Municipal Solid Waste as a Source of Lignocellulosic Fiberand Plastic for Composite Industries

Alireza AshoriDepartment of Chemical Industries, Iranian Research Organization for Scienceand Technology (IROST), Tehran, Iran

Municipal solid wastes (MSWs) generated each year containpotentially useful and recyclable materials for composites. Interestis high for the use of MSWs in composites, thus providing costand environmental benefits. The main objective of this study wasto show the potential of municipal solid waste materials for makingwood plastic composites. The possibility of using recycled materialsin the development of composites is very attractive, especially withrespect to the large quantity of wood and plastic waste generateddaily. Waste wood and paper can meet all the requirements in orderto replace inorganic fillers in thermoplastic composites. Advantagesassociated with biocomposite products include lighter weight andimproved acoustic, impact, and heat reformability properties—allat a cost less than that of comparable products made from plasticsalone. In addition, these composites can possibly be reclaimed andrecycled for the production of second-generation composites.

Keywords Biodegradable; Composite; Green chemistry,Mechanical properties; Waste materials

INTRODUCTION

The word ‘‘waste’’ typically conjures up a vision ofmaterial with no value or useful purpose. The generation ofsolid and industrial wastes, however, is increasing at analarming rate. It is difficult to dispose of the growing volumeof municipal solid wastes (MSWs) in landfills because mostpeople will not tolerate MSWs in their neighborhood. Ifpresent trends continue, the majority of our landfills will beclosed in the near future. As political and conservation pres-sures increase, the recovery and=or reduction of recyclablematerials from the solid-waste stream are urgently needed[1].

When two or more materials with different propertiesare combined together, they form a composite material[2].The properties of composite materials, in general, aresuperior in many respects to those of the individualconstituents. This has provided the main motivation forthe research and development of composite materials.

The properties of polymeric composite materials aremainly determined by three constitutive elements: the poly-mer, the reinforcement (such as particles and fibers), andthe interface between them[3]. The composite industryalways looks into alternative low-cost lignocellulosicsources that can decrease overall manufacturing costsand increase stiffness of the materials. However, greenchemistry technology is evolving that holds promise forusing waste or recycled wood, paper, and plastics to makean array of high-performance products that are, in them-selves, potentially recyclable. A number of studies havebeen reported[1,4,5,6,7] that describe recycled plastics suchas polyethylene, polypropylene, or polyethylene terephtha-late, which can be combined with wood fiber waste to makeuseful wood-plastic composites (WPCs).

The overall goal of this study is to illustrate the avail-ability and potential of waste materials from MSW streamsand the desirability of developing the means to recyclethem.

MUNICIPAL SOLID WASTE AS A SOURCEOF LIGNOCELLULOSIC FIBER AND PLASTICS

MSW comes from residential, commercial, institutional,and industrial sources and includes such things as durableand nondurable goods, containers and packaging, foodscraps, yard trimmings, and miscellaneous inorganicwaste[8]. Waste wood, waste paper, and waste plastics aremajor components of MSW and offer great opportunitiesas recycled ingredients in wood-plastic composites(WPCs)[5].

With a rising level of prosperity in industrializedcountries, an increasing number of products and servicesare being produced and consumed. This development isreflected in the amount of waste generated. Data fromthe past three decades show that the total amount ofmunicipal solid waste is continuously rising. Figure 1shows the quantities of household waste (without demo-lition waste) in a number of European countries. A riseof about 2–3% each year can be seen[9].

Address correspondence to A. Ashori, Iranian ResearchOrganization for Science and Technology (IROST), P.O. Box15815-3538, Tehran, Iran. E-mail: ashori@irost.ir

Polymer-Plastics Technology and Engineering, 47: 741–744, 2008

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print/1525-6111 online

DOI: 10.1080/03602550802188565

741

Iran’s basic approach to MSW is: (1) waste preventionand minimization, (2) promotion of recycling, and (3)environmentally-sound final disposal. The generation ofwaste is controlled at the source by households and busi-ness enterprises. Recyclable components of such wasteare disposed of separately to facilitate recycling. The datain Table 1 include all the domestic residential waste pro-ducts, but not all the industrial waste materials. Data areinvluded for the total weight and percentage of certainTehran (capital of Iran) MSW streams, but lack infor-mation for wood (including timber, leaves, bark, sawdust)and industrial production wastes. In 2006 the total quanti-ties of MSW in Tehran added up to 84.2 thousand tons,generated by the population of 7.728 million. This meansthat about 1.1 kg of waste is generated per capita perday. Paper, paperboard, and plastics in the MSW streamaccounted for approximately 18.6 and 9.4 thousand tons,respectively. Vast quantities of low-grade wood, woodresidues, and industry-generated wood waste in the form

of sawdust, planer shavings, and chips are now beingburned. In addition, a number of problems are associatedwith the use of these waste materials, some of whichinclude collection, separation, clean up, uniformity, form,and costs. Assuming that these problems can be overcomeon a cost effective basis, some of the resultant reclaimedmaterials should be useful ingredients for a range ofvaluable composites, from low-cost, high-volume materialsto high-cost, low-volume materials for a wide range ofend-use applications[1].

Source separation and recycling not only extend the lifeof landfills by removing materials from the MSW stream,but they also make available large volumes of valuableraw materials for use by industry in place of virginresources. Industrial use of such materials reduces the costsfor raw materials and the energy it takes to make a fini-shed product. The main requirement is that the recycledingredients meet the quality and quantity requirements ofthe consuming production operation[1].

USE OF WASTE MATERIALS IN WPC

WPCs are enjoying rapid growth due to their manyadvantages. Reasonable strength and stiffness, low cost,low density, absence of associated health hazards, easyfiber surface modification, wide availability, and relativenonabrasiveness[10] are some of these advantages. Inaddition, the processing is flexible, economical, and eco-logical. On the other hand, natural organic fibers fromrenewable natural resources offer the potential to act as asustainable and biodegradable reinforcing material alterna-tive for the use of glass or carbon fiber and inorganic fillers.Figure 2 shows the strength of different plant fiberscompared to glass. Considering the specific properties, aweight-saving potential of about 15% compared to glassfiber-reinforced materials is not unrealistic. At the moment,this is one of the most relevant, technical-driving forces forfurther developments[11].TABLE 1

Distribution of materials in Tehran (Iran) municipal solidwaste in 2006

Amount in municipal solid waste

Source Percentage Weight (�103 t)

Dried bread 42.1 35.5Paper and paperboard 22.1 18.6Miscellaneous inorganic 13.2 11.1Plastics 11.2 9.4Metals 9.0 7.6Glass 1.7 1.4Textiles 0.7 0.6Total 100 84.2

Source: Adapted from Recycling Organization of TehranMunicipal report. FIG. 2. Specific strength of plant fibers compared to glass.

FIG. 1. The development of municipal solid waste quantities in selected

European countries[9].

742 A. ASHORI

Wood-flour and sawdust have been used in the plasticsindustry for many years as filler to reduce the cost of fin-ished goods, as well as to improve properties such as stiff-ness, in the same manner as inorganic fillers. Theadvantages of wood over inorganic fillers include lowercost, reduced weight, the use of a renewable resource,and lower wear on processing equipment. In many usesWPCs can be opaque, colored, painted, or overlaid. Conse-quently, recovered fibers or resins used in these compositesdo not require the extreme cleaning and refinement neededwhen they are to be used as raw materials for printingpaper or pure plastic resins. This fact greatly reduces thecost of WPCs as raw materials and makes composite panelsan unusually favorable option for the recycling of three ofour most visible and troublesome classes of MSW. Wastewood, waste paper, and waste plastic bottles are majorcomponents of MSWs and offer great opportunities asrecycled ingredients in wood fiber-plastic composites[1]

Winandy et al. [5] reported that recycled sources of bothwood and plastic are commonly used in WPC’s (Table 2).

