“Lignocellulosic materials” refer to the organic matter produced by plants on the Earth in the form of grasses, shrubs, agricultural crops, and trees. Worldwide, this plant growth (also called biomass) serves two sustaining functions for our planet: it degrades carbon dioxide to oxygen and it has been the origin or storage media of all non-atmospheric carbon. Leaving aside the related critical issues of fossil fuel depletion and global warming/cooling, lignocellulosic materials growing on the surface also serve many commercial purposes: food production, fuel sources, structural materials for housing and industry, paper products, and chemicals.

Although lignocellulosic materials represent a sustainable resource base, the expanding use of paper and wood products has caused the developed countries to reevaluate the use and recovery of these natural biopolymerics. This issue of the MRS Bulletin explores some of the intricacies surrounding the recovery and reuse of these biomaterials. The applications for materials research are by no means exhaustively covered in these articles. Instead we illuminate the critical issues facing the paper recycling community and the technologies being applied to this resource to create marketable materials.

With the northeastern United States leading the way, tipping fees paid to landfill owners for solid waste disposal have increased as much as 533% since 1980. Fueled by the rapidly diminishing number of available landfills, these rates are expected to go only higher, adding to the public's frustration. Local, state, and federal officials are seeking solutions to mitigate the problem and the public outcry.

In an address at the May 14,1990 Waste-paper I Conference, James B. Malloy, president and chief operating officer of Jefferson Smurfit Corporation and Container Corporation of America, stated: “The bottom line is that our industry, not only in the U.S., but also around the world, must continue to strive for sensible waste reduction at the source as well as total integration of waste management options. In cooperation with, not in conflict with, the public sector we can continue to be positive, constructive participants in the search for workable solutions to the municipal solid waste challenge.”

Recycling is part of the solution. Paper, which contributes up to 40% of solid waste, offers an obvious solution (see Figure 1). The focus on recycling must remain high, encouraging the public to collect and sort waste paper as well as purchase recycled material. What follows is a description of some attempts to inject order into this otherwise complex issue.

The versatility of wood as a raw material is emphasized by the realization that the mass of wood consumed annually in the United States is nearly that of the combined total U.S. consumption of aluminum, plastics, cement, and steel (Figure 1). Partly as a result of the enormous quantities consumed, many wood and paper products also make up significant fractions of the materials disposed in landfills, despite accelerated recycling efforts, notably those of the paper industry. With a target recycle rate of 40% by 1995, the paper industry will make further progress in alleviating some of the disposal problems, but additional efforts to recycle wood and wood-fiber-based materials into other types of products will also be needed. Many of these opportunities have been described. A common denominator in these utilization schemes is to consider how the morphology of secondary wood-based materials may limit their use, and how the morphological characteristics of recycled fiber and wood may influence the properties of the materials produced from them. These considerations suggest, at least partly, a materials science approach to the utilization of recycled fiber and wood, particularly for the fabrication of wood-based composites.

Over the past few years, recycling within the pulp and paper industry has been brought sharply into focus. The primary motivating factors for this have been the crisis in the landfills, of which paper is the largest component, the ensuing legislation, greater public awareness of recycling as an issue, and a desire to recycle more.

In reality, recycling has always been a significant part of papermaking. On a worldwide basis, about one third of the fiber supply is recycled fiber (Table I). A further significant portion of the fiber supply comes from the use of residues from sawmills and other woodworking operations; thus, in the strictest sense, the recycled content is even higher.

The amount of recycled paper that is used varies from 45–50% for Japan and Continental Europe, which have limited forest resources, to about 10% for Canada and Scandinavia, which are rich in forest resources.

In the United States, the recycle rate is about 26% and increasing. Estimates of future usage vary, but the industry as a whole is moving toward a recycle rate close to about 40% or higher by the end of the decade.

It is important to understand the effect that recycling has on fiber properties and also the effect that adding recycled pulp can have on the final sheet properties. To arrive at this, it is worthwhile to review the main aspects of the recycling process and how the process affects pulp properties.

Large amounts of waste paper are generated every day and interest in its reuse has increased steadily due to environmental concerns and improved economics. In 1990 in the United States, for example, 28.9 million tons of recovered papers were collected for recycling. By 1995, that amount is expected to increase to almost 40 million tons with a collection rate of almost 40%. To facilitate the use of secondary fibers, sticky contaminants, or “stickies,” must be controlled.

Classification and Properties of Stickies

Recovered paper bales usually contain extraneous materials such as sand, glass, staples, nails, inks, coatings, plastic, styrofoam, wax, EVA (ethylene vinyl acetate), and SBR (styrene butadiene rubber). A particularly troublesome contaminant in recovered paper is “stickies” which, in their original state, were used as paper adhesives. Inks and coatings can also be a source of stickies. Inks are primarily composed of a pigment, liquid vehicle, binder, and modifier. Coating formulations contain several ingredients that can be classified as pigments, binders, and additives, such as plasticizers, thickeners, dispersants, dyes, preservatives, and defoamers. Note that both inks and coatings mixtures contain binders which contribute to the stickies problem. Common binders used in inks are hydrocarbon resins and rosin esters while those used in coating formulations include starch, soya protein, acrylics, and polyvinyl acetate. An overview of stickies was presented by Moreland.

