Utilization of Recycled Agriculture-Based Fiber for Composites - ACS

Chapter 29

Utilization of Recycled Agriculture-Based Fiber for Composites

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Roger M . Rowell Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, 1 Gifford Pinchot Drive, Madison, WI 53705-2366

Approximately 60 percent of the volume of solid waste in an average municipal waste stream consists of agro-based resources such as paper and paper-based products, wood, and yard wastes. These resources, along with a vast quantity of agricultural residues, can be utilized in natural fiber-based composites. These composites include geotextiles, filters, sorbents, structural and non-structural, molded, packaging, and combinations with other resources such as plastics, glass, and metals. Collection of these resources can be done through an agro refinery concept where breakdown, sorting, cleaning and processing into products can be done based on market needs.

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 (MSW) stream include waste wood, paper, and other agriculture wastes. There are also potentially millions of tons of wood fiber in timber thinnings, industrial wood waste, demolition waste, pallets, and pulp mill sludges not to mention the millions of tons of agricultural wastes generated each year. These resources offer great opportunities as recycled ingredients in natural fiber-based composites. Source separation and recycling not only extend the life of landfills by removing materials from the MSW stream but also make available large volumes of valuable raw materials for use by industry in place of virgin resources. Industrial use of such materials reduces both costs for raw materials and the energy it takes to make a finished product. The main requirement is that the recycled ingredients meet the quality and quantity requirements of the consuming production operation.

This chapter not subject to U.S. copyright Published 1995 American Chemical Society Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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PLASTICS, RUBBER, AND PAPER RECYCLING


Challenges in Recycling of Waste Agro-Based Resources A comprehensive waste management program must rely on the aggregate impact of several courses of action: waste reduction, recycling, waste-to-energy schemes, and landfill [7]. The greatest impact that is likely to resultfromfurther research is in the area of recycling. Increased use of recycled agro-based resources will allow the markets for fiber composites to grow without increasing the use of virgin timber. Therefore, forest products industries will benefit from such research because less expensive raw materials will be available for producing value-added composites [2]. In 1986, the United States generated almost 158 million tons of solid waste, almost 50 percent of the world's total [3]. It is projected that this total will increase to approximately 193 millions tons by the year 2000 [4,5]. In 1986, only about 17 million tons, or 9 percent of the total solid waste was recycled [6]. This is a waste of resources, energy, space, and labor. The word "waste" projects a vision of a material with no value or useful purpose. However, technology is evolving that holds promise for using waste or recycled wood, paper products, and other forms of agro-resources into an array of high-performance composite products that are in themselves potentially recyclable. When fibers, resins, and other resources are used as raw materials for products such as paper, they require extensive cleaning and refinement. When recovered fibers, resins, and other resources are used for the manufacture of composites, these materials do not require extensive preparation. This greatly reduces the potential cost of manufacturing. A case-in-point is the making of composites from recycled paper. In the United States, nearly 80 million tons of 6,000 different paper and paper board products are produced and over 70 million tons are discarded each year [ 7,8] Few of the paper products found in the MSW stream are produced solely from fiber and water. Each product consists of a fiber matrix to which some inorganic or organic chemical compound is added to enhance the utility of the product. Thus, many forms of wastepaper contain contaminants (extraneous materials). Whether they are adhesives, inks, inorganics, dyes, metal foils, or plastics, these contaminants may need to be separated from the wastepaper before the fiber can be recycled into another useful paper product. This is not the case withfiber-basedcomposites. In many uses, naturalfibercomposites of varying types are opaque, colored, painted, or overlaid. Consequently, recovered fibers, resins, or other resources used for composites do not require extensive cleaning and refinement. Thus, composites provide an unusually favorable option for the recycling of several highly visible and troublesome classes of MSW. A considerable amount of data is available regarding the inventory of the U.S. MSW stream (Table 1). In 1988, paper and paper board, wood, and plastics in the MSW stream accounted for approximately 71.8, 6.5, and 14.4 million tons respectively. By the year 2000, thesefiguresare expected to increase to 96.1, 8.4, and 21.1 million tons annually [8]. In addition to the wood fiber in the MSW stream, vast quantities of low-grade wood, wood residues, and industry-generated

Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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wood waste in the form of sawdust, planer shavings, and chips are now being burned or disposed of in other ways. Table 2 shows the data on the agro-based resources in the MSW as of 1988 [8]. The data includes all the residential waste products but not the industrial waste resources such as pallets, timber thinnings, production wastes, bark, and sawdust. There is also no data available on the total amount of potential agricultural wastes such as bagasse (from sugar cane) and seed hulls which are collected in central locations. There is also a vast amount of agricultural residues that are currently left in the fields. These could also be utilized for fiber. Many steps are associated with the use of waste resources, including collection, analysis, storage, separation, clean up, breakdown, uniformity, form, and processing into products. There are many different plans to handle these steps, but no matter how they are done, or in what order, they must be done economically. Desire does not drive markets! Markets are driven by economics. There are at least three issues that have caused great concern in the recycling industry. One is the cost of landfilling which has been one of the strong driving forces in the economics of recycling as the cost to landfill has risen sharply in the last few years. Another concern, is the inconsistency in the markets for recycled products. Many schemes have been proposed to use such wastes as old newspapers, plastic milk and soda pop bottles, etc., but the markets using these waste products have not been reliable. The final concern is the actual cost of recycled resources versus virgin resources. In most cases, the recycled resource is more costly to use than virgin so the use of recycled resources is not economically feasibly. There is little indication that the majority of the consuming public is willing to pay more for products made from recycled resources compared to virgin resources. The purpose of the research presented in this paper is to describe the potential for producing structural composites from waste wood [9], paper [70-/2], agricultural residues [73], and other forms of agro-resources [74]. For comparison, a mixed hardwoodfiber[10-11] and hemlockfiber[9] are included. The properties of all boards are compared to minimum standards as outlined by the American Hardboard Association [75]. Processing of Fiber Into Boards Materials The following recycled and agro-fibers were used to make fiberboards for testing: Hardwood - Mixture of several hardwood species processed from pulp-grade chips through a defibrator digester at 690 KPa steam pressure for 4 minutes and refining through a Bouer 400 refiner. Old Newspaper - Old newspaper hammer milled using a 25.4 mm screen, placed into a repulper for further fiberization, and then hammer milled again using a 6.3 mm screen. HW-ONP - 50-50 Percent by weight of hardwood and old newspaper fiber. Newspaper fiber was re-hammer milled using a 1.6 mm screen.



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Table 1.- Estimated distribution of resources in the municipal solid waste stream in the United States in 1988 [2]


Amount in MSW stream 6

Source

Percent

Weight (xlO tons)

Paper and paper board Yard waste Metals Food waste Glass Plastics Textiles Wood Rubber-leather Miscellaneous inorganics Other

40.0 17.6 8.5 7.3 7.0 8.0 2.2 3.6 2.6 1.5 1.7

71.8 31.6 15.3 13.2 12.5 14.4 3.9 6.5 4.6 2.7 3.1

(Total)

100.0

179.6

NOTE:

Some data from ref. 2.

TABLE 2 - Estimated portion of agro-based resources in municipal solid waste in 1988 [8] SOURCE

AMOUNT IN MSW PERCENT WEIGHT (million tons)

PAPER/PAPER BOARD NEWSPAPER CORRUGATED MIXED MAGAZINES YARD WASTE WOOD

38.8 (6.3) (7.9) (21.9) (0.7) 18.2 2.6

61.2 (9.9) (12.5) (34.5) (1.1) 28.7 4.2

TOTAL

59.6

94.1

NOTE:

Some data from ref. 8.



