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Cyanate ester resin (CE), a high-performance and low dielectric materials, was modified with amino hollow silica (HSMs-NH 2) and polyimide resin (PI) to form an IPN structure. Reducing the crosslinking density of the composite system and accompanying with its steric hindrance effect, PI increased the free volume of the composite material. The hollow structure introduced by HSMs-NH 2 further enhanced a low dielectric property. IPN structure and HSMs-NH 2 also significantly improved the impact toughness of HSMs-NH 2 /PI/CE composites. The bonding between the Si– O –Si and HSMs-NH 2 offered an excellent heat resistance and as well surface bonding capability to matrix, which reduced the decomposition and effectively improved their thermal stability. Simultaneously, profited by the hydrophobicity of Si– O –Si, HSMs-NH 2 /PI/CE composite materials enabled to keep low dielectric properties in humid environments. [Display omitted] • A composite material with low dielectric constant, high toughness, high temperature resistance, and moisture resistance. • HSMs-NH 2 as a lightweight nano filler has a large cavity structure. • The formation of IPN structure in CE by PI not only reduces the dielectric constant of CE, but also improves its toughness. • HSMs-NH 2 improves dielectric properties, heat and moisture resistance of PI/CE composite. [ABSTRACT FROM AUTHOR]

Waterborne polyurethane (WPU) is increasingly favored because of its affordability, eco-friendliness, and water-based storage convenience. However, the inclusion of hydrophilic groups can diminish its mechanical strength and water resistance. Herein, a range of bio-based waterborne polyurethanes were synthesized by using economical and sustainable poly(trimethylene ether) glycol (PO3G), isophorone diisocyanate (IPDI), and poly(propylene glycol) (PPG) as raw materials. They exhibited superior mechanical properties, transparency, and corrosion resistance. We explored the effect of PO3G content on the properties of these bio-based WPU emulsions and films. The findings revealed that films with over 30 % PO3G content demonstrated a high tensile strength (above 10 MPa) and maintained a high elongation at break (above 4000 %), matching or surpassing existing bio-based WPU systems. The corrosion resistance of these films was also exceptional, with a high inhibition efficiency (above 99.97 %). This research introduces a new approach for creating high-performance bio-based WPUs with promising applications in coatings, leather, and biomedical materials. [Display omitted] • Bio-based waterborne polyurethanes (WPUs) were synthesized by using sustainable PO3G. • Bio-based WPUs showed extremely high toughness with acceptable mechanical strength. • Bio-based WPUs exhibited high-efficency corrosion resistance to saline water (above 99.97 %). [ABSTRACT FROM AUTHOR]

Thermally expandable microspheres (TEMs) with different foaming temperatures were utilized to develop bimodal polypropylene (PP)/TEM composite foams through injection molding. The introduction of TEMs significantly enhanced the crystallization process of PP and optimized its viscoelastic behavior. As the TEM content increased, the foam density decreased. An optimal state where the cell structure remained intact was obtained at a 6.0 wt% TEM content and the composite foam exhibited the best comprehensive mechanical properties. Furthermore, with the introduction of a second type of high-temperature TEM as the co-blow agent, bimodal cells with size centralized at 12 μm and 57 μm were generated in the PP matrix. When the ratios of two TEMs were controlled at 3.0 wt% each, the PP/TEM 3 + 3 % foam with an equal amount of co-blowing agent achieved 7 %, 94 %, and 101 % improvement in tensile strength, toughness, and strain-at-break compared with the PP/TEM 6 % foam with sole DU300x TEM blowing agent, owing to the synergetic effects of stress dissipation and redirection within the bimodal cell structures and the transverse toughening of the rigid TEM microspheres. In addition, the composite foam exhibits a smooth surface appearance with a low surface roughness since the TEM shell could effectively prevent the burst of the microspheres during foaming. This work provides a simple and effective approach for manufacturing bimodal foams with high toughness and high-quality surfaces. [Display omitted] • Bi-modal PP foams made with two types of thermoplastic expandable microspheres. • Bi-modal cells form when high and low temperature TEMs ratios reach 3 %. • TEMs addition accelerated crystallization and enhanced PP matrix viscosity. • Bi-modal PP/TEM foam showed enhanced strength, modulus, toughness, and ductility. • The surface quality is improved by preventing the cells burst during injection. [ABSTRACT FROM AUTHOR]

The demand for innovative green materials that can viably replace environmentally harmful petrochemical plastics is escalating. To that end, novel gel materials were readily prepared in this study using a natural polymer (alginate) and a bio-friendly polyol solvent (glycerol), and then structurally characterized by Fourier-transform infrared spectroscopy and X-ray diffractometry. The optimal gel exhibited mechanical properties similar to those of common plastics (Young's modulus, ∼218 MPa; tensile strength, ∼24 MPa; work of extension, ∼17 MJ m−3; and fracture energy, ∼5130 J m−2). Additionally, a potent welding technique was devised to fuse gel fragments. The representative welded gel exhibited an exceptional adhesive strength (∼0.21 MPa) similar to cartilage–bone bonds, and was cross-sectionally analyzed by field-emission scanning electron microscopy. Importantly, the gels retained their properties even after prolonged exposure to ambient air (temperature, ∼26 °C; humidity, ∼60 %). They also exhibited a remarkable ability to withstand exposure to ultraviolet irradiation, temperature instability, and fluctuations in moisture levels. The synthesized high-performance gels could be used instead of traditional plastics in various practical settings. [Display omitted] • We synthesized mechanically robust, self-weldable Ca-alginate glycerol hydrogels. • The developed gels are moderately flexible and remarkably stiff and strong. • The gels show self-weldable behavior with excellent adhesive strength. • The prepared gels are highly stable in air under ambient conditions. • The gels can be used as alternatives to traditional plastics in pertinent settings. [ABSTRACT FROM AUTHOR]

The impact of three phosphonate oligomers with different unsaturation degrees on the flame retardancy, mechanical properties and optical performance of unsaturated polyester resins (UPRs) were investigated. The three phosphonate oligomers were poly(2-butyne-1,4-diol phenylphosphonate) (PY) containing C C, poly(cis -2-butene-1,4-diol phenylphosphonate) (PE) containing C C and poly(1,4-butanediol phenylphosphonate) (PO) without unsaturated bonds. The flame retardancy and UV-shielding effect of UPRs were positively correlated with the unsaturation degree of oligomers. Specifically, only adding 20 wt% PY made UPR pass UL-94 V-0 rating and 22 wt% PE was needed, while 22%PO/UPR was still in UL-94 NR rating. Further, PE containing C C exhibited the highest efficiency in improving the toughness of UPR. The impact strength and elongation at break of 22%PE/UPR were significantly improved by 460 % and 200 % respectively, compared with pure UPR. Meanwhile, the high transparency of UPRs benefits from the good compatibility between oligomers and matrix. This work provides the basis for development and utilization of novel high-performance and multifunctional UPRs with potential versatile applications. [Display omitted] • Three multifunctional flame retardant/toughening oligomers were prepared. • The flame retardancy, toughness and UV-shielding effect of UPRs were greatly strengthened. • The unsaturated degree of oligomers exerted significant influence on all the properties of UPRs. [ABSTRACT FROM AUTHOR]

