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119
SECTION III
SORPTION BEHAVIOR OF SELECTED ALDEHDYE SCAVENGING AGENTS
IN POLY(ETHYLENE TEREPHTHALATE) BLENDS
E.C. SULOFF, J.E. MARCY, B.A. BLAKISTONE,
S.E. DUNCAN, T.E. LONG, AND S.F. O’KEEFE
Formatted in Accordance with the Journal of Food Science Style Guide.
120
Chapter 6: Sorption behavior of selected aldehyde scavenging agents in poly(ethylene terephthalate) blends.
ABSTRACT
Poly(m-xylylene adipamide) (nylon MXD6), D-sorbitol, and α-cyclodextrin aldehyde
scavenging agents were blended with poly(ethylene terephthalate) and thermally pressed into
films. Films were stored in an acidified aqueous model solution (pH 3.6) containing a 25 µM
mixture of acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, and caproaldehyde for
1, 3, 7, and 14 days. The total amount of aldehydes sorbed by films was 2 to 10 times higher for
films containing aldehyde scavenging agents then non-blended films. Aldehyde scavenging
films demonstrated selective scalping, preferring smaller molecular weight aldehydes to larger
aldehydes. Partition coefficients for smaller aldehydes were 3 to 6 times greater for aldehyde
scavenging films then control film.
INTRODUCTION
Research studies investigating the scalping behavior of food packaging materials have
mainly focused on how this phenomenon negatively impacts the quality of foods and beverages.
Few researchers have addressed how scalping, particularly selective scalping, can be used to
improve the flavor profile of food systems. Polymer blends included with an agent that has an
affinity for specific compounds can be used to proactively remove deleterious substances in a
packaging environment (Del Nobile and others 2002; Hotchkiss 1997; Rooney 2000). The use
of such a packaging system can be referred to as active packaging.
Food and packaging firms are jointly pursuing new developments in packaging materials,
in the form of coatings and blends, in order to extend the quality and shelf-life of foods and
beverages. Reynolds (2002) writes that the use of drop-in material, in the form of polymeric
additives, that will not require any significant changes in injection-molding of performs or
blowing of performs to bottles are likely to emerge in beverage packages in the next two to ten
years. The use of polymeric blends in food and beverage containers will likely replace
multilayer structures to improve barrier properties and may be tailored to protect product quality
121
and extend shelf-life by sensing environmental and product changes. Active packaging in the
United States is expected to show a 19% compound annual growth over the next five years
(Reynolds 2002).
The use of nylons, polyols, and cyclodextrins are described in patent literature to reduce
residual acetaldehyde in PET and other polymers (Bobo 1993; Eckert and others 2001; Long and
others 2000; Wood and Beaverson 2000). Nylons and other polyamides react with carbonyl
compounds by the nucleophillic addition of the free amino group to aldehydes in order to form
imines (also known as Schiff bases). D-sorbitol reacts with aldehydes in a reversible
nucleophillic addition reaction. An acid catalyst protonates the carbonyl oxygen and
subsequently eliminates water from a hemiacetal intermediate to produce an acetal. Alpha-
cyclodextrin, as well as other cyclodextrins, form inclusion complexes with aldehydes through
weak intermolecular forces. Hydrophobic interactions and van der Waals forces are proposed to
be the driving forces for the formation of cyclodextrin-aldehyde complexes. In addition, α-
cyclodextrin is believed to form a more stable complex then β- or γ-cyclodextrins for smaller and
straight chain guests due to its smaller cavity diameter (Rekharsky and Inoue 1998).
The heat treatment of beverages often causes the formation of aldehyde and ketone off-
flavors. This is particularly true for extended shelf-life (ESL) milk products that undergo ultra-
high temperature (UHT) processing. The formation of aldehyde and ketone off-flavors in UHT
processed milk products do not occur immediately, but rather after several weeks of storage
(Badings 1991; Shipe and others 1978). ESL milk products often exhibit a stale flavor,
attributed to the formation of alkanals and methyl ketones during storage (Moio and others
1994; Shibamoto 1980).
Lipid oxidation contributes largely to the loss in quality in food products containing
lipids and fats. Lipid oxidation in food products can be initiated by a metal catalyst
(autoxidation) or radiant energy (photo-induced oxidation). However, hydroperoxides are
formed by both autoxidation and photo-induced oxidation of fatty acids and are the principle
source of off-flavors developed by lipid oxidation. Hydroperoxides are unstable and readily
breakdown to form, among other volatiles, aldehydes.
The mass transfer of substances from packaging material to a food product is known as
migration. The migration of low molecular weight compounds formed during the
polymerization, processing, and forming of packaging materials is particularly problematic. For
122
example, acetaldehyde is formed in the polyester poly(ethylene terephthalate) (PET) by the
thermal decomposition of the ethylene glycol hydroxy terminal group and main chain of the
polymer (Ikgarashi and others 1989). The migration of acetaldehyde from PET is well
documented and continues to be a problem with this packaging material.
An aliphatic series of aldehydes were selected as molecular probes in order to examine
the effects of molecular weight, chain length, and solubility on sorption affinity for similar
species. In addition, these compounds are readily formed by thermal processing, lipid oxidation,
and package migration during the storage of many foods and beverages and have extremely low
odor and flavor thresholds.
MATERIALS AND METHODS
Materials
The bulk polymer, PET (Eastpak Polymer 9921W), was supplied by Eastman Chemical
Co. (Kingsport, TN). Nylon MXD6 (MXD6-6001) was supplied by Mitsubishi Gas Chemical
Co. (New York, NY). D-sorbitol was purchased from Aldrich Chemical Co. (Milwaukee, WI)
and α-cyclodextrin was supplied by Cerestar (Hammond, IN). Acetaldehyde, propionaldehyde,
butyraldehyde, valeraldehyde, and caproaldehyde were purchased from Aldrich Chemical Co.
(Milwaukee, WI).
Preparation of Polymer Films
PET and nylon MXD6 pelletized resin were reduced in size to allow for uniform
compounding. Resin pellets were freeze fractured into a fine powder by submerging the pellets
in liquid nitrogen for 5 min and grinding them in a Vortec Impact Mill Model M-1 (Vortec
Products Co., Long Beach, CA). The freeze fracture process was repeated two additional times
in order to obtain particles with a suitable size prior to compounding. D-sorbitol and α-
cyclodextrin were not further reduced in size prior to compounding. Bulk polymer (95) and
aldehyde scavenging agents (5) were combined as a dry mixture in 250 g batches. Mixtures
were shaken on IKA Model VXR S1 platform shaker (IKA Works, Inc., Wilmington, NC)
123
operating at motor setting 1000 for 48 hrs in order to achieve a homogeneous mixture. Mixtures
were then dried at 60°C overnight in a vacuum oven at reduced pressure.
