TY - THES A1 - Shabir Mahr, Muhammad T1 - Wood modification with titania and silica based precursors - a novel approach to prepare multifunctional sol-gel derived TiO2 / SiO2 wood-inorganic composites N2 - This dissertation is devoted to explicitly investigate the suitability of titania and silica based precursors for wood modification. Novel TiO2 / SiO2 wood inorganic composites were prepared by two-step process. In first step, freshly prepared precursor solutions of silicon and titanium alkoxides were vacuum impregnated (one or more cycles) to oven dried pine sapwood (Pinius sylvestris L.). Precursor solutions with nano-scaled species and particulates (TiO2 and SiO2) were soaked by the entire wood matrix during this step. In (second) subsequent curing step, these penetrating liquids transformed into respective gel layers and depositions therein by sol-gel processing (in-situ hydrolysis-condensation). Sol-gel based depositions were evenly covered on the cell walls in the form of thin layers. These gel films were not crack-free however; very few cracks were visible in the gel coatings present within the wood matrix of composites prepared with precursors of low alkoxide content. In addition, the gels were randomly distributed, found to be mainly deposited in the wood cell lumen and also localized in the cell walls as ESEM-EDX mapping revealed. The impregnated samples show an increase in mass and volume expressed as weight percent gain (WPG) and bulking (B). Both of the parameters are decisive for tailoring a number of physical properties of the resultant composites. In general, moisture and water sorption capacities were decreased by 43 to 50 % while anti-swelling efficiency (ASE) and bending strength (MOE) of the precursor-modified wood (composite) were increased up to 34 % and 41 % respectively, when compared to unmodified wood. These improvements are attributed mainly to gel depositions in the wood structure that physically interact with the wood matrix consequently narrowing the main flow passages there and reinforcing strengths of the fiber. These materials show superior resistance against fire of different scenarios. In small scale fire, their flame was retarded markedly (up to 78 % in optimum case) in comparison to wood controls as studied by oxygen index test (LOI). Cone calorimetric investigations revealed their better fire retardancy in terms of time resolved heat release rates (HRR) in the developing fire scenario. A remarkable reduction of 40 % in the second peak of HRR was achieved through sol-gel treatment. Furthermore, fire hazards such as CO and total smoke production were considerably lowered for these materials. Beside these improvements, reductions in first peak HRR and in fire load (total heat evolved) were not worth considering in compliance to fire retardancy principles. In relation to the mechanism of protection, it can be concluded that stable gel layer (independence of material loading) inside the wood retards markedly the proceeding combustion processes (oxidation) after first pyrolysis by improving the overall protection properties of the fire residue. These materials show excellent resistance against bio-deterioration. Almost full decay protection was achieved against wood destroying brown rot fungi (Coniophora puteana and Poria placenta) in 10 weeks laboratory trials only with 1 mass% loadings (WPG). Mass loss in prolonged test (16 weeks) was similar to 10 week lasted test indicating that protection is permanent. In addition, composites imparted moderate resistances against soft rot fungi and very minor one against surface blue stain. The lowering in moisture content that discourages fungal colonization, gel layer that provides better shielding against fungal exposure and un-hydrolyzed alkoxides (organics) that probably induce biocidal effects are the main reasons for protection against biological attack in these materials. Composites are utmost leach resistant because of the insolubility of gel depositions in water as well as due to their fixture into the wood matrix. In addition to this intrinsic property, gel precipitates can also reduce substantially (70 to 80 %) the release of hazardous active agents (e.g. CuCl2) of wood preservatives into the environment. This anti-leaching effect is supposed to be due to the reduced ion mobility of active agents inside the wood by their encapsulations into the gel matrix, lowering of water penetration into the wood depths as well as due to the internal covering action of the gel layer. In short, it can be assessed that TiO2 / SiO2 