Surface properties,thermal, and mechanical characteristics of poly(vinyl alcohol)–starch‐bacterial cellulose composite films

Nanocomposite films for food packaging applications were developed using bacterial cellulose (BC) nanofibers in different amount in a poly(vinyl alcohol)/starch (PVA/St) matrix. In search of a better method to reduce the harmful ingredients in food packaging, the cellulose nanofibers were obtained by the mechanical defibrillation of BC pellicles thus avoiding the addition of chemicals in the final packaging material. Improved mechanical performances were obtained starting from just 1% BC nanofibers in PVA/St. Atomic force microscopy images showed a uniform dispersion of BC nanofibers on the surface of nanocomposites. A twofold increase of both tensile strength and modulus was obtained for 2 wt % BC in the composite. BC nanofibers have greatly improved the barrier properties of PVA/St matrix, a twofold increase of water vapor permeability being obtained for only 2 wt % BC nanofibers in the composite film. PVA/St/2BC was proposed as a high potential material for food packaging applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45800.     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of (Z)‐3‐hexen‐1‐yl acetate by lipase immobilized in polyvinyl alcohol nanofibers

Polyvinyl alcohol (PVA)‐nanofibers‐immobilized lipase were formed by electrospinning. The specific surface area of the nanofiber (5.96 m²/g) was about 250 times larger than that of PVA‐film‐immobilized lipase (0.024 m²/g). The PVA‐nanofibers‐immobilized lipase were used as the catalyst for the esterification of (Z)‐3‐hexen‐1‐ol (leaf alcohol) with acetic acid in hexane. The activity of the nanofiber is equivalent to that of commercially available immobilized lipase (Novozym‐435). The ester conversions of the nanofibers, Novozym‐435, the film and lipase powder reached 99.5% at 5 h, 100% at 5 h, 11.5% at 6 h, and 81.1% at 5.75 h, respectively. The nanofibers‐immobilized lipase showed higher activity for the esterification than the film‐immobilized lipase and lipase powder, probably because it has high specific surface area and high dispersion state of lipase molecules in PVA matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electrospun cellulose nanofiber reinforced soybean protein isolate composite film

This article presents the fabrication of cellulose nanofibrous mats (CNM) reinforced soybean protein isolate (SPI) composite with high visible light transmittance. The CNM was composed of cellulose nanofibers generated from electrospinning technique. The microstructure of the fractured surface of composite films was characterized by scanning electron microscopy (SEM). The light transmittance, mechanical properties, and swelling ratio of CNM/SPI composite were investigated in terms of CNM content in the composite. Because of the ultrafine diameter and superhigh length‐to‐diameter ratio of nanofibers, large amount of cellulose nanofibers fibers distribute in the SPI matrix to form an interpenetrating network (IPN) like composite material. It was found that strong interfacial interactions occurred at the cellulose nanofiber/SPI interfaces. The incorporation of 20 wt % cellulose nanofibers in the SPI matrix resulted in great improvement of mechanical strength and Young's modulus by respectively 13 and 6 times more than neat SPI film. More interestingly, this composite was translucent with light transmittance of over 75% at 700 nm. Furthermore, the swelling ratio of this IPN‐like CNM/SPI composite decreased from 106 to 22% as CNM content increased from 0 to 20 wt %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Extrusion processing of green biocomposites: Compounding,fibrillation efficiency,and fiber dispersion

The efficiency of twin‐screw extrusion process to fibrillate cellulose fibers into micro/nanosize in the same step as the compounding of green bionanocomposites of thermoplastic starch (TPS) with 10 wt % fibers was examined. The effect of the processing setup on micro/nanofibrillation and fiber dispersion/distribution in starch was studied using two types of cellulose fibers: bleached wood fibers and TEMPO‐oxidized cellulose fibers. A composite with cellulose nanofibers was prepared to examine the nanofiber distribution and dispersion in the starch and to compare the properties with the composites containing cellulose fibers. Optical microscopy, scanning electron microscopy, and UV/Vis spectroscopy showed that fibers were not nanofibrillated in the extrusion, but good dispersion and distribution of fibers in the starch matrix was obtained. The addition of cellulose fibers enhanced the mechanical properties of the TPS. Moisture uptake study revealed that the material containing TEMPO‐oxidized fibers had higher moisture absorption than the other composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39981.     