Neat PET and polymer mixtures were then pressed into films using a thermal press. Neat
PET and mixtures (5.0 ± 0.1 g) were evenly dispersed on a stainless steel metal frame measuring
10 cm x 10 cm with a thickness of 356 µm. Both sides of the stainless steel frame were lined
with Kapton film (DuPont, Wilmington, DE) in order to improve the removal of cast film from
the metal frame after cooling. The stainless steel frame was then placed between two larger
aluminum plates and placed in a PHI Precision Press Model GS 21-J-C-7 (Pasadena Hydraulics,
Inc., City of Industry, CA) operating at 270°C and 881 KPa. Films were pressed for 90 sec and
then immediately submerged in an ice bath. Films were removed from steel frame, dried with a
towel, and then cut into strips measuring 2 cm x 7.5 cm. Finally, film strips were placed in a
vacuum oven at 30°C overnight at reduced pressure. Characteristics of thermally pressed PET
films are listed in Table 2.
Density Analysis
The densities of powdered aldehyde scalping agents and cast films were determined by
gas pyconometry (Palacio and others 1999; Sartore and others 2002). Density analysis was
performed using Micromeritics AccuPyc 1330 pycnometer (Micromeritics Instrument Company,
Norcross, GA) operating at an ambient temperature and using helium as the displacement
medium.
Thermal Analysis
Differential scanning calorimetry (DSC) was used to determine the percent crystallinity
of cast films. Percent crystallinity for cast films was determined using a Perkin Elmer Pyris 1
DSC (Perkin Elmer, Inc., Wellesley, MA) equipped with Pyris Software Version 3.81 data
acquisition platform. Cast films were analyzed under an ambient atmosphere and a temperature
program of 25-200°C at 10°C/min. Percent crystallinity was calculated based on the area of the
crystallization peak on the first heating profile.
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The thermal stability of the aldehyde scavenging agents and cast films was determined by
thermal gravimetric analysis (TGA). TGA measurements were made using a TA Instruments Hi-
Res TGA 2950 Thermogravimetric Analyzer (TA Instruments, New Castle, DE) operating under
nitrogen and a temperature program of 25-600°C at 20°C/min. Degradation temperature (Td)
was calculated using TA Instruments Thermal Advantage Release 1.0 software.
Preparation of Aqueous Model Solutions
Stock solutions of molecular probes (0.01 M) were prepared in a cold room, 7 ± 4°C,
using 0.0001 N HCl (pH = 3.6 ± 0.2) as a solvent. Stock solutions were mechanically stirred for
20 min in tightly stoppered flasks to prevent loss of volatiles. Stock solutions were then diluted
1:40, using 0.0001 N HCl solvent, in a common volumetric flask in order to achieve a mixture
containing a concentration of 250 µM for each molecular probe. Solution was mechanically
stirred for 20 min in a tightly stoppered flask.
Preparation of Exposure Vials
The weight of each 15 cm2 film strip was recorded and then placed in a 40 mL exposure
vial fitted with a Teflon-fluorocarbon-resin lined cap. Precisely 9 mL of 0.001 N HCl solvent
and 1 mL of solution containing 250 µM concentrations of acetaldehyde, propionaldehyde,
butyraldehyde, valeraldehyde, and caproaldehyde were added to each exposure vial. Exposure
vials were prepared in triplicate in a cold room maintained at 7 ± 4°C. Aqueous model solution
(pH 3.6) used in exposure vials included 25 µM concentrations of aldehydes.
Exposure Conditions
Exposure vials were placed horizontally in test tube racks allowing test strips to be
completely submerged in model solution. Test tube racks were fitted in a Lab-Line Orbit
Environ-Shaker Model 3527 (Lab-Line Instruments, Inc., Melrose Park, IL) operating at 250
r.p.m. Exposure vials were gently shaken for 1, 3, 7, and 14 days at an ambient temperature.
125
2,4-Dinitrophenylhydrazine Derivatization Procedure for Molecular Probes
The 2,4-dinitrophenylhydrazine (DNPH) reagent was prepared daily in multiple 50 mL
glass centrifuge tubes. Forty-three mg of 2,4-dinitrophenylhydrazine (30% water w/w) (Aldrich
Chemical Co., Milwaukee, WI) was dissolved in 30 mL mixture of hydrochloric acid, water, and
acetonitrile (5:11:4). Carbonyl contamination contained within the DNPH reagent was removed
by extraction with carbon tetrachloride. Carbon tetrachloride (4 mL) was added to DNPH
reagent (30 mL) and was vigorously shaken for 5 min. The mixture was then centrifuged using a
Sorvall Refrigerated Superspeed Centrifuge Model RC-5B (DuPont Instruments, Wilmington,
De) at 949 G for 20 min in order to separate the phases. Extracted DNPH reagent was used for
derivatization reaction.
Exposure vials were removed from orbital shaker and chilled to 7 ± 4°C after 1, 3, 7, and
14 days. Film strips were quickly removed from molecular probe solution and were rinsed with
precisely 1 mL of water. Exposure vials were then immediately capped to avoid loss of volatile
aldehyde species. DNPH reagent (5 mL) was then added to exposure vials. Reaction vials were
then shaken using a Lab-Line Orbit Environ-Shaker Model 3527 operating at 250 r.p.m. for 5 hrs
at ambient temperature. Derivatization reaction conditions within reaction vial were 1.0 M HCl
and 2.5 mM DNPH (20 equiv. of total aldehyde concentration). These conditions were found to
be optimum for the formation of aldehyde-hydrazine complexes. Vials were then removed from
orbital shaker and diluted with 9 mL of acetonitrile to dissolve any aldehyde-hydrazine
precipitate formed during the derivatization reaction. Table 3 lists percent yields for conversion
of aldehydes to aldehyde-hydrazine complexes by this procedure.
High Performance Liquid Chromatography Analysis
Diluted samples were analyzed using Varian 9010 Solvent Delivery System (Varian, Inc.,
Palo Alto, CA) equipped with a Varian Model 9050 Variable Wavelength UV-VIS Detector and
Dynamax Autosampler Model AI-200 (Rainin Instrument Co., Woburn, MA). Data acquisition
and integration was performed using Varian LC Star System Workstation. Separation of
aldehydes was accomplished using Waters Nova-Pak C-18 guard column (3.9 mm x 20 mm) and
analytical column (3.9 mm x 300 mm) (Waters Corp., Milford, MA).
126
The eluent was pumped at a flow rate of 1 mL/min and the UV detector was operated at
360 nm. The injection volume was 50 µL. A gradient elution was followed from 50% (v/v)
acetonitrile in water to 100% acetonitrile over a period of 20 min. Quantification of aldehyde
species was accomplished using an external standard curve based on peak area. Retention times
and detector response factors for molecular probes are listed in Table 2.
