Crystallinity cellulose

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

Cellulose crystallinity has been shown to affect pyrolysis rates and Ea s (2,26,27). The initial low temperature decomposition is reported to occur first in the amorphous region (5,26,27). Also,... 

Accessible Cellulose in Wood Pulp, Linters and Regenerated Cellulose. Crystalline Reactivity and Yarn Properties2S... 

The FP cellulose per unit (ml) volume and enzyme yield per unit (g) cellulose or substrate obtained on wheat straw, wood, and CTMP in SSF were higher than those obtained in LSF on wheat straw and wood (Tables I, II, and III). And wheat straw proved to be a better substrate than wood for cellulose production in SSF. This could be attributed to the polysaccharides (cellulose and hemicelluloses) of wheat straw being more readily available for the organism s growth and cellulose synthesis than those of wood. The hemicelluloses and cellulose were presumably not as available in wood, because of its high lignin content and high cellulose crystallinity, as in wheat straw. 

The cellulose crystallite size is highest in ulvophycean and certain chlorophycean algae (114-169A), lowest in vascular plants (49-62A) and intermediate in Aceiobacter (70-84A) (1). It appears that cellulose crystalline dimensions are independent of the type of terminal cellulose synthesizing complex. The idea that cellulose biosynthesis is not exclusively responsible for determining its crystalline dimensions has been proposed previously by Marx-Figini (52). 

The relative influence of vibratory milling on the course of enzymatic and dilute acid hydrolysis of four cellulosic substrates was investigated. The four substrates—cotton linters, newsprint, Douglas fir, and red oak— were vacuum-dried and then milled for various time periods ranging up to 240 min. Assays were then made of rate and extent of hydrolysis, maximum yield of reducing sugar, and cellulose crystallinity. 

Adsorption of water is accompanied with swelling of wood. Since cellulose constitutes almost 50% of the wood substance, its fractional contribution to sorption is the highest. Swelling of wood is thus manifested by the adsorption of water by hydroxyl groups located on surface of micells and amorphous regions of cellulose, crystalline zones being impenetrable. Reduction in... 

The purposes of pretreatment of lignocellulosic materials are the removal of lignin and hemicellulose, reduction of cellulose crystallinity, and increase in the porosity of the materials. Among the physical methods, mechanical treatments, such as chipping, grinding and milling are used to reduce cellulose crystallinity. The... 

Cellulose Crystallinity and Crystal Lattice Type, Part II, J. Appl. Polym. Sci. (1964) 8, 1325-1341. 

Lignin > > > > > hemicelluloses > accessible cellulose > noncrystalline cellulose > > > crystalline cellulose... 

PROP Fine white fibrous particles from treatment of bleached cellulose from wood or cotton. Insol in water and most org solvs. SYNS ABICEL n P-AMYLOSE ARBOCEL ARBOCEL BC 200 ARBOCELL B 600/30 AVICEL AVICEL 101 AVICEL 102 AVICEL PH 101 AVICEL PH 105 CELLEX MX a-CELLULOSE CELLULOSE 248 CELLULOSE (ACGIH.OSHA) CELLULOSE CRYSTALLINE CELUFI CEPO CEPO CFM CEPO S 20 CEPO S 40 CHROMEDIA CC 31 ... 

In solid state, cellulose exists in mostly crystalline state. This state has been the subject of extensive studies for at least 100 years, and several important aspects need to be pointed out at the onset. Crystallinity is neither uniform (options exist) nor static (crystallinity can be lost as well as gained in relation to molecular mobility), nor is it permanent (conditions have been identified under which transitions of order take place). Cellulose crystallinity manifests itself through the existence of distinctive X-ray diffraction patterns. These patterns allow the determination of the overall dimensions of unit cells which are spatial units that represent the... 

Cellulose crystallinity is not uniform. A simple experiment of immersing cellulose in cold concentrated alkali, a process used for enhancing the dye-absorbing quality of cotton fabrics called mercerization, was found already in the 1930s on the basis of X-ray diffraction to produce a cellulosic allomorph with different unit cell dimensions [13,14]. This was given the... 

Cellulose pyrolysis has been studied in detail from a variety of points of view mainly related to chemical utilization of wood pyrolysis products or to fire related problems. Analytical pyrolysis of cellulose is not often used as a tool for cellulose detection, but it is a common procedure for studying the pyrolysis products. A variety of analytical procedures have been applied for this study, pyrolysis/gas chromatography/mass spectrometry (Py-GC/MS) being the most common [11-16]. Besides Py-GC/MS, other analytical procedures also have been utilized, such as Py-MS [17,18], Py-IR [19], and off-line Py followed by HPLC [20]. The Py-MS spectrum of cellulose was shown in Figure 5.4.1 (B). Some procedures applied GC/MS on derivatized pyrolysis products (off-line), the derivatization being done by silylation [21], permethylation, perbenzoylation [22], etc. Information about cellulose also has been obtained from the analysis of pyrolysis products of several cellulose derivatives, such as O-substituted cellulose [23]. Also the study of cellulose crystalline structure with X-ray during pyrolysis has been used [23a] to generate information about the pyrolysis mechanism. 

SYNONYMS P-amylose, a-cellulose, cellulose crystalline, flour cellulose, hydroxycel-lulose, pyrocellulose. 

The principal features of a mathematical model described for the enzymatic hydrolysis and fermentation of cellulose by Trichoderma reesei are the assumption of two forms of cellulose (crystalline and amorphous), two sugars (cellobiose and D-glucose), and two enzymes (cellulase and j3-D-glucosidase). An inducer-repressor-messenger RNA mechanism is used to predict enzyme formation, and pH effects are included. The model consists of 12 ordinary differential equations for 12 state variables and contains 38 parameters. The parameters were estimated from four sets of experimental data by optimization. The results appear satisfactory, and the computer programs permit simulation of a variety of system changes. 

The principal features of a mathematical model described for the enzymatic hydrolysis and fermentation of cellulose by Trichoderma reesei are the assumption of two forms of cellulose (crystalline and amorphous), two sugars... 

In nature, fibrous biopolymers have long been used in the reinforcement of extracellular biocomposites, inspiring the reproduction of this technology using native CNs as filler in a range of host polymer matrixes. Due to the highly crystalline nature of the cellulose nanoparticles, they possess attractive mechanical properties, such as an axial Young s Modulus of around 140 GPa, which is dependent on cellulose crystallinity and axial ratio [36]. When... 

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