Frank Bauer

Trialkoxysilane grafting onto nanoparticles for the preparation of clear coat polyacrylate systems with excellent scratch performance

Transparent reinforced polyacrylates were prepared using nanosized filler particles with radiation-curable acrylates. To improve embedding of the nanofillers within the acrylate matrix the filler surface was chemically modified. This modification of the silica and alumina nanoparticles was accomplished by trimethoxysilanes having methacryloxypropyl (MEMO), vinyl (VTMO), and n-propyl (PTMO) functionalities. Due to acid catalyzed condensation of organosilanes a polysiloxane shell was formed around the nanoparticles. This shell is bonded to OH groups on the filler surface. The appearance of covalent Si–O–Si–R bonds was clearly shown by multinuclear MAS NMR. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with different degrees of condensation. In the work presented, an acrylate-nanocomposite formulation contains up to 35 wt.% nanosized silica covered with polysiloxanes. For MEMO modification, surface-anchored methacryl groups can copolymerize with network acrylates. But also PTMO-modified composite materials exhibit markedly improved properties as compared to the neat acrylate polymer; e.g., an increased modulus and heat resistance, improved scratch and abrasion resistance. This makes polyacrylate nanocomposites a very promising new coating technology for many far reaching technical applications.

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 1 FTIR and multi‐nuclear NMR spectroscopy to the characterization of methacryl grafting

Nano-sized silica and alumina particles were used as fillers for polymer reinforcement and scratch resistant coatings. For favorable embedding within the polyacrylate matrix the surface of the fillers was chemically modified by reaction with methacroyloxy (propyl)-trimethoxysilane. The formation of covalent Si(Al)-O-Si-C bonds between functional groups from silane and OH groups on silica and alumina was demonstrated by means of FTIR and MAS NMR spectroscopy. The reactivity of the various surface silanols towards the coupling agent and the yield of surface Si-O-Si bonds were estimated by 29 Si CP MAS NMR data.

Preparation of Scratch and Abrasion Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 3. Effect of Filler Particles and Grafting Agents

After modification with different trialkoxysilanes, nano-sized silica and alumina particles were used as fillers in transparent UV/EB curable acrylates for polymer reinforcement, particularly to attain scratch and abrasion resistant coatings. The acid catalyzed condensation of the organosilanes forms a polysiloxane shell which covers the nanoparticle like a nanocapsule. CP MAS NMR spectroscopy and MALDI-TOF mass spectrometry proved to be useful for the characterization of the polysiloxane structures. Grafter oligomers with more than 20 monomeric units were observed. Nanoparticles modified by methacroyloxy(propyl)trimethoxysilane and vinyltri-methoxysilane can copolymerize with acrylates. Compared with the pure polymers, these crosslinked polyacrylate nanocomposites, containing up to 35 wt.-% silica, exhibit markedly improved surface mechanical properties. Promising scratch and abrasion resistance of radiation-cured nanocomposite materials were also obtained by propyltrimethoxysilane grafting which results in an organo-philation of pyrogenic silica. Both colloidal and pyrogenic nano-sized silica nanopowders were used as fillers in polyacrylate films. The concentration of colloidal SiO 2 in commercial acrylate formulations amounts up to 50 wt.-%, whereas pyrogenic silica, notwhithstanding their surface modification by silanes, results in a thickening effect which limits its content to about 35 wt.-%. Never-theless, a comparison showed a distinct improvement in the surface mechanical properties such as haze and diamond microscratch hardness for surface-modified pyrogenic silica.

Preparation of scratch and abrasion resistant polymeric nanocomposites by monomer grafting onto nanoparticles, 2 Characterization of radiation‐cured polymeric nanocomposites

By in situ grafting methacroyloxy functionalized-silanes on commercial nanoglobular silica polymerization-active silico-organic nanoparticles were prepared. In radiation (UV, EB) induced polymerization reactions these modified nanoparticles form covalent crosslinks to acrylate substrates, thus efficiently modifying their viscoelastic properties. The transparent nanopowder composites can be used as scratch resistants coatings. The composite films show excellent adhesion on PC and PVC and good abrasion resistance after the Taber abraser test with haze values of about 6% after 500 cycles.

Improvement of coke-induced selectivation of H-ZSM-5 during xylene isomerization

Abstract An improvement of coke-induced selectivation was achieved by an additional thermal treatment of the pre-coked H-ZSM-5 catalysts with hydrogen or alkanes. By means of the conventional pre-coking procedure using methanol as coke precursor, a sample containing only a small amount of carbonaceous deposits (≈0.3 wt.%) is effective in reducing the undesirable transalkylation products during xylene isomerization. However, upon additional post-treatment by propane, the modified H-ZSM-5 catalyst exhibited a lower xylene loss (≈1.1%) while maintaining a reasonable activity for ethylbenzene conversion (≈55%), as compared to that pre-coked with the xylene feed under high severity conditions.

