Lynne Wong's PhD thesis

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CHAPTER 5. ADSORPTION ISOTHERMS OF SUGAR CANE FIBRES In the previous chapter the Brix-free water content of the cane components are determined by means of a contact method. This chapter describes the experiments performed to determine the equilibrium moisture content, and hence adsorption properties, by means of a vapour sorption method of these cane component parts which enabled the determination of a number of thermodynamic parameters that provide insight into the microstructure of the fibre-water interface. 5.1 THE CONCEPT OF BOUND WATER IN FIBRE All biological systems have the ability to retain molecular hydration as a fundamental defensive mechanism against dehydration (Quioco et al., 1989). The structure, mobility and function of biological molecules are affected by the water molecules bound to the ionic, polar and hydrophilic sites of macromolecules (Vertucci and Leopold, 1987). Rascio et al. (1992) demonstrated the important role played by bound water in the plant's adaptation to the moderate stress of dehydration and related its tolerance towards dehydration to the quantity of bound water, the strength of binding and its ability to tolerate the removal of bound water without damage. However, the relationship between the quantity of bound water and water binding strength of plant tissues was not elucidated. In their review of moisture sorption isotherm characteristics of food products, Al-Muhtaseb et al. (2002) quoted that food preservation consisted of controlling the moisture content during the processing of foods, achieved either by removing it or binding it such that the food becomes stable to both microbial and chemical deterioration (Labuza, 1980). Later, the concept of water activity was introduced to indicate the ‘quality’ of the water content of food. It describes the degree of ‘boundness’ of water and hence, its availability to participate in physical, chemical and microbiological reactions. In a biological system, three aspects of water can be distinguished (Rizvi and Benato, 1984): 1) Structural, the position and orientation of water molecules in relation to each other and to macromolecules. 2) Dynamic, molecular motions of water molecules and their contribution to the hydrodynamic properties of the system.
3) Thermodynamic, water in equilibrium with its surroundings, at a certain relative humidity and temperature. Moreover, in a biological system, water is believed to exist with either unhindered or hindered mobility, referred to as free or bound water respectively. ‘Bound water’ is considered as that portion of water held in the material which exhibits physical properties significantly different from those of free water or bulk water (Berlin, 1981), through stronger hydrogen bonding than liquid water. Some of the characteristics of bound water are lower vapour pressure, high binding energy as measured during dehydration, reduced mobility, unfreezability at low temperature and unavailability as a solvent such as in the definition of Brix-free water (Labuza and Busk, 1979). Although each of these characteristics has been used to define bound water, each gives a different value for the amount of water which is bound. As a result of this, as well as the complexities and interactions of the binding forces involved, no universal definition of bound water has been adopted. 5.2 TYPES OF ADSORPTION AND ADSORPTION ISOTHERMS In this study the interaction of sugar cane fibres with water was studied. When a solid surface (in this case the sugar cane fibre) is exposed to a fluid (i.e. gas or liquid, and in this case water) adsorption occurs. It is understood to mean the increase in the density of the fluid in the vicinity of an interface. With certain systems, e.g. some metals exposed to hydrogen, oxygen or water, the adsorption process is accompanied by absorption, i.e. the penetration of the fluid into the solid phase. In such a case the term sorption is used and, in particular, when the adsorption and absorption processes cannot be distinguished experimentally. Distinction was made in the early 1930s between physical adsorption (physisorption) in which weak Van der Waals interactions are involved and chemical adsorption (chemisorption) in which the adsorbed molecules are attached by strong chemical bonding. The characteristic features distinguishing between the two types of adsorption may be summarised as follows: (a) Physisorption is a general phenomenon with a relatively low degree of specificity, whereas chemisorption is dependent on the reactivity of the adsorbent (solid 170
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THE BRIX-FREE WATER CAPACITY AND SO
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dissolved and hydrated waters, and
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ACKNOWLEDGEMENTS I am particularly
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Page 1.5 THE DELETERIOUS EFFECTS OF
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Page 2.2 THE PHENOMENON OF BRIX-FRE
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Page 3.4.3.3 Cane tops 83 3.4.4 Cha
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4.3.3 Temperature at which Brix-fre
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4.6.1 Materials 143 4.6.1.1 Samples
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CHAPTER 6. PROPERTIES OF THE SORBED
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APPENDIX 3. CALCULATIONS LEADING TO
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LIST OF FIGURES Page Figure 1.1. Fi
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Figure 3.1. Glucose and fructose an
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Figure 5.11. Residual plots for the
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total adsorbed water (m) and the pr
