Poor Toughness Research Articles

Construction of “organic–inorganic” hierarchical structure of carbon fibers and the effect on the properties of epoxy composites

AbstractThe demand for epoxy (EP) in semiconductor, aerospace, and other applications is currently on the rise. However, pure epoxy is difficult to meet these requirements, such as low thermal conductivity and poor toughness. Therefore, in this paper, sulfonamides (SAs) and core‐shell silica (SLC‐SiO2) were grafted onto the surface of short carbon fibers (SCF) with sizes of 0.1–6 mm by the chemical grafting method. As a result, the surface activity of SCF was improved and the interfacial properties of the EP composites were enhanced. The interfacial compatibility of SCF grafted with SAs and SLC‐SiO2 in EP is greatly improved, resulting in stronger mechanical interlocking and chemical bonding ability between EP and SCF. The results showed that when the content of SCF@SAs@SLC‐SiO2/EP composites reached 0.3 wt% of SCF@SAs@SLC‐SiO2, the impact and tensile strengths were increased from 12.15 kJ·m−2 and 43.4 MPa to 16.93 kJ·m−2 and 74.97 MPa compared with the pure epoxy, which were improved 39.3% and 72.7%. In addition, the thermal conductivity of SCF@SAs@SLC‐SiO2/EP composites was also improved by 12.5% from 0.205 W·(m·K)−1 to 0.2306 W·(m·K)−1 compared with the pure EP. This is due to improved chemical interactions and mechanical interlocking at the fiber‐epoxy interface. This study provides a new method for the preparation of high‐performance SCF/EP composites.Highlights The amino group of sulfonamides was grafted with short carbon fiber to increase the surface active group of short carbon fiber. Sulfonamides react with carboxyl groups on the surface of core‐shell silica to form an “organic–inorganic” structure. Improve the surface roughness of short carbon fiber, and make it evenly dispersed in epoxy resin, so as to improve the performance of epoxy composite materials.

Facile synthesis of polyester-polyether block copolyols for the sustainable high-performance polyurethane reactive hot melt adhesives

The presence of polyols with both polyester and polyether structures in polyurethane enhances bonding strength and facilitates easy curing. In this study, polyester-polyether block polyols with varying molecular weights (2500–3500) were synthesized through ring-opening polymerization (ROP) using l-lactide (LA) and ε-Caprolactone (CL). The chemical structure of the polyols was characterized using 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were employed to examine the crystalline morphology of the polyols. Subsequently, the synthesized polyols were combined with 4,4′-diphenylmethane diisocyanate (MDI) and other additives to prepare polyurethane reactive hot melt adhesives. It was observed that, in PCL-based polyurethane reactive hot melt adhesives, increasing the molecular weight of the polyols resulted in improved crystalline morphology, increased lap shear strength and tensile strength, and enhanced thermal stability. On the other hand, PLA-based polyurethane reactive hot melt adhesives exhibited low bonding strength and lacked practical application value due to the poor toughness of PLA. Interestingly, the bonding strength and tensile strength of PLA-based polyurethane reactive hot melt adhesives improved when physically blended with PCL-based polyurethane reactive hot melt adhesives. These polyols offer a novel approach for utilizing LA and CL in adhesive applications.

Effect of heat treatment on microstructure and mechanical anisotropy of direct energy deposited Ti-6.0Al-2.5Nb-2.2Zr-1.2Mo alloy

Ti-6.0Al-2.5Nb-2.2Zr-1.2Mo alloy (Ti-6321) exhibits excellent corrosion resistance and impact toughness, which can be used as a deep-sea pressure-resistant hull. However, the alloy tends to have high strength but low plasticity, poor impact toughness, and anisotropic mechanical properties by fabricating by direct energy deposition (DED) technology. In order to improve the impact toughness of DEDed Ti-6321 alloy while reducing its anisotropy of mechanical properties, this study manipulates the microstructure and mechanical properties of the alloy through heat treatment. The research finds that with the increase of the single-stage annealing temperature within the (α+β) two-phase region, the width of the α phase increases, the Ultimate Tensile Strength (UTS) remains essentially unchanged, the Yield Strength (YS) decreases, and the impact absorption energy significantly improves. For double annealing heat treatment at two-phase region, temperature increase at the first-stage annealing enlarges the width and decreases the aspect ratio of the primary α phase. Leading to the decrease of the UTS & YS and increase of the impact absorption energy, with a conversely tendency at 1000 °C. The increase in the second-stage annealing temperature raises the size and volume fraction of the secondary α phase, causing the alloy's UTS and YS to initially rise then fall, with a slight increase in impact absorption energy. The anisotropy in the mechanical properties of DEDed Ti-6321 alloy mainly addressed from the different distribution of α phase orientations at different loading directions, and can be eliminated through sufficient β single-phase zone annealing.

