Composites from Recycled Materials by xps54377

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									                     In: Maloney, T.M., ed. Proceedings of the 25th International
                         particleboard/composite materials symposium; 1991 April 9-11;
                         Pullman, WA. Pullman, WA: Washington State University; 1991:
                         301-314.

          COMPOSITES FROM RECYCLED MATERIALS



                                                                                  Presented by:

    ROGER M. ROWELL                   JOHN A. YOUNGQUIST                      DOBBIN MCNATT
  Forest Products Laboratory          Forest Products Laboratory           Forest Products Laboratory
         Madison, WI                         Madison. WI                          Madison. WI




                 ABSTRACT                                 Research and development needs for maximiz-
                                                          ing the benefits of using recovered waste mate-
      A reduction is urgently needed in the quan-         rials for composite products are discussed.
tities of industrial and municipal solid waste
materials that are being landfilled currently.
Major components of municipal solid waste                              INTRODUCTION
include waste wood, paper. plastics. fly ash.
gypsum. and other biomass fibers -- materials                  The word “waste” projects a vision of a
that offer great opportunities as recycled ingre-         material with no value or useful purpose. How-
dients in wood composites. This paper dis-                ever, technology is evolving that holds promise
cusses possibilities for manufacturing selected           for using waste or recycled wood and, in some
composites from these materials. Methods for              cases. even plastics to make an array of high-
producing the composites and the resultant prod-          performance composite products that are in
uct properties and attributes are described.              themselves potentially recyclable.

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     When fibers. resins. and other materials are          posite waste. The use of resources that coexist
used as raw materials for products such as                 with wood-based resources is also considered,
paper. they require extensive cleaning and re-             including a variety of plastics and other re-
finement. When recovered fibers. resins. and               sources that “contaminate” the wood-based re-
other materials are used for the manufacture of            source.
composites. these materials do not require ex-
tensive preparation. This greatly reduces the                    A comprehensive waste management pro-
potential cost of manufacturing.                           gram must rely on the aggregate impact of
                                                           several courses of action: waste reduction,
      A case-in-point is the making of compos-             recycling. waste-to-energy schemes. and land-
ites from recycled paper. In the United States.            fill (Kovacs 1988). The greatest impact that is
nearly 80 million tons of 6,000 different paper            likely to result from further research is in the
and paperboard products are produced and over              area of recycling. Increased use of recycled
70 million tons are discarded each year. Few of            biobased resources will allow the markets for
the paper products found in the municipal solid            fiber composites to grow without increasing the
waste (MSW) stream are produced solely from                use of virgin timber. Therefore. forest products
fiber and water. Each product consists of a fiber          industries will benefit from such research be-
matrix to which some mineral or chemical com-              cause less expensive raw materials will be avail-
pound is added to enhance the utility of the               able for producing high quality composites.
product. Thus, many forms of wastepaper con-
tain contaminants (extraneous materials).                       The purpose of this paper is to describe the
Whether they are adhesives, inks, dyes, metal              potential for producing selected composites from
foils, plastics, or ordinary household wastes,             waste wood, paper. plastics, fly ash, gypsum.
these contaminants may need to be separated                and other forms of waste biomass. First, the
from the wastepaper before the fiber can be                availability of waste materials from the MSW
recycled into another useful paper product. This           stream and the desirability of developing ways
is not the case with wood-based composites. In             to recycle these materials into useful, high-
many uses, wood fiber composites of varying                performing, value-added composites is dis-
types are opaque, colored. painted. or overlaid.           cussed. Then methods for making selected
Consequently. recovered fibers, resins. or other           composites are described briefly and product
materials used for composites do not require               properties and attributes are discussed. Next,
extensive cleaning and refinement. Thus. com-              composites made from combinations of wood
posites provide an unusually favorable option              with other biobased fibers are reviewed. Fi-
for the recycling of several highly visible and            nally, research and development needs for
troublesome classes of MSW – paper of vari-                maximizing the benefits of using recovered
ous types, waste wood. plastic bottles, fly ash.           waste materials for composite products are out-
gypsum, and other biobased fibers.                         lined.

