Synergism of enzymes in chemical pulp bleaching from an industrial point of view: A critical review

Enzymes are biological catalysts and are very specific, catalyzing either a single chemical reaction or a limited number of closely related reactions. For example, xylanases are enzymes that catalyze the cleavage of polymeric xylan and thereby break down this hemicellulose. The first xylanase enzyme preparations used in the bleaching process of chemical pulp also contained cellulase, which catalyzes the hydrolysis of cellulose. This obviously had an adverse effect on pulp yield and quality. Unfortunately, this setback gave enzyme-assisted pulp bleaching a negative reputation. At a later stage, enzyme producers managed to engineer enzyme production strains that generated cellulase-free xylanase preparations. However, due to the initial negative experiences with the earlier enzyme mixtures, only a limited number of companies in the pulp industry have seriously considered using these so-called second-generation enzymes in their bleach plants. It is apparent that these improved enzyme preparations would bring about significant benefits in terms of chemical cost savings and effluent quality. In addition to xylanase-aided bleaching, it is possible to improve the effectivity further by adding other enzymes, such as lipase and esterase, to create an enzyme cocktail. This may be particularly beneficial in the bleaching of hardwood pulp, such as white birch, which often encounters complex and troublesome problems with wood extractives. By adding different types of enzymes at more than one position in the fiberline, even further improvements are possible. The main objective of this review is to discuss the advantages of incorporating modern enzyme preparations in the bleaching of chemical pulp.     

Site-selective substitution and resulting magnetism in arc-melted perovskite ATiO3-δ (A = Ca,Sr, Ba)

Magnetic properties in perovskite titanates ATiO_3-δ (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis was conducted by powder synchrotron X-ray diffraction with Rietveld refinements. Quantitative chemical element analysis was carried out by X-ray photoelectron spectroscopy. Magnetic measurements were conducted by vibrating sample magnetometer and X-ray magnetic circular dichroism (XMCD). The magnetic properties are found to be affected by impurities of 3d elements such as Fe, Co, and Ni. Depending on the composition and crystal structure, the occupation of the magnetic ions in perovskite titanates is selectively varied, which is interpreted to be the origin of the different magnetic behaviors in arc-melted perovskite titanates ATiO_3-δ (A = Ca, Sr, Ba). In addition, both formation of oxygen vacancies and the reduction of Ti⁴⁺ to Ti³⁺ during arc-melting also play a role as proven by XMCD. Nevertheless, preferential site occupation of magnetic impurities is dominant in the magnetic properties of arc-melted perovskite ATiO_3-δ (A = Ca, Sr, Ba).     

Effects of a Nd—Fe—B magnetic filler on the crystallization of poly(phenylene sulfide)

The crystallization of poly(phenylene sulfide) (PPS) in a polymer–magnetic Nd—Fe—B powder suspension was studied. Isothermal crystallization behavior was analyzed by way of differential scanning calorimetry, and the kinetics were described via the Avrami equation. The Avrami parameters and the crystallization times were strongly affected by both the particle size and the presence of a coupling agent coated on the filler particles. The small Nd—Fe—B particles exhibited long induction and half‐times, whereas the large particles tended to have short crystallization times. Particles ranging from 38 to 150 μ appeared to have similar crystallization times and to have no significant change in the value of Avrami index with melt crystallization temperature. As a result of these analyses, the dynamic mechanical properties were determined to correlate the fundamental polymer crystallization characteristics and the physical properties of the PPS binder. The enhancement of the wetting of the filler to the binder was promoted through the coupling agent, as confirmed by dynamic mechanical testing performed on the samples. The storage modulus typically decreased because of the presence of the uncoated small particles. Conversely, the loss modulus was enhanced because of the presence of the coated small particles in the PPS binder. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1091–1102, 2002     

Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

The tert‐butoxy radical‐facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free‐radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP‐graft‐PMMA residues were detected by solid‐state ¹³C‐NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert‐butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1–2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 898–915, 2002     

Thermal crosslinking of collagen immobilized on poly(acrylic acid) grafted poly(ethylene terephthalate) films

Graft polymerization of acrylic acid onto plasma‐treated poly(ethylene terephthalate) (PET) films was used to prepare surfaces suitable for collagen immobilization by dip‐coating. Such surfaces could be used as matrices for smooth muscle cell cultures in tissue engineering. Contact angle measurements showed that plasma‐treated and grafted PET films undergo considerable surface reorganization during storage under ambient conditions. However, after collagen immobilization the contact angle remained relatively stable. The amount of collagen initially attached to the film surface increased with increasing poly(acrylic acid) graft density, but subsequent washing in water led to significant collagen loss. This loss could nevertheless be substantially reduced by thermal crosslinking of the collagen in the range 110–130 °C. Atomic force microscopy (AFM) observations suggested that the washed crosslinked collagen has a very similar structure to that of the un‐crosslinked collagen. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1874–1880, 2002     