Highly-toughened PLLA/PVA biodegradable blends: Graft copolymer tailored crystallization and phase morphology

Poly(l-lactic acid) (PLLA), recognized as a promising substitute for petroleum-based polymers, has garnered significant attention for its various advantages. However, the practical application of PLLA is limited by its poor toughness. This study introduces a novel approach, using a graft copolymer, poly(vinyl alcohol)-graft-poly(l-lactic acid) (PVA-g-PLLA), synthesized through a "grafting to" method to enhance the compatibility of PLLA/PVA blends. It is demonstrated that even though the graft copolymer promotes crystallization, the resultant ternary blends, especially with a mass ratio of 7:3:1, exhibited an 88.7 % elongation at break, representing a 1642 % improvement over pure PLLA and a 576 % increase over binary PLLA/PVA blends. In addition, incorporating PVA-g-PLLA significantly enhanced the toughness of the PLLA/PVA blends without sacrificing strength, thermal stability, or transparency. Remarkably, the Vicat softening temperature of the blends with a 7/3/1.5 ratio increased to about 94.4 °C, substantially higher than the 59.9 °C observed in PLLA/PVA blends. These findings suggest that the newly developed copolymer and the ternary blends hold substantial promise for creating biodegradable materials that do not compromise performance. It suggests a promising future for these materials in various applications where enhanced durability, thermal stability, and environmental sustainability are crucial.

Current status and challenges of shape memory scaffolds in biomedical applications

AbstractThe rapid evolution of clinical medicine, materials science, and regenerative medicine has rendered traditional implantable scaffolds inadequate for addressing the complex therapeutic demands of various diseases. Currently, implantable scaffolds in clinical practice are mainly made of metal, with the disadvantages of high stiffness, poor toughness, and low deformation. This paper offers a thorough review of shape memory scaffolds (SMSs), emphasizing their distinctive self‐recovery and adaptive functionalities that enhance compatibility with injured tissues, surpassing the capabilities of conventional metallic biomaterials. It delves into the limitations of current clinical scaffolds and the requisite performance metrics for effective implants and outlines the essential materials and fabrication methods for SMSs. Moreover, we enumerate the biomedical applications of SMMs with different response types, including thermology‐responsive, water‐responsive, and light‐responsive. The discussion extends to the burgeoning applications of SMSs in biomedical engineering, including their utility in bone tissue engineering, cardiovascular stenting, tubular structures, and cardiac patches, which underscore their potential in minimally invasive procedures and dynamic tissue interactions. This review concludes with an analysis of current challenges and prospects, providing valuable insights for developing and applying SMSs in the biomedical sector.

Magnetic casein/CaCO3/Fe3O4 microspheres stimulate osteogenic differentiation

The quality of life is significantly impacted by bone defects, which calls for the creation of optimum restorative materials with particular qualities. Current repair materials, such as metal alloys, polymer scaffolds, and bone cement, have a number of drawbacks, such as poor fracture toughness, non-degradability, and insufficient osteogenic ability. To address these challenges, we designed a novel magnetic casein/CaCO3/Fe3O4 microspheres (CCFM), combining biodegradability, osteoinductivity, osteoconductivity, and osteogenesis properties together. In vitro studies confirmed the outstanding biocompatibility and osteogenic differentiation effects on MC3T3-E1 cells of CCFM, highlighting their potential as a promising bone regeneration platform for clinical applications. As a novel bone repair material with superparamagnetic properties, CCFM not only possess good osteoinductivity, osteoconductivity, and osteogenesis properties but also can remain in the lesion location for a long time under an external magnetic field, representing a significant advancement in the field of bone tissue engineering and offering new possibilities for effective bone defect remediation and patient care.

