Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology

Подождите немного. Документ загружается.

Companies will need to plan accordingly for slower

printing speeds. Figure 13 shows a DataMax I-Series

RFID-enabled printer used in the University of

Florida Packaging Lab.

Portal. A portal is an RFID ‘‘gate’’ located at a dock or

a doorway. It usually has several antennas designed

to read tags on items passing through it. A pellet

load often contains tens to hundreds of cases, and

each case often holds tens of items. Entire pallet

loads move through portals. Wal-Mart requests that

only one pallet tag, representing the entire pallet, is

expected to be read from the portal. Figure 14 shows

a typical RFID portal, set up in the University of

Florida Packaging Lab.

Conveyor. In the supply chain, individual cases and

shippers often move on conveyor systems. The con-

veyor can be equipped with RFID antennas to detect

cases. Figure 15 shows a conveyor belt conﬁguration

in the University of Florida Packaging Lab.

Forklift/Mobile Reader. An alternative to the RFID

portal is an RFID enabled forklift. The RFID forklift

is equipped with a reader that records EPCs for

pallets carried (33). RFID enabled forklifts may also

need tags located at ﬁxed positions on ﬂoors, posts,

walls, doorways, and/or shelving in order to relate

pallets to locations.

Handheld Devices. Handheld devices, such as PDAs

(P ortable Digital Assistants) and PDTs (Portable Data

Terminals), are commonly used in retail environ-

ments to locate goods , set planograms (merchandise

presentation schematics), and stock merchandise.

Many are equipped with barcode scanners and wire-

less communication with a central server, although

some newer devices, such as the device pictured in

Figure 16, a re equipped with RFID capability.

Testing Apparatus. A typical testing apparatus would

consist of a conveyor belt, RFID hardware, machine vision

hardware, and a method of capturing and logging the

data, usually with a standard PC.

Table 4. Continued

Standard Description Applications Sample

POSTNET Encodes a Zip+4 code and optionally

a delivery point. To be replaced by

OneCode.

US Postal Service

OneCode Intended to replace POSTNET and

PLANET symbologies.

US Postal Service

MSI Based on Plessey. Store numeric

characters.

Inventory control

Telepen Encodes 128 ASCII characters

without the need to use ‘‘shift’’

characters.

Libraries

Interleaved 2 of 5

Figure 7. Databar-14.

Figure 8. Cognex InSight camera reading a label. (Photo by

Bruce Welt, University of Florida.)

1068 RADIO FREQUENCY IDENTIFICATION (RFID)

RFID Variables

To accurately test RFID read rates, several variables need

to be taken into account.

Frequency Variances. Different RFID tags operate at

different frequencies. In the supply chain, the most com-

mon are EPC compatible UHF tags.

Tag Technology (Class 1, gen-2, etc.). High-requency

EPC tags come in several variations. There are older

Class 0 (read only tags), Class 0+ (Class 0 tags with write

capability), Class 1 (writable tags), and the newer Gen 2

tags (writable). The older Class 0 and Class 1 tags have

been used on the supply chain and are not compatible with

one another, but they are being phased out in favor of the

newer Gen 2 tags. Many modern RFID devices are

compatible with all three tag types. Some older devices

can be updated to work with the newer tags.

Speed of Conveyor. Wal-Mart desires the ability to read

RFID tags on a conveyor belt moving at speeds of up to

600 ft/min. At the higher speeds, the RFID equipment has

less time to interrogate tags, making it more difﬁcult to

obtain accurate reads.

Reader and Antenna Variances. RFID readers may have

special settings that can be conﬁgured. Such variables

include RF power level and polling frequency. Higher

polling frequency typically leads to more reads within a

period of time. A higher power level may result in more

successful reads; however, it can also result in spurious

reads from nearby tags. Some RFID readers can be

conﬁgured to broadcast a signal when an external trigger

occurs, such as a carton breaking an infrared beam, (e.g.,

Intelletto Technologies LineMaster).

Figure 9. Cognex InSight software decoding EPC code in Data-

Matrix code and human readable form.

Figure 10. 2 2 DataMatrix symbol.

Figure 11. A slightly damaged 2D barcode. Although damaged,

much of the remaining data can still be used.

Figure 12. 2D barcodes used to encode digital sound data on

movie ﬁlm (public domain image).

