Indian Journal of Chemical Technology Vol. 1 0, November 2003, pp. 6 1 9-622

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Carboxymethylation of wood residues: Effect of etherification process variables

T 0 Egbuchunam* & F E Okieimen

University of Benin, Department of Chemistry, Benin City, Nigeria

Received I I July 2002; revised received 30 May 2003; accepted 26 June 2003

: 'A study .of carboxymethylation of wood residues from Terminalia superba (ash conten't 0.01.8; organic ��activeS, 2.14;-. holoceliulose, 76.45; a-cellulose, 55.87 % ; DP 331.86) was carried out Using "arious 'alkali/cellulose .t-a:tio\; <in" , variI}OS . organic " 'solvent mediums (benzene, methylene chloride) and organic ' .solvent':, mixtures l(benZene/isopropanol, . and acetoDitrile/ acetone). The extent of etherification was found to be d�pendent on the strength · of the aqueous alkali solution and was the highest (DS, 0.431) for cellulosic materials impregnated with CuS04 prior to 81kali treatment. It was found that an increase in the time of alkali-treatment from 0.5-24 h was accompanied by marked changes, of up to 44%, in the degree of substitution. The lowest 'OS (0.315) was obtained for c8rbo�ethyhition in methylene chloride and in acetonitrile/acetone (1:1) mixture and the highes� (0.438) in �ntVisoprop'anol (1:1) mixture. The viscosity of dilute aqueous solutions of carboxymethyl cellulose ,prepared, i�8s·pt�ured! "tc.ow shear rate (200 S·l) at varioJlS temperatures, in the presence of mono-, di':, and ,triv8lent CatiODs; jD:order i9:determioe the·reduction in viscosity with time.

Cellulose is the most abundant renewable organic raw material. It is the major constituent of the cell wall of plants, and occurs in cotton almost in the pure form. Although cellulose is widely distributed in nature, it is commercially available either from cotton or from pulp derived from different varieties of woods and raw woods. Carboxymethyl cellulose is one of the most important water-soluble derivatives of cellulose that has found use in cosmetics, pharmaceuticals, in food industry, and also as detergents and drilling mud additives etc. Several workers l . 1 O have reported the preparation, characterization and properties of carboxymethyl cellulose using cotton linters and wood pulps as raw material. Similar studies using cellulose derived from tropical plant resources are scanty. Work was carried out on preparation and characterization of carboxymethyl ether derivative from wood residues of Terminalia superba (white afara) , a widely distributed forestry wood in south­western part of Nigeria.

Experimental Procedure Raw materials

Wood (Terminalia superba) residue was collected from a sawmill in Benin City, Nigeria and sieved to a particle size of 0.3 mm using the ASTM mesh no. 5 .

*For correspondence (E-mail: tessychunam@ yahoo. com) Present address: College of Education, Department of Chemistry, P.M.B. 1 25 1 , Warri, Nigeria

Sodium hydroxide, potassium hydroxide, methylene chloride, benzene, ethanol, chloroacetic acid, acetonitrile, and acetone were of reagent grade and were used as received.

Characterisation of wood residue The wood meal was extracted with ethanollbenzene

mixture I I , and pulped using the chlorite pulping methodl2. The ash contentl3 and degree of polymerization of the holocellulose obtained from the wood meal are given in Table 1 .

Table l-Some characteristics of T. superba wood residues

Parameter

Density (g/mL) Organic extractives (%) Holocellulose content (%) a-cellulose content (%) Degree of polymerization

Value

0.649 2 . 1 4

76.45 55.87

33 1 .86

Carboxymethylation of cellulosic materials Carboxymethylation of holocellulose and u­

cellulose obtained from the wood residue was carried out using the monochloroacetate-sodium hydroxide method l6 at 29°C. Typical carboxymethylation of cellulose was a two-stage process viz: production of alkali cellulose and conversion of the alkali-cellulose by reaction with chloroacetic acid to ether.

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Alkalisation was carried out by steeping the cellulosic materials in various concentrations of aqueous solutions of sodium hydroxide and potassium hydroxide.

