Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology
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Q
QUALIFYING
Qualifying is the act of setting up and administering a
training program that ensures that the people who will be
interfacing with the packaging line are given a thorough
overview of the packaging line and a detailed program on
what they need to know to complete their tasks without
hesitation or guessing. All training must address the
following questions:
When should training be done?
What training should be done?
How should we do training?
Where should we do training?
How much is enough training?
Manuals and other self-help tools?
Performance reviews and continuing improvement?
Company standards and policy?
1049
R
RADIATION: EFFECT ON PACKAGING
MATERIALS
HYUN JIN PARK
Graduate School of
Biotechnology,
Korea University, Seoul,
Korea
DAE HOON JEON
Department of Food Packaging,
Korea Food and Drug
Administration, Seoul,
Korea
INTRODUCTION
Packaging makes food more convenient and improves
its shelf life by protecting it from micro-organisms, biolo-
gical or chemical changes, and physical damage. As a
result, packaging has become an indispensable element
in the food manufacturing process (1). Plastic mate-
rials are also used in medical devices or surgical prepara-
tions (2).
The treatment of prepackaged foods with ionizing
radiation such as g- or X-ray is gradually becoming more
popular as a food-preservation technique. The irradiation
of prepackaged foods helps prevent subsequent microbial
reinfection and insect increment (3). Generally, packaging
prevents water loss and mechanical damage of foods,
makes handling easier, and improves its marketability.
Good packaging materials must maintain functional qua-
lities such as impermeability, mechanical strength, seal
stability, color, and haze in the course of the radiation
process. Also, the packaging materials must not release
additives or radiation-induced reaction products into the
foods during irradiation, because these materials contam-
inate the prepackaged foods and affect the safety of
consumers. Most polymers listed in the U.S. Code of
Federal Regulation (CFR) 21 y179.45 were approved for
g-irradiation by the U.S. Food and Drug Administration
(FDA) in the 1960s through petitions by the Atomic
Energy Commission (p10 kGy) and the U.S. Army
(p60 kGy) (4–6). Polymers used to package food intended
for irradiation must currently receive separate U.S. FDA
approvals for electron-beam (e-beam), g-radiation, and X-
radiation. These three forms of irradiation in a vacuum
have virtually indistinguishable effects on polymers. How-
ever, in air, irradiation damage is favored by slow-dose
rates such as g-irradiation (7).
It is becoming more common to use ionizing radiation
instead of a high-pressure autoclave or ethylene oxide
treatment when sterilizing medical products (8). Specifi-
cally, radiation is popular because it is easier and more
economically efficient than using a high-pressure
autoclave or treating medical products with ethylene
oxide (9). When using ionization radiation for the sterili-
zation of medical devices, the International Atomic En-
ergy Agency (IAEA) recommends packaging polymers
such as polyethylene (PE), polyester, polypropylene (PP),
nylon, poly (vinyl chloride) (PVC), and so forth (8).
The effects of radiation on polymers may be classified
as scission, crosslinking, structural modifications, and
chemical reactions based on different values of the ab-
sorbed dose. Scission of the polymer chains results in a
decrease in molecular weight, whereas crosslinking re-
sults in an increase. Structural modifications are changes
in the number of unsaturated polymer chains and pre-
sence of charged units in polymer chains. Chemical reac-
tions lead to small volatile products and, eventually,
organic radicals, which are potential contaminants of
packaged foods (10, 11).