Polyrotaxane (PR) is a supramolecular polymer, in which an axial polymer extends through multiple cyclic molecules. PR specifically comprises polyethylene glycol, α -cyclodextrin, and adamantane as the axial polymer, cyclic molecule, and terminal blocking group, respectively. It is a useful stress-relaxing material because the cyclic polymers can freely slide and rotate in cyclic motions on the axial polymer. In this study, epoxy resin (DGEBA) cured with phenolic resin (PN) was blended with PR, which has methacryl groups at the ends of side chains of the cyclic molecules, as a toughness modifier. The effect of the methacryl group polymerization catalyst (DCP) on the cured properties of epoxy resin was reported. PR was homogeneously dispersed in the DGEBA/PN resin matrix. Increasing the PR concentration significantly improved the toughness, impact resistance, and adhesive properties of the DGEBA/PN/PR alloy. Moreover, adding DCP resulted in an increase in the glass transition temperature due to the decreased molecular mobility of the network. This phenomenon was attributed to the synergistic effect of the formation of an interpenetrating polymer network, which is an entangled network of the curing reaction of the DGEBA/PN resin and polymerization of PR, and the intermolecular hydrogen bonds between carbonyl and hydroxyl groups of PR and hydroxyl groups of the DGEBA/PN resin. In contrast, the increased interfacial adhesion between PR and the DGEBA/PN did not result in significant improvement of flexural properties. [Display omitted] • Polyrotaxane (PR) is a supramolecular polymer that acts a stress-relaxing material. • IPN is formed as entangled network of curing epoxy resin and PR polymerization. • Intermolecular hydrogen bonds between epoxy resin and PR improve heat resistance. • Increasing PR concentration substantially improves the toughness of epoxy resin. [ABSTRACT FROM AUTHOR]

The high brittleness of epoxy resin at cryogenic temperature restricts their wide application in cryogenic engineering. In this study, polyhedral oligomeric silsesquioxane (POSS) with -Si-O-Si- molecular chains were synthesized, and the mechanical properties of diglycidyl ether of bisphenol A (E51 epoxy resin) were significantly enhanced at room temperature (RT) by incorporating a 4% POSS and curing agent 4,4′-diamino-diphenylmethane (DDM) as the E51/POSS/DDM resin system. Subsequently, by adding different contents of epoxidation hydroxyl-terminated polybutadiene (EHTPB) into the E51/POSS/DDM resin system, the EHTPB-E51/POSS/DDM resin system was prepared. The investigation into the impact of EHTPB content on the mechanical properties of EHTPB-E51/POSS/DDM resin system at room temperature (RT) revealed that EHTPB-E51/POSS/DDM resin system with 10% EHTPB exhibited the most favorable results. Specifically, the elongation at break, flexural strength, and critical stress intensity factor (K IC) were measured to be 6.82%, 143.75 MPa, and 1.83 MPa m1/2, respectively. These values demonstrated a notable improvement of 53.3%, 26.9%, and 86.7% compared to those for the E51/DDM resin system. Concurrently, at 77 K, the elongation at break and critical stress intensity factor (K IC) increased by 37.8% and 73.5%, respectively. The toughening mechanism of the prepared EHTPB-E51/POSS/DDM resin system was further explored through resin-curing cross-linking simulation networks and SEM images of the fracture surface of resin samples. The study of EHTPB and POSS synergistically toughened epoxy resin provided a new efficient method to prepare epoxy resins with high toughness at low temperatures. [Display omitted] • Cross-linkable EHTPB and POSS synergistically improve the E51 toughness. • K IC and G IC values are 73.5% and 258.6% higher than the E51/DDM at 77 K. • Resin-cured crosslinking simulation network analyzed the toughening mechanism. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) foam is gaining increased attention as a biodegradable alternative to traditional petroleum-based plastic foams, which pose significant environmental pollution issues post-use. However, its potential application is greatly limited by inherent shortcomings such as brittleness and diminished heat resistance post-melting. Herein, high-performance biodegradable PLA/poly(butylene succinate) (PBS) blend foams with well-defined cell structure, high ductility, and enhanced heat resistance were fabricated using a core-back foam injection molding (FIM) process coupled with a straightforward annealing procedure. To enhance compatibility and tailor the dispersed phase morphology into a more fibrillar structure, an epoxy-functional chain extender (ADR) was incorporated. This addition resulted in a substantial increase in the notched impact strength, elevating it to 7.0 kJ/m2, compared to the mere 1.5 kJ/m2 of unmodified PLA foam. Moreover, with the inclusion of 1.0 phr ADR, the notched impact strength of the foam post-annealing soared to 20.7 kJ/m2, a 13.8-fold enhancement compared to pure PLA foam. The formation of a uniformly distributed and interlocked "shish-kebab" crystal structure in the blend facilitated effective stress transfer and distribution, leading to shear yield in the PLA matrix. Additionally, the heat deflection temperature of the annealed blend foam showed a significant increase significantly to 94.7 °C, in contrast to the mere 55.6 °C of pure PLA foam. This study demonstrates a viable and feasible strategy for preparing fully biodegradable PLA foams with high-toughness and heat resistance. [Display omitted] • Biodegradable PLA/PBS blend foams were fabricated using foam injection molding. • Changes in ADR content affect interface adhesion and tailor phase morphology. • An interlocking shish-kebab structure was achieved during the annealing process. • The resultant foams exhibited superior toughness and heat resistance. [ABSTRACT FROM AUTHOR]

Despite numerous studies, the relationship between network structure and fracture remains unclear. In this study, the fracture properties of end-linking networks were compared with those of loop-free analogs made from star prepolymers by performing phantom chain simulations. The networks were created from equilibrated sols of stoichiometric mixtures of linear prepolymers and f -functional linkers through end-linking reactions using Brownian dynamics schemes. The examined networks, with various f values (between 3 and 8) and strand-connection rates (φ s), were evaluated in terms of the primary loop fraction and the cycle rank ξ. These structural characteristics were consistent with mean-field theories that assume independent reactions. Energy minimization and uniaxial stretch were applied to the networks until they broke without Brownian motion. The fracture characteristics, including strain at break (ε b), stress at break (σ b), and work for fracture (W b), were obtained from stress-strain curves. The end-linking networks exhibited larger ε b and smaller σ b and W b than those for star networks due to primary loops, at the same set of f and φ s. However, ε b , σ b / ν b r and W b / ν b r (with ν b r being the branch point density) lie on the same master curves as those for star networks if they are plotted against ξ. This result implies that the fracture of end-linking networks is essentially the same as that for star analogs, and the effects of primary loops are embedded in ξ. [Display omitted] • Phantom chain simulations were performed for the fracture of end-linking networks. • The network structure was analyzed concerning the ratio of loops and cycle rank. • The cycle rank dominates fracture properties just as loop-free networks. [ABSTRACT FROM AUTHOR]