Carboxymethylation was carried out in various organic solvents such as benzene and methylene chloride, and other organic solvent mixtures like benzene/isopropanol and acetonitrile/acetone. The degree of substitution (OS) of the carboxymethyl cellulose was determined by the ash sulphate method 10, 1 7 .

Viscosity measurement The viscosity of the carboxymethyl cellulose

samples was determined by following a standard method described elsewhere1 7, using Bariod Hank Crank type rotatry viscometer of ASTM spindle size 1 8 at a shear rate of 200 S· I . Viscosity measurements were made on 0.25 and 1 .0 wt% aqueous solution and in the presence of mono-, di-, and trivalent cations and as a function of time over a period of 2 1 days.

Results and Discussion Some chemical characteristics of the wood residues

from T. superba are given in Table 1 . The ash content of the wood residue is somewhat lower than the values reported for Scandinavian wood species l 8, 0.3-0.4%, North American woods species l9, 0.28-0.40% and Canadian wood species2o, 0. 1 8-0.28%. The organic solvent extractives (wax content) of the wood residues is 2. 14%. The wax content reported for some common woods are as low as 0.3% in Ulmus america and Solix nigra

2 1 and as high as 9.55% in Pinus

ponderosa2 1 • Organic extractives from wood residues include aliphatic compounds, alcohols, ketones, acid esters, phenolic compounds, alkaloids, etc,22. Recent investigations showed that organic extractives from some tropical hardwood species are resistant to biodegradation23 and there is potential application of wood wax in the preservation of wood products. The a-cellulose content of T. superba is 55 .87% and compares favourably with the values reported for white cedar, Gossweilerodendron balsmiferun, white spruce and eastern hemlock as 44.5, 47 .7, 48.5 and 56.5% respectively22, The degree of polymerization of cellulose from T. superba (33 .86) lies between the range of 1 00-2000, acceptable for use in the petroleum paint and chemical industries24.

Oata in Table 2 give the values of degree of substitution (OS) of carboxymethyl cellulose (CMC)

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Indian J. Chern. Technol ., November 2003

Table 2-Effect of alkali treatment on the degree of carboxymethylation of T. superba wood residues

Alkali

NaOH KOH NaOH KOH NaOH KOH NaOH KOH NaOH KOH

Cellulose­alkali ratio (w/w)

1 :2 1 :2 1 :4 1 :4 1 :6 1 :6 1 :8 1 :8 1 : 1 0 1 : 10

Degree of substitution Holocellulose a-cellulose

0.328; 0.402" 0.385 0.320; 0.392" 0.355 0.378; 0.374" 0.346 0.366;0.358" 0.350 0.352;0.340'

0.360

0.373;0.400" 0.390 0.386;0.47 1 " 0.420 0.389;0.409" 0.382 0.366;0.358"

0.4 1 2 0.420;0.4 1 5" 0.400

a=cellulose material was steeped in aqueous solution of CUS04 (0.22 g/1O mL) before treatment with alkali

samples produced from T. superba wood residues as function of alkalization regent. The results show that impregnation of the cellulosic materials with CUS04 solution prior to alkali treatment gave CMC with the highest values of OS. The observed effectiveness of CUS04 treatment as a swelling agent for the cellulosic materials is similar to the results reported earlier25• The values of OS obtained by using NaOH and KOH solutions are almost of the same order of magnitude, but KOH tends to be a more effective swelling agent than NaOH, giving optimum value of OS at lower alkali strength.

The variations of the OS of the cellulosic materials with the time of alkali treatment are shown in Table 3 using the optimum cellulose/swelling agent ratio. It can be seen that on using CuSOJNaOH system, the values of OS obtained, appears to be largely independent of alkalization time (values of OS increasing by about 5%) whereas the values of OS obtained following the treatment with NaOH, increased by as much as 3 1 % and by 1 3% on treatment with KOH. Olaru et al. 1O reported the kinetics of carboxymethylation of wood pulp and cotton linters and observed that the rate of transformation of the more ordered regions of the cellulosic materials showed smaller reaction rates and determined the overall extent of etherification. Alkali treatment of cellulose is intended to reduce the ordered region of the material and make it accessible to subsequent etherification reaction. The results shown in Table 3, indicate that the effectiveness of the swelling agents in reducing the ordered region in the cellulosic materials is CuSOJNaOH>KOH>NaOH.