Stickies can be classified into three categories: hot melts, pressure-sensitive adhesives, and latexes. Although wax can be a contaminant, it is not included separately because it is similar to and an important ingredient of most hot melts.Contaminants such as plastics and styrofoam are also excluded from this discussion because they are not stickies.

Printing and writing paper represents 30% by weight of all domestically made paper products. Today, however, less than 50% of that paper is recycled. The problem with waste paper from homes and offices is that it contains dyes, inks, and chemicals. If these additives are not removed properly—with no fiber degradation—the recycled paper will be of an inferior quality for writing and printing.

Recycling, however, is the future. In 1990, 28.9 million tons of paper were collected for recycling, representing a collection rate of 33.5%. By the year 1995, the collection rate goal is 40%, with favorable economics supporting increased utilization of recovered paper. For example, a ton of paper made from 100% waste paper saves 17 trees, 4,100 kWh of energy (approximately 6 months of power used by the average home), 7,000 gallons of water, 60 pounds of air-polluting effluents, and 3 cubic yards of landfill.

Two of the issues facing recycled fiber utilization are the cost and visual quality of the final sheet. Paper brightness, opacity, and printability are the industry's biggest concerns when comparing the quality of recycled fibers to that of virgin fibers. The common approach to increasing brightness is to add a white filler pigment such as precipitated calcium carbonate (PCC), ground limestone, clay, and/or titanium dioxide. Chemical optical brighteners have also been used, but their use will decline as consumers ask what impact the brightening chemicals have on the environment.

Lignocellulosics represent that mass of organic matter produced by land-growing plants in the form of trees, shrubs, and agricultural crops. Lignocellulosics are renewable, and they sustain living conditions on our planet by recycling carbon dioxide to oxygen. Lignocellulosics serve the planet as a carbon sink. Chlorophyll is the essential catalyst and sunlight the necessary energy source that drive this carbon dioxide reduction to an organic mass that varies little from the carbon-to-oxygen ratio of carbon monoxide.

There is, however, no distinct “lignocellulose” molecule. Instead, nature has found it necessary to formulate a multiphase material consisting of cellulose, hemicelluloses, and lignin. The composition of this multiphase material can be likened to a fiber-reinforced organic glass where cellulose serves as lightweight fiber, lignin serves as a continuous (glassy) matrix, and hemicelluloses serve as coupling agents. The overall composition suggests that there is 35–45% cellulose, 25–35% hemicelluloses, 20–25% lignin, and various minor constituents.

In chemical terms, cellulose is a linear homopolysaccharide with a high degree of crystallinity. It consists of 1,4-β-linked D-glucopyranose units connected in syndiotactic fashion (on alternating sides of the main chain). Cellulose molecules in nature occur with molecular weights exceeding 2 million. Hemicelluloses, by contrast, are branched heterosaccharides of lesser molecular weight. They rarely exceed 20,000 daltons. Hemicelluloses are either rich in glucomannan chains (softwoods), or they consist primarily of branched xylans (hardwoods and annual crops). The chemical composition of hemicelluloses is extraordinarily similar to cellulose (i.e., polyanhydro-pyranoside), but their morphological structure is vastly different.

The Advanced Technology Center for Surface Engineered Materials (ATC-SEM) is a bold experiment in research management. Scientists from its five member institutions work independently within a central framework for overall planning and for the allocation of resources. Access to areas of expertise beyond the compass of the individual institutions more than offsets the logistical problems inherent in the distributed nature of the organization.

ATC-SEM had its origins in 1988 as one of a number of Advanced Technology Centers established by a grant from the New Jersey Commission on Science and Technology after approval of the Jobs, Education, and Competitiveness Bond Act. All the ATCs are dedicated to improving the competitiveness of New Jersey's industry through the application of technology.

The ATM-SEM is administered through Associated Institutions for Material Sciences (AIMS) which has six member institutions, five of which are universities. AIMS also administers other multicampus programs in New Jersey, including the New Jersey NASA space grant consortium and a SEMATECH Center of Excellence. The hallmark of each program is a collaborative effort which transcends the capabilities of any of the individual campuses. The consortium member institutions span the private, public, and industrial sectors and comprise the New Jersey Institute of Technology, Princeton University, Rutgers (the State University of New Jersey), Stevens Institute of Technology, the University of Medicine and Dentistry of New Jersey, and David Sarnoff Research Center (an independent contract research center).

If one defines a polymeric material as a piece of matter designed for a given and usable property, this property is not related simply to the chemical formula of the polymer. The chemical and stereochemical defects occurring during synthesis, structural organization, and processing must all be characterized, understood, and controlled.

Institute C. Sadron (ICS), established in 1954 by the French National Research organization (CNRS) as the Centre de Recherches sur les Macromolécules under the inspiration and direction of Prof. Ch. Sadron, has progressively shifted from polymer synthesis and characterization toward the understanding of the structure-property relationship in the sense just described. This has involved the creation of an engineering school staffed with equipment and research teams in rheology, processing, and mechanical properties. More than 60 permanent scientists and university professors work in the Institute; about 20 theses are submitted each year. ICS now covers a broad range of competencies, from synthesis to processing through most techniques of characterization and theoretical modeling at the molecular and macroscopic levels. This opens the way to a comprehensive research effort, which is illustrated here for polymer blends.