IRRADIATION OF PACKAGING MATERIALS
Status and Trends
Food irradiation is the treatment of food by a certain type
of energy. The process involves exposing the food, either
packaged or in bulk, to carefully regulated amounts of
ionizing radiation for a specific time to achieve certain
desirable objectives (12). The standard was adopted by the
Codex Alimentarius Commission, a joint body of the Food
and Agriculture Organization of the United Nations (FAO)
and the World Health Organization (WHO), which is
responsible for issuing food standards to protect consumer
health and facilitate fair practices in food trade; the WHO
represents more than 150 governments. The Codex Gen-
eral Standard for food irradiation was based on the
findings of a Joint Expert Committee on Food Irradiation
(JECFI) convened by the FAO, WHO and the Interna-
tional Atomic Energy Agency (IAEA) (13). The JECFI has
evaluated available data in 1964, 1969, 1976, and 1980. In
1980, it concluded that ‘‘the irradiation of any food com-
modity’’ up to an overall average dose of 10 kGy ‘‘presents
no toxicological hazard’’ and requires no more testing. It
stated that irradiation up to 10 kGy ‘‘introduces no special
nutritional or microbiological problems’’ in foods. In Sep-
tember 1997, a study group was jointly convened by the
WHO, FAO, and IAEA to evaluate the wholesomeness of
food irradiated with doses above 10 kGy. Food irradiation
technologies are considered safe as long as the sensory
qualities of food are maintained and harmful micro-organ-
isms are destroyed (14, 15). Polymers listed in the U.S.
CFR 21 y179.45 ‘‘Packaging Materials for Use during the
Irradiation of Pre-packaged Foods’’ are shown in Table 1
(16). These early submissions requested approval for g-
treatment only. Although electron beam treatment was
technically attainable, its use for routine polymer treat-
ment was not economically favorable (17). Commercializa-
tion
of X-ray treatment
was even less attractive than that
1051
of g-ray use. X-rays are produced at low yields through
electron beam bombardment of heavy metal targets. Over
the past 20 years, the unit cost of electron beam treat-
ment has declined steadily. The higher dose rates asso-
ciated with an electron beam and the ability to switch
radiation
ON and OFF have made the treatment attractive
to food processors. The economics of X-ray treatment still
do not favor their wide-scale use in food irradiation.
However, X-rays have the advantage of deep penetration,
and the major advantage of electron beams continues to be
that radiation can be switched
ON and OFF as needed. For
these reasons, the use of X-rays in the field of food
irradiation will be neglected (7).
The requirements for the certification and routine control
of the sterilization of medical devices by radiation are
mentioned in the European standard EN 552. EN 552
provides two possible approaches in setting up the steriliz-
ingdose.Oneistouseknowledgeofthenumberand
resistance to radiation (if known) of the inherent microbial
population present on or in the medical device. The other is
to use a minimum dose of 25 kGy. Because EN 552 was
published in 1994, there has been broad discussion and
debate about the degree to which this particular guidance
should be applied. As a result, a consensus has emerged that
evidence is required to support the effectiveness of 25 kGy
against both the numbers of contaminating micro-organ-
isms on the product and the resistance to radiation of these
organisms. Therefore, the Panel has developed a definition
of microbiological quality that encompasses both numbers of
micro-organisms and their resistance to radiation (18, 19).
Irradiation Mechanisms for Polymeric Packaging Materials
The types of radiation used in material treatments are
limited to radiations from high-energy g-rays, X-rays, and
accelerated electrons. X-rays with varying energies are
generated by machines. g-rays with specific energies come
from the spontaneous disintegration of radionuclides.
Naturally existing and man-made radionuclides, which
are also called radioactive isotopes or radioisotopes, emit
radiation as they spontaneously revert to a stable state.
There is a half-life specific for each radionuclide of a
distinct element. The becquerel (Bq) is the unit of radio-
activity and equals one disintegration per second (Table 2).
Energies from these radiation sources are too low to induce
radioactivity in any material, including food and medical
products. Cobalt-60 is a radionuclide used almost solely for
the irradiation of food and medical products by g-rays. It is
produced by neutron bombardment in a nuclear reactor of
the metal cobalt-59, and then it is doubly encapsulated in
stainless steel to prevent any leakage during its use in an
irradiator. The g-rays produced are highly penetrating and
can be used to treat full boxes of fresh or frozen food.
Cesium-137 is the only other g-emitting radionuclide ac-
ceptable for industrial processing of materials. It can be
obtained from used nuclear fuel elements (14). However,
there is no supply of commercial quantities of cesium-137.
