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Identification of off-flavor compounds in high-density polyethylene (HDPE) with different amounts of abscents.

INTRODUCTION

Earlier studies have shown that organoleptic or·gan·o·lep·tic
adj.
1. Relating to perception by a sensory organ.

2. Involving the use of sense organs.


organoleptic
 properties of drinking water drinking water

supply of water available to animals for drinking supplied via nipples, in troughs, dams, ponds and larger natural water sources; an insufficient supply leads to dehydration; it can be the source of infection, e.g. leptospirosis, salmonellosis, or of poisoning, e.g.
 are essential when using polyethylene pipes. Water plays an important role in the solubility solubility

Degree to which a substance dissolves in a solvent to make a solution (usually expressed as grams of solute per litre of solvent). Solubility of one fluid (liquid or gas) in another may be complete (totally miscible; e.g.
 of additives in polyolefins (1). There are three principal causes for organoleptic changes in water: dissolution of additives, oxidation of the internal surface of the pipe, and migration of external contaminants (2, 3). In addition, some studies have shown that odor-causing compounds like aldehydes and ketones Ketones
Poisonous acidic chemicals produced by the body when fat instead of glucose is burned for energy. Breakdown of fat occurs when not enough insulin is present to channel glucose into body cells.

Mentioned in: Diabetic Ketoacidosis, Urinalysis
, can be released from thermal oxidation In microfabrication, thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer (semiconductor). The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it.  of polyethylene, and these most unpleasant odors can be caused by carbonyl carbonyl /car·bon·yl/ (kahr´bah-nil) the bivalent organic radical, C:O, characteristic of aldehydes, ketones, carboxylic acid, and esters.

car·bon·yl
n.
The bivalent radical CO.
 compounds in a certain molecular weight range (4-6). Viebke et al. (7) also showed that the degradation of polyolefin pipes is one reason for the formation of carbonyl compounds. Ho et al. (8) considered nonanal as a major contributor of the off- odor due to its abundance and low odor threshold concentration. Rigal has studied the taste of HDPE HDPE
abbr.
high-density polyethylene
 by organoleptic tests and bad taste was caused by insufficiently controlled cooling conditions followed by formation of oxidation products (9). Berg has also investigated the origin of these off-flavors (10). Anselme et al. (2) have discussed some organoleptic problem sources and possible remedies.

There are many efforts to remove odor-causing compounds. Zambetti et al. (11) have compared the effect of different antioxidants Antioxidants
Substances that reduce the damage of the highly reactive free radicals that are the byproducts of the cells.

Mentioned in: Aging, Nutritional Supplements

antioxidants,
n.
 on reducing tastes and odors. Gioffre et al. (12) have eliminated organic odors from air using activated silicalite and zeolite zeolite

Any member of a family of hydrated aluminosilicate minerals that have a framework structure enclosing interconnected cavities occupied by large metal cations (positively charged ions)—generally sodium, potassium, magnesium, calcium, and barium—and water
 Y, Marcus has sequestered se·ques·ter  
v. se·ques·tered, se·ques·ter·ing, se·ques·ters

v.tr.
1. To cause to withdraw into seclusion.

2. To remove or set apart; segregate. See Synonyms at isolate.

3.
 ammonia and its odor using combined zeolites (13). Gustafsson et al. (14) have shown, that off-odor and off-taste compounds in polyolefin packaging materials can be eliminated with the aid of a new molecular sieve A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecules small enough to pass through the pores are adsorbed while larger molecules are not.
, Abscents, which is added to HDPE during compounding, Abscents is a combination of zeolites including (1:1) activated silicalite and zeolite LZ-10 (12). Abscents is a deodorizing powder and it is used in such products where odor is a problem. This molecular sieve is highly selective for adsorbing odor-causing compounds like aldehydes and ketones. Abscents is very effective to decrease the odor of molecules; it has organophilic pores that trap odor molecules within its structure. Abscents is different than other sieves due to its capacity for adsorbing odor-causing compounds even in the presence of water. One of the benefits of Abscents is its ability to remove many odorous compounds below their threshold detection level (14, 15).