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Hemlock - Pulp grade chips, steamed for 2 minutes at 0.759 MPa disk refined, and flashed dried at 160 C. Demolition wood - Wood shredded, hammer milled, cleaned and processed as given for hemlock. Mixed Office Waste - Mixed white office waste paper including envelopes was hammer milled using a 3.75 cm screen. Colored Paper - Mixed colored office waste paper including envelopes hammer milled using a 3.75 cm screen. Magazine Paper - Mixed magazine paper hammer milled using a 3.75 cm screen followed by a 1.25 cm screen. Bagasse - Fiber from a countercurrent diffusion extractor with a five-roller dewatering mill in Hawaii was screened to removefinesand dried to 30% moisture. Thefiberwas then hammer milled using a 1.25 cm screen. Kenaf - Kenaf bastfiberwas separated from the core using a air separation system. The bastfiberwas then hammer milled using a 1.25 cm screen. Resin Application and Board Fabrication The different fibers were sprayed separately in a laboratory blender with a watersoluble, 50% solids content, liquid phenolic resin. Different levels of resin were used for each board. Afinalfibermoisture content of approximately 10% was obtained for all fibers. The fiber was then hand-formed into a 508 mm x 508 mm randomly oriented mats and the mats pressed to a maximum pressure of 75 kg, with press platens at 190 C for 10-12 minutes. Testing of Board Properties Static bending Static bending tests were conducted on board specimens (50 by 200 mm) conditioned to 65% relative humidity (RH), according to ASTM standard D 1037 [16] using a 150 mm span. Modulus of rupture (MOR) and modulus of elasticity (MOE) were determined. Fifteen specimens for each cycle was tested and the results averaged. Tensile strength parallel to board surface Tensile strength parallel to the board surface was determined on board specimens (50 by 250 mm) conditioned to 65% relative humidity (RH), according to ASTM standard D 1037 [16]. Fifteen specimens for each cycle was tested and the results averaged. Water tests Oven dried, weighed specimens (5 by 5 by 1.27 cm) were placed in a 28 x 36 cm container, 5 cm deep. Thickness measurements were taken on a flatbed micrometer. Water was added to the container and the board thickness recorded as a function of time. Measurements were taken in time increments of 15, 30, and 45 minutes for the first hour, every hour for the first 6 hours, then once a day for 5 days. After 5 days, each specimen was again oven dried for 24 hours at 105 C and weights and thickness determined. Fifteen specimens for each cycle was tested and the results averaged.



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Relative humidity tests Oven dried, weighed specimens (5 by 5 by 1.27 cm) were placed in constant humidity rooms at 30%, 65%, and 90% RH and 27 C . After 31 days, the specimens were weighed to determine the equilibrium moisture content (EMC) and thickness measured to determine thickness swelling. Fifteen specimens for each cycle was tested and the results averaged. Linear expansion tests Tests were conducted according to ASTM standard D 1037 [16] on specimens 1.25 by 15 by 0.6 cm. Each specimen was conditioned at 50% RH, 27 C and length measured. The specimens were conditioned at 90% RH, 27 C for 21 days and length again measured. Linear expansion from 50 to 90% RH was then calculated. Five specimens of each type of board were tested and the results averaged. Results of Board Testing Because of the limited number of specimens per individual test, statistical analysis of the date was not appropriate. The results presented here should be considered as indicative of trends that a larger, statistically valid experiment should confirm. The results shown in Table 3 show that the fiberboard with the highest modulus of rupture was the boards made from mixed hardwood fiber followed closely by the 50/50 mixture of hardwood fiber and old newspaper fiber. The highest modulus of elasticity came from boards made from the 50/50 mixture of hardwood fiber and old newspaper fiber followed by the mixed hardwood fiber. Tensile strength was about the same for boards made from the 50/50 mixture, hardwoodfiberalone and hemlock fiber. All boards made from recycledfiberalone had lower MOR, MOE, and TS as compared to boards made from non-recycled fiber. All boards met the minimum ANSI standard for MOR except the boards made from mixed office waste, colored paper, and magazine paper. MOE and TS values are also very low for these same boards. The data in Table 4 show that thickness swelling was above the ANSI standard for all boards except for the boards made from mixed hardwood, 50/50 mixture, and bagassefiber.The boards madefrommixed office waste, colored paper, and magazine paper elongated in the water almost twice as much as all other boards. Part of the reason fiberboards made from magazine paper have such poor strength properties may be due to the inorganics present in the paper. Recycled resources that are only dry hammer milled before board formation result in particles offiberbundles which are held together by hydrogen bonding. These particles are then bonded together with a thermosetting matrix to form the boards. The mechanism of failure in these boards may be in the hydrogen bond matrix while the rest of the boards fail through thefibercell wall or the resin matrix. The primary objective of this research was to show that structural fiberboards can be made from recycled resources. While the strength properties of most of the boards made from 100% recycledfiberare lower than fiberboards made from virgin fiber, strength properties can be improved by changing the method of fiber processing and the type and amount of resin used. There are also many other non-structural.applications for recycledfiberin other types of composites.


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Table 3 Modulus of rupture (MOR) and modulus of elasticity (MOE) in bending and tensile strength (TS) parallel to the board surface offiberboardsmade from recycled fiber


Fiber Source

Level of Adhesive

HARDWOOD OLD NEWS PAPER HW-ONP HEMLOCK DEMOLITION WOOD MIXED OFFICE WASTE COLORED PAPER MAGAZINE PAPER BAGASSE KENAF

MOR

MOE

TS

%

MPa

GPa

MPa

7 7 7 10 10 8 8 8 5 8

96.7 44.1 88.3 50.6 43.2 13.2 12.1 7.0 13.9 47.1

4.83 2.14 5.44 3.66 3.23 0.48 0.36 0.31 1.4 4.6

38.7 21.3 39.4 33.0 28.3 11.6 10.0 5.2

ANSI STANDARD

— 31.0

31.0

TABLE4 - Thickness swelling (TSw) and linear expansion (LE) in water of fiberboards made from recycled fiber Fiber Source

Level of Adhesive

HARDWOOD OLD NEWS PAPER HW-ONP HEMLOCK DEMOLITION WOOD MIXED OFFICE WASTE COLORED PAPER MAGAZINE PAPER BAGASSE KENAF ANSI STANDARD

TSw

%

. %

7 7 7 10 10 8 8 8 5 8

13.4 35.0 20.3 25.2 29.8 29.8 33.7 30.3 24.1 37.3

LE 50-90 % RH ..

. %

..

0.26 0.32 0.39

0.64 0.60 0.44

>25



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GEOGRAPfflCAREA CITY

FARM

RECYCLED PAPER PRODUCTS

AGRICULTURAL RESIDUES

WASTE WOOD

TOTAL CROP

GRASS/LEAVES

WEEDS

PAPER

AGRICULTURAL WASTE

AGE© REFINERY

I

I

I

I

FOOD

FEED

FIBER

FUEL

I

COMPOST

I

I I

FERMENTATION

CHEMICALS Figure 1. Concept of an agrorefinery.


29.