Cobalt-60 has therefore become the chosen source for g-
radiation. Over 80% of the cobalt-60 available in the world
Table 1. Packaging materials for use during the irradiation of prepackaged foods listed in the U.S. CFR 21 y179.45. (16)
Packaging material
Approved
dose (kGy)
Nitrocellulose-coated cellophane 10
Vinylidene chloride copolymer-coated cellophane 10
Glassine paper 10
Wax-coated paperboard 10
Polyolefin film 10
Polyolefin film containing coatings made of a vinylidene chloride copolymer with one or more of the following
comonomers: acrylic acid, acrylonitrile, itaconic acid, methyl acrylate, and methyl methacrylate
10
Kraft paper (flour packaging only) 10
Polyethylene terephthalate film 10
Polyethylene terephthalate film containing coatings made of a vinylidene chloride copolymer with one or more of the
following comonomers: acrylic acid, acrylonitrile, itaconic acid, methyl acrylate, and methyl methacrylate
10
Polyethylene terephthalate film containing coatings made of polyethylene 10
Polystyrene film 10
Rubber hydrochloride film 10
Vinylidene chloride-vinyl chloride copolymer 10
Nylon-11 10
Ethylene-vinyl acetate copolymer film 30
Vegetable parchment 60
Polyethylene film 60
Polyethylene terephthalate film 60
Nylon-6 film 60
Vinyl chloride-vinyl acetate copolymer film 60
Table 2. Unit of radiation dose and radioactivity (14)
Absorbed dose Radioactivity
Unit gray (Gy) becquel (Bq)
Definition 1 Gy = 1 J/kg 1 Bq = 1 disintegration/s
Former unit rad curie (Ci)
Conversion 1 rad = 0.01 Gy 1 Ci = 3.7 10
10
Bq = 37 GBq
1 krad = 10 Gy 1 kCi = 37 TBq
1 mrad = 10 kGy 1 mCi = 37 PBq
1052 RADIATION: EFFECT ON PACKAGING MATERIALS
market is produced in Canada. Other source producers are
the Russian Federation, the People’s Republic of China,
India and South Africa (20). High-energy electron beams
can be produced from machines that can accelerate elec-
trons to near the speed of light using a linear accelerator.
Because electrons cannot penetrate very far into food and
medical products compared with g-radiation or X-rays, they
can only be used for processing food with thin packages. X-
rays of various energies are produced when a beam of
accelerated electrons bombards a metallic target. The
efficiency of conversion from electrons to X-rays is gener-
ally less than 10%. Radiation dose is the quantity of
radiation energy absorbed by the food or medical products
as it passes through the radiation field during processing.
It is measured using a unit called the gray (Gy). In terms of
energy relationships, 1 Gy equals 1 J of energy absorbed
per kilogram of food being irradiated. The maximum dose
of 10 kGy recommended by the Codex General Standard for
Irradiated Foods is equivalent to the heat energy required
to increase the temperature of water by 2.41C(Table2).
Irradiation is often referred to as a cold pasteurization
process because it can accomplish the same objective as the
thermal pasteurization of liquid foods, for example milk,
without any substantial increase in product temperature
(14). The use of X-rays is considered low-ionization-density
radiation. As a result, X-rays tend to reveal deep penetra-
tion of over 1.0 M in organic media and deposit their energy
in at most a few discrete steps. Incident electrons, in
contrast, are charged, have mass, and interact readily
with polymer electrons through coulombic repulsion. Their
energy tends to be dissipated in an almost linear fashion
through rapid interactions with countless polymer elec-
trons (7, 21). X-rays and g-rays are electromagnetic waves
with a much shorter wavelength than visible and ultravio-
let (UV) light. The energy levels of X-rays overlap with
g-rays. The X-ray is distinguished from g-ray by its origin.
g-rays originate from atomic nuclei through isotopic decay,
whereas X-rays are produced when high-energy electrons
decelerate on impact with the nucleus of another molecule
(22). When an X-ray or g-ray with greater energy than
ionization energy of the weakest electron collides with a
polymer, the weakest electron is thrown out from the
polymer and a positive ion remains.
