Structure and properties of composites compression‐molded from silk fibroin powder and waterborne polyurethane

The degummed silk filament was pulverized with a home‐made machine to obtain the silk fibroin (SF) powder with the diameter of around 3 µm. The resulting SF powder was blended with waterborne polyurethane (WPU) aqueous dispersion, and then was dried and compression‐molded to prepare novel blended materials with improved miscibility and mechanical properties. WPU acted as a plasticizer and one of the components for the blends during the compression‐molded process. The structure, morphology, and properties of the blended films were investigated. The results indicated that β‐sheet of SF existed in the blended films. The SEM images showed that the cross‐section of the blended films exhibited an overall homogeneous morphology. Furthermore, the transmission electron microscope observation exhibited that some sphere‐like SF particles were well dispersed in the WPU matrix. The hydrogen bond interaction between SF and WPU in the blended films led to an increase of the glass transition temperature for the soft segment of WPU in the blended films. The blended films showed an improved Young's modulus and tensile strength from 1.2 to 288.9 MPa and 0.3 to 16.5 MPa, respectively, with the increasing of SF up to a content of 70 wt%. The hydrogen‐bonding interactions existing in SF and WPU and compression molding method played the important role in improving the miscibility and mechanical properties of the blended films. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic linear dichroism FT-IR studies of synthetic spider silk

This work deals with the analysis of the orientation behavior of different segments of synthetic spider silk samples containing hard and soft segments. Two different types of spider silk were examined, one with an aliphatic hard segment (hexamethylene-diisocyanate) and an amorphous soft segment (polytetramethylene oxide) (A40) and the other with an aromatic hard segment (4,4′-methylene bisphenyl diisocyanate) and a semicrystalline soft segment (polyethylene oxide-polypropylene oxide- polyethylene oxide) (A143). In order to observe the orientation behavior of the hard and the soft segments it was necessary to define marker bands. While for both samples the chosen marker bands for the hard segments were the same, the marker bands for the soft segments were different. FT-IR spectra were recorded while strain was applied to the material at the same time. Two parameters, the dichroic ratio R and the order Parameter f were used to evaluate the behavior of these materials under conditions of strain. It was found that sample A143 broke at a strain level of 37,5 %, while sample A40 showed a high dynamic range up to a strain level of 307 %.     

Biobased PLA/NR-PMMA TPV with balanced stiffness-toughness: In-situ interfacial compatibilization,performance and toughening model

Using rubber to toughen polylactide (PLA) is always accompanied by the sharp reduction in stiffness. Herein, PLA/poly (methyl methacrylate) grafted natural rubber (NR-PMMA) thermoplastic vulcanizates (TPVs) with balanced stiffness-toughness were fabricated. With the addition of 40 wt % NR-PMMA, the impact strength and tensile toughness of PLA/NR-PMMA TPV significantly improved to about 102.7 kJ/m² and 66.1 MJ/m³, respectively, compared with those of 2.7 kJ/m² and 2.4 MJ/m³ for the pure PLA. Meanwhile, the yielding stress was maintained at 34.5 MPa. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of in-situ interfacial compatibilization between PLA and rubber phases. Both tensile and impact toughening mechanism were studied and deduced as considerable energy dissipation provided by the continuous rubber phase. Instrumented notched impact tests demonstrated that the energy dissipating in crack propagation process contributed to the main part of impact toughness. In addition, a novel toughening model based on bicontinuous structure was incorporated, which showed good applicability in predicting the impact strength of PLA/NR-PMMA TPVs.     

Development of Tough Thermoplastic Elastomers by Leveraging Rigid–Flexible Supramolecular Segment Interplays

Supramolecular interactions facilitate the development of tough multifunctional thermoplastic elastomers. However, the fundamental principles that govern supramolecular toughening are barely understood, and the rational design to achieve the desired high toughness remains daunting. Herein, we report a simple and robust method for toughening thermoplastic elastomers by rationally tailoring hard–soft phase separation structures containing rigid and flexible supramolecular segments. The introduced functional segments with distinct structural rigidities provide mismatched supramolecular interactions to efficiently tune the energy dissipation and bear an external load. The optimal supramolecular elastomer containing aromatic amide and acylsemicarbazide moieties demonstrates a record toughness (1.2 GJ m⁻³), extraordinary crack tolerance (fracture energy 282.5 kJ m⁻²), an ultrahigh true stress at break (2.3 GPa), good elasticity, healing ability, recyclability, and impact resistance. The toughening mechanism is validated by testing various elastomers, confirming the potential for designing and developing super-tough supramolecular materials with promising applications in aerospace and electronics.     