Electrospun polyvinyl alcohol/waterborne polyurethane composite nanofibers involving cellulose nanofibers

TEMPO‐oxidized cellulose nanofibers (TOCNs) were used as nanofillers in this work. Composite nanofibers of polyvinyl alcohol (PVA)/waterborne polyurethane (WPU) reinforced with TOCNs were produced by electrospinning. The reinforcing capability of TOCNs was investigated by tensile tests. Scanning electron microscopy (SEM), X‐ray diffraction, and thermogravimetry analyses were also carried out in order to characterize the appearance, crystallinity, and reinforcing effect of the cellulose nanofibers. SEM results showed that PVA/WPU/TOCNs composite nanofibers presented a highly homogeneous dispersion of TOCNs. The reinforced composites had about 44% increase in their mechanical properties with addition of only 5 wt % of TOCNs while about 42% decrease in elongation at break. The TOCNs reinforced composite nanofibers were more thermally stable than pure PVA/WPU nanofibers. The development of crystalline structure in the composite fibers was observed by XRD. Since PVA, WPU, and TOCNs are hydrophilic, non‐toxic, and biocompatible, and therefore, these nanocomposite nanofibers could be used for tissue scaffolding, filtration materials, and medical industries as wound dressing materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41051.     

Cellulose NANOFIBER‐polyethylene nanocomposites modified by polyvinyl alcohol

The uniform dispersion of cellulose nanofibers (CNFs) in non‐polar polymer matrices is a primary problem to overcome in creating novel nanocomposites from these materials. The aim of this study was to produce CNF‐polyethylene (PE) nanocomposites by melt compounding followed by injection molding to investigate the possibility of using polyvinyl alcohol (PVA) to improve the dispersion of CNF in the PE matrix. The tensile strength of CNF‐ filled composites was 17.4 MPa with the addition of 5 wt % CNF–PVA, which was 25% higher than the strength of neat PE. The tensile modulus of elasticity increased by 40% with 5% CNF–PVA addition. Flexural properties also significantly increased with increased CNF loading. Shear viscosity increased with increasing CNF content. The elastic moduli of the PE/CNF composites from rheological measurements were greater than those of the neat PE matrix because of the intrinsic rigidity of CNF. Melt creep compliance decreased by about 13% and 45% for the composites with 5 wt % CNF and 10 wt % CNF, respectively. It is expected that the PVA carrier system can contribute to the development of a process methodology to effectively disperse CNFs containing water in a polymer matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42933.     

The morphology and properties of poly(methyl methacrylate)‐cellulose nanocomposites prepared by immersion precipitation method

Poly(methyl methacrylate) (PMMA)‐cellulose nanofibers nanocomposite were prepared by an immersion precipitation method using various nanofiber contents. Solvent exchange was used to disperse the cellulose nanofibers in dimethylacetamide (DMAc) so that they could be easily mixed with PMMA solution. Atomic force microscopy images show that the thickness of the nanofibers dispersed in DMAc is around 2–3 nm. The nanocomposites obtained were translucent. The thermogravimetric and differential scanning calorimetry analyses show that with increasing cellulose nanofiber content the thermal stability and the glass transition temperature (T_g) of polymer matrix shift to higher temperature. The tensile modulus and strength increased with increasing nanofiber content. Dynamic mechanical analysis profiles show that the presence of cellulose nanofibers affects the storage modulus of PMMA nanocomposites over the whole range of temperatures studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Zwitterionic‐polymer‐functionalized poly(vinyl alcohol‐co‐ethylene) nanofiber membrane for resistance to the adsorption of bacteria and protein

