A reduction is urgently needed in the quantities of industrial and municipal solid waste materials that are currently being landfilled. Major components of municipal solid waste include waste wood, paper, agriculture wastes, and other biomass fibers. In 1990, there were approximately 80 million tons of 6,000 different paper and paperboard products and 5.8 million tons of wood in the municipal solid waste stream. There are also potential millions of tons of wood fiber in timber thinnings, industrial wood waste, demolition waste, pallets, and pulp mill sludges. These materials offer great opportunities as recycled ingredients in wood-based composites. This paper discusses possibilities for manufacturing selected composites from these materials as well as materials which coexist with the wood-based resources such as plastics, fly ash, and gypsum.

Recycling is not new to the paper industry. A lot of work was done during World War II, but following the war, the paper industry, for economic and technical reasons, moved away from recycling. The reasons are obvious. We have the trees, and we have them in great profusion. However, recycling came back to us with a vengeance along with the solid waste problem in the late ‘60’s and early ‘70’s. It was a big issue then largely in the federal, state and local government jurisdictions, but the general public did not really perceive it as a major issue until, Senator Gary Hart attempted to levy a tax on virgin materials in 1978. After that it went back on the back burner. It came back again in 1987 and 1988, when people started to pay more attention to the environment and when costs for waste disposal began increasing.

There are several clear trends in the recycling of paper. Firstly, the amount of recycle is increasing and will continue to do so. Secondly, recycled fiber is being used in greater quantities. Finally the recycled fiber is being introduced into higher quality paper grades which previously did not have any recycled content.

This means that on the one hand the quality of the recycled furnish is deteriorating in terms of contaminant level and strength, while on the other hand there is an increased expectation in terms of properties of the end product, the recycled fiber.

The major unit operations of recycling and general principles of system design are reviewed, methods for enhancing these properties and limits which can be achieved are discussed.

Wood is a major industrial raw material, with U.S. consumption approaching that of aluminum, plastics, cement, and steel combined. Partially as a result of the magnitude of wood and wood products in use, these products constitute a substantial portion of the solid waste stream. In order to reduce the amount of wood and wood fiber disposed in landfills, efforts to recycle these materials into useful products such as structural composites are needed. The success of such conversion depends in part on knowledge of the morphological characteristics of various sources of secondary wood and wood fibers, and the influence of wood element morphology on composite properties. An overview of wood and fiber morphology representative of major sources of secondary material is provided, with a discussion of how these morphological features may influence the properties of conventional wood composites and wood fiber/plastic composites.

For most products, processing recycled paper back into paper will require de-inking and removal of coatings and fillers. Paper to paper recycling will also require sorting the paper waste stream to insure that the stock used contains the type of fiber needed. These problems can be eliminated if the waste paper product stream is used to make fiber based composites. Mixed office waste, packaging materials, paperboard, newspaper, and many other types of paper fiber can be used directly for the production of thermosetting or thermoplastic fiber based composites. High levels of clay used in magazine paper can be tolerated in these composites. This paper will review research in making fiber based composites from several waste paper streams and the properties of these products.

Dry-process hardboard represents a favorable option for recycling old newspaper fibers. However, dry-process boards tend to be less dimensionally stable than boards processed by other methods. Our objective was to determine the effects of various wood fiber (WF) to old newspaper (ONP) ratios (100:0, 50:50, and 0:100 WF/ONP) on the mechanical strength and water resistance of dry-process hardboards made from these fibers. Untreated and acetylated hardboards were made with 3 or 7 percent resin and 0.5 percent wax. Boards were tested for static bending and tensile strength properties and water resistance. As expected, increasing the resin level from 3 to 7 percent generally improved all measured properties. Acetylation substantially improved the water resistance of all boards; increasing the amount of ONP caused a corresponding deterioration in both mechanical properties and water resistance.

The interaction and adhesion between fibers and the matrix in composite materials have a significant influence on the properties of the fiber composite. It is, therefore, of utmost importance to be able to evaluate the properties of the interface/ interphase of the fiber-matrix for optimization of the properties of the composites. Techniques that are currently used to evaluate the properties of this region will be discussed with special attention to lignocellulosicthermoplastic composites. Sample preparation, applicability, problems and advantages of each technique will be highlighted. Results obtained at our laboratory for wood-low molecular weight polyethylene systems using the pull-out test will be discussed.