EXPERIMENTAL

Sample Preparation

The samples were blue high-density polyethylene high-density polyethylene
n. Abbr. HDPE
A strong, relatively opaque form of polyethylene having a dense structure with few side branches off the main carbon backbone.
 (HDPE) pellets with four (0.10 wt%, 0.15 wt%, 0.20 wt%, 0.30 wt%) different amounts of Abscents, manufactured by UOP (micro OPeration) The "u" is the substitute letter for the µ symbol. See microinstruction. , Inc. (14). Polyethylene pellets were about 4 mm in diameter and 2 mm thick, Each pellet sample (32 g) was placed into 250 mL odor-free water (Ultra High Quality ELGA ELGA English Ladies' Golf Association (UK)  water) and shaken for four hours at room temperature (25 [degrees] C). These water samples (10 mL of each) were tested using gas chromatography/mass spectrometry/sniffing-methods.

Analysis

Instrumental analysis was carried out with a VG AutoSpec high resolution mass spectrometer spectrometer

Device for detecting and analyzing wavelengths of electromagnetic radiation, commonly used for molecular spectroscopy; more broadly, any of various instruments in which an emission (as of electromagnetic radiation or particles) is spread out according to some
 connected to a Hewlett Packard 5890 Series II gas chromatograph gas chromatograph
n.
An instrument used in gas chromatography to separate a sample of a volatile substance into its components.
. A Tekmar 2000 purge and trap-system (a dynamic headspace head·space  
n.
The volume left at the top of an almost filled jar, tin, or other container before sealing.

Noun 1. headspace - the volume left at the top of a filled container (bottle or jar or tin) before sealing
) was used to introduce the samples into the GC/MS GC/MS Gas Chromatograph/Mass Spectrometer
GC/MS Gas Chromatograph/Mass Spectrometry
GC/MS Gas Chromatograph/Mass Spectrograph
. The purge and trap operating conditions are shown in Table 1. The GC-column was a 25 m Noribond SE 54 (1 [[micro]meter] phase, i.d. 0.25 mm) and there were two identical columns. The eluted compounds from one column were sniffed at the same time as the peaks of the same compounds were detected by MS and appeared on the chromatogram chromatogram /chro·mato·gram/ (kro-mat´o-gram) the record produced by chromatography.

chro·mat·o·gram
n.
The pattern of separated substances obtained by chromatography.
 using the other column (16). An initial temperature for gas chromatography gas chromatography (GC)

Type of chromatography with a gas mixture as the mobile phase. In a packed column, the packing or solid support (held in a tube) serves as the stationary phase (vapour-phase chromatography, or VPC) or is coated with a liquid stationary phase
 of 40 [degrees] C for 5 minutes was used, followed by increasing the temperature at a rate of 5 [degrees] C/min to 250 [degrees] C and to a final hold for 10 minutes.
Table 1. The Operating Conditions of Purge and Trap Equipment.

Function                         Time/Temperature

standby temperature              30 [degrees] C
prepurge time                    3 min
preheat time                     3 min
sample temperature               100 [degrees] C
purge time                       12 min
dry purge time                   6 min
moisture control module          0 [degrees] C
cryo cooldown                    -120 [degrees] C
desorb preheat                   175 [degrees] C
desorb time/temperature          4 min/180 [degrees] C
inject time/temperature          0.85 min/250 [degrees] C
bake time/temperature            7 min/225 [degrees] C


RESULTS AND DISCUSSION

The Results of GC/MS/SNIFF Analysis

In leaching samples with water, 91 volatile compounds with molecular weight ranging from 46-184 were identified. Those compounds belonged mainly to the groups of hydrocarbons (alkanes The following is a list of straight-chain alkanes and their common names, sorted by number of carbon atoms.

Number of C atoms Formula Common name Synonyms
1 CH4 Methane marsh gas; methyl hydride; natural gas
2 C2H6
, alkenes) and carbonyl compounds (aldehydes and ketones). These compounds can partition into water, so they are probably also responsible for off-taste. Some of these compounds, like aldehydes, could be readily identified by their characteristic odors. The special focus in interpretation of mass spectra was concentrated on bad smelling compounds and their behavior with different percentages of Abscents.