Experimental Design and Statistical Analysis
A split-split-plot design was employed. The experiment included three sub-samples for
each set of conditions and was repeated three times in a completely randomized block design.
LSD analysis adjusted by Tukey-Kramer procedure was used for separation of treatment means.
A significance level of p < 0.05 was established to detect statistical differences. Statistical
analysis was performed using SAS release 8.2 software, (SAS Institute, Inc., Cary, NC) (SAS
Institute 1999).
RESULTS AND DISCUSSION
Density and Thermal Analysis of Aldehyde Scavenging Agents and Test Films
Density and thermal analysis results for aldehyde scavenging agents and test films are
listed in Tables 1 and 2. Nylon MXD6, D-sorbitol and ∝-cyclodextrin aldehyde scavenging
agents were determined to have densities of 1.19, 1.48, and 0.55 g/cm3. Although the densities
of neat aldehyde scavenging agents varied greatly, the densities of PET films containing these
same agents were similar. PET : nylon MXD6, PET : D-sorbitol, and PET : ∝-cyclodextrin were
determined to have densities of 1.338, 1.351, and 1.357 g/cm3. Aldehyde scavenging PET films
were slightly denser then neat PET films with a density of 1.272 g/cm3. In addition, aldehyde
scavenging PET films were more crystalline then neat PET films. The percent crystallinities of
PET : nylon MXD6, PET : D-sorbitol, and PET : ∝-cyclodextrin were 19, 19, and 20%. Neat
PET films were only 13% crystalline. Increased crystallinity of PET blends containing
immiscible adjuncts have been reported else where (Da Silva and others 2002; Guenther and
Baird 1996).
127
Nylon MXD6, D-sorbitol, and α-cyclodextrin are reported to have melting temperatures
of 237, 98, and 255°C. These same additives showed degradation temperatures of 396, 294, and
304°C. Thermal properties of neat aldehyde scavenging agents indicated that they were suitable
for use in PET blends requiring a processing temperature of 270°C. However, the thermal
properties of the aldehyde scavenging agents changed in the presence of PET.
Degradation temperatures for D-sorbitol and α-cyclodextrin in PET thermally pressed
films were 207 and 284°C, respectively. The Td of D-sorbitol decreased by more then 87°C in
the presence of PET. Similar results were found for α-cyclodextrin, where the Td decreased by
nearly 20°C. The Td of nylon MXD6 in thermally pressed film was not able to be determined
since its Td temperature is nearly equivalent to the Td of neat PET. The dramatic decrease in
thermal stability of D-sorbitol and α-cyclodextrin in PET films is difficult to explain. In fact,
one would expect neat aldehyde scavenging agents in powdered form to degrade at lower
temperatures then when present in PET films. The presence of terephthalic acid or ethylene
glycol might contribute to the degradation of D-sorbitol or α-cyclodextrin, however, the Td of
PET in films blended with those agents did not occur until 415 or 417°C. The presence of
terephthalic acid and ethylene glycol at temperatures below their Td is unlikely.
It is important to note that TGA thermograms for D-sorbitol and α-cyclodextrin indicate their
presence in thermally pressed PET films. The pressing conditions, 270°C at 881 KPa for 90 sec,
did not completely degrade these additives. Differences between the time temperature treatment
for additives by the thermal press and TGA analysis may explain their presence in the film.
Thermally pressed films underwent an instantaneous heat treatment of 270°C for 90 sec, whereas
the TGA temperature program included a shallow heating rate of 20°C/min.
2,4-Dinitrophenylhydrazine Derivatization and HPLC Analysis of Molecular Probes
The derivatization of aldehydes by 2,4-dinitrophenylhydrazine followed by their
separation by HPLC allowed for precise quantitative measurement of molecular probes at sub-
micromolar levels in the model solution. HPLC analysis of aldehyde-hydrazines offered more
precise results and a lower level of detection then was achieved by solvent extraction of test
films or solid phase microextraction gas chromatography of model solutions. Table 3 lists the
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percent yield of derivatization with molecular probes, retention times, and detector response
factors for molecular probes.
Total Aldehyde Concentration in Aqueous Model Solutions
The total aldehyde concentration in the aqueous model solution was calculated by taking
the sum of all molecular probe concentrations on a particular day. The total aldehyde
concentration for the aqueous model solution (control) and model solutions exposed with neat
PET, PET : nylon MXD6, PET : D-sorbitol, and PET : α-cyclodextrin film strips were 122, 117,
89, 70, and 58 µM after one day. These results indicate 4, 27, 43, and 52% reductions in total
aldehyde content in model solutions exposed with neat PET, PET : nylon MXD6, PET : D-
sorbitol, and PET : α-cyclodextrin film when compared to the control solution. Statistical
analysis after one day exposure showed differences between control and blended films, but did
not show any differences between control and neat PET. Differences were also found between
films containing aldehyde scavenging agents.
The control model solution and model solutions exposed with neat PET, PET : nylon
MXD6, PET : D-sorbitol, and PET : α-cyclodextrin films after three days of storage showed total
aldehyde concentrations of 117, 99, 77, 60, and 48 µM, respectively. These results account for
15, 34, 49, and 59% reductions in total aldehyde content in model solutions exposed to test
polymers when compared to control solution. Statistical analysis after three days of exposure
showed differences between control and all blended films, as well as neat PET. In addition, each
model solution exposed to test films were found to be different from the other three.
Total aldehyde concentrations in aqueous model solution control and solutions exposed
to test films were nearly identical for seven and fourteen days of storage. Total aldehyde
concentration in the aqueous model solution after fourteen days is shown on Figure 1. After
seven days of storage, the total aldehyde concentration in control solution and solutions
containing neat PET, PET : nylon MXD6, PET : D-sorbitol, and PET : α-cyclodextrin were 114,
91, 70, 56, and 45 µM. Reductions in total aldehyde content in model solutions after seven days
of exposure to test films were calculated to be 20, 39, 51, and 61%. Statistical analysis for seven
and fourteen day exposures showed identical results for differences among control and film
treatments. Model solutions exposed with neat PET and blended films were statistical different
129
from control solution. Differences between films were found in every instance, except when
comparing the PET : D-sorbitol treatment and PET : α-cyclodextrin treatment. No difference
was found between these two treatments.
The concentration of the aqueous model solution control showed minimal degradation
during the fourteen day experiment. The initial total aldehyde concentration after day one was
122 µM compared to 112 µM determined after fourteen days of storage. Similar degradation
results have been reported for aldehydes in acidified model solutions (Ayhan and others
2001; Konczal and others 1992; Pieper and others 1992).