Waterborne polyurethane-coated polyamide/fullerene composite films: Mechanical,thermal, and flammability properties

Novel waterborne polyurethane (WPU) was prepared and coated on nylon 12 (Ny12) and fullerene-C60 (Full-C60, 1–10 wt%) composite films using simple dip coating technique. In Ny12/Full-C60 composite, fullerene nanoparticles were dispersed in a wavy layered pattern, whereas coated WPU/Ny12/Full-C60 films depicted uniform pattern of non-overlapping scales. WPU/Ny12/Full-C60 1–10 showed higher values of tensile strength and modulus, 91.4–98.1 MPa and 52.2–57.9 GPa, respectively. In WPU/Ny12/Full-C60 1–10, maximum degradation temperature was increased to 598°C and char yield to 35%. Increasing fullerene content from 1 to 10 wt% decreased maximum peak heat release rate from 209 to 132 kW m^?2, i.e., 53% reduction in flammability compared to WPU.     

Bioinspired and Mechanically Strong Fibers Based on Engineered Non-Spider Chimeric Proteins

Silk-protein-based fibers have attracted considerable interest due to their low weight and extraordinary mechanical properties. Most studies on fibrous proteins focus on the recombinant spidroins, but these fibers exhibit moderate mechanical performance. Thus, the development of alternative structural proteins for the construction of robust fibers is an attractive goal. Herein, we report a class of biological fibers produced using a designed chimeric protein, which consists of the sequences of a cationic elastin-like polypeptide and a squid ring teeth protein. Remarkably, the chimeric protein fibers exhibit a breaking strength up to about 630 MPa and a corresponding toughness as high as about 130 MJ m⁻³, making them superior to many recombinant spider silks and even comparable to some native counterparts. Therefore, this strategy is a novel concept for exploring bioinspired ultrastrong protein materials through the development of new types of structural chimeric proteins.     

Tough and self‐recoverable hydrogels crosslinked by triblock copolymer micelles and Fe3+ coordination

Tough hydrogels have great potentials in soft robotics, artificial muscles, tissue replacement, and so on. Here we introduce novel tough hydrogels crosslinked by triblock copolymer (F127DA) micelles and metal coordination. The gels showed outstanding tensile strength (∼1–11 MPa), toughness (∼4–32 MJ m⁻³), and excellent self‐recovery properties (∼56.8–87.2% toughness recovery in 9 min at room temperature). The mechanical and self‐recovery properties could be manipulated by varying contents of micelles and/or COO⁻ groups. Dynamic mechanical analysis of the hydrogels revealed apparent activation energy and relaxations for both physical interactions. In situ small‐angle X‐ray scattering measurements on hydrogels upon stretching revealed micelle deformations. XPS measurements on hydrogels before and after stretching revealed significant changes in the binding energy of Fe³⁺ ions in the gels, suggesting the rupture of coordination bonds. The experimental results strongly suggest a synergistic effect from the micelle‐crosslinking and Fe³⁺–COO⁻ coordination on the strength, toughness, and self‐recovery of the hydrogels. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 865–876     

Mechanically Strong Globular‐Protein‐Based Fibers Obtained Using a Microfluidic Spinning Technique

Proteins used for the formation of light weight and mechanically strong biological fibers are typically composed of folded rigid and unfolded flexible units. In contrast to fibrous proteins, globular proteins are generally not regarded as a good candidate for fiber production due to their intrinsic structural defects. Thus, it is challenging to develop an efficient strategy for the construction of mechanically strong fibers using spherical proteins. Herein, we demonstrate the production of robust protein fibers from bovine serum albumin (BSA) using a microfluidic technique. Remarkably, the toughness of the fibers was up to 143 MJ m^?3, and after post‐stretching treatment, their breaking strength increased to almost 300 MPa due to the induced long‐range ordered structure in the fibers. The performance is comparable to or even higher than that of many recombinant spider silks or regenerated silkworm fibers. Thus, this work opens a new way for making biological fibers with high performance.     