     This paper focuses on wood-based re-
sources that either presently enter or could enter              MUNICIPAL SOLID WASTE AS
the recycling stream, both commercially and                       SOURCE OF MATERIALS
residentially. This includes newspaper, pack-                       FOR COMPOSITES
aging. and other forms of wood-based fiber
products. as well as all forms of industrial and                A considerable amount of data is related to
residential solid-wood and wood-based com-                 the inventory of the U.S. MSW stream (Table


                                                     302
 1). In 1988, paper and paperboard, wood, and             trial production wastes, bark, and sawdust. These
plastics in the MSW stream accounted for ap-              latter categories of wood waste also represent
                                           6
proximately 71.8, 6.5, and 14.4 x 10 ton,                 potentially valuable sources of raw materials.
respectively. By the year 2000, these figures are
                                                6
expected to increase to 96.1, 8.4, and 21.1 x 10                Many problems are associated with the use
ton annually (Environmental Protection Agency             of waste materials, including collection, analy-
1990). In addition to the wood fiber in the MSW           sis, separation, clean up, uniformity, form, and
stream, vast quantities of low-grade wood, wood           costs. Assuming that these problems can be
residues, and industry-generated wood waste in            overcome on a cost-effective basis, some of the
the form of sawdust, planer shavings, and chips           resultant reclaimed materials should be useful
are now being burned or otherwise disposed of.            ingredients for a range of valuable composites,
                                                          from low-cost, high-volume materials to high-
The data in Table 1 include all the residential           cost, low-volume materials for a wide range of
waste products, but not all the industrial waste          end uses.
materials. Data are available for the total vol-
ume or weight of certain wood-based products                   Source separation and recycling not only
in the MSW stream, such as paper, packaging,              extends the life of landfills by removing mate-
and pallets, but only incomplete information is           rials from the MSW stream, but also makes
available for timber thinnings, leaves, indus-            available large volumes of valuable raw materi-




       Table l.–Estimated distribution of materials generated in municipal solid waste
                      a
       stream in 1988

                                                                    Amount in MSW Stream
                                                                                Weight
                                                                                   6
               Source                                                 (%)     (x 10 ton)


       Paper and paperboard                                            40.0         71.8
       Yard Waste                                                      17.6         31.6
       Metals                                                           8.5         15.3
       Food waste                                                       7.3         13.2
       Glass                                                            7.0         12.5
       Plastics                                                         8.0         14.4
       Textiles                                                         2.2          3.9
       Wood                                                             3.6          6.5
       Rubber-leather                                                   2.6          4.6
       Miscellaneous inorganics                                         1.5          2.7
       Other                                                            1.7          3.1
       (Total)                                                       (100.0)      (179.6)
        1
            Adapted from EPA report (1990).

                                                    303
als for use by industry in place of virgin re-            ing and mixing: the mixture is extruded as
sources. Industrial use of such materials re-             sheets that are subsequently shaped by
duces both costs for raw materials and the                thermoforming into the final product. Limits on
energy it takes to make a finished product (New           the melt viscosity of the mixture restrict the
York Legislative Commission 1986). The main               amount of fiber or flour (to about 50 weight
requirement is that the recycled ingredients              percent) as well as the length of the fibers that
meet the quality and quantity requirements of             can be used. Fiber length is also limited by fiber
the consuming production operation.                       breakage as a result of the high shear forces
                                                          during melt mixing.