Sorption Amounts and Rates for Molecular Probes into Test Films
The amount and rate of sorption for molecular probes into test films are shown in Figures
2-6. The percentages of acetaldehyde sorbed by neat PET, PET : nylon MXD6, PET : D-
sorbitol, and PET : α-cyclodextrin test films after fourteen days were 14, 51, 82, and 90%. The
rate of sorption of acetaldehyde in blended films was much greater then neat PET. Nearly 95%
of acetaldehyde sorption occurred in blended films after one day. The rate of acetaldehyde
sorption for neat PET was more gradual. Only 36% of neat PET acetaldehyde sorption occurred
after one day.
Neat PET, PET : nylon MXD6, PET : D-sorbitol, and PET : α-cyclodextrin test films
sorbed 10, 39, 56, and 76% of propionaldehyde after fourteen days of exposure. The rate of
sorption for propionaldehyde was greater in blended test films then neat PET films. In addition,
maximum sorption for propionaldehyde occurred after seven days exposure. Less
propionaldehyde was removed from the aqueous model solution after fourteen days then seven
days. These results are confusing and only occurred for this molecular probe.
Butyraldehyde and valeraldehyde sorption by test films showed similar results to the
other molecular probes. Neat PET, PET : nylon MXD6, PET : D-sorbitol, and PET : α-
cyclodextrin test films sorbed 19, 40, 48, and 58% of butyraldehyde after fourteen days of
exposure. The percentages of valeraldehyde sorption after fourteen days for these same test
films were 27, 36, 40, and 48%. Neat PET, PET : nylon MXD6, PET : D-sorbitol, and PET : α-
cyclodextrin test films sorbed 23, 21, 26, and 23% of caproaldehyde after fourteen days of
exposure. However, a decrease in the amount of caproaldehyde sorbed by PET : α-cyclodextrin
130
occurred between seven and fourteen days. Again, the rate of sorption for the molecular probes
was greater in blended test films then neat PET film.
A relationship between the total amount and rate of molecular probes sorbed by blended
test films was established. For instance, blended films sorbed molecular probes with lower
molecular weights to greater extent then those with higher molecular weights. PET : nylon
MXD6 test films removed nearly 51% of acetaldehyde from the model solution compared to
only 21% of caproaldehyde. The differences between sorption of acetaldehyde and
caproaldehyde were even more pronounced for PET : D-sorbitol and PET : α-cyclodextrin films.
The percentages of acetaldehyde sorbed by PET : D-sorbitol and PET : α-cyclodextrin were 82
and 90%, compared to 26 and 23% of caproaldehyde sorbed for the same blended films.
Molecular probes with lower molecular weights were also found to be removed at a
greater rate then higher molecular weight probes in blended films. During the fourteen day
exposure period for the blended films, 92, 94, and 93% of acetaldehyde sorption occurred for
PET : nylon MXD6, PET : D-sorbitol, and PET : α-cyclodextrin after one day exposure.
Caproaldehyde sorption occurred at a more gradual rate. Only 19, 58, and 74% of total
caproaldehyde sorption occurred after one day exposure for the same films.
Trends associated with sorption amount and rate found for blended films were not similar
to trends found for neat PET films. In fact, the affect of molecular size on sorption amount for
neat PET films were exactly opposite of what was established for blended films. Neat PET films
sorbed a greater percentage of higher molecular weight aldehydes then lower molecular weight
aldehydes from the model solution. For example, only 14% of acetaldehyde was sorbed after
fourteen days of exposure with neat PET film compared to more then 23% sorption of
caproaldehyde for the same period. The rate of sorption for molecular probes in neat PET films
was much slower then what was seen in blended films. Most molecular probes did not reach
equilibrium conditions for sorption until seven days of exposure for neat PET films. Blended
films showed near equilibrium conditions after one or three days of exposure.
Sorption Affinities of Aldehydes into Test Films
Summarized in Figure 7 is the amount (mg) of acetaldehyde, propionaldehyde,
butyraldehyde, valeraldehyde, and caproaldehyde sorbed per unit volume (dm3) by neat PET,
131
PET : nylon MXD6, PET : D-sorbitol, and PET ∝-cyclodextrin after fourteen days of storage.
Values obtained from molecular probe sorption, per unit volume of polymeric materials, after
fourteen days were used to calculate equilibrium partition coefficients (K) (Table 4). Steady
state conditions were established for all molecular probes and test films after fourteen days of
exposure. The equilibrium partition coefficient was calculated using equation 1
( )sol
filmt
CVQQ
K/0 −
= (1)
where Q0 is the quantity (mg) of the molecular probe in the initial model solution (t=0), Qt is the
quantity (mg) of the molecular probe in the model solution after contact (t), Vfilm is the volume of
the test film (dm3), and Csol is the concentration (mg/L) in the solution at equilibrium (Lebossé
and others 1997). Partition coefficients with greater values indicate stronger affinities between
aldehydes and test films then partition coefficients with lower values.
Equilibrium partition coefficients for aldehydes and blended films were greater then
partition coefficients for neat PET films. PET : α-cyclodextrin test films showed the highest
partition coefficients for aldehdyes, followed by PET : D-sorbitol films and PET : nylon MXD6
films. The only exception to these trends occurred for caproaldehyde. The partition coefficient
between caproaldehyde and neat PET films was greater then PET : nylon MXD6 films. In
general, partition coefficients between lower molecular weight aldehydes and blended films were
greater then partition coefficients for higher molecular weight aldehydes. The opposite was true
for neat PET films. PET films showed greater affinities for higher molecular weight probes then
lower molecular probes. In another study, (Shimoda and others 1988), the partition coefficient
(plastic/solution) increased with molecular weight for a homologous series of saturated
aldehydes (hexanal through dodecanal).
The number of theoretical scavenging sites found in test films was not a good predictor of
sorption capacity for test films. For instance, the theoretical number of free amine groups for
nylon MXD6 in each test film is approximately 1.37 x 1018. This approximation was achieved
by multiplying the average molecular number, 16,500 g/mol, for nylon MXD6 by the amount
present in the test film (3.75 x 10-2 g) and then multiplying that value by 6.022 x 1023 active
132
sites/mol. This approximation assumes that only one amine site is available for scavenging per
mole of nylon MXD6.
The number of molecules for each molecular probe present in each vial is 1.51 x 1017.
This approximation was achieved by multiplying the molecular probe concentration (2.50 x 10-5
mol/L) by the volume of model solution in the test vial (0.01 L) and then multiplying this value
by 6.022 x 1023 molecules/mol. This attributes to a total of 7.55 x 1017 (1.51 x 1017 x 5
molecular probes) molecules of aldehyde compounds present in each vial. The ratio of
theoretical active sites to total aldehyde molecules present in the test vial is 1.81 for the PET :
nylon MXD6 film treatment. The number of theoretical scavenging sites for D-sorbitol and α-
cyclodextrin was calculated according to the same procedure discussed for nylon MXD6.
