High-Density Polyethylene (HDPE) Water Bottles

The bottle made of FDA approved food-grade HDPE is the lowest cost compared to PET and PC bottles. The common sizes are 1 and 2.5-gallon bottles. The rectangular 2.5-gallon bottle has a built-in handle and a dispensing valve. The 1-gallon bottles are available in two configurations, the "milk-jug" and the high profile bottle.

Three quality issues of HDPE bottles are: the taste problem, the fitting of the cap, and inadequate bottle strength during storage.

The Taste Problem
A plastic-like taste from water bottled in a HOPE bottle could be a result of one or more of the following causes:

• Bottles stored longer than one year
• Bottles stored in temperatures higher than 490 (120F) for more than 72 hours
• Contaminated air supply to the blow molding machine or high melting temperature greater than 2040 (400F) (Solvay, 1992)
• Short machine cycle time, less than 8 seconds in 4-head machine, less than 9 seconds in 6-head machine (Paxon, 1993)
• Presence of high level of oxidation products - aldehydes, ketones, and acids inside process stream during production of raw HOPE resin (Phillips 66 Company, 1993)

To quantify the plastic taste from HDPE bottles, a taste test is periodically conducted. The taste intensity of HDPE bottles depends on the quality of the blow molding process and is also impacted by any adverse storage conditions.

A fresh-made bottle with a strong taste, is often an indication of a need to verify the molding machine's operating parameters or the processing history of the related resin batch.

Cap Fitting Problem
Friction press-on closures are used in the 1-gallon and in the 2.5-gallon bottles. To seal properly, both the tear-band cap of the 1-gallon and the "push-pull" dispensing valve of the 2.5 gallon depend on the quality of the bottle spout finish, its smoothness and roundness.

HDPE bottles have a tendency to shrink. The bottle capacity decreases most rapidly in the first minutes following molding, then continues to decline with time. Higher bottle storage temperatures cause a greater rate of bottle shrinkage. After 10 days in storage, an 1-gallon bottle decreased 2% of its capacity when stored at 49C (120F); another bottle from the same batch decreased only 1.2% of its capacity when stored at a lower temperature of 23C (73F) (Phillips 66 Company, 1978). Although the shrinkage is marginal, when combined with the neck warpage this could cause the cap to leak. Slight increase in the blow time and blow pressure will correct the capacity deficiency and prevent the neck warpage.

The "milk-jug" 1-gallon bottle has a threading finish and utilizes a threaded plastic cap with polyethylene-foam liner. The cap is a mechanical break-away type with perforations along the lower part of the skirt which form a "breakline" in the closure (Nairn, et al., 1986). To seal well, the cap demands a smooth bottle spout and a correct application torque. Excessive application torque from the capper will damage the flatness of the bottle's sealing surface or that of the liner, causing leakage.

Thus, a preventive maintenance program to ensure a consistent application torque for the capper is necessary in the HOPE bottling operation.

Packaging the HDPE Water Bottles
HDPE bottles are packaged in corrugated boxes for distribution. Typical package sizes are a box of six bottles (1-gallon) or a box of two bottles (2.5-gallon). The boxes are stacked in three layers on a wood pallet then stretch-wrapped for transporting.

Full pallets are stacked two-high in the warehouse. This stacking arrangement is a cost-effective practice in warehousing the bottled water boxes. Field tests showed that the thickness of the boxes, especially for the 2.5-gallon water bottles, could be minimized without sacrificing the package integrity, provided the pallets are not stacked more than two high. Although the low stacking requires more space, the saving from using a lighter box is justified. It is also essential that HDPE water bottles are not stored longer than 90 days and that the stock be rotated regularly.