 COMPOSITES FROM WASTEPAPER,                                    In contrast. nonwoven mat technology in-
   WOOD FIBER, PLASTICS, AND                              volves room temperature air mixing of ligno-
     INORGANIC MATERIALS                                  cellulosic fibers (or even fiber bundles) with
                                                          thermoplastic fibers. The resultant mixture
                                                          passes through a needling step that produces a
     Wastepaper. wood. plastics, fly ash, gyp-            low-density mat in which the fibers are me-
sum, and other biomass fibers can be reclaimed            chanically entangled. The mat is then shaped
from industrial and MSW streams and used for              and densified by a thermoforming step. With
several kinds of composite products: wood                 this technology. the amount of lignocellulosic
fiber-plastic composites. dry-formed wood fi-             fiber can be greater than 90 weight percent. In
ber-based composites, inorganic bond wood                 addition. the lignocellulosic fiber can be
composites. and composites that combine wood              precoated with a thermosetting resin; for ex-
fibers with other lignocellulosic fibers, metals,         ample. phenol-formaldehyde.               After
and glass.                                                thermoforming. the product possesses good tem-
                                                          perature resistance. Because longer fibers are
                                                          required, this product can achieve better me-
      Thermoformable Wood-Plastic                         chanical properties than that obtained with the
            Fiber Composites                              melt-blending process. However. high wood
                                                          fiber contents lead to increased moisture sensi-
     Thermoformable composites are classified             tivity.
into two general types on the basis of the manu-
facturing process. Both processes-melt blend-                   It is virtually certain that virgin ingredients
ing and nonwoven mat formulation -- allow                 can be replaced by some recycled ingredients in
and require differences in composition and in             melt blending and nonwoven mat formation for
the lignocellulosic component.                            many applications. For example. the thermo-
                                                          plastic polymer might be totally or partially
      A typical composition for a melt-blended            replaced by high-density polyethylene (HDPE)
composite is 40 to 60 weight percent wood flour           from milk bottles. polyethylene terephthalate
or cellulose pulp fiber with a powdered or                (PET) from beverage bottles, or even
pelletized thermoplastic such as polypropylene            nonsegregated plastic mixtures from MSW.
or polyethylene. In the melt-blending process,            Large quantities of a variety of industrial waste
the wood-based fiber or flour is blended with             plastics are also available and should be consid-
the melted thermoplastic matrix by shearing or            ered. The virgin lignocellulosic component
kneading. Currently, the primary commercial               might be replaced by fibers from wastepaper or
process employs twin screw extruders for melt-            waste wood. These substitutions offer potential


                                                    304
benefits in reducing both MSW and the cost of                    examined several types of pulp fiber in compos-
the composite processes. In some cases, the                      ites made with polypropylene and HDPE.
properties of the composite will probably be                     Shiraishi and colleagues showed improvements
improved; for example, by substituting waste-                    in mechanical properties as a consequence of
paper fibers for wood flour in the melt-blending                 using high-molecular-weight maleated polypro-
process.                                                         pylene instead of normal polypropylene (Kishi
                                                                 et al. 1988, Takase and Shiraishi 1989). Finally,
     Currently, the primary application of                       Maiti and Hassan (1989) measured the effects
thermoformed composites, both melt and                           of wood flour on the melt rheology of polypro-
blended and air laid, is for interior door panels                pylene.
and trunk liners in automobiles. Additional
large-volume, low-to-moderate cost applica-                           At the Forest Products Laboratory (FPL) in
tions are expected in areas such as packaging                    Madison, Wisconsin, and the University of
(trays, cartons), interior building panels, and                  Wisconsin, Myers and others (in press, in prepa-
door skins.                                                      ration) investigated in some detail the influence
                                                                 of a low-molecular-weight maleated polypro-
                                                                                                     1
     The following sections are not intended to                  pylene (Eastman’s Epolene E-43) on the me-
be a comprehensive review of recent research                     chanical and physical properties of wood flour
on wood fiber-thermoplastic composites. The                      and polypropylene-extruded composites. Ex-
effects of some important composition and pro-                   periments by Kolosik and others (unpublished
cessing variables in the composite processes are                 data) indicated that the E-43 probably is not
described, including preliminary indications of                  acting as a true coupling agent, but instead has
the effects of recycled ingredients.                             some effectiveness as a dispersing agent.