AB ! AB
þ
þ e
Generally, the amount of energy needed to create this ion
pair is about 32.5 eV, and this ionization effect is com-
pleted within about 10
12
s.
Free radicals are formed from the production of ion
pairs and immediately results in molecular dissociation:
ABd ! A
þ
þ Bd þ e
If the energy transferred to an electron is less than the
ionization potential of the atom, then there may still be
enough energy to promote the electron from its ground
state to its excited state, which is referred to as excitation.
AB ! AB
Often, these excited states are identical with optical
excitation states, and the excited molecules produce radia-
tion-induced chemical reactions that are similar to those
that result from excited states produced by the absorption
of a quantum of light (21). As a result, the products of
radiolysis are at least qualitatively similar to the products
of photolysis in many systems.
Applications for Irradiation of Packaged Foods and Medical
Products
With the exception of applications such as: (a) sprout
inhibition in potatoes or onions, (b) insect disinfestation
in bulk grains, or (c) the delay of post-harvest ripening of
fruits, food irradiation processes are usually carried out on
packaged food. There may be different reasons for the use
of packaging: (1) prevention of microbial reinfection or
insect growth, (2) prevention of water loss, (3) exclusion of
oxygen, (4) prevention of mechanical damage during
transport, or (5) improvement of handling and marketing.
The packaging material used must not release radiation-
induced degradation or addition products or additives into
the food, and it should not lose functional qualities such as
mechanical strength, seal stability, or impermeability
after irradiation (23, 24).
Plastic films laminated with aluminum foil are routi-
nely sterilized by radiation as part of the manufacturing
process. They are used for sealed ‘‘bag-in-a-box’’ products,
such as tomato paste, fruit juices, and wines. Other
aseptic packaging materials, dairy product packaging,
and single-serving containers, for example, cream and
wine bottle corks, are also routinely sterilized by irradia-
tion prior to filling and sealing to prevent product con-
tamination. Other types of materials used to wrap food or
other products are also routinely processed by radiation in
many countries. The radiation process is used to crosslink
the polymer chains for greater strength and heat resis-
tance, for example, heat-shrink wrap (14).
The principles of International Standardization Orga-
nization (ISO) dose-setting Method 1 (ISO 11137) are
basically identical to those embodied in Association for
Advancement of Medical Instrumentation (AAMI) Method
B1, which are described originally in the American Na-
tional Standards Institute (ANSI)/AAMI ST 32-1991. The
method for substantiation of 25 kGy as a medical products
sterilization dose, given in ISO/TR 13409, is an adaptation
of the same AAMI dose-setting method (25, 26).
PHYSICOCHEMICAL CHANGES OF POLYMERIC
PACKAGING MATERIALS DURING IRRADIATION
Molecular Weight
The chemical behaviors of polystyrene (PS) and PVC at a
dose of a 100-kGy electron beam were studied by size
exclusion chromatography (SEC). After this treatment,
the value of the weight average molecular weights (Mw)
and z-average molecular weights (Mz) increased compared
with control polymers. Thus, it suggested that the process
of crosslinking had taken place in two polymers by in
electron beam radiation. In addition, there was a slight
RADIATION: EFFECT ON PACKAGING MATERIALS 1053
decrease in the number of average molecular weight (Mn)
after treatment. This change confirms that a splitting
process occurred because Mn is sensitive to a reduction
in small macromolecular species contained within the
polymers (2). Degradation was the major occurrence after
the initial step of g- and electron-beam radiation of PP,
which was not related to the atmosphere and/or antiox-
idant. However, double bond formation increased the
production of branching and crosslinking reactions. A PP
with a high melt strength at low dose was obtained, which
indicates that controlling the branching reaction was
useful for producing a polymer with special rheological
properties (27).