based sol-gel precursor treatment of wood has a possibility to be commercialize in near future due to easy handling and non-toxic nature of the precursor used. Resultant end products (composites) are also novel and promising multifunctional materials that can be used for multi-purposes in relation to use class 3 (outdoor but without ground contact according to EN 335 2006) environments. KW - Precursor solutions KW - Sol-gel process KW - Gel depositions KW - Wood modification KW - Composite materials KW - Fire retardancy KW - Cone calorimeter KW - Flammability KW - Anti-fungal efficacy KW - Brown rot fungi KW - Soft rot fungi KW - Leach resistance PY - 2013 SN - 978-3-95404-570-9 SP - 1 EP - 110 PB - Cuvillier CY - Göttingen AN - OPUS4-29988 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Hübert, Thomas A1 - Mahr, Muhammad Shabir ED - Klein, Lisa ED - Aparicio, Mario ED - Jitianu, Andrei T1 - Sol-Gel wood preservation N2 - The sol–gel-based modification of wood introduces chemical substances into wood in order to improve its characteristics and impart new properties. It stabilizes dimensions of wood (timber) components, increases its strength and resistance to water, and reduces cracking. Many sol–gel-based impregnations aim to protect against wood rot and fire. In most cases, the treatments are performed with alkoxysilanes, polysiloxanes, colloidal silica, or organically modified silica. In addition further substances such as titania, copper, and boron compounds have been applied on different types of wood. The precursor solutions were introduced by immersion, painting, or spray coating of wood followed by a drying and heat treatment process. The structure of the impregnated wood was investigated by SEM, EDX, TEM, FT-IR, NMR, and XRD. Frequently, test procedures according to standards were applied in order to assess the improvement in properties. Investigations demonstrate that silica and titania impregnations change properties first of all with increasing the amount of absorbed inorganic material (WPG), which is determined by the concentration of precursors, amount and size of particles in the sol, and the impregnation method. Sol–gel impregnation can be considered as an environmentally friendly approach of wood preservation. Various improvements in wood properties can be achieved such as reduced water uptake and volume swelling, improved weather stability, resistance against biodegradation, and fire retardancy. KW - Titania KW - Sol-Gel KW - Wood Protection KW - Silica PY - 2017 SN - 978-3-319-32099-1 DO - https://doi.org/10.1007/978-3-319-19454-7_106-2 SP - 1 EP - 48 PB - Springer AN - OPUS4-41095 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shabir Mahr, Muhammad A1 - Hübert, Thomas A1 - Sabel, Martin A1 - Schartel, Bernhard A1 - Bahr, Horst A1 - Militz, H. T1 - Fire retardancy of sol-gel derived titania wood-inorganic composites N2 - Sol–gel technology was applied in tailoring novel wood-made-inorganic composites with improved thermal and fire properties. In practice, composites materials were prepared by impregnating pine sapwood wood with nano-scaled precursor solutions derived from titanium(IV) isopropoxide followed by a thermal curing process. Thermal and fire properties were evaluated by thermal analysis and cone calorimetry, whereas flammability was specified by oxygen index (LOI) and UL 94 test. Peak heat release rates were moderately reduced indicating fire retardance potential in terms of flame spread attributed to the appropriate protection layer action of the titania-based depositions. LOI (oxygen index) values of these composites were increased up to 38 vol.% in comparison to 23 vol.% for untreated wood. The flame retardancy performance depends on the fire scenario and is strongly influenced by wood loading and crackfree deposition of the titania layers inside the composite. PY - 2012 DO - https://doi.org/10.1007/s10853-012-6628-3 SN - 0022-2461 SN - 1573-4803 VL - 47 IS - 19 SP - 6849 EP - 6861 PB - Springer Science + Business Media B.V. CY - Norwell, Mass. AN - OPUS4-26235 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shabir Mahr, Muhammad A1 - Hübert, Thomas A1 - Schartel, Bernhard A1 - Bahr, Horst A1 - Sabel, Martin A1 - Militz, H. T1 - Fire retardancy effects in single and double layered sol-gel derived TiO2 and SiO2-wood composites N2 - Sol–gel derived TiO2 and SiO2-wood inorganic composites are prepared by direct vacuum infiltration of silicon and titanium alkoxide based precursors in pine sapwood in one or two cycles followed by a controlled thermal curing