Sol–gel coating of cellulose fibres with antimicrobial and repellent properties

Multifunctional, water and oil repellent and antimicrobial finishes for cotton fibres were prepared from a commercially available fluoroalkylfunctional water-born siloxane (FAS) (Degussa), nanosized silver (Ag) (CHT) and a reactive organic–inorganic binder (RB) (CHT). Two different application procedures were used: firstly, one stage treatment of cotton fabric samples by FAS sol (i), as well as by a sol mixture constituted from all three precursors (Ag–RB–FAS, procedure 1S) (ii), and secondly, two stage treatment of cotton by Ag–RB sol and than by FAS sol (Ag–RB + FAS, procedure 2S) (iii). The hydrophobic and oleophobic properties of cotton fabrics treated by procedures (i)–(iii) before and after consecutive (up to 10) washings were established from contact angle measurements (water, diiodomethane and n-hexadecane) and correlated with infrared and XPS spectroscopic measurements. The results revealed that even after 10 washing cycles cotton treated with Ag–RB + FAS (2S) retained an oleophobicity similar to that of the FAS treated cotton, while the Ag–RB–FAS (1S) cotton fibres exhibited a loss of oleophobicity already after the second washing, even though fluorine and C–F vibrational bands were detected in the corresponding XPS and IR spectra. The antibacterial activity of cotton treated by procedures (i)–(iii) was tested by its reduction of the bacteria Escherichia coli and Staphylococcus aureus following the AATCC 100-1999 standard method and EN ISO 20743:2007 transfer method. The reduction in growth of both bacteria was nearly complete for the unwashed Ag–RB and Ag–RB–FAS (S1), but for the unwashed Ag–RB + FAS (S2) treated cotton no reduction of S. aureus and 43.5 ± 6.9% reduction of E. coli was noted. After the first washing, the latter two finishes exhibited nearly a complete reduction of E. coli but for the Ag–RB treated cotton the reduction dropped to 88.9 ± 3.4. None of the finishes retained antibacterial properties after 10 repetitive washings. The beneficial and long-lasting low surface energy effect of FAS finishes in the absence of Ag nanoparticles, which led to the “passive” antibacterial properties of FAS treated cotton fabrics, was established by applying the EN ISO 20743:2007 transfer method. The results revealed a reduction in bacteria of about 21.9 ± 5.7% (FAS), 13.1 ± 4.8% (Ag–RB–FAS (S1)) and 41.5 ± 3.7% (Ag–Rb + FAS (S2)), while no reduction of the growth of bacteria was observed for cotton treated with Ag nanoparticles after 10 repetitive washings. The physical properties (bending rigidity, breaking strength, air permeability) of finished cotton samples were determined, and showed increased fabric softness and flexibility as compared to the Ag–RB treated cotton, but a slight decrease of breaking strength in the warp and weft directions, while air permeability decreased for all type of finishes.     

Synthesis and thermal stability of a novel phosphorus-nitrogen containing intumescent flame retardant

A novel phosphorus-nitrogen containing intumescent flame retardant （P-N IFR） was prepared via the reaction of dichlor-opentate with N-methylaniline. The structure of the product was confirmed by ^1H NMR, ^31p NMR, MS and IR. TGA analysis showed it has effective thermal stability.     

Novel multifunctional water- and oil-repellent,antibacterial, and flame-retardant cellulose fibres created by the sol–gel process

This research aimed to prepare cotton fibres with novel multifunctional water- and oil-repellent, antibacterial, and flame-retardant properties. A three-component equimolar sol mixture, which included 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride, and P,P-diphenyl-N-(3-(trimethoxysilyl)propyl) phosphinic amide, was applied to the cotton fabric using the sol–gel process. The presence of the coating on the cotton fibres was confirmed by Fourier transform-infrared spectroscopy and X-ray photoelectron spectroscopy. The functional properties of the coated cotton fabric were determined from liquid contact angle measurements and antibacterial activity, burning behaviour, and thermo-oxidative stability studies. The results demonstrate that a unique, compatible, and uniform organic-inorganic hybrid polymer network was formed on the fabric surface, which preserved its simultaneous hydrophobic (water contact angle of 135 ± 2°), oleophobic (n-hexadecane contact angle of 117 ± 1°), and bactericidal (bacterial reduction of 100 %) properties and incorporated the enhanced thermo-oxidative stability of the modified cellulose fibres.     

