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Comparison of Acid-Base Characterization Techniques on Lignocellulosic Surfaces. Which One is Right

Overview. IntroductionDescription of methods and materialsReview of basic wood chemistryEvaluation of contact angle acid-base techniquesEvaluation of inverse gas chromatography acid-base techniquesConclusions. Second International Symposium on Acid-Base Interactions. Introduction. Why study acid-base interactions of lignocellulosic surfaces?Wood adhesive bonding and paper chemistry is dependent on strong secondary forces, ie., acid-base interactions..

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Comparison of Acid-Base Characterization Techniques on Lignocellulosic Surfaces. Which One is Right

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    1. Comparison of Acid-Base Characterization Techniques on Lignocellulosic Surfaces. Which One is Right? Douglas J. Gardner, Sheldon Q. Shi and William T. Tze University of Maine Orono, Maine

    2. Overview Introduction Description of methods and materials Review of basic wood chemistry Evaluation of contact angle acid-base techniques Evaluation of inverse gas chromatography acid-base techniques Conclusions

    3. Introduction Why study acid-base interactions of lignocellulosic surfaces? Wood adhesive bonding and paper chemistry is dependent on strong secondary forces, ie., acid-base interactions.

    4. Methods Contact angle analysis Wilhelmy plate on wood veneer, pulp fibers and paper Wicking measurements on particles and pulp fibers Inverse gas chromatography

    5. Materials Wood particles and veneer Bleached Kraft pulp fiber Thermomechanical pulp fiber Bleached kraft paper Sized Kraft paper AKD AKD-Alum Rosin

    6. Wood Chemistry Cellulose Hemicellulose Lignin Extractives Vicinal Water

    7. Paper and Sizing Chemistry

    8. Contact Angle Analysis Good-van Oss Chaudhury (GVOC) Theory Chang’s Model

    9. Values of surface tension components and Parameters for Probe Liquids

    10. Calculation Methods To determine the ? LW, (Pd) first using the Geometric mean equation (one non polar liquid). To determine the ? LW, (Pd) first using the Geometric mean equation (all liquids). To determine ? LW, ? +, and ? -, or Pd, Pa, and Pb using multiple regression.

    11. Geometric Mean

    12. GVOC Theory

    13. Chang Model

    14. Effect of Calculation Methods on GVOC Model Multiple regression results in low polar component of surface energy; One-liquid higher dispersive and total energies; All- liquid method the polar portion is higher.

    15. Effect of Calculation Methods on Chang’s Model Using multiple regression method to determine the three unknowns is not reasonable. Also, one-liquid method gives higher dispersive and total energy.

    16. Comparison of Dispersive Energy Determined by One Liquid and All Liquids (mJ/m2) Using one liquid gives the same dispersive energy as the probe liquid when the contact angle is zero for higher energy surfaces .

    17. Summary for Calculation Methods It appears best to determine the dispersive component first using all the probe liquids followed by determining the acid-base components.

    18. Comparison of the Wood Surface Energy Components Determined by GVOC Model ?Stot and ?SAB for veneers are higher than particles; More electron donating ?-sites are present on both veneer and particle surfaces than the electron-accepting ?+sites.

    19. Comparison of the Wood Surface Energy Components Determined by Chang’s Model ?Stot and ?SAB for veneers are higher than particles; The surfaces of both the veneer and particle surfaces were found to be amphoteric.

    20. Total Surface Energy of Different Wood Species Determined by GVOC and Chang Models

    21. Summary of the Results for the Comparison of GVOC and Chang Models Used for Wood The total surface energies determined by the GVOC and Chang models for wood surfaces are usually within 1 mJ/m2 of each other; Total surface energy for veneers is higher than particles; and this is mainly due to the difference of ?SAB between the surfaces of veneers and particles; More electron donating ?-sites are present on the veneer surfaces than the electron-accepting ?+sites. GVOC theory shows that basicity dominates the lignocellulose surface; Chang’s model shows the lignocellulose surfaces are more amphoteric.