Electron paramagnetic resonance (EPR) spectroscopy
was used to characterize free radicals in g-ray-irradiated
biodegradable polymers. In general, polymers with high
melting points and crystallinity had the highest yields of
radicals at room temperature (28). Electron beam radia-
tion was performed at both room temperature (293 K) and
77 K (29). The effects of g-irradiation on the physicochem-
ical characteristics of biaxially stretched poly (ethylene
terephthalate) (PET) packaging film were investigated in
the range of 0–200 kGy. The diethylene glycol (DEG)
contents in PET chains were increased at low doses
(5 and 10 kGy), whereas these values decreased at doses
in the range of 30–200 kGy. Molecular weights, intrinsic
viscosity, and the levels of carboxy end groups decreased
slightly after treatment with a 60-kGy dose (30).
Polymer Structure
Polymer structure undergoes crosslinking at high doses of
g-radiation. Styrene-acrylonitrile copolymers and polybu-
tadiene (PB) are not as resistant to radiation compared
with PS but are still fairly stable. As in PS, the aromatic
ring structure absorbs a large part of the radiation energy.
Polybutadiene easily undergoes both crosslinking and
degradation (11).
Mechanical Properties
The results of evaluations of (a) resistance to g-radiation
(0–25 kGy), (b) tensile strength, and (c) elongation at
break for plastic films such as low-density polypropylene
(LDPE) and bidirection copolypropylene were reported.
When the radiation dose was increased to a range of 10–
25 kGy, the tensile strength rate and elongation at break
lowered slightly compared with the samples irradiated at
a 5-kGy dose, although these samples still had values
higher than those obtained from the unirradiated LDPE.
This reveals that the mechanical properties of LDPE
irradiated at these doses were improved. This correlates
to the relation between gel formation and radiation dose.
When samples of nylon/sarin/polyethylene or bidirection
copolypropylene were irradiated at a dose of 5 kGy, there
was a significant increase in tensile strength rate, and the
elongation at break lowered slightly compared with uni-
rradiated samples (8). In another study, the effects of g-
irradiation on ethylene vinyl alcohol copolymer (EVOH)
were investigated. Irradiation increased tensile strength
(TS) and elongation at break (%E) of EF-CR; whereas
the TS of EF-XL was not significantly changed and %E of
EF-XL decreased. Irradiation had no effect on TS and %E
of nylon/EVOH/PP (31).
Gas Permeability
PP film samples were prepared with isotactic PP granules,
which were hot pressed and cooled by three different
methods to obtain three different crystalline states with
various thicknesses and were g-irradiated with a dose of
25 kGy. The diffusion of oxygen has an inverse relation-
ship with crystallinity and film thickness (32). Irradiation
of nylon/poly (vinylidene chloride) (PVDC)/ethylene viny-
lacetate (EVA) barrier film caused changes in mass trans-
fers of the packaging material. g-radiation induced higher
amounts of mass transfer than beta radiation. Oxygen
permeability was affected by irradiation. These concerns
are particularly important in cases where barrier materi-
als are used for maintaining the quality of prepackaged
products, which are irradiated to obtain a longer shelf life
(33). Oxygen permeability decreased as g-irradiation dose
increased in nonoriented and biaxially oriented EVOH
and nylon/EVOH/PP (31).
Thermal Characteristics
The effect of g irradiation and electron-beam irradiation on
thermal characteristics of PP is examined with differential
scanning calorimetry (DSC) and thermogravimetric analy-
sis (TGA) coupled with Fourier transform infrared (FTIR).
In the case of the higher doses, the loss of crystallinity is
gr
eater
for g-ray-treated PP than for electron-beam-treated
PP. This suggests that both types of radiation cause a
decrease in the length of the macromolecular chains, cross-
linking, and other modifications in the crystal domains.
This degradation mechanism is emphasized by the pre-
sence of air, which leads simultaneously to oxidation (34).
The thermal properties of an LDPE/high-density polyethy-
lene (HDPE) (75/25) blend after exposure to g-radiation up
to 2000 kGy have been measured. The melting and crystal-
lization temperatures tended to decrease as the radiation
dose increased and show a tendency to stabilize at higher
values (35). The effects of g-radiation dose on the isother-
mal and nonisothermal crystallization of LLDPE, LDPE
and HDPE by DSC were studied (36). This includes a
qualitative comparison of nonisothermal data and quanti-
tative data for crystallization rate and nucleation mode.
