Surface chemical functionalization of cellulose nanocrystals by 3-aminopropyltriethoxysilane.

Surface functionalization of cellulose nanocrystals (CNCs) is valuable option to tailor properties as well as increase opportunities for their application. In this study, the surface of CNCs was functionalized with 3-aminopropyltriethoxysilane (APTES), without using hazardous solvents and by a direct, simple and straightforward method. APTES was firstly hydrolyzed in water and then adsorbed onto CNC through hydrogen bonds, finally the chain hydrocarbon was covalently linked to the surface of CNC through SiOC bonds which formed via the condensation reaction between hydroxyl and silanol groups. The chemical modification of the CNCs surface was confirmed by ATR-IR and NMR spectroscopy. Experiments conducted by AFM and XRD showed no significant change in the CNC dimensions and crystalline structure as a result of the modification. The EDX and XPS results confirmed the exsistence of APTES onto the CNCs. Silylated CNC exhibited good thermal stability and a greater amount of residual char was formed at 500 °C compared to non-chemically modified CNC. Thus, The silylation of CNCs may offer applications in composite manufacturing, where these nanoparticles have limited dispersibility in hydrophobic polymer matrices, and as nano-adsorbers due to the presence of amino groups attached on the surface.

Branched poly(ethyleneimine): a versatile scaffold for patterning polymer brushes by means of remote photocatalytic lithography.

Patterning of functional surfaces is one of the cornerstones of nanotechnology as it allows the fabrication of sensors and lab-on-a-chip devices. Here, the patterning of self-assembled monolayers of branched poly(ethyleneimine) (bPEI) on silica was achieved by means of remote photocatalytic lithography. Moreover, when 2-bromoisobutyryl-modified bPEI was used, the resulting pattern could be amplified by grafting polymer brushes by means of surface-initiated atom transfer radical polymerization. In contrast to previous reports for the patterning of bPEI, the present approach can be conducted in minutes instead of hours, reducing the exposure time to UV radiation and enhancing the overall efficiency. Furthermore, our approach is much more user-friendly, allowing a facile fabrication of patterned initiator-modified surfaces and the use of inexpensive instrumentation such as a low-power UV source and a simple photomask. Considering the versatility of bPEI as a scaffold for the development of biosensors, patterning by means of remote photocatalytic lithography will open new opportunities in a broad field of applications.

Ammoxidized Fenton-Activated Pine Kraft Lignin Accelerates Synthesis and Curing of Resole Resins.

Ammoxidation of pine kraft lignin in aqueous 5 wt % ammonia affords a novel type of phenol substitute that significantly accelerates resole synthesis and curing as demonstrated for 40 wt % phenol replacement. Compared to non-ammoxidized lignin, which already shortens significantly the cooking time required to reach a resole viscosity of 1000 Pa·s (250 vs. 150 s) and reduces the typical curing B-time by about 25% at 100 °C, the use of ammoxidized lignin has an even more pronounced impact in this respect. Activation of lignin by Fenton-type oxidation prior to ammoxidation further boosts both synthesis and curing of the resole. This is presumably due to the intermediary formation of polyvalent cross-linkers like N,N,N-tris (methylol) trimethylene triamine triggered by saponification of a larger fraction of nitrogenous moieties present in such a treated lignin (ammonium salts, amide-type nitrogen, urea) and reaction of the released ammonia with formaldehyde. Except for the fact that phenol replacement by ammoxidized lignin results in a somewhat less brittle cured adhesive polymer and higher elastic modulus, the aforementioned acceleration in curing could no longer be observed in the presence of wood, where a significantly delayed wood-adhesive bond formation was observed for the lignin-containing adhesives as evident from the automated bonding evaluation system.

Exploring Network Formation of Tough and Biocompatible Thiol-yne Based Photopolymers.

This work deals with the in-depth investigation of thiol-yne based network formation and its effect on thermomechanical properties and impact strength. The results show that the bifunctional alkyne monomer di(but-1-yne-4-yl)carbonate (DBC) provides significantly lower cytotoxicity than the comparable acrylate, 1,4-butanediol diacrylate (BDA). Real-time near infrared photorheology measurements reveal that gel formation is shifted to higher conversions for DBC/thiol resins leading to lower shrinkage stress and higher overall monomer conversion than BDA. Glass transition temperature (Tg ), shrinkage stress, as well as network density determined by double quantum solid state NMR, increase proportionally with the thiol functionality. Most importantly, highly cross-linked DBC/dipentaerythritol hexa(3-mercaptopropionate) networks (Tg ≈ 61 °C) provide a 5.3 times higher impact strength than BDA, which is explained by the unique network homogeneity of thiol-yne photopolymers.

Lignocellulose Nanofiber-Reinforced Polystyrene Produced from Composite Microspheres Obtained in Suspension Polymerization Shows Superior Mechanical Performance.

A facile approach to obtaining cellulose nanofiber-reinforced polystyrene with greatly improved mechanical performance compared to unreinforced polystyrene is presented. Cellulose nanofibers were obtained by mechanical fibrillation of partially delignified wood (MFLC) and compared to nanofibers obtained from bleached pulp. Residual hemicellulose and lignin imparted amphiphilic surface chemical character to MFLC, which enabled the stabilization of emulsions of styrene in water. Upon suspension polymerization of styrene from the emulsion, polystyrene microspheres coated in MFLC were obtained. When processed into polymer sheets by hot-pressing, improved bending strength and superior impact toughness was observed for the polystyrene-MFLC composite compared to the un-reinforced polystyrene.