Egbuchunam & Okieimen: Carboxymethylation of wood residues

Table 4 gives the effect of the etherification medium on the values of DS of the cellulosic materials treated with 40% NaOH solution. It can be seen that benzene/isopropanol mixtures containing 50 and 70% benzene afforded modified cellulosic materials with the highest values of DS . The observed difference in the effect of the etherifying media on the degree of substitution of the cellulosic materials is thought to be due to the difference in the polarity of the reaction media. For instance, Olaru et al. 1O

reported that carboxymethylation of cellulose in ethanol/acetone mixtures gave higher degree of substitution than in the single solvents and explanations in terms of the dielectric constant of the solvent mixtures were offered.

The viscosity of aqueous solutions of CMC in different concentrations of Na+, Ca2+ and Ae+ ions are given in Table 5 . The results show that the cations markedly affected the dilute solution viscosity of CMC. It can be seen that four-fold increase in the concentration of the metal ions was accompanied with 39.9, 62.5, and 73.8% reductions in viscosity of dilute solutions of CMC in the presence of Na+ , Ca2+, and A 1 3+ ions respectively. The reduction in the viscosity of CMC solution is thought to result from gel (network) formation in the presence of the metal ions26-28 . Viscosity retention in the presence of cation is a desirable property in materials for use in oil-well flooding and enhanced crude oil recovery operations. The results in Table 5 show that CMC samples derived from T. superba wood residues may be useful as viscosity builder in petroleum production activities.

Measurement of solution viscosity of polymer materials as a function of time has been used to estimate the extent of biodegradation29,3o. The reductions in the viscosity of dilute solutions of CMC stored up for 21 days are given in Table 6. It can be seen that dilute aqueous solution of CMC are relatively stable to biodegradation, showing less than 3% reduction in viscosity in 7 days. It would appear that storage of aqueous solution of CMC beyond 10 days leads to rapid degradation of the polymer. The relatively high viscosity retention of solution of the CMC derived from T. superba suggests a potential application in oil production processes.

Conclusion Processing of wood into timber and commercial

wood products generate large quantities of waste materials which often constitute/contribute to urban wastelhealth hazard; and sometimes used as domestic

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Table 3-Rate of carboxymethylation of a-cellulosic material from T. superba isopropanol as a function of alkali-treatment

Time Degree of substitution A B

0.5 0.303 0.460 1 .0 0.438 0.468 1 .5 0.435 0.443 2.0 0.436 0.450 1 2.0 0.430 0.465

A cellulose-alkali ratio (w/w) 1 :8; alkali NaOH B cellulose-alkali ratio (w/w) 1 :4; alkali KOH

C

0.483 0.502 0.497 0.500 0.500

C sample pre-treated with CUS04 solution (0.22 g/1 O mL) and then with NaOH; cellulose-alkali ratio 1 :4

Table 4--Effect of etherification medium on a-cellulose materials

Etherification medium

Benzene Methylene chloride Benzene/isopropanol mixture (% benzene) 70 50 30 1 0 Acetonitrile/acetone mixture 50% acetone

Degree 9f substitution

0.395 0.3 1 5

0.430 0.438 0.362 0.334

0.3 1 5

Alkalisation I h, cellulose; alkali ratio 1 :8; alkali NaOH

Table 5--Solution viscosity of carboxymethyl cellulose obtained from T. superba wood residues in the presence of some cations

Metal ion

0.0 0.2 0.4 0.6 0.8

Viscosity of 1 wt% CMC solution CP

53.4 56.3 37.4 33.8 32.0

30.0 2 1 .2 20.4 20.0

28.4 1 6.7 1 5.4 14.0

Table 6--Biodegradation of aqueous solution of carboxymethyl cellulose obtained from T. superba wood residues

Time (days) 1 5 7 1 0 1 4 2 1

Reduction i n viscosity" (%) 0.0 0.0 1 .2 5.0 14.0 32.5

a = viscosity of 2 wt% solution of CMC aged at 29°C was measured at 50°C

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fuel. The results from this study show that ether derivatives suitable for industrial applications can be prepared from these waste materials that are available in large quantities and at little cost.

