Surface characterization of ashtree wood meal by inverse gas chromatography

02007 Science in China PressSurface characterization of ashtree wood mealby inverse gas chromatograpZHAo Shu, LIN Xu, SONG JingWei&SHIBaoLiFlame Materials Preparation and Molecule Design Key Laboratory of Heilongjiang Province, Northeast Forestry University, HarbinInverse gas chromatography(IGc)is a sensitive and convenient method to characterize surface prop-erties and thermodynamic parameters of solid materials Surface properties of ashtree wood meal weredetermined by inverse gas chromatography in this work. the dispersive component of the surface freenergy and acid-base parameters of the ashtree wood meal were characterized. the dispersive component of surface free energy was within 36-39 mJ/m the Lewis acidic number K, was 0.53, and thebasic number K was 0.21, respectively. The results show that ashtree is amphoteric and predominantlyacidic woodashtree, inverse gas chromatography, acid-base properties, surface free energyThe surface free energy is one of the most important the thermodynamics of adsorption and the surface acidparameters in characterization of wood surface proper- base properties of polymer materials 5-7. Kamdem18)ties. It also plays a significant role in the interactions of characterized the surface properties of birch wood mealwood with plastics of composite. The surface free en- by IGC. The surface properties of ashtree wood meal areergy of wood consists of dispersive component and researched in this paper. The dispersive component ofacid-base component. The acid-base interactions are the surface free energy was characterized, and the Lewissummation of hydrogen bonding, charge transfer com- acidity and basicity were investigated. To know well theplexes, acid-base type interactions, dipole moments and surface properties of wood, that can afford theoreticalelectron acceptor-donor complexes". These properties bases to improve the interface performance of wood andaffect directly the interfacial compatibility of wood and plastics compounds, would have an important referenceplastics. Generally, surface free energy of wood is de- value for selecting and molecularly designing adhesivestermined by the contact angle method, However, the for different wood in the production of wood-basedacid-base interactions of wood surface cannot be char-acterized well. And the determined contact angle waseasily effected for some reasons, such as the coarseness 1 Inverse gas chromatographyof wood surface, temperature, and time, so the surfacefree energy cannot represent well the properties of wood IGC technique is a method, which uses organic vapor asprobes with very small volumes. a gas having no inter-various techniques can be used to characterize solid action with stationary phase is taken as carier gas. Thesurface acid-base properties, e.g. isoelectric point(EP),tested solid is packed into the column and taken as sta-indicator dye adsorption, XPS, and calorimetry or in-verse gas chromatography (IGC). IGC is a sensitive Received July 10, 200 accepted november 21. 2006and convenient method to characterize surface proper- 'c中国煤化工ties of solid materials. It has been widely used to studCN Go of NEFU of Chinawww.scichina.comwww.springerink.comChinese Science Bulletin I May 2007 I vol. 52 I no. 9 11178-1181tionary phase. The probe molecules are diluted by car- sorption free energy between stationaryrier gas. So, there is no interactions between probe mole- molecule iscules. Whenuilibrium state of adsorption is△Ga=△G0+△G,reached between the stationary phase and fluid phase, where aGa is dispersive free energy of adsorption,andthe retention time of probe solvents is measured, andAGa is the free energy of adsorption by Lewis acid-basethen the retention volumes are calculated from the reten- interactions. From the AG of molecules with differenttion time. The surface