process. The resulting flame retardancy effect is investigated under two different fire scenarios using cone calorimetry and oxygen index (LOI). Heat release rates (HRR) especially the values for the second peak, are reduced moderately for all single layered composites. This effect is more pronounced for double layered composites where HRR was reduced up to 40 % showing flame retardancy potential in developing fires. Beside this, smoke release was lowered up to 72 % indicating that these systems had less fire hazards compared to untreated wood, whereas no meaningful improvement is realized in terms of fire load (total heat evolved) and initial HRR increase. However impressively, the LOI of the composites were increased up to 41 vol% in comparison to 23 vol% for untreated wood displaying a remarkable flame retardancy against reaction to a small flame. An approximate linear interdependence among the fire properties and the material loading as well as fire residue was observed. A residual protection layer mechanism is proposed improving the residue properties for the investigated composites. KW - Wood KW - Sol-gel KW - Composite materials KW - Cone calorimeter KW - Fire retardance KW - Flammability PY - 2012 DO - https://doi.org/10.1007/s10971-012-2877-5 SN - 0928-0707 SN - 1573-4846 VL - 64 IS - 2 SP - 452 EP - 464 PB - Kluwer Academic Publ. CY - Dordrecht AN - OPUS4-27618 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shabir Mahr, Muhammad A1 - Hübert, Thomas A1 - Stephan, Ina A1 - Militz, H. T1 - Decay protection of wood against brown-rot fungi by titanium alkoxide impregnations N2 - Decay resistance of pine sapwood treated with titanium alkoxide solutions was tested against the brown-rot fungi Coniophora puteana and Poria placenta for exposure times of 10 and 16 wk. In practice, wood-specimens were vacuum-impregnated by alcoholic solutions of titanium alkoxide with concentrations in the range of 5–16 mass % (solid content in solution) and subsequently cured under different humidity conditions. Results reveal that treated wood degraded up to 5% in comparison to untreated one that deteriorated 38% and 50%, respectively against both wood-decay fungi. Even full protection (mass loss below 3%) was achieved against brown rot with titanium alkoxide solution containing solid content of around 5 mass% with a weight percentage gain (WPG) of 9 mass%. With increased concentration, fungal resistance decreased slightly which was associated with more cracks and imperfections formed in the deposited layers of titanium dioxide in the adjacent wood matrix. Thermal analysis verified that a considerable amount of precursor remained in the wood structure as un-hydrolyzed organic residues. These organics, being bioactive, had the tendency to induce similar fungicidal effects as those of conventional fungicides. The amount of organic residues is correlated with the decay resistance of the tested samples. In a prolonged decay test, mass losses of 16-wk incubated samples do not show behavior different from that of the wood samples incubated for 10 wk. This result implies that the decay protection is permanent and confirms further the fungicidal activity of titanium-alkoxide-treated wood. KW - Precursor solutions KW - Sol-gel process KW - Equivalent solid content KW - Brown rot KW - Coniophora puteana KW - Poria placenta KW - Fungal colonization KW - Biocidal effect PY - 2013 DO - https://doi.org/10.1016/j.ibiod.2012.04.026 SN - 0964-8305 VL - 77 SP - 56 EP - 62 PB - Elsevier Ltd. CY - Barking AN - OPUS4-27622 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shabir Mahr, Muhammad A1 - Hübert, Thomas A1 - Stephan, Ina A1 - Bücker, Michael A1 - Militz, H. T1 - Reducing copper leaching from treated wood by sol-gel derived TiO2 and SiO2 depositions N2 - The antileaching efficacy of sol-gel-derived TiO2- and SiO2-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step process, wood was vacuum impregnated by the precursor solutions containing CuCl2. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl2 solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl2-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO2/SiO2 gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu. KW - Copper leachability KW - SiO2-based gel KW - Sol-gel treatment of wood KW - TiO2-based gel KW - Wood impregnation KW - Wood protection PY - 2013 DO - https://doi.org/10.1515/hf-2012-0105 SN - 0018-3830 SN - 1437-434X VL - 67 IS - 4 SP - 429 EP - 435 PB - De Gruyter CY - Berlin AN - OPUS4-28892 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -