Reaction-induced Phase Separation Research Articles

Cardo poly (ether sulfone) toughened E51/DETDA epoxy resin and its carbon fiber composites

A toughener that can effectively improve the interlaminar toughness in carbon fiber composites is crucial for various applications. We investigated, the toughening effects of phenolphthalein-based cardo poly (ether sulfone) (PES-C) on E51/ DETDA epoxy and its carbon fiber composites (CFCs). Scanning electron microscopy showed that the phase structures of PES-C/epoxy blends change from island (of dispersed phase) structures to bi-continuous structures (of the matrix) as the PES-C content increased, which is associated with reaction-induced phase separation. After adding 15 phr PES-C, the glass transition temperature (Tg) of the blends increased by 51.5 °C, and the flexural strength, impact strength and fracture toughness of the blends were improved by 41.1%, 186.2% and 42.7%, respectively. These improvements could be attributed to the phase separation structure of the PES-C/epoxy system. A PES-C film was used to improve the mode-II fracture toughness (GIIC) of CFCs. The GIIC value of the 7 μm PES-C film toughened laminate was improved by 80.3% compared to that of the control laminate. The increase in GIIC was attributed to cohesive failure and plastic deformation in the interleaving region.

Preparation and size control of epoxy resin multilevel structures with SiO2 particles

In the process of preparing porous epoxy materials using reaction-induced phase separation (RIPS), the introduction of an appropriate amount of SiO2 particles enables the control of the phase separation behavior of the system and its ultimate phase structure. This study examined the role of SiO2 particles in the preparation and size control of epoxy resin multilevel structures by analyzing the phase separation and reaction kinetics in an epoxy resin blend system and characterizing the ultimate phase structure. It was found that fumed SiO2 particles (0–3 wt%) added to the DGEBA/DDCM/PEG200 blends resulted in significant interfacial stabilization, delaying phase separation. With an increase in the fumed SiO2 particle content, the phase structure stopped evolving at an earlier stage of phase separation. In addition, the fumed SiO2 particles dispersed in the porogen-enriched phase helped to stabilize the system, i.e., preventing or slowing down the segregation and aggregation of the components in the system, which may inhibit secondary phase separation in the porogen-enriched phase. When 350 nm SiO2 particles were used, an increase in the particle size resulted in a larger phase structure. The SiO2 particles were dispersed within the pore-forming agent phase, increasing the proportion of the pore-forming agent and exerting an occupancy effect, which diminished with decreasing SiO2 particle size and increasing hydrophobicity. Notably, the surface of the epoxy porous material skeleton was decorated with small pits formed by the acid etching of the SiO2 particles, and this multilevel structure contributed to the specific surface area. The multilevel structure can be precisely controlled by adjusting the size, content, and wettability of the SiO2 particles. The results of this study are universal and instructive for the preparation of porous materials using a phase separation method in combination with solid particles.

Dissipative Particle Dynamics Simulation for Reaction-Induced Phase Separation of Thermoset/Thermoplastic Blends.

Reaction-induced phase separation occurs during the curing reaction when a thermoplastic resin is dissolved in a thermoset resin, which enables toughening of the thermoset resin. As resin properties vary significantly depending on the morphology of the phase-separated structure, controlling the morphology formation is of critical importance. Reaction-induced phase separation is a phenomenon that ranges from the chemical reaction scale to the mesoscale dynamics of polymer molecules. In this study, we performed curing simulations using dissipative particle dynamics (DPD) coupled with a reaction model to reproduce reaction-induced phase separation. The curing reaction properties of the thermoset resin were determined by ab initio quantum chemical calculations, and the DPD parameters were determined by all-atom molecular dynamics simulations. This enabled mesoscopic simulations, including reactions that reflect the intrinsic material properties. The effects of the thermoplastic resin concentration, molecular weight, and curing conditions on the phase-separation morphology were evaluated, and the cure shrinkage and stiffness of each cured resin were confirmed to be consistent with the experimental trends. Furthermore, the local strain field under tensile deformation was visualized, and the inhomogeneous strain field caused by the phase-separated structures of two resins with different stiffnesses was revealed. These results can aid in understanding the toughening properties of thermoplastic additives at the molecular level.