Multifunctional hydrogels with high electrical conductivity and mechanical flexibility are widely used as flexible strain sensors in different fields such as artificial intelligence, electronics and flexible sensing. However, when the temperature drops below the freezing point, the solidification of water leads to solidify or even failure of the hydrogel, severely limiting the application in low temperature environments. Thus, the hydrogel was prepared by a freeze-thaw method using polyvinyl alcohol, polyvinylpyrolidone, sodium chloride, glycerol and sodium carboxymethyl cellulose. The hydrogel exhibited excellent electrical conductivity and mechanical property in −40 °C–20 °C. Simultaneously, the hydrogel sensor possessed prominent sensitivity and cyclic stability to accurately monitor human motion in real time, including large-scale human motion such as wrist, elbow, and knee flexion movements as well as subtle human motion. There were no adverse reactions after the hydrogel into mice during14 days, indicating good biocompatibility of the hydrogel. Furthermore, the hydrogel could be printed in different shapes by 3D printing. The investigation provides a new route for the development of multi-functional hydrogel wearable sensors. The hydrogel exhibited concurrently enhanced mechanical property, freezing resistance, water retention ability and biocompatibility by introducing Sodium carboxymethyl cellulose, which could serve as wearable sensor for monitoring human motions. [Display omitted] • Hydrogels exhibited anti-freezing and water retention and biocompatibility. • Sodium carboxymethyl cellulose possesses biocompatibility and biodegradability. • Hydrogel sensor can detect the movement characteristics of various human joints. • Hydrogel no adverse reactions after the hydrogel into mice during14 days. [ABSTRACT FROM AUTHOR]

Epitaxy crystalline structure and multilayer alternated structure can both improve the toughness. In this work, these two structures are simultaneously introduced into one iPP/HDPE blend sample by a self-designed multi-flow vibration injection molding (MFVIM) device. As a result, there is a synergistic influence on enhancing the impact strength. The impact strength of this sample reaches to 76.04 kJ/m2, which is much higher than the sample fabricated by conventional injection molding, 3.27 kJ/m2. The characterization of crystalline structure and macroscopic hierarchical structure is carried out by PLM, SEM, SAXS, WAXD and DSC. It is found that these two structures cause an associated deformation by providing various paths of external force and prolonging its transmitted path during fast impact loading. These results provide a novel method to enhance the toughness of polymer material by toughening it from different scales. Image 1 • Multilayer structure and epitaxy structure were inducedinto one injection molded PP/PE part. • Great toughness enhancement was realized without sacrificing strength. • An associated deformation happened from oriented lamellae andmacroscopic layer. [ABSTRACT FROM AUTHOR]

In this work the mechanical properties of high internal phase emulsion templated Ring-opening Metathesis Polymerization cured poly(dicyclopentadiene) (pDCPD) foams of 90% porosity prepared with varying surfactant amounts are studied. Using tensile-testing instead of conventionally compression testing of foam samples reveals a distinct influence of the surfactant loading on the mechanical properties. Although void sizes (and similarly window sizes) linearly decrease with increasing surfactant amounts, the strength and toughness do not. The strength of the foams is greatly unaffected by variations of the surfactant amount in the regime of 1–5 vol%. Above these levels the strength decreases with increasing surfactant loading. The modulus of toughness increases with increasing surfactant amount until a maximum is reached at around 2–4 vol% of surfactant. More surfactant causes a decrease in toughness. Accordingly, in terms of mechanical properties an optimal surfactant amount of 3 vol% in respect to DCPD is found. Applying this formulation to the preparation of foams with 80, 70, 60, and 50% nominal porosity gives materials with high strength (Young's moduli in between 116 and 416 MPa) and toughness (moduli of toughness between 600 kJ/m3 to 2 MJ/m3). Image 1026 • PolyHIPEs of 90% porosity were prepared by Ring-Opening Metathesis Polymerization of dicyclopentadiene. • The influence of surfactant loading on the morphological and mechanical properties was investigated. • The mechanical properties were probed by tensile testing allowing for evaluating the strength and toughness of the foams. • The surfactant amount critically influenced both the strength and toughness. [ABSTRACT FROM AUTHOR]

Abstract A strong and tough self-healing elastomer is prepared based on double reversible networks consisting of ionic interactions and Diels-Alder (D-A) crosslinks. The elastomer is synthesized through one-pot copolymerization of a pair of oppositely charged monomers and furan functionalized methacrylate (FMA), which is then crosslinked with 1,1'-(Methylenebis(4,1-phenylene))bis(1H-pyrrole-2,5-dione) (BMI) via Diels-Alder (D-A) reaction. The oppositely charged monomers form ionic bonds which can segregate into aggregates with a wide distribution of size. Under heating or external force, the aggregates can dissociate from small to big ones to dissipate amount of energy and endow the materials with high mechanical properties (13 MPa in strength, 480% in stretchability). While the D-A crosslinks act as covalent bonds at room temperature and endow the materials with high elasticity and fast shape recovery ability. These two reversible networks with different dynamics contribute to the multi-scale self-healing properties of the elastomer. As a result, the self-healing efficiency of the elastomer is as high as 86%. Graphical abstract A strong and tough self-healing elastomer with high mechanical properties (13 MPa in fracture strength, 480% in stretchability) and self-healing efficiency (86%) is prepared based on double reversible networks consisting of ionic interactions and Diels-Alder (D-A) crosslinks. Image 1 Highlights • The elastomers have high mechanical properties (13 MPa in fracture strength, 480% in stretchability) and self-healing efficiency (86%). • The ionic aggregates have wide size distribution which can desegregate progressively to dissipate energy. • The D-A crosslinks endow the sample with fast recovery ability. • The ionic bonds are dynamic at room temperature while the D-A crosslinks are dynamic at high temperature. [ABSTRACT FROM AUTHOR]

In our earlier contribution, it was shown that with the addition of 1 wt% functionalized multiwall carbon nanotube (f-MWNT), an unprecedented 152% increase in PP impact strength without a significant loss in stiffness and ductility can be achieved. In the context of these observations, this work examined the impact fracture mechanism of such PP/f-MWNT nanocomposite, in which the PP interphase was tailored by the same co-solvent solution process. The nanotube-matrix stress transfer efficacy in PP/f-MWNT as compared to that of PP/pristine MWNT (p-MWNT) was determined by Raman spectroscopy. The calculated interfacial shear strength ( τ i ) is 17.8 MPa in PP/f-MWNT and 2.2 MPa in PP/p-MWNT, suggesting improved matrix-CNT adhesion in the former. This strong interfacial adhesion allows CNTs to bridge the opening crack, absorb fracture energy and promote local plastic deformation of the polymer matrix. Such process was demonstrated using SEM fractography where breakage/pull out of the CNTs, microcracks, and the intensive fibril formation accompanied with the extension of the PP matrix were captured at the impact fracture surface. Both the interfacial shear strength and the SEM fractography supported the hypothesis that better matrix-CNT adhesion can be achieved through interphase engineering. [ABSTRACT FROM AUTHOR]

