1997 Volume 2

Microbial contaminants will decrease the quality of pigments and fillers in paper and board industry . Microbe-caused spoilage of these raw materials as well as indirect deteriorative effects of these spoiled
additives on the machine housekeeping, production and hygienic properties of paper products are well-known problems at the mills.

The traditional analysis of colony forming units helps both the manufacturer ofraw material and his client to understand, what are the major contaminants and their densities in the raw material studied.
These methods, unfortunately, are unsatisfying when rapid microbiological analyses are needed in urgent situations (trouble shooting, prevention of process contamination) . Their shortage as indicators of the effects of biocides on the activity of microbes is also evident . Three “rapid methods” were regarded as promising alternatives of colony count analyses in the control of paper and board
machine’s processes: detection of microbial growth by impedance method or turbidity test and measurement of biomass by luminometric ATP assay . When tested for mineral additive control, difficulties were arisen in every case: inhibitive effect of sedimentation of the sample in direct impedance measurement, poor interpretation of slow growth responses in indirect impedance method and the adsorptive effects of turbidity on the light emission (ATP assay) or on the background
absorbance (turbidometry) . For these reasons, strong dilutions of samples were needed and only high microbial densities (over 1000000 CFU/ml) were practically measurable by these methods. Integration of total impedance change may help to estimate low microbial densities by impedance methods, and more effective extraction and fractioning of microbial ATP may increase the sensitivity of ATP assay . Turbidometry seems to be a rather finished method, but its weak point is the long incubation period needed. Some efforts to develop all methods for the control of mineral additives seems thus to be necessary.

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The role played by AKD vapours during internal sizing was investigated using commercial AKD waxes and model surfaces. The model surfaces consist of cellulose and cellulose acetate films deposited on smooth glass slides. These cellulosic films were exposed to AKD vapours at temperatures ranging from 80’C to 175oC for different periods of time. The extent of sizing was followed by measuring the advancing contact angle of water over the treated surfaces. A simple model, considering both physisorption and chemical reaction, was developed and validated with experimental data. The energy of activation of 61 .4 kJ/mole was derived from the Arrhenius plot . From a series of indirect techniques, it is concluded that the establishment of a covalent bond between cellulose and AID is essential in order to introduce permanent hydrophobicity to cellulosic surfaces . The effect of “sizing promoters” on the reaction rate was also examined.

Both NaHC03 and cationic PEI failed to catalyze sizing between cellulose and AKD vapours. The mechanism proposed and the model will shed new light on the phenomena of AKD sizing treatment and sizing migration.

Mechanisms of retention of AKD are studied in terms of effects of cationic polymer additions, and roles of fines and carboxyl groups of pulp fibers. Handsheets were prepared from normal pulp and fines-free pulp under various conditions, and AKD contents in the handsheets were determined by pyrolysis-gas chromatography (PY-GC). The addition of cationic polymer (PAE) to pulp suspension was clearly effective in promoting AKD sizing for both cured and noncured handsheets, resulting from higher
retention of AKD in the sheet by cationic PAE molecules. Potential measurement indicated that the originally cationic AKD emulsions come to have amphoteric surface charges in pulp suspension . The effective AKD retention by PAE may, therefore, be due to ionic bond formation between anionic sites of AKD emulsion surfaces and anionic pulp fibers or fines through cationic PAE molecules. The experiments using fines-free pulp showed that most of the added AKD was adsorbed on fines of beaten pulp . Blocking of carboxyl groups in pulp with nonionic methylamide groups resulted in nearly no sizing degrees and quite low AKD contents. Therefore, it is clear that dissociated carboxyl groups in pulp fibers and fines are the actual retention sites of AKD emulsion particles at the usual addition levels of AM Among chitosan salts and PAE used at 0.1-0.4 addition levels, chitosan AcOH salt gave the highest effect on AKD retention as well as sizing degrees. Good correlation between AKD
contents and sizing degrees was obtained ; sizing behavior of AKD-sized handsheets was explainable in terms of their AKD contents determined by PY-GC, and thus retention of AKD is the significant first step for AKD sizing. Solid-state ,3C-NMR analysis of cellulase-treated residues of 13C-labelled
AKD-sized handsheets showed that size components were present in papersheet as structures of either the original AKD or ketones, hydrolyzed AKD, without forming ß-ketoesters . SEM observations of AKD-sized handsheets indicated that the effect of curing on AKD sizing is explained in terms of melting of size molecules and their spreading over pulp fiber surfaces .