References I Yokota H, J Appl Polym Sci, 30 ( 1 985) 263 2 Majdanac L D, Poleti D & Teodrovic M J, Act Polymucia, 48

( 1 99 1 ) 32 1 3 Isserlis V I, Karoh C G, Gorodnor V D, Pozdniakova T L,

Vasiilier B V & Jegalova N N, Cell Chern Techllol, 25 ( 1 99 1 ) 2 1 1

4 Xi quam L, Tingzhu Q & Shaoqui Q, Acta Polymerica, 4 1 ( 1990) 220

5 Olaru N, Olaru L A, Stoleriu A & Leanca M, Proc lilt Symp on Wood and Pulping Chemistry. vol III (Helsinki). 1995. 1 36

6 Sikema D & Janssen H. Macromolecules, 22 ( 1 989) 364 7 Westra J. Macromolecules. 22 ( 1 989) 367 8 Dolz-Planas M, Nonald-Garcia C, Herraez-Dominguez J &

Belda-Maximino R, J Pharm Sci, 80 ( 199 1 ) 75 9 Ghannam M T & Esmail M N. Ind Eng Chem Res, 37 ( 1 998)

1 335 10 Olaru N, Olaru L, Stoleriu A & Timpu D, J Appl Polym Sci,

67 ( 1 998) 48 1 I I ASTM, American Society for Testing Materials ASTM 1974-

62 Test for alcohol-benzene soluble matter in cellulose Philadelphia Pa, 1 968

1 2 Wise L E , Murphy M & Addieco A A , Paper Trade J. 122 ( 1 946) 35

1 3 Ash in pulp Eastom Pa, Tappi Technical Association of the Paper and Pulp Industry Tappi T22 1 -M58, 1 97 1

622

Indian J. Chern. Technol ., November 2003

14 Solubility of pulp in cold sodium hydroxide Easton Pa, Tappi, Technocal association of the Paper and Pulp industry Pappi 23 1 -M58, 197 1

1 5 Alexander W J & Mitche R L, Anal Chem, 2 1 ( 1 949) 1 297 16 Testing sodium carboxymethyl cellulose. Philadelphia Pa,

ASTM American Society for Testing Materials. ASTM D 1439-65, 1 967

17 Grossman F, Klauss W, Mergenthaler E & Soucji S W, Lebellsm Z Vnters Forsch, 1 5 ( 1 964) 143

1 8 Rydholm S A , Pulping Processes (Wiley Interscience New York), 1965, 96

1 9 Timell T , Tappi J, 40( 17) ( 1 957) 586 20 Clermont L P & Schwart H, Pulp Pap Mag Can, 52( 12)

( 195 1 ) 1 03 2 1 Mutton D B, Wood Extractives. edited by Hillis W E

(Academic Press New York), 1 962, 331 22 Hillis W E Wood Extractives edited by Hillis W E

(Academic Press New York), 1 962, 481 23 Unzeodu U N, Studies ill the Biodeterioration of Wood

Treated with Organic Extractives of Some Tropical Hardwoods, 1 996 (unpublished)

24 Snell F D & Ettre L S (Eds) Encyclopedia of Industrial Chemical Analysis vol 9 (Interscience New York), 1 970, 59

25 Scott C D, Biotechnol Bioeng, 39 ( 1 992) 1 064 26 Glicksman M, Gum ill Food Industry (Academic Press New

York), 1 969, 245 27 El-Molloa M M & EI-Sayad H S, Adv Polym Technol, 20( 1 )

(200 1 ) 58 28 Edali E, Esmail M N & Vatristas G H, J Appl Polm Sci, 79

(200 1 ) 1 787 29 Okieimen F E, J App/ Polym Sci, (in press) 30 Singh R P, Tripathy T, Panda J, Kannan K, Jain S K & Lan

N T, Polym Eng Sci, 40 (2000) 46