Using GC/MS/SNIFF analysis, seven ketones and four aldehydes were identified that caused off-odors. Some of those compounds only appeared and caused odors when the added percentage of Abscents was the lowest (0.10%) as seen in Fig. 1. These bad-smelling compounds were heptanal, octanal, nonanal of aldehydes, and five ketones: 3,3-dimethylcyclobutanone ([C.sub.6]-ketone), methyl isobutyl ketone Methyl isobutyl ketone (MIBK) is a ketone that is widely used as a solvent. Unlike the other common ketone solvents, acetone and MEK, MIBK has quite low solubility in water, allowing it to be used for liquid-liquid extraction.  (MIK MIK More in Kitchen ), 3, 4-dimethyl-2-hexanone ([C.sub.8]-ketone) and isopropylcyclohexanone and 4,6-dimethyl-5-hepten-2-one ([C.sub.9]ketones). The calculated concentrations of these carbonyl compounds with different amounts of Abscents are shown in Table 2.

In leaching water with a minimum percentage of Abscents there were many bad smells compared with the leachate leach·ate  
n.
A product or solution formed by leaching, especially a solution containing contaminants picked up through the leaching of soil.
 of pellets when the maximum amount of Abscents (0.30%) was used. As shown in Fig. 1, the concentrations of off-flavor compounds and the intensifies of odors decreased or disappeared thoroughly when the maximum percentage of Abscents was added. The strongest odor was caused by [C.sub.9]-ketone; isopropylcyclohexanone (pungent). The intensity of this odor decreased notably using the maximum amount of Abscents. The odor was then described as very weak and solvent-like.

The off-odors of other carbonyl compounds (nonanal, octanal, heptanal, MIK, 3, 3-dimethylcyclobutanone) and their behavior with increasing amount of Abscents are indicated in Fig. 1. The odor descriptions became more pleasant. Using the maximum amount of Abscents, the concentrations of some ketones were below the threshold odor concentration (TOC) and thereby caused no odor. Some of these ketones were removed completely with a higher percentage of Abscents (0.20%, 0.30%). Additionally, one aldehyde aldehyde (ăl`dəhīd) [alcohol + New Lat. dehydrogenatus=dehydrogenated], any of a class of organic compounds that contain the carbonyl group, and in which the carbonyl group is bonded to at least one hydrogen; the general , decanal Dec´a`nal

a. 1. Pertaining to a dean or deanery.
His rectorial as well as decanal residence.
- Churton.

Decanal side
the side of the choir on which the dean's tall is placed.
, appeared only when a minimum amount (0.10%) of Abscents was used.
Table 2. Concentration of Off-Flavor Compounds in Leachates (mg/L).

Compound              0.10 wt%    0.15 wt%    0.20 wt%    0.30 wt%

methytbutenone        0.002       0.001         -          -
dimothylbutanone      0.008       0.006        0.005      0.003
MIK                   0.002       0.0012       0.0013     0.0006
methylheptadienone    0.003       0.001        0.001       -
heptanal              0.05        0.03         0.03       0.01
dimethylhexanone      0.002       0.001        0.001      0.001
dimethylheptenone     0.009       0.005        0.006      0.004
octanal               0.13        0.06         0.07       0.03
isopropylhexanone     0.010       0.005        0.007      0.003
nonanal               0.27        0.12         0.11       0.04
decanal               0.036        -            -          -
TOTAL                 0.52        0.23         0.23       0.09


As seen in Fig. 2, the total amounts of carbonyl compounds were very low (0.09 mg/L), being 0.30% of Abscents. When the amount of Abscents was minimum (0.10%) the total carbonyl concentration was 0.52 mg/L. Such a high total content of off-flavor compounds was especially caused by aldehydes. This was particularly noticed in tile case of decanal; this aldehyde appeared only in the sample with 0.10% of Abscents.

