Sea‐island polyurethane/polycarbonate composite nanofiber fabricated through electrospinning

Sea‐island polyurethane (PU)/polycarbonate (PC) composite nanofibers were obtained through electrospinning of partially miscible PU and PC in 3 : 7 (v/v) N,N‐dimethylformamide (DMF) and tetrahydrofuran (THF) mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were influenced by composition ratio in the binary mixtures. The pure PC nanofiber was brittle and easy to break. With increasing the PU content in the PU/PC composite nanofibers, PU component not only facilitated the electrospinning of PC but improved the mechanical properties of PU/PC nanofibrous mats. In a series of nanofibrous mats with varied PU/PC composition ratios, PU/PC 70/30 showed excellent tensile strength of 9.60 Mpa and Young's modulus of 55 Mpa. After selective removal of PC component in PU/PC composite nanofibers by washing with acetone, the residual PU maintained fiber morphology. However, the residual PU nanofiber became irregular and contained elongated indents and ridges along the fiber surface. PU/PC composite fibers showed sea‐island nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. At PC content below 30%, the PC domains were small and evenly dispersed in the composite nanofibers. As PC content was over 50%, the PC phases became large elongated aggregates dispersed in the composite nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cocontinuous cellulose acetate/polyurethane composite nanofiber fabricated through electrospinning

Cocontinuous cellulose acetate (CA)/polyurethane (PU) composite nanofibers were obtained through electrospinning of partially miscible CA and PU in 2:1 N,N‐dimethylacetamide (DMAc)/acetone mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were affected by component ratio in the binary mixtures. PU component not only facilitated the electrospinning of CA at CA concentration down to 12 wt%, but reinforced the tensile strength of CA/PU nanofibrous mats, while semirigid component CA in the composite nanofibers could greatly improve the rigidity and dimensional stability of CA/PU nanofibrous mats. In a series of nanofibrous mats with varied CA/PU composition ratios, CA/PU 20/80 showed excellent tensile strength and Young's modulus. The residual product after selective removal of any one of the components in CA/PU composite nanofibers by washing with proper solvent maintained the fiber structure but greatly reduced the fiber size, suggesting CA/PU composite fibers showed a cocontinuous nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Wet-spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

Polyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet-spinning route in this work. Based on nonsolvent-induced phase separation theory, N,N-dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46950.     

Fluorescent poly(p-phenylene vinylene)/poly(ethylene oxide) nanofibers obtained by electrospinning

Poly(p-phenylene vinylene) (PPV)/poly(ethylene oxide) (PEO) hybrid nanofibers were prepared by electrospinning a composite solution of PPV precursor/PEO in a mixture of ethanol and water, followed by thermal conversion. The precursor/PEO composite solutions were successfully electrospun into nanofibers with diverse helical, helical and linear, and helical bead-on-string morphologies by controlling the amount of aqueous PEO solution in a composite solution. Moreover, adding aqueous PEO solution to a precursor ethanol solution decreased the diameters of the fibers. The experimental data suggest that the viscosity, conductivity, and surface tension of the electrospinning solution are the main factors that influence the morphology of the fibers. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) investigations indicated that the PPV precursor reacts with PEO during thermal conversion. Ultraviolet–visible (UV-vis) and photoluminescence (PL) spectra of the PPV-PEO nanofibers exhibited appreciable blue shifts with the addition of PEO, which made it possible to fabricate nanofibers with fluorescence ranging from yellow-green to blue. These highly fluorescent PPV/PEO nanofibers with various morphologies are potentially interesting for many applications, such as micro- and nanooptoelectronic devices and systems.     

Green electrospun nanocuprous oxide–poly(ethylene oxide)–silk fibroin composite nanofibrous scaffolds for antibacterial dressings