A zwitterionic poly(vinyl alcohol‐co‐ethylene) (PVA‐co‐PE) nanofiber membrane for resistance to bacteria and protein adsorption was fabricated by the atom transfer radical polymerization of sulfobetaine methacrylate (SBMA). The PVA‐co‐PE nanofiber membrane was first surface‐activated by α‐bromoisobutyryl bromide, and then, zwitterionic SBMA was initiated to polymerize onto the surface of nanofiber membrane. The chemical structures of the functionalized PVA‐co‐PE nanofiber membranes were confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The morphologies of the PVA‐co‐PE nanofiber membranes were characterized by scanning electron microscopy. The results show that the poly(sulfobetaine methacrylate) (PSBMA) was successfully grafted onto the PVA‐co‐PE nanofiber membrane, and the surface of the nanofiber membrane was more hydrophilic than that of the pristine membrane. Furthermore, the antibacterial adsorption properties and resistance to protein adsorption of the surface were investigated. This indicated that the PSBMA‐functionalized surface possessed good antibacterial adsorption activity and resistance to nonspecific protein adsorption. Therefore, this study afforded a convenient and promising method for preparing a new kind of soft and nonwoven dressing material with antibacterial adsorption and antifouling properties that has potential use in the medical field. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44169.     

Mechanical reinforcement of electrospun water‐soluble polymer nanofibers using nanodiamonds

Optimization of the mechanical properties is necessary in the applications of electrospun nanofibrous matrices. In this work, mechanical reinforcement of electrospun nanofiber membranes of water‐soluble polymer by the incorporation of commercial nanodiamonds (NDs) was studied. Through an ND/poly(vinyl alcohol) (ND/PVA) model system, it is demonstrated that 155% improvement of Young's modulus, 89% increase in tensile strength, and 336% elevation in energy to break are achieved by the addition of only 2 wt% ND. Fourier transform infrared spectroscopy results suggest the existence of molecular interactions between NDs and PVA matrix, which contributes to the effective load transfer from the polymer matrix to the fillers. However, higher level of ND addition (>2 wt%) aggravates the agglomeration of nanofillers in PVA matrix and offsets the reinforcing effect, as ND agglomerates may act as flaws in composite nanofibers. Furthermore, NDs have optimizing effect on the morphology of ND/PVA nanofibers through increasing the conductivity of the electrospinning solution. Therefore, ND nanofillers possess the potential to improve the mechanical performance of water‐soluble polymer‐based nanofiber membranes. POLYM. COMPOS., 34:1735–1744, 2013. © 2013 Society of Plastics Engineers     

Fabrication of Core/Shell Nanofibers with Desirable Mechanical and Antibacterial Properties by Pickering Emulsion Electrospinning

To endow nanofibers with the desirable antibacterial and mechanical properties, a facile strategy using Pickering emulsion (PE) electrospinning is proposed to prepare functional nanofibers with core/shell structure for the first time. The water‐in‐oil (W/O) Pickering emulsion stabilized by oleic acid (OA)‐coated magnetite iron oxide nanoparticles (OA‐MIONs) is comprised of aqueous vancomycin hydrochloride (Van) solution and poly(lactic acid) (PLA) solution. The core/shell structure of the electrospun Van/OA‐MIONs‐PLA nanofibers is confirmed by scanning electron microscopy and transmission electron microscopy observation. Sustained release of Van from the PE electrospun nanofiber membrane is achieved within the time of 600 h. Compared with the neat PLA electrospun nanofiber membrane, 57% increase of tensile strength and 36% elevation of elongation at break are achieved on PE electrospun nanofiber membrane. In addition, the PE electrospun nanofiber membrane demonstrates excellent antibacterial property stemming from the combinational antibacterial activities of OA‐MIONs and Van. The Van‐loaded PE electrospinning nanofibers with sustained antibacterial performance possess potential applications in tissue engineering and drug delivery.

     

Comparison of prolonged antibacterial activity and release profile of propolis‐incorporated PVA nanofibrous mat,microfibrous mat,and film

Propolis as a natural antibacterial agent was incorporated into the poly(vinyl alcohol) (PVA) in different forms of nanofiber, microfiber, and film. The successful fabrication of uniform nanofibers with 85–314 nm diameters and microfibers with 2.02 μm diameter was proved by scanning electron microscopy. Structural analysis by Fourier transform infrared spectroscopy and X‐ray diffraction and swelling properties confirmed the formation PVA hydrogel and its H‐bonding to the propolis. Evaluation and comparison of antimicrobial properties of produced samples against Staphylococcus aureus strains revealed that nanofiber mat with 19 mm inhibition zone has 11.76 and 26.67% higher efficiency against bacteria than microfiber mat and film with 17 and 15 mm inhibition zone, respectively. Nanofibrous mat showed sustained release during 96 h by maintaining full antibacterial activity up to 51 h which is of great importance in burn wounds. These results confirm the advanced performance of natural propolis in the form of nanofiber substrate as wound dressing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45794.     

