Homogeneous dispersion of chitin nanofibers in polylactic acid with different pretreatment methods

Chitin nanofibers extracted from crab shell were used to reinforce polylactic acid (PLA) by extrusion molding. The dispersion problem of nanofibers in PLA matrix was solved by three pretreatment methods, including water pretreatment, polyethylene glycol (PEG) pretreatment, and polyethylene oxide (PEO) pretreatment. The results demonstrated that chitin nanofibers were distributed uniformly on the fracture surface of the PLA matrix with three different pretreatment methods. However, the aspect ratio of nanofibers with was reduced with the PEG and PEO pretreatment methods. Therefore, the bending modulus (MOE), bending strength (MOR) and impact toughness of the chitin nanofibers/PLA composites prepared by the water pretreatment method were much higher than those of the composites prepared by the PEG and the PEO pretreatment method. Furthermore, the reinforcing effect with the PEG method is slightly better than that with the PEO method. Although it was found that both PEG and PEO were good interfacial compatibilizers for nanofibers and PLA, the reinforcing effect of the composites prepared by PEG and PEO pretreat methods was suppressed due to the decrease of the aspect ratio for chitin nanofibers.     

Synthesis,Characterization, and Hydrolytic Degradation of Polylactide/Poly(ethylene glycol)/Nano-silica Composite Films

Poly(lactic acid) (PLA)/PEG/nano-silica composite degradable films have been prepared by solvent casting method. IR measurements showed that vibration of C–O–C group was confined by silica network. SEM results showed that nano-silica particles were dispersed uniformly in the PLA/PEG matrix. TGA results indicated that the thermal decomposition temperature rose with the increase of nano-silica content. The tensile strength of composite film increased by the addition of nano-silica particles into PLA/PEG matrix. The degradation rate of PLA/PEG/nano-silica composites increased with the acidic medium of degradation. On the other hand, the slower degradation was obtained in the neutral buffer solution. PLA/PEG/nano-silica composites were found to exhibit almost similar degradation behavior as that of PLA/PEG films.     

Supercritical Carbon Dioxide Isolation of Cellulose Nanofibre and Enhancement Properties in Biopolymer Composites

The physical properties, such as the fibre dimension and crystallinity, of cellulose nanofibre (CNF) are significant to its functional reinforcement ability in composites. This study used supercritical carbon dioxide as a fibre bundle defibrillation pretreatment for the isolation of CNF from bamboo, in order to enhance its physical properties. The isolated CNF was characterised through zeta potential, TEM, XRD, and FT-IR analysis. Commercial CNF was used as a reference to evaluate the effectiveness of the method. The physical, mechanical, thermal, and wettability properties of the bamboo and commercial CNF-reinforced PLA/chitin were also analysed. The TEM and FT-IR results showed the successful isolation of CNF from bamboo using this method, with good colloidal stability shown by the zeta potential results. The properties of the isolated bamboo CNF were similar to the commercial type. However, the fibre diameter distribution and the crystallinity index significantly differed between the bamboo and the commercial CNF. The bamboo CNF had a smaller fibre size and a higher crystallinity index than the commercial CNF. The results from the CNF-reinforced biocomposite showed that the physical, mechanical, thermal, and wettability properties were significantly different due to the variations in their fibre sizes and crystallinity indices. The properties of bamboo CNF biocomposites were significantly better than those of commercial CNF biocomposites. This indicates that the physical properties (fibre size and crystallinity) of an isolated CNF significantly affect its reinforcement ability in biocomposites. The physical properties of isolated CNFs are partly dependent on their source and production method, among other factors. These composites can be used for various industrial applications, including packaging.     

Fabrication and enhanced mechanical properties of porous PLA/PEG copolymer reinforced with bacterial cellulose nanofibers for soft tissue engineering applications

