Jinghuan Chen

Highly Thermostable, Flexible, and Conductive Films Prepared from Cellulose, Graphite, and Polypyrrole Nanoparticles

In this study, graphite powder (GP) was introduced into the conductive cellulose/polypyrrole (PPy) composite films to increase their conductivity and thermal stability. The GP was dispersed in ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) before the dissolution of cellulose, and the cellulose/GP/PPy films were prepared by in situ chemical polymerization of PPy nanoparticles on the film surface. The structural characteristics and properties of the composite films were investigated in detail. The GP flakes, which were embedded in the cellulose matrix, increased the thickness and decreased the density of the films, leading to the decrement of mechanical properties. However, the thermal stability of the films was significantly improved by the incorporation of graphite, and the composite film could even substantially maintain the original shape after being burned. In addition, the electrical conductivity of the films was increased seven times, leading to the excellent electromagnetic interference shielding effectiveness. The cellulose/GP/PPy film could be considered as a potential candidate for the effective lightweight electromagnetic interference shielding materials in electronics, radar evasion, aerospace, and other applications.

Cellulose acetate fibers prepared from different raw materials with rapid synthesis method

Transesterification is a mild process to prepare cellulose acetate (CA) as compared with the traditional method. In this study, CA fibers were produced from six cellulose raw materials based on a simple and rapid transesterification method. The properties of the CA solutions and the obtained CA fibers were investigated in detail. Results showed that all of the cellulose raw materials were esterified within 15 min, and spinning dopes could be obtained by concentrating the CA solutions via vacuum distillation. The XRD, FT-IR, (1)H, (13)C and HSQC NMR analysis confirmed the successful synthesis of CA. The degree of substitution (DS) of the obtained CA was significantly affected by the degree of polymerization (DP) of cellulose raw materials, which further influenced the viscosity of CA solutions as well as the structural, thermal and mechanical properties of the CA fibers.

Effects of polymorphs on dissolution of cellulose in NaOH/urea aqueous solution

This study focused on the effect of cellulose crystal type on the dissolution of cellulose in aqueous NaOH/urea. Cellulose I, II, IIII, and IVI were prepared and characterized. Subsequently, the solubility of these cellulose samples in aqueous NaOH/urea was tested and the mechanism was determined by a combination of (1)H NMR spectroscopy and differential scanning calorimetry (DSC). The results indicated that, compared with the degree of polymerization (DP) and crystallinity index of cellulose, the cellulose crystal type had greater impact on cellulose dissolution. Specially, the solubility of the cellulose I, II, and III was progressively decreased, probably due to different hydrogen bond network and packing energy in it. The ability of cellulose I, II, III, and IV to form hydrogen bonds with sodium hydroxides was nearly the same, while gradually increased when cellulose preparations were associated with urea. Moreover, all the cellulose solutions showed good thermal stability.

Chapter 6 – Steam Explosion

This chapter introduces the mechanism, key parameters, and operation mode of steam explosion, and emphasizes the recent investigations in biorefinery as a pretreatment or fractionation process. Although many kinds of pretreatment processes have been explored and developed, none of them has been employed industrially for second-generation bioethanol production in view of the cost and economical efficiency. Steam explosion, as a physicochemical treatment, has specific characteristic advantages over the others and has been considered extensively as a promising pretreatment for improving the enzymatic bioconversion. The biorefinery concept designates that the total utilization of lignocellulosic biomass and high-value-added production from main components is forward direction. This review summarizes the basic theoretic issues of steam explosion and provides the latest data of its applications on the production of ethanol or sugars.

Regulating effect of hemicelluloses on the preparation and properties of composite Lyocell fibers

Composite Lyocell fibers were successfully prepared from cotton linter pulp and bamboo hemicelluloses with N-methyl-morpholine-N-oxide as a solvent. The viscosity of the spinning solutions, as well as the structural and mechanical properties of the composite fibers were investigated to understand the effect of hemicelluloses on the dissolution process and the properties of fibers. The addition of hemicelluloses raised the concentration of spinning dopes and reduced the average molecular weight of raw materials, leading to the increase and then decrease of the viscosity of solution. The crystal and morphological structure of the fibers were slightly influenced by the presence of hemicelluloses, while the tensile strength and modulus of the fibers were improved by adding appropriate amount of hemicelluloses. Moreover, the distribution of hemicelluloses in the solution and composite fiber were proposed to illustrate this regulating effect. This study provided an alternate way to improve the properties of Lyocell fibers and enlarge the utilization of hemicelluloses.