We propose a facile method for preparing toughening epoxies using self-assembled scaffolds formed by organogels. 1,3:2,4-dibenzylidene sorbitol (DBS) is a sugar derivative that is capable of self-assembling into a 3-D nanofibrillar network at relatively low concentrations in certain organic solvents to form organogels. In this work, we induced the formation of such nanofibrils in the most frequently used epoxy monomer, di-glycidyl ether of bisphenol A (DGEBA). Subsequently, we cured DGEBA in the presence of a curing agent with various amounts of DBS. The resulting materials were transparent and homogeneous epoxies with DBS nanofibrillar networks. The DBS nanofibrils in the epoxy matrix acted as reinforcing materials that enhanced the hardness and stiffness of the epoxies. Moreover, due to the entangled network structures, the toughness of the epoxies increased with increasing amounts of DBS (the maximum being an approximately 5-fold improvement). In addition, the thermal stability of the epoxies was improved by the addition of DBS, including the glass transition temperatures and thermal degradation temperatures. [ABSTRACT FROM AUTHOR]

Poly( l -lactic acid) (PLLA) sheets with dramatic improvement of mechanical properties, especially toughness, were obtained by uniaxial pre-stretching around T g . It was found that a network structure consisting of cohesional entanglements was formed during the usual compression molding process, leading to the brittleness of PLLA, and the destruction of the network structure due to disentanglement after pre-stretching, leading to the toughness of PLLA. The network structure could not be destroyed when pre-stretching ratio (PSR) was in the elastic deformation region I and strain softening region II (PSR < 0.2). However, when PSR got into the strain hardening region III (PSR = 0.2), the network structure was destroyed resulting from the disentanglement, leading to the brittle to ductile transition. With PSR increasing from 0.2 to 0.4, the orientation was formed in pre-stretched PLLA, leading to further increase of the elongation at break. And then the degree of orientation increased along with the occurrence of the mesophase (PSR ≥ 0.5), therefore, the modulus and strength increased, while the elongation at break decreased. However, the elongation at break was still larger than that of undrawn PLLA. [ABSTRACT FROM AUTHOR]

Polystyrene (PS) was blended with shape memory polyurethanes (SMPU). Styrene blocks were grafted onto PU chains during SMPU synthesis to yield a modified SMPU with a higher affinity towards PS. Furthermore, blends containing a compatibilizer, poly (styrene-co-maleic anhydride) (SMA), were also prepared by melt mixing the components. The non-compatibilized blends display phase separated structures with PS rich and SMPU rich phases, which were less evident in blends prepared with either the modified SMPU or SMA compatibilizer. The elastic storage modulus of PS was less affected when blended with SMPU in samples containing modified SMPU with styrene grafts. The impact strength of the blends with higher contents of SMPU modified with styrene blocks (25 and 50 wt.%), after shape recovery, was higher than the impact strength of neat PS. The incorporation of shape memory polymers into a brittle polymer matrix is a potential strategy to improve the toughness by external stimuli. [ABSTRACT FROM AUTHOR]

Interface has been long time recognized as crucial for changing and optimizing mechanical properties of polymer composites and nanocomposites. Spectroscopic identification of this interface, however, remains a great challenge. This study combining solid-state 13 C NMR spectroscopy with a principal component analysis (PCA) proposes a novel strategy to explore the role of interfacial area at vicinity of filler particles on toughness of polymer composites. Samples of commercial-grade isotactic polypropylene (PP), both neat and modified with various types of calcium carbonate (CaCO 3 ) microparticles, were subjected to a combination of fracture mechanical testing and solid-state NMR analysis. Temperature-induced transformation between the free and constrained amorphous phases was monitored using the factor analysis of 13 C MAS NMR spectra. The three-dimensional correlation plots clearly separated the prepared PP/CaCO 3 microcomposites into the well-defined clusters, allowing the systems with differing quantities of partially ordered amorphous domains to be identified. These differences perfectly correlated with the toughness of the prepared composites. The results thus confirmed that the changes in the toughness of the microcomposites are closely related to the increased formation of the partially ordered trans -crystalline fraction of PP chains. [ABSTRACT FROM AUTHOR]

A novel hyperbranched polyether epoxy (HBPEE) bearing a stiff fluorene unit and flexible aliphatic chains has been synthesized using a one-pot approach and used as a toughener for bis-benzoxazine resin (MDA-BOZ). Effects of loadings and molecular weight of HBPEE on curing behavior, rheology properties, static mechanical, dynamic mechanical and thermal properties of the hybrid systems have been studied. Results show hybrids containing medium-M n (i.e. ∼3900) HBPEE-2 modifier possesses optimal comprehensive properties. Synchronous improvement of impact strength, flexural strength and storage modulus was found in hybrids containing 5% HBPEE-2 and 5% HBPEE-3, where HBPEE served as a non-phase-separation modifier confirmed by SEM and DMA. Notably, there was a 2.8-fold improvement in impact strength for hybrids containing 10% HBPEE-2, compared to the same properties of samples without HBPEE. This was achieved without any compromise of flexural modulus, flexural strength, E′, thermal stability and glass transition temperature (T g ). The results demonstrate that multiple factors, such as enhanced crosslinking density ( v e ), rigidity of the toughener, reduced hydrogen bond network and higher fractional free volume, contributed to such improvement. [ABSTRACT FROM AUTHOR]

Polymer alloys are increasingly being used in engineering applications. These multicomponent polymeric systems are one of the fastest growing segments of today's plastics industry. This review examines the state-of-the-art and recent developments in the field of high performance reactively toughened ternary and quaternary polymeric alloys of encapsulated (core-shell) morphology. These alloys consist of a functionalized elastomeric polymer that functions as both dispersant and impact modifier for the resulting multiphase system. The chemical reaction of the impact modifier during melt processing gives rise to its interfacial localization and development of a core-shell structure for dispersed components. It is well-established that the dispersed composite nano/micro-domains in these blends provide a superior stiffness-toughness balance with improved processability at lower rubber contents compared with traditional toughened binary blends containing homogeneous rubbery domains. The thermodynamic and kinetic issues governing the development of an encapsulated morphology are presented. The impacts of processing conditions, microstructural (molecular, architectural, rheological, and physical) characteristics of blend components, and various blending parameters on the formation and evolution of core-shell nano/micro-morphology are reviewed thoroughly in conjunction with their subsequent influences on the macroscopic mechanical response of the blends. Special focus is on detailed discussion of the involved nano- and micro-mechanics of deformations associated with different phase structures, interphase adhesions, and dispersion states of core-shell nano/micro-structures during both high-speed impact and quasi-static fracture mechanics tests. The use of volume-strain measurements for determining the relative contribution of various dilatational and non-dilatational nano/micro-deformations accompanying the failure process during macroscopic mechanical loadings is examined profoundly. The theoretical models proposed for prediction of modulus and strength of multiphase systems comprising core-shell structured domains as well as the design criteria deduced from these models to develop high-performance materials of high impact resistance with low rigidity loss are highlighted. Finally, future research perspectives and possible directions for further progress in this field are outlined. [Display omitted] [ABSTRACT FROM AUTHOR]