Effect of plastic deformability and fracture behaviour on interfacial toughening mechanism at Fe/Ni interfaces

Fracture at interface causes plastic deformation in the vicinity region. Conventional plastic energy dissipation theory indicates that ductile vicinity toughens the interface by absorbing plastic deformation energy. However, the microstructure in the vicinity directly affects local plastic deformability and fracture behaviour, implying a more complicated toughening mechanism. In this study, the effect of microstructure and hardness on fracture behaviour of Fe/Ni interface was investigated. By experimental approach, interfaces with and without dynamic recrystallization (DRX) were fabricated by controlling the bonding conditions. It showed that compression-induced plastic deformation is the main source of the hardening behaviour in the vicinity. Moreover, the interfaces with hardened DRX vicinities exhibited improved fracture toughness, which is inconsistent with the plastic energy dissipation theory. To clarify this observation, the crystal plasticity finite element method (CPFEM) approach was employed to distinguish the effects of plastic deformation and interfacial microstructure. The result showed that although higher plastic deformability in the vicinity absorbs more dissipated plastic energy, severe stress concentration at the interface leads to early fracture and poor toughness. On the other hand, the interfacial hardened DRXed grains disperse interfacial stress distribution and provide potential sub-crack sites. A combined result of uniform plastic deformation and fracture energy dissipation is responsible for the improved toughness at interfaces with DRXed grains.

Numerical investigation on the impact resistance of ceramic-based composite structure with hybrid architecture

As known, ceramics possess desirable strength, hardness and low density, which have been extensively applied in engineering fields. However, the inherent brittleness makes the ceramics present poor toughness and consequently impact resistance as well. In recent decades, some ingenious architectures of biomaterials employed to improve the mechanical properties of brittle bulk materials, such as laminate and brick-mud, have become increasingly popular. Here, in order to further enhance the impact resistance of ceramics, a kind of hybrid ceramic-based composite structure is designed according to the gradient feature in dactyl club of mantis shrimp. The impact resistance performances of bulk, laminate, brick-mud and hybrid structures are investigated by finite element simulation. The results show that the hybrid structure can effectively avoid catastrophic failure, thereby having large scope of deformation area to store energy. Moreover, the damage mass of impactor for the hybrid plate is the largest due to the beginning hard collision between impactor and target plate and long cumulative damaging time of impactor. As a result, with the highest internal energy and eroding kinetic energy of impactor simultaneously, the hybrid structure dissipates the most energy of impactor. Further, under extreme working conditions of oblique and high velocity impact, the hybrid structure still exhibits optical impact resistance performance.

Nacre inspired supertough and flame-retardant reduced graphene oxide composite films

Nacre-like graphene composite films (GCFs) with high strength have been highly developed. However, the GCFs usually exhibit relatively poor toughness and poor flame resistance, seriously limiting their applications as structural materials. Here, reduced graphene oxide (rGO), halloysite nanotubes (HNTs), and flame-retarding modified lignin (F-lignin) were compounded to fabricate the rGO-HNTs-(F-lignin) film. In the rGO-HNTs-(F-lignin) film, the F-lignin binds the rGO sheets and HNTs, enhancing the entanglement of HNTs and the interactions between HNTs and rGO sheets, and the macromolecular F-lignin also improves the ductility of the rGO-HNTs-(F-lignin) film, while the entangled HNTs conversely reinforce the F-lignin to prevent the F-lignin from fracture when the rGO-HNTs-(F-lignin) film is under stress, further increasing the ductility of the rGO-HNTs-(F-lignin) film. The HNTs and F-lignin promote each other to enhance the strengthening and toughening effect on the rGO-HNTs-(F-lignin)-film, and endowing the rGO-HNTs-(F-lignin)-film with the superior mechanical properties of the tensile strength of 634 ± 38 MPa, tensile fracture strain of 8.17 ± 0.59 %, and toughness of 25.35 ± 2.95 MJ/m3, respectively. The rGO-HNTs-(F-lignin) film also exhibits improved flame-retardant properties due to the high flame retardancy of HNTs and F-lignin. These excellent integrated properties of the rGO-HNTs-(F-lignin) film will promote its potential applications as structural materials.