A new class of polylactic acid (PLA)/polyethylene glycol (PEG) copolymer reinforced with bacterial cellulose nanofibers (BC) was prepared using a solvent casting and particulate leaching methods. Four weight fractions of BC (1, 2.5, 5, and 10 wt%) were incorporated into copolymer via silane coupling agent. Mechanical properties were evaluated using response surface method (RSM) to optimize the impact of pore size, porosity, and BC contents. Compressive strength obtained for PLA/PEG-5 BC wt% was 9.8 MPa, which significantly dropped after developing a porous structure to 4.9 MPa. Nielson model was applied to investigate the BC stress concentration on the PLA/PEG. Likewise, krenche and Hapli-Tasi model were employed to investigate the BC nanofiber reinforcement and BC orientation into PLA/PEG chains. The optimal parameters of the experiment results found to be 5 wt% for BC, 230 μm for pore size, and 80% for porosity. Scanning electron microscopy (SEM) micrograph indicates that uniform pore size and regular pore shape were achieved after an addition of BC-5% into PLA/PEG. The weight loss of copolymer-BC with scaffolds enhanced to the double values, compared with PLA/PEG-BC % without scaffolds. Differential Scanning Calorimetric (DSC) results revealed that the BC nanofiber improved glass transition temperature (T_g) 57 °C, melting temperature (T_m) 171 °C, and crystallinity (χ %) 43% of PLA/PEG reinforced-BC-5%.     

On the use of plant cellulose nanowhiskers to enhance the barrier properties of polylactic acid

Polylactic acid (PLA) nanocomposites were prepared using cellulose nanowhiskers (CNW) as a reinforcing element in order to asses the value of this filler to reduce the gas and vapour permeability of the biopolyester matrix. The nanocomposites were prepared by incorporating 1, 2, 3 and 5 wt% of the CNW into the PLA matrix by a chloroform solution casting method. The morphology, thermal and mechanical behaviour and permeability of the films were investigated. The CNW prepared by acid hydrolysis of highly purified alpha cellulose microfibers, resulted in nanofibers of 60–160 nm in length and of 10–20 nm in thickness. The results indicated that the nanofiller was well dispersed in the PLA matrix, did not impair the thermal stability of this but induced the formation of some crystallinity, most likely transcrystallinity. CNW prepared by freeze drying exhibited in the nanocomposites better morphology and properties than their solvent exchanged counterparts. Interestingly, the water permeability of nanocomposites of PLA decreased with the addition of CNW prepared by freeze drying by up to 82% and the oxygen permeability by up to 90%. Optimum barrier enhancement was found for composites containing loadings of CNW below 3 wt%. Typical modelling of barrier and mechanical properties failed to describe the behaviour of the composites and appropriate discussion regarding this aspect was also carried out. From the results, CNW exhibit novel significant potential in coatings, membranes and food agrobased packaging applications.     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.     

Synthesis,characterization, and hydrolytic degradation of polylactide/poly(ϵ-caprolactone)/nano-silica composites

Poly(lactic acid) (PLA)/poly(?-caprolactone) (PCL)/nano-silica composite degradable films were prepared by a solvent casting method. SEM results showed that the nano-silica particles were dispersed uniformly in the PLA/PCL matrix. TGA results indicated that the thermal decomposition temperature rose with the increase of nano-silica content. The tensile strength of the composites was enhanced with the increase of nano-silica content up to 2%. The tensile strength increased with the silica content and reached its maximum (22.51 Mpa). The improvement in the water uptake ratio in the PLA/PCL/silica nanocomposites may be attributable to the presence of silica nanoparticles in the PLA/PCL matrix. After 15 weeks total processing time for the solution of alkaline and phosphate buffer, the performances of 16.23% and 3.65% for degradation.     

Effect of cellulose nanofibers on induced polymerization of aniline and formation of nanostructured conducting composite

Cellulose nanofibers (CNFs), derived from the most abundant and renewable biopolymer, are known as natural one-dimensional nanomaterials because of their high aspect ratio. CNFs also are rich in hydroxyl groups, offering opportunities for functionalization toward development of high-value nanostructured composites. Herein, CNFs were extracted from poplar wood powder by chemical pretreatment combined with high-intensity ultrasonication, and then coated with polyaniline (PANI) through in situ polymerization. The PANI-coated CNFs formed nanostructured frameworks around PANI, thereby conferring the CNF/PANI composite with stability and higher charge transport. The optimum PANI content to achieve maximum conductivity of CNF/PANI composites was determined. The morphology, crystall structure, chemical composition, and conductivity of the samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and four-point probe method, respectivily. Our results demonstrated that CNFs can be effective as a template for a flexible and stable conducting polymer to form higher-order nanostructures.     

