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     

丝素蛋白与聚氨酯共混膜的制备及结构和性能

采用溶液共混法制备了一系列不同组成的聚氨酯/丝素共混膜.利用红外光谱和广角X-射线衍射表征聚氨酯/丝素共混膜的结构;扫描电镜观察共混膜的断面;紫外-可见光谱测定共混膜的透光性;运用拉伸实验研究不同配比聚氨酯/丝素共混膜的力学性能.结果表明聚氨酯和丝素蛋白分子间存在较强的氢键相互作用.当丝素含量低于3 wt%时,试膜的断面较光滑,丝素蛋白分子进入聚氨酯网状结构中,破坏了聚氨酯分子内硬段和软段间的氢键作用.随着丝素含量进一步增大,丝素小颗粒均匀分散在聚氨酯基体中,二者之间具有较好的相容性.本实验所采用的制膜条件有利于促进丝素蛋白大分子的结晶.丝素蛋白对聚氨酯具有良好的增强效果,当丝素含量从0到5.6 wt%变化时,共混试片的断裂强度由0.56 MPa增大到4.60 MPa,杨氏模量由0.14 MPa增大到1.71 MPa,断裂伸长率从1065%下降到988%.丝素蛋白增强聚氨酯共混膜的强度显著增加,但弹性基本保持不变.     

Preparation and Characterization of Nanocomposite Films from Chitin Whisker and Waterborne Poly(ester-urethane) With or Without Ultra-Sonification Treatment

Two series of nanocomposite films were prepared from waterborne poly(ester-urethane) and chitin whisker with and without ultrasound treatment coded as CW/WPU and CHW/WPU, respectively. The effects of ultra-sonification method and chitin whisker content on the chemical compositions, crystallization behavior and miscibility were studied by attenuated total reflection Fourier transform infrared (ATR-FTIR), wide-angle X-ray diffraction (WXRD), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). Thermal stability and mechanical properties of the films were measured by thermogravimetric analysis (TGA) and tensile test, respectively. The results revealed that both nanocomposite films exhibited a certain degree of miscibility when chitin whisker content was lower than 30 wt%, resulting in higher thermal stability and tensile strength than the pure waterborne poly(ester-urethane) film. Interestingly, the composite films CW/WPU with ultrasound treatment possessed better miscibility, storage modulus, thermal stability and tensile strength than those without ultrasound treatment over the entire composition range studied here. The difference can be attributed to the relatively higher dispersion level of whisker within poly(ester-urethane) matrix resulting in relatively stronger entanglement and interaction between both components. The ultrasound treatment can effectively improve the miscibility and mechanical properties of the casting nanocomposite films with nano-meter size chitin whisker added. This indicated that the structure, miscibility and mechanical properties of the nanocomposite films depended significantly on the preparation method.     

Structure–property relationships of blended polysaccharide and protein biomaterials in ionic liquid

Cellulose and silk blended biomaterial films were regenerated from ionic liquid solution and investigated to characterize and understand the effect of inter- and intra-molecular interactions upon the morphology and thermal properties. The blended films were dissolved in 1-allyl-3-methylimidazolium chloride ionic liquid, coagulated and regenerated with water. Various characterization techniques were implemented to characterize structural, morphological and thermal properties: FTIR, SEM, TGA, DSC and X-ray scattering. The results showed that the cellulose microcrystalline structure and β-sheets from the silk can be disrupted by inter- and intra-molecular hydrogen bonds forming intermediate semicrystalline or amorphous structures. The SEM showed morphological effects of such interactions that cause varying thermal degradation and glass transition temperature. The X-ray scattering confirms such findings at the molecular level, demonstrating that the cellulose microfibril diameter decreases as the silk content increases. It also shows that the β-sheets size increases as the cellulose content increases. These various techniques provide evidence that suggest the hydrogen bonds between the β-sheets and the glucose units in the cellulose chains control the thermal and structural properties of the blended films, changing the morphology and physicochemical properties.     