Degradation of the mechanical properties of NbMoTaW refractory high-entropy alloy in tension

The mechanical properties of the bcc refractory high-entropy alloy (RHEA) NbMoTaW with columnar and equiaxed microstructures and a nanoscale metal oxide layer on the grain boundaries are investigated at ambient temperatures (RT) to 1200 °C. Under compression, the alloy shows a yield strength, σy, of ⁓1390 ± 20 MPa at RT and retains a high yield strength, σy, of ⁓301.5 MPa at 1200 °C. However, in tension, the fracture strengths, σf, of both columnar and equiaxed microstructures are far lower - below 70 MPa - and the material fails in the elastic regime without showing any measurable ductility at all temperatures. The fracture mechanisms in tension transition from transgranular cleavage at RT to a mixture of transgranular and intergranular fracture at 800 °C to a complete intergranular fracture at 1200 °C due to selective weakening of the metal oxide layer on the grain boundaries driven by a structural change. The transition in the fracture mechanism in the equiaxed microstructure promotes extrinsic toughening at higher temperatures, resulting in a ⁓6.4 times higher fracture toughness (KIc ⁓10.3 MPa√m) at 1200 °C compared to that at RT. NbMoTaW is a well-known RHEA, but the poor tensile strength and fracture toughness measured in this study highlight the critical importance of investigating the mechanical properties of these high-temperature RHEAs in tension.

Study on the physico-mechanical properties and mechanisms of poplar wood co-modified by anoxic high-temperature heat treatment and impregnation with silica sol/phenolic resin

Addressing the challenges of fast-growing poplar wood in construction, decoration, and furniture, including low density, insufficient strength, poor toughness, and suboptimal dimensional stability, this study introduces an innovative organic/inorganic impregnation-heat treatment technique. This method significantly enhances the physico-mechanical properties of poplar wood and overcomes issues associated with thermosetting resin modification, such as reduced impact toughness, uneven resin penetration, and wood swelling. Utilizing in situ polymerization with silica sol and phenolic resin, specifically with particle sizes between 8 and 15 nm, the process markedly improves wood permeability and overall properties through vacuum pressure impregnation and heat treatment. The findings indicate a 54.42 % increase in the wood's density. Optimized heat treatment at 180 °C for 1 h significantly enhances dimensional stability and reduces water absorption, with the ASE value reaching up to 69.3 %. Furthermore, the impregnation-heat treated wood exhibits a 50.19 % increase in bending strength to 81.6 MPa, a 103.93 % increase in modulus of elasticity to 16.5 GPa, and a 29.42 % increase in impact toughness to 92.5 kJ/m2, demonstrating substantial improvements over the raw material. FT-IR analysis reveals the presence of Si-O-Si vibration peaks, indicating the effective penetration of silica sol. TGA analysis displays the treated material's superior thermal stability compared to the raw material. XRD analysis confirms that the impregnation and heat treatment processes have not adversely affected the wood's crystalline regions but have instead reduced hygroscopicity and enhanced stability. SEM analysis showed that the composite impregnation liquid effectively penetrated and distributed within the wood cells. These results open new theoretical and technical pathways for enhancing the physico-mechanical properties of fast-growing poplar wood.

Effect of cooling rate in the mid-temperature region on fatigue crack propagation rate of bainitic steel

Controlling continuous cooling is an important means to control the most important mechanical properties of bainitic steel for frogs in railroad applications. In this paper, a bainitic steel for railway frogs is taken as the research object. By designing different cooling rates in the bainitic transformation medium temperature region, the effect of cooling rate on fatigue crack propagation rate was studied. The results show the sample of 4 °C/s cooling rate exhibits higher strength and impact toughness, while the crack propagation rate near the threshold is significantly lower and the threshold is relatively higher at 0.1 °C/s cooling rate. This is related to the fact that more massive blocky retained austenite and coarse microstructure in the sample at 0.1 °C/s cooling rate are more favorable to the occurrence of crack closure effect, especially in the near-threshold region. The fatigue crack propagation rate of the tested steel in the stable propagation region at 4 °C/s cooling rate is slightly higher than that at 0.1 °C/s. This is related to its complex interface distribution characteristics. However, with the increase of Δ K, the tested steel at 0.1 °C/s cooling rate tends to preferentially fail, which is related to its poor toughness.