Research on Melt-Blended                                              Publications are beginning to appear on the
Composites                                                       effect of recycled ingredients on the behavior of
                                                                 melt-blended lignocellulosic-polyolefin com-
     The 1980s brought a resurgence of re-                       posites. Selke and colleagues showed that com-
search into various aspects of melt-blended                      posites from aspen fiber and once-recycled blow-
composites made from wood-based flour or                         molding HDPE from milk bottles possessed
fiber in virgin thermoplastic matrices. For                      essentially equivalent strength and modulus
example, Kotka and colleagues published many                     properties as those of composites made from
papers in this area, emphasizing improvements                    virgin HDPE; however, impact energy was re-
in the filler-matrix bond throughcoupling agents                 duced (Selke et al. 1988, Yam et al. 1988).
and grafting of polymers on cellulosic fiber                     Woodhams and others (1990) found that com-
surfaces (Kotka et al. 1990, Maldas et al. 1988,                 posites made from polypropylene and pulp fi-
Maldas et al. 1989). Klason and colleagues                       bers or fiberized old newspaper possessed
carried out extensive investigations on the ef-                  strength and impact properties very similar, and
fects of several polymer and fiber types and the                 apparently much superior, to those of compos-
influence of a variety of processing aids and                    ites made from wood flour-polypropylene sys-
coupling agents (Dalvag et al. 1985, Klason et                   tems. In preliminary work at the FPL, the
al. 1984). Woodhams and others (1984, 1990)                      properties of wood flour-polypropylene and

1
    The use of trade or firm names in this paper is for reader information and does not imply endorsement by the U. S.
    Department of Agriculture of any product or service.

                                                           305
wood flour-HDPE systems have been com-                    erts’ patents were assigned to the Weyerhaeuser
pared with the properties of a fiberized old              Company.
newspaper-HDPE composite. The differences
between wood flour-polypropylene and wood                      From 1966 to 1968, a series of patents
flour-HDPE systems were qualitatively consis-             (Caron and Allen 1966.1968; Caron and Grove
tent with expectations based on the lower                  1966a, b, c; Grove and Caron 1966) were issued
strength and greater flexibility of HDPE rela-            and assigned to the Weyerhaeuser Company.
tive to polypropylene. Also. strength was im-             These patents cover the use of a wood fiber-
proved by substituting fiberized old newspaper            thermoplastic resin system in conjunction with
for wood flour.                                           a thermosetting resin system. In the early 1970s.
                                                          Brooks (1990) developed a process that pro-
Research on Nonwoven Web                                  duced a very flexible mat using a thermoplastic
Composites                                                Vinyon fiber in combination with a thermoset-
                                                          ting resin system. The mat was fed through an
     Numerous articles and technical papers               oven to melt and set the Vinyon fiber without
have been written and several patents have been           affecting the setting of the thermosetting resin
issued on both the manufacture and use of                 component. This process was patented in 1984
nonwoven fiber webs containing combinations               by Doerer and Karpik and was assigned to the
of textile and cellulosic fibers. This technology         Van Dresser Corporation.
is particularly well-known in the consumer prod-
ucts industry. For example. Sciaraffa and oth-                  Brooks also developed an interesting
ers (1982) were issued a patent for producing a           method of recycling waste cellulosic materials
nonwoven web that has both fused spot bonds               for the production of medium density fiber-
and patterned embossments for use as a liner              board and paper (Brooks 1973). After being
material for disposable diapers. Bither (1980)            shredded. sorted from other waste materials like
found that polyolefin pulps can serve as effec-           plastic and metal. and steamed. the cellulosic
tive binders in nonwoven products. Many addi-             fibers and fiber bundles are abraided under heat
tional references could be cited in this area.            and pressure to break down any hydrogen bonds
                                                          and to soften any lignin and other resins. The
     Brooks (1990) published a review of the              resultant cellulose fibers are then mixed with
history of technological development for the              resin. formed into a mat. and consolidated under
production and use of moldable wood products              pressure to form flat fiberboard and paper prod-
and air-laid. nonwoven. moldable mat processes            ucts.
and products. The first moldable wood product
using the wet slurry process was developed by                  Youngquist and Rowell (1989) reviewed
Deutche Fibrit during 1945 to 1946 in Krefeld,            opportunities for combining wood with
West Germany (Brooks 1990). A moldable                    nonwood materials. This review included a
cellulose composition containing pine wood                discussion of the materials and properties of
resin was patented by Roberts (1955) as well as           composites consisting of wood fibers and bio-
a process for producing molded products from              mass. metal. plastic, glass, or synthetic fibers.
this composition (Roberts 1956). The compo-               In a recently published paper. Youngquist and
sition consisted of a mixture of comminuted               others (1990) reported on the mechanical and
cellulose material and at least 10 percent of a           physical properties of wood-plastic fiber com-
thermoplastic pine wood resin derived from the            posites made with air-formed dry-process tech-
1
  solvent refining of crude rosin. Both of Rob-           nology. This paper reported the effect of spe-