RADIO FREQUENCY IDENTIFICATION (RFID) 1069

Antenna positioning also plays an important role in

RFID. Various studies have been conducted to determine

optimal positioning of the antennas. Antennas also come

in various shapes and sizes, which can also cause varia-

tions in read rates.

Environment. Environment can affect read rates of RFID

tags. Factors such as heat, humidity, and corrosion can

hinder successful reads. Many tags can decay or be more

likely to fail under some conditions. Figure 17 shows Gen-2

RFID tags after being exposed to air for several weeks.

2D Barcode Variables

To implement a 2D barcode system, some variables must

also be taken into account.

Types of Barcodes. There are several standards of 2D

barcodes, along with ‘‘stacked’’ linear barcodes. One of the

most common is DataMatrix, which has been used by the

Department of Defense and other organizations to identify

items. Other standards include Aztec, MaxiCode (used by

the United Parcel Service, based in Sandy Springs, Geor-

gia), and PDF417.

Figure 13. Datamax, Inc. (Orlando, FL) Model I-4210 RFID-

enabled thermal transfer printer in the packaging laboratory at

the University of Florida. (Photo by Bruce Welt University of

Florida.)

Figure 14. A pallet passes through an RFID portal in the

packaging laboratory at the University of Florida. (Photo by

Bruce Welt, University of Florida.)

Figure 15. Tagged cartons pass RFID antennas on a conveyor

belt in packaging laboratory at the University of Florida. (Photo

by Bruce Welt, University of Florida.)

Figure 16. Symbol Personal Digital Assistant (PDA) with em-

bedded barcode reader and RFID functionality.

1070 RADIO FREQUENCY IDENTIFICATION (RFID)

In addition to standard 2D barcodes, some companies

have experimented with color barcodes. One such example

is the High Capacity Color Barcode, developed by Micro-

soft (Redmond, WA) to complement standard UPC bar-

codes on DVDs and video games. The barcodes can be read

using camera phones or webcams to link the user to

special content (31).

Speed of Conveyor. As with RFID, the speed of the

conveyor system is also a factor. With 2D barcodes,

the conveyor speed can have a signiﬁcant impact on the

accuracy of reads.

A typical 2D barcode system uses a CCD array (cam-

era) to read symbols; and with a standard camera, the

exposure time and aperture size have an impact. A shorter

exposure time will result in a better picture for moving

objects, but with result in less light entering the lens.

More light can be let into the camera by increasing the

aperture size; however, this reduces depth of ﬁeld that can

be used for focusing.

This problem can be countered by using a light source

to illuminate the barcode while it is being read, in a

similar manner as a ﬂash on a camera. High-speed strobes

are often used to freeze images of moving items when

using imaging systems. Companies such as Advanced

Illumination (Rochester, VT) offer such equipment.

Printing Methods and Materials. The method of printing

may have some variances in the results, and also the

durability of the labels. Thermal transfer is one of the

most common methods of printing labels; however, laser,

dot matrix, and inkjet printers can also be used.

Thermal Contact Paper. Thermal contact paper is an-

other method used in label printers. With this method, the

paper is chemically treated such that it will change color

when heated. This method is common for printing receipts

at a point-of-sale. Since other heat sources will continue to

darken thermal contact paper and markings may fade

over time, this method is not used when persistence of

critical data is required.

Laser Engraving. Laser engraving (also known as laser

etching) is a method of using lasers to burn designs

directly onto a surface, including woods and plastics. Since

laser engraving does not require (a) physical contact and

(b) messy and expensive inks or solvents, this approach is

gaining marketshare in many industries. Figure 18 shows

a simple laser engraving apparatus.

Light Variations. Lighting can play a factor in reading

barcodes. External lighting can overexpose or underex-

pose an image captured by a camera, and the reﬂectivity of

some surfaces can hinder successful reads. Thermal trans-

fer, for example, may cause problems if the transfer

reﬂects light from a light source directly into the image

sensor.

General Testing Laboratory

A facility involved in testing RFID and related technolo-

gies should maintain certain basic equipment and cap-

abilities. These include the following:

Conveyor Systems. The conveyor is the main platform

across which tagged items travel. Materials and

construction may play a role in testing.

Computer Systems. The ability to run various soft-

ware applications is required.

