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diffusion increases while solubility decreases), (4)

glass-transition temperature, and (5) the presence of

plasticizers and ﬁllers.

Diffusion Coefﬁcient. In Fick’s law, the diffusion coefﬁ-

cient D is a parameter that relates the ﬂux of a penetrant

in a medium to its concentration gradient. A diffusion-

coefﬁcient value is always given for a particular molecule–

polymer pair. For solid polymers, the diffusion coefﬁcient

values may range from 1 10

8

to 1 10

13

/s. The

diffusion theory shows that diffusion is an activated

phenomenon that follows Arrhenius’ law. In addition to

temperature, penetrant concentration and plasticizers

also affect the value of the diffusion coefﬁcient. Excellent

references covering the diffusion process are the books by

Crank (23) and by Crank and Park (24).

Permeability Coefﬁcient. The permeability coefﬁcient

(P) combines the effect of the diffusion and solubility

coefﬁcients. The barrier characteristic of a polymer is

commonly associated with its permeability coefﬁcient

value. The well-known relationship P = DS holds when D

is concentration independent and S follows Henry’s law.

Methods for measuring the permeability to organic com-

pounds are described by Hernandez et al. (25). ASTM E96

describes a method for measuring the water-vapor trans-

mission rate (WVTR). ASTM D1434 covers a method for

the determination of oxygen permeability.

Solubility Coefﬁcient. The solubility coefﬁcient indicates

the sorption capacity of a polymer with respect to a

particular sorbate. The simplest solubility coefﬁcient is

deﬁned by Henry’s law of solubility, which is valid at low

concentration values. The solubility of CO

in PET at high

pressure is described by combining Henry’s and Lang-

muir’s laws (26). In the case of organic compounds, the

Flory–Huggins equation is applicable (24); and for sorption

of water in nylons, a special model has been proposed (27).

SURFACE AND ADHESION

Adhesive Bond Strength. Adhesive bond strength be-

tween an adhesive and a solid substrate is a complex

phenomenon and is controlled (at least in part) by the

values of surface tension, solubility parameters, and ad-

hesive viscosity. To obtain wettability and adhesion be-

tween a polymeric substrate and an adhesive, the surface

tension of the adhesive must be lower than that of the

substrate. Usually, the difference between the two values

must be at least 10 dyn/cm. The similarity in solubility

parameters between the two phases indicates the similar-

ity of the intermolecular forces between the two phases.

For good compatibility, the values of the solubility para-

meters must be very close. Low viscosity in the adhesive is

necessary for good spreadability and wettability of the

substrate (28).

Blocking. Blocking is the tendency of a polymer ﬁlm to

stick to itself simply by physical contact. This effect is

controlled by the adhesion characteristic of the polymer.

Blocking is enhanced by surface smoothness and by

pressure on the ﬁlms present in stacked sheets or com-

pacted rolls. Blocking can be measured by the perpendi-

cular force needed to separate two sheets, and it can be

minimized by incorporating additives such as talc in the

polymer ﬁlm. ASTM D1893, ASTM D3354, and Packaging

Institute procedure T3629 present methods to evaluate

blocking.

Cohesive Bond Strength. Cohesive bond strength is the

force within the adhesive itself when bonding two sub-

strates. The cohesive bond strength depends mainly on

the intermolecular forces of the adhesive, molecular mass,

and temperature.

Friction. The coefﬁcient of friction (COF) is a measure

of the friction forces between two surfaces, and it char-

acterizes a ﬁlm’s frictional behavior. The COF of a surface

is determined by the surface adhesivity (surface tension

and crystallinity), additives (slip, pigment, and antiblock

agents), and surface ﬁnish. Cases in which the material’s

COF values require careful consideration include ﬁlm

passing over free-running rolls, bag forming, the wrapping

of ﬁlm around a product, and the stacking of bags and

other containers. Besides the intrinsic variables affecting

a material’s COF, environmental factors such as machine

speed, temperature, electrostatic buildup, and humidity

also have considerable inﬂuence in its ﬁnal value. The

static COF is associated with the force needed to start

moving an object. It is usually higher than the kinetic

coefﬁcient, which is the force needed to sustain movement.

Determination of static COF is described in TAPPI stan-

dard T503 and ASTM D1894. Thompson (29) has also

analyzed the action of additives on the value of COF of

polypropylene.

Heat Sealing. An important property for wrapping,

bagmaking, or sealing a ﬂexible structure is the heat

sealability of the material. At a given thickness, heat-

sealing characteristics of ﬂexible web material are deter-

mined by the material’s composition (which controls

strength), average molecular mass (controlling tempera-

ture and strength), molecular-mass distribution (setting

temperature range and molecular entanglement), and the

thermal conductivity (controlling dwell time (30). Tests

normally conducted to evaluate the heat sealability of a

polymeric material are the cold-peel strength (ASTM F88)

and the hot-tack strength (31). Hot tack is the melt

strength of a heat seal when the seal interface is still

liquid and without mechanical support. The hot adhesiv-

ity is associated with the molecular entanglement of the

polymer chains, viscosity, and intermolecular forces of the

material.

Surface Tension. In solids and liquids, the forces asso-

ciated with inside molecules are balanced because each

molecule is surrounded by like molecules. On the other

hand, molecules at the surface are not completely sur-

rounded by the same type of molecules, thereby generat-

ing unbalanced forces. Therefore, at the surface, these

molecules show additional free surface energy. The

998 POLYMER PROPERTIES

intensity of the free energy is proportional to the inter-

molecular forces of the material. The free surface energy

of liquids and solids, called surface tension, can be ex-

pressed in mJ/m

(millijoules per square meter) or dyn/cm

(dynes per centimeter). Values of surface tension in poly-

mers range from 20 dyn/cm for Teﬂon to 46 dyn/cm for

nylon 6,6. The measurement of surface tension by contact-

angle measurement is covered by ASTM D2578. Several

independent methods are used to estimate surface tension

of liquids and solid polymers, including the molar para-

chor (1).

When two condensed phases are in close contact, the

free energy at the interface is called interfacial energy.

Interfacial energy and surface energy in polymeric mate-

rials control adhesion, wetting, printing, surface treat-

ment, and fogging.

Wettability. Adhesion and printing operations on a

plastic surface depend on the value of the substrate

wettability or surface tension. A measure of the wettabil-

ity of a surface is given by a material’s surface tension as

described in ASTM D2578.

