Review Articles

The rate and extent of transport of macromolecules and other solutes into cellulosic materials and fibers have important applications in such fields as papermaking, textiles, medicine, and chromatography. This review considers how diffusion and flow affect permeation into wood, paper, and other lignocellulosic materials. Because pore sizes within such materials can range from nanometers to millimeters, a broad perspective will be used, also considering some publications related to other porous materials. Factors that limit the rate or extent of polymer or other solute transport into pores can involve thermodynamics (affecting the driving motivation for permeation), kinetics (if there is insufficient time for the system to come to equilibrium), and physical barriers. Molecular flow is also affected by the attributes of the solute, such as molecular mass and charge, as well as those of the substrate, such as the pore size, interconnectedness, restricted areas, and surface characteristics. Published articles have helped to clarify which of these factors may have a controlling influence on molecular transport in different situations.

Laccases (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) are multi-copper oxidases that are widely distributed among plants, insects, and fungi. They have been described in different genera of ascomycetes, some deuteromycetes, and mainly in basidiomycetes. These enzymes catalyze the one-electron oxidation of a wide variety of organic and inorganic substrates, including mono-, di-, and polyphenols, aminophenols, methoxyphenols, aromatic amines, and ascorbate, with the concomitant four electron reduction of oxygen to water. Laccase is currently the focus of much attention because of its diverse applications, such as delignification of lignocellulosics, crosslinking of polysaccha-rides, bioremediation applications, such as waste detoxification, and textile dye transformation, food technologic uses, personal and medical care applications, and biosensor and analytical applications. This review helps to understand the properties of this important enzyme for efficient utilization for its biotechnological and environmental applications.

In the future liquid biofuels will need to be renewable, sustainable, as well as technically and economically viable. This paper provides an overview of the challenges that the biochemical production of cellulosic ethanol process still faces. The main emphasis of the paper is on challenges that emerge from the scale of liquid biofuel production. These challenges include raw material availability, other consumables, and side stream handling. The pretreatment, C5 fermentation, and concentration of sugars in processing need improvements, too. Sustainability issues and greenhouse gas reduction also pose a challenge for implementation and require development of internationally recognized sustainability principles and standards, and certification of sustainable operation. Economics of cellulosic ethanol processes are still also an area under development and debate. Yet, the Energy Independence and Security Act mandate together with the European Union Renewable Energy Directive and other local targets are driving the development and implementation forward towards more significant contribution of biofuels in the transportation sector.

For over 2000 years the manual craft of papermaking has been practiced all over the world utilizing a variety of techniques. This review describes the evolution of hand papermaking and its cultural significance. Paper’s evolution has been shaped by the structure and chemical composition of the fibers. Almost every aspect of modern papermaking technology has been foreshadowed by traditional practices. Such practices were passed down for many generations within families of papermakers. The main sources of cellulosic fiber evolved as the ancient craft migrated from its birthplace in China to Korea and Japan, the Islamic world, and then to Europe and America. Though most paper made today comes from automated, continuous production systems, handmade paper has enjoyed a resurgence, both as a traditional craft and as an art-form. In addition, traditional papermaking methods can provide insights to help in modern applications involving cellulosic fibers.

This paper reviews recent results in the field of chemical modification of wood with linear chain anhydrides. Though the main focus is on work performed by the author, this is described in the context of related progress in the field. The combined research has demonstrated the effectiveness of chemical modification applied to solid wood and wood raw material for composites production in overcoming the main disadvantages of wood. Wood samples and wood chips/strands have been chemically modified with a series of anhydrides at equivalent levels of modification, under identical conditions, and the question was to determine which is the primary factor controlling the biological durability, the degree of cell wall bulking by the bonded adduct, or the extent of hydroxyl substitution. The results have clearly indicated that the degree of cell wall bulking caused by the adduct, rather than the extent of hydroxyl substitution, is the primary factor controlling the biological durability and water vapour sorption. Despite the large difference in OH substitution level, reaction with different anhydrides results in the same level of protection against decay, marine borers and termites, and in the same level of water vapour sorption. These observations suggest that the mechanism of protection is not chemical/biochemical in origin, but relates to the bulking of the cell wall by the reacted adduct.