Microstructure evolution and mechanical properties of Fe–Cr–B alloys with varying Mo additions

The continuously net-like morphology of borides accounts for the poor toughness of Fe–Cr–B wear-resistant alloys. To effectively modify the morphology of Fe2B, Mo element has been introduced in Fe–Cr–B alloys, and the microstructure evolution and mechanical properties have been systematically investigated. The results show Fe–Cr–B alloys are mainly composed of martensite, M2B, M23(B, C)6 and lamellar M3B2 after Mo addition. With the increase of Mo addition, the content of M3B2 increases gradually while that of M23(B, C)6 increases firstly and then decreases. Consequently, the net-like structure of M2B can be effectively broken to acquire the isolated bulk-like morphology, which is mainly attributed to the growth inhibition effect of lamellar structure M3B2. In addition, the hardness varies depending on the volume fraction of borides. However, the fracture toughness of Fe–Cr–B alloy can be dramatically improved by 34.3% with Mo addition increasing from 1 to 4%. Grain morphology modification of M2B plays the predominant role in the toughness improvement because the crack propagation path can be blocked. Furthermore, the lamellar M3B2 structure can effectively hinder the cracking propagation so as to improve the alloy's fracture toughness. Mo addition has been proved to be an effective way to modify the grain morphology of M2B hard phase.

A new Ti–Al–Cr–Mo–Zr titanium alloy welding wire: Stability, microstructure and mechanical properties

In order to improve the plasticity of titanium alloy welded joints, relevant scholars currently focus primarily on studying the mechanism of action of alloying elements Mo and V, such as reducing the phase transition temperature of the welded seam and ensuring a certain amount of β phase residue in the welded seam. In addition to improving the stability and strengthening ability of titanium alloy welded joint, it can also maintain a certain degree of plasticity of the welded joint. However, the poor impact toughness is still the key problem that restricts its long-term stable service in the harsh environment. Our work designed and developed a new Ti–Al–Cr–Mo–Zr solid welding wire, with the synergistic effect of Al, Cr, Mo and Zr, the welded seam microstructure and grain can be refined while ensuring the enough stiffness of the welding wire and its flatness during wire feeding into the designated working area. It ensures good wetting and spreading flow performance of the liquid molten pool metal in the welding process, so better welded seam formation can be obtained. The relative contents of α′ martensite and β phase in the welded seam are 76.79% and 23.21%, respectively. The residual β phase is interspersed between the α′ martensite of the slats. The β phase provides a path for the plastic deformation of the welded joint, making it easier for dislocation slip to pass the β/α′ interface. At the same time, more dislocation slip channels and a small number of fine twins can be found in the interior of α′ martensite, which can ensure the strength while taking into account the toughness. After testing, it is found that the average tensile strength of welded joints is 901 MPa, which is close to 95% of the base metal (BM), the average post-fracture elongation of welded joints is 21%, and the impact toughness value at room temperature is distributed between 25 J and 33 J, which meets the requirements of the synergistic effect of welded joint strength and plastic toughness. It is suitable for long-term stable service of Ti64 titanium alloy welding structure under harsh working conditions.

Achieving exceptional strain-hardening ability in nanocrystalline Ni–W coatings through compositionally modulated multilayer approach

Nanocrystalline Ni–W coatings show exceptional strength; however, they exhibit poor toughness due to limited ductility and high residual stresses which impede their use in practical applications as a potential hard chrome replacement. In the present study, compositionally modulated multilayer (CMM) coatings with alternate layers of Ni-1 at% W (soft) and Ni-15 at% W (hard) of three different layer thicknesses of 1, 0.5, and 0.1 μm are developed by pulse reverse electrodeposition to achieve the strength-ductility synergy, thereby enhanced wear resistance. Microcompression test results reveal that all the CMM coatings exhibit remarkably higher strain-hardening ability than the homogenous coatings. Significant fluctuations in the strain-hardening rate and a positive shift in the onset stress for the work-hardening stages were observed with the layer thickness. This suggests a strong interplay between the hard and soft layers on the deformation characteristics of multilayer coatings. Detailed electron microscopy of the cross-section of the deformed micropillars shows substantial evidence of co-deformation of both layers. A mechanism is proposed to explain the enhanced strain-hardening in multilayers involving the strength incompatibility arising in the layers leading to lateral constraints, resulting in strain gradient plasticity, stabilizing of local shear by the soft layers, and the barrier effect of the interfaces.

