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Functionalization of Cellulose—Chemical Approach
Published in Narendra Pal Singh Chauhan, Functionalized Polymers, 2021
Merin Sara Thomas, Prasanth K.S. Pillai, Sabu Thomas, Laly A. Pothen
Chemical modification by silylation procedure is relatively cheap since silylation agents are effective and not costly. Silane coupling agents are usually adopted for creating a perfect bonding by improving the degree of crosslinking in the interface region. The number of cellulose hydroxyl groups at the fiber-matrix interface may be reduced by the action of silane coupling agents. In the presence of moisture, hydrolysable alkoxy groups lead to the formation of silanols, which further react with the hydroxyl group of the fiber, forming a stable covalent bond with the cell wall. Yu et al. (2019) fabricated hydrophobic cellulosic materials via gas-solid silylation reaction for oil/ water separation. Laitinen et al. (2017) prepared low-cost, ultralight, highly porous, hydrophobic, and reusable super absorbing cellulose nanofibril aerogel via silylation of cellulose nanofibrils. Two important silylating agents that were used for the silylation process are methyltrimethoxysilane and hexadecyltrimethoxysilane (Laitinen et al. 2017). More recently, ene- or thiol-functionalized silanes were also covalently grafted on NFC-based films and consequently clicked with appropriate moieties through thiol-ene click chemistry (Huang et al. 2014).
Cellulose Fibers and Nanocrystals: Preparation, Characterization, and Surface Modification
Published in Vineet Kumar, Praveen Guleria, Nandita Dasgupta, Shivendu Ranjan, Functionalized Nanomaterials I, 2020
Djalal Trache, Ahmed Fouzi Tarchoun, Mehdi Derradji, Oussama Mehelli, M. Hazwan Hussin, Wissam Bessa
Similar to the esterification process, silylation is the reaction in which the silyl group (R3Si−) reacts either with alcohols, amines, or carboxylic acids and later forms the covalent bond. In the past, Gousse et al. (Gousse et al., 2004) studied a series of alkyldimethyl chlorosilanes used as stabilizers for CNCs in organic solvent, as shown in Figure 11.10. Due to the newly developed hydrophobic characteristics from the long chain structures, the CNC particles were observed to be soluble in some hydrophobic organic solvents. Nevertheless, silylation results in the particle chain on the surface being soluble in the reaction medium, hence it diminishes the cellulose microfibrillar features (Gousse et al., 2004). Scheme for the reaction of cellulose with silane derivatives. Here, R represents various alkyldimethylchlorosilanes such as C3H7, C4H9, C8H17, and C12H25.
Derivatization Reactions in Trace Chemical Analysis
Published in Pradyot Patnaik, Handbook of Environmental Analysis, 2017
Sylilation reactions involve replacement of active hydrogen from acids, alcohols, thiols, amines, and amides with trimethylsilyl groups. Enolizable aldehydes and ketones likewise are converted to their trimethylsilyl derivatives. Nonvolatile samples are converted into volatile silyl derivatives for their GC analysis. Also, the substitution of active hydrogen atom with silyl group in the molecule reduces the hydrogen bonding and polarity in the compound. Many hydroxyl and amino compounds are nonvolatile and often unstable above 250°C. Silylation yields more stable and volatile derivatives and therefore is an effective pathway to analyze such substances. Silylation involves nucleophilic substitution reaction of the second-order proceeding through the SN2 mechanism. For example, the substitution of active hydrogen in a compound containing –OH functional group using trimethylchlorosilane as a silylation reagent would yield the corresponding trimethylsilyl derivative as the end product. The reaction is shown below: Sample–OH+(CH3)3SiCl→Sample–O–Si(CH3)3+HCl
Humic acid attachment on chitosan-modified silica gel as an economical, efficient, and selective adsorbent for thorium and uranium removal
Published in Environmental Technology, 2023
Erik Prasetyo, Kazuhiro Toyoda
Among the low-cost materials proposed for adsorbent synthesis, humic acid and silica gel are considered suitable raw materials. Humic acid (unstable but possesses a high binding capacity) and silica gel (inert but possesses a low binding capacity) are combined as a functional group and a supporting material. One of the most common routes for attaching a functional group, such as humic acid, to the silica gel surface is silylation, which addressed in numerous publications [24–27]. However, despite its effectiveness, silylation is considered an expensive and complicated process that involves hazardous chemicals and generates additional waste.