Composites of biomass fibers with hydrophobic polymers like polypropylene (PP) represent material systems with poor or no interfacial adhesion because of the inherent incompatibility between the respective components. Block and graft copolymers can function as compatibilizers to improve interfacial adhesion and provide composites with an improved and unique balance of properties. Various approaches to improving interfacial adhesion with an emphasis on our work on the compatibilization of biofibers (lignocellulosics) with polypropylene is presented. The biofiber-reinforced polypropylene composite was prepared by reactive extrusion. The compatibilizer which is the graft copolymer produced by reaction of maleated polypropylene with the cellulosic component of the biofiber, was generated insitu during reactive extrusion processing. Maleated polypropylene (MAPP) was produced by the peroxide catalyzed grafting of maleic anhydride (MA) on polypropylene (PP) in the extruder. It was subsequently alloyed with the biofiber by use of a catalyst to form covalent bonds between the components. Alternatively, all the processing steps i.e. maleation, graft formation and the alloying were done in a single extruder run. The chemistry occurring during the two reactive extrusion processing modes and its effect on the properties of the resultant materials is discussed.

Wood-plastic composites have been produced utilizing a phenol-formaldehyde pretreatment of the wood. The use of additives to cross link the plastics and increase the interfacial bond between the wood and plastic were also investigated. These preliminary results suggest that pretreatment of the wood with a thermosetting resin may increase the stiffness of the composite. The use of an octylphenol as a plastic compatabilizer did not reliably increase stiffness in this system, although additional study is warranted. An interaction between the wood and the polystyrene in the plastic mixture may be indicated.

In addition to its use in recycled paper products, recovered lignocellulosic fiber can be used as a reinforcement filler in composites with polyolefins. However, problems in both processing and product performance are often caused by the incompatibilities of surface energies between hydrophilic cellulose and non-polar polyolefin. This poor match in surface polarities is detrimental to strong adhesive bonding between olefin and cellulose. This work examines the effect of surface energy on the adhesion properties of polypropylene and cellulose. In particular, three materials accepted as paper-sizing agents were used to change the cellulosic fiber's surface energy to make it more compatible withthe surface energy of polypropylene.

Cellulose fibers were treated by various methods with (1) alkyl ketene dimer, (2) alkenyl succinic anhydride, and (3) stearic acid and were characterized by their surface energies as determined by single fiber wettability measurements using the Wilhelmy technique. These measurements are discussed in detail. Results from these measurments can be related to differences in adhesion between treated cellulose and polypropylene, which can be measured by internal bond tests on hot-pressed composite sheets.

Results indicate that the use of sizing agents reduces the acid/base (hydrogen bonding) character of the cellulose surface. Interactions involving hydrogen bonding are important in cellulose/modified-polypropylene composites. Reduction of these interactions appears to lead to a corresponding reduction in adhesion between cellulose and polypropylene.

We examined the influence of several variables on the mechanical properties of wood fiber-polyolefin composites blended in a thermokinetic mixer. A pure cellulose fiber and fibers from old newspaper provided similar performance in matrices of virgin polypropylene or recycled milk bottles (high density polyethylene). Relative to wood flour, these fibrous fillers led to greater strength and modulus with both plastics, to lower impact energy with polyethylene, and to similar impact energy with polypropylene. Compared with the existing commercial wood flour-polypropylene system, the totally recycled polyethylene-newspaper composite provided equivalent strength and modulus, along with greater notched impact energy. Little difference was seen in composites containing a maleated polypropylene additive in the form of the solid anhydride or the emulsified potassium salt, indicating that the additive acted as a dispersing agent and not as a strong coupling agent.

Polypropylene (PP)-wood veneer laminates were used as a model system to investigate adhesion in wood-polypropylene composites. Wood veneers were treated with maleated polypropylene waxes (MA-PP). PP films were then compression molded to the wood surfaces and peel forces were measured.

Low MA-PP treatment levels increased the peel adhesion over that for untreated surfaces. High MA-PP treatment levels decreased the peel adhesion and intermediate MA-PP levels had no effect on the peel adhesion. Microscopy of the fracture surfaces indicated PP penetration into lumens in both treated and untreated wood veneer. Untreated surfaces also exhibited PP penetration into pits and intercellular spaces, while treated surfaces exhibited only hindered penetration on this scale. The penetrated PP formed tendrils during fracture. DSC of PP on wood and cellulose surfaces showed higher PP crystallization temperatures on untreated surfaces than on treated surfaces.

The usefulness of solubility parameters in identifying miscible polymer blends is reviewed. The use of wood fibers in mixtures of recycled thermoplastics is of current interest. These composites do not require miscible blends of polymers, but must exhibit compatibility in order to have good adhesion and physical properties. The use of solubility parameters to design improved composites is cited. This approach is then applied to wood fiber/polyolefin thermoplastic composites.

