Cellulose-based materials

Cellulose represents the most abundant renewable and biodegradable polymeric material on earth. Due to its low cost and functional versatility, cellulose has been a key feedstock for the production of chemicals with various properties and applications over the past century. In 2000, the world produces 187 million tons of wood pulp annually. Most of it is used as raw material in the production of paper and cardboard products; only ten percent is transformed into cellulose derivatives. 2 This crystalline and rigid homopolymer has not yet reached its full application potential due to its essential insolubility in most common solvents. Chemical modification of the hydroxyl groups overcomes this obstacle and offers considerable opportunities for preparing cellulosebased polymeric materials. The objective of this research was to investigate new paths for the preparation of cellulose derivatives with a variety of structural features to obtain advanced materials suitable for different applications. New synthesis methods were proposed for cellulose modification and the already existing synthetic approaches were explored using new reagents. This study investigated modification of cellulose through reactive dissolution approaches (heterogeneous modification) using organic solvents, such as pyridine, N,Ndimethylacetamide (DMA) and N,N-dimethylformamide (DMF) (I, II & III) and under homogeneous conditions, using ionic liquids (ILs) as the reaction medium (IV). Esterification of cellulose is among the most versatile modifications leading to a wide variety of commercially produced polymers with valuable properties. The acylation can be carried out efficiently through a reactive dissolution approach in pyridine (I). This means that the reaction is initially heterogeneous, in the absence of costly and toxic directdissolution solvents. As the reaction proceeds, it produces a homogenous mixture. The obtained cellulose esters usually show a high degree of substitution (DS) and polymerization (DP) and are soluble in organic solvents. Esterification can also be conducted in DMF (III). Chloroacetyl cellulose was first obtained via the reaction of chloroacetyl chloride with cellulose in DMF and used as starting materials for further reactions with amines and thiols. Highly substituted aminoacetyl cellulose and thioacetyl cellulose were achieved via this method. In addition, simple distillation can easily recover DMF in good yield, which attaches a more recyclable process to this important synthon, chloroacetyl cellulose, compared to other reported media. Carbamate derivatives of cellulose have also gained industrial significance recently. The reactive dissolution approach can also be used for carbamoylation of celluloses (II). Reactions with cellulose, or pulp and aromatic isocyanates, were initiated as heterogeneous mixtures in hot pyridine. However, attempts to synthesize highly substituted cellulose carbamates with aliphatic isocyanates in pyridine failed, as they did not achieve homogeneous solutions, even after long reaction times. Consequently, aliphatic cellulose carbamates were prepared via reactive dissolution in DMA, with dibutyltin dilaurate (DBTL) as catalyst. Lately, ionic liquids (ILs) have received much attention in cellulose chemistry because of their potential as green solvents in shaping processes, fractionation of lignocellulosic biomasses, and homogeneous synthesis of polysaccharide derivatives. Homogeneous carbonylation of cellulose can be accomplished by applying dialkylcarbonates in a novel solvent system composed of methyl trioctylphosphonium acetate [P8881][OAc] as solvent/catalyst and dimethyl sulfoxide as cosolvent (IV). Cellulose dialkylcarbonates with moderate degrees of substitution are accessible via this procedure. All derivatives prepared in this study were thoroughly characterized with numerous techniques for their structure, degree of substitution (DS), molecular weight, thermal properties, and other physiochemical properties. Various pulp samples, with different hemicellulose contents, provided the sources of starting material, in order to investigate both the suitability of cheaper pulp samples and the pulp’s degree of influence on reactivity. In short, identical results were obtained with all pulps when compared with microcrystalline cellulose (MCC) derivatives. The purpose of this study was to provide an alternative look into the use of the wellknown renewable biopolymer ‘cellulose’ to develop highly engineered materials, using