                                                    306
cies, wood flour to polypropylene ratio, and               nation with wood and polyester homopolymer
type of plastic fiber or plastic fiber-thermoset-          fibers, formed a composite with greatly im-
ting resin blends on mechanical and dimen-                 proved mechanical properties compared to that
sional stability properties of pressed panels hav-         of the other two composite formulations tested.
                                3
ing a density of 1 g/cm . Kryzysik and
Youngquist (in press) reported on the bonding              Wood-Plastic Fiber Mat
of air-formed wood-polypropylene as a cou-                 Composites
pling agent between the hydrophilic wood and
the hydrophobic polyolefin materials.                           Wood and plastic fibers can be formed into
                                                           a web using nonwoven web technology. The
     A number of preliminary trials were con-              fibers are introduced into a turbulent air stream,
ducted at the FPL using recycled office waste-             transferred via this air stream to a moving sup-
paper. shredded old newspapers. dry fiberized              port bed. and subsequently formed into a con-
old newspaper, and fiberized demolition waste              tinuous mat with low or high density. This mat
wood. The raw paper materials, which did not               of intertwined fibers is then passed through a
have the ink removed, were reduced to a suit-              needling operation where fish-hook-type needles
able form using several reduction methods.                 further intertwine and strengthen the fibers.
                                                           The ratio of wood to plastic in this matrix can be
      The demolition waste was first sorted me-            in the 95/5 weight percent range. The plastic
chanically and then manually to remove                     material (5%) can also be replaced with a long
nonwood materials, washed. and fiberized us-               wood fiber-like jute or kenaf.
ing a pressurized refiner. The recycled wood-
based fibers were then air mixed with virgin                     One interesting application for low-den-
polyester or polypropylene. transferred by an              sity fibermats is for mulch around newly planted
air stream to a moving support bed, needled, and           seedlings. The mats provide the benefits of
subsequently formed into a continuous. low-                natural mulch: in addition. controlled-release
density mat of intertwined fibers.                         fertilizers, repellents. insecticides, and herbi-
                                                           cides can be added to the mats as needed.
      When polyester fibers were used, the wood            Research results on the combination of mulch
fibers were sprayed with a liquid phenolic resin           and pesticides in agronomic crops have been
prior to web formation. The use of a thermo-               promising (Crutchfield et al. 1985). The addi-
plastic polyolefin-like polypropylene greatly              tion of such chemicals could be based on silvi-
improved the dimensional stability of the com-             cultural prescriptions to ensure seedling sur-
posite compared to that of the polyester copoly-           vival and early development on planting sites
mer-containing composite. These results can                where severe nutritional deficiencies, animal
probably be explained by the fact that the                 damage. insect attack, and weed problems are
polypropylene melts and. to some extent, par-              anticipated. The Forest Service is conducting
tially encapsulates the wood fibers. In all cases,         preliminary research on using fiber mats to
the ability of the polyester copolymer-contain-            improve the survival of loblolly pine seedlings
ing composite to absorb impact energy was                  in southern Louisiana.
superior to that of the polypropylene-contain-
ing composite. This can be attributed to the fact               Low-density fiber mats can also be used to
that the polyester maintains a fibrous matrix              replace dirt or sod for grass seedling around new
whereas the polypropylene fibers melt and flow             homesites or along highway embankments. The
under heat pressure. Phenolic resin, in combi-             grass seed can be incorporated in a wood or jute