The importance of dietary carbohydrates

Forty years ago carbohydrates (CHO) were regarded as a simple energy source whereas they are now recognized as important food components. The human diet contains a wide range of CHO, the vast majority of which are of plant origin. Modern techniques based on chemical classification of dietary CHO replaced the traditional "by difference" measurement. They provide a logical basis for grouping into categories of specific nutritional importance. The physiological effects of dietary CHO are highly dependent on the rate and extent of digestion and absorption in the small intestine and fermentation in the large intestine, interactions which promote human health. Current knowledge of the fate of dietary CHO means that the potentially undesirable properties of many modern foods could be altered by using processing techniques that yield foods with more intact plant cell wall structures. Such products would more closely resemble the foods in the pre-agriculture diet with respect to the rate of digestion and absorption of CHO in the small intestine. The potentially detrimental physiological consequences of eating sugars and starch that are rapidly digested and absorbed in the small intestine suggest that, as fibre, the form, as well as the amount of starch should be considered. Increasing consumer awareness of the relationship between diet and health has led to demands for more widespread nutrition labelling. The entry "carbohydrate" is required in most countries, and the value is usually obtained "by difference" and used in the calculation of energy content. However, the value provides no nutritional information per se. Food labels should provide values that aid consumers in selecting a healthy diet.     

Combinatorial synthesis of new cationic lipids and high-throughput screening of their transfection properties

Here we describe the first synthesis-screening approach for the identification and optimization of new cationic lipids for gene transfer in various cell lines. Combinatorial solid-phase chemistry was used to synthesize a library of new cationic lipids based on 3-methylamino-1,2-dihydroxypropane as the polar, cationic lipid part. As the nonpolar lipid part, different hydrocarbon chains were bound to the amino group of the scaffold and the amino group was further methylated to afford constantly cationic lipids. Lipids were synthesized in both configurations and as racemates, and the counter ions were also varied. By using a fully automated transfection screening method and COS-7 cells, the cationic lipid N,N-ditetradecyl-N-methyl-amino-2,3-propanediol (KL-1-14) was identified as a candidate lipid for the development of an improved transfection reagent. Screening the transfection properties of KL-1-14 in numerous combinations with the helper lipids dioleoylphosphatidylethanolamine (DOPE) and cholesterol (Chol) revealed that Chol is the most suitable helper lipid and the best KL-1-14/Chol ratio is 0.5-0.7. Compared to the standard transfection lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulfate (DOTAP), transfection efficiency was improved by a factor of about 40. Furthermore, by using R- and S-configured KL-1-14, it could be shown that the configuration of the lipids had no significant influence on its transfection efficiency. The highest transfection efficiencies were achieved with chloride as the counter ion. The new lipofection reagent was further tested to transfect the cell lines MDA-MB-468, MCF-7, MDCK-C7, and primary dentritic cells (DC), which are important for the development of new anticancer gene therapy strategies. Even in these cells, KL-1-14/Chol (1:0.6) had improved transfection efficiencies, which were about two to four times higher than for DOTAP.     

Effect of FA chain length on normal- and reversed-phase HPLC of phospholipids

Forty-seven saturated synthetic diacyl PA, PC, PE, PG, and PS and five unsaturated diacyl phospholipids (PL) underwent normal- and reversed-phase (RP) HPLC with isocratic isopropanol/hexane/water (5∶4∶1) and methanol/chloroform/acetonitrile/water (79.5∶9∶8∶3.5) mobile phases, respectively. For normal-phase HPLC, capacity factors (k′ _i ) decrease with chain length (n) of the two identical PL FA residues, whereas the opposite occurs with RP (C₁₈)-HPLC. Plots of In k′ _i vs. n for individual PL classes are in general curved, violating the linear free-energy relationship. For PL of the same n but with different head groups, k′ _i with normal-phase HPLC varies as PE<PG<PA<PS<PC, except when n≥16, when the order is PE<PS≈PA≈PG<PC. For RP-HPLC, the order of k′ _i values is PG<_A≈PS≤PC≈PE until n≥16, when it is PA≈PG<PS≪PC≈PE. With normal-phase HPLC, k′ _i values of PL with unsaturated FA of n=18 are ordered as PE<PA<PC. Increasing degrees of unsaturation lead to increasing k′ _i .     

Synthesis and characterization of dehydroabietic acid derivatives suitable for surfactant synthesis

The syntheses of derivatives of dehydroabietic acid suitable for further manipulation into surfactants are presented. The compounds are produced at very high yields and purity. They contain several different functional groups, e.g., carboxylic acid, amine, ester, alcohol, and an aromatic group. The functional groups are useful as the linking unit to the hydrophilic part in synthesizing surfactants.     

Thermoreversible Gelcasting: A Novel Ceramic Processing Technique

A new ceramic processing method, thermoreversible gelcasting (TRG), has been developed. The method uses a gelation process that can be reversed multiple times. Two Al₂O₃ systems have been explored with the use of a specific triblock copolymer to form a binding gel network. The mixture becomes a free-flowing liquid on heating above 60°C. However, on cooling below 60°C, the slurry instantaneously transforms to a physical gel. This process can be reversed easily (essentially with an infinite processing time window) while the solvent is present in the system, which is advantageous when trying to produce high-quality dense pieces if initial casting irregularities occur. Near-theoretically dense specimens have been produced with properties consistent with reported values of high-density Al₂O₃.