Metabolic engineering of novel lignin in biomass crops

Lignin, a phenolic polymer in the secondary wall, is the major cause of lignocellulosic biomass recalcitrance to efficient industrial processing. From an applications perspective, it is desirable that second-generation bioenergy crops have lignin that is readily degraded by chemical pretreatments but still fulfill its biological role in plants. Because plants can tolerate large variations in lignin composition, often without apparent adverse effects, substitution of some fraction of the traditional monolignols by alternative monomers through genetic engineering is a promising strategy to tailor lignin in bioenergy crops. However, successful engineering of lignin incorporating alternative monomers requires knowledge about phenolic metabolism in plants and about the coupling properties of these alternative monomers. Here, we review the current knowledge about lignin biosynthesis and the pathways towards the main phenolic classes. In addition, the minimal requirements are defined for molecules that, upon incorporation into the lignin polymer, make the latter more susceptible to biomass pretreatment. Numerous metabolites made by plants meet these requirements, and several have already been tested as monolignol substitutes in biomimetic systems. Finally, the status of detection and identification of compounds by phenolic profiling is discussed, as phenolic profiling serves in pathway elucidation and for the detection of incorporation of alternative lignin monomers

Improving the properties of flexible hybrid-silica aerogels: addition of pores for a more lightweight material

Silica aerogels with their remarkable properties such as low density and thermal conductivity are prime candidates for a wide range of different applications, such as insulation materials in aviation. While pure silica aerogels are very brittle and difficult to handle, adapting the sol-gel process can result in organic-inorganic hybrid-materials with a high mechanical flexibility and a good hydrophobicity while still retaining a remarkable insulation performance. They were first investigated by Hayase et al. and are based on methyltrimethoxysilane (MTMS) and dimethoxydimethylsilane (DMDMS). For aviation applications the properties of this aerogel still have to be improved. Starting with recipes patented by the German Aerospace Center (DLR), the synthesis route was first investigated towards varying precursors and their ratios, using different solvents and mixtures, as well as testing a wide range of surfactants and catalysts. Mechanical, thermal, chemical and morphological properties of the samples were analyzed. With this presentation we will report on a set of experiments reducing the density. In a first approach gas bubbles were included in the aerogel network by distributing nitrogen gas into the sol during the gelation process. And in a second one the formation of large-scale pores was carried out using suitable filler-materials which can later be removed during washing processes. Both attempts result in an even lighter lightweight material and in addition lead to improved thermal and acoustic insulation performance, while still retaining a high mechanical flexibility and a good hydrophobicity. Those resulting aerogels can possibly outperform the state-of-the-art compressed fiberglass-mats in aviation applications

Flexible Hybrid Silica-Aerogels: Studying the Influences of Different Geometries and Shapes

Silica aerogels with their remarkable properties such as low density and thermal conductivity are prime candidates for a wide range of different applications, such as insulation materials in aviation. While pure silica aerogels are very brittle and difficult to handle, adapting the sol-gel process can result in organic-inorganic hybrid-materials with a high mechanical flexibility and a good hydrophobicity while still retaining a remarkable insulation performance. They were first investigated by Hayase et al. [1] and are based on methyltrimethoxysilane (MTMS) and dimethoxydimethylsilane (DMDMS). For aviation applications the properties of this aerogel still have to be improved. Our research is based on a patented recipe of the German Aerospace Center (DLR) [2]. The synthesis was varied towards precursors and their ratios, using different surfactants and catalysts, as well as focusing on shaping the final aerogels into beads and monoliths. Mechanical, thermal, chemical, and morphological properties of the samples were analyzed. With this presentation we will report on a set of experiments focused on synthesizing bead-shaped particles in an emulsion process and comparing their thermal properties to standard monolithic samples. The densities of packed beads and mats is compared, since lightweight is one of the most necessary properties of the final material in aircraft application. Sample sizes vary from lower millimeter (1 - 5 mm) to upper centimeter (> 30 cm) range. Those resulting aerogels can possibly outperform the state-of-the-art compressed fiberglass-mats in aviation applications. The authors gratefully acknowledge funding by the Federal Ministry for Economic Affairs and Climate Action (BMWK) and its Aviation Research Program “LuFo VI-1”. (FKZ: 20Q1908C) [1] G. Hayase, K. Kanamori, K. Nakanishi, J. Mater. Chem. 21, 17077-17079 (2011) [2] R. Fener, P. Niemeyer, European Patent EP3042884A1 (2015

Enhancing flexible hybrid silica aerogels: integrating new functionality through addition of different precursors

Hybrid silica aerogels can overcome one of the main drawbacks of classical silica aerogels, which are unsuitable for many industrial applications due to their brittle network. By modifying the synthesis through changes in the sol-gel, drying or post-treatment processes, different properties like the mechanical flexibility can be enhanced. This was done by Hayase in 2011 through addition of one or two methylgroups to the tetravalent Si-precursors, resulting in flexible silica aerogels known as marshmallows. These are used as basis for further improvements and modifications, allowing the investigation towards more potential uses. By modifying different parts of the synthesis, changes on a chemical and physical level can be introduced. In this work, we went from Hayase's binary to a ternary precursor system. One component investigated was tetraethoxysilane (TEOS), often used for classical silica aerogels, with the goal reduce the overall pore sizes, changing the aerogels behavior. This however comes at the expense of flexibility. Another precursor with potential for functionalization is vinylmethyldimethoxysilane (VMDMS). The vinyl- groups allow the binding of additional molecules through radical polymerization, giving rise to the possibility to create hybrids otherwise not possible

Improving the properties of flexible hybrid-silica aerogels

Silica aerogels with their remarkable properties such as low density and thermal conductivity are prime candidates for a wide range of different applications, such as insulation materials in aviation. While pure silica aerogels are very brittle and difficult to handle, adapting the sol-gel process can result in organic-inorganic hybrid-materials with a high mechanical flexibility, a good hydrophobicity while still retaining a sufficient insulating performance. They were first investigated by Hayase et al. [1] and are based on methyltrimethoxysilane (MTMS) and dimethoxydimethylsilane (DMDMS). For further improvement of the material s properties, the synthesis needs to be tuned. Starting with recipes filed for patenting by the German Aerospace Center (DLR) [2], the synthesis route was first investigated towards varying precursors and their ratios, using different solvents and mixtures, as well as testing a wide range of surfactants and catalysts. Mechanical, thermal, chemical and morphological properties of the samples were investigated. After further polymeric crosslinking the metal-oxygen bonds can be partially substituted by the more lightweight carbon-backbone, while retaining the flexibility of the material. Therefore, investigations using a consistent precursor system of MTMS and dimethoxymethylvinylsilane (DMMVS) are carried out. The above-mentioned properties are required in the field of aviation, and the resulting aerogels can possibly outperform the state-of-the-art compressed fiberglass-mats