However, the stochiometry of D-sorbitol for acetal production by aldehydes is 2:1 and is
hypothesized to be approximately 1:1 for α-cyclodextrin complexation. The number of
theoretical scavenging sites for D-sorbitol and α-cyclodextrin films was calculated to be 6.20 x
1019 and 2.32 x 1019. The ratios of theoretical sites to total aldehyde molecules present in test
vials for PET : D-sorbitol, and PET : α-cyclodextrin treatments are 82.1 and 30.7. PET : D-
sorbitol and PET : α-cyclodextrin treatments were the most effective in removing aldehydes from
the model solution, but nylon MXD6 was the most efficient agent in removing aldehydes from
solution.
Factors Affecting Sorption Affinity, Capacity, and Rate for Molecular Probes and Test
Films
The principal variables affecting the sorption process of low molecular weight
compounds into polymeric packaging materials include the chemical composition of the
packaging material and sorbate molecule, polymer morphology, temperature, initial
concentration of the sorbate, sorption capacity of the polymer, and sorbate diffusivity. The
dynamics of the sorption process and therefore the time in which to reach equilibrium is
controlled by sorbate diffusivity, while the remaining variables determine the specific change in
sorbate concentration at equilibrium (Konczal and others 1992).
The polarity of a packaging material (sorbent) and molecular probe (sorbate) can
dramatically affect their affinities toward one another. In general, sorbents and sorbates with
133
similar polarities have higher affinities for one another due the universal rule, “like dissolves
like”. PET is a relatively polar polymer, therefore, it was not surprising that blended PET films
sorbed higher molecular weight saturated aldehydes to a lesser extent then lower molecular
weight aldehydes. With increasing carbon length, the polarity of saturated aldehydes decreases
and consequently, their sorption decreases.
The solubility of molecular probes in an aqueous solution is related to their polarity.
More soluble compounds are sorbed to a lesser degree by polymers in solution then less soluble
compounds (Kwapong and Hotchkiss 1987). Therefore, one would expect that the sorption of a
molecular probe with low water solubility, such as caproaldehyde, would be much greater then a
probe with very high water solubility, such as acetaldehyde. These results were consistent with
findings for neat PET, however, were not found to be true for PET blends, which showed the
opposite relationship. The differences found between neat PET and PET blends are likely to be
attributed to polymer crystallinity and morphology.
Absorption and diffusion of low molecular weight compounds take place in the
amorphous area of a polymer (Crank 1968). The crystalline region consists of tightly packed
lamellae, which impede the diffusion of molecules. According to this theory, more crystalline
polymers show less sorption of small molecular weight compounds then less crystalline
polymers. This trend was established for citrus flavor volatiles and aldehydes in polyolefins
(Charara and others 1992; Sadler and Braddock 1991; Shimoda and others 1988).
The sorption of water molecules in the amorphous region of a polymer has a plasticizing
affect on polymers. Differences in the sorption behavior of aldehydes in the blended films were
probably due to differences in their polarity and hydrogen bonding with sorbed water in the
polymer. Aldehydes, in which hydrogen bonding occurs more readily, are drawn into the
amorphous region of the polymer by water vapor. This process brings aldehydes in close
proximity to the aldehyde scavenging sites present in the PET blends. Interactions between
aldehydes and scavenging agents are stronger than their hydrogen bonding with water molecules.
Thus, aldehydes become irreversibly or reversibly attached to a functional group within the
polymer matrix. This phenomenon was not shown for neat PET, since no aldehyde scavenging
agents impeded the return of aldehyde compounds into solution once equilibrium conditions are
established for water sorption in the polymer.
134
Finally, polymer morphology may have influenced the sorption behavior of molecular
probes. Charara and others (1992) report absorption of orange oils in LDPE causes large fissures
and ridges on the polymer surface. He confirmed these findings by the use of scanning electron
microscopy (SEM). The creation of uneven surfaces on the polymer surface may promote more
extensive adsorption. Kwapong and Hotchkiss (1987) report adsorption to be the dominant
sorption mechanism for polymers below their glass transition temperature (Tg). PET materials
investigated in this study were well below their Tg.
CONCLUSIONS
Low molecular weight aldehyde compounds compromise the quality of many food and
beverage products. Many of these compounds are degradation products produced from thermal
processing, lipid oxidation, and package migration. The addition of nylon MXD6, D-sorbitol,
and α-cyclodextrin to PET thermally pressed films were shown to effectively remove aldehydes
from an aqueous model solution. The sorption amount and rate for aldehydes in aldehyde
scavenging films are related to their water solubility and the crystalline structure of the polymer.
135
TABLES AND FIGURES INCLUDED FOR PUBLICATION
Table 1 - Characteristics of aldehyde scavenging agents used in PET blends
Additive Mwa
(g / mol) Densitya
(g / cm3) Tm
a (°C)
Tdb
(°C) Nylon MXD6 ≈16,500 1.19 237 396 D-Sorbitol 182 1.48 98 294 α-Cyclodextrin 972 0.55 255-260 304 a Specifications from manufacturers. b Degradation temperature determined by TGA.
136
Table 2 - Characteristics of thermally pressed PET films
Exposure Material Densitya (g / cm3)
% Crystallinityb
Thicknessc
(mm) Td
d (°C) Bulke Additivef
PET (100) 1.272 13 0.34 413 - PET (95): Nylon MXD6 (5) 1.338 19 0.34 406 NDg
PET (95) : D-Sorbitol (5) 1.351 19 0.35 415 207 PET (95) : α-Cyclodextrin (5) 1.357 20 0.33 417 284 a Density measurement by gas pyconometry. b Percent crystallinity measurement by DSC and based on peak area and first heating profile. c Thickness measured by micrometer. d Degradation temperature determined by TGA. e Degradation temperature of bulk PET polymer. f Degradation temperature of aldehyde scalping additive added to bulk polymer. g Td not able to be detected from TGA thermogram.
137
Table 3 - Derivatization and HPLC characteristics of molecular probes used in aqueous
model solution
Molecular Probe Concentrationa
(uM) (mg / L) tR
b (min)
% DNPH Conversionc
Response Factor
Acetaldehyde 25 1.40 6.89 98 292 Propionaldehyde 25 1.80 8.86 97 259 Butyraldehyde 25 2.25 10.67 93 287 Valeraldehyde 25 2.66 12.52 93 267 Caproaldehyde 25 3.07 14.25 89 316 a Initial target concentration for molecular probes in aqueous model solution. b Retention times for aldehyde-hydrazine complexes. c Percent aldehyde-hydrazine complex formed from derivatization procedure. d Relative molar response factor for UV-Vis detector at 360 nm.
