymerized with two types of intermonomer linkages. That is, thermally reversible Diels–Alder (DA) bonds from the reaction between furan and maleimide groups, and thermally irreversible bonds from the reaction between epoxide and anhydride groups. These two types of bonds provide the polymer with thermal remendability and load‐bearing capacity, respectively. Compared with N,N‐diglycidylfurfurylamine, which was previously developed by the authors and has a similar structure to FGE but with fewer furan rings, FGE can react with maleimide with lower activation energy and the DA bonds formed exhibit higher reversibility. Consequently, improved crack healability of the cured FGE characterized by nearly full recovery of fracture toughness was revealed using double cleavage drilled compression tests. Copyright © 2010 Society of Chemical Industry     

Reactive compatibilization of PP/PBT blends by a mixture of PP‐g‐MA and epoxy resin

In this study, dual compatibilizers composed of the commercially available maleic anhydride‐grafted polypropylene (PP–MA) and a multifunctional epoxy resin were demonstrated to effectively compatibilize the immiscible and incompatible blends of PP and poly(butylene terephthalate) (PBT). The PP–MA with a low MA content is totally miscible with PP to make the PP phase quasi‐functionalized, so that the multifunctional epoxy has the chance to react with PBT and PP–MA simultaneously to form PP–MA‐co‐epoxy‐co‐PBT copolymers at the interface. These desired copolymers are able to anchor along the interface and serve as efficient compatibilizers. The compatibilized blends, depending on the quantity of dual compatibilizers employed, exhibit higher viscosity, finer phase domain, and improved mechanical properties. Epoxy does not show compatibilization effects for the PP/PBT blends without the presence of PP–MA in the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2272–2285, 2001     

Annealing effect on the shape memory properties of polylactic acid (PLA)/thermoplastic polyurethane (TPU) bio-based blends

PLA and TPU were melt-blended to form shape memory bio-based blends with or without post-annealing effect. To the authors’ best knowledge, this is the first work to discuss the annealing effect on the PLA-based SMP blends. Annealed TPU showed regularly fractured surfaces unlike the macro-phase segregated domains for non-annealed TPU. After 3 h-annealing treatment, spherulites were observed for PLA, but not for TPU. The crystallinity of PLA increased, close to 3-fold increment, for annealed blends in comparison with non-annealed blends. The shape memory behaviors of PLA/TPU blends predeformed under three different predeformation temperatures (25, 80, 120 °C) were investigated. The annealing effect was helpful in enhancing the shape fixing ratio of the PLA/TPU (60/40) blend at high predeformation temperature of 120 °C in comparison with 25 °C. However, the suitable selection of the optimum predeformation temperature at 80 °C outweighed the annealing effect to attain the high shape fixing ratio, even in the case of non-annealed blends. The annealing effect often increased the perfection of crystal domains/interfaces and the larger crystal sizes, which would be detrimental to the molecular extensibility. The overall annealing effect on the shape recovery ratios were quite effective for both PLA/TPU blends of 80/20 and 60/40 without sacrificing the shape fixing ratios at the optimum predeformation temperature of 80 °C, attributing to the increased crystallinity of PLA and homogenized phase domains of TPU. Particularly, the annealing treatment did significantly increase the recovery ratio of the blends, more than 2-fold increment, especially for PLA/TPU (60/40) blend. At both lower or higher predeformation temperatures, the stress concentration between the increased crystalline domains and amorphous regions tended to dominate the annealing effect, leading to a negative contribution to the shape recovery processes.     

Multiple shape memory effects of trans‐1,4‐polyisoprene and low‐density polyethylene blends

A novel series of shape memory blends of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) were prepared using a simple physical blending method. The mechanical, thermal and shape memory properties of the blends were studied and schemes proposed to explain their dual and triple shape memory behaviors. It was found that the microstructures played an important role in the shape memory process. In TPI/LDPE blends, both the TPI crosslinking network and LDPE crystalline regions could work as fixed domains, while crystalline regions of LDPE or TPI could act as reversible domains. The shape memory behaviors were determined by the components of the fixed and reversible domains. When the blend ratio of TPI/LDPE was 50/50, the blends showed excellent dual and triple shape memory properties with both high shape fixity ratio and shape recovery ratio. © 2017 Society of Chemical Industry     

Diels–Alder‐based crosslinked self‐healing polyurethane/urea from polymeric methylene diphenyl diisocyanate

Crosslinked self‐healing polyurethane/urea based on a Diels–Alder reaction (C‐PMPU–DA) was synthesized from a multiple‐furan monomer and a commercial bismaleimide. The multiple‐furan monomer (PMPU–furan) was obtained from a functionalized prepolymer (polymeric MDI: PBA‐2000 = 2:1) by furfuryl amine. The structures of both the PMPU–furan and C‐PMPU–DA were characterized by attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and ¹H‐NMR. The Diels–Alder bonds enabled C‐PMPU–DA thermal reversibility, which was investigated by ATR–FTIR spectroscopy, ¹H‐NMR, gel–solution–gel experiments, and viscosity tests. Meanwhile, the self‐healing properties of C‐PMPU–DA were also investigated by the recovery of the mechanical properties. The results showed that C‐PMPU–DA exhibited good thermal reversibility and self‐healing properties. C‐PMPU–DA exhibited thermosetting properties at room temperature, although it exhibited thermoplastic properties at higher temperatures and may find applications in self‐healing materials, recyclable materials, or removable materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40234.     