                                                     307
fiber mat. Fiber mats promote seed germination                    There is a great opportunity to produce
and good moisture retention. High-density fi-               fiber-based composites of varying densities from
ber mats can be used for air filters or other types         recycled wood fibers. One family of products,
of filters. The density of the mats can be varied,          called Homasote, was first produced in 1916
depending on the material being filtered and the            and is made from old newspapers and other
volume of material that passes through the mat              groundwood paper (Post 1990). Other fiber-
per unit of time. The FPL is conducting prelimi-            board-type products now on the market also use
nary work on developing wood fiber mats for                 all or partly recycled wood fiber as the raw
filters. All of the applications discussed for              material base stock. Uses for these types of
wood fiber mats can provide excellent outlets               products include insulating acoustical board;
for recycled wood fiber.                                    carpet board: wall. ceiling. and floor acoustical
                                                            insulation panels; nail baseboard; and floor and
          Dry-Formed Wood-Fiber-                            roof insulation boards. It is anticipated that
             Based Composites
                                                            many other uses for wood fiber-based products
     Wood fiber-based composites are made                   will be developed as collection, separation, and
                                                            clean-up processes are further refined and de-
from reconstituted wood: the wood is first
reduced to fibers or fiber bundles and then put             veloped.
back together by special manufacturing pro-
cesses into panels of relatively large size and                  Research is now being conducted at FPL to
                                                            determine the dimensional stability, moisture
moderate thickness. In final form, the panel
materials retain some properties of the original            resistance, stiffness, and strength properties of
                                                            dry-process hardboards. The hardboards are
wood, but because of the manufacturing meth-
                                                            made from varying blends of virgin wood fiber
ods, the materials also gain some different prop-
erties. Because these products are manufac-                 and old newsprint fiber.
tured, they can be and are tailored to satisfy a
particular end-use or group of end-uses.
                                                               Inorganic-Bonded Wood Composites
      Essentially, wood fiber-based composites
are made by breaking down wood to fibers                          Wood particles or fibers held together with
through thermal-mechanical or mechanical pro-               an inorganic matrix, such as Portland cement or
cesses. The fibers are interfelted in the reconsti-         gypsum, form a composite that can be used in a
tution process and are characterized by a bond              variety of structural and industrial applications
produced by the interfelting. The composites                (Moslemi 1990). These composites have an
are frequently classified as fibrous-felted board           unique advantage over some conventional build-
products. At certain densities under controlled             ing materials because they combine the charac-
conditions of hot pressing, rebonding of the                teristics of both the wood fiber and mineral
lignin effects a further bond in the resultant              matrix. Some of these composites are water
panel product. Binding agents and other mate-               resistant and can withstand the rigors of outdoor
rials may be added during manufacture to in-                applications, and almost all are either fireproof
crease strength or resistance to fire, moisture, or         or highly fire-resistant and are very resistant to
decay. These materials include rosin, alum,                 attack by decay fungi.
asphalt. paraffin, synthetic and natural resins,
preservative and fire-resistant chemicals, and                    These types of composites, which provide
drying oils. Wax sizing is commonly added to                another major future recycling opportunity to
improve water resistance.                                   utilize waste wood and other postconsumer

                                                      308
wastes, are made by blending proportionate                to be recycled will somewhat dictate the type of
amounts of the wastes with inorganic materials.           size-reduction or comminution equipment se-
The most apparent and widely used example is              lected to process the waste wood. The type of
cement. Portland cement, when combined with               equipment, in turn, will determine the final size
water, immediately begins to react in a process           and character of the resulting aggregate. For
called hydration to eventually solidify into a            example, certain types of size-reduction equip-
solid stonelike mass. When fine sand and                  ment (shredders, pulverizers, hammermills,
coarse stone, the traditional aggregates, are             augers) might be best suited to convert waste
blended with the cement and water paste, the              wooden pallets, wood reels, stumps, and hous-
materials are bound together to form concrete.            ing demolition material into shredded fiber
The strong bond between the paste and the                 bundles for use as concrete aggregate. On the
aggregate occurs as each cement particle estab-           other hand. a completely different kind of ma-
lishes a type of surface growth that spreads by           chine (wood chipper or chunker) might be pre-
linking with other cement particles and the               ferred for reducing unmerchantable trees and
aggregate.                                                tree trimmings into chips or chunks.