High strength,high stiffness and toughness,defect-tolerant waterborne polyurethane with healing and antibacterial abilities

The nature creates many biomaterials such as spider silk which exhibits a combination of stiffness, strength and toughness. However, most of synthetic unfilled materials suffer from a trade-off between toughness and stiffness. Inspired by the structure of spider silk but beyond it, we proposed a novel molecular design to achieve transparent unfilled waterborne polyurethane (WPU) with simultaneously enhanced stiffness (280.9 MPa), tensile strength (25.1 MPa) and toughness (140.0 MJ/m³) as well as good elasticity (710%). The designed WPU comprised homogeneous continuous phase (soft segments) and diverse H-bonds (hard segments) dispersed in it. The increase of rigid molecular chain content and H-bonds contributed to the high stiffness of WPU. Furthermore, the mismatch of stiffness between hard domains and soft segments might promote crack deflection and branching, which endowed the robust WPU with fracture energy of 81.16 kJ/m². The robust WPU film could be healed to recover most of its original mechanical properties (strength for 24.4 MPa and elongation for 610%) under heating. In addition, the WPU films demonstrated good antibacterial performance against Staphylococcus aureus and Escherichia coli after chlorination.     

基于CuAAC反应链间自交联有机-无机杂化水性聚氨酯的合成及性能

利用4,4’-二羟甲基-1,4-庚二炔功能单体作为扩链剂合成了一系列炔基接枝量不同的水性聚氨酯（WPU）,然后基于铜催化的叠氮-炔基环加成（CuAAC）反应,采用3-叠氮基丙基三乙氧基硅烷（APTES-N₃）改性炔基功能化WPU,制备了室温链间自交联有机-无机杂化WPU. 采用红外光谱（FTIR）和核磁氢谱（¹H NMR）表征了自交联有机-无机杂化WPU. 探讨了APTES-N₃接枝量对WPU膜性能和WPU乳液形态的影响. 结果表明,随着APTES-N₃含量增加,WPU膜的结晶性逐渐下降;耐水性、耐溶剂性和热稳定性逐渐增强;WPU乳液粒子黏连程度增加. 当APTES-N₃质量分数从0增大到12%时,WPU膜的拉伸强度从14.3 MPa增加到28.6 MPa.     

Silk Fibroin/Wool Keratin Composite Scaffold with Hierarchical Fibrous and Porous Structure

The present study describes a silk microfiber reinforced meniscus scaffold (SMRMS) with hierarchical fibrous and porous structure made from silk fibroin (SF) and wool keratin (WK) using electrospinning and freeze-drying technology. This study focuses on the morphology, secondary structure, mechanical properties, and water absorption properties of the scaffold. The cytotoxicity and biocompatibility of SMRMS are assessed in vivo and in vitro. The scaffold shows hierarchical fibrous and porous structure, hierarchical pore size distribution (ranges from 50 to 650 µm), robust mechanical properties (compression strength can reach at 2.8 MPa), and stable biodegradability. A positive growth condition revealed by in vitro cytotoxicity testing indicates that the scaffold is not hazardous to cells. In vivo assessments of biocompatibility reveal that only a mild inflammatory reaction is present in implanted rat tissue. Meniscal scaffold made of SF/WK composite shows a potential application prospect in the meniscal repair engineering field with its development.     

Structure and properties of the nanocomposite films of chitosan reinforced with cellulose whiskers

Bio‐based nanocomposite films were successfully developed using cellulose whiskers as the reinforcing phase and chitosan as the matrix. Cellulose whiskers, with the lengths of 400 ± 92 nm and diameters of 24 ± 7.5 nm on average, were prepared by hydrolyzing cotton linter with sulfuric acid solution. The effects of whisker content on the structure, morphology and properties of the nanocomposite films were characterized by SEM, XRD, FTIR, UV‐vis spectroscopy, DMA, TG, tensile testing, and swelling experiment. The results indicated that the nanocomposites exhibited good miscibility, and strong interactions occurred between the whiskers and the matrix. With increasing whisker content from 0 to 15–20 wt %, the tensile strength of the composite films in dry and wet states increased from 85 to 120 MPa and 9.9 to 17.3 MPa, respectively. Furthermore, the nanocomposite films displayed excellent thermal stability and water resistance with the incorporation of cellulose whiskers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1069–1077, 2009     