RFID Software. To interface with the RFID devices,

one may need to use a middleware package. These

packages can interface with different brands of

readers and process the data.

Vision Software. To decode 2D barcodes, vision soft-

ware is needed. Some cameras, such as Cognex Inc.’s

(Natick, MA) InSight series, include a programma-

ble interface to input a trigger signal, capture

an image, decode the image, and output data

to a serial or Ethernet connection. The intelligent

Figure 17. Oxidation apparent on Gen-2 RFID inlays antennas

after several weeks exposure to ambient air of the packaging

laboratory at the University of Florida.

Figure 18. Laser engraving technology.

RADIO FREQUENCY IDENTIFICATION (RFID) 1071

camera may be programmed with or without a host

PC. Some cameras do not include software and

simply relay images to computers for processing

(e.g., Cognex Inc’s VisionPro).

Intelligent cameras are generally more expensive,

but do not require a host computer to perform all func-

tions. This results in lower overall power and space

requirements.

A software-based camera, such as Point Gray Re-

search’s (Vancouver, BC, Canada) Flea, does not have

on-board programming capability and must interface

with a computer to be of use. One advantage of software-

based cameras is the ease of using multiple cameras and

the increased power and ﬂexibility of a computer for image

processing

Development Software. To transfer data between the

camera software, hardware, and a database inter-

face, development software may be desired. Micro-

soft Visual Studio, for example, includes Application

Programming Interfaces (APIs) to interface with

serial ports and TCP/IP. Cognex’s VisionPro also

includes an interface for use with Visual Studio

and can generate applications that can be compiled

and edited from within Visual Studio. Other solu-

tions also exist, such as those by Borland and Sun

Microsystems.

Database software. A database may be desired to log

data captured from RFID, barcode, and/or machine

vision devices. Some packages available include

Microsoft SQL Server (commercial product), Micro-

soft SQL Express (free), MySQL (free), and Micro-

soft Access (commercial). The programming

environment can interface with the database using

ODBC or JDBC drivers.

PLC. A programmable logic controller may be desired

to control trigger signals. The Flea camera, for

example, is designed to input 3.3-V signals, while

the Cognex Insight will take a 24-V signal.

Sensors. Instead of constantly searching for a tag, an

RFID sensor and/or camera can be conﬁgured to

read a tag when triggered. A common way to do this

is by using a simple optical sensor.

Light Source. The read rate of 2D barcodes can be

improved signiﬁcantly at higher speeds with the use

of an external light source. Modern light-emitting

diodes (LEDs) can emit a bright light onto the

barcode, allowing more light to be captured by the

camera.

RFID Devices. There are several different types of

RFID devices available on the market. Some include

built-in antennas, while others use external anten-

nas. Some devices are designed as original equip-

ment manufacturer (OEM) devices and are also

designed to be combined with or embedded within

another device. Such devices will only have basic

RFID functionality. One such example of an OEM

device is the Sirit Inc.’s (Toronto, Ontario, Canada)

InFinity 210 (shown in Figure 19), which could serve

as an RFID core for a branded RFID reader. Data

are transmitted to and from the device using special

serial commands. It can use either an on-board

antenna or connected to a larger external antenna.

Other devices are designed for direct interfacing

with the user. They may have a user-friendly inter-

face and come with additional features and inter-

faces. One such example is Intelletto’s (Markham,

Ontario, Canada) Linemaster, a device designed to

be used in conjunction with a barcode scanner

(Figure 20).

Antennas. Most supply chain RFID implementations

use UHF RFID tags, and as such, will require UHF

compatible antennas. Some readers are compatible

with multiple frequencies, but may require dedi-

cated antennas for each frequency. Figure 21 shows

different antennas used for high-frequency and ul-

tra-high Frequency RFID tags.

Image Sensor. For standard one-color 2D barcodes, a

monochrome camera is all that is required and may

perform better than a color camera. A color camera

can also be used, but for monochrome symbols the

color information will be discarded by the symbol

Figure 19. Sirit InFinity 210 OEM device.

Figure 20. Intelletto, Inc. Model Linemaster RFID device.

1072 RADIO FREQUENCY IDENTIFICATION (RFID)

reading algorithm. A hardware-based camera may

interface with the host system using a serial or

Ethernet connection, while a software-based camera

will use an IEEE 1394 (Firewire) interface for fast

data transfer.