Improving delamination resistance of 3D printed continuous fiber-reinforced thermoset composites by multi-scale synergistic toughening of mono-component polyetherketone-cardo

Continuous fiber-reinforced thermoset composites (CFRTCs) 3D printing offers a promising solution to fabricate lightweight, high-strength sophisticated composite structures. However, the delamination resistance of 3D printed CFRTCs is decreased by the weak fiber-matrix and interlayer adhesion caused by the process principle. To increase the interlayer toughness of 3D printed CFRTCs, this study developed a printing matrix toughened by various polyetherketone-cardo (PEK-C) forms by modulating its dissolution state. The results showed that the interlaminar toughening effects of the particle dispersion and dissolved dual form of PEK-C were superior to the insoluble particles or the dissolved PEK-C. As a result, the mode I and mode II interlaminar fracture toughness increased by 112.38 % and 189.01 %, respectively. And the synergistic effect of dual-form PEK-C was determined. Fractographic investigation revealed that the dissolved PEK-C experienced the reaction-induced phase separation initiating a nanoscale thermoplastic phase and developing a multi-scale PEK-C toughening system with the microscale PEK-C particles. Moreover, morphological observation of the particle and PEK-C phases demonstrate multi-scale synergistic toughening mechanisms of mono-component PEK-C. This study presents an innovative technique for interlayer toughening applicable to the CFRTCs 3D printing, illustrates the toughening principle, and shows its promise as a general strategy.

Improvement of persistent hydrophilicity and pore uniformity of polyvinyl chloride ultrafiltration membranes by in-situ crosslinking reaction assisted phase separation

A novel in-situ crosslinking reaction assisted phase separation strategy was proposed for persistent hydrophilization and pore size regulation of polyvinyl chloride (PVC) membranes. In-situ cross-linking between PVC molecular chains was achieved through grafting of 3-aminopropyltrimethoxysilane (APTMS) during the dissolution process and cross-linking reactions between siloxanes in APTMS molecules initiated by the coagulation bath (water). The effect of in-situ crosslinking reaction on the structure, separation and anti-fouling performance of the PVC membranes was studied. Through in-situ crosslinking reaction induced phase separation, the migration and curing of polymer molecular chains in the phase separation process were regulated, which endowed the modified membrane with improved hydrophilicity, higher porosity and narrow pore size distribution. The pure water flux of the obtained membrane increased 3.5 times as much as that of the pure PVC membrane. In addition, the flux recovery rate (FRR) of the obtained membrane was increased by 15.9% and the strength was also increased slightly at the same time. The stability of the membranes was also improved, without chemical agents leaching during filtration, avoiding secondary pollution to our environment.

Preparation of Porous Epoxy Resin Materials by Reaction-Induced Phase Separation Regulated Using Fumed Silica

Significant attention has been paid to improving the microstructure of polymer blends by stabilizing their phase interface with inorganic nanoparticles. During the preparation of porous epoxy resin materials by reaction-induced phase separation, the microstructure of the porous epoxy resin materials is controlled by fumed silica. The phase separation and chemical kinetics have been monitored by optical microscopy, differential scanning calorimetry, and rheometry, and the microstructure has been characterized by scanning electron microscopy and mercury porosimetry. Upon comparison of the phase separation process of the epoxy blend before and after the addition of fumed silica, it is evident that the fumed silica are preferentially dispersed in the pore-forming agent phase; at the phase interface, the coarsening rate of the phase structure is decreased, the reaction rate is decreased, and the gelation is delayed. With an increase in the mass fraction of the fumed silica, the pore size of the porous epoxy resin materials decreases gradually, and the structure is fined. This result provides an approach for the fine control of the microstructure of porous epoxy resin materials. In addition, the fumed silica in the porous epoxy resin material can be removed by acid etching without affecting the structure of the porous material. Furthermore, the effect of the fumed silica on the structure of the closed-hole epoxy resin system has been investigated.