Mechanically Strong Globular-Protein-Based Fibers Obtained Using a Microfluidic Spinning Technique

Proteins used for the formation of light weight and mechanically strong biological fibers are typically composed of folded rigid and unfolded flexible units. In contrast to fibrous proteins, globular proteins are generally not regarded as a good candidate for fiber production due to their intrinsic structural defects. Thus, it is challenging to develop an efficient strategy for the construction of mechanically strong fibers using spherical proteins. Herein, we demonstrate the production of robust protein fibers from bovine serum albumin (BSA) using a microfluidic technique. Remarkably, the toughness of the fibers was up to 143 MJ m⁻³, and after post-stretching treatment, their breaking strength increased to almost 300 MPa due to the induced long-range ordered structure in the fibers. The performance is comparable to or even higher than that of many recombinant spider silks or regenerated silkworm fibers. Thus, this work opens a new way for making biological fibers with high performance.     

Water-Resistant and Stretchable Conductive Ionic Hydrogel Fibers Reinforced by Carboxymethyl Cellulose

Conductive ionic hydrogels (CIH) have been widely studied for the development of stretchable electronic devices, such as sensors, electrodes, and actuators. Most of these CIH are made into 3D or 2D shape, while 1D CIH (hydrogel fibers) is often difficult to make because of the low mechanical robustness of common CIH. Herein, we use gel spinning method to prepare a robust CIH fiber with high strength, large stretchability, and good conductivity. The robust CIH fiber is drawn from the composite gel of sodium polyacrylate (PAAS) and sodium carboxymethyl cellulose (CMC). In the composite CIH fiber, the soft PAAS presents good conductivity and stretchability, while the rigid CMC significantly enhances the strength and toughness of the PAAS/CMC fiber. To protect the conductive PAAS/CMC fiber from damage by water, a thin layer of hydrophobic polymethyl acrylate (PMA) or polybutyl acrylate (PBA) is coated on the PAAS/CMC fiber as a water-resistant and insulating cover. The obtained PAAS/CMC-PMA and PAAS/CMC-PBA CIH fibers present high tensile strength (up to 28 MPa), high tensile toughness (up to 43 MJ/m³), and good electrical conductivity (up to 0.35 S/m), which are useful for textile-based stretchable electronic devices.     

Hydrogen‐Bonding Toughened Hydrogels and Emerging CO2‐Responsive Shape Memory Effect

A double hydrogen bonding (DHB) hydrogel is constructed by copolymerization of 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine (hydrophobic hydrogen bonding monomer) and N,N‐dimethylacrylamide (hydrophilic hydrogen bonding monomer) with polyethylene glycol diacrylates. The DHB hydrogels demonstrate tunable robust mechanical properties by varying the ratio of hydrogen bonding monomer or crosslinker. Importantly, because of synergistic energy dissipating mechanism of strong diaminotriazine (DAT) hydrogen bonding and weak amide hydrogen bonding, the DHB hydrogels exhibit high toughness (up to 2.32 kJ m⁻²), meanwhile maintaining 0.7 MPa tensile strength, 130% elongation at break, and 8.3 MPa compressive strength. Moreover, rehydration can help to recover the mechanical properties of the cyclic loaded–unloaded gels. Attractively, the DHB hydrogels are responsive to CO₂ in water, and demonstrate unprecedented CO₂‐triggered shape memory behavior owing to the reversible destruction and reconstruction of DAT hydrogen bonding upon passing and degassing CO₂ without introducing external acid. The CO₂ triggering mechanism may point out a new approach to fabricate shape memory hydrogels.     

Bioinspired and Mechanically Strong Fibers Based on Engineered Non‐Spider Chimeric Proteins

Silk‐protein‐based fibers have attracted considerable interest due to their low weight and extraordinary mechanical properties. Most studies on fibrous proteins focus on the recombinant spidroins, but these fibers exhibit moderate mechanical performance. Thus, the development of alternative structural proteins for the construction of robust fibers is an attractive goal. Herein, we report a class of biological fibers produced using a designed chimeric protein, which consists of the sequences of a cationic elastin‐like polypeptide and a squid ring teeth protein. Remarkably, the chimeric protein fibers exhibit a breaking strength up to about 630 MPa and a corresponding toughness as high as about 130 MJ m^?3, making them superior to many recombinant spider silks and even comparable to some native counterparts. Therefore, this strategy is a novel concept for exploring bioinspired ultrastrong protein materials through the development of new types of structural chimeric proteins.     