     A special category of concrete is structural              Besides wood waste, other postconsumer
lightweight concrete. Because lightweight con-            wastes such as glass and plastic can also be used
crete is made entirely or partially with light-           as concrete aggregate. Depending on the type
weight aggregates, such as burnt clay, pumice,            or types of aggregate used and the proportionate
expanded blast furnace slag, and expanded ver-            blend of materials in the resulting concrete, the
miculite, its principal unique property is its            end properties may differ somewhat, but gener-
lower density compared to normal-weight con-              ally, the product would be classified as low- to
crete. This makes lightweight concrete attrac-            medium-strength concrete, for which there are
tive for reducing dead loads in structures with           many potential applications.
concrete floor or roof fills. Generally, light-
weight concrete also has superior insulating                   Other inorganic waste materials that can be
properties. Concrete made with waste wood                 added to the concrete mix or used indepen-
will be lightweight and have high insulating              dently to produce a different kind of composite
value.                                                    material are fly ash and flue gas gypsum. The
                                                          extremely finely grained fly ash, which is pro-
     As an aggregate for concrete, wood can be            duced during the combustion process and espe-
used in many forms. The wood aggregate may                cially during the incineration of coal fuels, is
be a gradation of wood chunks, wood chips                 collected by mechanical or electrostatic pre-
(typical of the chips used by the pulp and paper          cipitators. Flue gas gypsum, now being pro-
industry), shredded fiber bundles, sawdust, and           duced in very large quantities because of Clean
even individual wood fibers (such as in a pulp            Air Act regulations, is the result of introducing
slurry or that produced from recycled wastepa-            lime into the combustion process to reduce
per). For example, the North Central Forest               sulphur dioxide emissions. By 1995, more than
Experiment Station of the USDA Forest Ser-                100 power plants throughout the United States
vice in Houghton, Michigan, is developing a               will be producing gypsum. Flue gas gypsum
product called Chunkrete, which uses wood                 can be used in lieu of mined gypsum.
chunks, particles, or fibers to substitute for or
partially replace gravel or stone aggregate. The              Gypsum-bonded wood-fiber panels are
type or character of bulky wood waste material            used as replacements for gypsum wallboard and

                                                    309
are reported to have strong nail- and screw-               produce composites for various applications–
holding properties: high moisture and fire resis-          from furniture to structural wall panels.
tance; and improved impact. mold, and mildew
resistance (Donnell 1990). Other reported ad-
vantages include improved anti-sag properties                          RESEARCH AND
(for ceiling boards), better sound insulation,                      DEVELOPMENT NEEDS
and easy installation (‘joints do not require tap-
ing).                                                            The USDA Forest Service. by virtue of its
                                                           role as steward of the National Forests, its
      The combination of wood fibers with inor-            research mission, and its longstanding expertise
ganic binders provides an unique opportunity to            in wood-based composites and recycling re-
utilize recycled, waste, and low-grade wood                search at the FPL, is actively engaged in a high-
fiber. Research has indicated clearly that inor-           priority research program on alternative uses
ganic-bonded wood composites can meet struc-               for recovered materials from the MSW stream.
tural and industrial needs.                                The FPL research program is focusing on devel-
                                                           oping value-added composites from waste ma-
                                                           terials, including wood-plastic fiber compos-
     Wood-Biomass Fiber Composites                         ites, dry-formed wood fiber-based composites,
                                                           and composites fabricated with inorganic bind-
     Wood is only one biobased resource in the             ers. For each of these program areas, we are:
waste stream. Other biobased resources include
yard waste, water plants, and agricultural resi-                1. Developing methods for converting
dues. Yard waste is a major co-mingled source                      recovered fibers into forms suitable
of biobased fiber that is now considered only for                  for subsequent processing into altema-
composting. This is a vast resource that could                     tive end-use applications.
be combined with the wood-based resource to
produce composites of many different types.                    2. Optimizing laboratory methods for
Many lakes and waterways suffer from an over-                     making prototype products.
production of water plants. These unwanted
plants create another large waste stream that                  3. Developing a performance data base,
could also be considered as a valuable source of                  including determining mechanical and
industrial fiber if they could be collected and                   physical properties of wood-based
processed economically and combined with the                      products and conducting analytical
wood-based resource to produce composites.                        tests.
Because most recycling plans call for the
composting or burning of this portion of the                   4. Determining the potential for recy-
waste stream. very little thought has been given                  cling composites with minimal loss of
to using yard waste and water plants for com-                     properties.
posites.
                                                               5. Studying product applications and
      Agricultural residues, such as straw, rice                  economic viability of alternative end-
hulls, bagasse, and corn stalks, also represent a                 use applications.
vast resource that can be used to make compos-
ites of many different types. In some parts of the             In each of these research areas, economic
world, these products are already being used to            and laboratory studies are being conducted on