ELECTRICAL PROPERTIES

Electrical conductivity, dielectric constants, dissipation

factors, and triboelectric behavior are electrical properties

of polymers subject to low electric-ﬁeld strength. Materi-

als can be classiﬁed as a function of their conductivity (k)

in (O/cm)

1

(reciprocal ohms per centimeter) as follows:

conductors, 0–10

5

; dissipatives, 10

5

–10

12

; and insula-

tors, X10

12

. Plastics are considered nonconductive ma-

terials (i.e., not counting the newly developed conducting

materials).

Dielectric Constant. The relative dielectric constant of

an insulating material (e) is the ratio of the electric

capacities of parallel-plate condenser with and without

the material between the plates. A correlation between the

dielectric constant and the solubility parameter (d)is

given by the relationship of dE7.0e (1). There is also a

relationship between resistivity R (inverse of conductivity)

and the dielectric constant at 298 K: log R =232e (1).

Values of e for polymers are presented in Refs. (1) and (2).

Triboelectric Behavior. When two polymers are rubbed

against each other, one becomes positively charged and

the other becomes negatively charged, depending on the

relative electron donor–acceptor characteristics of the

polymers. A triboelectric series is the listing of polymers

according to their charge intensity, which goes from the

most negative charge (electron acceptor) to the most

positive (electron donor). The charge of polymer ﬁlms

also takes place by friction during industrial operations

such as form/ﬁll/seal. The most negative polymers are

(value in parentheses is the dielectric constant): PP

(e = 2.2), PE (e = 2.3), and PS (e = 2.6); neutral charged

polymers include PVC (e = 2.8), PVDC (e = 2.9), and PAN

(e = 3.1); and positively charged polymers include cellulose

(e = 3.7) and nylon 6,6 ( e = 4.0). As these values suggest, the

tribolectric series of dry polymers can be correlated with

the polymer dielectric constant. Since hydrophilic poly-

mers absorb water, they become more conductive, and

their dielectric constants increase. Standard methods for

measuring the triboelectric charge of ﬁlms and foams are,

at the time of this article, still under consideration by

ASTM Committee D10.13 (32).

OPTICAL APPEARANCE

Among the most important optical properties of polymers

are absorption, reﬂection, scattering, and refraction. Ab-

sorption of light takes place at the molecular level, when

the electromagnetic energy is absorbed by atoms or group

of atoms. If visible light is absorbed, a color will appear;

however, most polymers show no speciﬁc absorption with

visible light and, therefore, are colorless. Reﬂection is the

light that is remitted on the surface and depends on the

refractive indices of air and polymer. Scattering of light is

caused by optical inhomogeneities reﬂecting the light in

all directions. Refraction is the change in direction of light

due to the difference between the polymer and air refrac-

tion indices. Transparency, opacity, and gloss of a polymer

are not directly related to the chemical structure or

molecular mass; they are determined mainly by the poly-

mer morphology. Optical appearance properties are of two

types: optical morphological properties, which correlate

with transparency and opacity; and optical surface proper-

ties, which produce the specular reﬂectance and attenu-

ated reﬂectance (1, 33).

Gloss. Gloss is the percentage of incident light that is

reﬂected at an angle equal to the angle of the incident rays

(normally 451). It is a measure of the ability of a surface to

reﬂect the incident light. If the specular reﬂectance is near

zero, the surface is said to be ‘‘mat.’’ A surface with high

reﬂectance has a high gloss, which produces a sharp image

of any light source and gives a pleasing sparkle. Surface

roughness, irregularities, and scratches all decrease gloss.

Test method is covered by ASTM 2457.

Haze. Haze

is the percentage

of transmitted light that,

in passing through the sample, deviates by more than 2.51

from an incident parallel beam. The appearance of haze is

caused by light being scattered by surface imperfections

and nonhomogeneity. The measurement of haze is de-

scribed in ASTM D1003.

Transparency and Opacity. Transmittance is the per-

cent of incident light that passes through the sample

and is determined by the intensity of the absorption and

scattering effects. The absorption in polymers is insignif-

icant; thus, if the scattering is zero, the sample will be

transparent. An opaque material has low transmittance

and, therefore, large scattering power. The scattering

power of a polymer results from morphological inhomo-

geneities and/or the presence of crystals. Then, an amor-

phous homogeneous polymer such as ‘‘crystal’’ polystyrene

will have little or no scattering power and therefore will be

transparent, while a highly crystalline polymer such as

POLYMER PROPERTIES 999

HDPE will be mostly opaque. Transmittance can be

determined according to standard ASTM D1003. A trans-

parent material has a transmittance value above 90%.

BIBLIOGRAPHY

1. D. W. Van Krevelen, Properties of Polymers, 3rd edition,

Elsevier, New York, 1990.

2. J. Brandup, and E. Immergut, eds., Polymer Handbook, 3rd

edition, Wiley-Interscience, New York, 1989.

3. D. Braun, Identiﬁcation of Plastics, 2nd edition, Hanser

Publishers, New York, 1986.

4. American Society for Testing and Materials, Vols. 08.01–

08.03, 1988.

5. R. C. Progelhof and J. L. Thorne, Polymer Engineering

Principles, Hanser Publishers, New York, 1993.

6. Guide to Plastics Property and Speciﬁcation Charts, Modern

Plastics, McGraw-Hill, New York, 1987, pp. 46–48.

7. B. Wunderlich, S. Cheng, and K. Loufakis, in J. I. Kroschwitz,

ed., Encyclopedia of Polymer Science and Engineering, Vol.

16, Wiley, New York, 1989, pp. 767–807.

8. D. Rosato, Rosato’s Plastic Encyclopedia and Dictionary,

Hanser Publishers, New York, 1993.

9. G. Kampf, Characterization of Plastic by Physical Methods,

Hansen Publishers, New York, 1986.

10. A. Birley, B. Harworth, and J. Batchelor, Physics of Plastics,

Hansen Publishers, New York, 1992.

11. R. P. Brown, ed., Handbook of Plastic Testing, 2nd edition,

Pitman Press, Bath, UK, 1981.

12. S. H. Hamid, M. B. Amin, and A. G. Maadhah, eds., Handbook

of Polymer Degradation, Marcel Dekker, New York, 1992.

13. R. J. Hernandez, J. Food Eng. 22, 495–505 (1991).

14. J. J. Strebel, Polym. Test. 14, 189–202 (1995).

15. C. P. Fenimore and F. J. Martin, Modern Plast. 44, 141 (1966).

16. F. L. Fire, Combustion of Plastics, Van Nostrand Reinhold,

New York, 1991.