Synergistic preparation of a straw fiber/polylactic acid composite with high toughness and strength through interfacial compatibility enhancement and elastomer toughening

Plant fiber-reinforced polylactic acid (PLA) composites are extensively utilized in eco-friendly packaging, sports equipment, and various other applications due to their environmental benefits and cost-effectiveness. However, PLA suffers from brittleness and poor toughness, which restricts its use in scenarios demanding high toughness. To expand the application range of plant fiber-reinforced PLA-based composites and enhance their poor toughness, this study employed a two-step process involving wheat straw fiber (WF) to improve the interfacial compatibility between WF and PLA. Additionally, four elastomeric materials—poly (butylene adipate-co-terephthalate) (PBAT), poly (butylene succinate) (PBS), polycaprolactone (PCL), and polyhydroxyalkanoate (PHA)—were incorporated to achieve a mutual reactive interface enhancement and elastomeric toughening. The results demonstrated that Fe3+/TsWF/PLA/PBS exhibited a tensile strength, elongation at break, and impact strength of 34.01 MPa, 14.23 %, and 16.2 kJ/m2, respectively. These values represented a 2.4 %, 86.7 %, and 119 % increase compared to the unmodified composites. Scanning electron microscopy analysis revealed no fiber exposure in the cross-section, indicating excellent interfacial compatibility. Furthermore, X-ray diffraction and differential scanning calorimetry tests confirmed improvements in the crystalline properties of the composites. This work introduces a novel approach for preparing fiber-reinforced PLA-based composites with exceptional toughness and strength.

The effect of the vanillin‐derived Si‐containing compound on the curing behavior, thermal and mechanical properties of bismaleimide resins

AbstractBismaleimide (BMI) resins is widely used in the aerospace field because of its excellent properties, but its poor toughness limits the possibility of its application in a wider range of fields. Therefore, a novel bio‐compound, 4‐(allyloxy)‐3‐methoxy‐N‐(3‐(triethoxysilyl)propyl)benzamide (AMTPM), was designed and synthesized from renewable vanillin, which has Schiff‐base structure, silico‐oxygen bond structure, and allyl structure. The chemical structure of AMTPM has been characterized and validated by Fourier transform infrared (FTIR) and hydrogen nuclear magnetic resonance (1H NMR). It was found that the addition of AMTPM can effectively promote the curing behavior of BD resins (BMI and diallyl bisphenol A (DBA) was mixed and cured at the ratio of 1:0.87, named BD resins). AMTPM can affect the thermal stability and improve the mechanical properties of BD‐AMTPM resins (BD resins modified by AMTPM in different addition), and the detailed discussion was conducted. With the increase of AMTPM content, the thermal stability of BD‐AMTPM resins was deteriorated while the residual weight percentage at 800°C (Yc) was increased. When the content of AMTPM reached 12 wt%, the results showed that Yc achieved the values at a magnitude of 37.57%. Meanwhile, the glass transition temperature (Tg) achieved 320°C. Among the BD‐AMTPM resins system, the BD‐6 wt% AMTPM has the best toughness and mechanical properties. The impact strength was increased by 29.2%, the tensile strength was increased by 22.1% and the elongation at break was increased by 44%. The fracture morphology of BD‐AMTPM resins was also studied by scanning electron microscopy (SEM) to support the mechanical experimental conclusions. This study provides a more environmentally friendly and convenient modifier, which is of great significance for expanding the application of bismaleimide resin.Highlights A bio‐based modifying agent (AMTPM) was designed and successfully synthesized. AMTPM has both Si‐O and Schiff‐base structures. AMTPM can effectively improve the toughness of BD‐AMTPM resins through impact and tensile tests.