138
Figure 1 – Total aldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 14 days. a Different letters represent statistical differences among exposure materials at p < 0.05.
a 112
b91
c70
d55
d43
0
20
40
60
80
100
120
140
Exposure Material
Tota
l Ald
ehyd
e C
once
ntra
tion
( µµ µµM
)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
139
Figure 2 – Sorption of acetaldehyde by neat PET and aldehyde scavenging PET films in
aqueous model solutions.
0
20
40
60
80
100
0 2 4 6 8 10 12 14Time (days)
Perc
ent S
orpt
ion
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
140
Figure 3 – Sorption of propionaldehyde by neat PET and aldehyde scavenging PET films in
aqueous model solutions.
0
20
40
60
80
100
0 2 4 6 8 10 12 14Time (days)
Perc
ent S
orpt
ion
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
141
Figure 4 – Sorption of butyraldehyde by neat PET and aldehyde scavenging PET films in
aqueous model solutions.
0
20
40
60
80
100
0 2 4 6 8 10 12 14Time (days)
Perc
ent S
orpt
ion
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
142
Figure 5 – Sorption of valeraldehyde by neat PET and aldehyde scavenging PET films in
aqueous model solutions.
0
20
40
60
80
100
0 2 4 6 8 10 12 14Time (days)
Perc
ent S
orpt
ion
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
143
Figure 6 – Sorption of caproaldehyde by neat PET and aldehyde scavenging PET films in
aqueous model solutions.
0
20
40
60
80
100
0 2 4 6 8 10 12 14Time (days)
Perc
ent S
orpt
ion
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
144
Figure 7 – Sorption of molecular probes per unit volume of neat PET and aldehyde
scavenging PET films in aqueous model solutions after 14 days of exposure.
0
5
10
15
20
25
30
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
Exposure Material
Sorp
tion
(mg
prob
e / d
m3 p
olym
er)
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
145
Table 4 – Partition coefficients for m
olecular probes after 14 days of contact with neat PE
T and aldehyde scavenging PE
T
films in aqueous m
odel solutions
Contact M
aterial A
cetaldehyde (K
) Propionaldehyde
(K)
Butyraldehyde
(K)
Valeraldehyde
(K)
Caproaldehyde
(K)
PET 234
162 328
454 382
PET : Nylon M
XD
6 892
676 698
621 367
PET : D-Sorbitol
1485 1007
863 717
465 PET : α-C
yclodextrin 1616
1357 1045
865 587
146
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149
CHAPTER 6 APPENDIX
Table 5 - Solubility characteristics of molecular probes used in aqueous model solutions
No. Molecular Probe Mw (g/mol)
kHcp a
(M/atm) P0
b
(atm) Max. Water Solubility
(M) (mg/L) 1 Acetaldehyde 44.05 1.85E+01 1.15E+00 2.12E+01 9.34E+05 2 Propionaldehyde 58.08 1.82E+01 4.16E-01 7.57E+00 4.40E+05 3 Butyraldehyde 72.11 1.37E+01 1.47E-01 2.01E+00 1.45E+05 4 Valeraldehyde 86.13 9.21E+00 4.48E-02 4.13E-01 3.56E+04 5 Caproaldehyde 100.16 1.00E-01 1.42E-02 1.00E-01 1.00E+04
a Henry’s law constant (Staudinger and Roberts 2001; Zhou and Mopper 1990). b Vapor pressure of pure molecular probe (Green and Maloney 1997).
150
Table 6 - Odor and flavor thresholds of molecular probes in water and milka
Molecular Probe Odor Threshold in Water (ppm)
Flavor threshold in Water (ppm)
Flavor Threshold in Milk (ppm)
Acetaldehyde 1.20E-04 to 1.50E+01 1.50E-08 to 1.30E-05 1.30E+00 Propionaldehyde 9.50E-03 1.70E-01 - Butyraldehyde 9.00E-03 to 7.00E-03 7.00E-02 - Valeraldehyde 1.20E-02 to 1.20E+00 7.00E-01 1.30E-01 Caproaldehyde 5.00E-03 to 3.00E-02 1.60E-02 to 2.00E-01 5.00E-02 a Odor and flavor thresholds obtained from literature (Fazzalari 1978).
151
Figure 8 - T
GA
thermogram
of nylon MX
D6.
152
Figure 9 - TG
A therm
ogram of D
-sorbitol .
153
Figure 10 - TG
A therm
ogram of ααα α-cyclodextrin.
154
Figure 11 - D
SC therm
ogram of neat PE
T therm
ally pressed film.
155
Figure 12 - D
SC therm
ogram of PE
T : nylon M
XD
6 thermally pressed film
.
156
Figure 13 - D
SC therm
ogram of PE
T : D
-sorbitol thermally pressed film
.
157
Figure 14 - D
SC therm
ogram of PET : ααα α-cyclodextrin therm
ally pressed film.
158
Figure 15 - T
GA
thermogram
of neat PET
thermally pressed film
.
159
Figure 16 - T
GA
thermogram
of PET
: nylon MX
D6 therm
ally pressed film.
160
Figure 17 - T
GA
thermogram
of PET
: D-sorbitol therm
ally pressed film.
161
Figure 18 - TG
A therm
ogram of PET : ααα α-cyclodextrin therm
ally pressed film.
162
Figure 19 – T
GA
thermogram
s of neat PET
and aldehyde scavenging PET
films.
163
Figure 20 - HPL
C chrom
atograms of (1) acetaldehyde, (2) propionaldehyde, (3) butyraldehyde, (4) valeraldehyde, and
(5) caproaldehyde exposed to (A) N
eat PET
, (B) PE
T : nylon M
XD
6 blend, (C) PE
T : D
-sorbitol blend, and (D) PE
T : ααα α-
cyclodextrin blend for 1 day in aqueous solutions.
164
Figure 21 - HPL
C chrom
atograms of (1) acetaldehyde, (2) propionaldehyde, (3) butyraldehyde, (4) valeraldehyde, and
(5) caproaldehyde exposed to (A) N
eat PET
, (B) PE
T : nylon M
XD
6 blend, (C) PE
T : D
-sorbitol blend, and (D) PE
T : ααα α-
cyclodextrin blend for 3 days in aqueous solutions.
165
Figure 22 - HPL
C chrom
atograms of (1) acetaldehyde, (2) propionaldehyde, (3) butyraldehyde, (4) valeraldehyde, and
(5) caproaldehyde exposed to (A) N
eat PET
, (B) PE
T : nylon M
XD
6 blend, (C) PE
T : D
-sorbitol blend, and (D) PE
T : ααα α-
cyclodextrin blend for 7 days in aqueous solutions.