The isothermal crystallization allowed for the observation
of changes in the crystallization rate related to a decrease
in the crystallization temperature caused by the cross-
linking of the polymer. In nonisothermal crystallization,
the development of crystallites depends on the crystal sizes
in the polymer.
Effects of Stabilizers in Polymer
The effect of g-irradiation on PS without additives is
negligible even when high doses are used. However, the
role of antioxidants and stabilizers are decisive in PB and
butadiene-containing copolymers (11). Dioctyl phthalate
(DOP) and epoxy soybean oil (ESO) were added to PVC
and irradiated up to 50 kGy. Mechanical properties, opti-
cal properties, and viscosity were measured and compared
1054 RADIATION: EFFECT ON PACKAGING MATERIALS
with nonirradiated PVC. In conclusion, DOP and ESO
were shown to be effective in stabilizing the radiolytic
abstraction of HCl from PVC. Both plasticizers gave good
color stability and overall properties to the products (37).
A breakage test on bending has shown that the PP
containing a plasticizer and antioxidant improved radia-
tion stability as compared with PP alone. Also the excel-
lent color stability has shown in formulated PP not PP
alone after irradiation treatments (38).
RELEASE OF ADDITIVES AND THEIR DEGRADATION
PRODUCTS DURING IRRADIATION
Additives in Polymeric Packaging Films
Packaging has become an essential element in the food
manufacturing process, and different types of additives,
such as antioxidants, stabilizers, lubricants, antistatic
agents, and anti-blocking agents have also been developed
to improve the performance either during manufacturing
or in the use of these polymeric packaging (1). In general,
Commission of the European Communities (CEC) Direc-
tives introduced limits on the overall migration from
plastics into food and food simulants. In addition, specific
migration limits for free monomers in the final article
have been set for some monomers. Currently, the limit for
overall migration was set at 10 mg/dm or 60 mg/kg of a
food simulant. It also includes the lists of permitted
monomers together with the restrictions that apply to
specific monomers (39). In the United States, the regula-
tions include both the basic polymer resins used in food
packaging and the adjuvants, which are added to a poly-
mer in the process of manufacturing the final food package
articles. Regulations frequently contain specifications for
the resin, such as residual monomer content. The time,
temperature, and solvent conditions for the short-term
extraction tests are also referred to in the regulations (40).
A large amount of research regarding the migration of
volatiles, additives, monomers, and oligomers from plastic
packaging materials into food were investigated.
Identification of Volatile Transformation Products After
Irradiation
The volatile g-radiolysis products of six medical polymers:
PS, methyl methacrylate-acrylonitrile-butadiene-styrene
(MABS), nylon, PVC, and PP, by thermal desorption (TDS)-
gas chromatography (GC)-mass spectrometry (MS) after
sterilizing doses of B25 kGy were identified (41, 42). The
main radiolysis products of PS are acetophenone, benzal-
dehyde, phenol, 1-phenylethanol, and phenylacetaldehyde.
The same volatiles are observed in MABS, which gives
some separate aliphatic compounds. The main products of
PVC and PP are fragments of additives, i.e., of stabilizers
and phenol-type antioxidants, respectively. The volatile
compounds produced in flexible food packaging materials,
LDPE, EVA, and PET/PE/EVOH/PE, during electron-beam
irradiation using the purge and trap technique and by
combined GC-MS. Both primary, i.e., methyl-derivates,
and so on, as well as secondary, i.e., oxidation products,
ketones, aldehydes, alcohols, carboxylic acid, and so on, are
produced during irradiation with doses of 5, 20, and 100 ky
were isolated and identified (3). The polymer materials, PE,
PP, PET, polyamide (PA), PS, and PVC were investigated
after treating with an g-radiation dose of 44 kGy. The
quantitative changes in compositions of radiolysis products
of each packaging material were measured. The polyolefine
materials such as PE and PP showed an increase of low
volatility compounds after irradiation due to an oxidative
decomposition of the polymer, oligomers and additives.
