Supra-molecular ecobionanocomposites based on polylactide and cellulosic nanowhiskers: synthesis and properties

Successful filler dispersion and establishment of good interfacial contact with the surrounding matrix are essential for optimized reinforcement in polymeric nanocomposites. In particular, in renewable-based composites this can be challenging, where hydrophilic attractions between nanofillers facilitate aggregation. Here an innovative approach to prepare cellulosic nanowhisker (CNW) reinforced polylactide (PLA) is presented. The lactide ring-opening polymerization is initiated from CNW surface hydroxyl groups after partial acetylation to control the grafting density. Grafting of PLA chains is verified by Fourier transform infrared spectroscopy. The resulting nanocomposites display exceptional properties; a heat distortion temperature of 120 °C is achieved at 10 wt % CNW loading and can be further enhanced to reach 150 °C at 15 wt % CNW. The formation of a percolating network is verified by comparison of modulus data with an established theoretical model. Additionally, nucleation by CNWs reduces the crystallization half-time to 15 s compared with 90 s for PLA. Melt-pressed films retain transparency indicating good filler dispersion.     

Injectable nanocomposites of single-walled carbon nanotubes and biodegradable polymers for bone tissue engineering

We have investigated the dispersion of single-walled carbon nanotubes (SWNTs) and functionalized SWNTs (F-SWNTs) in the unsaturated, biodegradable polymer poly(propylene fumarate) (PPF) and examined the rheological properties of un-cross-linked nanocomposite formulations as well as the electrical and mechanical properties of cross-linked nanocomposites. F-SWNTs were produced from individual SWNTs by a diazonium-based method and dispersed better than unmodified SWNTs in both un-cross-linked and cross-linked PPF matrix. Cross-linked nanocomposites with F-SWNTs were superior to those with unmodified SWNTs in terms of their mechanical properties. Specifically, nanocomposites with 0.1 wt % F-SWNTs loading resulted in a 3-fold increase in both compressive modulus and flexural modulus and a 2-fold increase in both compressive offset yield strength and flexural strength when compared to pure PPF networks, whereas the use of 0.1 wt % SWNTs gained less than 37% mechanical reinforcement. These extraordinary mechanical enhancements considered together with Raman scattering and sol fraction measurements indicate strong SWNT-PPF interactions and increased cross-linking densities resulting in effective load transfer. With enhanced mechanical properties and capabilities of in situ injection and cross-linking, these SWNT/polymer nanocomposites hold significant implications for the fabrication of bone tissue engineering scaffolds.     

Preparation and properties of banana fiber-reinforced composites based on high density polyethylene (HDPE)/Nylon-6 blends

Banana fiber (BaF)-filled composites based on high density polyethylene (HDPE)/Nylon-6 blends were prepared via a two-step extrusion method. Maleic anhydride grafted styrene/ethylene–butylene/styrene triblock polymer (SEBS-g-MA) and maleic anhydride grafted polyethylene (PE-g-MA) were used to enhance impact performance and interfacial bonding between BaF and the resins. Mechanical, crystallization/melting, thermal stability, water absorption, and morphological properties of the composites were investigated. In the presence of SEBS-g-MA, better strengths and moduli were found for HDPE/Nylon-6 based composites compared with corresponding HDPE based composites. At a fixed weight ratio of PE-g-MA to BaF, an increase of BaF loading up to 48.2 wt.% led to a continuous improvement in moduli and flexural strength of final composites, while impact toughness was lowered gradually. Predicted tensile modulus by the Hones–Paul model for three-dimensional random fiber orientation agreed well with experimental data at the BaF loading of 29.3 wt.%. However, the randomly-oriented fiber models underestimated experimental data at higher fiber levels. It was found that the presence of SEBS-g-MA had a positive influence on reinforcing effect of the Nylon-6 component in the composites. Thermal analysis results showed that fractionated crystallization of the Nylon-6 component in the composites was induced by the addition of both SEBS-g-MA and PE-g-MA. Thermal stability of both composite systems differed slightly, except an additional decomposition peak related to the minor Nylon-6 for the composites from the HDPE/Nylon-6 blends. In the presence of SEBS-g-MA, the addition of Nylon-6 and increased BaF loading level led to an increase in the water absorption value of the composites.     

Nanoreinforcement of poly(propylene fumarate)-based networks with surface modified alumoxane nanoparticles for bone tissue engineering

A novel composite material has been fabricated for bone tissue engineering scaffolds utilizing the biodegradable polymer poly(propylene fumarate)/poly(propylene fumarate)-diacrylate (PPF/PPF-DA) and surface-modified carboxylate alumoxane nanoparticles. Various surface-modified nanoparticles were added to the polymer including a surfactant alumoxane, an activated alumoxane, a mixed alumoxane containing both activated and surfactant groups, and a hybrid alumoxane containing both groups within the same substituent. These nanocomposites, as well as polymer resin and unmodified boehmite composites, underwent flexural and compressive mechanical testing and were examined using electron microscopy. Hybrid alumoxane nanoparticles dispersed in PPF/PPF-DA exhibited over a 3-fold increase in flexural modulus at 1 wt % loading compared to polymer resin alone. No significant loss of flexural or compressive strength was observed with increased loading of hybrid alumoxane nanoparticles. These dramatic improvements in flexural properties may be attributed to the fine dispersion of nanoparticles into the polymer and increased covalent interaction between polymer chains and surface modifications of nanoparticles.     

Novel biobased nanocomposites from soybean oil and functionalized organoclay

Novel biobased nanocomposites have been prepared by the cationic polymerization of conjugated soybean oil (CSOY) or conjugated LoSatSoy oil (CLS) with styrene (ST) and divinylbenzene (DVB), and a reactive organomodified montmorillonite (VMMT) clay as a reinforcing phase. This filler has been prepared by the cationic exchange of sodium montmorillonite with (4-vinylbenzyl)triethylammonium chloride in aqueous solution. The nanostructures of the nanocomposites have been determined by using wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM), respectively. The results from WAXD and TEM indicate that a heterogeneous structure consisting of intercalation and partial exfoliation or an intercalation structure exists in the nanocomposites, depending on the amount of VMMT in the polymer matrix. The thermal, mechanical, and organic vapor barrier properties of the nanocomposites have been evaluated by dynamic thermal analysis, thermogravimetric analysis, mechanical testing, and toluene absorption. A significant improvement is observed in the thermal stability, the dynamic bending storage modulus, the compressive modulus, the compressive strength, the compressive strain at failure, and the vapor barrier performance for the CSOY-- and CLS-based nanocomposites with 1-2 wt % VMMT loading, where some individual exfoliated silicate platelets occur. For example, the CLS-based nanocomposite with 1-2 wt % VMMT exhibits increases of 100-128%, 86-92%, and 5-7% in compressive modulus, compressive strength, and compressive strain at failure, respectively. CLS with higher unsaturation and reactivity affords nanocomposites with higher thermal stability and higher mechanical properties than CSOY.     

Thermal properties and flammability of polylactide nanocomposites with aluminum trihydrate and organoclay

Biodegradable polylactide (PLA) nanocomposites with aluminum trihydrate (ATH) and modified montmorillonite (MMT) were prepared via direct melt compounding using a twin-screw micro extruder. The exfoliated and intercalated structures of clay in the matrix were observed by TEM and XRD. The thermal oxidative degradation temperature and activation energy of the PLA/ATH/MMT nanocomposite determined by thermogravimetric analysis are higher than that without addition of ATH and organoclay. The incorporation of layered silicates into the PLA/ATH composite results in further stabilization throughout the degradation step. The V-0 rating (UL94 V) of the PLA nanocomposite has been achieved, and the melt dripping was reduced during combustion. Results showed that high loading of the conventional flame retardant ATH yielded brittle PLA composites; however, replacing a portion of the ATH with modified MMT in the PLA matrix improved this result.     

"Green" nanocomposites from cellulose acetate bioplastic and clay: effect of eco-friendly triethyl citrate plasticizer

"Green" nanocomposites have been successfully fabricated from cellulose acetate (CA) powder, eco-friendly triethyl citrate (TEC) plasticizer and organically modified clay. The effect of the amount of plasticizer varying from 15 to 40 wt % on the performance of the nanocomposites has been evaluated. The morphologies of these nanocomposites were evaluated through X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) studies. The mechanical properties of nanocomposites are correlated with the XRD and TEM observations. Cellulosic plastic-based nanocomposites with 20 wt % TEC plasticizer and 5 wt % organoclay showed better intercalation and an exfoliated structure than the counterpart having 30/40 wt % plasticizers. The tensile strength, modulus and thermal stability of cellulosic plastic reinforced with organoclay showed a decreasing trend with an increase of plasticizer content from 20 to 40 wt %. The nano-reinforcement at the lower volume fractions (phi < or = 0.02) reduced the water vapor permeability of cellulosic plastic by 2 times and the relative permeability better fits with larger platelet aspect ratios (alpha = 150).     

Obtaining of new magnetic nanocomposites based on modified polysaccharide

The study presents the preparation of some composite materials with magnetic properties by two different encapsulation methods of magnetite (Fe₃O₄) in a polymer matrix based on carboxymethyl starch-g-polylactic acid (CMS-g-PLA). The copolymer matrix used to obtain the magnetic nanocomposites was synthesized by grafting reaction of carboxymethyl starch (CMS) with d,l-lactic acid (DLLA), in the presence of Sn octanoate [Sn(Oct)₂] as catalyst. Magnetite was obtained by co-precipitation from aqueous salt solutions FeCl₂/FeCl₃ (molar ratio 1/2). The magnetic composites were prepared by precipitation method in acetone (non-solvent) of the DMSO solutions of magnetite and copolymer, and synthesis in situ of the nanocomposites. In the first case, the particle size measured by DLS-technique was 168 nm, and the magnetization was 46.82 emu/g, while after in situ synthesis, the composite materials showed smaller size (141 nm), but the magnetization was reduced (3.04 emu/g). The higher magnetization in the first case is due to the great degree of encapsulation of the magnetite, which was about 43.4 wt.%, compared to 4.37 wt.% for the in situ synthesis (determined by thermogravimetry). The CMS-g-PLA copolymer, magnetite, and the nanocomposites were characterized by infrared spectroscopy (FTIR), near infrared chemical imagistic (NIR-CI), dynamic light scattering (DLS) technique, X-ray diffraction (WAXD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and thermal analyses. Since the polymer matrix and magnetite are biodegradable and biocompatible, the magnetic nanocomposites can be used for conjugation of some drugs. The polymer matrix CMS-g-PLA acts as a shell, and vehicle for the active component, whereas magnetite is the component which makes targeting possible by external magnetic field manipulation.     

Morphology and properties of soy protein isolate thermoplastics reinforced with chitin whiskers

Environmentally friendly thermoplastic nanocomposites were successfully developed using a colloidal suspension of chitin whiskers as a filler to reinforce soy protein isolate (SPI) plastics. The chitin whiskers, having lengths of 500 +/- 50 nm and diameters of 50 +/- 10 nm on average, were prepared from commercial chitin by acid hydrolysis. The dependence of morphology and properties on the chitin whiskers content in the range from 0 to 30 wt % for the glycerol plasticized SPI nanocomposites was investigated by dynamic mechanical thermal analysis, scanning electron microscopy, swelling experiment, and tensile testing. The results indicate that the strong interactions between fillers and between the filler and SPI matrix play an important role in reinforcing the composites without interfering with their biodegradability. The SPI/chitin whisker nanocomposites at 43% relative humidity increased in both tensile strength and Young's modulus from 3.3 MPa for the SPI sheet to 8.4 MPa and from 26 MPa for the SPI sheet to 158 MPa, respectively. Further, incorporating chitin whisker into the SPI matrix leads to an improvement in water resistance for the SPI based nanocomposites.     

A glucose biosensor based on TiO(2)-Graphene composite

A novel glucose biosensor was developed based on the adsorption of glucose oxidase at a TiO(2)-Graphene (GR) nanocomposite electrode. A TiO(2)-GR composite was synthesized from a colloidal mixture of TiO(2) nanparticles and graphene oxide (GO) nanosheets by an aerosol assisted self-assembly (AASA). The particle morphology of all TiO(2)-GR composites was spherical in shape. It was observed that micron-sized TiO(2) particles were encapsulated by GR nanosheets and that the degree of encapsulation was proportional to the ratio of GO/TiO(2). The amperometric response of the glucose biosensor fabricated by the TiO(2)-GR composite was linear against a concentration of glucose ranging from 0 to 8mM at -0.6V. The highest sensitivity was noted at about 6.2μA/mMcm(2). The as prepared glucose biosensor based on the TiO(2)-GR composite showed higher catalytic performance for glucose redox than a pure TiO(2) and GR biosensor.     

Fibrous cellulose nanocomposite scaffolds prepared by partial dissolution for potential use as ligament or tendon substitutes

Fibrous cellulose nanocomposites scaffolds were developed and evaluated for their potential as ligament or tendon substitute. The nanocomposites were prepared by partial dissolution of cellulose nanofiber networks using ionic liquid at 80 °C for different time intervals. Scanning electron microscopy study indicated that partial dissolution resulted in fibrous cellulose nanocomposites where the dissolved cellulose nanofibers formed the matrix phase and the undissolved or partially dissolved nanofibers formed the reinforcing phase. Mechanical properties of the composites in simulated body conditions (37 °C and 95% RH) after sterilization using gamma rays was comparable to those of natural ligaments and tendons. Stress relaxation studies showed stable performance towards cyclic loading and unloading, further confirming the possibility for using these composites as ligament/tendon substitute. In vitro biocompatibility showed a positive response concerning adhesion/proliferation and differentiation for both human ligament and endothelial cells. Prototypes based on the cellulose composite were developed in the form of tubules to be used for further studies.     

Photoelectrocatalytic treatment of pentachlorophenol in aqueous solution using a rutile nanotube-like TiO2/Ti electrode.

Taking pentachlorophenol (PCP) as a reference, we investigated the photoelectrocatalytic degradation of organic pollutants using a rutile nanotube-like TiO(2)/Ti film electrode. The nanotube-like TiO2 electrode was prepared by first oxidizing the surface of a titanium sheet to form rutile TiO2 and then treating it to form the tubular structure in NaOH aqueous solution. The occurrence of PCP degradation was indicated by the decrease in pH, concentration of PCP and TOC, and by the formation of chloride ions. The photoelectrochemical (PEC) efficiency of the nanotube-like TiO2/Ti electrode has been determined in terms of degradation of PCP and the incident photo-to-current conversion efficiency (IPCE). The experimental results showed that PCP could be degraded more efficiently by a photoelectrocatalytic process than by a photocatalytic or electrochemical oxidation alone. A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using a nanotube-like TiO2 electrode was over 60% higher than that using a TiO2 film electrode. It is noted that chloride ion and hydrogen ion concentration increased with irradiation time in the PEC degradation of PCP; PCP was gradually mineralized and the complete minimization of PCP took more time than its degradation.     

New intercalated layer silicate nanocomposites based on synthesized starch-g-PCL prepared via solution intercalation and in situ polymerization methods: As a comparative study

Starch-g-polycaprolacton (Starch-g-PCL) nanocomposites have been prepared with graft polymerization through in situ ring-opening polymerization of ε-caprolacton in the presence of starch and Sn(Oct)₂ (Tin(II) 2-ethyl hexanoate) as an initiator/catalyst. A surface-modified montmorillonite by dimethyl (hydrogenated tallow alkyl) ammonium cation, was used. In fact, the related nanocomposites prepared via two methods in solution and in situ with introducing different amount of loading clay. The effect of swelling time on d-spacing of silicate layers was investigated and the obtained nanocomposites were analyzed using X-ray diffraction technique. The morphology of the synthesized nanocomposites examined using Scanning Electron Microscopy (SEM) and also the thermal degradation behavior of the prepared nanocomposites accomplished with using TGA.     

Optimisation of the Photonic Efficiency of TiO2 Decorated on MWCNTs for Methylene Blue Photodegradation

MWCNTs/TiO₂ nanocomposite was prepared by oxidising MWCNT in H₂SO₄/HNO₃ then decorating it with TiO₂-p25 nanopowder. The composites were characterised using XRD, TEM, FT-IR PL and UV−vis spectroscopy. The TEM images have shown TiO₂ nanoparticles immobilised onto the sidewalls of the MWCNTs. The UV-vis spectrum confirms that the nanocomposites can significantly absorb more light in the visible regions compared with the commercial TiO₂ (P25). The catalytic activity of these nanocomposites was determined by photooxidation of MB aqueous solution in the presence of visible light. The MWCNTs/TiO₂ (1:3) mass ratio showed maximum degradation efficiency. However, its activity was more favourable in alkaline and a neutral pH than an acidic medium.     

Preparation and mechanical properties of chitosan/carbon nanotubes composites

Biopolymer chitosan/multiwalled carbon nanotubes (MWNTs) nanocomposites have been successfully prepared by a simple solution-evaporation method. The morphology and mechanical properties of the chitosan/MWNTs nanocomposites have been characterized with field emission scanning electron microscopy (SEM), bright field transmission electron microscopy (TEM), optical microscopy (OM), wide-angle X-ray diffraction (XRD), and tensile as well as nanoindentation tests. The MWNTs were observed to be homogeneously dispersed throughout the chitosan matrix. When compared with neat chitosan, the mechanical properties, including the tensile modulus and strength, of the nanocomposites are greatly improved by about 93% and 99%, respectively, with incorporation of only 0.8 wt % of MWNTs into the chitosan matrix.     

Photocatalytic disinfection of Giardia intestinalis and Acanthamoeba castellani cysts in water

In this study, disinfection of water containing Giardia intestinalis and Acanthamoeba castellani cysts with TiO2 and modified catalyst silver loaded TiO2 (Ag-TiO2) was investigated. Destruction of the parasites was evaluated after UV illumination of the suspension consisting 5 x 10(8)-13.5 x 10(8)cysts/mL in the presence of 2g/L neat or modified TiO2 at neutral pH. In the initial stage, the solid photocatalyst particles penetrated the cyst wall and then oxidant species produced by TiO2/UV destroyed both cell wall and intracellular structure. In the case of G. intestinalis inactivation (disinfection) performance of TiO2/UV system reached 52.5% only after 25 min illumination and total parasite disinfection was achieved after 30 min illumination. However, silver loaded TiO2 seemed to be more effective as this loading provided better catalytic action as well as additional antimicrobial properties. Cell viability tests showed that parasite cysts, their walls in particular, were irreversibly damaged and cysts did not re-grow. Nevertheless the studied system seemed to be ineffective for the inactivation of A. castellani. Inactivation percentages of TiO2/UV and Ag-TiO2/UV systems were far lower than that of UV alone, being 50.1% and 46.1%, respectively.     

Biological control of the size and reactivity of catalytic Pd(0) produced by Shewanella oneidensis

The interaction between Shewanella oneidensis MR-1 and the soluble metal Pd(II) during the reductive precipitation of Pd(0) determined the size and properties of the precipitated Pd(0) nanoparticles. Assessment of cell viability indicated that the bioreduction of Pd(II) was a detoxification mechanism depending on the Pd(II) concentration and on the presence and properties of the electron donor. The addition of H₂ in the headspace allowed S. oneidensis to resist the toxic effects of Pd(II). Interestingly, 25 mM formate was a less effective electron donor for bioreductive detoxification of Pd(II), since there was a 2 log reduction of culturable cells and a 20% decrease of viable cells within 60 min, followed by a slow recovery. When the ratio of Pd:cell dry weight (CDW) was below 5:2 at a concentration of 50 mg l⁻¹ Pd(II), most of the cells remained viable. These viable cells precipitated Pd(0) crystals over a relatively larger bacterial surface area and had a particle area that was up to 100 times smaller when compared to Pd(0) crystals formed on non-viable biomass (Pd:CDW ratio of 5:2). The relatively large and densely covering Pd(0) crystals on non-viable biomass exhibited high catalytic reactivity towards hydrophobic molecules such as polychlorinated biphenyls, while the smaller and more dispersed nanocrystals on a viable bacterial carrier exhibited high catalytic reactivity towards the reductive degradation of the anionic pollutant perchlorate.     