Effects of Rice Straw Powder (RSP) Size and Pretreatment on Properties of FDM 3D-Printed RSP/Poly(lactic acid) Biocomposites

To develop a new kind of environment-friendly composite filament for fused deposition modeling (FDM) 3D printing, rice straw powder (RSP)/poly(lactic acid) (PLA) biocomposites were FDM-3D-printed, and the effects of the particle size and pretreatment of RSP on the properties of RSP/PLA biocomposites were investigated. The results indicated that the 120-mesh RSP/PLA biocomposites (named 120#RSP/PLA) showed better performance than RSP/PLA biocomposites prepared with other RSP sizes. Infrared results showed that pretreatment of RSP by different methods was successful, and scanning electron microscopy indicated that composites prepared after pretreatment exhibited good interfacial compatibility due to a preferable binding force between fiber and matrix. When RSP was synergistically pretreated by alkaline and ultrasound, the composite exhibited a high tensile strength, tensile modulus, flexural strength, and flexural modulus of 58.59, 568.68, 90.32, and 3218.12 MPa, respectively, reflecting an increase of 31.19%, 16.48%, 18.75%, and 25.27%, respectively, compared with unmodified 120#RSP/PLA. Pretreatment of RSP also improved the thermal stability and hydrophobic properties, while reducing the water absorption of 120#RSP/PLA. This work is believed to provide highlights of the development of cost-effective biocomposite filaments and improvement of the properties of FDM parts.     

A method for simultaneously improving the flame retardancy and toughness of PLA

In order to modify the brittleness and flame retardant properties of poly(lactic acid) (PLA), a series of flame retardant toughened PLA composites were prepared using poly(ethylene glycol) 6000 (PEG6000) as a toughening and charring agent together with ammonium polyphosphate (APP) as an acid source and blowing agent. The fire and thermal behavior of PLA/PEG/APP composites was evaluated by limiting oxygen index (LOI), UL‐94, cone calorimeter, and thermogravimetric analysis (TGA). The results showed that the PLA/PEG/APP system had good charring ability and could improve the flame retardancy of PLA. When the content of APP in the composites was more than 5 wt%, all samples could reach UL‐94 V‐0 rating. The results of mechanical property tests demonstrated that the brittleness of PLA was also improved after blended with PEG6000. All the PLA/PEG/APP composites with an APP content of less than 10 wt% showed an obvious neck and fracture behavior, that is, the tensile behavior of PLA was changed from brittle to ductile. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of cellulose nanofibers on the rheological behavior of silica-based shear-thickening fluid

In this work, the influence of cellulose nanofibers (CNFs) on the rheological behavior of silica-based shear-thickening fluid (STF) is investigated. CNFs of 150–200 nm in diameter were extracted from cotton fibers using a supermasscolloider. CNF-reinforced STF of different concentrations (0.1–0.3 wt.%) was prepared via an ultrasonication technique. The presence of CNFs and their interaction with the silica nanoparticles in the STF were analyzed using SEM and FTIR. The addition of a minute quantity of CNF to the STF (0.3% CNF-reinforced STF) caused a marked increase in the peak viscosity, from 36.8 (unmodified STF) to 139.0 Pa s (0.2% CNF-reinforced STF), and a concomitant decrease in the critical shear rate from 33.45 to 14.8 s^?1 . The presence of a large number of hydroxyl groups on the CNFs enhanced their interaction with the nanoparticles via hydrogen bonding, which induced shear thickening. The mechanism of the interaction between silica nanoparticles and CNF was also demonstrated. Oscillatory dynamic rheological analysis showed that the addition of even a small amount of CNF led to higher elastic behavior in the system at lower shear rates. In contrast, a more viscous nature was demonstrated at higher angular frequencies. As the concentration of  nanofibers in the STFs increased, the crossover point between storage and loss modulus shifted to higher angular frequencies, implying stronger interaction between the constituents of the STF. The dynamic viscosity profile of all samples also exhibited shear-thickening behavior.     

The influence of organo-modified sepiolite on the flame-retardant and thermal properties of intumescent flame-retardant polylactide composites