Cuprous oxide (Cu₂O) nanoparticles have attracted extensive attention because of their excellent optical, catalytic, antibacterial, and antifungal properties and low cost. Nano-Cu₂O–poly(ethylene oxide) (PEO)–silk fibroin (SF) composite nanofibrous scaffolds (CNSs) were fabricated through green electrospinning to impart excellent antibacterial properties onto nanofibrous scaffolds. Scanning electron microscopy revealed that the nanofibers became more nonuniform and appeared more and more as beads in the nanofibers with increasing nano-Cu₂O concentration, and no obvious morphological changes were observed after 75% EtOH vapor treatment. Transmission electron microscopy and X-ray photoelectron spectroscopy demonstrated that nano-cuprous oxide (nano-Cu₂O) was successfully loaded into the PEO–SF nanofibers. Fourier transform infrared–attenuated total reflectance spectroscopy results indicate that nano-Cu₂O did not induce SF conformation from random coils to β sheets. The SF conformation converted from random coils to β sheets after 75% EtOH vapor treatment. The results of water contact angle testing and swelling property measurement clarified that nano-Cu₂O–PEO–SF CNSs possessed outstanding hydrophilicity. Nano-Cu₂O–PEO–SF CNSs exhibited better antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria than PEO–SF nanofibrous scaffolds, and the antibacterial activity increased with increasing nano-Cu₂O concentration. Cell viability studies with pig iliac endothelial cells demonstrated that nano-Cu₂O–PEO–SF CNSs had no cytotoxicity. Nano-Cu₂O–PEO–SF CNSs are expected to be ideal biomimetic antibacterial dressings for wound healing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47730.     

Aureole nanofibers by electrospinning of PAMAM‐PEO solution

Poly(amido amine) (PAMAM) dendrimer‐polyethylene oxide (PEO) nanofibers as dendrimeric‐polymeric composite nanofibers were prepared via electrospinning of PEO solution containing PAMAM dendrimer. The resultant fibers were characterized by means of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology and thermal properties of PEO nanofibers with and without PAMAM dendrimer were compared and the effect of PAMAM concentration on morphology and thermal properties of the resultant fibers was studied. The fibers had a size range of about 400–1300 nanometer in diameter with aureole morphology in most regions. The phase change temperature, phase transition heat, and the crystallinity of the produced composite fibers were determined by DSC analyses. TGA was also used to confirm the presence of PAMAM and to determine the amount of it within the fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospun polyurethane patch in combination with cedarwood and cobalt nitrate for cardiac applications

The growth in nanotechnology led to the fabrication of scaffold at a low cost with high productivity and high surface area. The present research aims to fabricate a novel cardiac scaffold utilizing polyurethane (PU) added with cedarwood (CW) and cobalt nitrate (CoNO₃) nanofibers. Morphological analysis showed that the mean fiber diameter of the PU nanofibers was reduced owing to the incorporation of CW and CoNO₃. Infrared and thermal analysis revealed the interaction of PU with CW and CoNO₃. Contact angle studies showed that the electrospun PU/CW displayed hydrophobic nature while PU/CW/CoNO₃ showed hydrophilic behavior compared to the pristine PU. The tensile strength of PU nanofibers increased with CW and CoNO₃ addition. Atomic force microscopy analysis depicted that the PU/CW was rougher while the PU/CW/CoNO₃ as smoother surfaces than the pristine PU. According to the coagulation assay data, the blood compatibility of the electrospun composites was enhanced compared to the pristine PU. In addition, PU and its composite nanofibers exhibited non-toxic to human dermal fibroblast cells and improved cell proliferation rates compared to the control plates. To conclude, the improved physicochemical and biological response of the electrospun composites would be putative for cardiac tissue engineering. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48226.     

Chain conformation,crystallization behavior,electrical and mechanical properties of electrospun polymer-carbon nanotube hybrid nanofibers with different orientations

An improved electrospinning technique was used to produce poly(ethylene oxide) (PEO) and PEO-multi-walled carbon nanotube (MWCNT) hybrid nanofibers. By this technique, both the orientation of MWCNTs in the electrospun PEO nanofibers and the orientation of electrospun PEO–MWCNT hybrid nanofibers can be controlled. The morphologies of the as-spun PEO–MWCNT hybrid nanofibers and the dispersion and orientation of MWCNTs in the fiber matrix were observed by scanning and transmission electron microscopy. The effect of electrospinning process and the incorporation of MWCNTs on the chain conformation and semicrystalline framework of PEO were examined by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and differential scanning calorimetry, and compared with pure PEO and PEO–MWCNT films prepared by casting. Finally, to investigate how the fiber assemblies affect the mechanical and electrical properties of the hybrid materials, tensile testing and impedance analysis were performed on randomly oriented, uniaxially and biaxially oriented PEO–MWCNT hybrid nanofiber mats. The results indicated that both the uniaxially and biaxially oriented assembled hybrid materials have better tensile strength, modulus, and electrical conductivity compared with random nanofibers.     