Sample Performance Comparison

Tests with such systems are common in the University of

Florida Packaging Science Laboratory.

A description of a simple performance comparison

between a speciﬁc RFID installation and machine vision

capture of Datamatrix barcodes follows.

Materials and Methods

Gen-2 Tags. Tags used for the RFID tests included 96-

bit Class 1 Gen-2 tags (Figure 22). Each box of tags

included 506 tags. The tags were packaged in a static-

resistant bag on a spindle in a corrugated regular slotted

container. The tags used are actually RFID ‘‘inlays’’ that

are designed to be incorporated into conventional labels.

For this work, the inlays were used directly.

Programming. Tags were programmed manually using

the Sirit InFinity 210 reader. Once all the tags were

programmed, data were veriﬁed, with defective tags being

replaced.

Upon testing, read rates were reasonable using empty

boxes on a conveyor, but not close to the 100% requirement

desired by Wal-Mart. Some tags functioned well during

the ﬁrst few trials, but stopped functioning on later trials.

Environment. The inlays did not hold up very well to the

lab environment without additional protection. Oxidation

was readily apparent on RFID tag antennas.

Read Methods. RFID tags were read with a Sirit In-

ﬁnity 210 RFID device. For initial testing, tags were

placed on empty corrugated ﬁberboard containers and

placed on a conveyor belt. Reads were performed when a

container tripped an IR sensor. In addition to RFID, a

machine vision system using Cognex’s VisionPro software

package was used to read 2D DataMatrix barcodes. The

2D barcodes were each placed in a similar location on each

carton.

Results and Findings. Data showed that the vision sys-

tem had more accurate reads. When boxes were placed on

the conveyor belt with uniform direction, the vision sys-

tem was able to pick up every box that passed through.

The RFID rates, however, were signiﬁcantly lower. In

addition to tags not being picked accurately by the reader,

some tags failed completely.

Results of this particular test (shown in Figure 23)

show some actual read rates from a trial using 10 tags,

each sent along the conveyor ﬁve times each. Also notable

is Tag #2, which did not have any RFID reads after being

successfully coded and veriﬁed. This indicates that the tag

had stopped functioning and needed to be replaced. Tag

#1, however, worked all ﬁve times, indicating that there

may be inter-tag differences. While this example does not

represent a comprehensive comparison between vision

systems and RFID, it does suggest that RFID may not

Figure 21. UHF (left) and HF (right) RFID antennas.

Figure 22. Gen-2 tags used for testing.

RADIO FREQUENCY IDENTIFICATION (RFID) 1073

be without competition for collecting serialized identiﬁca-

tion codes going forward.

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Figure 23. Sample results of trial with 10 tags, each repeated

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1074 RADIO FREQUENCY IDENTIFICATION (RFID)

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RECYCLING

JOHN K. BORCHARDT

Southhaven Communications,

Houston, Texas

INTRODUCTION

Recycling is steadily increasing in both developed and

underdeveloped countries. World population is both grow-

ing rapidly and becoming more concentrated in urban

areas. Increased urbanization will increase the concentra-

tion of packaging wastes, thus improving collection eco-

nomics. A United Nations study indicates that increased

recycling rates are accompanied by job creation and im-

proved living conditions (see also Environmental Laws,

North America and International Org).

In the United States, the recycling industry employs

about 1.1 million people, with an annual payroll of $37

billion (1).

Paper and board are the most widely used packaging

materials in terms of weight. In the United Kingdom,

paper and board account for 43% by weight of all packa-

ging (2). Paper and board packaging make up 6.4% of the

overall content of typical household waste. For further

information on paper and cardboard recycling, see Waste

Watch’s Paper information sheet. Plastics account for 20%

of the weight of all packaging. Glass accounts for 20% of

the weight of all packaging and 10% of all goods are

packaged in glass.