Mechanical properties of reactive polyetherimide-modified tetrafunctional epoxy systems

Highly crosslinked multifunctional epoxy resins are commonly brittle. Thermoplastic toughening agents have been used to improve the fracture toughness of crosslinked epoxy resins. However, toughness improvement is limited due to poor interfacial adhesion between epoxy matrix and thermoplastic toughener. Furthermore, it is desired that toughness improvements should not come at the expense of other properties, including modulus, thermal properties and processability. In this work, amine functionalized reactive polyetherimide (rPEI) having two different molecular weights and loading levels were incorporated in tetraglycidyl-4, 4′-diaminodiphenyl methane (TGDDM) epoxy resin to study the structure-property relationship, including effects of reaction-induced phase separation on fracture toughness. Results demonstrate that the phase morphologies of rPEI in an epoxy resin can be drastically affected by the functionality, molecular weight and loading levels of rPEI. The mode-I fracture toughness (KIC) of rPEI-toughened epoxy is increased by up to 140% versus untoughened epoxy control. An investigation into the fracture mechanisms of rPEI-toughened TGDDM epoxy showed evidence of rPEI particle bridging as one of the key mechanisms of toughening. Our work further demonstrated that the rPEI-toughened TGDDM epoxy maintained both high modulus and high Tg, rendering it suitable for a wide range of applications.

Miscibility, thermal degradation and rheological analysis of epoxy/MABS blends.

The effect of the addition of the methyl methacrylate acrylonitrile butadiene styrene (MABS) copolymer on the miscibility, thermal degradation and rheological properties of epoxy systems is described. Epoxy resin/MABS blends containing 5, 10, 15 and 20 phr MABS were prepared using the solution mixing technique. Homogenous blends obtained using this technique have undergone a polymerization reaction induced phase separation process by the introduction of the curing agent 4,4'-diaminodiphenyl sulfone (DDS). The isothermal rheology at four different temperatures, 150, 160, 170 and 180 °C, was used to examine the effect of MABS on the gelation and vitrification time. The evolution of storage modulus, loss modulus and tan delta was found to be closely related to the evolution of complex phase separation. The increase in the complex viscosity during curing was determined by in situ rheometry and theoretically analysed by fitting with the Williams-Landell-Ferry equation. An exponential increase in complex viscosity was observed, which was induced by cross-linking. The variation of Tg before and after curing was studied using DSC analysis and dynamic kinetic modeling of the curing process was carried out by utilizing dynamic DSC scans. Thermal stability studies of completely cured epoxy/MABS blends using thermogravimetric analysis revealed that all the blends and neat epoxy exhibited single step degradation. Thermal degradation kinetics was calculated using the Coats Redfern equation.

Reaction-induced phase separation towards in situ network in epoxy resins for simultaneously improving thermal conductivity and fire safety

Simultaneously improving the thermal conductivity and fire safety of the polymeric thermal management materials (PTMMs) still remains a challenge. In this work, through reaction-induced phase separation (RIPS), co-continuous networks were in situ formed between polyetherimide (PEI) and epoxy resin (EP) cured with either commercially available 4,4′-diaminodiphenyl sulfone (DDS) or the synthesized bis(4-aminophenyl) phenylphosphonate (BAPP). Boron nitride nanosheets (BNNSs) were selectively localized in the interfacial region between the EP-rich and PEI-rich phases as the thermally conductive fillers; therefore the thermally conductive networks were constructed. BNNSs and BAPP simultaneously endowed the composites with enhanced thermal conductivity and expected fire safety. In detail, the EPBAPP/PEI/BNNS composite with barely 1 wt% BNNSs showed a thermal conductivity increment over 67%; and both the heat and smoke release were greatly suppressed in cone calorimetry: the peak heat release rate (PHRR) reduced by 58%, total heat release (THR) by 56% and total smoke production (TSP) by 46%, compared with the reference. The successful application of the RIPS method in constructing in situ thermally conductive networks provided promising perspectives for designing versatile PTMMs.