17. C. J. Hilado, Flammability Handbook for Plastics, 4th edition,

Technomic, Lancaster, PA, 1990.

18. P. N. Son, ‘‘UV Stabilizers’’ in Modern Plastics Encyclopedia

Handbook, McGraw-Hill, 1994, p. 119.

19. G. M. Bristow and W. F. Watson, Trans. Faraday, Soc. 54,

1731,1742 (1958).

20. H. Mark and A. V. Tobolsky, Physical Chemistry of High

Polymers, 2nd edition, Interscience, New York, 1950.

21. A. F. M. Barton, Handbook of Polymer-Liquid Interaction

Parameters and Solubility Parameters, CRC Press, Boca

Raton, FL, 1990.

22. D. Braun, Simple Methods for Identiﬁcation of Plastics, 2nd

edition, Hanser Publishers, New York, 1986.

23. J. Crank, The Mathematics of Diffusion, 2nd edition, Clar-

endon Press, London, 1975.

24. J. Crank and G. S. Park, Diffusion in Polymers, Academic

Press, New York, 1968.

25. R. J. Hernandez, J. R. Giacin, and A. L. Baner, J. Plast. Film

Sheet. 2,

187–211 (1986).

26. W.

R. Vieth, J. M. Howell, and J. Hsieh, J. Membrane Sci. 1,

177 (1976).

27. R. J. Hernandez and R. Gavara, J. Polym. Sci., Part B 32,

2367–2374 (1994).

28. D. E. Packham, Handbook of Adhesives, John Wiley & Sons,

New York, 1993.

29. K. I. Thompson, TAPPI J., 157 (September 1988).

30. J. W. Spink, R. J. Hernandez, and J. R. Giacin, TAPPI

Proceedings Polymer, Laminations and Coating Conference,

1991, pp. 579–587.

31. H. Theller, J. Plast. Film Sheet. 5(1), 66 (1989).

32. C. W. Hall, S. Singh, and G. Burgess, J. Test. Evaluation, 21,

57–61 (1993).

33. M. Born and E. Wolf, Principle of Optics, 6th edition, Perga-

mon Press, Oxford, 1980.

Cited Publications

Ruben J. Hernandez, in A. L. Brody and K. S. Marsh, The Wiley

Encyclopedia of Packaging Technology, 2nd ed., 1997, pp. 758–

765.

POLYMERIC OXYGEN SCAVENGING SYSTEMS

KAY COOKSEY

Michigan State University, East

Lansing, Michigan

Oxygen scavengers are mainly used for food and pharma-

ceutical applications but also can be used for any product

that needs a low oxygen storage atmosphere. Essentially,

oxygen scavengers are so named because they preferen-

tially absorb oxygen within the environment, thus, pre-

venting the oxygen from reacting with the product. Many

other terms have been used to describe oxygen scavengers,

which include the following: antioxidants, interceptors,

controllers, and absorbers. According to Brody, the deﬁni-

tion of an oxygen scavenger is a material in which a

chemical (or combination of reactive compounds); incorpo-

rated into a package structure may combine with oxygen

and effectively remove oxygen from the inner package

environment. The purpose of an oxygen scavenger is to

limit the amount of oxygen available for deteriorative

reactions that can lead to reduced functionality of the

product. For foods and pharmaceutical products, deteriora-

tive reactions include lipid oxidation, nutritional loss,

changes in ﬂavor and aroma, alteration of texture, and

microbial spoilage. Typically, oxygen scavengers are used

in packages that have air tight seals and are used in

conjunction with other means of preservation, such as

chemical preservatives, reduced water activity, reduced

pH, vacuum packaging, or modiﬁed atmosphere packaging.

BACKGROUND AND HISTORY

Research on oxygen scavengers began in the 1920s for

enclosed packages using a ferrous sulfate and moisture

absorbing mixture (1). Rooney (2) indicates that a British

patent from 1938 used iron, zinc, or manganese to sca-

venge oxygen from canned foods. Research continued

1000 POLYMERIC OXYGEN SCAVENGING SYSTEMS

throughout the 1940s with the bulk of the work performed

in the United Kingdom and by the U.S. Army for military

rations. During the 1970s the ﬁrst major commercial

oxygen scavenger was introduced by Mitsubishi Gas and

Chemical Company in Japan, which was available in the

United States by the late 1970s. The product eventually

became known under the tradename Ageless

and func-

tions using permeable sachet that contains a reduced iron

salt and moisture absorbent material. Another company

from Japan, Toppan Printing Company, also produced a

commercially available oxygen scavenging system, but it

functioned using ascorbic acid-based reaction. During the

1970s and 1980s, more oxygen scavenging systems were

introduced by Japanese and American companies using

several scavenging methods (1–2). During the 1980s, work

began on oxygen scavenger development using singlet

oxygen reaction by the Commonwealth Scientiﬁc Indus-

trial Research Organization (CSIRO) in Australia. See

sachets shown in Figures 1 and 2.

According to de Kruijf (3), oxygen scavengers are the

most patented of all active packaging technologies with at

least 50 patents through 1989 and 20 issued from 1990 to

1994. In the 1990s work focused more heavily on technol-

ogies to incorporate oxygen scavengers directly into ﬁlm

and other package forms such as closure liners, thermo-

formed cups, tubs, and trays rather than sachets. Part

of the reason for this change was related to concern

over consumers accidentally using the sachets as ‘‘ﬂavor

packets’’ and incidents whereupon the contents of the

sachet may seep out into the food. These problems

can lead to loss of product quality and can also lead to

serious consumer safety concerns. For example, iron in

concentrated amounts, can be toxic to children or pets,

because of their small body mass. For this reason, the FDA

mandated that iron-based sachets must be labeled with

‘‘Do not eat’’ on the sachets sold in the United States to

avoid accidental ingestion of the contents. (4).

Based on information made available in 2002, oxygen

scavengers in bottles made up the largest portion of the

market with 43.8% of the market, followed by cap/liner/

lidding representing 31.5%, sachets with 22.6%, and oxy-

gen absorbing ﬁlm with 2%.