Morphology profiles obtained by reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems

The reaction‐induced phase separation in epoxy/aromatic diamine formulations simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF), has been studied. The epoxy monomer was based on the diglycidyl ether of bisphenol A (DGEBA) and the aromatic diamine was 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) (MCDEA). Phase‐separation conversions are reported for various PSF/PEI proportions for blends containing 10 wt% total TP. On the basis of phase‐separation results, a conversion–composition phase diagram at 200 °C was compiled. This diagram was used to design particular cure cycles in order to generate different morphologies during the phase‐separation process. It was found that, depending on the PSF/PEI ratio employed, a particulate or a morphology characterized by a distribution of irregular PEI‐rich domains dispersed in an epoxy‐rich phase was obtained for initially miscible blends. Scanning electron microscopy (SEM) characterization revealed that the PEI‐rich phase exhibits a phase‐inverted structure and the epoxy‐rich matrix presents a bimodal size distribution of TP‐rich particles. For PSF/PEI ratios near the miscibility limit, slight temperature change result in morphology profiles. Copyright © 2005 Society of Chemical Industry     

Recyclable,shape‐memory,and self‐healing soy oil‐based polyurethane crosslinked by a thermoreversible Diels–Alder reaction

The recyclable, shape‐memory, and self‐healing soy oil‐based polyurethane (S‐PU) networks were constructed by the thermoreversible Diels–Alder (DA) reaction between S‐PU (sealed with furfuryl alcohol) and 1,5‐bis(maleimido)‐2‐methylpentane. The DA and retro‐DA reactions between furan and maleimide were investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, solubility, and recycle testing. Moreover, the shape‐memory properties of the S‐PU networks were studied by qualitative recovery testing and quantitative cyclic tensile testing. Furthermore, the self‐healing properties of S‐PU networks were confirmed by cut, scratch, and tensile testing. The results showed that, compared to the traditional S‐PU, the novel S‐PU prepared in this work was recyclable and self‐healing. And although both of them have shape‐memory effect, the novel S‐PU has a higher shape fixed rate and shape recovered rate than the traditional S‐PU. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46049.     

Toughening of an epoxy resin with hydroxy‐terminated poly(arylene ether nitrile) with pendent tertiary butyl groups

Hydroxy‐terminated poly(arylene ether nitrile) oligomers with pendent tert‐butyl groups (PENTOH) were synthesized by the nucleophilic aromatic substitution reaction of 2,6‐dichlorobenzonitrile with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone medium with anhydrous potassium carbonate as a catalyst at 200°C in a nitrogen atmosphere. The PENTOH oligomers were blended with diglycidyl ether of bisphenol A epoxy resin and cured with 4,4′‐diaminodiphenyl sulfone. The curing reaction was monitored with infrared spectroscopy and differential scanning calorimetry. The morphology, fracture toughness, and thermomechanical properties of the blends were investigated. The scanning electron micrographs revealed a two‐phase morphology with a particulate structure of the PENTOH phase dispersed in the epoxy matrix, except for the epoxy resin modified with PENTOH with a number‐average molecular weight of approximately 4000. The storage modulus of the blends was higher than that of the neat epoxy resin. The crosslink density calculated from the storage modulus in the rubbery plateau region decreased with an increase in PENTOH in the blends. The fracture toughness increased more than twofold with the addition of PENTOH oligomers. The tensile strength of the blends increased marginally, whereas the flexural strength decreased marginally. The dispersed PENTOH initiated several toughening mechanisms, which improved the fracture toughness of the blends. The thermal stability of the epoxy resin was not affected by the addition of PENTOH to the epoxy resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Evaluation of Norbornene‐Based Adhesives to Amine‐Cured Epoxy for Self‐Healing Applications