An investigation concerning the interactions between cationic starch and peroxide bleached thermomechanical pulp (TMP) has been carried out. The influence of electrolytes, pH, temperature, a fixing agent and charge density of the starch is discussed. The adsorption of cationic starch onto dispersed and dissolved wood substances and unwashed fibres was reduced by an increase in NaCl concentration. The adsorption onto washed fibres, however, showed a maximum with increasing NaCl concentration. The adsorption onto dispersed and dissolved substances and unwashed fibres increased and reached a plateau level as function of increasing pH.

Onto washed fibres, the adsorption was reduced as pH was increased from 5 to 8. An increase in temperature affected only the adsorption onto washed fibres. A fixing agent retained the dispersed and dissolved wood substances more effectively than the ordinary cationic starch but the amount of adsorbed cationic starch remained unaffected by the presence of the fixing agent. Cationic starch of medium charge density (degree of substitution, D.S ., : 0.035) aggregated turbid substances more effectively than cationic starches of low charge density (D.S . 0.015) and of high charge density (D.S . 0.05) .

Novel comb copolymer with long polyacrylamide backbones bearing very short polyethylene glycol (PEG) pendant chains were prepared by the free-radical copolymerisation of acrylamide (AM) and PEG acrylate macromonomers. The copolymers are effective retention aids for mechanical pulps in retaining fines and precipitated calcium carbonate (PCC). The optimum copolymer stricture had a molecular weight greater than 3 million and contained 0.5 – 1 .0 % of PEG pendant chains with 9 to 23 polyether repeat units. The retention of fines induced by copolymer/phenolic resin (PFR) dual-polymer system follows the mechanism called “complex bridging flocculation” . According to this mechanism, the copolymer molecules aggregate in the presence of PFR to form a colloidal dispersed polymer complex which hetero-flocculates with fine particles. The interpolymer complex formation were experimentally observed through precipitate isotherms measurement, dynamic viscosity measurement and fluorescent microscopy.

The flocculation of three colloidal dispersions (precipitated calcium carbonate (PCC), T’02 and a calcined clay) using a combination of polymeric flocculants and cofactors was investigated . The flocculants used were PEO (MW = 9×10′), CPAM (a cationic copolymer of acrylamide) and POLYPAM-CO-PEG (a non-ionic comb copolymer (MW = 5×100 consisting of a polyacrylamide backbone with – I mole % pendent PEG chains). The cofactors were based on polyvinyl phenol-co-sodium acrylate) and polyvinyl phenol-co-sodium styrene sulfonic acid). The amount of flocculation induced was dependent on the components present in each system. Cofactors containing sulfonic acid were more calcium ion
tolerant than the cofactors containing carboxyl groups. These latter cofactors formed a precipitate when exposed to > 0.6 mM Ca”. Maximum flocculation of PCC was obtained by using POLYPAM-CO-PEG with a cofactor containing 23 mole % of sulfonated groups . TiO, was not flocculated when PEO was employed due to the adsorbed layer thickness of this flocculant being approximately equal to half the Debye screening length in 0.001 M NaCl. However, T’02 was flocculated by POLYPAM-CO-PEG and CPAM, the best flocculation being obtained when POLYPAM-CO-PEG was used with either a
cofactor containing 19 mole % sulfonated groups, or a cofactor containing 14 mole % acrylic acid groups . Overall, the easiest colloid to flocculate was the calcined clay ; maximum flocculation being obtained when PEO was combined with a cofactor containing 19 mole % sulfonated groups.

In general, the flocculation was most sensitive to the charge of the cofactors. It is proposed that the hydrophobic character of the vinyl phenol based cofactor is important. Hydrophobic interaction may be a part of the cofactor interaction with PEO and subsequent complex adsorption on surfaces.

A model is presented for the entrapment of a distribution of particles by a distribution of pores. The fraction of particles retained and their distribution of sizes can be calculated for evolving and static porous structures. For evolving structures the change in distribution and fractional retention through the structure can be calculated. Also, the variance in these parameters between zones in the plane of the sheet can be calculated. The agreement between the theory and experimental data is good . The theory has relevance to the retention of fillers and fines in the papermaking process and to more general problems of stochastic porous media.

Paper properties can be controlled by mixing different furnishes . The outcome of the elastic, strength and toughness properties is analyzed in this work using results from other fields of material science . particularly from composites . We discuss the micromechanics of reinforcement fibres, their conformability to the background fibre web and the fracture processes in reinforced paper. Reinforcement fibres should have high ductility and they be similar to the mechanical furnish iii their
micromechanical stiffness.