TYPES AND MECHANISMS OF ACTION

Iron-Based Systems. Iron-based sachets are the type of

oxygen scavenging system that has been used commer-

cially for many years. It generally involves a reaction

between iron powder contained in a permeable sachet

that also may contain a dessicant. Iron powder reacts

with oxygen using the following reaction (6, 7):

Fe ! Fe

2þ

þ 2e



þ H

O þ2e



! 2OH



2þ

þ 2OH



! FeðOHÞ

FeðOHÞ

O ! FeðOHÞ

Oxygen Scavenging Polymer Materials. Many polymers

have been developed using a wide variety of chemistries

(2), however, the most commercially successful materials

have been homogenous blends of reactive substances with

polymers. An effective oxygen scavenging polymer was

developed in which dissolved reagents of known chemistry

were incorporated into a polymer, and the trigger mechan-

ism was light, which excited the reactive components in

Figure 2. Multisorb Freshpax.

Figure 1. Mitsubishi Ageless Sachets.

POLYMERIC OXYGEN SCAVENGING SYSTEMS 1001

the ﬁlm, thus, inﬂuencing oxygen diffusion into the poly-

mer. The oxygen has to be in an excited singlet state,

which required the use of a photsensitizing dye and

exposure to visible light. Another approach was based on

transition-metal-catalyzed oxidation of an aromatic nylon.

The transition metal in this case was cobalt or cobalt salt.

This material eventually became known under the trade-

name Oxbart The material easily could be blended with

polyester eventually to become important for packaging

wine and beer in plastic bottles, because it effectively

could prevent oxidation in both products. Amoco Chem-

cials introduced a material called Amosorbt, which

blended polyester and polybutadiene and was catalyzed

by a transition metal salt. When the catalyst was added

late in the injection molding process, the resulting mate-

rial became an oxidizable polymer. Another material using

light as a triggering mechanism was developed by Speer

and coworkers (8). This patent process used a transition

metal catalyst and a photosensitizer. The reaction was

designed in such a way as to prevent the rupture of the

polymer backbone as might normally occur through oxida-

tion. The material was composed of unsaturated polymers

such as poly(1,2 butdiene), which could scavenge ground

state oxygen as opposed to singlet oxygen. This product is

marketed under the trade name OS 1000t or 2000t by

Cryovac Division of Sealed Air (Figure 3).

Other materials that incorporate active components

into the polymer include material marketed by Chevron

Chemical Company, which works by auto-oxidation of

unsaturated groups on the polymer backbone. Oxidation

of aromatic nylons and hydrocarbon polymers with active

side groups use light to trigger the oxygen scavenging

process. One method that differs from the light triggering

systems involves the light excitation of a photoreducible

component such as phenolic compound, which is reduced

by oxygen, thereby scavenging oxygen.

Designing an oxygen scavenging system for speciﬁc

types of packaging is quite complex and still not well

understood except by the vendors who specialize in such

systems. Most oxygen scavengers are designed for packa-

ging based on the removal of a speciﬁed amount of oxygen

from the interior of the package over a period of a few

days. Tewari and coworker (9) studied the oxygen absorp-

tion kinetics of six commercial oxygen scavengers that

differed in oxygen scavenging capacity as well as oxygen

scavenging methods (i.e., iron-based and enzyme based).

It was determined that oxygen concentration was the

primary limiting factor in the kinetics of oxygen scaven-

gers in atmosphere of less than 500 ppm but other factors

such as temperature, capacity, and variation between

types of scavengers also occurred. Miltz and Perry (10)

studied the performance of iron-based oxygen sachets to

improve methods to apply them more effectively because

their cost and lack of technical understanding has limited

their use. Based on their study, the actual scavenging

capacity was higher than the manufacturers speciﬁca-

tions. They also found that, in modiﬁed atmosphere

packages containing carbon dioxide, the sachets also

absorbed the carbon dioxide as well as oxygen. Oxygen

sachets were found to reduce the transient period time

(time to reach equilibrium) for active modiﬁed atmosphere

packaging by nearly half compared to passive modiﬁed

atmosphere packaging without a sachet. This effect al-

lowed the shelf life to be extended because of optimal

atmosphere as soon as quickly as possible (11).

APPLICATIONS

Oxygen scavengers were initially used by the U.S. military

for the meals ready to eat (MRE) rations. Foods with

oxygen scavengers for MREs include the following: white

and whole wheat bread, pound cake, fudge brownies,

wheat snack bread, potato sticks, chow mein noodles,

nut raisin mix, pretzels, wafﬂes, and hamburger buns

(1). In the retail market, typical uses in the United States

include fresh pasta, beef jerky, pepperoni, beer (cap liner

and some bottles), ketchup, juice, case-ready meats, pre-

pared foods, and shredded cheese. Use of oxygen sachets is

more prevalent and diverse in Japan for products such as

seasonings, cheese, aseptically packaged cooked rice, dry

pet foods, cough capsules, plant growth hormone, anti-

biotics, vitamins pills and tablets, medical kits to preserve

reagents, kidney dialysis kits, and other products.

CURRENT RESEARCH ON SPECIFIC APPLICATIONS

Meat Packaging. Oxygen scavengers are used in meat

packaging to control color in red meat packages. When the

pigment for red meat (myglobin) is exposed to oxygen, the

Figure 3. Cryovac OS1000 oxygen scavenging ﬁlm.

1002 POLYMERIC OXYGEN SCAVENGING SYSTEMS

meat appears as a bright red color, which is associated

with freshness and overall acceptability. However, when

meat is exposed to too much oxygen over time, the pigment

converts to metmyoglobin, which appears as a brown color

and is not visually acceptable to consumers. Many studies

have used oxygen scavengers in modiﬁed atmosphere

packages to extend the display life of red meat packages.