High adhesive strengths are essential in self‐healing polymers. In these novel materials, healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to an embedded chemical initiator triggers ring‐opening metathesis polymerization (ROMP), bonding the crack faces closed. In order to improve self‐healing efficiencies in these systems, it is necessary to improve the adhesion of the polymerized healing agent with the epoxy matrix. In this study, the adhesive shear strength between different norbornene‐based healing agents and an amine‐cured epoxy resin was evaluated using single lap shear specimens. The healing agents tested include endo‐dicyclopentadiene (DCPD), 5‐ethylidene‐2‐norbornene (ENB) and DCPD/ENB blends. 5‐Norbornene‐2‐methanol (NBM) and 5‐norbornene‐2‐exo,3‐exo‐dimethanol (NBDM) were used as adhesion promoters because they contain hydroxyl groups which can form hydrogen bonds with the amine‐cured epoxy adherend. A custom synthesized norbornene‐based crosslinking agent was also added to improve the adhesion of the polymerized ENB by increasing its crosslink density after ROMP. The effects of catalyst loading, polymerization time and cure temperature on the adhesive bond strength are studied in detail.

     

Reaction‐induced phase separation and resulting thermomechanical and surface properties of epoxy resin/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) blends cured with 4,4′‐diaminodiphenylsulfone

We investigated the phase separation, cure kinetics and thermomechanical properties of diglycidyl ether of bisphenol‐A/4,4′‐diaminodiphenylsulfone/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (TBCP) blends. Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy revealed that the blends exhibited heterogeneous phase morphology in which the TBCP formed dispersed domains in epoxy matrix, due to reaction induced phase separation. A fraction of phase‐separated PEO phase underwent partial crystallization whereas another fraction formed interphases between the dispersed domains and epoxy matrix. Moreover, the dispersed PEO chains improved the compatibility and interfacial adhesion between the matrix and domains and, consequently, significantly improved the mechanical properties of epoxy resin. Furthermore, the thermal degradation studies and contact angle measurements disclosed that the dispersed domains were well protected by the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44406.     

Thermally reversible and self‐healing novolac epoxy resins based on Diels–Alder chemistry

The modified novolac epoxy resins with furan pendant groups were prepared by novolac epoxy resin and furfuryl alcohol and then crosslinked by bifunctional maleimide via Diels–Alder (DA) chemistry to obtain the thermally reversible and self‐healing novolac epoxy resins. The as‐prepared crosslinked novolac epoxy resins were characterized by FT‐IR, NMR, TGA, and DMA. The results indicate that the novel crosslinked novolac epoxy resins present higher storage modulus (2.37 GPa at 30°C) and excellent thermal stability (348°C at 5% mass loss). Furthermore, the thermal reversible and self‐healing properties were studied in detail by DSC, SEM, thermal re‐solution, and gel–solution–gel transition experiments. All the results reveal that the crosslinked novolac epoxy resins based on DA reaction can be used as smart material for the practical application of electronic packaging and structural materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42167.     

Synthesis and self‐healing behavior of thermoreversible epoxy resins modified with nitrile butadiene rubber

Cracks may generate in epoxy resins, which can affect the comprehensive property and shorten service life. The problem is expected to be resolved by endowing epoxy resin with self‐healing performance. Herein, a new kind of self‐healing epoxy resin containing both Diels–Alder (DA) bonds and nitrile butadiene rubber (NBR) has been developed. The self‐healing performance and mechanical properties of as‐prepared epoxy resins are investigated by qualitative observation and quantitative measuring. Results reveal that the as‐prepared epoxy resins exhibit excellent self‐healing performance and multiple repair ability, and the self‐healing behavior is based on dual actions of thermal reversibility of DA reaction and thermal movement of molecular chains. Furthermore, the thermoreversible DA bonds contribute much to the recovery of mechanical property, while the incorporated thermoplastic NBR accelerates the whole healing process. The self‐healing efficiency of epoxy resins can be enhanced markedly by introducing thermoplastic NBR. In addition, the self‐healing epoxy resins also exhibit outstanding reprocessing performance, which makes it possible of recycling waste epoxy resin. POLYM. ENG. SCI., 59:1603–1610 2019. © 2019 Society of Plastics Engineers     

Toughening of thermoset/thermoplastic composites via reaction‐induced phase separation: Epoxy/phenoxy blends

Phase morphology and phase separation behavior of amine‐cured bisphenol‐A diglycidyl ether epoxy and phenoxy mixtures have been investigated by means of time‐resolved small angle light scattering, optical microscopy, and scanning electron microscopy. The starting reactant mixtures composed of epoxy, phenoxy, and curing agents such as diaminodiphenyl sulfone (DDS) and methylene dianiline (MDA) were found to be completely miscible. Upon curing with DDS at 180°C, phase separation took place in various epoxy/phenoxy blends (compositions ranging from 10–40% phenoxy), whereas the MDA curing showed no indication of phase separation. The mechanical and physical properties of single‐phase and two‐phase networks were examined, in that the DDS‐cured epoxy/phenoxy blends having a two‐phase morphology showed improved ductility and toughness without significantly losing other mechanical and thermal properties such as modulus, tensile strength, glass transition and heat deflection temperatures. The energy absorbed to failure during the drop weight impact event was also found to improve relative to those of the single‐phase MDA‐cured blend as well as of the neat epoxy. Such property enhancement of the DDS‐cured blends has been discussed in relation to the two‐phase morphology obtained via scanning electron microscopy micrographs of fractured surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1257–1268, 2000     

