Heat capacity of lignin

The molar heat capacity (Cp) of a pure compound at constant pressure is defined 

Adjust the sensitivity, heating rate, baseline, and other parameters of the DSC apparatus. Place the empty sample pans in the sample and reference holders. The initial and end temperatures (T, and Tc) (Fig. 4.8.13) for scanning are set and the sample and reference holders are maintained at T, for a suitable time to obtain the straight line I. Scanning at a heating rate of 5 or lOK/min is conducted from T, to Tc to obtain DSC curve II. The sample and reference holders are maintained at Te for some time to obtain the straight line, III. 

The reference material (e.g., sapphire or A1203) is placed in the reference pan which is placed in the reference holder, and scanning from T, to Tc is carried out to obtain curve IV. 

Scanning from T, to Tc is performed with the sample in the sample pan to obtain curve V. If the three curves, 11, IV, and V, do not meet at T, and Tc, adjust the apparatus to obtain the correct baseline and repeat the procedure. 

Because of the temperature fluctuation of sample holders in the initial period of scanning, the use of data from the initial stage for calculating heat capacity should be avoided 

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FIGURE 8.6 Heat capacity of dioxane lignin (DL) and wood cellulose. 

T Hatakeyama, K Nakamura, H Hatakeyama. Smdies on heat capacity of ceUulose and lignin by differential scanning calorimetry. Polymer 23 1801-1804, 1982. 

The second class comprises conventional solids, defined by a chemical formula, but whose property requirements are very minimal. In this class we included lignin, cellulose, mannan, galactan, xylan, arabinan and the biomass. The properties specified in the database include molecular weight, heat of formation, solid molar volume, and solid heat capacity. 

As an amorphous polymer, lignin undergoes chain segment motion upon heating. This motion, a glass transition, is characteristic of all amorphous polymers, and is indicated by an endothermic shift in the DTA or DSC curves. This glass transition is accompanied by abrupt changes in free volume, heat capacity, and thermal expansion coefficient. 

Fig. 4.8.14. Heat capacity (Cp) curves of quenched (cooled rapidly) and annealed (heat-treated) dioxane lignin A quenched from 423 K to 310 K, B annealed at 395 K for — 60 min, — lOOmin, - 940min, 1300min (Hatakeyama et al 1982)...

Heat capacities (Cp) of DL [25] and wood cellulose [53] (crystallinity 38%, calculated from X-ray diffractometry [49]), are shown in Figure 8.6. The Cp values of lignin were higher than those of cellulose, which monotonically increased with increasing temperature. The effect of crystallinity on Cp values of cellulose is reported elsewhere [25]. 

Acrylic acid-modified Ficus carica lignocellulosic fiber was used as adsorbent. And the removal of Cr(VI) was evaluated in the presence of various metal ions aqueous solutions [87]. The F. carica fibers were washed, dried at 50°C for 24 h, and soxhlet extracted with acetone for 12 h in order to remove waxes and lignin. Then it was dried at 50°C for 5h and then cut into pieces of 1.0-1.5mm-size. The F. carica fibers were immersed in 100 ml of double distilled water for 24 h in order to activate the reactive sites. A known amount of ceric ammonium nitrate, concentrated nitric acid, and acrylic acid was added to the flask containing the fiber. The mixture was heated to constant temperature for a definite time. The modified F carica fibers were washed with ethanol and dried at 50°C to a constant weight. The maximum adsorption capacity of Cr(VI) onto adsorbent was found to be 28.90 mg g". ... 

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