    22. Total Surface Energy of Sized and Unsized Papers The surface energy of the paper fibers is decreased after sizing.

    23. Correlation of Total Surface Energy and Sizing Performance The total surface energy of the sized paper fibers determined using the Chang model correlates well with the HST test with 1% formic acid ink.

    24. Surface Energy Components of Sized and Unsized Papers Determined by GVOC Model Compared to the un-sized paper, the ?sAB, ?s-, and ?s- of the sized paper are smaller in magnitude.

    25. Surface Energy Components of Sized and Unsized Papers Determined by the Chang Model Compared to the unsized paper, the ?sAB of the sized paper is lower; After sizing, the surfaces of AKD and AKD alum sized paper become basic. There is a repulsive effect on the surface energy. Therefore, the total surface energy is lower.

    26. Calculation of Acid-Base Interaction Directly Using Square Root Coefficients Determined by Multiple Regression (GVOC*)

    27. Surface Energy of AKD-Sized Paper (mJ/m2)

    28. Correlation of Total Surface Energy and Sizing Performance The total surface energy of the sized paper fibers determined using the Chang model and GVOC* calculation correlates well with the HST test with 1% formic acid ink.

    29. Summary of the Results for the Comparison of GVOC and Chang Models Used for Sized Fibers An apparent benefit of the Chang model is its ability to determine attractive-repulsive characteristics of a surface. The conventional GVOC acid-base components ? + and ? - may not be representative of a surface which has attractive or repulsive characteristics; The GVOC equation can be used to calculate the attractive or repulsive characteristics of the acid-base interaction if the coefficients obtained by multiple regression (? +)1/2 and (? - )1/2 are used directly (GVOC*). The ?stot and ?sAB determined by both Chang model and GVOC* show similar values.

    30. Inverse Gas Chromatography The experiment was conducted on a Hewlett Packard HP 5890 Gas Chromatograph equipped with a flame ionization detector and an automatic injector. The retention time of thirteen probes was measured at three temperatures (30°C, 45°C, and 60°C). The dispersive energies were calculated using the increment of the free energy of a methylene group in the n-alkanes series. The acid-base (specific) interactions were determined using the retention data of polar probes

    31. Liquid Probes Used in the IGC

    32. Net Specific Retention Volume (Vg)

    33. Determination of Acid-Base Interaction (Isp) Papirer’s method: Isp is obtained by the plot of RTlnVg versus the logarithm of the saturation vapor pressure (log P0). Schultz’s method: Isp is obtained through the plot of RTlnVg versus surface tension and cross section [a(?Ld)1/2].

    34. Using Papirer’s Method to Determine Specific Interaction

    35. Using Schultz’s Method to Determine Specific Interaction Plot of RTlnVg Versus a(?Ld)1/2 at 60 oC

    36. Enthalpy of Specific Adsorption (KJ/mol) Determined by Schultz and Papirer Methods for Maple Particles with Various Probes

    37. Determination of the Acid-Base Parameters

    38. Correlation of the Acid-Base Parameters Determined by Schultz and Papirer Methods

    39. Comparison of the Surface Properties of TMP and Kraft Fiber Determined by Different Methods

    40. Correlation of Ka Vs. ?+ There is poor correlation between Ka (IGC) and ?+ (GVOC)

    41. Correlation of Kb Vs. ?- There is poor correlation between Kb (IGC) and ?- (GVOC)

    42. Summary on IGC Results Negative enthalpy of specific adsorption was found for the wood materials; A poor correlation exists between Ka, Kb (IGC) and ?+ and ?- (GVOC); Good correlation exists between the Schultz and Papirer methods for the Ka and Kb coefficients.

    43. Conclusions and Recommendations Using all liquids to first determine the dispersive component is the best way for calculating total surface energy for both the GVOC and Chang Models; The GVOC and Chang models provide nearly identical results if the GVOC calculation is performed in the manner proposed (GVOC*); Surface energy analysis of sized paper shows the importance of being able to measure attractive-repulsive character in acid-base measurements; In IGC, a good correlation was found between the Schultz and Papirer method to determined Ka and Kb.

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