In situ phase separation of novel phosphorus-containing polyester in epoxy resins towards simultaneously improved thermal conductivity and fire safety

Polymeric thermal management materials (PTMMs) attained with expected thermally conductive performance and flame retardancy are still urgently being required. Herein, a novel phosphorus-containing polyester named poly(bis(1,1’-biphenoxyl)hexyl 5-(diphenylphosphoryl-amino)isophthalate) (PBHPI) was synthesized and incorporated into the epoxy resin (EP). After curing with 4,4’-diaminodiphenyl sulfone (DDS), in situ networks were obtained via reaction-induced phase separation (RIPS) between PBHPI and EPDDS, which induced the preferable distribution of boron nitride nanosheets (BNNSs) at the interface between the PBHPI-rich and EP-rich phases; therefore the photon transmission pathways were constructed. Due to the flame inhibition activity of PBHPI and the physical barrier effect of BNNSs, EPDDS/PBHPI/BNNSs composites exhibited expected fire safety performance of heat insulation and smoke suppression in cone calorimetry: the peak heat release rate (PHRR) reduced by 60%, total heat release (THR) by 40% and total smoke production (TSP) by 41%, compared with EPDDS. In addition, the incorporation of barely 1 wt% BNNSs improved the thermal conductivity of the composites. This work combining the molecular design of the novel phosphorus-containing polyester and the RIPS methods to construct in situ networks provided a feasible solution and unique insight into the design of PTMMs in a facile and convenient way.

Constructing PA6/PS composite foam with porous and hybrid isolation structure to synergistically control absorption and electromagnetic interference shielding effectiveness

AbstractIsolation structure has been proven to be an effective method for constructing electromagnetic shielding composites, achieving high electrical conductivity with shallow filler content and high‐efficiency electromagnetic shielding. However, there are still many challenges in further optimizing the design and improving absorption. This article designed a hybrid isolation structure using nylon magnetic microspheres and polystyrene (PS). First, we prepared PA magnetic microspheres (Ni@PA6M) with Ni nanoparticles uniformly dispersed by the reaction induced phase separation (RIPS) method, then mixed with MWCNT and PS at high speed and formed by hot pressing. Under the optimized ratio, the hybrid structure has more interfaces and a more complete conductive network. Simultaneously, the magnetic microspheres can promote the absorption of electromagnetic waves, thereby improving the electromagnetic shielding performance of the material. When the MWCNT content is 7 wt%, Ni@PA6M:PS = 7:3, the total shielding effectiveness (EMI SET) and reflection coefficient (R) of the composite reached 28.6 dB and 0.77, respectively, while the EMI SET and R of the composite constructed with pure nylon microspheres and PS are 26.1 dB and 0.74, respectively. Further, using supercritical CO2 foaming technology to foam the PS phase in the composite to form many cells can improve the impedance matching and absorption of electromagnetic waves. The results show that introducing the cell structure reduces the reflection coefficient (R) from 0.77 to 0.69, and the EMI SET drops to a certain extent. Introducing the hybrid isolation and porous structure we designed provides a new idea for creating electromagnetic shielding materials for isolation structures.

Synergistic toughening on hybrid epoxy nanocomposites by introducing engineering thermoplastic and carbon-based nanomaterials

