Pulp samples

In the preparation of citrus pulp samples by this revised method the likelihood of contamination appeared to be eliminated providing the tools and work area were free of contaminants and the manipulations were carefully executed. However, the samples so prepared do not contain any of the pulp from the area immediately adjacent to the peel and to that extent are not totally representative. 

Stone Fruit Types. Very preliminary studies of DDT or parathion penetration into peach fruits were completed. The pulp samples were prepared by immersing the intact fruits in boiling water for 1 minute, slipping the skins off, rinsing thoroughly with water and removing the seeds. 

Preliminary Remarks. The material to be hydrolyzed should be in a milled or pulverized condition or reduced to minute pieces. Wood and pulp samples should be extracted with ethanol-benzene and ethanol according to TAPPI-Standard T6m-59. Each method described below can be applied to 2-50 mg of material. The evaporator for removing the TFA should be kept in a hood. Contact of the acid with skin and eyes must be avoided. 

Filter the pulp sample (fibre-water suspension) through a Schleicher Schuell Black ribbon no 5891 ashless filter paper with water suction. Immerse the calibrated Ca(II)-ISE and the Ag/AgCl/3M KC1 reference electrode in the filtrate and record the potential (E (mV)) until a stable reading ( + 0.5 mV) is obtained. Calculate the Ca(II) activity of the pulp sample by using the calibration plot. 

The concentration (activity) of free Ca(II) of pulp samples determined by Ca(II)-ISEs may be significantly lower than the total Ca(II) concentration due to complexation of Ca(II) by different components in pulp samples. This should be kept in mind when comparing results obtained by the Ca(II)-ISE with other methods, such as ICP-AES. 

Table II. Average Nutrient Per iod (6 ) Composition of Citrus Pulp Samples Collected During a 13-year ...

The hydrogenated pulp, sample 33, was obtained by hydrogenating sample 7 in the presence of a solid catalyst, palladium-on-activated carbon (5%) [16]. 

The rest of the pulp samples listed in Table I (8 to 13) were provided by Dr. C.-H. Tay of Abitibi-Price Inc., Mississauga, Ontario, Canada. These samples were in the form of handsheets and were stored in the dark in a freezer at -18°C until used. 

Raman spectra obtained from pulp samples 4 to 13 are shown in Figures 2 to 4. For these samples, pulping and bleaching processes produced changes in the 850 to 1850 cm-1 spectral region. The features in these spectra are typical of lignocellulosic materials (authors unpublished work). 

Spruce Mechanical Pulps and Treatments. When spruce pulp sample 4 was treated with borohydride, the pulp became brighter (Table I). In the Raman spectrum of the bleached pulp, bands at 1620 and 1654 cm-1 declined in intensity (Table III). These changes were probably caused by the removal or modification, or both, of chromophores and aromatic carbonyl groups. It is known that... 

Figure 7. Relative band intensity of 1654 cm-1 Raman band in various wood and pulp samples. Samples are identified in Table I.

Simple lignin-like para- and ort/to-quinoid structures were impregnated onto cellulose and mechanical pulp and photolyzed with a xenon lamp. The photo-reversion properties of these impregnated pulp samples were monitored as a function of time. The results of these studies indicate that in general not all quinoid type structures contribute to further photo-yellowing of mechanical pulp. 

Hydrolysis on an analytical scale and work-up procedure. The wood or pulp sample (2.000g), suspended in 100 ml of buffer solution, was refluxed for 19 hours. After being cooled to room temperature, the mixture was filtered through a Buchner... 

The natural content of stilbenes is considered to be very low in spruce wood lignin and this was confirmed in the present work (Figure 5). Analysis of the aqueous extracts after mild acidic hydrolysis revealed, however, that from wood to unbleached pulps and further to bleached pulps a stepwise conversion of diarylpropane to diguaiacyl stilbene structures takes place (Figure 5). The content of diarylpropane structures was found to be 25% less in the unbleached pulp samples than in the wood with a simultaneous increase in the content of stilbene structures. After hydrogen peroxide bleaching, the content of diarylpropane structures further decreased and the... 

Vanillin structures can be considered to be minor lignin end groups and compounds containing vanillin moieties were isolated from all wood and pulp samples. The yields were, however, much lower than those of either coniferyl alcohol... 

Pulp Samples. The samples used in the study were commercial unbleached and peroxide-bleached spruce (Picea abies) groundwood (GW), unbleached and peroxide-bleached spruce, and unbleached and peroxide-bleached aspen chemimechanical pulp (CTMP). 

Figure 6 shows a difference spectrum between an irradiated pulp sample of peroxide-bleached groundwood and the same sample after storage for 24 hours. The relative reflectance decreases in the UV-region decrease and increases in the visible region. 

The following gives a brief compilation of procedures to determine hexenuronic acids in cellulosic pulp samples. The common methods are based on hydrolysis of HexA moieties from pulp, either enzymatically or chemically, with subsequent quantification of the hydrolysis products either directly or after chemical conversion into UV active compounds. A comparison of these three methods is given by Tenkanen et al. [136]. For comparison rather than exact determination of HexA, e.g., during bleaching stages, the diffuse reflection UV VIS method can be applied [137]. A photoacoustic FTIR procedure based on chemometric analysis has been described as well [138]. In Table 3, the available methods to analyze HexA moieties in cellulosic material are summarized. 

Fig. 15 UV radiation of celiuiose for different times (h). ADSco plots of a pulp without hemicellulose left) and with hemicellulose (right). The ADSco plots show the MW-dependent differences in the carbonyl content between the respective irradiated pulp samples and the non-irradiated starting material (SM). Reprinted with permission from Holzforschung (2004) 58 597. Copyright (2002) Walter de Gruyter...

Materials. A number of papermaking pulp samples, including bleached and unbleached, sulfite and sulfate, hardwood and softwood, and semichemical varieties, were analyzed thermogravimetrically. Some of these pulps, artificially aged at elevated temperatures and humidity, were also included. A list of the pulps and the codes assigned to them for easier reference are given in Table I. 

---