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Table 2.18. Moisture content in sug
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Page Table 4.4. Results of the dete
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Page Table 4.24. Analysis of varian
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Page Table 5.13. Table 5.14. Equili
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Table 6.3. Heat of sorption of the
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GLOSSARY OF TERMS Absorption is the
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Filterability of a raw sugar is mea
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Sorption is the generic term used w
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LIST OF MAIN SYMBOLS Symbol Descrip
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s c s Slope of Caurie I isotherm pl
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number of 255, and cane land covere
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Nouvelle Mon In Trésor ustrie and
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Figure 1.3. Cane sampling by core s
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In Mauritius, most of the sugar fac
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are: cane tops, dry and green leave
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1.4 TRENDS IN CANE QUALITY RECEIVED
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campaign was launched to encourage
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The level of extraneous matter in c
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In Australia (Cargill, 1976), cane
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The effect of soil on factory perfo
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leaves increased the level of impur
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• From 1976 to 1980, when the pro
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Clerget purity of molasses 40 Clerg
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CHAPTER 2. IMPACT OF EXTRANEOUS MAT
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Since the extrapolated purity of mo
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Figure 2.1. Jeffco cutter grinder.
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2.1.4 Results The analytical result
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Table 2.3. Analytical results of re
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Table 2.5. Composition of dry trash
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Table 2.7. Predicted factory perfor
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Boiling house recovery 91.0 89.8 89
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0 5 10 15 20 % EM in cane y = 0.572
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% EM in cane 0 5 10 15 20 0 -2 -4 -
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1 y = 0.020 (% D) R 2 = 1.00 = 0.03
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% EM in cane 0 5 10 15 20 0 -2 y =
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esulting in 0.015 unit sucrose loss
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2.2.1 Experimental procedure Cane m
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filter paper, rejecting the first f
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Table 2.9. Effect of increased addi
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Table 2.11. Effect of increased add
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Table 2.13. Effect of increased add
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various components such as stalk fi
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in the presence of dry leaves, if c
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Table 2.17. Moisture content in sug
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CHAPTER 3. SEPARATION OF THE SUGAR
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Table 3.1. It can be seen that the
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Table 3.2. Fibrous physical composi
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R 579 R 570 M 1557/70 M 1400/86 74
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loosen the fibre. The woody core is
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agitate the mixture in the pot, and
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Figure 3.7. Custom-built fibre-pith
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The extraction of fibres starting f
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pre-treatment in a Jeffco cutter-gr
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Figure 3.19. Stalk cake washed free
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not have many dry leaves attached t
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Table 3.5. Masses of cane samples a
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Table 3.7. Masses of cane samples a
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Table 3.9. Masses of cane component
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3 57.6 126.3 23.7 97.2 31.1 53.8 11
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Table 3.12. Material loss (%) from
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3.5.3 Fibre/pith ratios in cane com
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Table 3.15. Effect of extraneous ma
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Snow (1974) investigated the season
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from Figure 2.9 that the change in
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Table 3.18. Fibre % cane results by
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110
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(a). Dry leaf (b). Green leaf (c).