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Collection of Recycled Resources One of the key issues in the recycling arena is how to collect recycled resources. We offer a system for collection and processing based on the same principal as a petroleum refinery. In a refinery based on petroleum, crude oil is brought into the refinery and the computer decides what products will be made based on market demand. The same principal could be applied to the agro-based industry. Figure 1 shows the basic concept of an agro refinery. In any geographic area, all agro-based resources are brought to the refinery. No predetermined markets are assumed and, as with the petroleum refinery, decisions as to processing and final product selection are made by market demands. From the cities within the geographic area comes recycled paper products, waste wood, grass, leaves, and other agricultural wastes. From the rural area comes these same resources along with all agricultural products. No separation of grainfromcob or stock is made on the land. Everything is cut off at the ground and brought in. The refinery then has many options to produce food, feed, fiber, fuel, or used as a media for fermentation, produce chemicals, or convert part to compost. The market structure determines what processing will be done and the best decisions based on total needs will be made. Since it has been shown that farm land must have some of the crop residue left on the land, it is important that part of the products produced include some type of compost. The compost produced can be better than the original plant residues as it can be enriched with other needed ingredients. Our present paradigm in the food growing industry is to grow grain for food and use the residue for feed. In many parts of the United States, however, there is excess grain and there are schemes to burn grain for fuel. Plants, such as kenaf, are now grown for fiber on lands that once were used to grow grain. We have, for generations, used herbicides to remove weeds from food and feed crops, but, if we are after fiber, the "weeds" may be the best crop. There are schemes to ferment grains to ethanol to be used as an additive to gasoline. There are also schemes to convert agro-based resources to methanol, phenols, and other chemicals. Instead of all of these product decisions made in advance, the agro refinery would be the central processing and decision making hub for the entire agro-based industry. It will lead to many more options for the use of this valuable resource. Literature Cited 1. Kovacs, W.L. Ecology Law Quarterly, 1988 15(4),537-625 2. Rowell, R.M., Spelter, H., Arola, R.A., Davis, P., Friberg, T., Hemingway, R.W., Rials, T., Luneke, D., Narayan, R., Simonsen,J.,and White, D. Forest Prod. J, 1993, 43(1) 55-63 3. New York Legislation Commission on Solid Waste Management. The economics of recycling municipal waste, 1986.



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4. U.S. Environmental Protection Agency, Report EPA/530-SW-90-042, 1990, Washington, DC. 5. U.S. Congress, Facing America's trash: What's next for municipal solid waste, 1989, Office of Tech. Assessment, OTA-0-424, Washington, D.C. 6. U.S. Environmental Protection Agency, Characterization of municipal solid waste in the United States,1960to 2000, 1988, EPA, Washington, D.C. 7. Focus '95+. Landmark paper recycling symposium, 1991, Atlanta, GA, 8. Franklin Associates, Ltd. Environmental Protection Agency Report, NTIS No PB87-178323, 1988, Prairie Village, KS 9. English, B., Youngquist, J.A., and Krzysik, A.M., Lignocellulosic composites. In, Cellulosic polymers, blends and composites, R.D. Gilbert, Ed. Hanser Publishers, 1994, New York, NY, 115-130 10. Krzysik, A.M., Youngquist, J.A., Muehl, J.M., Rowell, R.M., Chow, P., and Shook, S.R. Dry-process hardboards from recycled newsprint paper fibers. In, Materials interactions relevant to recycling of wood-based materials, R.M. Rowell, T.L. Laufenberg, and J.K. Rowell, eds, 1992, Materials Research Society, Pittsburgh, PA, Vol 266, 73-78. 11. Krzysik, A.M., Youngquist, J.A., Rowell,.R.M., Muehl, J.M., Chow, P., and Shook, S.R., 1993, ForestProd.J., 43(7/8) 53-58. 12. Rowell, R.M. and Harrison, S. Fiber based composites from recycled mixed paper and magazine stock, In, Materials interactions relevant to recycling of wood-based materials, R.M. Rowell, T.L. Laufenberg, and J.K. Rowell, eds. Materials Research Society, Pittsburgh, PA, 1992, Vol 266, 65-72. 13. Rowell, R. M., and Harrison, S. E., 1993, Proceedings, Fifth Annual International Kenaf Conference, Bhangoo, M. S., Ed., California State University Press, Fresno, CA, 129. 14. Rowell, R.M. and Keany, F. Wood and Fiber Sci., 1991, 23(1) 15-22 15. American National Standard. Basic hard board. ANSI/AH A 135.4, American Hardboard Association, 1982, Palatine, IL. 16. American Society for Testing and Materials Standard D 1037-38, Standard methods for evaluating properties of wood-based fiber and particle panel materials, 1982, Philadelphia, PA. RECEIVED August 2, 1995


Utilization of Recycled Agriculture-Based Fiber for Composites - ACS

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