In the United States, approximately 251 million tons of

MSW was generated in 2006 (3). Containers and packa-

ging comprised 40.2% (79.6 million tons) of total municipal

solid waste generation. Excluding composting, the amount

of MSW recycled increased to 60 million tons, an increase

of 1.26 million tons from 2005. The tons recovered for

composting rose slightly to 21 million tons in 2006, up

from 20.6 million tons in 2005. The recovery rate for

recycling (including composting) was 32.5% in 2006 up

from 32.1% in 2005

Major sources of packaging wastes are grocery stores,

restaurants, and ofﬁce buildings. Residential collection of

waste materials is increasing, although sorting of the

wastes is often a major expense. The average composition

of U.S. municipal solid wastes (2006) is given in Table 1.

Both economic factors and governmental regulation are

driving recycling. Energy costs associated with recycling

are almost always less than in manufacture of products

from virgin materials. For example, recycled aluminum

requires only about 2.8 kWh/kg of metal produced, while

primary aluminum production requires about 45 kWh/kg

of metal produced (4). Steel and glass recycling consume

about 50% of the energy needed to make these products

from ore and silica. Plastics recycling takes only 10–15% of

the energy needed to reﬁne petroleum and manufacture

virgin resins. Incineration of plastics is a less efﬁcient

means of saving energy. For example, 100 lb (45.4 kg) of

high-density polyethylene (HDPE) has a fuel value of

20 10

Btu (19 kJ). Recycling saves twice this: 40 10

Btu (38 kJ). Lower energy consumption associated with

recycling reduces emissions of carbon dioxide, a green-

house gas believed to be associated with global warming.

For example, producing aluminum by recycling creates

only about 4% as much CO

as is created when virgin

aluminum is produced (4).

Both economic and environmental factors have led to

government regulations designed to promote recycling.

Economic concerns are related to balance of payment

issues when virgin raw materials for packaging products

are imported. For example, in China and Japan, limited

forest resources means that many paper products have to

be imported. Recycling reduces these imports. In fact,

Japan imports used paper products from the United

States and elsewhere to recycle them.

In some areas, the number of landﬁll sites is becoming

limited. Although the number of landﬁlls in the United

States is declining, the remaining sites are large, modern

facilities. Concerns about landﬁll disposal costs are becom-

ing less of a factor in promoting North American recycling.

Environmental concerns include forest depletion and the

effects of wastes on the environment. One concern receiving

much publicity is the harmful effects that plastics, when

eaten,canhaveonmarineanimallifesuchasdolphins.

SEPARATION OF COMMINGLED MATERIALS

Solid wastes, particularly from residential curbside collec-

tion programs, arrive at material recovery facilities

Table 1. Composition of U.S. Municipal Solid Wastes

Component Percent by Weight

Paper 33.9

Plastics 11.7

Metals 7.6

Glass 5.3

Rubber, leather, textiles 7.3

Yard trimmings 12.9

Food scraps 12.4

Source: Reference 3.

RECYCLING 1075

(MRFs) as a complex mixture. MRFs are typically built to

process 100–500 tons of waste per day (5). Unit operations

are summarized in Figure 1. The wastes are dumped on a

tipping ﬂoor, where paper products are separated from

metals and plastics. Metals and plastics, mostly contain-

ers, are pushed onto a conveyer belt. Two types of mag-

netic separators remove steel and aluminum from plastics

and glass. Density differences or manual sorting are used

to separate glass from plastics. The glass containers are

hard-sorted by color. The plastics are separated into

individual polymer types by the MRF or in separate

reclaiming facilities (5). Plastic bottles are classiﬁed into:

clear poly(ethylene terephthalate) (PET) soft-drink bot-

tles; green PET soft-drink bottles; translucent high-den-

sity polyethylene milk, water, and juice bottles; pigmented

HDPE detergent bottles; poly(vinyl chloride) (PVC) water

bottles; and food containers such as polypropylene

ketchup bottles (5).

METALS

Ferrous Metals

Iron and steel scrap account for more than one-third of the

cast iron and steel produced in the United States. Much of

this is ‘‘home scrap’’ produced during production of cast

iron and steel. Home scrap is always recycled. ‘‘Prompt

industrial scrap’’ is produced by industries while manu-

facturing products from steel or cast iron. Postcon-

sumer scrap comes primarily from automobiles. Other

sources include railroad rails and other machinery. Muni-

cipal solid waste is a growing source of postconsumer

scrap in the United States. In some countries with low

labor costs, ship breaking is a major source of postcon-

sumer scrap.

