Research Articles

Medium or high charge density cationic polyelectrolytes are frequently used for water treatment. In the papermaking wet-end they are used as retention agents or as flocculating aids. Negative polyelectrolytes that enter the papermaking system increase the demand for cationic polyelectrolytes. Polyelectrolyte concentration can be determined by the colloidal titration method, using either of two options for detecting the endpoint: i) visual observation or spectrophotometric determination of the colour change of an indicator, or ii) streaming current measurement. This work discusses the best conditions for the application of the titration using spectrophotometric measurement for the end point detection. Poly-diallyldimethylammonium chloride was used as the cationic polyelectrolyte, potassium polyvinyl sulphate as the negative polyelectrolyte, and o-toluidine blue as the positive indicator dye. The polyelectrolyte concentration range, interference from the metal ions affecting the indicator color change, the optimal indicator concentration to avoid precipitation problems, and the effect of adding a surfactant to the indicator solution were also considered. Titration curves were analyzed and optimized. Under these conditions the technique provided results with acceptable precision.

The sorption properties of lignin-wool composites towards oil pollution at different concentrations of the contamination were studied. The release ability of oil pollutant was studied by a gravimetric method and by determining the chemical oxygen demand of cleaned water. It has been established that technical hydrolysis lignin–wool composites display a low release ability of oil-based pollutants and a slow rate for achieving release equilibrium.

In order to make full use of rice straw (RS) produced at large quantity in China and to reduce the production cost of L-lactic acid, attempts were made to utilize the hydrolysate of RS as sole carbon source and the lignocellulose as inert support for producing L-lactic acid using solid state fermentation (SSF). The pretreated rice straw was enzymatically hydro- lyzed by cellulase, and the hydrolyzate, containing reducing sugars supplemented with a minimum of (NH4)2SO4, MnSO4, and yeast extract, was used as moistening agent to impregnate 5g of RS, which was used as the inert support for SSF. Maximum L-lactic acid production of 3.467g per 5g of support was obtained at 37 oC, using Lactobacillus casei as inoculum, after 5 days of fermentation with optimized process parameters such as 72% moisture content, 4g per 5g support of reducing sugars, 2.5ml per 5g support of inoculum size, 3g per 5g support of CaCO3, and pH 6.5.

The response of kraft pulp of Melocanna baccifera (Muli bamboo) to different conditions of oxygen delignification and subsequent bleaching using CEHH sequence was studied. Oxygen delignification caused the kappa number of the pulp to drop between 40 and 75% over the range of temperature 70-100 °C, oxygen pressure 2-7 bar, alkali charge 2-4%, and reaction time 5-60 min. The oxygen-delignified pulp could be bleached to a brightness level of 86%. The conditions that favored greater kappa reduction also caused a greater reduction in the pulp viscosity, which called for an economic balance between the environmental benefits and the degradation of the pulp. Reaction temperature during oxygen delignification had an effect on the fiber curl and kink, while other variables such as oxygen pressure, alkali dose, and the reaction time had no significant effect on fiber deformation.

Bonding and activation in paper were studied with the help of laboratory test sheets and common paper strength tests. Different papermaking furnishes and raw material treatments were used to examine the effects they have on bonding and activation. Furthermore, various boundary conditions during drying were included to single out the influence of bonding and activation on paper properties. It was found that bonding is clearly increased by beating of kraft pulp, starch addition, and thermomechanical pulp fines, whereas activation benefited most from beating and addition of reinforcement fibers to mechanical pulp based furnishes. Subjecting test sheets to increasing amounts of drying stress affected activation positively, and bonding negatively. The increase in activation did not seem to be dependent on the beating degree of chemical pulp fibers. Bonding, on the other hand, deteriorated more significantly in sheets made of extensively beaten kraft fibers, i.e. in sheets where the initial bonding potential was higher. Commonly used paper strength measurements provide dependable and accurate tools for assessing the effect of different variables on both bonding and activation. A short literature survey of bonding and activation is also provided.