Polyhedral oligomeric silsesquioxane copolymerized with butyl acrylate (BA), methyl methacrylate (MMA), and acrylic acid (AA) induced ca. twofold increase of fracture energy Γ and of Young's modulus E of cast films at only 1 wt% content. The copolymer of composition BA:MMA:AA:POSS 56:41:2:1 mol% was synthesized in situ by seeded semi-batch emulsion polymerization. Films cast from the corresponding emulsions were optically transparent and transmission electron microscopy (TEM) showed that POSS was predominantly dispersed at nearly single unit in the acrylic matrix. Shear rheology and time-temperature superposition (TTS) analysis demonstrated an entangled state with the absence of terminal regime, and POSS increased the segmental relaxation time τ e and the rubbery modulus G e , hence the free volume and packing length p decreased, relative to the neat copolymer. The efficient dispersion of POSS and its size smaller than the virtual tube diameter suggests that POSS is intercalating the molecular mesh. Therefore, the entanglement density increased and induced an increase of tensile mechanical modulus. The mesh intercalation by POSS means that it did not act as stress concentrator and consequently the critical fracture strain ε* and the fracture energy Γ also increased. These results evidenced the topological constraints imposed by the bulky POSS to hinder chains past each other thus inducing an increase of entanglement density and this manifested in simultaneous mechanical reinforcement and resistance to fracture. [Display omitted] • POSS simultaneously increased mechanical modulus and toughness of acrylic nanocomposite. • Well-dispersed POSS intercalated the macromolecular mesh. • The intercalation increased the entanglement density and hence induced mechanical reinforcement. • The intercalated POSS did not act as stress concentrator. [ABSTRACT FROM AUTHOR]

In recent years, rubber toughened polypropylene (PP) blends have been extensively investigated with special regard to the importance of PP matrix properties (e.g., crystal morphology and structure) in tailoring the toughening efficiency. Unfortunately, although high melt flowability is indispensable to the processing of polymers into complex thin-wall products, it remains a huge challenge to achieve a marvelous balance between stiffness and toughness in the blends with relatively low matrix molecular weight. Herein, taking PP/EPR (ethylene-propylene copolymer) blends as an example, the combined effects of matrix molecular weight and crystallinity on the mechanical properties of PP/EPR blends have been examined in both experiment and theory. The experimental results show that decreasing molecular weight leads to significant deterioration in notched impact toughness, tensile strength and Young's modulus. Impressively, the toughness loss caused by the decrease of molecular weight can be well-compensated by a slight reduction in the matrix crystallinity, without evidently sacrificing the strength and modulus, demonstrating an improved stiffness-toughness balance. Theoretical analysis indicates that the impact toughness of PP/EPR blends is heavily dependent on the chain entanglement density (v e) of PP matrix, and a linear relationship between critical interparticle distance (ID c) and the v e 1/3 has been verified from both experiment and theory. Moreover, it is interesting to find that decreasing matrix crystallinity can increase the v e of low-molecular-weight PP matrix, which enables the effective toughening at lower concentration of EPR and thus gives rise to less loss in the strength and modulus. We believe this work not only gives a new insight into the role of chain entanglement in the toughening but also provides a promising guidance for the design of high-performance PP with high melt flowability. [Display omitted] • Combined effects of M n and crystallinity on the toughening efficiency of PP/EPR blends were studded. • The relationship between the ID c and v e of PP matrix i.e. ID c ∼ v e 1/3 , was given for the first time. • Matrix with higher M n or lower crystallinity has higher v e , exhibiting larger ID c. • Toughness loss caused by decreasing M n can be compensated by reducing crystallinity. • Low-viscosity PP/EPR blends with good toughness-stiffness balance were obtained. [ABSTRACT FROM AUTHOR]

In this study, a facile approach to fabricate a novel bio-based hybrid (BBH) with core/shell structure is presented by taking advantage of plant-derived resources. The BBH developed herein comprises of an inorganic core of ammonium polyphosphate (APP), covered with an organic shell that is constructed via layer-by-layer assembly of a novel bio-based polyelectrolyte (BPE) and polyethylenimine (PEI). BBH can simultaneously enhance the flame retardancy and toughness of polylactic acid (PLA) with very high efficiency. The flame retardant PLA composite can pass UL94 V0 rating at the BBH loading content of 10 wt%. The efficient flame retardant performance is due to its effectiveness in both gas and condensed phases. More importantly, the flame retardant PLA composite containing 10 wt% BBH exhibits ductile fracture with an elongation at break of 27.3%, which is much higher than that of neat PLA (8%). The debonding and plastic void deformation of the PLA matrix around the BBH are responsible for the enhanced toughness. This work provides important hints for devising highly efficient multifunctional flame retardant and broadening the application field of renewable resources. [ABSTRACT FROM AUTHOR]

Introducing reversible hydrogen bonds as sacrificial bonds is an emerging strategy to improve the toughness of elastomers. However, binary hydrogen bonds are not strong enough and highly dynamic, and thus have only a moderate toughening effect. Here we demonstrate that quadruple hydrogen bonds have a remarkable toughening effect for diene elastomers. To fabricate the quadruple hydrogen bonds toughened elastomer, we graft 2-ureido-4[1H]-pyrimidinone (UPy) groups onto the backbone of polyisoprene (PI). The UPy groups dimerize to form strong hydrogen bonds which have higher bond energy than binary hydrogen bonds. Compared with weak hydrogen bonds with the same mole fraction, the strong hydrogen bonds lead to higher reversible crosslinking density and slower chain mobility of the elastomer; this enables higher energy dissipation as the elastomer is subjected to deformation. As a result, the introduction of UPy significantly increases both the toughness and the tensile strength of the elastomer. Moreover, unlike covalent sacrificial bonds, the hydrogen bonds of UPy are dynamic and show the re-association of sacrificial bonds at room temperature, as evidenced by recovery of hysteresis loop during cyclic tensile tests. This work will not only greatly extend our understanding on the different toughening effects of weak and strong hydrogen bonds, but also help us to rationally design tougher elastomers. [ABSTRACT FROM AUTHOR]

Melt blending of poly(butylene succinate) (PBS) with poly(lactic acid) (PLA) to fine tune the mechanical properties of PLA needs to be aware of immiscibility. The present work proposed the random poly(butylene succinate- co -lactic acid) (rPBSL), and for the first time about its multi-functions as compatibilizer, plasticizer, and film clarity enhancer. Based on PLA/PBS (80/20%wt) with rPBSL (3–5 phr), the films obtained show the smooth surface with compatibility and clarity. A significant decrease in T g (from 52 °C to 43 °C) and a noteworthy increase in elongation at break (four-fold) confirms the role of plasticizer. A decrease in T c (from 103 °C to 85 °C), together with increases in degree of crystallinity and spherulite growth rate with homogeneously dispersed spherulite suggests how the rPBSL effectively induces rapid nucleation. By balancing the crystal and amorphous domains including the initiation of rapid and small spherulites, it is seen that rPBSL performs as a multi-functional additive for PLA/PBS blends. [ABSTRACT FROM AUTHOR]

