SYNOPSISThe effect of press-drying temperature on the surface chemistry of chimicothernomechanical pulp fibers has been studied using electron spectroscopy for chemical analysis (ESCA). The chemical composition showed no significant variation for press-dried samples at temperatures between 25 and 140°C. On the other hand, ESCA showed that lignin content increased whereas hemicelluloses content decreased on the surface of press-dried samples at 175OC. By its hydrophobic nature, lignin gives to paper and paperboards better dimensional stability and resistance to moisture and water. However, lignin does not intervene in fiber bonding because the specific bond strength does not vary with press-drying temperature.
SynopsisHandsheets of post-treated chemithermomechanical pulps (CTMP) and a sample of Whatman paper no. 1 were analyzed using an ESCA spectrometer. All of these samples revealed the presence of the C,, C,, and C, components in the carbon (1s) peak and the 0, component in the oxygen (1s) peak; the 0, peak component which was present in the other samples was missing from the Whatman paper. Pulp sulfonation produced a reduction in C, representing the group of carbon not bonded to oxygen, and an increase in C, with C, remaining relatively constant. These changes imply reductions in lignin and extractives and a corresponding increase in cellulose content on the fiber surface. Extrapolation of the C,, C,, C,/C,, and O/C curves of CTMP to zero percent sulfonation yielded the same values as those obtained for pure TMP. ESCA analysis allows us to monitor the increase of sulfur content as a function of sulfonation in accordance with results obtained from bulk pulp sulfonate content titration. INTRODUCTIONDespite the growth in the synthetic polymer industry, products made from wood fibers and cellulose still constitute the most important quantity of organic polymeric materials. Although the chemical composition of those materials are well characterized, much less is known about their surface chemistry, which in turn affects the properties of the final product. In the case of paper, for example, the quality of fiber-to-fiber bonding depends largely on the chemical nature of the fiber surface, which in turn determines the physical strength of paper and even its resistance to weathering and to photodegradation.Surface spectroscopic techniques, such as electron spectroscopy for chemical analysis (ESCA), reflectance (ATR) infrared spectroscopy, wettability measurements, and scanning electron microscopy (SEM) have potential of yielding chemical information for interfaces with a resolution of 10 A or better.','Since the ESCA technique is based on a direct analysis of the kinetic energy of electrons that have been excited by high energy x-rays and pulled away from their atomic environment, this technique is a powerful tool for the chemical analysis of surfaces of synthetic p~l y m e r s~-~ and natural or modified textiles fiber^.^^^ In fact, ESCA has already been employed in the characterization of the surface composition of wood fibers8*' and cotton fibers," and the results obtained seem very promising for the pulp and papers industries. The main objective of this study is to use the ESCA technique to characterize the changes in the surface chemistry of chemithermomechanical (CTMP) fibers when treated to various degrees of sulfonation. ESCA spectra of these fibers were also compared to the spectrum of Whatman paper no. 1, a material which was shown to have a surface composition rather close to that of cellulose. '-lo EXPERIMENTAL CTMP samples obtained from Kruger Inc. were cooked in a pressure bomb (1 L) for various periods of time ranging from 0 to 8.5 h in order to reach various degrees of sulfonation. The pulp sulfonation was d...
This study investigates alternatives that can improve the internal bond strength (IBS) of paper by pulp refining and paper press-drying (PD). The improvement mechanisms of IBS and their impact on the strength development of high-yield pulps are discussed. All experiments were conducted using a factorial design where the factors were four pulp types (one spruce thermomechanical (TMP) and three chemi-thermomechanical (CTMP) from spruce, birch, and aspen), three refining levels, three PD temperatures and three pressures. The effects of these treatments on the physical and mechanical properties of paper were studied using an analysis of variance. Refining changed the fibre surface, thereby promoting mechanical adhesion. PD temperature softened the fibres and changed their surface chemistry, while PD pressure improved the contact area between fibres. These changes led to an important improvement in IBS which explained, to a large extent, the variations in paper properties. Compared to air-dried paper, PD paper showed much higher properties for most tested pulps at all refining levels. These results were due to the increase in bonded areas. PD at 175°C substantially improved the wet tensile strength of paper due to the flow of lignin on the fibre surface, which protects the hydrogen bonds from moisture.
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