Polylactide (PLA) composites based on intumescent flame-retardant (IFR) and organo-modified sepiolite (OSEP) were prepared via direct melt compounding. The uniform dispersion of OSEP in the PLA matrix was observed by TEM, but some agglomerates still existed at the high loading. Tensile results showed that high loading of the conventional IFR led to a reduction in tensile strength of PLA composites; however, replacing a portion of the IFR with modified sepiolite in the PLA matrix improved this result. The thermal degradation temperature of the PLA/IFR/OSEP composites determined by thermogravimetric analysis was lower than that of neat PLA, as a consequence of the catalyzed carbonization induced by the addition of IFR and OSEP. The formulation with 13 mass% IFR and 2 mass% OSEP exhibited the highest LOI value of 32 vol% and also reached UL-94 V-0 rating in the vertical burning tests. Furthermore, the co-addition of IFR and OSEP gave rise to a significant reduction in peak heat release rate (PHRR) and total heat release (THR) of PLA composites during combustion, particularly in the case of PLA/IFR13/OSEP2 (82% reduction in PHRR and 69% in THR). The excellent fire resistance of PLA/IFR13/OSEP2 could be attributed to that IFR catalyzed carbonization of PLA to form the char, while OSEP resulted in further stabilization in the charred layers.     

Nanocomposites of natural rubber and polyaniline-modified cellulose nanofibrils

Cellulose nanofibrils (CNF) were isolated from cotton microfibrils (CM) by acid hydrolysis and coated with polyaniline (PANI) by in situ polymerization of aniline onto CNF in the presence of hydrochloride acid and ammonium peroxydisulfate to produce CNF/PANI. Nanocomposites of natural rubber (NR) reinforced with CNF and CNF/PANI were obtained by casting/evaporation method. TG analyses showed that coating CNF with PANI resulted in a material with better thermal stability since PANI acted as a protective barrier against cellulose degradation. Nanocomposites and natural rubber showed the same thermal profiles to 200 °C, partly due to the relatively lower amount of CNF/PANI added as compared to conventional composites. On the other hand, mechanical properties of natural rubber were significantly improved with nanofibrils incorporation, i.e., Young’s modulus and tensile strength were higher for NR/CNF than NR/CNF/PANI nanocomposites. The electrical conductivity of natural rubber increased five orders of magnitude for NR with the addition of 10 mass% CNF/PANI. A partial PANI dedoping might be responsible for the low electrical conductivity of the nanocomposites.     

Decorating silver nanoparticles on electrospun cellulose nanofibers through a facile method by dopamine and ultraviolet irradiation

In this paper, a new method is introduced for producing multi-functional cellulose nanofibers in order to achieve the biodegradable materials for various applications with a minimal amount of potentially toxic materials. Cellulose nanofibers (CNFs) were fabricated by electrospinning cellulose acetate solution followed by deacetylation. The CNFs were then treated with silver nitrate, ammonia, and sodium hydroxide and subsequently with dopamine as reducing and adhesive agent. Ag ions on the CNF surface were photo-reduced to Ag nanoparticles (NPs) using UVA irradiation to produce a dense layer of silver nanoparticles on the nanofibers. This is based on the simultaneous formation of polydopamine and Ag NPs on CNFs. Overall, this is a fast, simple, and efficient procedure that takes place in a conventional method at ambient temperature. The crystalline structure of CNFs decorated with AgNPs was studied by X-ray diffraction. Field-emission scanning electron microscopy and energy-dispersive X-ray patterns showed uniform distribution of silver nanoparticles on the CNF surface. Incorporation of AgNPs on the CNF surface via dopamine improved the electrical conductivity and also the tensile strength of the nanomat. The CNFs decorated with AgNPs exhibited a low electrical resistivity around 35 KΩ/square and a tensile strength of 87% higher than untreated CNFs.     

Resin impregnation of cellulose nanofibril films facilitated by water swelling

Flexible composite films were produced by impregnating aqueous phenol formaldehyde (PF) resin into water-swollen cellulose nanofibril (CNF) films. CNF films were prepared using a pressurized filtration method in combination with freeze drying. The freeze-dried films were swollen with water then impregnated with PF resin by soaking in aqueous resin solutions of varying concentrations. Small amounts of PF slightly enhanced the tensile properties of CNF films. The formulation with the best mechanical properties was CNF/PF films with 8 wt % resin exhibiting tensile stress and toughness of 248 MPa and 26 MJ/m³, respectively. Resin concentrations higher than about 8 % resulted in composites with decreased tensile properties as compared to neat CNF films. The wet strength of the composite films was significantly higher than that of the neat CNF films. The resulting composites showed greater resistance to moisture absorption accompanied by reduced thickness swelling when soaked in water as compared to neat CNF films. The composites also showed decreased oxygen permeability at low humidity compared to neat films, but the composites did not show improved barrier properties at high humidity.     

Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.     