In this study, epoxy-anhydride thermoset was initially modified with polyethersulfone (PESU) at 0‐15 wt% loading. The various mass ratios at 0.50 wt% total content of graphene nanoplatelets (GNPs)/carbon nanotubes (CNTs) were further introduced to comprehensively study the simultaneous incorporation of different tougheners on morphological, thermal, and mechanical properties of engineering thermoplastic modified epoxy. The binary blend of PESU/epoxy reveals two-phase morphologies due to reaction induced phase separation, showing particulate morphology at 5 wt% PESU and co-continuous morphology at 10‐15 wt% PESU. It was found that the presence of PESU at 5 wt% not only improved thermal stability but also provide the optimum mechanical properties, showing 35% and 40% increasing in tensile strength and fracture toughness, respectively. From fracture surface analysis, crack deflection from the PESU dispersed particles was observed as a main toughening mechanism for this binary blend. With introducing GNPs and/or CNTs, hybrid nanocomposite based on 5 wt% PESU modified epoxy matrix showed similar morphology and thermo-mechanical properties to the binary blends. Additionally, the remarkable Young's modulus were observed in all hybrid PESU/carbon-based nanofillers toughened epoxy composites. PESU and GNPs dispersed phase contribute greatly in enhancing fracture toughness (KIc) of hybrid PESU/nanofillers system. KIc of PESU/epoxy blends with 0.5 wt% GNPs was measured at 0.86 MPa m1/2, counting as ∼60% and ∼18% improvement from pristine epoxy and 0.5 wt% GNPs modified neat epoxy, respectively. Apart from crack deflection of PESU, GNPs cluster effectively deviates and bifurcates the crack path, indicating the synergistic effect on PESU/GNPs epoxy nanocomposite. Interestingly, these two tougheners also dominates the toughening mechanism in PESU/GNPs/CNTs epoxy nanocomposites. Meanwhile, the influence of CNTs on fracture toughness was not clearly demonstrated on hybrid nanocomposite system.

Enhanced Electromagnetic Interference Shielding Properties of Immiscible Polyblends with Selective Localization of Reduced Graphene Oxide Networks.

Herein, an effective technique of curing reaction-induced phase separation (CRIPS) was used to construct a reduced graphene oxide (RGO) network in the immiscible diglycidyl ether of the bisphenol A/polyetherimide (DGEBA/PEI) polyblend system. The unique chemical reduction of RGO facilitated the reduction of oxygenated groups and simultaneously appended amino groups that stimulate the curing process. The selective interfacial localization of RGO was predicted numerically by the harmonic and geometric mean technique and further confirmed by field emission transmission electron microscopy (FETEM) analysis. Due to interfacial localization, the electrical conductivity was increased to 366 S/m with 3 wt.% RGO reinforcement. The thermomechanical properties of nanocomposites were determined by dynamic mechanical analysis (DMA). The storage modulus of 3 wt.% RGO-reinforced polyblend exhibited an improvement of ~15%, and glass transition temperature (Tg) was 10.1 °C higher over neat DGEBA. Furthermore, the total shielding effectiveness (SET) was increased to 25.8 dB in the X-band region, with only 3 wt.% RGO, which represents ~99.9% shielding efficiency. These phase separation-controlled nanocomposites with selective localization of electrically conductive nanofiller at a low concentration will extend the applicability of polyblends to multifunctional structural nanocomposite applications.

Effect of GO modification and curing on formation of ordered structures in epoxy composites

Modifications of GO by polymer chains may promote, in addition to exfoliation, also formation of ordered structures in epoxy. However, the contribution of self- assembly in the uncured matrix and reaction-induced phase separation to this process is not clear. SAXS study of analogous liquid and cured epoxy reveals that single grafted GO forms ordered structures only due to RIPS of grafted rubber. The marked self-assembly of bimodally grafted GO (BGO) before curing indicates that such modification changes its ordering performance substantially. Moreover, formation of ordered lamellar structures in liquid epoxy accompanied by easy migration of BGO may lead to formation of these arrays at the interface in carbon fibre composites. As a result, in-situ formation of effective nacre-like structures on the surface of CF, increasing delamination resistance, can be achieved.

