SECTION III SORPTION BEHAVIOR OF SELECTED ALDEHDYE ...with Kapton film (DuPont, Wilmington, DE) in order to improve the removal of cast film from the metal frame after cooling. The

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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.

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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

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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

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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)

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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.

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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).

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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).

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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

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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

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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,

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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

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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

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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


0

20

40

60

80

100

0 2 4 6 8 10 12 14Time (days)

Perc

ent S

orpt

ion


141

Figure 4 – Sorption of butyraldehyde by neat PET and aldehyde scavenging PET films in


0

20

40

60

80

100

0 2 4 6 8 10 12 14Time (days)

Perc

ent S

orpt

ion


142

Figure 5 – Sorption of valeraldehyde by neat PET and aldehyde scavenging PET films in


0

20

40

60

80

100

0 2 4 6 8 10 12 14Time (days)

Perc

ent S

orpt

ion


143

Figure 6 – Sorption of caproaldehyde by neat PET and aldehyde scavenging PET films in


0

20

40

60

80

100

0 2 4 6 8 10 12 14Time (days)

Perc

ent S

orpt

ion


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


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



eat PET

, (B) PE

T : nylon M

XD

6 blend, (C) PE

T : D


T : ααα α-

cyclodextrin blend for 3 days in aqueous solutions.

165

Figure 22 - HPL

C chrom



eat PET

, (B) PE

T : nylon M

XD

6 blend, (C) PE

T : D


T : ααα α-


166

Figure 23 - HPL

C chrom



eat PET

, (B) PE

T : nylon M

XD

6 blend, (C) PE

T : D


T : ααα α-


167


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

)


168


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

)


169


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

)


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


Molecular Probe

Mol

ecul

ar P

robe

Con

cent

ratio

n ( µµ µµ

M)


171


neat PET and aldehyde scavenging PET blends after 3 days of exposure.

0

5

10

15

20

25

30


Molecular Probe

Mol

ecul

ar P

robe

Con

cent

ratio

n ( µµ µµ

M)


172



0

5

10

15

20

25


Molecular Probe

Mol

ecul

ar P

robe

Con

cent

ratio

n ( µµ µµ

M)


173



0

5

10

15

20

25

30


Molecular Probe

Mol

ecul

ar P

robe

Con

cent

ratio

n ( µµ µµ

M)


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


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


0

5

10

15

20

25

30


Exposure Time

Buty

rald

ehyd

e C

once

ntra

tion

( µµ µµM


177

Figure 34 – Valeraldehyde concentration in aqueous model solutions after exposure to neat


0

5

10

15

20

25

30


Exposure Time

Val

eral

dehy

de C

once

ntra

tion

( µµ µµM


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


Exposure Time

Cap

roal

dehy

de C

once

ntra

tion

( µµ µµM


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


Exposure Material

Sorp

tion

(mg

prob

e / d

m3 p

olym

er)


180


scavenging PET blends after 3 days of exposure.

0

5

10

15

20

25


Exposure Material

Sorp

tion

(mg

prob

e / d

m3 p

olym

er)


181


scavenging PET blends after 7 days of exposure.

0

5

10

15

20

25

30


Exposure Material

Sorp

tion

(mg

prob

e / d

m3 p

olym

er)


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


Exposure Material

Sorp

tion

(mg

acet

alde

hyde

/ dm

3 pol

ymer

)


183

Figure 40 – Sorption of propionaldehyde per unit volume for neat PET and aldehyde


0

5

10

15

20

25

30


Exposure Material

Sorp

tion

(mg

prop

iona

ldeh

yde

/ dm

3 pol

ymer

)


184

Figure 41 – Sorption of butyraldehyde per unit volume for neat PET and aldehyde


0

5

10

15

20

25


Exposure Material

Sorp

tion

(mg

buty

rald

ehyd

e / d

m3 p

olym

er)


185

Figure 42 – Sorption of valeraldehyde per unit volume for neat PET and aldehyde


0

5

10

15

20

25


Exposure Material

Sorp

tion

(mg

vale

rald

ehyd

e / d

m3 p

olym

er)


186

Figure 43 – Sorption of caproaldehyde per unit volume for neat PET and aldehyde


0

2

4

6

8

10

12

14

16

18


Exposure Material

Sorp

tion

(mg

capr

oald

ehyd

e / d

m3 p

olym

er)


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.

188

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.

189

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.






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.






192


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.






193


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.






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.





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.






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SECTION III SORPTION BEHAVIOR OF SELECTED ALDEHDYE ...with Kapton film (DuPont, Wilmington, DE) in order to improve the removal of cast film from the metal frame after cooling. The