Gill and McGinnis (12) studied the conditions under which

commercially available scavengers with an oxygen absorb-

ing capacity of 200 ml/sachet could prevent transient

discoloration of nitrogen ﬂushed ground beef. The rate of

oxygen absorption decreased with decreasing oxygen con-

centration when the oxygen concentration was between 10

and 20%, but the rate of oxygen absorption became

exponentially proportional with time when the oxygen

concentration was less than 1%. Oxygen concentration

in packages needed to be reduced below 10 ppm in 30

minutes at 2 1C or 2 hours at 1.5 1C to prevent transient

discoloration. It was determined that to achieve this, more

sachets than were economically feasible would have been

required at that time. Continued work on prevention of

transient discoloration of beef was done by Tewari and

others (13), who determined that steaks removed from a

controlled atmosphere masterpack had less discoloration

when packaged with an oxygen scavenger and that the

number of sachets had more impact on discoloration

prevention than the type of scavenger used. The same

research group also studied the effect of oxygen scaven-

gers inside retail trays, lidding and over-wrapped trays,

which were all equally effective for extending the accep-

table shelf life of modiﬁed atmosphere, display ready beef

and pork cuts (14). They also found that eight oxygen

scavengers with a capacity sufﬁcient to achieve an oxygen

half life of 0.6–0.7 were needed when oxygen concentra-

tion could otherwise remain at less than 500ppm during

storage. Isdell (15) measured the redness of meat 96 hours

after removal from a gas ﬂushed mother pack. They found

that redness of meat packaged in a retail tray containing

oxygen scavengers was better than retail trays that

did not contain an oxygen scavenger. In another study,

researchers (16) found that, combined with a controlled

atmosphere mother pack (outer bag), double ﬂushed

with 50% carbon dioxide and 50% nitrogen was effective

for maintaining the display shelf life of variety of red

meat cuts. The oxygen scavenger helped maintain a

low level of oxygen (0.1%) to prevent formation of

metmyoglobin.

Payne and others, (17) studied vacuum controlled

atmosphere packaging with carbon dioxide, carbon diox-

ide ﬂushed packages containing iron-based oxygen sca-

venging sachets, and packages that contain oxygen

scavengers alone for beef stored for up to 20 weeks at

1.5 1C. Beef packaged with oxygen scavenger alone

provided the best results with regard to drip loss, micro-

bial and sensory properties. Martinez and coworkers (18)

found that fresh pork sausages packaged in a 20% carbon

dioxide, 80% nitrogen atmosphere with an iron-based

oxygen scavenging sachet, had reduced psychrotropic

aerobic counts and extended shelf life with regard to color

and lipid stability for 20 days at 2 1C. Catﬁsh steaks were

packaged in barrier ﬁlm and vacuum packaged with and

without an iron-based sachet. Shelf life was extended 10

days (20 days with sachet v. 10 days without sachet) with

the aid of the sachet based on sensory, microbiological,

and volatile base nitrogen analysis. The oxygen in the

packages containing the sachets reached 0.42% within 24

hours of packaging (19). Labels are manufactured that

absorb 10–20 mL of oxygen, and larger labels are starting

to become available that scavenge 100–200 mL O

(7).

Besides labels, oxygen scavengers also can be incorporated

into the polymer ﬁlm. The ﬁlm is capable of reducing

oxygen in the headspace to less than 1 ppm in 4–10 days

for products such as dried, smoked meat as well as

processed meat products (20).

Bakery Products. Baked goods such as bread, pastries,

cakes, and cookies can have an extended shelf life with use

of oxygen scavengers combined with modiﬁed atmosphere

packaging. The low-oxygen condition retard molds and

other spoilage bacteria and also reduces lipid oxidation,

which can produce off ﬂavors. According to Kotsianis and

coworkers (21), an advantage over using an oxygen sca-

venger system compared to modiﬁed atmosphere packa-

ging alone was because of the fact that lower oxygen levels

could be achieved, and oxygen can be reduced in case of

leakage through defective seals. The disadvantages could

be cost and possible consumer objection to a packet in-

serted inside the package that could become loose and

cause accidental ingestion by a child or pet. A few studies

have reported on the effectiveness of oxygen scavengers for

bakery products. Sponge cakes (0.8–0.9 a

) were packed in

a modiﬁed atmosphere package (MAP) with oxygen absor-

ber sachets of two different absorption capacities (100 and

210 mL). The cakes were analyzed for mold growth over a

period of 28 days at 25 1C storage. MAP alone provided

some beneﬁts regarding mold prevention; however, com-

bining oxygen scavengers (using either 100 or 210 mL)

with modiﬁed atmosphere (30% CO

) prevented mold

growth entirely during the 28 days of storage. The results

also indicated that a greater beneﬁt existed for cakes with

a higher a

(0.9) compared to lower a

(0.8) (22).

In another study (23), oxygen absorbers were added to

wheat crackers formulated with high levels of oil for

storage in hermetically sealed cans used as military

rations. The study included storage at 15, 25, and 35 1C.

Shelf life was assessed using sensory panels as well as

hexane concentration and headspace oxygen measure-

ments. As storage temperature increased, headspace oxy-

gen decreased within the can. Overall, cans of crackers

without oxygen sachets reached unacceptable levels of

rancidity within 24 weeks at 25 and 351C. Cans of crackers

with oxygen sachets did not have rancid odors after 44

weeks of storage, regardless of storage temperature. Thus,

shelf life of canned crackers was extended for 20 weeks

with oxygen absorbers added to the can.

Other Products. In a study by Zerdin and coworkers

(24), orange juice contained in aseptic packages with an

oxygen scavenging barrier layer had better retention of

ascorbic acid than packages with plain oxygen barrier

ﬁlm. Packages that contained oxygen scavengers had less

mold growth on cheddar cheese compared to packages

POLYMERIC OXYGEN SCAVENGING SYSTEMS 1003

without the oxygen scavengers over a 16 week refriger-

ated storage period (25).

Milk processed using ultra-high temperature proces-

sing, (UHT) was packaged and stored in aseptic pouches

that contain an oxygen scavenging ﬁlm or a pouch without

the scavenging ﬁlm. The milk in the oxygen scavenging

pouch had signiﬁcantly lower levels of dissolved oxygen

and levels of volatiles associated with staleness (26).

Hazelnuts were packaged under controlled atmosphere

conditions with and without iron-based oxygen sachets.

The nuts packaged using the sachets were signiﬁcantly

less oxidized compared to the nuts without the sachets.

However, when the sachets were analyzed for volatile

compounds, other ﬂavor compounds were also scavenged

by the sachets (27)

REGULATORY STATUS

A program was developed by the EU Fair R&D program to

establish and implement active and intelligent packaging

technologies within existing EU regulations, which would

enable technologies to be used and allow for products to be

globally competitive with other technologies. The program

included, inventory, classiﬁcation, evaluation, and recom-

mendations for regulation of active and intelligent packa-

ging systems. Oxygen scavenging systems were examined

as part of the evaluation step and was tested for migration

into a variety of food simulants. It was determined (3) that

migration from oxygen scavengers varied signiﬁcantly

depending upon type of system (sachet, cap, crown, or

ﬁlm) and food stimulant. For example, migration of oxy-

gen scavenger in water (mg/sample) was 620, 74, 1.0, and

0.2 for sachet, cap, crown, and ﬁlm, respectively. Based on

a study by Lopez-Cervantes and coworkers (23), migration

into liquid, solid, and gelled food stimulants using

two different types of oxygen sachets were tested. Migra-

tion from oxygen scavengers did not exceed European

Union migration limits as long as the sachet was properly

located in the package, and the packaging process did not

favor the content becoming wet from water released from

the food.