Irradiation of Crosslinked, Poly(Vinyl Alcohol) Blended Hydrogel for Wound Dressing

In order to obtain a more ideal hydrogel wound dressing, crosslinked hydrogel films blended with polyvinyl alcohol (PVA), polyvinyl pyrrolidone, kappa-carrageenan (KC), and powder silk were prepared by electron beam, and their physiochemical properties were investigated as a combination of function factors. The experimental results showed that the gel fraction of the hydrogel films depended mainly on irradiation dose and the monomer concentration of the polymers, the properties of hydrogel could be greatly extended or improved by blending homopolymers. The rate of gel formation of the hydrogel was raised, and the water evaporation from hydrogel could be retarded after mixing with KC, while the tensile strength of hydrogel films were obviously increased after mixing with silk. Toxicity and healing effect of PVA/PVP/KC/silk blended hydrogel films as wound dressings were evaluated. The irradiated blended hydrogel showed satisfactory properties for wound dressing, the hydrogel did not induceany acute general toxic effects, and it is effective for fast healing of wound.     

Hydrogen‐bonding,crystallinity, and morphological properties of poly(silicic acid)/waterborne polyurethane nanocomposites

Unique nanocomposites consisting of poly(silicic acid) nanoparticles (PNs) and waterborne polyurethane (WPU) were prepared. The aliphatic WPU prepared in this study was end‐capped with a silanol group, which could react with PNs via a sol–gel process. PNs were modified with phenyltrimethoxysilane (PTMS) and 3‐(trimethoxysilyl)propyl ester (TMPE) and then blended with WPU. The structure–property relationships were examined. Solid‐state ²⁹Si NMR spectra of WPU showed that structures T₁, T₂, and T₃ of WPU decreased and structures Q₃ and Q₄ of PN/WPU nanocomposites increased gradually. When the PN concentration increased to 10 wt %, PN/WPU nanocomposites exhibited the maximum fraction of hydrogen‐bonded carbonyl groups. In the PTMS–PN and TMPE–PN systems, the fraction of hydrogen‐bonded carbonyl groups fluctuated stably when the concentrations of PTMS–PN and TMPS–PN exceeded 5 wt %. The X‐ray diffraction results revealed that α‐form, γ‐form, or triclinic crystallization could be found in the WPU matrix. A differential scanning calorimetry spectrum showed that the crystalline structure of the hard segment of WPU was influenced by the nanoparticle concentration. The degrees of crystallinity were 88% for the PN/WPU nanocomposites, 41% for the PTMS–PN/WPU nanocomposites, and 54% for the TMPE–PN/WPU nanocomposites when the PN, PTMS–PN, and TMPE–PN concentrations were 5 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1076–1089, 2005     

Silk Sericin Retards the Crystallization of Silk Fibroin

Summary: The thermal and structural analysis of silk fibroin (SF) and silk sericin (SS) blend films reveals that the crystallization of SF is retarded in the presence of SS. Although a phase separation was observed, there might be a strong interaction at the boundary of the SF and SS through intermolecular hydrogen bonding, which restricts the conformational transition of SF.

TEM image of the cross‐section of the SF/SS blend (75:25) film (magnification: ×15 000).     