properties of solid can be calculated from the retention volumes, Vn is calculated acpolarities, combining eq (6)with eq (9),AGcording to the following equationV=( -to)FC,(1)the enthalpy of Lewis acid-base interactions AHa iswhere t is the retention time of probe solvent, to is the calculated from eq (10). The Lewis acid number Ka andretention time of non-interacting probe(such as meth-ane), F is the flow rate of camier gas, and C is a correcLewis base number Kb are calculated according to eq(10tion factor calculated by the following expression:d(n vn)C=1-B0-△H=R(10)d(/T△H=KXDN+ KLXAN,(11)where PH o is the saturated vapor pressure of water atwhere DN and aN' are the donor number and acceptorambient temperature, Po is the atmospheric pressure Jis number of polar molecules. Plotting -AHA /AN* vSthe compression correction factor for unideal gas prop- DN/AN*, one gets K, as the slope, and Kb as the inter-erties determined as follows:3(P/P)2-12(P/P2 Experimentalwhere Pi and Po are the inlet and outlet pressures of 2.1 Materialscolumn, respectivelyThe adsorption free energy of probe molecules andThe material is ashtree wood meal made in the saidstationary phase,-AGa, has a relationship with the ad- laboratory. The non-polar probe molecules were n-hesion work of probe molecules and stationary phase, hexane(C6), n-heptanes(C,), n-octane( C)and n-nonane( C9). Polar probe molecules were trichloro--△G4=NaW,(4) methane(CHCI3), acetone(Acet,) and tetrahydrofuranwhere N is the Avogadro number, and a is the surface(THF). Methane was taken as non-interacting probe.These solvents were of analytical grade and purchasedarea of probe molecules. When n-alkanes are used, only from Tianjin Kermel Chemical Reagents Developmentdispersive forces exist=24)(n)Center, China. The characteristics of probe solvents are(5) listed in Table 1where ys is dispersive component of surface free energyof solid phase, and n is surface free energy of probe Table 1 Properties of the proba basic relation exists in IGC technology(A)(ml/m2)nC651.5AG=RTInva+KCombining eqs. (4),(5)and (6), the following equa- nC8 63.0 213tion holds.nc969.022.7RTInv, =2Na(x )(n)2+KcHCl440259227When a series of n-alkanes are used, plotting RTiInVn171be calculated from the sleTuu中国煤化工When polar probe is injected into the column, the ad-CNMHGZHAO Shu et al. Chinese Science Bulletin I May 2007 I vol. 52I no. 911178-11812.2 IGC instrument3.2 Lewis acid-base parameters Ka and K, of ashtreeThe instrument was a GC-900A gas chromatography wood meal(Shanghai Tianpu Analytical Instrument Ltd, China), There are dispersive interaction and acid-base interacequipped with a flame ionization detector( FID). Nitro- tion between the surface of ashtree wood meal and polargen was used as the carrier gas. The flow rate was 11.2 probes. And the total free energy of adsorption -AGa ismL/min, measured with a soap bubble flow meter. The the sum of free energy of adsorption by dispersive in-injector and FiD were heated to 130C. The injection teraction -AGa and free energy of adsorption by acidvolumes were 0.1 HL, being injected at least for three base interaction-AGa. The free energy of adsorptiontimeby dispersive interaction is eqlal to the freAshtree was prepared as wood meal of 60-80 mesh. adsorption between ashtree wood meal surface and non-After being extracted by benzene and ethanol for 6 h and polar probes. Figure 2 is the plot of RTnV, vs a(nd"2atdried, the wood meal was packed into the column. The323. 