Block copolyesters of poly(pentamethylene p,p′‐bibenzoate) and poly(tetramethylene adipate)

Hydroxy‐terminated poly(pentamethylene p,p′‐bibenzoate) oligomers with different molecular weights were prepared. The poly(pentamethylene p,p′‐bibenzoate) oligomers showed rather high crystallinity, and some of them exhibited a monotropic smectic phase. Block copolyesters with hard segments of poly(pentamethylene p,p′‐bibenzoate) and soft segments of poly(tetramethylene adipate) were prepared by coupling the poly(pentamethylene p,p′‐bibenzoate) oligomer and a poly(tetramethylene adipate)glycol with methylene‐4,4′‐diphenylene diisocyanate in solution. The block copolyesters were characterized by IR, ¹H NMR, differential scanning calorimetry, a polarized microscope, and X‐ray diffraction. The thermal transitions of the block copolyesters were dependent on the composition and the molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used. The hard segments in the block copolyesters showed no liquid crystallinity and exhibited rather low crystallinity or were even amorphous. The molecular weight of the poly(pentamethylene p,p′‐bibenzoate) oligomer used influences the glass‐transition temperature and crystalline properties of the soft segments in the block copolyesters significantly. The effect on the glass‐transition temperature of the soft segments is described as the difference in miscibility between the hard and soft segments. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2626–2636, 2002     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Ion‐Specific Assembly of Strong,Tough, and Stiff Biofibers

Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle. Many biological materials realize this objective through multiscale (i.e., atomic‐ to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials. Inspired from the architecture of such biological structures, we here present flow‐assisted organization and assembly of renewable native cellulose nanofibrils (CNFs), which yields highly anisotropic biofibers characterized by a unique combination of high strength (1010 MPa), high toughness (62 MJ m^?3) and high stiffness (57 GPa). We observed that properties of the fibers are primarily governed by specific ion characteristics such as hydration enthalpy and polarizability. A fundamental facet of this study is thus to elucidate the role of specific anion binding following the Hofmeister series on the mechanical properties of wet fibrillar networks, and link this to the differences in properties of dry nanostructured fibers. This knowledge is useful for rational design of nanomaterials and is critical for validation of specific ion effect theories. The bioinspired assembly demonstrated here is relevant example for designing high‐performance materials with absolute structural control.     

Ion‐Specific Assembly of Strong,Tough, and Stiff Biofibers

Designing engineering materials with high stiffness and high toughness is challenging as stiff materials tend to be brittle. Many biological materials realize this objective through multiscale (i.e., atomic‐ to macroscale) mechanisms that are extremely difficult to replicate in synthetic materials. Inspired from the architecture of such biological structures, we here present flow‐assisted organization and assembly of renewable native cellulose nanofibrils (CNFs), which yields highly anisotropic biofibers characterized by a unique combination of high strength (1010 MPa), high toughness (62 MJ m^?3) and high stiffness (57 GPa). We observed that properties of the fibers are primarily governed by specific ion characteristics such as hydration enthalpy and polarizability. A fundamental facet of this study is thus to elucidate the role of specific anion binding following the Hofmeister series on the mechanical properties of wet fibrillar networks, and link this to the differences in properties of dry nanostructured fibers. This knowledge is useful for rational design of nanomaterials and is critical for validation of specific ion effect theories. The bioinspired assembly demonstrated here is relevant example for designing high‐performance materials with absolute structural control.     

Preparation and characterization of waterborne polyurethane/attapulgite nanocomposites

In this paper, waterbrone polyurethane (WPU)/attapulgite (AT) nanocomposites have been prepared by direct emulsion blending. The WPU was synthesized from poly(tetramethylene glycol), 4,4-diphenylmethane diisocyanate, dimethylol butanic acid, and neutralized by triethylamine. SEM examination of fractured surfaces showed that AT particles were irregularly dispersed in the WPU matrix. FTIR analysis suggested no major chemical structural changed in the presence of a small amount of AT. DMA results showed that the storage modulus of WPU/AT nanocomposites was increased and the glass transition temperatures of both soft and hard segments shifted to higher temperature compared to the pristine WPU. Thermal resistance of the samples measured by TGA was improved with the addition of AT. The mechanical properties of the nanocomposites, examined by tensile tests, showed higher tensile strength and elongation at break than that of the pristine WPU.     