Porous composite scaffolds of hydroxyapatite/silk fibroin via two‐step method

A two‐step method was used to fabricate the hydroxyapatite (HAP)/silk fibroin (SF) scaffolds, i.e. the nano‐sized HAP/SF composite powders were prepared by co‐precipitation, which were then blended with SF solution to fabricate the HAP/SF composite scaffolds. The obtained scaffolds showed a 3D porous structure. The porosity was higher than 90% with the average macropore size of 214.2 µm. Moreover, the nano‐sized HAP/SF composite powders were uniformly dispersed in the silk fibroin matrix, which provided the scaffolds enhanced compressive properties. The cell culture assay showed that the scaffolds fabricated by the two‐step method could improve the cell proliferation and osteogenic differentiation when compared with those prepared by the conventional one‐step blending method. The results suggested that the two‐step method could promote the uniform dispersion of HAP in the SF matrix and efficient combination between the HAP and the matrix, which may provide a potential application in the composite scaffold preparation for tissue engineering. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and thermal properties of antimony doped tin oxide/waterborne polyurethane nanocomposite films as heat insulating materials

The waterborne polyurethane (WPU) was synthesized from the polycondensation between isophorone diisocyanate (IPDI) and polyoxypropylene glycol (N‐210) and then dispersed into water. Subsequently, the WPU emulsion was modified with antimony doped tin oxide (ATO) nanoparticle by ultrasonic dispersion. The ATO/WPU emulsion was cast onto Teflon molds. After being dried, ATO/WPU films were prepared. TEM indicated that the ATO nanoparticles were homogeneously dispersed in the polymer matrix at the nanometer scale. DSC showed that the ATO/WPU nanocomposites displayed increased glass transition temperatures compared to the control WPU. The mechanical properties of the films were characterized by dynamic‐mechanical analysis (DMA). The higher glass transition temperature and storage modulus indicates the superior mechanical properties of WPU modified by ATO nanoparticles over the conventional unmodified WPU. The thermal behaviors of the films were evaluated by thermogravimetric analysis (TGA). It could be found that the incorporation of ATO into WPU can improve the thermal stability dramatically. The results from UV–visible–near infrared spectra indicated that the ATO/WPU films could decrease the infrared transmission effectively. The heat‐insulation measurements showed that glass coated with ATO/WPU films possessed better heat‐insulating effect than empty glass. Copyright © 2010 John Wiley & Sons, Ltd.     

Tri-component bio-composite materials prepared using an eco-friendly processing route

We report on the blending of three natural polymers, raw cotton, silk and wool, using ionic liquids as the dissolving media. We find that with increased content of wool and silk the thermal degradation temperature of the new bio films increases. This is due to an increase in the hydrogen bond network between the blended polymers. We also investigated the role of the coagulating solvent by coagulating the bio films using water, methanol or isopropanol. Again, we find the coagulating solvent impacts the final properties of the bio films with water shown to coagulated films with the best material properties.     

纤维素/甲壳素共混膜的结构表征与抗凝血性能

以 6wt %NaOH 4wt%尿素为纤维素的新溶剂 ,采用溶液共混法制备出纤维素 甲壳素共混膜 ,为甲壳素在碱性溶液中制膜提供了新的方法 .红外光谱、X 射线衍射、扫描电镜和力学性能、抗凝血性能测试结果表明 ,共混膜中甲壳素含量低于 4 0wt%时 ,纤维素与甲壳素分子间具有良好的相容性 ;在纤维素中引入适量甲壳素可提高共混膜的抗张强度 ,共混膜的干、湿态抗张强度在甲壳素含量 10wt%时最大 ,其值分别为 89 1MPa和 4 3 7MPa ,比纯态纤维素膜的干、湿态抗张强度分别提高了 6 7%和 11 5 % ;甲壳素的引入可明显降低血小板在共混膜表面的粘附、凝聚与变性 ,增大共混膜的抗凝血参数 ,甲壳素含量达到 5 0wt%时 ,该共混膜具有良好的抗凝血性能     

Preparation of Antibacterial Waterborne Polyurethane/silver Nanocomposite

Stable aqueous dispersions of silver (Ag) nanoparticles were prepared by reducing silver nitrate solutions with sodium borohydride (NaBH₄) in the presence of waterborne polyurethane as a stabilizing agent. WPU/Ag nanocomposites were obtained after evaporating water. Transmission electron microscope (TEM) shows nanoscale Ag particles are well dispersed in WPU matrix at a lower concentration, while particles exhibit a little aggregation at a higher concentration. UV‐visible spectra, X‐ray powder diffraction, and energy dispersive X‐ray spectrometer (EDS) confirm the existence of Ag particle in WPU matrix. The WPU/Ag composite films show good antibiotic ability.     