Other packaging materials such as PET, PA, and PS did
not show a meaningfully change their amount of solvent-
extractable compounds after irradiation with 44 kGy.
The PVC packaging material used in this study was not
resistant to irradiation treatment. Because of the release of
hydrochloric acid during irradiation, a large amount
of volatile substances could be extracted from the
PVC sheet. Most attention should be paid to low-volatility
radiolysis products, which are the most likely to migrate
into a foodstuff or a pharmaceutical product (43). Volatile
radiolysis products of LDPE and PP films were investi-
gated by TDS-GC-MS after absorbed doses of up to 25 kGy.
The radiation-induced compounds are mainly hydro-
carbons, aldehydes, ketones, and carboxylic acids with
concentrations one order of magnitude below that of
the residual hydrocarbons. The radiolysis products are
retained for considerable times in LDPE films, and they
remained in PP films much longer than in LDPE
films (42). Four volatile compounds: e-caprolactam, 2-pro-
pyldecanol, 2-butyloctanol, and 2,3-diethyl-2,3-dimethyl-
1,4-butanediol, were detected after g-irradiation of
EVOH. (31)
The Presence of Extractable Antioxidants After Irradiation
The effect of electron-beam irradiation on the migration
behavior of additives present in food packaging material
was studied with PP pouches that contained aqueous food
simulants. The loss of some products of antioxidant de-
gradation from the material can be correlated to the
presence of these same products in the food simulants.
This observation led us to assume that components of the
packaging material could migrate into the aqueous food
simulants (44). The chromatograms from reversed-phase
(RP)–high-performance liquid chromatography (HPLC)
for the extraction solutions corresponding to the PP con-
trol
and those treated
with g-ray and electron beam were
obtained. Two compounds were identified; the first is the
antioxidant tris-(2,4-di-tert-butylphenyl) phosphite (Irga-
fos 168) and the second corresponds to its degradation
product phosphate. For the lower dose of 25 kGy, irradia-
tion induces a large decrease of phosphate levels but has
little effect on the levels of phosphite. In the case of g-ray-
treated PP, the levels of phosphite antioxidant decrease as
the absorbed irradiation dose increases. There were no
noticeable trends in the electron-beam-treated PP. The
amount of the phosphate compound is considerably
lower after both radiation treatments (34). Tris-(2,4-
di-tert-butylphenyl) phosphite (Irganox 168) and its corre-
sponding phosphate in HDPE food trays as a function
of g-irradiation were identified and quantified. The com-
plete degradation of phosphate to phosphate occurs at low
RADIATION: EFFECT ON PACKAGING MATERIALS 1055
g-irradiation doses, i.e., 5 kGy. Because treatment with
such a low dose of g-irradiation leads to the conversion of
phosphite to mainly phosphate, the formation of phos-
phate during melt processing and radiation sterilization of
these HDPE trays must take into account products
from the irradiation of phosphate (45). Thermal deso-
rption indicated the formation and release of 1,3-di-
tert-butylbenzene (1,3-DTBB) during g-irradiation of the
HDPE (46). After g-radiation of PE, PP, and PS, the
contents of antioxidants significantly decreased. Irgafos
168 disappeared the fastest. 2,4-DTBP was detected not
only after irradiation but also before irradiation, whereas
1,3-DTBB and 2,6-di-tert-butyl-p-benzoquione (2,6-DTB
BQ) were detected only after irradiation (47, 48). Ninety-
six percent of the initial phenolic stabilizer was undetect-
able after electron-beam radiation. A phosphite stabilizer
and its reaction products accounted for 35% of the initial
amount. The sum of all potential migrants derived from
the additives accounted for less than 1% of global migra-
tion. This extensive migration was mainly caused by
oligomers (49). Polyolefin polymers may undergo degrada-
tion through oxidation by air and UV light. Antioxidants
are added to stabilize the polymer because they will be
preferentially degraded. Hindered phenol and triphenyl
phosphite as antioxidants are widely used in the polyolefin
industry. Unfortunately, these compounds and their de-
composed products can be released onto the foods during
irradiation. Tests are still underway to determine the
genetic effects, if any, of these compounds (1).