The pulp and paper industry has started applying new, ecologically sound technology (biotechnology) in its manufacturing processes. Many interesting enzymatic applications have been proposed. Implemented technologies tend to change the existing industrial process as little as possible. Enzymes have great potentials in solving many problems associated with the use of recycled fiber, especially related to deinking, drainability, hornification, refining, and stickies. Based on the promising results of mill-scale trials, several mills in the world have started using enzymes for deinking. The potentials of cellulase enzymes have also been demonstrated for reducing the energy requirement in pulp refining, improving the machine runnability and stickies control when using recycled fiber. They have the important benefits in that they can be considered a “green” product. They are natural occurring compounds with little adverse impact on the environment. This paper deals with the importance of recycling of paper, problems associated with the recycling, and potentials of enzymes in solving these problems. A few case studies have also been included.

Embrittlement threatens the useful lifetime of books, maps, manuscripts, and works of art on paper during storage, circulation, and display in libraries, museums, and archives. Past studies have traced much of the embrittlement to the Brønsted-acidic conditions under which printing papers have been made, especially during the period between the mid 1800s to about 1990. This article reviews measures that conservators and collection managers have taken to reduce the acidity of books and other paper-based materials, thereby decreasing the rates of acid-catalyzed hydrolysis and other changes leading to embrittlement. Technical challenges include the selection of an alkaline additive, selecting and implementing a way to distribute this alkaline substance uniformly in the sheet and bound volumes, avoiding excessively high pH conditions, minimizing the rate of loss of physical properties such as resistance to folding, and avoiding any conditions that cause evident damage to the documents one is trying to preserve. Developers have achieved considerable progress, and modern librarians and researchers have many procedures from which to choose as a starting point for further developments.

Chitosan obtained by alkaline deacetylation of chitin is a non-toxic, biocompatible, and biodegradable natural polymer. Chitosan-based hydrogel polymeric beads have been extensively studied as micro- or nano-particulate carriers in the pharmaceutical and medical fields, where they have shown promise for drug delivery as a result of their controlled and sustained release properties, as well as biocompatibility with tissue and cells. To introduce desired properties and enlarge the scope of the potential applications of chitosan, graft copolymerization with natural or synthetic polymers on it has been carried out, and also, various chitosan derivatives have been utilized to form beads. The desired kinetics, duration, and rate of drug release up to therapeutical level from polymeric beads are limited by specific conditions such as beads material and their composition, bead preparation method, amount of drug loading, drug solubility, and drug polymer interaction. The present review summarizes most of the available reports about compositional and structural effects of chitosan-based hydrogel polymeric beads on swelling, drug loading, and releasing properties. From the studies reviewed it is concluded that chitosan-based hydrogel polymeric beads are promising drug delivery systems.

Plant-derived cellulosic materials play a critical role when organic wastes are composted to produce a beneficial amendment for topsoil. This review article considers publications dealing with the science of composting, emphasizing ways in which the cellulosic and lignin components of the composted material influence both the process and the product. Cellulose has been described as a main source of energy to drive the biological transformations and the consequent temperature rise and chemical changes that are associated with composting. Lignin can be viewed as a main starting material for the formation of humus, the recalcitrant organic matter that provides the water-holding, ion exchange, and bulking capabilities that can contribute greatly to soil health and productivity. Lignocellulosic materials also contribute to air permeability, bulking, and water retention during the composting process. Critical variables for successful composting include the ratio of carbon to nitrogen, the nature of the cellulosic component, particle size, bed size and format, moisture, pH, aeration, temperature, and time. Composting can help to address solid waste problems and provides a sustainable way to enhance soil fertility.

This paper reviews the physical and chemical characteristics of fibers from the stem, fronds, and empty fruit bunches of oil palm tree in relation to their papermaking properties. Challenges regarding the use of this nonwood material for papermaking are raised, and possible solutions to them are given. A vision for the complete utilization of oil palm biomass is also outlined.