In 2002 Trex, the largest supplier of wood-plastic com-posite lumber, purchased on average over 227,000 kg of plas-tic scrap each day[12]. CorrectDeck uses about half virginplastic and the other half is obtained from recycled grocerybags and used pallet wrap[13]. Anderson developed engineeredWPC materials for its Renewal line of windows from a

wood-PVC composite material made from wood and PVCmaterial partially reclaimed from its wood window plants(Table 2). Boise has recently developed and introduced itsnew HomePlate siding made with 50% recycled polyethyleneand 50% reprocessed ‘‘urban’’ wood fiber. In total, the wood-plastic industry in North America consumed an estimated 204million kg of plastic in 2001, of which more than 95% of itwas recycled. Of all the polyolefins reclaimed from the post-consumer waste stream, 38% ended up in wood-plastic com-posites[12]. Because a large portion of the plastic waste streamis already commonly used in WPCs, it is becoming more dif-ficult to secure recycled raw material sources. Many commer-cial WPC manufacturers use a combination of recycledwood-based materials and recycled plastics.[5].

Unlike the traditional engineering fibers—e.g., glass andcarbon fibers, and mineral fillers—the lignocellulosic fibersare able to impart to a composite certain benefits such aslow density, less machine wear during processing than thatproduced by mineral reinforcements, no health hazards,and a high degree of flexibility[14].

In WPC manufacturing, virgin thermoplastic materials(e.g., high and low density polyethylene [HDPE andLDPE], polypropylene [PP], poly vinyl chloride [PVC])are widely used. Similar to virgin plastics, any recycledplastic which can melt and be processed below the degra-dation temperature of wood or other lignocellulosic fillers

TABLE 2Listing of common sources for the plastic and wood fiber used in some commercial wood plastic composite products

commercially marketed in the United States[5]

Company name Plastic source Wood source Plastic type

Plasticcontent

(%)

Woodcontent

(%)

Trex Recycled Pallets and furniture waste PE mix 50 50Crane Plastics Virgin Recycled oak wood flour HDPE 50 50Fiber composites Recycled and

virginOak and pine from millwork HDPE, LDPE, PVC 50 50

AERT Recycled andvirgin

Reclaimed cedar wood chips,oak millwork

PE

USPL Recycled Wood and natural fiber HDPE 65 35Anderson Recycled and

virginPine scrap PVC 50 50

Nexwood Recycled Rice hull flour HDPE 40 60LP specialty

productsRecycled All sawmill waste PE 50 50

Mikron Virgin Hardwood and softwood flour HDPE, LDPECertain teed Recycled fiber PVC Max. 65 Max. 45Kadant composites Recycled Recycled paper fiber HDPE 40 60Dura products Recycled Pallets and post-industrial

oak fiberHDPE

Correct buildingproducts

Virgin Oak and pine wood fiber PP 40 60

SOLID WASTE AS A SOURCE OF FIBER AND PLASTIC 743

(200�C) is usually suitable for manufacturing WPCs. Plasticwastes are one of the major volumes of global municipalsolid waste and present a promising raw material sourcefor new value-added products (WPCs) thanks to their largeamount of daily generation and low cost[15]. The utilizationof recycled plastics has been considered for the manufac-ture of WPCs. The results have shown that properties ofcomposites made from waste plastics are similar to thosemade from virgin materials[16,17].

CONCLUSION

Reductions are urgently needed in the quantities of MSWmaterials that are currently being landfilled. Waste wood,waste paper, and waste plastics are major components ofMSW and offer great opportunities as recycled ingredientsin wood-plastic composites. The possibility of using recycledmaterials in the development of composites is very attractive,especially with respect to the large quantity of plastic wastegenerated daily. For environmental, technical, and cost rea-sons there is increased interest in replacing inorganic filler(e.g., talcum or chalk) and reinforcement materials (glassfiber) with waste wood and=or paper fibers. Advantages asso-ciated with these composites include lighter weight andimproved acoustic, impact, and heat reformability proper-ties—all at a cost less than that of comparable products madefrom plastics alone. In addition, biocomposite products canpossibly be reclaimed and recycled for the production ofsecond-generation composites.

ACKNOWLEDGMENTS

Financial support (F. No. 600-47) from the IranianResearch Organization for Science and Technology(IROST) is gratefully acknowledged. The author alsowishes to thank Dr. M. H. Eikani for his help and adviceduring this work.

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