A composite made from palladium nanoparticles and carbon nanofibers for superior electrocatalytic oxidation of formic acid

We report on a novel type of nanocomposite for use in the electrooxidation of formic acid in fuel cells. The material is composed of palladium nanoparticles (Pd-NPs) and carbon nanofibers (CNFs) and was prepared by electrospinning of the precursors Pd(acac)₂ and polyacrylonitrile, respectively, followed by thermal treatment to generate in-situ Pd-NPs that are well dispersed within the CNF framework. The nanocomposite was characterized by TEM, high-resolution TEM, SEM, XRD, Raman spectroscopy, and XPS. The size of the Pd-NPs ranges from 12 to 82 nm, depending on the temperature for carbonization (700–1,000 °C). The length and width of the CNF is in the order of tens of micrometers and 300 to 500 nm, respectively. TEM and XPS studies indicate that the Pd-NPs are firmly embedded in the CNF, resulting in a good electrochemical stability of the composite. The electrocatalytic properties of the composite with respect to the oxidation of formic acid were studied by cyclic voltammetry and chronoamperometry. They showed a distinctly improved electrocatalytic activity and stability compared to a commercial Pd-on-carbon catalyst. The Pd/CNF composite carbonized at 900 °C was found to display the best performance.

Fe–N/C nanofiber electrocatalysts with improved activity and stability for oxygen reduction in alkaline and acid solutions

Fe–N/C nanofiber (Fe–N/CNF) electrocatalysts were prepared by impregnating electrospun polyacrylonitrile nanofibers with iron nitrate (Fe(NO₃)₃) solution and subsequent heat treatment, exhibiting improved activity and stability during oxygen reduction reaction (ORR) both in 0.1 M KOH (pH?=?13) and 0.5 M H₂SO₄ (pH?=?0) electrolyte solutions. Higher treatment temperature and NH₃ atmosphere were preferred by the Fe–N/CNF catalysts, and especially the concentration of Fe(NO₃)₃ solution exerted great effects on the surface morphology, structure, and thus electrocatalytic performance of the catalysts. The Fe–N/CNFs prepared using 0.5 wt% Fe(NO₃)₃ solution showed relatively higher ORR activity in alkaline and acid solutions and better stability especially in 0.5 M H₂SO₄ solution than the catalyst without Fe, probably because Fe could promote the graphitization of the polymer-converted carbon species, enhancing the resistance to electrochemical oxidation and thus the stability of the Fe–N/CNF catalysts.     

Polycarbonate carbon nanofiber composites

Carbon nanofiber (CNF) composites have the potential for creating inexpensive, semiconducting polymers. These composites require a homogeneous dispersion within the polymer. Many groups have focused on high shear methods such as twin screw extrusion. Although high shear methods produce a homogeneous dispersion, the aspect ratio of the nanofibers is reduced by the mechanical force. In this report, we present results for low shear composite formation via in situ polymerization of cyclic oligomeric carbonates. The composites were characterized by thermal gravimetric analysis, electrical conductivity, scanning electron microscopy and transmission electron microscopy. The composites exhibit minimal aggregation of the carbon nanofibers even at high weight percents. The polycarbonate/CNF composites exhibit an electrical conductivity percolation threshold of 6.3 wt% which is higher compared with similar CNF composites. The composites also show an increase in thermal stability of 40 °C as the CNF loading increases from 0 to 9 wt%.     

Thermal characterization and electrical properties of Fe-modified cellulose long fibers and micro crystalline cellulose

Thermal properties of polylactic acid (PLA) filled with Fe-modified cellulose long fibers (CLF) and microcrystalline cellulose (MCC) were studied using thermo gravimetric analysis (TG), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The Fe-modified CLFs and MCCs were compared with unmodified samples to study the effect of modification with Fe on electrical conductivity. Results from TG showed that the degradation temperature was higher for all composites when compared to the pure PLA and that the PLA composites filled with unmodified celluloses resulted in the best thermal stability. No comparable difference was found in glass transition temperature (T _g) and melting temperature (T _m) between pure PLA and Fe-modified and unmodified CLF- and MCC-based PLA biocomposites. DMA results showed that the storage modulus in glassy state was increased for the biocomposites when compared to pure PLA. The results obtained from a femtostat showed that electrical conductivity of Fe-modified CLF and MCC samples were higher than that of unmodified samples, thus indicating that the prepared biocomposites have potential uses where conductive biopolymers are needed. These modified fibers can also be tailored for fiber orientation in a matrix when subjected to a magnetic field.