FUTURE OF OXYGEN SCAVENGERS

New methods of producing oxygen scavengers will

continue to be developed. For example, Alteiri and cow-

orkers (29), suggested the use of aerobic microorganisms

as the mechanism for oxygen scavenging. The microorgan-

isms can be trapped in poly-vinyl alcohol and used as a

coating for high humidity foods. Another use that may

see increased application is addition of an oxygen sachet

with biopolymer ﬁlm. Polylactic acid ﬁlm did not have

oxygen barrier properties equal to the polyester ﬁlm

typically used for packaging semi-hard cheese (30).

However, when an oxygen scavenger was added to the

package, lipid oxidation of the cheese was signiﬁcantly

reduced and continued to improve with dark storage

(Tables 1, 2).

Another new method may involve radiation treatment

of ethyl vinyl alcohol copolymers. Researchers (30), irra-

diated EVOH (29% ethylene) with 30 and 90 kGy dosages

and found that as the dosage increased, the longer the

polymer was able to react with oxygen.

Oxygen scavengers that function better under a variety

of temperatures will also be used. A patent was issued for

an oxygen scavenging ﬁlm that acts under ambient and

refrigerated conditions and can be incorporated uniformly

into a multilayer ﬁlm (32). Another development involves

a patent that indicates that the activation of the oxygen

scavenging component of a ﬁlm can be triggered upon

packaging with the product to prevent loss of scavenging

capacity in ﬁlms that may be active while ﬁlm is in storage

(prior to product packaging). The ﬁlm would receive an

initial trigger using actinic radiation, which would not be

sufﬁcient to activate the ﬁlm fully and would receive the

total dose necessary to trigger the oxygen scavenging

component when desired (33).

An oxygen scavenger that also indicates the level of

oxygen present has been developed, which makes it both

an active, and intelligent package component. The sca-

venger is in a pouch form with a layer in the pouch that

has a color changing substance that can be viewed

through a clear window (34).

Table 1. Oxygen Scavenging Components

Sulﬁtes

Boron

Glycols and sugar alcohols

Unsaturated fatty acids and hydrocarbons

Palladium catalysts

Enzymes

Yeast

Ferrous-iron

Organometallic ligands

Photosensitive Dyes

Polydiene block copolymers

Polymer-bound oleﬁns

Aromatic nylon

Table 2. Commercially Available Oxygen Scavenging

Systems

Ageless

Mitsubisihi Gas and Chemical Co., Japan

ATCO

Emco Packaging Systems, UK; Standa

Industries, France

Freshilizers series Toppan Printing, Japan

Freshpax

Freshmax

Multisorb Technologies, Inc. USA

Bioka

Bioka, Finland

Smartcap ZapatA Industries, USA

Daraform, Cryovac

OS 1000

Cryovac, Division of Sealed Air, USA

Oxyguard Toyo Seikan Kaisha, Japan

Oxbart Carnaud Metal Box, UK

Zero

t CSIRO, Southcorp Packaging, Australia

Amsorb

Amoco Chemicals, USA

1004 POLYMERIC OXYGEN SCAVENGING SYSTEMS

REFERENCES

1. A. L. Brody, E. R. Strupinsky, and L. R. Kline. Active

Packaging for Food Applications, CRC Press, Boca Raton,

FL, 2001.

2. M. L. Rooney, in J. H. Han, ed. Innovations in Food Packaging.

Elsevier Academic Press, San Diego, CA., 2005, pp. 123–137.

3. N. de Kruijf, M. van Beest, R. Rijk, T. Spilainen-Malm, P.

Paserio Losada, and B. De Meulenaer, Food Add. and Contam,

19 Supplement, 144–162 (2002).

4. M. Ozdemir and J. D. Floros, Crit. Rev. Fd. Sci. and Nutri. 44,

185–193 (2004).

5. A. Brody, Active Packaging: Beyond Barriers. Packaging

Strategies, West Chester, PA and BRG Townsend, Mt. Olive,

NJ (2002).

6. F. Charles, J. Sanchez, N. Gontard, J. Fd. Eng, 72, 1–7 (2006).

7. J. P. Kerry, M. N. O’Grady,S. A. Hogan. Meat Sci, 74, 113–130

(2006).

8. U. S. Patent 5,211,875, D. V. Speer, W. P. Roberts, and C. R.

Morgan, 1993.

9. G. Twari, L. E. Jeremiah, D. S. Jayas, R. A. Holley, Internat. J.

Fd. Sci. & Tech. 37, 199–207 (2002).

10. J. Miltz, M. Perry, Packag. Technol. Sci. 18, 21–27 (2005).

11. F. Charles, J. Sanchez, N. Gontard, J. Fd. Sci. 70, E443–E449

(2005).

12. C. O. Gill and J. C. McGinnis, Meat Sci. 41, 19–27 (1995).

13. G. Twari, D. S. Jayas, E. Jeremiah, and R. A. Holley, J. Fd.

Sci. 66, 506–510 (2001).

14. G. Twari, Jayas, D. S., Jeremiah, L. E., and Holley, R. A.

Internatl. J. Fd. Sci. and Tech., 37, 209–217 (2002).

15. E. Isdell, P. Allen, A. Doherty, and F. Butler, Internat. J. Fd.

Sci. & Tech., 34, 71–80 (1999).

16. E. Isdell, P. Allen, A. Doherty, and F. Butler, Internat. J. Fd.

Sci. & Tech., 38, 623–632 (2003).

17. S. R. Payne, C. J. Durham, S. M. Scott, and C. E. Devine, Meat

Sci., 49, 277–287 (1998).

18. L. Martinez, D. Djenane , I. Cilla, J. A. Beltran, and P.

Roncales, Fd. Chem., 94,219–225 (2006).

19. C. O. Mohan, C. N. Ravishankar, T. K. Srinivasagopal, J. Sci

Fd. Agric., 88, 442–448 (2008).