Shredders received whole or baled vehicle bodies from

salvage yards. Typical shredders process 200–1500 cars

per day. All major automobile producing countries

have adequate capacity to shred their available supply of

discarded automobiles. In the United States, approxi-

mately 1.21 million tons of steel are recovered annually

from 9 million scrap vehicles (6). Steel fuel tanks are

removed from automobiles before the vehicles are

shredded. These are sold for metal recovery.

A hammermill shreds the vehicle into ﬁst-sized frag-

ments. These are separated into a magnetic fraction

(ferrous metals) and a nonmagnetic fraction. The non-

magnetic fraction is separated using air or water to form a

low-density nonmetallic fraction and a high-density frac-

tion consisting mostly of zinc, copper, and aluminum.

Tin must be removed when recycling tinplate cans. As

little as 0.01% tin can form hard spots in steel and causes

difﬁculties in rolling (6). Therefore, only low levels of steel

can scrap can be used directly in furnaces. By processing

cans with hot caustic and an oxidizing agent, tin can be

removed from tinplated steel cans. The use of steel bev-

erage cans is declining. Those used often contain no tin.

Therefore, few mills operate detinning operations. Can

scrap has been used as a precipitant in copper leaching

mining. However, this is a low-volume application.

Minimills using electric arc furnaces use scrap iron and

steel as their only feedstock. The amount of scrap that

may be used in basic oxygen furnishes is limited to about

33% of the charge because the only heat source for melting

the scrap is carbon and silicon added with iron ore.

Nonferrous Metals

When processing municipal solid wastes, an eddy-current

separation unit is often used to separate aluminum and

other nonferrous metals from the waste stream. This is

done after removal of the ferrous metals (Figure 1). The

eddy-current separator produces an electromagnetic ﬁeld

through which the waste passes. The nonferrous metals

produce currents having a magnetic moment that is

phased to repel the moment of the applied magnetic

ﬁeld. The repulsion causes the nonferrous metals to be

thrown out of the process stream away from nonmetallic

objects (7).

Another separation device that may be used is the

mineral jig. This unit produces a loose vibrating bed of

particles in a liquid medium. The vibrations segregate the

solids into layers by density. The dense nonferrous me-

tals—primarily lead, zinc, and copper—are at the bottom,

while organics are at the top. The middle layer is primar-

ily glass.

Aluminum is the largest-volume nonferrous metal

recovered and recycled. More than 95% of beer and

carbonated soft-drink containers are two-piece aluminum

cans (8). Aluminum is also used for aerosol cans and as

foil–plastic–paper laminates to package cereal and frozen

foods. Aluminum is also used for food trays and pie plates.

All of these are found in and collected from municipal solid

wastes.

The energy savings associated with recycling alumi-

num are driving the aluminum energy to increasingly rely

upon remelting of aluminum scrap and less on primary

production (9).

Aluminum produced from recycled material requires

only about 2.8 kWh/kg, while primary aluminum pro-

duction requires about 45 kWh/kg of metal produced

(10). Primary aluminum production relies on electricity

Figure 1. Basic unit operations in sorting waste plastics.

1076 RECYCLING

produced largely by coal-ﬁred electricity generating

plants, while recycling uses natural gas. Natural gas

combustion produces less air pollutants and greenhouse

gases than does burning coal.

The Aluminum Industry Technology Roadmap issued

in 2003 set a U.S. target to recycle 100% of aluminum by

2020 (11). Achieving this goal will require:

. Designing remelting furnaces that minimize melt

lost while increasing melt rates, cost effectiveness,

energy efﬁciency, and safety while reducing emis-

sions of polluting gases.

. Developing low-cost aluminum puriﬁcation processes

to remove impurities such as magnesium, iron, lead,

lithium, silicon, and titanium to produce high-purity

aluminum from mixed scrap.

. Developing alloys that better match scrap to speciﬁ-

cations, allowing for increased utilization.

. Minimizing aluminum loss caused by oxidation and

dross formation during remelting.

. Improving separation of metal from dross or salt

cake.

Another advantage is that ﬂuoride emission, long

a major concern in aluminum smelting, is reduced

to the degree that the plant processes recycled aluminum

(12). (The U.S. aluminum industry uses 15 kg of ﬂuoride

ion per metric ton of virgin aluminum produced. About

10–15% of this ﬂuoride is lost during the production

process.)