Influence on fracture toughness arising from controlled morphology of multiphase toughened epoxy resins in the presence of fibre reinforcement

Numerous studies found in the literature focus on enhancing the fracture toughness of thermosetting polymers by incorporating various toughening agents. The resulting gains in fracture toughness are mostly attributed to an expansion in the volume of the plastic deformation zone ahead of the propagating crack and the modified resin blends are subsequently introduced as matrices for fibre reinforced composite materials. It is often assumed that improvements in fracture toughness of the polymer matrix are directly transferred to the resulting fibre reinforced composites. This paper shows that this is not necessarily the case. The present study is focused on the fracture behaviour and phase morphology of the continuous carbon fibre reinforced polymer composites (CFRPs) based on resin systems modified by including carbon nanotubes and a phase separating thermoplastic (TP) toughener. It is shown that the presence of fibre reinforcement influences the phase distribution in TP modified epoxies, where the toughening potential of the deformable TP phase is curtailed. Incorporating high aspect-ratio CNTs is an effective means to control and enhance the uniformity of the multiphase morphology, hence further improving the interlaminar properties of CFRPs. This is shown to be due to the interference of the CNTs in the kinetics of the reaction induced phase separation by affecting the polymer diffusion rate.

Self-assembled nanostructured viscoelastic and thermally stable high performance epoxy based nanomaterial for aircraft and automobile applications: An experimental and theoretical modeling approach

Nanostructured self-assembled and high-performance epoxy/epoxidized poly(styrene-block-butadiene-block-styrene) block copolymer blends with 55 mol% epoxidation degree [eSBS 55 ]- 0,5,10 and 20 phr- 4, 4′diaminodiphenyl methane (DDM) material were successfully synthesized by using solvent casting method. The role of the highest epoxidized SBS (eSBS 55 ) as a modifier and its concentration on the effect of nanostructured morphology, viscoelastic properties, reaction induced phase separation and thermal degradation kinetics of epoxy/eSBS 55 system were investigated in detail. Various theoretical models such as Coats-Redfern method, Broido method and Horowitz- Metzger method were applied for the first time on epoxy/eSBS systems to calculate the thermodynamic parameters and correlate experimental results. These highly enhanced viscoelastic & thermal properties and nanoscale morphology of as synthesized novel epoxy/eSBS 55 material have proved that ‘eSBS 55 ’is an outstanding modifier to epoxy resin for creating superior high-performance properties required for various coating and structural applications such as in aircrafts, floorings, automobiles and constructions. Viscoelastic and thermal properties of nanostructured epoxy/eSBS 55 systems • Nanostructured and high performance epoxy-amphiphilic blends were synthesized. • eSBS 55 wt% act as an excellent modifier and produced good compatibility with epoxy. • Excellent viscoelastic properties and thermal properties of blends were achieved. • Correlation of TGA experimental results with theoretical models for the first time. • eSBS 55 wt% produced superior performance properties for various coating applications.

Biphasic epoxy-ionic liquid structural electrolytes: minimising feature size through cure cycle and multifunctional block-copolymer addition

Structural electrolytes provide mechanical properties approaching structural resin combined with a high degree of ionic conductivity. Here, structural electrolytes based on bisphenol A diglycidyl ether and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM-TFSI) were synthesised through reaction induced phase separation (RIPS) using isophorone diamine (iPDA) as a curing agent. The microstructure and properties of the resulting materials were controlled through both the initial formulations and the curing temperature. Curing at room temperature generated a bi-continuous structure and improved both mechanical performance and ionic conductivity of the resulting structural electrolytes. The balance between properties can be systematically adjusted; for example, a promising Young’s modulus of 800 MPa was obtained simultaneously with an ionic conductivity of 0.28 mS cm−1, for a formulation containing 35 vol% EMIM-TFSI. The lengthscale of the structural features was reduced by an order of magnitude by introducing multifunctional block-copolymers (MF-bcP) based on glycidyl methacrylate (GMA) and quaternised (2-dimethylamino)ethyl methacrylate (DMAEMA). Small angle neutron scattering (SANS), obtained during curing, identified at least two structural phases of different length scale, for the formulations containing MF-bcP, in agreement with microstructures observed using scanning electron microscopy. Such structural electrolytes may be required when using structural electrodes that also have finer characteristic lengthscales. The addition of the MF-bcP to formulations containing 35 vol% EMIM-TFSI produced structural electrolytes with a Young’s modulus of 530 MPa and an ionic conductivity of 0.64 mS cm−1.