Surface modification of nanoparticles for radiation curable acrylate clear coatings

Abstract To obtain transparent, scratch and abrasion resistant coatings a high content of nanosized silica and alumina filler was embedded in radiation-curable acrylate formulations by acid catalyzed silylation using trialkoxysilanes. 29SiMAS NMR and MALDI-TOF mass spectrometry were employed to elucidate the structure of the surface-grafted methacryloxypropyl-, vinyl- and n-propyl-trimethoxysilane. In accordance with NMR findings, MALDI-TOF MS showed highly condensed oligomeric siloxanes of more than 20 monomeric silane units. A ladder-like structure of bound polysiloxanes is proposed rather than a simplified picture of tridentate silane bonding. Hence, silane coupling agents do not only modify the chemical nature of the filler surface but also strongly effect the rheological properties of the acrylate nanodispersions.

Characterization of mesoporous materials by vibrational spectroscopic techniques

Abstract Vibrational spectroscopic techniques (i.e. infrared, Raman-spectroscopy and inelastic neutron scattering) are employed for the characterization of the wall structure and the nature of active sites in ordered mesoporous MCM-41 materials. Supported by nitrogen physisorption measurements our results provide unambiguous evidence for the destruction of mesoporous pore structures under a pressure usually used for the preparation of wafers for transmission IR spectroscopy. Avoiding pressure treatment of the samples, vibrational spectroscopic studies are suited to yield information about the effects of isomorphous substitution and calcination on the framework structure of mesoporous materials. The utilization of 18 O isotope labelling and N -methylpyrrolidine adsorption revealed the heterogeneity of hydroxyl groups in MCM-41 materials.

TG-FTIR and isotopic studies on coke formation during the MTG process

Abstract The removal of carbonaceous deposits formed during the conversion of methanol to hydrocarbons on zeolite H-ZSM-5 was investigated in a thermobalance system coupled with an IR spectrometer. Using different carrier gases, the effect of thermal treatment increased in the order helium

Hydroisomerization of long-chain paraffins over nano-sized bimetallic Pt–Pd/H-beta catalysts

The hydroisomerization of long-chain n-paraffins was studied in the temperature range of 205–230 °C at pH2 = 50 bar using a pilot-scale trickle-bed continuous-flow reactor over bimetallic catalysts consisting of mixtures of platinum and palladium supported on commercially available nano-sized zeolite beta (nSi/nAl = 12.5 and 25, respectively) extruded with an alumina binder. For n-hexadecane conversion, high yields of isomers (25 and 45 wt.% of mono- and multibranched isomers, respectively) without extensive cracking (>10 wt.%) were obtained at a conversion of 80%. Long-term tests with n-hexadecane and blends of solid n-paraffins for 30–60 days on-stream clearly indicate that a minor loss in catalyst activity can easily be compensated for by increasing the reaction temperature from 220 °C to 225 °C. The zeolite with a “mild acidity” exhibits a low hydrocracking activity with isomerization yields of up to 70 wt.% and high stability over more than 60 days on-stream. Carbonaceous deposits formed during n-paraffin hydroisomerization were investigated by elemental analysis, TGA, ATR-FTIR and 13C MAS NMR spectroscopy, showing the formation of hydrogen-rich coke which leads to pore blocking.

Radiation-cured polymeric nanocomposites of enhanced surface-mechanical properties

Though polymerisation-active metallo-organic nanoparticles have proven exceedingly efficient in modifying the viscoelastic properties of UV and EB crosslinked polymeric nanocomposites, they are obviously unsuitable for practical applications. Rather, adequate polymerisation-activity was imparted on inorganic nanoparticles, e.g. silica and alumina, by grafting onto them functionalised trialkoxysilanes, yielding covalent-bonded, hydrolysis-stable surface compounds. Extensive spectroscopic studies of their siloxane structure led to the idea of a core-shell nanocapsule. The polysiloxane shell formed around the inorganic nanoparticle is not only of major importance to the rheological behaviour of the nanodispersion but, moreover, also admits a sufficiently high nanofiller content for a pronounced reinforcement of the nanocomposite coating. In recent work, organophilation of the inorganic nanoparticles could be accomplished by just applying adsorptive means, thus evading the formation of the precarious alcohols and alkyl acrylates. In the event, round milled corundum micro-particles turned out to be efficient synergists in further improving the respective coatings.