Polyethylene containers

Ethyl indole-2-carboxylate (45.2 g, 0.238 mmol) was dissolved in abs. EtOH (450 ml) in a 11 polyethylene container and cooled in a dry icc-cthanol bath. The solution was saturated with dry HCl gas until the volume increased to 875 ml, Granular tin metal (84.2g, 0.7l0mmol) was added to the slurry and... 

Fluoroboric acid and some fluoroborate solutions are shipped as corrosive material, generally in polyethylene-lined steel pads and dmms or in rigid nonretumable polyethylene containers. Acid spills should be neutralized with lime or soda ash. 

Titanium trifluoride can be stored in tightly closed polyethylene containers for several years. Shipping regulations classify the material as a corrosive sohd and it should be handled in a fully ventilated area or in a chemical hood. The ACGIH adopted toxicity values (1992—1993) for TiF is as TWA for fluorides as F 2.5 mg/m. ... 

Sodium Hypochlorite (Liquid Bleach). Commercial strength Hquid bleach used by industries, laundries, and in swimming pool sanitation, contains 12—15% av CI2 and is sold in 3.8- and 7.6-L polyethylene bottles and 23—57-L carboys, 205-L dmms, and tank tmcks of about 3-kI capacity and greater. Household bleach contains about 5% av CI2 and is sold in 1—5.7-L polyethylene containers. Shipping is limited within a short radius of the plant... 

Heavy metal contamination of pH buffers can be removed by passage of the solutions through a Chelex X-100 column. For example when a solution of 0.02M HEPES [4-(2-HydroxyEthyl)Piperazine-l-Ethanesulfonic acid] containing 0.2M KCl (IL, pH 7.5) alone or with calmodulin, is passed through a column of Chelex X-100 (60g) in the K" " form, the level of Ca ions falls to less than 2 x 10" M as shown by atomic absorption spectroscopy. Such solutions should be stored in polyethylene containers that have been washed with boiling deionised water (5min) and rinsed several times with deionised water. TES [, N,N, -Tetraethylsulfamide] and TRIS [Tris-(hydroxymethyl)aminomethane] have been similarly decontaminated from metal ions. 

Weathering in a tropical climate causes polyethylene containers to crack, polypropylene (PP) ropes to rupture, and ABS telephones to foil. Polystyrene (PS) and cellulose acetate films used as packing materials also fail due to weathering. 

Such an experience with one plastic, PVC, makes it doubly important to carefully examine any plastic to be used with a food product. The basic question to be answered is Does the plastic container provide adequate protection to the food product during the entire life cycle of the container Adequate protection of a food product in a polyethylene container implies that there is no undesirable change in the chemical content of the food during storage in the container. Thus, our study is concerned with the ways in which food products can change when stored in polyethylene containers. 

Perhaps the best way to examine the relationship between polyethylene containers and liquid food products is to examine several applications which posed problems related to one or more of the above four attributes. 

If a change occurs in the food product after storage in a plastic container, some part of the change could be caused by absorption in the container wall. The important components such as flavor oils or emulsifiers exist in relatively small quantities. The type and thickness of the polyethylene container can influence this variable. If the before and after taste test shows no difference between storage in the plastic container and storage in glass, absorption in the wall is considered insignificant. 

Low molecular weight fractions can be detected by smelling the inside of almost any freshly made polyethylene container. The amount varies with the specific polyethylene resin and the type of processing that have been used. 

On occasion the polyethylene has been blamed for odors caused by other parts of the container design such as screw cap liners, printing inks on the bottle exterior, adhesives used to laminate polyethylene to paper, and the fiberboard or the lining of material used in the separate exterior overpack in which a polyethylene container is held. Careful selection of all of these related materials is always advisable with liquid food products. 

As it is ordinarily prepared, polyethylene contains an appreciable number of nonlinear units. Its total structure therefore is not as simple as here represented see below. 

Commercial samples of polyethylene contain varying amounts of defects at the molecular level, depending upon the method of prepara-... 

High density polyethylene, shown in Fig. 18.2 a), consists primarily of linear hydrocarbon chains of the type shown in Fig. 18.1. We commonly abbreviate its name to HDPE. As with all other polymers, high density polyethylenes contain a distribution of molecular weights. The molecules have few, if any, branches. 

Figure 18,2 d) illustrates the general structure of very low density polyethylene, which we also call ultra low density polyethylene. In common with linear low density polyethylene, these resins are copolymers of ethylene and 1-alkenes. The comonomer level ranges from approximately 8 to 14 mole %. We normally refer to these polymers as VLDPE or ULDPE. The molecules of very low density polyethylene contain a distribution of lengths and branch placements. 

Robertson [ 57 ] has measured the adsorption of zinc, caesium, strontium, antimony, indium, iron, silver, copper, cobalt, rubidium, scandium, and uranium onto glass and polyethylene containers. Radioactive forms of these elements were added to samples of seawater, the samples were adjusted to the original pH of 8.0, and aliquots were poured into polyethylene bottles, Pyrex-glass bottles and polyethylene bottles contained 1 ml concentrated hydrochloric acid to bring the pH to about 1.5. Adsorption on the containers was observed for storage periods of up to 75 d with the use of a Nal(Tl) well crystal. Negligible adsorption on all containers was registered for zinc, caesium, strontium, and... 

The first aim of this work was to study the influence of an unwashed membrane filter on the cadmium, lead, and copper concentrations of filtered seawater samples. It was also desirable to ascertain whether, after passage of a reasonable quantity of water, the filter itself could be assumed to be clean so that subsequent portions of filtrate would be uncontaminated. If this were the case, it should be possible to eliminate the cleaning procedure and its contamination risks. The second purpose of the work was to test the possibility of long-term storage of samples at their natural pH (about 8) at 4 °C, kept in low-density polyethylene containers which have been cleaned with acid and conditioned with seawater. 

Table 1.11 gives the results of analytical measurements on aliquots of a conditioning seawater stock, stored at about 4 °C for three and five months in old low-density polyethylene containers (acid-washed for four days and conditioned for more than two months). 

Low-density polyethylene containers are suitable for storing seawater samples at 4 °C and natural pH, provided that they are thoroughly cleaned (in 2 M hydrochloric acid for at least a week) and adequately conditioned (with prefiltered seawater for at least one to two weeks). Storage can be prolonged for at least three months (or five months for cadmium) without significant concentration changes. For lead and copper, adsorption losses are observed after five months. 

Scarponi et al. [781] studied the influence of an unwashed membrane filter (Millpore type HA, 47 mm diameter) on the cadmium, lead, and copper concentrations of filtered seawater. Direct simultaneous determination of the metals was achieved at natural pH by linear-sweep anodic stripping voltammetry at a mercury film electrode. These workers recommended that at least 1 litre of seawater be passed through uncleaned filters before aliquots for analysis are taken the same filter can be reused several times, and only the first 50-100 ml of filtrate need be discarded. Samples could be stored in polyethylene containers at 4 °C for three months without contamination, but losses of lead and copper occurred after five months of storage. 

Duplicate samples were processed onshore after a variety of storage procedures. All samples were analysed for copper and iron by GFA-AS. Only samples filtered (< 1 pm), acidified, and stored frozen gave extractable copper and iron results comparable with those for samples extracted immediately after collection. Cold storage with sample acidification in polyethylene containers appeared less satisfactory. Organic extracts from samples processed onboard are best retained in all-Teflon containers pending complete digestion and analysis onshore. Unless clean (ultra-filtered air) conditions can be ensured onboard, the estuarine water samples are best returned in a filtered, acidified, and frozen condition for onshore processing. 

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