In this study, the poly( l -lactide)/thermoplastic poly(ester urethane) (PLA/TPU) blend was employed as the matrix for preparation of nanocomposites with several halloysite nanotube (HNT) concentrations. This design was hypothesized based on a morphological conversion according to the assessment of thermodynamic equilibrium calculated by the contact angle measurements. HNTs as nanoparticles were applied to create PLA/TPU nanocomposites with more polymer interfaces for greater interactions, more compatibility, and a higher toughness. The addition of adequate HNTs, which have a thermodynamic inclination of settling in the low viscosity PLA phase, penetrates in the PLA phase and saturates the surface of this phase, as a result, the sea-islands transforms to quasi-cocontinuous morphology. If the added HNT is more, the nanoparticles not only disperse in the PLA phase and the interface but also penetrate into the TPU and agglomerate in some areas. The predicted morphology and microstructure were observed by the SEM and elemental analyses. The chemical structure changes and thermal properties of composites were investigated by the FTIR, DSC and TGA, respectively. The thermal stability of nanocomposites was investigated and shown that this property was improved by the presence of HNT in the nanocomposites. Also, the mechanical properties of the prepared composites, including elongation at break, tensile strength, elastic modulus, toughness, impact strength and hardness were reinforced. The melt flow properties of the designed composites were also investigated by the dynamic rheological analysis. Due to the reinforced thermal stability, fortified mechanical properties, high toughness and high melt elasticity, the designed composites are capable of being used in several applications such as packaging, thermal sealing, thermoforming, and melt spinning of plastics. [ABSTRACT FROM AUTHOR]

Finite tensile behavior and fracture toughness of double-network (DN) and triple-network (TN) hydrogels synthesized from 3-sulfopropyl acrylate potassium salt (SAPS) and acrylamide (AAm) are discussed. The mechanical behavior of pseudo-semi-interpenetrating polymer network (pseudo-SIPN), pseudo-interpenetrating polymer network (pseudo-IPN) and TN hydrogels prepared from the two types of DN networks are considered. In general, the mechanical behavior of tough hydrogels is dependent upon the crosslink densities of the first and second networks in DN and TN hydrogels and the covalent connectivity of the second or third network to the previous network architecture. Pseudo-SIPN hydrogels, where no crosslinking agent is used to make the second network, exhibit necking for tensile deformations. When a very low concentration of crosslinking agent is used in the second polymerization step (pseudo-IPN), necking is suppressed and strain hardening occurs. Increasing the crosslink density of the second network produces more pronounced strain hardening, but also embrittlement of the hydrogel. For tough hydrogels where the first network is very brittle, i.e., very high crosslink density, it is difficult to prevent necking. The formation of a third, loosely crosslinked network within pseudo-SIPN and pseudo-IPN hydrogels that exhibit necking prevents necking and produces strain hardening. Loading – unloading tensile experiments conducted on DN hydrogels indicated that regardless of the stretch ratio used (high strains above or low strains below the yield point), the sample exhibited plastic flow and a residual strain. The value of the residual strain was insensitive to the magnitude of the strain at which the load was removed. [ABSTRACT FROM AUTHOR]

A new strategy to toughen epoxy resins through control of topological structure of cross-linking network has been presented. With a tertiary amine initiator, the curing proceeded via chain-wise polymerization. The impact strength of epoxy resin increased to above 84 kJ/m 2 by only increasing the curing temperature, which is much higher than the reported value of 10–30 kJ/m 2 for pure epoxy resin. Meanwhile, yielding was found during uniaxial tensile and three-point bending measurements. At the molecular scale, the cross-linking density showed a bimodal distribution and decreased with increasing curing temperature. A mechanism based on controlled topology of cross-linking network has been proposed to explain these changes. The cross-linking of epoxy resins occurs via a continuous anionic ring-opening polymerization, resulting in well interpenetrated chains. The chain transfer converts active alkoxide anions into inactive hydroxyls, limiting the linear growth and cross-linking. The resultant branching structures display lower cross-linking density, serving as native tougheners at the segment scale. Chain transfer accelerates with temperature, thus the ductility increases monotonically with curing temperature. This mechanism was confirmed by deliberately introducing branching chains through a short time of high-temperature reaction at the first stage of curing. The impact strength was enhanced by 2.5 times in comparison to the samples without the initial high-temperature curing. This unique and facile strategy shows potential in directly obtaining more ductile epoxy resins materials by controlling the topology of cross-linked networks. [ABSTRACT FROM AUTHOR]

Curing epoxies with a mixture of low- and high-T g diamines has been proposed as a way to increase thermoset toughness. We seek here to understand the origins of toughness enhancement in systems comprised of the diamines poly(oxypropylene)diamine (POPDA) and diethyltoluenediamine (DETDA) together with the epoxy resin diglycidyl ether of bisphenol A (DGEBA) via control of network isomerization. Two curing protocols at constant overall DGEBA/DETDA/POPDA 2:1 amine:epoxy stoichiometric composition are compared: (i) curing a liquid mixture of DGEBA, DETDA and POPDA, and (ii) partially curing DGEBA with POPDA (60% of amines reacted), then adding DETDA and more DGEBA to continue to a fully cured stoichiometric sample; the latter is referred to as the “partially reacted substructure” (PRS) method. PRS samples are 50% tougher than the compositionally-identical mixed samples yet have higher T g 's than the mixed samples. We show here that MD simulations of model systems provide a molecular-level rationale for this observation. First, MD yields reasonably accurate densities and T g 's. Lower T g 's in the mixed systems are correlated to larger thermal fluctuations in positions of monomer centers enabled by more uniform dispersion of the POPDA molecules. Furthermore, the onset of crosslink bond stretching under steady uniaxial tensile strain occurs at lower strains in the mixed samples, which correlates to their lower experimental ductility. This behavior is shown to arise from POPDA molecules in the PRS system more easily deforming from their unstrained conformations than they can in the mixed systems. These findings provide further guidance in the use of control over network isomerization at constant composition to enhance toughness of thermoset systems. [ABSTRACT FROM AUTHOR]

In this work, we report that super-toughened and high-strength polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends can be successfully prepared by interfacial compatibilization and dynamic vulcanization during reactive melt-blending with small amounts (0.5–3 wt %) of epoxy-functional styrene-acrylic oligomers (ESA). The results show that the compatibilization is realized with the grafting of some PLA and PBAT chains onto ESA backbones to in-situ generate PLA- graft -PBAT copolymers at the blend interface. Meanwhile, the ESA-mediated vulcanization gives rise to the highly cross-linked PBAT particles with a unique network-like distribution in the PLA matrix. Both the strengthened interfaces and networked PBAT particles are favorable to the triggering of massive matrix plastic deformation required for effective energy dissipation and thus the toughening effect is substantially enhanced. Impressively, the notched Izod impact toughness and elongation at break of the PLA/PBAT (70/30) blends can reach as high as 62.4 kJ/m2 and 232%, while the tensile strength increases from 44.2 MPa to 51.5 MPa, indicating a balanced toughness and strength. Most notably, it is demonstrated that tuning the molecular structure of ESA (i.e., epoxy group density and backbone length) is essential to improving the interfacial adhesion and phase morphology, enabling high toughening efficiency. Our facile yet robust strategy presents an unprecedented opportunity for the development of high-performance fully biodegradable PLA blends. [Display omitted] • Full biodegradable PLA/PBAT blends with balanced toughness and strength are prepared. • Dynamic vulcanization leads to the highly cross-linked PBAT domains in PLA matrix. • Copolymers are in-situ generated at the interface for effective compatibilization. • The formation of PBAT particle network is responsible for the desired properties. • The key role of ESA structure in tailoring the morphology and properties is verified. [ABSTRACT FROM AUTHOR]