Microfibrillated Lignocellulose Enables the Suspension-Polymerisation of Unsaturated Polyester Resin for Novel Composite Applications.

A new route towards embedding fibrillated cellulose in a non-polar thermoset matrix without any use of organic solvent or chemical surface modification is presented. It is shown that microfibrillated lignocellulose made from cellulose with high residual lignin content is capable of stabilising an emulsion of unsaturated polyester resin in water due to its amphiphilic surface-chemical character. Upon polymerisation of the resin, thermoset microspheres embedded in a microfibrillated cellulose network are formed. The porous network structure persists after conventional drying in an oven, yielding a mechanically stable porous material. In an application experiment, the porous material was milled into a fine powder and added to the polyester matrix of a glass fibre-reinforced composite. This resulted in a significant improvement in fracture toughness of the composite, whereas a reduction of bending strength and stiffness was observed in parallel.

Microwave-Assisted Syntheses in Recyclable Ionic Liquids: Photoresists Based on Renewable Resources.

The copoly(2-oxazoline) pNonOx80 -stat-pDc(=) Ox20 can be synthesized from the cationic ring-opening copolymerization of 2-nonyl-2-oxazoline NonOx and 2-dec-9'-enyl-2-oxazoline Dc(=) Ox in the ionic liquid n-hexyl methylimidazolium tetrafluoroborate under microwave irradiation in 250 g/batch quantities. The polymer precipitates upon cooling, enabling easy recovery of the polymer and the ionic liquid. Both monomers can be obtained from fatty acids from renewable resources. pNonOx80 -stat-pDc(=) Ox20 can be used as polymer in a photoresist (resolution of 1 µm) based on UV-induced thiol-ene reactions.

Versatile thiol-based reactions for micrometer- and nanometer-scale photopatterning of polymers and biomolecules.

Thiol-based chemistry provides a mild and versatile tool for surface functionalization. In the present work, mercaptosilane films were patterned by utilizing UV-induced photo-oxidation of the thiol to yield sulfonate groups via contact and interferometric lithography (IL). These photo-generated sulfonic acid groups were used for selective immobilization of amino-functionalized molecules after activation with triphenylphosphine ditriflate (TPPDF). Moreover, protein-resistant poly(oligoethyleneglycolmethacrylate) (POEGMA) brushes were grown from the intact thiol groups by a surface-induced polymerization reaction. Exploiting both reactions it is possible to couple amino-labelled nitrilotriacetic acid (NH2-NTA) to sulfonate-functionalized regions, enabling the site-specific binding of green fluorescent protein (GFP) to regions defined lithographically, while exploiting the protein-resistant character of POEGMA brushes to prevent non-specific protein adsorption to previously masked areas. The outstanding reactivity of thiol groups paves the way towards novel strategies for the fabrication of complex protein nanopatterns beyond thiol-ene chemistry.

Ex situ and in situ characterization of patterned photoreactive thin organic surface layers using friction force microscopy.

Photolithographic methods allow an easy lateral top-down patterning and tuning of surface properties with photoreactive molecules and polymers. Employing friction force microscopy (FFM), we present here different FFM-based methods that enable the characterization of several photoreactive thin organic surface layers. First, three ex situ methods have been evaluated for the identification of irradiated and non-irradiated zones on the same organosilane sample by irradiation through different types of masks. These approaches are further extended to a time dependent ex situ FFM measurement, which allows to study the irradiation time dependent evolution of the resulting friction forces by sequential irradiation through differently sized masks in crossed geometry. Finally, a newly designed in situ FFM measurement, which uses a commercial bar-shaped cantilever itself as a noncontact shadow mask, enables the determination of time dependent effects on the surface modification during the photoreaction.

Water-developable poly(2-oxazoline)-based negative photoresists.

Copoly(2-oxazoline)-based photoresists are prepared from pEtOx(80) Bu(=) Ox(20) and pPhOx(80) Dc(=) Ox(20) , respectively, a tetrathiol, and a photosensitive initiator. It is possible to prepare copoly(2-oxazoline)s bearing unsaturated side chains in a microwave reactor on a decagram scale in reaction times of 100 min or shorter. UV irradiation of dried polymer films through a quartz mask induces the thiol-ene reaction in the illuminated areas. Subsequent development of the polymer films in halogen-free solvents reproduces the negative pattern of the mask with a resolution of 2 µm. The pEtOx(80) Bu(=) Ox(20) -derived photoresists can also be developed in water.

Reversible photochromism of polynorbornenes bearing spiropyran side groups.

ABSTRACT: In this paper, the synthesis and characterization of poly(norbornene) homo- and copolymers bearing spiropyran side groups are described. Difficulties in the homopolymerization of spiropyrans due to the opened merocyanine form were observed leading to low polymerization yields for homopolymers while copolymers with 10 mol% spiropyran content were prepared in good yield. Spiropyrans are characterized by their reversible photochromism, which was conserved in the polymers as shown by UV-Vis spectroscopy and FT-IR spectroscopy. The switching between the apolar spiropyran form and the zwitterionic merocyanine form also leads to switchable wettability as evidenced by contact angle measurements.