Preparation and characterization of electrospun polyurethane–polypyrrole nanofibers and films

Polyurethane (PU)–polypyrrole (PPy) composite films and nanofibers were successfully prepared for the purpose of combining the properties of PU and PPy. Pyrrole (Py) monomer was polymerized and dispersed uniformly throughout the PU matrix by means of oxidative polymerization with cerium(IV) [ceric ammonium nitrate Ce(IV)] in dimethylformamide. Films and nanofibers were prepared with this solution. The effects of the PPy content on the thermal, mechanical, dielectric, and morphological properties of the composites were investigated with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR)–attenuated total reflection (ATR) spectroscopy, dielectric spectrometry, and scanning electron microscopy. The Young's modulus and glass-transition temperatures of the composites exhibited an increasing trend with increases in the initially added amount of Py. The electrical conductivities of the composite films and nanofibers increased. The crystallinity of the composites were followed with DSC, the mechanical properties were followed with DMA, and the spectroscopic results were followed with FTIR–ATR spectroscopy. In the composite films, a new absorption band located at about 1650 cm⁻¹ appeared, and its intensity improved with the addition of Py. The studied composites show potential for promising applications in advanced electronic devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on the mechanical properties of hybrid reinforced rigid polyurethane composite foam

The mechanical properties of hybrid reinforced rigid polyurethane (PU) foams were investigated with the reinforcing agent SiO₂ and fibers. The effect of content of SiO₂ and fibers and the effect of length of fibers on the properties of the PU composite foam were emphatically analyzed. The experiment results show that the tensile strength of the PU composite foam is optimal when the content of SiO₂ and glass fiber is 20 and 7.8%, respectively. Furthermore, the reinforcing effect of glass fiber, Nylon‐66 fiber, and PAN‐matrix carbon fiber were compared and the results show that the tensile strength of the PU composite foam reinforced with 3–5% carbon fiber is optimal. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1493–1500, 2004     

Polystyrene bioactive nanofibers using orange oil as an ecofriendly solvent

Solution blow spun polystyrene (PS) nanofibers were produced from 20 to 30 wt % PS solutions using toluene (industrial solvent) and orange oil (green solvent). The latter being composed of d -limonene (97.06%) as determined by gas chromatography–mass spectroscopy. The rheological behavior and volatility of the solvents and polymer solutions were correlated with fiber morphology, accessed by scanning electron microscopy. Thermal analysis was used to determine the thermal behavior of fibers. The antimicrobial activity of orange oil was tested for potential applications of the spun mats in active food packaging. Results showed that the nanofibers spun from orange oil solutions had average diameters of 306 ± 74 nm as opposed to 441 ± 110 nm for toluene. Moreover, when compared with fiber spun from toluene solutions, orange oil yielded more flexible fibers with slightly lower contact angles and better antimicrobial properties due to the presence of residual oil confirmed by Fourier-transform infrared spectroscopy. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47337.     

Preparation and characterization of octadecane/polyurea nanocapsule‐embedded poly(ethylene oxide) nanofibers

This article describes the preparation and characterization of latent heat storage poly(ethylene oxide) nanofibers (LHS‐PEO nanofibers) with octadecane/polyurea (PCM/PU) nanocapsules. PCM/PU nanocapsules were prepared by interfacial polycondensation from toluene 2,4‐diisocyanate and ethylene diamine in a resin‐fortified emulsion system. LHS‐PEO nanofibers were prepared using an electrospinning procedure with varying PCM/PU nanocapsules content, i.e., from 0 to 8 wt %. The PCM/PU nanocapsules were polydisperse with an average diameter of 200 nm. The melting and freezing temperatures were determined as 23.7 and 28.2°C, respectively, and the corresponding latent heats were determined as 123.4 and 124.1 kJ kg^?1, respectively. The encapsulation efficiency of the PCM/PU nanocapsules was 78.1%. The latent heat capacity of the LHS‐PEO nanofibers increased as the PCM/PU nanocapsules content increased. Defects, such as holes and disconnection of the nanofibers, were observed, particularly inside the LHS‐PEO nanofibers. For packaging applications, mats were fabricated from the nanocapsules‐embedded nanofibers with varying nanocapsule content and the mats’ surface temperatures were monitored with a thermal imaging camera. The results proved the feasibility of using the LHS‐PEO nanofibers for thermal energy storage and functional packaging materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42539.     