20. B. Butler, Proceedings of Worldpak 2002 East Lansing, MI,

USA., (2002).

21. I. S. Kotsianis, V. Giannou, C. Tzia, Trends in Food Sci. and

Tech., 13, 319–324 (2002).

22. M. E. Guynot,V. Sanchis ,A. J. Ramos, and S. Marı

n, J

. Fd Sci.

68,

2547–2552 (2003).

23. S. Berenzon and I. S. Saguy, Lebens.-Wisse und Tech., 31, 1–5

(1998).

24. K. Zerdin, M. Rooney, and J. Vermue, Fd. Chem., 82, 387–395

(2003).

25. E. Oyugi and E. Mbuy., Internat. J. Dairy Tech. 60, 89–95

(2007).

26. M. Perkins, K. Zerdin, M. L. Rooney, B. R. D’Arcy, and H. C.

Deeth, Packg. Technol. Sci. 20, 137–146 (2007).

27. S. Pastorelli, S. Valzacchi, A. Rodriguez, and C. Simoneau, Fd.

Contam., 23, 1236–1241 (2006).

28. J. Lopez-Cervantes, D. I. Sanchez-Machado, S. Pastorelli, R.

Rijk, and P. Paserio-Losada, Fd. Add. Contam., 20, 291–299

(2003).

29. C. Altieri, M. Sinigaglia, M. R. Corbo, G. G. Buonocore, P.

Falcone, and M. A. Del Nobile, Lebensm.-Wiss. u.-Technol.,

37, 9–15 (2004).

30. V. K. Holm, G. Mortensen, M. Vishart, M. A. Petersen,

Internat. Dairy j., 16, 931–939 (2006).

31. A. Lopez-Rubio, J. M. Lagaron, T. Yamamoto, and R. Gavara.

J. Appl. Poly. Sci., 105, 2676–2682 (2007).

32. U. S. Patent 7,078,100 B2, C. L. Ebner, A. E. Matthews,

and T. O Millwood, for Cryovac Division of Sealed Air,

(2006).

33. U. S. Patent 7,238,300, J. A. Solis, R. Dayrit, S. W. Beckwith,

B. L. Butler, R. L. Cotterman, D. V. Speer and T. D. Kennedy,

(2007).

34. European Patent Application EP 1 676 790 A1, W. Yang, Y.

Yang, and L. Xiuzhi, (2006).

General References

M. L. Rooney, in M. L. Rooney (ed.) Active Food Packaging.

Blackie Academic Professional, London, UK, pp. 145–165

(1995).

F. N. Teumac, in M. L. Rooney (ed.) Active Food Packaging.pp.

193–202 (1995).

G. Robertson, in G. Robertson (ed.) Food Packaging, Principles

and Practices 2nd ed. CRC Press, Boca Raton, FL pp. 292–293

(2006).

V. Daniel, and F. L. Lambert. Available at http://palimpsest.

stanford.edu/waac/wn/wn15/wn15-2/wn15-206.html. Accessed

November 7, 2008.

POLYPROPYLENE

R.C. MILLER

Montell USA, Inc., Wilmington,

Delaware

Updated by Staff

INTRODUCTION

Polypropylene is an extremely versatile material in the

packaging industry. The reason for its adaptability is the

ease with which its polymer structure and additive

packages can be tailored to meet diverse requirements.

Many useful properties are inherent in polypropylene. It

has low density (high yield), excellent chemical resistance,

a relatively high melting point, and good strength, at

modest cost.

GENERAL CATEGORIES AND DEFINITIONS

Polypropylene is the result of linking a large number

(typically 1000 to over 30,000) of propylene molecules to

build long polymer chains (see Figure 1). Polymers made

up only of propylene are called homopolymers. If another

monomer is added (typically ethylene), the polymer is

POLYPROPYLENE 1005

called a copolymer. The order and regularity of the mono-

mer units in the polymer control the properties of the

product.

One end of a propylene molecule is different from the

other. The end with three hydrogens is called the head; a

head-to-tail linkage is called stereoregular. If the process

links the monomers head-to-head about as often as they

are linked head-to-tail, the resulting polymer has little

order and does not crystallize (1). At room temperature,

this material has a density of about 0.850 g/cm

.Itis

called atactic or amorphous polypropylene and is soft,

tacky, and soluble in many solvents. Such polymers are

useful in hot-melt adhesives (see Adhesives) and several

other applications.

If monomers are connected head-to-tail almost every

time, the polymer is said to be isotactic and crystallizes

(see Figure 2). Crystallinity is the reason for the solvent

resistance, stiffness, and heat resistance of the commer-

cial plastic material. At normal conditions, isotactic poly-

propylene is usually about half crystalline and has a

density of 0.90270.005 g/cm

. Normal polypropylene

melts at about 3291F (1651C) when heated slowly and

contains roughly 5% of atactic material as well as inter-

mediate structures. In this article, the term polypropylene

(PP) implies the plastic of commerce.

When discussing copolymers and alloys, an additional

level of complexity is added. Alloys, also called blends, are

mixtures of polymers. Copolymers are the result of poly-

merizing two or more monomers together. There are many

possible types (structures) of copolymer (2), not all of

which are useful.

Random copolymers result when a small amount

of comonomer, usually ethylene, is polymerized at random

intervals along the PP chain. Typical ethylene levels are

from 1 to 5 wt%, and the product has only one phase.

These copolymers are relatively clear and have lower

and broader melting points than PP homopolymers.

The lowering of the melting point is proportional to

the randomness of incorporation and the amount of como-

nomer incorporated. At ethylene levels well above 10%,

the product becomes less crystalline and is called

EPR, or ethylene–propylene rubber. One cannot make

an alloy (polymer blend) that resembles a random

copolymer.

Impact copolymers generally contain larger amounts

of ethylene monomer, typically 4 to W25%, and are

heterophasic. The ethylene may be polymerized in the

form of polyethylene and/or EPR. Usually, such products

are made by polymerizing a homopolymer and changing

the conditions to add ethylene to the polymer chain.

Reasonably comparable materials can be made by me-

chanically blending polypropylene with EPR and/or

polyethylene. If crystalline EPR or polyethylene is pre-

sent, it can be detected by a second melting point at

224–2711F (118–1331C). These products are characterized

by lower stiffness, much enhanced toughness at low

temperatures, and a relatively opaque appearance (see

Table 1).