The reactions of methylenediphenyl 4,4’-diisocyanate (MDI) with hydroxy-terminated 4-armed star-shaped l -lactide oligomer (H4LAO n ) and 4-armed star-shaped ε-caprolactone oligomer (H4CLO n ) with the degree of polymerization per one arm, n = 3, 5 or 10 produced conetworks [MH4(LA/CL)O n s] with the feed H4LAO n /H4CLO n weight ratios of 75/25, 50/50 and 25/75. The formation of conetwork structures with different crosslinking densities was confirmed by the swelling test and FT-IR spectral analysis. Scanning electron microscopic analysis revealed that the oligolactate (LAO) and oligocaprolactone (CLO) segments are compatibilized for all the conetworks except for MH4(LA/CL)O 10 25/75. Differential scanning calorimetry and dynamic mechanical analyses revealed that all the conetworks are substantially amorphous, and that only one glass transition temperature ( T g ) was observed for each of the conetworks except for MH4(LA/CL)O 10 25/75. Tensile properties of MH4(LA/CL)O n s were largely affected by the influence of the T g value which changes according to the LAO/CLO ratio. MH4(LA/CL)O 5 50/50 ( T g : 33.3 °C) exhibited the highest tensile toughness among all the conetworks. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs) isolated from kenaf bast fibers were used to reinforce unsaturated polyester resin (UPR) composites toughened with liquid natural rubber (LNR). The surface of the CNCs was modified with silane, and the effects of this treatment on the morphological, tensile, and thermal properties of the resulting composites were studied. Electron micrographs show that the CNCs are well dispersed in the UPR and the rubber phase and that the rubber particles are smaller in the nanocellulose composites. Tensile tests show that untreated CNC–LNR–UPR composites are as strong as toughened UPR. The tensile modulus increases significantly with either treated or untreated CNC content of the composites. The impact resistance of UPR increases as LNR and then CNCs are added, with the best results obtained with silane-treated CNCs. The viscoelastic behavior and the thermal resistance of the composites also improve upon addition of both treated and untreated CNCs. [ABSTRACT FROM AUTHOR]

Hybrid gels featuring interpenetrating covalent and ionic crosslinked networks have recently been shown to exhibit both high toughness and recoverability of strain-induced network damage. The high toughness results from the energy dissipated as entropically strained network strands are released by the dissociation of ionic crosslinks. As in the so-called double network hydrogels, the toughening process is inherently linked to network damage. This damage, however, can be recovered to a large degree in hybrid gels due to the reformation of ionic associations when the gel is unloaded. The stability of the ionic network under load is here investigated and it is shown that these networks show large stress relaxation at constant strain, time dependent stress-strain behaviour and rate-dependent toughness. A double exponential model is invoked to mathematically describe the stress relaxation of the hybrid gels indicating at least two relaxation mechanisms. The rate-dependent toughness and the relaxation behaviour of the hybrid gels are attributed to the labile unzipping of the ionic crosslinks which is assumed to be load and time dependent. [ABSTRACT FROM AUTHOR]

This work attempts to introduce polyhedral oligomeric silsesquioxane compounds as a novel toughening agent for thermosetting systems. For this purpose, an acrylic/melamine thermosetting system was modified by OH-functional silsesquioxane nano-cage. Mechanical and thermo-mechanical behavior of resultant nanocomposites were studied by tensile and DMTA techniques. It was found that low content of silsesquioxane building blocks is sufficient to shift the mechanical behavior of the matrix from a brittle character to a flexible tough one. Various morphological techniques (SEM and TEM equipped with elemental analyzer together with XRD) were also utilized to clarify how nano-cages have been oriented within the matrix. It was revealed that nano-cages have been well dispersed in a molecular scale within the thermosetting network. The good dispersion of silsesquioxane compounds was assigned to the high compatibility within the matrix owing to their compact structure and OH-functional groups available on the cage. [ABSTRACT FROM AUTHOR]

This study aims to explore the origin of toughness in β-phase isotactic polypropylene (i-PP). Samples of commercial-grade i-PP, both neat and nucleated with a specific β-nucleating agent (N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide), were subjected to a combination of structure-sensitive methods and fracture mechanical testing. In addition to common structural characterisation methods, solid-state NMR data were collected to obtain information about the dynamics of the polymer segments as well as the structure. In particular, temperate-induced transformation between the free and constrained amorphous phase was monitored by variable-temperature 13 C MAS NMR, whereas T 1ρ ( 1 H) relaxation was used to estimate correlations times of segmental motions. Lower thermodynamic stability of rigid amorphous fraction was found in the β-crystalline systems. In contrast helical chains in crystalline and constrained amorphous phase were found to be more restrained in the α-crystalline system. Overall, the results indicate larger restrictions in chain mobility in the amorphous phase of the α-polymorphic PP system than in that of the β-crystalline ones. [ABSTRACT FROM AUTHOR]

Propionate-hexanoate mix ester of paramylon (PaPrHe), a bio-based β-(1,3)- d -glucan photosynthesized by Euglena, was blended with poly(butylene succinate- co -adipate) (PBSA) and analysed for its physical properties. The morphology of the blend was revealed using a combination of selective enzymatic etching and SEM. The morphology changed from phase separated to co-continuous and then uniform dispersion with increasing PBSA content. In particular, the 10% PaPrHe loading had a unique sub-micron level dispersion with a median particle diameter of 0.6 μm. This ratio also had the highest toughness (67.3 kJ/m2) among all the ratios, surpassing even neat PBSA (53.2 kJ/m2). X-ray analyses of thermally stretched films showed high degree of orientation (94%) and crystallinity in the PBSA rich blends, leading to a 160–400% increase in the tensile strength. All the blend ratios had high thermal stability and melt-processability making the PBSA/PaPrHe green blend a sustainable alternative for packaging and mulch-film applications. [Display omitted] • Bio-based blends from PaPrHe and PBSA were prepared using melt-extrusion. • 90/10 PBSA/PaPrHe had a sub-micron level dispersion with median particle dia: 0.6 μm. • The elongation at break and toughness could be tuned based on PBSA loading. • X-ray analyses of stretched films show high degree of orientation and crystallinity. • All the blend ratios had high thermal stability suitable for several applications. [ABSTRACT FROM AUTHOR]

Polymer blending is a typical and conventional approach for integrating the excellent physical/chemical properties of individual polymer components. Specifically, the mechanical toughness and strength of polyamide-6 (PA6)/polyketone (PK) blend are substantially enhanced compared to either PA6 or PK individual component. Nevertheless, there are few atomic-level insights into such mechanical property enhancement. In this study, solid-state nuclear magnetic resonance (NMR) is utilized as a main tool to understand the molecular origin of the mechanical enhancement of PA6/PK blends. The proton relaxation times are used to evaluate the miscibility and domain sizes in PA6/PK blends, and to determine the crystallinity of each component, where both conventional DSC and WAXD experiments fail because of similar crystallization/melting behaviors of PA6 and PK components. 2D 1H–13C WISE (wideline separation) and HETCOR (heteronuclear correlation) solid-state NMR spectroscopy were performed to further reveal the nano-heterogeneous structures and hydrogen bonding interactions in PA6/PK blend. With further combination with FTIR and SEM results, the previous characteristic morphological model for elucidating the toughening mechanism for PA6/PK blends is refuted, and it is proposed that the superior performance of PA6/PK blend is resulted from the synergistic effects of enhanced interfacial adhesion and interconnected interphase percolated in the bulk PA6/PK blends via hydrogen bonds. We envisage the detailed molecular level insights provided by solid-state NMR spectroscopy could assist in the bottom-up design of high performance polymer blend materials. [Display omitted] • The locations of hydrogen bonding between PA6 and PK are precisely determined. • The strength of hydrogen bonding interactions is semi-quantitatively characterized. • A complementary approach for studying crystallization of polymer blends is provided. • Insights into the toughening mechanism via solid-state NMR techniques are obtained. [ABSTRACT FROM AUTHOR]