Development of a gel spinning process for high‐strength poly(ethylene oxide) fibers

This article describes a new gel‐spinning process for making high‐strength poly(ethylene oxide) (PEO) fibers. The PEO gel‐spinning process was enabled through an oligomer/polymer blend in place of conventional organic solvents, and the gelation and solvent‐like properties were investigated. A 92/8 wt% poly(ethylene glycol)/PEO gel exhibited a melting temperature around 45°C and was highly stretchable at room temperature. Some salient features of a gel‐spun PEO fiber with a draw ratio of 60 are tensile strength at break = 0.66 ± 0.04 GPa, Young's modulus = 4.3 ± 0.1 GPa, and a toughness corresponding to 117 MJ/m³. These numbers are significantly higher than those previously reported. Wide‐angle x‐ray diffraction of the high‐strength fibers showed good molecular orientation along the fiber direction. The results also demonstrate the potential of further improvement of mechanical properties. POLYM. ENG. SCI., 54:2839–2847, 2014. © 2014 Society of Plastics Engineers     

Characterization of mechanically reinforced electrospun dextrin‐polyethylene oxide sub‐microfiber mats

Dextrin and dextrin‐polyethylene oxide (DEX/PEO) fibers in the submicron range were produced by electrospinning of single and blend polymer solutions. The morphology, intermolecular interactions, and mechanical properties of dextrin microfibers with and without PEO were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, nuclear magnetic resonance spectroscopy, and uniaxial tensile testing. Spectroscopic results confirmed hydrogen bond formation, evidencing dextrin as a molecular entanglement source for fiber mechanical reinforcement. The uniaxial tensile tests demonstrated a synergistic mechanical reinforcement effect that varied with blend composition. Equal weight ratio blends supported a maximum tensile strength with a high elastic modulus and demonstrated to be more elastic and resistant to breaking, even than pristine PEO fibers. Moreover, elastic moduli of blend fiber mats were found to lie within the value range for human skin, thus providing the DEX/PEO meshes with potential applicability as skin tissue scaffolds. This synthesis approach proved the feasible and inexpensive fabrication process of natural‐synthetic polymer hybrid fibers that combine the biocompatibility, biodegradability, and encapsulating capability of dextrin with the mechanical strength and flexibility of PEO for the development of scaffolds for tissue engineering and topical drug delivery applications in skin wound healing. POLYM. ENG. SCI., 59:1778–1786, 2019. © 2019 Society of Plastics Engineers     

Modification of thermoplastic polyurethane nanofiber membranes by in situ polydopamine coating for tissue engineering

To improve the interaction between cells and scaffolds, the appropriate surface chemical property is very important for tissue engineering scaffolds. In this work, the dopamine (DA) was first introduced into thermoplastic polyurethane (TPU) matrix to obtain TPU/DA nanofibers by electrospinning. Subsequently, the TPU@polydopamine (PDA) composite nanofibers with core/shell structure were fabricated by in situ polymerization of PDA. In comparison with TPU nanofibers, the uniformization of PDA coating layer on the surface of TPU/DA composite nanofibers significantly increased due to the addition of DA, which used as the active sites to guide the PDA particles accumulated along with the fiber direction. The hydrophilicity and water uptake ability of TPU@PDA composite nanofibers were larger than those of TPU nanofibers. The TPU@PDA composite nanofibers possess excellent comprehensive mechanical properties of high strength, stiffness, elasticity, and recoverability because of the hydrogen bonding occurrence between PDA and DA, as well as between PDA and TPU matrix. The attachment and viability of mouse embryonic osteoblasts cells (MC3T3-E1) cultured on TPU@PDA composite nanofibers were obviously enhanced compared with TPU nanofibers. Those results suggested that the modified TPU@PDA composite nanofibers have superior mechanical and biological properties, which promoting them potentially useful for tissue engineering scaffolds.     

Investigation of Properties of Polymer/Textile Fiber Composites

Polymer-based composite structures have advantages over other materials. The most important advantage is the higher mechanical properties obtained from the composites when supported by fiber reinforcement. The mechanical and thermal properties of fiber-reinforced composite structures are affected by the amount of fibers in the structures, orientation of the fiber and fiber length. Silk and cotton fibers are used in many fields but especially in clothing and textiles. However, there is not enough research on their usage as reinforcement fibers in composite structures. Silk fibers as a textile material have better physical and mechanic properties than other animal fibers. It is very important that the improvement of the mechanical and physical properties of the composite structures allows them to be used in many areas. From economical, technological and environmental points of view, the improved the mechanical and physical properties of polymeric materials are receiving much attention in the recent studies.