166
Figure 23 - HPL
C chrom
atograms of (1) acetaldehyde, (2) propionaldehyde, (3) butyraldehyde, (4) valeraldehyde, and
(5) caproaldehyde exposed to (A) N
eat PET
, (B) PE
T : nylon M
XD
6 blend, (C) PE
T : D
-sorbitol blend, and (D) PE
T : ααα α-
cyclodextrin blend for 14 days in aqueous solutions.
167
Figure 24 – Total aldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 1 day of exposure. a Different letters represent statistical differences among exposure materials at p < 0.05.
a122 a
117
b89
c70
d58
0
20
40
60
80
100
120
140
Exposure Material
Tota
l Ald
ehyd
e C
once
ntra
tion
( µµ µµM
)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
168
Figure 25 – Total aldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 3 days of exposure. a Different letters represent statistical differences among exposure materials at p < 0.05.
a 117
b99
c77
d60
e48
0
20
40
60
80
100
120
140
Exposure Material
Tota
l Ald
ehyd
e C
once
ntra
tion
( µµ µµM
)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
169
Figure 26 – Total aldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 7 days of exposure. a Different letters represent statistical differences among exposure materials at p < 0.05.
a 114
b91
c70
d56
d45
0
20
40
60
80
100
120
140
Exposure Material
Tota
l Ald
ehyd
e C
once
ntra
tion
( µµ µµM
)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
170
Figure 27 – Molecular probe concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 1 day of exposure.
0
5
10
15
20
25
30
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
Molecular Probe
Mol
ecul
ar P
robe
Con
cent
ratio
n ( µµ µµ
M)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
171
Figure 28 – Molecular probe concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 3 days of exposure.
0
5
10
15
20
25
30
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
Molecular Probe
Mol
ecul
ar P
robe
Con
cent
ratio
n ( µµ µµ
M)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
172
Figure 29 – Molecular probe concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 7 days of exposure.
0
5
10
15
20
25
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
Molecular Probe
Mol
ecul
ar P
robe
Con
cent
ratio
n ( µµ µµ
M)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
173
Figure 30 – Molecular probe concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 14 days of exposure.
0
5
10
15
20
25
30
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
Molecular Probe
Mol
ecul
ar P
robe
Con
cent
ratio
n ( µµ µµ
M)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha-Cyclodextrin
174
Figure 31 – Acetaldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Time
Ace
tald
ehyd
e C
once
ntra
tion
( µµ µµM
)Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
175
Figure 32 – Propionaldehyde concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Time
Prop
iona
ldeh
yde
Con
cent
ratio
n ( µµ µµ
M)
Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
176
Figure 33 – Butyraldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Time
Buty
rald
ehyd
e C
once
ntra
tion
( µµ µµM
)Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
177
Figure 34 – Valeraldehyde concentration in aqueous model solutions after exposure to neat
PET and aldehyde scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Time
Val
eral
dehy
de C
once
ntra
tion
( µµ µµM
)Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
178
Figure 35 – Caproaldehyde concentration in aqueous model solutions after exposure to
neat PET and aldehyde scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Time
Cap
roal
dehy
de C
once
ntra
tion
( µµ µµM
)Aqueous Model Solution Neat PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
179
Figure 36 – Sorption of molecular probes per unit volume for neat PET and aldehyde
scavenging PET blends after 1 day of exposure.
0
5
10
15
20
25
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
Exposure Material
Sorp
tion
(mg
prob
e / d
m3 p
olym
er)
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
180
Figure 37 – Sorption of molecular probes per unit volume for neat PET and aldehyde
scavenging PET blends after 3 days of exposure.
0
5
10
15
20
25
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
Exposure Material
Sorp
tion
(mg
prob
e / d
m3 p
olym
er)
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
181
Figure 38 – Sorption of molecular probes per unit volume for neat PET and aldehyde
scavenging PET blends after 7 days of exposure.
0
5
10
15
20
25
30
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
Exposure Material
Sorp
tion
(mg
prob
e / d
m3 p
olym
er)
Acetaldehyde Propionaldehyde Butyraldehyde Valeraldehyde Caproaldehyde
182
Figure 39 – Sorption of acetaldehyde per unit volume for neat PET and aldehyde
scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
Day 1 Day 3 Day 7 Day 14
Exposure Material
Sorp
tion
(mg
acet
alde
hyde
/ dm
3 pol
ymer
)
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
183
Figure 40 – Sorption of propionaldehyde per unit volume for neat PET and aldehyde
scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
30
Day 1 Day 3 Day 7 Day 14
Exposure Material
Sorp
tion
(mg
prop
iona
ldeh
yde
/ dm
3 pol
ymer
)
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
184
Figure 41 – Sorption of butyraldehyde per unit volume for neat PET and aldehyde
scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
Day 1 Day 3 Day 7 Day 14
Exposure Material
Sorp
tion
(mg
buty
rald
ehyd
e / d
m3 p
olym
er)
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
185
Figure 42 – Sorption of valeraldehyde per unit volume for neat PET and aldehyde
scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
5
10
15
20
25
Day 1 Day 3 Day 7 Day 14
Exposure Material
Sorp
tion
(mg
vale
rald
ehyd
e / d
m3 p
olym
er)
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
186
Figure 43 – Sorption of caproaldehyde per unit volume for neat PET and aldehyde
scavenging PET blends after 1, 3, 7, and 14 days of exposure.
0
2
4
6
8
10
12
14
16
18
Day 1 Day 3 Day 7 Day 14
Exposure Material
Sorp
tion
(mg
capr
oald
ehyd
e / d
m3 p
olym
er)
PET PET : Nylon MXD6 PET : D-Sorbitol PET : Alpha Cyclodextrin
187
Prediction of Sorption in a Beverage Container
Materials and Methods
The surface area of beverage containers was determined using a prototype surface
analyzer (CS Technologies, OmniSurface Machine Vision System, American Fork, UT). This
analyzer projects light onto the object that is being analyzed and casts a shadow of the object on
a shadow box. The object is rotated on a manual turntable connected to a computer workstation.
A digital camera, connected to the computer workstation, takes a digital image of the object’s
shadow at 8° increments when the turntable is rotated. The computer workstation then calculates
the surface area of the object based on the area of 45 two-dimensional images. Translucent and
transparent packaging materials required the application of thin epoxy paint in order to prevent
transmission of light. Surface area measurements for beverage containers showed excellent
precision demonstrated by small standard deviations among containers tested.