Thermal and flame retardant properties of epoxy resin cured by a novel phosphorus-containing 4,4′-bisphenol novolac curing agent

A novel flame retardant curing agent for epoxy resin (EP), i.e., a DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing 4,4'-bisphenol novolac (BIP-DOPO) was synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, ³¹P NMR spectroscopy, and gel permeation chromatography. The epoxy resin cured by BIP-DOPO itself or its mixture with a commonly used bisphenol A-formaldehyde novolac resin (NPEH720) was prepared. The flame retardancy of the cured EP thermosets were studied by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT), and the thermal properties by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the cured epoxy resin EPNP/BI/3/1, which contains 2.2% phosphorus, possesses a value of 26.2% and achieves the UL 94 V-0 rating. The data from cone calorimeter test demonstrated that the peak release rate, average heat release rate, total heat release decline sharply for the flame retarded epoxy resins, compared with those of pure ones. DSC results show that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA indicates that the incorporation of BIP-DOPO promotes the decomposition of epoxy resin matrix ahead of time and leads to higher char yield. The surface morphological structures of the char residues reveal that the introduction of BIP-DOPO benefits to the formation of a continuous and solid char layer on the epoxy resin material surface during combustion.     

Synergistic flame retardant effect of melamine in ethylene–vinyl acetate/layered double hydroxides composites

Mg–Al–Fe ternary layered double hydroxides (LDHs) were synthesized based on Bayer red mud by a calcination–rehydration method, and characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TG). The synergistic effects between melamine and LDHs in ethylene–vinyl acetate (EVA) composites were studied using limiting oxygen index (LOI), UL 94, cone calorimeter test (CCT), smoke density test (SDT), and thermogravimetry–fourier transform infrared spectrometry (TG–IR). Though melamine decreases the LOI values of EVA/LDHs/melamine composites, a suitable amount of melamine can apparently improve UL 94 rating; the composite with 45 % LDHs and 5 % melamine can pass UL 94 test. The CCTs results indicate that heat release rates (HRR) of EVA/LDHs/melamine composites decreased in comparison with that of EVA/LDHs composites. The SDT results show that melamine is helpful to smoke suppression. The TG–IR data show that the ternary composites have a higher thermal stability than that of the binary composites.     

Modification of cellulose fibres with organosilanes: Under what conditions does coupling occur?

Different cellulose substrates and organosolv lignin were treated heterogeneously with organic solutions of trialkoxysilanes bearing variable function on the forth substituent. It was shown unambiguously for the first time that Si-OR does not react with the hydroxy groups of cellulose even at high temperature, whereas it condenses with the phenolic OH of lignin. The addition of moisture to these systems induces the partial hydrolysis of the siloxane moieties and the ensuing silanol groups can then react with the cellulose OH, but only at high temperature. Using the latter systems and a siloxane bearing a polymerizable function, it was possible to attach poly(methylmethacrylate) chains to the surface of cellulose fibres through a two-step procedure.     

Multifunctional superhydrophobic/oleophobic and flame-retardant cellulose fibres with improved ice-releasing properties and passive antibacterial activity prepared via the sol–gel method