The amounts of all ketones (Table 2) were also the largest with the minimum percentage of Abscents. The concentration of methyl isobutyl ketone (MIK) was twice as big (0.002 mg/L) when the added amount of Abscents was 0.10% compared with amounts of 0.15% and 0.20% Abscents. The concentration of MIK was the lowest (0.0006 mg/L) when the amount of Abscents was the highest. The concentration of isopropylcyclohexanone ([C.sub.9]-ketone), the source of the strongest odor, was three times smaller (0.003 mg/L) with a maximum amount (0.30%) of Abscents compared to samples with an added minimum percentage (0.10%) of Abscents (0.010 mg/L). Furthermore, some ketones were removed completely when the percentage of Abscents was more than 0.20%.

CONCLUSION

A purge and trap-system connected to the GC/MS with simultaneous sniffing is a very useful technique for solving the off-flavor problems of HDPE used in pipe applications. Bad smelling areas were chosen for more detailed studies and closer investigations showed that the unpleasant odors in waters were due to carbonyl compounds.

The combined zeolite, Abscents, was used to reduce carbonyl compounds. Four different percentages (0.10%, 0.15%, 0.20% and 0.30%) of Abscents were investigated. For 0.10% of Abscents, off-flavor compounds appeared. There was no significant difference in concentrations of off-flavor compounds when the percentage of Abscents was varied between 0.15% and 0.20%. When the added amount of Abscents was the highest (0.30%), almost all carbonyl compounds disappeared. The intensities of odors also decreased or disappeared thoroughly.

The acceptability for pipes made for drinking water for less off-odor in water appears to be possible. This study unquestionably un·ques·tion·a·ble  
adj.
Beyond question or doubt. See Synonyms at authentic.



un·question·a·bil
 showed that higher percentages of Abscents in HDPE pellets lead to lower concentrations of off-flavor compounds.

ACKNOWLEDGMENT

This study was financially supported by Neste Foundation, Finland.

REFERENCES

1. U. W. Gedde, J. Viebke, H. Leijstrom, and M. Ifwarson, Polym. Eng. Sci., 34, 1773 (1994).

2. C. Anselme, K. N Guyen, A. Bruchet, and J. Mallevialle, Environ. Tech. Lett. 6, 477 (1985).

3. H. Flogstad, World Water, December 1984, p. 27.

4. A. Hoff and S. Jacobsson, J. Appl Poly. Sci., 26, 3409 (1981).

5. A. Bravo and J. H. Hotchkiss, J. Appl. Polym. Sci., 47, 1741 (1993).

6. J. Koszinowski and O. Piringer, J. Plast. Film. Sheet., 2, 40 (1986).

7. Y. C. Ho, K. L. Yam, S. S. Young, and P. F. Zambetti, J. Plast. Film Sheet., 10, 194 (1994).

8. J. Viebke, E. Elble, and U. W. Gedde, Polym. Eng. Sci., 36, 458 (1996).

9. S. Rigal, Wat. Sci. Tech., 25, 41 (1992).

10. N. Berg, 3rd International Symposium on Migration, Hamburg (1980).

11. P. F. Zambetti, S. L. Baker, and D. C. Kelley, Tappi J., 4, 167 (1995).

12. A. J, Gioffre and B. K. Marcus. U.S. Pat. Appl. 67, 977.4,795,482 (1989)

13. B. K. Marcus, U.S. Pat. Appl. 67,977.5,013,335 (1991).

14. B. Gustafsson, S. Olsson, and B. Friman, WO pat. 13, 029. SE Appl. 91/181 (1992).

15. A. J. Gioffre, Nonw. World, 6 (1989).

16. A. Veijanen, An Integrated Sensory and Analytical Method for Identification of Off-flavour Compounds, academic dissertation, Jyvaskyla, Finland (1990).
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No portion of this article can be reproduced without the express written permission from the copyright holder.
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Author:Villberg, Kirsi; Veijanen, Anja; Gustafsson, Irma
Publication:Polymer Engineering and Science
Date:Jun 1, 1998
Words:1809
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