                                                     310
an iterative basis as a means of setting rs-search         ber recycling program. As part of this effort. the
priorities and guiding process development.                FPL has formed a multidisciplinary team of
The research will focus on the components of               government. university. and industry special-
successful recycling systems through determin-             ists to prepare a detailed problem analysis to
ing the supply and availability of waste wood              focus research on composite from recycled
fiber. analyzing the economic efficiency of pro-           materials. Some material in this problem analy-
cessing concepts. and studying the market po-              sis was used in the preparation of this paper. We
tential for products made from recovered fiber.            wish to acknowledge the following individuals
Studies will examine the effect of new tech-               who are participating in this effort.
nologies on the environment. such as the pro-
jected impact on the landfill burden and on the
quality of the air. forests, soil. and water. The                  Government Representatives
studies will also examine the broader economic
impact of these technologies on timber markets                 Rodger A. Arola
and trade.                                                     USDA Forest Service
                                                               North Central Forest Experiment Station
                                                               Forestry Sciences Laboratory
        CONCLUDING REMARKS                                     Forest Hill Road
                                                               Houghton, MI 49931
     Recycling is a critical element in the long-
term management of renewable resources. A                      Richard W. Hemingway
successful approach to recycling requires full                 USDA Forest Service, Southern Station
cooperation between the government and the                     Alexandria Forestry Center
private sector. Government cannot logically                    2500 Shreveport Highway
mandate the increase use of recyclable materi-                 Pineville, LA 71360
als without the involvement of industry – the
industrial sector has the technical knowledge                  Henry Spelter
and equipment to separate and process solid                    USDA Forest Service. Forest Products
waste and to make useful, economically viable                    Laboratory
products from waste materials. Industry pro-                   One Gifford Pinchot Drive
vides the market for recycled resources. and it                Madison, WI 53705
must be a full partner in all aspects of the
process. It is believed that by using recovered
wood and fiber for wood-based composites                            University Representatives
tremendous opportunities are presented for
growth. for progress. and for further industry                 John Simonsen
competitiveness in a world that is rapidly con-                USDA Forest Service. Forest Research
suming many nonrenewable resources at an                          Laboratory
ever increasing rate.                                          Oregon State University
                                                               3015 SW Western Avenue
                                                               Corvallis, OR 97331
         ACKNOWLEDGEMENTS
                                                               Ramani Narayan
   The USDA Forest Service is developing a                     Michigan State University
comprehensive wastepaper and waste wood fi-                    Michigan Biotechnology Institute

                                                     311
    3900 Collins Road                                         duced by using this mat process. Pro-
    P. O. Box 27609                                           ceedings, 1990 Tappi Nonwovens Con-
    Lansing. MI 48909                                        ference. pp. 87-108.

    Don White                                         Caron, Phillip E. and Allen, G. D. 1968. Rein-
    University of Arizona                                    forced Moldable Wood Fiber Mat and
    College of Engineering and Mines                         Method of Manufacture. U.S. Patent
    Tucson, AR 85721                                         3,367,820. U. S. Patent Office. Wash-
                                                             ington. D. C.

         Industry Representatives                     Caron, Phillip E. and Grove, G. A. 1966a.
                                                             Process for Manufacturing Moldable
    Phil Davis                                               Fibrous Panels. U.S. Patent 3,230,287.
    Environmental Recovery Systems, Inc.                     U. S. Patent Office. Washington, D.C.
    1625 Broadway, Suite 2600
    Denver. CO 80210
                                                      Caron, Phillip E. and Grove, G. A. 1966b.
                                                             Production of Hot-Pressed Three-Di-
    Tom Friberg
                                                             mensional Fiber Articles. U. S. Patent
    Weyerhaeuser
                                                             3,261,898. U. S. Patent Office. Wash-
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                                                             ington, D. C.
    Tacoma. WA 98477

    David Leneke                                      Caron, Phillip E. and Grove, G. A. 1966c.
    Wilsey & Ham Pacific                                     Method of Die-Baking Moldable Wood
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    Portland, OR 97201                                       Patent Office. Washington, D. C.

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