The molecular weight (related to the average number of

monomer units in a chain) and the molecular-weight

distribution (MWD) are signiﬁcant polymer characteris-

tics. High-molecular-weight (HMW) polymers are highly

viscous when melted and are difﬁcult to injection-mold or

push through restrictive dies, but they have high tough-

ness and good ‘‘melt strength’’ (melt elasticity). Melts

of low-molecular-weight (LMW) polymers are more ﬂuid.

They have less toughness and lower melt strength. In a

narrow-MWD polymer, there is less variation in the length

of the chains than in a broad-MWD polymer. Narrow

MWD allows retention of the toughness of HMW grades

(3) in a more easily processed material. Narrow MWD

materials do not generally have high melt strength.

They offer advantages in ﬁber spinning and injection

molding.

Substantial modiﬁcation in properties can be achieved

by the use of additives (see Additives, plastics) and

ﬁllers. Virtually all commercial grades are stabilized to

increase resistance to oxidation on aging or at elevated

temperatures. Additives can confer resistance to sunlight,

reduce the tendency to retain static electric charges,

modify the coefﬁcient of friction, and prevent surface

tackiness.

The additives should be selected for the application. In

food packaging, the stabilization should be chosen to avoid

transfer of taste and odor to the package contents. Anti-

stats reduce static electricity, which attracts dust and

makes packages appear dirty. In sunlight, the damaging

wavelengths are in the UV range. UV resistance is im-

portant for items that may be stored outdoors. Coefﬁcient

of friction and antiblocking properties are important in

the winding and handling of ﬁlm (see Slitting/rewinding).

Frictional characteristics are also important in threaded

closures (see Closures).

Fillers can greatly increase stiffness, improve proces-

sing behavior, confer conductivity, and change the

Figure 1. Polypropylene.

Figure 2. Comparison of the structures of isotactic and atactic

polypropylenes: (a) isotactic PP–methyl groups in orderly align-

ment; (b) atactic PP–methyl groups in random alignment.

1006 POLYPROPYLENE

appearance of PP. Commonly used ﬁllers are talc, calcium

carbonate (usually powdered marble), glass ﬁber, mica,

carbon black, clays, cellulose ﬁbers, lubricants, and pig-

ments. Many exotic ﬁllers have been used for special

purposes. The use of ﬁllers in PP usually reduces tough-

ness and raises density and cost per volume.

PROCESSING

Melt-ﬂow rate (MFR) is one of the key variables in the

processing of PP. ASTM International (formerly The

American Society for Testing and Materials) (4) speciﬁes

that PP is to be tested at 4461F (2301 C) under a pressure

exerted by a nominal 4.4-1b (2-kg) mass in the apparatus

speciﬁed under ASTM Standard D-238. The result is the

weight of material extruded through the standard oriﬁce

in 10 min.This test is a crude measure of the melt viscosity

of the plastic under low shear rate. Melt viscosity corre-

lates to the weight-average molecular weight of the poly-

mer. Commercial PP grades of interest in packaging span

a MFR range of 0.3–40 g/10 min. The low ﬂow grades (up to

about 2.5 g/10 min) are used in sheet extrusion (see Ex-

trusion) and blow molding (see Blow molding). Film is

manufactured from intermediate-ﬂow grades (MFR 2–

15 g/10 min). Injection-molding processes (see Injection

molding) ordinarily use PP with MFR of 3–40 g/10 min

(see Table 2).

Thermoforming

Sheet extrusion for thermoforming (see Thermoforming) is

a small, rapidly growing segment of the PP market. Until

the late 1970s, few converters were willing to attempt

thermoforming of PP. Since that time, thermoforming

techniques and grades have been improved. Random co-

polymers and impact copolymers have a broader tempera-

ture ‘‘window’’ and are more easily formed than

homopolymers. Several grades are available that promise

excellent forming characteristics, even in homopolymers.

The several available high-melt strength PP grades ease

manufacture via improved material distribution and

higher forming rates. The factors that promote the use of

PP in thermoforming are low odor and taste transfer, good

moisture barrier, chemical resistance, and adequate clarity

in thin sections.

Blow Molding

In blow molding, most of the resin consumed is for consumer

products. High melt strength is required for extrusion blow

molding, which is used to produce relatively large contain-

ers up to 5.3 gal (20 L) in size. Injection blow molding

usually requires MFR of 1 –2.5 g/10 min. This process is

particularly useful for relatively small containers. The

ability to withstand temperatures or aggressive chemicals

that would stress-crack or attack other materials is usually

Table 2. Effect of Molecular Weight (Melt Flow) on Homopolymer Properties

Property Values

Melt-ﬂow condition L, g/10 min 0.4 2 12 35

Tensile strength (yield), psi (MPa) 4800 (33.1) 5000 (34.5) 5100 (35.2) 4600 (31.7)

Yield elongation, % 13 11 10 12

Flexural modulus (1% secant), psi (MPa) 190,000 (1310) 220,000 (1520) 220,000 (1520) 170,000 (1170)

Hardness Rockwell R (HRR) 92 91 90 88

Heat-deﬂection temperature (66 psi or

455 kPa), 1F(1C)

207 (97) 203 (95) 207 (97) 201 (94)

Notched Izod, 231C, ft lbf/in. (J/m) 1 (53) 0.8 (43) 0.7 (37) 0.6 (32)

Application Sheet extrusion,

thermoforming,

blow molding

Sheet extrusion,

thermoforming,

blow molding

Injection molding, ﬁlm Injection molding

Table 1. Typical Polypropylene Properties

Values

Property Homopolymer

Clariﬁed Random

Copolymer Impact Copolymer

High-Impact

Copolymer

Melt ﬂow condition L, g/10 min 4 10 4 4

Tensile strength (yield), psi (MPa) 4900 (33.8) 4300 (29.6) 3900 (26.9) 3000 (20.7)

Yield elongation (%) 11 9 9 8

Flexural modulus, (1% secant), psi

(MPa)

200,000 (1,380) 150,000 (1,030) 175,000 (1210) 130,000 (900)

Hardness Rockwell R (HRC) 86 77 73 70

Heat-deﬂection temperature (66 psi or

455 kPa), 1F(1C)

199 (93) 189 (87) 189 (87) 176 (80)

Notched Izod, 231C, ft lbf/in. (J/m) 0.7 (37) 1.4 (75) 1.8 (96) W10 W500

Application Injection molding Injection molding Injection molding Injection molding

POLYPROPYLENE 1007