In this research, a two-component sol–gel inorganic–organic hybrid coating was prepared on a cotton fibre surface. An equimolar sol mixture of the precursors 1H,1H,2H,2H-perfluorooctyltriethoxysilane (SiF) and P,P-diphenyl-N-(3-(trimethoxysilyl)propyl) phosphinic amide (SiP) was applied to cotton fabric samples using the pad-dry-cure method. The surfaces of the untreated and coated cotton fibres were characterised using scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight-secondary ion mass spectrometry. The functional properties of the coated cotton fabric samples were investigated using static contact angle measurements with water and n-hexadecane, the ice-releasing test, antibacterial testing against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, thermogravimetric analysis in an air atmosphere, and vertical flammability tests. The results reveal the formation of a nanocomposite two-component inorganic–organic hybrid polymer network that is homogenously distributed over the cotton fibre surface. The presence of the SiP component in the two-component inorganic–organic hybrid coating did not hinder the functional properties imparted by the presence of the SiF component and vice versa, illustrating their compatibility. The cooperative action of the SiF and SiP components in the two-component coating provided the cotton fabric with exceptional multifunctionality, including simultaneous superhydrophobicity and high oleophobicity, passive antibacterial activity, and improved thermo-oxidative stability.     

Steady-shear and viscoelastic properties of cellulose nanofibril–nanoclay dispersions

We have investigated the steady-shear and viscoelastic properties of composite dispersions of cellulose nanofibrils (CNFs) with medium or high charge density and two different nanoclays, viz. rod-like sepiolite or plate-like bentonite. Aqueous dispersions of CNFs with medium charge density displayed significantly lower steady-state viscosity and storage modulus but higher gelation threshold compared with CNFs with high charge density. Dynamic light scattering (DLS) results showed that the apparent hydrodynamic radius of bentonite particles increased when CNFs were added, implying that CNFs adsorbed onto the amphoteric edges of the plate-like bentonite particles. The sepiolite network in CNF–sepiolite dispersions was relatively unaffected by addition of small amounts of CNFs, and DLS showed that the hydrodynamic radius of sepiolite did not change when CNFs were added. Addition of CNFs at concentrations above the gelation threshold resulted in drastic decrease of the steady-shear viscosity of the sepiolite dispersion, suggesting that the sepiolite network disintegrates and the rod-like clay particles are aligned also at low shear rate. The relative change in the rheological properties of the clay-based dispersions was always greater on addition of CNFs with high compared with medium charge density. This study provides insight into how the rheology of CNF–nanoclay dispersions depends on both the nanoclay morphology and the interactions between the nanoclay and nanocellulose particles, being of relevance to processing of nanocellulose–clay composites.     

Hydrophobic modification of cellulose fibres by cationic-modified polyacrylate latex with core–shell structure

In cellulose fibre-based green packaging, the poor resistance or barrier against water or water vapour has remained as one of the key challenges. In this work, cationic polymer latex, butyl acrylate-co-styrene/2-ethylhexylacrylate-co-methyl methacrylate (BA-co-St/EHA-co-MMA), with core–shell structure was especially synthesized and used as a wet-end additive to render the fibre or paper hydrophobic. TEM observation confirmed that the latex particles obtained indeed possessed desired characteristic of core–shell structure. The experimental results showed that the cationic polymer was especially suitable for use in papermaking processes due to its high retention with cellulose fibres. The surface modification of the natural fibre by the adsorption of cationic latex on the fibre surfaces potentially created the thin films of polymers on fibre surfaces. The resulting paper is highly hydrophobic with improved barrier property, as demonstrated by the high contact angles and relatively low WVTR value. Moreover, the mechanical properties of paper were maintained or even improved in the presence of an appropriate level of the latex.     

Synthesis of functionalized α-zirconium phosphate modified with intumescent flame retardant and its application in poly(lactic acid)

A novel functionalized α-zirconium phosphate (F-ZrP) modified with intumescent flame retardant was synthesized by co-precipitation method and characterized. Poly (lactic acid) (PLA)/F-ZrP nanocomposites were prepared by melt blending method. The thermal stability and combustion behavior of PLA/F-ZrP nanocomposites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL-94), scanning electronic microscopy (SEM), and cone calorimeter test (CCT). The results showed that the addition of flame retardant F-ZrP slightly affect PLA's thermal stability, but significantly improve the flame retardancy of PLA composites. In comparison with neat PLA, the LOI value of PLA/F-ZrP was increased from 19.0 to 26.5, and the UL-94 rating was enhanced to V-0 as the loading of F-ZrP at 10%. SEM results suggested the introduction of F-ZrP in the PLA system can form compact intumescent char layer during burning. All these results showed that the F-ZrP performed good flame retardancy for PLA.     