Physical characteristics and properties of waterborne polyurethane materials reinforced with silk fibroin powder

Degummed silk filament was pulverized with a home‐made machine to obtain silk fibroin (SF) powder, and the structure, morphology, and particle size of the SF powder were investigated. The individual spherical particles and aggregates with different morphology of silk fibroin coexisted in water. A waterborne polyurethane (WPU) aqueous dispersion was blended with the SF powder to prepare novel blended materials with improved physical properties. The average particle size and zeta potential of the WPU/SF aqueous dispersions were characterized. The result showed that the WPU/SF dispersion with higher SF content exhibited a less negative zeta potential and a larger average particle size. Furthermore, the effect of SF content on the morphology, miscibility, and mechanical properties of the resulting blended films was studied by scanning electron microscopy, wide‐angle X‐ray diffraction, dynamic mechanical thermal analysis, and tensile testing. The films showed an improved Young's modulus and tensile strength from 0.3 to 33.8 MPa, and 0.6 to 5.2 MPa, respectively, with the increasing of SF up to a content of 26 wt %. The negative charges in the periphery and the small particle size made a good effort on dispersing SF powder into the WPU matrix as small aggregates, and the SF powder led to the efficient strengthening of WPU materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 940–950, 2010     

Multifunctional poly(2,5‐benzimidazole)/carbon nanotube composite films

The AB‐monomer, 3,4‐diaminobenzoic acid dihydrochloride, was recrystallized from an aqueous hydrochloric acid solution and used to synthesize high‐molecular‐weight poly(2,5‐benzimidazole) (ABPBI). ABPBI/carbon nanotube (CNT) composites were prepared via in situ polymerization of the AB‐monomer in the presence of single‐walled carbon nanotube (SWCNT) or multiwalled carbon nanotube (MWCNT) in a mildly acidic polyphosphoric acid. The ABPBI/SWCNT and ABPBI/MWCNT composites displayed good solubility in methanesulfonic acid and thus, uniform films could be cast. The morphology of these composite films was studied by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results showed that both types of CNTs were uniformly dispersed into the ABPBI matrix. Tensile properties of the composite films were significantly improved when compared with ABPBI, and their toughness (～200 MPa) was close to the nature's toughest spider silk (～215 MPa). The electrical conductivities of ABPBI/SWCNT and ABPBI/MWCNT composite films were 9.10 × 10^?5 and 2.53 × 10^?1 S/cm, respectively, whereas that of ABPBI film was 4.81 × 10^?6 S/cm. These values are ～19 and 52,700 times enhanced by the presence of SWCNT and MWCNT, respectively. Finally, without acid impregnation, the ABPBI film was nonconducting while the SWCNT‐ and MWCNT‐based composites were proton conducting with maximum conductivities of 0.018 and 0.017 S/cm, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1067–1078, 2010     

A Double Network Hydrogel with High Mechanical Strength and Shape Memory Properties

Double network (DN) hydrogels as one kind of tough gels have attracted extensive attention for their potential applications in biomedical and load-bearing fields. Herein, we import more functions like shape memory into the conventional tough DN hydrogel system. We synthesize the PEG-PDAC/P(AAm-co-AAc) DN hydrogels, of which the first network is a well-defined PEG (polyethylene glycol) network loaded with PDAC (poly(acryloyloxyethyltrimethyl ammonium chloride)) strands, while the second network is formed by copolymerizing AAm (acrylamide) with AAc (acrylic acid) and cross-linker MBAA (N, N'-methylenebisacrylamide). The PEG-PDAC/P(AAm-co-AAc) DN gels exhibits high mechanical strength. The fracture stress and toughness of the DN gels reach up to 0.9 MPa and 3.8 MJ/m³, respectively. Compared with the conventional double network hydrogels with neutral polymers as the soft and ductile second network, the PEG-PDAC/P(AAm-coAAc) DN hydrogels use P(AAm-co-AAc), a weak polyelectrolyte, as the second network. The AAc units serve as the coordination points with Fe³⁺ ions and physically crosslink the second network, which realizes the shape memory property activated by the reducing ability of ascorbic acid. Our results indicate that the high mechanical strength and shape memory properties, probably the two most important characters related to the potential application of the hydrogels, can be introduced simultaneously into the DN hydrogels if the functional monomer has been integrated into the network of DN hydrogels smartly.