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     

Microstructure and characterization of electrospun poly(vinyl alcohol) nanofiber scaffolds filled with graphene nanosheets

Graphene nanosheets (GNSs) have attracted significant scientific attention because of their remarkable features, including exceptional electron transport, excellent mechanical properties, high surface area, and antibacterial functions. Poly(vinyl alcohol) (PVA) solutions filled with GNSs were prepared for electrospinning, and their spinnability was correlated with their solution properties. The effects of GNS addition on solution rheology and conductivity were investigated. The as‐spun fibers were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The results revealed the effects of GNS on the microstructure, morphology, and crystallization properties of PVA/GNS composite nanofibers. The addition of GNSs in PVA solution increased the viscosity and conductivity of the solution. The electrospun fiber diameter of the PVA/GNS composite nanofiber was smaller than that of neat PVA nanofiber. GNSs were not only embedded at the fibers but also formed protrusions on the fibers. In addition, the crystallinity of PVA/GNS fiber decreased with higher GNS content. The possible application of PVA/GNS fibers in tissue engineering was also evaluated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41891.     

ZnO nanocrystallites/cellulose hybrid nanofibers fabricated by electrospinning and solvothermal techniques and their photocatalytic activity

ZnO nanocrystallites have been in situ embedded in cellulose nanofibers by a novel method that combines electrospinning and solvothermal techniques. Zn(OAc)₂/cellulose acetate (CA) precursor hybrid nanofibers with diameter in the range of 160–330 nm were first fabricated via the electrospinning technique using zinc acetate as precursor, CA as the carrier, and dimethylformamide (DMF)/acetone(2 : 1) mixture as cosolvent. The precursor nanofibers were transformed into ZnO/cellulose hybrid fibers by hydrolysis in 0.1 mol/L NaOH aqueous solution. Subsequently, these hybrid fibers were further solvothermally treated in 180°C glycerol oil bath to improve the crystallite structure of the ZnO nanoparticles containing in the nanofibers. The structure and morphology of nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. It was found that hexagonal structured ZnO nanocrystallites with the size of ～ 30 nm were dispersed on the nanofiber surfaces and within the nanofibers with diameter of about 80 nm. The photocatalytic property of the ZnO/cellulose hybrid nanofibers toward Rhodamine (RhB) was tested under the irradiation of visible light. As a catalyst, it inherits not only the photocatalytic ability of nano‐ZnO, but also the thermal stability, good mechanical property, and solvent‐resistibility of cellulose nanofibers. The key advantages of this hybrid nanofiber over neat ZnO nanoparticles are its elasticity, dimensional stability, durability, and easy recyclability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of graphene oxide/poly(vinyl alcohol) composite nanofibers via electrospinning

Graphene oxide (GO) was well dispersed in poly(vinyl alcohol) (PVA) diluted aqueous solution, and then the mixture was electrospun into GO/PVA composite nanofibers. Electron microscopy and Raman spectroscopy on the as‐prepared and calcined samples confirm the uniform distribution of GO sheets in the nanofibers. The thermal and mechanical properties of the nanofibers vary considerably with different GO filler contents. The decomposition temperatures of the GO/PVA composite nanofiber dropped by 38–50°C compared with pure PVA. A very small loading of 0.02 wt % GO increases the tensile strength of the nanofibers by 42 times. A porous 3D structure was realized by postcalcining nanofibers in H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical reinforcement of hydrogels by nanofiber network undergoing biaxial deformation