In this study, various lengths (1 mm–2.5 mm and 5 mm) of waste silk and waste cotton fibers were added to high-density polyethylene (HDPE) and polypropylene (PP) polymer in the mixing ratios of (polymer:fiber) 100%:0%, 97%:3%, and 94%:6% to produce composite structures. On the other hand, known lengths (1–2.5–5 mm) of waste silk and waste cotton fibers were added to recycled polyamide-6 (PA₆) and polycarbonate (PC) polymers in mixing quantities of 100%-0%, 97%-3%. A twin-screw extruder was employed for the production of composites. Tensile strength, % elongation, yield strength, elasticity modulus, Izod impact strength, melt flow index (MFI), heat deflection temperature (HDT), and Vicat softening temperature properties were determined. In order to determine the materials' thermal transition and microstructure properties, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used. Results have shown that cotton and silk fibers behave differently than in the composite structure. Waste silk fiber composites give better mechanical properties than waste cotton fiber.     

Mechanical and thermal properties of toughened polypropylene composites

The mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of silk fiber to the mechanical and thermal properties of its biodegradable composites

In recent years, natural fiber‐reinforced biodegradable thermoplastics are being recognized as an emerging new environmentally friendly material for industrial, commercial, and biomedical applications. Among different types of natural fibers, silk fiber is a common type of animal‐based fiber, has been used for biomedical engineering and surgical operation applications for many years because of its biocompatible and bioresorbable properties. On the basis of our previous study, a novel biodegradable biocomposite for biomedical applications was developed by mixing chopped silk fiber and polylactic acid (PLA) through the injection molding process. This article is aimed at studying the dynamic mechanical and thermal properties of the composite in relation to its biodegradation effect. At the beginning, it was found that the initial storage modulus of a silk fiber/PLA composite increased while its glass transition temperature decreased as compared with a pristine PLA sample. Besides, the coefficient of linear thermal expansions (CLTE) of the composite was reduced by 28%. This phenomenon was attributed to the fiber–matrix interaction that restricted the mobility of polymer chains adhered to the fiber surface, and consequently reduced the T_g and CLTE. It was found that the degraded composite exhibited lower initial storage modulus, loss modulus and tan delta (tan δ) but the T_g was higher than the silk fiber/PLA composite. This result was mainly due to the increase of crystallinity of the composite during its degradation process. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Analysis of the tensile modulus of poly(p‐hydroxybenzoate)/poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) ternary polyester composite fibers

Liquid crystalline polymer reinforced plastics were prepared by compounding (PHB/PEN/PET) blends. A fibrillar PHB structure was formed in situ in the PEN/PET matrix under a high elongational flow field during melt‐spinning of the composite fibers. The formation of PHB microfibrils in the composite fiber with different PHB contents and winding speeds was observed. The PHB microfibril reinforced PEN/PET composite fibers exhibited an unexpectedly low tensile modulus. We have evaluated the tensile modulus of the fibers using the non‐modified 22 and a modified 23 Halpin–Tsai model. From the analysis of both models, large differences were found between the theoretical and experimental values of the tensile modulus, and the low value of the tensile modulus of the composite fiber could not adequately be explained by either model. Thus, we analyzed the observed modulus values using the Takayanagi model, 24 which describes the concept of mechanical discontinuities in semi‐crystalline polymers. Using the Takayanagi model, the effective fraction of continuous or discontinuous microfibrils was evaluated. Consequently, we could successfully explain the very low modulus of the PHB/PEN/PET composite fiber, having a large number of PHB microfibrils, using the Takayanagi model. Copyright © 2003 Society of Chemical Industry     

Study of nanoreinforced shape memory polymers processed by casting and extrusion

Multi‐walled carbon nanotubes (CNTs) and cellulose nanofibers (CNFs) reinforced shape memory polyurethane (PU) composite fibers and films have been fabricated via extrusion and casting methods. Cellulose nanofibers were obtained through acid hydrolysis of microcrystalline cellulose. This treatment aided in achieving stable suspensions of cellulose crystals in dimethylformamide (DMF), for subsequent incorporation into the shape memory matrix. CNTs were covalent functionalized with carboxyl groups (CNT‐COOH) and 4,4′‐methylenebis (phenylisocyanate) (MDI) (CNT‐MDI) to improve the dispersion efficiency between the CNT and the polyurethane. Significant improvement in tensile modulus and strength were achieved by incorporating both fillers up to 1 wt% without sacrificing the elongation at break. Electron microscopy was used to investigate the degree of dispersion and fracture surfaces of the composite fibers and films. The effects of the filler (type and concentration) on the degree of crystallinity and thermal properties of the hard and soft segments that form the PU sample were studied by calorimetry. Overall, results indicated that the homogeneous dispersion of nanotubes and cellulose throughout the PU matrix and the strong interfacial adhesion between nanotubes and/or cellulose and the matrix are responsible for the enhancement of mechanical and shape memory properties of the composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers