Bismuth Phosphinates in Bi-Nanocellulose Composites and their Efficacy towards Multi-Drug Resistant Bacteria.

A series of poorly soluble phenyl bis-phosphinato bismuth(III) complexes [BiPh(OP(=O)R1 R2 )2 ] (R1 =R2 =Ph; R1 =R2 =p-OMePh; R1 =R2 =m-NO2 Ph; R1 =Ph, R2 =H; R1 =R2 =Me) have been synthesised and characterised, and shown to have effective antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The bismuth complexes were incorporated into microfibrillated (nano-) cellulose generating a bismuth-cellulose composite as paper sheets. Antibacterial evaluation indicates that the Bi-cellulose materials have analogous or greater activity against Gram positive bacteria when compared with commercial silver based additives: silver sulfadiazine loaded at 0.43 wt % into nanocellulose produces a 10 mm zone of inhibition on the surface of agar plates containing S. aureus whereas [BiPh(OP(=O)Ph2 )2 ] loaded at 0.34 wt % produces an 18 mm zone of inhibition. These phenyl bis-phosphinato bismuth(III) complexes show potential to be applied in materials in healthcare facilities, to inhibit the growth of bacteria capable of causing serious disease.

Polyamide-amine-epichlorohydrin (PAE) induced TiO2 nanoparticles assembly in cellulose network.

HYPOTHESIS: TiO2-NPs-Cellulose composites functionality depends on the retention and dispersion of NPs in the composites. SAXS and SEM can be combined to reveal the effect PAE has on the NPs aggregation, retention and interaction mechanisms in the composites. EXPERIMENTS: TiO2-NPs-Cellulose sheets were made by first preparing PAE-cellulose suspensions of different PAE dosages (10 and 50 mg of PAE/g fibres). The TiO2 NPs suspension (at different NPs loading) was then added to the cellulose-PAE suspension. The final suspension was used to make flexible paper-like composites sheets. SEM and SAXS quantified NPs retention and aggregation state. FINDINGS: PAE dosage of 20 mg/g cellulose provides full surface coverage of cellulose fibres. A 10 mg of PAE/g cellulose covers half the cellulose surface area and no free PAE remains in the suspension. PAE dosage of 50 mg/g cellulose gives full cellulose surface coverage and provides a large amount of PAE (30 mg/g cellulose) free in the suspension. Surprisingly, at both PAE dosages, NP coagulates and the size of the aggregates increase with NPs loading. Aggregates of two particle sizes (10 and 35 nm) are formed and the number density of smaller particles is higher than larger particle. The NPs aggregates and their retention are similar at both PAE dosages, which is explained by different PAE-NPs bridging mechanisms.

Novel In-situ Precipitation Process to Engineer Low Permeability Porous Composite.

Inspired by the natural precipitation of minerals in soil and rocks, a novel, simple and industrially scalable in-situ precipitation process to produce low permeability porous composites is presented. This process relies on capillary flow in wettable porous composites to absorb and store liquid. In this process, a porous composite first absorbs a salt solution, after which the composite is dipped in a second salt solution. Salts are selected such as they react to form an insoluble precipitate. As big pores absorb more liquid than small pores, the precipitated particles are formed specifically for each pore. In this paper, precipitation of CaCO3 nanoparticles in cellulose nanofibre (CNF) films was demonstrated as an example. Precipitation of 1 wt% of CaCO3 nanoparticles in the CNF film reduced the pore volume by 50%, without changing the density. This reduced the water vapour and oxygen transmission rates by one order of magnitude to 4.7 g/m2.day and 2.7 cc/m2.day, respectively. The barrier properties of in-situ precipitated composites showed superior performance to previously reported CNF films in literature. The concept is general and of very high industrial interest as it can easily be retrofitted to current continuous industrial processes.

Effect of nanoparticles size and polyelectrolyte on nanoparticles aggregation in a cellulose fibrous matrix.

Controlling nanoparticles (NPs) aggregation in cellulose/NPs composites allows to optimise NPs driven properties and their applications. Polyelectrolytes are used to control NPs aggregation and their retention within the fibrous matrix. Here, we aim at evaluating how a polyelectrolyte (Cationic Polyacrylamide; CPAM, molecular weight: 13MDa, charge: 50%, Radius of gyration: 30-36nm) adsorbs and re-conforms onto the surface of silica(SiO2) NPs differing in diameter (8, 22 and 74nm) and to investigate the respective NPs aggregation in cellulose matrices. SEM shows the local area distribution of NPs in composites. Ultra-SAXS (USAXS) allows to evaluate the average NPs size distribution and the inter-particle interactions at length scale ranging from 1 to 1000nm. USAXS data analysis reveals that CPAM covers multiple NPs of the smaller diameter (8nm), presumably with a single chain to form large size NPs aggregates. As the NPs diameter is increased to 22nm, CPAM re-conforms over NP surface forming a large shell of thickness 5.5nm. For the composites with NPs of diameter 74nm, the CPAM chain re-conforms further onto NP surface and the surrounding shell thickness decreases to 2.2nm. Structure factor analysis reveals higher structural ordering for NPs as increases their diameter, which is caused by different conformations adopted by CPAM onto NPs surface.

Water Resistant Cellulose - Titanium Dioxide Composites for Photocatalysis.

Novel water resistant photocatalytic composites of microfibrillated cellulose (MFC)-polyamide-amine-epichlorohydrin (PAE)-TiO2 nanoparticles (NPs) were prepared by a simple two-step mixing process. The composites produced are flexible, uniform, reproducible and reusable; they can readily be removed from the pollutant once used. Small amount of TiO2 NPs are required for the loaded composites to exhibit a remarkable photocatalytic activity which is quantified here as achieving at least 95% of methyl orange degradation under 150 min of UV light irradiation for the composite with best combination. The cellulose network combined with PAE strongly retains NPs and hinders their release in the environment. PAE dosage (10 and 50 mg/g MFC) controls the NP retention in the cellulose fibrous matrix. As TiO2 content increases, the photocatalytic activity of the composites levels off to a constant; this is reached at 2wt% TiO2 NPs for 10 mg/g PAE and 20wt% for 50 mg/g PAE. SEM and SAXS analysis confirms the uniform distribution of NPs and their formation of aggregates in the cellulose fibre network. These economical and water resistant photocatalytic paper composites made by a simple, robust and easily scalable process are ideal for applications such as waste water treatment where efficiency, reusability and recyclability are important.

Cationic polyacrylamide induced nanoparticles assembly in a cellulose nanofiber network.

Polyacrylamides of different molecular weight, charges and dosages allow to control the retention and distribution of nanoparticles (NPs) in composites, and optimise composite properties and functionality. Our aim is to evaluate the effect of high molecular weight (13 MDa) cationic polyacrylamide (CPAM) charge and dosage on SiO2 (74 nm) NP's assembly in cellulose nanofibers composites. Engineered cellulose/SiO2 composites were investigated by SEM, SAXS and DLS. SEM images show the local area retention of NPs into the cellulose matrix. SAXS provides an average NPs distribution and inter-NPs distance over complete volume of composite. DLS gives the hydrodynamic radius of CPAM adsorbed onto SiO2 NPs in a suspension. SAXS analysis reveals a structure conformation made of spherical SiO2 NPs core of diameter 74 nm surrounded by a CPAM polyelectrolyte shell 2.5 nm thick. Surprisingly, CPAM induced assembly of SiO2 NPs with constant inter-nanoparticle distance, which is irrelevant of polymer charge density. However, NPs retention in the cellulose fibre network increases with CPAM dosage. The assembly mechanism is governed by the balance of electrostatic and steric forces following CPAM coverage onto NPs and the inter-nanoparticle CPAM bridging conformation. This maintains the constant inter-nanoparticle distance and the assembly of NPs in the cellulose network.