Hydrogels can encapsulate large quantities of water within a three‐dimensional crosslinked polymer network. Polyvinyl alcohol (PVA) hydrogels have been widely used in tissue engineering, wound dressing, and drug delivery. However, the inferior mechanical properties of PVA hydrogels limit their utility in load‐bearing applications. To alleviate this deficiency, we used a hybrid electrospinning/solution casting continuous process to reinforce PVA hydrogels using polyurethane nanofibers. In this process, the nanofibers were electrospun into the wet solution cast film prior to solidification. The reinforcement of PVA hydrogels at a series of extent of water swelling was determined using a custom built bubble biaxial stretching device. The results showed that nanofibers have substantial enhancement effect on mechanical properties particularly in thin hydrogel films at high water concentrations. Reduction of nanofiber diameter was also found to increase this reinforcement due to increased interfacial area between nanofibers and hydrogels. POLYM. COMPOS., 37:709–717, 2016. © 2014 Society of Plastics Engineers     

Single‐wall carbon nanotubes dispersion behavior and its effects on the morphological and mechanical properties of the electrospun nanofibers

The dispersion behavior of single‐walled carbon nanotube (SWCNT) has important effects on morphological and mechanical properties of SWCNT composite nanofibers. The relationship of the dispersion conditions with morphological and mechanical characteristics for SWCNT / polyacrylonitrile (PAN) / polyvinylpyrrolidone (PVP) composite nanofibers have been examined. The SEM and TEM analyses of the nanofibers revealed that the deformation in the nanofiber structures increases with increasing concentration of SWCNTs. Tensile results showed that only 2 wt% SWCNT loading to the electrospun composite nanofibers gave rise to 10‐fold and 3‐fold increase in the tensile modulus and tenacity of nanofiber layers, respectively. Essentially, high mechanical properties and uniform morphology of the composite nanofibers were found at SWCNT concentration of ∼2 wt% due to their stable and individual dispersion. POLYM. COMPOS., 33:1951–1959, 2012. © 2012 Society of Plastics Engineers     

Thermal and morphological properties of PVA/4‐vinylbenzene boronic acid hybrid nanofibrous

The aim of this study was to investigate the preparation and characterization of PVA and PVA/4‐VBBA (4‐Vinylbenzene boronic acid) hybrid electrospun nanofiber mat. PVA was mixed with cross‐linkable 4‐Vinylbenzene boronic acid (4‐VBBA), enabling the polymer to cross‐link upon UV irradiation. The photo‐cross‐linking reaction was characterized by a Fourier transform infrared spectroscopy. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy (SEM). SEM images showed that the nanofiber diameter and the nanostructured morphology depended on solution viscosity, applied electric voltage(AV), tip to collector distance (TCD), and the amount of the 4‐VBBA. The thermal properties of PVA and PVA/4‐VBBA hybrid nanofibers were investigated by thermo gravimetric analysis. The photo‐crosslinked nanofibers were insoluble in water. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

A comprehensive study on Plantago ovata/PVA biocompatible nanofibers: Fabrication,characterization, and biological assessment

In this study, a biocompatible nanofiber is fabricated using Plantago ovata mucilage (POM) combined with polyvinyl alcohol (PVA), which is considered as a non-toxic polymer. High quality nanofibers were produced by controlling the electrospinning parameters after selecting an appropriate solvent for the POM/PVA combination (12% PVA and 3% POM). Electrospinning parameters, including high voltage, distance from collector to tip, feed rate and POM to PVA proportion were optimized following preparation of an aqueous POM/PVA solution. Using the results of scanning electron microscopy, the optimized electrospinning conditions for producing POM/PVA nanofibers were determined (high voltage = 18 kV, distance = 15 cm, feed rate = 0.125 ml/hr, PMM/PVA = 50/50) and uniform nanofibers with an average diameter of 250 nm were produced. The POM/PVA nanofiber sample was evaluated by determining the mechanical strength, characterization of produced nanofiber morphology, and investigating the cell viability by applying MTT assay. The bands for both POM and PVA from FTIR results showed that the samples remained stable. The tensile strength results showed that blending POM with PVA solution enhanced the Young's modulus by factor of 3.2 (0.2 MPa to 0.64 MPa). The MTT analysis on POM/PVA cell lines proved that the produced nanofiber considerably enabled the cellular proliferation. Enhancement in these analysis indicated how POM-based nanofibers is a promising scaffold for cell culture, drug delivery systems and food additives.