Major projects are underway in our laboratory focusing on mildly acidic (pH>3) and alkaline (pH<10) pretreatments of hardwood chips prior to incineration for electric power or prior to pulping for paper manufacture. Production of lignocellulosic ethanol from the hemicelluloses in the hydrolyzates will be attempted. It is of great interest to quantify the concentrations of lignin in these hydrolyzates, since lignin fragments are suspected as fermentation inhibitors. UV spectroscopy is normally used to estimate the concentration of aqueous soluble lignin. However, the 203 nm absorbance gave unreliable results for these hydrolyzates, and on some occasions the 278 nm absorbance was unduly influenced by high absorbance in the 260-265 nm range. A credible method that uses chlorination to generate methanol from the methoxyl groups in lignin will be described. Model compound experiments showed that syringyl lignin units, with two methoxyl groups, gave a methanol yield of ~1.0 mmole/ mmole of aromatic rings.

Handsheets produced from corn stalks and wheat straw soda AQ pulps were recycled in the lab. Pulping of corn stalks resulted in a low pulp yield, low bonding strength, and low recyclability. Conversely, wheat straw fiber had a better yield, very good tensile properties, and showed a considerably better response to recycling. The tensile index of wheat straw fibers retained 67% of its original value after four cycles. It could be shown that recycling caused only small changes in chemical compo-sition, but that the crystallinity index increased considerably. To be able to understand the behavior of wheat straw fiber as part of a commercial papermaking furnish, a paper containing 20% wheat straw fiber was produced on a 24 inch pilot paper machine and was recycled using a handsheet mold with white water return. Chemical analysis of the control (no wheat fiber) and the wheat-containing paper demonstrated slightly higher xylan content for the wheat-containing material. Recyclability increased slightly with addition of wheat fibers to a commercial furnish.

High-value, large-volume utilization of forest thinning materials from U.S. National Forests is a potentially important contributor to sustainable forest health. This study demonstrated the utilization of wood chips produced from thinnings for the production of thermomechanical pulp (TMP). Both whole-log chips (primarily from small-diameter logs, tops, and reject logs) and sawmill “residue” chips from a HewsawTM system (Mäntyharju, Finland) were evaluated. The residue chips produced in this study were substituted for a TMP mill’s standard residue chips up to about 50%. The whole-log chips were substituted for the mill’s whole-log chips up to about 30%. The results show that substitution of chips produced from forest thinnings reduced refining energy in all trials. Pulp quality was maintained throughout all trials.

Sodium aluminosilicate has been precipitated in-situ as filler on hardwood bleached kraft pulp fibers using papermaker’s alum and sodium silicate. The filler was produced in two ways, first in the absence of the fibers and second in the presence of fibers, i.e. in-situ precipitation of filler. The filler produced in absence of fiber was then added to the pulp slurry. Various pulp and paper properties were compared for direct loading of market filler, fresh filler loading, and filler prepared in-situ with fibers. In-situ precipitation technology provided paper with significant improvements in various properties of paper as compared to fillers directly added to the stock. Bulk and stiffness of the handsheets prepared with in-situ precipitation were much higher as compared to those of sheets prepared with fillers directly added to the pulp. There was no appreciable increase in brightness and whiteness of paper with in-situ precipitation, as an appreciable proportion of filler was precipitated inside the fibers. In-situ filler loaded pulps showed a higher filler retention value as compared to directly filler loaded pulps, as a high dose of retention aid was needed with the fillers directly added to the stock.

The lignosulphonate/polymer complex, in which the macromolecules of both components are linked together by physico-chemical bonds, has been applied as a new effective lignin-based soil conditioner (LSC). lt has an adhesive affinity both for mineral soil particles and the organic surface of lignocellulosic mulch. The modification of the mulch particles with aqueous solutions of the developed conditioner by means of impreg-nation makes it possible not only to anchor mulch to sandy soil and, thereby, to diminish significantly the evaporation from the soil surface, but also, due to mulch biodegradation, to enrich soil with the main nutrient elements and to create favourable conditions for plant growth. The effect of the mulch modification is determined by the complex composition and depends on its content in the aqueous solution and the application rate.