Physico-mechanical properties of chemically treated palm and coir fiber reinforced polypropylene composites

In this work, palm and coir fiber reinforced polypropylene bio-composites were manufactured using a single extruder and injection molding machine. Raw palm and coir were chemically treated with benzene diazonium salt to increase their compatibility with the polypropylene matrix. Both raw and treated palm and coir fiber at five level of fiber loading (15, 20, 25, 30 and 35 wt.%) was utilized during composite manufacturing. Microstructural analysis and mechanical tests were conducted. Comparison has been made between the properties of the palm and coir fiber composites. Treated fiber reinforced specimens yielded better mechanical properties compared to the raw composites, while coir fiber composites had better mechanical properties than palm fiber ones. Based on fiber loading, 30% fiber reinforced composites had the optimum set of mechanical properties.     

Toward "strong" green nanocomposites: polyvinyl alcohol reinforced with extremely oriented cellulose whiskers

To exploit the maximum potential of cellulose whiskers (CWs), we report here for the first time the successful fabrication of nanocomposites reinforced with highly oriented CWs in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a colloidal suspension of cotton-derived CWs. The macroscopically homogeneous PVA-CW suspensions were extruded into cold methanol to form gel fibers followed by a hot drawing. Compared to the neat PVA fiber, the as-spun fiber containing a small amount of CWs (5 wt % of solid PVA) showed higher drawability, leading to an extremely high orientation of CWs with the matrix PVA. The stress-transfer mechanism, a prime determining factor for high mechanical properties of nanocomposites, was studied by X-ray diffraction. The stress on the incorporated CWs was monitored by applying an in situ nondestructive load to the composite fibers. The applied stress to the whole sample was found to be effectively transferred to the CWs inside the composites, suggesting strong interfacial bonding between the filler and the matrix. Effective stress transfer to the oriented whiskers resulted in outstanding enhancement in mechanical properties of the nanocomposites.     

Chromate reduction by immobilized palladized sulfate-reducing bacteria

Resting cells of Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans NCIMB 8307 were used for the hydrogenase-mediated reduction of Pd(II) to Pd(0). The resulting hybrid palladium bionanocatalyst (Bio-Pd(0)) was used in the reduction of Cr(VI) to the less environmentally problematic Cr(III) species. The reduction of Cr(VI) by free and agar-immobilized Bio-Pd(0) was evaluated. Investigations using catalyst suspensions showed that Cr(VI) reduction was similar ( approximately 170 nmol Cr(VI)/h/mg Bio-Pd(0)) when Bio-Pd(0) was produced using D. vulgaris or D. desulfuricans. Continuous-flow studies using D. vulgaris Bio-Pd(0) with agar as the immobilization matrix investigated the effect of Bio-Pd(0) loading, inlet Cr(VI) concentration, and flow rate on the efficiency of Cr(VI) reduction. Reduction of Cr(VI) was highest at a D. vulgaris Bio-Pd(0) loading of 7.5 mg Bio-Pd(0)/mL agar (3:1 dry cell wt: Pd(0)), an input [Cr(VI)] of 100 microM, and a flow rate of 1.75 mL/h (approx. 3.5 column volumes/h). A mathematical interpretation predicted the activity of the immobilized Bio-Pd(0) for a given set of conditions within 5% of the value found by experiment. Considering the system as an 'artificial enzyme' analog and application of applied enzyme kinetics gave an apparent K(m) value (K(m app)) of 430 microM Cr(VI) and a determined value of flow-through reactor activity which differed by 11% from that predicted mathematically.