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dry fibre, or a factor, is used in
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Steuerwald (1912) applied sucrose s
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solution/fibre ratio was lowered fr
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leave some residual moisture on the
Page 171 and 172: instead of 150 g of 10° Brix sucro
Page 173 and 174: Table 4.2. Determination of Brix-fr
Page 175 and 176: Table 4.3. Comparison of Brix-free
Page 177 and 178: Table 4.4. Results of the determina
Page 179 and 180: In order to test for homogeneity of
Page 181 and 182: Table 4.7. Results of the repeat de
Page 183 and 184: The experiment was repeated with th
Page 185 and 186: e any residual moisture in the samp
Page 187 and 188: By means of the same technique, Won
Page 189 and 190: was still hot. Since the filter was
Page 191 and 192: value determined could be corrected
Page 193 and 194: Qin and White’s finding was confi
Page 195 and 196: A sample size of 3.5 g with 75 g co
Page 197 and 198: Figure 4.4. Fibre samples drying in
Page 199 and 200: - One large fibre sample (rind) of
Page 201 and 202: Table 4.18. Brix-free water values/
Page 203 and 204: Table 4.20. Brix-free water values/
Page 205 and 206: 4.7.3 Statistical analysis It is es
Page 207 and 208: Table 4.23. Analysis of variance (B
Page 209 and 210: pointing out that at 52 weeks old,
Page 211 and 212: The crop of R 570 sampled in 2001 w
Page 213 and 214: 4.7.4. Estimated Brix-free water co
Page 215 and 216: The main difference in the two sets
Page 217 and 218: Table 4.27. Predicted Brix-free wat
Page 219 and 220: 4.8 SUMMARY AND CONCLUSIONS An anal
Page 221: component parts, and verify the Bri
Page 225 and 226: Langmuir (1916, 1917, 1918) propose
Page 227 and 228: to determine the moisture sorption
Page 229 and 230: Table 5.1. Some commonly used isoth
Page 231 and 232: Lomauro et al. (1985) found that wi
Page 233 and 234: and on agricultural products such a
Page 235 and 236: Bruijn (1963) studied the mass incr
Page 237 and 238: After measuring the EMC of dry corn
Page 239 and 240: approached, that is, either by adso
Page 241 and 242: Table 5.4. Water activity (a w ) of
Page 243 and 244: 5.6.3 Procedure to determine equili
Page 245 and 246: 5.6.4 Results and discussion An exa
Page 247 and 248: Table 5.8. Equilibrium moisture con
Page 249 and 250: Table 5.10. Equilibrium moisture co
Page 251 and 252: Table 5.12. Equilibrium moisture co
Page 253 and 254: 30 o C 45 o C 55 o C 60 o C Water w
Page 255 and 256: m/m of 96% activity, a w (g/100g dr
Page 257 and 258: vaporisation generally decreases fr
Page 259 and 260: 30 o C isotherm 45 o C isotherm 55
Page 261 and 262: 4 0 Stalk fibre 5 0 Stalk pith 5 0
Page 263 and 264: 5.6.4.4 Fitting of sorption models
Page 265 and 266: Table 5.19. Parameters of the sorpt
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Table 5.27. Parameters of the sorpt
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Modified GAB Kuhn Iglesias - Chirif
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Table 5.28. Classification of resid
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Stalk fibre Stalk pith Rind fibre 4
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5.6.4.5 Calculated EMC values of re
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Table 5.30. Calculated equilibrium
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m/m of 96% Table 5.32. Calculated e
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Table 5.33. Parameters of the Hailw
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CHAPTER 6. PROPERTIES OF THE SORBED
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where m is the equilibrium moisture
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6.2 THE NUMBER OF ADSORBED MONOLAYE
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6.3 TOTAL SOLID SURFACE AREA AVAILA
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Thus, for each cane component of ea
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abscissa. For each moisture level (
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A similar procedure was followed to
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10 0 Stalk fibre Stalk pith Rind fi
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Moreover, if T β > T hm the proces
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Table 6.5. Characteristic parameter
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Binding energy/kJ (kg mol) -1 2 0 0
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6.8 CALCULATION OF BOUND WATER AND
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The values of K 1 , K 2 and W were
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Table 6.7. Separation of the total
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Table 6.7. (Contd.) Sample 30 o C 4
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3 0 S talk fibre 4 0 Stalk pith 3 0
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3 0 Reconstituted cane at 30 o C 3
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when water is added to dry wood, wh
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It is evident that in some cases ma
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The number of adsorbed monolayers,
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Data in Tables 2.9 and 2.11 show th
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particular fibre is systematically
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Anon. (1985b). Laboratory manual fo
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Blanchi R.H. and A.G. Keller (1952)
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Day D.L. and G.L. Nelson (1965). De
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Heyrovsky J. (1970). Determination
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Kuhn I.J. (1964). A new theoretical
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Madamba P.S., R.H. Driscoll and K.A
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Prinsen Geerligs, H.C. (1897). Stud
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Sing K.S.W., D.H. Everett, R.A.W. H
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Van der Pol C., C.M. Young and K. D
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Lynne Wong's PhD thesis

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