Fractionation of Regenerated Silk Fibroin and Characterization of the Fractions

The molecular weight (MW) of regenerated silk fibroin (RSF) decreases during degumming and dissolving processes. Although MW and the MW distribution generally affect polymer material processability and properties, few reports have described studies examining the influences of MW and the distribution on silk fibroin (SF) material. To prepare different MW SF fractions, the appropriate conditions for fractionation of RSF by ammonium sulfate (AS) precipitation process were investigated. The MW and the distribution of each fraction were found using gel permeation chromatography (GPC) and SDS-polyacrylamide electrophoresis (SDS-PAGE). After films of the fractionated SFs formed, the secondary structure, surface properties, and cell proliferation of films were evaluated. Nanofiber nonwoven mats and 3D porous sponges were fabricated using the fractionated SF aqueous solution. Then, their structures and mechanical properties were analyzed. The results showed AS precipitation using a dialysis membrane at low temperature to be a suitable fractionation method for RSF. Moreover, MW affects the nanofiber and sponge morphology and mechanical properties, although no influence of MW was observed on the secondary structure or crystallinity of the fabricated materials.     

Bacterial cellulose films with controlled microstructure–mechanical property relationships

Bacterial cellulose (BC) films with different porosities have been developed in order to obtain improved mechanical properties. After 13 days of incubation of Gluconobacter xylinum bacteria in static culture, BC pellicles have been set. BC films have been compression molded after water dispersion of BC pellicles and filtration by applying different pressures (10, 50, and 100 MPa) to obtain films with different porosities. Tensile behavior has been analyzed in order to discuss the microstructure–property relationships. Compression pressure has been found as an important parameter to control the final mechanical properties of BC films where slightly enhanced tensile strength and deformation at break are obtained increasing mold compression pressure, while modulus also increases following a nearly linear dependence upon film porosity. This behavior is related to the higher densification by increasing mold compression pressure that reduces the interfibrillar space, thus increasing the possibility of interfibrillar bonding zones. Network theories have been applied to relate film elastic properties with individual nanofiber properties.     

Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate

Blend films of poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. This blend films were characterized by tensile strength test, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The miscibility in the blends of PVA and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition‐dependent glass transition temperatures (T_gs), indicating that the blends are miscible. FT‐IR studies indicate that there is the intermolecular hydrogen bonding interactions, i.e. –OH…^?OOC– in PVA/NaAlg blends. The blend films also exhibited the higher thermal stability and their mechanical properties improved compared to those of homopolymers.     

Development of the morphology and crystalline state due to hybridization of reinforced toughened nylon containing a liquid‐crystalline polymer

A hybrid composite consisting of rubber‐toughened nylon‐6,6, short glass fibers, and a thermotropic liquid‐crystalline polymers (LCP) was investigated by the LCP content being varied. The thermal behavior, morphology, and crystallization behavior due to hybridization were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and wide‐angle X‐ray scattering (WAXS). DSC results indicated that the crystallinity of the glass‐fiber‐reinforced toughened nylon‐6,6 was reduced by LCP addition, particularly 5–10 wt % LCP. DMA data showed that the miscibility between the blended components was maximum at the 5 wt % LCP composition, and the miscibility decreased with increasing LCP content. SEM photomicrographs revealed information consistent with the thermal behavior on miscibility. It was also observed that the 10 wt % LCP composition showed predominantly an amorphous character with FTIR and WAXS. WAXS results indicated that LCP hybridization increased the interplanar spacing of the hydrogen‐bonded sheets of the nylon crystals rather than the spacing between the hydrogen‐bonded chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 549–559, 2003