Tailor‐Made Functional Polymethacrylates with Dual Characteristics of Self‐Healing and Shape‐Memory Based on Dynamic Covalent Chemistry

New shape memory polymers with self‐healing behavior are obtained by thermoreversible Diels–Alder (DA) cross‐linking of a furfuryl group‐containing star‐block copolymer with 1,1′‐(methylenedi‐4,1‐phenylene)bismaleimide. The star‐block copolymer consisting of a 3‐arm polycaprolactone (PCL) core and a polyfurfuryl methacrylate shell is synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. For this, a 3‐arm macro‐RAFT agent based on PCL is converted with an appropriate amount of furfuryl methacrylate in the presence of a radical initiator. Films of the DA network are partly insoluble at ambient temperatures. After annealing at 120 °C the films become completely soluble because of the progressing retro‐DA reaction. Evaporation of the solvent and subsequent annealing at 60 °C restores the original insoluble state of the material. By means of a scratch test and tensile tests on cut and subsequently mended samples it is shown that the retro‐DA reaction facilitates self‐healing. Additionally, the films show pronounced shape memory effects with reasonable shape recovery and fixity ratios, which are attributed to the melting and crystallization of the PCL phase.     

High-efficiency shape memory copolymers of polycaprolactone/thermoplastic polyurethane fabricated via in situ ring-opening polymerization

Shape memory blends of polycaprolactone/thermoplastic polyurethane (PCL/TPU) were prepared by in situ ring-opening polymerization (ROP) of ε-caprolactone (CL) and thermoplastic polyurethane (TPU). Fourier infrared spectrometer and ¹H-NMR were used to characterize the chemical structure of PCL/TPU copolymers. The results show that TPU has been involved in the ROP of CL, leading to the formation of copolymers with homogeneous morphologies. Besides, pure PCL and all the blends exhibit an excellent shape fixation ratio of 100%, due to their high crystallinity. When a small amount of TPU is introduced, the crystallinity of PCL decreases, and as a result, the shape recovery ratio of the copolymer is enhanced compared with pure PCL. However, with the increased loading of TPU, the content of PCL as the reversible phase decreases and the storage modulus of the PCL/TPU blend declines, so the driving force for the blends to return from the temporary shape to the initial shape becomes smaller, leading to a decrease in the shape recovery ratio. Notably, when the amount of TPU is only 5%, the shape recovery ratio of the blend could reach 83.3%, which is 26% higher than that of pure PCL, and meanwhile, the tensile strength of the blend decreases slightly. This study provides a new strategy for the design of shape-memory materials with high shape-memory properties.     

Mechanical properties of epoxy resin/hydroxyl‐terminated polyester blends: effect of two‐phase structure

In this paper, the effect of two‐phase structure on the mechanism of rubber‐toughening of epoxy resins was studied. Three types of hydroxyl‐terminated polyesters with different molecular weights were synthesized in order to modify epoxy resins to obtain single‐phase (P‐1), critical phase separation (P‐2) and two‐phase (P‐3) structures. The results of dynamical mechanical analysis and scanning electron microscopy distinguished the dissolved and phase‐separated polyesters in the epoxy matrix. The P‐1 system showed the highest dissolved content of polyester in the epoxy matrix, while the P‐3 system exhibited the lowest content. Both dissolved and phase‐separated polyesters proved to be capable of increasing the toughness of modified epoxy resins. The phase‐separated polyester was found to contribute much more to the improvement of toughness. Copyright © 2005 Society of Chemical Industry     

Regeneration efficiency of composites containing two‐sized capillaries

The aim of this work is to develop a composite material containing a regeneration system and to demonstrate its self‐healing properties. For this purpose, we will study the self‐healing behavior of composites that are fabricated with a regeneration system consisting of two‐sized capillaries filled with epoxy resin and hardener. Composites with restorative systems containing identical microtube diameters can be found in the literature, but until now no comparative studies with multiple diameter structures have been published. We will prove that a regeneration system containing two types of capillaries with diameters of 100 and 50 μm is more efficient (68% recovery of bending strength and Young's modulus after third regeneration) than a regeneration system containing capillaries with the same diameter (44% recovery of bending strength and 44% recovery of Young's modulus after third regeneration). POLYM. COMPOS. 37:1223–1230, 2016. © 2014 Society of Plastics Engineers