Organic coatings must be removed before the recovered

aluminum can be used to make new sheet stock (7). This is

done in special furnaces. About 90% of recovered alumi-

num cans is converted into new cans. The remainder are

used to make other aluminum products.

Removing tin from steel cans is the only U.S. domestic

source of this metal. As noted earlier, treatment of steel

cans with caustic and an oxidizing agent is used to

separate the tin. Recycled lead amounts to about 60% of

the U.S. lead industry production. Most recycled lead

comes from automobile batteries.

Total U.S. recovery of nonferrous metals from vehicle

shredding is 0.8 million tons annually (6). The metals are

mostly zinc, copper, and aluminum. About 8 kg of copper

can be recovered from each automobile copper radiator.

Their recovery and sale contributes signiﬁcantly to shred-

der proﬁts.

Precious metals are recovered proﬁtably from automo-

bile catalytic converters.

GLASS

Three-quarters of glass container shipments are for bev-

erages. The largest glass packaging markets are soft

drink, beer, wine, and hard-liquor bottles (13). Some glass

bottles are used in food, drugs, and cosmetics packaging.

About 75% of the containers are narrow-neck bottles (14).

Energy costs drop about 2–3% for every 10% cullet used in

the manufacturing process. For every six tons of recycled

container glass used, one less ton of carbon dioxide, a

greenhouse gas, is reduced compared to manufacturing

glass.

When processing municipal solid wastes, glass is gen-

erally removed by hand sorting after separating paper and

metals. The mineral jig may be used to separate glass

particles from other particles. Particles should be less

than 5 cm in their longest dimension. Glass occurs in the

middle layer of the slurry formed by the mineral jig. Froth

ﬂotation may be used to separate glass particles from

denser particles. Froth ﬂotation is most efﬁcient for

particles less than 850 mm in size. A cationic fatty-acid

amine surfactant has been used to improve the efﬁciency

of froth ﬂotation of glass.

The color distribution of glass in municipal solid waste

averages 65% colorless, 20% amber, and 15% green. [As

manufactured, 85% of container glass is clear (13).] Hand

sorting of containers or optical sorting of particles can be

used to separate glass of different colors. In optical sort-

ing, interruption of a light beam by a colored or opaque

particle will activate an air jet that blows the particle out

of the process stream. Mixed colored glass can be used in

amber and green glass bottle furnaces in proportions of

r5% and r20%, respectively.

Most collected glass containers are used in the manu-

facture of new glass containers (15). The amount of cullet

(recovered glass) used in glass production typically con-

stitutes 46% of the charge used to manufacture amber

soda-lime container glass. About 25% of this cullet is from

postconsumer sources, while the rest is waste from the

glassmaking process. Recycled glass used at levels as high

as 80 percent when available (14). Since glass has an

unlimited life, it can be recycled repeatedly.

While most recycled glass is used in the manufacture of

new glass, glass can be used without puriﬁcation or other

processing by other industries. Crushed glass is used in

construction as aggregate for roadways, in building bricks,

in synthetic slate products, and for glass-wool insulation

and honeycomb structural materials.

PAPER

2006, a record

53.4% of the paper consumed in the U.S.

(53.5 million tons) was recovered for recycling (16).

The primary process steps in recycling old corrugated

containers (OCCs) and other paper packing materials are

pulping, high-density cleaning, coarse and ﬁne screening,

centrifugal (reverse) cleaning, ﬁber fractionation, and

reﬁning. Pulping disintegrates the containers into indivi-

dual ﬁbers dispersed in water. High-density cleaning

removes large dense particles such as nails and large

staples (17). Coarse screening removes large low-density

contaminants such as unpulped tapes and large adhesive

particles (18). Coarse screen hole size ranges from 6 to

20 mm. Fine screens are ﬁtted with slots as small as 0.15–

0.30 mm. These separate smaller (Z250-mm) contaminant

particles such as plastic, wax, and adhesive particles (19).

A type of hydrocyclone device called a centrifugal or

reverse cleaner is used to remove low-density (adhesive)

particles in the 70 to 250-mm size range (17).

Despite the use of screening and reverse cleaning to

remove adhesive particles or ‘‘stickies,’’ their removal is

RECYCLING 1077