Results and Discussion
The amount (mg) of molecular probes sorbed per unit volume (dm3) for test films after
one, three, seven, and fourteen days were calculated and are presented in Figures 1-4. Previous
trends discussed for sorption amounts and rates by test films are also seen in this presentation
format. However, sorption amounts calculated on a per volume or surface area basis for
packaging material allows one to determine the theoretical concentration of molecular probes
that can be removed from a container. The volume of packaging material found in a container
can easily be calculated after accurately weighing the empty container and determining the
density of the packaging material. Alternatively, one can measure the surface area of a beverage
container in order to predict scalping capacity. The surface area of simply shaped containers
such as cylinders and cubes can be calculated using geometric equations, however, most
beverage containers will require more sophisticated equipment for surface area measurement.
The sorption capacity of molecular probes by several beverage containers in different
sizes and geometric shapes was predicted from data obtained for sorption amount after fourteen
days of exposure (Figures 44-50). Predictions assume containers were manufactured from neat
PET and blended PET materials. Storage conditions and composition of the aqueous model
solution are also assumed.
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The sorption capacity for molecular probes by larger containers is greater then smaller
containers due to their increased overall surface area. For instance, predicted sorption amounts
for acetaldehyde by 8 fl. oz. and 1 gallon containers consisting of PET : α-cyclodextrin material
are 345 and 2,171 µg. However, the concentration of molecular probe removed by the container
is related to its surface area to volume ratio. An 8 fl. oz. container which has a surface area to
volume ratio of 1.12 cm2 / mL consisting of PET : α-cyclodextrin material can remove 1,463 ppb
of acetaldehyde. A 1 gallon container comprised of the same material with a surface area to
volume ratio of 0.44 cm2 / mL is only predicted to remove 574 ppb of acetaldehyde from
solution.
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Figure 44 - Surface area measurementsa and theoretical scalping abilityb of 8 fl. oz.
beverage container.
Brand 8th Continent Product Soy milk – Low fat – Vanilla Size (fl. oz.) 8 Size (mL) 236 Packaging material HDPE (white) Surface area (cm2) 263 ± 7 Surface area (cm2) : Volume (mL)ratio 1.12 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 53 224 196 830 316 1337 345 1463 Propionaldehyde 41 175 167 707 241 1020 326 1381 Butyraldehyde 76 324 157 667 188 799 229 972 Valeraldehyde 101 429 134 569 150 637 182 772 Caproaldehyde 84 356 78 332 96 407 122 517 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
190
Figure 45 - Surface area measurementsa and theoretical scalping abilityb of 12 fl. oz. beverage container.
Brand Land O’ Lakes Line description Grip ‘n Go Product 2% Reduced fat milk Size (fl. oz.) 12 Size (mL) 355 Packaging material HDPE (white) Surface area (cm2) 344 ± 1 Surface area (cm2) : Volume (mL)ratio 0.97 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 69 195 256 722 413 1163 452 1272 Propionaldehyde 54 152 218 615 315 887 426 1201 Butyraldehyde 100 282 206 580 247 694 300 845 Valeraldehyde 133 373 176 495 197 554 238 671 Caproaldehyde 110 309 103 289 126 354 160 450 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
191
Figure 46 – Surface area measurementsa and theoretical scalping abilityb of 14 fl. oz. beverage container.
Brand Hershey Product Chocolate milk – Fat free – Calcium fortified Size (fl. oz.) 14 Size (mL) 414 Packaging material HDPE (white) Surface area (cm2) 377 ± 6 Surface area (cm2) : Volume (mL)ratio 0.91 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 76 183 281 678 452 1093 495 1195 Propionaldehyde 59 143 239 578 345 833 467 1129 Butyraldehyde 110 265 226 545 270 653 329 794 Valeraldehyde 145 351 193 465 215 520 261 631 Caproaldehyde 120 291 112 271 138 333 175 423 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
192
Figure 47 - Surface area measurementsa and theoretical scalping abilityb of 16 fl. oz. beverage container.
Brand Nestle Line description Nesquik Product Chocolate milk Size (fl. oz.) 16 Size (mL) 473 Packaging material PET (clear) Surface area (cm2) 410 ± 1 Surface area (cm2) : Volume (mL)ratio 0.87 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 83 174 305 646 492 1040 538 1138 Propionaldehyde 64 136 260 550 375 793 508 1074 Butyraldehyde 119 252 245 519 294 621 358 756 Valeraldehyde 158 334 209 443 234 495 284 600 Caproaldehyde 131 277 122 258 150 317 190 402 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
193
Figure 48 - Surface area measurementsa and theoretical scalping abilityb of 32 fl. oz. beverage container.
Brand Kroger Product Grade A Skim milk Size (fl. oz.) 32 Size (mL) 946 Packaging material HDPE (white) Surface area (cm2) 640 ± 6 Surface area (cm2) : Volume (mL)ratio 0.68 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 129 136 477 504 768 812 840 888 Propionaldehyde 100 106 406 429 586 619 793 838 Butyraldehyde 186 197 383 405 459 485 558 590 Valeraldehyde 247 261 327 346 366 387 443 469 Caproaldehyde 204 216 191 202 234 247 297 314 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
194
Figure 49 - Surface area measurementsa and theoretical scalping abilityb of 0.5 gal. beverage container.
Brand Valley Rich Product 2% Reduced fat milk Size (U.S. gal.) 0.5 Size (mL) 1890 Packaging material HDPE (opaque) Surface area (cm2) 1115 ± 10 Surface area (cm2) : Volume (mL)ratio 0.59 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 224 119 830 439 1338 708 1464 774 Propionaldehyde 175 92 708 374 1021 540 1382 731 Butyraldehyde 324 171 668 353 799 423 972 514 8Valeraldehyde 430 227 569 301 637 337 772 409 Caproaldehyde 356 188 332 176 407 216 517 274 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.
195
Figure 50 - Surface area measurementsa and theoretical scalping abilityb of 1 gal. beverage container.
Brand Valley Rich Product 2% Reduced fat milk Size (fl. oz.) 1.0 Size (mL) 3780 Packaging material HDPE (opaque) Surface area (cm2) 1654 ± 6 Surface area (cm2) : Volume (mL)ratio 0.44 a Surface area measurements performed using OmniSurface Machine Vision System.
Molecular probe PET (µg) (ppb)
PET:Nyl. MXD6 (µg) (ppb)
PET:D-Sorbitol (µg) (ppb)
PET:α-Cdex. (µg) (ppb)
Acetaldehyde 333 88 1232 326 1985 525 2171 574 Propionaldehyde 259 69 1050 278 1514 401 2050 542 Butyraldehyde 481 127 990 262 1185 314 1442 382 Valeraldehyde 637 169 845 223 945 250 1146 303 Caproaldehyde 528 140 493 130 604 160 767 203 b Calculated absorption of molecular probes assumes the following conditions: 1) PET packaging material, 2) ambient storage temperature, 3) exposure time of fourteen days.