Enhancing the effectiveness of a laccase–TEMPO treatment has a biorefining effect on sisal cellulose fibres

Enhancing the effectiveness of a laccase–TEMPO treatment on sisal pulp by increasing pulp consistency was for the first time found to increase the biorefining potential of this enzyme–mediator system. The operating conditions used were those previously found to maximize oxidative functionalization and paper strength. Prior to the enzyme treatment, the pulp was refined at a variable intensity (0, 3,000 and 4,500 revolutions) in order to ascertain whether the increased surface area would lead to enhanced functionalization and boost the refining effect as a result. Increasing pulp consistency increased the contents in aldehyde and carboxyl groups by 130% and 94%, respectively. Also, it resulted in more marked reduction of pulp viscosity during the enzyme treatment, especially at a high refining intensity; this had a detrimental effect on fibre strength and significantly reduced tear strength in the refined pulp. Oxidized pulp exhibited a considerably increased water retention value with respect to the initial pulp, particularly after refining. Dry tensile index was increased by 21, 18 and 12%, and burst index by 23, 16 and 13% at 0, 3,000 and 4,500 rev, respectively, by the laccase–TEMPO treatment as a result of increased inter-fibre hydrogen bonding offsetting the loss of fibre strength, an effect that can provide substantial savings in refining energy. Based on the results, a laccase–TEMPO treatment is an enzymatic booster of mechanical refining with the added advantages of providing unaltered drainability and increased air permeability. The most salient effect of the laccase–TEMPO treatment was an increase in wet tensile strength (by 160, 553 and 588% at 0, 3,000 and 4,500 rev, respectively) that can be ascribed to inter-fibre covalent bonding through hemiacetal linkages promoted by aldehyde groups. The improvement was much greater than that obtained at a lower consistency under identical conditions.     

Preparation and characterization of a water resistance flame retardant and its enhancement on charring–forming for polycarbonate

Hexakis(4-nitrophenoxy) cyclotriphosphazene (HNTP) was synthesized and was added into polycarbonate (PC) functioned as intumescent flame retardant and charring agent. The chemical structure of HNTP was confirmed by hydrogen and phosphorus nuclear magnetic resonance (¹H-NMR, ³¹P-NMR), energy-dispersive spectroscopy and Fourier transform infrared (FTIR). Flame retardancy and charring–forming behaviors of HNTP- and PC-based composites were extensively investigated with the limiting oxygen index, UL-94 vertical burning test, microscale combustion calorimeter (MCC) and thermogravimetric analysis. The water resistance of PC-based composites was studied by stationary water contact angle measurements. Furthermore, TG/FTIR was used to research their gaseous products and their releasing intensity during the decomposition. The morphology and chemical structure of residual char were used to study scanning electron microscopy (SEM) analyses and FTIR spectroscopy. The mechanical properties of samples were compared by tensile and impact tests.     

Synthesis, characterization and antibacterial properties of multifunctional hindered amine light stabilizers

A series of novel hindered amine light stabilizers containing an N-halamine moiety were designed and synthesized. Their structures were characterized by FT-IR, 1H NMR, and MS. The compounds were tested for antibacterial activity against Candida albicans, Staphylococcus aureus, and Escherichia coll. At a concentration of 0.5 mmol/L, these compounds all exhibited satisfactory antibacterial activity against all the three types of bacteria.     