To evaluate the chemical or toxicological risk caused by
irradiation, it is necessary to identify and quantify the
compounds (50). The residues of antioxidants pentaery-
thrityl-tetra-kis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)pro-
pionate] (Irganox 1010) and Irganox 1076 in PVC, PP, and
PE were tested. Incremental increases in g-radiation
proportionally reduced the extractable levels of these
compounds. Individual reductions were dictated by poly-
mer and antioxidants type but were approximately 30% at
10 kGy (7). 2,4-DTBP and tris-(2,4-DTBP) phosphate come
from Irgafos 168, and 2,6-DTBBQ comes from the Irganox
1010, after the irradiating of PP with electron beams at
doses 2.5 and 10 kGy. Also, the above compounds were
found in aqueous food simulants. Because the absorbed
dose by food simulants could be lower than the dose
absorbed by PP and the migrated compounds from PP
were decomposed into unknown products, the quantities
of the migrated compounds in food simulants were lower
than those of compounds in PP (44, 50). A dose of B7 kGy
g-radiation in HDPE was required to drive the Irgafos 168
concentration to zero as determined by using infrared (IR)
spectroscopy (45). The 2,4-DTBP was detected in the tray
samples by thermal desorption, followed by GC-MS, and it
may come from the storage hydrolysis of Irgafos 168 in
HDPE (46). The kinetics of antioxidant migration from PP
into fatty food simulants was studied via the diffusion
coefficients (51).
The long-term influence of electron beam irradiation
(2.5 and 10 kGy) on food packaging materials and or-
iented polypropylene (OPP) was studied. It was shown
that a partial or complete disappearance of the antiox-
idants (Irganox 1010 and Irgafos 168) occurred over time
and that a new compound was released as a result of
antioxidant degradation (50). Effects of g-irradiation
on residual and migration levels of the antioxidants,
tris-(2,4-di-tert-butylphenyl) phosphite (Irgafos 168),
and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) pro-
pionate (Irganox 1076), as well as their radiolysis pro-
ducts, were investigated in the linear LDPE (LLDPE)
packaging samples treated with doses from 0 to 200 kGy.
Irgafos 168 was not detected in 5 kGy-treated samples,
and the levels of Irganox 1076 decreased by 34.9% from
the initial level in 10 kGy-treated samples. The radiolysis
products 2,4-DTBP, 1,3-DTBB, and toluene were identi-
fied, and their concentrations gradually increased as the
irradiation dose increased. Migration of Irgafos 168 from
the LLDPE pouch into food simulants, distilled water,
acetic acid (4 mL/100 mL distilled water), or ethanol
(20 mL/100 mL distilled water) was not detected at dose
levels up to 200 kGy, whereas that of the Irganox 1076
was detected in a decreasing manner with an increase in
dose (52). The food packaging polymers PS, polycarbo-
nate (PC), PA-6, and PVC, were irradiated with doses in
the range of 5–200 kGy. The quantities of corresponding
monomer residues (styrene monomer, bisphenol-A, e-ca-
prolactam,
and vinyl chloride)
released from target ma-
terials were analyzed using a SIM mode of GC/MSD.
Styrene monomers in PS showed a slight increase from
740 to 777 ppm at 5–30 kGy and then decreased as the
dose increased from 30 to 200 kGy. Bisphenol-A in PC
was dose independent at the low doses of 5, 10, and
30 kGy, but its level increased from 173 to 473 ppm at
30 kGy and thereafter remained unchanged through 200
kGy. e-Caprolactam in PA-6 was also dose independent in
the range of 5–200 kGy, but its level (122–164 ppm) was
found to be higher than those of nonirradiated samples
(71 ppm). As for PVC, the quantity of vinyl chloride
tended to increase from 8 to 18 ppm at 5–200 kGy (53).
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