Polyurethane elastomer nanocomposites are strategically important due to their indispensable applications in daily life and high-tech fields. Herein, a series of nanocomposites with extraordinary strength, toughness and energy dissipation are reported, which are enabled by multiple dynamic moieties including dynamic boronic ester covalent bonds, boron-nitrogen coordination bonds in the matrix and on the interface. The surface-modified silica nanoparticles with amino-silane coupling agent (D-SiO 2) were added to the polyurethane matrix that contains boron-nitrogen coordination. The presence of interfacial coordination significantly improves the dispersion of D-SiO 2 and enhances the interface interaction of polyurethane composites (SPU/D-SiO 2), which is evidenced by scanning electron microscopy, transmission electron microscopy and rheological investigation. Through mechanical experiment analysis, these modified polyurethane composites exhibit high tensile strength and toughness. The tensile strength of SPU/10D-SiO 2 increases to 19.5 ± 0.2 MPa and its tensile toughness achieves 216.9 MJ/m3, which is 35% of increase as compared with the pristine SPU that had a record-high toughness. In addition, the coordination bonds in the matrix and interface in the composites provide versatile and efficient energy dissipation during the tensile process. This work offers a facile method to improve the mechanical robustness of the newly developed supramolecular polyurethane elastomers. [Display omitted] • The interfacial coordination significantly improves the dispersion of D-SiO 2 and enhances the interfacial interaction. • The tensile toughness of SPU/10D-SiO 2 achieves 216.9 MJ/m3, which is 35% of increase as compared with the pristine SPU. • The extraordinary strength, toughness and energy dissipation are enabled by multiple dynamic moieties. [ABSTRACT FROM AUTHOR]

Reversible addition-fragmentation chain transfer (RAFT) processes in polymer systems have shown great utility in controlling radical polymerizations. Due to the reversible chain transfer mechanism, RAFT agents have been extensively used to synthesize monodisperse linear polymers and block copolymers in solution or emulsion polymerization. On the other hand, little is known about the effects of RAFT agents on the polymerization kinetics and thermo-mechanical properties of cross-linked materials. This work investigates the effect of RAFT agents on photopolymerization behavior and ultimate polymer properties in urethane acrylate systems. Our results indicate that RAFT agent addition has a significantly different impact on network development depending on inherent system characteristics, i.e., systems with glass transition temperature (T g) below room temperature (LT) or those with T g above room temperature (HT). When polymerizing with RAFT agents, photopolymerization rate decreases and can be tuned using different concentrations of RAFT agent. The final materials also show increased elongation at break with decreased Young's modulus. However, ultimate thermo-mechanical behavior and mechanical properties are different based on T g. With RAFT addition decreased T g is observed from HT polyurethane networks. Tensile toughness is also doubled in comparison to neat HT films. On the other hand, although the T g of RAFT modified LT polyurethane networks does not change significantly, toughness of the final polymer films varies significantly with RAFT agent concentration. Enhanced toughness is only observed from films with low RAFT agent concentration while toughness decreases with higher loading of RAFT agent. These results demonstrate that the polymer network and thermo-mechanical properties can be modified by introducing RAFT agent which enables dynamic polymer chain rearrangements in both LT- and HT-acrylate network systems. [Display omitted] • Photopolymerization rates are much higher in RAFT controlled high T g systems. • Addition of RAFT agents decreases cross-link density and T g. • RAFT modification enables significantly increased elongation. • RAFT modified high T g systems maintain tensile modulus and enhance toughness. [ABSTRACT FROM AUTHOR]

Here, we described a simple approach for the development of advanced composites based on Nylon 12 by selectively modified multiwalled carbon nanotubes (MWCNTs). Prior mixing, MWCNTs were modified by a new combination of plasma treatment i.e. oxygen + nitrogen (PL-MWCNTs) in order to improve its dispersion in the nylon matrix and enhance the interfacial adhesion by increasing the compatibility. With incorporation of only 1.2 wt % PL-MWCNTs, the tensile strength, Young's modulus, elongation at break and storage modulus of Nylon 12 were dramatically improved by ∼66%, 64%, 69% and 39%, respectively. These results were found to be higher than individual plasma treated CNTs. Such large increments were due to the effects of excellent homogeneous dispersion of PL-MWCNTs in the Nylon matrix and strong interfacial adhesion within themselves, which is believed to be effects of both oxygenated and nitrogenated functional groups generated on the surface of CNTs during plasma treatment. [ABSTRACT FROM AUTHOR]

In the work, ethylene–octene copolymer (POE) toughened isotatic polypropylene (PP) blends with different phase morphologies and crystalline structures were successfully fabricated and their influence on the toughness of PP blends was discussed. POE domains not only played the role of stress concentration to induce stress field around them, but also acted as stress deliverer to transmit stress to the deep into the PP matrix. Elongated domains transmitted stress better, but spherical ones induced a larger stress field. As for the crystalline structure of PP matrix, compared with the “bundle-like” β-crystals, well-developed β-spherulites could induce a larger stress field. The toughness of the blends with different combinations of phase morphology and crystalline structure was also discussed. Only the blend with elongated POE domains and well-developed β-spherulites could achieve super-high toughness. To achieve this goal requires simultaneous optimization of nucleating agent content, POE content and composition, and processing conditions. This work provides a good example to better understand the influence of phase morphology of rubbers and crystalline structure of matrix in rubber-toughed polymer system. [ABSTRACT FROM AUTHOR]

Abstract: The remarkably high toughness of double network (DN) hydrogels is related to the energy dissipation that occurs due to the scission of network strands in the most tightly crosslinked of its two interpenetrating networks. The loading curve during tensile testing of DN hydrogels usually takes a complex shape and sometimes shows yielding. Wang and Hong recently proposed a model [1] based on the successive scission of the shortest remaining elastically active strands during tensile loading that predicts the shape of the loading curve of one DN hydrogel reasonably well. In the present study, the model was modified slightly and applied to five different DN gels prepared with different crosslink densities in the first (tight) network. The model fit parameters provide a description of the network strand length distribution in the tight network and show that the network strand concentration increases and the network strand length decreases when a higher crosslinker concentration was used to prepare the tight network. Such network strand distributions estimated from analysis of the tensile loading and unloading curves may be one of the first successful attempts to estimate the molecular weight distribution of a crosslinked polymer. [Copyright &y& Elsevier]