Double polymerization synergy to sharpen structural toughness of melamine resin foam

Melamine resin foam (Mfoam) is a porous heat-cured amino resin material with excellent flame retardancy, thermal insulation, and noise reduction capabilities. However, some fatal shortcomings like easy brittle breakage, easy powderization and poor toughness directly limit its wide application and further development. In this paper, hydroxypropyl acrylate (HPA) was used to participate in the synthesis of melamine resin oligomers (Moli) in order to link the vinyl group to molecular skeleton. As a result, both vinyl and hydroxymethyl active groups are present in Moli which provide Moli with the ability to perform free radical polymerization reaction and polycondensation polymerization reaction, named double polymerization reaction (DPR), and produce synergistic effects to form a structurally toughened melamine resin foam (TMfoam). The research shows that the scheme can effectively solve the problems of brittle breakage and easy powderization of Mfoam. And under apparent density (Ad) of 40 ± 2 kg/m3, the prepared TMfoam has good toughness, with the bending strength of 405.2 kPa, the compression strength of 352.5 kPa, and the pulverization rate of 1.18 %. Meanwhile, the combustion grade of the TMfoam can reach to B1 grade, and the thermal conductivity is 0.0328 W/(m·K). Also the absorption coefficient of TMfoam can reach up to 0.92 under frequency of 3045 Hz. All the facts indicate that the DPR showed good synergistic effect during the forming and setting stages from Moli to TMfoam. At the same time, the bubble chamber of TMfoam changes from metastable state to stable state, and its strength and toughness are significantly improved in step. This research has great and practical significance for expanding the wide application of Mfoam type materials.

Effect of nucleating agent incorporation on the crystallization and mechanical properties of polylactide/polyamide elastomer blends

ABSTRACT The widespread application of polylactide (PLA) has been limited by its slow crystallization rate and poor toughness. In the present work, a low molecular weight nucleator, TMC 301, and polyamide elastomer (PAE) were incorporated into PLA through melt blending to mediate both the crystallization capability and impact toughness. It was found that the introduction of TMC 301 decreased the crystallization temperature of PLA during the cooling process, while enhancing its cold crystallization capacity of PLA in the heating scan. Accordingly, the presence of TMC 301 shortened the half-crystallization time of PLA at 95°C in the ternary blends with minimal influence on the Avrami index. Moreover, the dispersion size of PAE decreased when the concentration of TMC 301 increased to 0.3 wt%, leading to a substantial increase in the tensile toughness and the impact strength of the PLA/PAE/TMC 301 blend. It is suggested that the size of the elastomer particles is a critical factor influencing the toughening efficiency of TMC301 in PLA/PAE blends.

Flame retardant, toughened, reinforced, transparent and long shelf-life one-component epoxy resins via a P/N/Si-containing hyperbranched polymer

One-component epoxy resins (OCEPs) cured from latent imidazole-based curing agents that exhibit high toughness, high strength, high fire safety, long shelf life, low dielectric properties and transparency are eagerly awaited in advanced manufacturing. However, existing research on latent imidazole-based curing agents/OCEPs mainly focuses on simultaneously improving their flame retardancy and shelf life, but neglects their poor toughness, strength and dielectric properties, and often compromises their transparency. Herein, a hyperbranched polymer (Si-DP) containing P/N/Si was fabricated to further improve the flame retardancy, toughness, strength and dielectric properties of EP10 (the transparent OCEPs comprising the latent imidazole-based curing agent PHI-HPP). EP10 containing Si-DP (EP10/Si-DP) boasted a shelf life longer than 81 days. The synergistic flame-retardant effect of P, N and Si elements enabled EP10/Si-DP3 to achieve a UL-94 V-0 rating with a limiting oxygen index of 33.9 %, the peak heat release rate and total smoke production of EP10/Si-DP5 were reduced by 44.4 % and 25.5 %, respectively, compared with EP10. The increased free volume and Si-O flexible bonds resulted in a 261.1 % higher impact strength of EP10/Si-DP5 than EP10. The excellent interfacial bonding of Si-DP with epoxy resins and the increased rigidity groups led to 74.0 % and 60.7 % higher tensile and flexural strengths of EP10/Si-DP5 than EP10, respectively. The intramolecular cavities and the low-polar Si-C bonds of Si-DP reduced the dielectric constant and dielectric loss of EP10/Si-DP. Meanwhile, EP10/Si-DP maintained inherent excellent transparency and high glass transition temperature (Tg). Carbon fiber epoxy composites prepared from EP10/Si-DP5 exhibited remarkable improvement in flame retardancy, smoke suppression as well as mechanical and interfacial performances. Overall, this research proposes an effective approach for preparing long shelf-life OCEPs with excellent overall performance.