Beneficial utilization of wastepaper and wood in cement-based materials is reviewed. Wastepaper presents a source of reinforcing fibers for thin-sheet cement products; these fibers help overcome the problems with the brittle nature of failure and low cracking resistance of plain cement products. Wood waste and sawdust can be used in concrete as light-weight aggregates capable of enhancing the weight-to-strength ratio, insulation properties and toughness characteristics of concrete materials.

Lignin, a complex natural polymer produced by all vascular terrestrial plants is second in abundance only to cellulose and is the matrix holding plant fibres together. Lignins are recovered mainly as byproducts from woodpulping processes with about 100 million tons produced annually worldwide.

Large volume uses for lignin byproduct other than for generation of energy (kraft process) are most likely to be in materials applications.

In the last decades many studies aimed to the recycling of different lignins (sulfite, kraft, organosolv, steam exploded, hydrolytic, etc.) in polymeric systems based on thermoplastics, thermosettings, elastomers, adhesives, sealants, etc.

Among all the technical lignins, sulfate lignins are chemically the most reactive and are therefore used to modify polymers. The oldest and the most familiar application of lignin as a component of polymeric materials involves the reinforcement of rubber. Multicomponent materials can be created by combination with other macromolecules like polyethylene, polypropylene, or poly(vinyl alcohol) to produce polyblends, block copolymers or interpenetrating polymer networks.

The present communication will try to present such examples of polymeric systems based on recycled lignin, and synthetic polymers such as: polyurethane, epoxy, acrylics, silicones.

Using standard laboratory procedures it was found that different pulp types showed very different recycling effects. Mechanical pulp fibres became flatter and more flexible giving a denser, stronger sheet. Beaten chemical pulp fibres “hornified”, resulting in a bulkier, weaker sheet. Unbeaten chemical pulp fibres were initially curly; recycling removed the curl. A mechanical/chemical pulp blend revealed that these effects occur at different rates. In no case was there evidence of fibre strength loss, or of fibre embrittlement. In these laboratory experiments, fines loss during sheetmaking affected the magnitude of the sheet properties, but not the trends.

The reduced interfiber bonding capability and reduced conformability of recycled fibers compared to virgin wood pulp fibers is caused by the drying phase of the first papermaking cycle. Changes in the fiber result in stiffness. This effect is more pronounced in chemical pulps than in high lignin content mechanical pulps. This chapter describes methods for restoring some or all the interfiber bonding. In an attempt to develop a “dry” newspaper recycling process, the water-intensive repulping and paper-forming steps were replaced with dry-fiberizing, air-forming, gas-phase ozone and ammonia treatments, and pressdrying. The tensile strength of the dry-recycled paper approached that of the original newsprint.

Recent advances in understanding the structure of cellulose are used as the basis for analyzing the structural changes that occur in pulp fibers during papermaking, particularly in the drying stage. These changes are responsible for the degradation of papermaking properties, and they must be reversed during recycling if the maximum papermaking potential of the virgin fibers is to be recovered. A number of studies have assessed the structural transformations that can occur in cellulosic fibers upon exposure to elevated temperatures. The researchers have invariably observed that the changes occur at the secondary and tertiary levels of structure, the levels that can have significant effects on the properties of fibers. In addition, some studies have focused specifically on the structural effects of recycling; clear correlations of structural change with changes in paper characteristics have been reported. The results of the various studies point to directions for further investigations into enhancing the recovery of papermaking value from recycled fibers.

Recycling of fiber into structural papers for the corrugated container industry, paper tubes, cartonboard or other paperboard with structural performance needs may require enhancement of properties through changes in the papermaking process. The loss of bonding capability, coupled with a degree of fiber shortening and fiber inflexibility, reduces the utility of recycled fiber and thus their competitiveness with their virgin counterparts. Traditional means for enhancing performance includes addition of starches or other binders, mechanical beating, or heat treatments. Other means for achieving heightened performances are reviewed which include alternative drying technologies, optimal placement of fibers within the paper sheet and forming technologies that provide structural enhancement. KEYWORDS: Fibers. fractionation, swelling, drying methods, fiber bonding. fiber alignment, pulp molding.

Newsprint represents a readily identifiable and valuable fiber source. Although the use of old newspapers fibers to make new newsprint is increasing, this activity must compete with the export market and other established usages like paperboard, insulation and speciality product manufacturing.