Reaction-Induced Phase Separation and Morphology Evolution of Benzoxazine/Epoxy/Imidazole Ternary Blends.

Introducing multiphase structures into benzoxazine (BOZ)/epoxy resins (ER) blends via reaction-induced phase separation has proved to be promising strategy for improving their toughness. However, due to the limited contrast between two phases, little information is known about the phase morphological evolutions, a fundamental but vital issue to rational design and preparation of blends with different phase morphologies in a controllable manner. Here we addressed this problem by amplifying the difference of polymerization activity (PA) between BOZ and ER by synthesizing a low reactive phenol-3,3-diethyl-4,4′-diaminodiphenyl methane based benzoxazine (MOEA-BOZ) monomer. Results indicated that the PA of ER was higher than that of BOZ. The use of less reactive MOEA-BOZs significantly enlarged their PA difference with ER, and thus increased the extent of phase separation and improved the phase contrast. Phase morphologies varied with the content of ER. As for the phase morphological evolution, a rapid phase separation could occur in the initial homogeneous blends with the polymerization of ER, and the phase morphology gradually evolved with the increase in ER conversion until the ER was used up. The polymerization of ER is not only the driving-force for the phase separation, but also the main factor influencing the phase morphologies.

Effects of curing temperature on the structure and properties of epoxy resin-poly(ε-caprolactam) blends

Improving the toughness of epoxy resins (EP) with diverse thermoplastic polymers through curing reaction induced phase separation (RIPS) has been widely studied, with the prerequisite of designing and tailoring the phase morphology evolution of the blend. Herein, two typical amine-type curing agents, 4,4′-diamino diphenylmethane (DDM) with precuring temperature at around 150 °C and diethylenetriamine (DETA) at 80 °C were utilized to regulate and control the phase structures of EP-poly(ε-caprolactone) (PCL) blends. The curing temperature above or below the melting temperature (Tm) of PCL resulted in different states of PCL. The effect of curing temperature on the miscibility between EP matrix and PCL phase, and the correlation between phase morphology evolution and thermomechanical behavior, mechanical properties were comprehensively investigated for the first time. Results revealed that when the curing temperature of EPDDM-PCL blends was higher than the Tm of PCL, curing took place without phase separation; while distinct phase separation took place when EPDETA-PCL was cured at a temperature below the Tm of PCL. When the curing temperature was high, the PCL was able to dissolve completely in the resin before crosslinking began, so that semi-interpenetrating networks were formed; and that when the curing temperature was low, the PCL was unable to dissolve, and therefore formed separate particles. Consequently, the EPDDM-PCL blends exhibited all-leading mechanical properties due to the entanglement and slippage between PCL chains and EP networks. The strength of EPDETA-PCL was reduced but the toughness was improved for island-shaped PCL particles bridging or pinning the cracks during failure. These results elucidated the effect of the phase morphologies formed at different curing temperature on mechanical properties, and provided significant insights regarding the toughening of thermosets.

Damping properties of carbon fiber reinforced composites hybridized with polysulfone (PSF)/cellulose nanocrystal (CNC) interleaves

Damping properties are critical for many applications of carbon fiber reinforced epoxy composites (CF/EP). In this paper, polysulfone (PSF)/cellulose nanocrystal (CNC) nanofibrous membranes were fabricated by electrospinning as hybrid interleaves in CF/EP composites. The damping properties of the interleaved CF/EP composites were measured by the cantilever percussion free-decay method and dynamic mechanical analysis (DMA). The strength and modulus values of the interleaved composites were obtained by tensile and flexural tests. The obtained results showed that after interleaving by the 10%PSF/0.5%CNC membranes, the damping properties of CF/EP composites were enhanced with little loss of mechanical properties. The damping mechanisms were examined and analyzed with the aid of scanning electron microscopy (SEM). It was concluded that the enhanced damping properties were due to the different energy dissipation mechanisms associated with the PSF nanoparticles generated by reaction induced phase separation and the incorporated CNCs in the EP matrix.