15 K, and the line is the plot of n-alkanes. The diflength of the column was 650 mm, i d. was 2.56 mm,ference of polar probes and n-alkanes is-AGa. Theand o d, was 3.00 mm. It was washed with acetone priorenthalpy of acid-base interactions AHa is calculatedto use. The column was conditioned at 90c for 12 h. from -AG Table 3 lists the results.The IGC experiments were performed at 50, 55, 60, 65and70℃, respectively3 Results and discussion3.1 Dispersive component of surface free energy ysof the ashtree wood mealAccording to eq(7), plotting RTInVn vs a(n 2 (Figure Acet-Ad1), the dispersive component of surface free energy 7sof the wood meal at different temperatures is calculatedfrom the slopes. Table 2 lists the resultsa(D a(A'(mI/m2y?Figure 2 Plot of RTinV, vs a(n" for polar probesTable 3 -AG,' and -AH, of acid-based interaction of ashtree woodT(K-△G:(k/mo)32315328.533.15338.15343.15(Jmo)cHCl31.261.571862553.3031.23Ac.-3.26-3.10-264-2.31-1.7128.12THF-2.10-149-087-0.2906545.19220240260280300320340In eg.(11), Ka and Kb are acid and base numbersatvr/a(A'(mJ/m)9which is the accepting and donor power. From the plotFigure1 Plot of RTnV, vsa(n"for n-alkanes.of -AHa/AN*VS DNAN*( Figure 3), the slope is Ka,and the intercept is Kb. The Lewis acidic number Ka is0.53 and the basic number kb is 0.21Table 2 Dispersive component of surface free energy y, of ashtreewood meAlthough acid and base action exists at the surface,3231532815333.15338.15343.15the last surface acid-base properties are decided byn(mm2)36.323690380338463900Ky/K2+YH中国煤化工8 e is expressed withthe acid-base con-CNMHGZHAO Shu et al. Chinese Science Bulletin I May 2007 I vol. 52I no. 9 I1178-1181stants of ashtree wood meal. It shows clearly that theacidity of ashtree wood meal is stronger than basicproperty. It would be expected that the ashtree wood hasa strong adhesivity with basic plastics and basic gluesY=05256X+020914 ConclusionsR=09919The experiments show that IGC is a method of characterizing the surface properties of wood. IGC can meas-CHOure the dispersive component of surface free energy andLewis acid-base numbers of wood at certain temperatureDNAN'range. The free energy of adsorption by dispersivecomponent of ashtree wood meal is 36.32, 36.90, 38.03Figure 3 Determination of k, and K for the surface Lewis acid-base of 38.46 and 39.00 mJ/m2 at 50. 55, 60, 65. and 70C. re.spectively. The surface Lewis acidic number Ka and theTable 4 K, and kh of ashtree wood mealbasic number Kb are 0.53 and 0.21, respectively. Theresult indicates that ashtree wood meal is a lewis acidicKb/K0.21040.74natural polymer, and its total acid-basic ability Ka+kb is0.74I Santos JMRCA, Guthrie J T. Analysis of interactions in multi-matography at infinite dilution Ill. Determination of the acid-basecomponent polymeric systems: The key-role of inverse gas chromproperties of some solid substrates(polymers, oxides and carbon fi-tography Mat Sci Eng R, 2005, 50(3): 79-107bres): a new model J Chromatogr A, 2002, 969(1-2): 37-472 Sun C H, Berg J C. A review of the different techniques for so7 Uhlmann P, Schneider S. Acid-base and surface energy characteri-surface acid-base characterization. Adv Colloid Interfac, 2003zation of grafted polyethylene using inverse gas chromatography. J05(13):151-1753 Bao F C, Wang Z, Guo w. Study on the surface properties of poplarChromatogr A2002,9691-2)73-80and Chinese fir wood. Sci Sil Sin (in Chinese), 2004, 40(1): 131-1368 Kamdem D P, Bose SK Luner P Inverse gas chromatography char-lukhopadhyay P, Schreiber H P. Aspects of acid-base interactionsacterization of birch wood meal. Langmuir, 1993. 9: 3039-3044and use of inverse gas chromatography. Colloid Surface A, 1995, 100:9 Santos J MRCA, Fagelman K, Guthrie J T Characterisation of the5 Jandura P, Riedl B, Kokta B V Inverse gas chromatography study orinverse gas chromatography. J Chromatogr A, 2002, 969(1-2)rtially esterified paper fiber. J Chromatogr A, 2002, 969(1-2)111-118301-31110 Santos JMRCA, Guthrie J T Study of a core-shell type impact6 Hamieh T, Fadlallaha M-B, Schultz J. New approach to characterizemodifier by inverse gas chromatography. J Chromatogr A, 2005physicochemical properties of solid substrates by inverse gas chro-I070(12):147-154中国煤化工CNMHGZHAO Shu et al. chinese Science Bulletin I May 2007 I vol. 52 I no. 911178-11811181