Preparation of 2CaO·3B2O3·H2O nanomaterials and evaluation of their flame retardant properties by a thermal analysis method

Different morphologies of calcium borate 2CaO·3B₂O₃·H₂O, nanoribbon, bundle-like nanostructure and fan-shaped non-nanostructure, have been prepared under hydrothermal conditions, which were characterized by XRD, FT-IR, TGA and SEM. Their flame retardant properties to the polypropylene were investigated by thermal analysis method (including TG, DSC and non-isothermal decomposition kinetics) and oxygen index method. With the decrease in TG mass loss, the increase in heat absorption for DSC in N₂ atmosphere, the increase in LOI values, and the increase in apparent activation energy E_a, the flame retardant properties of prepared 2CaO·3B₂O₃·H₂O samples increased gradually from non-nanostructure to bundle-like nanostructure and then to nanoribbon. This trend may be ascribed to their sizes being decreased accordingly. The flame retarding mechanism has been proposed. The mechanical property of polypropylene/2CaO·3B₂O₃·H₂O composite material has also been evaluated. It can be predicted that 2CaO·3B₂O₃·H₂O nanoribbon could serve as an excellent flame retardant.

     

How does the never-dried state influence the swelling and dissolution of cellulose fibres in aqueous solvent?

The swelling and dissolution capacity of dried and never-dried hardwood and softwood pulps and cotton linters was compared in two aqueous solvents, N-methylmorpholine-N-oxide (NMMO)-water at 90 °C with water contents ranging from 16 to 22% and NaOH—water at −6 °C with NaOH contents ranging from 5 to 8%. Swelling and dissolution mechanisms were observed by optical microscopy and dissolution efficiency was evaluated by recovering insoluble fractions. The results show a contrasted picture towards the effect of the never-dried state on the swelling and the dissolution capacity depending on the origin of the fibres and the type of aqueous solvent. In the case of NMMO—water, the presence of water within and around the fibre does not seem to favour dissolution initiation but after 2 h of mixing the dissolution yield appears to be similar for either dried or never-dried state. The limiting factor for dissolution in NMMO—water is not the penetration of the solvent inside the cellulose fibres, but only the local concentration of NMMO molecules around the fibre. For NaOH—water, both optical microscopy observations on individual fibres and dissolution yield measurements show that the never-dried state is more reactive for softwood pulps and cotton linters and has no significant effect on hardwood pulps. In this case, the local decrease of solvent strength is counteracted by the opening of the structure in the never-dried state which should enable the Na⁺ hydrated ions to penetrate easier.     

Disintegration of periodate–chlorite oxidized hardwood pulp fibres to cellulose microfibrils: kinetics and charge threshold

Periodate–chlorite oxidized bleached hardwood kraft pulp fibre samples with six levels of charge densities ranging from 0.5 to 1.8 mmol/g were gradually disintegrated to microfibrils using a high-shear homogenizer. The disintegration kinetics and mechanisms were studied by a flow fractionation method, and the properties of the resulting particles were determined using low shear viscosity and transmittance measurements. The particles formed during the disintegration were visualized with a charge-coupled device camera and by field-emission scanning electron microscopy. The result showed that cellulose fibres with a low charge density disintegrated at a low rate and produced ragged fibres and bunches of microfibrils via bursting of the fibre walls, whereas those with a higher charge density broke down at a high rate and microfibrils were formed through swelling and the creation of balloon structures. A carboxyl content of 1.2 mmol/g was found to be the threshold value for the efficient formation of high aspect ratio microfibrils and also for the change in the disintegration mechanism in the high-shear homogenizer.     

Effect of a magnetic field on the rheological properties of the systems hydroxypropyl cellulose–ethanol and hydroxypropyl cellulose–dimethyl sulfoxide

With the use of viscometry, the cloud-point method, polarization microscopy, the turbidity-spectrum method, and a polarization photoelectric apparatus, the relaxation pattern of the rheological behaviors, phase transitions, and structures of the systems hydroxypropyl cellulose–ethanol and hydroxypropyl cellulose–dimethyl sulfoxide are studied. The regions of existence of isotropic and anisotropic phases and the concentration dependence of the sizes of supramolecular particles are determined. It is found that a magnetic field increases the viscosities of solutions. The concentration dependences of viscosity and particle size are described by curves with maxima.